Alcohol and gene interactions

Subjective response to alcohol and ADH polymorphisms in a select sample of young adult male East Indians and Africans in Trinidad and Tobago

OBJECTIVE

Level of response to alcohol has been associated with risk of alcohol dependence in a number of ethnic groups. In the present study, subjective and objective responses to alcohol were evaluated in Indo-Trinidadians (Indo-T) and Afro-Trinidadians (Afro-T). Associations of alcohol dehydrogenase polymorphisms with response to alcohol, using the Subjective High Assessment Scale (SHAS), and breath alcohol concentrations (BrAC) were tested.

METHOD

Regular male drinkers without alcohol dependence (n = 112) ages 18-25 years participated in alcohol challenge sessions consisting of placebo and two doses of alcohol (target BrAC: 0 g/dl for placebo, .04 g/dl low dose, and .08 g/dl high dose) and genotyped for variants in ADH1B*3 and ADH1C*2.

RESULTS

Indo-T had significantly higher BrAC, pulse rates, and cortisol levels when compared with Afro-T but did not have significantly higher SHAS values. Higher responses on the SHAS items muddle/confused and nauseated were significantly associated with the presence of at least one ADH1B*3 allele following the high dose of alcohol in Afro-T. Indo-T with at least one ADH1C*2 allele displayed significantly different Drug × Time interactions for the SHAS item effects of alcohol at the low dose and for the SHAS items clumsy, muddle/confused, effects of alcohol, floating, drunk, and total at the high dose from Indo-T with two ADH1C*1 alleles.

CONCLUSIONS

This is the first study that has investigated individual sensitivity to alcohol in a Caribbean population and in people of East Indian descent. Indo-T with at least one ADH1C*2 allele may be at higher risk for heavy drinking by feeling less of the effects of alcohol, including nausea. In Afro-T, having at least one ADH1B*3 allele appears to exert a protective effect by enhancing the unpleasant effects of alcohol, such as nausea and confusion.

Alcohol intake

Alcohol consumption and its association with health or illness states are of great interest from the nutritional genomics point of view. This interest is centered not only on investigating the genetic variants that can modulate the effects of alcoholic beverages on different intermediate and final disease phenotypes (mainly cardiovascular diseases and cancer), but also on finding out how the genome influences the amount of alcohol consumed and consumption habits. This chapter reviews the latest findings on alcohol consumption trends, the methodological limitations in the analysis of alcohol consumption, and the main genes and polymorphisms related to alcohol intake, including the inconsistent results from genome-wide association studies (GWASs). It also reviews the effects of alcohol consumption on cardiovascular diseases and cancer and the studies analyzing the interactions between different genetic polymorphisms and alcohol in phenotypes related to these diseases, discussing the studies' advantages and limitations as well as future research perspectives.

Alcohol dehydrogenase 1B genotype and fetal alcohol syndrome: a HuGE minireview

Fetal alcohol syndrome (FAS), 1 of the most common developmental disabilities in the United States, occurs at a rate of 0.5-2.0:1000 live births. Animal model, family, and twin studies suggest a genetic component to FAS susceptibility. Alcohol dehydrogenases (ADHs) catalyze the rate-limiting step in alcohol metabolism. Studies of genetic associations with FAS have focused on the alcohol dehydrogenase 1B (ADH1B) gene, comparing mothers and children with the alleles ADH1B*2 or ADH1B*3, associated with faster ethanol metabolism, with those homozygous for ADH1B*1. While most studies have found a protective effect for genotypes containing ADH1B*2 or ADH1B*3, results have been conflicting, and further investigation into the association between the ADH1B genotype and FAS is needed. Whether increased alcohol intake accounts for the elevated risk reported for the ADH1B*1/ADH1B*1 genotype should be addressed, and future studies would benefit from consistent case definitions, enhanced exposure measurements, larger sample sizes, and careful study design.

Gene-alcohol interactions in the metabolic syndrome

AIMS

Recent studies have reported that moderate alcohol consumption is associated with a lesser prevalence of the metabolic syndrome (MetS). However, this relationship is still confusing and the presence of gene-environment interactions has been suggested. Our aim is to summarize evidence for gene-alcohol interactions in the MetS.

DATA SYNTHESIS

Research in gene-alcohol interactions applied to MetS is very complex due to the difficulties surrounding the definition of phenotype, environment and genotype, as well as in estimating the influence of the social context. In the MetS there is a constellation of metabolic disturbances the definition of which is still changing. Thus, most studies that have reported on gene-alcohol interactions have done so by analyzing isolated components. Likewise, the definition of alcohol consumption is also complex given that apart from the amount of ethanol consumed, the type of drink, the frequency of consumption, etc., may be important. No less difficult is the definition of genotype as there are many candidate genes involved, including not only those relevant for each phenotype studied, but also those related with alcohol metabolism, as well as those related to alcohol intake.

