New insight on why people with Down syndrome invariably develop Alzheimer’s disease

A new study by researchers at Sanford-Burnham Medical Research Institute reveals the process that leads to changes in the brains of individuals with Down syndrome—the same changes that cause dementia in Alzheimer’s patients. The findings, published in Cell Reports, have important implications for the development of treatments that can prevent damage in neuronal connectivity and brain function in Down syndrome and other neurodevelopmental and neurodegenerative conditions, including Alzheimer’s disease.

Down syndrome is characterized by an extra copy of chromosome 21 and is the most common chromosome abnormality in humans. It occurs in about one per 700 babies in the United States, and is associated with a mild to moderate intellectual disability. Down syndrome is also associated with an increased risk of developing Alzheimer’s disease. By the age of 40, nearly 100 percent of all individuals with Down syndrome develop the changes in the brain associated with Alzheimer’s disease, and approximately 25 percent of people with Down syndrome show signs of Alzheimer’s-type dementia by the age of 35, and 75 percent by age 65. As the life expectancy for people with Down syndrome has increased dramatically in recent years—from 25 in 1983 to 60 today—research aimed to understand the cause of conditions that affect their quality of life are essential.

"Our goal is to understand how the extra copy of chromosome 21 and its genes cause individuals with Down syndrome to have a greatly increased risk of developing dementia," said Huaxi Hu, Ph.D., professor in the Degenerative Diseases Program at Sanford-Burnham and senior author of the paper. "Our new study reveals how a protein called sorting nexin 27 (SNX27) regulates the generation of beta-amyloid—the main component of the detrimental amyloid plaques found in the brains of people with Down syndrome and Alzheimer’s. The findings are important because they explain how beta-amyloid levels are managed in these individuals."

Beta-Amyloid, Plaques and Dementia

Xu’s team found that SNX27 regulates beta-amyloid generation. Beta-amyloid is a sticky protein that’s toxic to neurons. The combination of beta-amyloid and dead neurons form clumps in the brain called plaques. Brain plaques are a pathological hallmark of Alzheimer’s disease and are implicated in the cause of the symptoms of dementia.

"We found that SNX27 reduces beta-amyloid generation through interactions with gamma-secretase—an enzyme that cleaves the beta-amyloid precursor protein to produce beta-amyloid," said Xin Wang, Ph.D., a postdoctoral fellow in Xu’s lab and first author of the publication. "When SNX27 interacts with gamma-secretase, the enzyme becomes disabled and cannot produce beta-amyloid. Lower levels of SNX27 lead to increased levels of functional gamma-secretase that in turn lead to increased levels of beta-amyloid."

SNX27’s Role in Brain Function

Previously, Xu and colleagues found that SNX27 deficient mice shared some characteristics with Down syndrome, and that humans with Down syndrome have significantly lower levels of SNX27. In the brain, SNX27 maintains certain receptors on the cell surface—receptors that are necessary for neurons to fire properly. When levels of SNX27 are reduced, neuron activity is impaired, causing problems with learning and memory. Importantly, the research team found that by adding new copies of the SNX27 gene to the brains of Down syndrome mice, they could repair the memory deficit in the mice.

The researchers went on to reveal how lower levels of SNX27 in Down syndrome are the result of an extra copy of an RNA molecule encoded by chromosome 21 called miRNA-155. miRNA-155 is a small piece of genetic material that doesn’t code for protein, but instead influences the production of SNX27.

With the current study, researchers can piece the entire process together—the extra copy of chromosome 21 causes elevated levels of miRNA-155 that in turn lead to reduced levels of SNX27. Reduced levels of SNX27 lead to an increase in the amount of active gamma-secretase causing an increase in the production of beta-amyloid and the plaques observed in affected individuals.

"We have defined a rather complex mechanism that explains how SNX27 levels indirectly lead to beta-amyloid," said Xu. "While there may be many factors that contribute to Alzheimer’s characteristics in Down syndrome, our study supports an approach of inhibiting gamma-secretase as a means to prevent the amyloid plaques in the brain found in Down syndrome and Alzheimer’s."

