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Organic anion transporters (OATs) belong to a subgroup of the solute carrier 22 transporter family. OATs have a central role in xenobiotic disposition affecting the toxicokinetics of its substrates and inter-individual differences in their expression, activity and function impact both toxicokinetics and toxicodynamics. Amongst OATs, OAT1 (solute carrier family 22 member 6) is involved in the urinary excretion of many xenobiotics bringing substrates into renal proximal tubular cells which can then be secreted across the apical membrane into the tubule lumen. The mycotoxin ochratoxin A has been shown to have a high affinity for OAT1, which is an important renal transporter involved in its urinary excretion. Nowadays, molecular modeling techniques are widely applied to assess protein-ligand interactions and may provide a tool to depict the mechanistic of xenobiotic action be it toxicokinetics or toxicodynamics. This work provides a structured pipeline consisting of docking and molecular dynamic simulations to study OAT1-ligand interactions and the impact of OAT1 polymorphisms on such interactions. Such a computational structure-based analytical framework allowed to: i) model OAT1-substrate complex formation and depict the features correlating its sequence, structure and its capability to recruit substrates; and ii) investigate the impact of OAT1 missense mutations on substrate recruitment. Perspectives on applying such a structured pipeline to xenobiotic-metabolising enzymes are discussed.

As an expansion investigation of drug-drug interaction (DDI) from previous clinical trials, additional plasma endogenous metabolites were quantitated in the same subjects to further identify the potential biomarkers of organic anion transporter (OAT) 1/3 inhibition. In the single dose, open label, three-phase with fixed order of treatments study, 14 healthy human volunteers orally received 1000 mg probenecid alone, or 40 mg furosemide alone, or 40 mg furosemide at 1 hour after receiving 1000 mg probenecid on days 1, 8, and 15, respectively. Endogenous metabolites including kynurenic acid, xanthurenic acid, indo-3-acetic acid, pantothenic acid, p-cresol sulfate, and bile acids in the plasma were measured by liquid chromatography–tandem mass spectrometry. The Cmax of kynurenic acids was significantly increased about 3.3- and 3.7-fold over the baseline values at predose followed by the treatment of probenecid alone or in combination with furosemide respectively. In comparison with the furosemide-alone group, the Cmax and area under the plasma concentration–time curve (AUC) up to 12 hours of kynurenic acid were significantly increased about 2.4- and 2.5-fold by probenecid alone, and 2.7- and 2.9-fold by probenecid plus furosemide, respectively. The increases in Cmax and AUC of plasma kynurenic acid by probenecid are comparable to the increases of furosemide Cmax and AUC reported previously. Additionally, the plasma concentrations of xanthurenic acid, indo-3-acetic acid, pantothenic acid, and p-cresol sulfate, but not bile acids, were also significantly elevated by probenecid treatments. The magnitude of effect size analysis for known potential endogenous biomarkers demonstrated that kynurenic acid in the plasma offers promise as a superior addition for early DDI assessment involving OAT1/3 inhibition. SIGNIFICANCE STATEMENT This article reports that probenecid, an organic anion transporter (OAT) 1 and OAT3 inhibitor, significantly increased the plasma concentrations of kynurenic acid and several uremic acids in human subjects. Of those, the increases of plasma kynurenic acid exposure are comparable to the increases of furosemide by OAT1/3 inhibition. Effect size analysis for known potential endogenous biomarkers revealed that plasma kynurenic acid is a superior addition for early drug-drug interaction assessment involving OAT1/3 inhibition.

BackgroundEndogenous biomarkers are promising tools to assess transporter-mediated drug–drug interactions early in humans.MethodsWe evaluated on a common and validated in vitro system the selectivity of 4-pyridoxic acid (PDA), homovanillic acid (HVA), glycochenodeoxycholate-3-sulphate (GCDCA-S) and taurine towards different renal transporters, including multidrug resistance-associated protein, and assessed the in vivo biomarker sensitivity towards the strong organic anion transporter (OAT) inhibitor probenecid at 500 mg every 6 h to reach close to complete OAT inhibition.ResultsPDA and HVA were substrates of the OAT1/2/3, OAT4 (PDA only) and multidrug resistance-associated protein 4; GCDCA-S was more selective, having affinity only towards OAT3 and multidrug resistance-associated protein 2. Taurine was not a substrate of any of the investigated transporters under the in vitro conditions tested. Plasma exposure of PDA and HVA significantly increased and the renal clearance of GCDCA-S, PDA and HVA decreased; the magnitude of these changes was comparable to those of known clinical OAT probe substrates. PDA and GCDCA-S were the most promising endogenous biomarkers of the OAT pathway activity: PDA plasma exposure was the most sensitive to probenecid inhibition, and, in contrast, GCDCA-S was the most sensitive OAT biomarker based on renal clearance, with higher selectivity towards the OAT3 transporter.ConclusionsThe current findings illustrate a clear benefit of measuring PDA plasma exposure during phase I studies when a clinical drug candidate is suspected to be an OAT inhibitor based on in vitro data. Subsequently, combined monitoring of PDA and GCDCA-S in both urine and plasma is recommended to tease out the involvement of OAT1/3 in the inhibition interaction.

Context Relinqing granules (RLQ) are being used alone or in combination with antibacterial drugs to treat urological disorders. Objective This study investigates the pharmacokinetics of RLQ in humans and the potential for RLQ-perpetrated interactions on transporters. Materials and methods Twelve healthy subjects (six women and six men) participated to compare single- and multiple-dose pharmacokinetics of RLQ. In the single-dose study, all 12 subjects received 8 g of RLQ orally. After a 7-d washout period, the subjects received 8 g of RLQ for seven consecutive days (t.i.d.) and then a single dose. Gallic acid (GA) and protocatechuic acid (PCA) in plasma and urine samples were analysed using LC-MS/MS. The transfected cells were used to study the inhibitory effect of GA (50–5000 μg/L) and PCA (10–1000 μg/L) on transporters OAT1, OAT3, OCT2, OATP1B1, P-gp and BCRP. Results GA and PCA were absorbed into the blood within 1 h after administration and rapidly eliminated with a half-life of less than 2 h. The mean peak concentrations of GA (102 and 176 μg/L) and PCA (4.54 and 7.58 μg/L) were lower in males than females, respectively. The 24 h urine recovery rates of GA and PCA were about 10% and 5%, respectively. The steady-state was reached in 7 d without accumulation. GA was a potent inhibitor of OAT1 (IC50 = 3.73 μM) and OAT3 (IC50 = 29.41 μM), but not OCT2, OATP1B1, P-gp or BCRP. Discussion and conclusions GA and PCA are recommended as PK-markers in RLQ-related pharmacokinetic and drug interaction studies. We should pay more attention to the potential for RLQ-perpetrated interactions on transporters.

