Posts tagged medicine

Scientists from the Florida campus of The Scripps Research Institute have described findings that could enable the development of more effective drugs for addiction with fewer side effects.

The study, published in the August 2, 2013 issue of the Journal of Biological Chemistry, showed in a combination of cell and animal studies that one active compound maintains a strong bias towards a single biological pathway, providing insight into what future drugs could look like.

The compound examined in the study, known as 6’- guanidinonaltrindole (6’-GNTI), targets the kappa opioid receptor (KOR). Located on nerve cells, KOR plays a role in the release of dopamine, a neurotransmitter that plays a key role in drug addiction. Drugs of abuse often cause the brain to release large amounts of dopamine, flooding the brain’s reward system and reinforcing the addictive cycle.

“There are a number of drug discovery efforts ongoing for KOR,” said Laura Bohn, a TSRI associate professor, who led the study. “The ultimate question is how this receptor should be acted upon to achieve the best therapeutic effects. Our study identifies a marker that shows how things normally happen in live neurons—a critically important secondary test to evaluate potential compounds.”

While KOR has become the focus for drug discovery efforts aimed at treating addiction and mood disorders, KOR can react to signals that originate independently from multiple biological pathways, so current drug candidates targeting KOR often produce unwanted side effects. Compounds that activate KOR can decrease the rewarding effects of abused drugs, but also induce sedation and depression.

The new findings, from studies of nerve cells in the striatum (an area of the brain involved in motor activity and higher brain function), reveal a point on the KOR signaling pathway that may prove to be an important indicator of whether drug candidates can produce effects similar to the natural biological effects.

“Standard screening assays can catch differences but those differences may not play out in live tissue,” Bohn noted. “Essentially, we have shown an important link between cell-based screening assays and what occurs naturally in animal models.”

(Source: scripps.edu)

The results of a new study by neurological researchers at Rush University Medical Center show that a sudden decrease of testosterone, the male sex hormone, may cause Parkinson’s like symptoms in male mice. The findings were recently published in the Journal of Biological Chemistry.

(Image credit)

One of the major roadblocks for discovering drugs against Parkinson’s disease is the unavailability of a reliable animal model for this disease.

“While scientists use different toxins and a number of complex genetic approaches to model Parkinson’s disease in mice, we have found that the sudden drop in the levels of testosterone following castration is sufficient to cause persistent Parkinson’s like pathology and symptoms in male mice,” said Dr. Kalipada Pahan, lead author of the study and the Floyd A. Davis endowed professor of neurology at Rush. “We found that the supplementation of testosterone in the form of 5-alpha dihydrotestosterone (DHT) pellets reverses Parkinson’s pathology in male mice.”

“In men, testosterone levels are intimately coupled to many disease processes,” said Pahan. Typically, in healthy males, testosterone level is the maximum in the mid-30s, which then drop about one percent each year. However, testosterone levels may dip drastically due to stress or sudden turn of other life events, which may make somebody more vulnerable to Parkinson’s disease.

“Therefore, preservation of testosterone in males may be an important step to become resistant to Parkinson’s disease,” said Pahan.

Understanding how the disease works is important to developing effective drugs that protect the brain and stop the progression of Parkinson’s disease. Nitric oxide is an important molecule for our brain and the body.

"However, when nitric oxide is produced within the brain in excess by a protein called inducible nitric oxide synthase, neurons start dying,” said Pahan.

“This study has become more fascinating than we thought,” said Pahan.  “After castration, levels of inducible nitric oxide synthase (iNOS) and nitric oxide go up in the brain dramatically. Interestingly, castration does not cause Parkinson’s like symptoms in male mice deficient in iNOS gene, indicating that loss of testosterone causes symptoms via increased nitric oxide production.”

“Further research must be conducted to see how we could potentially target testosterone levels in human males in order to find a viable treatment,” said Pahan.

Other researchers at Rush involved in this study were Saurabh Khasnavis, PhD, student, Anamitra Ghosh, PhD, student, and Avik Roy, PhD, research assistant professor.

