Current Alzheimer Research - Volume 12, Issue 4, 2015

Accumulating evidence has suggested the involvement of oxidative stress in the pathogenesis of Alzheimer’s disease (AD). The main endogenous antioxidant, glutathione (GSH), has been shown to decline with ageing and in several age-related degenerative diseases, including AD. Potential options for replenishing GSH levels as a therapeutic target to treat these conditions include the administration of GSH itself, and low toxicity forms of the limiting amino acid for GSH synthesis; cysteine. However, passive GSH uptake is limited due to an unfavourable concentration gradient between the plasma and cytosol. Similarly, cysteine prodrugs have demonstrated limited efficacy to elevate depleted GSH levels in several in vivo and in vitro models of disease. It has been suggested that the decline in GSH levels in AD, may be associated with down regulation of GSH homeostasis rather than substrate limitation. Cellular GSH homeostasis is regulated by non-allosteric feedback inhibition exerted by GSH on glutamate cysteine ligase (GCL), which is responsible for the synthesis of the GSH precursor γ-glutamylcysteine (GGC). In conditions involving down regulated GSH homeostasis, GGC serves as a crucialrate-limiting substrate for GSH synthetase, the main enzyme responsible for condensing glycine with GGC to form the final thiol tripeptide, GSH. In this review, we focus on the therapeutic potential of GGC to elevate cellular GSH levels. We also discuss the efficacy of GGC prodrugs which would be taken up and converted by the unregulated GS to GSH, and the administration of modified GSH compounds, such as GSH esters that could potentially overcome the concentration gradient that prohibits passive GSH uptake, in AD.

Alzheimer’s disease (AD) is the most common cause of dementia, affecting more than 36 million people worldwide. Octodon degus, a South American rodent, has been found to spontaneously develop neuropathological signs of AD, including amyloid-β (Aβ) and tau deposits, as well as a decline in cognition with age. Firstly, the present work introduces a novel behavioral assessment for O. degus - the burrowing test - which appears to be a useful tool for detecting neurodegeneration in the O. degus model for AD. Such characterization has potentially wide-ranging implications, because many of these changes in species-typical behaviors are reminiscent of the impairments in activities of daily living (ADL), so characteristic of human AD. Furthermore, the present work characterizes the ADlike neuropathology in O. degus from a gene expression point of view, revealing a number of previously unreported AD biomarkers, which are found in human AD: amyloid precursor protein (APP), apolipoprotein E (ApoE), oxidative stressrelated genes from the NFE2L2 and PPAR pathway, as well as pro-inflammatory cytokines and complement proteins, in agreement with the known link between neurodegeneration and neuroinflammation. In summary, the present results confirm a natural neuropathology in O. degus with similar characteristics to AD at behavioral, cellular and molecular levels. These characteristics put O. degus in a singular position as a natural rodent model for research into AD pathogenesis and therapeutics against AD.

Apolipoprotein E4 (apoE4), the most prevalent genetic risk factor for Alzheimer's disease (AD), is associated with neuronal and vascular impairments. Recent findings suggest that retina of apoE4 mice have synaptic and functional impairments. We presently investigated the effects of apoE4 on retinal and choroidal vasculature and the possible role of VEGF in these effects. There were no histological differences between the retinal and choroidal vasculatures of naïve apoE3 and apoE4 mice. In contrast, laserdriven choroidal injury induced higher levels of choroidal neovascularization (CNV) in apoE4 than in apoE3 mice. These effects were associated with an inflammatory response and with activation of the Muller cells and asrocytic markers gluthatione synthetase and GFAP, all of which were more pronounced in the apoE4 mice. CNV also induced a transient increase in the levels of the synaptic markers synaptophysin and PSD95 which were however similar in the apoE4 and apoE3 naive mice. Retinal and choroidal VEGF and apoE levels were lower in naïve apoE4 than in corresponding apoE3 mice. In contrast, VEGF and apoE levels rose more pronouncedly following laser injury in the apoE4 than in apoE3 mice. Taken together, these findings suggest that the apoE4-induced retinal impairments, under basal conditions, may be related to reduced VEGF levels in the eyes of these mice. The hyper-neovascularization in the apoE4 mice might be driven by increased inflammation and the associated surge in VEGF following injury.

