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Kenichi Inui - One of the best experts on this subject based on the ideXlab platform.
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inhibitory effects of vandetanib on creatinine transport via renal Organic Cation Transporter oct2
European Journal of Pharmaceutical Sciences, 2021Co-Authors: Yuko Tanihara, Kenichi Inui, Satohiro MasudaAbstract:Abstract Vandetanib (ZD6474, Zactima®, Caprelsa®) is a newly developed dual tyrosine kinase inhibitor of vascular endothelial growth factor and epidermal growth factor receptor. Recently, several reports have indicated the interaction of vandetanib with tyrosine kinase inhibitors and Transporters. However, these characteristics of vandetanib remain unclear. We examined the interaction of vandetanib with the human Organic Cation Transporter 2 (hOCT2) stably expressed in human embryonic kidney (HEK) 293 cells. The specific uptake of vandetanib was not observed in hOCT2-expressing HEK293 cells. Vandetanib inhibited the uptake of creatinine mediated by hOCT2 in a dose-dependent manner. The IC50 value for vandetanib inhibition of creatinine uptake by hOCT2 was 3.7 ± 1.0 μM (average ± SE of three separate experiments). The IC50 value of cimetidine and trimethoprim for hOCT2 were 100 ± 13.5 and 52.1 ± 8.0 μM, respectively. Vandetanib showed markedly higher affinity for hOCT2 than cimetidine and trimethoprim. These results suggest that hOCT2 may play a crucial role in elevating the serum creatinine levels, as well as increasing the risk of renal impairment during vandetanib administration.
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Organic Cation Transporter oct slc22a and h Organic Cation antiporter mate slc47a are key molecules for nephrotoxicity of platinum agents
Biochemical Pharmacology, 2011Co-Authors: Atsushi Yonezawa, Kenichi InuiAbstract:Platinum agents have been widely used in cancer chemotherapy for a long time. Cisplatin, carboplatin, oxaliplatin and nedaplatin have a common chemical structure consisting of platinum, carrier groups and leaving groups, and undergo the similar mechanism of cytotoxicity. However, each agent differs in its efficacy and adverse effects, although the molecular mechanism involved is unclear. Recently, it was reported that Organic Cation Transporter OCT/SLC22A, and multidrug and toxin extrusion MATE/SLC47A play a role in the pharmacokinetics of platinum agents. Only cisplatin induces nephrotoxicity and the toxicity is kidney-specific. Kidney-specific OCT2 mediates the transport of cisplatin and is the determinant of cisplatin-induced nephrotoxicity. In addition, cisplatin and oxaliplatin are substrates for these Transporters, but carboplatin and nedaplatin are not. Substrate specificity could regulate the features of platinum agents. In this commentary, we will discuss the characteristics of OCT and MATE, and demonstrate the recent topics about the relationship between the transport of platinum agents by Organic Cation Transporters and their pharmacological characteristics.
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protective effect of concomitant administration of imatinib on cisplatin induced nephrotoxicity focusing on renal Organic Cation Transporter oct2
Biochemical Pharmacology, 2009Co-Authors: Yuko Tanihara, Toshiya Katsura, Satohiro Masuda, Kenichi InuiAbstract:Although the Organic Cation Transporter 2 (OCT2/SLC22A2) mediate renal tubular uptake of cisplatin from the circulation, neither apical multidrug and extrusion (MATE) 1 or MATE2-K mediate tubular secretion of the agent. Therefore, the highly concentrated tubular cisplatin potentiates nephrotoxicity, and these are considered to be a critical mechanism for cisplatin-induced nephrotoxicity. In the present study, we examined the protective effect of imatinib, a Cationic anticancer agent, on that nephrotoxicity. Imatinib markedly reduced cisplatin-induced cytotoxicity and platinum accumulation in OCT2-expressing HEK293 cells, but almost no change was found in the cells expressing human MATE1, MATE2-K and rat MATE1. In rats, the renal accumulation of platinum and subsequent nephrotoxicity, based on the blood urea nitrogen, plasma creatinine and creatinine clearance, were significantly decreased with the oral administration of imatinib. The orally administered imatinib significantly increased the area under the plasma concentration-time curve of intravenously administered cisplatin for 3 min by an average of 120%. In additional, the concomitant administration of imatinib clearly avoided the severe renal impairment by the histological examination. In conclusion, the concomitant administration of imatinib with cisplatin prevents cisplatin-induced nephrotoxicity inhibiting the OCT2-mediated renal accumulation of cisplatin.