"Our next step is to develop and implement a screening test to identify molecules that can reduce the levels of miRNA-155 and hence restore the level of SNX27, and find molecules that can enhance the interaction between SNX27 and gamma-secretase. We are working with the Conrad Prebys Center for Chemical Genomics at Sanford-Burnham to achieve this," added Xu.

New Research on Walnuts and the Fight Against Alzheimer’s Disease

A new animal study published in the Journal of Alzheimer’s Disease indicates that a diet including walnuts may have a beneficial effect in reducing the risk, delaying the onset, slowing the progression of, or preventing Alzheimer’s disease.

Research led by Abha Chauhan, PhD, head of the Developmental Neuroscience Laboratory at the New York State Institute for Basic Research in Developmental Disabilities (IBR), found significant improvement in learning skills, memory, reducing anxiety, and motor development in mice fed a walnut-enriched diet.

The researchers suggest that the high antioxidant content of walnuts (3.7 mmol/ounce) may have been a contributing factor in protecting the mouse brain from the degeneration typically seen in Alzheimer’s disease. Oxidative stress and inflammation are prominent features in this disease, which affects more than five million Americans.

“These findings are very promising and help lay the groundwork for future human studies on walnuts and Alzheimer’s disease – a disease for which there is no known cure,” said lead researcher Dr. Abha Chauhan, PhD. “Our study adds to the growing body of research that demonstrates the protective effects of walnuts on cognitive functioning.”

The research group examined the effects of dietary supplementation on mice with 6 percent or 9 percent walnuts, which are equivalent to 1 ounce and 1.5 ounces per day, respectively, of walnuts in humans. This research stemmed from a previous cell culture study led by Dr. Chauhan that highlighted the protective effects of walnut extract against the oxidative damage caused by amyloid beta protein. This protein is the major component of amyloid plaques that form in the brains of those with Alzheimer’s disease.

Someone in the United States develops Alzheimer’s disease every 67 seconds, and the number of Americans with Alzheimer’s disease and other dementias are expected to rapidly escalate in coming years as the baby boom generation ages. By 2050, the number of people age 65 and older with Alzheimer’s disease may nearly triple, from five million to as many as 16 million, emphasizing the importance of determining ways to prevent, slow or stop the disease. Estimated total payments in 2014 for all individuals with Alzheimer’s disease and other dementias are $214 billion.

Walnuts have other nutritional benefits as they contain numerous vitamins and minerals and are the only nut that contains a significant source of alpha-linolenic acid (ALA) (2.5 grams per ounce), an omega-3 fatty acid with heart and brain-health benefits. The researchers also suggest that ALA may have played a role in improving the behavioral symptoms seen in the study.

Aluminium and its likely contribution to Alzheimer’s disease

A world authority on the link between human exposure to aluminium in everyday life and its likely contribution to Alzheimer’s disease, Professor Christopher Exley of Keele University, UK, says in a new report that it may be inevitable that aluminium plays some role in the disease.

He says the human brain is both a target and a sink for aluminium on entry into the body – “the presence of aluminium in the human brain should be a red flag alerting us all to the potential dangers of the aluminium age. We are all accumulating a known neurotoxin in our brain from our conception to our death. Why do we treat this inevitability with almost total complacency?”

Exley, Professor in Bioinorganic Chemistry, Aluminium and Silicon Research Group in The Birchall Centre, Lennard-Jones Laboratories at Keele University, writes in Frontiers in Neurology about the ‘Aluminium Age’ and its role in the ‘contamination’ of humans by aluminium. He says a burgeoning body burden of aluminium is an inevitable consequence of modern living and this can be thought of as ‘contamination’, as the aluminium in our bodies is of no benefit to us it can only be benign or toxic.

Professor Exley says: “The biological availability of aluminium or the ease with which aluminium reacts with human biochemistry means that aluminium in the body is unlikely to be benign, though it may appear as such due to the inherent robustness of human physiology. The question is raised as to ‘how do you know if you are suffering from chronic aluminium toxicity?’ How do we know that Alzheimer’s disease is not the manifestation of chronic aluminium toxicity in humans?

