The role of gastrointestinal factors in alcohol metabolism

Although the liver is the major organ responsible for ethanol metabolism, such metabolism also occurs in the gastrointestinal (GI) tract. However, compared to the liver, GI metabolism of ethanol is quantitatively much lower. Various enzyme systems have been characterized in GI mucosal cells including various isozymes of alcohol dehydrogenase (ADH), cytochrome P450 2E1 (CYP 2E1) and catalase. Gastric ADH activity is one factor by which first pass metabolism (FPM) is influenced and its activity is modulated by genetics, gender, age, drugs and gastric morphology. Another important factor in FPM of ethanol is the speed of gastric emptying. In addition to mucosal ethanol metabolism, ethanol can also be oxidized by many bacterial species in the upper GI tract including oropharynx and stomach as well as in the large intestine. GI metabolism of ethanol may influence systemic bioavailability of ethanol and may lead to local toxicity most likely mediated by acetaldehyde. Such toxicity could be of importance in ethanol-associated carcinogenesis.