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The Wnt/ß-catenin signaling pathway is dysregulated in diseases and Wnt inhibitors like PRI-724 are in clinical development. This study evaluated the regulatory actions of PRI-724 and other Wnt inhibitors on the transport activity of human renal Organic anion transporters (OATs) and Organic anion transporting polypeptides (OATPs). The substrate uptake by OAT4 and OATP2B1 was markedly decreased by PRI-724 (Vmax/Km: ∼26% and ∼17% of corresponding control), with less pronounced decreases in OAT1, OAT3 and OAT1A2. PRI-724 decreased the plasma membrane expression of inhibited OATs/OATPs but didn't affect their total cellular expression. Two model Wnt inhibitors - FH535 and 21H7 - were also tested in comparative studies. Like PRI-724, they also strongly decreased the activities and membrane expression of multiple OATs/OATPs. In contrast, FH535 didn't affect the substrate uptake by organic cation transporters. In control studies, the EGFR inhibitor lapatinib did not inhibit the function of some OATs/OATPs. Together these findings suggest that Wnt inhibitors selectively modulate the function of multiple organic anions transporters, so their clinical use may have unanticipated effects on drug entry into cells. These findings are pertinent to current clinical trials that have been designed to understand the safety and efficacy of new Wnt inhibitor drugs.

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Organic anion transporting polypeptides (OATPs) are important transporter proteins that are expressed at the plasma membrane of cells, where they mediate the influx of endogenous and exogenous substances including hormones, natural compounds and many clinically important drugs. OATP1A2, OATP2B1, OATP1B1 and OATP1B3 are the most important OATP isoforms and influence the pharmacokinetic performance of drugs. These OATPs are highly expressed in the kidney, intestine and liver, where they determine the distribution of drugs to these tissues. Herbal medicines are increasingly popular for their potential health benefits. Humans are also exposed to many natural compounds in fruits, vegetables and other food sources. In consequence, the consumption of herbal medicines or food sources together with a range of important drugs can result in drug-herb/food interactions via competing specific OATPs. Such interactions may lead to adverse clinical outcomes and unexpected toxicities of drug therapies. This review summarises the drug-herb/food interactions of drugs and chemicals that are present in herbal medicines and/or food in relation to human OATPs. This information can contribute to improving clinical outcomes and avoiding unexpected toxicities of drug therapies in patients.

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The organic anion transporting polypeptides (OATPs) are important membrane proteins that mediate the cellular uptake of drugs and endogenous substances. OATP1A2 is widely distributed in many human tissues that are targeted in drug therapy; defective OATP1A2 leads to altered drug disposition influencing therapeutic outcomes. 5'-AMP-activated protein kinase (AMPK) signaling plays an important role in the pathogenesis of the metabolic syndrome characterized by an increased incidence of type II diabetes and nonalcoholic fatty liver disease. This study investigated the regulatory role of AMPK in OATP1A2 transport function and expression. We found that the treatment of AMPK-specific inhibitor compound C (dorsomorphin dihydrochloride) decreased OATP1A2-mediated uptake of estrone-3-sulfate in a concentration- and time-dependent manner. The impaired OATP1A2 function was associated with a reduced Vmax [154.6 ± 17.9 pmol × (µg × 4 minutes)-1 in compound C-treated cells vs. 413.6 ± 52.5 pmol × (µg × 4 minutes)-1 in controls]; the Km was unchanged. The cell-surface expression of OATP1A2 was decreased by compound C treatment, but total cellular expression was unchanged. The impaired cell-surface expression of OATP1A2 was associated with accelerated internalization and impaired targeting/recycling. Silencing of the AMPK α1-subunit using specific small interfering RNA corroborated the findings with compound C and revealed a role for AMPK in regulating OATP1A2 protein stability. Overall, this study implicated AMPK in the regulation of the function and expression of OATP1A2, which potentially impacts on the disposition of OATP1A2 drug substrates that may be used to treat patients with the metabolic syndrome and other diseases.

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1. Human solute carrier transporters (SLCs) are important membrane proteins mediate the cellular transport of many endogenous and exogenous substances. Organic anion/cation transporters (OATs/OCTs) and organic anion transporting polypeptides (OATPs) are essential SLCs involved in drug influx. Drug-drug/herb interactions through competing for specific SLCs often lead to unsatisfied therapeutic outcomes and/or unwanted side effects. In this study, we comprehensively investigated the inhibitory effects of five clinically relevant alkaloids (dendrobine, matrine, oxymatrine, tryptanthrin and chelerythrine) on the substrate transport through several OATs/OCTs and OATPs. 2. We performed transport functional assay and kinetic analysis on the HEK-293 cells over-expressing each SLC gene. 3. Our data showed tryptanthrin significantly inhibited the transport activity of OAT3 (IC50 = 0.93 ± 0.22 µM, Ki = 0.43 µM); chelerythrine acted as a potent inhibitor to the substrate transport mediated through OATP1A2 (IC50 = 0.63 ± 0.43 µM, Ki = 0.60 µM), OCT1 (IC50 = 13.60 ± 2.81 µM) and OCT2 (IC50 =10.80 ± 1.16 µM). 4. Our study suggested tryptanthrin and chelerythrine could potently impact on the drug transport via specific OATs/OCTs. Therefore, the co-administration of these alkaloids with drugs could have clinical consequences due to drug-drug/herb interactions. Precautions should be warranted in the multi-drug therapies involving these alkaloids.