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regulation of basal core promoter activity of human Organic Cation Transporter 1 oct1 slc22a1
American Journal of Physiology-gastrointestinal and Liver Physiology, 2008Co-Authors: Moto Kajiwara, Masayo Aoki, Tomohiro Terada, Iwao Ikai, Toshiya Katsura, Junichi Asaka, Kenichi InuiAbstract:Human Organic Cation Transporter 1 (OCT1/SLC22A1) plays important roles in the hepatic uptake of Cationic drugs. The functional characteristics of this Transporter have been well evaluated, but molecular information regarding transcriptional regulation is limited. In the present study, therefore, we examined the gene regulation of OCT1 gene focusing on basal core expression. An approximately 2.5-kb fragment of the OCT1 promoter region was isolated, and promoter activity was measured by luciferase assay in the human liver cell lines Huh7 and HepG2. Deletion analysis suggested that the region spanning -141/-69 was essential for the basal core transcriptional activity and that this region contained the sequence of a cognate E-box (CACGTG). The E-box is known to be bound by the basal transcription factors, upstream stimulating factors (USFs), and the functional involvements of USF1 and USF2 were confirmed by a transactivation effect, a mutational analysis of the E-box, and an electrophoretic mobility shift assay. The transactivation effect of USFs on the OCT1 promoter was further stimulated by hepatocyte nuclear factor 4alpha, a liver-enriched transcription factor. There were no polymorphisms in the proximal promoter region (about 400 bp) of OCT1 gene (n = 109). These findings indicated that both USF1 and USF2 bind to an E-box sequence located in the OCT1 core promoter region and are required for the basal gene expression of this Transporter.
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kidney specific expression of human Organic Cation Transporter 2 oct2 slc22a2 is regulated by dna methylation
American Journal of Physiology-renal Physiology, 2008Co-Authors: Masayo Aoki, Tomohiro Terada, Moto Kajiwara, Ken Ogasawara, Iwao Ikai, Osamu Ogawa, Toshiya Katsura, Kenichi InuiAbstract:Human Organic Cation Transporter 2 (OCT2/SLC22A2), which is specifically expressed in the kidney, plays critical roles in the renal secretion of Cationic compounds. Tissue expression and membrane localization of OCT2 are closely related to the tissue distribution, pharmacological effects, and/or adverse effects of its substrate drugs. However, the molecular mechanisms underlying the kidney-specific expression of OCT2 have not been elucidated. In the present study, therefore, we examined the contribution of DNA methylation of the promoter region for the OCT2 gene to its tissue-specific expression using human tissue samples. In vivo methylation status of the proximal promoter region of OCT2 and that of OCT1, a liver-specific Organic Cation Transporter, were investigated by bisulfite sequencing using human genomic DNA extracted from the kidney and liver. All CpG sites in the OCT2 proximal promoter were hypermethylated in the liver, while hypomethylated in the kidney. On the other hand, the promoter region of OCT1 was hypermethylated in both the kidney and liver. The level of methylation of the OCT2 promoter was especially low at the CpG site in the E-box, the binding site of the basal transcription factor upstream stimulating factor (USF) 1. In vitro methylation of the OCT2 proximal promoter dramatically reduced the transcriptional activity, and an electrophoretic mobility shift assay showed that methylation at the E-box inhibited the binding of USF1. These results indicate that kidney-specific expression of human OCT2 is regulated by methylation of the proximal promoter region, interfering with the transactivation by USF1.
Akira Tsuji - One of the best experts on this subject based on the ideXlab platform.
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carnitine Organic Cation Transporter octn2 slc22a5 is responsible for renal secretion of cephaloridine in mice
Drug Metabolism and Disposition, 2009Co-Authors: Takashi Kano, Yukio Kato, Yoshiyuki Kubo, Kimihiro Ito, Takuo Ogihara, Akira TsujiAbstract:Carnitine/Organic Cation Transporter (OCTN) 2 (SLC22A5) plays a pivotal role in renal tubular reabsorption of carnitine, a vitamin-like compound, on apical membranes of proximal tubules, but its role in relation to therapeutic drugs remains to be clarified. The purpose of the present study was to elucidate the involvement of OCTN2 in renal disposition of a β-lactam antibiotic, cephaloridine (CER), based on experiments with juvenile visceral steatosis (jvs) mice, which have a functional deficiency of the octn2 gene. Renal clearance of CER during constant intravenous infusion in wild-type mice was much higher than could be accounted for by glomerular filtration, but was decreased by increasing the infusion rate with minimal change in kidney-to-plasma concentration ratio, suggesting the existence of saturable transport mechanism(s) across the apical membranes. The plasma concentration profile and kidney-to-plasma concentration ratio after intravenous injection in jvs mice were higher than those in wild-type mice, whereas renal clearance in jvs mice was much lower than that in wild-type mice and could be accounted for by glomerular filtration. Uptake of CER by mouse OCTN2 was shown in Xenopus laevis oocytes expressing mouse OCTN2. The CER transport by OCTN2 exhibited saturation with Km of ∼3 mM, which is similar to the renal CER concentration exhibiting saturation in renal clearance in vivo. The OCTN2-mediated CER transport was inhibited by carnitine and independent of Na+ replacement in the medium. These results show OCTN2 on apical membranes of proximal tubules plays a major role in renal secretion of CER in mice.
