Neuroscience

One of the most controversial topics in neurology today is the prevalence of serious permanent brain damage after traumatic brain injury (TBI). Long-term studies and a search for genetic risk factors are required in order to predict an individual’s risk for serious permanent brain damage, according to a review article published by Sam Gandy, MD, PhD, from the Icahn School of Medicine at Mount Sinai in a special issue of Nature Reviews Neurology dedicated to TBI.

About one percent of the population in the developed world has experienced TBI, which can cause serious long-term complications such as Alzheimer’s disease (AD) or chronic traumatic encephalopathy (CTE), which is marked by neuropsychiatric features such as dementia, Parkinson’s disease, depression, and aggression. Patients may be normal for decades after the TBI event before they develop AD or CTE. Although first described in boxers in the 1920s, the association of CTE with battlefield exposure and sports, such as football and hockey, has only recently begun to attract public attention.  

"Athletes such as David Duerson and Junior Seau have brought to light the need for preventive measures and early diagnosis of CTE, but it remains highly controversial because hard data are not available that enable prediction of the prevalence, incidence, and individual risk for CTE," said Dr. Gandy, who is Professor of Neurology and Psychiatry and Director of the Center for Cognitive Health at Mount Sinai. "We need much more in the way of hard facts before we can advise the public of the proper level of concern."

Led by Dr. Gandy, the authors evaluated the pathological impact of single-incident TBI, such as that sustained during military combat; and mild, repetitive TBI, as seen in boxers and National Football League (NFL) players to learn what measures need to be taken to identify risk and incidence early and reduce long-term complications.

Mild, repetitive TBI, as is seen in boxers, football players, and occasionally military veterans who suffer multiple blows to the head, is most often associated with CTE, or a condition called “boxer’s dementia.” Boxing scoring includes a record of knockouts, providing researchers with a starting point in interpreting an athlete’s risk. But no such records exist for NFL players or soldiers on the battlefield.

Dr. Gandy and the authors of the Nature Reviews Neurology piece suggest recruiting large cohorts of players and military veterans in multi-center trials, where players and soldiers maintain a TBI diary for the duration of their lives. The researchers also suggest a genome-wide association study to clearly identify risk factors of CTE. “Confirmed biomarkers of risk, diagnostic tools, and long-term trials are needed to fully characterize this disease and develop prevention and treatment strategies,” said Dr. Gandy.  

Amyloid imaging, which has recently been approved by the U.S. Food and Drug Administration, may be useful as a monitoring tool in TBI, since amyloid plaques are a hallmark symptom of AD-type neurodegeneration. Amyloid imaging consists of a PET scan with an injection of a contrast agent called florbetapir, which binds to amyloid plaque in the brain, allowing researchers to visualize plaque deposits and determine whether the diagnosis is CTE or AD, and monitor progression over time. Tangle imaging is expected to be available soon, complementing amyloid imaging and providing an affirmative diagnosis of CTE. Dr. Gandy and colleagues recently reported the use of amyloid imaging to exclude AD in a retired NFL player with memory problems under their care at Mount Sinai.  

Clinical diagnosis and evaluation of mild, repetitive TBI is a challenge, indicating a significant need for new biomarkers to identify damage, report the authors. Measuring cerebrospinal fluid (CSF) may reflect damage done to neurons post-TBI. Previous research has identified a marked increase in CSF biomarkers in boxers when the CSF is taken soon after a fight, and this may predict which boxers are more likely to develop detrimental long-term effects. CSF samples are now only obtained by invasive lumbar puncture; a blood test would be preferable.

"Biomarkers would be a valuable tool both from a research perspective in comparing them before and after injury and from a clinical perspective in terms of diagnostic and prognostic guidance," said Dr. Gandy. "Having the biomarker information will also help us understand the mechanism of disease development, the reasons for its delayed progression, and the pathway toward effective therapeutic interventions."

Currently, there are no treatments for boxer’s dementia or CTE, but these diseases are preventable. “With more protective equipment, adjustments in the rules of the game, and overall education among athletes, coaches, and parents, we should be able to offer informed consent to prospective sports players and soldiers. With the right combination of identified genetic risk factor, biomarkers, and better drugs, we should be able to dramatically improve the outcome of TBI and prevent the long-term, devastating effects of CTE,” said Dr. Gandy.

