title: CYP2A6 genotype, phenotype, and the use of nicotine metabolites as biomarkers during ad libitum smoking.
abstract: CYP2A6 inactivates nicotine to cotinine and cotinine to 3-hydroxycotinine. We investigated which of plasma nicotine and metabolites were most related to CYP2A6 genotype and smoking levels. We assessed demographic and smoking histories in 152 Caucasian ad libitum smokers, measured breath carbon monoxide (CO) levels, and determined plasma nicotine, cotinine, and 3-hydroxycotinine by high-performance liquid chromatography and CYP2A6 genotypes by PCR. Cigarettes per day was most closely related to CO (r = 0.60, P < 0.001) followed by plasma cotinine (r = 0.53, P < 0.001), whereas plasma cotinine was most strongly correlated with CO levels (r = 0.74, P < 0.001), confirming that cotinine is a good indicator of smoking levels; this was not limited by CYP2A6 variants. 3-Hydroxycotinine/cotinine is reported to be a good marker of CYP2A6 activity, and we found that the 3-hydroxycotinine/(cotinine + nicotine) ratio was most correlated with CYP2A6 genotype (r = 0.38, P < 0.001). Inclusion of the CYP2A6*12A allele strengthened the correlation (r = 0.46, P < 0.001), suggesting that the identification of novel alleles will continue to improve this relationship. Nicotine metabolism is slower in smokers, and we have shown that CYP2A6 is reduced by nicotine treatment in monkeys. Here, we found that plasma nicotine levels were inversely correlated with CYP2A6 activity (3-hydroxycotinine/cotinine, r = -0.41, P < 0.001) among those without CYP2A6 variants, suggesting a reduction in metabolism with higher nicotine levels. Together, these findings (a) confirm the use of plasma cotinine and CO as indicators of Caucasians' smoking levels, and that this is not limited by CYP2A6 genetic variation; (b) indicate that 3-hydroxycotinine/cotinine and 3-hydroxycotinine/(cotinine + nicotine) are moderately good indicators of the CYP2A6 genotype; and (c) support that nicotine exposure may reduce its own metabolism.
authors.affiliation: Department of Pharmacology, Center for Addiction and Mental Health, University of Toronto, 1 King's College Circle, Toronto, Ontario, Canada M5S 1A8.
authors.forename: Viba
authors.initials: V
authors.lastname: Malaiyandi
authors.forename: Shari D
authors.initials: SD
authors.lastname: Goodz
authors.forename: Edward M
authors.initials: EM
authors.lastname: Sellers
authors.forename: Rachel F
authors.initials: RF
authors.lastname: Tyndale
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000483:Alleles; D000704:Analysis of Variance; D001189:Aryl Hydrocarbon Hydroxylases / Q000097:blood / Q000187:drug effects* / Q000235:genetics*; D015415:Biomarkers / Q000097:blood; D001944:Breath Tests; D002170:Canada / Q000453:epidemiology; D002248:Carbon Monoxide / Q000097:blood; D002851:Chromatography, High Pressure Liquid; D003367:Cotinine / Q000031:analogs & derivatives / Q000097:blood; D065637:Cytochrome P-450 CYP2A6; D005260:Female; D014644:Genetic Variation / Q000235:genetics; D005838:Genotype; D006801:Humans; D008297:Male; D008875:Middle Aged; D006899:Mixed Function Oxygenases / Q000097:blood / Q000187:drug effects* / Q000235:genetics*; D009538:Nicotine / Q000008:administration & dosage* / Q000097:blood / Q000378:metabolism*; D018722:Nicotinic Agonists / Q000008:administration & dosage* / Q000097:blood / Q000378:metabolism*; D010641:Phenotype; D016133:Polymerase Chain Reaction; D012680:Sensitivity and Specificity; D012907:Smoking / Q000097:blood / Q000208:ethnology / Q000235:genetics* / Q000378:metabolism*; D044465:White People / Q000235:genetics
chemical_list: D015415:Biomarkers; D018722:Nicotinic Agonists; C001381:hydroxycotinine; D009538:Nicotine; D002248:Carbon Monoxide; D006899:Mixed Function Oxygenases; D001189:Aryl Hydrocarbon Hydroxylases; C585710:CYP2A6 protein, human; D065637:Cytochrome P-450 CYP2A6; D003367:Cotinine