Apolipoprotein E epsilon 4 is associated with hippocampal volume reduction in females with alcoholism

Brain DNA damage and behavioral changes after repeated intermittent acute ethanol withdrawal by young rats

RATIONALE

Alcohol addiction causes severe problems, and its deprivation may potentiate symptoms such as anxiety. Furthermore, ethanol is a neurotoxic agent that induces degeneration and the consequences underlying alcohol-mediated brain damage remain unclear.

OBJECTIVES

This study assessed the behavioral changes during acute ethanol withdrawal periods and determined the levels of DNA damage and reactive oxygen species (ROS) in multiple brain areas.

METHODS

Male Wistar rats were subjected to an oral ethanol self-administration procedure with a forced diet where they were offered 8% (v/v) ethanol solution for 21 days followed by five repeated 24-h cycles alternating between ethanol withdrawal and re-exposure. Control animals received an isocaloric control diet without ethanol. Behavioral changes were analyzed on ethanol withdrawal days in the open-field (OF) and elevated plus-maze (EPM) tests within the first 6 h of ethanol deprivation. The pre-frontal cortex, hypothalamus, striatum, hippocampus, and cerebellum were dissected for alkaline and neutral comet assays and for dichlorofluorescein ROS testing.

RESULTS

The repeated intermittent ethanol access enhanced solution intake and alcohol-seeking behavior. Decreased exploratory activity was observed in the OF test, and the animals stretched less in the EPM test. DNA single-strand breaks and ROS production were significantly higher in all structures evaluated in the ethanol-treated rats compared with controls.

CONCLUSIONS

The animal model of repeated intermittent ethanol access induced behavioral changes in rats, and this ethanol exposure model induced an increase in DNA single-strand breaks and ROS production in all brain areas. Our results suggest that these brain damages may influence future behaviors.

Neuropathology of alcoholism

Chronic alcohol consumption results in structural changes to the brain. In alcoholics without coexisting thiamine deficiency or liver disease this is largely restricted to a loss of white-matter volume. When it occurs, neuronal loss is limited in anatomic distribution and only detected with quantitative techniques. This relative paucity of neurodegeneration is reflected in studies of gene and protein expression in postmortem brain where findings are subtle and discordant between studies. In alcoholics with coexisting pathologies, neuronal loss is more marked and affects a wider range of anatomic regions, especially subcortical nuclei. Although this more widespread damage may reflect a more severe drinking history, there is evidence linking thiamine deficiency and the consequences of liver disease to the pathogenesis of alcohol-related brain damage. Furthermore, a range of other factors, such as cigarette smoking and mood disorders, that are common in alcoholics, have the potential to influence studies of brain pathology and should be considered in further studies of the neuropathology of alcoholism.

Apolipoprotein E epsilon 4 allele is associated with ventricular expansion rate and surface morphology in dementia and normal aging

The apolipoprotein E epsilon 4 allele (ApoE-ε4) is the strongest known genetic risk factor for late onset Alzheimer's disease. Expansion of the lateral ventricles occurs with normal aging, but dementia accelerates this process. Brain structure and function depend on ApoE genotype not just for Alzheimer's disease patients but also in healthy elderly individuals, and even in asymptomatic young individuals. Therefore, we hypothesized that the ApoE-ε4 allele is associated with altered patterns of longitudinal ventricular expansion, in dementia and normal aging. We tested this hypothesis in a large sample of elderly participants, using a linear discriminant analysis-based approach. Carrying more ApoE-ε4 alleles was associated with faster ventricular expansion bilaterally and with regional patterns of lateral ventricle morphology at 1- and 2-year follow up, after controlling for sex, age, and dementia status. ApoE genotyping is considered critical in clinical trials of Alzheimer's disease. These findings, combined with earlier investigations showing that ApoE is also directly implicated in other conditions, suggest that the selective enrollment of ApoE-ε4 carriers may empower clinical trials of other neurological disorders.

DNA damage and neurotoxicity of chronic alcohol abuse

Chronic alcohol abuse results in a variety of pathological effects including damage to the brain. The causes of alcohol-induced brain pathology are presently unclear. Several mechanisms of pathogenicity of chronic alcoholism have been proposed, including accumulation of DNA damage in the absence of repair, resulting in genomic instability and death of neurons. Genomic instability is a unified genetic mechanism leading to a variety of neurodegenerative disorders. Ethanol also likely interacts with various metabolic pathways, including one-carbon metabolism (OCM). OCM is critical for the synthesis of DNA precursors, essential for DNA repair, and as a methyl donor for various methylation events, including DNA methylation. Both DNA repair and DNA methylation are critical for maintaining genomic stability. In this review, we outline the role of DNA damage and DNA repair dysfunction in chronic alcohol-induced neurodegeneration.