CONCLUSIONS

Although various studies exist that show statistically significant interactions between alcohol consumption and MetS components, a greater integration of variables as well as greater homogeneity in definitions is required.

ADH1C*2 allele is associated with alcohol dependence and elevated liver enzymes in Trinidad and Tobago

Variants in alcohol dehydrogenase (ADH) genes differ between ethnic groups and have, in some studies, been found to be associated with alcohol dependence and alcoholic liver disease. This study sought to determine whether an association exists between ADH (ADH1C previously ADH3, ADH1B*2 previously ADH2*2) genotypes, alcohol dependence, drinking history, and liver function tests in the two major ethnic groups of Trinidad and Tobago (TT). One hundred and forty-five alcohol-dependent individuals of both East Indian (Indo-TT) and African (Afro-TT) ancestry, and 108 controls matched by age, sex, and education participated in the study. Serum levels of alanine and aspartate aminotransferase (ALT, AST), alkaline phosphatase (ALP), lactate dehydrogenase (LDH), and gamma-glutamyltransferase (GGT) as well as presence of HIV, hepatitis B surface antigen, and anti-hepatitis C virus antibody were determined. There was a significant difference in the distribution of ADH1C allele polymorphisms between the ethnic groups (P<.0001). Forty-three percent of the Indo-TT were found to have one ADH1C*2 allele and 5% were homozygous, whereas, only 23% of Afro-TT had one allele and one was homozygous. Only three individuals had an ADH1B*2 allele (one Indo-TT alcohol dependent, two Indo-TT controls). The ADH1C*2 allele was significantly associated with alcohol dependence overall and within Indo-TT ancestry, however, it was not associated with current or heaviest alcohol consumption levels. Individuals with at least one ADH1C*2 allele also had significantly elevated levels of ALP (P<.02) and GGT (P<.02) as compared to individuals homozygous for ADH1C*. Additionally, GGT levels were also found to be elevated (P<.02) within Indo-TT alcohol dependents with at least one ADH1C*2 allele but not within the Afro-TT alcohol dependents with that allele. A linear regression that included alcohol dependence and levels of alcohol consumption confirmed that levels of serum GGT were significantly associated with the ADH1C*2 genotype. These results suggest that ADH1C polymorphisms are associated with alcohol dependence and alcohol associated elevations of liver enzymes in a population with a low frequency of ADH1B2 alleles.

Ethanol-responsive genes: identification of transcription factors and their role in metabolomics

Transcription factors (TFs) and their combinatorial control on cis-regulatory elements play critical role in the co-expression of genes. This affects the interaction of genes in the transcriptome and thus may affect signals that cascade through cellular pathways. Using a combination of bioinformatic approaches, we sought to identify such common combinations of TFs in a set of ethanol-responsive (ER) genes and assess the role of ethanol in affecting multiple pathways through their co-regulation. Our results show that the metallothionein genes are regulated by TF motifs cAMP responsive element binding protein (CREB) and metal-activated transcription factor 1 and primarily involved in zinc ion homeostasis. We have also identified new target genes, Synaptojanin 1 and tryptophan hydroxylase 1, potentially regulated by this module. Altered arrangement of TF-binding sites in the module may direct the action of these and other target genes in intracellular signaling cascades, cell growth and/or maintenance. In addition to CREB, other key TFs identified are ecotropic viral integration site-1 and SP1. These modulate the contribution of the target ER genes in cell cycle regulation and apoptosis or programmed cell death. Multiple lines of evidence confirm the above findings and indicate that different groups of ER genes are involved in different biological processes and their co-regulation most likely results from different sets of regulatory modules. These findings associate the role of the ER genes studied and their potential TF modules with alcohol response pathways and phenotypes.

Alcohol and the liver

PURPOSE OF REVIEW

To apprise the reader of advances in 2005 in the epidemiology, pathogenesis, prognosis and treatment of alcoholic liver disease. Alcohol use has declined in developed countries, but the opposite is true elsewhere; alcoholic liver disease is a considerable burden worldwide.

RECENT FINDINGS

Genetic mechanisms for alcoholic liver disease are being discovered in addition to aggravating cofactors, such as hepatitis C, obesity and iron overload, and ameliorating ones, like coffee and tea drinking. The involvement of the innate immune system and the mechanisms of apoptosis in alcoholic liver disease are better appreciated, especially the emerging role of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Steroid use and nutrition for alcoholic hepatitis are being refined, and the validity of the model for end-stage liver disease (MELD) score in predicting the outcome of alcoholic liver disease is upheld. Recidivism after liver transplantation for alcoholic liver disease adversely impacts long-term survival.

SUMMARY

Inroads are being made into the genetics of alcoholic liver disease and new phenomena are being uncovered in its pathogenesis, but safe and effective therapies for both alcoholic hepatitis and alcoholic cirrhosis are still wanting.