Halogenated tyrosine/phenylalanine derivatives have been developed for use in tumor imaging and targeted alpha therapy. 3-Fluoro-α-methyl-l-tyrosine (FAMT), targeting amino acid transporter LAT1 (SLC7A5), is a cancer-specific positron emission tomography probe that exhibits high renal accumulation, which is supposed to be mediated by organic anion transporter OAT1 (SLC22A6). In the present study, we investigated the structural requirements of FAMT essential for interaction with OAT1. OAT1 transported FAMT with a K m of 171.9 μM. In structure-activity relationship analyses, removal of either the 3-halogen or 4-hydroxyl group from FAMT or its structural analog 3-iodo-α-methyl-l-tyrosine greatly decreased the interaction with OAT1, reducing the [14C]p-aminohippurate uptake inhibition and the efflux induction. By contrast, the α-methyl group, which is essential for LAT1 specificity, contributed to a lesser degree. In fluorinated tyrosine derivatives, fluorine at any position was accepted by OAT1 when there was a hydroxyl group at the ortho-position, whereas ortho-fluorine was less interactive when a hydroxyl group was at meta- or para-positions. The replacement of the ortho-fluorine with a bulky iodine atom greatly increased the interaction. In in vivo studies, probenecid decreased the renal accumulation (P < 0.001) and urinary excretion (P = 0.0012) of FAMT, whereas the plasma concentration was increased, suggesting the involvement of OAT1-mediated transepithelial organic anion excretion. LAT1-specific 2-fluoro-α-methyltyrosine, which had lower affinity for OAT1, exhibited lower renal accumulation (P = 0.0142) and higher tumor uptake (P = 0.0192) compared with FAMT. These results would provide a basis to design tumor-specific compounds that can avoid renal accumulation for tumor imaging and targeted alpha therapy. SIGNIFICANCE STATEMENT: We revealed the structural characteristics of halogenated tyrosine derivatives essential for interaction with the organic anion transporter responsible for their renal accumulation. We have confirmed that such interactions are important for renal handling and tumor uptake. The critical contribution of hydroxyl and halogen groups and their positions as well as the role of α-methyl group found in the present study may facilitate the development of tumor-specific compounds while avoiding renal accumulation for use in tumor imaging and targeted alpha therapy.

Mercury is a widespread pollutant. Mercuric ions uptake into tubular cells is supported by the Organic anion transporter 1 (Oat1) and 3 (Oat3) and its elimination into urine is through the Multidrug resistance-associated protein 2 (Mrp2). We investigated the effect of recombinant human erythropoietin (Epo) on renal function and on renal expression of Oat1, Oat3, and Mrp2 in a model of mercuric chloride (HgCl2)-induced renal damage. Four experimental groups of adult male Wistar rats were used: Control, Epo, HgCl2, and Epo + HgCl2. Epo (3000 IU/kg, b.w., i.p.) was administered 24 h before HgCl2 (4 mg/kg, b.w., i.p.). Experiments were performed 18 h after the HgCl2 dose. Parameters of renal function and structure were evaluated. The protein expression of Oat1, Oat3 and Mrp2 in renal tissue was assessed by immunoblotting techniques. Mercury levels were determined by cold vapor atomic absorption spectrometry. Pretreatment with Epo ameliorated the HgCl2-induced tubular injury as assessed by histopathology and urinary biomarkers. Immunoblotting showed that pretreatment with Epo regulated the renal expression of mercury transporters in a way to decrease mercury content in the kidney. Epo pretreatment ameliorates HgCl2-induced renal tubular injury by modulation of mercury transporters expression in the kidneys.

Background and Objectives Citrus flavonoids are not only components of daily nutrition, they are also promoted as dietary supplements and are important ingredients in traditional medicines. Interactions of flavonoids with synthetic drugs represent an often neglected issue. We therefore investigated in vitro whether the polymethoxyflavones nobiletin, sinensetin, and tangeretin and the flavonoid rutinosides didymin, hesperidin, and narirutin can inhibit human organic anion transporting polypeptides (OATP) 1B1, 1B3, and 2B1, which are important transporters mediating drug-drug and food-drug interactions. Methods Inhibition was investigated by quantifying the decreased uptake of the fluorescent OATP1B1 and OATP1B3 substrate 8-fluorescein-cAMP in HEK293 cells overexpressing OATP1B1 or OATP1B3 and of the fluorescent OATP2B1 substrate 4′,5′-dibromofluorescein in HEK293 cells overexpressing OATP2B1. Results We demonstrate that all flavonoids investigated inhibit OATP2B1 in the lower micromolar range (IC50 between 1.6 and 14.2 µM), but only the polymethoxyflavones also inhibit OATP1B1 and 1B3 (IC50 between 2.1 and 21 µM). Conclusions All flavonoids investigated might contribute to the intestinal OATP2B1-based interactions with drugs observed with citrus juices or fruits. In contrast, the concentration of the polymethoxyflavones after consumption of citrus juices or fruits is most likely too low to reach relevant systemic concentrations and thus to inhibit hepatic OATP1B1 and OATP1B3, but there might be a risk when they are consumed as medicines or as dietary supplements.

Relation between the renal function and the membrane environment where the organic anion transporters Oat1 and Oat3 are localized is scarce. The aim of this study was to examine the Oat1 and Oat3 distribution in different cellular fractions under physiological conditions as well as the effects of extrahepatic cholestasis on membrane distribution of both proteins. Besides, the potential role of jaundice serum on the Oat1 and Oat3 expression in suspensions of renal tubular cells was evaluated. Cellular and membrane fractions of renal cortex were obtained from control rats to evaluate Oat1 and Oat3 protein expressions. Other rats were subjected to bile duct ligation (BDL) or Sham operation to determine the membrane distribution of Oat1 and Oat3 between lipid raft domains (LRD) and non-LRD. Incubation of renal cortical cells with serum from Sham and BDL were also performed to study Oat1 and Oat3 protein expressions. In physiological conditions, Oat1 and Oat3 were concentrated in LRD. The pathology induced a shift of Oat1 from LRD to non-LRD, while Oat3 showed no changes in its distribution. In cells exposed to BDL serum, Oat1 protein expression in membranes significantly increased. For Oat3, no difference between groups was observed. The Oat1 redistribution to non-LRD in BDL could be favoring the increase in renal transport of organic anions previously observed. This change was specific to Oat1. The in vitro experiment allows to conclude that some component present in BDL serum is responsible for the alterations observed in Oat1 expression in cortical membranes.

