Apolipoprotein E4 Effects in Alzheimer’s Disease are Mediated by Synaptotoxic Oligomeric Amyloid-β

mind. 2012 may 26. [Epub ahead of print]

Apolipoprotein E4 results in Alzheimer’s illness are mediated via synaptotoxic oligomeric amyloid-β

Koffie RMHashimoto TTai HCKay KRSerrano-Pozo AJoyner DHou SKopeikina KJFrosch MPLee VMHoltzman DMHyman BTSpires-Jones TL.

source

1 Massachusetts common medical institution, Harvard clinical faculty, 114 sixteenth street, Charlestown, MA 02129, america.

abstract

The apolipoprotein E ε4 gene is crucial genetic risk issue for sporadic Alzheimer’s illness, however the link between this gene and neurodegeneration remains unclear. using array tomography, we analysed >50 000 synapses in brains of 11 sufferers with Alzheimer’s diseaseand 5 non-demented keep watch over subjects and found that synapse loss round senile plaques in Alzheimer’s illness correlates with the burden of oligomeric amyloid-β within the neuropil and that this synaptotoxic oligomerized peptide is present at a subset of synapses. further prognosis finds apolipoprotein E εfour sufferers with Alzheimer’s illness have significantly larger oligomeric amyloid-β burden and exacerbated synapse loss around plaques in comparison with apolipoprotein E εthree sufferers. Apolipoprotein E4 protein colocalizes with oligomeric amyloid-β and enhances synaptic localization of oligomeric amyloid-β by using >5-fold. Biochemical characterization shows that the amyloid-β enriched at synapses via apolipoprotein E4 contains sodium dodecyl sulphate-secure dimers and trimers. In mouse primary neuronal culture, lipidated apolipoprotein E4 enhances oligomeric amyloid-β association with synapses by the use of a mechanism involving apolipoprotein E receptors. together, these information recommend that apolipoprotein E4 is a co-factor that enhances the toxicity of oligomeric amyloid-β both through increasing its ranges and directing it to synapses, offering a hyperlink between apolipoprotein E ε4 genotype and synapse loss, an immense correlate of cognitive decline in Alzheimer’sdisease.

Citation

 

Nutrition in Severe Dementia

Current Gerontology and Geriatrics Research Volume 2012 (2012), Article ID 983056, 7 pages doi:10.1155/2012/983056

Behavior Neurology Section, Federal University of São Paulo (UNIFESP), 04025-000 São Paulo SP, Brazil

Received 17 December 2011; Revised 18 February 2012; Accepted 21 February 2012

Academic Editor: Andrea Fuso

Copyright © 2012 Glaucia Akiko Kamikado Pivi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

An increasing proportion of older adults with Alzheimer’s disease or other dementias are now surviving to more advanced stages of the illness. Advanced dementia is associated with feeding problems, including difficulty in swallowing and respiratory diseases. Patients become incompetent to make decisions. As a result, complex situations may arise in which physicians and families decide whether artificial nutrition and hydration (ANH) is likely to be beneficial for the patient. The objective of this paper is to present methods for evaluating the nutritional status of patients with severe dementia as well as measures for the treatment of nutritional disorders, the use of vitamin and mineral supplementation, and indications for ANH and pharmacological therapy.

1. Introduction

Dementia is one of the most common and most significant health problems in the elderly and is one of the main causes of disability in older age [1] A growing proportion of older adults with Alzheimer disease (AD) or other dementias are now surviving to more advanced stages of the illness [23].

Much clinical attention and research effort has been directed towards early diagnosis and mild stages of dementia, and prodromal stages, formerly classified as mild cognitive impairment (MCI). The later stages of the disease are as important as, if not more important than, the earlier stages because of the unique characteristics and events which occur affecting the lives of patients and their carers. Severe dementia (SD) is still relatively neglected and its prevalence is unclear, but it is estimated that one-third of dementia patients are in the severe stages [46].

There are several causes for concern in SD, when many impairments become more apparent: functional disabilities mean that carers have to take over more practical tasks, such as bathing, toileting, and feeding; there are special considerations with palliative care and ethical issues of terminal care along with physical problems [79].

SD, including AD, is associated with feeding problems, including difficulty in swallowing, leading to choking, chewing but failing to swallow, and active resistance to hand feeding. Because patients with dementia have limited language and communication abilities, it is difficult to identify the source of aversive behavior [910]. Nevertheless eating and drinking may well be a sensory pleasure for people with SD. That potential source of pleasure should be maximized while at the same time ensuring optimum nutrition and hydration [11].

In addition, weight loss is a frequent complication of AD and occurs in patients at all stages, even in the early stages before diagnosis is possible. Malnutrition (namely, undernutrition) contributes to the alteration of general health status, to the frequency and gravity of complications, especially infections, and to a faster loss of independence. These states of malnutrition can be prevented or at least improved if an early intervention strategy is set up, but management must be rapid and appropriate. Weight loss is a phenomenon whose kinetics may vary; it can be a dramatic loss of several kilograms in a few months (severe weight loss) or a moderate but continuous loss as the disease progresses (progressive weight loss) [1213].

With progressive dementia, patients become incompetent to make decisions. As a result, complex situations may arise in which physicians and families decide whether artificial nutrition and hydration (ANH) is likely to be beneficial for the patient [1416]. Many people with SD will ultimately experience dysphagia, which in turn is associated with aspiration pneumonia. Decisions about how to respond when someone develops swallowing problems are discussed elsewhere in this paper [17].

Artificial nutrition is the provision of liquid nutritional supplement by the enteral or parenteral route. The decision whether or not to provide artificial nutrition often evokes a powerful emotional response. Because surrogates and other loved ones agonize over the withholding and/or withdrawal of artificial nutrition, healthcare providers need to be ready to discuss the most current data regarding efficacy, complications, and the ethical and legal issues [1820].

