In Vitro Inhibition of Renal OCT2 and MATE1 Secretion by Antiemetic Drugs.

The organic cation transporter 2 (OCT2) and multidrug and toxin extrusion protein 1 (MATE1) mediate the renal secretion of drugs. Recent studies suggest that ondansetron, a 5-HT3 antagonist drug used to prevent nausea and vomiting, can inhibit OCT2- and MATE1-mediated transport. The purpose of this study was to test the ability of five 5-HT3 antagonist drugs to inhibit the OCT2 and MATE1 transporters. The transport of the OCT2/MATE1 probe substrate ASP+ was assessed using two models: (1) HEK293 kidney cells overexpressing human OCT2 or MATE1, and (2) MDCK cells transfected with human OCT2 and MATE1. In HEK293 cells, the inhibition of ASP+ uptake by OCT2 listed in order of potency was palonosetron (IC50: 2.6 µM) > ondansetron > granisetron > tropisetron > dolasetron (IC50: 85.4 µM) and the inhibition of ASP+ uptake by MATE1 in order of potency was ondansetron (IC50: 0.1 µM) > palonosetron = tropisetron > granisetron > dolasetron (IC50: 27.4 µM). Ondansetron (0.5-20 µM) inhibited the basolateral-to-apical transcellular transport of ASP+ up to 64%. Higher concentrations (10 and 20 µM) of palonosetron, tropisetron, and dolasetron similarly reduced the transcellular transport of ASP+. In double-transfected OCT2-MATE1 MDCK cells, ondansetron at concentrations of 0.5 and 2.5 µM caused significant intracellular accumulation of ASP+. Taken together, these data suggest that 5-HT3 antagonist drugs may inhibit the renal secretion of cationic drugs by interfering with OCT2 and/or MATE1 function.

Antiseizure medications and fetal nutrients: Effects on choline transporters in a human placental cell line.

OBJECTIVE: Many nutrients essential to the fetus and for proper function of the placenta itself cannot freely diffuse across membrane barriers, and their transplacental transfer depends on transporters. Our previous studies provided evidence for altered expression of transporters for folic acid in trophoblasts exposed to antiseizure medications (ASMs). The goal of the current study was to explore the effects of older and newer ASMs on the expression and function of uptake transporters for choline, which interacts with folate at pathways for methyl group donation. METHODS: BeWo cells were incubated for 2 or 5 days with valproate (42, 83, or 166 µg/ml), carbamazepine (6 or 12 µg/ml), levetiracetam (10 or 30 µg/ml), lamotrigine (3 or 12 µg/ml), lacosamide (5, 10, or 20 µg/ml), or their vehicles (n = 6/treatment group). Quantitative polymerase chain reaction (PCR) analysis was utilized to study the effects of ASMs on the transcript levels of the choline transporters SLC44A1 (CTL1) and SLC44A2 (CTL2). Transporter protein expression in valproate-treated cells was assessed by western blot analysis. Choline and acetylcholine were quantified in cell lysates by a choline/acetylcholine assay kit. RESULTS: Compared with controls, valproate and levetiracetam at high therapeutic concentrations (83 and 30 µg/ml, respectively) lowered choline transporter transcript levels by up to 42% and 26%, and total choline levels by 20% and 21%, respectively (p < .05). At 83 µg/ml, valproate additionally reduced CTL1 and CTL2 protein expression, by 39 ± 21% and 61 ± 13% (mean ± SD), respectively (p < .01). Carbamazepine reduced SLC44A1 transcript levels, whereas lacosamide modestly decreased the expression of SLC44A2. Lamotrigine did not alter choline transporter expression. SIGNIFICANCE: Antiseizure medications, particularly at high therapeutic concentrations, can interfere with the placental uptake of choline. In line with current knowledge from pregnancy registries and clinical studies, the present in vitro findings further support careful adjustment of maternal ASM doses during pregnancy.

27-Hydroxycholesterol regulates human SLC22A12 gene expression through estrogen receptor action.

