Cloning of transporters for anionic drugs and the application to pharmacokinetic analysis

本研究的目的是确定SLC22家族有机阴离子转运体的新成员，这些新成员对于了解各种药物和外源生物的药代动力学是必不可少的。这项研究的最终目的是通过揭示人体转运蛋白的功能以及组织和细胞分布来确定有机阴离子转运蛋白在药物动力学中的作用。在本研究中，我们鉴定了SLC22家族的6个新成员，包括OAT4(有机阴离子转运体4)、OAT5、OAT6、OAT7、CT2(肉碱转运体2)和URAT1(尿酸盐转运体1)。OAT4、OAT5和OAT7表现出相似的底物选择性，更倾向于硫酸雌酮等硫酸盐结合物。OAT4和OAT5分别存在于人和大鼠肾近端小管的顶膜。相反，OAT7存在于肝细胞的窦状膜中。因此，推测肝细胞中形成的硫酸盐结合物通过OAT7进入血液，并被肾近端小管上皮细胞通过基底膜上的OAT1和OAT3摄取，通过顶膜OAT4或OAT5排泄到尿液中。URAT1存在于肾近端小管的顶膜上，作为一种有机阴离子交换器，转运尿酸盐、乳酸、吡啶羧酸盐和烟酸盐。URAT-1负责尿酸盐的肾脏重吸收。它的遗传缺陷被证明是特发性肾低尿酸血症的原因之一。CT2和OAT6是具有不同性质的肉碱转运蛋白。值得注意的是，CT2在睾丸中特异表达，并被认为对精子成熟起重要作用。此外，通过建立稳定表达人有机阴离子转运体的细胞系，并利用这些细胞系分析各种有机化合物的转运特性，我们证明了这些细胞系在药物-药物相互作用的体外预测中是非常有用的。

The purpose of this study is to identify new members of organic anion transporters of SLC22 family essential for the understanding of the pharmacokinetics of various drugs and xenobiotics. The final goal of this research is to establish the role of organic anion transporters in the pharmacokinetics by revealing the functions and tissue and cellular distribution of the human transporters. In the present study, we have identified six new members of the SLC22 family including OAT4 (organic anion transporter 4), OAT5, OAT6, OAT7, CT2 (carnitine transporter 2) and URAT1 (urate transporter 1). OAT4, OAT5 and OAT7 exhibit similar substrate selectivity preferring sulfate conjugates such as estrone sulgfate. OAT4 and OAT5 are present in the apical membrane of renal proximal tubules of human and rat, respectively. In contrast, OAT7 is present in the sinusoidal membrane of hepatocytes. Therefore, it is proposed that the sulfate conjugates formed in hepatocytes move into blood through OAT7 and taken up by renal proximal tubule epithelial cells via OAT1 and OAT3 on the basolateral membrane and excreted into urine via apical membrane OAT4 or OAT5. URAT1 is present in the apical membrane of renal proximal tubules and functions as an organic anion exchanger transporting urate, lactate, pyradine carboxylate and nicotinate. URAT 1 is responsible for the renal reabsorption of urate. Its genetic defect has turned out to be a cause of idiopathic renal hypouricemia. CT2 and OAT6 are carnitine transporters with different properties. It is notable that CT2 is expressed specifically in testis and is suggested to be important for sperm maturation. In addition, by generating cell lines stably expressing human organic anion transporters and analyzing the properties of the transport of various organic compounds using the cell lines, we have demonstrated that those cells lines are quite useful in the in vitro prediction of drug-drug interactions.