Organic anion transporter 1 (OAT1), expressed at the basolateral membrane of renal proximal tubule epithelial cells, mediates the renal excretion of many clinically important drugs. Previous study in our laboratory demonstrated that ubiquitin conjugation to OAT1 leads to OAT1 internalization from the cell surface and subsequent degradation. The current study showed that the ubiquitinated OAT1 accumulated in the presence of the proteasomal inhibitors MG132 and ALLN rather than the lysosomal inhibitors leupeptin and pepstatin A, suggesting that ubiquitinated OAT1 degrades through proteasomes. Anticancer drugs bortezomib and carfilzomib target the ubiquitin-proteasome pathway. We therefore investigate the roles of bortezomib and carfilzomib in reversing the ubiquitination-induced downregulation of OAT1 expression and transport activity. We showed that bortezomib and carfilzomib extremely increased the ubiquitinated OAT1, which correlated well with an enhanced OAT1-mediated transport of p-aminohippuric acid and an enhanced OAT1 surface expression. The augmented OAT1 expression and transport activity after the treatment with bortezomib and carfilzomib resulted from a reduced rate of OAT1 degradation. Consistent with this, we found decreased 20S proteasomal activity in cells that were exposed to bortezomib and carfilzomib. In conclusion, this study identified the pathway in which ubiquitinated OAT1 degrades and unveiled a novel role of anticancer drugs bortezomib and carfilzomib in their regulation of OAT1 expression and transport activity. SIGNIFICANCE STATEMENT Bortezomib and carfilzomib are two Food and Drug Administration–approved anticancer drugs, and proteasome is the drug target. In this study, we unveiled a new role of bortezomib and carfilzomib in enhancing OAT1 expression and transport activity by preventing the degradation of ubiquitinated OAT1 in proteasomes. This finding provides a new strategy in regulating OAT1 function that can be used to accelerate the clearance of drugs, metabolites, or toxins and reverse the decreased expression under disease conditions.

The multispecific organic anion transporters, OAT1 (SLC22A6) and OAT3 (SLC22A8), the main kidney elimination pathways for many common drugs, are often considered to have largely-redundant roles. However, whereas examination of metabolomics data from Oat-knockout mice (Oat1 and Oat3KO) revealed considerable overlap, over a hundred metabolites were increased in the plasma of one or the other of these knockout mice. Many of these relatively unique metabolites are components of distinct biochemical and signaling pathways, including those involving amino acids, lipids, bile acids, and uremic toxins. Cheminformatics, together with a “logical” statistical and machine learning-based approach, identified a number of molecular features distinguishing these unique endogenous substrates. Compared with OAT1, OAT3 tends to interact with more complex substrates possessing more rings and chiral centers. An independent “brute force” approach, analyzing all possible combinations of molecular features, supported the logical approach. Together, the results suggest the potential molecular basis by which OAT1 and OAT3 modulate distinct metabolic and signaling pathways in vivo. As suggested by the Remote Sensing and Signaling Theory, the analysis provides a potential mechanism by which “multispecific” kidney proximal tubule transporters exert distinct physiological effects. Furthermore, a strong metabolite-based machine-learning classifier was able to successfully predict unique OAT1 versus OAT3 drugs; this suggests the feasibility of drug design based on knockout metabolomics of drug transporters. The approach can be applied to other SLC and ATP-binding cassette drug transporters to define their nonredundant physiological roles and for analyzing the potential impact of drug–metabolite interactions.

Small changes to molecules can have profound effects on their pharmacological activity as exemplified by the addition of the two-carbon acetyl group to make drugs more effective by enhancing their pharmacokinetic or pharmacodynamic properties. N-acetyl-d,l-leucine is approved in France for vertigo and its l-enantiomer is being developed as a drug for rare and common neurological disorders. However, the precise mechanistic details of how acetylation converts leucine into a drug are unknown. Here we show that acetylation of leucine switches its uptake into cells from the l-type amino acid transporter (LAT1) used by leucine to organic anion transporters (OAT1 and OAT3) and the monocarboxylate transporter type 1 (MCT1). Both the kinetics of MCT1 (lower affinity compared to LAT1) and the ubiquitous tissue expression of MCT1 make it well suited for uptake and distribution of N-acetyl-l-leucine. MCT1-mediated uptake of a N-acetyl-l-leucine as a prodrug of leucine bypasses LAT1, the rate-limiting step in activation of leucine-mediated signalling and metabolic process inside cells such as mTOR. Converting an amino acid into an anion through acetylation reveals a way for the rational design of drugs to target anion transporters.

Multiple doses of tenofovir disoproxil fumarate (TDF) together with emtricitabine is effective for HIV preexposure prophylaxis (PrEP). TDF is converted to tenofovir (TFV) in circulation, which is subsequently cleared via tubular secretion by organic ion transporters (OATs; OAT1 and OAT3). Using in vitro kinetic parameters for TFV and the OAT1 and OAT3 inhibitor probenecid, a bottom‐up physiologically‐based pharmacokinetic model was successfully developed for the first time that accurately describes the probenecid–TFV interaction. This model predicted an increase in TFV plasma exposure by 60%, which was within 15% of the observed clinical pharmacokinetic data, and a threefold decrease in renal cells exposure following coadministration of a 600 mg TDF dose with 2 g probenecid. When compared with multiple‐dose regimens, a single‐dose probenecid‐boosted TDF regimen may be effective for HIV PrEP and improve adherence and safety by minimizing TFV‐induced nephrotoxicity by reducing TFV accumulation in renal cells.

