Posts tagged beta amyloid

Without a steady supply of blood, neurons can’t work. That’s why one of the culprits behind Alzheimer’s disease is believed to be the persistent blood clots that often form in the brains of Alzheimer’s patients, contributing to the condition’s hallmark memory loss, confusion and cognitive decline.

New experiments in Sidney Strickland’s Laboratory of Neurobiology and Genetics at Rockefeller University have identified a compound that might halt the progression of Alzheimer’s by interfering with the role amyloid-β, a small protein that forms plaques in Alzheimer’s brains, plays in the formation of blood clots. This work is highlighted in the July issue of Nature Reviews Drug Discovery.

For more than a decade, potential Alzheimer’s drugs have targeted amyloid-β, but, in clinical trials, they have either failed to slow the progression of the disease or caused serious side effects. However, by targeting the protein’s ability to bind to a clotting agent in blood, the work in the Strickland lab offers a promising new strategy, according to the highlight published in print on July 1.

This latest study builds on previous work in Strickland’s lab showing amyloid-β can interact with fibrinogen, the clotting agent, to form difficult-to-break-down clots that alter blood flow, cause inflammation and choke neurons.

“Our experiments in test tubes and in mouse models of Alzheimer’s showed the compound, known as RU-505, helped restore normal clotting and cerebral blood flow. But the big pay-off came with behavioral tests in which the Alzheimer’s mice treated with RU-505 exhibited better memories than their untreated counterparts,” Strickland says. “These results suggest we have found a new strategy with which to treat Alzheimer’s disease.”

RU-505 emerged from a pack of 93,716 candidates selected from libraries of compounds, the researchers write in the June issue of the Journal of Experimental Medicine. Hyung Jin Ahn, a research associate in the lab, examined these candidates with a specific goal in mind: Find one that interferes with the interaction between fibrinogen and amyloid-β. In a series of tests that began with a massive, automated screening effort at Rockefeller’s High Throughput Resource Center, Ahn and colleagues winnowed the 93,000 contenders to five. Then, test tube experiments whittled the list down to one contender: RU-505, a small, synthetic compound. Because RU-505 binds to amyloid-β and only prevents abnormal blood clot formation, it does not interfere with normal clotting. It is also capable of passing through the blood-brain barrier.

“We tested RU-505 in mouse models of Alzheimer’s disease that over-express amyloid-β and have a relatively early onset of disease. Because Alzheimer’s disease is a long-term, progressive disease, these treatments lasted for three months,” Ahn says. “Afterward, we found evidence of improvement both at the cellular and the behavioral levels.”

The brains of the treated mice had less of the chronic and harmful inflammation associated with the disease, and blood flow in their brains was closer to normal than that of untreated Alzheimer’s mice. The RU-505-treated mice also did better when placed in a maze. Mice naturally want to escape the maze, and are trained to recognize visual cues to find the exit quickly. Even after training, Alzheimer’s mice have difficulty in exiting the maze. After these mice were treated with RU-505, they performed much better.

“While the behavior and the brains of the Alzheimer’s mice did not fully recover, the three-month treatment with RU-505 prevents much of the decline associated with the disease,” Strickland says.

The researchers have begun the next steps toward developing a human treatment. Refinements to the compound are being supported by the Robertson Therapeutic Development Fund and the Tri-Institutional Therapeutic Discovery Institute. As part of a goal to help bridge critical gaps in drug discovery, these initiatives support the early stages of drug development, as is being done with RU-505.

“At very high doses, RU-505 is toxic to mice and even at lower doses it caused some inflammation at the injection site, so we are hoping to find ways to reduce this toxicity, while also increasing RU-505’s efficacy so smaller doses can accomplish similar results,” Ahn says.

(Source: newswire.rockefeller.edu)

A specific preparation of cocoa-extract called Lavado may reduce damage to nerve pathways seen in Alzheimer’s disease patients’ brains long before they develop symptoms, according to a study conducted at the Icahn School of Medicine at Mount Sinai and published June 20 in the Journal of Alzheimer’s Disease (JAD).  

Specifically, the study results, using mice genetically engineered to mimic Alzheimer’s disease, suggest that Lavado cocoa extract prevents the protein β-amyloid- (Aβ) from gradually forming sticky clumps in the brain, which are known to damage nerve cells as Alzheimer’s disease progresses.

