Glucuronidation of the lung carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) by rat UDP-glucuronosyltransferase 2B1.

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone and its major metabolite, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), are potent lung carcinogens in animals. UDP-glucuronosyltransferase (UGT)-mediated glucuronidation of NNAL is a potentially important detoxification pathway for these carcinogens. To identify the UGT isozyme(s) involved in this pathway, we examined the glucuronidation of NNAL in rat liver microsomes and homogenates from cell lines overexpressing specific UGT isozymes. NNAL glucuronidation was induced in liver microsomes from rats treated with family 2 UGT inducers including phenobarbitol and 3, 5-di-tert-butyl-4-hydroxytoluene, which exhibited 1.7- and 2.6-fold higher rates of glucuronidation than microsomes from control rats. The rates of NNAL glucuronidation in liver microsomes from GUNN (deficient in family 1 UGTs) and RHA parental control rats were similar. All rat liver microsomes used in the present study catalyzed the glucuronidation of (S)-NNAL at a rate between 3.5 and 5.5 times that of the glucuronidation of (R)-NNAL. Liver microsomes from Wistar rats exhibiting the low-androsterone glucuronidation phenotype characteristic of the UGT2B2-deficient genotype glucuronidated NNAL at a rate similar to microsomes from Wistar rats exhibiting the high-androsterone glucuronidation phenotype/UGT2B2 [+] genotype. Homogenates from UGT2B1-overexpressing cells catalyzed the glucuronidation of NNAL at a K(m) of 745 microM. As with rat liver microsomes, NNAL-Gluc I was the major diastereomer formed by UGT2B1. Glucuronidation of NNAL was not detected with homogenates from UGT2B12-overexpressing cells. These results suggest that UGT2B1 plays an important role in the glucuronidation of NNAL in the rat.