Current Alzheimer Research - Volume 9, Issue 1, 2012

Alzheimer's disease (AD) represents one of the most important future therapeutic targets, both with regards to basic and translational research, due to the progressive aging of most westernized countries. Estimates in 2006 indicated that the worldwide prevalence of AD was nearing 27 million cases [1] and with greater and greater proportions of the world population living beyond 60 years of age, nearly 1 in 85 people worldwide may suffer from AD in the mid-part of this century. The potential economic, social and healthcare burden of a progressive disease of this prevalence clearly presents one of the most important future threats to worldwide health. Since AD currently has no effective therapeutic cure, and it gradually renders people incapable of tending to their own needs, long-term assistive caregiving essentially is the only treatment. The need for this long-term assisted (or ‘informal’) care of AD patients also means that the social and healthcare burden also affects collateral populations and may also detrimentally affect their standard of living. A recent European Union (EU) study was created to focus upon this specific aspect of the socioeconomic burden of AD. In the 2008 Eurocode Study [2], it was estimated that 7.23 million people suffered from dementia in 27 EU countries (EU27) in 2008. The total costs of illness for dementia disorders in the EU27 was estimated to be 160 billion Euros, of which more than half was attributed to the costs of informal healthcare. Considering the tremendous future social and economic threat posed by the increasing prevalence of AD, there are worryingly few new therapeutic strategies to effectively tackle this disease [3]. Many lines of research have focused intently upon issues such as direct disease mechanisms, but have failed thus far to generate any significant therapeutic breakthroughs. Considering the profound prevalence of AD in westernized societies, the current AD pharmacopeia is significantly lacking. Four pharmacotherapeutics are currently approved by regulatory agencies such as the U.S. Food and Drug Administration and the European Medicines Agency to treat the cognitive manifestations of AD. Reinforcing the paucity of the range of available and effective AD therapies, three of these four compounds belong to the same drug class, i.e. acetylcholinesterase inhibitors (donepezil, galantamine, rivastigmine) while the other, memantine, is an N-methyl-D-aspartic acid (NMDA) receptor modulator. In contrast to this limited capacity to treat AD, a similarly prevalent disorder, i.e. hypertension, can be medicated by multiple forms of therapeutic comopounds including, diuretics (e.g. acetazolamide, amiloride), calcium channel blocking agents (e.g. amlodipine, diltiazem), angiotensin converting enzyme inhibitors (e.g. captopril, enalapril), angiotensin receptor II antagonists (e.g. losartan, valsartan), centrallyacting alpha adrenoceptor agonists (e.g. clonidine, doxazosin), catecholamine depleting agents (e.g. reserpine), beta adrenoceptor antagonists (e.g. atenolol, carvedilol) and up to eighteen different forms of combination therapeutics (e.g. amiloriode-hydrochlorothiazide, felodipine-elanapril). Therefore our range of AD therapies is seriously limited. In addition to this rather pessimistic observation, only donepezil is approved for treatment of advanced AD dementia [4]. Unfortunately the use of the anti-AD therapies in cases of mild cognitive impairment (MCI) has failed to demonstrate any significant efficacy in delaying of the onset of AD [5]. In addition to their rather limited therapeutic actions many of the currently approved AD therapies also cause physiological effects likely to reduce drug compliance, i.e. nausea, vomiting, bradycardia, decreased appetite, weight loss and increased gastric acid production and irritation. To combat this current lack of multiple efficacious anti-AD strategies, over four hundred different pharmaceutical agents are currently under investigation around the world, with nearly one hundred of these nearing the later stages of clinical review [6]. The areas of research occupied by these agents currently in development include, agents that reduce amyloid beta through vaccination processes, reduce oxidative stress via metal ion chelation or attenuate the long term inflammatory responses associated with AD [7-10].....

Alzheimer's disease and other related neurodegenerative diseases are highly debilitating disorders that affect millions of people worldwide. Efforts towards developing effective treatments for these disorders have shown limited efficacy at best, with no true cure to this day being present. Recent work, both clinical and experimental, indicates that many neurodegenerative disorders often display a coexisting metabolic dysfunction which may exacerbate neurological symptoms. It stands to reason therefore that metabolic pathways may themselves contain promising therapeutic targets for major neurodegenerative diseases. In this review, we provide an overview of some of the most recent evidence for metabolic dysregulation in Alzheimer's disease, Huntington's disease, and Parkinson's disease, and discuss several potential mechanisms that may underlie the potential relationships between metabolic dysfunction and etiology of nervous system degeneration. We also highlight some prominent signaling pathways involved in the link between peripheral metabolism and the central nervous system that are potential targets for future therapies, and we will review some of the clinical progress in this field. It is likely that in the near future, therapeutics with combinatorial neuroprotective and ‘eumetabolic’ activities may possess superior efficacies compared to less pluripotent remedies.