2. Definition of Severe Dementia

SD can be defined as the stage of the disease process of dementia in which cognitive deficits are of sufficient magnitude as to impair an otherwise healthy person’s ability to independently perform the basic activities of daily life, such as dressing, bathing, and toileting. Definitions of SD vary from those which use a specific cutoff on a cognitive scale such as the Mini Mental State Examination. In accordance with the literature, we defined SD as follows [4]:(i)score of less than 10 in the Mini Mental State Examination (MMSE) [21] or(ii)score of 3 or higher in the Clinical Dementia Rating (CDR) [22], or(iii)categories 6a to 7f in the Functional Assessment Staging Test (FAST) [23], or(iv)score of 6 or 7 on the Global Deterioration Scale (GDS) [24].

Some investigators state that the incorporation of these instruments into clinical trials has allowed the rate of worsening or improvement of patients to be quantified in advanced stages. Moreover, they have permitted better stratification of this long stage known as SD, which includes patients with very different cognitive, behavioral, and functional profiles. Thus, among patients classified as CDR 3, known as SD, there are individuals who still communicate verbally and walk without support, but also others who are confined to bed, unable to lift their heads, or already in the fetal position. The advantages of better classification of advanced dementia include the possibility of better studies designed to validate interventions in cognition, behavioral, and functional status, as well as better approaches in terminal dementia using palliative care [525].

Although by definition the functional impairment in dementia must be related to the cognitive decline, there are a number of other factors such as parkinsonism and comorbid disorders that by themselves contribute significantly to the functional disability [26].

So, unlike the dying trajectory in more-acute illnesses, patients with dementia have a long period of severe functional and cognitive impairment before death [27].

3. Nutritional Evaluation of Patients with Advanced Dementia

Cachexia and weight loss are common signs among AD patients. These findings have been studied to see if there is any correlation between organic deficiency caused by low-energy intake and the acute state of hypercatabolism these patients present. Undernourishment has been suggested to be a factor in the etiology of dementia and other psychiatric, and cognitive disorders, although nothing has been proven in this respect [2829].

Weight loss in AD may be correlated to the presence of higher rates of infection, the burning of energy due to repetitive movements and cognitive deficit that compromises the patient’s independence [3031].

This process increases the risk of infections, skin ulcers and stimulates loss of body temperature, which consequently compromises the quality of life of patients with AD [32].

There is a theory behind the weight loss seen in AD patients that is based on the morphology and that has to do with the brain lesions caused by the disease, and a significant association has been found between low body weight and atrophy of the mesial temporal cortex in the region of the central nervous system responsible for eating behavior [33].

Guérin et al. [12] observed two forms of weight loss, one slow and progressive, the other rapid and severe. A severe weight loss was related to the seriousness of the disease, the higher number of hospital admissions, clinical events, and institutionalization, which led the researchers to conclude that these patients might benefit from nutritional interventions.

Munõz et al. [34] found that there is impairment of the energy and muscle reserves at all stages of the disease, but that there is a greater impairment of the Body Mass Index (BMI), and brachial fatty and lean mass, in the advanced stage.

Given these findings, evaluation of their nutritional status is crucially important for these patients. The result of the nutritional evaluation will guide the management to be followed in each case.

The nutritional evaluation of these patients may be carried out using a number of traditional methods based on objective evaluations such as anthropometry, the evaluation of clinical signs that are indicative of malnutrition, evaluation of food intake, the subjective Mini Nutritional Assessment (MNA), and by NSI-Nutrition Screening Initiative [35].

The MNA was developed in order to assess the risk of malnutrition in the elderly and identify those who could benefit from early intervention. This evaluation is made of 18 items including: anthropometry, nutritional evaluation, global clinical evaluation and self-perception of health, and may be used both in screening and to evaluate the nutritional status; any trained health professional can apply it [36].

The NSI is a self-applied questionnaire made up of 10 questions, created in order to assess primary health care; however, its use is not widely recommended since it has shown limited power of prediction for mortality in the elderly [37].

Most authors, despite these methods, consider the use of anthropometrical measurements to be the gold standard for nutritional evaluation, along with outpatient tests for total lymphocytes, albumin, blood cholesterol, hemoglobin, and transferrin [38].

A nutritional evaluation study made in a long-stay institution with dementia syndrome, depression, and cardiovascular diseases, using anthropometric data gathering, found that 36.6% of these patients were malnourished, demonstrating the importance of early nutritional intervention [39].

Spaccavento et al. [13], using MNA to investigate the role of the nutritional status, correlating it to cognitive, functional, and neuropsychiatric deficits in AD patients, found that patients at risk of malnutrition showed greater impairment, both in simple instrumental daily life activities (DLA and IDLA) and a greater likelihood of presenting hallucinations, apathy, aberrant and nocturnal motor behavior on the sub-scales of the Neuropsychiatric Index (NPI).

Weight loss has a negative impact on the prognosis of AD since the more severe the malnutrition is the faster will be the clinical progression leading to the death of patients [40].

4. Nutritional Management of Patients with Advanced Dementia

4.1. Does Oral Nutritional Therapy (ONT) in Patients with Advanced Dementia Bring Benefit for the Nutritional Status?

In patients with advanced dementia there is a reduced capacity for communication, loss of pleasure in eating, changes in mastication leading to difficulty in swallowing certain consistencies of food, and culminating in dysphagia [41].

These patients tend to present reduced mobility leading to loss of muscle mass even when not malnourished. In these cases nutritional therapy plays an essential role since it aims to provide comfort in the eating process and assure the patient’s dignity [31].

As AD advances, the difficulty of keeping these patients’ weight up through conventional feeding increases, and in these cases it is recommended to use high-calorie concentrates [42].

ESPEN, the European Society for Clinical Nutrition and Metabolism [43], classifies as evidence level C the use of dietary supplements to maintain the nutritional status of patients with dementia.

Pivi et al. [44], in their study of oral nutritional therapy with patients at different stages of AD, found that an additional 690 kcal/day in these patients’ diets led to an improvement of the nutritional indices BMI, BC (brachial circumference), BMC (brachial muscle circumference), and TLC (total lymphocyte count), demonstrating that nutritional supplementation is in fact effective at any stage of the disease.

Carver and Dobson [45] likewise found that dietary supplementation significantly increases body weight, tricipital skin fold, and brachial muscle circumference in hospitalized elderly dementia patients.

