All posts by Stephanie Liou

Lamotrigine

control medium

Drug Summary: Lamotrigine belongs to a group of medications called anticonvulsants, which are used to control seizure disorders. Lamotrigine acts on the central nervous system to control the number and severity of seizures. It is thought to suppress the activity of certain parts of the brain and the abnormal firing of nerve cells that cause seizures. In psychiatry, lamotrigine may be used as a mood stabilizer. In the laboratory, researchers have found that lamotrigine also inhibits release of the neurotransmitter glutamate. This is important because glutamate may play a role in nerve cell degeneration in the brains of people with HD, so reducing the amount of glutamate released makes lamotrigine a potential treatment for HD.

Problem: Glutamate sensitivity^

Many factors contribute to the degeneration and death of nerve cells in people with HD. One aspect of HD is that nerve cells are particularly sensitive to glutamate. Glutamate is a neurotransmitter that is used to pass messages along from one nerve cell to another. (For more information on glutamate and HD click here.) Researchers have observed that because glutamate receptors in some nerve cells of people with HD are more sensitive than in people without HD, they are activated more frequently than normal receptors. This increased activity and sensitivity to glutamate has been associated with nerve cell death.

One way to prevent the overstimulation of a nerve cell by glutamate is to inhibit glutamate release from the nerve cells that communicate with it. In order to understand this kind of treatment, we must first understand the steps involved in the nerve impulse. (For more information on how nerve impulses work, click here.) It is important that we understand the steps of the nerve impulse because different treatments can be used to inhibit glutamate release by interfering at different steps. A nerve impulse involves receiving a message at one end of a cell and transmitting it via an electric signal to the other end of the cell. Neurotransmitters such as glutamate are stored at the end of the cell and are released in the last step. They act as a chemical signal, transmitting the message to a neighboring cell.

An important step in the electrical transmission of the nerve impulse involves sodium (Na+) channels. Most of the time, charged particles called ions line up along the inside and outside of the nerve cell membrane, giving the membrane a small electric voltage. Many different types of channels are located in the membrane, acting like guards at an exclusive community, only letting certain molecules in and out. Some of these channels open or close depending on what the membrane voltage is. One of these voltage-gated channels is the sodium channel, and it opens when the inside of the membrane becomes more electrically positive than usual. When the channel opens, sodium ions are free to enter the cell and continue the messaging cascade that ultimately leads to the release of neurotransmitters such as glutamate.

After the sodium channel lets enough sodium into the cell so that it reaches a maximum voltage, the channel temporarily becomes inactivated. An inactivated channel means that not only can no more sodium get through to relay the current message, but also the channel cannot be immediately reset, and thus will let no new messages be relayed. This intermediate stage between open and closed is called the refractory period. The sodium channel returns to the closed position only after the membrane voltage returns to a normal level (restoring the normal voltage involves the exit and entry of different ions). Once the channel is back in the closed position it can be opened again when the voltage rises enough. (See figure L-5 for a representation of the different sodium channel positions.)

Fig L-5: Sodium Channels

How can lamotrigine reduce glutamate release?^

Studies have shown that lamotrigine may inhibit the release of glutamate. While lamotrigine may act in several different ways, it is primarily thought to act as an anti-glutamate drug by interfering with sodium channels. These channels are a necessary step in the nerve impulse and for normal release of glutamate by a nerve cell. In this way, lamotrigine’s inhibition of glutamate release is similar to that of the drug riluzole. (For more information on riluzole click here.)

Lamotrigine exerts its effects during the refractory period by binding to sodium channels. In overactive nerve cells such as in people with seizure disorders or HD, it takes longer for sodium channels to transition from the open period to the inactivated refractory period. An extended open period is what allows so much glutamate to be released in overactive cells. Lamotrigine targets these overactive cells that are slow to inactivate, leaving normal areas of the brain unaffected. Lamotrigine acts by prolonging the inactive refractory period so that sodium channels cannot return to the closed position. Since the channel must first be closed before it can be re-opened, prolonging the inactive period decreases the time of the open period, thus decreasing glutamate release. To put it another way, during the inactive refractory period, no more sodium can get in, so the membrane’s voltage is stabilized. When sodium is kept out, no more messages can be relayed, and thus no more glutamate is released. Therefore, lamotrigine inhibits glutamate release by interfering with sodium channels.

Research on lamotrigine^

Kremer, et al. (1999) recognized that prolonged exposure to glutamate leads to the gradual decline and death of nerve cells in diseases such as HD. They therefore hypothesized that inhibiting the release of glutamate would prevent or at least slow the progression of HD. Lamotrigine is known to inhibit glutamine release in vitro, and has been successfully applied to protect nerve cells in other experiments using animal models. Building on these results, the researchers ran a clinical trial on humans lasting 30 months to see if lamotrigine would slow the progression of HD in people who had experienced physical symptoms for less than five years.

The researchers studied the effects of lamotrigine on 28 people with HD; they also gave a placebo to 27 people with HD to control for psychological effects of treatment as well as to have a comparison group. This was a double-blind study, meaning neither the researchers nor the patients knew which group received the lamotrigine and which received the placebo. (The purpose of a double-blind study is to remove any experimenter or patient bias in evaluating the treatment.) The efficacy of the drug was primarily measured using the total functional capacity (TFC) scale. Patients were also assessed using a variety of cognitive and physical tests.

Over the course of the 30 months of the study, both groups significantly declined in their TFC scores, without any significant difference between the group receiving lamotrigine treatment and the group receiving a placebo pill. This led the researchers to conclude that lamotrigine is not effective in slowing the progression of HD. However, there was slightly less deterioration in terms of the physical symptoms known as chorea in the group receiving lamotrigine. Also, when asked about their various symptoms (mood, physical, etc.), a larger percentage of patients in the group receiving lamotrigine reported an improvement. Despite this perception, both groups declined in their performance on physical tasks. In addition, not much change was observed in the cognitive tests, although the placebo group performed better than the lamotrigine group on one test due to better learning.

Sixteen (of 28) people receiving lamotrigine treatment reported several side effects, including nausea, skin rash, insomnia, and severe depression. Eight (of 27) people receiving a placebo reported mild side effects.

While the study reported the overall inefficacy of lamotrigine, it is important to consider the relatively small sample size and the fact that deterioration varied widely among participants. This is why the researchers have not fully ruled out lamotrigine’s ability to treat early HD. The positive results of the study (decreased chorea and improved symptoms such as mood) may be a result of what lamotrigine is already used for – as an anticonvulsant and mood elevator. A possible reason why the clinical results on humans were not as favorable as those on animals is because the effective dose in animals is much too high for humans to tolerate. Increasing the dose in people is not an option because of the harmful side effects associated with the drug.

Higgins, et al. (2002) also focused on decreasing the amount of glutamate released in nerve cells. Since lamotrigine is known to inhibit the release of glutamate, this group tested the safety of various doses of the drug and how well it was tolerated in HD patients. They conducted an open-label study, meaning that the patients knew they were receiving an actual drug and not a placebo. Over the course of seven weeks the researchers increased the amount of lamotrigine given and then continued giving the maximum dose up to six months. The effects of the drug were tested using the Unified Huntington’s disease Rating Scale (UHDRS) and cognitive tests.

The researchers studied only twenty people with HD and ended up collecting data from fifteen (two people’s symptoms got worse while three people did not report back). The researchers did not find any changes in the UHDRS (this includes motor, functional, and behavioral aspects of HD). However, significant improvements were seen in two parts of the cognitive tests, Verbal Fluency and Symbol Digit Modalities.

Overall, the researchers found that the patients were able to tolerate the drug well and that it was safe to use. They were not able to reproduce the results seen in a previous study that found lamotrigine could reduce chorea. Researchers will need to follow up on this study with a longer lasting investigation that is not open-label and includes more patients.

For further reading^

  1. Kremer, et al. Influence of lamotrigine on progression of early Huntington’s disease. 1999. Neurology 53(5): 1000. Online.
    This is a research article about a clinical trial of lamotrigine and HD. It describes the study’s methods and results in great detail and is directed toward a scientific audience.
  2. Higgins, et al. Safety and tolerability of lamotrigine in Huntington’s disease. 2002. Movement Disorders 17(S5): S324.
    This is a short description of medium difficulty of a clinical trial using lamotrigine as presented at the 7th international congress of Parkinson’s disease and movement disorders.
  3. Hurley, Stephen C. Lamotrigine update and its use in mood disorders. 2002. The Annals of Pharmacotherapy 36(5): 860-873. Online.
    This article reviews known information about lamotrigine and evaluates its use in treating mood disorders. It is not directly related to HD, but the section on pharmacology on page 861 is helpful in understanding how lamotrigine works on nerve cells.

-K. Taub, 11/21/04

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Riluzole

complicated ph

Update: Riluzole is no longer considered to be a promising avenue of research; it failed a phase III clinical trial in 2007. The trial ran for 3 years and included 537 adult HD patients, who were randomly assigned to either the treatment group (receiving 50 mg of riluzole twice a day) or the control group (which received a placebo instead). The 379 patients who completed the study were measured with the Unified Huntington’s Disease Rating Scale (UHDRS), a test commonly used in clinical trials to measures factors such as motor control, independence, and mental function. The scientists performing the study concluded that riluzole has no benefit for the treatment of HD, as it was not significantly better than the placebo; it does not slow the progression of HD, nor does it improve symptoms.

Previous studies found some improvement in motor control for patients who took riluzole. However, these studies were complicated by the fact that other drugs, such as antipsychotics, were taken at the same time to control chorea. Therefore, this study was careful to look at the effects of riluzole separate from all other treatments; patients who participated in the study exclusively used drugs prescribed for the study.

For more information, click here.

Drug Summary: Riluzole has been shown to have energy-buffering and anti-glutamate properties. It has been associated with increased energy metabolism efficiency and inhibition of glutamate activity, and is currently used as a treatment for Amyotrophic Lateral Sclerosis (ALS), a disease that is also hypothesized to involve glutamate toxicity. Huntington’s disease is associated with these both problems in energy metabolism and glutamate toxicity; let us discuss some of these problems and the ways in which riluzole might alleviate them.

Problem: Aerobic inefficiency

Energy metabolism is the process by which cells produce energy. Normally, cells prefer a form of energy metabolism called aerobic respiration due to its efficiency and high-energy yield. The altered huntingtin protein in people with HD is believed to interfere with aerobic respiration, resulting in the inability of HD cells to perform aerobic respiration efficiently. Instead, HD cells must resort to anaerobic respiration, another form of energy metabolism that is less efficient. This impairment in energy metabolism results in various negative effects that eventually lead to cell death.

Studies have reported that riluzole treatment improves motor abnormalities associated with administration of a toxin that blocks energy metabolism. The improvements indicate that riluzole may have positive effects on cells with defective metabolism. However, the mechanism by which riluzole improves energy metabolism is still unknown.

Problem: Glutamate Sensitivity

One of the effects of the impairment in energy metabolism in HD cells is an increased sensitivity to glutamate. Glutamate is one of the major neurotransmitters in the nervous system, used to transmit messages from nerve cell to another. (For more on glutamate, click here.) Increased activation of receptors that receive glutamate has been observed in people with HD. Increased glutamate activity, in turn, has been associated with nerve cell death.

Studies have demonstrated that riluzole may act as an anti-glutamate drug in two ways: 1) by inhibiting the release of glutamate and 2) by interfering with the effects of glutamate on nerve cells.

Fig L-3: Riluzole Inhibits Glutamate Release

It is thought that riluzole inhibits the release of glutamate by interfering with sodium (Na+) channels that are required for normal glutamate release. Figure L-3 shows how riluzole inhibits glutamate release.

The mechanism by which riluzole disrupts the effects of glutamate on target cells is slightly more complicated. Let us first go over what happens in a normal glutamate-receiving cell in order to understand the effects of riluzole on these cells in a patient with HD.

Various types of glutamate receptors are found in nerve cells. One type of glutamate receptor allows the entry of ions into the cell upon glutamate binding, resulting in various changes inside the cell. Among these receptors are NMDA receptors, discussed in the section HD and Glutamate. A second type of glutamate receptors causes cellular changes by initiating a messenger cascade, which involves the activation and deactivation of various molecules and pathways that can cause changes inside the nerve cell.

In a messenger cascade, the binding of glutamate is a “message” that is being sent to the nerve cell. This message is passed on from one molecule to another, until it reaches its final destination. Scientists have discovered that glutamate binding “tells” the cell to release calcium from its stores.

Fig L-4: Messenger Cascades

In HD cells, the overactivation of the glutamate receptors results in overactivation of the messenger cascades and consequently, increased calcium release. High amounts of calcium in the nerve cells are known to cause cell death, which is one possible explanation of how HD nerve cells die. Figure L-4 shows a diagram depicting the molecules involved in the messenger cascade as well as the final effects of the cascade.

Riluzole may disrupt glutamate activity by interfering with the activity of certain proteins involved in the messenger cascade. Once the cascade is inhibited, changes induced by glutamate such as calcium release and the associated cell death might eventually be delayed.

Research on Riluzole

Bensimon, et al. (1994) hypothesized that riluzole may have beneficial effects on people with diseases such as amyotrophic lateral sclerosis (ALS) which involve overactivation of glutamate receptors. ALS is a progressive and fatal disorder affecting nerve cells. The cause of the disease is unknown, and no treatment is available that influences survival.

Many hypotheses about the cause of the disease are currently being studied. One of these hypotheses involves glutamate. Studies have reported that increased glutamate concentrations in the brain result in nerve cell death. Given this possible role of glutamate in ALS progression, the researchers sought to assess the effects of riluzole in people with ALS.

The researchers conducted a trial in 155 participants with ALS in France for one year. The participants were given either 50-mg of riluzole twice a day or a placebo. Survival and changes in ability to function were used as tests for the drug’s effectiveness. A secondary test used to examine the drug’s effectiveness was change in muscle strength.

After 12 months, 58 percent in the placebo group were still alive, compared with 74 percent in the riluzole group. The deterioration of muscle strength and functional ability was significantly slower in the riluzole group than in the placebo group.

Side effects of riluzole included stiffness, mild increase in blood pressure, and increase in the levels of the enzyme aminotransferase, which sometimes result in elevations of toxic ammonia. High levels of ammonia have been associated with brain damage, although the reason for ammonia toxicity is still unknown. While aminotransferase elevations were more frequent with riluzole treatment, the elevations were well tolerated and did not cause severe adverse effects in most of the participants in this study. More studies need to be conducted to understand this side effect of riluzole.

On the whole, it appears that these reported side effects may worsen the quality of life, but such consequences may be outweighed by the effect of the drug in improving muscle function and survival rates. The mechanism by which riluzole improves muscle function and survival rates is still unknown. However, the results of this study indicate that riluzole may have a beneficial effect in people with diseases that involve glutamate toxicity such as ALS and HD.