In both men and women, age-related loss of sex steroid hormones has been linked to an increased risk for Alzheimer's disease (AD). The primary female hormone estrogen, and the primary male hormone testosterone have numerous protective effects in the brain relevant to the prevention of AD such as the promotion of neuron viability, reduction of β- amyloid accumulation and alleviation of tau hyperphosphorylation. Therefore it has been hypothesized that the precipitous loss of these hormones either through menopause or normal aging, can increase susceptibility to AD pathogenesis. This review will discuss the basic science research and epidemiological evidence largely supporting this hypothesis, as well as the estrogen-based hormone therapy clinical findings that have recently shed doubt on this theory. The complications associated with estrogen-based hormone therapy such as the inclusion of a progestogen, hormone responsiveness with age, and natural vs. synthetic hormones will be discussed. Further, we will outline the cancer risks facing both estrogen and testosterone-based hormone therapy. Most importantly, this review will discuss the present and future strategies to translate the neuroprotective properties of sex steroid hormones into safe and efficacious treatments for AD. One of the most promising translational tools thus far may be the development of selective estrogen and androgen receptor modulators. However, additional research is needed to optimize these and other translational tools towards the successful use of hormone therapies in both men and women to delay, prevent, and or treat AD.

Alzheimer's disease [AD] is the most common cause of dementia in North America. Despite 30+ years of intense investigation, the field lacks consensus regarding the etiology and pathogenesis of sporadic AD, and therefore we still do not know the best strategies for treating and preventing this debilitating and costly disease. However, growing evidence supports the concept that AD is fundamentally a metabolic disease with substantial and progressive derangements in brain glucose utilization and responsiveness to insulin and insulin-like growth factor [IGF] stimulation. Moreover, AD is now recognized to be heterogeneous in nature, and not solely the end-product of aberrantly processed, misfolded, and aggregated oligomeric amyloid-beta peptides and hyperphosphorylated tau. Other factors, including impairments in energy metabolism, increased oxidative stress, inflammation, insulin and IGF resistance, and insulin/IGF deficiency in the brain should be incorporated into all equations used to develop diagnostic and therapeutic approaches to AD. Herein, the contributions of impaired insulin and IGF signaling to AD-associated neuronal loss, synaptic disconnection, tau hyperphosphorylation, amyloid-beta accumulation, and impaired energy metabolism are reviewed. In addition, we discuss current therapeutic strategies and suggest additional approaches based on the hypothesis that AD is principally a metabolic disease similar to diabetes mellitus. Ultimately, our ability to effectively detect, monitor, treat, and prevent AD will require more efficient, accurate and integrative diagnostic tools that utilize clinical, neuroimaging, biochemical, and molecular biomarker data. Finally, it is imperative that future therapeutic strategies for AD abandon the concept of uni-modal therapy in favor of multi-modal treatments that target distinct impairments at different levels within the brain insulin/IGF signaling cascades.

Ethnobotany encompasses the cultural uses of plants by humans, including their uses as medicines (ethnopharmacology). The reputed medicinal properties of plants have been documented for centuries in different cultures, and there are many plant species that have been traditionally used for memory disorders, which are now being explored to determine any scientific basis for their reputed uses. Plants have been a valuable source of drugs, and phytochemicals have also provided templates to develop synthetic drugs (e.g. rivastigmine, based on the chemical structure of physostigmine from Physostigma venenosum). Although drug development from botanical origin is one aim, the use of plants as herbal medicines is still popular. Scientific evidence for efficacy and safety has been explored for many species, although more research is needed, particularly to identify active phytochemicals to produce standardised herbal products. For Alzheimer's disease (AD) there are relatively few drugs available to treat symptoms, and there is a lack of successful therapies that modulate disease progression. Since two of the currently licensed drugs for AD are based on natural products (galantamine and rivastigmine), it is not surprising that many plants are now being investigated as a potential source of new therapies for AD. This review discusses those plants that have ethnobotanical uses suggestive of alleviation of AD pathology and associated symptoms, for cognitive and for behavioural and psychological symptoms of dementia (BPSD). An emphasis is placed on those plants that have shown some promising effects in clinical studies with dementia patients (e.g. Crocus sativus, Ginkgo biloba, Salvia species), but other plants and their phytochemicals showing relevant mechanistic effects for AD (e.g. Bacopa monnieri, Centella asiatica, Ptychopetalum olacoides) are also discussed.

