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

我们对肾脏中表达的有机离子转运体的结构、功能和肾小管定位进行了研究，以系统阐明离子药物肾脏排泄过程的机制。有机阳离子转运体家族：我们证明了OCT1和OCT2有机阳离子转运体识别具有相似底物亲和力的多种阳离子药物。免疫细胞化学研究表明，OCT1和OCT2定位于肾脏不同管段的基底膜。此外，我们还发现OCT2在男性肾脏中的表达高于女性肾脏，而OCT1和Oct3在男性肾脏中的表达不高于女性肾脏，并且OCT2表达的性别差异受性激素的调节。有机阴离子转运蛋白家族：我们使用各种异源表达系统表征了有机阴离子转运蛋白OAT1和OAT-K1的底物特异性。OAT1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。我们发现非甾体抗炎药(NSAIDs)如消炎痛和水杨酸盐竞争性地抑制了OAT1介导的甲氨蝶呤转运，表明OAT1是转运体介导的甲氨蝶呤与NSAIDs相互作用的主要部位。此外，我们还成功克隆了一种新的有机阴离子转运蛋白OAT-K2。功能分析表明，OAT-K2还能识别OAT-K1等多种疏水性有机阴离子。这些观察结果将有助于我们评估和预测肾脏药物的排泄。此外，估计每个转运体的底物亲和力可能有助于预测转运体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.