Matsunaga Norikazu, Wada Sho, Nakanishi Takeo, Ikenaga Miho, Ogawa Mikio, Tamai Ikumi
Department of Membrane Transport and Biopharmaceutics, Faculty of Pharmaceutical Sciences, Institute of Medical, Pharmaceutical and Health Sciences, Kanazawa University , Kakuma-machi, Kanazawa, 920-1192, Japan.
Mol Pharm. 2014 Feb 3;11(2):568-79. doi: 10.1021/mp400513k. Epub 2013 Dec 13.
In recent years, it has become increasingly important to test the safety of circulating metabolites of novel drugs as part of drug discovery and development programs. Accordingly, it is essential to develop suitable methods for identifying the major metabolites and their disposition in animal species and in humans. Mycophenolic acid (MPA), a selective inosine-5'-monophosphate dehydrogenase (IMPDH) inhibitor, is metabolized by glucuronidation and enterohepatic circulation of MPA-glucuronides is an important factor in the continuous systemic exposure of MPA. In humans, about 90% of the administered MPA dose is finally excreted as MPA phenyl-glucuronide (MPAG) in urine. Notably, the plasma concentration of MPAG is much higher than that of MPA. These factors suggest that, after its formation in hepatocytes, MPAG is excreted into bile and is also transported across the basolateral membrane to enter the circulation. In the present study, we performed metabolic/hepatobiliary transport studies of MPA and MPAG using sandwich-cultured human hepatocytes (SCHH) and constructed mathematical models of their hepatic disposition. We also performed vesicular transport studies to identify which human multidrug resistance-associated proteins (MRPs) are involved in the transport of MPAG from hepatocytes. MPAG was a preferred substrate for the biliary excretion transporter MRP2 and the hepatic basolateral transporters MRP3 and MRP4 in conventional and metabolic/hepatobiliary transport studies using SCHH and vesicular transport studies using human MRP-expressing membrane vesicles. The resulting mathematical model suggested that the basolateral transport plays an important role in the hepatic disposition of MPAG formed in hepatocytes. Our findings suggest that mathematical modeling of metabolic/hepatobiliary transport studies using SCH will provide useful information for determining the fate of metabolites formed in hepatocytes.
近年来，作为药物发现和开发项目的一部分，测试新型药物循环代谢物的安全性变得越来越重要。因此，开发合适的方法来鉴定主要代谢物及其在动物和人类体内的处置情况至关重要。霉酚酸（MPA）是一种选择性肌苷-5'-单磷酸脱氢酶（IMPDH）抑制剂，通过葡萄糖醛酸化进行代谢，MPA-葡萄糖醛酸苷的肠肝循环是MPA持续全身暴露的一个重要因素。在人类中，约90%的MPA给药剂量最终以MPA苯葡萄糖醛酸苷（MPAG）的形式经尿液排出。值得注意的是，MPAG的血浆浓度远高于MPA。这些因素表明，MPAG在肝细胞中形成后，会排泄到胆汁中，也会穿过基底外侧膜进入循环。在本研究中，我们使用夹心培养的人肝细胞（SCHH）对MPA和MPAG进行了代谢/肝胆转运研究，并构建了它们肝脏处置的数学模型。我们还进行了囊泡转运研究，以确定哪些人类多药耐药相关蛋白（MRPs）参与了MPAG从肝细胞的转运。在使用SCHH的常规和代谢/肝胆转运研究以及使用表达人类MRP的膜囊泡的囊泡转运研究中，MPAG是胆汁排泄转运体MRP2以及肝脏基底外侧转运体MRP3和MRP4的优选底物。所得的数学模型表明，基底外侧转运在肝细胞中形成的MPAG的肝脏处置中起重要作用。我们的研究结果表明，使用SCH进行代谢/肝胆转运研究的数学建模将为确定肝细胞中形成的代谢物的命运提供有用信息。