People in their 20s don’t have much on their middle-aged counterparts when it comes to some fine motor movements, researchers from UT Arlington have found.

In a simple finger-tapping exercise, study participants’ speed declined only slightly with age until a marked drop in ability with participants in their mid-60s.

Priscila Caçola, an assistant professor of kinesiology at The University of Texas at Arlington, hopes the new work will help clinicians identify abnormal loss of function in their patients. Though motor ability in older adults has been studied widely, not a lot of research has focused on when deficits begin, she said.

The journal Brain and Cognition will include the study in its June 2013 issue. It is already available online.

“We have this so-called age decline, everybody knows that. I wanted to see if that was a gradual process,” Caçola said. “It’s good news really because I didn’t see differences between the young and middle-aged people.”

Caçola’s co-authors on the paper are Jerroed Roberson, a senior kinesiology major at UT Arlington, and Carl Gabbard, a professor in the Texas A&M University Department of Health and Kinesiology.

The researchers based their work on the idea that before movements are made, the brain makes a mental plan. They used an evaluation process called chronometry that compares the time of test participants’ imagined movements to actual movements. Study participants – 99 people ranging in age from 18 to 93 – were asked to imagine and perform a series of increasingly difficult, ordered finger movements. They were divided into three age groups – 18-32, 40-63 and 65-93 – and the results were analyzed.

“What we found is that there is a significant drop-off after the age of 64,” Roberson said. “So if you see a drop-off in ability before that, then it could be a signal that there might be something wrong with that person and they might need further evaluation.”

The researchers also noted that the speed of imagined movements and executed actions tended to be closely associated within each group. That also could be useful knowledge for clinicians, the study said.

“The important message here is that clinicians should be aware that healthy older adults are slower than younger adults, but are able to create relatively accurate internal models for action,” the study said.

Caçola is a member of UT Arlington Center for Health Living and Longevity. She has published previous research on the links between movement representation and motor ability in children.

Researchers at Washington University School of Medicine in St. Louis have identified a new set of genetic markers for Alzheimer’s that point to a second pathway through which the disease develops.

Much of the genetic research on Alzheimer’s centers on amyloid-beta, a key component of brain plaques that build up in the brains of people with the disease.

In the new study, the scientists identified several genes linked to the tau protein, which is found in the tangles that develop in the brain as Alzheimer’s progresses and patients develop dementia. The findings may help provide targets for a different class of drugs that could be used for treatment.

The researchers report their findings online April 24 in the journal Neuron.

"We measured the tau protein in the cerebrospinal fluid and identified several genes that are related to high levels of tau and also affect risk for Alzheimer’s disease,” says senior investigator Alison M. Goate, DPhil, the Samuel and Mae S. Ludwig Professor of Genetics in Psychiatry. “As far as we’re aware, three of these genes have no effect on amyloid-beta, suggesting that they are operating through a completely different pathway.”

A fourth gene in the mix, APOE, had been identified long ago as a risk factor for Alzheimer’s. It has been linked to amyloid-beta, but in the new study, APOE appears to be connected to elevated levels of tau. Finding that APOE is influencing more than one pathway could help explain why the gene has such a big effect on Alzheimer’s disease risk, the researchers say.

“It appears APOE influences risk in more than one way,” says Goate, also a professor of genetics and co-director of the Hope Center for Neurological Disorders. “Some of the effects are mediated through amyloid-beta and others by tau. That suggests there are at least two ways in which the gene can influence our risk for Alzheimer’s disease.”

The new research by Goate and her colleagues is the largest genome-wide association study (GWAS) yet on tau in cerebrospinal fluid. The scientists analyzed points along the genomes of 1,269 individuals who had undergone spinal taps as part of ongoing Alzheimer’s research.

Whereas amyloid is known to collect in the brain and affect brain cells from the outside, the tau protein usually is stored inside cells. So tau usually moves into the spinal fluid when cells are damaged or die. Elevated tau has been linked to several forms of non-Alzheimer’s dementia, and first author Carlos Cruchaga, PhD, says that although amyloid plaques are a key feature of Alzheimer’s disease, it’s possible that excess tau has more to do with the dementia than plaques.

“We know there are some individuals with high levels of amyloid-beta who don’t develop Alzheimer’s disease,” says Cruchaga, an assistant professor of psychiatry. “We don’t know why that is, but perhaps it could be related to the fact that they don’t have elevated tau levels.”