Rosas, et al. (1999) hypothesized that riluzole treatment may have beneficial effects in people with HD. The researchers conducted a 6-week trial of riluzole in eight participants with HD. The participants were treated with 50 mg of riluzole twice a day and were observed for changes in chorea (involuntary dance-like movements), dystonia (prolonged muscle contractions), and total functional capacity (TFC) scores. TFC is a standardized scale used to assess the capacity to work, handle finances, perform domestic chores and self-care tasks, and live independently. The brain lactate evels of the participants were also studied. Lactate is a by-product of anaerobic metabolism that is often used as a measure of energy metabolism efficiency in cells. Low lactate levels would indicated high aerobic respiration and high energy yields. High lactate levels on the other hand, would indicate that cells are unable to perform aerobic respiration and had to resort to the less-efficient anaerobic respiration instead. Changes in lactate levels were then used by the researchers to test the effects of riluzole on energy metabolism.

The researchers found that the chorea rating score of the participants who took riluzole improved by 35% compared to their scores before treatment. Discontinuation of treatment resulted in worsened chorea, indicating that riluzole was indeed associated with the improved chorea. No significant changes were seen on the dystonia or TFC scores.

Lactate levels were lower in the riluzole-treated participants compared to their levels before treatment. However, the researchers reported concerns about inaccuracies in lactate measurements due to limitations in their instruments and measuring methods. Whether or not the decreased lactate levels associated with riluzole indicate improved energy metabolism remains to be determined.

In this study, no significant adverse effects were observed after 6 weeks of treatment. The most frequent side effect was diarrhea; other symptoms quickly resolved without the need for medical intervention.

The results of this study also suggest a possible role for riluzole in the treatment of chorea in people with HD. However, the mechanism by which riluzole might alter or prevent disease progression is still ambiguous. More studies need to be conducted to determine whether and how riluzole can slow the progression of HD and protect nerve cells.

For further reading

  1. Bensimon, et al. “A Controlled Trial of Riluzole in Amyotrophic Lateral Sclerosis (ALS).” The New England Journal of Medicine. 1994; 330(9): 585-591. Online.
    This study reported that riluzole treatment resulted in increased survival rates and improved muscle function in people with ALS.
  2. Rosas, et al. “Riluzole Therapy in Huntington’s Disease (HD).” Movement Disorders. 1999; 14(2): 326-330.
    This study reproted that riluzole treatment resulted in decreased chorea and lactate levels in people with HD.
  3. Landwehrmeyer GB, Dubois B, de Yébenes JG, Kremer B, Gaus W, Kraus PH, Przuntek H, Dib M, Doble A, Fischer W, Ludolph AC; European Huntington’s Disease Initiative Study Group. Riluzole in Huntington’s disease: a 3-year, randomized controlled study. Ann Neurol. 2007 Sep;62(3):262-72.

This study concluded that Riluzole has no benefit for HD.

-E. Tan, 1-15-02, updated by M. Hedlin 7-1-11

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Remacemide

Drug Summary: Remacemide (RMC) is a drug that HD researchers hope can alleviate glutamate toxicity in the brains of HD patients. Remacemide is an NMDA antagonist – it inhibits the binding of glutamate to NMDA receptors, preventing glutamate from exerting its toxic effects on the nerve cell. Although, it has been shown to transiently improve motor performance in mouse models of HD, the few human clinical trials that have been performed have not produced statistically significant improvements in brain or motor function. Patients have also experienced side effects such as lightheadedness, dizziness, vomiting, nausea, and gastrointestinal disturbance.

inhibitor-01

The lowered amount of energy available in the nerve cells of patients with HD is thought to cause NMDA receptors to be oversensitive to glutamate. Therefore, normal physiological levels of glutamate can cause overexcitation of the NMDA receptor, leading to the influx of calcium ions into the cell. Excess calcium ion entry can lead to cell death through a combination of events. (For more information, click here.)

Remacemide, sometimes referred to as Remacemide Hydrochloride, is under investigation as a treatment for HD because it acts as a non-competitive inhibitor of the NMDA receptor. This means that remacemide decreases the receptor’s ability to bind glutamate by docking to a site on the receptor other than the glutamate binding site, and changing the shape of the receptor such that glutamate has a difficult time binding. Researchers hope that by inhibiting the NMDA receptor, the toxic effects of glutamate in the neurons of patients with HD can be lessened.

Clinical trials have examined the effectiveness of remacemide in curbing or stopping the neurodegenerative effects of HD in humans. Although remacemide treatment has not produced statistically significant improvement in these trials, in some patients it seems to transiently improve certain motor symptoms caused by HD such as chorea. Side effects such as dizziness, nausea, vomiting, lightheadedness, and gastrointestinal disturbances tended to accompany treatment.

Experiments done on mouse models of HD have been more positive.

Research on Remacemide

Kieburtz, et al. (1996) conducted a study on the effects of remacemide in 31 participants in the early-stages of HD. The study was conducted over a 5-week period and the participants were divided into three treatment groups:

• 10 received 200 mg of remacemide per day
• 10 received 600 mg of remacemide per day
• 11 received a placebo (no medication at all)

The total functional capacity (TFC) of the participants was used as the criteria of the drug’s effectiveness. TFC is a standardized scale used to assess capacity to work, handle finances, perform domestic chores and self-care tasks, and live independently. The TFC scale ranges from 13 (normal) to 0 (severe disability). The HD Motor Rating Scale (HDMRS) was also used to assess the motor capabilities of the participants. The HDMRS consists of 14 items that assess the relevant motor features of HD including chorea and other motor functions. Other psychological tests were also conducted to measure the effectiveness of the drug in improving cognitive function.

Following treatment, the researchers concluded that there was no statistically significant difference between the three treatment groups. However, a trend towards improvement in chorea was observed among the participants who received 200 mg of remacemide per day. No major side effects were observed in most of the participants. However, one of the participants who received 600 mg/day did not complete the study due to persistent nausea and vomiting, which was believed to be a result of the medication.

The researchers concluded that remacemide could have short-term effects in improving chorea experienced by people in the early stages of HD. No statistically significant changes in cognitive performances were seen in the treatment groups. Larger, long-term controlled studies of remacemide are needed to determine the duration of tolerability and potential benefits of remacemide and other NMDA blockers.

The Huntington Study Group (2001) conducted a clinical trial involving 347 early-stage HD patients at 23 sites in the United States and Canada, monitored between July 1997 and June 1998. Participants in the study were assigned to four different treatments:

• 25% received remacemide (200 mg thrice a day)
• 25% received CoQ10 (300 mg twice a day)
• 25% received a combination of remacemide and CoQ10
• 25% received a placebo (no medication at all)

The primary measure of the drug’s effectiveness was change in total functional capacity (TFC) of the people with HD. A score of 13 represents a normal degree of function and a score of 0 represents a severely disabled state. The average TFC score of the participants before the study was 10.2. None of the treatments significantly altered the decline in TFC.

The condition of the participants who were treated with remacemide worsened by 2.3 points on the TFC scale, showing that the drug had no beneficial effect on slowing the functional decline experienced by people with HD. However, there was a trend toward an improvement in the degree of chorea in the participants treated with remacemide. Although this effect was not statistically significant, the effect was seen during the patient’s first visit after treatment began, suggesting that remacemide may decrease chorea. These findings suggest that antiglutamate therapies could be useful in controlling chorea even if they have no impact on slowing functional decline. However, remacemide was associated with side effects that included dizziness, lightheadedness and nausea. A trend towards a decrease in TFC decline was seen in the participants treated with CoQ10. (For information on CoQ10, click here.)

Ferrante et al. (2002) studied the potential therapeutic effects of remacemide, coenzyme Q10, and the combination of the two drugs on transgenic mouse models of Huntington’s Disease. They found that oral administration of either coenzyme Q10 or remacemide significantly extended survival and delayed the development of motor deficits, weight loss, cerebral atrophy, and neuronal intranuclear inclusions in the R6/2 transgenic mouse model of HD. The combined treatment, using CoQ10 and remacemide together, was even more effective than either compound alone.

For further reading

  1. Kieburtz, et al. “A controlled trial of remacemide hydrochloride in Huntington’s disease.” Movement Disorders. 1996, May; 11(3): 273-7.
    This article contains the full details on the study by Kieburtz, et al.
  2. The Huntington Study Group. “A randomized, placebo-controlled trial of coenzyme Q10 and remacemide in Huntington’s disease.” Neurology. 2001, Aug 14; 57(3): 397-404.
    This article contains details on the study done by The Huntington Study Group.
  3. Schilling, et al. “Coenzyme Q10 and remacemide hydrochloride ameliorate motor deficits in a Huntington’s disease transgenic mouse model.” Neuroscience Letters. 2001, Nov 27; 315(3): 149-153.
  4. Ferrante, et al. “Therapeutic Effects of Coenzyme Q10 and Remacemide in Transgenic Mouse Models of Huntington’s Disease.” Journal of Neurosience. 2002, Mar 1; 22(5): 1592-1598.

-P. Chang, 7/5/04

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Mithramycin

control

Drug Summary: Mithramycin (also known as MIT and plicamycin) is an antibiotic that binds to DNA to regulate transcription. It attaches to specific regions of DNA that are rich in guanine and cytosine. While it is currently prescribed for the treatment of certain types of cancer and a few other conditions, recent research shows that it is helpful in treating motor symptoms and prolonging life in a mouse model of HD.

How could Mithramycin treat HD?

Normally in the course of Huntington’s disease certain genes are prevented from being expressed in their normal protein products. This abnormal repression of genes is referred to as transcriptional dysregulation. Remember that “transcription” is the process by which the information of DNA is copied into messengers that are then used as templates for protein synthesis. Many of the genes that are prevented from being expressed are important for nerve cell health and survival. So, when these genes are blocked from producing their respective proteins, they cannot help to prevent the neurodegeneration that is typical of HD. This repression is caused by the mutant huntingtin protein, which interacts with molecules that would normally aid in the transcription of these helpful genes. The proteins that are encoded by the repressed genes have a wide variety of functions, which may explain why there are so many different symptoms associated with HD. One possible way to prevent many of these symptoms is to restore normal transcription, which is the proposed function of the drug mithramycin.

How does Mithramycin work?

A number of hypotheses exist for how mithramycin acts in the body, but a group of researchers recently discovered what may be the key mechanism by which it prevents gene repression. One way that genes are repressed, or “silenced,” is through a process called methylation. Before explaining exactly what methylation is, we will first review how DNA is organized.

The entire DNA code is extremely long, and in order to be able to fit it into each cell, it needs to be very tightly compacted into chromosomes. (For more information on chromosomes, click here.) To accomplish this compression, the DNA is wound around structures called nucleosomes. You can think of a nucleosome as a spool and the DNA as the thread. Nucleosomes are made up of smaller proteins called histones. There are four different core histones (H2A, H2B, H3, and H4), and two of each are present in every nucleosome, along with one helper histone (H1). Histones play a very important role in the regulation of transcription.

By controlling access to DNA, histones determine if and when transcription occurs. When the histones keep the DNA tightly wound up, transcription factors cannot access the DNA, and it therefore cannot be transcribed. Different chemical groups (a chemical group can be a single atom or a small molecule) can be added to the histones in specific spots, causing the DNA to coil up to prevent transcription or causing the DNA to uncoil to allow transcription.

One way to control transcription is by methylation. In methylation, a chemical group called a methyl group is added to histone H3 or H4 at specific spots. When a histone is methylated at one of these spots, a protein called HP1 recognizes this signal and binds to the methyl group. These HP1 proteins also recognize each other and bind together, winding the DNA up into the coiled form of chromosomes in the process. Remember that in this coiled form, transcription factors cannot bind to the DNA so transcription cannot occur: the genes have been silenced. Methylation is a fairly permanent way of controlling transcription, so it can be devastating for an important section of the DNA to be wrongly methylated.

5b dna methylation final-revised

According to an important hypothesis, mithramycin helps restore normal transcription by regulating methylation. Researchers have discovered in a mouse model of HD that histone H3 was hypermethylated (methylated more that usual) at its ninth amino acid (recall that histones are proteins made up of amino acids in a long string or “chain”). It is already well known that increased methylation at this particular spot affects transcription. After conducting several experiments, the researchers concluded that mithramycin exerts its neuroprotective effects by preventing this hypermethylation and restoring normal transcription. Exactly how mithramycin prevents the hypermethylation has yet to be decisively determined, but the researchers have proposed a likely explanation.

Mithramycin is known to bind to areas of DNA that are rich in guanine (G) and cytosine (C), two DNA bases. (For more information on DNA bases, click here.) By binding to a GC-rich section of DNA, mithramycin likely prevents another molecule, which plays a role in methylation, from binding. Such molecules that aid in methylation could be either transcription factors or a type of enzyme called histone methyltransferase (HMT). HMT adds methyl groups to histones, causing the DNA to coil up as noted earlier and make it inaccessible for transcription. Transcription factors can also play a role in gene silencing by recruiting HMT. One type of transcription factor (TF) is already known to recruit an HMT that specifically binds to histone H3 at the ninth amino acid. These transcription factors bind to the DNA and recruit a specific HMT. The HMT then methylates the histone, preventing transcription. While a transcription factor that binds to GC-rich areas of DNA has yet to be found, researchers hypothesize that if there is such a molecule, mithramycin displaces it, preventing methylation. By preventing hypermethylation, mithramycin restores normal transcription, preventing much of the neurodegeneration typical of HD in the mouse model.

Research on Mithramycin

Ferrante, et al. (2004) tested the effects of mithramycin on a transgenic mouse model of HD. The researchers daily injected one group of mice with one of five different doses of mithramycin and another group of mice with a placebo to serve as a comparison group. The mice were tested for body weight twice a week, motor performance once a week at first and later twice a week, and observed twice a day for survival. The researchers found that the dose of mithramycin influenced how long the mice lived. The benefits of mithramycin peaked at a dose of 150 micrograms per kilogram per day, since lower doses were less effective and higher doses were not well tolerated (and even resulted in death). The optimal dose of mithramycin led to the longest extension of survival ever seen in the HD transgenic mouse, extending survival by 29.1%. While this finding is very encouraging, we must remember that the experiment was done on mice and issues with drug safety and tolerability may prevent mithramycin from being so effective in humans.

In addition to their longer lives, the mithramycin-treated transgenic mice also performed better than the placebo-treated mice on the motor performance test each time they were tested. Motor performance was tested using the “rotarod” apparatus, which is a rotating rod on which the mice are placed and timed for how long they can stay on. The total motor improvement over placebo-treated mice was 42.6%. Mithramycin did not appear to affect the body weight of the transgenic mice.

When HD in the transgenic mice had become so advanced that they were no longer able to feed or move when prodded, they were euthanized and their brains examined. Amazingly, the researchers found that the mice that were treated with mithramycin had almost none of the typical brain deterioration seen in HD. The mithramycin-treated mice did not exhibit brain atrophy, enlarged ventricles, or loss of nerve cells in the striatum, which are typical symptoms of HD in both mice and humans. (For more information on HD and the brain, click here.) While the placebo-treated mice had a 21.3% reduction in brain weight, those treated with mithramycin experienced only a 2.8% reduction in brain weight. Also, the size of the nerve cells in placebo-treated mice decreased by 41.9%, while the mithramycin-treated mice did not have any significant decrease in nerve cell size compared to non-HD mice. These results show that mithramycin improves survival and is neuroprotective, since fewer nerve cells in the brain die and they remain at the normal size.