“At some point in time the accumulation of aluminium in the brain will achieve a toxic threshold and a specific neurone or area of the brain will stop coping with the presence of aluminium and will start reacting to its presence. If the same neurone or brain tissue is also suffering other insults, or another on-going degenerative condition, then the additional response to aluminium will exacerbate these effects. In this way aluminium may cause a particular condition to be more aggressive and perhaps to have an earlier onset - such occurrences have already been shown in Alzheimer’s disease related to environmental and occupational exposure to aluminium.” 

Professor Exley argues that the accumulation of aluminium in the brain inevitably leads to it contributing negatively to brain physiology and therefore exacerbating on-going conditions such as Alzheimer’s disease. He suggests that this is a testable hypothesis and offers a non-invasive method of the removal of aluminium from the body and the brain. He says the aluminium hypothesis of Alzheimer’s disease will only be tested if we are able to lower the body and hence brain burden of aluminium and determine if such has any impact upon the incidence, onset or aggressiveness of Alzheimer’s disease.

Professor Exley adds: “There are neither cures nor effective treatments for Alzheimer’s disease. The role of aluminium in Alzheimer’s disease can be prevented by reducing human exposure to aluminium and by removing aluminium from the body by non-invasive means. Why are we choosing to miss out on this opportunity? Surely the time has come to test the aluminium hypothesis of Alzheimer’s disease once and for all?”

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Novel culture system replicates course of Alzheimer’s disease, confirms amyloid hypothesis

An innovative laboratory culture system has succeeded, for the first time, in reproducing the full course of events underlying the development of Alzheimer’s disease. Using the system they developed, investigators from the Genetics and Aging Research Unit at Massachusetts General Hospital (MGH) now provide the first clear evidence supporting the hypothesis that deposition of beta-amyloid plaques in the brain is the first step in a cascade leading to the devastating neurodegenerative disease. They also identify the essential role in that process of an enzyme, inhibition of which could be a therapeutic target.

"Originally put forth in the mid-1980s, the amyloid hypothesis maintained that beta-amyloid deposits in the brain set off all subsequent events – the neurofibrillary tangles that choke the insides of neurons, neuronal cell death, and inflammation leading to a vicious cycle of massive cell death," says Rudolph Tanzi, PhD, director of the MGH Genetics and Aging Research Unit and co-senior author of the report receiving advance online publication in Nature. “One of the biggest questions since then has been whether beta-amyloid actually triggers the formation of the tangles that kill neurons. In this new system that we call ‘Alzheimer’s-in-a-dish,’ we’ve been able to show for the first time that amyloid deposition is sufficient to lead to tangles and subsequent cell death.”

While the mouse models of Alzheimer’s disease that express the gene variants causing the inherited early-onset form of the disease do develop amyloid plaques in their brains and memory deficits, the neurofibrillary tangles that cause most of the damage do not appear. Other models succeed in producing tangles but not plaques. Cultured neurons from human patients with Alzheimer’s exhibit elevated levels of the toxic form of amyloid found in plaques and the abnormal version of the tau protein that makes up tangles, but not actual plaques and tangles.

Genetics and Aging Research Unit investigator Doo Yeon Kim, PhD, co-senior author of the Nature paper, realized that the liquid two-dimensional systems usually used to grow cultured cells poorly represent the gelatinous three-dimensional environment within the brain. Instead the MGH team used a gel-based, three-dimensional culture system to grow human neural stem cells that carried variants in two genes – the amyloid precursor protein and presenilin 1 – known to underlie early-onset familial Alzheimer’s Disease (FAD). Both of those genes were co-discovered in Tanzi’s laboratory.