Physical activity has been correlated with a reduced incidence of cognitive decline and Alzheimer's disease in human populations. Although data from intervention-based randomized trials is scarce, there is some indication that exercise may confer protection against age-related deficits in cognitive function. Data from animal models suggests that exercise, in the form of voluntary wheel running, is associated with reduced amyloid deposition and enhanced clearance of amyloid beta, the major constituent of plaques in Alzheimer's disease. Treadmill exercise has also been shown to ameliorate the accumulation of phosphorylated tau, an essential component of neurofibrillary tangles in Alzheimer's models. A common therapeutic theme arising from studies of exercise-induced neuroprotection in human populations and in animal models involves reduced inflammation in the central nervous system. In this respect, physical activity may promote neuronal resilience by reducing inflammation.

Dynamic circadian rhythms contribute to memory formation, and the hormonal and neurochemical changes that follow circadian patterns are frequently dysregulated with aging. The effect of aging on circadian rhythms is a doubleedged sword; on one hand, poor sleep quality compromises neuronal structure and function in regions that support cognition, and on the other hand, perturbation of central and peripheral oscillators changes the hormonal milieu, with consequences for neuroplasticity. In the current review, recent developments surrounding the circadian regulation of memory formation are described, with reference to how mechanisms that support temporal coding might change with advancing age. The cognitive consequences of changes in sleep patterns are also discussed. New roles for the circadian clock genes period-1, period-2, and bmal1 in memory formation are discussed in the context of age-related cognitive decline. The potential for chronobiological approaches to the treatment and prevention of Alzheimer's disease merits further exploration from a pharmacotherapeutic perspective, as the timing of drug delivery could potentiate or diminish treatment efficacy.

Excess tumor necrosis factor (TNF) plays a pivotal role in the pathogenesis of Alzheimer's disease(AD). Clinical improvement following perispinal administration of etanercept in patients with Alzheimer's disease and other forms of dementia and brain dysfunction is characteristically evident within minutes. The rapidity and constellation of the clinical effects across multiple domains (cognition, mood, memory, motor function, and attention) suggest they are mediated by non-synaptic signaling mechanisms previously unrecognized for etanercept. These mechanisms likely extend beyond the known roles of TNF as a gliotransmitter that modulates synaptic strength, synaptic scaling, and AMPA receptor trafficking. Preliminary basic science and clinical investigation suggests that perispinal administration of etanercept may lead to its rapid penetration into the cerebrospinal fluid (CSF) within the cerebral ventricles. Diffusion of large molecules into the periventricular brain parenchyma is known to occur, but this process may not be sufficient to explain the rapidity of the clinical effects. There exist populations of cells, including CSF-contacting neurons and modified ependymal cells called tanycytes, that have receptive surfaces in direct contact with the CSF. It is hypothesized that the rapid clinical effects of perispinal etanercept involve non-synaptic signal transduction across the ependymal barrier and into neuronal networks via these CSF-contacting cells. This hypothesis challenges the dogma that penetration of a therapeutic into the cerebral parenchyma through the endothelium of the cerebral vasculature (the so-called blood- brain barrier) is necessary to produce rapid clinical effects in AD. CSF-contacting cells may constitute a therapeutic target for a diverse group of brain, psychiatric and spinal disorders.

The extensive prevalence of Alzheimer's disease (AD) places a tremendous burden physiologically, socially and economically upon those directly suffering and those caring for sufferers themselves. Considering the steady increases in numbers of patients diagnosed with Alzheimer's, the number of effective pharmacotherapeutic strategies to tackle the disease is still relatively few. As with many other neurodegenerative mechanisms, AD, is characterized by the continued presence and accumulation of cytotoxic protein aggregates, i.e. of beta-amyloid and the microtubule associated protein, tau. Therefore, one novel therapeutic avenue for the treatment of AD may be the actual targeting of factors that control protein synthesis, packaging and degradation. One of the prime cellular targets that, if effectively modulated, could accomplish this is the endoplasmic reticulum (ER). The ER can not only control cellular protein synthesis, trafficking and degradation but it is also closely associated with cytoprotective mechanisms, including calcium ion regulation and unfolded protein responses. This review will delineate some of the most important functional physiological features of the ER that, if effectively modulated, could result in beneficial amelioration or remediation of the negative cellular aspects of AD initiation and progression. While not a classical drug target, even with minimal levels of beneficial modulation, its multifactorial efficacy may amplify small effects resulting in significant therapeutic efficacy.

