Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.24.64 (MPP)
 1,876 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The aim of this study is to investigate the placental transport mechanism of cationic compounds by comparison of the uptake of an organic cation into human placental basal membrane vesicles (BLMVs) with that into organic cation transporter 3 (OCT3)-expressing cells. Reverse transcription-polymerase chain reaction analysis demonstrated that OCT3 is the only OCT isoform expressed in the human placenta. The function of OCT3 was investigated by measuring the uptake of 1-methyl-4-phenylpyridinium (MPP(+)) into human embryonic kidney (HEK)293 cells stably expressing OCT3 (HEK/OCT3 cells). The OCT3-mediated uptake of MPP(+) was sodium- and chloride-independent and saturable, with a Michaelis constant (K(m)) of 82.5 microM. The OCT3-mediated uptake was inhibited by various cationic drugs in a concentration-dependent manner but not by anionic compounds, such as p-aminohippuric acid and captopril, or a zwitterion, carnitine. Western blotting analysis of membrane vesicles prepared from human term placenta revealed that OCT3 is expressed only in BLMVs but not in microvillous membrane vesicles. The uptake of MPP(+) into BLMVs was membrane potential-dependent and saturable, with a K(m) value of 51.8 muM, which is similar to that in HEK293/OCT3 cells. The inhibitory spectrum of various compounds on MPP(+) uptake by BLMVs was also similar to that in HEK293/OCT3 cells. These results suggest that OCT3 is expressed on the basal membrane of human trophoblast cells and plays an important role in the placental transport of cationic compounds.
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PMID:Functional analysis of organic cation transporter 3 expressed in human placenta. 1608 76

The positively charged fluorescent dyes ethidium (Et(+)) and propidium (Pr(2+)) are widely used as DNA and necrosis markers. Et(+) is cytotoxic and mutagenic. The polyspecific organic cation transporters OCT1 (SLC22A1), OCT2 (SLC22A2), and OCT3 (SLC22A3) mediate electrogenic facilitated diffusion of small (< or =500 Da) organic cations with broad specificities. In humans, OCT2 mediates basolateral uptake by kidney proximal tubules (PT), whereas in rodents OCT1/2 are involved. In mouse kidney, perfused Et(+) accumulated predominantly in the S2/S3 segments of the PT, but not Pr(2+). In cells stably overexpressing human OCTs (hOCTs), Et(+) uptake was observed with K(m) values of 0.8 +/- 0.2 microM (hOCT1), 1.7 +/- 0.5 microM (hOCT2), and 2.0 +/- 0.5 microM (hOCT3), whereas Pr(2+) was not transported. Accumulation of Et(+) was inhibited by OCT substrates quinine, 3-methyl-4-phenylpyridinium (MPP(+)), cimetidine, and tetraethylammonium (TEA(+)). For hOCT1 and hOCT2, the IC(50) values for MPP(+), TEA(+), and cimetidine were higher than for inhibition of previously tested transported substrates. For hOCT2, the inhibition of Et(+) uptake by MPP(+) and cimetidine was shown to be competitive. Et(+) also inhibited transport of 0.1 microM [(3)H]MPP(+) by all hOCT isoforms with IC(50) values between 0.4 and 1.3 microM, and the inhibition of hOCT1-mediated uptake of MPP(+) by Et(+) was competitive. In Oct1/2(-/-) mice, Et(+) uptake in the PT was almost abolished. The data demonstrate that Et(+) is taken up avidly by the PT, which is mediated by OCT1 and/or OCT2. Considering the high affinity of OCTs for Et(+) and their strong expression in various organs, strict safety guidelines for Et(+) handling should be reinforced.
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PMID:Organic cation transporters OCT1, 2, and 3 mediate high-affinity transport of the mutagenic vital dye ethidium in the kidney proximal tubule. 1935 79