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involvement of carnitine Organic Cation Transporter octn2 slc22a5 in distribution of its substrate carnitine to the heart
Drug Metabolism and Pharmacokinetics, 2008Co-Authors: Daisuke Iwata, Yoshimichi Sai, Tomohiko Wakayama, Shoichi Iseki, Yukio Kato, Yoshiyuki Kubo, Akira TsujiAbstract:This study was designed to clarify the pharmacological role of carnitine/Organic Cation Transporter (Octn) family members in mouse heart. Immunohistochemical analysis revealed that Octn1 was exclusively expressed on endothelial cells in blood vessels. Octn2 was detected on the plasma membrane of cardiac muscle cells by immunoelectron microscopy. Octn3 was not detected in the heart. Integration plot analysis showed that coadministration of unlabeled L-carnitine reduced distribution of L-[3H]carnitine to the heart. L-[3H]Carnitine uptake in heart slices was reduced by carnitine analogs and various Octn2 substrates. L-[3H]Carnitine uptake by heart slices from juvenile visceral steatosis (jvs) mice, which have a hereditary octn2 gene deficiency, was negligible. Distribution of [3H]quinidine, another Octn2 substrate, to the heart was not reduced by L-carnitine, and [3H]quinidine uptake in heart slices was Na(-)-independent and inhibited by Cationic drugs, but not carnitine analogs. [3H]Quinidine uptake by heart slices from jvs mice was similar to that of wild-type mice. These results demonstrate that OCTN2 is functionally expressed on the plasma membrane of muscle cells and is involved in distribution of carnitine to the heart. Some mechanism(s) other than OCTN2 is involved in the distribution of quinidine to the heart.
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transport of carnitine and acetylcarnitine by carnitine Organic Cation Transporter octn 2 and octn3 into epididymal spermatozoa
Reproduction, 2007Co-Authors: Daisuke Kobayashi, Junichi Nezu, Ikumi Tamai, Yasuto Kido, Yoshimichi Sai, Kazuhiro Yoshida, Tomohiko Wakayama, Shoichi Iseki, Akira TsujiAbstract:Carnitine and acetylcarnitine are important for the acquisition of motility and maturation of spermatozoa in the epididymis. In this study, we examined the involvement of carnitine/Organic Cation Transporter (OCTN) in carnitine and acetylcarnitine transport in epididymal spermatozoa of mice. Uptake of both compounds by epididymal spermatozoa was time-dependent and partially Na(+)-dependent. Kinetic analyses revealed the presence of a high-affinity transport system in the spermatozoa, with K(m) values of 23.6 and 6.57 muM for carnitine and acetylcarnitine respectively in the presence of Na(+). Expression of OCTN2 and OCTN3 in epididymal spermatozoa was confirmed by immunofluorescence analysis. The involvement of these two Transporters in carnitine and acetylcarnitine transport was supported by a selective inhibition study. We conclude that both Na(+)-dependent and -independent carnitine Transporters, OCTN2 and OCTN3, mediate the supply of carnitine and acetylcarnitine to epididymal spermatozoa in mice.
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molecular and physiological evidence for multifunctionality of carnitine Organic Cation Transporter octn2
Molecular Pharmacology, 2001Co-Authors: Rikiya Ohashi, Junichi Nezu, Noriyoshi Hashimoto, Miyuki Shimane, Hiroko Nikaido, Ikumi Tamai, Akira TsujiAbstract:OCTN2 is an Na+-dependent Transporter for carnitine, which is essential for fatty acid metabolism, and its functional defect leads to fatal systemic carnitine deficiency (SCD). It also transports the Organic Cation tetraethylammonium (TEA) in an Na+-independent manner. Here, we studied the multifunctionality of OCTN2, by examining the transport characteristics in cells transfected with mouse OCTN2 and in juvenile visceral steatosis (jvs) mice that exhibit a SCD phenotype owing to mutation of the OCTN2 gene. The physiological significance of OCTN2 as an Organic Cation Transporter was confirmed by usingjvs mice. The embryonic fibroblasts fromjvs mice exhibited significantly decreased transport of [14C]TEA. Pharmacokinetic analysis of [14C]TEA disposition demonstrated that jvsmice showed decreased tissue distribution and renal secretory clearance. In transport experiments using OCTN2-expressing cells, TEA and carnitine showed mutual trans-stimulation effects in their transport, implying a carnitine/TEA exchange mechanism. In addition, Na+ affected the affinity of carnitine for OCTN2, whereas Na+ is unlikely to be involved in TEA transport. This is the first molecular and physiological demonstration of the operation of an Organic Cation Transporter in renal apical membrane. The results are consistent with the physiological coupling of carnitine reabsorption with the secretion of Organic Cations.
