METABOLISM AND MACROMOLECULAR INTERACTION OF THE TOBACCO-SPECIFIC CARCINOGEN 4-(METHYLNITROSAMINO)-1-(3-PYRIDYL)-1-BUTANONE IN CULTURED EXPLANTS AND EPITHELIAL-CELLS OF HUMAN BUCCAL MUCOSA

Metabolism and macromolecular interaction of the tobacco-specific carc inogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) were studi ed in human buccal mucosa in vitro. Microautoradiographic analysis of [5-H-3]NNK-exposed explant cultures demonstrated a uniform distributio n of bound radioactivity in the mucosal epithelium, without significan t binding in the underlying connective tissue. The metabolism of [5-H- 3]NNK at concentrations of both 6 and 100 muM resulted in seven identi fied metabolites in both explant and epithelial cell cultures. Formati on of 4-(methylnitros-amino)-1-(3-pyridyl)butan-1-ol by carbonyl reduc tion of NNK accounted for almost 95% of the total metabolism, whereas the proportions of other metabolites obtained by alpha-carbon hydroxyl ation and pyridine N-oxidation reactions varied from undetectable leve ls to approximately 2% in both experimental systems. A positive correl ation between concentration and the metabolic route associated with th e formation of DNA methylating intermediates (alpha-hydroxylation at t he N-methylene carbon) was found, i.e. when the concentration of NNK w as raised from 6 to 100 muM, keto-acid formation which in part reflect s DNA methylation was increased preferentially over ketoalcohol produc tion, an index of DNA pyridyloxobutylation. Both the total rate of NNK metabolism and the amount of protein adducts were higher in cells fro m primary cultures up to the third passage than in explants cultured f or 1 day. Between 10(-9) to 10(-4) M, neither NNK nor its precursor al kaloid nicotine affected the colony forming efficiency of normal and t umorous buccal epithelial cells, although at 10(-3) M each agent inhib ited this function. Taken together, the results demonstrate the capabi lity of human buccal mucosal epithelium to metabolize NNK by three maj or pathways, including those involved in the formation of adducts with cellular macromolecules.