Influence of Genetic Variations of Ethanol-Metabolizing Enzymes on Phenotypes of Alcohol-Related Disorders

Mitochondria and Alcohol-Associated Liver Disease: Pathogenic Role and Target for Therapy

Alcohol-associated liver disease (ALD) is one of the leading causes of chronic liver disease and a major cause of liver-related death. ALD is a multifactorial disease triggered by the oxidative metabolism of alcohol which leads to the activation of multiple factors that promote the progression from steatosis to more advanced stages like alcohol-associated steatohepatitis (AH) that culminate in alcohol-associated cirrhosis and hepatocellular carcinoma. Poor understanding of the complex heterogeneous pathology of ALD has limited drug development for this disease. Alterations in mitochondrial performance are considered a crucial event in paving the progression of ALD due to the crucial role of mitochondria in energy production, intermediate metabolism, calcium homeostasis, and cell fate decisions. Therefore, understanding the role of mitochondria in eliciting steatosis and progression toward AH may open the door to new opportunities for treatment. In this review, we will cover the physiological function of mitochondria, its contribution to ALD in experimental models and human disease, and explore whether targeting mitochondria may represent a game changer in the treatment of ALD.

Understanding the exceptional pre-vaccination Era East Asian COVID-19 outcomes

During the first year of the pandemic, East Asian countries have reported fewer infections, hospitalizations, and deaths from COVID-19 disease than most countries in Europe and the Americas. Our goal in this paper is to generate and evaluate hypothesis that may explain this striking fact. We consider five possible explanations: (1) population age structure (younger people tend to have less severe COVID-19 disease upon infection than older people); (2) the early adoption of lockdown strategies to control disease spread; (3) genetic differences between East Asian population and European and American populations that confer protection against COVID-19 disease; (4) seasonal and climactic contributors to COVID-19 spread; and (5) immunological differences between East Asian countries and the rest of the world. The evidence suggests that the first four hypotheses are unlikely to be important in explaining East Asian COVID-19 exceptionalism. Lockdowns, in particular, fail as an explanation because East Asian countries experienced similarly good infection outcomes despite vast differences in lockdown policies adopted by different countries to control the COVID-19 epidemic. The evidence to date is consistent with our fifth hypothesis - pre-existing immunity unique to East Asia - but there are still essential parts of this story left for scientists to check.

Alcohol-Induced Oxidative Stress and the Role of Antioxidants in Alcohol Use Disorder: A Systematic Review

Alcohol use disorder (AUD) is a highly prevalent, comorbid, and disabling disorder. The underlying mechanism of ethanol neurotoxicity and the involvement of oxidative stress is still not fully elucidated. However, ethanol metabolism has been associated with increased oxidative stress through alcohol dehydrogenase, the microsomal ethanol oxidation system, and catalase metabolic pathways. We searched the PubMed and genome-wide association studies (GWAS) catalog databases to review the literature systematically and summarized the findings focusing on AUD and alcohol abstinence in relation to oxidative stress. In addition, we reviewed the ClinicalTrials.gov resource of the US National Library of Medicine to identify all ongoing and completed clinical trials that include therapeutic interventions based on antioxidants. The retrieved clinical and preclinical studies show that oxidative stress impacts AUD through genetics, alcohol metabolism, inflammation, and neurodegeneration.

Alcohol Addiction: One Entity or Different Entities? A DSM-4-Based Attempt Toward a Geographicization of Alcohol Addiction and Abuse

AIM

To examine whether in Europe perceptions of 'alcoholism' differ in a discrete manner according to geographical area.

METHOD

Secondary analysis of a data set from a European project carried out in 2013-2014 among 1767 patients treated in alcohol addiction units of nine countries/regions across Europe. The experience of all 11 DSM-4 criteria used for diagnosing 'alcohol dependence' and 'alcohol abuse' were assessed in patient interviews. The analysis was performed through Multiple Correspondence Analysis.

RESULTS

The symptoms of 'alcohol dependence' and 'alcohol abuse', posited by DSM-IV, were distributed according to three discrete geographical patterns: a macro-area mainly centered on drinking beer and spirit, a culture traditionally oriented toward wine and a mixed intermediate alcoholic beverage situation.

CONCLUSION

These patterns of perception seem to parallel the diverse drinking cultures of Europe.

Genome-wide associations between alcohol consumption and blood DNA methylation: evidence from twin study

Aim: Alcohol intake alters DNA methylation profiles and methylation might mediate the association between alcohol and disease, but limited number of positive CpG sites repeatedly replicated. Materials & methods: In total, 57 monozygotic (MZ) twin pairs discordant for alcohol drinking from the Chinese National Twin Registry and 158 MZ and dizygotic twin pairs in the Swedish Adoption/Twin Study of Aging were evaluated. DNA methylation was detected using the Infinium HumanMethylation450 BeadChip. Results: Among candidate CpG sites, cg07326074 was significantly correlated with drinking after adjusting for covariates in MZ twins in both datasets but not in the entire sample or dizygotic twins. Conclusion: The hypermethylation of cg07326074, located in the tumor-promoting gene C16orf59, was associated with alcohol consumption.

Alcohol consumption and breast cancer risk in Japan: A pooled analysis of eight population-based cohort studies

Although alcohol consumption is reported to increase the incidence of breast cancer in European studies, evidence for an association between alcohol and breast cancer in Asian populations is insufficient. We conducted a pooled analysis of eight large-scale population-based prospective cohort studies in Japan to evaluate the association between alcohol (both frequency and amount) and breast cancer risk with categorization by menopausal status at baseline and at diagnosis. Estimated hazard ratios (HR) and 95% confidence intervals were calculated in the individual cohorts and combined using random-effects models. Among 158 164 subjects with 2 369 252 person-years of follow-up, 2208 breast cancer cases were newly diagnosed. Alcohol consumption had a significant association with a higher risk of breast cancer in both women who were premenopausal at baseline (regular drinker compared to nondrinker: HR 1.37, 1.04-1.81, ≥23 g/d compared to 0 g/d: HR 1.74, 1.25-2.43, P for trend per frequency category: P = .017) and those who were premenopausal at diagnosis (≥23 g/d compared to 0 g/d: HR 1.89, 1.04-3.43, P for trend per frequency category: P = .032). In contrast, no significant association was seen in women who were postmenopausal at baseline or at diagnosis, despite a substantial number of subjects and long follow-up period. Our results revealed that frequent and high alcohol consumption are both risk factors for Asian premenopausal breast cancer, similarly to previous studies in Western countries. The lack of a clear association in postmenopausal women in our study warrants larger investigation in Asia.

