Genes and gene expression in the brain of the alcoholic

Sex differences in GABAA receptor subunit transcript expression are mediated by genotype in subjects with alcohol-related cirrhosis of the liver

Male and female human subjects show contrasting propensities to misuse drugs of addiction, including alcohol. These differences lead to different psychological and neurological consequences, such as the likelihood of developing dependence. The pattern and extent of brain damage in alcohol-use disorder cases also varies with comorbid disease. To explore mechanisms that might underlie these outcomes, we used autopsy tissue to determine mRNA transcript expression in relation to genotype for two GABAA receptor subunit genes. We used quantitative Real-Time PCR to measure GABRA6 and GABRA2 mRNA concentrations in dorsolateral prefrontal and primary motor cortices of alcohol-use disorder subjects and controls of both sexes with and without liver disease who had been genotyped for these GABAA receptor subunit genes. Cirrhotic alcohol-use disorder cases had significantly higher expression of GABRA6 and GABRA2 transcripts than either controls or non-cirrhotic alcohol-use disorder cases. Differences were observed between sexes, genotypes and brain regions. We show that sex differences in subjects with GABRA6 and GABRA2 variants may contribute to differences in susceptibility to alcohol-use disorder and alcohol-induced cirrhosis.

Correlation between the epigenetic modification of histone H3K9 acetylation of NR2B gene promoter in rat hippocampus and ethanol withdrawal syndrome

Patients with alcohol use disorder may develop acute ethanol withdrawal syndrome (EWS). Previous studies showed that an epigenetic modification of the N-methyl-D-aspartate (NMDA) receptor, especially NMDA receptor 2B subunit (NR2B), was involved in the pathological process of EWS. However, the relationship between the epigenetic regulation of the NR2B gene in the rat hippocampus region and EWS were inconsistent. The purpose of this study was to explore the role of the histone H3K9 acetylation of the NR2B gene in the rat hippocampus region in EWS. A rat model of chronic ethanol exposure was established. EWS score and the behavioral changes were recorded at different time points. The NR2B expression levels and the histone H3K9 acetylation level in the NR2B gene promoter region were measured using qRT-PCR, Western blot, immunofluorescence, and chromatin immunoprecipitation, respectively. Finally, the relationship between the epigenetic modification of histone H3K9 acetylation of NR2B gene promoter and EWS were examined. Our ultimate results showed that the EWS score was increased at 2 h, peaked at 6 h after withdrawal of ethanol, and reduced to the level parallel to the normal control group at day 3 after ethanol withdrawal. The NR2B mRNA expression and protein levels showed similar patterns. Further correlation analyses indicted that both histone H3K9 acetylation in NR2B gene promoter and the expression levels of NR2B were positively associated with EWS. Our results suggest that chronic ethanol exposure may result in epigenetic modification of histone H3K9 acetylation in NR2B gene promoter in rat hippocampus, and the expression levels of NR2B were found to be positively correlated with ethanol withdrawal syndrome.

GABA-A and NMDA receptor subunit mRNA expression is altered in the caudate but not the putamen of the postmortem brains of alcoholics

Chronic consumption of alcohol by humans has been shown to lead to impairment of executive and cognitive functions. Here, we have studied the mRNA expression of ion channel receptors for glutamate and GABA in the dorsal striatum of post-mortem brains from alcoholics (n = 29) and normal controls (n = 29), with the focus on the caudate nucleus that is associated with the frontal cortex executive functions and automatic thinking and on the putamen area that is linked to motor cortices and automatic movements. The results obtained by qPCR assay revealed significant changes in the expression of specific excitatory ionotropic glutamate and inhibitory GABA-A receptor subunit genes in the caudate but not the putamen. Thus, in the caudate we found reduced levels of mRNAs encoding the GluN2A glutamate receptor and the δ, ε, and ρ2 GABA-A receptor subunits, and increased levels of the mRNAs encoding GluD1, GluD2, and GABA-A γ1 subunits in the alcoholics as compared to controls. Interestingly in the controls, 11 glutamate and 5 GABA-A receptor genes were more prominently expressed in the caudate than the putamen (fold-increase varied from 1.24 to 2.91). Differences in gene expression patterns between the striatal regions may underlie differences in associated behavioral outputs. Our results suggest an altered balance between caudate-mediated voluntarily controlled and automatic behaviors in alcoholics, including diminished executive control on goal-directed alcohol-seeking behavior.

