Alcohol-metabolizing enzyme polymorphisms and alcoholism in Japan

The role of acetaldehyde in the actions of alcohol (update 2000)

BACKGROUND

Recent advances in the field of acetaldehyde (AcH) research have raised the need for a comprehensive review on the role of AcH in the actions of alcohol. This update is an attempt to summarize the available AcH research.

METHODS

The descriptive part of this article covers not only recent research but also the development of the field. Special emphasis is placed on mechanistic analyses, new hypotheses, and conclusions.

RESULTS

Elevated AcH during alcohol intoxication causes alcohol sensitivity, which involves vasodilation associated with increased skin temperature, subjective feelings of hotness and facial flushing, increased heart and respiration rate, lowered blood pressure, sensation of dry mouth or throat associated with bronchoconstriction and allergy reactions, nausea and headache, and also reinforcing reactions like euphoria. These effects seem to involve catecholamine, opiate peptide, prostaglandin, histamine, and/or kinin mechanisms. The contribution of AcH to the pathological consequences of chronic alcohol intake is well established for different forms of cancer in the digestive tract and the upper airways. AcH seems to play a role in the etiology of liver cirrhosis. AcH may have a role in other pathological developments, which include brain damage, cardiomyopathy, pancreatitis, and fetal alcohol syndrome. AcH creates both unpleasant aversive reactions that protect against excessive alcohol drinking and euphoric sensations that may reinforce alcohol drinking. The protective effect of AcH may be used in future treatments that involve gene therapy with or without liver transplantation.

CONCLUSIONS

AcH plays a role in most of the actions of alcohol. The individual variability in these AcH-mediated actions will depend on the genetic polymorphism, not only for the alcohol and AcH-metabolizing enzymes but also for the target sites for AcH actions. The subtle balance between aversive and reinforcing, protecting and promoting factors will determine the overall behavioral and pathological developments.

A genetic association with the development of alcohol and other substance use behavior in Asian Americans

Studies of Asian adults have found that alcohol use and alcohol dependence are related to variation in the aldehyde dehydrogenase (ALDH2) gene. To investigate the association of ALDH2 with the development of drug involvement, the authors analyzed retrospective information about the onset and regular use of alcohol and other substances as reported by 180 Asian American college students. Possession of an ALDH2*2 allele was not related to initiation of alcohol use or having ever been intoxicated, but individuals with ALDH2*2 alleles were less likely to be regular drinkers, were less likely to have engaged in a binge-drinking episode, reported a lower number of maximum drinks consumed in a 24-hr period, and were less likely to have used tobacco regularly than those without this genetic variant. These findings suggest that ALDH2 is associated with the development of not only alcohol-related behavior but other substance use behavior as well.

Alcohol and aldehyde dehydrogenase polymorphisms in Japanese patients with alcohol-induced chronic pancreatitis

In order to clarify the genetic factors in alcohol-related chronic pancreatitis among Japanese, we determined the genotype of two major alcohol-metabolizing enzymes, alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH). The restriction fragment-length polymorphisms of the ADH2 and the ALDH2 genes were analyzed in 47 normal subjects and 31 patients with alcoholic pancreatitis. No significant difference between the patient and control groups was found in the ADH2 genotypes. A significant genetic difference between the two groups was found in the ALDH2 locus. The frequency of the ALDH2*1 allele was found to be 0.681 and that of the ALDH2*2 allele was 0.319 in the controls, while these values were 0.935 and 0.065 in the patients, respectively. Most of the patients (27 of 31) were ALDH2*1/2*1, only four were ALDH2*1/2*2, and none of the patients were ALDH2*2/2*2. These results indicate that genetic polymorphism of the ALDH2 gene influences the risk of developing alcoholic pancreatitis in Japanese.

Chinese alcoholic patients with esophageal cancer are genetically different from alcoholics with acute pancreatitis and liver cirrhosis

OBJECTIVE

It is a mystery why some alcoholic patients acquire certain organ-specific complications of alcoholism, whereas other alcoholic patients acquire different ones. The aim of this study was to investigate the differences among Chinese alcoholic patients with esophageal cancer, acute pancreatitis, and liver cirrhosis by studying the genetic polymorphisms of ADH2, ADH3, ALDH2, and P4502E1.

METHODS

Liver alcohol dehydrogenase (ADH), aldehyde dehydrogenase (ALDH), and cytochrome P4502E1 (P4502E1) are polymorphic at the ADH2, ADH3, and ALDH2 loci and the 5'-flanking region of the P4502E1. Using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method, we determined the polymorphism of the above-mentioned alcohol metabolizing genes in 59 alcoholics with carcinoma of the esophagus (alcoholic esophageal Ca), 87 acute alcoholic pancreatitis patients, 116 alcoholics with liver cirrhosis (alcoholic cirrhosis), 19 alcoholics with both liver cirrhosis and acute pancreatitis (alcoholic P plus C), and 241 nonalcoholic patients.