Stellera chamaejasme L. is a traditional Chinese medicine with a long history to treat stubborn skin ulcer, and it also has antiviral and antitumor effects. Neochamaejasmine B (NCB), Neochamaejasmine A (NCA) and Chamaechromone (CMC) are the major components in dried roots of Stellera chamaejasme L.. Our studies suggested that NCB, NCA and CMC are inhibitors of Organic anion transporter 1 (OAT1). OAT1 is encoded by solute carrier family 22 member 6 gene (SLC22A6) in humans and plays a critical role in the organic anion drug uptake and excretion in the kidney. Lamivudine is the typical substrate of OAT1 and is frequently used in combination with other antiviral drugs in clinical antiviral treatments. The aim of this study is to investigate the interaction and its mechanism between these bi-flavone components in Stellera chamaejasme L. and lamivudine via OAT1 both in vitro and in vivo. In vitro, the uptake studies in Madin-Darby canine kidney (MDCK) cells overexpressing OAT1 suggested that NCB inhibited the uptake of 6-CFL and lamivudine.Similar results were obtained for NCA and CMC. NCB was a noncompetitive and competitive inhibitor interaction with OAT1. IC50 values of NCB, NCA and CMC for inhibiting OAT1-mediated lamivudine transport were 2.46, 8.35 and 0.61 μmol·L-1, respectively. In vivo, the pharmacokinetic results of lamivudine in rats showed that the mean area under the plasma concentration-time curve (AUC0-∞) and maximal plasma concentration (Cmax) of lamivudine after co-administration is increased 2.94-fold and 1.87-fold, respectively, compared to lamivudine administration alone. The results of interactions between lamivudine and these bi-flavone components in Stellera chamaejasme L. extracts via OAT1 in vivo are consistent with studies in vitro. The inhibition of OAT1-mediated uptake of lamivudine by NCB, NCA and CMC is the possible mechanism for Stellera chamaejasme L. extracts improving the oral bioavailability of lamivudine in rats.

Rheumatoid arthritis patients can be prescribed a combination of immunosuppressive drug leflunomide (LEF) and the antiviral drug acyclovir to reduce the high risk of infection. Acyclovir is a substrate of organic anion transporter (OAT) 1/3 and multidrug resistance-associated protein (MRP) 2. Considering the extraordinarily long half-life of LEF’s active metabolite teriflunomide (TER) and the kidney injury risk of acyclovir, it is necessary to elucidate the potential impact of LEF on the disposition of acyclovir. Here we used a specific MRP inhibitor MK571 and probenecid (OAT1/3 and MRP2 inhibitor) to assess the effects of MRP2 and OAT1/3 on the pharmacokinetics and tissue distribution of acyclovir in rats. We showed that LEF and probenecid, but not MK571 significantly increased the plasma concentration of acyclovir. However, kidney and liver exposures of acyclovir were increased when coadministered with LEF, probenecid or MK571. The kidney/plasma ratio of acyclovir was increased to approximately 2-fold by LEF or probenecid, whereas it was increased to as much as 14.5-fold by MK571. Consistently, these drugs markedly decreased the urinary excretion of acyclovir. TER (0.5−100 μmol/L) dose-dependently increased the accumulation of acyclovir in MRP2-MDCK cells with an IC 50 value of 4.91 μmol/L. TER (5 μmol/L) significantly inhibited the uptake of acyclovir in hOAT1/3-HEK293 cells. These results suggest that LEF/TER increased the kidney accumulation of acyclovir by inhibiting the efflux transporter MRP2, which increased its kidney/plasma ratio and renal injury risk. However, the inhibitory effects of LEF/TER on OAT1/3 reduced the tubular cells’ uptake of acyclovir and increased the plasma concentration.

Hyperuricaemia, which results from the overproduction and underexcretion of uric acid, has been linked with chronic renal dysfunction, cardiovascular diseases, diabetes and metabolic syndrome. However, available clinical drugs cannot simultaneously target the production and excretion of uric acid. Norathyriol, a natural xanthone, was expected to have the dual actions. We previously reported that norathyriol possessed potent anti-hyperuricaemic activity related to the inhibition of uric acid production. Here, we investigated the uricosuric actions in hyperuricaemic animals and explored the possible molecular mechanisms associated with renal urate transporters and xanthine oxidase (XO). The results showed that norathyriol (0.5–4.0 mg/kg) dose- and time-dependently decreased serum urate levels in uric acid-induced hyperuricaemic mice and markedly increased the fractional excretion of urate in oxonate-induced hyperuricaemic rats, demonstrating a promotion of urate excretion in the kidney. Further evidence showed that norathyriol markedly increased renal mRNA and protein expression of the secretory organic anion transporter 1 (OAT1) in hyperuricaemic mice and strengthened its transport function in vitro. Moreover, norathyriol also upregulated the mRNA expression of the secretory transporters OAT3, ATP-binding cassette transporter G2 and multidrug resistance protein 4, but not their protein expression. Changes in the expression of the reabsorptive transporters were not observed. This is the first report that norathyriol has uricosuric effects by targeting OAT1. Moreover, norathyriol significantly inhibited XO activity in an uncompetitive manner. Taken together, these findings suggest that norathyriol has the potential to be developed as a new anti-hyperuricaemic agent with dual actions that activate OAT1 and inhibit XO activity.

A bioactivity guided program exploring the interaction of phytochemicals in the entire plant Primula macrocalyx with the organic anion transporters (OAT1 and OAT3) and microorganisms led to the elucidation of ten known flavones (1–4, 6–10, 12) and two previously undescribed flavones (5, 11). The structures of the compounds were determined by extensive analysis of spectroscopic data, as well as by comparison with data from previous reports. Two known flavones (9, 12) are reported for the first time from the family Primulaceae. All compounds were evaluated for inhibition of OAT1 and OAT3. Six flavones (2, 3, 6–8, 12) showed potent inhibitory activity on OAT1, while seven flavones (2, 3, 6–9, 12) showed marked inhibitory activity on OAT3, with IC50 ≤ 10.0 µM. Antimicrobial activities of crude fractions against sixteen microorganisms were tested to give a target yeast strain Candida rugosa for further evaluation of MICs on the isolates. Three flavones (7, 8, 12) showed marked antifungal activity with MIC µM. To our knowledge, this study is the first to evaluate these flavones as inhibitors of the OAT1 and OAT3, and as antifungal agents.