Although dietary supplementation shows benefits for nutritional status, only 11% of outpatients use them, as a study by Trelis and López [46] showed. This study highlighted the importance of the entire team involved in the treatment of dementia patients being able to perceive the onset of nutritional deficit and so refer the patient to the nutritionist to indicate the best type of supplement for each case.

Other studies with nondemented elderly patients with other clinical needs also showed the effectiveness of using dietary supplements in addition to the habitual diet. Volkert et al. [47] showed that elderly patients over 75 who were given calorific supplementation of 500 kcal/day improved their convalescence and recovery from deficiency states.

It is important to mention that there are lines of research that recommend the prescription of dietary supplements only for patients with low BMIs, since they may abandon their habitual diets in favor of dietary supplements [48].

Young et al. [49] also demonstrated this concern in a study with use of dietary supplements for 21 days in addition to their habitual diets. Those patients who received nutritional supplements were observed to have less likelihood of increasing energy intake in their habitual diets. The researchers stressed out that patients with low body weight have a greater chance of benefitting from the use of nutritional supplements.

This whole discussion leads us to observe that a natural diet ingested by mouth promotes patient comfort and dignity and may not shorten survival, since there are reports of patients who survived two years exclusively feeding by mouth [31]. There is evidence that dietary supplementation may enhance the nutritional status of dementia patients, regardless of the phase at which they are. The significance of this nutritional improvement has yet to be determined for the rate of cognitive and functional decline.

5. Use of Vitamins and Minerals in Alzheimer’s Patients

No specific or definitive environmental risk factor has been identified as the likely cause of AD, but there are research lines that correlate diet as a preventive and improving factor for the dementia states.

There is evidence of worsening of the cognitive condition linked to the increase of homocysteine, whereas the consumption of fats and red grapes seems to have a protective effect for AD patients [50].

De Jong et al. [51] studied patients who followed dietary instructions and consumed foods supplemented daily with 0.25 mg of folic acid and 2.5 mg B6 vitamin; they found that these participants showed a reduction in the serum concentration of homocysteine of around 25%. This result suggests that a low concentration of homocysteine may inhibit the development of dementia.

Morris et al. [52] studied nurses who consumed polyunsaturated fatty acids at least once a week; although results were not conclusive, they suggested that this cohort had a lower risk of developing AD.

Polyphenols, in particular resveratrol, found in great quantities in red grapes, are believed to reduce the incidence of AD owing to their antioxidant properties, although this has not yet been proved [5354].

A study of supplementation with low concentration of folic acid and B vitamin complex were made to investigate the association of these substances with enhanced cognitive function. It raised the prospect of reduction of dementia risk, but researchers emphasized that more studies are needed to prove this [55].

Study with AD patients in the mild phase who received micronutrient supplementation for six months found that, when compared to the control group, there was no benefit in the supplementation for the evolution of the disease, the nutritional status, the biochemical parameters, the cognitive function, and the behavior and eating disorders that these patients commonly present [56].

Despite the evidences, caution must be taken in adopting such approaches, since more studies on micronutrient supplementation need to be performed in order to observe real benefits for dementia.

6. Indication of Artificial Nutrition and Hydration in Advanced Dementia Patients

The use of Enteral Nutrition Therapy (ENT) or Artificial Nutrition and Hydration (ANH) is only indicated when there is a risk of malnutrition and severe impairment of the swallowing process, with the possible consequence of aspiration pneumonia [57].

According to ASPEN—American Society for Parenteral and Enteral Nutrition [58], an ENT in patients with advanced dementia is classified as category E, not obligatory in those cases. The decision for ENT must be based on effective communication with the caregivers to decide whether it should be used or not.

The use of nasogastric or nasoenteric tubes in patients with dementia is not recommended as they may pull out the tube, leading to discomfort for patient and family both, since the patient will have to be reintubated [59]. Gastrostomy is normally indicated as the route for alternative feeding, since it is already commonplace and laid down in rules when the duration of ENT is over six weeks [60].

ANH using feeding tubes or gastrostomy has been routinely indicated for patients in advanced stage of dementia who present serious problems swallowing, in order to prevent malnutrition, hydrate the patient properly, and provide comfort. Some studies, however, have put forward issues for the nonuse of ANH in these patients [59].

See Table 1 setting out the major studies in this field and their recommendations regarding ANH in advanced dementia patients:

tab1
Table 1: Results of the main studies in artificial nutrition and hydration (ANH) in patients with severe dementia.

The use of ANH in patients with dementia is very controversial being necessary identification of the goals for an intelligent and rational judgment [65].

Deciding whether to use ANH in dementia patients is a challenge and many caregivers may take their decisions without adequate information and based on an over-optimistic view of the future clinical course of this patient. Health professionals, relatives, and patients should be aware of the realistic expectations of tube feeding and of its risks and benefits before taking such a decision [18].

Ethical dilemmas are related to ANH and it is useful in cases of severe dementia, being necessary to make valid clinical judgments and to guide patients and their families to exchange options related to initiating, withholding, or withdrawing ANH. All this process should be comprehensive and understood from theory to practice. The use of informed consent for competent caregivers is important in those cases [66].

7. Pharmacologic Therapies

Several randomized controlled trials have been published on atypical antipsychotic therapy for behavioral and psychological symptoms in patients with SD.

Some results suggested no significant difference between any of the treatments compared with placebo. They also support the recommendation for the use of atypical antipsychotics only in the presence of severe agitation, aggression, or psychosis that places the patient or those in their environment at risk. Other psychotropic drugs include the antidepressants and anticonvulsants. On balance, the efficacy of the atypical antipsychotics appears to be superior to that of other classes of drugs despite the increased risks. However, there are few, if any, head-to-head comparisons to truly characterize all risks and benefits [7]. In a meta-analysis adverse events of atypical antipsychotics were mainly somnolence and urinary tract infection or incontinence across drugs, and extrapyramidal symptoms or abnormal gait were observed with risperidone or olanzapine. There was no evidence for increased injury, falls, or syncope. But there was a significant risk for cerebrovascular events, especially with risperidone [67]. With all these studies it is possible to imagine that management of behavioral disorders could improve nutritional status. We also know that some antipsychotic drugs could improve appetite, and we could use these drugs to improve food intake. But more studies are needed to better assess clinical significance and effectiveness of these hypotheses.