Once the researchers determined the effectiveness of mithramycin in treating HD mice, they tested several different hypotheses to find out how exactly the drug works. These experiments ruled out several mechanisms. They found out that mithramycin does not reduce the amount that the HD allele is transcribed (which would result in less of the harmful huntingtin protein); it does not change the amount of glutamate receptors or their activity (which would reduce the amount of excitotoxicity); and it does not change the permeability of mitochondria (which would reduce programmed cell death). The final hypothesis left was that mithramycin prevents the mutant huntingtin protein from interfering with transcription of specific genes that are important for nerve cell survival. There are several ways that mithramycin could restore normal transcription, and the researchers determined that it was by preventing methylation at a specific spot of histone H3 (as explained earlier). By preventing too much methylation, mithramycin allows genes to be expressed that promote survival in the presence of mutant huntingtin.

This initial study of mithramycin on the HD transgenic mouse shows very promising results. While the drug is already approved by the Food and Drug Administration (FDA) for the treatment of cancer and other diseases, it is too early to tell if mithramycin will be useful in treating people with HD. Since HD is a chronic condition, it important to determine whether a potential treatment can safely be used for long periods of time. Unfortunately, mithramycin is not well-tolerated in people at the typical dose for long-term use. In fact, the typical human dose is 25-30 micrograms per kilogram per day (recall that the optimal dose given to mice was much larger at 150 micrograms per kilogram per day) and is only given up to ten days. Mithramycin has been shown to cause unpleasant side effects, including nausea and vomiting, and long-term use has been shown to lead to excessive bleeding. Research on humans with HD will have to be conducted to test the efficacy of mithramycin given at non-continuous doses and/or smaller doses.

For further reading

  1. Ferrante, et al. “Chemotherapy for the Brain: The Antitumor Antibiotic Mithramycin Prolongs Survival in a Mouse Model of Huntington’s Disease.” The Journal of Neuroscience. 2004; 24(46): 10335-10342.
    This is a very technical, scientific article. It details the experiment where mithramycin was given to HD mice and discusses the drug’s likely mechanism of action.
  2. Mithramycin.” Online.
    This is an excellent summary of the drug mithramycin and Ferrante et al.’s findings. It is of medium to high difficulty.
  3. Zhang and Reinberg. “Transcription regulation by histone methylation: interplay between different covalent modifications of the core histone tails.” Genes & Development. 2001; 15(18): 2343-2360. Online.
    This is an extremely technical article that goes into detail about transcriptional regulation and histone methylation. It is only recommended to the most scientifically literate audiences.

-K. Taub, 8-10-05

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Arginine

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Arginine and Huntington’s Disease:

Arginine is an amino acid produced naturally in the body and has a significant effect on human brain chemistry. Amino acids are the building blocks of proteins and, in humans, are either produced in the body or consumed in the diet. Scientists hope that through investigating the way arginine interacts with the brain, they can learn more about the mental decline associated with age-related dementia, Parkinson’s disease, and Huntington’s disease (HD) to search for potential solutions.

How the Body uses Arginine

Arginine is a non-essential amino acid meaning that the human liver can make its own arginine, so, in most cases, it does not need to be obtained from food. It can stimulate the secretion of growth hormone, which as the name suggests causes growth and cell regeneration. Thus, it can aid in the healing time of damaged tissues.

Arginine is also the dietary precursor of nitric oxide (NO), which is a gas that can serve as a cellular messenger in both the brain and body. NO plays an important role in a variety of biological functions, including blood vessel dilation, immune responses and neurotransmission.

Arginine: Neurotoxic or Neuroprotective?

NO serves multiple functions in maintaining brain chemistry in non-HD brains. Depending on its concentrations in local tissues, NO can be both neuroprotective – protecting nerve cells from damage – and neurotoxic – toxic to nerve cells, possibly causing apoptosis or cell death. Since NO serves many different purposes, scientists are uncertain whether increases in NO levels would be helpful or harmful to the brain, and how much of an effect it would have. Therefore, using dietary arginine as a treatment for HD – which would increase levels of NO – could be either beneficial or harmful.

Overproduction of NO can be toxic to nerve cells. NO combines with superoxide, a very unstable and reactive molecule, to make peroxynitrite. Peroxynitrite is able to alter proteins, fragment DNA, and interfere with the energy metabolism of cells- all of which are toxic to nerve cells and contribute to HD.

On the other hand, NO can be neuroprotective. Because NO production depletes free radicals like superoxide O2-, NO is considered to be an anti-oxidant and prevents the damage to nerve cells caused by free radicals. However, it is this very characteristic that allows NO to combine with peroxynitrite, the nerve cell toxin described above. Since arginine in the diet increases NO, arginine supplements could have two completely opposite outcomes, like two sides of a coin – and researchers are working to understand how this coin toss plays out in the body.

Role of NO and arginine in HD

NO may also be involved in HD, although scientists are still debating its role in the disease. One HD-related change in the brain is increased blood flow to the brain, or cerebral blood flow (CBF). In 1986, scientists found that heart attack drugs, which were designed to widen blood vessels, also released NO. They suspected that NO might play a part in widening blood vessels. The correlations between arginine, NO, blood flow, and changes in CBF associated with HD led to studies investigating the link between arginine and HD.

Studies from the past decade are inconclusive as to whether or not a lack of NO contributes to HD. In one study, researchers at the University of Connecticut fed aged HD transgenic mice (For more information on animal models, click here.) diets of differing concentrations (0, 1.2 or 5%) of arginine. They looked at the effect of dietary arginine on three symptoms of HD: weight loss, loss of motor control, and increase in CBF:

  • In mice that did not receive arginine (0% group), there was no weight loss and no change in CBF. The degree of motor decline associated with HD was not reduced.
  • In mice given the highest amount of arginine (5% group), the severity and onset of weight loss and motor problems was accelerated and CBF at rest was increased.
  • Mice receiving 1.2% arginine had weight loss and CBF that was intermediate between the other groups, while, interestingly, motor function was better than the groups given higher or lower arginine concentrations.

Both the 1.2 and 5% groups had elevated levels of peroxynitrite, which suggests that excess NO is can be toxic to nerve cells, though a slight increase in NO, as seen in the 1.2% group, seems to be beneficial to motor function.

These findings are supported by earlier studies which showed that decreasing NO levels in the body with a compound, 7-nitroindazole, which blocks the enzyme that synthesizes NO, called nitric oxide synthase (NOS), reduced resting CBF by 17-27% in rats and 30% in humans.

Arginine as a Possible Diagnostic Tool for HD

Arginine could also potentially be used to measure degeneration in HD patients. In a recent study of HD pathology, patients were injected with arginine and tested for levels of growth hormone in the blood. Growth hormone levels can indicate whether there is any impairment in the hypothalamus, a part of the brain responsible for many metabolic processes, so researchers were hoping this could be another method to measure the progression of HD. Results showed that there were two subgroups of HD patients: those with the normal response of increased growth hormone levels, and those that did not show an increase in growth hormone levels. It remains unclear whether the two subgroups exist due to different stages of the disease or to different patterns of neurodegeneration. Further research needs to be conducted in this area.

Future of Arginine in HD Research and Treatment

Scientists are still unsure whether NO plays a part in primary or secondary disease mechanisms of HD. In other words, it is unknown if NO itself causes HD symptoms or is only a part of a chain of events in the brain leading to nerve cell death. Both arginine and NOS inhibitors will remain in the experimental phase for HD treatments until more studies are done.

For further reading

  1. Deckel, et al. “Dietary arginine alters time of symptom onset in Huntington’s disease transgenic mice.” Brain Research Volume 875, Issues 1-2 , 1 September 2000, Pages 187-195. Online
    This is a study that tested the outcome of feeding HD transgenic mice varying levels of dietary arginine.
  2. Deckel, A. Wallace. “Nitric Oxide and Nitrous Synthase in Huntington’s disease.” Journal of Neuroscience Research. 2001 Apr 15;64(2):99-107. Online
    This paper gives some basic information about the role of nitric oxide in the body and in neurodegenerative diseases.
  3. Salvatore E, Rinaldi C, Tucci T et al. (2011) Growth hormone response to arginine test differentiates between two subgroups of Huntington’s disease patients. J Neurol Neurosurg Psychiatry 82:543–547. This paper investigated the role of growth hormone levels in the pathology of HD.

-A. Zhang, 10-11-11

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Vitamin E

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Drug Summary: Vitamin E is commonly found in the diet, in oils, margarine, and dressings. It is a lipid-soluble vitamin that protects cell membranes and other lipid-containing substances in the body, by interacting directly with free radicals and neutralizing them to prevent oxidative damage. Vitamin E could potentially help treat neurodegenerative diseases such as HD by protecting nerve cell membranes (which are made of lipids) from oxidation by free radicals, which can lead to cell death. (For more information on free radical damage, click here.) Studies in people with Parkinson’s disease or Alzheimer’s disease have shown some correlation between higher vitamin E intake and decreased risk of developing these diseases. (For more information on Alzheimer’s and Parkinson’s, click here.) However, there have been contradictory results in studies that tested whether vitamin E treatment could slow the progression or improve the symptoms of these diseases. Not many studies have been conducted to test the effects of vitamin E in people with HD. Unfortunately, the few results that exist have been inconclusive, with some indicating only slight benefits among some patients with mild symptoms, while others suggesting that vitamin E could potentially even have negative effects on health.

What is vitamin E’s role inside the body?

Vitamin E is lipid-soluble, meaning that it dissolves in fats. It has to be ingested with minimal amounts of dietary fat to be properly absorbed in the gastrointestinal (GI) tract. Vitamin E exists in eight different chemical forms, but the most common form in the human body is called alpha-tocopherol (α-tocopherol). Alpha-tocopherol’s main role inside the body is to act as an antioxidant. Alpha-tocopherol is lipid-soluble, so it mostly exerts its antioxidant effects on parts of the cell that are also lipid-soluble, such as the cell membrane, an important part of the cell that is made of lipids. Because cell membranes are made of lipid molecules, they are vulnerable to oxidation by free radicals, which can lead to cell death. Alpha-tocopherol plays a very big role in protecting cell membranes by donating its own electrons to free radicals in order to neutralize them.(For more information on free radical damage, click here.)  Although alpha-tocopherol loses its antioxidant activity once it donates an electron, other antioxidants like vitamin C can restore alpha-tocopherol’s antioxidant properties. (For more information on vitamin C, click here.)

antiox

Besides protecting cell membranes, alpha-tocopherol has also been shown to protect low density lipoproteins (LDL) from oxidation by free radicals. LDL’s are particles made of both lipids and proteins that carry fats and cholesterol through our bloodstream. Research shows that oxidized LDL may increase a person’s risk of developing heart disease. Alpha-tocopherol may therefore exert positive effects in people with HD not only by protecting nerve cell membranes, but also by helping to prevent other complications such as heart disease. (For more information on heart disease and other complications of HD, click here.)

In addition to having these antioxidant effects, alpha-tocopherol affects several other cellular mechanisms and is known to act as a blood-thinner. Blood thinners can help reduce one’s risk of heart attack and stroke by preventing the formation of blood clots in blood vessels. It is important to remember that taking high doses of a blood-thinning compound like vitamin E along with other blood thinners is not advised, and anyone who wishes to take vitamin E as a blood thinner should first consult their doctors.

Could vitamin E supplementation become a potential treatment for HD?

Several laboratory studies have shown that vitamin E has great potential as an antioxidant. One such study showed that another form of vitamin E, alpha-tocotrienol, protected nerve cells from increased free radical damage and toxicity caused by the neurotransmitter glutamate (Khanna, et al. 2003). Because the nerve cells of people with HD are especially sensitive to glutamate, the prevention of glutamate-induced oxidative damage is very important. (For more information on glutamate toxicity, click here.) In this laboratory study, treatment of nerve cells with alpha-tocotrienol not only decreased cell death but also helped them grow at a normal rate even when treatment with glutamate was continued.

Fig K-5: Alpha-Tocotrienol Inhibits 12-LOX

The same researchers found that alpha-tocotrienol not only protects nerve cells by reacting with free radicals directly, but can also prevent free radicals from forming. Alpha-tocotrienol can prevent excessive oxidative damage by inhibiting an enzyme called 12-lipoxygenase (12-LOX), an effect independent of its antioxidant properties. Increased levels of glutamate around the nerve cells cause activation of 12-LOX within the cells, which when activated leads to a cascade of events that lead to production of free radicals and an influx of calcium ions into the nerve cells. These events eventually lead to nerve cell death. Alpha-tocotrienol inhibits 12-LOX from setting off this cascade by binding to it close to its active site. The active site is the spot where an enzyme would normally bind to other molecules, or substrates, in order to set off a reaction in the cell. 12-LOX normally binds to a molecule called arachidonic acid to set off the above-mentioned cascade of events. By binding close to the active site, alpha-tocotrienol prevents 12-LOX from binding arachidonic acid and setting off the reactions that would eventually lead to nerve cell death.

Besides laboratory findings, there is also some clinical evidence that increased intake of vitamin E may help reduce the risk of developing Parkinson’s and Alzheimer’s disease, both of which also involve increased oxidative stress. However, studies that tested whether vitamin E supplementation could help reduce symptoms or slow the progression of these diseases have had varied results. One study of a total of 341 people with Alzheimer’s disease showed that treatment with alpha-tocopherol was associated with a delay in the progression of cognitive symptoms when compared to the placebo group. The group treated with alpha-tocopherol also demonstrated a slower decline in their abilities to perform everyday functions. Research on the protective properties of vitamin E in Parkinson’s disease has been inconclusive in both animals and humans; some studies have shown vitamin E to be protective and others have not.

Peyser, et al. (1995) conducted a 1-year clinical trial with 73 HD patients who were randomly assigned to receive either alpha-tocopherol treatment or a placebo. Since vitamin E interferes with the absorption of vitamin A in the intestines, these researchers decided that subjects in the treatment group should also take a vitamin A supplement in order to prevent the potential development of Vitamin A deficiency. Because vitamin C can restore vitamin E’s antioxidant abilities after it has neutralized a free radical, the treatment group also received daily vitamin C supplements.

These researchers reported that they unfortunately were not able to obtain placebo vitamin A and C pills for the control group, so both the vitamin E treatment group and the control group ended up taking vitamin A and C supplements, which are also antioxidants. Giving both groups these additional vitamins could not produce the same strong evidence as would the use of completely neutral placebo pills. The control group may have also showed some sort of improvement simply because they were given these two vitamins. Furthermore, the vitamin E treatment group may have benefited from the additional vitamins. However, the researchers were still able to establish some specific effects of adding vitamin E to the vitamin A and C combination.

These researchers realized that participants responded differently to the vitamin E supplementation depending on which stage of HD they were in when they started treatment. In order to analyze the results, they split both the treatment and placebo group in two based on the participants’ initial scores on a neurological test. Participants who entered the study with a score of 45 or less were considered to be in the early stages of HD, and participants who had initial scores of more than 45 were considered to be in the late stages. Based on this grouping, the researchers showed that on average, early-stage participants who were treated with vitamin E improved on the neurological examination by the end of the study. Meanwhile, late-stage participants did not show this improvement. This study is important because it shows that vitamin E may have potential to slow HD progression caused by free radical damage, but only if treatment is started before severe nerve cell damage takes place.