After growing for six weeks, the FAD-variant cells were found to have significant increases in both the typical form of beta-amyloid and the toxic form associated with Alzheimer’s. The variant cells also contained the neurofibrillary tangles that choke the inside of nerve cells causing cell death. Blocking steps known to be essential for the formation of amyloid plaques also prevented the formation of the tangles, confirming amyloid’s role in initiating the process. The version of tau found in tangles is characterized by the presence of excess phosphate molecules, and when the team investigated possible ways of blocking tau production, they found that inhibiting the action of an enzyme called GSK3-beta – known to phosphorylate tau in human neurons – prevented the formation of tau aggregates and tangles even in the presence of abundant beta-amyloid and amyloid plaques

"This new system – which can be adapted to other neurodegenerative disorders – should revolutionize drug discovery in terms of speed, costs and physiologic relevance to disease," says Tanzi. "Testing drugs in mouse models that typically have brain deposits of either plaques or tangles, but not both, takes more than a year and is very costly. With our three-dimensional model that recapitulates both plaques and tangles, we now can screen hundreds of thousands of drugs in a matter of months without using animals in a system that is considerably more relevant to the events occurring in the brains of Alzheimer’s patients."

Exercise key to warding off dementia

EXERCISE is one of the best ways to protect against dementia in later life and the earlier you start, the greater the effect, research suggests.

Participating in intellectually stimulating leisure activities, paid work, volunteer work or study can also help protect against memory loss and reduce the risk of developing Alzheimer’s disease.

UWA adjunct clinical professor Nicola Lautenschlager, who led a review of strategies to delay cognitive decline, says there is a growing body of evidence that suggests exercise is beneficial for brain health.

"The knowledge we have so far basically makes it very clear that regular physical activity, even at an older age, can be very beneficial for protecting cognition," she says.

"Beyond that it’s also very effective for protecting or maintaining mental health, especially in relation to symptoms of depression or anxiety."

Prof Lautenschlager, who is based at the University of Melbourne, says older people who are well enough are advised to do 150 minutes of physical activity a week, such as going for walks.

"When it comes [to] brain health…it would be good if the walking speed isn’t very slow, so it shouldn’t be a stroll but rather what we call moderate pace," she says.

"Research has shown that the level of physical activity has to have a certain intensity so that the brain benefits."

Enjoyable hobbies key to brain health

Hobbies that keep the brain active, such as playing an instrument, going to concerts or joining a book club, can also be very helpful as long as it is an activity a person enjoys, Prof Lautenschlager says.

"The minute you prescribe an activity they hate doing…most likely the effect in terms of being beneficial for brain health is lost," she says.

"It produces so much stress in the body not wanting to do it that the stress is more harmful than the benefit of keeping the brain active."

Prof Lautenschlager says middle age is a crucial time for making lifestyle decisions that will determine a person’s health in later life.

"Usually we are talking about when you move into your 30s, definitely the 40s and also still the 50s," she says.

"Things like a high blood pressure or carrying too much weight, if you do that in these decades, it seems to harm the brain long-term in terms of how healthy a person is in their 70s or 80s."

Ideally people should aim for a healthy lifestyle from childhood but luckily research shows lifestyle changes still have an effect on brain health if a person is already old, Prof Lautenschlager says.

"Even programs…with seniors in their 70s and 80s can still make a difference," she says.

The research was published this month in the journal Maturitas.

Worry, jealousy, moodiness linked to higher risk of Alzheimer’s in women

Women who are anxious, jealous, or moody and distressed in middle age may be at a higher risk of developing Alzheimer’s disease later in life, according to a nearly 40-year-long study published in the October 1, 2014, online issue of Neurology®, the medical journal of the American Academy of Neurology.

"Most Alzheimer’s research has been devoted to factors such as education, heart and blood risk factors, head trauma, family history and genetics," said study author Lena Johannsson, PhD, of the University of Gothenburg in Gothenburg, Sweden. "Personality may influence the individual’s risk for dementia through its effect on behavior, lifestyle or reactions to stress."

For the study, 800 women with an average age of 46 were followed for 38 years and given personality tests that looked at their level of neuroticism and extraversion or introversion, along with memory tests. Of those, 19 percent developed dementia.

Neuroticism involves being easily distressed and personality traits such as worrying, jealousy or moodiness. People who are neurotic are more likely to express anger, guilt, envy, anxiety or depression. Introversion is described as shyness and reserve and extraversion is associated with being outgoing.