Pharmacological therapies for the improvement of cognition include cholinesterase inhibitors and memantine, suggesting that this class of medication improves cognition, function, behavior, and global measures. There is a consensus to recommend their use in patients with severe Alzheimer’s disease.

The most common side effects are gastrointestinal and include anorexia, nausea, vomiting, and diarrhea [7]. It is therefore very important to pay attention to these problems so as not to impair food intake. There are no studies in the literature to demonstrate whether cholinesterase inhibitors or memantine could improve the nutritional status.

It is also important to register that there are no well-designed randomized studies to demonstrate benefits of appetite stimulant drugs. We know that it is common medical practice, but evidence of the mechanisms, safety, and efficacy is lacking.

8. Final Remarks

There have been studies to develop drugs and treatments to understand nonpharmacological measures, to find epidemiological factors that affect the natural history of this disease, but they are not conclusive to define ways to approach the end of life or to look into issues such as suitable nutrition for these patients. The long drawn-out course and uncertain time frame of the prognosis raise considerable doubts as to decisions to be taken by the team of carers and by the relatives.

This paper demonstrates the palliative care that should be given in order to improve the patient’s quality of life. All aspects of the treatment of these patients should therefore be part of the responsibilities of the multiprofessional team. It should act cohesively to help relatives take the best decisions in choosing treatment for their loved ones.

This view of comfort and of the right proportions between actions taken and the principle of nonharm may serve as a guide in decision making, especially as regards nutrition issues [8].

Acknowledgments

The authors want to acknowledge SUPPORT Advanced Medical Nutrition/Danone—Division Brazil and Severe Dementia Clinic—Behavior Neurology Section, Federal University of São Paulo—UNIFESP for their contribution to the realization of this paper.

Citation

 

Recent Alzheimer’s Disease Research Highlights

Editorial

As co-editors of Alzheimer’s Research and Therapy we would like to highlight several of the major translational research advances that have occurred over the past year, during which a tremendous amount of superb science relevant to the study of Alzheimer’s disease (AD) has been published. Our selection is, of course, influenced by our own biases, and selecting particular advances to highlight was challenging. Nevertheless, many major scientific questions relevant to developing better therapies and diagnostics for AD remain. The advances we have chosen to highlight represent evolving areas of research in AD that raise as many questions as they answer, but offer some promise that may help us to reach our shared goal of translating research advances into real advances that benefit patients.

Better cellular models of Alzheimer’s disease?

For many years the lack of truly faithful cellular and animal models of AD has imposed some limitation on what can be inferred from these experimental models. With the technological advances demonstrating that human fibroblasts can be converted into pluripotent stem (iPS) cells and subsequently into neurons, and the promise of this technology to provide new cellular models of human neurodegenerative disease, it was only a matter of time for this technology to be applied to the study of AD.

Over the past year, the first of what are likely to be a plethora of studies examining culture models of AD based on neuronally differentiated iPS cells derived from familial and sporadic AD patients and Down syndrome were published. The first of these demonstrated that fibroblasts from familial AD patients with presenilin 1 or 2 mutations showed altered processing of amyloid β protein precursor (APP) and increased production of total amyloid β protein (Aβ) with increased relative production of Aβ42 [1]. The second included neuronally differentiated iPS cells from reprogrammed fibroblasts of two APP gene duplication carriers, two patients with sporadic AD and two controls [2]. In the neuronally differentiated iPS cell lines from familial and one of the two sporadic AD patients, there was higher secretion of Aβ40. A further finding in these three AD cell lines provided a suggestion of interactions with mechanisms of tau pathology: higher levels of phospho-tau and active glycogen synthase kinase (GSK)3β. The third and most recent paper conducted similar studies using neuronally differentiated iPS cells from Trisomy 21 patients[3].When differentiated, these cells showed increased production of Aβ42, increased phospho-tau and perhaps most interesting, the accumulation of Aβ42 aggregates.

Although the alterations in APP and Aβ observed were largely anticipated, based on previous data from human fibroblasts and other biological samples [4], the alterations in tau and GSK3β activity are somewhat surprising. Even more surprising was the demonstration of extracellular Aβ42 aggregates in long-term iPS Trisomy 21 neuronal cultures. Indeed, no previous culture system to date has reproducibly produced such plaque-like aggregates. If this is reproducible and confirmed to result in a plaque-like structure, it may be possible to utilize such cells to more precisely understand plaque formation under physiologic culture conditions.

Of course with any new technology there remain a number of concerns, and it is not clear whether issues of scale and reproducibility will enable this technology to totally overcome limitations of studying a degenerative brain disease in a culture dish. Though the consistency of the findings across the three studies is reassuring, they still only report on the phenotypes of a handful of cell lines from those at risk for AD. One future application that will be very intriguing is whether iPS cell technology may offer a way to obtain insights into biological mechanisms of genes implicated as risk modifiers in late onset AD [5,6]. Hopefully, such future studies will be conducted with appropriate experimental blinding and sufficient power to ensure that the results obtained are widely reproducible.

Insights into the mechanistic basis for the regional distribution and spread of AD pathology

Classic postmortem studies have framed the characteristic progression and regional distribution of tau and Aβ pathology in the brain. In AD, tau pathology characteristically spreads from the entorhinal cortex into limbic and association cortices as AD evolves [7]. Several studies that have appeared this year provide mechanistic insights into the distribution and spread of tau pathology[8,9].

