CYP2B6, CYP3A4, and CYP2C19 are responsible for the in vitro N-demethylation of meperidine in human liver microsomes.
Meperidine is an opioid analgesic metabolized in the liver by N-demethylation to normeperidine, a potent stimulant of the central nervous system. The purpose of this study was to identify the human cytochrome P450 (P450) enzymes involved in normeperidine formation. Our in vitro studies included 1) screening 16 expressed P450s for normeperidine formation, 2) kinetic experiments on human liver microsomes and candidate P450s, and 3) correlation and inhibition experiments using human hepatic microsomes. After normalization by its relative abundance in human liver microsomes, CYP2B6, CYP3A4, and CYP2C19 accounted for 57, 28, and 15% of the total intrinsic clearance of meperidine. CYP3A5 and CYP2D6 contributed to < 1%. Formation of normeperidine significantly correlated with CYP2B6-selective S-mephenytoin N-demethylation (r = 0.88, p < 0.0001 at 75 > microM meperidine, and r = 0.89, p < 0.0001 at 350 microM meperidine, n = 21) and CYP3A4-selective midazolam 1'-hydroxylation (r = 0.59, p < 0.01 at 75 microM meperidine, and r = 0.55, p < 0.01 at 350 microM meperidine, n = 23). No significant correlation was observed with CYP2C19-selective S-mephenytoin 4'-hydroxylation (r = 0.36, p = 0.2 at 75 microM meperidine, and r = 0.02, p = 0.9 at 350 microM meperidine, n = 13). An anti-CYP2B6 antibody inhibited normeperidine formation by 46%. In contrast, antibodies inhibitory to CYP3A4 and CYP2C8/9/18/19 had little effect (<14% inhibition). Experiments with thiotepa and ketoconazole suggested inhibition of microsomal CYP2B6 and CYP3A4 activity, whereas studies with fluvoxamine (a substrate of CYP2C19) were inconclusive due to lack of specificity. We conclude that normeperidine formation in human liver microsomes is mainly catalyzed by CYP2B6 and CYP3A4, with a minor contribution from CYP2C19.
Ramírez
Jacqueline
J
University of Chicago, Department of Medicine, Section of Hematology-Oncology, 5841 S. Maryland Avenue, MC2115, Chicago, IL 60637, USA.
Innocenti
Federico
F
Schuetz
Erin G
EG
Flockhart
David A
DA
Relling
Mary V
MV
Santucci
Raymond
R
Ratain
Mark J
MJ
D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics / Q000378:metabolism*; D065702:Cytochrome P-450 CYP2B6; D065731:Cytochrome P-450 CYP2C19; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism*; D016666:Fluvoxamine / Q000378:metabolism / Q000494:pharmacology; D006801:Humans; D006900:Hydroxylation / Q000187:drug effects; D007527:Isoenzymes / Q000378:metabolism; D007654:Ketoconazole / Q000378:metabolism / Q000494:pharmacology; D008614:Meperidine / Q000031:analogs & derivatives* / Q000378:metabolism* / Q000494:pharmacology; D008617:Mephenytoin / Q000737:chemistry / Q000378:metabolism; D008862:Microsomes, Liver / Q000201:enzymology*; D006899:Mixed Function Oxygenases / Q000235:genetics / Q000378:metabolism*; D010089:Oxidoreductases, N-Demethylating / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D013852:Thiotepa / Q000378:metabolism / Q000494:pharmacology
D007527:Isoenzymes; D011994:Recombinant Proteins; D003577:Cytochrome P-450 Enzyme System; D013852:Thiotepa; D008614:Meperidine; D006899:Mixed Function Oxygenases; D001189:Aryl Hydrocarbon Hydroxylases; C585599:CYP2B6 protein, human; C045793:CYP2C19 protein, human; C104464:CYP3A protein, human; C510164:CYP3A5 protein, human; D065702:Cytochrome P-450 CYP2B6; D065731:Cytochrome P-450 CYP2C19; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D010089:Oxidoreductases, N-Demethylating; C002752:normeperidine; D016666:Fluvoxamine; D008617:Mephenytoin; D007654:Ketoconazole