Characterization of the novel CYP2A6*21 allele using in vivo nicotine kinetics

Objective: The impact of CYP2A6*21 (K476R) on in vivo nicotine metabolism and disposition was investigated. Methods: A two-step allele-specific PCR assay was developed to detect the 6573A > G single nucleotide polymorphism (SNP) in CYP2A6*21. Nicotine metabolism phenotypes from a previously described intravenous labeled nicotine and cotinine infusion study [1] was used to assess the impact of CYP2A6*21. Genomic DNA samples from 222 (111 monozygotic and dizygotic twin pairs) Caucasian subjects were genotyped for CYP2A6 alleles (CYP2A6*1X2, -*1B, -*2, -*4, -*7, -*9, -*10, -*12, and -*21). The pharmacokinetic parameters were compared between individuals with no detected CYP2A6 variants (CYP2A6*1/*1, n=163) and individuals heterozygous for the CYP2A6*21 allele (CYP2A6*1/*21, n=9). Results: The frequency of the CYP2A6*21 allele was found to be 2.3% in Caucasians (n=5/222 alleles, evaluated in one twin from each twin pair). In vivo pharmacokinetic parameters, such as nicotine clearance (1.32 +/- 0.37 vs. 1.18 +/- 0.20 L/min), fractional clearance of nicotine to cotinine (1.02 +/- 0.36 vs. 0.99 +/- 0.23 L/min), nicotine half-life (111 +/- 37 vs. 116 +/- 29 min), and the trans-3'-hydroxycotinine to cotinine ratio (1.92 +/- 1.0 vs. 1.55 +/- 0.58) indicated no substantial differences in nicotine metabolism between those without the variant (CYP2A6*1/*1, n=163) and those with the variant (CYP2A6*1/*21, n=9), respectively. Conclusion: CYP2A6*21 does not have a detectable impact on nicotine metabolism in vivo. Our data suggest that CYP2A6*21 may not be important for future studies of nicotine metabolism and the resulting impacts on smoking behaviors.