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na dependent carnitine transport by Organic Cation Transporter octn2 its pharmacological and toxicological relevance
Journal of Pharmacology and Experimental Therapeutics, 1999Co-Authors: Rikiya Ohashi, Junichi Nezu, Miyuki Shimane, Hikaru Yabuuchi, Ikumi Tamai, Yoshimichi Sai, Asuka Oku, Akira TsujiAbstract:Carnitine deficiency, either primary or drug-induced, causes critical symptoms and is thought to involve alteration of active transport of carnitine across the plasma membrane of tissues as the underlying mechanism. Recently, we showed that human Organic Cation Transporter, hOCTN2, cloned as a member of the Organic Cation Transporter family, is a physiologically important Na+-dependent high-affinity carnitine Transporter in humans. In this study, we further characterized the functional properties of hOCTN2 and examined the interaction between hOCTN2-mediated carnitine transport and clinically used drugs to assess possible toxicological effects. When expressed in human embryonic kidney (HEK)293 cells, hOCTN2 showed low but significant stereospecific transport activity:d-carnitine was transported with lower affinity ( Km = 10.9 μM) than thel-isomer ( Km = 4.3 μM). One Na+ appeared to be associated with the transport of one carnitine molecule. hOCTN2-mediated transport of acetyl-l-carnitine was also Na+-dependent and of high affinity, with a Km value of 8.5 μM. To examine the transport activity for Organic Cations other than carnitine and the possible relationship of drug-induced carnitine deficiency with hOCTN2, the inhibitory effect of several drugs on hOCTN2-mediated l-carnitine transport was examined. Many zwitterionic drugs, such as cephaloridine, and many Cationic drugs, such as quinidine and verapamil, exhibited significant inhibitory effects. Among these inhibitors, tetraethylammonium, pyrilamine, quinidine, verapamil, and valproate were found to be transported by hOCTN2. The results suggest that the carnitine deficiency-related toxicological effects by long-term treatment with such drugs might be ascribed to a functional alteration of hOCTN2-mediated carnitine transport.
Kathleen M. Giacomini - One of the best experts on this subject based on the ideXlab platform.
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the effect of uremic solutes on the Organic Cation Transporter 2
Journal of Pharmaceutical Sciences, 2017Co-Authors: Lei Zhang, Kit Wun Kathy Cheung, Chia Hsiang Hsueh, Ping Zhao, Timothy W Meyer, Shiewmei Huang, Kathleen M. GiacominiAbstract:Chronic kidney disease (CKD) is characterized by the accumulation of uremic solutes; however, little is known about how these solutes affect drug absorption and disposition. The goal of this study is to evaluate the effect of uremic solutes on the Organic Cation Transporter, OCT2, which plays a key role in the renal secretion of many basic drugs. As a second goal, we reviewed the literature to determine whether there was evidence for the effect of CKD on the renal secretion of basic drugs. We first screened 72 uremic solutes as inhibitors of [14C]-labeled metformin uptake by OCT2. Seven were identified as inhibitors and 3 of them were determined to be clinically relevant. Of the 7 solutes, dimethylamine, malondialdehyde, trimethylamine, homocysteine, indoxyl-β-d-glucuronide, and glutathione disulfide were novel OCT2 inhibitors. For 6 drugs that are known OCT2 substrates, both secretory clearance and glomerular filtration rate declined in parallel with progression of CKD from stage 2 to 4, suggesting that selective effects of uremic solutes on net tubular secretion of Organic Cations do not occur. Further clinical studies are warranted with a broader range of OCT2 substrates to determine whether CKD may differentially affect tubular secretion of drugs especially in patients with advanced CKD.
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discovery of competitive and noncompetitive ligands of the Organic Cation Transporter 1 oct1 slc22a1
Journal of Medicinal Chemistry, 2017Co-Authors: Eugene C Chen, Andrej Sali, Yong Huang, Natalia Khuri, Xiaomin Liang, Adrian Stecula, Huanchieh Chien, Sook Wah Yee, Kathleen M. GiacominiAbstract:Organic Cation Transporter 1 (OCT1) plays a critical role in the hepatocellular uptake of structurally diverse endogenous compounds and xenobiotics. Here we identified competitive and noncompetitive OCT1-interacting ligands in a library of 1780 prescription drugs by combining in silico and in vitro methods. Ligands were predicted by docking against a comparative model based on a eukaryotic homologue. In parallel, high-throughput screening (HTS) was conducted using the fluorescent probe substrate ASP+ in cells overexpressing human OCT1. Thirty competitive OCT1 ligands, defined as ligands predicted in silico as well as found by HTS, were identified. Of the 167 ligands identified by HTS, five were predicted to potentially cause clinical drug interactions. Finally, virtual screening of 29 332 metabolites predicted 146 competitive OCT1 ligands, of which an endogenous neurotoxin, 1-benzyl-1,2,3,4-tetrahydroisoquinoline, was experimentally validated. In conclusion, by combining docking and in vitro HTS, competit...
