Predictors of Variation in CYP2A6 mRNA, Protein, and Enzyme Activity in a Human Liver Bank: Influence of Genetic and Nongenetic Factors.
Cytochrome P450 2A6 CYP2A6: metabolizes several clinically relevant substrates, including nicotine, the primary psychoactive component in cigarette smoke. Smokers vary widely in their rate of inactivation and clearance of nicotine, altering numerous smoking phenotypes. We aimed to characterize independent and shared impact of genetic and nongenetic sources of variation in CYP2A6 mRNA, protein, and enzyme activity in a human liver bank (n = 360). For the assessment of genetic factors, we quantified levels of CYP2A6, cytochrome P450 oxidoreductase (POR), and aldo-keto reductase 1D1 (AKR1D1) mRNA, and CYP2A6 and POR proteins. CYP2A6 enzyme activity was determined through measurement of cotinine formation from nicotine and 7-hydroxycoumarin formation from coumarin. Donor DNA was genotyped for CYP2A6, POR, and AKR1D1 genetic variants. Nongenetic factors assessed included gender, age, and liver disease. CYP2A6 phenotype measures were positively correlated to each other (r values ranging from 0.47-0.88, P < 0.001). Female donors exhibited higher CYP2A6 mRNA expression relative to males (P < 0.05). Donor age was weakly positively correlated with CYP2A6 protein (r = 0.12, P < 0.05) and activity (r = 0.20, P < 0.001). CYP2A6 reduced-function genotypes, but not POR or AKR1D1 genotypes, were associated with lower CYP2A6 protein (P < 0.001) and activity (P < 0.01). AKR1D1 mRNA was correlated with CYP2A6 mRNA (r = 0.57, P < 0.001), protein (r = 0.30, P < 0.001), and activity (r = 0.34, P < 0.001). POR protein was correlated with CYP2A6 activity (r = 0.45, P < 0.001). Through regression analyses, we accounted for 17% (P < 0.001), 37% (P < 0.001), and 77% (P < 0.001) of the variation in CYP2A6 mRNA, protein, and activity, respectively. Overall, several independent and shared sources of variation in CYP2A6 activity in vitro have been identified, which could translate to variable hepatic clearance of nicotine.
Campbell Family Mental Health Research Institute, Centre for Addiction and Mental Health (CAMH), Toronto, Ontario, Canada (J-A.T., R.F.T.); Department of Pharmacology and Toxicology (J-A.T., R.F.T.) and Department of Psychiatry (R.F.T.), University of Toronto, Toronto, Ontario, Canada; Department of Pharmaceutics (B.P., K.G.C, K.E.T.) and Center for Exposures, Diseases, Genomics, and Environment (P.S.), University of Washington, Seattle, Washington; Department of Pharmaceutical Sciences, St. Jude Children's Research Hospital, Memphis, Tennessee (A.C., E.G.S.).
Julie-Anne
JA
Tanner
Campbell Family Mental Health Research Institute, Centre for Addiction and Mental Health (CAMH), Toronto, Ontario, Canada (J-A.T., R.F.T.); Department of Pharmacology and Toxicology (J-A.T., R.F.T.) and Department of Psychiatry (R.F.T.), University of Toronto, Toronto, Ontario, Canada; Department of Pharmaceutics (B.P., K.G.C, K.E.T.) and Center for Exposures, Diseases, Genomics, and Environment (P.S.), University of Washington, Seattle, Washington; Department of Pharmaceutical Sciences, St. Jude Children's Research Hospital, Memphis, Tennessee (A.C., E.G.S.).
Bhagwat
B
Prasad
Campbell Family Mental Health Research Institute, Centre for Addiction and Mental Health (CAMH), Toronto, Ontario, Canada (J-A.T., R.F.T.); Department of Pharmacology and Toxicology (J-A.T., R.F.T.) and Department of Psychiatry (R.F.T.), University of Toronto, Toronto, Ontario, Canada; Department of Pharmaceutics (B.P., K.G.C, K.E.T.) and Center for Exposures, Diseases, Genomics, and Environment (P.S.), University of Washington, Seattle, Washington; Department of Pharmaceutical Sciences, St. Jude Children's Research Hospital, Memphis, Tennessee (A.C., E.G.S.).
