Analysis of the factors governing the elimination route of therapeutic agents

施用于身体的治疗剂通常通过肝脏和肾脏中的代谢和/或排泄而消除。药物的消除途径（肝脏或肾脏）被认为主要取决于药物的理化性质。近年来，分子生物学的研究表明，多种药物转运蛋白在两种器官中都有表达，并参与药物的体内分布。因此，本研究的重点是这些转运蛋白在体内的功能，以确定药物消除途径。我们建立了Ntcp和Oatp 1的基因转染系统，并分析了它们的底物特异性。许多类型的治疗剂被确定为Oatp 1的底物，而Ntcp在胆汁酸内具有窄的底物特异性。通过比较肝细胞和转染子之间的转运活性，我们估计了Oatp 1对肝细胞对每种底物的总体摄取的贡献率。在这项研究中，我们还确定了新的克隆，燕麦3和燕麦4，这是在肝脏中表达。检测了在肝基底外侧膜上表达的Mrp 3的底物特异性。我们发现，Mrp 3接受胆汁酸作为底物，并参与其流出的肝细胞在离体大鼠肝灌注系统。胆汁淤积状态以及苯巴比妥治疗导致Mrp 3的过度表达，其至少部分来自mRNA水平的增加。由于Mrp 3接受多种类型的有机阴离子作为底物，这些发现意味着，应考虑特定的运输系统参与药物从肝脏到血液的外排。

Therapeutic agents administered to the body are generally eliminated by the metabolism and/or excretion both in the liver and kidney. The elimination route (liver or kidney) of the drugs has been believed to mainly depend on the physicochemical properties of the drugs. However, the recent advance in the molecular biology revealed that many types of drug transporters are expressed in both organs and involved in drug disposition. Therefore, the present study focused on the function of such transporters in vivo to determine the drug elimination route. We have established the gene transfectant systems both for Ntcp and Oatp1 and analyzed their substrate specificity. Many types of therapeutic agents were identified as substrates of Oatp1 whereas Ntcp has the narrow substrate specificity within the bile acids. By comparing the transport activity between the hepatocytes and such transfectants, we have estimated the contribution ratio of Oatp1 to the overall uptake of each substrate by hepatocytes. In this study we also identified new clones, Oat3 and Oat4, which are expressed in the liver. Substrate specificity of Mrp3 which is expressed on the basolateral membrane of the liver was examined. We found that Mrp3 accepts bile acids as substrates and is involved in their efflux from the hepatocytes in the isolated rat liver perfusion system. Cholestatic condition as well as phenobarbital treatment results in the overexpression of Mrp3 which come from at least partially the increase in mRNA level. Since Mrp3 accept many types of organic anions as substrates, these findings imply that the specific transport systems should be considered to be involved in the efflux of drugs from the liver to blood.