A newer study by Kasparova et al. (2006) done on rat models of HD showed that administration of a combination of vitamin E and coenzyme-Q10 (For more information on coenzyme-Q10, click here.) could have potential benefits for HD patients. The rats received coenzyme-Q10 and vitamin E for 10 days before they were injected with 3-NP, a chemical that would create lesions in the striatum, resulting in symptoms similar to HD. Results showed that the increase of creatine kinase, an indicator of brain energy metabolism dysfunction, as well as the decrease of coenzyme-Q10, were prevented in the brain tissue of these rats as compared those in the control group.  However, coenzyme-Q10 and vitamin E were not effective in preventing the decline of electron transport chain function (For more information on electron transport chain function and abnormalities in energy metabolism, click here.).

Risks of Vitamin E supplements

In recent years, researchers at John Hopkins University have reported that patients who take high doses of vitamin E (more than 400IU) had higher risks of death, although it remains unclear why. Vitamin E supplements typically contain 400-800IU (1IU = 2/3 mg), which meets the criterion for high dosage. The data is still inconclusive as to whether lower doses of vitamin E are also associated with this risk. Furthermore, the studies were conducted on older adults, and many of them had heart diseases and other diseases. Nevertheless, HD patients taking high doses of vitamin E should consult with their doctors and might want to consider taking other types of antioxidants.

Conclusion

In conclusion, while vitamin E has beneficial antioxidant effects, it may be toxic at higher doses. Further research needs to be completed to determine whether vitamin E can be a safe and effective therapeutic treatment for Huntington’s disease. As of Spring 2012, not many studies have been conducted investigating the relationship between vitamin E and Huntington’s disease specifically.

For further reading

  1. For a good overview of what vitamin E does inside the body, how it is linked to other medical conditions and how it relates to diet and nutrition, visit Oregon State University’s Linus Pauling Institute website.
  2. Fariss, et al. “Vitamin E therapy in Parkinson’s disease.” Toxicology. 2003 Jul 15;189(1-2):129-46.
    This is a fairly complicated article that explains the role of oxidative stress in Parkinson’s disease and then reviews all the research that has been done on vitamin E treatment in Parkinson’s.
  3. Khanna, et al. “Molecular basis of vitamin E action.” The Journal of Biological Chemistry. 2003 Oct. 31;278(44):43508-15.
    This is a very technical article that describes the experiments that showed that alpha-tocotrienol helps prevent nerve cell death by inhibiting 12-LOX.
  4. Peyser, et al. “Trial of d-alpha-tocopherol in Huntington’s disease.” The American Journal of Psychiatry. 1995 Dec;152(12):1771-5.
    This article is of medium difficulty and describes the 1995 clinical trial of alpha-tocopherol in 73 people with HD.
  5. Sano, et al. “A controlled trial of selegiline, alpha-tocopherol, or both as treatment for Alzheimer’s disease.” The New England Journal of Medicine. 1997 Apr 24;336(17):1216-22.
    This is an article of medium difficulty that describes the clinical study of 341 people with Alzheimer’s disease that tested the effects of alpha-tocopherol treatment along with another drug.

– A. Milczarek, 05/03/05, updated A. Zhang, 4/18/12

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Vitamin C

Drug summary: Vitamin C, also known as ascorbic acid, has been shown to have antioxidant properties. Research shows that in nerve cells, vitamin C has the ability to directly react with free radicals to prevent oxidative stress, which contributes to the progression of the HD disease process. (For more information on free radicals and antioxidants, click here.) Vitamin C may also have the potential to prevent toxicity caused by a neurotransmitter called glutamate. (For more information on glutamate toxicity, click here.)

What is vitamin C?

In the 1970’s, famous Nobel Prize-winning scientist Linus Pauling advocated Vitamin C use to prevent and cure anything from the common cold to heart disease and cancer. While the recommended daily intake of vitamin C is around 60-75 mg, Pauling himself supposedly took 12,000 mg daily and increased that value to 40,000 mg if he felt a cold coming on! While most doctors and researchers have never agreed with Pauling about the wonders vitamin C could work, there is now evidence that vitamin C actually plays an important role in protecting nerve cells from oxidative damage, which may prove vitamin C supplementation to be a promising treatment for people with HD.

Vitamin C, or ascorbic acid, is a water-soluble vitamin. While most animals can make their own vitamin C, humans and a few closely related animals have lost this ability because of a mutation in their DNA that occurred earlier in their evolution. This means that we have to supply the body with small daily amounts of vitamin C through our diet. In the body, vitamins work as coenzymes, meaning that they help enzymes facilitate necessary reactions. Vitamin C’s job is to help in the reactions by which the body makes necessary molecules. One of these is collagen, which makes up connective tissue throughout the body. Another is the molecule carnitine, which shuttles fats into the mitochondria, where they are converted into energy. (For more information on how carnitine can help treat HD, click here.) Vitamin C is also necessary in the synthesis of the excitatory neurotransmitter noradrenaline (also called norepinephrine).

Vitamin C also has antioxidant properties that may prove to be helpful in treating HD. Inside the body, ascorbic acid (vitamin C) changes form to become the negatively charged ascorbate. Ascorbate can then directly neutralize very reactive free radicals by donating its own electrons to them. In this way ascorbate can protect other cell components from oxidation by free radicals. Oxidation can cause cell components to lose their ability to function normally, and excessive oxidative damage may eventually lead to nerve cell death. It has even been found that ascorbate prevents free radicals from oxidizing its fellow vitamin, vitamin E! (For more information on vitamin E, click here .)

How are ascorbate and HD related?

In humans, there is normally a very high concentration of ascorbate in the part of the brain called the striatum. Interestingly, the striatum is the same part of the brain that is most affected by HD. (For more information about the brain and HD, click here.) Most of the ascorbate in this part of the brain exists in the extracellular fluid, or in the spaces between the nerve cells. Scientists now know that ascorbate is actually released from the nerve cells into the extracellular space during times of motor activity. Researchers recently found that in HD mice, this releasing mechanism does not work as well as it does in normal mice. This finding suggests that a decline in motor functions in HD could be tied to lowered levels of ascorbate in specific areas of the brain.

How can ascorbate protect nerve cells in HD?

The release of ascorbate from nerve cells is actually linked to the uptake of another molecule into the nerve cells. This molecule is glutamate, an excitatory neurotransmitter that can be toxic to nerve cells. It can exert toxic effects either when it is present in large amounts or when the nerve cells are overly sensitive to it, as are nerve cells in many people with HD. Because glutamate is excitatory, it is often released by nerve cells during times of motor activity. When it is released by one nerve cell, it travels to the next nerve cell to stimulate it. (For more information on nerve cells, click here.) When glutamate has done its job as messenger, it can either be broken down or taken back up by the nerve cells that released it.

Fig K-4: Release of Ascorbate in the Brain

Researchers found that when glutamate is taken back up by the nerve cells, these cells simultaneously release ascorbate. Because glutamate release is tied to increased production of free radicals, this ascorbate release mechanism might have evolved in order to protect nerve cells. The more glutamate that is released by the nerve cell, the more is taken back up later. Because glutamate is “exchanged” with ascorbate when it goes back into the nerve cell, the cell can regulate how much ascorbate it releases based on how much glutamate was originally released. This mechanism allows the cell to release appropriate amounts of ascorbate because it can measure how much free radical production may have been stimulated by the glutamate release. But glutamate is not the only factor responsible for increasing free-radical formation during this time. When a cell is more active, it has to carry out more metabolic processes, and at a faster rate, which also increases the natural production of free radicals. Therefore, the levels of extracellular ascorbate should be highest during times of motor activity: this is a time when the cells are most likely producing increased levels of free radicals themselves and may need extra protection from glutamate toxicity.

Researchers recently found that nerve cells in the striatum of HD mice release much less ascorbate during motor activity than do the nerve cells of normal mice. Because it is also known that loss of ascorbate in the striatum can impair motor behavior, they decided to test whether injections of ascorbate could improve the motor symptoms of HD mice. They found that injections of ascorbate allowed the nerve cells of HD mice to release normal amounts of ascorbate when they were active. The researchers also found that HD mice treated with ascorbate performed better on two out of three motor tests than did untreated HD mice. These studies show that an inadequate amount of ascorbate in the striatum of HD mice may play a role in worsening their symptoms. While some studies have also shown a connection between increased vitamin C intake and decreased risk of developing Alzheimer’s disease, there are still no studies on the effect of the vitamin on people with HD. Researchers first need to find out if these animal model findings translate to humans with HD before considering ascorbate as a possible treatment.

Research on vitamin C and HD:

Rebec, et al. (2002) discovered that the nerve cells in the striatum of HD mice release much lower quantities of ascorbate than do nerve cells of normal mice. The researchers used two groups of mice: one group was composed of HD mice, and the other was the control group (composed of normal mice). They first put both groups of mice under anesthesia so that they could place electrodes into the striatum of the brain that would measure ascorbate levels. When the mice were under anesthesia, the levels of ascorbate in the striatum were the same in both groups. As the normal mice woke up, their ascorbate levels increased and continued increasing as they became more active. As the HD mice woke up, their ascorbate levels actually decreased by up to 50% below the anesthesia level. The HD mice also went on to engage in less motor behavior and spent more time resting than the control mice. These findings suggest that the brains of HD mice are unable to release the normal amounts of ascorbate when necessary.

Rebec, et al. (2003) went on to test whether treatment with ascorbate would help alleviate motor symptoms in HD mice. This time there were four groups of mice: two groups of HD mice and two groups of normal mice; only one group of HD mice and one group of normal mice was treated with ascorbate. These groups received injections of ascorbate 4 days of the week and then were allowed 3 days of recovery. The two groups that were not treated (one of the HD mice, the other, normal mice) got injections of a placebo to control for any effects that the actual injections and handling may have had on the mice. Treatment and observation went on for three weeks and ascorbate levels in the striatum of the mice were measured twice during the study.

In order to measure the ascorbate levels, the mice were once again put under anesthesia. When they were in this state, mice in all four groups had similar levels of extracellular ascorbate. As they woke up, both groups of normal mice, whether they had been treated with ascorbate or not, showed the expected increase in ascorbate. HD mice that had not been treated with ascorbate showed the same decrease in extracellular ascorbate that had been seen in Rebec, et al.’s previous study (2002, see above). However, HD mice that had been treated showed an increase in ascorbate levels that was similar to the increase seen in both groups of normal mice. These findings are important because they show that treatment with ascorbate can help restore the ascorbate-releasing ability to active nerve cells in HD mice. They also show that treatment with ascorbate only affected the HD mice, since normal mice that were treated did not show a greater increase in ascorbate release than was expected.

Next, the behavior of the mice was observed to determine whether ascorbate treatment actually helped improve motor symptoms. The researchers used three motor tests and behaviors as their criteria. The first was the performance of a repetitive grooming movement that is a sign of nerve cell damage in the HD mice. The next was a test of motor flexibility that recorded how often the mice would choose to turn left or right instead of going straight through a maze, with more turns indicating more flexibility. The final test measured general movement in an open area. The researchers found that HD mice treated with ascorbate performed the repetitive grooming movement less often and had increased flexibility in the maze than did untreated HD mice, suggesting that ascorbate treatment is beneficial to these mice (specifically, by acting as an antioxidant in the striatum). Despite the fact that there was no significant difference between the two groups in the third overall movement test, the researchers still believe that continued study of ascorbate (and vitamin C) may be helpful in understanding more about nerve cell damage in HD.

For further reading

  1. Rebec, et al. “Ascorbate treatment attenuates the Huntington behavioral phenotype in mice.” Neuroreport. 2003 Jul 1; 14(9): 1263-5.
    This is the original article that documents the results of ascorbate treatment in HD mice. It is very technical and meant for a scientific audience.
  2. Rebec, et al. “Dysregulation of ascorbate release in the striatum of behaving mice expressing the Huntington’s disease gene.” The Journal of Neuroscience. 2002 Jan 15; 22(2): RC202.
    This highly technical article explains the differences in ascorbate release between normal and HD mice.
  3. Rice, Margaret E. “Ascorbate regulation and its neuroprotective role in the brain.” Trends in Neuroscience. 2000 May; 23(5): 209-16.
    This is a very technical article that explains the many roles ascorbate plays in the brain as well as the mechanism by which ascorbate moves into and out of nerve cells.

A. Milczarek, 12/24/04

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Lipoic Acid

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Treatment summary: Lipoic acid is a coenzyme present in the mitochondria of cells. It helps to produce energy by aiding enzymes in breaking down sugar during the Krebs cycle. The body makes enough lipoic acid to fulfill its basic metabolic functions, but the compound can also act as an antioxidant when it is in excess. Lipoic acid is special because it is the only antioxidant that is able to deactivate free radicals that are both fat-soluble and water-soluble. (For more information on free radicals and antioxidants, click here.) Because of its antioxidant properties, lipoic acid is being investigated as a possible treatment for HD.

Lipoic acid can be found in many common foods such as potatoes, carrots, broccoli, yeasts, beets, yams, and red meat. This antioxidant is slowly becoming recognized as having unique properties in the prevention of and therapy for a broad range of diseases. For example, lipoic acid protects the liver from damage caused by alcohol, shields the lungs from damage caused by smoke, and enhances glucose disposal in type II diabetes (and reduces associated neuropathy and cataracts). Since humans are not usually deficient in lipoic acid, no recommended dietary allowance (RDA) has been established, but supplementation may help in some conditions. Few studies have investigated the effects and safety of lipoic acid supplementation in humans.

Research on lipoic acid

Andreassen, et al. (2001) investigated the effects of lipoic acid supplementation in two mouse models of HD (we’ll call them strain 1 and strain 2). The researchers mixed lipoic acid into the food of 17 strain 1 mice and 11 strain 2 mice. Other mice were not given lipoic acid and were used as a comparison (there were 55 strain 1 mice and 22 strain 2 mice that did not receive lipoic acid). The mice were weighed each week and successful treatment was evaluated based on weight changes and survival.

The strain 1 mice that were given lipoic acid did not lose weight as fast those not given lipoic acid and continually weighed more than the untreated group. However, the weight of the strain 2 mice was not significantly affected by lipoic acid treatment.

Regardless of its effect on weight, both types of mice receiving lipoic acid survived longer than the untreated mice. The strain 2 mice receiving lipoic acid survived an average of a week longer than untreated strain 2 mice, while the strain 1 mice receiving lipoic acid survived an average of about 11 days longer than untreated strain 1 mice.

These results, while positive, are not as significant and extensive as those found for some other supplements such as creatine (For more information on creatine, click here.) Furthermore, these are only the results of one experiment and much more research needs to be done to find out the safety and efficacy of lipoic acid in humans with HD. However, this study does confirm the role of oxidative damage in HD and suggests that lipoic acid may act to slow its progression.

For further reading

  1. Andreassen, et al. Lipoic acid improves survival in transgenic mouse models of Huntington’s disease. 2001. Neuroreport 12(15):3371-3373. Online.
    This is a scientific article of moderate difficulty reporting the results of a study of lipoic acid in the mouse model of HD.

-K. Taub, 11/21/04

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Selenium

Drug Summary: Selenium is a mineral found in small quantities that is essential to the diet. Selenium contributes to the normal functioning of the immune system and the thyroid gland. It is the central element in glutathione peroxidase (GPx), an antioxidant enzyme that protects cells against the oxidative damage caused by peroxides and free radicals. (For more information on free radicals and antioxidants, click here.)

