Factors associated with resistance to dementia despite high Alzheimer disease pathology

Neuropathologic alterations in mild cognitive impairment: a review

Mild cognitive impairment (MCI), the earliest clinically detectable phase of the trajectory toward dementia and Alzheimer's disease (AD), led to the need for even earlier detection and prevention of AD. Although it is a clinical diagnosis, its underlying neuropathological findings are just being defined. MCI is best studied in longitudinally followed patients in centers that are experienced in dementing disorders. In this review of the few major clinical-pathological reports of longitudinally followed patients, it appears that most autopsied amnestic MCI (aMCI) patients are on a pathway toward AD. Neurofibrillary pathology in entorhinal cortex, hippocampus, and amygdala--not amyloid plaques--is the major substrate for aMCI and for memory decline. In addition, many MCI patients have other concomitant pathological alterations, the most common of which are strokes, but also include argyrophilic grains and Lewy bodies. These findings are not surprising because most MCI autopsied cases have been in the older (80 to 90 year) range where these findings are common. In early AD, the phase following MCI, the significant change is an increase in neurofibrillary tangles in the neocortex that correlates with an increase in Braak score and the observed clinical progression.

Alzheimer disease pathology in cognitively healthy elderly: a genome-wide study

Many elderly individuals remain dementia-free throughout their life. However, some of these individuals exhibit Alzheimer disease neuropathology on autopsy, evidenced by neurofibrillary tangles (NFTs) in AD-specific brain regions. We conducted a genome-wide association study to identify genetic mechanisms that distinguish non-demented elderly with a heavy NFT burden from those with a low NFT burden. The study included 299 non-demented subjects with autopsy (185 subjects with low and 114 with high NFT levels). Both a genotype test, using logistic regression, and an allele test provided consistent evidence that variants in the RELN gene are associated with neuropathology in the context of cognitive health. Immunohistochemical data for reelin expression in AD-related brain regions added support for these findings. Reelin signaling pathways modulate phosphorylation of tau, the major component of NFTs, either directly or through β-amyloid pathways that influence tau phosphorylation. Our findings suggest that up-regulation of reelin may be a compensatory response to tau-related or beta-amyloid stress associated with AD even prior to the onset of dementia.

Reduced gray matter volume in normal adults with a maternal family history of Alzheimer disease

OBJECTIVE

A consistently identified risk factor for Alzheimer disease (AD) is family history of dementia, with maternal transmission significantly more frequent than paternal transmission. A history of maternal AD may be related to AD-like glucose consumption in cognitively healthy subjects. In this cross-sectional study, we tested whether cognitively healthy people with a family history of AD have less gray matter volume (GMV), an endophenotype for late-onset AD, than individuals with no family history, and whether decreases in GMV are different in subjects with a maternal family history.

METHODS

As part of the Kansas University Brain Aging Project, 67 cognitively intact individuals with a maternal history of late-onset AD (FHm, n = 16), a paternal history of AD (FHp, n = 8), or no parental history of AD (FH-, n = 43), similar in age, gender, education, and Mini-Mental State Examination score, were scanned at 3 T. We used voxel-based morphometry to examine GMV differences between groups, controlling for age, gender, and apoE4.

RESULTS

Cognitively healthy individuals with a family history of late-onset AD had significantly decreased GMV in the precuneus, middle frontal, inferior frontal, and superior frontal gyri compared with FH- individuals. FHm subjects had significantly smaller inferior frontal, middle frontal, precuneus, and lingual gyri compared with FH- and FHp subjects.

CONCLUSIONS

Overall, maternal family history of Alzheimer disease (AD) in cognitively normal individuals is associated with lower gray matter volume in AD-vulnerable brain regions. These data complement and extend reports of cerebral metabolic differences in subjects with a maternal family history.

Visual aspects of neurologic protein misfolding disorders

PURPOSE OF REVIEW

This article reviews topics of interest to the ophthalmologist relating to the most common neurologic protein misfolding disorders.

