Nicotine and NNK Glucuronidation Pathways on Smokers

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Tobacco use is responsible for 90% of all lung cancers. A large prospective study carried out by the investigators of Project 1 of this POI reported a 2-5 fold difference among US racial/ethnic minorities in the risk of lung cancer due to cigarette smoking. The overall hypothesis of this program project grant is that this differential cancer risk is due to dissimilarities in exposure and response to tobacco smoke carcinogens. The exposure of a smoker to tobacco carcinogens is driven by nicotine addiction. Their response to nicofine and to most carcinogens is directiy influenced by the metabolism of these compounds. Two key routes of nicotine and carcinogen metabolism are P450-catalyzed oxidation and UGT-catalyzed conjugation. 4- (Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a tobacco specific nitrosamine, is a designated human carcinogen. It is the overall goal of this project to characterize racial/ethnic differences in the glucuronidation pathway of nicotine and NNK metabolism and to determine the SNPs present in UGTs associated with these differences. Three glucuronidation pathways will be studied: nicofine glucuronidation, and the glucuronidation oftwo NNK metabolites, NNAL and a-hydroxymethylNNK. The pathways will be assessed by urinary levels of glururonide metabolites and UGT variants will be characterized in vitro. Our preliminary data provided evidence of lower nicotine glucuronidation in African Americans relative to European Americans, and this project will focus on these two groups. However, through interactions with the large genome wide association study of carcinogen exposure and metabolism in project 1 we will extend our studies to other ethnic/racial groups. Our aims are to confirm the observed ethnic/racial difference in nicotine glucuronidation, and to extend our studies to NNAL glucuronidation. We will test the hypothesis that the extent of NNAL /V-glucuronidation is lower in racial/ethnic groups with a higher risk of smoking related lung cancer. NNAL glucuronidation is a key detoxification pathway of NNK. In the rat we have identified a 2"'^ potentially more important NNK detoxification pathway, glucuronidation of a-hydroxymethylNNK. In the last two aims of this project we will develop the methodology to quantify this glucuronide in smokers and to test our hypothesis that its formation in smokers is critical to the regulation of DNA adduct formation and potentially cancer risk.