RxPG News : Huntington's

Link between Huntington's and abnormal cholesterol levels in brain discovered

Sun, 03 Dec 2006 15:10:07 PST

( from http://www.rxpgnews.com ) Mayo Clinic researchers have discovered a protein interaction that may explain how the deadly Huntington's disease affects the brain. The findings, published in and featured on the cover of the current issue of Human Molecular Genetics, show how the mutated Huntington's protein interacts with another protein to cause dramatic accumulation of cholesterol in the brain.

"Cholesterol is essential for promoting the connection network among brain cells and in maintaining their membrane integrity. Both the level of cholesterol and its delivery to the proper locations in the cell are essential for the survival of neurons," explains Mayo Clinic molecular biologist Cynthia McMurrary, Ph.D.

"Our discovery that the mutant Huntington's disease protein derails the cholesterol delivery system and causes cholesterol accumulation in neurons provides us with key results and solid clues to the mechanism of this disease," says Dr. McMurray. "Fully understanding the mechanism of toxicity is the key to developing treatments."

Huntington's disease -- sometimes called Huntington's chorea or St. Vitus' dance -- is a progressive, degenerative condition that causes nerve cells in the brain to waste away. Symptoms include uncontrolled movements, emotional disturbances and mental deterioration.

The mutant protein of Huntington's attacks the railroad system of brain cells and impairs transport of essential materials required for neurons to function. When this transportation system goes awry in the parts of the brain affected in Huntington's disease, motor skills, cognitive skills and even speech can be affected. A person cannot move without shaking, and physical control gradually deteriorates, often with accompanying personality changes, depression and increased risk of suicide. Those who have Huntington's commonly die from complications of the disease, such as falls or infections.

Mouse control neuron (left) and neuron showing cholesterol accumulation in Huntington's disease.

Approximately 30,000 Americans have Huntington's disease. Another 150,000 carry the gene and have a 50 percent risk of passing it on to their children. The disease is easily diagnosed by a blood test, but symptoms usually don't appear until middle age.

Their findings, say the researchers, provide the first direct link between the Huntington's protein and the protein that controls capture and trafficking inside the cell. Their research suggests a possible means by which Huntington's disease functions.

Because no one knows how the disease is incurred or spreads, this new information is critical and establishes a clear path for investigations to move forward.

The Mayo researchers observed the abnormal accumulation of cholesterol in cultured neuronal cells in the laboratory and in the brains of animal models. They found that this happens only when the mutant Huntington's protein is expressed together with the molecule, caveolin-1. Caveolin-1 is the major structural protein of small vesicles called caveolae, which capture cholesterol and move it in and out of the neuronal membranes. When the researchers "knocked out" expression of caveolin, the neurons expressing mutant Huntington's protein stopped accumulating cholesterol.

PARP1 inhibitors can protect Huntington's disease affected cells from damage

Sun, 30 Jul 2006 02:40:37 PST

( from http://www.rxpgnews.com ) An enzyme known to be critical for the repair of damaged cells and the maintenance of cellular energy may be a useful target for new strategies to treat Huntington's disease (HD) and other disorders characterized by low cellular energy levels. In the August issue of Chemistry & Biology, a research team from the MassGeneral Institute for Neurodegenerative Disease (MIND) describes their discovery of a novel inhibitor of Poly (ADP-ribose) polymerase (PARP1) and their findings that PARP1 inhibitors can protect HD-affected cells from damage in laboratory assays.

"While PARP1 is essential for the repair of damaged DNA, we also know that, if overactivated, it can cause cell death by excessive energy depletion," says Aleksey Kazantsev, PhD, director of the MIND High Throughput Drug Screening Laboratory, who led the current study. "It has recently been shown that neurons from patients with Huntington's appear to be energy-deficient, so we hypothesized that modest stresses that would be tolerated by healthy cells could send HD cells below a viable energy threshold and that blocking PARP1 activation could be protective."

