By using this human "knockout model" for deficient acetaldehyde removal, we found that in addition to oral microflora, acetaldehyde in saliva may also originate from the oxidation of ethanol in the parotid gland. When combined with earlier epidemiological data, these results offer a strong evidence for the local carcinogenic action of acetaldehyde in humans.

A single dose of 4-MP before ethanol ingestion reduces ethanol elimination rate, the flushing reaction, and both blood and salivary acetaldehyde levels in ALDH2-deficient subjects but not in subjects with the normal ALDH2 genotype. These results suggest that the role of oral mucosal and glandular ADHs in salivary acetaldehyde production is minimal and support earlier findings indicating that salivary acetaldehyde production is mainly of microbial origin in subjects with normal ALDH2.

This article represents the proceedings of a symposium at the 2000 ISBRA Meeting in Yokohama, Japan. The chairs were Helmut K. Seitz and Shohei Matsuzaki. The presentations were (1) Alcohol dehydrogenase-2 and aldehyde dehydrogenase-2 genotype and cancer risk for upper aerodigestive tract in Japanese alcoholics, by Akira Yokoyama; (2) The role of acetaldehyde in alcohol-associated carcinogenesis, by Nils Homann; (3) High salivary acetaldehyde levels after a moderate dose of alcohol in ALDH2-deficient subjects, by Satu Väkeväinen; (4) Alcohol and vitamin A interactions, by Xian Dong Wang; and (5) Alcohol and colorectal cancer, by Helmut K. Seitz.

This study demonstrated that certain bacterial species or groups that originate from the oral cavity are responsible for the bulk of acetaldehyde production in the hypochlorhydric stomach. These findings provide new information with the respect to the local production of carcinogenic acetaldehyde in the upper digestive tract of achlorhydric human subjects.