Lavado cocoa is primarily composed of polyphenols, antioxidants also found in fruits and vegetables, with past studies suggesting that they prevent degenerative diseases of the brain.  

The Mount Sinai study results revolve around synapses, the gaps between nerve cells. Within healthy nerve pathways, each nerve cell sends an electric pulse down itself until it reaches a synapse where it triggers the release of chemicals called neurotransmitters that float across the gap and cause the downstream nerve cell to “fire” and pass on the message.

The disease-causing formation of Aβ oligomers – groups of molecules loosely attracted to each other –build up around synapses. The theory is that these sticky clumps physically interfere with synaptic structures and disrupt mechanisms that maintain memory circuits’ fitness. In addition, Aβ triggers immune inflammatory responses, like an infection, bringing an on a rush of chemicals and cells meant to destroy invaders but that damage our own cells instead.

“Our data suggest that Lavado cocoa extract prevents the abnormal formation of Aβ into clumped oligomeric structures, to prevent synaptic insult and eventually cognitive decline,” says lead investigator Giulio Maria Pasinetti, MD, PhD, Saunders Family Chair and Professor of Neurology at the Icahn School of Medicine at Mount Sinai. “Given that cognitive decline in Alzheimer’s disease is thought to start decades before symptoms appear, we believe our results have broad implications for the prevention of Alzheimer’s disease and dementia.

Evidence in the current study is the first to suggest that adequate quantities of specific cocoa polyphenols in the diet over time may prevent the glomming together of Aβ into oligomers that damage the brain, as a means to prevent Alzheimer’s disease.  

The research team led by Dr. Pasinetti tested the effects of extracts from Dutched, Natural, and Lavado cocoa, which contain different levels of polyphenols. Each cocoa type was evaluated for its ability to reduce the formation of Aβ oligomers and to rescue synaptic function. Lavado extract, which has the highest polyphenol content and anti-inflammatory activity among the three, was also the most effective in both reducing formation of Aβ oligomers and reversing damage to synapses in the study mice.  

“There have been some inconsistencies in medical literature regarding the potential benefit of cocoa polyphenols on cognitive function,” says Dr. Pasinetti. “Our finding of protection against synaptic deficits by Lavado cocoa extract, but not Dutched cocoa extract, strongly suggests that polyphenols are the active component that rescue synaptic transmission, since much of the polyphenol content is lost by the high alkalinity in the Dutching process.”  

Because loss of synaptic function may have a greater role in memory loss than the loss of nerve cells, rescue of synaptic function may serve as a more reliable target for an effective Alzheimer’s disease drug, said Dr. Pasinetti.

The new study provides experimental evidence that Lavado cocoa extract may influence Alzheimer’s disease mechanisms by modifying the physical structure of Aβ oligomers. It also strongly supports further studies to identify the metabolites of Lavado cocoa extract that are active in the brain and identify potential drug targets.

In addition, turning cocoa-based Lavado into a dietary supplement may provide a safe, inexpensive and easily accessible means to prevent Alzheimer’s disease, even in its earliest, asymptomatic stages.

(Source: mountsinai.org)

Scientists at NYU Langone Medical Center have identified a compound, called 2-PMAP, in animal studies that reduced by more than half levels of amyloid proteins in the brain associated with Alzheimer’s disease. The researchers hope that someday a treatment based on the molecule could be used to ward off the neurodegenerative disease since it may be safe enough to be taken daily over many years.  

“What we want in an Alzheimer’s preventive is a drug that modestly lowers amyloid beta and is also safe for long term use,” says Martin J. Sadowski, MD, PhD, associate professor of neurology, psychiatry, and biochemistry and molecular pharmacology, who led the research to be published online June 3 in the journal Annals of Neurology. “Statin drugs that lower cholesterol appear to have those properties and have made a big impact in preventing coronary artery disease. That’s essentially what many of us envision for the future of Alzheimer’s medicine.”

The 2-PMAP molecule that Dr. Sadowski’s team identified is non-toxic in mice, gets easily into the brain, and lowers the production of amyloid beta and associated amyloid deposits.

