Nicotine Metabolism and Smoking Behaviour in Vulnerable Populations

The rate of nicotine metabolic inactivation varies widely among different populations, influencing smoking behaviors and associated disease risk. African American smokers metabolize nicotine more slowly and report lower cigarette consumption compared to Caucasian smokers, but suffer disproportionately from lung cancer risk. In addition to ethnic/racial differences, altered physiological states, for example during pregnancy, may lead to variation in the rate of nicotine metabolism, smoking behaviors, and reproductive toxicity in pregnant smokers. We sought to characterize sources of variability in the rate of nicotine metabolism, and resultant influences on smoking behaviors in these vulnerable populations. We demonstrate variation in UDP-glucuronosyltransferase 2B10 and 2B17 (UGT2B10 and UGT2B17) and flavincontaining monooxigenase 3 (FMO3) do not substantially alter nicotine metabolism or tobacco consumption in African Americans. We further demonstrate the metabolism of cotinine, the primary metabolite of nicotine, is influenced by variation in UGT2B10 altering the utility of cotinine as a biomarker of nicotine intake in African American smokers. Most analytical methods for measuring nicotine’s urinary metabolites involve enzymatic or chemical deglucuronidation for quantification of the glucuronide-conjugated metabolites. We developed a direct liquid chromatography-tandem mass spectrometry (LCMS/MS) assay that provides more accurate estimates of the nicotine metabolism rate, intake and impact of genetic variation in smokers. We then utilized this direct LCMS/MS approach to evaluate nicotine metabolism during pregnancy and postpartum. We identified distinct patterns of nicotine metabolites, and an overall faster rate of nicotine metabolism during pregnancy. We demonstrate nicotine metabolism was accelerated likely through induction of CYP2A6 and UGT2B10 activity leading to faster nicotine C-oxidation and N-glucuronidation, respectively. We further biochemically characterized the level of nicotine intake, and thus tobacco exposure, during pregnancy and postpartum. We demonstrate the intake of nicotine was higher during pregnancy and postpartum than is suggested by self-reported cigarettes per day. Lastly, we found cotinine underestimated nicotine intake during pregnancy compared to postpartum. Overall, our findings provide insight into the patterns of nicotine metabolism, CYP2A6 and UGT2B10 genetic variation, and tobacco exposure in two vulnerable, biologically and physiologically distinct, populations, and expand on our knowledge of genetic and non-genetic sources of variation in the rate of nicotine metabolism.Ph.D