GABA Receptors Genes Polymorphisms and Alcohol Dependence: No Evidence of an Association in an Italian Male Population

Objective

The genes encoding for gamma-aminobutyric acid (GABA) A and B receptors may be considered as candidates for alcoholism; genetic alterations at this level may produce structural and functional diversity and thus play a role in the response to alcohol addiction treatment. To investigate these aspects further, we conducted a preliminary genetic association study on a population of Italian male alcohol addicts, focusing on GABA A and B receptors.

Methods

A total of 186 alcohol-dependent subjects (in the first phase 139, then 47 more samples) and 182 controls were genotyped for 25 single nucleotide polymorphisms (SNPs) of genes encoding the alpha-1 subunit of GABA A receptor (GABRA1) and subunits 1 and 2 of GABA B receptor (GABBR1 and GABBR2). The chi-squared test for allele and genotype distributions and Hardy-Weinberg equilibrium analysis of both subjects and controls were performed. Bonferroni's correction for multiple comparisons was applied.

Results

Preliminary results comparing 139 alcohol-dependent subjects and 182 controls showed differences in genotype distribution in the former for SNP rs29253, located in the intron region of the GABBR1 gene. In order to clarify the meaning of this association, 47 more samples from alcohol-dependent subjects were tested for this SNP only: the previously found association was not confirmed.

Conclusion

The lack of significant differences between the two groups does not provide evidence that GABRA 1 and GABBR1 and 2 genes are candidates for alcoholism in this population. Further studies with larger samples are needed, together with investigation of other components of the GABA pathway.

Reduced expression of α-synuclein in alcoholic brain: influence of SNCA-Rep1 genotype

α-Synuclein has recently been implicated in the pathophysiology of alcohol abuse due to its role in dopaminergic neurotransmission. In these studies, genetic variability in the α-synuclein gene influences its expression which may contribute to susceptibility to chronic alcohol abuse. Real-time PCR was used to quantify α-synuclein mRNA expression in autopsy samples of human dorsolateral prefrontal cortex. Because of the association between length of the α-synuclein-repeat 1 microsatellite marker and expression levels of the gene, this marker was genotyped in a Caucasian sample of 126 controls and 117 alcoholics using capillary gel electrophoresis. The allele and genotype frequencies of α-synuclein-repeat 1 marker differed significantly between alcoholics and controls. Alcoholics had greater frequencies of the shortest allele found (267 bp). The shortest allele of the α-synuclein-repeat 1 marker was associated with decreased expression of α-synuclein in prefrontal cortex. Individuals with at least one copy of the 267 bp allele were more likely to exhibit an alcohol abuse phenotype. These results suggest that individuals with the 267 bp allele may be at increased risk of developing alcoholism and that genetic variation at the α-synuclein-repeat 1 locus may influence α-synuclein expression in the prefrontal cortex.

Electrically evoked synaptosomal amino acid transmitter release in human brain in alcohol misuse

Severe chronic alcohol misuse leads to neuropathological changes in human brain, with the greatest neuronal loss in the dorsolateral prefrontal cortex. In this region, GABA(A) receptors are selectively upregulated, and show altered subunit expression profiles only in alcoholics without comorbid disease, whereas glutamate(NMDA) subunit expression profiles are selectively downregulated only in alcoholics with comorbid cirrhosis of the liver. To determine whether these outcomes might be conditional on synaptic transmitter levels, evoked release was studied in well-characterized synaptosome suspensions preloaded with L-[(3)H]glutamate and [(14)C]GABA and stimulated electrically (±10 V contiguous square waves, 0.4 ms, 100 Hz, 1.5 min) with and without Ca(2+). Stimulation elicited brief peaks of both radioisotopes that were larger in the presence of Ca(2+) ions (p < 0.01). A repeat stimulus evoked a second, smaller (p < 0.01) peak. Ca(2+)-dependent L-[(3)H]glutamate release, but not [(14)C]GABA release, was higher overall in alcoholics than in controls (p < 0.05). With comorbid cirrhosis, L-[(3)H]glutamate release showed a graded response, whereas [(14)C]GABA release was lowest in noncirrhotic alcoholics. Release patterns did not differ between cortical regions, or between males and females. Neither age nor postmortem interval was a significant confounder. The released transmitters may differentially alter receptor profiles on postsynaptic cells.