The prime target for Alzheimer’s prevention is amyloid beta. Decades before dementia begins, this small protein accumulates in clumps in the brain. Modestly lowering the production of amyloid beta in late middle age, and thus removing some of the burden from the brain’s natural clearance mechanisms, is believed to be a good prevention strategy. Researchers two years ago reported that something like this happens naturally in about 0.5 percent of Icelanders, due to a mutation they carry that approximately halves amyloid beta production throughout life. These fortunate people show a slower cognitive decline in old age, live longer, and almost never get Alzheimer’s.

Prevention of Alzheimer’s dementia is now considered more feasible than stopping it after it has begun, when brain damage is already severe. Every prospective Alzheimer’s drug in clinical trials has failed even to slow the disease process at that late stage. “The key is to prevent the disease process from going that far,” Dr. Sadowski says.

Dr. Sadowski and colleagues screened a library of compounds and found that 2-PMAP reduced the production of amyloid beta’s mother protein, known as amyloid precursor protein (APP). The APP protein normally is cut by enzymes in a way that leaves amyloid beta as one of the fragments. Dr. Sadowski’s team found that 2-PMAP, even at low, non-toxic concentrations, significantly reduced APP production in test cells, lowering amyloid beta levels by 50 percent or more.

The scientists subsequently found that 2-PMAP had essentially the same impact on APP and amyloid beta in the brains of living mice. The mice were engineered to have the same genetic mutations found in Alzheimer’s patients with a hereditary form of the disease, causing overproduction of APP and Alzheimer’s-like amyloid deposits. A five-day treatment with 2-PMAP lowered brain levels of APP and, even more so, levels of amyloid beta. Four months of treatment sharply reduced the amyloid deposits and prevented the cognitive deficits that are normally seen in these transgenic mice as they get older.

Dr. Sadowski and his laboratory are now working to make chemical modifications to the compound to improve its effectiveness. But 2-PMAP already seems to have advantages over other amyloid-lowering compounds, he says. One is that it can cross efficiently from the bloodstream to the brain, and thus doesn’t require complex modifications that might compromise its effects on APP.

The compound also appears to have a highly selective effect on APP production, by interfering with the translation of APP’s gene transcript into the APP protein itself. The best known candidates for Alzheimer’s preventives lower amyloid by inhibiting the secretase enzymes that cleave amyloid beta from APP, tending to cause unwanted side-effects via their off target interference with the processing of other client proteins cleaved by these enzymes. A clinical trial of one secretase inhibitor was halted in 2010 after it was found to worsen dementia and cause a higher incidence of skin cancer.

Alzheimer’s disease, the most common form of dementia, currently afflicts more than five million Americans, according to the Alzheimer’s Association. Unless preventive drugs or treatments are developed, the prevalence of Alzheimer’s is expected to triple by 2050.

(Source: communications.med.nyu.edu)

In surprise findings, scientists at The Scripps Research Institute (TSRI) have discovered that a protein with a propensity to form harmful aggregates in the body when produced in the liver protects against Alzheimer’s disease aggregates when it is produced in the brain. The results suggest that drugs that can boost the protein’s production specifically in neurons could one day help ward off Alzheimer’s disease.

“This result was completely unexpected when we started this research,” said TSRI Professor Joel N. Buxbaum, MD. “But now we realize that it could indicate a new approach for Alzheimer’s prevention and therapy.”

Buxbaum and members of his laboratory report their latest finding in the May 21, 2014 issue of the Journal of Neuroscience.

First Hints

The study centers on transthyretin (TTR), a protein that is known to function as a transporter, carrying the thyroid hormone thyroxine and vitamin A through the bloodstream and cerebrospinal fluid. To do this job, it must come together in a four subunit structure called a tetramer. Certain factors such as old age and TTR gene mutations can make these tetramers prone to fall apart and misfold into tough aggregates called amyloids. TTR amyloids accumulate in the heart, kidneys, peripheral nerves and other tissues and cause life-shortening diseases including familial amyloid polyneuropathy and senile systemic (cardiac) amyloidosis.

Starting in the mid 1990s, however, reports from several laboratories hinted that TTR in the brain might protect against other amyloids—particularly the Alzheimer’s-associated protein amyloid beta. In test tube experiments, TTR seemed able to grab hold of amyloid beta and prevent it from aggregating. In transgenic “Alzheimer’s mice,” which overproduce amyloid beta, TTR expression was increased in affected brain tissue, compared to control mice, as one would expect from a protective response.

“I didn’t really believe those reports at the time,” Buxbaum said.

