Metabolism of a glucuronide conjugate of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in rats

Abstract

Besides 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), [4-(methylnitrosamino)-1-(3-pyridyl)but-1-yl]-β-O-d-glucosiduronic acid (NNAL-Glu) is another important metabolite of the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) which has been detected in the urine of tobacco users and non-smokers heavily exposed to sidestream cigarette smoke. In order to evaluate the toxicological significance of NNAL-Glu formation and excretion, the metabolism of [5-³H]-NNAL-Glu was studied in rats. Five male F344 rats were administered 3.7 mg/kg [5-³H]-NNAL-Glu by i.v. injection and the metabolites in urine analysed by HPLC. More than 90% of the radioactivity was excreted in urine within the first 24 h. Unchanged NNAL-Glu accounted for 81.2±3.1% of the total radioactivity; the remaining part of the dose appears to be deconjugated resulting in the urinary excretion of NNAL (3.6±1.7%) and its α-hydroxylation (11.5±2.2%) and N-oxidation (3.6±1.6%) products. The presence of α-hydroxylation products of NNAL-Glu in urine suggests that this NNK metabolite may be activated in vivo to carcinogenic intermediates.