The polyspecific organic cation transporters OCT1 (SLC22A1), OCT2 (SLC22A2) and OCT3 (SLC22A3) mediate facilitated and bidirectional diffusion of small (< or = 500Da) organic cations with broad specificities for endogenous substrates such as choline, acetylcholine and monoamine neurotransmitters, as well as a variety of xenobiotics. Importantly, besides a wide range of clinically used drugs, these also include several toxins like the neurotoxin 1-methyl-4-phenylpyridinium (MPP(+)) and herbicide paraquat. OCT2-OCT-3 display differential tissue distribution: OCT1 is predominantly found in liver of humans, and liver and kidney in rodents; OCT2 is most strongly expressed in both human and rodent kidney, whereas is OCT3 primarily expressed in placenta, but also more widely detected in various tissues, including brain and lung. The physiological roles of OCTs as transporters for biogenic amines or acetylcholine in these tissues are still debated, in contrast to their involvement in providing access pathways for harmful/toxic cationic substrates into the body and particular tissues. This review highlights a novel role of human and rodent OCTs as carriers of the toxic fluorescent dye ethidium, as opposed to the less harmful related phenanthridine compound propidium, which is not transported. Additional uptake and efflux pathways for ethidium in pro- and eukaryotes are discussed. OCT-mediated pathways may determine major entry routes for ethidium into the body where toxicity via specific mechanisms may develop in tissues expressing OCTs. Considering the high affinity of OCTs for ethidium (K(m) = 1-2 microM) and their strong expression in various organs, strict safety guidelines for the handling of ethidium should be reinforced.
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PMID:Organic cation transporters: physiology, toxicology and special focus on ethidium as a novel substrate. 1970 34

The organic cation transporter (OCT, SLC22) family is a family of polyspecific transmembrane proteins that are responsible for the uptake or excretion of many cationic drugs, toxins, and endogenous metabolites in a variety of tissues. Many of the OCTs have been previously characterized, but there are a number of orphan genes whose functions remain unknown. In this study, two novel rat SLC22 genes, SLC22A17 (BOCT1) and SLC22A23 (BOCT2), were cloned and characterized. Northern blot analysis showed that BOCT1 and BOCT2 mRNA was expressed in a wide variety of tissues. BOCT1 was strongly expressed in brain, primary neurons and brain endothelial cells, with highest expression in choroid plexus. BOCT2 was also abundantly expressed in brain, as well as in liver. To characterize the products of these genes, BOCT1 cDNA was isolated from a rat blood-brain barrier cDNA library, and BOCT2 cDNA was isolated from rat brain capillary and from cultured neurons using PCR techniques. Plasmids expressing BOCT1 and BOCT2 were transfected into HEK-293 cells, as were control cDNAs for OCT1 and OCTN2. Recombinant cell surface protein was verified by western blot and fluorescence microscopy. Transport activity of BOCT1 and BOCT2 was evaluated using radioisotope uptake assays. The OCT1- and OCTN2-expressing cells transported the canonical substrates, 1-methyl-4-phenyl-pyridinium (MPP(+)) and carnitine, respectively. However, BOCT1 and BOCT2-expressing cells did not show transport activity for these substrates or a number of other SLC22 substrates. These novel family members have a nonconserved amino terminus, relative to other OCTs, that may preclude typical SLC22 transport function.
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PMID:Expression and analysis of two novel rat organic cation transporter homologs, SLC22A17 and SLC22A23. 2135 64

The organic cation/carnitine transporters OCTN1 and OCTN2 are related to other organic cation transporters (OCT1, OCT2, and OCT3) known for transporting oxaliplatin, an anticancer drug with dose-limiting neurotoxicity. In this study, we sought to determine whether OCTN1 and OCTN2 also transported oxaliplatin and to characterize their functional expression and contributions to its neuronal accumulation and neurotoxicity in dorsal root ganglion (DRG) neurons relative to those of OCTs. [(14)C]Oxaliplatin uptake, platinum accumulation, and cytotoxicity were determined in OCTN-overexpressing human embryonic kidney (HEK) 293 cells and primary cultures of rat DRG neurons. Levels of mRNA and functional activities of rat (r)Octns and rOcts in rat DRG tissue and primary cultures were characterized using reverse transcription-polymerase chain reaction and uptake of model OCT/OCTN substrates, including [(3)H]1-methyl-4-phenylpyridinium (MPP(+)) (OCT1-3), [(14)C]tetraethylammonium bromide (TEA(+)) (OCT1-3 and OCTN1/2), [(3)H]ergothioneine (OCTN1), and [(3)H]l-carnitine (OCTN2). HEK293 cells overexpressing rOctn1, rOctn2, human OCTN1, and human OCTN2 showed increased uptake and cytotoxicity of oxaliplatin compared with mock-transfected HEK293 controls; in addition, both uptake and cytotoxicity were inhibited by ergothioneine and L-carnitine. The uptake of ergothioneine mediated by OCTN1 and of L-carnitine mediated by OCTN2 was decreased during oxaliplatin exposure. rOctn1 and rOctn2 mRNA was readily detected in rat DRG tissue, and they were functionally active in cultured rat DRG neurons, more so than rOct1, rOct2, or rOct3. DRG neuronal accumulation of [(14)C]oxaliplatin and platinum during oxaliplatin exposure depended on time, concentration, temperature, and sodium and was inhibited by ergothioneine and to a lesser extent by L-carnitine but not by MPP(+). Loss of DRG neuronal viability during oxaliplatin exposure was inhibited by ergothioneine but not by L-carnitine or MPP(+). OCTN1 and OCTN2 both transport oxaliplatin and are functionally expressed by DRG neurons. OCTN1-mediated transport of oxaliplatin appears to contribute to its neuronal accumulation and treatment-limiting neurotoxicity more so than OCTN2 or OCTs.
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PMID:Oxaliplatin transport mediated by organic cation/carnitine transporters OCTN1 and OCTN2 in overexpressing human embryonic kidney 293 cells and rat dorsal root ganglion neurons. 2160 77

