PT - JOURNAL ARTICLE AU - Doris Wiener AU - Daniel R. Doerge AU - Jia-Long Fang AU - Pramod Upadhyaya AU - Philip Lazarus TI - CHARACTERIZATION OF <em>N-</em>GLUCURONIDATION OF THE LUNG CARCINOGEN 4-(METHYLNITROSAMINO)-1-(3-PYRIDYL)-1-BUTANOL (NNAL) IN HUMAN LIVER: IMPORTANCE OF UDP-GLUCURONOSYLTRANSFERASE 1A4 AID - 10.1124/dmd.32.1.72 DP - 2004 Jan 01 TA - Drug Metabolism and Disposition PG - 72--79 VI - 32 IP - 1 4099 - http://dmd.aspetjournals.org/content/32/1/72.short 4100 - http://dmd.aspetjournals.org/content/32/1/72.full SO - Drug Metab Dispos2004 Jan 01; 32 AB - The nicotine-derived tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), is one of the most potent and abundant procarcinogens found in tobacco and tobacco smoke and is considered to be a causative agent for several tobacco-related cancers. Glucuronidation of the major metabolite of NNK, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), has been implicated as an important mechanism for NNK detoxification. To characterize NNAL metabolism by N-glucuronidation in humans, high-pressure liquid chromatography was used to detect glucuronide conjugates of NNAL formed in human liver microsomes in vitro. In addition to peaks corresponding to the O-glucuronides of NNAL (NNAL-O-Gluc), a second series of peaks were observed in human liver microsomes that were identified by liquid chromatography-mass spectrometry to be NNAL N-glucuronides (NNAL-N-Gluc). Microsomes prepared from liver specimens from individual subjects (n = 42) exhibited substantial variability in the levels of NNAL-N-Gluc (49-fold variability) and NNAL-O-Gluc (49-fold variability) formed in vitro. This variability was likely not due to differences in tissue quality, as substantial variability (5-fold) was also observed in the ratio of NNAL-N-Gluc/NNAL-O-Gluc formation, with a mean ratio of 1.7 in the 42 specimens. Liver microsomes from smokers (n = 14) exhibited no significant difference in the levels of either NNAL-N-Gluc or NNAL-O-Gluc formation, or in the ratio of NNAL-N-Gluc/NNAL-O-Gluc formation, as compared with liver microsomes from never smokers (n = 28). Overexpressed UDP-glucuronosyltransferase (UGT) 1A4 exhibited significant levels of N-glucuronidating activity (Vmax/Km = 3.11 μl · min–1 · g–1) in vitro; no NNAL-N-glucuronide formation was detected for the 11 other overexpressed UGT enzymes tested in these studies. These results demonstrate the importance of N-glucuronidation in the metabolism of NNAL and the role of UGT1A4 in this pathway. The American Society for Pharmacology and Experimental Therapeutics