The association between alcohol metabolism and genetic variants of ADH1A, SRPRB, and PGM1 in Korea

BACKGROUND

Excessive alcohol consumption is a major public health problem in East Asian countries. Alcohol use leads to a cascade of problems including increased chances of risky behavior and a wide range of negative health consequences, from alcoholic liver disease to upper gastric and liver cancer. These alcohol effects are known to be influenced by ethnic variability and genetics.

METHODS

In this study, subjects were administered a single dose of alcohol (0.6 g/kg for men or 0.4 g/kg for women), and blood alcohol and acetaldehyde concentrations were measured eight times over 5 hours. To investigate genetically susceptible factors to alcohol metabolism, we selected single-nucleotide polymorphisms (SNP) of genes identified by prior genetic association studies for alcohol metabolism, alcohol consumption, alcohol dependence, and related traits, and performed genotyping on all subjects (n = 104).

RESULTS

We identified variations in the ADH1A, SRPRB, and PGM1 genes, which are directly associated with blood alcohol or acetaldehyde concentrations. Namely, the T allele of SRPRB rs17376019 and the C allele of PGM1 rs4643 were associated with lower blood alcohol levels, while the ADH1 rs1229976 C allele group exhibited markedly higher blood acetaldehyde levels than those of the ADH1 rs1229976 T allele group.

CONCLUSION

This study demonstrates that genetic variations in ADH1A, SRPRB, and PGM1 are associated with variations in blood alcohol and acetaldehyde concentration after alcohol intake.

Acetaldehyde inhibits retinoic acid biosynthesis to mediate alcohol teratogenicity

Alcohol consumption during pregnancy induces Fetal Alcohol Spectrum Disorder (FASD), which has been proposed to arise from competitive inhibition of retinoic acid (RA) biosynthesis. We provide biochemical and developmental evidence identifying acetaldehyde as responsible for this inhibition. In the embryo, RA production by RALDH2 (ALDH1A2), the main retinaldehyde dehydrogenase expressed at that stage, is inhibited by ethanol exposure. Pharmacological inhibition of the embryonic alcohol dehydrogenase activity, prevents the oxidation of ethanol to acetaldehyde that in turn functions as a RALDH2 inhibitor. Acetaldehyde-mediated reduction of RA can be rescued by RALDH2 or retinaldehyde supplementation. Enzymatic kinetic analysis of human RALDH2 shows a preference for acetaldehyde as a substrate over retinaldehyde. RA production by hRALDH2 is efficiently inhibited by acetaldehyde but not by ethanol itself. We conclude that acetaldehyde is the teratogenic derivative of ethanol responsible for the reduction in RA signaling and induction of the developmental malformations characteristic of FASD. This competitive mechanism will affect tissues requiring RA signaling when exposed to ethanol throughout life.

Correlations of ALDH2 rs671 and C12orf30 rs4767364 polymorphisms with increased risk and prognosis of esophageal squamous cell carcinoma in the Kazak and Han populations in Xinjiang province

OBJECTIVE

Genetic polymorphisms in ALDH2 and C12orf30 genes have been reported to increase the risk of developing esophageal squamous cell carcinoma (ESCC). This study aims to investigate the relationship between ALDH2 rs671 and c12orf30 rs4767364 polymorphisms in the chromosome 12q24 gene, and risk and prognosis of individuals developing esophageal cancer (ESCC) in Xinjiang Kazak and Han populations.

METHODS

The case group consisted of 127 ESCC patients. The control group comprised of 125 healthy individuals. Subjects that were recruited all come from Xinjiang province. TaqMan and the Hardy-Weinberg equilibrium were the main methods employed to detect and examine the distribution of genotypes of rs671 and rs4767364.

RESULTS

The genotype frequencies of ALDH2 rs671 between the Kazak case and control groups were statistically significant, while no significant difference was observed between the Han case and control groups (P>.05). Moreover, ALDH2 rs671 (G>A) was associated with poor prognosis of ESCC in both Kazak and Han populations, and c12orf30 rs4767364 (A>G) was also connected with poor prognosis of ESCC in Kazak but not in Han population.

CONCLUSION

In the chromosome 12q24 locus, ALDH2 rs671 (G>A) is related to the susceptibility to ESCC in Kazak populations, and it is also associated with poor prognosis of EC in Kazak and Han populations. Furthermore, c12orf30 rs4767364 (A>G) may be correlated with poor ESCC prognosis in Kazak population.

Genetic Association and Gene-Gene Interaction Reveal Genetic Variations in ADH1B, GSTM1 and MnSOD Independently Confer Risk to Alcoholic Liver Diseases in India