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targeted disruption of Organic Cation Transporter 3 attenuates the pharmacologic response to metformin
Molecular Pharmacology, 2015Co-Authors: Eugene C Chen, Ligong Chen, Xiaomin Liang, Sook Wah Yee, Ethan G Geier, Sophie L Stocker, Kathleen M. GiacominiAbstract:Metformin, the most widely prescribed antidiabetic drug, requires Transporters to enter tissues involved in its pharmacologic action, including liver, kidney, and peripheral tissues. Organic Cation Transporter 3 (OCT3, SLC22A3), expressed ubiquitously, transports metformin, but its in vivo role in metformin response is not known. Using Oct3 knockout mice, the role of the Transporter in metformin pharmacokinetics and pharmacodynamics was determined. After an intravenous dose of metformin, a 2-fold decrease in the apparent volume of distribution and clearance was observed in knockout compared with wild-type mice (P < 0.001), indicating an important role of OCT3 in tissue distribution and elimination of the drug. After oral doses, a significantly lower bioavailability was observed in knockout compared with wild-type mice (0.27 versus 0.58, P < 0.001). Importantly, metformin's effect on the plasma glucose concentration-time curve was reduced in knockout compared with wild-type mice (12 versus 30% reduction, respectively, P < 0.05) along with its accumulation in skeletal muscle and adipose tissue (P < 0.05). Furthermore, the effect of metformin on phosphorylation of AMP activated protein kinase, and expression of glucose Transporter type 4 was absent in the adipose tissue of Oct3(-/-) mice. Additional analysis revealed that an OCT3 3' untranslated region variant was associated with reduced activity in luciferase assays and reduced response to metformin in 57 healthy volunteers. These findings suggest that OCT3 plays an important role in the absorption and elimination of metformin and that the Transporter is a critical determinant of metformin bioavailability, clearance, and pharmacologic action.
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profiling of a prescription drug library for potential renal drug drug interactions mediated by the Organic Cation Transporter 2
Journal of Medicinal Chemistry, 2011Co-Authors: Yasuto Kido, Par Matsson, Kathleen M. GiacominiAbstract:Drug–drug interactions (DDIs) are major causes of serious adverse drug reactions. Most DDIs have a pharmacokinetic basis in which one drug reduces the elimination of a second drug, leading to potentially toxic drug levels. As a major organ of drug elimination, the kidney represents an important site for DDIs. Here, we screened a prescription drug library against the renal Organic Cation Transporter OCT2/SLC22A2, which mediates the first step in the renal secretion of many Cationic drugs. Of the 910 compounds screened, 244 inhibited OCT2. Computational analyses revealed key properties of inhibitors versus noninhibitors, which included overall molecular charge. Four of six potential clinical inhibitors were Transporter-selective in follow-up screens against additional Transporters: OCT1/SLC22A1, MATE1/SLC47A1, and MATE2-K/SLC47A2. Two compounds showed different kinetics of interaction with the common polymorphism OCT2-A270S, suggesting a role of genetics in modulating renal DDIs.
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effect of genetic variation in the Organic Cation Transporter 1 oct1 on metformin pharmacokinetics
Clinical Pharmacology & Therapeutics, 2008Co-Authors: Chaline Brown, Claire M Brett, Richard A Castro, Ryan P Owen, Steven A. Sheardown, Esteban G Burchard, Kathleen M. GiacominiAbstract:The goal of this study was to determine the effects of genetic variation in the Organic Cation Transporter 1, OCT1, on the pharmacokinetics of the antidiabetic drug, metformin. Twenty healthy volunteers with known OCT1 genotype agreed to participate in the study. Each subject received two oral doses of metformin followed by collection of blood and urine samples. OCT1 genotypes had a significant (P<0.05) effect on metformin pharmacokinetics, with a higher area under the plasma concentration–time curve (AUC), higher maximal plasma concentration (Cmax), and lower oral volume of distribution (V/F) in the individuals carrying a reduced function OCT1 allele (R61C, G401S, 420del, or G465R). The effect of OCT1 on metformin pharmacokinetics in mice was less than in humans possibly reflecting species differences in hepatic expression level of the Transporter. Our studies suggest that OCT1 genotype is a determinant of metformin pharmacokinetics.
Vadivel Ganapathy - One of the best experts on this subject based on the ideXlab platform.