Effects of chronic alcohol consumption on expression levels of APP and Aβ-producing enzymes

Chronic alcohol consumption contributes to numerous diseases, including cancers, cardiovascular diseases, and liver cirrhosis. Epidemiological studies have shown that excessive alcohol consumption is a risk factor for dementia. Along this line, Alzheimer's disease (AD) is the most common form of dementia and is caused by the accumulation of amyloid-β (Aβ plaques in neurons. In this study, we hypothesized that chronic ethanol consumption is associated with pathological processing of APP in AD. To investigate the relationship between chronic alcohol consumption and Aβ production, brain samples from rats fed an alcohol liquid diet for 5 weeks were analyzed. We show that the expression levels of APP, BACE1, and immature nicastrin were increased in the cerebellum, hippocampus, and striatum of the alcohol-fed group compared to the control group. Total nicastrin and PS1 levels were induced in the hippocampus of alcohol-fed rats. These data suggest that the altered expression of APP and Aβ-producing enzymes possibly contributes to the chronic alcohol consumption-mediated pathogenesis of AD.

Long-term effects of methamphetamine exposure on cognitive function and muscarinic acetylcholine receptor levels in mice

Exposure to methamphetamine during brain development impairs cognition in humans and rodents. In mice, these impairments are more severe in females than males. Genetic factors, such as apolipoprotein E genotype, may modulate the cognitive effects of methamphetamine. Methamphetamine-induced alterations in the brain acetylcholine system may contribute to the cognitive effects of methamphetamine and may also be modulated by apolipoprotein E isoform. We assessed the long-term effects of methamphetamine exposure during brain development on cognitive function and muscarinic acetylcholine receptors in mice, and whether apolipoprotein E isoform modulates these effects. Mice expressing human apolipoprotein E3 or E4 were exposed to methamphetamine (5 mg/kg) or saline once a day from postnatal days 11-20 and behaviorally tested in adulthood. Muscarinic acetylcholine receptor binding was measured in the hippocampus and cortex. Methamphetamine exposure impaired novel location recognition in female, but not male, mice. Methamphetamine-exposed male and female mice showed impaired novel object recognition and increased number of muscarinic acetylcholine receptors in the hippocampus. The cognitive and cholinergic effects of methamphetamine were similar in apolipoprotein E3 and E4 mice. Thus, the cholinergic system, but not apolipoprotein E isoform, might play an important role in the long-term methamphetamine-induced cognitive deficits in adulthood.

Proton magnetic resonance spectroscopy in alcohol use disorders: a potential new endophenotype?

BACKGROUND

Current effort is directed at defining new classification schemes for alcohol use disorders (AUD) based on genetic/biological, physiological, and behavioral endophenotypes.

METHODS

We describe briefly findings of in vivo brain proton magnetic resonance spectroscopy ((1)H MRS) studies in AUD and propose that they be further explored and expanded regarding their value as a potential endophenotype for AUD.

RESULTS

In vivo (1)H MRS, as part of the emerging field of "imaging genomics," may provide readily accessible, objective, functionally significant and region-specific neurobiological measures that successfully link genotypes to neurocognition and to psychiatric symptomatology in relatively small patient cohorts. We discuss several functional gene variants that may affect specific (1)H MRS-detectable metabolites and provide recent data from our own work that supports the view of genetic effects on metabolite measures.

CONCLUSIONS

MRS-genetics research will not only offer clues to the functional significance and downstream effects of genetic differences in AUD, but, via monitoring and/or predicting the efficacy of pharmacological and behavioral interventions as a function of genotype, has the potential to influence future clinical management of AUD.