RECENT FINDINGS

Many neurodegenerative diseases are pathologically associated with misfolded proteins. These diseases cause a profound impact of disability to the individual and society. Alzheimer's disease costs alone are estimated to be over US$225 billion annually in the USA. The ophthalmologist is often asked to provide an opinion regarding the cause of visual symptoms in patients with these unique disorders.

SUMMARY

The categorization of neurodegenerative diseases has evolved based on advances in genetic, molecular and pathological research. In many neurodegenerative diseases, aggregation of a misfolded protein is responsible for the development of pathologic inclusions. When the misfolded protein is tau or synuclein, these diseases are called tauopathies or synucleinopathies, respectively. This article focuses on ophthalmic findings in some of the most common tauopathies and synucleinopathies: Alzheimer's disease, progressive supranuclear palsy, Parkinson's disease, dementia with Lewy bodies and multisystem atrophy.

Changing perspectives regarding late-life dementia

Individuals over 80 years of age represent the most rapidly growing segment of the population, and late-life dementia has become a major public health concern worldwide. Development of effective preventive and treatment strategies for late-life dementia relies on a deep understanding of all the processes involved. In the centuries since the Greek philosopher Pythagoras described the inevitable loss of higher cognitive functions with advanced age, various theories regarding the potential culprits have dominated the field, ranging from demonic possession, through 'hardening of blood vessels', to Alzheimer disease (AD). Recent studies suggest that atrophy in the cortex and hippocampus-now considered to be the best determinant of cognitive decline with aging-results from a combination of AD pathology, inflammation, Lewy bodies, and vascular lesions. A specific constellation of genetic and environmental factors (including apolipoprotein E genotype, obesity, diabetes, hypertension, head trauma, systemic illnesses, and obstructive sleep apnea) contributes to late-life brain atrophy and dementia in each individual. Only a small percentage of people beyond the age of 80 years have 'pure AD' or 'pure vascular dementia'. These concepts, formulated as the dynamic polygon hypothesis, have major implications for clinical trials, as any given drug might not be ideal for all elderly people with dementia.

Dietary composition modulates brain mass and solubilizable Abeta levels in a mouse model of aggressive Alzheimer's amyloid pathology

OBJECTIVE

Alzheimer's disease (AD) is a progressive neurodegenerative disease of the central nervous system (CNS). Recently, an increased interest in the role diet plays in the pathology of AD has resulted in a focus on the detrimental effects of diets high in cholesterol and fat and the beneficial effects of caloric restriction. The current study examines how dietary composition modulates cerebral amyloidosis and neuronal integrity in the TgCRND8 mouse model of AD.

METHODS

From 4 wks until 18 wks of age, male and female TgCRND8 mice were maintained on one of four diets: (1) reference (regular) commercial chow; (2) high fat/low carbohydrate custom chow (60 kcal% fat/30 kcal% protein/10 kcal% carbohydrate); (3) high protein/low carbohydrate custom chow (60 kcal% protein/30 kcal% fat/10 kcal% carbohydrate); or (4) high carbohydrate/low fat custom chow (60 kcal% carbohydrate/30 kcal% protein/10 kcal% fat). At age 18 wks, mice were sacrificed, and brains studied for (a) wet weight; (b) solubilizable Abeta content by ELISA; (c) amyloid plaque burden; (d) stereologic analysis of selected hippocampal subregions.

RESULTS

Animals receiving a high fat diet showed increased brain levels of solubilizable Abeta, although we detected no effect on plaque burden. Unexpectedly, brains of mice fed a high protein/low carbohydrate diet were 5% lower in weight than brains from all other mice. In an effort to identify regions that might link loss of brain mass to cognitive function, we studied neuronal density and volume in hippocampal subregions. Neuronal density and volume in the hippocampal CA3 region of TgCRND8 mice tended to be lower in TgCRND8 mice receiving the high protein/low carbohydrate diet than in those receiving the regular chow. Neuronal density and volume were preserved in CA1 and in the dentate gyrus.

