Metabolism in the F344 Rat of 4-(N-Methyl-N-nitrosamino-1-(3-pyridyl)-1-butanone, a Tobacco-specific Carcinogen

The metabolism of the tobacco-specific carcinogen, 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK), was studied in the F344 rat, in which it induces tumors of the nasal cavity, liver, and lung. When NNK was incubated with rat liver microsomes and a reduced nicotinamide adenine dinucleotide phosphate-generating system, metabolites resulting from a-hydroxylation, carbonyl reduction, and N-oxidation were isolated. a-Hydroxylation at the methylene carbon gave 4-oxo-4-(3-pyridyl)butanal, whereas a-hydroxylation at the methyl carbon gave myosmine and 4-hydroxyl-1-(3-pyridyl)butan-1-one. The formation of these products involved the intermediacy of electrophilic diazohydroxides or carbonium ions which may be proximate or ultimate carcinogens of NNK. Carbonyl reduction gave 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)butan-1-ol and N-oxidation yielded 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl-N-oxide)-1-butanone. When rats were gavaged with NNK, the microsomal products of a-hydroxylation were not detected in the 48-hr urine. Compounds which presumably resulted from further oxidation or reduction of these products, 4-oxo-4-(3-pyridyObutyric acid, 4-hydroxy-4-(3-pyridyl)butyric acid, and 4-hydroxy-1-(3-pyridyl)butan-1-ol, were isolated. 4-(N-Methyl-N-nitrosamino)-1-(3-pyridyl)butan-1-ol and 4-(N-methyl-N-ni-trosamino)-1-(3-pyridyl-N-oxide)-1-butanone were also urinary metabolites.