Tumorigenicity and metabolism of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol enantiomers and metabolites in the A/J mouse

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), a major metabolite of the tobacco-specific pulmonary carcinogen 4-(methylnitrosamino)-1-(3-pyrid yl)-1-butanone (NNK), has a chiral center but the tumorigenicity of the NNA L enantiomers has not been previously examined. In this study, we assessed the relative tumorigenic activities in the A/J mouse of NNK, racemic NNAL, (R)-NNAL, (S)-NNAL and several NNAL metabolites, including [4-(methylnitros amino)-1-(3-pyridyl)but-(S)-1-yl] beta-O-D-glucosiduronic acid [(S)-NNAL-Gl uc], 4-(methylnitrosamino)-1-(3-pyridyl N-oxide)-1-butanol, 5-(3-pyridyl)-2 -hydroxytetrahydrofuran, 4-(3-pyridyl)butane-1,4-diol and 2-(3-pyridyl) tet rahydrofuran, We also quantified urinary metabolites of racemic NNAL and it s enantiomers and investigated their metabolism with A/J mouse liver and lu ng microsomes. Groups of female A/J mice were given a single i.p. injection of 20 mu mol of each compound and killed 16 weeks later. Based on lung tum or multiplicity, (R)-NNAL (25.6 +/- 7.5 lung tumors/mouse) was as tumorigen ic as NNK (25.3 +/- 9.8) and significantly more tumorigenic than racemic NN AL (12.1 +/- 5.6) or (S)-NNAL (8.2 +/- 3.3) (P < 0.0001). None of the NNAL metabolites was tumorigenic, The major urinary metabolites of racemic NNAL and the NNAL enantiomers were 4-hydroxy-4-(3-pyridyl)butanoic acid (hydroxy acid), NNAL-N-oxide and NNAL-Gluc, in addition to unchanged NNAL, Treatmen t with (R)-NNAL or (S)-NNAL gave predominantly (R)-hydroxy acid or (S)-hydr oxy acid, respectively, as urinary metabolites. While treatment of mice wit h racemic or (S)-NNAL resulted in urinary excretion of (S)-NNAL-Gluc, treat ment with (R)-NNAL gave both (R)-NNAL-Gluc and (S)-NNAL-Gluc in urine, appa rently through the metabolic intermediacy of NNK, (S)-NNAL appeared to be a better substrate for glucuronidation than (R)-NNAL in the A/J mouse. Mouse liver and lung microsomes converted NNAL to products of alpha-hydroxylatio n, to NNAL-N-oxide, to adenosine dinucleotide phosphate adducts and to NNK, In lung microsomes, metabolic activation by alpha-hydroxylation of (R)-NNA L was significantly greater than that of (S)-NNAL. The results of this stud y provide a metabolic basis for the higher tumorigenicity of (R)-NNAL than (S)-NNAL in A/J mouse lung, namely preferential metabolic activation of (R) -NNAL in lung and preferential glucuronidation of (S)-NNAL.