Cytochrome P450 2A6 (CYP2A6) is the primary human enzyme involved in nicotine metabolism. The objective of this study was to characterize two nonsynonymous single nucleotide polymorphisms in CYP2A6* 24, 594G>C (Val110Leu) and 6458A>T (Asn438Tyr). We determined their haplotype, allele frequencies, effect on CYP2A6 activity in vivo, as well as their stability and ability to metabolize nicotine in vitro. CYP2A6* 35 (6458A>T) occurred at a frequency of 2.5-2.9% among individuals of black African descent, 0.5-0.8% among Asians and was not found in Caucasians. In addition, we identified two novel alleles, CYP2A6* 36 (6458A>T and 6558T>C (Ile471Thr)) and CYP2A6* 37 (6458A>T, 6558T>C and 6600G>T (Arg485Leu)). In vivo, CYP2A6* 35 was associated with lower CYP2A6 activity as measured by the 3HC/COT ratio. In vitro, CYP2A6.35 had decreased nicotine C-oxidation activity and thermal stability. In conclusion, we identified three novel CYP2A6 alleles (CYP2A6* 35, *36 and *37); the higher allele frequency variant CYP2A6* 35 was associated with lower CYP2A6 activity.
Bibliographical noteFunding Information:
This study was supported by the Centre for Addiction and Mental Health, Canadian Institutes for Health Research (CIHR) MOP86471 and CA91912 (JSA). We thank Bin Zhao, Ewa B Hoffmann, Qian Zhou, Jill C Mwenifumbo, Man Ki Ho and Evan Dorey for technical assistance; Rabindra Shivnaraine for valuable input in data analyses and Sandy Faheim for careful review of the paper. We acknowledge the generous contribution of Dr Benowitz’s Lab in measuring the 3HC and COT levels among the African–American population. We also thank Dr Elizabeth Gillam for generous gift of the CYP2A6 construct and Dr Linda Ashworth for generously providing us with cosmid DNA clones 19296, 19019 and 27292 that contain CYP2A6, CYP2A7 and CYP2A13. NK receives funding from CIHR-Strategic Training Program in Tobacco Use in Special Populations (TUSP) and Ontario Graduate Scholarship program (OGS). RFT holds a Canada Research Chair in Pharmacogenetics.