Kilicarslan T, Haining R L, Rettie A E, Busto U, Tyndale R F, Sellers E M
Department of Pharmacology, University of Toronto, Toronto, Canada.
Drug Metab Dispos. 2001 Apr;29(4 Pt 1):460-5.
We have identified CYP2C19 and CYP3A4 as the principal cytochrome P450s involved in the metabolism of flunitrazepam to its major metabolites desmethylflunitrazepam and 3-hydroxyflunitrazepam. Human CYP2C19 and CYP3A4 mediated the formation of desmethylflunitrazepam with Km values of 11.1 and 108 microM, respectively, and 3-hydroxyflunitrazepam with Km values of 642 and 34.0 microM, respectively. In human liver microsomes (n = 4) formation of both metabolites followed biphasic kinetics. Desmethylflunitrazepam formation was inhibited 31% by S-mephenytoin and 78% by ketoconazole, suggesting involvement of both CYP2C19 and CYP3A4. Formation of 3-hydroxyflunitrazepam was also significantly inhibited by ketoconazole (94%) and S-mephenytoin (18%). In support of these chemical inhibition data, antibodies directed against CYP2C19 and CYP3A4 selectively inhibited formation of desmethylflunitrazepam by 26 and 45%, respectively, while anti-CYP3A4 antibodies reduced 3-hydroxyflunitrazepam formation by 80%. Our data also suggest that CYP1A2, -2B6, -2C8, -2C9, -2D6, and -2E1 are not involved in either of these metabolic pathways. We estimate that the relative contributions of CYP2C19 and CYP3A4 to the formation of desmethylflunitrazepam in vivo are 63 and 37%, respectively, at therapeutic flunitrazepam concentrations (0.03 microM). We conclude that the polymorphic enzyme CYP2C19 importantly mediates flunitrazepam demethylation, which may alter the efficacy and safety of the drug, while CYP3A4 catalyzes the formation of 3-hydroxyflunitrazepam.
我们已确定CYP2C19和CYP3A4是参与氟硝西泮代谢为其主要代谢产物去甲基氟硝西泮和3-羟基氟硝西泮的主要细胞色素P450酶。人CYP2C19和CYP3A4介导去甲基氟硝西泮的形成，其Km值分别为11.1和108微摩尔，介导3-羟基氟硝西泮的形成，其Km值分别为642和34.0微摩尔。在人肝微粒体（n = 4）中，两种代谢产物的形成均遵循双相动力学。S-美芬妥英抑制去甲基氟硝西泮形成31%，酮康唑抑制78%，提示CYP2C19和CYP3A4均参与其中。酮康唑（94%）和S-美芬妥英（18%）也显著抑制3-羟基氟硝西泮的形成。为支持这些化学抑制数据，针对CYP2C19和CYP3A4的抗体分别选择性抑制去甲基氟硝西泮形成26%和45%，而抗CYP3A4抗体使3-羟基氟硝西泮形成减少80%。我们的数据还表明CYP1A2、-2B6、-2C8、-2C9、-2D6和-2E1均不参与这些代谢途径中的任何一条。我们估计，在治疗性氟硝西泮浓度（0.03微摩尔）下，CYP2C19和CYP3A4对体内去甲基氟硝西泮形成的相对贡献分别为63%和37%。我们得出结论，多态性酶CYP2C19重要地介导氟硝西泮去甲基化，这可能改变药物的疗效和安全性，而CYP3A4催化3-羟基氟硝西泮的形成。