The women were also asked if they had experienced any period of stress that lasted one month or longer in their work, health, or family situation. Stress referred to feelings of irritability, tension, nervousness, fear, anxiety or sleep disturbances. Responses were categorized as zero to five, with zero representing never experiencing any period of stress, to five, experiencing constant stress during the last five years. Women who chose responses from 3 and 5 were considered to have distress.

The study found that women who scored highest on the tests for neuroticism had double the risk of developing dementia compared to those who scored lowest on the tests. However, the link depended on long-standing stress.

Being either withdrawn or outgoing did not appear to raise dementia risk alone, however, women who were both easily distressed and withdrawn had the highest risk of Alzheimer’s disease in the study. A total of 16 of the 63 women, or 25 percent, who were easily distressed and withdrawn developed Alzheimer’s disease, compared to eight out of the 64 people, or 13 percent, of those who were not easily distressed and were outgoing.

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Memory loss associated with Alzheimer’s reversed for first time

Since its first description over 100 years ago, Alzheimer’s disease has been without effective treatment. That may finally be about to change: in the first, small study of a novel, personalized and comprehensive program to reverse memory loss, nine of 10 participants, including the ones above, displayed subjective or objective improvement in their memories beginning within 3-to-6 months after the program’s start. Of the six patients who had to discontinue working or were struggling with their jobs at the time they joined the study, all were able to return to work or continue working with improved performance. Improvements have been sustained, and as of this writing the longest patient follow-up is two and one-half years from initial treatment. These first ten included patients with memory loss associated with Alzheimer’s disease (AD), amnestic mild cognitive impairment (aMCI), or subjective cognitive impairment (SCI; when a patient reports cognitive problems). One patient, diagnosed with late stage Alzheimer’s, did not improve.

The study, which comes jointly from the UCLA Mary S. Easton Center for Alzheimer’s Disease Research and the Buck Institute for Research on Aging, is the first to suggest that memory loss in patients may be reversed, and improvement sustained, using a complex, 36-point therapeutic program that involves comprehensive changes in diet, brain stimulation, exercise, optimization of sleep, specific pharmaceuticals and vitamins, and multiple additional steps that affect brain chemistry.

The findings, published in the current online edition of the journal Aging, “are very encouraging. However, at the current time the results are anecdotal, and therefore a more extensive, controlled clinical trial is warranted,” said Dale Bredesen, the Augustus Rose Professor of Neurology and Director of the Easton Center at UCLA, a professor at the Buck Institute, and the author of the paper.

In the case of Alzheimer’s disease, Bredesen notes, there is not one drug that has been developed that stops or even slows the disease’s progression, and drugs have only had modest effects on symptoms. “In the past decade alone, hundreds of clinical trials have been conducted for Alzheimer’s at an aggregate cost of over a billion dollars, without success,” he said.

Other chronic illnesses such as cardiovascular disease, cancer, and HIV, have been improved through the use of combination therapies, he noted. Yet in the case of Alzheimer’s and other memory disorders, comprehensive combination therapies have not been explored. Yet over the past few decades, genetic and biochemical research has revealed an extensive network of molecular interactions involved in AD pathogenesis. “That suggested that a broader-based therapeutics approach, rather than a single drug that aims at a single target, may be feasible and potentially more effective for the treatment of cognitive decline due to Alzheimer’s,” said Bredesen.

While extensive preclinical studies from numerous laboratories have identified single pathogenetic targets for potential intervention, in human studies, such single target therapeutic approaches have not borne out. But, said Bredesen, it’s possible addressing multiple targets within the network underlying AD may be successful even when each target is affected in a relatively modest way. “In other words,” he said, “the effects of the various targets may be additive, or even synergistic.”

The uniform failure of drug trials in Alzheimer’s influenced Bredesen’s research to get a better understanding of the fundamental nature of the disease. His laboratory has found evidence that Alzheimer’s disease stems from an imbalance in nerve cell signaling: in the normal brain, specific signals foster nerve connections and memory making, while balancing signals support memory loss, allowing irrelevant information to be forgotten. But in Alzheimer’s disease, the balance of these opposing signals is disturbed, nerve connections are suppressed, and memories are lost.