But he was working on TTR amyloidoses and had the tools needed to investigate the issue genetically. He and his colleagues at TSRI did those experiments, and found, to their surprise, that overproducing TTR in “Alzheimer’s mice” did indeed protect the animals: it reduced their memory deficits as well as the accumulations of amyloid beta aggregates in their brains. Since that 2008 study, Buxbaum and colleagues have gone on to publish additional experiments examining the mechanism of the protection including two last year, in collaboration with the Wright and Kelly laboratories at TSRI and Roberta Cascella in Florence, that showed how TTR tetramers can bind to amyloid beta and inhibit the latter from forming the more harmful types of aggregate.

Context Is Everything

In the latest study, Buxbaum and his team, including lead authors Xin Wang and Francesca Cattaneo, at the time both postdoctoral fellows in the Buxbaum laboratory, found another key piece of evidence for TTR’s protective role.

TTR is known to be produced principally in the liver and in the parts of the brain where cerebrospinal fluid is made. Prior studies in the Buxbaum group found evidence that TTR can also be produced in neurons, albeit at low levels. Still, it has remained unclear how TTR production, in neurons or in other cells, would be increased in response to amyloid beta accumulation.

To start, the team analyzed a segment of DNA near the TTR gene called the promoter region, where, in principle, special DNA-binding proteins called transcription factors could increase TTR gene activity. The analysis suggested that Heat Shock Factor 1 (HSF1), known as a master switch for a broad protective response against certain types of cellular stress, could bind to the TTR gene’s promoter.

Further experiments showed that HSF1 does indeed bind to this region and that two known stimulators of HSF1—heat and a compound called celastrol—also boost HSF1 binding to the TTR promoter, in addition to boosting TTR production. Remarkably, though, the researchers found that HSF1’s dialing-up of TTR production seemed to occur only in neuronal-type cells, not in liver cells where most TTR is produced.

In fact, the researchers found that in liver cells the HSF1 response somehow brought about a modest decrease in TTR production. That result may seem puzzling, but it is consistent with the idea that liver-cell TTR, which is produced at 15 to 20 times the levels of neuronal TTR, is more likely to be hazardous than protective.

Using genetic techniques to force cells to overproduce HSF1, the researchers again saw jumps in TTR gene activity and protein production, but only in neuronal cells. In liver cells TTR activity rose when HSF1 was blocked, suggesting that HSF1 normally helps keep a lid on liver TTR production.

“It’s becoming more and more evident in biology that the same molecule can do very different things in different contexts,” Buxbaum said.

To underscore the relevance to Alzheimer’s, his team examined neurons from the hippocampus brain region in ordinary lab mice and in amyloid-beta-overproducing Alzheimer’s mice. Again consistent with the concept of TTR as protective in neurons, they found that the frequency of HSF1 binding to the TTR gene promoter, and the numbers of resulting TTR gene transcripts, were both doubled in the Alzheimer’s mice compared to the ordinary lab mice.

Buxbaum and his colleagues plan to do further research on this apparent TTR-mediated stress response in neurons to determine, among other things, precisely how Alzheimer’s-associated amyloid beta switches it on. But they have already begun to think about developing a small molecule compound, suitable for delivery in a pill, that at least modestly boosts HSF1 activity and/or TTR production in neurons—and thus might prevent or delay Alzheimer’s dementia.

(Source: scripps.edu)

Neuroscientists at Mayo Clinic in Florida have defined a subtype of Alzheimer’s disease (AD) that they say is neither well recognized nor treated appropriately.

The variant, called hippocampal sparing AD, made up 11 percent of the 1,821 AD-confirmed brains examined by Mayo Clinic researchers — suggesting this subtype is relatively widespread in the general population. The Alzheimer’s Association estimates that 5.2 million Americans are living with AD. And with nearly half of hippocampal sparing AD patients being misdiagnosed, this could mean that well over 600,000 Americans make up this AD variant, researchers say.

In an oral presentation at the annual meeting of the American Academy of Neurology in Philadelphia, scientists say hippocampal sparing AD often produces symptoms that are substantially different from the most commonly known form of AD, which affects the hippocampus, the center of memory.

The patients, mostly male, are afflicted at a much younger age, and their symptoms can be bizarre — behavioral problems such as frequent and sometimes profane angry outbursts, feelings that their limbs do not belong to them and are controlled by an “alien” unidentifiable force, or visual disturbances in the absence of eye problems, researchers say.