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structure function and regional distribution of the Organic Cation Transporter oct3 in the kidney
American Journal of Physiology-renal Physiology, 2000Co-Authors: Wei Huang, Ramesh Kekuda, Haiping Wang, Simon J Conway, Frederick H Leibach, Malliga E Ganapathy, Vadivel GanapathyAbstract:We examined in this study the expression of the potential-sensitive Organic Cation Transporter OCT3 in the kidney. A functionally active OCT3 was cloned from a mouse kidney cDNA library. The cloned Transporter was found to be capable of mediating potential-dependent transport of a variety of Organic Cations including tetraethylammonium. This function was confirmed in two different heterologous expression systems involving mammalian cells and Xenopus laevis oocytes. We have also isolated the mouse OCT3 gene and deduced its structure and organization. The OCT3 gene consists of 11 exons and 10 introns. In situ hybridization studies in the mouse kidney have shown that OCT3 mRNA is expressed primarily in the cortex. The expression is evident in the proximal and distal convoluted tubules. The expression of OCT3 in human kidney was confirmed by RT-PCR. We have also cloned OCT3 from human placenta and human kidney. Human OCT3 exhibits 86% identity with mouse OCT3 in amino acid sequence. Human OCT3 was found to transport tetraethylammonium and a variety of other Organic Cations. The transport process was electrogenic. We conclude that OCT3 is expressed in mammalian kidney and that it plays an important role in the renal clearance of Cationic drugs.
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structural and functional characteristics and tissue distribution pattern of rat octn1 an Organic Cation Transporter cloned from placenta
Biochimica et Biophysica Acta, 2000Co-Authors: Ronald L George, Haiping Wang, Simon J Conway, Frederick H Leibach, Wei Huang, Vadivel GanapathyAbstract:This report describes the structure, function, and tissue distribution pattern of rat OCTN1 (novel Organic Cation Transporter 1). The rat OCTN1 cDNA was isolated from a rat placental cDNA library. The cDNA is 2258 bp long and codes for a protein of 553 amino acids. Its amino acid sequence bears high homology to human OCTN1 (85% identity) and rat OCTN2 (74% identity). When expressed heterologously in mammalian cells, rat OCTN1 mediates Na(+)-independent and pH-dependent transport of the prototypical Organic Cation tetraethylammonium. The Transporter interacts with a variety of structurally diverse Organic Cations such as desipramine, dimethylamiloride, cimetidine, procainamide, and verapamil. Carnitine, a zwitterion, interacts with rat OCTN1 with a very low affinity. However, the transport of carnitine via rat OCTN1 is not evident in the presence or absence of Na(+). We conclude that rat OCTN1 is a multispecific Organic Cation Transporter. OCTN1-specific mRNA transcripts are present in a wide variety of tissues in the rat, principally in the liver, intestine, kidney, brain, heart and placenta. In situ hybridization shows the distribution pattern of the transcripts in the brain (cerebellum, hippocampus and cortex), kidney (cortex and medulla with relatively more abundance in the cortical-medullary junction), heart (myocardium and valves) and placenta (labyrinthine zone).
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functional characteristics and tissue distribution pattern of Organic Cation Transporter 2 octn2 an Organic Cation carnitine Transporter
Journal of Pharmacology and Experimental Therapeutics, 1999Co-Authors: Xiang Wu, Puttur D Prasad, Deva P Rajan, Pankaj Seth, Jinwen Chen, Simon J Conway, Frederick H Leibach, Wei Huang, Vadivel GanapathyAbstract:We have demonstrated in the present study that novel Organic Cation Transporter (OCTN) 2 is a Transporter for Organic Cations as well as carnitine. OCTN2 transports Organic Cations without involving Na+, but it transports carnitine only in the presence of Na+. The ability to transport Organic Cations and carnitine is demonstrable with human, rat, and mouse OCTN2s. Na+ does not influence the affinity of OCTN2 for Organic Cations, but it increases the affinity severalfold for carnitine. The short-chain acyl esters of carnitine are also transported by OCTN2. Two mutations, M352R and P478L, in human OCTN2 are associated with loss of transport function, but the protein expression of these mutants is comparable to that of the wild-type human OCTN2. In situ hybridization in the rat shows that OCTN2 is expressed in the proximal and distal tubules and in the glomeruli in the kidney, in the myocardium, valves, and arterioles in the heart, in the labyrinthine layer of the placenta, and in the cortex, hippocampus, and cerebellum in the brain. This is the first report that OCTN2 is a Na+-independent Organic Cation Transporter as well as a Na+-dependent carnitine Transporter and that OCTN2 is expressed not only in the heart, kidney, and placenta but also in the brain.