This research was supported by a grant from the National Institutes of Health that received the highest score for its scientific merit in the particular cycle it was reviewed.

Parkinson’s is a slowly progressive disease that affects a small area of cells within the mid-brain known as the substantia nigra. Gradual degeneration of these cells causes a reduction in a vital chemical neurotransmitter, dopamine. The decrease in dopamine results in one or more of the classic signs of Parkinson’s disease that includes resting tremor on one side of the body; generalized slowness of movement; stiffness of limbs and gait or balance problems. The cause of the disease is unknown. Both environmental and genetic causes of the disease have been postulated.

Parkinson’s disease affects about 1.2 million patients in the United States and Canada. Although 15 percent of patients are diagnosed before age 50, it is generally considered a disease that targets older adults, affecting one of every 100 persons over the age of 60. This disease appears to be slightly more common in men than women.

(Source: rush.edu)

The development of new drugs for improving treatment of Alzheimer’s and Parkinson’s disease is a step closer after recent research into how stem cells migrate and form circuits in the brain.

The results from a study by researchers at The University of Auckland’s Centre for Brain Research may hold important clues into why there is less plasticity in brains affected by Parkinson’s and Alzheimer’s disease, and links to insulin resistance and diabetes.

The major five-year project to understand how stem cells start and stop migrating in the brain has also helped to unlock the secrets of how stem cells migrate during development and in adulthood.

The study revealed new information on how connectivity between brain cells is improved or worsened, says senior study author, Dr Maurice Curtis who conceived and directed the research. The experiments were carried out at the Centre for Brain Research laboratories by Dr Hector Monzo. Collaborators included a director of the CBR, Distinguished Professor Richard Faull, Dr Thomas Park, Dr Birger Dieriks, Deidre Jansson and Professor Mike Dragunow.

“We have begun testing new novel drug compounds that target how polysialic acid is removed from the cell in the hope of improving neuron connectivity,” says Dr Curtis.

He explains that stem cells in the brain are immature brain cells that must migrate from their birthplace to a position in the brain where they will connect with other brain cells, turn into adult brain cells (neurons) and become part of the brain’s circuitry.

“Even once the neuron has found its location, the neuron’s tentacles (or dendrites) need to forage to find other neurons to connect with to form circuits. This would be easy except that in the adult brain the cells are surrounded by a fairly rigid matrix (extracellular matrix) and so migration or foraging becomes almost impossible in this high friction environment.”

“The way the cell overcomes this ‘friction’ is by placing large amounts of a special slippery molecule called ‘polysialic acid-neural cell adhesion molecule’ onto the cell surface,” says Dr Curtis. “This allows the cell to migrate or forage with only a fraction of the friction it once had and this also reduces the energy requirements of the cell.”

Once the cell has migrated to its destination, the slippery coating is removed and the cell becomes locked in place ready to connect with other cells. In the case of the dendritic foraging, the polysialic acid must be removed in order for the dendrite to connect with another cell (synapse formation).

“We have known for at least 20 years that this process occurs but despite extensive studies by a number of groups internationally we have been in the dark about what controls this process,” he says. “Studies in my laboratory have demonstrated what happens to the slippery molecules once the cell no longer needs them.”

There were three possibilities for this process:

• that enzymes cut them off the outside of the cell
• that the friction wears it off the cell or
• the cell internalises the slippery substance and recycles it ready for future use.

“For the past five years, we have systematically studied how this process is controlled,” says Dr Curtis. “Our findings have demonstrated that cells internalise the slippery molecule after receiving two specific cues.”

One of these cues is from collagen which makes up part of the rigid structure outside of the cell and the other is from a gaseous molecule called nitric oxide which triggers the outer membrane of the cell to internalise the slippery molecules.

“What we also discovered is that when there is an increased amount of insulin and insulin-like growth factor 1 (which has some similar functions to insulin) present in the culture, the cell cannot internalise the slippery molecules and instead they remain on the cell surface.”

