常见肠、肝、肾疾病以及糖尿病状态下相关药物转运体的变化及其应用意义

转运体是位于细胞膜上的功能性膜蛋白。目前研究证明转运体在药物的吸收、分布以及排泄过程中发挥着重要的作用,其中以肠道、肝脏以及肾脏转运体的作用最为明显。疾病状态下转运体的表达和功能会发生改变,影响药物在体内的处置过程,使药物的药代动力学发生明显改变而对疾病的药物治疗产生影响。本文综述了常见肠道疾病、肝脏疾病、肾脏疾病以及糖尿病状态下相关转运体的变化及其对临床药物治疗的影响。     

疾病状态下有机阴离子转运体表达和功能的变化及其机制研究进展

有机阴离子转运体属于溶质转运体22亚家族成员，是一类重要的摄取类转运体，其有多个亚型。有机阴离子转运体在体内介导多种小分子内源性物质的转运，起到维持机体内环境稳态的作用。此外，临床上许多药物也是有机阴离子转运体的底物。研究表明某些疾病可能导致有机阴离子转运体表达和功能的异常改变，进而影响药物的疗效或导致机体内源性物质水平紊乱。对有机阴离子转运体的分布和功能进行简要介绍，并综述了疾病状态下有机阴离子转运体表达和功能变化及其机制的研究进展。     

肝脏的药物转运体及其临床意义的研究进展

介绍肝脏的药物转运体的功能、分布、底物特征及其对药物的体内处置过程的影响。按照肝脏药物转运体系统、体内处置的影响进行分类归纳总结。肝脏作为机体对内源物和外源物(药物)的代谢和排泄的重要器官,除了药物代谢酶外,肝脏转运体在其中也发挥着一定的作用。当药物转运体的功能受到影响时,往往会使其底物性药物的有效性和安全性发生改变。     

转运体在药物肾脏排泄中的重要作用

转运体是细胞膜上的功能性蛋白,在肾脏中表达广泛,对许多内源性或外源性物质的肾脏分泌及重吸收起到了至关重要的作用。许多药物（包括有机阴离子药物、有机阳离子药物及肽类药物等）在肾脏排泄的过程中,经主要集中在近端肾小管的转运体主动转运介导。临床合用某些药物时可能在肾脏发生转运体介导的相互作用。从肾脏主要转运体的分布及功能出发,综述其在药物肾脏排泄中的作用。     

转运体介导中药与化学药相互作用研究进展

ATP结合盒转运体家族和溶质转运体家族的转运体参与众多的中药与化学药相互作用过程,因其可介导内外源性药物及其代谢物的跨膜转运。转运体同细胞色素P450酶类似,会对特征底物的血药浓度和组织分布产生一定影响,从而改变药物的药效或者毒副作用。本文综述了具有重要临床意义的P-糖蛋白、乳腺癌耐药蛋白、有机阴离子转运体、有机阳离子转运体和有机阴离子转运多肽等5种转运体所介导的中药与化学药相互作用,以期为临床联合用药提供一定的理论依据。     

有机阳离子转运体的基因多态性研究进展

人体的肝脏、肾脏和肠道上广泛分布有各种转运蛋白,其中有机阳离子转运体（OCTs）负责转运一些内、外源性的有机阳离子的转运。在此我们主要讨论的是OCTs家族的成员OCT1和OCT2的基因多态性以及其功能意义。同时我们也就OCT对于药物代谢动力学以及药效学的影响进行阐述,以及OCTs在药物相互作用上的意义。     

肾脏转运体和/或代谢酶介导药物排泄及药物相互作用的研究进展

肾脏是人体最重要的排泄器官。肾单元近端小管细胞具有多种药物转运体和代谢酶,在药物及其代谢物处置中发挥关键作用。近端小管细胞中主要转运体包括有机阴离子转运体、有机阳离子转运体、有机阳离子/肉毒碱转运体、多药及毒素外排转运蛋白、P-糖蛋白、乳腺癌耐药蛋白和多药耐药相关蛋白;主要代谢酶包括细胞色素P450酶,UDP-葡萄糖醛酸基转移酶、磺酸基转移酶、谷胱甘肽S-转移酶。肾脏转运体和/或代谢酶介导药物相互作用(DDIs)是临床关注的重要问题。肾脏转运体和代谢酶存在密切协作关系,在肾脏也存在多种相互作用现象(包括转运-转运相互作用,代谢-代谢相互作用和转运-代谢相互作用),其显著影响药物肾脏处置、临床疗效和肾毒性。本文系统阐述了这些相互作用对药物及其代谢物的肾脏排泄、药动学、DDIs和肾毒性的影响。今后需要进一步阐明肾脏转运-代谢相互作用机制,将有助于研究体内药物肾脏处置和DDIs,促进临床合理用药。     