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cloning and functional characterization of a potential sensitive polyspecific Organic Cation Transporter oct3 most abundantly expressed in placenta
Journal of Biological Chemistry, 1998Co-Authors: Ramesh Kekuda, Puttur D Prasad, Haiping Wang, Frederick H Leibach, Xiang Wu, Vadivel GanapathyAbstract:Abstract We have isolated a cDNA from rat placenta which, when expressed heterologously, mediates the transport of a wide spectrum of Organic Cations. The cDNA codes for a protein of 551 amino acids containing 12 putative transmembrane domains. Northern blot analysis indicates that this Transporter is expressed most abundantly in the placenta and moderately in the intestine, heart, and brain. The expression is comparatively low in the kidney and lung and is undetectable in the liver. This Transporter is distinct from the previously cloned Organic Cation Transporters (OCT1, OCT2, NKT, NLT, RST, and OCTN1). When expressed in HeLa cells, the cDNA induces the transport of tetraethylammonium and guanidine. Competition experiments indicate that this transport process recognizes a large number of Organic Cations, including the neurotoxin 1-methyl-4-phenylpyridinium, as substrates. The cDNA-induced transport is markedly influenced by extracellular pH. However, when expressed in Xenopus laevisoocytes, the cDNA-induced transport is electrogenic, associated with the transfer of positive charge into the oocytes. Under voltage clamp conditions, tetraethylammonium evokes inward currents that are concentration- and potential-dependent. This potential-sensitive Organic Cation Transporter, designated as OCT3, represents a new member of the OCT gene family.
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cdna sequence transport function and genomic organization of human octn2 a new member of the Organic Cation Transporter family
Biochemical and Biophysical Research Communications, 1998Co-Authors: Xiang Wu, Puttur D Prasad, Frederick H Leibach, Vadivel GanapathyAbstract:Abstract We have cloned OCTN2, a new member of the Organic Cation Transporter family, from a human placental trophoblast cell line. The hOCTN2 cDNA codes for a protein of 557 amino acids with twelve putative transmembrane domains. Theoctn2gene, located on human chromosome 5q31, consists of ten exons. The OCTN2-specific transcript, 3.5 kb in size, is expressed widely in human tissues and in cell lines of human origin. At the level of amino acid sequence, OCTN2 is more closely related to OCTN1 than to OCT1, OCT2 and OCT3. When expressed heterologously in HeLa cells, OCTN2 mediates the transport of tetraethylammonium, a prototypical Organic Cation, in a pH-dependent manner. Several Organic Cations, including the neurotoxins 1-methyl-4-phenylpyridinium, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, and methamphetamine, compete for the OCTN2-mediated transport process.
Edgar Schomig - One of the best experts on this subject based on the ideXlab platform.
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increased ergothioneine tissue concentrations in carriers of the crohn s disease risk associated 503f variant of the Organic Cation Transporter octn1
Gut, 2009Co-Authors: D Taubert, Norma Jung, T Goeser, Edgar SchomigAbstract:Accumulating evidence suggests that genetic susceptibility to Crohn’s disease (CD) is driven by loss-of-function mutations in established risk genes such as IBD5 , NOD2/CARD15 , ATG16L1 or IL23R conferring defects in the innate immune response.1 2 Within the IBD5 locus, a coding variant of the Organic Cation Transporter OCTN1 ( SLC22A4 ) has been associated with the risk of CD in Caucasian populations.3 4 However, the causal involvement of OCTN1 in CD pathogenesis is unclear, because the OCTN1 variant is in linkage disequilibrium with other IBD5 alleles, in particular with a promoter variant of the carnitine Transporter OCTN2 ( SLC22A5 ).3 We have previously demonstrated that the food ingredient ergothioneine (ET), not arising from mammalian metabolism or intestinal flora, represents the key substrate of OCTN15 and that the CD risk-associated variant 503F (1672T) exhibits a …
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catecholamine transport by the Organic Cation Transporter type 1 oct1
British Journal of Pharmacology, 1998Co-Authors: Tilo Breidert, Dirk Gründemann, Folker Spitzenberger, Edgar SchomigAbstract:1 Liver and kidney extract adrenaline and noradrenaline from the circulation by a mechanism which does not seem to be one of the classical catecholamine Transporters. The hypothesis that OCT1 is involved–the Organic Cation Transporter type 1 which exists in rat kidney and liver–was tested. 2 Based on human embryonic kidney cells (293), we constructed a cell line which stably expresses OCT1r (293OCT1r cells). Transfection with OCT1 resulted in a transport activity not only for prototypical known substrates of OCT1 such as 3H-1-methyl-4-phenylpyridinium and 14C-tetraethylammonium but also for the catecholamines 3H-adrenaline, 3H-noradrenaline (3H-NA) and 3H-dopamine (3H-DA), the indoleamine 3H-5-hydroxytryptamine (3H-5HT) as well as the indirect sympathomimetic 14C-tyramine. 