Katrina G
KG
Claw
Campbell Family Mental Health Research Institute, Centre for Addiction and Mental Health (CAMH), Toronto, Ontario, Canada (J-A.T., R.F.T.); Department of Pharmacology and Toxicology (J-A.T., R.F.T.) and Department of Psychiatry (R.F.T.), University of Toronto, Toronto, Ontario, Canada; Department of Pharmaceutics (B.P., K.G.C, K.E.T.) and Center for Exposures, Diseases, Genomics, and Environment (P.S.), University of Washington, Seattle, Washington; Department of Pharmaceutical Sciences, St. Jude Children's Research Hospital, Memphis, Tennessee (A.C., E.G.S.).
Patricia
P
Stapleton
Campbell Family Mental Health Research Institute, Centre for Addiction and Mental Health (CAMH), Toronto, Ontario, Canada (J-A.T., R.F.T.); Department of Pharmacology and Toxicology (J-A.T., R.F.T.) and Department of Psychiatry (R.F.T.), University of Toronto, Toronto, Ontario, Canada; Department of Pharmaceutics (B.P., K.G.C, K.E.T.) and Center for Exposures, Diseases, Genomics, and Environment (P.S.), University of Washington, Seattle, Washington; Department of Pharmaceutical Sciences, St. Jude Children's Research Hospital, Memphis, Tennessee (A.C., E.G.S.).
Amarjit
A
Chaudhry
Campbell Family Mental Health Research Institute, Centre for Addiction and Mental Health (CAMH), Toronto, Ontario, Canada (J-A.T., R.F.T.); Department of Pharmacology and Toxicology (J-A.T., R.F.T.) and Department of Psychiatry (R.F.T.), University of Toronto, Toronto, Ontario, Canada; Department of Pharmaceutics (B.P., K.G.C, K.E.T.) and Center for Exposures, Diseases, Genomics, and Environment (P.S.), University of Washington, Seattle, Washington; Department of Pharmaceutical Sciences, St. Jude Children's Research Hospital, Memphis, Tennessee (A.C., E.G.S.).
Erin G
EG
Schuetz
Campbell Family Mental Health Research Institute, Centre for Addiction and Mental Health (CAMH), Toronto, Ontario, Canada (J-A.T., R.F.T.); Department of Pharmacology and Toxicology (J-A.T., R.F.T.) and Department of Psychiatry (R.F.T.), University of Toronto, Toronto, Ontario, Canada; Department of Pharmaceutics (B.P., K.G.C, K.E.T.) and Center for Exposures, Diseases, Genomics, and Environment (P.S.), University of Washington, Seattle, Washington; Department of Pharmaceutical Sciences, St. Jude Children's Research Hospital, Memphis, Tennessee (A.C., E.G.S.).
Kenneth E
KE
Thummel
Campbell Family Mental Health Research Institute, Centre for Addiction and Mental Health (CAMH), Toronto, Ontario, Canada (J-A.T., R.F.T.); Department of Pharmacology and Toxicology (J-A.T., R.F.T.) and Department of Psychiatry (R.F.T.), University of Toronto, Toronto, Ontario, Canada; Department of Pharmaceutics (B.P., K.G.C, K.E.T.) and Center for Exposures, Diseases, Genomics, and Environment (P.S.), University of Washington, Seattle, Washington; Department of Pharmaceutical Sciences, St. Jude Children's Research Hospital, Memphis, Tennessee (A.C., E.G.S.) r.tyndale@utoronto.ca.
Rachel F
RF
Tyndale
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D065637:Cytochrome P-450 CYP2A6 / Q000235:genetics* / Q000378:metabolism*; D005260:Female; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D014644:Genetic Variation; D005838:Genotype; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008099:Liver / Q000201:enzymology*; D008297:Male; D008875:Middle Aged; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D009538:Nicotine / Q000494:pharmacology; D010088:Oxidoreductases / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D014015:Tissue Banks; D014468:Umbelliferones / Q000494:pharmacology; D055815:Young Adult
D012333:RNA, Messenger; D014468:Umbelliferones; C031477:7-hydroxycoumarin; D009538:Nicotine; D010088:Oxidoreductases; D065637:Cytochrome P-450 CYP2A6; C021936:3-oxo-5 beta-steroid delta 4-dehydrogenase; D009251:NADPH-Ferrihemoprotein Reductase