Neuroprotective strategies in drug abuse-evoked encephalopathy

Encephalopathy is evidenced as an altered mental state with various neurological symptoms, such as memory and cognitive problems. The type of a substance-evoked encephalopathy will depend on the drug, substance, or combination being abused. The categories into which we could place the various abused substances could be tentatively divided into stimulants, amphetamines, hallucinogens, narcotics, inhalants, anesthetics, anabolic steroids, and antipsychotics/antidepressants. Other factors that may underlie encephalopathy, such as infectious agents, environmental, and other factors have also to be taken into account. Drugs of abuse can be highly toxic to the CNS following acute, but more so in chronic exposure, and can produce significant damage to other organs, such as the heart, lungs, liver, and kidneys. The damage to these organs may be at least partially reversible when drug abuse is stopped but CNS damage from repeated or prolonged abuse is often irreversible. The major pathways for the organ and CNS toxicity could be related to ischemic events as well as increased cell damage due to metabolic or mitochondrial dysfunction resulting in increased excitotoxicity, reduced energy production, and lowered antioxidant potential. These susceptibilities could be strengthened by the use of antioxidants to combat free radicals (e.g., vitamin E, lipoic acid); trying to improve energy generation by using mitochondriotropic/metabolic compounds (e.g., thiamine, coenzyme Q10, carnitine, riboflavin); by reducing excitotoxicity (e.g., glutamate antagonists) and other possible strategies, such as robust gene response, need to be investigated further. The drug-abuse-evoked encephalopathy still needs to be studied further to enable better preventative and protective strategies.

Association of polymorphisms in RGS4 and expression of RGS transcripts in the brains of human alcoholics

Chronic alcoholism leads to neurotoxic effects in the central nervous system. Neuroadaptive changes in the brain may lead to tolerance to, and dependence on, alcohol as a result of alterations in synaptic complexity. G-proteins are negatively regulated by RGS proteins, which are integral to many neural pathways that include neurotransmission, hormonal responses, and chemotactic signals. These considerations, together with findings from microarray analyses of human autopsy brain, suggest that proteins involved in G-protein signalling, specifically the RGS protein family, may play an important role in the functioning of neural systems that are affected by chronic alcohol abuse. We used Real Time PCR to measure the expression of two members of the RGS family, RGS4 and RGS7, in the superior frontal gyrus and primary motor cortex from alcoholic and non-alcoholic cases. Overall, cirrhotic alcoholics had lower expression levels of RGS4 mRNA than controls and non-cirrhotic alcoholics. We also report that the four RGS4 SNPs (SNP1, 4, 7 and 18) may be associated with alcoholism in European Caucasians at the haplotype level. The haplotype T-C-G (SNP1-4-18) may exert a protective effect against alcoholism.

Neurocognitive correlates of white matter quality in adolescent substance users

BACKGROUND

Progressive myelination during adolescence implicates an increased vulnerability to neurotoxic substances and enduring neurocognitive consequences. This study examined the cognitive manifestations of altered white matter microstructure in chronic marijuana and alcohol-using (MJ+ALC) adolescents.

METHODS

Thirty-six MJ+ALC adolescents (ages 16-19) and 36 demographically similar controls were evaluated with diffusion tensor imaging (Bava et al., 2009) and neurocognitive tests. Regions of group difference in fractional anisotropy (FA) and mean diffusivity (MD) were analyzed in relation to cognitive performance.

RESULTS

In users, lower FA in temporal areas related to poorer performance on attention, working memory, and speeded processing tasks. Among regions where users had higher FA than controls, occipital FA was positively associated with working memory and complex visuomotor sequencing, whereas FA in anterior regions was negatively associated with verbal memory performance.

CONCLUSIONS

Findings suggest differential influences of white matter development on cognition in MJ+ALC using adolescents than in non-using peers. Neuroadaptation may reflect additive and subtractive responses to substance use that are complicated by competing maturational processes.