Alzheimer's disease (AD) is the most common form of dementia characterized by progressive loss of memory and other cognitive functions among older people. Senile plaques and neurofibrillary tangles are the most hallmarks lesions in the brain of AD in addition to neurons loss. Accumulating evidence has shown that oxidative stress–induced damage may play an important role in the initiation and progression of AD pathogenesis. Redox impairment occurs when there is an imbalance between the production and quenching of free radicals from oxygen species. These reactive oxygen species augment the formation and aggregation of amyloid-β and tau protein hyperphosphorylation and vice versa. Currently, there is no available treatments can modify the disease. However, wide varieties of antioxidants show promise to delay or prevent the symptoms of AD and may help in treating the disease. In this review, the role of oxidative stress in AD pathogenesis and the common used antioxidant therapies for AD will summarize.

Objective. This research aims to determine whether residence (rural vs. urban) at different life stages (childhood, adulthood, and late life) is associated with increased risk of incident dementia in a population-based cohort of older Spaniards. Methods. In this prospective study, 2,711 participants aged 65 years and older were assessed at baseline and 3 years later. All cases of incident dementia were diagnosed using DSM-IV criteria. The relationship between residence and the relative risk of dementia was analysed using Cox's regression models. Demographics, comorbidity index, consumption (tobacco / alcohol) and doubtful dementia diagnosis were considered as possible confounders. Results. At the three-year follow-up, 91 cases of dementia were detected. Lower education and occupational attainment were associated with a higher incidence of dementia three years later. Rural residence in adulthood was associated with a significantly higher risk of dementia at the follow-up. Childhood rural residence revealed a marked trend for risk of dementia (p = 0.08), but it was nonsignificant in later life. The risk of dementia was considerably higher for the rural/low-education group than for the urban/high-education group, for both childhood and adulthood residence. Finally, people from areas with the lowest socio- economic status Arévalo (rural, blue-collar) and Margaritas (urban, blue-collar) showed higher risk of dementia than people from Lista (urban, mixed white/blue collar). Conclusion. In this cohort, early and mid-life stages rural residence was a risk factor for dementia, but not later-life rural residence. The rural residence effect was noticeably higher in people with a lower educational level.

Alzheimer’s disease-related pathology results in tremendous structural and functional changes in the brain. These morphological changes might lead to a less precise performance of automated brain segmentation techniques in AD-patients, which in turn could possibly lead to false allocations of gray matter, white matter or cerebrospinal fluid. FreeSurfer has been shown to operate as an accurate and reliable instrument to measure cortical thickness and volume of neuroanatomical structures. Considering the principal role of FreeSurfer in the imaging field of AD, the present study aims to investigate the robustness of FreeSurfer to capture morphological changes in the brain against varying processing variables in comparison to manual measurements (the gold standard). T1-weighted MRI scan data were used pertaining to a sample of 53 individuals (18 healthy participants, 18 patients with mild cognitive impairment, and 18 patients with mild AD). Data were analyzed with different FreeSurfer versions (v4.3.1, v4.5.0, v5.0.0, v5.1.0), on a custom-built cluster (LINUX) and a Macintosh (UNIX) workstation. Group differences across versions and workstations were most consistent for both the hippocampus and posterior cingulate, regions known to be affected in the earliest stages of the disease. The results showed that later versions of FreeSurfer were more sensitive to identify group differences and corresponded best with the results of gold standard manual volumetric methods. In conclusion, later versions of FreeSurfer were more accurate than earlier versions, especially in medial temporal and posterior parietal regions. This development is very promising for future applications of FreeSurfer in research studies and encourages the future role of FreeSurfer output as a candidate marker in clinical practice.