To test this hypothesis the MIND researchers first ran a computer search of their small-molecule library for potential novel inhibitors of PARP1, searching for those with structural similarities to known inhibitors. "Safety and efficacy of human drugs depends on many factors, so it's hard to predict which inhibitor would be most effective against a specific disorder. The more diverse novel inhibitors can be identified, the more chances there are of developing safe and effective drugs," Kazantsev explains.

Two candidate molecules were identified as potential PARP1 inhibitors based on their structure, and both of them were confirmed to inhibit the enzyme's activity in an in vitro assay. However, when tested using cultured human and rat cells, only one of the candidate molecules, K245-14, successfully prevented the death of cells in which PARP1 had been overactivated.

The next assays examined whether blocking PARP1 activity with K245-14 could reduce energy depletion in cells with the HD genetic mutation. Using cells from human HD patients and from a mouse model of the disorder, the MIND researchers compared the reactions of HD cells to oxidative stress caused by the application of hydrogen peroxide with the reactions of normal cells. Although all of the cells reacted with a loss of ATP, a key source of cellular energy, the HD cells which had much lower ATP levels to begin with were much more vulnerable to stress-induced energy loss. Inhibiting PARP1 by means of K245-14 reduced ATP loss in all tested cells and significantly protected against both energy loss and cell death in the HD cells.

"While we were pleased to observe these predicted protective effects in our experiments, validation of PARP1 as a useful HD drug target will require the testing of inhibitors in animal trials," Kazantsev explains. "The process of identifying the best candidates for trials will be very complex, since any drug treating a central nervous system disorder needs to penetrate the blood-brain barrier. We will be working with our collaborators at the Scripps Research Institute world leaders in computational chemistry to conduct a more comprehensive virtual screen and select additional promising candidates for drug development.

"Inhibition of PARP1 activity is thought to be potentially beneficial for treatment of cancer, neurodegenerative conditions such as Parkinson's disease, and over twenty other human disorders," he adds. "We envision broad therapeutic applications for small molecule inhibitors of PARP1." Kazantsev is an assistant professor of Neurology at Harvard Medical School.

Gene therapy protects neurons in Huntington's disease

Fri, 30 Jun 2006 03:01:37 PST

( from http://www.rxpgnews.com ) Researchers at Rush University Medical Center, Chicago, and Ceregene Inc., San Diego, have successfully used gene therapy to preserve motor function and stop the anatomic, cellular changes that occur in the brains of mice with Huntington's disease (HD). This is the first study to demonstrate that, using this delivery method, symptom onset might be prevented in HD mice with this treatment.

"This could be an important step toward a disease modifying therapy," says co-author Jeffrey H. Kordower, PhD, director of the Research Center for Brain Repair at Rush. "We could potentially be stopping the disease process in its tracks, delaying symptoms from ever showing up."

Huntington's disease is an inherited degenerative disease that progressively robs patients of the ability to think, judge appropriately, control their emotions and perform coordinated tasks. HD typically begins in mid-life, between the ages of 40 and 50. There is no effective treatment or cure for this fatal illness that affects 30,000 Americans and places another 75,000 at risk.

Kordower says this research, if eventually applied to humans, could help those who have HD or, due to the presence of a genetic test, are known to be destined to get HD.

"Each child of an affected parent has a 50 percent risk for inheriting the disease. Genetic testing can identify mutated gene carriers destined to suffer from HD. Unlike other neurodegenerative disorders, identification of the genetic markers provides a unique opportunity to intercede therapeutically before or extremely early in the disease processonly a small fraction of potential carriers get tested. But, if there was a treatment, especially one that altered the natural course of disease, potentially halting it, we would hope every potential patient would get tested so they could avail themselves to the therapy."

Researchers used a defective virus, adenoassociated viral vector, (AAV) to deliver gene therapy (glial-derived neurotrophic factor (GDNF) directly to the brain cells of mice.

GDNF is one of two closely related, naturally-occurring nutrients that strengthen and protect brain cells that would normally die in this disease. The other neural nutrient is called neurturin (NTN). GDNF and NTN also increase production of the chemical neurotransmitter dopamine, which sends signals in the brain that enable people to move smoothly and normally. Ceregene, Inc, whose scientists co-authored this paper, is developing AAV-NTN (called CERE-120) as a potential treatment for several neurodegenerative diseases, while using AAV-GDNF for 'proof of principle' research studies.