Phellodendri Chinensis Cortex (PC) is a traditional medicinal material used to treat gout and hyperuricemia (HUA) in China. Berberine (BBR), the main component of PC, possesses anti-hyperuricemic and anti-gout effects. However, BBR exhibits low bioavailability due to its extensive metabolism and limited absorption. Thus, the metabolites of BBR are believed to be the potential active forms responsible for its in vivo biological activities. Berberrubine (BRB), one of the major metabolites of BBR, exhibits appreciable biological activities even superior to BBR. In this work, the anti-hyperuricemic efficacy of BRB was investigated in HUA model mice induced by co-administration with intraperitoneal potassium oxonate (PO) and oral hypoxanthine (HX) for 7 days. Results showed that administration with BRB (6.25, 12.5, and 25.0 mg/kg) significantly decreased the serum levels of uric acid (UA) by 49.70%, 75.35%, and 75.96% respectively, when compared to the HUA group. In addition, BRB sharply decreased the levels of serum creatinine (CRE) (by 19.62%, 28.98%, and 38.72%, respectively) and blood urea nitrogen (BUN) (by 16.19%, 25.07%, and 52.08%, respectively) and reversed the PO/HX-induced renal histopathological damage dose-dependently. Additionally, BRB lowered the hepatic XOD activity, downregulated the expressions of glucose transporter 9 (GLUT9) and urate transporter 1 (URAT1), upregulated expressions of organic anion transporter 1/3 (OAT1/3) and ATP-binding cassette transporter subfamily G member 2 (ABCG2) at both protein and mRNA levels, and suppressed the activation of the JAK2/STAT3 signaling pathway. In addition, BRB significantly decreased the levels of inflammatory mediators (IL-1β, IL-6, and TNF-α). In conclusion, our study indicated that BRB exerted anti-hyperuricemic effect, at least in part, via regulating the urate transporter expressions and suppressing the JAK2/STAT3 signaling pathway. BRB was believed to be promising for further development into a potential therapeutic agent for HUA treatment.

Human OAT1 and OAT3 play major roles in renal drug elimination and drug-drug interactions. However, there is little information on the interactions of drug metabolites with transporters. The goal of this study was to characterize the interactions of drug metabolites with OAT1 and OAT3 and compare their potencies of inhibition with those of their corresponding parent drugs. Using HEK293cells stably transfected with OAT1 and OAT3, 25 drug metabolites and their corresponding parent drugs were screened for inhibitory effects on OAT1-and OAT3-mediated 6-carboxyfluorescein uptake at a screening concentration of 200μM for all but 3 compounds. 20 and 24 drug metabolites were identified as inhibitors (inhibition>50%) of OAT1 and OAT3, respectively. Seven drug metabolites were potent inhibitors of either or both OAT1 and OAT3 with Ki values less than 1μM. 22 metabolites were more potent inhibitors of OAT3 than OAT1. Importantly, one drug and four metabolites were predicted to inhibit OAT3 at unbound plasma concentrations achieved clinically (Cmax,u/Ki values≥0.1). In conclusion, our study highlights the potential interactions of drug metabolites with OAT1 and OAT3 at clinically relevant concentrations, suggesting that drug metabolites may modulate therapeutic and adverse drug response by inhibiting renal drug transporters.

Over the course of more than 500 million years, the kidneys have undergone a remarkable evolution from primitive nephric tubes to intricate filtration-reabsorption systems that maintain homeostasis and remove metabolic end products from the body. The evolutionarily conserved solute carriers organic cation transporter 2 (OCT2) and organic anion transporters 1 and 3 (OAT1/3) coordinate the active secretion of a broad range of endogenous and exogenous substances, many of which accumulate in the blood of patients with kidney failure despite dialysis. Harnessing OCT2 and OAT1/3 through functional preservation or regeneration could alleviate the progression of kidney disease. Additionally, it would improve current in vitro test models that lose their expression in culture. With this review, we explore OCT2 and OAT1/3 regulation from different perspectives: phylogenetic, ontogenetic, and cell dynamic. Our aim is to identify possible molecular targets both to help prevent or compensate for the loss of transport activity in patients with kidney disease and to enable endogenous OCT2 and OAT1/3 induction in vitro in order to develop better models for drug development.

Biapenem is a carbapenem antibiotic. It is excreted predominantly through the kidney as unchanged forms. However, the molecular mechanism of renal excretion of biapenem and potential drug-drug interactions (DDIs) were still unknown. In the present study, the role of organic anion transporters (OAT) 1/3 and organic cation transporters (OCT) 2 in the renal excretion of biapenem, and the potential DDIs between biapenem and six clinical commonly prescribed antibiotics and antiviral drugs that acted as substrates or inhibitors of OAT3 were evaluated in vitro. Further, the effect of probenecid on the pharmacokinetics of biapenem was explored in the rats. We observed that biapenem could not inhibit the transport activities of OAT1 or OCT2, while mildly inhibited OAT3 (IC50 >500 μM). Among the tested antibiotics and antiviral drugs, the relatively high DDI index values (maximal unbound plasma concentration over IC50, Imax,u/IC50) were found for piperacillin, linezolid and benzylpenicillin, which were 2.84, 1.7 and 0.62, respectively. Although probenecid had the highest DDI index (27.1) in vitro, no significant impact of it on the pharmacokinetics of biapenem was observed in the rats. Our results indicated that biapenem was primarily eliminated by the glomerular filtration, while OAT3-mediated renal tubular secretion was a minor route. Biapenem is not a clinically relevant substrate or inhibitor because of its low affinity to OAT3. According to current results, it would be safe to use biapenem with other antibiotics and antiviral drugs that acted as substrates or inhibitors of OAT3.

Cisplatin is an anticancer drug commonly used for solid tumors. However, it causes nephrotoxicity. OAT1 and OAT3 are organic anion transporters known to contribute to the uptake of cisplatin into renal tubular cells. The present study was designed to examine the protective role of ellagic acid nanoformulation (ellagic acid nano) on cisplatin-induced nephrotoxicity in rats, and the role of OAT1/OAT3 in this effect. Four groups of male Wistar rats were used (n = 6): (1) control, (2) cisplatin (7.5 mg/kg single dose, intraperitoneal), (3) cisplatin + ellagic acid nano (1 mg/kg), and (4) cisplatin + ellagic acid nano (2 mg/kg). Nephrotoxic rats treated with ellagic acid nano exhibited a significant reduction in elevated serum creatinine, urea, and oxidative stress marker, malondialdehyde (MDA). Additionally, ellagic acid nano restored renal glutathione (GSH), superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx). Ellagic acid nano improved the histopathological changes induced by cisplatin, such as tubular dilatation, necrosis, and degeneration. Interestingly, OAT1 and OAT3 showed significantly lower expression at both mRNA and protein levels following ellagic acid nano treatment relative to the cisplatin-exposed group. These findings reveal a potential inhibitory role of ellagic acid antioxidant on OAT1 and OAT3 expression and thus explains its nephroprotective effect against cisplatin nephrotoxicity.