慢性肾脏病对药物转运和代谢的影响

本文介绍了慢性肾脏病状态下,肾脏、肝脏及肠道中主要代谢酶和药物转运体介导药物转运和代谢的最新研究进展,以期为临床合理用药提供参考。肾脏疾病对肾脏、肝脏和肠道转运体及代谢酶均有一定的影响,是与肾脏本身器质性病变协同进展而表现出来的病理生理过程。在科研及临床实践中,有必要将肾脏疾病对其他器官的影响一并分析、综合考虑,以作出最客观最合理的判断。     

血脑屏障上ABC转运体与中枢神经系统疾病相关性的研究进展

ABC转运体作为血脑屏障上一类重要的外排转运体,介导了内源性物质、药物及环境毒素的外排过程。疾病状态下,ABC转运体的功能及表达会发生改变,有些疾病会导致转运体过表达或者活性增强,引发耐药现象;还有一些疾病会引起转运体损伤,导致毒素蓄积脑内,加剧疾病的发展。将各种脑部疾病与ABC转运体之间的关系研究清楚,将有助于阐明致病机制,并可为改善脑部耐药及治疗中枢神经疾病提供思路和策略。本文就这一问题,综述了血脑屏障ABC转运体在多种疾病状态下功能与表达的变化,及这些改变对疾病产生的影响,并初步探讨了相关机制,提出了一些改善耐药和治疗疾病的策略。     

肾脏有机阳离子转运体家族研究进展

肾脏转运体在肾脏处置药物过程中发挥重要作用.临床所用药物与肾脏有机阳离子转运体家族密切相关.本文对肾脏有机阳离子转运体家族的主要成员及其特征、影响因素以及实验方法等研究进展进行综述.     

Organic Cation Transporter OCTs (SLC22) and MATEs (SLC47) in the Human Kidney

In the kidney, human organic cation transporters (OCTs) and multidrug and toxin extrusion proteins (MATEs) are the major transporters for the secretion of cationic drugs into the urine. In the human kidney, OCT2 mediates the uptake of drugs from the blood at the basolateral membrane of tubular epithelial cells, and MATE1 and MATE2-K secrete drugs from cells into the lumen of proximal tubules. However, the expression of these transporters depends on the species of the animal. In the rodent kidney, OCT1 and OCT2 are expressed at the basolateral membrane, and MATE1 localizes at the brush-border membrane. Together, these transporters recognize various compounds and have overlapping, but somewhat different, substrate specificities. OCTs and MATEs can transport important drugs, such as metformin and cisplatin. Therefore, functional variation in OCTs and MATEs, including genetic polymorphisms or inter-individual variation, may seriously affect the pharmacokinetics and/or pharmacodynamics of cationic drugs. In this review, we summarize the recent findings and clinical importance of these transporters.     

Organic cation transporters (OCTs, MATEs), in vitro and in vivo evidence for the importance in drug therapy

Organic cation transporters (OCTs) of the solute carrier family (SLC) 22 and multidrug and toxin extrusion (MATE) transporters of the SLC47 family have been identified as uptake and efflux transporters, respectively, for xenobiotics including several clinically used drugs such as the antidiabetic agent metformin, the antiviral agent lamivudine, and the anticancer drug oxaliplatin. Expression of human OCT1 (SLC22A1) and OCT2 (SLC22A2) is highly restricted to the liver and kidney, respectively. By contrast, OCT3 (SLC22A3) is more widely distributed. MATEs (SLC47A1, SLC47A2) are predominantly expressed in human kidney. Data on in vitro studies reporting a large number of substrates and inhibitors of OCTs and MATEs are systematically summarized. Several genetic variants of human OCTs and in part of MATE1 have been reported, and some of them result in reduced in vitro transport activity corroborating data from studies with knockout mice. A comprehensive overview is given on currently known genotype-phenotype correlations for variants in OCTs and MATE1 related to protein expression, pharmacokinetics/-dynamics of transporter substrates, treatment outcome, and disease susceptibility.     