The microtubule associated protein tau has traditionally been thought to be a cytoplasmic protein. It has been known for some time that soluble tau can be detected in CSF, but its presence in a body fluid was attributed to leakage from dead or dying cells [10]. More recent data from both cell culture studies and in vitro microdialysis suggest that tau and tau aggregates can be constitutively secreted from cells [11]. Moreover, there is evidence that extracellular tau aggregates can seed intracellular aggregation. Two papers published in the last year suggest that tau secretion and subsequent seeding of aggregation can occur in vivo and account for the progression of tau pathology in vivo [8,9]. Both of these papers describe studies using transgenic mice expressing the frontotemporal dementia-associated tau P301L mutant in the entorrhinal cortex, and both demonstrated that tau pathology begins in the entorrhinal cortex in these mice but spreads along anatomically connected networks, possibly through synaptic connections. These data are important conceptually as they provide further evidence that tau pathology in AD may spread through a prion-like conformation-dependent templating reaction mediated by release of tau aggregates from one cell and subsequent internalization by a neighbouring cell. They also provide an explanation for the potential efficacy of anti-tau immunotherapy [12]. Although it is possible that anti-tau antibodies modulate tau pathology by somehow entering neurons and altering tau aggregation, these data would suggest that some anti-tau antibodies may block spread of tau pathology from one cell to another by targeting the extracellular tau transmitted from one cell to another.

Does epigenetic modification offer new insights for developing treatment strategies?

The role of epigenetic mechanisms, that is, the ability of non-genetic factors to cause genes to express themselves differently without changing their underlying DNA structure, is becoming apparent in an ever increasing number of biological and medical fields and may offer insights into why therapeutic strategies targeting amyloid pathology have been unsuccessful to date. An elegant study reported recently in Nature provides evidence that Aβ may constrain the expression of some memory- and learning-related genes [13]. After these have been ‘switched off’ by Aβ they cannot be ‘switched on’ again just by removing the Aβ. This process seems to be mediated via a histone deacetylase, HDAC2, which the authors have shown to be activated in brain tissue from both transgenic mouse models, where it reduced synaptic density and memory function, and human AD sufferers. They went on to show that inhibiting HDAC2 restored synaptic plasticity and improved some aspects of memory, although it did not boost the number of surviving neurons in the mice. The pathway is a complex one that also involves the glucocorticoid receptor, GR1.

The implied possibility of reversing pathology, in contrast to slowing decline, is an exciting one but needs further evaluation. HDAC inhibitors are already used or being explored in a number of conditions, for example, oncology, and some pharmaceutical companies are exploring their potential in AD. However, we also need to understand whether such drugs might affect other important but unrelated aspects of genetic function. Roles of epigenetic mechanisms in aging and AD are likely to be a strong focus of future translational research.

Towards Alzheimer’s disease prevention

Over the past few years the challenges of disease modification in symptomatic patients have become increasingly apparent. Preclinical studies almost invariably show diminishing efficacy with increasing pathology at initiation of treatment. There have been several failed phase III clinical trials with disease modifying agents, though many of these agents were suboptimal with respect to potency, therapeutic window, or brain penetrance. Moreover, even phase II studies with more optimal disease modifying agents fail to show evidence for significant efficacy.

Thus, a clinical highlight of the past year has been a renewed emphasis on designing and implementing more appropriate clinical trial methodology for evaluating disease-modifying treatment in AD. Editorials and reviews have emphasized that disease-modifying treatment in established AD at the stage of dementia may be too late – the greatest benefit could come from preventing the chain of events that leads to neurodegeneration and irreversible structural changes in the brain [14-17]. Biomarkers exist that are able to identify AD pathology, particularly amyloid deposition, long before cognitive decline begins, and sensitive cognitive tests and paradigms using functional magnetic resonance imaging are showing alterations even during what has been termed ‘preclinical AD’ [16] and the ‘asymptomatic at risk’ individual [18] and new diagnostic research criteria have been proposed by two working groups.

Treatment trials are at an advanced level of planning in two groups of people at risk for AD. Programmes to clinically identify and characterize carriers of mutations in the presenilin or APP genes, and also systematic initiatives that aim to assess and evaluate biomarkers during these presymptomatic stages are under way. The Alzheimer Prevention Initiative [17] has planned a clinical trial in a large population of presenilin 1 E280A mutation-carriers in Colombia, whose natural history and transition from asymptomatic through early symptoms and cognitive deficits to overt dementia has been precisely mapped in a landmark 15 year follow-up study [19]. The international Dominantly Inherited Alzheimer Network group has enrolled and characterized people with different APP and presenilin mutations [20] and is planning an intervention clinical trial in at risk carriers who test positive for amyloid biomarkers. Another initiative more closely relevant to sporadic AD proposes to identify amyloid carriers among elderly subjects who are not cognitively impaired and study their outcomes, using cognitive and imaging measures, over a period of two years [16].

In summary, this has been an exciting year for all of us working to improve treatment for people with AD. Greater understanding of the underlying pathological mechanisms, gained from research using transgenic animals and new stem cell-based technologies, have revealed possible novel therapeutic strategies targeting the underlying pathologies, that is, both Aβ and tau pathology. These developments are complemented by the move to identify pre-dementia AD and improve trial design. Together they provide hope for the future.

Abbreviations

Aβ: amyloid β protein; AD: Alzheimer ‘s disease; APP: amyloid β protein precursor; GSK: glycogen synthase kinase; HDAC: histone deacetylase; iPS: induced pluripotent stem;

Competing interests

DG serves on data and safety monitoring boards for clinical trials for Janssen and Elan Pharmaceuticals and for Balance Pharmaceuticals. He is a consultant for Elan Pharmaceuticals, Phloronol, Inc., and United BioSource. TG has served on advisory boards related to preclinical studies for Janssen, Novarits, Bristol-Myers Squib and Elan Pharmaceuticals. He has received sponsored research grants from Lundbeck and Myriad Pharmaceuticals in the past. GW has served on advisory boards to a number of pharmaceutical companies, including Jannsen, Shire Pharmaceuticals, Lundbeck, Cambridge Neurodiagnostics and Roche. He is a consultant to TauRx. DG, TG and GW are Editors-in-Chief of Alzheimer’s Research & Therapy and receive an annual honorarium.

Citation

 

Alzheimer’s Disease Spreads Through Linked Nerve Cells, Brain Imaging Studies Suggest

Alzheimer’s disease and other forms of dementia may spread within nerve networks in the brain by moving directly between connected neurons, instead of in other ways proposed by scientists, such as by propagating in all directions, according to researchers who report the finding in the March 22 edition of the journal Neuron.

