Ethnic Differences in Gastric α‐Alcohol Dehydrogenase Activity and Ethanol First‐Pass Metabolism

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Abstract
We assessed whether the low α-alcohol dehydrogenase (ADH) activity in Japanese (compared with Caucasians) affects the first-pass metabolism of ethanol. ADH isozyme activities were determined in endoscopic biopsies of the gastric corpus from 24 Japanese and 41 Caucasian men by starch gel electrophoresis and by comparing the reduction of m-nitrobenzaldehyde (a preferred substrate of α-ADH) with that of acetaldehyde (a preferred substrate of γ-ADH) and the glutathione-dependent formaldehyde oxidation (a specific reaction of χ-ADH). Alcohol pharmacokinetics was compared in 10 Japanese and 10 Caucasians after administration of ethanol (300 mg/kg of body weight) intravenously or orally, using 5 and 40% oral solutions. Japanese exhibited lower α-ADH activity than Caucasians, with no difference in the other gastric isozymes. With 5% ethanol, first-pass metabolism was strikingly lower in Japanese than in Caucasions. Blood alcohol levels were similar because of the high elimination rate in Japanese due to the hepatic β2-ADH variant. With 40% ethanol, the first-pass metabolism increased in both groups to comparable levels, suggesting an additional contribution by χ-ADH at high ethanol concentrations. These results indicate that α-ADH activity contributes significantly to gastric ethanol oxidation and its lower activity in Japanese is associated with lesser first-pass metabolism.