“The key to the breakthrough was in determining that the process by which the polysialic acid is added to the cell surface was so persistent that it needed to be stopped in order to study how the polysialic acid was removed,” says Dr Curtis. “This required extensive trialling of many different cell growth conditions, enzyme concentrations and growing the cells in many different extracellular matrices.”

This is interesting because it is well known that in Parkinson’s disease and Alzheimer’s disease the brain is less sensitive to insulin, he says.

“In our studies in cells the insulin blocks the removal of polysialic acid and therefore the cell cannot connect properly and form synapses with other nearby cells.”

“This may hold major clues to why there is less plasticity in brains affected by Parkinson’s and Alzheimer’s disease in adults as well as helping to unlock the secrets of how stem cells migrate during development of the brain”, says Dr Curtis.

The Gus Fisher Postdoctoral Fellowship, the Auckland Medical Research Foundation and the Manchester Trust were the main sponsors of this research work.

The study results were published online this month in an ‘ahead of print’ version of The Journal of Neurochemistry.

(Source: auckland.ac.nz)

A gene related to neural tube defects in dogs has for the first time been identified by researchers at the University of California, Davis, and University of Iowa.

The researchers also found evidence that the gene may be an important risk factor for human neural tube defects, which affect more than 300,000 babies born each year around the world, according to the U.S. Centers for Disease Control and Prevention. Neural tube defects, including anencephaly and spina bifida, are caused by the incomplete closure or development of the spine and skull.

The new findings appear this week in the journal PLOS Genetics.

“The cause of neural tube defects is poorly understood but has long been thought to be associated with genetic, nutritional and environmental factors,” said Noa Safra, lead author on the study and a postdoctoral fellow in the laboratory of Professor Danika Bannasch in the UC Davis School of Veterinary Medicine.

She noted that dogs provide an excellent biomedical model because they receive medical care comparable to what humans receive, share in a home environment and develop naturally occurring diseases that are similar to those found in humans. More specifically, several conditions associated with neural-tube defects are known to occur naturally in dogs. All DNA samples used in the study were taken from household pets, rather than laboratory animals, Safra said.

She and colleagues carried out genome mapping in four Weimaraner dogs affected by spinal dysraphism, a naturally occurring spinal-cord disorder, and in 96 such dogs that had no neural tube defects.  Spinal dysraphism, previously reported in the Weimaraner breed, causes symptoms that include impaired motor coordination or partial paralysis in the legs, abnormal gait, a crouched stance and abnormal leg or paw reflexes.

Analysis of a specific region on canine chromosome eight led the researchers to a mutation in a gene called NKX2-8, one of a group of genes known as “homeobox genes,” known to be involved with regulating patterns of anatomical development in the embryo.

The researchers determined that the NKX2-8 mutation occurred in the Weimaraner breed with a frequency of 1.4 percent — 14 mutations in every 1,000 dogs.

Additionally, they tested nearly 500 other dogs from six different breeds that had been reported to be clinically affected by neural tube defects, but did not find copies of the NKX2-8 gene mutation among the non-Weimaraner dogs.

“The data indicate that this mutation does not appear as a benign mutation in some breeds, while causing defects in other breeds,” Safra said. “Our results suggest that the NKX2-8 mutation is a ‘private’ mutation in Weimaraners that is not shared with other breeds.”

The researchers say that identification of such a breed-specific gene may help veterinarians diagnose spinal dysraphism in dogs and enable Weimaraner breeders to use DNA screening to select against the mutation when developing their breeding plans.

In an effort to investigate a potential role for the NKX2-8 mutation in cases of neural tube defects in people, the researchers also sequenced 149 unrelated samples from human patients with spina bifida. They found six cases in which the patients carried mutations of the NKX2-8 gene but stress that further studies are needed to confirm whether these mutations are responsible for the diagnosed neural tube defects.

