title: O-Dealkylation of fluoxetine in relation to CYP2C19 gene dose and involvement of CYP3A4 in human liver microsomes.
abstract: This work evaluated the kinetic behavior of fluoxetine O-dealkylation in human liver microsomes from different CYP2C19 genotypes and identified the isoenzymes of cytochrome P450 involved in this metabolic pathway. The kinetics of the rho-trifluoromethylphenol (TFMP) formation from fluoxetine was determined in human liver microsomes from three homozygous (wt/wt) and three heterozygous (wt/m1) extensive metabolizers (EMs) and three poor metabolizers (PMs) with m1 mutation (m1/m1) with respect to CYP2C19. The formation rate of TFMP was determined by gas chromatograph with electron-capture detection. The kinetics of TFMP formation was best described by the two-enzyme and single-enzyme Michaelis-Menten equation for liver microsomes from CYP2C19 EMs and PMs, respectively. The mean intrinsic clearance (V(max)/K(m)) for the high- and low-affinity component was 25.2 microl/min/nmol and 3.8 microl/min/nmol of cytochrome P450 in the homozygous EMs microsomes and 12.8 microl/min/nmol and 2.9 microl/min/nmol of cytochrome P450 in the heterozygous EMs microsomes, respectively. Omeprazole (a CYP2C19 substrate) at a high concentration and triacetyloleandomycin (a selective inhibitor of CYP3A4) substantially inhibited O-dealkylation of fluoxetine. Furthermore, fluoxetine O-dealkylation was correlated significantly with S-mephenytoin 4'-hydroxylation at a low substrate concentration and midazolam 1'-hydroxylation at a high substrate concentration in liver microsomes of 11 Chinese individuals, respectively. Moreover, there were obvious differences in the O-dealkylation of fluoxetine in liver microsomes from different CYP2C19 genotypes and in microsomal fractions of different human-expressed lymphoblast P450s. The results demonstrated that polymorphic CYP2C19 and CYP3A4 enzymes were the major cytochrome P450 isoforms responsible for fluoxetine O-dealkylation, whereas CYP2C19 catalyzed the high-affinity O-dealkylation of fluoxetine, and its contribution to this metabolic reaction was gene dose-dependent.
authors.affiliation: Pharmacogenetics Research Institute, Xiang-Ya School of Medicine, Central South University, Changsha, Hunan, People's Republic of China.
authors.forename: Zhao-Qian
authors.initials: ZQ
authors.lastname: Liu
authors.forename: Bing
authors.initials: B
authors.lastname: Zhu
authors.forename: Yun-Fu
authors.initials: YF
authors.lastname: Tan
authors.forename: Zhi-Rong
authors.initials: ZR
authors.lastname: Tan
authors.forename: Lian-Sheng
authors.initials: LS
authors.lastname: Wang
authors.forename: Song-Lin
authors.initials: SL
authors.lastname: Huang
authors.forename: Yan
authors.initials: Y
authors.lastname: Shu
authors.forename: Hong-Hao
authors.initials: HH
authors.lastname: Zhou
mesh_terms: D000465:Algorithms; D001189:Aryl Hydrocarbon Hydroxylases; D002849:Chromatography, Gas; D065731:Cytochrome P-450 CYP2C19; D051544:Cytochrome P-450 CYP3A; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism*; D018076:DNA, Complementary / Q000096:biosynthesis; D003640:Dealkylation; D004563:Electrochemistry; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005473:Fluoxetine / Q000378:metabolism*; D018628:Gene Dosage; D005838:Genotype; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D008862:Microsomes, Liver / Q000201:enzymology*; D006899:Mixed Function Oxygenases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D017367:Selective Serotonin Reuptake Inhibitors / Q000378:metabolism*
chemical_list: D001189:Aryl Hydrocarbon Hydroxylases; D065731:Cytochrome P-450 CYP2C19; D051544:Cytochrome P-450 CYP3A; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System; D018076:DNA, Complementary; D004791:Enzyme Inhibitors; D005473:Fluoxetine; D006899:Mixed Function Oxygenases; D011994:Recombinant Proteins; D017367:Selective Serotonin Reuptake Inhibitors; C045793:CYP2C19 protein, human; C104464:CYP3A protein, human; C510163:CYP3A4 protein, human