ROLE OF CATALASE IN IN-VITRO ACETALDEHYDE FORMATION BY HUMAN COLONIC CONTENTS

Ingested ethanol is transported to the colon via blood circulation, an d intracolonic ethanol levels are equal to those of the blood ethanol levels. In the large intestine, ethanol is oxidized by colonic bacteri a, and this can lead to extraordinarily high acetaldehyde levels that might be responsible, in part, for ethanol-associated carcinogenicity and gastrointestinal symptoms. It is believed that bacterial acetaldeh yde formation is mediated via microbial alcohol dehydrogenases (ADHs). However, almost all cytochrome-containing aerobic and facultative ana erobic bacteria possess catalase activity, and catalase can, in the pr esence of hydrogen peroxide (H2O2), use several alcohols (e.g., ethano l) as substrates and convert them to their corresponding aldehydes. In this study we demonstrate acetaldehyde production from ethanol in vit ro by colonic contents in a reaction catalyzed by both bacterial ADH a nd catalase. The amount of acetaldehyde produced by the human colonic contents was proportional to the ethanol concentration, the amount of colonic contents, and the length of incubation time, even in the absen ce of added nicotinamide adenine dinucleotide or H2O2. The catalase in hibitors sodium azide and 3-amino-1,2,4-triazole (3-AT) markedly reduc ed the amount of acetaldehyde produced from 22 mM ethanol in a concent ration dependent manner compared with the control samples (0.1 mM sodi um azide to 73% and 10 mM 3-AT to 67% of control). H2O2 generating sys tem [beta-D(+)-glucose + glucose oxidase] and nicotinamide adenine din ucleotide induced acetaldehyde formation up to 6- and 5-fold, respecti vely, and together these increased acetaldehyde formation up to Ii-fol d. The mean supernatant catalase activity was 0.53 +/- 0.1 mu mol/min/ mg protein after the addition of 10 mM H2O2, and there was a significa nt (p < 0.05) correlation between catalase activity and acetaldehyde p roduction after the addition of the hydrogen peroxide generating syste m. Our results demonstrate that colonic contents possess catalase acti vity, which probably is of bacterial origin, and indicate that in addi tion to ADH, part of the acetaldehyde produced in the large intestine during ethanol metabolism can be catalase dependent.