Current Alzheimer Research - Volume 8, Issue 7, 2011

Alzheimer's disease (AD) affects memory and neurogenesis. Adult neurogenesis plays an important role in memory function and impaired neurogenesis contributes to cognitive deficits associated with AD. Increased physical/ cognitive activity is associated with both reduced risk of dementia and increased neurogenesis. Previous attempts to restore hippocampal neurogenesis in transgenic mice by voluntary running (RUN) and environmental enrichment (ENR) provided controversial results due to lack of non-transgenic (non-Tg) control and inclusion of social isolation as “standard“ housing environment. Here, we determine the effect of RUN and ENR upon hippocampal neurogenesis in a triple transgenic (3xTg-AD) mouse model of AD, which mimics AD pathology in humans. We used single and double immunohistochemistry to determine the area density of hippocampal proliferating cells, measured by the presence of phosphorylated Histone H3 (HH3), and their potential neuronal and glial phenotype by co-localizing the proliferating cells with the immature neuronal marker doublecortin (DCX), mature neuronal marker (NeuN) and specific astroglial marker (GFAP). Our results show that 3xTg-AD mice in control environment exhibit impaired hippocampal neurogenesis compared to non-Tg animals at 9 months of age. Exposure to RUN and ENR housing restores hippocampal neurogenesis in 3xTg-AD animals to non-Tg control levels. Differentiation into neurones and glial cells is affected neither by transgenic status nor by housing environment. These results suggest that hippocampus of 3xTg-AD animals maintains the potential for cellular plasticity. Increase in physical activity and/or cognitive experience enhances neurogenesis and provides a potential for stimulation of cognitive function in AD.

Alzheimer's disease (AD) is a degenerative disorder that leads to progressive, irreversible cognitive decline. It develops as a result of over-production and aggregation of β-amyloid (Aβ) peptides in the brain. We have recently shown that stress exacerbates, while nicotine prevents long-term memory impairment induced by β-Amyloid. In this study, we evaluated the effect of chronic psychosocial stress on synaptic plasticity (Late-phase long-term potentiation; L-LTP, and long-term depression; LTD) in the β-Amyloid rat model of AD, and the positive impact of chronic nicotine treatment. Chronic psychosocial stress was induced by an intruder method. The Rat AD model was induced by 14-day i.c.v. osmotic pump infusion of a 1:1 mixture of 300 pmol/day Aβ1-40/Aβ1-42. The rats were treated with nicotine (2 mg/kg/day) for 6 weeks. In vivo electrophysiological recordings of L-LTP, and LTD in hippocampal area CA1 showed that chronic stress by itself did not affect L-LTP. However, it markedly aggravated the impairment of this response as well as LTD in Aβ- treated rats. The effects of Aβ and the combination of stress and Aβ were totally prevented by chronic nicotine treatment. Immunoblot analysis revealed that stress and/or Aβ significantly increased the basal levels of calcineurin and prevented the expected L-LTP-induced increase in CREB phosphorylation, and CaMKIV levels. These effects were not seen in Aβ- infused rats chronically treated with nicotine. The changes in synaptic plasticity-related molecules may explain the effects of stress and/or chronic nicotine on L-LTP in Aβ animals.

Chlorpyrifos (CPF) is an organophosphate pesticide widely used in intensive agriculture. Various studies have demonstrated delayed neurotoxic effects in adult mammals after acute CPF exposure. This pesticide induces oxidative stress and neuronal damage, which suggests a possible relationship between CPF exposure and Alzheimer's disease (AD). In the present study, we examined in a mice model of AD, long-term changes in the behavior and brain levels of amyloid β after acute CPF exposure. Fifty mg/kg of CPF were subcutaneously injected to Tg2576 (Tg) mice carrying the Swedish amyloid-β protein precursor (AβPP) mutation for AD. General status, body weight, acetyl cholinesterase (AChE) inhibition, and behavioral changes were assessed. Amyloid β fragment (1-40 and 1-42) levels were also measured in the cortical and hippocampal brain regions. A significant and transient decrease in body weight was observed 72 hr after treatment, while no autonomic effects were noted. Motor activity was decreased in Tg mice seven months after CPF treatment. Acquisition learning in a water maze task was not affected, but retention was ameliorated in CPF-exposed Tg mice. Amyloid β levels increased in the brains of treated Tg mice eight months after CPF exposure. The results of this study show that some behavioral changes persisted or emerged months after acute CPF exposure, while amyloid β levels increased. These findings raise concern about the risk of developing neurodegenerative diseases following moderate exposure to CPF in vulnerable subjects.