Genetic susceptibility is an important modifier of clinical outcome and natural history of progression in Alcoholic liver disease (ALD). While the significance of ethnicity in this evolution is very clear, subtle inter-individual genetic variant(s) might be important and thus we investigated those in an Indian population. Fourteen markers were genotyped within two alcohol metabolism genes [Alcohol dehydrogenase (ADH) gene clusters (ADH1B and ADH1C) and Aldehyde dehydrogenase (ALDH2)], one microsomal ethanol oxidizing enzyme cytochrome p450 (CYP2E1) and three oxidative stress response (OSR) genes (MnSOD, GSTT1 and GSTM1) among 490 Bengali individuals (322 ALD and 168 control) from Eastern and North-Eastern India and validation was performed in a new cohort of 150 Bengali patients including 100 ALD and 50 advanced non-alcoholic steatohepatitis (NASH). Out of 14 genetic variants, carriage of 5 genotypes (rs2066701CC in ADH1B, rs1693425TT in ADH1C, rs4880TT in MnSOD and GSTT1/GSTM1 null, p-value <0.05) were noted significantly higher among ALD patients while inter or intra group gene-gene interaction analysis revealed that addition of risk genotype of any OSR gene enhanced the possibility of ALD synergistically. Multiple logistic regression analysis showed independent association of rs2066701CC, rs4880TT and GSTM1 null genotype with ALD while lower frequencies of those genotypes in advanced NASH patients further confirmed their causal relation to ALD. Thus these findings suggest that the three variants of ADH1C, MnSOD and GSTM1 can be used to identify individuals who are at high risk to develop ALD and may be helpful in proper management of Indian alcoholics.

Prognostic Value of Drinking Status and Aldehyde Dehydrogenase 2 Polymorphism in Patients With Head and Neck Squamous Cell Carcinoma

Background

The association between alcohol drinking, aldehyde dehydrogenase 2 (ALDH2) polymorphism, and survival in patients with head and neck squamous cell carcinoma (HNSCC) remains unclear.

Methods

We performed a retrospective cohort study of 267 HNSCC patients at Aichi Cancer Center. Of these, 65 patients (24%) were non-drinkers, 104 (39%) were light drinkers (ethanol <46 g or <5 days/week), 46 (17%) were moderate drinkers (ethanol intake 46–68 g/day and ≥5 days/week), and 52 (20%) were heavy drinkers (ethanol intake ≥69 g and ≥5 days/week). The prognostic value of pre-treatment drinking status and ALDH2 polymorphism was investigated using multivariate proportional hazard models.

Results

Drinking status was associated with disease-free survival (DFS) in HNSCC patients, with marginal statistical significance (5-year DFS: 67.9% [95% confidence interval {CI}, 53.8–78.4%] for non-drinkers, 57.6% [95% CI, 47.4–66.6%] for light drinkers, 46.1% [95% CI, 30.8–60.1%] for moderate drinkers, and 43.5% [95% CI, 29.3–56.9%] for heavy drinkers; P = 0.088). However, this association lost significance when multivariate analyses were adjusted for established prognostic factors. ALDH2 genotype was not significantly associated with DFS in HNSCC patients (5-year DFS: 85.7% [95% CI, 53.9–96.2%] for Lys/Lys, 56.2% [95% CI, 47.4–64.1%] for Glu/Lys, and 50.5% [95% CI, 40.3–59.7%] for Glu/Glu; P = 0.154). After stratification by ALDH2 genotype, we observed a significant positive dose-response relationship between drinking status and DFS in HNSCC patients with ALDH2 Glu/Glu (P_trend = 0.029).

Conclusions

In this study, we identified a significant positive dose-response relationship between pre-treatment drinking status and DFS in HNSCC patients with ALDH2 Glu/Glu. To confirm this association, further study is warranted.

Metabolic methanol: molecular pathways and physiological roles

Methanol has been historically considered an exogenous product that leads only to pathological changes in the human body when consumed. However, in normal, healthy individuals, methanol and its short-lived oxidized product, formaldehyde, are naturally occurring compounds whose functions and origins have received limited attention. There are several sources of human physiological methanol. Fruits, vegetables, and alcoholic beverages are likely the main sources of exogenous methanol in the healthy human body. Metabolic methanol may occur as a result of fermentation by gut bacteria and metabolic processes involving S-adenosyl methionine. Regardless of its source, low levels of methanol in the body are maintained by physiological and metabolic clearance mechanisms. Although human blood contains small amounts of methanol and formaldehyde, the content of these molecules increases sharply after receiving even methanol-free ethanol, indicating an endogenous source of the metabolic methanol present at low levels in the blood regulated by a cluster of genes. Recent studies of the pathogenesis of neurological disorders indicate metabolic formaldehyde as a putative causative agent. The detection of increased formaldehyde content in the blood of both neurological patients and the elderly indicates the important role of genetic and biochemical mechanisms of maintaining low levels of methanol and formaldehyde.

Preventive effects of Chlorella on skeletal muscle atrophy in muscle-specific mitochondrial aldehyde dehydrogenase 2 activity-deficient mice

Background

Oxidative stress is involved in age-related muscle atrophy, such as sarcopenia. Since Chlorella, a unicellular green alga, contains various antioxidant substances, we used a mouse model of enhanced oxidative stress to investigate whether Chlorella could prevent muscle atrophy.

Methods

Aldehyde dehydrogenase 2 (ALDH2) is an anti-oxidative enzyme that detoxifies reactive aldehydes derived from lipid peroxides such as 4-hydroxy-2-nonenal (4-HNE). We therefore used transgenic mice expressing a dominant-negative form of ALDH2 (ALDH2*2 Tg mice) to selectively decrease ALDH2 activity in the muscles. To evaluate the effect of Chlorella, the mice were fed a Chlorella-supplemented diet (CSD) for 6 months.

Results

ALDH2*2 Tg mice exhibited small body size, muscle atrophy, decreased fat content, osteopenia, and kyphosis, accompanied by increased muscular 4-HNE levels. The CSD helped in recovery of body weight, enhanced oxidative stress, and increased levels of a muscle impairment marker, creatine phosphokinase (CPK) induced by ALDH2*2. Furthermore, histological and histochemical analyses revealed that the consumption of the CSD improved skeletal muscle atrophy and the activity of the mitochondrial cytochrome c oxidase.

Conclusions

This study suggests that long-term consumption of Chlorella has the potential to prevent age-related muscle atrophy.