Cholinergic hypofunction is a trait of Alzheimer's disease and vascular dementia and countering it is one of the main therapeutic strategies available for these disorders. Cholinergic transporters control cellular mechanisms of acetylcholine (ACh) synthesis and release at presynaptic terminals. This study has assessed the influence of 4 week treatment with two different cholinergic enhancing drugs, the cholinergic precursor choline alphoscerate (alpha-glyceryl-phosphorylcholine) or the acetylcholinesterase (AChE) inhibitor galantamine on high affinity choline uptake transporter (CHT) and vesicular ACh transporter (VAChT) expression in the brain of spontaneously hypertensive rats (SHR). SHR represent an animal model of cerebrovascular injury characterized by cholinergic hypofunction. Analysis was performed by immunochemistry, ELISA and immunohistochemistry on frontal cortex, striatum and hippocampus. Immunochemical and ELISA analysis was extended to peripheral blood lymphocytes (PBL), used as a peripheral reference of changes of brain cholinergic markers. An increased expression of VAChT and CHT was observed in brain areas investigated and in PBL of SHR. The similar trend for cholinergic transporters observed in brain and PBL suggests these cells may represent a marker of brain cholinergic transporters. Treatment with choline alphoscerate increased CHT and to a greater extent VAChT expression. Treatment with galantamine countered the increase of CHT and VAChT. The different activity of the cholinergic precursor and of the AChE inhibitor on parameters investigated is likely related to their mechanism of action. Choline alphoscerate increases ACh synthesis and release. This requires an augmentation of systems regulating neurotransmitter uptake and storage. The effect of choline alphoscerate on CHT and VAChT observed in this study suggests an improved synaptic efficiency elicited by the compound. The AChE inhibitor slows-down ACh degradation in the synaptic cleft. A greater availability of neurotransmitter elicited by galantamine counters the enhanced activity of cholinergic transporters compensating cholinergic deficits. Differences in the activity of the cholinergic precursor and AChE inhibitor investigated on CHT and VAChT suggests that association between choline alphoscerate and AChE/cholinesterase inhibitors may represent a strategy for potentiating deficient cholinergic neurotransmission worthwhile of being investigated in clinical trials.

Diagnosis and therapeutic strategies in Alzheimer's disease (AD) might greatly benefit of the present multidisciplinary approach for studying the molecular pathogenesis of the disorder. Gene expression profile at peripheral level could be a promising tool for pathogenic studies as well as for early diagnosis of AD. A dysregulated inflammatory response, as well as other systemic disorders, have been described in AD. Therefore, we investigated the expression, at peripheral level, of a number of genes involved in the inflammatory, oxidative stress and proliferative response of a well defined, small cohort of sporadic AD patients. Firstly, the mRNA expression of inflammatory, stress and proliferation/ differentiation genes were evaluated, using SuperArray, in mitogen-stimulated peripheral blood mononuclear cells (PBMC) from a group of 12 well-characterized, sporadic AD patients with various levels of dementia, by comparison with aged-matched controls. Real-time RT-PCR confirmed the trend of alteration in 16 genes out of the 36 supposed to be dysregulated in AD patients, by the preliminary screening. The expression level of the NFKB1(p105/50Kd) gene was significantly higher in AD with respect to adult age-matched controls (AA) and was related to the Mini-Mental State Examination (MMSE) score of the same patients. In addition, the expression of various NF-κB target genes and of both NF-κBp50 and NF-κBp65 DNA-binding activity were increased in PBMC from AD patients in comparison with those from AA. Our results suggest that NF-κB activation at peripheral blood cell level could be a potential new hallmark of AD progression and sustain a rationale to more deeply investigate the therapeutic potential of specific NF-κB inhibitors in AD.

In Alzheimer's disease, histochemically visualized cholinesterases with altered pH optimum for activity and inhibitable by indoleamines and the protease inhibitor bacitracin emerge in association with plaques and tangles. It has been suggested that these cholinesterases may participate in the pathologic process. However, it is not known whether the properties of cholinesterases observed in Alzheimer's disease are due to requirements of histochemical procedures or actual biochemical properties of these enzymes. Using biochemical assays of acetylcholinesterase and butyrylcholinesterase activities, we demonstrate here that serotonin and bacitracin result in a significantly greater and dose-dependent inhibition of cholinesterases in Alzheimer's disease cortex when compared with age-matched controls. In contrast, variations in pH did not distinguish cholinesterases in Alzheimer's disease and control cortex. We also confirmed significant reduction of acetylcholinesterase activity in Alzheimer's disease cortex and increased butyrylcholinesterase activity that only approached significance. We conclude that inhibition by indoleamines and bacitracin is a biochemical characteristic of a proportion of cholinesterases in Alzheimer's disease that most likely represents the pool associated with plaques and tangles. Most of the available cholinesterase inhibitors are relatively incapable of inhibiting cholinesterases associated with plaques and tangles. The findings of the present investigation open the way for attempts to isolate cholinesterases associated with plaques and tangles and design or discovery of inhibitors specifically targeted to cholinesterases in these lesions