In chronic kidney disease (CKD), the secretion of uremic toxins is compromised leading totheir accumulation in blood, which contributes to uremic complications, in particular cardiovasculardisease. Organic anion transporters (OATs) are involved in the tubular secretion of protein-bound uremictoxins (PBUTs). However, OATs also handle a wide range of drugs, including those used for treatmentof cardiovascular complications and their interaction with PBUTs is unknown. The aim of this study wasto investigate the interaction between commonly prescribed drugs in CKD and endogenous PBUTs withrespect to OAT1-mediated uptake.We exposed a unique conditionally immortalized proximal tubule cellline (ciPTEC) equippedwithOAT1 to a panel of selected drugs, including angiotensin-converting enzymeinhibitors (ACEIs: captopril, enalaprilate, lisinopril), angiotensin receptor blockers (ARBs: losartan andvalsartan), furosemide and statins (pravastatin and simvastatin), and evaluated the drug-interactionsusing an OAT1-mediated fluorescein assay.We show that selected ARBs and furosemide significantlyreduced fluorescein uptake,with the highest potency forARBs. Thiswas exaggerated in presence of somePBUTs. Selected ACEIs and statins had either no or a slight effect at supratherapeutic concentrationson OAT1-mediated fluorescein uptake. In conclusion, we demonstrate that PBUTs may compete withco-administrated drugs commonly used in CKD management for renal OAT1 mediated secretion,thus potentially compromising the residual renal function.

The role of the renal organic anion transporters OAT1 (also known as SLC22A6, originally identified as NKT) and OAT3 (also known as SLC22A8) in chronic kidney disease (CKD) remains poorly understood. This is particularly so from the viewpoint of residual proximal tubular secretion, a key adaptive mechanism to deal with protein-bound uremic toxins in CKD. Using the subtotal nephrectomy (STN) model, plasma metabolites accumulating in STN rats treated with and without the OAT inhibitor, probenecid, were identified. Comparisons with metabolomics data from Oat1-KO and Oat3-KO mice support the centrality of the OATs in residual tubular secretion of uremic solutes, such as indoxyl sulfate, kynurenate, and anthranilate. Overlapping our data with those of published metabolomics data regarding gut microbiome-derived uremic solutes - which can have dual roles in signaling and toxicity - indicates that OATs play a critical role in determining their plasma levels in CKD. Thus, the OATs, along with other SLC and ABC drug transporters, are critical to the movement of uremic solutes across tissues and into various body fluids, consistent with the remote sensing and signaling theory. The data support a role for OATs in modulating remote interorganismal and interorgan communication (gut microbiota-blood-liver-kidney-urine). The results also have implications for understanding drug-metabolite interactions involving uremic toxins.

Organic anion transporters (OATs) are transmembrane proteins which belong to SLC22 subfamily. They are responsible for the uptake of various endo- and xenobiotics into the cells of different organs and tissues. Following our previous work on characterization of zebrafish Oat1 and Oat3, in this study we analyzed interaction of various classes of environmental contaminants with these membrane transporters using the transport activity assay with HEK293 Flp-In cell line stably overexpressing zebrafish Oat1 and Oat3, respectively. Based on the initial screening of a series of 36 environmental contaminants on their ability to interact with zebrafish Oat1 and Oat3, the most potent interactors were selected, their IC50 values calculated and type of interaction determined. Finally, to further confirm the type of interaction and initially evaluate their toxic potential, the cytotoxicity assays were performed. Broad ligand selectivity and similarity of zebrafish Oat1 and Oat3 with mammalian orthologs was confirmed and potent interactors among environmental contaminants identified.

Plasma pyridoxic acid (PDA) and homovanillic acid (HVA) were recently identified as novel endogenous biomarkers of organic anion transporter (OAT) 1/3 function in monkeys. Consequently, this clinical study assessed the dynamic changes and utility of plasma PDA and HVA as an initial evaluation of OAT1/3 inhibition in early-phase drug development. The study was designed as a single-dose randomized, three-phase, crossover study; 14 Indian healthy volunteers received probenecid (PROB) (1000 mg orally) alone, furosemide (FSM) (40 mg orally) alone, or FSM 1 hour after receiving PROB (40 and 1000 mg orally) on days 1, 8, and 15, respectively. PDA and HVA plasma concentrations remained stable over time in the prestudy and FSM groups. Administration of PROB significantly increased the area under the plasma concentration-time curve (AUC) of PDA by 3.1-fold (dosed alone; P 0.05) and 2.1-fold (P

Phytochemical investigation of Camphorosma lessingii has resulted in the isolation of four previously unreported isoflavones (1–4) and eight known compounds (5–12). Nine of these compounds (1–6, 8–10) are reported for the first time from members of the family Amaranthaceae. The structures of all isolated compounds were determined by spectroscopic methods, primarily one-dimensional and two-dimensional nuclear magnetic resonance and mass spectrometry. The absolute configuration of 6 was confirmed by circular dichroism. Inhibition of the organic anion transporters, OAT1 and OAT3, by the isolated compounds was evaluated. Among them, 7, 2′-dihydroxy- 6,8-dimethoxyisoflavone (1), 2′-hydroxy-6,7,8-trimethoxyisoflavone (2), 6,2′-dihydroxy-7,8-dimethoxyisoflavone (3), and 7-methoxyflavone (5) showed a significant inhibitory effect on 6-carboxyfluorescein uptake mediated by OAT1 and OAT3.

Although arachnoid mater epithelial cells form the blood-arachnoid barrier (BAB), acting as a blood-CSF interface, it has been generally considered that the BAB is impermeable to water-soluble substances and plays a largely passive role. Here, we aimed to clarify the function of transporters at the BAB in regulating CSF clearance of water-soluble organic anion drugs based on quantitative targeted absolute proteomics (QTAP) and in vivo analyses. Protein expression levels of 61 molecules, including 19 ATP-binding-cassette (ABC) transporters and 32 solute-carrier (SLC) transporters, were measured in plasma membrane fraction of rat leptomeninges using QTAP. Thirty-three proteins were detected; others were under the quantification limits. Expression levels of multidrug resistance protein 1 (Mdr1a/P-gp/Abcb1a) and breast cancer resistance protein (Bcrp/Abcg2) were 16.6 and 3.27 fmol/μg protein (51.9- and 9.82-fold greater than in choroid plexus, respectively). Among those organic anion transporters detected only at leptomeninges, not choroid plexus, organic anion transporter 1 (oat1/Slc22a6) showed the greatest expression (2.73 fmol/μg protein). On the other hand, the protein expression level of oat3 at leptomeninges was 6.65 fmol/μg protein, and the difference from choroid plexus was within two-fold. To investigate oat1's role, we injected para-aminohippuric acid (PAH) with or without oat1 inhibitors into cisterna magna (to minimize the contribution of choroid plexus function) of rats. A bulk flow marker, FITC-inulin, was not taken up from CSF up to 15 min, whereas uptake clearance of PAH was 26.5 μL/min. PAH uptake was completely blocked by 3 mM cephalothin (inhibits both oat1 and oat3), while 17% of PAH uptake was inhibited by 0.2 mM cephalothin (selectively inhibits oat3). These results indicate that oat1 and oat3 at the BAB provide a distinct clearance pathway of organic anion drugs from CSF independently of choroid plexus.