Genetic differences in response to alcohol

The level of response to alcohol, which reflects individual differences in sensitivity to the pharmacologic effects of alcohol, is considered to be an important endophenotype of alcohol use disorder (AUD). By comparing monozygotic and dizygotic twins, the heritability of the level of response to alcohol has been estimated to be 60%. Many genes have been implicated as potential contributors toward heavy drinking, alcohol-related problems, and AUD through a low level of response to alcohol, each with a small effect. Identified are genes for gamma-aminobutyric acid (GABA) receptors, serotonin transporter, opioid receptor, and nicotinic acetylcholine receptor, but the most well-characterized genes that have a strong impact on the level of response to alcohol are those for alcohol-metabolizing enzymes. Although two genetic variations in alcohol and aldehyde dehydrogenases, which have been the most intensively studied, exist almost exclusively in Asian populations, studies on the effect of genetic variations in alcohol-metabolizing enzymes on the response to alcohol are gradually expanding in non-Asian populations. In this chapter, we focus on genetic studies in humans. After analyzing the overall influence of genetic factors on the response to alcohol, we explore individual genes that may influence the response to alcohol. Lastly, we review studies examining the effects of genetic variations in alcohol-metabolizing enzymes on the level of response to alcohol.

Genetic influences on response to alcohol and response to pharmacotherapies for alcoholism

Although very many individuals drink alcohol at safe levels, a significant proportion escalates their consumption with addiction as the end result. Alcoholism is a common, moderately heritable, psychiatric disorder that is accompanied by considerable morbidity and mortality. Variation in clinical presentation suggests inter-individual variation in mechanisms of vulnerability including genetic risk factors. The development of addiction is likely to involve numerous functional genetic variants of small effects. The first part of this review will focus on genetic factors underlying inter-individual variability in response to alcohol consumption, including variants in alcohol metabolizing genes that produce an aversive response (the flushing syndrome) and variants that predict the level of subjective and physiological response to alcohol. The second part of this review will report on genetic variants that identify subgroups of alcoholics who are more likely to respond to pharmacotherapy to reduce levels of drinking or maintain abstinence. Genetic analyses of the level of response to alcohol, particularly of the functional OPRM1 A118G polymorphism and 5' and 3' functional polymorphisms in SLC6A4, are beginning to provide insights into the etiology of alcoholism and also genotype-stratified subgroup responses to naltrexone and SSRIs/ondansetron respectively. Because of large inter-ethnic variation in allele frequencies, the relevance of these functional polymorphisms will vary between ethnic groups. However there are relatively few published studies in this field, particularly with large sample sizes in pharmacogenetic studies, therefore it is premature to draw any conclusions at this stage.

Genetic influences on the development of alcoholism

Alcoholism has a substantial heritability yet the detection of specific genetic influences has largely proved elusive. The strongest findings are with genes encoding alcohol metabolizing enzymes. A few candidate genes such as GABRA2 have shown robust associations with alcoholism. Moreover, it has become apparent that variants in stress-related genes such as CRHR1, may only confer risk in individuals exposed to trauma, particularly in early life. Over the past decade there have been tremendous advances in large scale SNP genotyping technologies allowing for genome-wide associations studies (GWAS). As a result, it is now recognized that genetic risk for alcoholism is likely to be due to common variants in very many genes, each of small effect, although rare variants with large effects might also play a role. This has resulted in a paradigm shift away from gene centric studies toward analyses of gene interactions and gene networks within biologically relevant pathways.

Genome-wide DNA methylation patterns in discordant sib pairs with alcohol dependence

INTRODUCTION

Alcohol dependence is a complex disease caused by a confluence of environmental and genetic factors. Epigenetic mechanisms have been shown to play an important role in the pathogenesis of alcohol dependence.

METHODS

To determine if alterations in gene-specific methylation were associated with alcohol dependence, a genome-wide DNA methylation analysis was performed on peripheral blood mononuclear cells from alcohol-dependent patients and siblings without alcohol dependence as controls. The Illumina Infinium Human Methylation450 BeadChip was used and gene-specific methylation of DNA isolated from peripheral blood mononuclear cells was assessed. Genes ALDH1L2, GAD1, DBH and GABRP were selected to validate beadchip results by pyrosequencing.

RESULTS

Compared to normal controls, 865 hypomethylated and 716 hypermethylated CG sites in peripheral blood mononuclear cell DNA in alcohol-dependent patients were identified. The most hypomethylated CG site is located in the promoter of SSTR4 (somatostatin receptor 4) and the most hypermethylated CG site is GABRP (gamma-aminobutyric acid A receptor). The results from beadchip analysis were consistent with that of pyrosequencing.

DISCUSSION

DNA methylation might be associated with alcohol dependence. Genes SSTR4, ALDH1L2, GAD1, DBH and GABRP may participate in the biological process of alcohol dependence.

Genetics of alcohol dependence and social work research: do they mix?

Since completion of the mapping of the human genome in early 2000, tremendous progress has been made in the identification of many different genes associated with our health and across diseases. Although social work researchers are not expected to conduct genetic research at the molecular level, it is imperative that we are able to understand the basic genetic findings related to behavioral problems and are able to translate and integrate this information into psychosocial treatment approaches and program development. This article is an introduction and overview of genetic approaches, using studies of the genetics of alcoholism to exemplify important issues. The literature review is not comprehensive and focuses primarily on the Collaborative Study on the Genetics of Alcoholism project as an example of a multidisciplinary and integrative approach to the genetic study of a major health problem often encountered in social work practice.

Pharmacogenetics of alcohol, nicotine and drug addiction treatments

The numerous premature deaths, medical complications and socio-economic repercussions of drug and alcohol addiction suggest that improvements in treatment strategies for addictive disorders are warranted. The use of pharmacogenetics to predict response to medication, side effects and appropriate dosages is relatively new in the field of drug addiction. However, increasing our understanding of the genetic factors influencing these processes may improve the treatment of addiction in the future. We examined the available scientific literature on pharmacogenetic advancements in the field of drug addiction with a focus on alcohol and tobacco to provide a summary of genes implicated in the effectiveness of pharmacotherapy for addiction. In addition, we reviewed pharmacogenetic research on cocaine and heroin dependence. Thus far, the most promising results were obtained for polymorphisms in the OPRM1 and CYP2A6 genes, which have been effective in predicting clinical response to naltrexone in alcoholism and nicotine replacement therapy in smoking, respectively. Opinions differ as to whether pharmacogenetic testing should be implemented in the clinic at this time because clinical utility and cost-effectiveness require further investigation. However, the data summarized in this review demonstrate that pharmacogenetic factors play a role in response to addiction pharmacotherapy and have the potential to aid in the personalization of addiction treatments. Such data may lead to improved cessation rates by allowing physicians to select medications for individuals based, at least in part, on genetic factors that predispose to treatment success or failure rather than on a trial and error basis.