The excretion and reabsorption of uric acid both to and from urine are tightly regulated by uric acid transporters. Metabolic syndrome conditions, such as obesity, hypercholesterolemia, and insulin resistance, are believed to regulate the expression of uric acid transporters and decrease the excretion of uric acid. However, the mechanisms driving cholesterol impacts on uric acid transporters have been unknown. Here, we show that cholesterol metabolite 27-hydroxycholesterol (27HC) upregulates the uric acid reabsorption transporter URAT1 encoded by SLC22A12 via estrogen receptors (ER). Transcriptional motif analysis showed that the SLC22A12 gene promoter has more estrogen response elements (EREs) than other uric acid reabsorption transporters such as SLC22A11 and SLC22A13, and 27HC-activated SLC22A12 gene promoter via ER through EREs. Furthermore, 27HC increased SLC22A12 gene expression in human kidney organoids. Our results suggest that in hypercholesterolemic conditions, elevated levels of 27HC derived from cholesterol induce URAT1/SLC22A12 expression to increase uric acid reabsorption, and thereby, could increase serum uric acid levels.

Expression of the organic cation/carnitine transporter family (Octn1,-2 and-3) in mdx muscle and heart: Implications for early carnitine therapy in Duchenne muscular dystrophy to improve cellular carnitine homeostasis.

INTRODUCTION: Carnitine is essential for long-chain fatty acid oxidation in muscle and heart. Tissue stores are regulated by organic cation/Cn transporter plasmalemmal Octn2. We previously demonstrated low carnitine in quadriceps/gluteus and heart of adult mdx mice. METHODS: We studied protein and mRNA expression of Octn2, mitochondrial Octn1 and peroxisomal Octn3 in adult male C57BL/10ScSn-DMD mdx/J quadriceps, heart, and diaphragm compared to C57BL/10SnJ mice. RESULTS: We demonstrated reduction in mOctn2 expression on Western blot and similar expression of mOctn1 and mOctn3 in mdx quadriceps, heart and diaphragm. There was a significant upregulation of mOctn1 and mOctn2 mRNA by qRT-PCR in mdx quadriceps and of mOctn2 and mOctn3 mRNA in mdx heart. We showed upregulation of mdx mOctn1 and mOctn3 mRNA but no increase in protein expression. DISCUSSION: Dystrophin deficiency likely disrupts Octn2 expression decreasing muscle carnitine uptake thus contributing to membranotoxic long-chain acyl-CoAs with sarcolemmal and organellar membrane oxidative injury providing a treatment rationale for early L-carnitine in DMD.

Protein expression of ABCC2 and SLC22A3 associates with prognosis of pancreatic adenocarcinoma.

ATP-binding cassette (ABC) and solute carrier (SLC) transporters translocate diverse substances across cellular membranes and their deregulation may cause drug resistance of cancers. This study investigated significance of protein expression and cellular localization of the previously suggested putative prognostic markers ABCC2 and SLC22A3 in pancreatic cancer patients. Protein localization and brush border staining intensity of ABCC2 and SLC22A3 was assessed in tumor tissue blocks of 65 pancreatic cancer patients and associated with clinical data and survival of patients with regard to therapy. Negative SLC22A3 brush border staining in pancreatic tumors significantly increased the risk of both disease progression and patient´s death in univariate analyses. Multivariate analyses confirmed the association of SLC22A3 expression with progression-free survival of patients. A subgroup analysis of patients treated with regimens based on nucleoside analogs suggested that patients with negative brush border staining or apical localization of SLC22A3 in tumor cells have worse overall survival. The combination of positive ABCC2 and negative SLC22A3 brush border staining predicted worst overall survival and patients with positive brush border staining of both proteins had best overall and progression-free survival. The present study shows for the first time that the protein presence and to some extent also localization of SLC22A3 significantly associate with prognosis of pancreatic cancer in both unstratified and chemotherapy-treated patients. The combination of ABCC2 and SLC22A3 brush border staining also needs further attention in this regard.