RESULTS

The results showed that the allele frequency of ALDH2*2 was significantly higher in the alcoholic esophageal Ca group than in the alcoholic pancreatitis and alcoholic cirrhosis groups. The allele frequency of ADH2*1 was significantly higher in the alcoholic esophageal Ca patients than in nonalcoholic control groups. The ALDH2*2 was significantly lower in alcoholic groups (except the alcoholic esophageal Ca group) than in nonalcoholic control groups. The allele frequencies of ADH2*1 and ALDH2*2 are higher in alcoholic patients with esophageal Ca than alcoholic patients without it. The genotype distribution of P4502E1, detected by RsaI and PstI, was not different among alcoholic patients with different organ diseases.

CONCLUSIONS

The allele frequency of ADH2*1 and ALDH2*1 are different among subpopulations of alcoholics, suggesting that alcoholic patients with different specific types of organ damage are genetically different. The Chinese alcoholic patients with the ADH2*1 and ALDH2*2 allele are more susceptible to esophageal Ca.

Genetic polymorphism of alcohol dehydrogenase in europeans: the ADH2*2 allele decreases the risk for alcoholism and is associated with ADH3*1

Polymorphism at the ADH2 and ADH3 loci of alcohol dehydrogenase (ADH) has been shown to have an effect on the predisposition to alcoholism in Asian individuals. However, the results are not conclusive for white individuals. We have analyzed the ADH genotype of 876 white individuals from Spain (n = 251), France (n = 160), Germany (n = 184), Sweden (n = 88), and Poland (n = 193). Peripheral blood samples from healthy controls and groups of patients with viral cirrhosis and alcohol-induced cirrhosis, as well as alcoholics with no liver disease, were collected on filter paper. Genotyping of the ADH2 and ADH3 loci was performed using polymerase chain reaction-restriction fragment length polymorphism methods on white cell DNA. In healthy controls, ADH2*2 frequencies ranged from 0% (France) to 5.4% (Spain), whereas ADH3*1 frequencies ranged from 47. 6% (Germany) to 62.5% (Sweden). Statistically significant differences were not found, however, between controls from different countries, nor between patients with alcoholism and/or liver disease. When all individuals were grouped in nonalcoholics (n = 451) and alcoholics (n = 425), ADH2*2 frequency was higher in nonalcoholics (3.8%) than in alcoholics (1.3%) (P =.0016), whereas the ADH3 alleles did not show differences. Linkage disequilibrium was found between ADH2 and ADH3, resulting in an association of the alleles ADH2*2 and ADH3*1, both coding for the most active enzymatic forms. In conclusion, the ADH2*2 allele decreases the risk for alcoholism, whereas the ADH2*2 and ADH3*1 alleles are found to be associated in the European population.

Relationship between alcohol drinking, ADH2 and ALDH2 genotypes, and risk for hepatocellular carcinoma in Japanese

The polymorphism in the ALDH2 gene plays a central role in Asian alcohol hypersensitivity and has been associated with the risk for esophageal cancer. In the present study, we attempted to examine associations between the ADH2 and ALDH2 polymorphisms, alcohol drinking and hepatocellular carcinoma (HCC) development in a case-control study in Japan. One hundred and two patients with HCC (85 males and 17 females) and 125 control subjects (101 males and 24 females) were enrolled in the study. Higher cumulative amounts of alcohol consumption (drink-years of > or = 40 drinks/day x year) showed a significant association with HCC development (odds ratio, OR = 2.7; 95% CI = 1.3-5.5, adjusted for age and smoking). By contrast, we could find no association of the ALDH2 genotypes with HCC development (adjusted OR for ALDH2*1/*2 = 1.1; 95% CI = 0.6-2.1). Likewise, the ADH2 genotypes were not associated with HCC development (adjusted OR for ADH2*2/*2 = 0.8; 95% CI = 0.5-1.5). The present results do not support a contribution of acetaldehyde, an active metabolite of ethanol, to HCC development and rather indicate a direct involvement of ethanol in hepatocarcinogenesis.

