Molecular diversity of organic ion transporters and their roles in the renal drug excretion

本研究通过对肾脏表达的有机离子转运蛋白的结构、功能和肾小管定位的研究，系统阐明离子型药物的肾脏排泄机制.有机阳离子转运蛋白家族：我们证明了OCT 1和OCT 2有机阳离子转运蛋白识别多种具有相似底物亲和力的阳离子药物。免疫细胞化学研究显示，OCT 1和OCT 2定位于不同肾小管节段的基底外侧膜。此外，我们发现OCT 2在雄性肾脏中的表达高于雌性肾脏，而OCT 1和OCT 3则没有，并且OCT 2表达的性别差异受性别差异的调节.有机阴离子转运蛋白家族：我们已经使用各种异源表达系统表征了有机阴离子转运蛋白OAT 1和OAT-K1的底物特异性。OAT 1识别相对亲水性的有机阴离子，而OAT-K1运输疏水性的有机阴离子。我们证明，OAT 1介导的甲氨蝶呤转运竞争性抑制非甾体抗炎药（NSAID），如吲哚美辛和水杨酸盐，表明OAT 1是甲氨蝶呤和NSAID之间的转运介导的相互作用的主要网站。此外，我们还成功克隆了一个新的有机阴离子转运蛋白OAT-K2。功能分析表明，OAT-K2与OAT-K1一样，也能识别多种疏水性有机阴离子。这些结果将有助于我们评估和预测肾脏药物排泄。此外，估计每个转运蛋白的底物亲和力可能有助于预测转运蛋白介导的药物相互作用。

We have studied the structure, function and tubular localization of organic ion transporters expressed in the kidney to systematically elucidate the mechanisms of renal excretion process of ionic drugs.1. Organic cation transporter family : We demonstrated that OCT1 and OCT2 organic cation transporters recognized a variety of cationic drugs with similar substrate affinity. Immunocytochemical studies revealed that OCT1 and OCT2 were localized at the basolateral membrane of different tubular segments in the kidney. In addition, we found that the expression of OCT2, but not OCT1 and OCT3, was higher in the male kidney than the female kidney, and that the gender difference in OCT2 expression was regulated by sex hormones.2. Organic anion transporter family : We have characterized the substrate specificity of organic anion transporters, OAT1 and OAT-K1, using various heterologous expression systems. OAT1 recognized relatively hydrophilic organic anions, while OAT-K1 transports hydrophobic organic anions. We demonstrated that OAT1-mediated transport of methotrexate was competitively inhibited by nonsteroidal anti-inflammatory drugs (NSAIDs) such as indomethacin and salicylate, suggesting that OAT1 is the major site of the transporter-mediated interaction between methotrexate and NSAIDs. In addition, we succeeded in cloning of a new organic anion transporter, OAT-K2. Functional analysis indicated that OAT-K2 also recognized a variety of hydrophobic organic anions like OAT-K1.These observations will help us to evaluate and predict the renal drug excretion. In addition, estimation of substrate affinity for each transporter could be useful to predict transporter-mediated drug interactions.