Karjalainen Marjo J, Neuvonen Pertti J, Backman Janne T
Department of Clinical Pharmacology, University of Helsinki, Haartmaninkatu 4, FIN-00290 Helsinki, Finland.
Drug Metab Dispos. 2006 Dec;34(12):2091-6. doi: 10.1124/dmd.106.011965. Epub 2006 Sep 19.
Rofecoxib was recently found to greatly increase plasma concentrations of the CYP1A2 substrate drug tizanidine in humans, but there are no published in vitro studies on the CYP1A2-inhibiting effects of rofecoxib. Our objective was to investigate whether rofecoxib is a direct-acting or metabolism-dependent inhibitor of CYP1A2 in vitro. The effect of rofecoxib on the O-deethylation of phenacetin (20 microM) was studied using human liver microsomes. The effect of preincubation time on the inhibitory potential of rofecoxib was also studied, and the inhibitor concentration that supports half the maximal rate of inactivation (KI) and the maximal rate of inactivation (kinact) were determined. Rofecoxib moderately inhibited phenacetin O-deethylation (IC50 23.0 microM), and a 30-min preincubation with microsomes and NADPH considerably increased its inhibitory effect (IC50 4.2 microM). Inactivation of CYP1A2 by rofecoxib required NADPH, and was characterized by a KI of 4.8 microM and a kinact of 0.07 min(-1). Glutathione, superoxide dismutase, mannitol, or dialysis could not reverse the inactivation of CYP1A2 caused by rofecoxib. Fluvoxamine decreased the rofecoxib-caused inactivation of CYP1A2 in a concentration-dependent manner. In conclusion, rofecoxib is a potent, metabolism-dependent inhibitor of CYP1A2, a cytochrome P450 form contributing to rofecoxib metabolism. The results provide a mechanistic explanation for the interactions of rofecoxib with CYP1A2 substrates and may partially explain its nonlinear pharmacokinetics.
最近发现罗非昔布可显著提高人体中CYP1A2底物药物替扎尼定的血浆浓度，但尚未有关于罗非昔布对CYP1A2抑制作用的体外研究发表。我们的目的是在体外研究罗非昔布是CYP1A2的直接作用抑制剂还是代谢依赖性抑制剂。使用人肝微粒体研究了罗非昔布对非那西丁（20微摩尔）O-去乙基化的影响。还研究了预孵育时间对罗非昔布抑制潜力的影响，并确定了支持半数最大失活速率（KI）和最大失活速率（kinact）的抑制剂浓度。罗非昔布中度抑制非那西丁O-去乙基化（IC50为23.0微摩尔），与微粒体和NADPH预孵育30分钟可显著增强其抑制作用（IC50为4.2微摩尔）。罗非昔布使CYP1A2失活需要NADPH，其特征为KI为4.8微摩尔，kinact为0.07分钟-1。谷胱甘肽、超氧化物歧化酶、甘露醇或透析均不能逆转罗非昔布引起的CYP1A2失活。氟伏沙明以浓度依赖性方式降低罗非昔布引起的CYP1A2失活。总之，罗非昔布是一种强效的、代谢依赖性CYP1A2抑制剂，CYP1A2是参与罗非昔布代谢的一种细胞色素P450形式。这些结果为罗非昔布与CYP1A2底物的相互作用提供了机制解释，并可能部分解释其非线性药代动力学。