Apolipoprotein E gene polymorphism and previous alcohol withdrawal seizures

Aim of this study was to investigate the possible association of apolipoprotein E (ApoE) gene polymorphism with a history of alcohol withdrawal seizures. We included 194 patients with alcohol dependence who were divided into patients with (SZ+) and without (SZ-) previous alcohol withdrawal seizures. ApoE genotypes were determined using PCR. For statistical analysis we examined the number of ApoE alleles (ApoE2: n=36; ApoE3: n=311; ApoE4: n=41). A significant positive association with a positive history of withdrawal seizures (SZ+) was found in the ApoE3 allele group (Fisher's exact test: p=0.006) while a significant negative association was observed in the ApoE2 allele group (Fisher's exact test: p=0.029). For the ApoE4 allele group no significant differences were found regarding a history of withdrawal seizures. Our findings suggest an association between the apolipoprotein E3 gene variant and an elevated risk of alcohol withdrawal seizures. These preliminary results must be validated in further studies.

Apolipoprotein E polymorphism, homocysteine serum levels and hippocampal volume in patients with alcoholism: an investigation of a gene-environment interaction

There is growing evidence that disadvantageous influences of the apolipoprotein E4 allele in the central nervous system are modified by environmental and dietary conditions. The present study investigated the gene-environment interaction of apolipoprotein E4 with homocysteine serum levels in patients with alcohol dependence with regard to alcohol-related hippocampal volume loss using volumetric high-resolution magnetic resonance imaging. We included 52 patients with alcohol-dependence. ApoE genotypes, homocysteine serum levels and hippocampal volumes were determined. We found a significant impact of homocysteine (F=13.2; df=1; P<0.001; 1-beta=0.95), not for ApoE4 genotype (F=0.482; df=1; P=0.49; 1-beta=0.05) on hippocampal volume. There was a significant interaction between both factors (ApoE4 x Hcy; F=8.8; df=1; P=0.005; 1-beta=0.80). The ApoE4 allele constitutes a risk factor for hippocampal volume loss in patients with alcohol dependence under the conditions of hyperhomocysteinemia. We suggest that the disadvantageous effects of apolipoprotein E4 on alcohol-related brain volume loss are based on certain gene-environment interactions.

Obsessive-compulsive alcohol craving is not associated with Apolipoprotein E genotype

This study examined a possible association with obsessive and compulsive alcohol craving in 192 alcohol-dependent patients undergoing detoxification treatment. Statistical analysis revealed no significant association between Apolipoprotein E polymorphism and obsessive-compulsive alcohol craving (analysis of variance: F=1.11, P=0.358).

Premorbid effects of APOE on synaptic proteins in human temporal neocortex

APOE affects the risk of Alzheimer's disease (AD) and course of several other neurologic diseases. Experimental studies suggest that APOE influences synaptogenesis. We measured the concentration of two presynaptic proteins, synaptophysin and syntaxin 1, and also postsynaptic density-95 (PSD95), in superior temporal cortex from 42 AD and 160 normal brains, and determined the APOE genotypes. The concentration of both presynaptic proteins was approximately two-thirds lower in AD than normal brains and that of PSD95 one-third lower. No effect of APOE on synaptic proteins was found in advanced AD. However, in normal brain, epsilon4 was associated with lower concentrations of all three synaptic proteins and epsilon2 with significantly elevated PSD95 (p=0.03). A combined measure of synaptic proteins showed a significant linear decrease from epsilon2 through epsilon3 to varepsilon4 (p=0.01). APOE influences the concentration of synaptic proteins in normal superior temporal cortex and may thereby affect the response to injury, and the risk and outcome of a range of neurologic diseases.

Apolipoprotein E4 genotype is not associated with short-term cognition deficits during alcohol withdrawal

Aim of this prospective study was to investigate a possible association between the apolipoprotein E4 (ApoE4) genotype and clinically well-known cognition deficits during alcohol withdrawal. We examined 172 patients with alcohol dependence (137 men, 35 women) during withdrawal treatment. The ApoE genotype was determined in all patients using polymerase chain reaction. Cognitive function was assessed applying the c.I.-Test on day 0 (admission) and on day 7 of withdrawal treatment. Using Pearson's chi2 test we found no significant association between the ApoE4 genotype and cognition deficits for both dates (day 0: p=.463; day 7: p=.760). Moreover, multivariate logistic regression analyses revealed no significant association between presence of the ApoE4 allele and cognitive dysfunction. Even though ApoE4 plays an important role in alcoholism-related brain atrophy and cognition deficits in demented as well as in nondemented healthy elderly people, this study provides no evidence for an association with short-term cognition deficits during alcohol withdrawal.