Direct determination of usual (Caucasian-type) and atypical (Oriental-type) alleles of the class I human alcohol dehydrogenase-2 locus

Genetic polymorphisms in ethanol metabolism: issues and goals for physiologically based pharmacokinetic modeling

Chronic exposure to excessive ethanol consumption has adverse effects on virtually all organs and tissues in the body, including but not limited to the liver, pancreas, reproductive organs, central nervous system, and the fetus. Exposure to ethanol can also enhance the toxicity of other chemicals. Not all persons exposed to the same amount of ethanol experience the same degree of adverse effects. For example, only 12% to 13% of alcohol abusers develop cirrhosis. Possible factors which may alter susceptibility include age, sex, nutritional status, health status (i.e., smokers) and race. Some of these factors affect susceptibility because they alter ethanol metabolism, which occurs primarily in the liver by alcohol dehydrogenase (ADH). Genetic polymorphisms for ADH partially account for the observed differences in ethanol elimination rates among various populations but the relative contribution to susceptibility is not completely understood. Incorporation of the kinetic parameters associated with ADH polymorphisms into a physiologically based pharmacokinetic (PBPK) model for ethanol will aid in assessing the relative contribution to susceptibility. The specific information required to develop this model includes Km and Kcat values for each ADH isoform and the amount of each isoform present in the liver. Blood ethanol concentrations (BEC) from various populations with known ADH phenotypes are also necessary to validate the model. The impact of inclusion of these data on PBPK model predictions was examined using available information from adult white and African American males.

Contribution of two missense mutations (G71R and Y486D) of the bilirubin UDP glycosyltransferase (UGT1A1) gene to phenotypes of Gilbert's syndrome and Crigler-Najjar syndrome type II

In our mutation analyses of bilirubin UDP glycosyltransferase (UGT1A1) gene, we encountered six patients with Crigler-Najjar syndrome type II who were double homozygotes for G71R and Y486D, a patient with Gilbert's syndrome who was a single homozygote for G71R and six patients with Gilbert's syndrome who were single heterozygote for G71R. To clarify the role of each mutation in the occurrence of the two syndromes, we made four mutant expression models. Relative UGT1A1 activity of a single homozygous model of G71R was 32.2+/-1.6% of normal, that of a single homozygous model of Y486D was 7.6+/-0.5%, that of a double homozygous model of G71R and Y486D was 6.2+/-1.6% and that of a heterozygous model of G71R was 60.2+/-3.5%. The decreased activities of the single homozygous model of G71R and the double homozygous model were at an appropriate level to be diagnosed as Gilbert's syndrome and CN-II, respectively. The activity of a single heterozygous model of G71R was somewhat high to develop to the phenotype of Gilbert's syndrome, suggesting the presence of additional factors for the etiology of Gilbert's syndrome.

The contribution of polymorphism in the alcohol dehydrogenase beta subunit to alcohol sensitivity in a Japanese population

In humans, ingested alcohol is mainly metabolized by the combination of class I alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH). In Orientals, there are highly frequent polymorphisms both in the class I ADH beta subunit (ADH2) and in the low Km ALDH (ALDH2). We characterized the three genotypes of ALDH2 in a Japanese population. In the present study, we evaluated the effects of the ADH2 polymorphism in the same population (424 males and 100 females) controlling for the effects of the ALDH2 polymorphism. In the ALDH2(1)/ALDH2(2) group, the frequency of facial flushing with one glass of beer was significantly higher in the ADH2(1)/ADH2(2) and ADH2(2)/ADH2(2) genotype than in the ADH2(1)/ADH2(1) genotype. Likewise, the proportion of persons with positive results for ethanol-induced cutaneous erythema differed significantly depending on the ADH2 genotype in both the ALDH2(1)/ALDH2(1) and ALDH2(1)/ALDH2(2) genotypes. However, drinking habits were not significantly associated with the ADH2 genotype, suggesting that the ADH2 genotype influences the metabolism of ethanol only in the peripheral tissues.

