title: Identification of CYP3A4 and CYP2C8 as the major cytochrome P450 s responsible for morphine N-demethylation in human liver microsomes.
abstract: 1. The aim was to identify the cytochrome P450 (CYP) enzymes responsible for the N-demethylation of morphine in vitro. 2. In human liver microsomes, normorphine formation followed Michaelis-Menten kinetics with mean Km and Vmax of 12.4 +/- 2.2 mM and 1546 +/- 121 pmol min(-1) mg(-1), respectively. In microsomes from a panel of 14 human livers phenotyped for 10 CYP enzymes, morphine N-demethylation correlated with testosterone 6beta-hydroxylation (r=0.91, p<0.001) and paclitaxel 6-alpha hydroxylation (r=0.72, p<0.001), two specific markers of CYP3A4 and CYP2C8, respectively. Normorphine formation decreased when incubated in the presence of troleandomycin or quercetin (by 46 and 33-36%, respectively), which further corroborates the contribution of CYP3A4 and CYP2C8. 3. Among eight recombinant human CYP enzymes tested, CYP3A4 and CYP2C8 exhibited the highest intrinsic clearance. More than 90% of morphine N-demethylation could be accounted for via the action of both CYP3A4 and CYP2C8. 4. The in vitro findings suggest that hepatic CYP3A4, and to a lesser extent CYP2C8, play an important role in the metabolism of morphine into normorphine.
authors.affiliation: Faculté de Pharmacie, Université de Montréal, Montréal, Québec, Canada.
authors.forename: D
authors.initials: D
authors.lastname: Projean
authors.forename: P-E
authors.initials: PE
authors.lastname: Morin
authors.forename: T M
authors.initials: TM
authors.lastname: Tu
authors.forename: J
authors.initials: J
authors.lastname: Ducharme
mesh_terms: D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000378:metabolism*; D002460:Cell Line; D065727:Cytochrome P-450 CYP2C8; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D018076:DNA, Complementary; D006801:Humans; D006900:Hydroxylation; D007313:Insecta; D008745:Methylation; D008862:Microsomes, Liver / Q000201:enzymology* / Q000378:metabolism; D015394:Molecular Structure; D009020:Morphine / Q000378:metabolism*; D009022:Morphine Derivatives / Q000032:analysis / Q000378:metabolism
chemical_list: D018076:DNA, Complementary; D009022:Morphine Derivatives; D009020:Morphine; D003577:Cytochrome P-450 Enzyme System; D001189:Aryl Hydrocarbon Hydroxylases; C450259:CYP2C8 protein, human; C104464:CYP3A protein, human; D065727:Cytochrome P-450 CYP2C8; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; C010616:normorphine