title: Role of CYP2C9 and its variants (CYP2C9*3 and CYP2C9*13) in the metabolism of lornoxicam in humans.
abstract: CYP2C9 is an important member of the cytochrome P450 enzyme superfamily with some 12 CYP2C9 alleles (*1-*12) being previously reported. Recently, we identified a new CYP2C9 allele with a Leu90Pro mutation in a Chinese poor metabolizer of lornoxicam [Si D, Guo Y, Zhang Y, Yang L, Zhou H, and Zhong D (2004) Pharmacogenetics 14:465-469]. The new allele, designated CYP2C9*13, was found to occur in approximately 2% of the Chinese population. To examine enzymatic activity of the CYP2C9*13 allele, kinetic parameters for lornoxicam 5'-hydroxylation were determined in COS-7 cells transiently transfected with pcDNA3.1 plasmids carrying wild-type CYP2C9*1, variant CYP2C9*3, and CYP2C9*13 cDNA. The protein levels of cDNA-expressed CYP2C9*3 and *13 in postmitochondrial supernatant (S9) from transfected cells were lower than those from wild-type CYP2C9*1. Mean values of Km and Vmax for CYP2C9*1, *3, and *13 were 1.24, 1.61, and 2.79 microM and 0.83, 0.28, and 0.22 pmol/min/pmol, respectively. Intrinsic clearance values (Vmax/Km) for variant CYP2C9*3 and CYP2C9*13 on the basis of CYP2C9 protein levels were separately decreased to 28% and 12% compared with wild type. In a subsequent clinical study, the AUC of lornoxicam was increased by 1.9-fold and its oral clearance (CL/F) decreased by 44% in three CYP2C9*1/*13 subjects, compared with CYP2C9*1/*1 individuals. This suggests that the CYP2C9*13 allele is associated with decreased enzymatic activity both in vitro and in vivo.
authors.affiliation: College of Life Science, Jilin University, No.115 Jiefang Road, Changchun, 130023, China.
authors.forename: Yingjie
authors.initials: Y
authors.lastname: Guo
authors.forename: Yifan
authors.initials: Y
authors.lastname: Zhang
authors.forename: Ying
authors.initials: Y
authors.lastname: Wang
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Chen
authors.forename: Dayong
authors.initials: D
authors.lastname: Si
authors.forename: Dafang
authors.initials: D
authors.lastname: Zhong
authors.forename: J Paul
authors.initials: JP
authors.lastname: Fawcett
authors.forename: Hui
authors.initials: H
authors.lastname: Zhou
mesh_terms: D000483:Alleles; D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D019556:COS Cells; D002522:Chlorocebus aethiops; D065729:Cytochrome P-450 CYP2C9; D014644:Genetic Variation / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D010894:Piroxicam / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology
chemical_list: D010894:Piroxicam; C450260:CYP2C9 protein, human; D065729:Cytochrome P-450 CYP2C9; D001189:Aryl Hydrocarbon Hydroxylases; C059451:lornoxicam