Abstract

1. Mycophenolic acid (MPA) has become a cornerstone of immunosuppressive therapy, in particular for transplant patients. In the gastrointestinal tract, the liver and the kidney, MPA is mainly metabolized into phenyl-β-d glucuronide (MPAG). Knowledge about the interactions between MPA/MPAG and membrane transporters is still fragmented.

2. The aim of the present study was to explore these interactions with the basolateral hepatic MRP4 transporter. The inhibition of the MRP4-driven transport by various drugs which can be concomitantly prescribed was also evaluated.

3. In vitro experiments using vesicles overexpressing MRP4 showed an ATP-dependent transport of MPAG driven by MRP4 (Michaelis–Menten constant of 233.9 ± 32.8 µM). MPA was not effluxed by MRP4. MRP4-mediated transport of MPAG was inhibited (from −43% to −84%) by ibuprofen, cefazolin, cefotaxime and micafungin. An in silico approach based on molecular docking and molecular dynamics simulations rationalized the mode of binding of MPAG to MRP4. The presence of the glucuronide moiety in MPAG was highlighted as key, being prone to make electrostatic and H-bond interactions with specific residues of the MRP4 protein chamber. This explains why MPAG is a substrate of MRP4 whereas MPA is not.

摘要

1. 麦考酚酸（MPA）已成为免疫抑制疗法的基石，尤其是对于移植患者而言。在胃肠道，肝脏和肾脏中，MPA主要代谢为苯基-β - d葡糖醛酸苷（MPAG）。关于MPA / MPAG与膜转运蛋白之间相互作用的知识仍然是零碎的。

2. 本研究的目的是探讨与基底外侧肝MRP4转运蛋白的这些相互作用。还评估了各种药物对MRP4驱动的转运的抑制作用，这些药物可以同时服用。

3. 使用过表达MRP4的囊泡进行的体外实验显示，由MRP4驱动的MPAG依赖ATP的转运（Michaelis-Menten常数为233.9±32.8 µM）。MPA没有被MRP4释放。布洛芬，头孢唑林，头孢噻肟和米卡芬净抑制了MRP4介导的MPAG转运（从-43％到-84％）。基于分子对接和分子动力学模拟的计算机方法合理化了MPAG与MRP4的结合模式。MPAG中葡糖醛酸苷部分的存在被强调为关键，易于与MRP4蛋白腔室的特定残基发生静电和H键相互作用。这解释了为什么MPAG是MRP4的底物，而MPA不是。