β-amyloid protein (Aβ)-induced neurotoxicity is the main component of Alzheimer7apos;s disease (AD) neuropathogenesis. Inhalation anesthetics have long been considered to protect against neurotoxicity. However, recent research studies have suggested that the inhalation anesthetic isoflurane may promote neurotoxicity by inducing apoptosis and increasing Aβ levels. We therefore set out to determine whether isoflurane can induce dose- and time-dependent dual effects on Aβ-induced apoptosis: protection versus promotion. H4 human neuroglioma cells, primary neurons from naive mice, and naive mice were treated with Aβ and/or isoflurane, and levels of caspase-3 cleavage (activation), apoptosis, Bcl-2, Bax, and cytosolic calcium were determined. Here we show for the first time that the treatment with 2% isoflurane for six hours or 30 minutes potentiated, whereas the treatment with 0.5% isoflurane for six hours or 30 minutes attenuated, the Aβ-induced caspase-3 activation and apoptosis in vitro. Moreover, anesthesia with 1.4% isoflurane for two hours potentiated, whereas the anesthesia with 0.7% isoflurane for 30 minutes attenuated, the Aβ-induced caspase-3 activation in vivo. The high concentration isoflurane potentiated the Aβ-induced reduction in Bcl-2/Bax ratio and caused a robust elevation of cytosolic calcium levels. The low concentration isoflurane attenuated the Aβ-induced reduction in Bcl-2/Bax ratio and caused only a mild elevation of cytosolic calcium levels. These results suggest that isoflurane may have dual effects (protection or promotion) on Aβ-induced toxicity, which potentially act through the Bcl-2 family proteins and cytosolic calcium. These findings would lead to more systematic studies to determine the potential dual effects of anesthetics on AD-associated neurotoxicity.

Treatment of Alzheimer's disease (AD) with acetylcholinesterase inhibitors (AChEI) enhances cholinergic activity and alleviates clinical symptoms. In the present functional magnetic resonance imaging (fMRI) study, we investigated the effect of the AChEI rivastigmine on cognitive function and brain activation patterns during a face recognition memory task. Twenty patients with newly-diagnosed mild AD were administered a single oral dose of placebo, a single dose of rivastigmine (acute), and twice-daily treatment with rivastigmine for 4 weeks (chronic). After each treatment, the patients underwent a facial recognition task during fMRI. The prefrontal areas known to be involved in face recognition memory processing demonstrated greater fMRI activity in both the acute and chronic rivastigmine conditions compared to the placebo condition. In the same brain areas, differences in both fMRI activation at the map level and regional fMRI signal intensity measures between the placebo and chronic treatment conditions correlated negatively with the Mini- Mental State Examination score. In the chronic rivastigmine condition, patients with better preserved cognitive abilities demonstrated less enhanced prefrontal activity, whereas patients with poorer cognition showed greater prefrontal activity. These findings suggest that the prefrontal attention/working memory systems are already impaired in the early stages of AD and that the effect of cholinergic medication in the brain areas involved in recognition memory, i.e., increased or decreased fMRI activation patterns, depends on the severity of the disease. These findings also suggest the importance of early AChEI treatment in the course of AD, at the point when there is still some cognitive reserve available and the therapy has the highest potential efficacy.

Apolipoprotein E (APOE) ε4 allele and sigma-1 receptor (SIGMAR1) c.5C (Q2P) polymorphisms have been acknowledged as risk factors for developing Alzheimer's disease (AD). However, whether these polymorphisms influence the disease process is unclear. Therefore, two cohorts with a clinical diagnosis of AD were recruited, a postmortem confirmed Australian cohort (82 cases) from the Australian Brain Bank Network, and a Chinese cohort with detailed clinical assessments recruited through an epidemiology study in Shanghai and through the neurology department outpatients clinic of Shanghai Ruijin Hospital (330 cases). SIGMAR1 Q2P and APOE genotyping was performed on all cases. Dementia severity in the Chinese cohort was assessed using MMSE scores, and the stages of senile plaques and neurofibrillary tangles (NFT) assessed in the Australian cohort. Associations between SIGMAR1 Q2P and APOE genotypes and disease severity were assessed using SPSS. Results confirmed that APOE ε4 allele associated with increased NFT stages and cognitive decline, with carriers with one APOE ε2 or ε3 allele often having better clinical outcomes compared to carriers with none or two ε2 or ε3 alleles respectively. SIGMAR1 c.5C polymorphism alone did not associate with MMSE score variability in Chinese or with pathological stages in Caucasians. However, the association studies revealed a significant genetic interaction between the APOE ε4 allele and SIGMAR1 2P carriers in both populations, i.e., in APOE non ε4 allele carriers, SIGMAR1 2P variant had increased cognitive dysfunction and more advanced stages of NFT. Our data demonstrate that SIGMAR1 and APOE interact to influence AD severity across ethnic populations.

To evaluate the effects of galantamine withdrawal, and compare this with uninterrupted therapy, two 6-week double-blind withdrawal studies (Studies 1 and 2) were performed. These enrolled individuals who had completed one of two 3- or 5-month randomized clinical trials (parent trials) involving patients with mild to moderate Alzheimer's disease (AD). In Study 1 (GAL-USA-11; n'723), patients continuously treated with galantamine 16 mg/day exhibited a mean (± standard error [SE]) improvement in 11-item cognitive subscale of the Alzheimer's Disease Assessment Scale score of 1.8 (± 0.46) points at Week 6 compared with the parent trial baseline, (p<0.001 vs placebo; observed cases analysis). Over the same period, patients switched from galantamine to placebo and those who had received continuous placebo, exhibited mean (± SE) deteriorations of 0.7 (± 0.49) and 1.2 (± 0.49) points, respectively. Similar trends were apparent in Study 2 (GAL-USA-5; n=118). In Study 1, subgroup analyses demonstrated cognitive benefits with continuing galantamine treatment and deterioration associated with galantamine withdrawal in patients with advanced moderate AD (baseline Mini- Mental State Examination score ≤14) and in individuals deemed non-responsive in terms of Clinician's Interview-Based Impression of Change-plus Caregiver Input (CIBIC-plus) evaluation at the end of the parent trial (CIBIC-plus score >4). No safety issues were identified. In patients with mild to moderate AD who have exhibited cognitive benefits from up to 5 months' galantamine treatment, continuing therapy reinforces previously achieved benefit, whereas in patients in whom galantamine is discontinued, although no safety concerns arise, the natural progression of AD is apparent.