Interaction of organic cations with a newly identified plasma membrane monoamine transporter

Many endogenous compounds and xenobiotics are organic cations that rely on polyspecific organic cation transporters (OCTs) to traverse cell membranes. We recently cloned a novel human plasma membrane monoamine transporter (PMAT) that belongs to the equillibrative nucleoside transporter (ENT) family. We have reported previously that, unlike other ENTs, PMAT (also known as ENT4) is a Na+-independent and membrane potential-sensitive transporter that transports monoamine neurotransmitters and the neurotoxin 1-methyl-4-phenylpyridinium (MPP+). These compounds are the known substrates for OCTs, which raises the possibility that PMAT functions as a polyspecific transporter like the OCTs. In the present study, we analyzed the interaction of PMAT with a series of structurally diverse organic cations using MDCK cells stably expressing human PMAT. Our study showed that PMAT interacts with many organic cations that have heterogeneous chemical structures. PMAT transports classic OCT substrates, such as tetraethylammonium, guanidine, and histamine. Prototype OCT inhibitors, including cimetidine, and type II cations (e.g., quinidine, quinine, verapamil, and rhodamine123) are also PMAT inhibitors. An analysis of molecular structures and apparent binding affinities revealed that charge and hydrophobicity are the principal determinants for transporter-substrate/inhibitor interaction. A planar aromatic mass seems to be important for high affinity interaction. trans-Stimulation and efflux studies demonstrate that PMAT is able to mediate bidirectional transport. These functional properties of PMAT are strikingly similar to those of the OCTs. We therefore conclude that PMAT can function as a polyspecific organic cation transporter, which may play a role in organic cation transport in vivo.     

Drug uptake systems in liver and kidney

The hepatobiliary system and the kidneys are the main routes by which drugs and their metabolites leave the body. Compounds that are mainly excreted into bile in general have relatively high molecular weights, are amphipathic and highly bound to plasma proteins. In contrast, compounds that are predominantly excreted into urine have relatively low molecular weights, are more hydrophilic and generally less protein bound. The first step in drug elimination in liver and kidney is uptake into hepatocytes or into proximal tubular cells. The substrate specificity and affinity of the uptake carriers expressed at the basolateral membranes of hepatocytes and proximal tubular cells could therefore play an important role for the determination of the main elimination route of a compound. This review discusses the tissue distribution, substrate specificity, transport mechanism, and regulation of the members of the organic anion transporting polypeptide (Oatp/OATP) superfamily (solute carrier family SLC21A) and the SLC22A family containing transporters for organic cations (OCTs) and organic anions (OATs). The Oatps/OATPs are mainly important for the hepatic uptake of large amphipathic organic anions, organic cations and uncharged substrates, whereas OCTs and OATs mediate uptake of predominantly small organic cations and anions in liver and kidney.     

Membrane transport function in primary cultures of human proximal tubular cells

To further develop primary cultures of human proximal tubular (hPT) cells for study of drug disposition, we determined kinetics and protein expression of several key transporters for organic anions and cations, peptides, and neutral amino acids. p-Aminohippurate uptake exhibited similar kinetics as published values, was inhibited by cephaloridine, cimetidine, methotrexate, and urate, consistent with function of both organic anion transporter 1 (OAT1) and OAT3. Transport rates by organic cation transporters (OCTs) were up to three-fold higher than those of OATs. Of the OCT substrates tested, triethanolamine exhibited the highest transport rates across the basolateral membrane (BLM). OCTN1 exhibited high-affinity, low-capacity BLM transport of l-carnitine. Glycylsarcosine transport by PepT2 was rapid and comparable to that of OCTs. Amino acid System L on the BLM exhibited comparable kinetic parameters for transport of l-leucine as the OATs. Efflux of verapamil across the brush-border membrane by P-glycoprotein was very rapid. Expression of carriers was generally maintained throughout 5 days of culture. Of the four OAT proteins studied (OAT1-4), expression of OAT1 and OAT3 was the most readily detected and exhibited interindividual variation. OCTN2 was the major OCT in hPT cells. Expression was also quantified for multidrug resistance-associated proteins 2 and 5 and P-glycoprotein. These results show that primary cultures of hPT cells express a diverse array of transporters for major classes of important drugs and are suitable for study of drug transport and disposition and assessment of potential drug-drug interactions in human kidney.     