Association of a restriction fragment length polymorphism in the alcohol dehydrogenase 2 gene with Japanese alcoholic liver cirrhosis

BACKGROUND/AIMS

The association of ADH2 polymorphisms with alcoholic liver cirrhosis has not been clearly demonstrated.

METHODS

We investigated the association of two alleles in the ADH2 gene marked by restriction fragment length polymorphisms in patients with alcoholic liver cirrhosis. The ADH2 restriction fragment polymorphisms with Mae III were determined using the polymerase chain reaction on lymphocytes from 76 male Japanese alcoholics (non-cirrhotic patients; 34 cases, cirrhotic patients; 42 cases) and 60 healthy male subjects.

RESULTS

The frequency of the ADH2(1)/ADH2(1) genotype was significantly higher in the alcoholics than in the healthy subjects p < 0.001). In the alcoholics, the genotype ADH2(2)/ADH2(2) was significantly more prevalent in the cirrhotic group than in the non-cirrhotic group (p < 0.05).

CONCLUSIONS

These results suggest that the Mae III polymorphisms of the ADH2 gene may be associated not only with susceptibility to alcoholic liver cirrhosis, but also with the development of alcoholism in Japanese patients.

Polymorphisms in alcohol metabolizing enzyme genes and alcoholic cirrhosis in Japanese patients: a multivariate analysis

Alcohol dehydrogenase (ADH), aldehyde dehydrogenase (ALDH), and P450IIE1 are the primary enzymes that catalyze the conversion of ethanol to acetaldehyde and then to acetate. Genetic polymorphisms have been reported in ADH2, ADH3, ALDH2, and the 5'-flanking region of P450IIEI. In this study, we used multivariate analysis to determine which genetic polymorphisms in alcohol metabolizing enzymes were independently associated with the development of alcoholic cirrhosis. Thirty-four noncirrhotic alcoholic patients, including 27 with fatty liver and 7 with nonspecific changes, and 46 patients with alcoholic liver cirrhosis were studied. Restriction fragment length polymorphisms (RFLPs) in the ADH2 and P450IIE1 genes were detected by digestion of polymerase chain reaction (PCR)-amplified DNA with MaeIII and RsaI, respectively. In the ALDH2 gene, RFLPs were detected by differences in the MboII site after PCR amplification. By multivariate analysis of four significant factors including total alcohol intake, ADH, ALDH, and P450IIE1 using the multiple logistic regression model, genotype ADH2(2)/ADH2(2) (P = .029) and genotype c1/c1 of P450IIE1 (P = .013) were found to be independently associated with alcoholic cirrhosis. The odds ratios for ADH2(2)/ADH2(2) genotype and the type A genotype of P450IIE1 (c1/c1) were 4.600 and 4.006, respectively. These results suggest that ADH2 and P450IIE1 gene polymorphisms may be independently associated with the development of alcoholic liver cirrhosis in Japan.

Alcohol-metabolizing enzyme polymorphisms and alcoholism in Japan

The liver enzymes, alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH), which are responsible for the oxidative metabolism of ethanol, are polymorphic in humans. Cytochrome P450IIE1, an ethanol-inducible isozyme of liver microsomal P450, is also important in ethanol metabolism. Genetic polymorphisms in the 5'-flanking region of the human cytochrome P450IIE1 gene have recently been reported. We hypothesized that the polymorphisms of ADH, ALDH, and P450IIE1 modify the susceptibility to development of alcoholism. We determined the genotypes of the ADH2, ALDH2, and P450IIE1 loci of 96 Japanese alcoholics and 60 healthy male subjects, using leukocyte DNA by the restriction fragment-length polymorphism by polymerase chain reaction. The alcoholics had significantly higher frequencies of the ADH2(1) and ALDH2(1) alleles than did the healthy subjects. No significant difference in the frequency of the P450IIE1 genotype was observed between the alcoholics and the healthy subjects. In conclusion, genetic polymorphisms of the ADH and ALDH genes, but not of the P450IIE1 gene, influence the risk of developing alcoholism in Japanese.