Because of its antioxidant role, selenium has been studied for its potential to protect the body from many degenerative diseases, including Parkinson’s disease and cancer. (For a comparison between Parkinson’s and HD, click here.) Selenium is thought to protect against cancer because a form of selenium from yeast was found to have caused cancer cells in test tubes and in animals to undergo apoptosis, or programmed cell death.

Selenium can be found in a variety of foods including brazil nuts, yeast, whole grains, and seafood. Plant foods in most countries are also major dietary sources of selenium. The Recommended Dietary Allowance (RDA) is the average daily dietary intake level that is sufficient to meet the nutritional requirements of nearly all healthy individuals in each life-stage and gender group. The RDAs for selenium in adults is 55 micrograms (mcg), for pregnant women it is 60 mcg, and for lactating (breast feeding) women it is 70 mcg. While selenium can be taken as a supplement, most healthy adults get enough from the diet alone. One brazil nut alone has 100 mcg, an egg has 12 mcg, and a slice of whole wheat bread has 11 mcg of selenium.

selenium-01

People who eat foods grown primarily on selenium-poor soils are at risk for deficiency, but selenium deficiencies are rare in Western countries. However, studies have shown that the amount of selenium found in the blood decreases significantly with age and that decreased amounts of selenium might be a risk factor for dementia.

Research on selenium

Santamaría, et al. (2003) recognized that in neurodegenerative diseases such as HD, oxidative stress and free radicals contribute to the degeneration of nerve cells. In order to study these effects and a possible treatment, these researchers gave rats a substance called quinolinic acid (QUIN). QUIN has traditionally been used to produce a model of HD in rats and primates because it mimics what the nerve cells of someone with HD would look like. QUIN causes damage to nerve cells by producing free radicals and causing oxidative stress. This is similar to what occurs in HD: damaged mitochondria produce free radicals, which contribute to the progression of the disease. Researchers can then study the effects of different substances on these cells.

In this study, researchers at the National Institute of Neurology in Mexico City, Mexico tested how selenium affected the QUIN rats. They did this by studying the effects of selenium both in vitro and in vivo. The in vitro studies looked at the brain cells directly (outside of the body, after death), while the in vivo studies look at the effects on the bodies of the living rats as a whole. The researchers measured the activity of the enzyme GPx in the cells because it depends on selenium for its antioxidant properties. They also looked at the physical behavior of the rats. To determine the degree of damage, the researchers examined the rat brains and counted samples for how many nerve cells were preserved and how many were damaged.

Because of its antioxidant effects, selenium was able to reduce toxicity caused by QUIN in rats. Different concentrations were found to be effective in different parts of the brain, but selenium specifically reduced the damage caused by QUIN in the and striatum and and hippocampus. The animals that were given QUIN alone had nerve cells that were very damaged; many of these nerve cells died. The animals that were given QUIN and then treated with selenium had only a few sick nerve cells and most were healthy. Selenium decreased nerve cell degeneration by 70%. As expected, the presence of selenium increased GPx activity, most likely helping to reduce the toxic effects on the nerve cells.

Rats treated with selenium did not differ in bodyweight significantly compared to rats not receiving treatment. Moreover, an equal number of rats died in the treated and non-treated groups (two in each). Because of these results, the researchers concluded that this level of selenium does not cause any harmful side effects in rats.

Since selenium was found to protect against QUIN-related damage, and QUIN causes damage similar to that present in HD, treatment with selenium could possibly slow the progression of Huntington’s disease.

Zafar, et al. (2003) studied the effects of selenium on protecting nerve cells in the brains of rat models of Parkinson’s disease. Damage to nerve cells caused by free radicals and oxidative stress contributes to the progression of both Parkinson’s and Huntington’s diseases.

The researchers gave rats selenium in the chemical form of sodium selenite for seven days before inducing Parkinson’s-like symptoms. They were then tested for a variety of things including antioxidant activity and behavioral effects.

Rats treated with selenium were found to have greater antioxidant activity compared to those not treated. In the physical tests, selenium treatment was found to significantly lessen the harmful effects of Parkinson’s on the rats. They were less prone to circling around, had better muscle coordination, and wasted less time in traveling a specific distance.

These results confirm the fact that selenium plays an important role in decreasing oxidative stress. This study and others suggest that selenium may be helpful in treating neurodegenerative diseases such as Parkinson’s and HD.

For further reading

  1. Santamaría, et al. Protective effects of the antioxidant selenium on quinolinic acid-induced neurotoxicity in rats: in vitro and in vivo studies. 2003. Journal of Neurochemistry 86(2): 479-488. Online.
    This article presents the research findings of a study of selenium in QUIN-treated rats. It is highly technical and meant for a scientific audience.
  2. Wilkins, Joanna. Selenium. 2013. A Healthy Me. Online.
    This is a very informative web page that explains the importance of selenium and how to get enough of it.
  3. Zafar, et al. Dose-dependent protective effect of selenium in rat model of Parkinson’s disease: neurobehavioral and neurochemical evidences. 2003. Journal of Neurochemistry 84(3): 438. Online.
    This article presents the research findings of a study of selenium in a rat model of Parkinson’s disease. It is highly technical and meant for a scientific audience. While it does not directly pertain to HD the findings are important because both diseases involve nerve cell death related to oxidative damage.

-K. Taub, 11/21/04

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Coenzyme-Q10

altered

Huntington’s Disease (HD) is associated with a genetic mutation that results in an expanded polyglutamine chain in the huntingtin protein. In HD, huntingtin becomes a misfolded protein, which can cause many problems for the nerve cell. Scientists have not yet found a straightforward way to explain how a single genetic mutation can lead to the complex symptoms of HD. It is thought that misfolded huntingtin damages the nerve cell in many different ways.

One proposed mechanism suggests that misfolded huntingtin damages an organelle in the nerve cell called the mitochondrion. Mitochondria are important because they help the cell produce energy and regulate the number of free radicals in the cell. When the mitochondria are not working correctly, oxidative damage occurs in the cell because there are too many free radicals. This is thought to contribute to nerve cell death in HD. Therapies that reduce the amount of free radicals in the nerve cell might prevent some HD symptoms.

One potential treatment to reduce free radicals involves a molecule called coenzyme-Q10, which is naturally produced throughout the body. It plays a role in the electron transport chain and helps produce ATP, the cell’s major source of energy. (For more information on coenzyme-Q10 and the electron transport chain, click here.) Coenzyme-Q10 also reduces oxidative damage by interacting directly with free radicals, inactivating them so they cannot damage the cell. The level of coenzyme-Q10 in the brains of HD patients is lower than normal, potentially reducing the ability of affected nerve cells to manage free radicals that accumulate. Because the nerve cells can no longer deactivate all of the free radicals, they become damaged. Drug supplements may be useful to raise the level of coenzyme-Q10 in the brain and prevent the damage caused by free radicals.

Initial Findings on Coenzyme-Q10

This section describes several studies that tested the effects of coenzyme-Q10 treatment in both humans and mice. The studies show that coenzyme-Q10 is at least somewhat effective in delaying the symptoms of HD and increasing survival, and could serve as a potential treatment for HD and other neurodegenerative disorders.

Ferrante, et al. (2002) tested coenzyme-Q10 as a treatment in a mouse model of late stage HD. In this study, they found that coenzyme-Q10 given to transgenic mice increased survival by 14.5%. Human trials did not show that coenzyme-Q10 significantly affects survival, so it was thought that coenzyme-Q10 would not make an effective treatment for HD patients. Later research that studied the effects of coenzyme-Q10 in human patients with neurodegenerative disorders similar to HD, such as Parkinson’s disease and ALS, showed that higher doses of coenzyme-Q10 than those previously used produced more promising results. The patients had a significantly declined rate of nerve cell death and symptom progression. (For more information on other neurodegenerative and related diseases, click here.)

The Huntington Study Group (2001) conducted a clinical trial involving 347 early-stage HD patients at various sites in the United States and Canada. The trial was done to test the efficacy of coenzyme-Q10 and remacemide, an anti-glutamate drug. The participants were monitored between July 1997 and June 1998 and were assigned to four different treatments:

The primary measure of the drug’s effectiveness was change in Total Functional Capacity (TFC) of the people with HD. TFC is a standardized scale used to assess capacity to work, handle finances, perform domestic chores and self-care tasks, and live independently. The TFC scale ranges from 13 (normal) to 0 (severe disability). The average TFC score of the participants before the study was 10.2. None of the treatments significantly altered the decline in TFC. However, subjects treated with coenzyme-Q10 showed a delayed decline in the TFC compared to subjects who were not treated translating into approximately one more year of independence for people with HD. The supplement was well-tolerated by the study participants and showed no adverse effects on the participant’s other capacities. No changes in the decline in TFC relative to the placebo group were seen in the participants treated with remacemide. However, improvements in chorea were observed. (For more information on remacemide, an anti-glutamate drug, click here.)

The researchers concluded that although there was a trend toward slowing of the progression of HD with coenzyme-Q10 treatment, the effects were not large enough to recommend coenzyme-Q10 as a treatment for early HD. In part, this is because the financial costs of coenzyme-Q10 are considerable. Since coenzyme-Q10 is a nutritional supplement, it is worth remembering that it is not subjected to the same quality and content regulations as pharmaceutical drugs are. Different brands and formulations of coenzyme-Q10 may differ chemically or may contain additives, and there is little information about how these different contents might affect a person with HD. Finally, it should be emphasized that the findings of this study are not applicable to people at risk for HD, or for people at the intermediate or advanced stages of HD.

Nevertheless, the results of the study suggest that therapies that affect the energy supply in cells can affect the course of HD. Additional studies are called for to identify dosage effects and to study effectiveness for people in different stages of HD.

Koroshetz, et al. (1997) treated 18 early-stage HD patients with oral coenzyme-Q10 for 2 to 8 weeks. The patients were recruited from the Massachusetts General Hospital HD Unit and were all able to walk, with half of them still working. Brain lactate level was used as the criteria to measure the effectiveness of the supplement. They hypothesized that treatment with coenzyme-Q10 could increase the efficiency of the respiratory chain, and consequently, lower lactate levels. (For more on lactate, click here.)

The researchers discovered that upon treatment with coenzyme-Q10, the participants experienced significant decreases in brain lactate levels. Lactate levels reversed back to their original levels following withdrawal of therapy, indicating that the findings were indeed due to coenzyme-Q10 treatment. This study supports the theory that coenzyme-Q10 could increase the amount of energy available in cells, perhaps by increasing the efficiency of the respiratory chain.

New Discoveries

Scientists have been testing coenzyme-Q10 recently in order to discover the optimal dosage and preparation of the supplement.

Smith, et al. (2006) tested higher doses of coenzyme-Q10 with a late stage HD mouse model. This model demonstrated some features of human HD, including progressive loss of motor function. They also compared two commercially-available preparations of coenzyme-Q10, one from a company called Tishcon and one from a company called Chemco. The researchers administered different doses of each substance, seeking an optimal dosage to treat HD.

Results showed that higher doses of coenzyme-Q10 significantly slowed the progression of HD symptoms, such as declining motor performance and grip strength. Smith tested several different doses and found that for the Chemco formulation of coenzyme-Q10, 5000 mg/kg/day was the most effective dosage in extending the lifespan of HD mice. Tishcon coenzyme-Q10 extended survival by a greater amount and at a lower dosage of 1000 mg/kg/day. Moreover, HD mice treated with higher doses of coenzyme-Q10 did not lose as much weight, have as much nerve cell death, or form as many huntingtin aggregates as untreated HD mice. Administering high doses of coenzyme-Q10 to mice in the form of a pellet significantly raised the level of coenzyme-Q10 in their bloodstream and nerve cells. These findings suggest that oral administration of the drug would be effective. Finally, high doses of coenzyme-Q10 also significantly reduced the amount of OH8dG (8-hydroxydeoxyguanosine) in the brain. OH8dG is a molecule that appears in unusually high concentrations in the brains of HD patients, and is associated with oxidative stress in the nerve cell. In summary, this study shows that high doses of coenzyme-Q10 can prevent some motor symptoms, prolong lifespan, and reduce oxidative stress and nerve cell death in HD mice. However, doses that are too high are less effective, possibly because of side effects.

In comparing the effectiveness of two commercially available coenzyme-Q10 preparations, the study found that the supplement produced by Tishcon was 5 times more effective in extending lifespan than that produced by Chemco. More of the coenzyme-Q10 in the Tishcon pellet was absorbed into the bloodstream in comparison to the Chemco pellet. It is important to remember that coenzyme-Q10 is a nutritional supplement and can be bought in many different prepared forms. Nutritional supplements are not regulated by Food & Drug Administration (FDA) guidelines Often there is little standardization and poor quality control for these supplements. Little is known about how each of these prepared forms may affect HD patients differently, and so more comparative studies are needed.

Current Studies

The Cure HD Initiative (CHDI), a nonprofit drug development research organization for HD, has recently begun to work on creating treatments for HD using coenzyme-Q10. On August 2, 2006 CHDI announced a partnership with Edison Pharmaceuticals, Inc. Edison is a small company that specializes in drug development for diseases related to problems with mitochondria, oxidative damage, and energy levels in the cell. This partnership will be an opportunity for Edison to specifically focus on oxidative damage in HD. The partnership hopes to develop a second generation coenzyme-Q10 molecule to be used to treat HD. Scientists at Edison Pharmaceuticals will contribute their expertise in the biology and pharmacology of free radicals and oxidative damage, while members of CHDI Foundation will contribute their expertise in HD and drug development.

In early 2009, the Huntington Study Group received funding from the NIH to test safety and tolerability of coenzyme-Q10 in individuals who have tested positive for HD but do not show any motor signs of HD. The study is called PREQUEL (Study in PRE-manifest Huntington’s disease of coenzyme Q10 (UbiquinonE) Leading to preventive trials). The study was conducted at 10 clinical sites throughout the nation and was the first therapeutic research study in pre-manifest HD. The results of this study were published in late 2017 and can be seen here.

Summary

Numerous studies conducted in the past decade show that coenzyme-Q10 may prove to be an effective drug in treating HD since it can enhance ATP production. Studies in the past have shown it to significantly delay HD symptoms and increase survival, especially in mice. However, side effects are still common, with gastrointestinal upset being the most common side effect in both human and animal trials. The PREQUEL clinical trial will study the effectiveness of coenzyme-Q10 in delaying the onset of HD in individuals who do not yet exhibit the symptoms of the disease. Overall, coenzyme-Q10 holds promise as a supplement to treat HD.