Transporter-mediated renal handling of nafamostat mesilate

Nafamostat mesilate (NM) is a serine-protease inhibitor that is rapidly eliminated from the circulation and accumulated in the kidney. This study was conducted to characterize the mechanism of NM transport in the kidney because a serious side effect of NM-induced hyperkalemia may be related to accumulation of NM in the kidney. Measurements of uptake of NM in vivo by the kidney uptake index (KUI) method and of transport in an in vitro-cultured LLC-PK1 cell system suggested the involvement of an organic cation transporter (OCT). To clarify the involvement of OCTs located in the basolateral membrane of proximal tubules, we evaluated NM transport by OCTs expressed in Xenopus laevis oocytes. The IC(50) values of NM on [(14)C]TEA ([(14)C]tetraethylammonium) uptake by rOCT1, rOCT2, and hOCT2 were 50, 0.5, and 20 microM, respectively, and NM was concluded to be a substrate of OCTs. To investigate the transport of NM across the brush-border membrane, we examined the uptake of NM into brush-border membrane vesicles (BBMVs) isolated from rat renal cortex. NM was taken up into the BBMVs, and the uptake was decreased by unlabeled NM and temperature, implying that a transporter(s) is also involved in NM transport across the apical membrane. NM was not a substrate of hOCTN1, hOCTN2, or P-gp, implying the involvement of some unknown transporter(s). Thus, renal accumulation of NM can be explained by the involvement of the basolateral OCTs, though the influence of the apical membrane transporter remains to be clarified.     

The inhibitory effects of camptothecin (CPT) and its derivatives on the substrate uptakes mediated by human solute carrier transporters (SLCs)

1.?Camptothecin (CPT) and its derivatives are potent candidate compounds in treating cancers. However, their clinical applications are largely restricted by severe toxicities.

2.?The solute carrier transporters (SLCs), particularly the organic anion transporting polypeptides and organic anion/cation transporters (OATs/OCTs) are widely expressed in human key organs and responsible for the cellular influx of many substances including endogenous substrates and many clinically important drugs. Drug–drug interactions through SLCs often result in unsatisfied therapeutic outcomes and/or unexpected toxicities.

3.?This study investigated the inhibitory effects of CPT and its eight derivatives on the cellular uptake of specific substrates mediated by the essential SLCs in over-expressing Human embryonic kidney 293 cells.

4.?Our data revealed that CPT, 10-hydroxycamptothecin (HCPT), 10-methoxycamptothecin (MCPT) and 9-nitrocamptothecin (9NC) significantly inhibit the uptake activity of OAT3. 9NC also inhibited the substrate transport mediated by OAT1. The substrate uptakes of OAT1, OCTN1 and OCTN2 were significantly decreased in the presence of CZ112, while CPT-11 potently down-regulated the transport activity of OCT1 and OCT3.

5.?In summary, our study demonstrated that CPT and its eight derivatives selectively inhibit the substrate uptakes mediated by the essential SLCs. This information contributes to understanding the localized toxicity of CPTs and provides novel molecular targets for the therapeutic optimization of CPTs in the future.     

Activation of ATP-sensitive K+ channels by ADP and K+ channel openers: homology model of sulfonylurea receptor carboxyl-termini

The multispecific organic anion transporters have been indicated to be involved in the transmembrane transport of various anionic substances. The kidney and liver possess the distinct organic anion transport pathways for the elimination of potentially toxic anionic drugs and metabolites. In the kidney, proximal tubular cells actively excrete organic anions of both endogenous and exogenous origin. We have isolated the renal multispecific organic anion transporter, OAT1 (organic anion transporter 1), from the rat kidney. OAT1 is a 551-amino acid residue protein with 12 putative membrane spanning domains. OAT1 mediates sodium-independent, anion exchange for a variety of organic anions including p-aminohippurate, cyclic nucleotides, prostanoides, dicarboxylates, and anionic drugs including beta-lactams, non-steroidal antiinflammatory drugs, diuretics and antiviral drugs. So far, three other isoforms have been identified. OATs comprise a new family of multispecific organic anion transporter, i.e., the OAT family. OATs show weak structural similarity to organic cation transporters (OCTs) and OCTN/carnitine transporters. All of the members of the OAT family are commonly expressed in the kidney, suggesting its significance in the renal organic anion excretion. In addition, OAT members appear to be responsible for the distribution/elimination of water soluble anionic drugs into/from the liver, brain and fetus.