Differential expression and immunoreactivity of thyroid hormone transporters MCT8 and OATP1C1 in rat ovary.

Thyroid hormones (THs) regulate several physiological processes in female mammals, many of which are related to reproduction such as steroidogenesis in the ovary, oocyte and granulosa cells maturation, follicular development and differentiation, and ovulation. THs actions require the presence of THs transporters to facilitate their cellular uptake and efflux. MCT8 and OATP1C1 are the principal THs transporters. The aim of the present study was to determine the gene expression and cellular localization of MCT8 and OATP1C1 in the rat ovary during the diestrus-II cycle phase. Ovaries of virgin adult rats were histologically processed. Reverse Transcription-PCR and immunohistochemistry analyses for MCT8 and OATP1C1 were done. MCT8 gene expression level was significantly higher (P ≤ 0.01) than that of OATP1C1 in the rat ovary. MCT8 and OATP1C1 were found in all types of ovarian cells but with different immunoreactivity. MCT8 showed stronger immunoreactivity in tertiary and Graafian follicles, corpus luteum and blood vessels, whereas OATP1C1's immunoreactivity was stronger in stroma cells, tunica albuginea, and blood vessels. Our results provide evidence that THs and their transporters are both necessary for ovarian function and that any alteration in these transporters could interfere with reproductive processes such as ovulation and steroidogenesis, compromising fertility.

Organic cation transporter 3 (Oct3) is a distinct catecholamines clearance route in adipocytes mediating the beiging of white adipose tissue.

Beiging of white adipose tissue (WAT) is a particularly appealing target for therapeutics in the treatment of metabolic diseases through norepinephrine (NE)-mediated signaling pathways. Although previous studies report NE clearance mechanisms via SLC6A2 on sympathetic neurons or proinflammatory macrophages in adipose tissues (ATs), the low catecholamine clearance capacity of SLC6A2 may limit the cleaning efficiency. Here, we report that mouse organic cation transporter 3 (Oct3; Slc22a3) is highly expressed in WAT and displays the greatest uptake rate of NE as a selective non-neural route of NE clearance in white adipocytes, which differs from other known routes such as adjacent neurons or macrophages. We further show that adipocytes express high levels of NE degradation enzymes Maoa, Maob, and Comt, providing the molecular basis on NE clearance by adipocytes together with its reuptake transporter Oct3. Under NE administration, ablation of Oct3 induces higher body temperature, thermogenesis, and lipolysis compared with littermate controls. After prolonged cold challenge, inguinal WAT (ingWAT) in adipose-specific Oct3-deficient mice shows much stronger browning characteristics and significantly elevated expression of thermogenic and mitochondrial biogenesis genes than in littermate controls, and this response involves enhanced ß-adrenergic receptor (ß-AR)/protein kinase A (PKA)/cyclic adenosine monophosphate (cAMP)-responsive element binding protein (Creb) pathway activation. Glycolytic genes are reprogrammed to significantly higher levels to compensate for the loss of ATP production in adipose-specific Oct3 knockout (KO) mice, indicating the fundamental role of glucose metabolism during beiging. Inhibition of ß-AR largely abolishes the higher lipolytic and thermogenic activities in Oct3-deficient ingWAT, indicating the NE overload in the vicinity of adipocytes in Oct3 KO adipocytes. Of note, reduced functional alleles in human OCT3 are also identified to be associated with increased basal metabolic rate (BMR). Collectively, our results demonstrate that Oct3 governs ß-AR activity as a NE recycling transporter in white adipocytes, offering potential therapeutic applications for metabolic disorders.

Effects of chronic caffeine exposure during adolescence and subsequent acute caffeine challenge during adulthood on rat brain serotonergic systems.

