EFFECTS OF PHENOBARBITAL AND 3-METHYLCHOLANTHRENE INDUCTION ON THE FORMATION OF 3 GLUCURONIDE METABOLITES OF 4-(METHYLNITROSAMINO)-1-(3-PYRIDYL)-1-BUTANONE, NNK

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a tobacco spec ific carcinogen believed to be a causative agent for human lung cancer . To exert its carcinogenic potential, NNK must be metabolically activ ated, by alpha-hydroxylation, at either the methyl or methylene carbon s adjacent to the N-nitroso group. We recently reported the presence o f a glucuronide conjugate of hydroxymethylnitrosamino)-1-(3-pyridyl)-1 -butanone (alpha-hydroxymethylNNK-Gluc) in the urine of Phenobarbital (PB) treated rats, and in the media of PB induced hepatocytes incubate d with NNK. PB induces the alpha-hydroxylation of NNK, which generates the aglycon, as well as several UDP-glucuronosyl transferases. In the study presented here, we compared the metabolism of NNK to alpha-hydr oxymethylNNK-Gluc by PB induced, 3-methylcholanthrene (3-MG) induced a nd control rat hepatocytes. Media was analyzed for the products of alp ha-hydroxylation, N-oxidation and glucuronidation by radioflow HPLC. P B induced both N-oxidation and alpha-hydroxylation of NNK. 3-MG did no t induce N-oxidation but induced alpha-hydroxylation more than 10-fold . alpha-HydroxymethylNNK-Gluc was not detected (< 0.05% total metaboli tes) when control hepatocytes were incubated with 1 to 100 mu M NNK. W hen 3-MG and PB induced hepatocytes were incubated with 1-100 mu M NNK alpha-hydroxymethylNNK-Gluc, expressed as the average percent of meta bolites, accounted for 0.725+/-0.27 and 1.35+/-0.24% (+/-S.D.) of the NNK metabolites, respectively. The percent of NNK metabolized to alpha -hydroxymethylNNK-Gluc is small. But this glucuronide is potentially i mportant in NNK carcinogenesis, since its formation results in the dir ect conjugation of an active metabolite responsible for DNA adduct for mation. When PB induced rats were injected with NNK the level of NNK h emoglobin adducts, which can serve as surrogates for DNA adducts, decr eased 50% compared to control rats administered NNK. Hepatic microsoma l metabolism increased 2-fold and urinary alpha-hydroxymethylNNK-Gluc increased more than 10-fold in PB treated rats. One explanation for th e decrease in NNK hemoglobin adducts may be a PB induced increase in t he glucuronidation of alpha-hydroxymethylNNK, the metabolite responsib le for adduct formation. (C) 1997 Elsevier Science Ireland Ltd.