Cytochrome P450 2C9 catalyzes indomethacin O-demethylation in human liver microsomes.
Indomethacin is a widely used nonsteroidal anti-inflammatory drug. We studied the human cytochrome P450 (CYP) isoform responsible for indomethacin O-demethylation, the major metabolic pathway for indomethacin. For indomethacin O-demethylase activities, the KM value was 34.6 +/- 5.4 muM and the Vmax value was 14.1 +/- 3.9 pmol/mg/min in human liver microsomes (N = 4). Indomethacin O-demethylase activity in human liver microsomes was competitively inhibited by sulfaphenazole, (S)-warfarin, and tolbutamide and was not affected by alpha-naphthoflavone, (S)-mephenytoin, or erythromycin. Indomethacin O-demethylase activities in microsomes from nine human livers were significantly correlated with tolbutamide hydroxylase activities (r = 0.750, p < 0.05) and not with (S)-mephenytoin 4'-hydroxylase activities. When the capacity for indomethacin O-demethylation in microsomes of B lymphoblastoid cells expressing human CYPs was investigated at an indomethacin concentration of 5 microM, cDNA-expressed CYP2C9 exhibited 6-fold greater activity than did CYP2C19. At an indomethacin concentration of 50 microM, cDNA-expressed CYP1A2 and CYP2D6 also exhibited slight activities. The KM values were 9.9 +/- 1.2 and 117.1 +/- 13.8 microM and the Vmax values were 0.33 +/- 0.05 and 0.24 +/- 0.04 pmol/min/pmol CYP in microsomes with cDNA-expressed CYP2C9 and CYP2C19, respectively (N = 4). Considering the 16-fold higher intrinsic clearance of CYP2C9, compared with that of CYP2C19, and these expression levels in human livers, the contribution of CYP2C19 to indomethacin O-demethylation was considered to be negligible. Indomethacin appears to be O-demethylated exclusively by CYP2C9 in humans.
Nakajima
M
M
Department of Clinical Pharmacy, School of Pharmaceutical Sciences, Showa University, Tokyo, Japan.
Inoue
T
T
Shimada
N
N
Tokudome
S
S
Yamamoto
T
T
Kuroiwa
Y
Y
D000478:Alkylation; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000378:metabolism; D001189:Aryl Hydrocarbon Hydroxylases; D019388:Cytochrome P-450 CYP1A2 / Q000502:physiology; D065731:Cytochrome P-450 CYP2C19; D065729:Cytochrome P-450 CYP2C9; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000235:genetics; D006801:Humans; D007213:Indomethacin / Q000378:metabolism*; D007527:Isoenzymes / Q000502:physiology; D007700:Kinetics; D008862:Microsomes, Liver / Q000201:enzymology*; D006899:Mixed Function Oxygenases / Q000378:metabolism / Q000502:physiology; D015394:Molecular Structure; D010090:Oxidoreductases, O-Demethylating / Q000502:physiology; D039181:Steroid 16-alpha-Hydroxylase; D013250:Steroid Hydroxylases / Q000502:physiology*; D013426:Sulfaphenazole / Q000494:pharmacology; D014044:Tolbutamide / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D014859:Warfarin / Q000494:pharmacology
D000894:Anti-Inflammatory Agents, Non-Steroidal; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D013426:Sulfaphenazole; D014859:Warfarin; D003577:Cytochrome P-450 Enzyme System; D014044:Tolbutamide; D006899:Mixed Function Oxygenases; D010090:Oxidoreductases, O-Demethylating; D013250:Steroid Hydroxylases; C450260:CYP2C9 protein, human; D065729:Cytochrome P-450 CYP2C9; D001189:Aryl Hydrocarbon Hydroxylases; C504573:CYP1A2 protein, human; C045793:CYP2C19 protein, human; D019388:Cytochrome P-450 CYP1A2; D065731:Cytochrome P-450 CYP2C19; D039181:Steroid 16-alpha-Hydroxylase; C053553:tolbutamide 4-hydroxylase; D007213:Indomethacin