In addition to APOE, the researchers found that a gene called GLIS3, and the genes TREM2 and TREML2 also affect both tau levels and Alzheimer’s risk.

Goate says she suspects changes in tau may be good predictors of advancing disease. As tau levels rise, she says people may be more likely to develop dementia. If drugs could be developed to target tau, they may prevent much of the neurodegeneration that characterizes Alzheimer’s disease and, in that way, help prevent or delay dementia.

The new research also suggests it may one day be possible to reduce Alzheimer’s risk by targeting both pathways.

“Since two mechanisms apparently exist, identifying potential drug targets along these pathways could be very useful,” she says. “If drugs that influence tau could be added to those that affect amyloid, we could potentially reduce risk through two different pathways.”

Human diseases caused by misfolded proteins known as prions are some of most rare yet terrifying on the planet—incurable with disturbing symptoms that include dementia, personality shifts, hallucinations and coordination problems. The most well-known of these is Creutzfeldt-Jakob disease, which can be described as the naturally occurring human equivalent of mad cow disease.

Now, scientists from the Florida campus of The Scripps Research Institute (TSRI) have for the first time identified a pair of drugs already approved for human use that show anti-prion activity and, for one of them, great promise in treating these universally fatal disorders.

The study, led by TSRI Professor Corinne Lasmézas and performed in collaboration with TSRI Professor Emeritus Charles Weissmann and Director of Lead Identification Peter Hodder, was published this week online ahead of print by the journal Proceedings of the National Academy of Sciences.

The new study used an innovative high-throughput screening technique to uncover compounds that decrease the amount of the normal form of the prion protein (PrP, which becomes distorted by the disease) at the cell surface. The scientists found two compounds that reduced PrP on cell surfaces by approximately 70 percent in the screening and follow up tests.

The two compounds are already marketed as the drugs tacrolimus and astemizole.

Tacrolimus is an immune suppressant widely used in organ transplantation. Tacrolimus could prove problematic as an anti-prion drug, however, because of issues including possible neurotoxicity.

However, astemizole is an antihistamine that has potential for use as an anti-prion drug. While withdrawn voluntarily from the U.S. over-the-counter market in 1999 because of rare cardiac arrhythmias when used in high doses, it has been available in generic form in more than 30 countries and has a well-established safety profile. Astemizole not only crosses the blood-brain barrier, but works effectively at a relatively low concentration.

Lasmézas noted that astemizole appears to stimulate autophagy, the process by which cells eliminate unwanted components. “Autophagy is involved in several protein misfolding neurodegenerative diseases such as Alzheimer’s, Parkinson’s and Huntington’s diseases,” she said. “So future studies on the mode of action of astemizole may uncover potentially new therapeutic targets for prion diseases and similar disorders.”

The study noted that eliminating cell surface PrP expression could also be a potentially new approach to treat Alzheimer’s disease, which is characterized by the build-up of amyloid β plaque in the brain. PrP is a cell surface receptor for Aβ peptides and helps mediate a number of critical deleterious processes in animal models of the disease.

The initial clinical trial of a novel approach to treating amyotrophic lateral sclerosis (ALS) – blocking production of a mutant protein that causes an inherited form of the progressive neurodegenerative disease – may be a first step towards a new era in the treatment of such disorders. Investigators from Massachusetts General Hospital (MGH) and Washington University School of Medicine report that infusion of an antisense oligonucleotide against SOD1, the first gene to be associated with familial ALS, had no serious adverse effects and the drug was successfully distributed thoughout the central nervous system.

"This therapy directly targets the cause of this form of ALS – a mutation in SOD1, which was originally discovered here at the MGH by my mentor Robert Brown," says Merit Cudkowicz, MD, chief of Neurology at MGH and senior author of the report in Lancet Neurology, which has been released online. “It’s very exciting that we have reached a stage when we can start clinical trials against this type of ALS.”

ALS causes the death of motor neurons in the brain and spinal cord, stopping transmission of neural signals to nerve fibers and leading to weakness, paralysis and usually death from respiratory failure. Only 10 percent of ALS cases are inherited, and mutations in SOD1 – which produce an aberrant, toxic form of the protein – account for about 20 percent of familial cases. Although that first SOD1 mutation was identified 20 years ago by the team lead by Brown – who is now professor and chief of Neurology at the University of Massachusetts Medical School – a technology that directly addresses such mutations became available only recently.