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Human oligopeptide transporter 1 (hPepT1) mediates the absorption of dietary peptides and a range of clinically relevant drugs. According to the predicted topological structure, hPepT1 contains multiple asparagine residues in putative N-glycosylation sites. This study investigated the influence of the six putative N-glycosylation sites within the extracellular region between transmembrane domains 9 and 10 on hPepT1 transporter function and expression in HEK-293T cells. Our study confirmed that hPepT1 is N-glycosylated in HEK-293T cells with the glycosylated and fully deglycosylated isoforms exhibiting apparent molecular masses of ∼78 and ∼55 kDa, respectively. Transport uptake of Glycylsarcosine (Gly-sar) by the hPepT1-N562Q variant, but not by other single mutants, was moderately impaired. We also constructed multiple N-glycosylation mutants based on the hPepT1-N562Q mutant by mutagenizing the additional asparagine residues N404Q, N408Q, N439Q, N509Q, and N514Q. Transport function showed a graded decrease as the number of mutagenized residues increased and simultaneous removal of all six asparagine residues essentially abolished transport activity. Kinetic studies indicated that the Vmax values for Gly-sar transport by low activity mutants were decreased compared to those of wild-type, which suggested that the cell surface expression and/or turnover rate of hPepT1 mutants was impaired; Km values were unchanged in most cases. Using immunoblotting and immunofluorescence, the plasma membrane and total cellular expression of the mutant transporters were decreased in accordance with functional impairments. In summary, we provide the first molecular evidence that hPepT1 is modified by N-glycosylation and that all six asparagine residues in the large extracellular loop between transmembrane domains 9 and 10 are subject to N-glycosylation. This information enhances our understanding of the role of the large extracellular loop in hPepT1 regulation and could facilitate the development of new hPepT1 substrate drugs with improved bioavailability.

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ETHNOPHARMACOLOGICAL RELEVANCE: Previous studies conducted on animals linked consumption of Nigella sativa L. seeds (NS) to decreased anxiety and improved memory. The present study, which was carried out at a boarding school in Bangladesh, was designed to examine probable effect of NS on mood, anxiety and cognition in adolescent human males. MATERIALS AND METHODS: Forty-eight healthy adolescent human males aged between 14 to 17 years were randomly recruited as volunteers and were randomly split into two groups: A (n=24) and B (n=24). The treatment procedure for group A and B were one capsule of 500 mg placebo and 500 mg NS respectively once daily for four weeks. All the volunteers were assessed for cognition with modified California verbal learning test-II (CVLT-II), mood with Bond-Lader scale and anxiety with State-Trait Anxiety Inventory (STAI) at the beginning and after four weeks of either NS or placebo ingestion. RESULTS AND DISCUSSION: No parameter showed statistically significant variation between A and B in measurements in the beginning, but after 4 weeks of one capsule of NS 500 mg intake, there was statistically significant variation of mood within group B but there was not statistically significant variation between group A and B. No significant variation was found in state anxiety within groups and between group A and B but in case of trait anxiety, significant variation was found within group B but not between group A and B. In case of CVLT II, there was significant variation within B in immediate short-term recall at trial 4 and 5 whereas this difference was found only in case of trial 5 between group A and B. Within group B, short term-free recall, long-term free recall and long-term cued recall had statistical difference whereas between group A and B long-term free recall and long-term cued recall had statistical difference. No parameters had significant variation within group A after placebo intake for 4 weeks. CONCLUSIONS: Over the 4 weeks study period, the use of NS as a nutritional supplement been observed to- stabilize mood, decrease anxiety and modulate cognition positively. However, long term study is suggested before using NS extensively.

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ETHNOPHARMACOLOGICAL RELEVANCE: There is very limited information regarding plants used by traditional healers for treating diabetes in Bangladesh, let alone compilation on the use of those. This study aimed at collecting and documenting information on antidiabetic plants traditionally used in the treatment of diabetes. MATERIALS AND METHODS: The survey was carried out in a period of almost 2 years. Fieldwork was undertaken in total of 15 districts of Bangladesh. Open-ended and semi structured questionnaire were used to interview a total of 1060 people including traditional healers, Ayurvedic/Unani drug manufacturers and local people. RESULTS: A total of 83 plant species of 38 families were listed. Leaves were the most cited plant part used against diabetes. Most of the reported species were tree in nature and decoction is the mode of preparation of major portions of the plant species. Most of the plant species were very common and were cultivated or planted in homestead or roadsides. CONCLUSION: Conventional use of many antidiabetic plants of Bangladesh can be rationalized by the presence of active compounds found in those plants. The documentation could be important for the conservation of these plants and represent the preliminary information required for future phytochemical investigation.

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