The Activity of Class I, II, III, and IV Alcohol Dehydrogenase Isoenzymes and Aldehyde Dehydrogenase in Colorectal Cancer

Chronic ethanol consumption is associated with an increased risk for cancer of the colorectum. The highly toxic and carcinogenic compound is acetaldehyde, the product of ethanol metabolism. Ethanol is metabolized to acetaldehyde by alcohol dehydrogenase (ADH) in colorectal mucosa and bacteria. The enzyme responsible for oxidation of acetaldehyde is aldehyde dehydrogenase. The aim of this study was to compare ADH isoenzymes and ALDH activity in colorectal cancer with the activity in normal colonic mucosa. Total ADH activity was measured by a photometric method with p-nitrosodimethylaniline (NDMA) as substrate, and ALDH activity by a fluorometric method with 6-methoxy-2-naphthaldehyde as a substrate. For measurement of the activity of class I and II isoenzymes we employed fluorometric methods, with class-specific fluorogenic substrates. The activity of class III ADH was measured by the photometric method with n-octanol as substrate, and class IV with m-nitrobenzaldehyde as substrate. Samples were taken surgically during routine operations of colorectal carcinomas from 32 patients. The activities of total ADH and, the most important in colon mucosa, class I ADH were significantly higher in cancer than in healthy tissues. The other tested classes of ADH had a tendency to higher-level activity in cancer cells than in healthy mucosa. ALDH activity was not significantly lower in the cancer cells. The activities of all tested enzymes and isoenzymes were not significantly higher in drinkers than in nondrinkers both in colorectal cancer and in normal mucosa. The differences in activities of total ADH and class I isoenzyme between cancer tissues and normal colon mucosa might be a factor for metabolic changes and disturbances in low-mature cancer cells and, additionally, might be a reason for the higher level of acetaldehyde, which can intensify carcinogenesis.