Interaction between the functional polymorphisms of the alcohol-metabolism genes in protection against alcoholism

The genes that encode the major enzymes of alcohol metabolism, alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH), exhibit functional polymorphism. The variant alleles ADH2*2 and ADH3*1, which encode high-activity ADH isoforms, and the ALDH2*2 allele, which encodes the low-activity form of ALDH2, protect against alcoholism in East Asians. To investigate possible interactions among these protective genes, we genotyped 340 alcoholic and 545 control Han Chinese living in Taiwan at the ADH2, ADH3, and ALDH2 loci. After the influence of ALDH2*2 was controlled for, multiple logistic regression analysis indicated that allelic variation at ADH3 exerts no significant effect on the risk of alcoholism. This can be accounted for by linkage disequlibrium between ADH3*1 and ADH2*2 ALDH2*2 homozygosity, regardless of the ADH2 genotypes, was fully protective against alcoholism; no individual showing such homozygosity was found among the alcoholics. Logistic regression analyses of the remaining six combinatorial genotypes of the polymorphic ADH2 and ALDH2 loci indicated that individuals carrying one or two copies of ADH2*2 and a single copy of ALDH2*2 had the lowest risk (ORs 0.04-0.05) for alcoholism, as compared with the ADH2*1/*1 and ALDH2*1/*1 genotype. The disease risk associated with the ADH2*2/*2-ALDH2*1/*1 genotype appeared to be about half of that associated with the ADH2*1/*2-ALDH2*1/*1 genotype. The results suggest that protection afforded by the ADH2*2 allele may be independent of that afforded by ALDH2*2.

Genetic polymorphism of CYP2E1, ADH2, and ALDH2 in Mexican-Americans

The major enzymes involved in the metabolism of ethanol are alcohol dehydrogenases (ADH) and aldehyde dehydrogenase (ALDH). Some of the isozymes of ADH are expressed polymorphically. Studies investigating a causal link between ADH expression and alcoholic liver disease (ALD) have so far produced conflicting results. The cytochrome P450 2E1 (CYP2E1) represents a second enzyme that can metabolize ethanol. Although normally a minor route of metabolism, its role in chronic alcoholics may be proportionately greater than in nonalcoholics because CYP2E1 is inducible by ethanol. An Rsa I restriction fragment length polymorphism (RFLP) in the 5'-flanking region of the CYP2E1 gene has been identified. Studies have shown that the mutant allele demonstrates greater transcriptional rate, protein level, and enzyme activity when compared with the wild-type allele. The association between the Rsa I site polymorphism and ALD has been reported. In this report, we examined the genotypes of ADH2(2), ALDH2(2), and CYP2E1 in a group of healthy subjects of Mexican-American descent. The ADH2(2) and ALDH2(2) frequencies are 6% and 0%, respectively, which are similar to those which have been reported for Caucasians. In contrast, the Rsa I allele frequency of the CYP2E1 gene is 16%, which is significantly higher than in Caucasians. The high RsaI allele frequency found in Mexican-Americans suggests that it might play a role in the development of ALD in this rapidly growing minority population where ALD is common.

The genetics of alcoholism

Recently, the first genome-wide searches for genes predisposing to or protecting against the development of alcohol dependence in humans have been carried out. Genetic studies in animal models of alcohol-related behaviors have also identified candidate chromosomal regions and potential candidate genes that can be tested in human populations.

Association of polymorphism in the alcohol dehydrogenase 2 gene with alcohol-related organ injuries, especially liver cirrhosis

The class I hepatic alcohol dehydrogenases (ADHs) are primarily responsible for ethanol metabolism in humans. Genetic polymorphism at the ADH2 locus results in the inheritance of isozymes of strikingly different catalytic properties. In European and Caucasian American populations, β1, which is encoded by ADH2(1) , is the most common form of the enzyme, while β2, encoded by the ADH2(2) allele, is found primarily in Orientals. The β2β2 enzyme encoded by ADH2(2) /ADH2(2) is approximately 20 times more active in ethanol oxidation than the β1β1 enzyme. In vivo the kinetic differences of ADH2 isozymes may influence individual risk for the effects of ethanol. This article will review the role of polymorphisms at the ADH2 loci in genetic predisposition to alcoholism and alcohol-related organ injury, especially alcoholic cirrhosis.

