−日中医学協会助成事業−

 Alcohol consumption is a probable risk factor with regard to colorectal neoplasm. Genetic polymorphisms, aldehyde dehydrogenase 2 (ALDH2) Glu487Lys and alcohol dehydrogenase 2 (ADH2) His47Arg, which have a strong impact on alcohol metabolism, are common in Japanese population but their significance for colorectal neoplasm remains to be clarified in detail. We therefore conducted a case-control study with 224 asymptomatic colorectal adenoma cases and 230 population-based controls matched for age and sex. After adjustment for sex, age, BMI, smoking status, drinking status, exercise, multivitamin consumption and family history of colorectal adenomas or cancers, the ADH2 Arg allele was found to be associated with increased risk, the odds ratios (ORs) being 1.41 (95%CI: 0.92-2.18) and 2.40 (1.00-5.78) for the His/Arg and Arg/Arg genotypes, respectively. Whereas no significant association was found for ALDH2 genotypes. In heavy drinkers, having ALDH2 Lys+ with ADH2 Arg+ showed ORs of 8.39 (1.69-41.54), compared with non drinkers, having ALDH2 Glu/Glu with ADH2 His/His. In conclusion, the present study suggests the polymorphisms of ADH2 and ALDH2 can modify the influence of alcohol consumption on colorectal adenomas risk

　

Key Words　 colorectal adenomas, drinking, gene-environment interaction, ALDH2, ADH2.

　

 The majority of colorectal cancer is thought to arise from adenomas, Alcohol consumption is a probable risk factor with respect to colorectal adenomas and colorectal cancers¹⁾. This increased risk might be caused by ethanol via cocarcinogenesis, induction of DNA hypomethylation, or tumor promotion, but might also result from its metabolite acetaldehyde, which was qualified as a probable carcinogen to humans. Alcohol is oxidized to acetaldehyde by the alcohol dehydrogenase enzymes (ADHs), especially by ADH2. Acetaldehyde is further oxidized into acetate by aldehyde dehydrogense enzymes (ALDHs), and this oxidation owes much to ALDH2. Encoding genes for these two representative alcohol-oxidizing capabilities and drinking behavior. Regarding ADH2 Arg/His, the 47His allele represents a superactive subunit of ADH2 that has about a 40 times higher than the less-active Arg/Arg from of ADH2. As for the ALDH2 Glu487Lys polymorphism, the 487Lys allele, encodes a catalytically inactive subunit. Individuals with the ALDH2 Glu/Lys genotype have only 6.25% of normal ALDH2 487Glu protein; indicating a dominant effect of ALDH2 487Lys. The ADH2 47His and ALDH2 487Lys alleles leading to high acetaldehyde concentrations, are clustered in East Asian popuiations such as Japanese and Chinese. Therefore, these two genetic polymorphisms modify the drinking habit and are expected to affect CRC and colorectal adenomas risk. However, rare evidence is available for the combined impact of ADH2 and ALDH2 polymorphisms on colorectal adenomas risk by alcohol drinking.

 The primary aim of this case-control study is to investigate the impact of ADH2 and ALDH2 polymorphisms on colorectal adenomas risk. We also evaluated potential interactions between the two polymorphisms and alcohol consumption with regard to colorectal adenomas risk.

　

Subject selection and data collection:

 The participants and data collection method for this case-control study have been described previously in detail²⁾. Briefly, 224 colorectal adenoma cases (159 men, 65 women) and 230 healthy controls (160 men, 70 women), frequency matched for age and sex, were recruited. Detailed information on demographic characteristics, personal medical history, usual physical activity, cigarette smoking and drinking habits, intake of multivitamins, and history of colorectal adenomas or cancer in the first-degree relatives were collected by trained interviewers. Alcohol use was categorized into never and ever use with consumption of <30 or ≧ 30ml of ethanol per day.

Genotyping of ALDH2 and ADH2:

 DNA of each subject was extracted from the buffy coat fraction. Genotyping was based upon duplex PCRs with the confronting two-pair-primer (PCR-CTPP) method ³⁾. Briefly, four primers for the ADH2 polymorphism and four primers for the ALDH2 polymorphism were mixed in a 25μl volume with 0.2mMdNTPs, 0.5U of AmpliTaq Gold DNA polymerase and 2.5μl×10 PCR buffer including 15 mM Mgcl2. The results were confirmed by the PCR restriction fragment length polymorphism method using MslI for both polymorphisms.