In our previous study, we described synchronized activity of organic cation transporter 3 (OCT3/SLC22A3) and multidrug and toxin extrusion 1 (MATE1/SLC47A1) transporter in the passage of organic cations across the rat placenta and the role of these transporters in fetal defense; in this study, we hypothesized that changes in placental levels of OCT3 and MATE1 throughout gestation might affect the fetal protection and detoxification. Using quantitative RT-PCR, Western blot analysis, and immunohistochemistry, we were able to detect Oct3/OCT3 and Mate1/MATE1 expression in the rat placenta as early as on Gestation Day (gd) 12 with increasing tendency toward the end of pregnancy. Comparing first versus third trimester human placenta, we observed stable expression of OCT1 and decreasing expression of OCT2 and OCT3 isoforms. Contrary to the current literature, we were able to detect also MATE1/MATE2 isoforms in the human placenta, however, with considerable inter- and intraindividual variability. Using infusion of 1-methyl-4-phenylpyridinium (MPP(+)), a substrate of OCT and MATE transporters, into pregnant dams, we investigated the protective function of the placenta against organic cations at different gds. The highest amount of MPP(+) reached the fetus on gd 12 while from gd 15 onward, maternal-to-fetal transport of MPP(+) decreased significantly. We conclude that increased expression of placental OCT3 and MATE1 along with general maturation of the placental tissues results in significantly lower transport of MPP(+) from mother to fetus. In contrast, decreasing expression of OCT3 and MATE1 in human placenta indicates these transporters may play a role in fetal protection preferentially at earlier stages of gestation.
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PMID:Organic cation transporter 3 (OCT3/SLC22A3) and multidrug and toxin extrusion 1 (MATE1/SLC47A1) transporter in the placenta and fetal tissues: expression profile and fetus protective role at different stages of gestation. 2330 78

Human organic cation transporter 1 (hOCT1) and human organic cation transporter 3 (hOCT3) are highly expressed in hepatocytes and play important roles in cationic drug absorption, distribution, and elimination. A previous study demonstrated that downregulation of hOCT1 and hOCT3 mRNA was related to hepatocellular carcinoma (HepG2) prognosis and severity. Whether these transporters expressed in HepG2 cells serve for cationic drug delivery has not been investigated. Besides radioactive transport, options for assessing hOCTs in hepatocytes are limited. This study clarified the significant roles of hOCTs in HepG2 by comparing cationic fluorescent 4-(4-(dimethylamino)styryl)-N-methylpyridinium (ASP+ ) with traditional [3 H]-1-methyl-4-phenylpyridinium (MPP+ ). The results showed ASP+ was preferably transported into HepG2 compared to [3 H]-MPP+ with high affinity and a high maximal transport rate. Selective transport of ASP+ mediated by hOCTs was influenced by extracellular pH, temperature, and membrane depolarization, corresponding to hOCT1 and hOCT3 expressions. Furthermore, transport of cationic drugs, metformin, and paclitaxel in HepG2 cells was blunted by OCT inhibitors, suggesting that hOCT1 and hOCT3 expressed in HepG2 cells exhibit notable impacts on cationic drug actions. The fluorescent ASP+ -based in vitro model may also provide a rapid and powerful analytical tool for further screening of cationic drug actions and interactions with hOCTs, particularly hOCT1 and hOCT3 in hepatocellular carcinoma.
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PMID:High affinity of 4-(4-(dimethylamino)styryl)-N-methylpyridinium transport for assessing organic cation drugs in hepatocellular carcinoma cells. 3188 48