Alzheimer's MRI

© 2011 East Portland Neurology

Led by neurologist and MacArthur Foundation “genius award” recipient William Seeley, MD, from the UCSF Memory and Aging Center, and post-doctoral fellow Helen Juan Zhou, PhD, now a faculty member at Duke-NUS Graduate Medical School in Singapore, the researchers concluded that a nerve region’s connectedness to a disease hot spot trumps overall connectedness, spatial proximity and loss of growth-factor support in predicting its vulnerability to the spread of disease in some of the most common forms of dementia, including Alzheimer’s disease.

The finding, based on new magnetic resonance imaging research (MRI), raises hopes that physicians may be able to use MRI to predict the course of dementias – depending on where within an affected network degenerative damage is first discovered – and that researchers may use these predicted outcomes to determine whether a new treatment is working. Network modeling combined with functional MRI might serve as an intermediate biomarker to gauge drug efficacy in clinical trials before behavioral changes become measurable, according to Seeley.

“Our next goal is to further develop methods to predict disease progression, using these models to create a template for how disease will progress in the brain of an affected individual,” Seeley said. “Already this work suggests that if we know the wiring diagram in a healthy brain, we can predict where the disease is going to go next. Once we can predict how the network will change over time we can predict how the patient’s behavior will change over time and we can monitor whether a potential therapy is working.”

The new evidence suggests that different kinds of dementias spread from neuron to neuron in similar ways, even though they act on different brain networks, according to Seeley. His previous work and earlier clinical and anatomical studies showed that the patterns of damage in the dementias are linked to particular networks of nerve cells, but until now scientists have found it difficult to evaluate in humans their ideas about how this neurodegeneration occurs.

Probing the Ways Dementias Might Spread

In the current study, the researchers modeled not only the normal nerve network that can be affected by Alzheimer’s disease, but also those networks affected by frontotemporal dementia (FTD) and related disorders, a class of degenerative brain diseases identified by their devastating impact on social behaviors or language skills.

The scientists mapped brain connectedness in 12 healthy people. Then they used data from patients with the five different diseases to map and compare specific regions within the networks that are damaged by the different dementias.

“For each dementia, we looked at four ideas that scientists often bring up to explain how dementia might target brain networks,” Seeley said. “The different proposed mechanisms lead to different predictions about how a region’s place in the healthy network affects its vulnerability to disease.”

In the “nodal stress” hypothesis, small regions within the brain that serve as hubs to carry heavy signaling traffic would undergo wear and tear that gives rise to or worsens disease. In the “trophic failure” mechanism, breakdowns in connectivity would disrupt transport through the network of growth factors needed to maintain neurons. In the “shared vulnerability” mechanism, specific genes or proteins common to neurons in a network would make them more susceptible to disease. But predictions from the “trans-neuronal spread” mechanism model best fit the network connectivity maps constructed by the researchers.

“The trans-neuronal spread model predicts that the more closely connected a region is to the node of disease onset – which we call the epicenter – then the more vulnerable that region will be once the disease begins to spread,” Seeley said. “It’s as if the disease is emanating from a point of origin, but it can reach any given target faster if there is a stronger connection.”

The scientists tracked and analyzed linkages within nerve networks that the dementias target. They used a technique called functional connectivity MRI to measure and spatially represent activity in specific regions of key networks in the brains of the healthy subjects. The MRI readout allowed the researchers to model each region within the network as a distinct but interconnected node. They ranked the nodes that most consistently fired together as being the most closely connected.

Across the five diseases investigated in the study, trans-neuronal spread was the proposed mechanism for which the data best matched the predictions. Previous studies of animals and cells in the laboratory also support the idea that disease-related proteins can spread from an affected neuron to other neurons via intercellular connections.

For more than three decades researchers have been noticing that regions affected by Alzheimer’s disease are connected by axons that branch between and connect neurons, Seeley said. Trans-neuronal spread is a proven hallmark of certain rare neurodegenerative diseases – such as Creutzfeldt-Jakob disease – that are propagated by misfolded cell-surface proteins called prions, which induce neighboring proteins to change shape, aggregate and wreak havoc.

While Alzheimer’s disease and FTD are not considered infectious, abnormal protein structures also are implicated in these common dementias. Recent experiments in which researchers transplanted post-mortem, human brain extracts from dementia patients into genetically modified mice have resulted in disease, Seeley said, “But it is difficult to explore these ideas in humans, and we wanted to begin to bridge this knowledge gap.”

The findings of the UCSF researchers are reinforced by a study conducted independently and published in the same edition of the journal by a research team led by Ashish Raj, PhD, who was at San Francisco VA Medical Center (SFVAMC) and UCSF at the time of the study and is currently at Cornell University, and senior author Michael Weiner, MD, director of the SFVAMC Center for Imaging of Neurodegenerative Diseases. The scientists used another MRI technique, called diffusion tensor imaging, to examine connectedness in affected nerve networks, obtaining similar results.

UCSF is a leading university dedicated to promoting health worldwide through advanced biomedical research, graduate-level education in the life sciences and health professions, and excellence in patient care.

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Nanotechnology Breakthrough Could Dramatically Improve Medical Tests

A laboratory test used to detect disease and perform biological research could be made more than 3 million times more sensitive, according to researchers who combined standard biological tools with a breakthrough in nanotechnology.

Light-Enhancing Material
Princeton researchers dramatically improved the sensitivity of immunoassays, a common medical test, using the nanomaterial shown here. The material consists of a series of glass pillars in a layer of gold. Each pillar is speckled on its sides with gold dots and capped with a gold disk. Each pillar is just 60 nanometers in diameter, 1/1,000th the width of a human hair. (Image: Stephen Chou/Analytical Chemistry)

The increased performance could greatly improve the early detection of cancer, Alzheimer’s disease and other disorders by allowing doctors to detect far lower concentrations of telltale markers than was previously practical.

The breakthrough involves a common biological test called an immunoassay, which mimics the action of the immune system to detect the presence of biomarkers – the chemicals associated with diseases. When biomarkers are present in samples, such as those taken from humans, the immunoassay test produces a fluorescent glow (light) that can be measured in a laboratory. The greater the glow, the more of the biomarker is present. However, if the amount of biomarker is too small, the fluorescent light is too faint to be detected, setting the limit of detection. A major goal in immunoassay research is to improve the detection limit.