Caffeine is the most commonly used drug in the world. However, animal studies suggest that chronic consumption of caffeine during adolescence can result in enhanced anxiety-like behavioral responses during adulthood. One mechanism through which chronic caffeine administration may influence subsequent anxiety-like responses is through actions on brainstem serotonergic systems. In order to explore potential effects of chronic caffeine consumption on brainstem serotonergic systems, we evaluated the effects of a 28-day exposure to chronic caffeine (0.3 g/L; postnatal day 28-56) or vehicle administration in the drinking water, followed by 24 h caffeine withdrawal, and subsequent challenge with caffeine (30 mg/kg; s.c.) or vehicle in adolescent male rats. In Experiment 1, acute caffeine challenge induced a widespread activation of serotonergic neurons throughout the dorsal raphe nucleus (DR); this effect was attenuated in rats that had been exposed to chronic caffeine consumption. In Experiment 2, acute caffeine administration profoundly decreased tph2 and slc22a3 mRNA expression throughout the DR, with no effects on htr1a or slc6a4 mRNA expression. Chronic caffeine exposure for four weeks during adolescence was sufficient to decrease tph2 mRNA expression in the DR measured 28 h after caffeine withdrawal. Chronic caffeine administration during adolescence did not impact the ability of acute caffeine to decrease tph2 or slc22a3 mRNA expression. Together, these data suggest that both chronic caffeine administration during adolescence and acute caffeine challenge during adulthood are important determinants of serotonergic function and serotonergic gene expression, effects that may contribute to chronic effects of caffeine on anxiety-like responses.

CircRNA_0023642 promotes migration and invasion of gastric cancer cells by regulating EMT.

OBJECTIVE: Non-coding circular RNAs (circRNAs) have displayed dysregulated expression in various tumor tissues. However, their role in the progression of cancers remains largely unknown. We aimed at examining the expression, functions, and molecular mechanisms of a new circRNA (circRNA_0023642) in gastric cancer (GC). PATIENTS AND METHODS: We evaluated the expression levels of circRNA_0023642 in GC tissues, adjacent normal tissues and cells lines using qRT-PCR. The functional roles of circRNA_0023642 in GC were determined by Cell Counting Kit-8 (CCK-8) assay, colony formation assay, transwell assay, and flow cytometric analysis. Western blot was used to analyze the effect of circRNA_0023642 on the expression of EMT-related proteins. RESULTS: We found that circRNA_0023642 was upregulated in GC tissues and cell lines. Functionally, down-regulation of circRNA_0023642 displayed the tumor-inhibitory effects by suppressing cell proliferation, migration, and invasion as well as inducing apoptosis. Mechanically, our results revealed that the abnormal expression of circRNA_0023642 could influence the EMT signaling pathway, which was demonstrated by measuring the expression levels of N-cadherin, vimentin snail, and E-cadherin. CONCLUSIONS: Our findings suggest that circRNA_0023642 serves as a metastasis activator by promoting EMT and may represent a novel molecular therapeutic target for GC.

Expression of MATE1, P-gp, OCTN1 and OCTN2, in epithelial and immune cells in the lung of COPD and healthy individuals.

BACKGROUND: Several inhaled drugs are dependent on organic cation transporters to cross cell membranes. To further evaluate their potential to impact on inhaled drug disposition, the localization of MATE1, P-gp, OCTN1 and OCTN2 were investigated in human lung. METHODS: Transporter proteins were analysed by immunohistochemistry in lung tissue from healthy subjects and COPD patients. Transporter mRNA was analysed by qPCR in lung tissue and in bronchoalveolar lavage (BAL) cells from smokers and non-smokers. RESULTS: We demonstrate for the first time MATE1 protein expression in the lung with localization to the apical side of bronchial and bronchiolar epithelial cells. Interestingly, MATE1 was strongly expressed in alveolar macrophages as demonstrated both in lung tissue and in BAL cells, and in inflammatory cells including CD3 positive T cells. P-gp, OCTN1 and OCTN2 were also expressed in the alveolar epithelial cells and in inflammatory cells including alveolar macrophages. In BAL cells from smokers, MATE1 and P-gp mRNA expression was significantly lower compared to cells from non-smokers whereas no difference was observed between COPD patients and healthy subjects. THP-1 cells were evaluated as a model for alveolar macrophages but did not reflect the transporter expression observed in BAL cells. CONCLUSIONS: We conclude that MATE1, P-gp, OCTN1 and OCTN2 are expressed in pulmonary lung epithelium, in alveolar macrophages and in other inflammatory cells. This is important to consider in the development of drugs treating pulmonary disease as the transporters may impact drug disposition in the lung and consequently affect pharmacological efficacy and toxicity.