They also decline at a much faster rate than do patients with the most common form of AD.

“Many of these patients, however, have memories that are near normal, so clinicians often misdiagnose them with a variety of conditions that do not match the underlying neuropathology,” says the study’s lead author, Melissa Murray, Ph.D., an assistant professor of neuroscience at Mayo Clinic in Florida.

Many of these patients are diagnosed with frontotemporal dementia, a disorder characterized by changes in personality and social behavior, or corticobasal syndrome, characterized by movement disorders and cognitive dysfunction. Language dysfunction is also more common in hippocampal sparing AD, although patients do not have vocal or hearing deficits.

“What is tragic is that these patients are commonly misdiagnosed and we have new evidence that suggests drugs now on the market for AD could work best in these hippocampal sparing patients — possibly better than they work in the common form of the disease,” Dr. Murray says.

The researchers benefit greatly from one of the largest brain banks in the country — more than 6,500 brain donations — as well as a collaborative environment between neuroscience research and neurology at Mayo Clinic, she says.

Both hallmark proteins of AD — amyloid beta (Aβ), which forms Aβ plaques, and tau, which produces tangles — are found across all subtypes of AD, including hippocampal sparing AD. The researchers developed a mathematical algorithm to classify AD subtypes using tangle counts. “What is fascinating is that all the AD patient subtypes had the same amount of amyloid, but for some reason tau tangles were found in strategic cortical regions disproportionate to the hippocampus.”

In these patients, tau preferentially damages and eventually destroys neurons in parts of the brain involved in behavior, motor awareness and recognition, as well as use of speech and vision, Dr. Murray says.

She says she hopes this research, the second high-profile Mayo study to highlight hippocampal sparing AD, will “open the minds” of clinicians who are trying to diagnose dementia, helping them understand that loss of memory is not present in every AD patient.

“Our studies support the notion that dementia related to AD does not necessarily equate to a loss of memory, and points to the need for more research in amyloid and tau imaging biomarkers to help clinicians accurately diagnose AD — regardless of subtype,” Dr. Murray says.

(Source: newsnetwork.mayoclinic.org)

Researchers at Lancaster University have invented a new imaging tool inspired by the humble sewing machine which is providing fresh insight into the origins of Alzheimer’s and Parkinson’s disease.

These diseases are caused by tiny toxic proteins too small to be studied with traditional optical microscopy.

Previously it was thought that Alzheimer’s was caused by the accumulation of long ‘amyloid’ fibres at the centre of senile plaques in the brain, due to improper folding of a protein called amyloid-β.

But new research suggests that these fibres and plaques are actually the body’s protective response to the presence of even smaller, more toxic structures made from amyloid-β called ‘oligomers’.

Existing techniques are not sufficient to get a good look at these proteins; optical microscopy does not provide enough resolution at this scale, and electron microscopy gives the resolution but not the contrast.

To solve the problem, Physicist Dr Oleg Kolosov and his team at Lancaster have developed a new imaging technique - Ultrasonic Force Microscopy (UFM) - inspired by the motion of a sewing machine. Their work has been published in Scientific Reports.

Dr Kolosov said: “By using a vibrating scanner, which moves quickly up and down like the foot of a sewing machine needle, the friction between the sample and the scanner was reduced – resulting in a better quality, and high contrast nanometre scale resolution image.”

It is one of a new generation of tools being developed worldwide to bring the oligomers into focus, enabling medical researchers to understand how they behave.

At Lancaster, Claire Tinker used UFM to image these oligomers. To help see them more clearly she needed to increase the contrast of the image and used poly-L-lysine (PLL) which kept the proteins stuck to the slides as the vibrating scanner was passed over them.

Lancaster University Biomedical Scientist Professor David Allsop said: “These high quality images are vitally important if we are to understand the pathways involved in formation of these oligomers, and this new technique will now be used to test the effects of inhibitors of oligomer formation that we are developing as a possible new treatment for Alzheimer’s disease.”

The technique worked so well that the team now hopes to develop it so that oligomer formation can be monitored as they are made in real time.

This would give researchers a clearer understanding of the early phases of Alzheimer’s and Parkinson’s and could potentially be one way of developing a future test for these diseases.

(Source: alphagalileo.org)