Correlation between Apolipoprotein-E polymorphism and Alzheimer's disease pathology

Genetics of Vascular Dementia: Systematic Review and Meta-Analysis

BACKGROUND

Vascular dementia (VaD) is the second most common type of dementia. So far, little is known about the contribution of genetic polymorphisms to the risk of VaD. Many candidate genetic polymorphisms have been examined in a large number of studies. However, due to the conflicting results, the genetics of VaD is still behind the shadow.

OBJECTIVE

We conducted a comprehensive meta-analysis on associations between genetic polymorphisms of any gene and VaD to investigate the genetics of VaD.

METHOD

We sought the published studies of associations between any genetic polymorphism and VaD and critically appraised them. We assessed the effects of genetic models by calculating pooled odds ratios (ORs), investigating the origin of heterogeneity by subgroup analysis, and testing the robustness by random effect model and sensitivity analysis.

RESULTS

69 studies with 4,462 cases and 11,583 controls were included. We identified APOE ɛ2/ɛ3/ɛ4 and additional four genetic polymorphisms including MTHFR C677T, PON1 L55M, TGF-β1 +29C/T, and TNF-α -850C/T associated with VaD. Tested by random effect model and sensitivity analysis, the pooled results show nice robustness.

CONCLUSIONS

Our comprehensive meta-analysis highlighted the genetic contribution to sporadic VaD. Because of the small amount of data on associations between genetic polymorphisms, except for APOE, and VaD, more studies are needed to test the existing genetic polymorphisms and detect other related genetic variants.

Apolipoprotein E ε4 allele and malondialdehyde level are independent risk factors for Alzheimer's disease

Background:

The ε4 allele of Apolipoprotein E is involved in lipid metabolism. Oxidative stress produces an increase in lipid peroxidation that has been implicated in the pathogenic cascade in Alzheimer’s disease. This study estimated the effect of the ε4 allele, malondialdehyde and lipid levels on the risk for Alzheimer’s disease.

Methods:

A total of 41 control subjects and 73 patients with Alzheimer’s disease were recruited. The Apolipoprotein E genotype was determined by amplification of exon 4 of the Apolipoprotein E by polymerase chain reaction (PCR); malondialdehyde concentration was determined by high-pressure liquid chromatography, and serum lipids were measured by routine photometric techniques.

Results:

Malondialdehyde levels were significantly higher in Alzheimer’s disease patients independent of the Apolipoprotein E genotype and ε4 allele. The ε4 allele increases the risk of Alzheimer’s disease by 5.114 times and elevated malondialdehyde levels increase the risk by 9.342.

Conclusion:

The presence of ε4 allele and elevated malondialdehyde levels are independent risk factors for Alzheimer’s disease. These findings support the hypothesis that lipid peroxidation and ε4 allele contribute to the pathogenic cascade in Alzheimer’s disease by different pathways.

Genetic risk factors and markers for Alzheimer's disease and/or depression in the VITA study

OBJECTIVES

In ageing population, both Alzheimer's disease (AD) and depression are common. Significant depressive symptoms are often co-morbid with cognitive impairment and dementia. In this study, we attempted to find various factors and markers for both AD and depression in a longitudinal cohort, the Vienna-Transdanube-Aging (VITA)-study.

METHODS

The VITA-Study consisted of 305 healthy subjects, 174 subjects with depression only, 55 subjects diagnosed with AD only and 72 subjects with depression as well as AD. Associations between AD and/or depression to gene polymorphisms APO E (epsilon4), choline acetyltransferase (ChAT) 4G to A, serotonin-transporter gene promoter-length, dopamine-D4-receptor, ciliary-neurotrophic-factor-null mutation and brain-derived neurotrophic factor (C270T) and to various known factors were analyzed.

RESULTS

AD and depression were significant associated. Significant risk factors found for AD were low education, low folic acid and depressive-symptoms, while for depression were low education and higher nonsteroidal anti-inflammatory drugs (NSAID) consume. Moreover, the ChAT polymorphism associated significant to depression. Gender, education, and ChAT significantly associated with the combination AD and/or depression.

CONCLUSION

Such studies must be conducted cautiously, as co-morbidities and gene-environmental-social influences may sway the results dramatically. We found in the VITA-study significant association between depression and AD and between ChAT polymorphism and depression.