Genetic polymorphisms of tobacco- and alcohol-related metabolizing enzymes and human esophageal squamous cell carcinoma susceptibility

Many human cancers are caused by synthetic or natural chemical compounds in the environment. Esophageal squamous cell carcinoma has been reported to be epidemiologically associated with tobacco and alcohol consumption. We studied the association between genetic polymorphisms of tobacco- and alcohol-related metabolizing enzymes and esophageal squamous cell carcinoma susceptibility. We examined genetic polymorphisms of the CYPIA1, GSTM1, CYPIIE1, ADH2, and ALDH2 genes in 94 Japanese patients with esophageal squamous cell carcinoma and 70 unrelated healthy Japanese persons. There were no significant differences between healthy controls and patients with esophageal cancer in the polymorphisms of the CYPIA1, GSTM1, and CYPIIE1 genes. On the other hand, there were significant differences in the ADH2 and ALDH2 polymorphisms between healthy controls and esophageal cancer patients. The ADH2(1)/ADH2(1) and ALDH2(1)/ALDH2(2) genotypes were independently and significantly higher in esophageal cancer patients than in healthy controls. Furthermore, persons with the combined genotypes ADH2(1)/ADH2(1) and ALDH2(1)/ALDH2(2) were at extraordinarily high risk for esophageal squamous cell carcinoma, with an odds ratio of 17.9 (p < 0.001). Thus polymorphisms of alcohol-metabolizing enzymes, that is, ADH2 and ALDH2, may be useful for screening patients at high risk for esophageal cancer, which might facilitate clarification of esophageal tumorigenesis and prevention of esophageal cancer.

Alcohol dehydrogenase and aldehyde dehydrogenase genotypes and alcoholism among Taiwanese aborigines

Previous population association studies have indicated that certain alleles of alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) genes may reduce the risk of alcoholism in Oriental populations. In this report we determined the genotypes for three genes, ADH2, ADH3, and ALDH2 among subjects with alcohol dependence (n = 159) and ethnically matched normal controls (n = 149) for the four largest aboriginal groups (Atayal, Ami, Bunun, and Paiwan) in Taiwan. The ethnicity matching used in this study was feasible because there are still few intergroup marriages between these aboriginal groups. On a group level, the rare frequencies of ALDH2*2, the inactive allele of ALDH2, among these aborigines may account partially for their vulnerability to alcohol use disorders. On an individual level, however, the genotypes controlling alcohol metabolism did not account for intragroup differences in vulnerability to alcoholism except in the case of ADH2 for the Ami ethnic group.

Cytochromes P4502E1 and P4501A1 genotypes and susceptibility to cirrhosis or upper aerodigestive tract cancer in alcoholic caucasians

Genetic polymorphisms of various cytochromes P450 have recently been described and could be implicated in the individual susceptibility of alcoholics to ethanol-related diseases. Rsal and Dral polymorphisms of CYP2E1 and Mspl polymorphism of CYP1A1 were studied in 260 controls and 511 alcoholic patients, without any clinical symptoms (n = 202) or with various ethanol-related diseases (n = 309), such as liver cirrhosis (n = 110), esophageal cancer (n = 62), upper aerodigestive tract cancer (n = 96), and other miscellaneous diseases (n = 41). Frequencies of the mutated alleles were found to be 2.5% (Rsal), 7.9% (Dral), and 8.7% (Mspl) in controls; 4%, 14.1%, and 12% in alcoholics without clinical symptoms; and 3.1%, 12.5%, and 11.2% in alcoholics with ethanol-related diseases. The only significant difference was found in the Dral polymorphism, whose frequency was enhanced in alcoholics with (p < 0.05) or without ethanol-related diseases (p < 0.01) when compared with controls. No differences were found between alcoholics without clinical symptoms and alcoholics with cirrhosis, esophageal cancer, or upper aerodigestive tract cancer. However, in liver cirrhosis and in ethanol-related cancers, the rare Dral-C allele was three times less frequent in patients under the age of 45 than in older patients, suggesting a protective role for this allele. In conclusion, our data indicate that the aforementioned mutations do not play a critical role in the development of cirrhosis, esophageal cancer, or upper aerodigestive tract cancers in Caucasians.

Alcohol-metabolising genes and alcoholism among Taiwanese Han men: independent effect of ADH2, ADH3 and ALDH2

BACKGROUND

Previous population association studies have indicated that certain alleles of alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) may reduce the risk of alcoholism in Asian populations. The association of ALDH2 and ADH2 with the development of alcoholism was found to be independent of each other and has been replicated in different Asian populations, while the effect of ADH3 is less studied.

METHOD

We genotyped the alcohol metabolism genes among Han men with alcohol dependence (n = 46) and their ethnically matched normal controls (n = 63) in Taiwan. Multiple logistic regression was then applied to assess the contribution of ADH3 to alcoholism by controlling the effect of ALDH2 and ADH2.

RESULTS

The results of multivariate analyses demonstrated that the odds ratios for an increment of one allele of ADH2*1, ADH3*2 and ALDH2*1 in the development of alcoholism were 4.18, 3.82, and 6.89, respectively.

CONCLUSIONS

These findings clearly indicate that all three alcohol-metabolising genes contribute to susceptibility to alcoholism.