3 For 3H-DA, 3H-5HT and 3H-NA, at non-saturating concentrations, the rate constants for inwardly directed substrate flux (kin) were 6.9±0.8, 3.1±0.2, and 1.2±0.1 μl min−1 mg protein−1. In wild type cells (293WT) the corresponding kin's were considerably lower, being 0.94±0.40, 0.47±0.08 and 0.23±0.05 μl min−1 mg protein−1 (n=12). The indirectly determined half-saturating concentrations of DA, 5HT, and NA were 1.1 (95% c.i.: 0.8, 1.4), 0.65 (0.49, 0.86), and 2.8 (2.1, 3.7) mmol l−1 (n=3). 4 Specific 3H-DA uptake in 293OCT1r cells was resistant to cocaine (1 μmol l−1), 3H-5HT uptake was resistant to citalopram (300 nmol l−1) and 3H-NA uptake was resistant to desipramine (100 nmoll−1), corticosterone (1 μmol l−1), and reserpine (10 nmol l−1) which rules out the involvement of classical Transporters for biogenic amines. 5 The findings demonstrate that OCT1 efficiently transports catecholamines and other biogenic amines and support the hypothesis that OCT1 is responsible for hepatic and renal inactivation of circulating catecholamines. British Journal of Pharmacology (1998) 125, 218–224; doi:10.1038/sj.bjp.0702065
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primary structure and functional expression of the apical Organic Cation Transporter from kidney epithelial llc pk1cells
Journal of Biological Chemistry, 1997Co-Authors: Dirk Gründemann, Nicola Ording, Annette D Schmidt, Fátima Martel, Jorg Babinebell, Edgar SchomigAbstract:Abstract Renal secretion of Organic Cations involves at least two distinct Transporters, located in the basolateral and apical membranes of proximal tubule cells. Whereas the basolateral Transporter has recently been cloned, sequence information about the apical type was not yet available. An Organic Cation Transporter, OCT2p, was cloned from LLC-PK1 cells, a porcine cell line with properties of proximal tubular epithelial cells. OCT2p was heterologously expressed and characterized in human embryonic kidney 293 cells. OCT2p-mediated uptake of the prototypical Organic Cation [14C]tetraethylammonium ([14C]TEA) into 293 cells was saturable. There was a highly significant correlation between the K i values for the inhibition of apical [14C]TEA uptake into LLC-PK1 cells and 293 cells transfected with OCT2p (r = 0.995;p < 0.001; n = 6). Although OCT2p is structurally related to OCT1r, the basolateral Organic Cation Transporter from rat kidney, the Transporters could be clearly discriminated pharmacologically with corticosterone, decynium22, andO-methylisoprenaline. The findings at hand suggest that OCT2 corresponds to the apical type of Organic Cation Transporter. Reverse transcriptase-polymerase chain reaction indicates that mRNA of OCT1r is limited to non-neuronal tissue, whereas OCT2r, the OCT2p homologue from rat, was found in both the kidney and central nervous regions known to be rich in the monoamine transmitter dopamine.
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primary structure and functional expression of the apical Organic Cation Transporter from kidney epithelial llc pk1 cells
Journal of Biological Chemistry, 1997Co-Authors: Dirk Gründemann, Nicola Ording, Annette D Schmidt, Fátima Martel, Jorg Babinebell, Edgar SchomigAbstract:Renal secretion of Organic Cations involves at least two distinct Transporters, located in the basolateral and apical membranes of proximal tubule cells. Whereas the basolateral Transporter has recently been cloned, sequence information about the apical type was not yet available. An Organic Cation Transporter, OCT2p, was cloned from LLC-PK1 cells, a porcine cell line with properties of proximal tubular epithelial cells. OCT2p was heterologously expressed and characterized in human embryonic kidney 293 cells. OCT2p-mediated uptake of the prototypical Organic Cation [14C]tetraethylammonium ([14C]TEA) into 293 cells was saturable. There was a highly significant correlation between the Ki values for the inhibition of apical [14C]TEA uptake into LLC-PK1 cells and 293 cells transfected with OCT2p (r = 0.995; p < 0.001; n = 6). Although OCT2p is structurally related to OCT1r, the basolateral Organic Cation Transporter from rat kidney, the Transporters could be clearly discriminated pharmacologically with corticosterone, decynium22, and O-methylisoprenaline. The findings at hand suggest that OCT2 corresponds to the apical type of Organic Cation Transporter. Reverse transcriptase-polymerase chain reaction indicates that mRNA of OCT1r is limited to non-neuronal tissue, whereas OCT2r, the OCT2p homologue from rat, was found in both the kidney and central nervous regions known to be rich in the monoamine transmitter dopamine.
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Transport of small Organic Cations in the rat liver. The role of the Organic Cation Transporter OCT1.
Naunyn-schmiedebergs Archives of Pharmacology, 1996Co-Authors: Fátima Martel, T. Vetter, Hermann Russ, Dirk Gründemann, Hermann Koepsell, Isabel Azevedo, Edgar SchomigAbstract:The kidneys and the liver are the principal organs for the inactivation of circulating Organic Cations. Recently, an Organic Cation Transporter (OCT1) has been cloned from rat kidney. In order to answer the question whether OCT1 is involved also in hepatic uptake of Organic Cations, the pharmacological characteristics of Organic Cation transport in hepatocytes were compared to the characteristics of transiently expressed OCT1.