(Source: news.ucdavis.edu)

Duke Medicine researchers have identified biochemical changes in people taking antidepressants – but only in those whose depression improves. These changes occur in a neurotransmitter pathway that is connected to the pineal gland, the part of the endocrine system that controls the sleep cycle, suggesting an added link between sleep, depression and treatment outcomes. The study, published on July 17, 2013, in the journal PLOS ONE, uses an emerging science called pharmacometabolomics to measure and map hundreds of chemicals in the blood in order to define the mechanisms underlying disease and to develop new treatment strategies based on a patient’s metabolic profile.

"Metabolomics is teaching us about the differences in metabolic profiles of patients who respond to medication, and those who do not," said Rima Kaddurah-Daouk, PhD, associate professor of psychiatry and behavioral sciences at Duke Medicine and leader of the Pharmacometabolomics Research Network.

"This could help us to better target the right therapies for patients suffering from depression who can benefit from treatment with certain antidepressants, and identify, early on, patients who are resistant to treatment and should be placed on different therapies."

Major depressive disorder – a form of depression characterized by a severely depressed mood that persists two weeks or more – is one of the most prevalent mental disorders in the United States, affecting 6.7% of the adult population in a given year.

Selective serotonin reuptake inhibitors (SSRIs) are the most commonly prescribed antidepressants for major depressive disorder, but only some patients benefit from SSRI treatment. Others may respond to placebo, while some may not find relief from either. This variability in response creates dilemmas for treating physicians where the only choice they have is to test one drug at a time and wait for several weeks to determine if a patient is going to respond to the specific SSRI.

Recent studies by the Duke team have used metabolomics tools to map biochemical pathways implicated in depression and have begun to distinguish which patients respond to treatment with an SSRI or placebo based on their metabolic profiles. These studies have pointed to several metabolites on the tryptophan metabolic pathway as potential contributing factors to whether patients respond to antidepressants.

Tryptophan is metabolized in different ways. One pathway leads to serotonin and subsequently to melatonin and an array of melatonin-like chemicals called methoxyindoles produced in the pineal gland. In the current study, the researchers analyzed levels of metabolites within branches of the tryptophan pathway and correlated changes with treatment outcomes.

Seventy-five patients with major depressive disorder were randomized to take sertraline (Zoloft) or placebo in the double-blind trial. After one week and four weeks of taking the SSRI or placebo, the researchers measured improvement in symptoms of depression to determine response to treatment, and blood samples were taken and analyzed using a metabolomics platform build to measure neurotransmitters.

The researchers observed that 60 percent of patients taking the SSRI responded to the treatment, and 50 percent of those taking placebo also responded. Several metabolic changes in the tryptophan pathway leading to melatonin and methoxyindoles were seen in patients taking the SSRI who responded to the treatment; these changes were not found in those who did not respond to the antidepressant.

The results suggest that serotonin metabolism in the pineal gland may play a role in the underlying cause of depression and its treatment outcomes, based on the biochemical changes that were seen to be associated with improvements in depression.

"This study revealed that the pineal gland is involved in mechanisms of recovery from a depressed state," said Kaddurah-Daouk. "We have started to map serotonin which is believed to be implicated in depression, but now realize that it may not be serotonin itself that is important in depression recovery. It could be metabolites of serotonin that are produced in the pineal gland that are implicated in sleep cycles.

"Shifting utilization of tryptophan metabolism from kynurenine to production of melatonin and other methoxyindoles seems important for treatment response but some patients do not have this regulation mechanism. We can now start to think about ways to correct this."

The identification of a metabolic signature for patients who have a milder form of depression and who can improve with use of placebo is critically important for streamlining clinical trials with antidepressants. The Duke team is the first to start to define in depth early biochemical effects of treatment with SSRI and placebo, and a molecular basis for why antidepressants take several weeks to start showing benefit.

In future studies, researchers may collect blood samples from patients during both the day and night to define how the circadian cycle, changes in sleep patterns, neurotransmitters and hormonal systems are modified in those who respond and do not respond to SSRIs and placebo. This can lead to more effective treatment strategies.

