title: Characterization of the novel CYP2A6*21 allele using in vivo nicotine kinetics.
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.
authors.affiliation: Centre for Addiction & Mental Health, and Department of Pharmacology, University of Toronto, Toronto, ON, Canada.
authors.forename: Nael
authors.initials: N
authors.lastname: Al Koudsi
authors.forename: Jill C
authors.initials: JC
authors.lastname: Mwenifumbo
authors.forename: Edward M
authors.initials: EM
authors.lastname: Sellers
authors.forename: Neal L
authors.initials: NL
authors.lastname: Benowitz
authors.forename: Gary E
authors.initials: GE
authors.lastname: Swan
authors.forename: Rachel F
authors.initials: RF
authors.lastname: Tyndale
mesh_terms: D000483:Alleles; D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics* / Q000378:metabolism*; D001483:Base Sequence; D065637:Cytochrome P-450 CYP2A6; D017931:DNA Primers / Q000235:genetics; D006207:Half-Life; D006239:Haplotypes; D006801:Humans; D006899:Mixed Function Oxygenases / Q000235:genetics* / Q000378:metabolism*; D009538:Nicotine / Q000378:metabolism* / Q000493:pharmacokinetics*; D010597:Pharmacogenetics; D020641:Polymorphism, Single Nucleotide; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic
chemical_list: D017931:DNA Primers; D009538:Nicotine; D006899:Mixed Function Oxygenases; D001189:Aryl Hydrocarbon Hydroxylases; C585710:CYP2A6 protein, human; D065637:Cytochrome P-450 CYP2A6