In vitro metabolism of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone by lung cells isolated from Syrian golden hamster

Effect of nicotine, cotinine and phenethyl isothiocyanate on 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) metabolism in the Syrian golden hamster

The effect of nicotine, cotinine and phenethyl isothiocyanate (PEITC) on metabolism of the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) was studied in the Syrian golden hamster. Urinary metabolite profiles were determined in 24 h urine after a single subcutaneous (s.c.) administration of [5-(3)H]NNK (80 nmol/kg, s.c.). Co-administration of either a 500-fold higher dose of nicotine (40 micromol/kg, s.c.) or a 5000-fold higher dose of cotinine (400 micromol/kg, s.c.) significantly (P<0.001) reduced metabolic activation of NNK by alpha-hydroxylation to 85 and 71% of control, respectively. Co-administration of a 300-fold higher dose of PEITC (1 micromol/g diet) slightly reduced alpha-hydroxylation of NNK (94% of control). Metabolism of NNK by reduction to 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) was increased by nicotine (155%), and significantly increased by cotinine (670%, P<0.001) and PEITC (219%, P<0.01). Detoxification of NNAL by glucuronidation was also increased by all three test agents. Detoxification of NNK and NNAL by N-oxidation was marginally increased by nicotine, reduced by PEITC, and significantly reduced by cotinine. The urinary metabolite profiles suggest that nicotine, which occurs in concentrations up to 30000-fold higher than NNK in mainstream cigarette smoke, and cotinine, its proximal metabolite, may have a significant protective effect against in vivo metabolic activation of NNK.

Stress, hormonal changes, alcohol, food constituents and drugs: factors that advance the incidence of tobacco smoke-related cancer?

The genotoxicity of the most potent carcinogen in cigarette smoke [4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)] is dependent on the relationship between its activation by cytochrome P450 enzymes and its detoxification by carbonyl reduction to NNK alcohol (NNAL) followed by glucuronidation. Recently, '11 beta-hydroxysteroid dehydrogenase' (11 beta-HSD 1) was identified to be responsible for NNK carbonyl reduction. It is now speculated that differences in tissue expression of 11 beta-HSD 1, as well as genetic polymorphisms, may have profound influences on the organospecificity and potency of NNK-induced cancerogenesis. Moreover, endogenous and exogenous substrates or inhibitors of 11 beta-HSD 1 may shift the NNK/NNAL equilibrium and favour NNK toxification in a variety of physiological and therapeutic situations. These issues are discussed here by Edmund Maser, who also describes how recent observations could provide the experimental base for epidemiological or clinical studies, which focus on polymorphisms in 11 beta-HSD 1 enzyme expression, as well as on implications of exposure to 11 beta-HSD 1 modulators and concurrent smoking.