The current study, the first author of which is Timothy Miller, MD, PhD, of Washington University, used what are called antisense oligonucleotides – small, single-stranded DNA or RNA molecules that prevent production of a protein by binding to its messenger RNA. While antisense medications have been tested against several types of disease, this was the first trial in a neurological disorder, making the assurance of safety – a primary goal of a phase 1 study – particular important. Studies in animal models led by Miller and others found that the experimental antisense drug used in this trial reduced expression of mutated and nonmutated SOD1 and slowed the progression of ALS.

Conducted at the MGH, Washington University, Johns Hopkins University and the Methodist Neurological Institute in Houston, the trial enrolled a total of 21 patients with SOD1 familial ALS. Four sequential groups of participants received spinal infusions over an 11-hour period of the antisense drug or a placebo, with the active drug being administered at one of four dosage levels. Since participants in one group were free to join a subsequent group more than 60 days later, seven received two infusions and two received a total of three.

Some of the participants reported the type of adverse effects typically associated with spinal infusions – headache and back pain – with no difference between the active drug and placebo groups. Participants who receive subsequent infusions reported fewer adverse effects. Cerebrospinal fluid samples taken immediately after infusion revealed the presence of the antisense oligonucleotidein all participants receiving  the drug at levels close to what was predicted based on animal studies. Analysis of spinal cord samples from one participant who had later died from ALS found drug levels highest at the site of the infusion and lowest at the furthest point and suggested that prior estimates of how long the drug would persist in the spinal cord were accurate.

Cudkowicz notes that the next step will be a larger study to address long-term safety and take a first look at the effectiveness of antisense treatment against ALS “This is a very important step forward for neurodegenerative disorders in general,” she explains. “There are other ALS gene mutations that antisense technology may be useful against. There also is an ongoing study of a different oligonucleotide against spinal muscular atrophy, and ongoing preclinical studies in Huntington’s disease, myotonic dystrophy and other neurological disorders are in development.

"The first person with ALS that I cared for had SOD1 ALS," she adds, "and I promised her a commitment to finding a treatment for this form of the disease. It’s so gratifying to finally be at the stage of knowledge where we can start testing this treatment in patients with SOD1 ALS. We also hope that this treatment may apply to the broader population of patient with sporadic ALS." Cudkowicz is the Julieanne Dorn Professor of Neurology at Harvard Medical School. 

The feeling of hunger itself may protect against Alzheimer’s disease, according to study published today in the journal PLOS ONE. Interestingly, the results of this study in mice suggest that mild hunger pangs, and related hormonal pathways, may be as important to the much-discussed value of “caloric restriction” as actually eating less.

Caloric restriction is a regimen where an individual consumes fewer calories than average, but not so few that they become malnourished. Studies in many species have suggested that it could protect against neurodegenerative disorders and extend lifespans, but the effect has not been confirmed in human randomized clinical trials.

Efforts to understand how cutting calories may protect the brain have grown increasingly important with news that American Alzheimer’s deaths are increasing, and because the best available treatments only delay onset in a subset of patients.

Study authors argue that hormonal signals are the middlemen between an empty gut and the perception of hunger in the brain, and that manipulating them may effectively counter age-related cognitive decline in the same way as caloric restriction.

“This is the first paper, as far as we are aware, to show that the sensation of hunger can reduce Alzheimer’s disease pathology in a mouse model of the disease,” said Inga Kadish, Ph.D., assistant professor in the Department of Cell, Developmental and Integrative Biology (CDIB) within the School of Medicine at the University of Alabama at Birmingham. “If the mechanisms are confirmed, hormonal hunger signaling may represent a new way to combat Alzheimer’s disease, either by itself or combined with caloric restriction.”

The team theorizes that feeling hungry creates mild stress. That, in turn, fires up metabolic signaling pathways that counter plaque deposits known to destroy nerve cells in Alzheimer’s patients. The idea is an example of hormesis theory, where damaging stressors like starvation are thought to be good for you when experienced to a lesser degree.

To study the sensation of hunger, the research team analyzed the effects of the hormone ghrelin, which is known to make us feel hungry. They used a synthetic form of ghrelin in pill form, which let them control dosage such that the ghrelin-treated mice felt steadily, mildly hungry.