The Princeton researchers tackled this limitation by using nanotechnology to greatly amplify the faint fluorescence from a sample. By fashioning glass and gold structures so small they could only be seen with a powerful electron microscope, the scientists were able to drastically increase the fluorescence signal compared to conventional immunoassays, leading to a 3-million-fold improvement in the limit of detection. That is, the enhanced immunoassay would require 3 million times fewer biomarkers to be present compared to a conventional immunoassay. (In technical terms, the researchers measured an improvement in the detection limit from 0.9 nanomolars to 300 attomolars.)

“This advance opens many new and exciting opportunities for immunoassays and other detectors, as well as in disease early detection and treatment,” said Stephen Chou, the Joseph C. Elgin Professor of Engineering, who led the research team. “Furthermore, the new assay is very easy to use, since for the person conducting the test, there will be no difference from the old one– they do the procedure in exactly the same way.”

The researchers published their results in two recent journal articles. One, published May 10 in Nanotechnology, describes the physics and engineering of the fluorescence-enhancing material. The other, published April 20 in Analytical Chemistry, demonstrates the effect in immunoassays. In addition to Chou, the authors include post-doctoral researchers Weihua Zhang, Liangcheng Zhou and Jonathan Hu and graduate students Fei Ding, Wei Ding, Wen-Di Li and Yuxuan Wang.

The work was funded by the Defense Advanced Research Project Agency and the National Science Foundation.

The key to the breakthrough lies in a new artificial nanomaterial called D2PA, which has been under development in Chou’s lab for several years. D2PA is a thin layer of gold nanostructures surrounded glass pillars just 60 nanometers in diameter. (A nanometer is one billionth of a meter; that means about 1,000 of the pillars laid side by side would be as wide as a human hair.) The pillars are spaced 200 nanometers apart and capped with a disk of gold on each pillar. The sides of each pillar are speckled with even tinier gold dots about 10 to 15 nanometers in diameter. In previous work, Chou has shown that this unique structure boosts the collection and transmission of light in unusual ways — in particular, a 1 billion-fold increase in an effect called surface Raman scattering. The current work now demonstrates a giant signal enhancement with fluorescence.

Immunoassay

Immunoassays are commonly performed in a set of glass vials such as the one shown here. The nanomaterial invested at Princeton to increase the sensitivity of the test could be added as a microscopic layer to the glass. (Photo: Frank Wojciechowski)

In a typical immunoassay, a sample such as blood, saliva or urine is taken from a patient and added to small glass vials containing antibodies that are designed to “capture” or bind to biomarkers of interest in the sample. Another set of antibodies that have been labeled with a fluorescent molecule are then added to the mix. If the biomarkers are not present in the vials, the fluorescent detection antibodies do not attach to anything and are washed away. The new technology developed at Princeton allows the fluorescence to be seen when very few antibodies find their mark.

In addition to diagnostic uses, immunoassays are commonly used in drug discovery and other biological research. More generally, fluorescence plays a significant role in other areas of chemistry and engineering, from light-emitting displays to solar energy harvesting, and the D2PA material could find uses in those fields, Chou said.

As next steps in his research, Chou said he is conducting tests to compare the sensitivity of the D2PA-enhanced immunoassay to a conventional immunoassay in detecting breast and prostate cancers. In addition he is collaborating with researchers at Memorial Sloan-Kettering Cancer Center in New York to develop tests to detect proteins associated with Alzheimer’s disease at a very early stage.

“You can have very early detection with our approach,” he said.

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Alzheimer’s Protein Structure Suggests New Treatment Directions

The molecular structure of a protein involved in Alzheimer’s disease — and the surprising discovery that it binds cholesterol — could lead to new therapeutics for the disease, Vanderbilt University investigators report in the June 1 issue of the journal Science.

Vanderbilt Center for Structural Biology investigators determined the structure of the C99 protein (shown in green and blue), which participates in triggering Alzheimer’s disease. Their discovery that C99 binds to cholesterol (shown in black, white and red) suggests a mechanism for cholesterol’s recognized role in promoting the memory-robbing disease and may lead to new therapeutics. (Credit: Charles Sanders and colleagues/Vanderbilt University

Charles Sanders, Ph.D., professor of Biochemistry, and colleagues in the Center for Structural Biology determined the structure of part of the amyloid precursor protein (APP) — the source of amyloid-beta, which is believed to trigger Alzheimer’s disease. Amyloid-beta clumps together into oligomers that kill neurons, causing dementia and memory loss. The amyloid-beta oligomers eventually form plaques in the brain — one of the hallmarks of the disease.

“Anything that lowers amyloid-beta production should help prevent, or possibly treat, Alzheimer’s disease,” Sanders said.

Amyloid-beta production requires two “cuts” of the APP protein. The first cut, by the enzyme beta-secretase, generates the C99 protein, which is then cut by gamma-secretase to release amyloid-beta. The Vanderbilt researchers used nuclear magnetic resonance and electron paragmagnetic resonance spectroscopy to determine the structure of C99, which has one membrane-spanning region.

They were surprised to discover what appeared to be a “binding” domain in the protein. Based on previously reported evidence that cholesterol promotes Alzheimer’s disease, they suspected that cholesterol might be the binding partner. The researchers used a model membrane system called “bicelles” (that Sanders developed as a postdoctoral fellow) to demonstrate that C99 binds cholesterol.

“It has long been thought that cholesterol somehow promotes Alzheimer’s disease, but the mechanisms haven’t been clear,” Sanders said. “Cholesterol binding to APP and its C99 fragment is probably one of the ways it makes the disease more likely.”

Sanders and his team propose that cholesterol binding moves APP to special regions of the cell membrane called “lipid rafts,” which contain “cliques of molecules that like to hang out together,” he said.

Beta- and gamma-secretase are part of the lipid raft clique.

“We think that when APP doesn’t have cholesterol around, it doesn’t care what part of the membrane it’s in,” Sanders said. “But when it binds cholesterol, that drives it to lipid rafts, where these ‘bad’ secretases are waiting to clip it and produce amyloid-beta.”