Effect of acute ethanol drinking on alcohol metabolism in subjects with different ADH and ALDH genotypes

The effect of different amounts of orally ingested ethanol on plasma alcohol dehydrogenase (ADH) and erythrocyte aldehyde dehydrogenase (ALDH), as well as on the blood ethanol and acetaldehyde levels, was examined in healthy nonalcoholic subjects. The genotypes at ADH2 and ALDH2 locus were identified in enzymatically amplified blood DNA by hybridization with allele-specific oligonucleotides. While the Japanese subject was found to be genotypically heterozygous for both ADH2 and ALDH2, the Caucasian subjects were genotypically homozygous normal for these alleles. A faster ethanol elimination associated with a higher blood acetaldehyde level was observed in the Japanese subject as compared to Caucasian subjects. However, no significant change in ADH and ALDH enzyme activities was detected as the result of acute ethanol intake.

[Genetically-induced variability of alcohol metabolism and its effect on drinking behavior and predisposition to alcoholism]

Alcoholism is one of the most challenging current health problems in the Western countries with far-reaching medical, social, and economic consequences. There are a series of factors that interact in predisposing or protecting an individual against alcoholism and alcohol-related disorders. This article surveys the state of our knowledge concerning the biochemical and genetic variations in alcohol metabolism and their implications in alcohol sensitivity, alcohol drinking habits, and alcoholism in different racial/ethnic groups. The major pathway for the degradation of ethanol is its oxidation to hydrogen and acetaldehyde--to which many of the toxic effects of ethanol can be attributed. Variations in alcohol and acetaldehyde metabolism via genetically determined polymorphisms in alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) seem to play an important role in individual and racial differences in acute and chronic reactions to alcohol, alcohol drinking habits, as well as vulnerability to organ damage after chronic alcohol abuse. Alcohol sensitivity and associated discomfort symptoms accompanying alcohol ingestion may be determinental for the significantly low incidence of alcoholism among the Japanese, Chinese and other Orientals of Mongoloid origin. An abnormal ALDH isozyme has been found to be widely prevalent among individuals of the Mongoloid race and is mainly responsible for the acute sensitivity to alcohol commonly observed in this race. Persons sensitive to alcohol by virtue of their genetically controlled ALDH isozyme deficiency may be discouraged from drinking large amounts of alcohol in their daily life due to the initial adverse reaction experienced after drinking alcohol. Indeed, a significantly low incidence of the mitochondrial ALDH isozyme deficiency has been observed in alcoholics as compared to psychiatric patients, drug dependents and healthy controls in Japan. How far any variation in ADH and/or ALDH activity among individuals of Caucasian origin will have similar effects has yet to be studied.

Genotype of alcohol dehydrogenase and aldehyde dehydrogenase loci in Japanese alcohol flushers and nonflushers

A much higher incidence of alcohol flushing among Orientals in comparison to Caucasians, i.e., greater than 50% vs 5%-10%, has been attributed to racial differences in alcohol-metabolizing enzymes. A large majority of Orientals are "atypical" in alcohol dehydrogenase-2 locus (ADH2), and their livers exhibit significantly higher ADH activity than the livers of most Caucasians. Approximately 50% of Orientals lack the mitochondrial aldehyde dehydrogenase (ALDH2) activity, and elimination of acetaldehyde might be disturbed. We determined by means of hybridization of genomic DNA samples with allele specific oligonucleotide probes, genotypes of the ADH2 and ALDH2 loci in Japanese alcohol flushers and nonflushers. We found that all individuals with homozygous atypical ALDH2(2)/ALDH2(2) and most of those with heterozygous atypical ALDH1(2)/ALDH2(2) were alcohol flushers, while all subjects with homozygous usual ALDH1(2)/ALDH1(2) were nonflushers. Frequency of the atypical ADH2(2) was found to be higher in alcohol flushers than in nonflushers, but the statistical significance was not established in the sample size examined.