The mice in this study were injected with the gene for GDNF encased in a harmless viral coating, which protects the gene and facilitates its delivery to brain cells. The virus coating (AAV vector) that carries the gene is well studied and has been used in several other gene transfer studies to deliver different genes for Parkinson's disease and Alzheimer's disease patients. The vector is no longer a true virus as it cannot replicate on its own and no longer contains any of its own genes. The vector has been engineered to transfer the gene for the brain nutrient selectively to the area of the brain where it is needed to protect the degenerating cells.

Three groups of mice were involved in the 4 month study. All mice were modeled to have the genetics of HD. The HD mice exhibited symptoms of motor deficits including loss of control, gait abnormalities, hypokinesia (abnormally decreased mobility and motor function), hind limb clasping behaviors and muscle weakness. One control group of mice did not receive any gene therapy. A second control group was injected with a placebo gene therapy. The third group received the active GDNF gene therapy.

To measure fine motor coordination, balance and fatigue, researchers evaluated mice walking on a rotating rod. Mice injected with the gene therapy performed significantly better than the other mice. These mice also showed diminished hind limb clasping, (a simulation of motor control behavior in HD patients). Perhaps most importantly, gene delivery of GDNF provided neuroprotection in the brain, with reduced density of brain inclusions and less cell death.

The authors wrote "Although GDNF's exact role in preventing cell death in mice modeled with HD remains to be established, we speculate the increase trophic support and inhibiting apoptosis (programmed cell death) via these two pathways likely played integral roles."

Kordower says the study suggests a new approach to forestall disease progression in newly diagnosed HD patients by delivering potent trophic factors with effects that are long-term and non-toxic." "If these results can be replicated in HD patients, it would represent a significant advance in the treatment of this tragic disease", agreed Dr. Jeffrey Ostrove, President and CEO of Ceregene.

"We are pleased with the results of this 'proof of concept' study with AAV-GDNF in HD mice", stated Raymond T. Bartus, Ph.D., Sr. Vice President, Clinical and Preclinical R&D and COO, Ceregene. "We now look forward to completing ongoing studies with our product, AAV-NTN (CERE-120), in HD mice, also performed in collaboration with Dr. Kordower and Rush University Medical Center", Bartus added.

Ceregene's lead program with CERE-120 is in Parkinson's disease (PD). The company completed enrollment of a Phase I trial with CERE-120 at UCSF and Rush University Medical Center, which was reported to be safe and well tolerated in PD patients at the American Association of Neurology meeting last spring. Initial efficacy results of this Phase I trial are expected to be presented this fall and a double-blinded, controlled Phase II trail in PD patients is planned for later this year.

Huntingtin cleavage is caused by caspase-6

Sat, 17 Jun 2006 20:09:37 PST

( from http://www.rxpgnews.com ) Researchers at the University of British Columbia's Centre for Molecular Medicine and Therapeutics (CMMT) have provided ground-breaking evidence for a cure for Huntington disease in a mouse offering hope that this disease can be relieved in humans.

Published today in Cell journal, Dr. Michael Hayden and colleagues discovered that by preventing the cleavage of the mutant huntingtin protein responsible for Huntington disease (HD) in a mouse model, the degenerative symptoms underlying the illness do not appear and the mouse displays normal brain function. This is the first time that a cure for HD in mice has been successfully achieved.

"Ten years ago, we discovered that huntingtin is cleaved by 'molecular scissors' which led to the hypothesis that cleavage of huntingtin may play a key role in causing Huntington disease", said Dr. Michael Hayden, Director and Senior Scientist at the Child and Family Research Institute's Centre for Molecular Medicine and Therapeutics. Dr. Hayden is also a Canada Research Chair in Human Genetics and Molecular Medicine.

