title: Alaska Native smokers and smokeless tobacco users with slower CYP2A6 activity have lower tobacco consumption, lower tobacco-specific nitrosamine exposure and lower tobacco-specific nitrosamine bioactivation.
abstract: Nicotine, the psychoactive ingredient in tobacco, is metabolically inactivated by CYP2A6 to cotinine. CYP2A6 also activates procarcinogenic tobacco-specific nitrosamines (TSNA). Genetic variation in CYP2A6 is known to alter smoking quantity and lung cancer risk in heavy smokers. Our objective was to investigate how CYP2A6 activity influences tobacco consumption and procarcinogen levels in light smokers and smokeless tobacco users. Cigarette smokers (n = 141), commercial smokeless tobacco users (n = 73) and iqmik users (n = 20) were recruited in a cross-sectional study of Alaska Native people. The participants' CYP2A6 activity was measured by both endophenotype and genotype, and their tobacco and procarcinogen exposure biomarker levels were also measured. Smokers, smokeless tobacco users and iqmik users with lower CYP2A6 activity had lower urinary total nicotine equivalents (TNE) and (methylnitrosamino)-1-(3)pyridyl-1-butanol (NNAL) levels (a biomarker of TSNA exposure). Levels of N-nitrosonornicotine (NNN), a TSNA metabolically bioactivated by CYP2A6, were higher in smokers with lower CYP2A6 activities. Light smokers and smokeless tobacco users with lower CYP2A6 activity reduce their tobacco consumption in ways (e.g. inhaling less deeply) that are not reflected by self-report indicators. Tobacco users with lower CYP2A6 activity are exposed to lower procarcinogen levels (lower NNAL levels) and have lower procarcinogen bioactivation (as indicated by the higher urinary NNN levels suggesting reduced clearance), which is consistent with a lower risk of developing smoking-related cancers. This study demonstrates the importance of CYP2A6 in the regulation of tobacco consumption behaviors, procarcinogen exposure and metabolism in both light smokers and smokeless tobacco users.
authors.affiliation: Centre for Addiction and Mental Health, Department of Psychiatry, University of Toronto, Toronto M5S 1A8, Ontario.
authors.forename: Andy Z X
authors.initials: AZ
authors.lastname: Zhu
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Binnington
authors.forename: Caroline C
authors.initials: CC
authors.lastname: Renner
authors.forename: Anne P
authors.initials: AP
authors.lastname: Lanier
authors.forename: Dorothy K
authors.initials: DK
authors.lastname: Hatsukami
authors.forename: Irina
authors.initials: I
authors.lastname: Stepanov
authors.forename: Clifford H
authors.initials: CH
authors.lastname: Watson
authors.forename: Connie S
authors.initials: CS
authors.lastname: Sosnoff
authors.forename: Neal L
authors.initials: NL
authors.lastname: Benowitz
authors.forename: Rachel F
authors.initials: RF
authors.lastname: Tyndale
mesh_terms: D000413:Alaska; D001711:Biotransformation; D019389:Cytochrome P-450 CYP2D6 / Q000378:metabolism*; D006801:Humans; D004930:Inuit; D009602:Nitrosamines / Q000493:pharmacokinetics / Q000633:toxicity*; D012907:Smoking / Q000378:metabolism*; D014026:Nicotiana
chemical_list: D009602:Nitrosamines; D019389:Cytochrome P-450 CYP2D6