Abstract
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.
Footnotes
-
↵1 Abbreviations used are: NNK, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone; NNAL, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol; UGT, UDP-glucuronosyltransferase; NNAL-N-Gluc, β-N-[4-(methylnitrosamino)-1-(3-pyridyl)-1-but-1-yl]-d-glucosiduronic acid; NNAL-O-Gluc, β-O-[4-(methylnitrosamino)-1-(3-pyridyl)-1-but-1-yl]-d-glucosiduronic acid; UDPGA, UDP-glucuronic acid; HPLC, high-pressure liquid chromatography; LC-MS/MS, liquid chromatography-tandem mass spectrometry.
-
These studies were supported by Public Health Service Grants DE13158 (National Institute of Dental and Craniofacial Research) to P. Lazarus, and CA68384 (National Cancer Institute; P. Lazarus, project leader; Steven Stellman, principal investigator) from the National Institutes of Health, Department of Health and Human Services.
-
These studies were presented at the American Association for Cancer Research, Washington, DC, July 2003.
- Received July 31, 2003.
- Accepted September 18, 2003.
- The American Society for Pharmacology and Experimental Therapeutics
DMD articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|