The role of GABA(A) receptors in the acute and chronic effects of ethanol: a decade of progress

The past decade has brought many advances in our understanding of GABA(A) receptor-mediated ethanol action in the central nervous system. We now know that specific GABA(A) receptor subtypes are sensitive to ethanol at doses attained during social drinking while other subtypes respond to ethanol at doses attained by severe intoxication. Furthermore, ethanol increases GABAergic neurotransmission through indirect effects, including the elevation of endogenous GABAergic neuroactive steroids, presynaptic release of GABA, and dephosphorylation of GABA(A) receptors promoting increases in GABA sensitivity. Ethanol's effects on intracellular signaling also influence GABAergic transmission in multiple ways that vary across brain regions and cell types. The effects of chronic ethanol administration are influenced by adaptations in GABA(A) receptor function, expression, trafficking, and subcellular localization that contribute to ethanol tolerance, dependence, and withdrawal hyperexcitability. Adolescents exhibit altered sensitivity to ethanol actions, the tendency for higher drinking and longer lasting GABAergic adaptations to chronic ethanol administration. The elucidation of the mechanisms that underlie adaptations to ethanol exposure are leading to a better understanding of the regulation of inhibitory transmission and new targets for therapies to support recovery from ethanol withdrawal and alcoholism.

A short review on the aetiology and pathophysiology of alcoholism

Alcoholism is a chronic remitting and relapsing condition; its aetiology and pathophysiology remains largely obscure despite recent advances. This review summarises the current knowledge about the causation (biological or psychological) of alcohol addiction. This involves heredity, candidate genes, alcohol metabolism regulation and the influence of alcohol in the pathophysiology of the different neurotransmitter systems. Alcohol addiction is a multifactorial phenomenon where personality structure, individual state of mind and social influences are in constant interaction with brain neurobiology and pathophysiology. This disorder influences different sexes in different ways and causes major problems, especially in developed societies.

Ethnic related selection for an ADH Class I variant within East Asia

Background

The alcohol dehydrogenases (ADH) are widely studied enzymes and the evolution of the mammalian gene cluster encoding these enzymes is also well studied. Previous studies have shown that the ADH1B*47His allele at one of the seven genes in humans is associated with a decrease in the risk of alcoholism and the core molecular region with this allele has been selected for in some East Asian populations. As the frequency of ADH1B*47His is highest in East Asia, and very low in most of the rest of the world, we have undertaken more detailed investigation in this geographic region.

Methodology/Principal Findings

Here we report new data on 30 SNPs in the ADH7 and Class I ADH region in samples of 24 populations from China and Laos. These populations cover a wide geographic region and diverse ethnicities. Combined with our previously published East Asian data for these SNPs in 8 populations, we have typed populations from all of the 6 major linguistic phyla (Altaic including Korean-Japanese and inland Altaic, Sino-Tibetan, Hmong-Mien, Austro-Asiatic, Daic, and Austronesian). The ADH1B genotyping data are strongly related to ethnicity. Only some eastern ethnic phyla or subphyla (Korean-Japanese, Han Chinese, Hmong-Mien, Daic, and Austronesian) have a high frequency of ADH1B*47His. ADH1B haplotype data clustered the populations into linguistic subphyla, and divided the subphyla into eastern and western parts. In the Hmong-Mien and Altaic populations, the extended haplotype homozygosity (EHH) and relative EHH (REHH) tests for the ADH1B core were consistent with selection for the haplotype with derived SNP alleles. In the other ethnic phyla, the core showed only a weak signal of selection at best.

Conclusions/Significance

The selection distribution is more significantly correlated with the frequency of the derived ADH1B regulatory region polymorphism than the derived amino-acid altering allele ADH1B*47His. Thus, the real focus of selection may be the regulatory region. The obvious ethnicity-related distributions of ADH1B diversities suggest the existence of some culture-related selective forces that have acted on the ADH1B region.

Links between nutrition, drug abuse, and the metabolic syndrome

Nutritional deficiency in combination with drug abuse may increase risk of developing the metabolic syndrome by augmenting cell damage, excitotoxicity, reducing energy production, and lowering the antioxidant potential of the cells. We have reviewed here the following points: effects of drugs of abuse on nutrition and brain metabolism; effects of nutrition on actions of the drugs of abuse; drug abuse and probability of developing metabolic syndrome; role of genetic vulnerability in nutrition/drug abuse and brain damage; and the role of neuroprotective supplements in drug abuse. Nutrition education is an essential component of substance abuse treatment programs and can enhance substance abuse treatment outcomes. The strategies available, in particular the nutritional approach to protect the drug abusers from the metabolic syndrome and other diseases are discussed.