Salt stress affects global protein expression profiles of extracellular membrane-derived vesicles of Listeria monocytogenes.

Our previous study has suggested that Listeria monocytogenes produces extracellular membrane vesicles (MVs) and its general stress transcription factor sigma B (σB) affects the production of MVs under energy stress. The objective of this study was to evaluate the production of MVs and perform global protein profiling for MVs with or without salt stress to understand the function of MVs in the pathogenesis of L. monocytogenes. When cells of L. monocytogenes were grown under 0.5 M salt stress, protein concentrations of MVs derived from wild-type strain and its isogenic ΔsigB mutant were approximately doubled compared to those of MVs derived from cells without salt stress. Proteomic analyses showed that the number of MV proteins expressed in wild-type strain was similar to that in ΔsigB mutant under salt stress. However, global protein expression profiles were dramatically changed under salt stress compared to those without salt stress. Fifteen σB dependent proteins were expressed in MVs of wild-type strain under salt stress, including osmolyte transporter OpuCABCD. In addition, MVs produced by salt stressed wild-type and ΔsigB mutant inhibited biofilm formation abilities of both strains. Taken together, our results suggest that salt stress can promote the production of MVs involved in carnitine transporter proteins, with σB playing a pivotal role in biological event.

Relationship between DNA Methylation in the 5' CpG Island of the SLC47A1 (Multidrug and Toxin Extrusion Protein MATE1) Gene and Interindividual Variability in MATE1 Expression in the Human Liver.

Multidrug and toxin extrusion protein 1 (MATE1), which is encoded by solute carrier 47A1 (SLC47A1), mediates the excretion of organic cations into bile and urine. Some genetic variants in human MATE1 altered its transport function in in vitro experiments; however, differences in the pharmacokinetics of substrate drugs cannot be explained by genetic variations in humans. In this study, we investigated whether DNA methylation was involved in interindividual variability in MATE1 expression in the human liver. Approximately 20-fold interindividual variability in MATE1 mRNA expression levels was observed in liver samples and mRNA expression levels negatively correlated with methylation levels of the CpG island in the 27 kb upstream of SLC47A1 DNA demethylation by treatment with 5-aza-2'-deoxycytidine increased MATE1 mRNA expression in MATE1-negative cell lines. The luciferase reporter assay showed that the CpG island increased the transcriptional activity of the SLC47A1 promoter. MATE1 mRNA expression levels were significantly lower in CpG island knockout HepG2 cells than in control cells. These results suggest that the 5' CpG island of SLC47A1 acts as an enhancer for SLC47A1, and DNA methylation in the CpG island plays an important role in interindividual differences in hepatic MATE1 expression.

Targeting miR-21 decreases expression of multi-drug resistant genes and promotes chemosensitivity of renal carcinoma.