Genetics of alcohol dependence

Twin, family, and adoption studies have consistently shown that genetic factors play an important role in the pathogenesis of alcohol dependence. Numerous studies have aimed to identify genes that contribute to susceptibility to alcohol dependence. Whole-genome linkage studies have identified several chromosomal regions that are linked with alcohol dependence. Association studies have also identified genes associated with alcohol dependence. Alcohol-metabolizing enzymes, such as alcohol dehydrogenase-1B and aldehyde dehydrogenase-2, are the most well-established genes that have polymorphisms associated with the risk for alcohol dependence. Polymorphisms in gamma-aminobutyric acid receptor genes are also reported to be associated with alcohol dependence. The polymorphism of opioid receptor mu 1 gene is of interest because it alters the treatment effects of naltrexone. Several genes related to neural transmission have been reported to be associated with alcohol dependence, but results are inconsistent among studies. One reason for these inconsistent results is the great heterogeneity of alcohol dependence. Classifying alcohol dependence into homogeneous phenotypes is a good strategy to solve this problem. Recently, several genome-wide association studies have been reported. Genome-wide association studies enable hypothesis-free genome mapping of vulnerability-contributing genes and are expected to add data to identify genes associated with the susceptibility to alcohol dependence. Knowledge of the genetic basis of alcohol dependence is growing and leads to a better understanding of the biological mechanisms of addiction, which can help with strategies to prevent and treat this disease.

Psychometric and genetic architecture of substance use disorder and behavioral disinhibition measures for gene association studies

Using large twin, family, and adoption studies conducted at the Minnesota Center for Twin and Family Research, we describe our efforts to develop measures of substance use disorder (SUD) related phenotypes for targets in genome wide association analyses. Beginning with a diverse set of relatively narrow facet-level measures, we identified 5 constructs of intermediate complexity: nicotine, alcohol consumption, alcohol dependence, illicit drug, and behavioral disinhibition. The 5 constructs were moderately correlated (mean r = .57) reflecting a general externalizing liability to substance abuse and antisocial behavior. Analyses of the twin and adoption data revealed that this general externalizing liability accounted for much of the genetic risk in each of the intermediate-level constructs, though each also exhibited significant unique genetic and environmental risk. Additional analyses revealed substantial effects for age and sex, significant shared environmental effects, and that the mechanism of these shared environmental effects operates via siblings rather than parents. Our results provide a foundation for genome wide association analyses to detect risk alleles for SUDs as well as novel insights into genetic and environmental risk for SUDs.

Haplotype-based study of the association of alcohol-metabolizing genes with alcohol dependence in four independent populations

BACKGROUND

Ethanol is metabolized by 2 rate-limiting reactions: alcohol dehydrogenases (ADH) convert ethanol to acetaldehyde that is subsequently metabolized to acetate by aldehyde dehydrogenases (ALDH). Approximately 50% of East Asians have genetic variants that significantly impair this pathway and influence alcohol dependence (AD) vulnerability. We investigated whether variation in alcohol metabolism genes might alter the AD risk in four non-East Asian populations by performing systematic haplotype association analyses to maximize the chances of capturing functional variation.

METHODS

Haplotype-tagging SNPs were genotyped using the Illumina GoldenGate platform. Genotypes were available for 40 SNPs across the ADH genes cluster and 24 SNPs across the two ALDH genes in four diverse samples that included cases (lifetime AD) and controls (no Axis 1 disorders). The case control sample sizes were the following: Finnish Caucasians: 232, 194; African Americans: 267, 422; Plains American Indians: 226, 110; and Southwestern American (SW) Indians: 317, 72.

RESULTS

In all four populations, as well as HapMap populations, 5 haplotype blocks were identified across the ADH gene cluster: (i) ADH5-ADH4; (ii) ADH6-ADH1A-ADH1B; (iii) ADH1C; (iv) intergenic; (v) ADH7. The ALDH1A1 gene was defined by 4 blocks and ALDH2 by 1 block. No haplotype or SNP association results were significant after correction for multiple comparisons; however, several results, particularly for ALDH1A1 and ADH4, replicated earlier findings. There was an ALDH1A1 block 1 and 2 (extending from intron 5 to the 3' UTR) yin yang haplotype (haplotypes that have opposite allelic configuration) association with AD in the Finns driven by SNPs rs3764435 and rs2303317, respectively, and an ALDH1A1 block 3 (including the promoter region) yin yang haplotype association in SW Indians driven by 5 SNPs, all in allelic identity. The ADH4 SNP rs3762894 was associated with AD in Plains Indians.

CONCLUSIONS

The systematic evaluation of alcohol-metabolizing genes in four non-East Asian populations has shown only modest associations with AD, largely for ALDH1A1 and ADH4. A concentration of signals for AD with ALDH1A1 yin yang haplotypes in several populations warrants further study.

Abacavir and metabolite pharmacokinetics in HIV-1-infected children and adolescents

OBJECTIVES

Abacavir (ABC) oral clearance, adjusted for body size, is approximately 2 times higher for children than adults with a corresponding difference in dose regimens. However, there are limited data available in the adolescent population. The pharmacokinetics (PKs) of ABC and primary metabolites were determined in HIV-1-infected children and adolescents to evaluate age and patient characteristics as a basis for adjusting ABC dose regimens and to assess the influence of metabolite formation on PK parameters.

