Winter H R, Wang Y, Unadkat J D
Department of Pharmaceutics, University of Washington, Seattle, Washington, USA.
Drug Metab Dispos. 2000 Aug;28(8):865-8.
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.
使用选择性细胞色素P450（CYP）抑制剂和临床浓度（4微摩尔）的氨苯砜（DDS），我们发现CYP2C9对人肝微粒体中氨苯砜N-羟基化（DDS-NHY）起主要作用，而CYP3A4和CYP2E1对其作用很小或几乎没有作用（≤10%）。磺胺苯吡唑（2.16微摩尔）和甲苯磺丁脲（500微摩尔），CYP2C9（或2C8/9）的选择性抑制剂，分别将DDS-NHY抑制了48±14%和41±15%。克隆的CYP2C8、CYP2C9、CYP2C18和CYP2C19对DDS-NHY的表观米氏常数Km值分别为75微摩尔、31微摩尔、25微摩尔和大于1毫摩尔。在4微摩尔DDS时，CYP3A4和CYP2E1无法进行DDS-NHY。S-美芬妥因（360微摩尔）分别使肝微粒体和CYP2C8介导的DDS-NHY活化了43±36%和193±16%。这种活化是细胞色素b5依赖性的。相反，S-美芬妥因分别使CYP2C9、CYP2C18和CYP2C19介导的DDS-NHY抑制了27±2%、49±1%和32±4%。由于CYP2C18和CYP19在人肝脏中的表达浓度较低，这些观察结果表明，在临床DDS浓度下，CYP2C9是DDS-NHY的主要贡献者，而CYP2C8可能是次要贡献者。
