Stomach and duodenal alcohol and aldehyde dehydrogenase isozymes in Chinese

Alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) isozyme phenotypes were determined in surgical and endoscopic biopsies of the stomach and duodenum by agarose isoelectric focusing. gamma-ADH was found to be the predominant form in the mucosal layer whereas beta-ADH was predominant in the muscular layer. Low-Km ALDH1 and ALDH2 were found in the stomach and duodenum. High-Km ALDH3 isozymes occurred only in the stomach but not in the duodenum. The isozyme patterns of gastric mucosal ALDH2 and ALDH3 remained unchanged in the fundus, corpus, and antrum. The stomach ALDH3 isozymes exhibited a Km value for acetaldehyde of 75 mM, and an optimum for acetaldehyde oxidation at pH 8.5. Since the Km value was high, ALDH3 contributed very little, if any, to gastric ethanol metabolism. The activities of ALDH in the gastric mucosa deficient in ALDH2 were 60-70% of that of the ALDH2-active phenotypes. These results indicate that Chinese lacking ALDH2 activity may have a lower acetaldehyde oxidation rate in the stomach during alcohol consumption.     

Polymorphism of aldehyde dehydrogenase and alcohol sensitivity

The metabolism of acetaldehyde has received considerable attention in the past years owing to its acute and chronic toxic effects in humans. Aldehyde dehydrogenase (ALDH) catalyzes the oxidation of acetaldehyde in liver and other organs. Two major isozymes of hepatic ALDH (ALDH I or E2 and ALDH II or E1), which differ in their structural and functional properties, have been characterized in humans. The ALDH I with a low Km for acetaldehyde is predominantly of mitochondrial origin and ALDH II which has a relatively higher Km is of cytosolic origin. An inherited deficiency of ALDH I isozyme has been found among Japanese and Chinese which is primarily responsible for producing acute alcohol sensitivity symptoms (flushing response) after drinking mild doses of alcohol. Biochemical, immunochemical and molecular genetics data indicate a structural mutation in the ALDH I isozyme gene responsible for the loss in catalytic activity. Population genetic studies indicate a wide prevalence of this ALDH polymorphism among individuals of Mongoloid race. Flushing response to alcohol shows familial resemblances and preliminary family data from Japan, China and Korea hint to an autosomal codominant inheritance for ALDH I isozyme deficiency. The ALDH polymorphism is apparently responsible for the low incidence of alcoholism in Japanese, Chinese and Koreans. Alcohol-induced sensitivity due to ALDH isozyme deficiency may act as an inhibitory factor against excessive alcohol drinking thereby imparting a protection against alcoholism.     

Structural mutation in a major human aldehyde dehydrogenase gene results in loss of enzyme activity.

Most Caucasians have two major liver aldehyde dehydrogenase isozymes, ALDH1 and ALDH2, while approximately 50% of Orientals have only ALDH1 isozyme, missing the ALDH2 isozyme. A remarkably higher frequency of acute alcohol intoxication among Orientals than among Caucasians could be related to the absence of the ALDH2 isozyme, which has a low apparent Km for acetaldehyde. Examination of liver extracts by two-dimensional crossed immunoelectrophoresis revealed that an atypical Japanese liver, which had no ALDH2 isozyme, contained an enzymatically inactive but immunologically cross-reactive material corresponding to ALDH2, beside the active ALDH1 isozyme. Therefore, the absence of ALDH2 isozyme in atypical Orientals is not due to regulatory mutation, gene deletion, or nonsense mutation, but must be due to a structural mutation in a gene for the ALDH2 locus, resulting in synthesis of enzymatically inactive abnormal protein.     

Liver alcohol and aldehyde dehydrogenase isozymes in a Chinese population in Hong Kong

The distribution of alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) isozymes in the livers of a Chinese population in Hong Kong was examined. Among the 90 livers examined, 7 were typical ADH phenotype consisting the normal beta 1-type isozymes and 83 were atypical phenotype consisting the beta 2-type isozymes. Livers of 48 subjects were of deficient type in ALDH containing ALDH-II alone and 42 were of normal type with both ALDH-I and ALDH-II. When the combination of ADH and ALDH isozymes is considered, the Chinese population in Hong Kong falls into 4 subgroups. For each group, the rates of ethanol and acetaldehyde clearance have a distinct and characteristic potential which is directly related to its particular combination of isozymes.     

Liver alcohol dehydrogenase in Japanese: high population frequency of atypical form and its possible role in alcohol sensitivity.

Electrophoretic and quantitative studies reveal that 85% of Japanese carry an atypical liver alcohol dehydrogenase (ADH). The frequency of ADH polymorphism is identical with the reported frequency of alcohol sensitivity in the Japanese population. This identity in population frequencies points to a causative relationship between the two phenomena and suggests that alcohol sensitivity might be due to the increased acetaldehyde formation in individuals carrying the atypical ADH gene.     