Clinically, Chaenomeles sinensis (Thouin) Koehne (C. sinensis) has been used to treat hyperuricemia and gout. However, the exact mechanism of action is still unknown. In the present study, the ethyl acetate fraction of C. sinensis fruit extract (CSF-E) was separated. Potassium oxonate (PO)-induced hyperuricemic mice and normal mice were administered with CSF-E at 60, 120 and 180 mg kg-1, respectively for 7 days. Serum uric acid, creatinine and BUN levels, liver oxidative damage, and serum and hepatic XOD activities were primarily measured using assay kits. The evaluation of its nephroprotective effects was carried out by renal histopathological analysis. Simultaneously, renal protein levels of organic anion transporters, such as mURAT1 and mOAT1, were detected using western blotting to elucidate the possible mechanisms. The results showed that CSF-E could significantly inhibit XOD activities in both serum and liver (p < 0.05), decreasing uric acid, creatinine and BUN levels in serum, and increasing levels in the excretion of uric acid by down-regulated of mURAT1 and up-regulated mOAT1 protein expression of kidney in hyperuricemic mice. Moreover, PO-induced alterations in the levels of MDA, hepatic SOD and GSH-Px activities and renal inflammation damage in hyperuricemic mice were effectively recovered by CSF-E at 120 mg kg-1. CSF-E possessed anti-hyperuricemic and nephroprotective effects by suppressing XOD activity, improving renal function and regulating renal mURAT1 and mOAT1 protein expression, which resulted in beneficial effects on hyperuricemia and gout prevention.

Lansoprazole, a proton pump inhibitor, potently inhibits human organic anion transporter, hOAT3 (SLC22A8). Lansoprazole has an asymmetric atom in its structure and is clinically administered as a racemic mixture of (R)-and (S)-enantiomers. However, little is known about the stereoselective inhibitory potencies of lansoprazole against hOAT3 and its homolog, hOAT1. In the present study, the stereoselective inhibitory effect of lansoprazole was evaluated using hOAT1-and hOAT3-expressing cultured cells. hOAT1 and hOAT3 transported [14C]p-aminohippurate and [3H]estrone-3-sulfate (ES) with Michaelis-Menten constants of 29.8 ± 4.0 and 30.1 ± 9.0 µmol/L respectively. Lansoprazole enantiomers inhibited hOAT1- and hOAT3-mediated transport of each substrate in a concentration-dependent manner. The IC50 value of (S)-lansoprazole against hOAT3-mediated transport of [3H]ES (0.61 ± 0.08 µmol/L) was significantly lower than that of (R)-lansoprazole (1.75 ± 0.31 µmol/L). In contrast, stereoselectivity was not demonstrated for the inhibition of hOAT1. Furthermore, (S)-lansoprazole inhibited hOAT3-mediated transport of pemetrexed and methotrexate (hOAT3 substrates) more strongly than the corresponding (R)-lansoprazole. This study is the first to demonstrate that the stereoselective inhibitory potency of (S)-lansoprazole against hOAT3 is greater than that of (R)-lansoprazole. The present findings provide novel information about the drug interactions associated with lansoprazole.

Bioluminescence (BL) imaging based on d -luciferin ( d -luc)–luciferase reaction allows noninvasive and real-time monitoring of luciferase-expressing cells. Because BL intensity depends on photons generated through the d -luc–luciferase reaction, an approach to increase intracellular levels of d -luc could improve the detection sensitivity. In the present study, we showed that organic anion transporter 1 (OAT1) is useful, as a d -luc transporter, in boosting the BL intensity in luciferase-expressing cells. Functional screening of several transporters showed that the expression of OAT1 in HEK293 cells stably expressing Pyrearinus termitilluminans luciferase (HEK293/eLuc) markedly enhanced BL intensity in the presence of d -luc. When OAT1 was transiently expressed in HEK293 cells, intracellular accumulation of d -luc was higher than that in control cells, and the specific d -luc uptake mediated by OAT1 was saturable with a Michaelis constant (Km) of 0.23 μM. The interaction between OAT1 and d -luc was verified using 6-carboxyfluorescein, a typical substrate of OAT1, which showed that d -luc inhibited the uptake of 6-carboxyfluorescein mediated by OAT1. BL intensity was concentration-dependent at steady states in HEK293/eLuc cells stably expressing OAT1, and followed Michaelis–Menten kinetics with an apparent Km of 0.36 μM. In addition, the enhanced BL was significantly inhibited by OAT1-specific inhibitors. Thus, OAT1-mediated transport of d -luc could be a rate-limiting step in the d -luc–luciferase reaction. Furthermore, we found that expressing OAT1 in HEK293/eLuc cells implanted subcutaneously in mice also significantly increased the BL after intraperitoneal injection of d -luc. Our findings suggest that because OAT1 is capable of transporting d -luc, it can also be used to improve visualization and monitoring of luciferase-expressing cells.

Background Apigenin is a flavonoid compound, widely distributed in natural plants. Various studies have suggested that apigenin has inhibitory effects towards several drug transporters, such as the organic anion transporting (OAT) polypeptides, 1B1 and 1B3 (OATP1B1 and OATP1B3). However, the mechanism by which apigenin interacts with OAT1 has not been well studied. Methods MDCK cells stably-expressing OAT1 were used to examine the inhibitory effects of apigenin on OAT1. UPLC–MS/MS was used to evaluate the in vitro and in vivo effects of apigenin on the uptake of acyclovir by OAT1. Cytotoxicity was determined by the cell viability, MTT assays. Results Apigenin effectively inhibited the activity of OAT1 in a dose-dependent manner with an IC50 value of 0.737 μM. Pre-incubation of cells with apigenin caused a time-dependent inhibition (TDI) of OAT1. Additionally, we examined the interactions between apigenin and acyclovir or adefovir. Data showed that apigenin (1 μM) significantly blocked the uptake of acyclovir by OAT1 in vitro with an inhibition rate of 55%. In vivo, apigenin could increase the concentration of acyclovir in plasma when co-administered with acyclovir. Importantly, the MTT assays showed that, at a dose of 50 μM, apigenin significantly reduced the cytotoxicity of adefovir and substantially increased cell viability from 50.6% to 112.62%. Conclusion Our results demonstrate that apigenin regulates OAT1, and can cause TDI or herb-drug interaction (HDI) when used in combination with acyclovir or adefovir. Therefore, apigenin could be used as a nephroprotective agent when used in combination with the substrates of OAT1.

