The effect of tobacco smoke, nicotine, and cotinine on the mutagenicity of4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL)

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) is a rodent carcinogen that is metabolically derived from carbonyl reduction of 4-(methyinitrosam ino)-1-(3-pyridyl)-1-butanone (NNK). NNAL can be pyridine N-oxidized to for m NNAL-N-oxide, or conjugated to form NNAL-glucuronide-non-genotoxic metabo lites that can be excreted in urine. Alternatively, NNAL can be alpha -hydr oxylated at the methyl and methylene carbons adjacent to the nitroso group to generate electrophiles that can react with biological macromolecules, su ch as DNA and proteins. Our laboratory has previously demonstrated that the mutagenicity of NNK was significantly inhibited by the aqueous extract of tobacco smoke, as well as pyridine alkaloids in cigarette smoke, such as ni cotine, cotinine and nornicotine. Given the structural similarity between N NK and NNAL, and the metabolic activation of both by cytochromes P450, we h ypothesized that there may be a similar inhibition of NNAL metabolism, and consequently, inhibition of the mutagenic activity of NNAL by tobacco smoke and its pyridine alkaloid constituents. In the present study, we evaluated the ability of two pyridine alkaloids (nicotine and cotinine) and aqueous cigarette smoke condensate extract (ACTE) to inhibit the mutagenicity of NN AL in Salmonella typhimurium strain TA 1535 in the presence of a metabolic activation system (S9). Both pyridine alkaloids tested, as well as ACTE inh ibited the mutagenicity of NNAL in a concentration-dependent manner. The ob served reductions in mutagen ici ty were not the result of cell killing due to cytotoxicity. These results demonstrate that tobacco smoke contains pyr idine alkaloids, as well as other unidentified constituents that inhibit th e mutagenicity of NNAL, a major metabolite of NNK. (C) 2001 Elsevier Scienc e B.V. All rights reserved.