Genotypes of alcohol-metabolizing enzymes in Japanese with alcohol liver diseases: a strong association of the usual Caucasian-type aldehyde dehydrogenase gene (ALDH1(2)) with the disease

Genetic polymorphisms of two major alcohol-metabolizing enzymes-i.e., one of the class I alcohol dehydrogenase isozymes (ADH2) and the mitochondrial aldehyde dehydrogenase (ALDH2)-exist in Japanese and other Orientals but not in Caucasians. Liver ADH activity of about 90% of Orientals is much higher than that of most Caucasians, while approximately 50% of Orientals lack the ALDH2 activity. The genetic differences have been implicated in the high incidence of alcohol sensitivity observed in Orientals. We determined, by means of hybridization of genomic DNA samples with allele-specific synthetic oligonucleotide probes, genotypes of the ADH2 and the ALDH2 loci of Japanese with alcoholic liver diseases and of control subjects. No significant difference between the patient and control groups was found in the ADH2 genotypes. A remarkable genetic difference between the two groups was found in the ALDH2 locus. The frequency of the typical (Caucasian-type) ALDH1(2) gene was found to be .65 and that of the atypical (Oriental type) ALDH2(2) gene was .35 in the controls, while these were .93 and .07, respectively, in the patients. Thus, most (20 of 23) of the Japanese patients were homozygous Caucasian type ALDH1(2)/ALDH1(2), only three were heterozygous ALDH1(2)/ALDH2(2), and none of the patients were homozygous Oriental type ALDH2(2)/ALDH2(2). The results indicate that Japanese with the atypical ALDH2(2) allele are at a much lower risk in developing the alcoholic liver diseases than are those with homozygous, usual (Caucasian-type) ALDH1(2)/ALDH1(2), presumably owing to their sensitivity to alcohol intoxication.     

Effects of alcohol consumption on mitochondrial aldehyde dehydrogenase isoenzymes in rat liver

The effects of long-term and short-term exposure of rats to ethanol on aldehyde dehydrogenase (ALDH) activity in the liver mitochondria were investigated. The specific activities of mitochondrial high Km ALDH and low Km ALDH after the prolonged administration of ethanol were both increased to levels about 2.5 times that of the control group. In contrast, high Km and low Km ALDH showed maximum activity 12 h after administration of a single large dose of ethanol, increasing 21 and 4.4 times, respectively, over the level in the control group. When ethanol was administered for a long time, the two ALDH isoenzyme levels showed approximately the same increase, while the high Km ALDH level was more significantly increased than the low Km ALDH level after a single large dose. These results suggest that the high Km ALDH level of the outer membrane was increased as a result of a transient increase in the level of acetaldehyde around the liver mitochondria after a single large dose of ethanol, and that high Km ALDH plays an important role in acetaldehyde metabolism. However, when ethanol was administered for a long time, the mitochondria were exposed to low concentrations of acetaldehyde over a long time, leading to an increase in levels of low and high Km ALDH in the matrix.     

Subcellular localization and capacity of beta-oxidation and aldehyde dehydrogenase in porcine liver

Porcine hepatocyte organelles were separated by isopycnic sucrose gradient centrifugation from livers of 6-month-old Yorkshire pigs. The presence of a peroxisomal palmitoyl-CoA oxidizing system and a peroxisomal NAD:aldehyde dehydrogenase (ALDH) with high Km for acetaldehyde was demonstrated. Peroxisomal palmitate oxidizing capacity was found to be equal to that of the surviving mitochondria. The high Km isozyme of ALDH was mainly located in the mitochondria (54%), with a significant portion in the peroxisome (32%). Remaining activity is distributed among the microsomes (8.3%) and cytosol (4.6%). The low Km isozyme was confined almost exclusively to the mitochondria. ALDH may exist in the peroxisome as a detoxification mechanism and contribute to shorter half-lives of reactive aldehydes in the cell. Species differences are discussed.     

The bifunctional Entamoeba histolytica alcohol dehydrogenase 2 (EhADH2) protein is necessary for amebic growth and survival and requires an intact C-terminal domain for both alcohol dahydrogenase and acetaldehyde dehydrogenase activity

The intestinal protozoan pathogen Entamoeba histolytica lacks mitochondria and derives energy from the fermentation of glucose to ethanol with pyruvate, acetyl enzyme Co-A, and acetaldehyde as intermediates. A key enzyme in this pathway may be the 97-kDa bifunctional E. histolytica alcohol dehydrogenase 2 (EhADH2), which possesses both alcohol dehydrogenase (ADH) and acetaldehyde dehydrogenase activity (ALDH). EhADH2 appears to be a fusion protein, with separate N-terminal ALDH and C-terminal ADH domains. Here, we demonstrate that EhADH2 expression is required for E. histolytica growth and survival. We find that a mutant EhADH2 enzyme containing the C-terminal 453 amino acids of EhADH2 has ADH activity but lacks ALDH activity. However, a mutant consisting of the N-terminal half of EhADH2 possessed no ADH or ALDH activity. Alteration of a single histidine to arginine in the putative active site of the ADH domain eliminates both ADH and ALDH activity, and this mutant EhADH2 can serve as a dominant negative, eliminating both ADH and ALDH activity when co-expressed with wild-type EhADH2 in Escherichia coli. These data indicate that EhADH2 enzyme is required for E. histolytica growth and survival and that the C-terminal ADH domain of the enzyme functions as a separate entity. However, ALDH activity requires residues in both the N- and C-terminal halves of the molecule.     

The metabolism of ethanol-derived acetaldehyde by alcohol dehydrogenase (EC 1.1.1.1) and aldehyde dehydrogenase (EC 1.2.1.3) in Drosophila melanogaster larvae.

Both aldehyde dehydrogenase (ALDH, EC 1.2.1.3) and the aldehyde dehydrogenase activity of alcohol dehydrogenase (ADH, EC 1.1.1.1) were found to coexist in Drosophila melanogaster larvae. The enzymes, however, showed different inhibition patterns with respect to pyrazole, cyanamide and disulphiram. ALDH-1 and ALDH-2 isoenzymes were detected in larvae by electrophoretic methods. Nonetheless, in tracer studies in vivo, more than 75% of the acetaldehyde converted to acetate by the ADH ethanol-degrading pathway appeared to be also catalysed by the ADH enzyme. The larval fat body probably was the major site of this pathway.