The findings suggest a new therapeutic strategy to reduce amyloid-beta production, he said.

“If you could develop a drug that blocks cholesterol from binding to APP, then you would keep the protein from going to lipid rafts. Instead it would be cleaved by alpha-secretase — a ‘good’ secretase that isn’t in rafts and doesn’t generate amyloid-beta.”

Drugs that inhibit beta- or gamma-secretase — to directly limit amyloid-beta production — have been developed and tested, but they have toxic side effects. A drug that blocks cholesterol binding to APP may be more specific and effective in reducing amyloid-beta levels and in preventing, or treating, Alzheimer’s disease.

The C99 structure had some other interesting details, Sanders said.

The membrane domain of C99 is curved, which was unexpected but fits perfectly into the predicted active site of gamma-secretase. Also, a certain sequence of amino acids (GXXXG) that usually promotes membrane protein dimerization (two of the same proteins interacting with each other) turned out to be central to the cholesterol-binding domain. This is a completely new function for GXXXG motifs, Sanders said.

“This revealing new information on the structure of the amyloid precursor protein and its interaction with cholesterol is a perfect example of the power of team science,” said Janna Wehrle, Ph.D., who oversees grants focused on the biophysical properties of proteins at the National Institutes of Health’s National Institute of General Medical Sciences (NIGMS), which partially funded the work. “The researchers at Vanderbilt brought together biological and medical insight, cutting-edge physical techniques and powerful instruments, each providing a valuable tool for piecing together the puzzle.”

“When we were developing bicelles 20 years ago, no one was saying, ‘someday these things are going to lead to discoveries in Alzheimer’s disease,’” he said. “It was interesting basic science research that is now paying off.”

The Vanderbilt team included lead authors Paul Barrett and Yuanli Song, Ph.D., as well as Wade Van Horn, Ph.D., Eric Hustedt, Ph.D., Johanna Schafer, Arina Hadziselimovic and Andrew Beel. The research was supported by grants from NIGMS (GM080513) and the Alzheimer’s Association.

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How to Tell Apart the Forgetful from Those at Risk of Alzheimer’s Disease

It can be difficult to distinguish between people with normal age-associated memory loss and those with amnestic mild cognitive impairment (aMCI). However people with aMCI are at a greater risk of developing Alzheimer’s disease (AD), and identification of these people would mean that they could begin treatment as early as possible. New research published in BioMed Central’s open access journal BMC Geriatrics shows that specific questions, included as part of a questionnaire designed to help diagnose AD, are also able to discriminate between normal memory loss and aMCI.

Loss of memory can be distressing for the person affected and their families and both the patient and people who know them may complain about their memory as well as difficulties in their daily lives. However memory problems can be a part of normal aging and not necessarily an indicator of incipient dementia. A pilot study had indicated that a simple, short, questionnaire (AQ), designed to identify people with AD by using informant-reported symptoms, was also able to recognize people with aMCI.

The AQ consists of 21 yes/no questions designed to be answered by a relative or carer in a primary care setting. The questions fall into five categories: memory, orientation, functional ability, visuospatial ability, and language. Six of these questions are known to be predictive of AD and are given extra weighting, resulting in a score out of 27. A score above 15 was indicative of AD, and between 5 and 14 of aMCI. Scores of 4 or lower indicate that the person does not have significant memory problems.

While validating the AQ researchers from Banner Sun Health Research Institute discovered that four of the questions were strong indicators of aMCI. Psychometrist Michael Malek-Ahmadi, who led the study, explained, “People with aMCI were more often reported as repeating questions and statements, having trouble knowing the date or time, having difficulties managing their finances and a decreased sense of direction.” He continued, “While the AQ cannot be used as a definitive guide to diagnosing AD or aMCI, it is a quick and simple-to-use indicator that may help physicians determine which individuals should be referred for more extensive testing.”

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New Method to Reveal Alzheimer’s Marker Shows Promise

Early study uses drug and imaging scans to pinpoint plaques associated with disease

New research adds to the growing pile of scientific strategies aimed at revealing beta-amyloid (protein) plaques, the brain-clogging fragments that have been associated with Alzheimer’s disease.

HealthDay news image

In a study funded by Bayer Healthcare Berlin, researchers report that they were able to use a drug and PET scans to successfully detect plaques in the brains of patients whose Alzheimer’s was confirmed after death.

More than 200 patients near death — including some with apparent Alzheimer’s disease — underwent the PET scans. They received doses of the drug florbetaben, which was used as a “tracer” to allow the PET scans to detect the plaques.

Thirty-one patients died and had autopsies to confirm that they had Alzheimer’s disease. The researchers determined that one way of interpreting the PET scan results correctly pinpointed Alzheimer’s disease 100 percent of the time and correctly ruled it out 92 percent of the time.

“These results confirm that florbetaben is able to detect beta-amyloid plaques in the brain during life with great accuracy and is a suitable biomarker,” study author Dr. Marwan Sabbagh, director of Banner Sun Health Research Institute in Sun City, Ariz., said in an American Academy of Neurology news release.

“This is an easy, noninvasive way to assist an Alzheimer’s diagnosis at an early stage. Also exciting is the possibility of using florbetaben as a tool in future therapeutic clinical research studies where therapy goals focus on reducing levels of beta-amyloid in the brain,” Sabbagh added.

Dr. William Jagust, a professor of neuroscience at the University of California, Berkeley’s Helen Wills Neuroscience Institute, said several companies are developing ways to detect beta-amyloid plaques. “It’s a very important development in our field,” he said. “The big practical question is how much is this going to cost — it may cost $2,000 or more to get a scan — and whether it is worth it considering what we can do for such patients.”

There’s no cure for Alzheimer’s and no way to reverse it, although drugs are available to treat symptoms. Still, Jagust said, detecting beta-amyloids may be helpful as a way to determine whether experimental drugs actually work.

The study is slated for presentation at the American Academy of Neurology’s annual meeting, which starts April 21 in New Orleans.

The data and conclusions should be viewed as preliminary until published in a peer-reviewed journal.

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