For further reading

  1. Smith KM, Matson S, Matson WR, Cormier K, Del Signore SJ, Hagerty SW, Stack EC, Ryu H, Ferrante RJ. Dose ranging and efficacy study of high-dose coenzyme Q10 formulations in Huntington’s disease mice. Biochimica et Biophysica Acta 1762 (2006) 616–626.
    This study demonstrates that larger doses of coenzyme-Q10 are more effective in treating HD mice. A fairly technical research article.
  2. Koroshetz, et al. “Energy Metabolism Defects in Huntington’s Disease and Effects of Coenzyme Q sub 10”. Annals of Neurology. 1997, Feb; 41(2): 160-5.
    This study used oral supplements of coenzyme-Q10 to raise energy metabolism in nerve cells and lower lactate levels in human HD patients. A technical research article.
  3. The Huntington Study Group. “A randomized, placebo-controlled trial of coenzyme Q10 and remacemide in Huntington’s disease.” Neurology. 2001, Aug 14; 57(3): 397-404.
    This experiment indicates that the use of remacemide and CoQ10 was not efficient enough to warrant study as a treatment. A fairly technical research article.
  4. Ferrante RJ, Andreassen OA, Dedeoglu A, Ferrante KL, Jenkins BG,Hersch SM, Beal MF. “Therapeutic effects of coenzyme Q10 and remacemide in transgenic mouse models of Huntington’s disease.” The Journal of Neuroscience, March 1, 2002, 22(5):1592-1599
    This article is the first study from the Ferrante group about treating mice with low doses of coenzyme-Q10. A technical article.

-A. Zhang, 6-8-10

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Ginkgo Biloba

Drug Summary: Ginkgo biloba has been shown to have antioxidant and anti-inflammatory properties. Because free radicals and inflammation are believed to be factors involved in the progression of HD, Ginkgo biloba may help in alleviating the symptoms of HD. However, no studies have been done yet on the effects of Ginkgo biloba on people with HD. Instead, preliminary research is being conducted to test the effects of Ginkgo biloba on diseases that also involve inflammation such as Alzheimer’s Disease.

Fig K-1: Gingko Biloba

Ginkgo biloba (G. biloba) is a type of tree that has existed for over 200 million years. Medicinal extracts are made from the dried leaves of the tree and have been used for 5000 years in traditional Chinese medicine for various purposes. The extract has been shown to have protective effects against mitochondrial damage and oxidative stress. Figure K-1 shows an image of Ginkgo leaves.

There are different variants of Ginkgo biloba extracts available on the market today. Among them are EGb 761, LI 1379, and Chinese Ginkgo extract ZGE. These extracts differ in their extraction process as well as composition. The principal constituents of Ginkgo biloba extract include flavonoids, terpenoids (ginkgolides and bilobalide) and different organic acids. The standardized extract usually contains 24% flavonoids and 6% terpenoids. Let us review the different biological activities of these components.

Flavonoids

The flavonoids contribute to Ginkgo’s antioxidant properties. They have been found to reduce the levels of free radicals, which are highly reactive molecules with unpaired electrons. One way by which flavonoids protect the cell is by reducing cell membrane lipid peroxidation. Lipid peroxidation is defined as the process whereby free radicals “steal” electrons from the lipids in our cell membranes, resulting in cell damage and increased production of free radicals. Lipids include molecules such as fatty acids, cholesterol, and other related compounds. As antioxidants, the flavonoids neutralize the free radicals in our cell, lowering the levels of free radicals available for lipid peroxidation. (For more on free radicals, click here.)

Terpenoids

The other major components of ginkgo extract are the terpenoids. The terpenoids include bilobalide and the ginkgolides A, B, C, M, and J.

Bilobalides are closely related in structure to the ginkgolides. Bilobalides have been proposed to have protective effects on nerve cells and on the nervous tissue through their role in motor nerve cell regeneration.

The ginkgolides inhibit the activity of the compound known as platelet-activating factor (PAF). PAF reduces inflammation by increasing permeability of blood vessels and contracting various involuntary muscles such as those in airways. (For more on inflammation, click here). PAF activation is also associated with the aggregation of platelets, which aid in blood clotting. Ginkgo supplementation has therefore been associated with anti-inflammatory effects as well as reduced blood clotting.

Fig K-2: Summary of the Effects of Gingko Biloba

Based on these biological properties of its constituent compounds, Ginkgo biloba supplementation may result in antioxidant, anti-inflammatory, and neuroprotective effects. Although the primary cause of HD is still unknown, prominent hypotheses center around injury caused by free radical oxidation damage and chronic inflammation. Given its antioxidant and anti-inflammatory properties, Ginkgo biloba may therefore be beneficial to people with HD. To date, no studies have been done regarding Ginkgo biloba’s effects on people with HD; however, some studies have investigated the effects of Ginkgo biloba on individuals with Alzheimer’s Disease (AD). AD is associated with disease mechanisms that are similar to HD, and so it is possible that some of these findings may be useful for future HD research.

In most of the clinical studies of Ginkgo biloba and Alzheimer’s patients, no serious side effects were noted. However, some case studies reported that people taking Ginkgo experience prolonged bleeding times due to its inhibition of PAF. Two case reports of hemorrhage were reported by people who were taking Ginkgo. Compounds such as aspirin and warfarin that are known to inhibit blood clotting have been found to result in bleeding complications when taken with Ginkgo. However, as of this writing (November 2001), the frequency and magnitude of bleeding complications with Ginkgo supplementation is still unclear.

Research on Ginkgo Biloba

Fig K-3: Effect of Gingko Biloba on Nerve Cells Exposed to H2O2

Oyama, et al. (1996) hypothesized that Ginkgo biloba treatment would have beneficial effects on cells exposed to the free radical hydrogen peroxide. The researchers first exposed nerve cells to hydrogen peroxide to see what happens to the cells after administration of hydrogen peroxide. They discovered that prolonged exposure to hydrogen peroxide resulted in the death of many nerve cells. To test the protective effects of Ginkgo biloba, nerve cells were treated with Ginkgo biloba extract for 1 hour before adding hydrogen peroxide. Ginkgo biloba treatment was found to increase the number of surviving nerve cells after hydrogen peroxide exposure. The researchers then compared the effects of Ginkgo biloba treatment 1 hour before, immediately after, and 1 hour after cells were exposed to hydrogen peroxide. They discovered that although Ginkgo biloba had protective effects when applied either immediately after or 1 hour after hydrogen peroxide exposure, the beneficial effects were weaker than that of treatment before hydrogen peroxide exposure. Figure K-3 shows a graph depicting the effects of Ginkgo biloba treatment.

Studies by other researchers showed that Ginkgo biloba extract exerted neuroprotective effects on nerve cells exposed to the hydroxyl radical, another type of free radical. The extract also had a scavenging effect on superoxide anions, which are also free radicals. Together with the results of the current study, it is believed that Ginkgo biloba may have neuroprotective effects on nerve cells suffering from cell damage induced by free radicals. Because free radical damage is hypothesized to play a role in the progression of HD, Ginkgo biloba treatment on HD cells may have beneficial effects.

Le Bars, et al. (1997) examined the effects of a particular extract of Ginkgo biloba on people with Alzheimer’s Disease (AD). Damage by free radicals and inflammation has been implicated as one of the mechanisms by which AD cells die. The researchers hypothesized that treatment with an antioxidant and anti-inflammatory molecule such as Ginkgo biloba may have beneficial effects on people with AD.

The extract the researchers used in this study was EGb 761, which is a particular extract of Ginkgo biloba used in Europe to alleviate symptoms associated with several cognitive disorders. Participants included 309 demented patients with mild to moderately severe cognitive impairment caused by Alzheimer’s Disease.

The participants were randomly assigned to treatment with Egb (120 mg/day) or a placebo. The trial was conducted for 52 weeks (13 months) in 6 research centers in the United States. The researchers assessed changes in 3 areas: cognitive impairment, daily living and social behavior, and overall psychopathology.

The results of the study indicated that Ginkgo biloba treatment was able to produce beneficial effects in 2 of the 3 outcomes: cognitive impairment and daily living and social behavior. No differences in overall psychopathology between the treated and placebo group were observed.

The results of this study indicated that Ginkgo biloba treatment may slow the deterioration of some people with AD. However, the researchers stated that more trials should be conducted to examine the effects of various dosages on slowing deterioration caused by AD to ensure that the proper dosage is administered. Furthermore, the exact mechanism of action by which Ginkgo biloba exerts its effects remains unknown. More research is also needed to reveal these mechanisms, in order to better explore the full therapeutic potential of Ginkgo biloba.

Mahdy et al. (2011) found that ginkgo biloba might repair some of the neurological problems caused by a toxin, 3-Nitropropionic acid (3-NP). When injected into the brains of mice, 3-NP mimics the effects of HD: it causes many of the biological and behavioral changes that are seen in people with HD. But mice that were treated with both 3-NP and ginkgo biloba showed milder neurodegenerative problems than those treated with 3-NP alone. Several biochemical changes that occur upon exposure to 3-NP were mitigated in animals that were treated with ginkgo biloba. Authors suggest that ginkgo biloba’s antioxidant properties, antiapoptotic effects, and improvement of energy metabolism were responsible for the neuroprotective effects.

For further reading

  1. Oyama, et al. “Ginkgo biloba extract protects brain neurons against oxidative stress induced by hydrogen peroxide.” Brain Research. 1996; 712:349-352.
    This study reported that G. biloba was able to protect nerve cells exposed to various free radicals.
  2. LeBars, et al. “A Placebo-Controlled, Double-Blind, Randomized Trial of an Extract of Ginkgo Biloba for Dementia.” JAMA. 1997; 278(16): 1327-1332.
    This study reported that G. biloba treatment resulted in cognitive and behavioral improvements in people with Alzheimer’s Disease.
  3. Mahdy HM, Tadros MG, Mohamed MR, Karim AM, Khalifa AE. The effect of Ginkgo biloba extract on 3-nitropropionic acid-induced neurotoxicity in rats. Neurochem Int. 2011 Jul 31. This technical study reported that Ginkgo biloba treatment in mice relieved some of the problems caused upon injection of 3-NP, a chemical that mimics HD

-E. Tan, 11-22-01; Updated by P. Chang, 5/6/03; updated by M. Hedlin, 8/11/11

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TUDCA: Tauroursodeoxycholic Acid

What in the world do black bears have to do with treating Huntington’s disease? Believe it or not, a compound found in large quantities in the bile (a digestive fluid) of black bears may help prevent the death of brain cells in people with HD. (TUDCA) Tauroursodeoxycholic acid is also found in small quantities in human bile. It is already being used to treat a liver disease in humans.

One complication that leads to the progression of Huntington’s disease is the death of nerve cells in certain areas of the brain. There are many theories as to what causes these cells to die. At least part of the story involves the cells undergoing apoptosis, or programmed cell death. (For more information on cell death and HD click here.) Scientists are working hard to find out both what causes nerve cells to initiate apoptosis as well as how to prevent it. This chapter discusses TUDCA, a drug that may help prevent nerve cell death.

What is the theory behind TUDCA?

A part of the cell that is especially involved in apoptosis is the mitochondrion (plural: mitochondria). Mitochondria are responsible for providing energy to the cell. If they are prevented from carrying out their jobs, the cell and its parts will not be able to perform all of their necessary functions and the cell will die. (For more information on energy and HD click here.) Mitochondria release and activate certain molecules that play a role in initiating apoptosis. When something perturbs the mitochondrial membrane, the mitochondria release a molecule called cytochrome c.

Cytochrome c then recruits enzymes called caspases to help initiate a cascade of events leading to apoptosis. Caspases are a key element in this process and are especially relevant to people with HD. The altered huntingtin protein resulting from the HD allele has more glutamines than the normal huntingtin protein. In people with HD, caspases work by cutting the altered huntingtin protein into little fragments. These fragments, in turn, activate more caspases and a vicious cycle begins. The caspases go on to participate in the cascade leading to apoptosis, while the huntingtin fragments enter the nucleus and form harmful protein aggregations called neuronal inclusions (NI). Both of these elements – many activated caspases and huntingtin fragments – contribute to a greater likelihood of early cell death in people with HD.

Much of what is known about TUDCA comes from studies done on liver cells. These studies found that TUDCA is able to prevent apoptosis and protect mitochondria from cellular elements that would otherwise interfere with energy production. One of these elements is a molecule called Bax. When Bax is transferred from the cytosol to the mitochondria, it aggravates the mitochondria s membrane, causing the membrane to release cytochrome c and initiate the apoptosis pathway. TUDCA plays an important role in preventing Bax from being transported to the mitochondria. It therefore protects the mitochondrial membrane, as well as preventing the mitochondria from activating caspases. The exact mechanism of how TUDCA works is unknown, but it has to do with protecting the mitochondria. By intervening at an early point in the apoptosis pathway and preventing the transfer of Bax to the mitochondria, TUDCA has the potential to save certain kinds of cells from early death.

How can TUDCA help treat HD?

A group of researchers tested TUDCA in animal models of HD to see if the above theory could translate into practice. In the mouse model of HD, the effects of TUDCA were observed in three ways. First, administering TUDCA helped nerve cells in the striatum both by preventing apoptosis and decreasing degeneration. (To learn more about parts of the brain affected in HD, click here.) In both people and mice with HD, the proteins formed from the HD allele tend to clump together and clog up the nucleus by forming aggregations called neuronal inclusions (NI). Second, the mice that were treated with TUDCA had fewer and smaller NIs compared to untreated mice. Finally, at the clinical level, treated mice showed decreased motor deterioration and other HD signs as compared to untreated mice.

What is the future of TUDCA in treating HD?

Animal studies using TUDCA to treat HD are showing some initial promise. The next step is to obtain funding and begin clinical trials to test the drug on humans with HD. Once researchers overcome this hurdle, this traditionally lengthy process may be sped up by a few key factors. First, since TUDCA is produced (albeit in very small amounts) in the human body, there should be virtually no side effects in using it as a drug. Second, it can cross the blood-brain barrier, which is usually a major obstacle to drug delivery in the central nervous system.

Delivering a drug involves getting it into the body as well as to the exact place where it will take action. Finally, TUDCA is already being used to treat a type of liver disease, so the U.S. Food and Drug Administration deems it safe for at least one particular use. Because of its neuroprotective effects, TUDCA may also be used to treat other conditions such as Alzheimer’s, Parkinson’s, and ALS. Despite all of these positive aspects of the drug, TUDCA has yet to be tested for its effects on humans with HD.

For further reading

  1. Bile acid inhibits cell death in Huntington’s disease. 2002. Huntington Society of Canada. Online.
    This article summarizes the research findings of TUDCA in the HD mouse model. It also provides a great low-tech explanation of apoptosis.
  2. Bile may treat Huntington’s. 2002. BBC News. Online.
    This short article concisely summarizes the research findings of TUDCA in the HD mouse model.
  3. Keene, C.D. et al. Tauroursodeoxycholic acid, a bile acid, is neuroprotective in a transgenic animal model of Huntington’s disease. 2002. Proceedings of the National Academy of Sciences of the U.S.A. 99(16): 10671-10676. Online.
    These are the published findings of the original study of TUDCA in the mouse model of HD. It is highly technical and only meant for a scientific audience.

-K. Taub, 11/14/2004

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Carnitine

Drug Summary: Carnitine acts to facilitate the entry of fatty acids into the mitochondria. Once these fatty acids are in the mitochondria, they can be used to produce energy. Because inefficient energy production is believed to contribute to the progression of HD, carnitine therapy could result in increased energy production, and could possibly delay HD progression.

essential

Carnitine as an energy buffer

Fig J-6: Food Breakdown

The food we eat is broken down into different sub-units. Carbohydrates are broken down into simple sugars, proteins into amino acids, and fats into fatty acids. Figure J-6 shows a diagram depicting an overview of the breakdown of the food we eat.

