Current Alzheimer Research - Volume 9, Issue 7, 2012

Donepezil is a reversible, non-competitive piperidine-type acetylcholinesterase inhibitor (AChEI) that is structurally unique compared with other currently available AChEIs. It was developed as a symptomatic treatment to compensate for the progressive loss of cholinergic signal between neurons, a consequence of neuronal cell loss in the brains of patients with Alzheimer's disease (AD). Clinical trials conducted over the 15 years since the drug was first licensed and available for use in patients with mild to moderate AD (1997) have shown that donepezil is efficacious and well tolerated at all stages of AD, from patients with mild or moderate impairment to those with severe disease. The published literature contains nearly 2000 papers on donepezil, and more than 200 of these articles relate to randomized controlled clinical trials. Trials in patients with mild cognitive impairment (MCI) failed to meet all of their primary objectives, but provided insights into patient selection and the design of trials. Overall, more than a decade of donepezil research has gradually changed attitudes toward therapy of AD from a general belief that no clinically useful treatment exists to the present day understanding that symptomatic therapy may be effective across the spectrum of dementia stages.

Purpose: The purpose of this study was to evaluate the macular and retinal nerve fiber layer (RNFL) thickness, and the electrical activity of the macula in patients with Alzheimer's disease (AD). Material and methods: 30 patients with AD and 30 age and sex matched healthy controls were studied. The thickness and the electrical activity of the macula were evaluated by means of optical coherence tomography (OCT) and multifocal-electroretinogram (mf-ERG). Results: Visual acuity, as well as visual fields and colour vision testing of all patients were normal. However, the mean foveal thickness was 148.50 μm (vs 171.50 μm in the control group, p=0.001) and the RNFL thickness was 104.5 μm in the superior area (vs 123 μm in the control group, p<0.0001) and 116.5 μm in the inferior area (vs 138 μm in the control group, p<0.0001) around the optic nerve. The mean P1 response density amplitude of the foveal area was 146.50 nV/deg2 (vs 293 nV/deg2 in the control group, p<0.0001) and the perifoveal area was 56.60 nV/deg2 (vs 81.50nv/deg2 in the control group, p<0.001). Conclusion: Our study showed that in patients with AD, even without visual failure there was a decrease in macular and RNFL thickness, as well as a decrease of the electrical activity of the macula.

In this study, we aimed to classify MR images for recognizing Alzheimer Disease (AD) in a group of patients who were recently diagnosed by clinical history and neuropsychiatric exams by using non-biased machine-learning techniques. T1 weighted MRI scans of 31 patients with probable AD and 31 age- and gender-matched cognitively normal elderly were analyzed with voxel-based morphometry and classified by support vector machine (SVM), a machine learning technique. SVM could differentiate patients from controls with accuracy of 74 % (sensitivity: 70 % and specificity: 77 %) when the whole brain was included the analyses. The classification accuracy was increased to 79 % (sensitivity: 65 % and specificity: 93 %) when the analyses restricted to hippocampus. Our results showed that SVM is a promising tool for diagnosis of AD, but needed to be improved.

Dementia is a known predictor of mortality, but little is known about disease duration. We therefore aimed to investigate the impact of dementia on survival by estimating years lived with the disease, in total and in different severity stages, and by comparing dementia to other major chronic disorders such as cancer and cardiovascular disease (CVD). During a 7.4-year follow-up of the Kungsholmen project, 371 incident dementia cases of the 1,307 dementia-free persons, aged 75+ at baseline, were clinically diagnosed (DSM-III-R criteria). Diagnoses of cancer and CVD were obtained from the national Stockholm Inpatient Registry System, active since 1969. Disease duration, hazard ratio (HR), and potential years of life lost (PYLL) were derived from Kaplan–Meier survival estimation, the Cox model, and standard life-table analysis, respectively. Dementia was a significant predictor of mortality (HR=1.7; 95% CI: 1.47–1.92) after adjustment for several covariates including comorbidity, accounting for 16% of all deaths. The mean (±SD) survival time after dementia diagnosis was 4.1 (±2.6) years, and more than 2 years were spent in moderate (14-month) and severe (12-month) stages. Women with dementia lived longer than men, as they survived longer in the severe stage (2.1 vs. 0.5 years among 75–84-year-old women compared to coetaneous men). The PYLL were 3.4 for dementia, 3.6 for CVD, and 4.4 for cancer. We found a similar impact of dementia and CVD on survival, but following diagnosis, persons with dementia, and especially women, spent half of their remaining lives in the severe disabling stages of the disease.

