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Entecavir (ETV) is a first-line antiviral agent for the treatment of chronic hepatitis B virus infection. Renal excretion is the major elimination path of ETV, in which tubular secretion plays the key role. However, the secretion mechanism has not been clarified. We speculated that renal transporters mediated the secretion of ETV. Therefore, the aim of our study was to elucidate which transporters contribute to the renal disposition of ETV. Our results revealed that ETV (50 M) remarkably reduced the accumulation of probe substrates in MDCK cells stably expressing human multidrug and toxin efflux extrusion proteins (hMATE1/2-K), organic cation transporter 2 (hOCT2), and carnitine/organic cation transporters (hOCTNs) and increased the substrate accumulation in cells transfected with multidrug resistance-associated protein 2 (hMRP2) or multidrug resistance protein 1 (hMDR1). Moreover, ETV was proved to be a substrate of the above-described transporters. In transwell studies, the transport of ETV in MDCK-hOCT2-hMATE1 showed a distinct directionality from BL (hOCT2) to AP (hMATE1), and the cellular accumulation of ETV in cells expressing hMATE1 was dramatically lower than that of the mock-treated cells. The accumulation of ETV in mouse primary renal tubular cells was obviously affected by inhibitors of organic anion transporter 1/3 (Oat1/3), Oct2, Octn1/2, and Mrp2. Therefore, the renal uptake of ETV is likely mediated by OAT1/3 and OCT2 while the efflux is mediated by MATEs, MDR1, and MRP2, and OCTN1/2 may participate in both renal secretion and reabsorption. C hronic hepatitis B virus (HBV) infection, with a high rate of morbidity, is one of the most important health problems worldwide. It is a major risk factor for cirrhosis and liver cancer (1). Entecavir (ETV) is a novel and highly selective deoxyguanosine analog with a high antiviral efficacy and a high genetic barrier to viral resistance (2). Since ETV was approved in 2005 by the U.S. FDA, it has been unanimously recommended as the fist-line antiviral agent for treatment of chronic HBV infection by global hepatology scientific societies, such as the American Association for the Study of Liver Diseases and the European Association for the Study of the Liver (3, 4).It was reported that about 73% of orally dosed ETV was eliminated in urine in an unchanged form. The renal clearance of ETV is independent of the dose and ranged from 360 to 471 ml/min in healthy volunteers, which is much greater than the glomerular filtration rate (GFR; 120 to 130 ml/min for normal humans) (5, 6), suggesting that tubular secretion accounts for the major part of the urinary excretion of ETV. Therefore, it is speculated that transporters expressed on the proximal tubular cells are involved in the process of tubular secretion of ETV. Furthermore, ETV is a hydrophilic weak base with a pK a value of 10.5 (Ͼ99% of ETV is positively charged at pH 7.4) and a logD value of Ϫ1.1 (pH 4 to 10), which implies that ETV is unlikely to penetrate the cell membrane by passive diffusion. Thus, transpor...

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BACKGROUND AND PURPOSENitidine chloride (NC), a benzophenanthridine alkaloid, has various biological properties including anticancer and analgesic activities. The aim of the present study was to evaluate the role of organic cation transporter 2 (OCT2) and multidrug and toxin extrusion 1 (MATE1) in the renal disposition and nephrotoxicity of NC. EXPERIMENTAL APPROACHMDCK cells stably expressing human OCT2 and/or hMATE1 were used to investigate the OCT2-and MATE1-mediated transport of NC. In addition, the accumulation of NC and its potential toxicity were studied in rat primary-cultured proximal tubular (rPCPT) cells and in rats in vivo. KEY RESULTSNC was found to be a high-affinity substrate of both OCT2 and MATE1 with high cytotoxicity in MDCK-hOCT2/hMATE1 and MDCK-hOCT2 compared to mock cells. The OCT2 inhibitors, cimetidine and (+)-tetrahydropalmatine ((+)-THP), significantly reduced NC accumulation and cytotoxicity in MDCK-hOCT2, MDCK-hOCT2/hMATE1 and rPCPT cells. Severe kidney damage with high levels of blood urea nitrogen and lactate dehydrogenase (LDH), reduced levels of alkaline phosphatase (ALP) and pathological changes were found in rats after 20 days of successive i.v. doses of NC (5 mg·kg À1 ·day À1 ). Concomitantly, the concentration of NC in the kidney reached similar high levels at 2 h after the last dose of the 20 day treatment as those observed at 0.5 h after a single i.v. dose of 5 mg·kg À1 . CONCLUSIONS AND IMPLICATIONSOur data indicate that NC-induced nephrotoxicity might be mainly attributed to OCT2-mediated extensive renal uptake and weak tubular secretion by MATE1.Abbreviations ASP + , 4-(4-(dimethylamino)styryl)-N-methylpyridinium iodide; ESI, electrospray ionization; HPC, hydroxypropyl cellulose; MATE1, multidrug and toxin extrusion 1; MPP

Sulpiride, a selective dopamine D2 receptor blocker, is used widely for the treatment of schizophrenia, depression and gastric/duodenal ulcers. Because the great majority of sulpiride is positively charged at physiological pH 7.4, and ~70% of the dose recovered in urine is in the unchanged form after human intravenous administration of sulpiride, it is believed that transporters play an important role in the renal excretion of sulpiride. The aim of the present study was to explore which transporters contribute to the renal disposition of sulpiride. The results demonstrated that sulpiride was a substrate of human carnitine/organic cation transporter 1 (hOCTN1) and 2 (hOCTN2), human organic cation transporter 2 (hOCT2), human multidrug and toxin efflux extrusion protein 1 (hMATE1) and 2-K (hMATE2-K). Sulpiride accumulation from the basolateral (BL) to the apical (AP) side in MDCK-hOCT2/pcDNA3.1 cell monolayers was much greater than that in MDCK-hOCT2/hMATE1 cells, and cimetidine dramatically reduced the intracellular accumulation of sulpiride from BL to AP. In addition, the accumulation of sulpiride in mouse primary renal tubular cells (mPRTCs) was markedly reduced by inhibitors of Oct2 and Octns. The results implied that OCTN1, OCTN2, OCT2, MATE1 and MATE2-K probably contributed to the renal transfer of sulpiride, in which OCT2 mediated the uptake of sulpiride from the bloodstream to the proximal tubular cells, while MATEs contributed to the sulpiride efflux from the proximal tubular cells to the renal lumen, and OCTNs participated in both renal secretion and reabsorption.