This section will focus on the processes by which fatty acids are used to supply our body’s energy.

Fig J-7: Fatty Acid Metabolism

Fatty acids must first be activated in the outer mitochondrial membrane before they can be used in the mitochondria. An enzyme called acyl-CoA synthetase is responsible for the activation of fatty acids. Once activation occurs, the fatty acids are transformed into molecules called acyl-CoA. Figure J-7 shows the reaction that takes place when fatty acids are activated.

Fig J-8: The Entry of Acyl-CoA into the Mitochondria

Long chain acyl-CoA molecules do not readily move through the mitochondrial membrane, and so a special transport chain is needed. Activated fatty acids in the form of acyl-CoA are carried across the mitochondrial membrane by carnitine. Once the acyl-CoA is in the mitochondria, carnitine is recycled back to the outer mitochondrial membrane to be reused again as an acyl-CoA transporter. Figure J-8 shows how carnitine transports the acyl-CoA molecule into the mitochondria.

Once inside the mitochondria, the acyl-CoA molecules will undergo a series of breakdown reactions collectively known as beta-oxidation. The most important end product of beta-oxidation is acetyl-CoA, a key molecule in the cell’s energy production. Acetyl-CoA can then enter the Krebs Cycle (one of the steps in energy metabolism) and lead to the production of ATP. (For more on the Krebs Cycle, click here.)

Aside from being an essential component of fatty acid metabolism, carnitine may contribute to normal cellular functioning by “stabilizing” the membrane against damage from harmful free radicals. Free radicals are by-products of energy metabolism and are reactive molecules that cause various cell damages.

As described in other chapters, impaired energy metabolism and damage by free radicals are two disease mechanisms believed to play a role in the progression of HD. Since carnitine is an acyl-Co-A transporter, scientists hypothesize that carnitine supplementation may increase metabolism efficiency by increasing the amounts of fatty acid available for processing in the mitochondria, thereby slowing HD progression. In addition, carnitine’s potential ability to decrease free radical damage also makes it a possible treatment for people with HD.

Various studies have investigated carnitine’s potential for improving conditions caused by mitochondrial dysfunction and impaired energy metabolism. In a recent (2000) clinical trial studying the potential efficacy of acetyl-L-carnitine (ALC), the active form of carnitine in the body, on slowing the rate of neurological decline in early-onset AD, treatment failed to affect the rate of decline. Research on the efficacy of ALC in treating mouse models of HD, however, have shown positive results. Below is a summary of some of the recent research done on acetyl-L-carnitine.

Research on Carnitine

Virmani, et al. (1995) studied the effects of acetyl-L-carnitine (ALC) in cells exposed to mitochondrial toxins (poisons). Exposure to mitochondrial toxins decreases metabolism efficiency. The researchers hypothesized that if ALC truly increases metabolism efficiency, then ALC treatment to cells exposed to mitochondrial toxins will show increased metabolism efficiency compared to cells exposed to toxins that are not treated with ALC.

Nerve cells of fetal rats were exposed to various mitochondrial toxins such as FCCP, Rotenone, NaCN, and 3-NP. All these toxins act to decrease metabolism efficiency by interfering with proteins in the mitochondria that are involved in energy metabolism.

Exposure to the toxins caused an increase in lactate levels and a decrease in mitochondrial activity. The increased lactate levels indicated that exposure to toxins decreased energy metabolism.

Part of the effect of ALC may also be related to the decrease in free-radical formation from the damaged mitochondria. Experiments by other scientists have shown that ALC protected rat nerve cells from damage caused by exposure to the free radical hydrogen peroxide.

Hagen, et al. (1998) investigated the effects of ALC in aging rats. Studies have reported that there is a decline in mitochondrial energy metabolism in normal aging. Researchers believe that mitochondrial DNA, proteins, and fats are continually damaged during our lifetime, resulting in a decline in mitochondrial function as we age. Furthermore, mutations accumulated in genes that encode the proteins needed by the mitochondria could alter the components of the electron transport chain, leading to inefficient electron transport. Inefficient electron transport is known to cause an increase in the production of free radicals, which causes further damage to the cell. Thus, mitochondrial dysfunction is speculated to be a contributing factor of the aging process.

Carnitine levels have also been found to decrease with age, depriving mitochondria of fatty acids for oxidation. The researchers found that treatment of aging rats with ALC increased cellular respiration and reversed the age-associated decline of certain molecules that contribute to the maintenance of the structure and function of the mitochondrial membrane.

Furthermore, ALC treatment improved the motor abilities of both young and old rats. ALC supplementation significantly restored overall activity levels in old animals, suggesting that decline in activity may be the result of mitochondrial damage. However, while ALC increased energy metabolism, it also led to an increase in the production of free radicals. This may indicate that while ALC can increase the supply of energy in cells, it cannot mask the age-associated loss of efficiency in the electron-transport chain. Long-term administration of ALC to animals must be done to determine whether it may improve mitochondrial dysfunction that occurs during the aging process and in pathological conditions such as HD.

Thal, et al. (2000) A 1-year, multicenter, double-blind, placebo-controlled, randomized trial was conducted. Two hundred twenty nine Alzheimer’s Disease patients ages 45 – 65 were enrolled in the study. They were treated with ALC (1 g tid) or placebo. Primary outcome measures were the Alzheimer’s Disease Assessment Scale-Cognitive Component and the Clinical Dementia Rating Scale.

Two-hundred twenty-nine patients were enrolled and randomized to drug treatment, with 117 taking placebo and 112 taking ALC. There were no significant differences between the two groups at baseline. For the primary outcome measures, there were no significant differences between the treatment groups on the change from baseline to endpoint in the intent-to-treat analysis. There were no significant differences in the incidence of adverse events resulting from treatment.

Overall, in a prospectively performed study in young-onset AD patients, ALC failed to slow decline. Less decline was seen on the MMSE in the completer sample only, with the difference being mediated by reducing decline in attention.

Vamos et al. (2010): A study of HD mice found that high doses of carnitine (45 mg/kg every day) caused improvements in HD mice. The treated HD mice lived 14.9% longer than untreated HD mice, and had improvements in motor activity: they moved more, and were faster. Furthermore, when the researchers performing the study looked at the brains of the treated HD mice, they found fewer neuronal inclusions, the clumps of mutant huntingtin. This suggests that carnitine is neuroprotective in HD mice, and might help treat HD.

For further reading

  1. Virmani, et al. “Protective action of L-carnitine and acetyl-L-carnitine on the neurotoxicity evoked by mitochondrial uncoupling or inhibitors.” Pharmacological Research. 1995; 32: 383-89.
    This article reports that carnitine can improve energy production initially inhibited by various toxins.
  2. Hagen, et al. “Acetyl-L-carnitine fed to old rats partially restores mitochondrial function and ambulatory activity.” Proc. Natl. Acad Sci USA 1998; 95: 9562-66.
    This article reports that carnitine treatment can lead to beneficial effects in aging rats.
  3. Thal, et al. “A 1-year controlled trial of acetyl-l-carnitine in early-onset AD.” Neurology. 2000 Sep 26;55(6):805-10
  4. For information on uncouplers and inhibitors, visit http://www.bmb.leeds.ac.uk/illingworth/oxphos/poisons.htm
    This page contains information on various mitochondrial toxins.
  5. For information on fatty acid oxidation, visit http://web.indstate.edu/thcme/mwking/fatty-acid-oxidation.html
    This page contains detailed, comprehensive information on fatty acid metabolism. Includes figures, structures of various lipid molecules, etc. Link to this page to learn more about carnitine, beta-oxidation, and how fats are used in our body.
  6. http://www.degussa-health-nutrition.com/degussa/html/e/health/eng/kh/l3.1.htm
    This page contains a good overview of fatty acids and fatty acid oxidation.
  7. Vamos E, Voros K, Vecsei L, Klivenyi P. Neuroprotective effects of L-carnitine in a transgenic animal model of Huntington’s disease. Biomed Pharmacother. 2010 Apr;64(4):282-6. Epub 2009 Oct 27. This technical paper describes the study of carnitine supplementation in HD mice.

-E. Tan, 9-22-01; Updated by P. Chang, 5-6-03, Updated by M. Hedlin 8-5-11

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Riboflavin

essential

Drug Summary: Riboflavin acts as an integral component of two coenzymes: FAD (flavin adenine dinucleotide) and FMN (flavin mononucleotide). These flavin coenzymes are critical for the metabolism of carbohydrates, fats, and proteins into energy. Because riboflavin is an important component of these flavin coenzymes, riboflavin supplementation is believed to increase the efficiency of energy metabolism in cells.

Riboflavin, also known as vitamin B2, is a water-soluble vitamin that is found naturally in the food we eat. Sources of riboflavin include organ meats (liver, kidney, and heart) and certain plants such as almonds, mushrooms, whole grain, soybeans, and green leafy vegetables.

In the body, riboflavin acts as an integral component of two coenzymes: FAD (flavin adenine dinucleotide) and FMN (flavin mononucleotide). A coenzyme is a molecule required for the activity of another enzyme. FAD and FMN are known as flavins since they are derived from riboflavin. These flavin coenzymes are critical for the metabolism of carbohydrates, fats, and proteins into energy. Specifically, FAD and FMN are involved in the activity of the electron transport chain, an essential component of energy metabolism that is known to be impaired in people with HD. (For more on metabolism, link to HD and Energy Metabolism).

Fig J-1: Role of NAD/NADH

In the electron transport chain, FMN is one of the components of complex I while FAD is involved in the activity of complex II. FAD acts as an electron carrier and takes part in both the Kreb’s Cycle and oxidative phosphorylation. It accepts electrons and is transformed into FADH2. FADH2 then transfers its electrons to complex II of the electron transport chain. For each pair of electrons from FADH2 passed along the electron transport chain, a number of ATP molecules are formed. FAD also affects enzymes that are responsible for the synthesis of other vital coenzymes such as NAD. Severe deficiencies in riboflavin can lower levels of coenzymes, leading to inefficient energy metabolism and consequent energy depletion. Figure J-1 shows the roles of FAD and FMN in the electron transport chain.

Impaired energy metabolism has been found to be associated with the progression of HD. Because of the role of riboflavin derivatives in the electron transport chain, scientists are looking into the possibility of riboflavin supplementation as a way of improving energy metabolism. Researchers hope that improving energy metabolism will slow or even stop the progression of HD. However, as of this time (October 2001), most studies done on riboflavin supplementation have concentrated on people with energy deficits due to mitochondrial disorders, rather than people with HD. Some of the disease mechanisms of these mitochondrial disorders are similar to those of HD. Because of these similarities, studies on people with mitochondrial disorders may be of interest to people with HD as well.

Research on Riboflavin

Bernsen, et al. (1993) evaluated the effects of riboflavin treatment in five (5) patients with mitochondrial myopathies. Mitochondrial myopathies are disorders often characterized by defects in the electron transport chain. Specifically, the participants in the study had a deficiency of Complex I, the largest of the electron transport chain enzymes.

Complex I removes electrons from NADH, an electron carrier, and passes them to ubiquinone. As mentioned above, complex I contains a flavin component, FMN, that is essential for the proper functioning of the complex. Riboflavin supplementation is hypothesized to improve the efficiency of the Complex I protein by increasing the concentrations of available FMN molecules in the cell.

Motor and muscle strength improvements, as well as lactate levels, were used by the researchers to measure the efficacy of riboflavin. Lactate levels are used by scientists as a measure of the efficiency of metabolism in the cell. In normal cells, a form of metabolism known as aerobic respiration is usually used for energy production. If aerobic respiration is impaired, such as in the case of people with HD and with mitochondrial disorders, cells switch to anaerobic respiration, a less efficient form of metabolism. Lactate is a by-product of anaerobic respiration and lactate levels indicate which form of metabolism is the primary form the cells use for its energy needs. High levels of lactate indicate low metabolism efficiency in that cells are “forced” to use anaerobic respiration. On the other hand, low levels of lactate indicate high metabolic efficiency in that aerobic respiration is the primary form of energy production.

Before treatment, the participants suffered from high lactate levels, exercise-induced weakness, muscle atrophy and other motor problems. Treatment with riboflavin resulted in varying degrees of improvement in three of the five patients. Two patients experienced no improvement, and the remaining three patients with improved conditions showed normalized lactate levels and improved muscle strength and motor abilities.

Ogle, et al. (1997) reported the effects of riboflavin in a case involving a female patient with a myopathy caused by Complex I deficiency. The patient had a mutation that caused instability in the assembly of the complex I protein and consequent deficiency in complex I activity. She suffered from frequent falls and could no longer climb the stairs due to muscle weakness. She also showed increased lactate levels.

Treatment with riboflavin during a 3-year period showed normalization in blood lactate levels. The participant was also able to walk longer distances and to rise from the floor without difficulty. An obvious worsening of symptoms occurred during one period when the participant failed to take riboflavin. Exercise tolerance deteriorated, muscle tone worsened, and lactate levels rose during the period when riboflavin was not used. The symptoms observed when riboflavin was not used suggest that the previous improvements were associated with riboflavin supplementation.

This case suggested that riboflavin may have beneficial effects on people with Complex I deficiencies.

For further reading

  1. Bernsen, et al. “Treatment of complex I deficiency with riboflavin.” Journal of the Neurological Sciences. 1993; 118: 181-87.
    This article reports that riboflavin treatment may have beneficial effects in some people with mitochondrial myopathies.
  2. Matthews, et al. “Neuroprotective Effects of Creatine and Cyclocreatine in Animal Models of Huntington’s Disease.” The Journal of Neuroscience. 1998, 18: 156-163.
    This article reports the Creatine supplementation results in decreased nerve cell lesions often found in cells with energy depletion.
  3. Ogle, et al. “Mitochondrial myopathy with tRNA sup Leu(UUR) mutation and complex I deficiency responsive to riboflavin.” Journal of Pediatrics. Januargy 1997; 130(1): 138-145.
    This article reports that riboflavin supplementation may improve the conditions of people with Complex I deficiency.
  4. Riboflavin available online
    Contains information about the possible beneficial effects of riboflavin on a variety of diseases.

-E. Tan, 9-22-01

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Dichloroacetate

Drug Summary: Dichloroacetate stimulates an enzyme called PDC that is essential for the production of energy in cells. Because inefficient energy production is believed to contribute to the progression of HD, dichloroacetate therapy could result in increased energy production, and could possibly help delay HD progression.

The altered huntingtin protein seen in the nerve cells of people with HD has been known to cause a decrease in the amount of energy available in cells by disrupting energy metabolism. (For more on metabolism, click here.) The mitochondria of HD cells appear to be damaged by the altered huntingtin and are unable to perform aerobic respiration, a form of energy metabolism. The mitochondrial damage forces cells to resort to anaerobic respiration, a less efficient form of energy metabolism. The inability to perform efficient aerobic respiration leads to decreased energy production. This energy deficit in HD cells leads to various consequences: the cell is unable to perform its different functions as efficiently as it used to and is more vulnerable to toxicity by various molecules.

