Galetin Aleksandra, Houston J Brian
School of Pharmacy and Pharmaceutical Sciences, University of Manchester, Oxford Road, Manchester, M13 9PL, UK.
J Pharmacol Exp Ther. 2006 Sep;318(3):1220-9. doi: 10.1124/jpet.106.106013. Epub 2006 Jun 8.
The contribution of the gut is not routinely incorporated into in vitro-in vivo predictions of either clearance or drug-drug interactions, and this omission may partially explain the general underprediction trend often observed. In the current study, the metabolic ability of hepatic and intestinal pooled microsomes was compared for eight CYP3A substrates (midazolam, triazolam, diazepam, alprazolam, flunitrazepam, nifedipine, testosterone, and quinidine) and paclitaxel, tolbutamide, S-mephenytoin, and bufuralol as CYP2C8, CYP2C9, CYP2C19, and CYP2D6 probes, respectively. A general agreement in the type of kinetics was observed between the two systems for the substrates investigated. Of the 16 pathways investigated, 75% of K(m) (S(50)) values obtained in intestinal microsomes (5.9-769 microM) were within 2-fold of hepatic estimates. Irrespective of the cytochrome P450 (P450) investigated and normalization of V(max) values for the P450 abundance, clearance was 4.5- to 50-fold lower in intestinal microsomes (0.0005-0.51 microl/min/P450) compared with the hepatic estimates (0.002-5.8 microl/min/P450), whereas the rank order was consistent between the systems. Assessment of two enterocyte isolation methods (mucosal scraping or enterocyte elution) was performed at the substrate concentrations corresponding to the determined V(max) conditions for 11 pathways. The activity difference between the methods (3-29-fold) was P450-related in the following rank order: CYP2C19 > CYP3A4 > CYP2C9 approximately CYP2D6. After correction for the loss of activity between the methods, the intrinsic activities of hepatic and intestinal CYP3A4, CYP2C9, CYP2C19, and CYP2D6 were comparable for the 16 pathways. The implications of these findings on the prediction of intestinal first-pass metabolism are discussed.
肠道的作用在体外-体内清除率或药物-药物相互作用预测中通常未被纳入，而这种遗漏可能部分解释了经常观察到的普遍预测不足趋势。在本研究中，比较了肝微粒体和肠微粒体混合后的代谢能力，其中包括8种CYP3A底物（咪达唑仑、三唑仑、地西泮、阿普唑仑、氟硝西泮、硝苯地平、睾酮和奎尼丁）以及分别作为CYP2C8、CYP2C9、CYP2C19和CYP2D6探针的紫杉醇、甲苯磺丁脲、S-美芬妥因和布非洛尔。在所研究的底物中，两个系统在动力学类型上达成了普遍共识。在所研究的16条途径中，肠微粒体中获得的75%的K(m)（S(50)）值（5.9 - 769 microM）在肝脏估计值的2倍以内。无论所研究的细胞色素P450（P450）如何，以及对P450丰度的V(max)值进行归一化处理后，与肝脏估计值（0.002 - 5.8微升/分钟/P450）相比，肠微粒体中的清除率低4.5至50倍（0.0005 - 0.51微升/分钟/P450），而两个系统之间的排序顺序是一致的。在对应于11条途径所确定的V(max)条件的底物浓度下，对两种肠上皮细胞分离方法（黏膜刮取或肠上皮细胞洗脱）进行了评估。方法之间的活性差异（3至29倍）与P450相关，顺序如下：CYP2C19 > CYP3A4 > CYP2C9 ≈ CYP2D6。在对方法之间的活性损失进行校正后，肝和肠CYP3A4、CYP2C9、CYP2C19和CYP2D6在16条途径中的内在活性相当。讨论了这些发现对肠道首过代谢预测的影响。