(Source: dukehealth.org)

Clinical trials of drug treatments for neurological diseases such as Alzheimer’s and Parkinson’s often fail because the animal studies that preceded them were poorly designed or biased in their interpretation, according to a new study from an international team of researchers. More stringent requirements are needed to assess the significance of animal studies before testing the treatments in human patients, the researchers say.

The team — led by John Ioannidis, MD, DSc, a professor of medicine at the Stanford University School of Medicine and an expert in clinical trial design — assessed the results of more than 4,000 animal studies in 160 meta-analyses of potential treatments for neurological disorders from Alzheimer’s disease, Parkinson’s disease, stroke, spinal-cord injury and a form of multiple sclerosis. (A meta-analysis is a study that compiles and assesses information and conclusions from many independent experiments of a treatment, or intervention, for a particular condition.).

They determined that only eight of the 160 studies of potential treatments yielded the statistically significant, unbiased data necessary to support advancing the treatment to clinical trials. In contrast, 108 of the treatments were deemed at least somewhat effective at the time they were published.

Ioannidis and his collaborators at the University of Edinburgh in Scotland and the University of Ioannina School of Medicine in Greece say that animal studies of potential interventions can be made more efficient and reliable by increasing average sample size, being aware of statistical bias, publishing negative results and making all the results of all experiments on the effectiveness of a particular treatment — regardless of their outcome — freely accessible to scientists.

"Some researchers have postulated that animals may not be good models for human diseases," said Ioannidis. "I don’t agree. I think animal studies can be useful and perfectly fine. The problem is more likely to be related to the selective availability of information about the studies conducted on animals." Although the researchers focused here on neurological disorders, they believe it is likely that similar bias exists in animal studies of other types of disorders.

Ioannidis, who directs the Stanford Prevention Research Center, is the senior author of the research, published online in PLoS Biology on July 16. Lecturer Konstantinos Tsilidis, PhD, and postgraduate fellow Orestis Panagiotou, MD, of the University of Ioannina share lead authorship of the study. Panagiotou is currently a researcher at the National Cancer Institute’s Division of Cancer Epidemiology and Genetics.

Ioannidis is known for his efforts to strengthen the way that research is planned, carried out and reported. He was called “one of the world’s foremost experts on the credibility of medical research” in a profile published in The Atlantic magazine in 2010. He outlined some of the problems he observed in a 2005 essay in PLoS-Medicine titled, “Why most published research findings are false.” The essay is one of the most-downloaded articles in the history of the Public Library of Science, according to the journal’s media relations office.

For the new study, Ioannidis and his colleagues evaluated results in a database of the thousands of animal studies compiled over the years through the CAMARADES initiative (Collaborative Approach to Meta-Analysis and Review of Animal Data in Experimental Studies), led by professor Malcolm MacLeod, PhD, from the University of Edinburgh, who is also a co-author of the study.

The team compared the number of experiments in the meta-analyses that would have been expected to yield positive results (based on their predicted statistical power) with the actual number of experiments with published positive results. The difference was striking: 919 expected versus the 1,719 that were published, implying that either negative results were not published, or that the results of the experiments were interpreted too optimistically.

"We saw that it was very common for these interventions to have published evidence that they would work," said Ioannidis. "It was extremely common to have results that suggest they would be effective in humans."

Furthermore, nearly half (46 percent) of the 160 meta-analyses showed evidence of small-study effects — a term used to describe the fact that a small study using fewer numbers of animals is more likely to find the intervention more effective than a larger study with many animals.

Ioannidis speculated that a reluctance to publish negative findings (that is, those that conclude that a particular intervention did not work any better than the control treatment) and a perhaps unconscious desire on the part of researchers to find a promising treatment has colored the field of neurological research. Obscuring access to studies that conclude a particular treatment is ineffective, while also publishing positive results that are likely to be statistically flawed, tilts the perception toward the potential effectiveness of an intervention and encourages unwarranted human clinical trials.