Renal cell carcinoma, the most common neoplasm of adult kidney, accounts for about 3% of adult malignancies and is usually highly resistant to conventional therapy. MicroRNAs are a class of small non-coding RNAs, which have been previously shown to promote malignant initiation and progression. In this study, we focused our attention on miR-21, a well described oncomiR commonly upregulated in cancer. Using a cohort of 99 primary renal cell carcinoma samples, we showed that miR-21 expression in cancer tissues was higher than in adjacent non-tumor tissues whereas no significant difference was observed with stages, grades, and metastatic outcome. In vitro, miR-21 was also overexpressed in renal carcinoma cell lines compared to HK-2 human proximal tubule epithelial cell line. Moreover, using Boyden chambers and western blot techniques, we also showed that miR-21 overexpression increased migratory, invasive, proliferative, and anti-apoptotic signaling pathways whereas opposite results were observed using an anti-miR-21-based silencing strategy. Finally, we assessed the role of miR-21 in mediating renal cell carcinoma chemoresistance and further showed that miR-21 silencing significantly (1) increased chemosensitivity of paclitaxel, 5-fluorouracil, oxaliplatin, and dovitinib; (2) decreased expression of multi-drug resistance genes; and (4) increased SLC22A1/OCT1, SLC22A2/OCT2, and SLC31A1/CTR1 platinum influx transporter expression. In conclusion, our results showed that miR-21 is a key actor of renal cancer progression and plays an important role in the resistance to chemotherapeutic drugs. In renal cell carcinoma, targeting miR-21 is a potential new therapeutic strategy to improve chemotherapy efficacy and consequently patient outcome.

Abl kinase regulation by BRAF/ERK and cooperation with Akt in melanoma.

The melanoma incidence continues to increase, and the disease remains incurable for many due to its metastatic nature and high rate of therapeutic resistance. In particular, melanomas harboring BRAFV600E and PTEN mutations often are resistant to current therapies, including BRAF inhibitors (BRAFi) and immune checkpoint inhibitors. Abl kinases (Abl/Arg) are activated in melanomas and drive progression; however, their mechanism of activation has not been established. Here we elucidate a novel link between BRAFV600E/ERK signaling and Abl kinases. We demonstrate that BRAFV600E/ERK play a critical role in binding, phosphorylating and regulating Abl localization and Abl/Arg activation by Src family kinases. Importantly, Abl/Arg activation downstream of BRAFV600E has functional and biological significance, driving proliferation, invasion, as well as switch in epithelial-mesenchymal-transition transcription factor expression, which is known to be critical for melanoma cells to shift between differentiated and invasive states. Finally, we describe findings of high translational significance by demonstrating that Abl/Arg cooperate with PI3K/Akt/PTEN, a parallel pathway that is associated with intrinsic resistance to BRAFi and immunotherapy, as Abl/Arg and Akt inhibitors cooperate to prevent viability, cell cycle progression and in vivo growth of melanomas harboring mutant BRAF/PTEN. Thus, these data not only provide mechanistic insight into Abl/Arg regulation during melanoma development, but also pave the way for the development of new strategies for treating patients with melanomas harboring mutant BRAF/PTEN, which often are refractory to current therapies.

OCTN1 Is a High-Affinity Carrier of Nucleoside Analogues.

Resistance to xenobiotic nucleosides used to treat acute myeloid leukemia (AML) and other cancers remains a major obstacle to clinical management. One process suggested to participate in resistance is reduced uptake into tumor cells via nucleoside transporters, although precise mechanisms are not understood. Through transcriptomic profiling, we determined that low expression of the ergothioneine transporter OCTN1 (SLC22A4; ETT) strongly predicts poor event-free survival and overall survival in multiple cohorts of AML patients receiving treatment with the cytidine nucleoside analogue cytarabine. Cell biological studies confirmed OCTN1-mediated transport of cytarabine and various structurally related cytidine analogues, such as 2'deoxycytidine and gemcitabine, occurs through a saturable process that is highly sensitive to inhibition by the classic nucleoside transporter inhibitors dipyridamole and nitrobenzylmercaptopurine ribonucleoside. Our findings have immediate clinical implications given the potential of the identified transport system to help refine strategies that could improve patient survival across multiple cancer types where nucleoside analogues are used in cancer treatment. Cancer Res; 77(8); 2102-11. ©2017 AACR.

Oct2 and Bob1 are sensitive and specific markers in lineage determination of B cell lymphomas with no expression of conventional B cell markers.