Now a decade later, this hypothesis has resulted in a landmark discovery. "This is a monumental effort that provides the most compelling evidence of this hypothesis to date", said Dr. Marian DiFiglia, Professor in Neurology, Massachusetts General Hospital, Harvard Medical School and one of the world's leading experts on Huntington disease. "Dr. Hayden and his team have shown in convincing fashion that many of the changes seen in HD patients can be erased in HD mice simply by engineering a mutation into the disease gene that prevents the protein from getting cleaved at a specific site".

To explore the role of cleavage, Dr. Hayden's team established an animal model of HD that replicated the key disease features seen in patients. A unique aspect of this particular animal model is that it embodied the human HD gene in exactly the same way seen in patients. This replication allowed researchers to examine the progression of HD symptoms including the inevitable cleavage of the mutant huntingtin protein. In the study, researchers confirmed that the deadly cleavage is caused by a key enzyme called caspase-6. By blocking the action of this target, they showed that the mouse did not develop any symptoms of Huntington disease.

Hayden's team is now trying to test this model of prevention in a mouse using drug inhibitors and then ultimately in humans. "Our findings are important because they tell us exactly what we need to do next", said Dr. Rona Graham, Post Doctoral Fellow at the CMMT and lead author in the study.

This work is also pivotal for the individuals and families affected by Huntington disease. "Patients of this disease should know that this is a research milestone for all and that this work brings the field closer to finding effective treatment for a devastating disorder", said Dr. DiFiglia.

The Huntington Society of Canada (HSC), a national network of volunteers and professionals united in the fight against HD, echoed this sentiment. "This ground-breaking research provides great hope for the Huntington community", said Don Lamont, the Society's CEO and Executive Director. "This research brings us closer to treatment and ultimately a cure".

Huntington disease is a degenerative brain disease that affects one in every 10,000 Canadians. One in 1,000 is touched by HD -- for example, as a person with HD, a family member, a person at risk, caregiver or friend. The disease results from degeneration of neurons in certain areas of the brain causing uncontrolled movements, loss of intellectual faculties, and emotional disturbances. Currently, there is no treatment to delay or prevent HD in patients.

Clioquinol, an antibiotic shows new promise for Huntington's Disease

Mon, 12 Sep 2005 18:13:38 PST

( from http://www.rxpgnews.com ) Clioquinol, an antibiotic that was banned for internal use in the United States in 1971 but is still used in topical applications, appears to block the genetic action of Huntington's disease in mice and in cell culture, according to a study reported by San Francisco VA Medical Center (SFVAMC) researchers.

The study, led by principal investigator Stephen M. Massa, MD, PhD, a neurologist at SFVAMC, was reported in the August 16, 2005 issue of Proceedings of the National Academy of Sciences.

Huntington's disease is a hereditary, degenerative, and ultimately fatal disease of the brain that causes changes in personality, progressive loss of memory and cognitive ability, and a characteristic uncontrolled jerking motion known as Huntington's chorea. There is no known cure or effective treatment. A person who carries the mutant Huntington's gene may pass it on unknowingly because the disease often manifests in early to late middle age after the carrier's children have already been born.

During the course of the disease, the Huntington's gene causes the production of a toxic protein, mutant huntingtin, in neurons (brain cells). Eventually the protein kills the neurons, causing the disease's degenerative effects.

In Massa's study, Clioquinol appeared to interrupt the production of mutant huntingtin. In the first part of his study, Massa and his research team tested the effect of Clioquinol on neurons in cell culture that contained a form of the mutant Huntington's gene. "We found that not only did cells look better and survive a bit longer when exposed to the drug, but they also seemed to make less of the toxic protein," observed Massa, who is also a clinical assistant professor of neurology at the University of California, San Francisco (UCSF).

Based on the in vitro results, Massa decided to test the drug in vivo, on mice bred to express the toxic huntingtin protein. The mice were given approximately 1 milligram of Clioquinol per day in water. After eight weeks of treatment, they had accumulated four times less toxic protein in their brains than control mice given water alone. The experimental animals lived 20 percent longer than the control animals, did better on tests of motor coordination, and had less weight loss.