Copy number variants (CNVs) are DNA regions that have gains (duplications) or losses (deletions) of genetic material. CNVs may encompass a single gene or multiple genes and can affect their function. They are hypothesized to play an important role in certain diseases. We previously examined the role of CNVs in late-onset Alzheimer's disease (AD) and mild cognitive impairment (MCI) using participants from the Alzheimer's Disease Neuroimaging Initiative (ADNI) study and identified gene regions overlapped by CNVs only in cases (AD and/or MCI) but not in controls. Using a similar approach as ADNI, we investigated the role of CNVs using 794 AD and 196 neurologically evaluated control non-Hispanic Caucasian NIA-LOAD/NCRAD Family Study participants with DNA derived from blood/brain tissue. The controls had no family history of AD and were unrelated to AD participants. CNV calls were generated and analyzed after detailed quality review. 711 AD cases and 171 controls who passed all quality thresholds were included in case/control association analyses, focusing on candidate gene and genome-wide approaches. We identified genes overlapped by CNV calls only in AD cases but not controls. A trend for lower CNV call rate was observed for deletions as well as duplications in cases compared to controls. Gene-based association analyses confirmed previous findings in the ADNI study (ATXN1, HLA-DPB1, RELN, DOPEY2, GSTT1, CHRFAM7A, ERBB4, NRXN1) and identified a new gene (IMMP2L) that may play a role in AD susceptibility. Replication in independent samples as well as further analyses of these gene regions is warranted.

Brain-derived neurotrophic factor (BDNF) is a growth factor implicated in neuronal survival. Studies have reported altered BDNF serum concentrations in patients with Alzheimer's disease (AD). However, these studies have been inconsistent. Few studies have investigated BDNF concentrations across multiple neurodegenerative diseases, and no studies have investigated BDNF concentrations in patients with frontotemporal dementia. To examine BDNF concentrations in different neurodegenerative diseases, we measured serum concentrations of BDNF using enzyme-linked immunoassay in subjects with behavioral–variant frontotemporal dementia (bvFTD, n=20), semantic dementia (SemD, n=16), AD (n=34), and mild cognitive impairment (MCI, n=30), as well as healthy older subjects (HS, n=38). BDNF serum concentrations were compared across diagnoses and correlated with cognitive tests and patterns of brain atrophy using voxelbased morphometry. We found small negative correlations between BDNF serum concentrations and some of the cognitive tests assessing learning, information processing speed and cognitive control in complex situations, however, BDNF did not predict disease group membership despite adequate power. These findings suggest that BDNF serum concentration may not be a reliable diagnostic biomarker to distinguish among neurodegenerative diseases.

The objective of the present work was to study a purported involvement of stress in amyloid pathology through the modulation of BACE expression. Early-life stressed rats (maternal separation, MS) showed significant increases in corticosterone levels, BACE expression and Aβ levels. The CpG7 site of the BACE promoter was significantly hypomethylated in MS, and corticosterone levels negatively correlated to the methylation status of CpG7. The activation of the stress-activated protein kinase JNK was also increased in MS rats. In SHSY-5Y neuroblastoma cells, corticosterone induced a rapid increase in BACE expression that was abolished by specific inhibiton of JNK activation or by spironolactone, a mineralocorticoid receptor antagonist, but not by mifepristone, a glucocorticoid receptor antagonist. Corticosterone was also able to increase pJNK expression and this effect was fully reverted by spironolactone. Mice chronically treated with corticosterone showed increased BACE and pJNK expression. These increases were reverted by treatment with spironolactone or with a JNK inhibitor. It is suggested that increased corticosterone levels associated to stress lead to increase BACE transcription both through epigenetic mechanisms and activation of JNK.

Alzheimer's disease (AD) is a neurodegenerative disorder that severely jeopardizes the health of aging populations all over the world. According to the amyloid cascade hypothesis, the pathological progression of AD is associated with the formation of amyloid plaques in the brain, resulting from the aggregation of amyloid-β (Aβ) peptides. Over the past few years, vast efforts have been dedicated to the development of amyloid probes and inhibitors for the diagnosis and effective treatment of AD. We review here recent advancements in luminescent probes for the detection of Aβ peptide and fibrils, and the current development of small molecule inhibitors of Aβ aggregation. We also highlight the key features in each specific example, as well as review new ideas and strategies that are crucial for researchers in this field.