AIMS: Rare cases of B cell lymphomas do not express conventional B cell markers (CD20, CD79a and PAX5), and these types of lymphomas include anaplastic lymphoma kinase (ALK)-positive large B cell lymphoma, plasmablastic lymphoma, primary effusion lymphoma and the solid variant of primary effusion lymphoma, extracavitary human herpesvirus 8 (HHV8)-positive large B cell lymphoma. Establishing accurate diagnoses of these B cell lymphomas can be challenging, and often requires a large panel of immunohistochemical stains, molecular assays and cytogenetic studies. B cell-specific transcription factors, Oct2 and Bob1, have been shown to be expressed consistently in most, if not all, B cell lymphomas, and therefore we investigated the utility of Oct2 and Bob1 immunohistochemistry in lineage determination of the aforementioned B cell lymphomas. METHODS AND RESULTS: We selected 34 cases of previously diagnosed B cell lymphomas with no or weak expression of CD20, CD79a and PAX5. Oct2 and Bob1 were positive in 74% (25 of 34) and 85% (29 of 34) of the cases, respectively. When we combined the results of these two immunostains, 94% (32 of 34) cases expressed at least one of these two markers. We also included 51 control cases of non-B cell neoplasms, and none of them expressed either Oct2 or Bob1. CONCLUSIONS: Oct2 and Bob1 are very reliable in determining B cell lineage in the absence of expression of other pan-B cell markers, and it should provide great diagnostic benefit to include them both in a panel of immunohistochemistry to assess undifferentiated malignant neoplasms.

Correlation of Organic Cation/Carnitine Transporter 1 and Multidrug Resistance-Associated Protein 1 Transport Activities With Protein Expression Levels in Primary Cultured Human Tracheal, Bronchial, and Alveolar Epithelial Cells.

Understanding how transporters contribute to the distribution of inhaled drugs in the lung is important for the discovery and development of such drugs. Protein expression levels may be useful to predict and understand drug distribution. As previously reported, organic cation/carnitine transporter 1 (OCTN1) and multidrug resistance-associated protein 1 (MRP1) have higher levels of protein expression among transporters in primary cultured human lung cells. Nevertheless, it is unclear to what extent transport activity correlates with transporter protein expression. The purpose is to evaluate whether differences in OCTN1 and MRP1 protein expression govern the respective transport activity in primary cultured human lung cells. The model substrates of 4-[4-(dimethylamino) styryl]-N-methylpyridinium iodide (ASP(+)) and carboxy-dichlorofluorescein (CDF) for OCTN1 and MRP1, respectively, were used in the lung cells from five donors. Significant correlation was found between the kinetic parameter Vmax for ASP(+) and OCTN1 protein expression in plasma membrane of tracheal, bronchial, and alveolar cells (r(2) = 0.965, 0.834, and 0.877, respectively), and between the efflux of CDF and MRP1 protein expression in plasma membrane of tracheal, bronchial, and alveolar cells (r(2) = 0.800, 0.904, and 0.790, respectively). These findings suggest that OCTN1 and MRP1 protein concentrations are determinants for drug distribution in the lung.

Organic cation transporter OCT6 mediates cisplatin uptake and resistance to cisplatin in lung cancer.