The significance of the cholinergic system in the brain during aging and in Alzheimer's disease

Acetylcholine is widely distributed in the nervous system and has been implicated to play a critical role in cerebral cortical development, cortical activity, controlling cerebral blood flow and sleep-wake cycle as well as in modulating cognitive performances and learning and memory processes. Cholinergic neurons of the basal forebrain complex have been described to undergo moderate degenerative changes during aging, resulting in cholinergic hypofunction that has been related to the progressing memory deficits with aging. Basal forebrain cholinergic cell loss is also a consistent feature of Alzheimer's disease, which has been suggested to cause, at least partly, the cognitive deficits observed, and has led to the formulation of the cholinergic hypotheses of geriatric memory dysfunction. Impaired cortical cholinergic neurotransmission may also contribute to beta-amyloid plaque pathology and increase phosphorylation of tau protein the main component of neurofibrillar tangles in Alzheimer's disease. Understanding the molecular mechanisms underlying the interrelationship between cortical cholinergic dysfunction, beta-amyloid formation and deposition, and tau pathology in Alzheimer's disease, would allow to derive potential treatment strategies to pharmacologically intervene in the disease-causing signaling cascade.

Histocompatibility antigens, aspirin use and cognitive performance in non-demented elderly subjects

HLA genotype and anti-inflammatory drug use have independently been associated with a lower risk of Alzheimer's disease (AD). We recently reported a negative association between aspirin use and AD. To investigate this further, we performed a cross-sectional study to investigate cognitive performance in 151 non-demented individuals in relation to HLA-DRB1 genotype and aspirin use. Aspirin and HLA-DRB1*01 were positive predictors of performance on logical memory (aspirin, p=0.04) and verbal fluency tests (HLA-DRB1*01, p=0.018), respectively. HLA-DRB1*05 had a negative impact on the Boston naming test (p=0.002). Our results suggest that aspirin use and inflammatory genotype may influence cognition in non-demented subjects.

Folate quenches oxidative damage in brains of apolipoprotein E-deficient mice: augmentation by vitamin E

We demonstrate that folate and vitamin E can compensate for the diminished oxidative buffering capacity of brains of apolipoprotein E-deficient mice. Normal and ApoE(tmlUne) homozygous 'knockout' mice were maintained for 1 month on a diet either lacking or supplemented with folate, vitamin E or iron as a pro-oxidant after which brain tissue was harvested and analyzed for for thiobarbituric acid-reactive substances (TBARs) as an index of oxidative damage. Normal mice exhibited no significant difference in TBARs following iron challenge in the presence or absence of vitamin E, folic acid or both. Similarly, ApoE knockout mice exhibited no significant differences following dietary iron challenge in the presence or absence of vitamin E. However, ApoE knockout mice accumulated significantly increased TBARs following iron challenge when folic acid was withheld, and accumulated even more TBARs when both folic acid and vitamin E were withheld. These findings demonstrate that ApoE knockout mice during vitamin deficiency are less capable of buffering the consequences of dietary iron challenge than are normal mice. Since the apolipoprotein E4 allele, which exhibits diminished oxidative buffering capacity, is linked to Alzheimer's disease (AD), these data underscore the possibility that critical nutritional deficiencies may modulate the impact of genetic compromise on neurodegeneration in AD.

Efficacy of vitamin E, phosphatidyl choline, and pyruvate on buffering neuronal degeneration and oxidative stress in cultured cortical neurons and in central nervous tissue of apolipoprotein E-deficient mice

Oxidative stress is a pivotal factor in neuronal degeneration. However, vitamin E was only marginally effective in clinical trials. We examined whether or not a mixture of vitamin E (as alpha-tocopherol), sodium pyruvate and phosphatidyl choline (PC), a mixture that promotes wound healing in non-neuronal systems, would provide neuroprotection beyond that observed with vitamin E alone. Combined treatment with these agents improved survival and neuritic spouting of murine embryonic cortical neurons in culture, and provided neuroprotection against oxidative damage following treatment with hydrogen peroxide. Dietary treatment with these three agents also compensated for the diminished oxidative buffering capacity of brains of apolipoprotein E-deficient mice, while vitamin E alone failed to do so. These data underscore the possibility that critical nutritional deficiencies may modulate the impact of genetic compromise on neurodegeneration.