METHODS

Pediatric subjects 9-18 years of age receiving antiretroviral therapy for HIV-1 infection were stratified by Tanner stage and given a single 8 mg/kg dose of ABC oral solution. Blood samples (n = 10) were obtained over 8 hours and measured for ABC, glucuronide, and carboxylate metabolites using high-performance liquid chromatography. PK parameters for children (Tanner stages 1-2; TS1) and adolescents (Tanner stages 3-5; TS2) were compared.

RESULTS

Twenty-five subjects were enrolled. ABC mean (range) maximum concentration (Cmax; microg/mL), area under the curve (microg.hr/mL), half-life (hours), and apparent clearance (CL/F; mL/min per kg) for TS1 and TS2 were 3.5 (1.2-5.6) vs 3.4 (1.8-5.9), 8.0 (2.1-18.6) vs 8.9 (3.1-17.2), 1.3 (0.7-2.5) vs 1.4 (0.9-1.9), and 22.1 (7.0-59.2) vs 18.4 (7.7-42.9) and not significantly different. Age, Tanner stage, and sex were not correlated with ABC clearance by univariate analysis. The ratios of metabolites to ABC area under the curve were correlated with ABC clearance as were the ratios of metabolites to ABC concentrations at the 6-hour time point.

CONCLUSIONS

ABC oral clearance in HIV-1-infected pediatric patients does not change during puberty, is similar to younger children, and is higher than previously published in adults. Therefore, dosing adolescents as adults should be reexamined. Intersubject PK variability is substantial and is not correlated with body size or age but more likely due to differences in metabolite formation that may be genetic in origin.

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.

An assessment of potential cancer risk following occupational exposure to ethanol

Recognition of the carcinogenic properties of ethanol has resulted from comprehensive evidence regarding the effect of consumption of alcohol; indeed, ethanol in alcoholic beverages is now considered a Group 1 carcinogen by the International Agency for Research on Cancer. However, there is little information on the effects of ethanol following exposure via the occupationally relevant routes of inhalation and dermal exposure. This review therefore focuses on these exposure routes, to assess potential carcinogenic risk associated with occupational exposure to ethanol. Inhalatory exposure at the current occupational exposure limit (OEL) for the United Kingdom (1000 ppm ethanol over an 8-h shift) was estimated to be equivalent to ingestion of 10 g ethanol (approximately 1 glass of alcohol) per day. However, in the occupational setting the dose-rate delivery of this amount of ethanol is low, allowing for its rapid and effective elimination, for the majority of individuals. Similarly, while dermal absorption in an occupational setting could potentially add to overall body ethanol burden, additional carcinogenic risk of such exposure is considered negligible. Thus, on balance, there appears little cause to suppose occupational exposure at or below the current OEL associates with any appreciable increase in risk of cancer. However, available occupational exposure data to confirm this view are currently limited. It is also suggested that adoption of a more flexible classification regime, considering risk in the context of hazard and exposure (such as that adopted by the German MAK commission), would represent an improvement over traditional occupational risk assessment practices.

Age-dependent neurodegeneration accompanying memory loss in transgenic mice defective in mitochondrial aldehyde dehydrogenase 2 activity

Oxidative stress may underlie age-dependent memory loss and cognitive decline. Toxic aldehydes, including 4-hydroxy-2-nonenal (HNE), an end product of lipid peroxides, are known to accumulate in the brain in neurodegenerative disease. We have previously shown that mitochondrial aldehyde dehydrogenase 2 (ALDH2) detoxifies HNE by oxidizing its aldehyde group. To investigate the role of such toxic aldehydes, we produced transgenic mice, which expressed a dominant-negative form of ALDH2 in the brain. The mice had decreased ability to detoxify HNE in their cortical neurons and accelerated accumulation of HNE in the brain. Consequently, their lifespan was shortened and age-dependent neurodegeneration and hyperphosphorylation of tau were observed. Object recognition and Morris water maze tests revealed that the onset of cognitive impairment correlated with the degeneration, which was further accelerated by APOE (apolipoprotein E) knock-out; therefore, the accumulation of toxic aldehydes is by itself critical in the progression of neurodegenerative disease, which could be suppressed by ALDH2.

Mendelian randomization: a novel test of the gateway hypothesis and models of gene-environment interplay

To determine if drinking behavior in adolescence provides a "gateway" leading to the misuse of other psychoactive substances and antisocial behavior, we genotyped 180 Asian adolescent adoptees to determine if they inherited the deficient from of the aldehyde dehydrogenase 2 (ALDH2) enzyme that is important in the metabolism of alcohol. Based on the gateway model, we hypothesized that those with normal enzyme activity (70% of the sample) who began to misuse alcohol would also misuse other drugs and display antisocial tendencies. Those with the enzyme deficiency (30%), because they experience unpleasant side effects associated with drinking, were expected to show less evidence of alcohol misuse and thus be less likely to progress to the misuse of other substances or engage in antisocial acts. Consistent with previous research, we found that ALDH2 deficiency was significantly associated with lower rates of drinking and getting drunk but not with ever having tried alcohol. Contrary to the gateway model, we found no evidence that ALDH2 deficiency was associated with lower rates of nonalcohol substance use or antisociality. Finally, in an examination of factors that may moderate the impact of the metabolic protection because of ALDH2 deficiency, we identified siblings rather than parents as the major source of familial environmental effect on adolescent drinking.

Association of ADH and ALDH genes with alcohol dependence in the Irish Affected Sib Pair Study of alcohol dependence (IASPSAD) sample

BACKGROUND

The genes coding for ethanol metabolism enzymes [alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH)] have been widely studied for their influence on the risk to develop alcohol dependence (AD). However, the relation between polymorphisms of these metabolism genes and AD in Caucasian subjects has not been clearly established. The present study examined evidence for the association of alcohol metabolism genes with AD in the Irish Affected Sib Pair Study of alcohol dependence.