"There are no standard rules that guide a decision to move from animal studies into human clinical trials," said Ioannidis, who also holds C.F. Rehnborg Professorship at Stanford. "Sometimes interventions are tested in humans with very little evidence that they may be effective. Of the 160 analyses we studied, only eight had what we would call strong evidence of potential effectiveness with no hint of bias in the preliminary animal studies. And of these eight, only two have given positive results in humans."

Ioannidis believes the development of consortiums of groups of researchers studying a particular intervention, coupled with the free sharing of all data about its effectiveness, or lack thereof, is a good first step in reducing bias in animal studies.

"Under the current conditions, only a tiny proportion of interventions that have published some promising results in animals have shown to be at all effective in humans. For example, while dozens of treatments on ischemic or hemorrhagic stroke seem to work in the animal literature, almost none of them have worked in humans," said Ioannidis. "It is hard to believe we could not improve upon that translation record. If we raise the bar for moving into human trials, centralize researchers’ efforts and make all results available, it will be much easier for researchers to know whether they have a potential winner, and it would increase the efficiency of human clinical trials enormously."

(Source: med.stanford.edu)

Amyotrophic Lateral Sclerosis (ALS) is a devastating motor neuron disease that rapidly atrophies the muscles, leading to complete paralysis. Despite its high profile — established when it afflicted the New York Yankees’ Lou Gehrig — ALS remains a disease that scientists are unable to predict, prevent, or cure.

Although several genetic ALS mutations have been identified, they only apply to a small number of cases. The ongoing challenge is to identify the mechanisms behind the non-genetic form of the disease and draw useful comparisons with the genetic forms.

Now, using samples of stem cells derived from the bone marrow of non-genetic ALS patients, Prof. Miguel Weil of Tel Aviv University’s Laboratory for Neurodegenerative Diseases and Personalized Medicine in the Department of Cell Research and Immunology and his team of researchers have uncovered four different biomarkers that characterize the non-genetic form of the disease. Each sample shows similar biological abnormalities to four specific genes, and further research could reveal additional commonalities. “Because these genes and their functions are already known, they give us a specific direction for research into non-genetic ALS diagnostics and therapeutics,” Prof. Weil says. His initial findings were reported in the journal Disease Markers.

Giving in to stress

To hunt for these biomarkers, Prof. Weil and his colleagues turned to samples of bone marrow collected from ALS patients. Though more difficult to collect than blood, bone marrow’s stem cells are easy to isolate and grow in a consistent manner. In the lab, he used these cells as cellular models for the disease. He ultimately discovered that cells from different ALS patients shared the same abnormal characteristics of four different genes that may act as biomarkers of the disease. And because the characteristics appear in tissues that are related to ALS — including in muscle, brain, and spinal cord tissues in mouse models of genetic ALS — they may well be connected to the degenerative process of the disease in humans, he believes.

Searching for the biological significance of these abnormalities, Prof. Weil put the cells under stress, applying toxins to induce the cells’ defense mechanisms. Healthy cells will try to fight off threats and often prove quite resilient, but ALS cells were found to be overwhelmingly sensitive to stress, with the vast majority choosing to die rather than fight. Because this is such an ingrained response, it can be used as a feature for drug screening for the disease, he adds.

The hunt for therapeutics

Whether these biomarkers are a cause or consequence of ALS is still unknown. However, this finding remains an important step towards uncovering the mechanisms of the disease. Because these genes have already been identified, it gives scientists a clear direction for future research. In addition, these biomarkers could lead to earlier and more accurate diagnostics.

Next, Prof. Weil plans to use his lab’s high-throughput screening facility — which can test thousands of compounds’ effects on diseased cells every day — to search for drug candidates with the potential to affect the abnormal expression of these genes or the stress response of ALS cells. A compound that has an impact on these indicators of ALS could be meaningful for treating the disease, he says.

Prof. Weil is the director of the new Cell Screening Facility for Personalized Medicine at TAU. The facility is dedicated to finding potential drugs for rare and Jewish hereditary diseases.

(Source: aftau.org)