Researchers believe that increasing the efficiency of aerobic respiration, and in turn, increasing the energy available to the cell, is one way of slowing the progression of HD.

aerobic-01

One way by which scientists measure the efficiency of metabolism is cells is by measuring the cells’ lactate levels. Lactate, a by-product of anaerobic respiration, is often found in higher concentrations in cells with decreased metabolism efficiency. High levels of lactate indicate that anaerobic respiration (the less efficient form of energy production) is the primary form of metabolism. On the other hand, low lactate levels indicate that aerobic respiration is the primary form of metabolism used by the cells.

Dichloroacetate in energy metabolism

Dichloroacetate has been found to decrease lactate production in cells by stimulating the pyruvate dehydrogenase complex (PDC), a critical group of enzymes involved in energy metabolism. The PDC is a large complex that is composed of multiple copies of three enzymes – E1, E2, and E3. The PDC serves as the vital enzyme involved in pyruvate oxidation, the step in aerobic respiration in which pyruvate is converted to acetyl-CoA. Pyruvate is a product of glycolysis, the first step in energy metabolism where sugar molecules from the carbohydrates we eat are transformed into pyruvate to be used for further processing in metabolism.

Each of the three enzymes that make up the PDC performs specific reactions that collectively transform pyruvate to acetyl-CoA. Acetyl-CoA is then transported into the mitochondria and enters the Kreb’s Cycle, a step in aerobic respiration. Once acetyl-CoA enters the Kreb’s Cycle, it undergoes various reactions that ultimately end in the production of large quantities of ATP. The PDC acts as a gatekeeper that facilitates and regulates the entry of pyruvate in to the Kreb’s Cycle.

In essence, the PDC determines whether the pyruvate molecules will be transformed into acetyl-CoA. If pyruvate is converted to acetyl-CoA, the cells can use the acetyl-CoA to undergo aerobic respiration. If pyruvate is unable to be converted to acetyl-CoA, the pyruvate is used in anaerobic respiration. If the PDC is damaged, fewer pyruvate molecules are converted to acetyl-CoA, which results in a decrease in the rate of aerobic respiration and a decrease in the number of ATP molecules produced. Instead, the pyruvate molecules stay in the cytosol and undergo anaerobic respiration, producing increased amounts of lactate. An abnormal lactate buildup results in various symptoms such as severe lethargy (tiredness) and poor feeding, especially during times of illness, stress, or high carbohydrate intake.

How is PDC activity regulated?

A family of enzymes called PDC Kinases acts to add phosphate groups to the E1 enzyme of the PDC. Adding a phosphate group to E1 inhibits the activity of the PDC complex. Acetyl-CoA usually activates these PDC kinases as a way to stop production of more acetyl-CoA when it is already present in large amounts and continued production is no longer needed.

Dichloroacetate therapy has been used to increase the efficiency of aerobic respiration. Researchers have reported that dichloroacetate stimulates the PDC by inhibiting the kinase that inactivates the PDC. Once the kinase is inhibited, the PDC continues to be activated and is able to perform its function of converting pyruvate to acetyl-CoA for use in aerobic respiration.

Given that impaired energy metabolism is implicated in the progression of HD, dichloroacetate treatment may improve metabolism and slow HD progression. In mouse models of HD, it is thought that the altered huntingtin protein interferes with the PDC kinases, causing a decrease in active PDC in nerve cells. This additional finding of decreased active PDC in HD nerve cells further supports the possibility of using dichloroacetate to stimulate the PDC and improve cell metabolism.

Dichloroacetate safety

There is some concern about the toxicity of dichloroacetate. Accumulations of dichloroacetate in groundwater have been described by some reports as a potential health hazard. However, concern about dichloroacetate toxicity is mainly based on data obtained in rats who were administered dichloroacetate at doses thousands of times higher than those to which humans are usually exposed. In these animals, chronic administration of dichloroacetate was found to cause liver problems and tumors. (Stacpoole, 1998.) In contrast, the dosage given to most humans is much lower than that administered to the rats. In clinical trials where dichloroacetate is used as a medical drug, no major side effects have been reported. Dichloroacetate is currently the most effective treatment for a disease known as congenital lactic acidosis (CLA). People with CLA have defective PDC enzymes and are thus unable to efficiently produce energy. In one study, patients with CLA were treated with 25-50 mg of dichloroacetate per 1 kg of body weight. No major complications were observed in the participants. (Stacpoole, 1997.) However, more research is currently being done to study the possible toxicity of dichlororacetate.

Issues of dichloroacetate toxicity have also arisen in research not directly related to HD. Dichloroacetate has also been found to protect against neuronal damage in the striatum of rats whose nerve cells have been deprived of blood flow. (Peeling, et al., 1996.) However, a recent report on an ongoing trial of dicholoroacetate treatment in people with mitochondrial disorders has reported that some patients developed new pathological symptoms and some had worsening in the transmission of nerve impulses. (Haas, et al., 2000.) Long-term trials are necessary to clarify the side effects associated with dichloroacetate and its role in HD treatment.

Research on Dichlororacetate

Gansted, et al. (1999) investigated whether dichloroacetate can improve the condition of people with mitochondrial myopathies (MM). The researchers hypothesized that dichloroacetate treatment in people with MM will result in improved energy metabolism.  Because a decrease in metabolism is hypothesized to also be associated with HD, results of studies on MM and dichloroacetate may lead clues to the efficacy of dichloroacetate in HD treatment.

The mitochondrial myopathies are a group of neuromuscular diseases caused by damage to the mitochondria. Some of the more common mitochondrial myopathies include Kearns-Sayre syndrome, myoclonus epilepsy with ragged-red fibers (MERRF), and mitochondrial encephalomyopathy lactic acidosis and stroke-like episodes (MELAS). Mitochondrial myopathies are often caused by mutations in the DNA encoding the electron transport protein complexes, resulting in decreased ATP production. Aerobic respiration is not as efficient, so the cells of people with MM have to resort to more anaerobic respiration for their energy needs. The increased anaerobic respiration results in accumulations of lactate during exercise and contributes to exercise intolerance.

Dichloroacetate treatment was administered for 15 days to 7 people with MM. The study showed that dichloroacetate administration lowered lactate levels in most of the patients, indicating that dichloroacetate may improve metabolism efficiency. However, three patients reported that dichloroacetate caused a considerable sedative effect.

Andreassen, et al. (2001) reported that dichloroacetate has therapeutic effects in two mouse models of HD. One model, called the R6/2 mice, had C-A-G repeat lengths of 141 to 152. These mice exhibited HD-like symptoms such as decreased weight, motor dysfunction, brain atrophy, neuronal inclusions, and an increased occurrence of diabetes. The second mouse model, called the N171-82Q mice, had 82 C-A-G repeats in their Huntington genes. These mice exhibited symptoms similar to those of the R6/2 mice except that their symptoms were less severe and more delayed in onset.

Dichloroacetate treatment began at 4 weeks of age and was terminated at 12 weeks of age. A dose of 100mg/kg of body weight was administered daily. The study showed that dicholoroacetate-treated mice of both models showed significantly improved survival and motor function, as well as delayed weight loss and nerve cell loss. The development of diabetes was also delayed. Dichloroacetate was also found to maintain normal amounts of the active form of PDC. However, formation of neuronal inclusions was not altered by dichloroacetate treatment. The results of this study raise the possibility that dichloroacetate might be a potential HD treatment with therapeutic benefits for people with HD.

For further reading

  1. Peeling, et al. Protective effect of dichloroacetate in a rat model of forebrain ischemia. Neuroscience Letters. 1996; 208: 21-24.
    Peeling, et al. reported that dichloroacetate was able to protect against neuronal damage in the striatum of rats whose nerve cells have been deprived of blood flow.
  2. Haas, et al. Results of the UCSD open label dichloroacetate trial in congenital lactic acidosis. In: Zullo SJ, ed. Mitochondrial Interest Group Minisymposium (Mitochondria: Interaction of Two Genomes). Bethesda, MD: NIH, 2000 p.2.
    Haas, et al. reported that some patients treated with dichloroacetate had developed new pathological symptoms and some had worsening in the transmission of nerve impulses.
  3. Gansted, et al. Dichloroacetate treatment of mitochondrial myopathy patients. Neurology. 1999; 52 (Suppl 2): A544.
    This article reports that dichloroacetate treatment resulted in lowered lactate levels (and consequently, increased energy production) in people with mitochondrial myopathies.
  4. Andreassen, et al. Dichloroacetate exerts therapeutic benefits in transgenic mouse models of Huntington’s disease. Annals of Neurology. 2001; 50(1): 112-6.
    This article reports that dichloroacetate treatment resulted in various beneficial effects in mouse models of HD.
  5. Stacpoole, et al. Clinical Pharmacology and Toxicology of Dichloroacetate. Environmental Health Perspectives. 1998; 106: Supplement 4.
    This article reports that rats treated with dichlororacetate at dosages thousands of times higher than normally prescribed to humans exhibited various pathological side effects.
  6. Stacpoole, et al. Treatment of congenital lactic acidosis with dichloroacetate. Archives of Disease in Childhood. 1997; 77: 535-541.
    This article reports that dichloroacetate treatment resulted in lower lactate levels in people with congenital lactic acidosis.

-P. Chang, 7/5/04

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Nicotinamide

Drug Summary: Nicotinamide (also referred to as Vitamin B3) is believed to cause improvements in energy production due to its role as a precursor of NAD (nicotinamide adenosine dinucleotide), an important molecule involved in energy metabolism. Increasing nicotinamide concentrations increase the available NAD molecules that can take part in energy metabolism, thus increasing the amount of energy available in the cell. Nicotinamide has been shown to be effective at curing motor symptoms in a mouse model of HD.

Nicotinamide and Energy Metabolism

Nicotinamide is a vitamin that plays an important role in the synthesis of components necessary for the production of ATP. A more familiar term for nicotinamide is Vitamin B3. Vitamin B3 can be found in various meats, peanuts, and sunflower seeds. Nicotinamide is the biologically active form of niacin (also known as nicotinic acid). Both nicotinamide and nicotinic acid, as well as a variation on nicotinic acid, called inosital hexaniacinate, are available as supplements.

The human body receives its necessary quantities of nicotinamide from two sources: diet, as described above, and by synthesizing nictonamide in the body itself. Our body is able to convert tryptophan, an amino acid regularly found in the body, into niacin. Niacin is then converted to nicotinamide, which the body uses for various purposes. Figure J-2 shows a diagram depicting how nicotinamide is produced in the body.

Nicotinamide is sometimes preferred as a supplement because it lacks some of the side effects of niacin. Niacin, but not nicotinamide, has been used as a drug to lower blood cholesterol levels. Nicotinamide, on the other hand, has been found to be effective in arthritis and early-onset Type I diabetes. Nicotinamide is also currently being studied for its effects in improving energy deficits caused by mitochondrial dysfunctions.

Fig J-3: Role of NAD/NADH

Various diseases such as Huntington’s disease, Parkinson’s disease, and mitochondrial disorders are associated with impaired energy metabolism due to various mitochondrial dysfunctions. Nicotinamide is believed to cause improvements in energy production due to its role as a precursor of NAD (nicotinamide adenosine dinucleotide) which is an important molecule involved in energy metabolism. NAD acts as an electron carrier, meaning that it can accept and donate electrons to various enzymes involved in energy metabolism. Specifically, NAD is transformed into NADH when it accepts electrons in a number of reactions involved in glycolysis and the Kreb’s cycle (steps in energy metabolism). NADH then donates its electron to complex I of the electron transport chain. For each pair of electrons passed along the electron transport chain from NADH, a number of ATP molecules are formed. Increasing nicotinamide concentrations increase the available NAD molecules that can take part in energy metabolism, thus increasing the amount of energy available in the cell. Figure J-3 shows an image tracing the role of NAD in the cell.

Nicotinamide can also increase cellular energy by inhibiting the enzyme poly-ADP-ribose polymerase. Under normal conditions, damage to DNA activates poly-ADP-ribose polymerase. When poly-ADP-ribose polymerase is activated, it depletes the supply of NAD by transferring poly-ADP-ribose subunits from NAD to various DNA repair enzymes. The depletion of NAD leads to the depletion of ATP due to the decrease in the activity of both glycolysis and the Kreb’s Cycle. When nicotinamide inhibits the poly-ADP ribose polymerase, it essentially prevents the NAD molecules from becoming depleted.

Relationship between Nicotinamide and Nicotine

Fig J-4: Structures of Nicotine and Nicotinamide

Nicotinamide was one of the first vitamins ever discovered. Around the same time that it was discovered, scientists also found that nicotine, the addictive substance in tobacco products, can be harmful to humans. One of the ways by which nicotine causes deterimental effects in humans is that it has a similar structure to nicotinamide and can interfere with the absorption and incorporation of the vitamin. Figure J-4 shows the structures of nicotinamide and nicotine.

Fig J-5: Competition between Nicotine and Nicotinamide

Nicotine competes with nicotinamide for the binding sites in the enzymes needed for the absorption of nicotinamide, thereby lowering the amounts of nicotinamide available to cells. Figure J-5 shows a diagram depicting the competition between nicotinamide and nicotine. This competition results in the depletion of NAD molecules that the cell needs to produce energy. This is one of the reasons why smoking can worsen the condition of people with mitochondrial dysfunction.

Research on Nicotinamide

Beal, et al. (1994) examined whether Coenzyme Q10, nicotinamide, or riboflavin can block brain lesions produced by a compound that causes a dysfunction in the mitochondria. Coenzyme Q10, also known as ubiquinone, is an antioxidant and an essential component of the electron transport chain. (For more on Coenzyme Q10, click here.) Riboflavin is a precursor of another coenzyme needed by the electron transport chain. (For more on Riboflavin, click here.)

The researchers administered the mitochondrial toxin, malonate, to a group of male rats. Malonate acts as an inhibitor of complex II of the electron transport chain and has been known to disrupt oxidative phosphorylation, leading to lowered ATP concentrations. Administration of malonate has been known to cause lesions in brains due to the deficit in energy.

The measures used by the researchers to assess the efficacy of the various supplements were lesion size after malonate administration and ATP concentrations. The researchers discovered that rats treated with coenzyme Q10 alone or nicotinamide alone showed decreased lesion size, while treatment with riboflavin had no effect on lesion size. Mice treated with a combination of coenzyme Q10 and nicotinamide showed the greatest reduction in lesion size. Furthermore, the combination of coenzyme Q10 and nicotinamide increased ATP concentrations and prevented ATP depletion caused by malonate.

These results suggest that coenzyme Q10 and nicotinamide can block ATP depletions and may improve the efficiency of the electron transport chain. It is therefore possible that coenzyme Q10 and/or nicotinamide may be able to slow the progression of HD, given that inefficiency of the electron transport chain contributes to the progression of HD.

Schulz, et al. (1995) studied the potential neuroprotective effects of Coenzyme Q10 and nicotinamide on mouse models of Parkinson’s disease (PD). Impaired energy metabolism has been found to be associated with some of the symptoms of PD.

To mimic the symptoms seen in people with PD, the researchers administered MPTP, a poison that is toxic to nerve cells. Administration of MPTP disrupts the energy metabolism of cells that release the neurotransmitter dopamine. Specifically, MPTP administration results in an inhibition of complex I of the electron transport chain of dopamine-releasing nerve cells. The impairment in the electron transport chain results in decreased ATP and increased