The effects of carotid and vertebral arterial morphological variations on cognitive function impairment remain unclear. We investigated the association between extracranial carotid and vertebral arterial variations and the risk of Alzheimer's disease (AD). A prospective study with a 5-year followup was conducted from July 2008 to June 2013. A total of 1741 subjects (50 years of age and older) were examined for carotid and vertebral arterial variations using computed tomography angiography (CTA) and completed the study follow-up. Variations of the carotid and vertebral arteries were classified as tortuosity, kinking and coiling, according to the Weibel and Fields criteria. Cognitive function was assessed using the Mini-Mental State Examination and the Activities of Daily Living scale. We analyzed the association between arterial variations and the risk of AD by using multivariate Cox proportional-hazards models. The prevalence of carotid arterial variations was 38.4%, and the prevalence of vertebral arterial variations was 86.6%. Among the 1741 subjects who completed the study follow-up, 134 AD cases were detected. The subjects diagnosed with AD displayed greater kinking and coiling in the carotid artery (P<0.01) and vertebral artery (P<0.05) than the subjects without AD. After adjusting for potential confounders, kinking and coiling (hazard ratio [HR]=1.93, 95% confidence interval [CI], 1.37 to 2.86, P<0.01) in the carotid artery were significantly associated with AD. Additionally, after adjusting for potential confounders, kinking and coiling (HR=1.73, 95% CI, 1.25 to 2.31, P<0.01) in the vertebral artery were significantly associated with the risk of AD. We determined that age, hypertension and smoking status were significant predictors of AD in the multivariable models with carotid and vertebral arterial variation. The results of the current study indicate that severe carotid and vertebral arterial variations are associated with a significantly increased risk of AD. Further investigation into the association between these variations and AD would be useful for preventing AD.

To investigate the effect of running exercise on myelinated fibers in the dentate gyrus (DG) of the hippocampus during Alzheimer's disease (AD), 6-month-old male APP/PS1 transgenic mice were randomly assigned to control or running groups. The running group mice were subjected to a running protocol for four months. The behaviors of the mice from both group mice were then assessed using the Morris water maze, and the total volume of the DG and the related quantitative parameters with characteristics of the myelinated nerve fiber and the myelin sheath in the DG were investigated using unbiased stereological techniques and electron microscopy. Learning and spatial memory performances were both significantly increased in the running group compared with the control group. There was no significant difference in the gratio of the myelinated axons between the two groups. However, the DG volume, the myelinated fiber length and volume in the DG, and the myelin sheath volume and thickness in the DG were all significantly increased in the running group mice compared with the control group mice. These results indicated that running exercise was able to prevent DG atrophy and delay the progression of the myelinated fiber loss and the demyelination of the myelin sheaths in the DG in an AD mouse model, which may underlie the running-induced improvement in learning and spatial memory. Taken together, these results demonstrated that running exercise could delay the progression of AD.

The common pathological hallmark of Alzheimer’s disease (AD) is β-amyloid plaque deposition. The ideal therapy would reduce the Aβ burden with a low inflammatory immune response. Passive immunotherapy is an advanced treatment that dramatically reduces brain Aβ pathologies in AD animal models. The objective of our study was to observe the effects of 5C8H5, a novel monoclonal antibody derived from 4Aβ1-15, on brain Aβ pathology in an APP/PS1 mouse model of AD. Six-month-old transgenic mice were administered 5C8H5, 4Aβ1-15 or IgG, and same-aged wild-type untreated C57Bl/6J mice were employed as controls. Inflammatory factors and Aβ40/42 levels were detected by ELISA, while Aβ plaques, microglial cell activation, microhemorrhages and neurogenesis were evaluated by immunohistochemical staining. Compared with 4Aβ1-15-treated mice, the mice in the 5C8H5 group induced more Aβ clearance with less microglial cell activation in a niche of Th2-polarized immune response. The levels of proinflammatory factors, including IL-1β, IL-6, TNF-α and IFN-γ, were significantly decreased in the CNS, while the level of antiinflammatory IL-4 was increased. Moreover, the mice in the 5C8H5 group induced more neurogenesis without microhemorrhage exacerbation and thereby performed better in behavioral assays than did the 4Aβ1-15 group. In conclusion, the novel monoclonal antibody induces more Aβ clearance and less microglial cell activation in the absence of inflammation, accompanied by an increased Th2-polarized immune response, which makes it a more promising therapeutic strategy. These data provide evidence that passive immunity could alleviate pathologic Aβ alterations by modulating inflammation and should be pursued further for the treatment of AD.