Characterization of N-glucuronidation of the lung carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) in human liver: importance of UDP-glucuronosyltransferase 1A4.
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 (V(max)/K(m) = 3.11 microl. 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.
Wiener
Doris
D
Cancer Epidemiology and Prevention Program, H. Lee Moffitt Cancer Center, Department of Interdisciplinary Oncology, University of South Florida, Tampa, USA.
Doerge
Daniel R
DR
Fang
Jia-Long
JL
Upadhyaya
Pramod
P
Lazarus
Philip
P
D002273:Carcinogens / Q000378:metabolism*; D002460:Cell Line; D002851:Chromatography, High Pressure Liquid; D020719:Glucuronides / Q000378:metabolism / Q000652:urine; D014453:Glucuronosyltransferase / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D008099:Liver / Q000201:enzymology / Q000378:metabolism*; D008175:Lung Neoplasms / Q000139:chemically induced*; D009602:Nitrosamines / Q000378:metabolism*; D014066:Palatine Tonsil / Q000378:metabolism; D011725:Pyridines / Q000378:metabolism*; D012907:Smoking / Q000378:metabolism; D014030:Tobacco, Smokeless
D002273:Carcinogens; D020719:Glucuronides; D009602:Nitrosamines; D011725:Pyridines; C019787:bilirubin glucuronoside glucuronosyltransferase; D014453:Glucuronosyltransferase; C099565:4-(methylnitrosamino)-1-(3-pyridyl)-1-butan-1-ol