title: CYP2C8/9 mediate dapsone N-hydroxylation at clinical concentrations of dapsone.
abstract: Using selective cytochrome P450 (CYP) inhibitors and clinical concentrations (4 microM) of dapsone (DDS), we found a major contribution of CYP2C9 and little or no contribution (< or = 10%) of CYP3A4 and CYP2E1 to dapsone N-hydroxylation (DDS-NHY) in human liver microsomes. Sulfaphenazole (2.16 microM) and tolbutamide (500 microM), selective inhibitors of CYP2C9 (or 2C8/9), inhibited DDS-NHY by 48 +/- 14 and 41 +/- 15%, respectively. The apparent Michaelis-Menten Km values for DDS-NHY by cloned CYP2C8, CYP2C9, CYP2C18, and CYP2C19 were 75 microM, 31 microM, 25 microM, and greater than 1 mM, respectively. CYP3A4 and CYP2E1 were incapable of DDS-NHY at 4 microM DDS. S-mephenytoin (360 microM) activated DDS-NHY by human liver microsomes and by CYP2C8 by 43 +/- 36 and 193 +/- 16%, respectively. This activation was cytochrome b5-dependent. In contrast, S-mephenytoin inhibited DDS-NHY by CYP2C9, CYP2C18, and CYP2C19 by 27 +/- 2, 49 +/- 1, and 32 +/- 4%, respectively. Because CYP2C18 and CYP19 are expressed at low concentrations in the human liver, these observations indicate that at clinical DDS concentrations, CYP2C9 is a major and CYP2C8 is a likely minor contributor to DDS-NHY in human liver microsomes.
authors.affiliation: Department of Pharmaceutics, University of Washington, Seattle, Washington, USA.
authors.forename: H R
authors.initials: HR
authors.lastname: Winter
authors.forename: Y
authors.initials: Y
authors.lastname: Wang
authors.forename: J D
authors.initials: JD
authors.lastname: Unadkat
mesh_terms: D017088:AIDS-Related Opportunistic Infections / Q000188:drug therapy; D000890:Anti-Infective Agents / Q000378:metabolism / Q000627:therapeutic use; D001189:Aryl Hydrocarbon Hydroxylases; D002384:Catalysis; D065727:Cytochrome P-450 CYP2C8; D065729:Cytochrome P-450 CYP2C9; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D003622:Dapsone / Q000378:metabolism* / Q000627:therapeutic use; D006801:Humans; D006900:Hydroxylation; D066298:In Vitro Techniques; D008099:Liver / Q000201:enzymology / Q000378:metabolism*; D011446:Prospective Studies; D039181:Steroid 16-alpha-Hydroxylase; D013250:Steroid Hydroxylases / Q000378:metabolism*
chemical_list: D000890:Anti-Infective Agents; D003622:Dapsone; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; C450260:CYP2C9 protein, human; D065729:Cytochrome P-450 CYP2C9; D001189:Aryl Hydrocarbon Hydroxylases; C450259:CYP2C8 protein, human; D065727:Cytochrome P-450 CYP2C8; D039181:Steroid 16-alpha-Hydroxylase