METHODS

We conducted a case-control association study with 575 independent subjects who met Diagnostic and Statistical Manual of Mental Disorders, 4th Edition, AD diagnosis and 530 controls. A total of 77 single nucleotide polymorphisms (SNPs) in the seven ADH (ADH1-7) and two ALDH genes (ALDH1A1 and ALDH2) were genotyped using the Illumina GoldenGate protocols. Several statistical procedures were implemented to control for false discoveries.

RESULTS

All markers with minor allele frequency greater than 0.01 were in Hardy-Weinberg equilibrium. Numerous SNPs in ADH genes showed association with AD, including one marker in the coding region of ADH1C (rs1693482 in exon6, Ile271Gln). Haplotypic association was observed in the ADH5 and ADH1C genes, and in a long haplotype block formed by the ADH1A and ADH1B loci. We detected two significant interactions between pairs of markers in intron 6 of ADH6 and intron 12 of ALDH2 (p = 5 x 10(-5)), and 5' of both ADH4 and ADH1A (p = 2 x 10(-4)).

CONCLUSION

We found evidence for the association of several ADH genes with AD in a sample of Western European origin. The significant interaction effects between markers in ADH and ALDH genes suggest possible epistatic roles between alcohol metabolic enzymes in the risk for AD.

Addiction science and its genetics

AIM

To assess the progress and impact of genetic studies in the addictions arena and to present this information in a form accessible to the general readership of Addiction.

METHODS

Review of the evidence that genes are involved in addiction, approaches to their identification, current findings and the potential implications.

RESULTS

Family, twin and adoption studies provide strong evidence that addiction runs in families and that this is determined in part by genetic factors. Two main molecular genetic approaches, namely linkage and association, have been adopted to identify the specific genes involved. Both methods are fraught with problems. Linkage is limited by issues of sensitivity, and association by false positives. Perhaps the strongest finding in psychiatric genetics to date is the impressive effect that a single genetic variant, in the aldehyde dehydrogenase 2 gene, has on drinking behaviour and reducing the risk of developing alcohol dependence. Other findings are currently less robust; however, the implications of elucidating the genetic underpinning of addiction will be profound.

CONCLUSIONS

Addiction genetics is a developing science that has yet to prove its worth in the clinical setting.

Transient receptor potential A1 mediates acetaldehyde-evoked pain sensation

Six transient receptor potential (TRP) ion channels expressed in the sensory afferents play an important role as body thermosensors and also as peripheral pain detectors. It is known that a number of natural compounds specifically activate those sensory neuronal TRP channels, and a well-known example is cinnamaldehyde for TRPA1. Here we show that human and mouse TRPA1 are activated by acetaldehyde, an intermediate substance of ethanol metabolism, in the HEK293T cell heterologous expression system and in cultured mouse trigeminal neurons. Acetaldehyde failed to activate other temperature-sensitive TRP channels expressed in sensory neurons. TRPA1 antagonists camphor and gadolinium, and a general TRP blocker ruthenium red inhibited TRPA1 activation by acetaldehyde. Camphor, gadolinium and ruthenium red also suppressed the acute nociceptive behaviors induced by the intradermal administration of acetaldehyde into the mouse footpads. Intradermal co-application of prostaglandin E2 and acetaldehyde greatly potentiated the acetaldehyde-induced nociceptive responses, and this effect was reversed by treatment with the TRPA1 antagonist camphor. These results suggest that acetaldehyde causes nociception via TRPA1 activation. Our data may also help elucidate the mechanisms underlying acetaldehyde-related pathological symptoms such as hangover pain.

Association of mu-opioid receptor gene polymorphism A118G with alcohol dependence in a Japanese population

Ethanol is considered to activate the brain reward system by increasing the release of an endogenous opioid receptor ligand, beta-endorphin. The polymorphism A118G in the mu-opioid receptor gene (OPRM1) causes the amino acid change Asn40Asp and has been reported to affect the affinity of the ligand for the receptor. The association of this polymorphism with the vulnerability to alcohol dependence has been studied in many populations, but not yet in Japanese people. In the present study, we compared the frequencies of the polymorphism OPRM1 A118G between patients with alcohol dependence and healthy control subjects living in a Japanese provincial prefecture. We also genotyped a polymorphism, G1510A, in the acetaldehyde dehydrogenase 2 gene (ALDH2), in which the A allele causes poor metabolism of acetaldehyde, a major metabolite of alcohol. Both OPRM1 118G and ALDH2 1510G were significantly associated with alcohol dependence. These results suggest that OPRM1 118G in addition to ALDH2 1510G might be one of the risk factors for alcohol dependence in Japanese people.

New findings on the genetic influences on alcohol use and dependence

PURPOSE OF REVIEW

Alcohol dependence is a complex disorder with a well documented highly hereditary nature. This article reviews the recent advances in our understanding of the direct and indirect genetic influences on alcohol use and dependence.

RECENT FINDINGS

Recent findings can be summarized as follows: (a) twin studies have defined and estimated the risks of general and specific alcohol-related vulnerabilities. (b) Linkage studies have provided largely inconsistent findings, though several chromosomal regions have been implicated. (c) Quantitative trait loci analyses in animals have identified that the Mpdz gene predisposes to alcohol dependence and withdrawal. (d) Examination of family-based samples has identified several genes including GABRA2 and CHRM2 thought to be associated with alcohol dependence.

SUMMARY

Despite great advances in understanding of genetic vulnerability in alcohol use disorders, only two gene complexes, ADH and ALDH2, have been identified as having defined effects on alcohol use and liability to dependence in humans. New genes associated with increased risks for the disorder will certainly be added to this list in the near future. Neurobiological analyses of the effects of these genes will surely contribute to further understanding of the cause of alcohol dependence and the interindividual differences in risks.