One early and prominent pathologic feature of Alzheimer's disease (AD) is the appearance of activated microglia in the vicinity of developing β-amyloid deposits. However, the precise role of microglia during the course of AD is still under discussion. Microglia have been reported to degrade and clear β-amyloid, but they also can exert deleterious effects due to overwhelming inflammatory reactions. Here, we demonstrate the occurrence of developing plaque populations with distinct amounts of associated microglia using time-dependent analyses of plaque morphology and the spatial distribution of microglia in an APP/PS1 mouse model. In addition to a population of larger plaques (>700μm2) that are occupied by a moderate contingent of microglial cells across the course of aging, a second type of small β-amyloid deposits develops (≤400μm2) in which the plaque core is enveloped by a relatively large number of microglia. Our analyses indicate that microglia are strongly activated early in the emergence of senile plaques, but that activation is diminished in the later stages of plaque evolution >150 days). These findings support the view that microglia serve to restrict the growth of senile plaques, and do so in a way that minimizes local inflammatory damage to other components of the brain.

Morphometric and neuropsychological retrospective studies of amnestic mild cognitive impairment (MCI) have demonstrated that regional atrophies and cognitive impairments may differentiate stable from progressing MCI. No measure has proved helpful prospectively. In this study, twenty five amnestic MCI patients and 25 healthy controls underwent structural MRI and comprehensive neuropsychological assessment. The groups' grey matter volumes were compared with voxel based morphometry and were also correlated with scores obtained on paired associates learning and category fluency tasks. MCI patients had significantly reduced grey matter volume in left mediotemporal and other neocortical regions compared with controls. Atrophy in perirhinal and anterior inferior temporal cortex was associated with poor scores on both category fluency and paired associates learning tasks. After 36 months, 44% of the MCI sample converted to dementia. Converter and non-converter MCI subgroups differed in paired associates learning and in category fluency scores, and showed limited differences in grey matter loss in the hippocampal complex. Variable atrophy in the hippocampus was not a relevant element in the converter/non converter distinction, but converters had significant volumetric reductions in the perhirinal cortex and in other anterior temporal and frontal neocortical areas. A high proportion of converters (91%) could be identified from baseline data using a combination of measures of regional atrophy in left temporal association cortex and poor scores on paired associates learning and category fluency tasks. This combined approach may offer a better option than using each measure alone to prospectively identify individuals at more immediate risk of conversion to dementia in the MCI population. The clinical advantage of this combination of structural MRI and neuropsychological measures in predicting conversion to dementia will need additional prospective validation.

While much uncertainty exists in the estimates of the global burden of Alzheimer's disease and about the potential impact of various interventions, there is a widespread acceptance of the fact that the steady increase in the incidence and prevalence of the condition worldwide is becoming a massive public health problem as well as a huge economic burden for all healthcare systems and societies. These heavy demands are further compounded by the poor quality of life of the affected individuals, of their families and of their caregivers. The epidemic proportion of Alzheimer's disease has triggered relentless attempts for development of treatment approaches during the past two decades by a multitude of pharmaceuticals and biotech companies. Commercial development of the acetylcholinesterase inhibitors has, until recently, virtually dominated the field and, although efficacy has been demonstrated for five different products, the longterm clinical results suggested that alternate approaches were warranted. Disease modifying strategies targeting the β- amyloid plaques (e.g., decreasing β-amyloid formation through β- and γ-secretase inhibition, diminishing β-amyloid aggregation through anti-aggregants or enhancement of β-amyloid clearance through active/passive immunization), targeting the neurofibrillary tangles through inhibition of tau protein hyperphosphorilation or, more recently, by increasing mitochondrial permeability, all these potential treatment modalities are facing major methodological challenges during the conduct of a myriad of clinical trials meant to bring the novel therapies to the market. Failure of more than 400 products tested in more than 800 clinical trials to date, with many of these failures occurring in late stage development (phase III) have triggered a paradigm shift toward targeting of the early stages of cognitive deficiencies (mild cognitive impairment- MCI) and a refinement of the investigative methodologies. The great heterogeneity of the disease entity itself (MCI) coupled with inadequate sensitivity, specificity and positive/negative predictive values of the many common diagnostic outcome scales, outcome measures, and of many of the currently used biomarkers expose the drug development professionals to the risk of methodological flaws rendering the products explored ineffective, while very expensive.