PURPOSE: The purposes of this study were to determine whether organic cation transporters (OCTs) can mediate platinum uptake, and whether OCT down-regulation confers resistance against cisplatin (CDDP) in cancer cells. METHODS: Two lung cancer cell lines, PC-6 and PC-14, and their CDDP-resistant derivatives, PC-6/CDDP and PC-14/CDDP, were analyzed. OCT expression levels were assayed using quantitative RT-PCR and Western blotting. Additionally, the effect of OCT6 overexpression, induced by transfection of the OCT6 gene SLC22A16 using a forced expression vector, on cellular sensitivity to CDDP and on intracellular platinum accumulation was measured using PC-14/CDDP cells. RESULTS: Both gene and protein expression of OCT6 were decreased in both CDDP-resistant cell lines compared with their expression in their respective parental cells. Intracellular accumulation of platinum was decreased in PC-14/CDDP cells compared with the parental cells after CDDP treatment. Furthermore, OCT6 overexpression induced by transfection of the OCT6 gene (SLC22A16) forced expression vector-sensitized PC-14/CDDP cells to CDDP and oxaliplatin (L-OHP) concomitant with increased intracellular concentration of platinum. CONCLUSION: OCT6 is a mediator of platinum uptake in cancer cells, and down-regulation of OCT6 is possibly one of the mechanisms of resistance against cisplatin in lung cancer.

Glutamine protects against cisplatin-induced nephrotoxicity by decreasing cisplatin accumulation.

Cisplatin is a chemotherapeutic drug but induces acute kidney injury (AKI). Cisplatin-induced AKI depends on several signaling pathways leading to apoptosis in tubular epithelial cells. Glutamine is a substrate for the synthesis of glutathione, the most abundant intracellular thiol and antioxidant, and plays an important role in protecting cells from apoptosis induced by different stimuli. In the present study, we investigated the protective effect of glutamine on cisplatin-induced AKI. Rats were divided into control, glutamine, cisplatin, and cisplatin plus glutamine groups. Glutamine ameliorated renal dysfunction, tissue injury, and cisplatin-induced apoptosis. Cisplatin increased cell death, caspase-3 cleavage, activation of MAPKs and p53, oxidative stress, and mRNA expression of TNF-α and TNFR1 in HK-2 cells. Glutamine treatment reduced cisplatin-induced these changes in HK-2 cells. Notably, glutamine reduced the cisplatin-induced expression of organic cation transporter 2 (OCT2) and cisplatin accumulation. Our results suggest that the protective effect of glutamine on cisplatin is specific for proximal tubular cells and the initial effects may be related to attenuation of cisplatin uptake. Thus, glutamine administration might represent a new strategy for the treatment of cisplatin-induced AKI.

Anti-hyperuricemic and nephroprotective effects of Rhizoma Dioscoreae septemlobae extracts and its main component dioscin via regulation of mOAT1, mURAT1 and mOCT2 in hypertensive mice.

Rhizoma Dioscoreae septemlobae (RDSE) has been widely used for the treatment of hyperuricemia in China. However, the therapeutic mechanism has been unknown. This study investigated the antihyperuricemic mechanisms of the extracts obtained from RDSE and its main component dioscin (DIS) in hyperuricemic mice. Hyperuricemic mice were induced by potassium oxonate (250 mg/kg). RDSE or DIS was orally administered to hyperuricemic mice at dosages of 319.22, 638.43, 1276.86 mg/kg/day for 10 days, respectively. Uric acid or creatinine in serum and urine was determined by HPLC or HPLC-MS/MS, respectively. The xanthine oxidase (XO) activities in mice liver were examined in vitro. Protein levels of organic anion transporter 1 (mOAT1), urate transporter 1 (mURAT1) and organic cation transporter 2 (mOCT2) in the kidney were analyzed by western blotting. The results indicated that uric acid and creatinine in serum were significantly increased by potassium oxonate, as compared to that of control mice. Compared saline-treated group, after RDSE treatment in the high and middle dose, the expression of mOAT1 increased 47.98 and 54.48 %, respectively, which accompanied with the decreased expression of mURAT1 (47.63 %) in high dose. After DIS treatment in high, middle and low dose, the expression of mOAT1 increased 23.93, 32.80 and 25.28 % compared to saline-treated group, respectively, which accompanied with the decreased expression of mURAT1 (51.07, 51.42 and 51.35 %). However, RDSE and DIS displayed a weak XO inhibition activity compared with allopurinol. Therefore, RDSE and DIS processed uricosuric and nephroprotective actions by regulation of mOAT1, mURAT1 and mOCT2.