Drug Metabolizing Enzyme and Transporter Gene Variation, Nicotine Metabolism, Prospective Abstinence, and Cigarette Consumption.

Andrew W Bergen,Timothy B Baker,Karen N Conneely,Gary E Swan,Denise Nishita,Christina N Lessov-Schlaggar,Transdisciplinary Research In Cancer Of The Lung Research Team ,Rachel F Tyndale,David V Conti,Neal L Benowitz,Ruth Krasnow,Sharon M Hall,Harold S Javitz,Hyman Hops,James W Baurley,Martha Michel,Jennifer B Mcclure,Andy Z X Zhu,Caryn Lerman

doi:10.1371/journal.pone.0126113

Abstract

The Nicotine Metabolite Ratio (NMR, ratio of trans-3’-hydroxycotinine and cotinine), has previously been associated with CYP2A6 activity, response to smoking cessation treatments, and cigarette consumption. We searched for drug metabolizing enzyme and transporter (DMET) gene variation associated with the NMR and prospective abstinence in 2,946 participants of laboratory studies of nicotine metabolism and of clinical trials of smoking cessation therapies. Stage I was a meta-analysis of the association of 507 common single nucleotide polymorphisms (SNPs) at 173 DMET genes with the NMR in 449 participants of two laboratory studies. Nominally significant associations were identified in ten genes after adjustment for intragenic SNPs; CYP2A6 and two CYP2A6 SNPs attained experiment-wide significance adjusted for correlated SNPs (CYP2A6 P ACT=4.1E-7, rs4803381 P ACT=4.5E-5, rs1137115, P ACT=1.2E-3). Stage II was mega-regression analyses of 10 DMET SNPs with pretreatment NMR and prospective abstinence in up to 2,497 participants from eight trials. rs4803381 and rs1137115 SNPs were associated with pretreatment NMR at genome-wide significance. In post-hoc analyses of CYP2A6 SNPs, we observed nominally significant association with: abstinence in one pharmacotherapy arm; cigarette consumption among all trial participants; and lung cancer in four case:control studies. CYP2A6 minor alleles were associated with reduced NMR, CPD, and lung cancer risk. We confirmed the major role that CYP2A6 plays in nicotine metabolism, and made novel findings with respect to genome-wide significance and associations with CPD, abstinence and lung cancer risk. Additional multivariate analyses with patient variables and genetic modeling will improve prediction of nicotine metabolism, disease risk and smoking cessation treatment prognosis.

Highlights

The predominant enzyme involved in nicotine and cotinine metabolism is CYP2A6 [1, 2], where nicotine is metabolized primarily to cotinine, and cotinine primarily to trans-3’-hydroxycotinine
After multiple test correction for 507 single nucleotide polymorphisms (SNPs), two CYP2A6 SNPs attained experiment-wide significance: rs4803381 (PACT = 4.53E-05) and rs1137115 (PACT = .0012), located in the promoter (c.-1013) and first exon (c.51) of CYP2A6. These SNPs are in strong linkage disequilibrium with each other (r2 = 0.63 and 0.62 and D’ = 0.99 and 1.00 in PKFAM and SMOFAM), and in ex vivo hepatic tissue have been shown to be associated with significantly reduced protein and activity [35]. rs4803381 and rs1137115 are assocated with many CYP2A6Ã star allele (Ã) haplotypes (Ã1B/ Ã1B2, Ã1B5, Ã1B6, Ã1B8, Ã1B9, Ã1B10, Ã1B11, Ã1D, Ã1J, Ã9A, Ã9B, Ã18C, Ã24A, Ã24B, Ã31A, Ã31B, Ã35A and Ã1A, Ã1B14, Ã1B17, Ã2, Ã14, Ã18B, Ã20, Ã21, Ã28A, Ã28B, Ã41, Ã42, Ã44, Ã45, respectively) [36]
In our analysis of indivdiuals randomized to nicotine replacement therapy (NRT) patch from two trials [18, 42], we find that a single CYP2A6 SNP is a statistically trending predictor where reduced nicotine metabolism implies increased nicotine plasma levels and increased abstinence

Summary

Introduction

The predominant enzyme involved in nicotine and cotinine metabolism is CYP2A6 [1, 2], where nicotine is metabolized primarily to cotinine, and cotinine primarily to trans-3’-hydroxycotinine. The Nicotine Metabolite Ratio (NMR) is the ratio of the metabolites trans-3’hydroxycotinine and cotinine. The ratio reflects the enzymatic activity of CYP2A6 and is a biomarker of the rate of nicotine clearance [3]. Significant correlations between the NMR and a) oral clearance of nicotine, b) oral clearance and t1/2 of cotinine, and c) lack of production of trans-3’-hydroxycotinine in individuals homozygous for null CYP2A6 alleles, support the validity of the NMR as a marker of CYP2A6 activity [3]. In addition to CYP2A6, genetic and biochemical studies have identified contributions of additional DMET loci to measures of nicotine metabolism in diverse samples and study designs. Gene variants associated with differences in nicotine metabolism [7] influence smoking behavior, tobacco exposures and attributable disease risks, and could serve as biomarkers for disease risk, and treatment prognosis [8]

Results

Discussion

Conclusion