Statistical analysis:

 Differences of characteristics between cases and controls were assessed using the Chi-square test. The Hardy-Weinberg equilibrium was checked with the Chi-square test. Unconditional logistic regression analysis was employed to estimate the odds ratios (ORs) and confidence intervals (95% CIs) for the association between genotypes and risk of colorectal adenomas. Adjustments were made for matching variables (age, sex) and for possible confounders. Covariates were identified as potential confounders by examining their distribution by case-control status. The covariates were included in the model if they changed the ORs by more than 20% or significantly changed the likelihood ratio statistic (p<0.05) on univariate analysis. All statistical tests were two-sided and differences were considered to be statistically significant at p < 0.05. All analyses were performed using SAS software, version 8.20 (SAS Institute, Inc. Cary, NC, USA).

　

 Demographic and lifestyle characteristics of the 224 colorectal adenoma cases and 230 controls are shown in Table 1. Differences were observed in the distribution of cigarette smoking between cases and controls (p = 0.001 for males). A significantly higher proportion of cases with a family history of colorectal adenomas or cancer than controls were found (p = 0.01). There were no significant differences in the distribution of sex, body mass index, drinking status, vigorous exercise, or multivitamin consumption between cases and controls.

 Table 2 shows genotype distributions for ADH2 and ALDH2 and combination, and their ORs and 95% CIs for colorectal adenomas. The genotype frequencies for all the polymorphisms were in accordance with the Hardy-Weinberg equilibrium in controls and allele frequencies were also in accordance with earlier reports in Japan. Significantly increased risk of colorectal adenomas was observed with Arg/Arg relative to His/His (OR: 2.45; 95%CI: 1.06-5.66; trend = 0.005 for model 1), whereas no significant elevation of risk was observed with the ALDH2 genotype alone. In the analysis for combination, compared with subjects having ALDH2 Glu/Glu with ADH2 His/His, age-sex adjusted ORs and 95% CIs for those with ALDH2 Glu/Glu and ADH2 Arg+, ALDH2 Lys+ and ADH2 His/His, and ALDH2 Lys+ and ADH2 Arg+ were 1.32 (0.81-2.16), 0.79 (0.49-1.29), and 1.56 (0.92-2.61), respectively. A model including confounders showed similar association.

 In Table3, the impact of combined genotypes on CRC risk stratified by alcohol drinking is presented as ORs adjusted for sex, age, BMI, smoking status, drinking status, exercise, multivitamin consumption and family history of colorectal adenomas or cancers. In heavy drinkers, having ALDH2 Lys+ with ADH2 Arg+ showed ORs of 8.39 (1.69-41.54), compared with non drinkers, having ALDH2 Glu/Glu with ADH2 His/His.

　

 In present study found subjects with ADH2 Arg allele had a higher risk of developing colorectal adenoma than those with ADH2 His/His genotype, and also found that high alcohol consumption most markedly increased the risk of colorectal adenomas in subjects with ADH2 Arg allele and ALDH2 Lys allele.

 Previous epidemiological studies also reported a significantly higher risk for colorectal cancer and esophageal cancer among Japanese with ADH2 Arg allele, compared to those with ADH2 His/His genotype^1,4,5). There are possible explanations for the effects of ADH2 on carcinogenesis. The high risk ADH2 encoded by ADH2 Arg allele might be exposed to lower dose of acetaldehyde following heavy alcohol drinking for hours. Especially, individuals with both the ADH2 Arg allele and ALDH2 Lys allele tend not to experience alcohol flushing, and diminished intensity of the aversive flushing response has been found to be positively associated with daily alcohol consumption⁶⁾. Subjects who consumed alcoholic beverages and carried susceptible genotypes experienced a increase in risk of developing colorectal adenomas, much higher than those who were non-drinkers and did not carry susceptible genotypes of ADH2 and ALDH2.

 The ADH2 Arg allele might, under certain conditions, increase the risk for colorectal adenomas via mechanisms of the interaction between genes and drinking behavior. Our present findings can provide additional information about the role of alcohol on colorectal adenomas in Japan.