Abstract
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.
Conclusions
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.
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Acknowledgements
The authors wish to thank Dr. L. Ashworth (Human genome center, Liverpool) for generously providing us with Cosmid DNA clones 19296, 19019, and 27292 that contain CYP2A6, CYP2A7, and CYP2A13, respectively. We sincerely thank Dr. Jason Yano for his helpful comments on the position and potential impact of CYP2A6*21 using the CYP2A6 crystal structure. We thank Drs. T. Inaba and E. Roberts for providing the human livers that provided data used as part of the rationale for this study. We are grateful for the participation of the twins without whom this work would not have been possible. CIHR, The Centre for Addiction & Mental Health and US Public Health Service grants awarded by the National Institutes on Drug Abuse, and carried out in part at the General Clinical Research Center at San Francisco General Hospital with support of the Division of Research Resources MOP-53248, DA11170, DA02277, DA12393 and NIH RR00083 supported this study. NA receives funding from CIHR-STPTR and OGS, JCM receives funding from CIHR-STPTR and SPICE, and RFT holds a Canadian Research Chair in Pharmacogenetics. All experiments conducted are in compliance with the current laws of U.S.A. and Canada inclusive of ethics approval.
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Nael Al Koudsi and Jill C. Mwenifumbo contributed equally to this work.
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Al Koudsi, N., Mwenifumbo, J.C., Sellers, E.M. et al. Characterization of the novel CYP2A6*21 allele using in vivo nicotine kinetics. Eur J Clin Pharmacol 62, 481–484 (2006). https://doi.org/10.1007/s00228-006-0113-3
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DOI: https://doi.org/10.1007/s00228-006-0113-3