Alcohol Dehydrogenase 2 His47Arg Polymorphism Influences Drinking Habit Independently of Aldehyde Dehydrogenase 2 Glu487Lys Polymorphism: Analysis of 2,299 Japanese Subjects

Although the functional effect of alcohol dehydrogenase 2 (ADH2) His(47)Arg polymorphism has been elucidated, its effect on habitual drinking remains unknown. Here, we conducted a cross-sectional study in 2,299 nonalcoholic Japanese subjects (989 men and 1,310 women). Drinking status, ethanol consumption, and physical reaction to one glass of beer were examined with regard to ADH2 and aldehyde dehydrogenase 2 (ALDH2) polymorphism. Strength of associations were assessed by age-, sex-, smoking status-, and genotype-adjusted odds ratios and their 95% confidence intervals. ADH2 His/Arg and Arg/Arg genotypes showed higher risk for habitual drinking. Among men, ALDH2 genotype- and confounder-adjusted odds ratios (95% confidence intervals) were 1.30 (0.89-1.89) and 3.16 (1.03-9.70), and this trend was significant (P = 0.024). A similar trend was observed among women. The combination genotypes of two polymorphisms revealed the clear effect of the ADH2 Arg allele among those with ALDH2 Glu/Lys in both sexes (P(trend) = 0.007 for men and 0.024 for women). Physical reactions, such as flushing and palpitation, were significantly less common in those with Arg/Arg compared with other ADH2 genotypes, and this was marked when combined with ALDH2 Glu/Lys. Heavy drinker status was also strongly associated with ADH2 Arg alleles. In conclusion, this study showed the strong effect of ADH2 His(47)Arg polymorphism on habitual drinking regardless of ALDH2 genotype.

Certain background factors exhibit an association with an increased risk for pancreatic calcification among Japanese male alcoholics

OBJECTIVE

This was a cross-sectional study conducted from April 2003 through March 2004 to investigate the background factors related to pancreatic calcification (PC) in male Japanese alcoholics.

METHODS AND RESULTS

Helical computed tomography examination revealed PC in 44 of 263 alcoholics, and this group was further divisible into 3 subgroups: "scant" (n = 24), "moderate" (n = 6), and "extensive" PC subgroups (n = 14). The extensive subgroup was associated with larger daily ethanol consumption (P = 0.05) and high-alcohol beverages, such as whisky (P = 0.02). The moderate subgroup was associated with a longer duration of habitual drinking (P = 0.04), whereas the scant PC group was associated with never having smoked (P = 0.05) and with low-alcohol beverages, such as beer (P = 0.09). None of the 40 subjects with inactive mitochondrial aldehyde dehydrogenase (ALDH2*2 allele) exhibited PC (P = 0.004). Heterozygous alcohol dehydrogenase 2 genotype (ADH2*1/2*2) exhibited an association with the scant subgroup (P = 0.02). The TG12 repeats in the cystic fibrosis transmembrane conductance regulator (CFTR) gene tended to have a weak association with PC.

CONCLUSION

Drinking behavior, smoking status, and genetic backgrounds are associated with PC and are likely to increase the risk for alcoholic chronic pancreatitis.

Differential teratogenic effect of alcohol on embryonic development between C57BL/6 and DBA/2 mice: a new view

BACKGROUND

Alcohol exposure during the fetal stage generates variable severity in different organs, as seen in fetal alcohol syndrome and fetal alcohol effect. Whether genetic factors or conditions of alcohol exposure influence the susceptibility to alcohol-related developmental impairment remains a question.

METHODS

To investigate the contribution of genotype to the susceptibility to alcohol-induced toxicity during development beyond confounding maternal factors and variables of alcohol exposures, the authors tested the effect of alcohol exposure under definitive concentration using a whole embryonic culture of two inbred strains previously known to be vulnerable (C57BL/6 [C6]) or resistant (DBA/2 [D2]) to alcohol. On gestational day 8, embryos from each group bearing three to six somites were collected and then cultured for 44 hr in a medium added with 400 mg/dl of ethanol. The viability and morphological malformations, as well as developmental staging of the embryos, were all scored at the end of the culture.

RESULTS

The authors found, in contrast to previous reports, that alcohol treatment retarded embryonic growth and induced abnormalities, including the neural tube opening and the hypoplasia of the optic vesicle in both strains. However, alcohol specifically compromised the heart and caudal neural tube in C6, whereas it specifically decreased the number of somites and the development of branchial bars among others in D2.

CONCLUSIONS

These results demonstrated that both strains of embryos are vulnerable to the same amount and pattern of alcohol exposures at the same developmental stage, but each with unique vulnerability in specific organs, with alcohol having greater teratogenic effects in D2 than in C6. These differential vulnerabilities are results of greater genetic influence, rather than the maternal influence or conditions of alcohol.

Alcohol and the liver

PURPOSE OF REVIEW

To highlight salient recent discoveries and results of clinical trials in alcoholic liver disease (ALD). The burden of care for ALD patients is hefty and the prevalence of alcohol abuse may be increasing in both the developed and the underdeveloped world.

RECENT FINDINGS

Molecular mechanisms of alcoholism are being identified but not of the predisposition to alcoholic liver injury, except perhaps for polymorphism of a cytotoxic T-cell antigen. The Mayo End-stage Liver Disease (MELD) score performs well in assessing the prognosis of ALD; serological biomarkers for predicting ALD outcome are of uncertain value. Concomitant liver disease (e.g., obesity, hepatitis C, and iron overload) aggravates the severity of ALD; conversely, alcohol abuse may be a cryptic co-factor in some cases of non-alcoholic fatty liver. For alcoholic hepatitis, nutritional support is the mainstay of treatment; steroids are considered by some (but not all) as safe and effective therapy, whereas manipulations of tumor necrosis factor-alpha activity have been disappointing, or of unproven benefit at best. In liver transplantation for ALD, methods are being devised to monitor recidivism and to ameliorate its risk and that of co-morbid psychiatric conditions.

SUMMARY

Much of the pathogenesis of ALD has been identified and headway has been made in predicting its prognosis. However, much remains to be done to elucidate the molecular genetics of the risk of developing ALD and in formulating safe, effective therapies for alcoholic hepatitis.