"It's a limited study, in that we used the same drug dose on all the animals as opposed to comparing different doses, but fairly convincing," Massa concluded. "Together, the in vitro and in vivo results suggest that Clioquinol has an effect of decreasing the symptoms of Huntington's, its pathology, and perhaps even the actual production of the toxic protein."

However, he noted, "the drug's mechanism of action remains unclear." The clearer the mechanism of the drug, he explained, the better the chance that researchers might eventually be able to create a medication that is both safe and effective.

Like some other antibiotics, Clioquinol is known to be a chelator -- that is, it binds metals in body tissues, particularly copper and zinc, and removes them when it is excreted. Massa and other researchers believe that this chelation effect may interfere with production of the mutant huntingtin protein in some way. "But there are still a couple of explanations we need to rule out," he said.

To that end, Massa's next studies will involve the creation of an in vitro system in which toxic and non-toxic forms of huntingtin are made in the same cell. He and his team will then evaluate the effects of Clioquinol on several phases of protein synthesis within the cell. Massa hopes these experiments will confirm initial indications that Clioquinol preferentially interferes with synthesis of the toxic form of the protein. "Then we can move on to trying to isolate the actual mechanism of the drug," he predicted.

"However," Massa cautioned, "the record of successfully translating drugs from animal to human use is not good."

Clioquinol has shown promise as a potential treatment for Alzheimer's disease in recent studies in mice and humans. Apparently through chelation, it interferes with the creation of beta-amyloid plaque in the brain, which has been implicated in the progression of Alzheimer's symptoms.

Currently, Clioquinol is banned for internal use in many countries because of its side effects. In Japan in the late 1950s and 60s, the drug was found to cause a neurologic condition called subacute myelo-optico-neuropathy (SMON), with symptoms including visual loss, muscle weakness, and numbness, in several thousand people. However, noted Massa, the doses given in current clinical trials are much smaller than were commonly prescribed in Japan. In addition, he explained, it has been found that vitamin B12, when taken along with the drug, protects against its potential toxic effects.

Potential therapeutic target for Huntington's disease

Thu, 07 Apr 2005 18:13:38 PST

( from http://www.rxpgnews.com ) Researchers studying yeast cells have identified a metabolic enzyme as a potential therapeutic target for treating Huntington's disease, a fatal inherited neurodegenerative disorder for which there is currently no effective treatment.

The group performed a genetic experiment known as a loss-of-function suppressor screen, which searches for genes that, when switched off, reduce the toxic effects of the mutant protein associated with Huntington's. One of the genes they identified encodes an enzyme, called KMO, that has been previously implicated in the disease. The enzyme functions in a metabolic pathway that is activated at early stages of the disease in people with Huntington's, as well as in animal models of the disease.

"The nice thing about this finding is that there is a chemical compound available that inhibits KMO activity," said Dr. Paul Muchowski, assistant professor of pharmacology at the UW, who led the study. "We're in the midst of testing that compound in a mouse model of Huntington's disease."

Further support for KMO as a therapeutic target for Huntington's disease comes from a recent study led by Dr. Aleksey G. Kazantsev of Harvard Medical School. In this study, researchers used cell-based experiments to screen about 20,000 chemical compounds, and identified one that suppresses neurodegeneration in a fly model of the disease. That compound has a very similar chemical structure as the drug that inhibits the target identified by Muchowski's group. The results appeared in the Jan. 18, 2005, issue of the Proceedings of the National Academy of Sciences.

In addition to finding a potential drug target for future Huntington's treatment, the study by Muchowski and his colleagues could take research on the disease in a new direction: towards microglial cells, which are immune cells in the brain. Previous research has focused exclusively on neuronal cells, but the enzyme KMO is found predominantly in microglial cells. Since inhibiting KMO activity has a direct effect on toxicity of the mutant protein associated with Huntington's, that could mean microgial cells are home to an important step in progression of the disease.

Huntington's affects an estimated 30,000 people in the United States. It is characterized by loss of motor control and cognitive functions, as well as by depression or other psychiatric problems.