If it could be developed, a treatment that affected biochemical pathways downstream of hunger signals might help delay cognitive decline without consigning people to a life of feeling hungry. Straight caloric restriction would not be tolerable for many persons over the long-run, but manipulating post-hunger signaling might.

This line of thinking becomes important because any protective benefit brought about by drugs or diets that mildly adjust post-hunger signals might be most useful if started in those at risk as early in life as possible. Attempts to treat the disease years later – when nerve networks are damaged enough for neurological symptoms to appear – may be too late. In the current study, it was long-term treatment with a ghrelin agonist that improved cognitive performance in mice tested when they had reached an advanced age.

Study details

The study looked at whether or not the feeling of hunger, in the absence of caloric restriction, could counter Alzheimer’s pathology in mice genetically engineered to have three genetic mutations known to cause the disease in humans.

Study mice were divided into three groups: one that received the ‘synthetic ghrelin’ (ghrelin agonist), a second that underwent caloric restriction (20 percent less food) and a third group that was fed normally. Study measures looked at each group’s ability to remember, their degree of Alzheimer’s pathology and their level of related, potentially harmful immune cell activation.

Results of such studies are most appropriately presented in terms of general trends in the data and statistical assessments of their likelihood if only chance factors were in play, a trait captured in each result’s P value (the smaller the better). Thus, the first formal result of the study are that, in mice with the human Alzheimer’s mutations, both the group treated with the ghrelin agonist LY444711 and the group that underwent caloric restriction performed significantly better in the a water maze than did than mice fed normally (p=0.023).

The water maze is the standard test used to measure mouse memory. Researchers put mice in a pool with an invisible platform on which they could rest, and measured how quickly the mice found the platform in a series of tests. Mice with normal memory will remember where the platform is, and find it more quickly each time they are placed in the pool. Ghrelin agonist-treated mice found the hidden platform 26 percent faster than control mice, with caloric restricted mice doing so 23 percent faster than control mice.

The second result was a measure of the buildup of a cholesterol-related protein called amyloid beta in the forebrain, an early step in the destruction of nerve cells that accompanies Alzheimer’s disease. The formal amyloid beta results show that mice either treated with the ghrelin agonist or calorically restricted had significantly less buildup of amyloid beta in the dentate gyrus, the part of the brain that controls memory function, than mice fed normally (i.e., control, 3.95±0.83; LY, 2.05±0.26 and CR, 1.28±0.17%, respectively; Wilcoxon p=0.04).

The above results translate roughly into a 67 percent reduction of this pathology in caloric-restricted mice as compared to control mice, and a 48 percent reduction of amyloid beta deposits when comparing the ghrelin-treated mice with the control group. These percentages are neither final nor translatable to humans, but are simply meant to convey the idea of “better.”

Finally, the team examined the difference in immune responses related to Alzheimer’s pathology in each of the three groups. Microglia are the immune cells of the brain, engulfing and removing invading pathogens and dead tissue. They have also been implicated in several diseases when their misplaced activation damages tissues. The team found that mice receiving the ghrelin agonist treatment had both reduced levels of microglial activation compared to the control group, similar to the effect of caloric restriction.

The ghrelin agonist used in the study does not lend itself to clinical use and will not play a role in the future prevention of Alzheimer’s disease, said Kadish. It was meant instead to prove a principle that hormonal hunger signaling itself can counter Alzheimer’s pathology in a mammal. The next step is to understand exactly how it achieved this as a prerequisite to future treatment design.

Ghrelin is known to create hunger signals by interacting with the arcuate nucleus in the part of the brain called the hypothalamus, which then sends out signaling neuropeptides that help the body sense and respond to energy needs. Studies already underway in Kadish’s lab seek to determine the potential role of these pathways and related genes in countering disease.

“Our group in the School of Public Health was studying whether or not a ghrelin agonist could make mice hungry as we sought to unravel mechanisms contributing to the life-prolonging effects of caloric restriction,” said David Allison, Ph.D., associate dean for Science in the UAB School of Public Health and the project’s initiator.

“Because of the interdisciplinary nature of UAB, our work with Dr. Allison led to an amazing conversation with Dr. Kadish about how we might combine our research with her longtime expertise in neurology because caloric restriction had been shown in early studies to counter Alzheimer’s disease,” said Emily Dhurandhar, Ph.D., a trainee in the UAB Nutrition Obesity Research Center and first study author. “The current study is the result.”