Alzheimer's disease (AD) is the most common age-related neurodegenerative disorder among the elderly. Nmethyl- D-aspartate receptor (NMDAR) overactivation has been implicated in early synaptic dysfunction that precedes late neurodegeneration in AD. Moreover, oligomers of amyloid-beta peptide (Aβ) 1-42 are considered the most synaptotoxic forms, responsible for early cognitive deficits in AD. In this work we evaluate the role of NMDARs on Aβ-evoked neuronal dysfunction and cell death through changes in microtubule polymerization in mature hippocampal cultures. Exposure to Aβ 1-42 caused a decrease in total and polymerized levels of beta-III tubulin and polymerized alpha-tubulin, suggesting microtubule disassembly. Moreover, Aβ induced DNA fragmentation in both neuronal and non-neuronal cells. Indeed, the effects of Aβ on beta-III tubulin polymerization were significantly correlated with reduced neurite length and neuronal DNA fragmentation. Interestingly, these effects were prevented by MK-801 and memantine, suggesting a role for extrasynaptic NMDARs in Aβ toxicity, and by ifenprodil, further indicating the involvement of GluN2B-containing NMDARs. Nevertheless, exposure to Aβ did not potentiate the effects caused by selective activation of NMDARs. Data largely suggest that Aβ-induced hippocampal neuronal dysfunction occurs through NMDAR-dependent microtubule disassembly associated to neurite retraction and DNA fragmentation in mature hippocampal cells.

Oscillatory activity in the entorhinal cortex has been associated with several cognitive functions. Accordingly, Alzheimer Disease-associated cognitive decline has been related to amyloid beta-induced disturbances in several of these oscillatory patterns. We have previously shown that acute application of amyloid beta inhibits the generation of slowfrequency oscillations (7-20 Hz). In contrast, alterations in faster oscillations recorded in Alzheimer Disease-transgenic mice that over-express amyloid beta have been controversial. Since transgenic mice may produce complex responses due to compensatory mechanisms, we tested the effect of acute application of amyloid beta on fast oscillations (beta-gamma bursts) generated by entorhinal cortex slices in vitro in a Mg2+-free solution. We also explored the participation of the enzyme glycogen synthase kinase 3 (GSK-3) in this effect. Our results show that bath application of a clinically relevant concentration of amyloid beta (10 nM) activates GSK-3 and reduces the power of beta-gamma bursts in the entorhinal cortex. The reduction of beta-gamma bursts by amyloid beta is blocked by inhibiting GSK-3 either with lithium or with SB 216763. Our results suggest that amyloid beta-induced inhibition of entorhinal cortex beta-gamma activity involves GSK-3 activation, which may provide a molecular mechanism for amyloid beta-induced neural network disruption and support the use of GSK-3 inhibitors to treat Alzheimer Disease.

Evidence from basic molecular biology has noted a critical role of GSK-3 in Alzheimer's disease (AD) pathogenesis such as beta-amyloid (Aβ) production and accumulation, the formation of neurofibrillary tangle (NFT), and neuronal degeneration. Aβ generation and deposition represents a key feature and is generated from APP by the sequential actions of two proteolytic enzymes: β-secretase and γ-secretase. GSK-3 could play a critical role in Aβ production via enhancing β-secretase activity. GSK-3 not only modulates APP processing in the process of Aβ generation, but regulates Aβ production by interfering with APP cleavage at the γ-secretase complex step since the APP and PS1 (a component of γ- secretase complex) are substrates of GSK-3 as well. GSK-3 may downregulate α-secretase through inhibiting PKC and ADAMs activity which are the substrates of GSK-3 contributing to Aβ production. Meanwhile, Aβ accumulation can induce GSK-3 activation through Aβ-mediated neuroinflammation and oxidative stress. Considering that active GSK-3 and some common GSK-3-shared factors induce the hyperphosphorylation of tau and neurofibrillary lesions, GSK-3 is a possible linking between amyloid plaques and NFT pathology. Additionally, GSK-3 could disrupt acetylcholine activity, and accelerate axon degeneration and failures in axonal transport, and lead to cognitive impairment in AD. Preclinical and clinical studies have supported that GSK-3β inhibitors could be useful in the treatment of AD. Consequently, an effective measure to inhibit GSK-3 activity may be a very attractive drug target in AD.