The model of multiple targets and an imbalance in signaling runs contrary to the popular dogma that Alzheimer’s is a disease of toxicity, caused by the accumulation of sticky plaques in the brain. Bredesen believes the amyloid beta peptide, the source of the plaques, has a normal function in the brain – as part of a larger set of molecules that promotes signals that cause nerve connections to lapse. Thus the increase in the peptide that occurs in Alzheimer’s disease shifts the memory-making vs. memory-breaking balance in favor of memory loss.

Given all this, Bredesen thought that rather than a single targeted agent, the solution might be a systems type approach, the kind that is in line with the approach taken with other chronic illnesses—a multiple-component system.

“The existing Alzheimer’s drugs affect a single target, but Alzheimer’s disease is more complex. Imagine having a roof with 36 holes in it, and your drug patched one hole very well—the drug may have worked, a single “hole” may have been fixed, but you still have 35 other leaks, and so the underlying process may not be affected much.”

Bredesen’s approach is personalized to the patient, based on extensive testing to determine what is affecting the plasticity signaling network of the brain. As one example, in the case of the patient with the demanding job who was forgetting her way home, her therapeutic program consisted of some, but not all of the components involved with Bredesen’s therapeutic program, and included:

(1) eliminating all simple carbohydrates, leading to a weight loss of 20 pounds; (2) eliminating gluten and processed food from her diet, with increased vegetables, fruits, and non-farmed fish; (3) to reduce stress, she began yoga; (4) as a second measure to reduce the stress of her job, she began to meditate for 20 minutes twice per day; (5) she took melatonin each night; (6) she increased her sleep from 4-5 hours per night to 7-8 hours per night; (7) she took methylcobalamin each day; (8) she took vitamin D3 each day; (9) fish oil each day; (10) CoQ10 each day; (11) she optimized her oral hygiene using an electric flosser and electric toothbrush; (12) following discussion with her primary care provider, she reinstated hormone replacement therapy that had been discontinued; (13) she fasted for a minimum of 12 hours between dinner and breakfast, and for a minimum of three hours between dinner and bedtime; (14) she exercised for a minimum of 30 minutes, 4-6 days per week.

The results for nine of the 10 patients reported in the paper suggest that memory loss may be reversed, and improvement sustained with this therapeutic program, said Bredesen. “This is the first successful demonstration,” he noted, but he cautioned that the results are anecdotal, and therefore a more extensive, controlled clinical trial is needed.

The downside to this program is its complexity. It is not easy to follow, with the burden falling on the patients and caregivers, and none of the patients were able to stick to the entire protocol. The significant diet and lifestyle changes, and multiple pills required each day, were the two most common complaints. The good news, though, said Bredesen, are the side effects: “It is noteworthy that the major side effect of this therapeutic system is improved health and an optimal body mass index, a stark contrast to the side effects of many drugs.”

The results for nine of the 10 patients reported in the paper suggest that memory loss may be reversed, and improvement sustained with this therapeutic program, said Bredesen. “This is the first successful demonstration,” he noted, but he cautioned that the results need to be replicated. “The current, anecdotal results require a larger trial, not only to confirm or refute the results reported here, but also to address key questions raised, such as the degree of improvement that can be achieved routinely, how late in the course of cognitive decline reversal can be effected, whether such an approach may be effective in patients with familial Alzheimer’s disease, and last, how long improvement can be sustained,” he said.

Cognitive decline is a major concern of the aging population. Already, Alzheimer’s disease affects approximately 5.4 million Americans and 30 million people globally. Without effective prevention and treatment, the prospects for the future are bleak. By 2050, it’s estimated that 160 million people globally will have the disease, including 13 million Americans, leading to potential bankruptcy of the Medicare system. Unlike several other chronic illnesses, Alzheimer’s disease is on the rise—recent estimates suggest that AD has become the third leading cause of death in the United States behind cardiovascular disease and cancer.

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