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

Abstract

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), a major metabolite of the tobacco-specific pulmonary carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), has a chiral center but the tumorigenicity of the NNAL 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-(methylnitrosamino)-1-(3-pyridyl)but-(S)-1-yl] beta-O-D-gluco-siduronic acid [(S)-NNAL-Gluc], 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) tetrahydrofuran. We also quantified urinary metabolites of racemic NNAL and its enantiomers and investigated their metabolism with A/J mouse liver and lung microsomes. Groups of female A/J mice were given a single i.p. injection of 20 micromol of each compound and killed 16 weeks later. Based on lung tumor multiplicity, (R)-NNAL (25.6 +/- 7.5 lung tumors/mouse) was as tumorigenic as NNK (25.3 +/- 9.8) and significantly more tumorigenic than racemic NNAL (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. Treatment with (R)-NNAL or (S)-NNAL gave predominantly (R)-hydroxy acid or (S)-hydroxy acid, respectively, as urinary metabolites. While treatment of mice with racemic or (S)-NNAL resulted in urinary excretion of (S)-NNAL-Gluc, treatment with (R)-NNAL gave both (R)-NNAL-Gluc and (S)-NNAL-Gluc in urine, apparently 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-hydroxylation, to NNAL-N-oxide, to adenosine dinucleotide phosphate adducts and to NNK. In lung microsomes, metabolic activation by alpha-hydroxylation of (R)-NNAL was significantly greater than that of (S)-NNAL. The results of this study 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.

The Aldo-Keto Reductase Superfamily and its Role in Drug Metabolism and Detoxification

“…Inhibition of NNKreductase activity by menadione and ethacrynic acid, but not barbital and pyrazole, is consistent with a major role of carbonyl reductase in the cytosolic metabolism of NNK (Atalla and Maser, 2001). Although reduction to alcohol decreases the carcinogenicity of NNK, the alcohol metabolite is not innocuous and is carcinogenic by itself; the S-stereoisomer being more tumorigenic in the mouse than the R-isoform (Upadhyaya et al, 1999). Cytosolic enzymes, including AKRs, produce more than 90% of S-stereoisomer, whereas microsomal enzymes produce more of the R-isomer, especially in lung and placenta.…”

Correlation between UDP-Glucuronosyltransferase Genotypes and 4-(Methylnitrosamino)-1-(3-Pyridyl)-1-Butanone Glucuronidation Phenotype in Human Liver Microsomes

“…Although the formation of NNAL is not a detoxification pathway for NNK, the glucuronidation of NNAL appears to be an important mechanism for NNK detoxification. This is supported by the fact that the glucuronidation of R-NNAL was significantly greater than S-NNAL after injection into A/J mice, a pattern consistent with the higher tumorigenicity exhibited by S-NNAL in the same experiments (12,13). In contrast to the relatively high tumorigenicity exhibited by both R-and S-NNAL, NNAL-Gluc is nontumorigenic after s.c. injection into A/J mice (12).…”

Glucuronidation of Nicotine and Cotinine by UGT2B10: Loss of Function by the UGT2B10 Codon 67 (Asp&gt;Tyr) Polymorphism

“…The amount of N-glucuronide formed was calculated based on the ratio of the radioactivity of the N-glucuronide versus total radioactivity. Nicotine-and cotinine-Nglucuronides were confirmed by sensitivity to h-glucuronidase as described previously (14). As controls, glucuronidation assays were regularly done using HLM and untransfected HEK293 microsomes as positive and negative controls, respectively, for glucuronidation activity.…”