INTERPRETATION

Dissociation of Abeta changes from brain mass changes raises the possibility that diet plays a role not only in modulating amyloidosis but also in modulating neuronal vulnerability. However, in the absence of a study of the effects of a high protein/low carbohydrate diet on nontransgenic mice, one cannot be certain how much, if any, of the loss of brain mass exhibited by high protein/low carbohydrate diet-fed TgCRND8 mice was due to an interaction between cerebral amyloidosis and diet. Given the recent evidence that certain factors favor the maintenance of cognitive function in the face of substantial structural neuropathology, we propose that there might also exist factors that sensitize brain neurons to some forms of neurotoxicity, including, perhaps, amyloid neurotoxicity. Identification of these factors could help reconcile the poor clinicopathological correlation between cognitive status and structural neuropathology, including amyloid pathology.

Preclinical properties of 18F-AV-45: a PET agent for Abeta plaques in the brain

beta-amyloid plaques (Abeta plaques) in the brain, containing predominantly fibrillary Abeta peptide aggregates, represent a defining pathologic feature of Alzheimer disease (AD). Imaging agents targeting the Abeta plaques in the living human brain are potentially valuable as biomarkers of pathogenesis processes in AD. (E)-4-(2-(6-(2-(2-(2-(18)F-fluoroethoxy)ethoxy)ethoxy)pyridin-3-yl)vinyl)-N-methyl benzenamine ((18)F-AV-45) is such as an agent currently in phase III clinical studies for PET of Abeta plaques in the brain.

METHODS

In vitro binding of (18)F-AV-45 to Abeta plaques in the postmortem AD brain tissue was evaluated by in vitro binding assay and autoradiography. In vivo biodistribution of (18)F-AV-45 in mice and ex vivo autoradiography of AD transgenic mice (APPswe/PSEN1) with Abeta aggregates in the brain were performed. Small-animal PET of a monkey brain after an intravenous injection of (18)F-AV-45 was evaluated.

RESULTS

(18)F-AV-45 displayed a high binding affinity and specificity to Abeta plaques (K(d), 3.72 +/- 0.30 nM). In vitro autoradiography of postmortem human brain sections showed substantial plaque labeling in AD brains and not in the control brains. Initial high brain uptake and rapid washout from the brain of healthy mice and monkey were observed. Metabolites produced in the blood of healthy mice after an intravenous injection were identified. (18)F-AV-45 displayed excellent binding affinity to Abeta plaques in the AD brain by ex vivo autoradiography in transgenic AD model mice. The results lend support that (18)F-AV-45 may be a useful PET agent for detecting Abeta plaques in the living human brain.

Does prevention for Alzheimer's disease exist?

The prevention of Alzheimer's disease is a growing public health concern amidst an ageing population. Meanwhile, there is no effective or curative treatment available where prevention could greatly reduce health costs. This review was based on reports of potential preventive factors, including modifiable lifestyle factors, as well as preventive pharmacological strategies. Although the present review was not systematic, the reports selected from PubMed using "Alzheimer's disease" and "prevention" as key-words, allow us to affirm that pursuing a healthy lifestyle; physical, cognitive, leisure activities; good social engagement; a high consumption of fish, low consumption of dietary fat and moderate consumption of wine, and control of vascular risk factors appear to be potential factors for delaying dementia.

Sex difference in pathology and memory decline in rTg4510 mouse model of tauopathy

Abnormal phosphorylation of tau protein is a common event in many neurodegenerative disorders, including Alzheimer's disease and other tauopathies. We investigated the relationship between hyperphosphorylated tau in brain extracts and mnemonic functions in rTg4510 mouse model of tauopathy. We report that rTg4510 mice showed rapid deterioration in spatial learning and memory, which paralleled a significant increase of hyperphosphorylated tau in the brain between 3 and 5.5 months of age. At 5.5 months, rTg4510 females showed significantly higher levels of hyperphosphorylated tau than males, with no evidence of differential tau transgene expression between the sexes. The increased levels of hyperphosphorylated tau in females were associated with more severe impairment in spatial learning and memory as compared to transgenic males. We also showed that within studied age range, the decrease in memory performance was accompanied by other behavioral disturbances in the water maze related to search strategy, like thigmotaxic swim and cue response. These findings suggest that the onset of abnormal tau biochemistry and coincident cognitive deficits in the rTg4510 mouse model is sex-dependent with females being affected earlier and more aggressively than males.