Biotransformation of the tobacco-specific carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in freshly isolated human lung cells

Metabolism of the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-p yridyl)-1-butanone (NNK) was characterized in human lung cells isolated fro m peripheral lung specimens obtained from 12 subjects during clinically ind icated lobectomy, NNK biotransformation was assessed in preparations of iso lated unseparated cells (cell digest), as well as in preparations enriched in alveolar type II cells, and alveolar macrophages. Metabolite formation w as expressed as a percentage of the total recovered radioactivity from [5-H -3]NNK and its metabolites per 10(6) cells per 24 h, 4-(Methylnitrosamino)- 1-(3-pyridyl)-1-butanol (NNAL) was the major metabolite formed in all lung cell preparations examined, and its formation ranged from 0.50 to 13%/10(6) cells/24 h, Formation of alpha-carbon hydroxylation end-point metabolites (bioactivation) and pyridine N-oxidation metabolites (detoxification), rang ed from non-detectable to 0.60% and from non-detectable to 1.5%/10(6) cells /24 h, respectively, reflecting a large degree of intercellular and inter-i ndividual variability in NNK metabolism. Formation of the alpha-hydroxylati on end-point metabolite 4-hydroxy-1-(3-pyridyl)-1-butanol (diol) was consis tently higher in alveolar type II cells than in cell digest or alveolar mac rophages (0.0146 +/- 0.0152, 0.0027 +/- 0.0037 and 0.0047 +/- 0.0063%/10(6) cells/24 h, respectively; n = 12; P < 0.05), SKF-525A was used to examine cytochrome P450 contributions to the biotransformation of NNK, SKF-525A inh ibited keto reduction of NNK to NNAL by 85, 86 and 74% in cell digest, type II cells, and macrophages, respectively (means of 11 subjects, P < 0.05), Type II cell incubates treated with SKF-525A formed significantly lower amo unts of total alpha-hydroxylation metabolites compared with type II cells w ithout SKF-525A (0.0776 +/- 0.0841 versus 0.1694 +/- 0.2148%/10(6) cells/24 h, respectively; n = 11; P < 0.05), The results of this first study examin ing NNK biotransformation in freshly isolated human lung cells indicate tha t NNK metabolism is subject to a large degree of inter-individual and inter cellular variability, and suggest a role for P450s in human lung cell NNK m etabolism. Both alveolar type II cells and alveolar macrophages may be pote ntial target cells for NNK toxicity based on their alpha-carbon hydroxylati on capabilities. In addition, carbonyl reduction of NNK to NNAL is SKF-525A sensitive in human lung cells.