Molecular basis for quantitative prediction of drug-drug interaction at excretion process

分子生物学的最新进展揭示了许多类型的异种转运蛋白在药物分泌到尿液和胆汁中的主导作用，导致药物在排泄过程中可能发生药物相互作用。因此，基于体外实验系统对相互作用进行预测是可望的。本研究旨在阐明预测药物在肝、肾排泄过程中相互作用的分子基础。作为排泄到胆汁和尿液中的模型药物，使用了新型尿酸生成抑制剂Y-700和新型利尿剂M17055。我们认为，肝脏对Y-700的摄取不同于OATP家族，而是依赖于Na~+的有机阴离子转运系统，部分Y-700摄取是由胆汁酸转运体NTCP介导的。我们还阐明了OAT1在M17055肾脏摄取中的重要作用。此外，我们还发现了表达在肾脏和/或小肠顶膜上的某些类型的转运蛋白与含有PDZ结构域的蛋白PDZK家族的直接相互作用，这意味着这种蛋白-蛋白相互作用可能在转运蛋白的顶端定位中发挥作用。在PDZ蛋白中，PDZK1与OCTN2共同定位于肾和小肠的顶膜上，并能刺激包括OCTN1、OCTN2和PEPT2在内的多种转运蛋白的转运活性。最后，我们重点研究了Na~+/H~+交换器(NHE)3对寡肽转运体PEPT1的功能调节，它还可以与PDZ蛋白结合并提供可被PEPT1用于转运活性的H~+梯度。NHE3影响PEPT1的转运活性、Na~(++)和H~(++)依赖性。因此，本研究提出了一个新的概念，即接头蛋白(如PDZK1)和其他膜蛋白(如NHE3)都具有与转运蛋白相互作用的潜力，可能是预测药物在排泄过程中相互作用的重要分子基础。

Recent progress in molecular biology has revealed predominant roles of many types of xenobiotic transporters in drug secretion into the urine and bile, leading to possible occurrence of drug-drug interaction at the excretion processes. Therefore, it is expected to predict the interaction based on in vitro experimental system. This study aimed to clarify molecular basis for the prediction of drug-drug interaction at the excretion process in liver and kidney. As model drugs that are excreted into the bile and urine, a novel uric acid generation inhibitor Y-700 and a novel diuretic M17055 were used. We have suggested involvement of Na^+-dependent organic anion transport system, other than OATP family, in hepatic uptake of Y-700, part of Y-700 uptake being mediated by bile acid transporter NTCP. We have also clarified important role of OAT1 in renal uptake of M17055. Furthermore, we have identified direct interaction of certain types of transporters, that are expressed on apical membranes in kidney and/or small intestine, with PDZ domain containing proteins PDZK family, implying that such protein-protein interaction may play a role in apical localization of the transporters. Among the PDZ proteins, PDZK1 is colocalized on apical membranes in kidney and small intestine with OCTN2, and can stimulate transport activity of several transporters including OCTN1, OCTN2 and PEPT2. Finally, we have focused on functional modulation of oligopeptide transporter PEPT1 by Na^+/H^+ exchanger (NHE) 3 that can also bind to the PDZ proteins and supply H^+ gradient that can be utilized by PEPT1 for transport activity. NHE3 affects transport activity, Na^+- and H^+- dependence of PEPT1. Thus, this study has proposed a novel concept that adaptor proteins (such as PDZK1) and other membrane proteins (such as NHE3), both having interaction potential with transporters, could be important molecular basis for prediction of drug-drug interaction at excretion processes.