Perturbation of organic anion transporter (OAT) 1- and OAT3-mediated transport can alter the exposure, efficacy, and safety of drugs. Although there have been reports of the endogenous biomarkers for OAT1/3, none of these have all of the characteristics required for a clinical useful biomarker. Cynomolgus monkeys were treated with intravenous probenecid (PROB) at a dose of 40 mg/kg in this study. As expected, PROB increased the area under the plasma concentration-time curve (AUC) of coadministered furosemide, a known substrate of OAT1 and OAT3, by 4.1-fold, consistent with the values reported in humans (3.1- to 3.7-fold). Of the 233 plasma metabolites analyzed using a liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based metabolomics method, 29 metabolites, including pyridoxic acid (PDA) and homovanillic acid (HVA), were significantly increased after either 1 or 3 hours in plasma from the monkeys pretreated with PROB compared with the treated animals. The plasma of animals was then subjected to targeted LC-MS/MS analysis, which confirmed that the PDA and HVA AUCs increased by approximately 2- to 3-fold by PROB pretreatments. PROB also increased the plasma concentrations of hexadecanedioic acid (HDA) and tetradecanedioic acid (TDA), although the increases were not statistically significant. Moreover, transporter profiling assessed using stable cell lines constitutively expressing transporters demonstrated that PDA and HVA are substrates for human OAT1, OAT3, OAT2 (HVA), and OAT4 (PDA), but not OCT2, MATE1, MATE2K, OATP1B1, OATP1B3, and sodium taurocholate cotransporting polypeptide. Collectively, these findings suggest that PDA and HVA might serve as blood-based endogenous probes of cynomolgus monkey OAT1 and OAT3, and investigation of PDA and HVA as circulating endogenous biomarkers of human OAT1 and OAT3 function is warranted.

d-Malate inhibits a Krebs cycle enzyme and the tubular transport of α-ketoglutarate, an intermediate of the Krebs cycle and the driving force for rat organic anion transporter 1 (rOAT1) and rOAT3 in the kidney. This study examined the effects of d-malate on the rat organic anion transport system. The uptake of 6-carboxyfluorescein by HEK293 cells expressing rOAT1 or rOAT3 was not affected by d-malate and l-malate. Up to 60 min after the intravenous injection of phenolsulfonphthalein (PSP), a typical substrate of the renal organic anion transporters, as a bolus to rats, 47.1% of the dose was recovered in the urine, and its renal clearance was estimated to be 8.60 ml/min/kg. d-Malate but not l-malate interfered with its renal excretion, resulting in the delayed elimination of PSP from plasma. No effect of d-malate was recognized on creatinine clearance or the expression level of rOAT3 in the kidney cortex. d-Malate increased the plasma concentration of α-ketoglutarate. In addition, the compound greatly stimulated the renal excretion of α-ketoglutarate, implying that d-malate inhibited its reabsorption. The content of α-ketoglutarate was significantly decreased in the kidney cortex of rats administered d-malate. Collectively, this study shows that d-malate abrogates the tubular secretion of PSP, and the reduction of the renal content of α-ketoglutarate was proposed to be one of the mechanisms. A relationship between the reabsorption of α-ketoglutarate and the basolateral uptake of organic anion in the kidney is suggested.

The organic anion transporters OAT1 (SLC22A6) and OAT3 (SLC22A8) have similar substrate specificity for drugs, but it is far from clear whether this holds for endogenous substrates. By analysis of more than 600 metabolites in the Oat3KO (Oat3 knockout) by LC/MS, we demonstrate OAT3 involvement in the movement of gut microbiome products, key metabolites, and signaling molecules, including those flowing through the gut–liver–kidney axis. Major pathways affected included those involved in metabolism of bile acids, flavonoids, nutrients, amino acids (including tryptophan-derivatives that are uremic toxins), and lipids. OAT3 is also critical in elimination of liver-derived phase II metabolites, particularly those undergoing glucuronidation. Analysis of physicochemical features revealed nine distinct metabolite groups; at least one member of most clusters has been previously validated in transport assays. In contrast to drugs interacting with the OATs, endogenous metabolites accumulating in the Oat1KO (Oat1 knockout) versus Oat3KO have distinct differences in their physicochemical properties; they are very different in size, number of rings, hydrophobicity, and molecular complexity. Consistent with the Remote Sensing and Signaling Hypothesis, the data support the importance of the OAT transporters in inter-organ and inter-organismal remote communication via transporter-mediated movement of key metabolites and signaling molecules (e.g. gut microbiome–to–intestine–to–blood–to–liver–to–kidney–to–urine). We discuss the possibility of an intimate connection between OATs and metabolite sensing and signaling pathways (e.g. bile acids). Furthermore, the metabolomics and pathway analysis support the view that OAT1 plays a greater role in kidney proximal tubule metabolism and OAT3 appears relatively more important in systemic metabolism, modulating levels of metabolites flowing through intestine, liver, and kidney.

In vitro data indicates that the kidney proximal tubule (PT) transporters of uremic toxins and solutes (e.g., indoxyl sulfate, p-cresol sulfate, kynurenine, creatinine, urate) include two “drug” transporters of the organic anion transporter (OAT) family: OAT1 (SLC22A6, originally NKT) and OAT3 (SLC22A8). Here, we have examined new and prior metabolomics data from the Oat1KO and Oat3KO, as well as newly obtained metabolomics data from a “chemical double” knockout (Oat3KO plus probenecid). This gives a picture of the in vivo roles of OAT1 and OAT3 in the regulation of the uremic solutes and supports the centrality of these “drug” transporters in independently and synergistically regulating uremic metabolism. We demonstrate a key in vivo role for OAT1 and/or OAT3 in the handling of over 35 uremic toxins and solutes, including those derived from the gut microbiome (e.g., CMPF, phenylsulfate, indole-3-acetic acid). Although it is not clear whether trimethylamine-N-oxide (TMAO) is directly transported, the Oat3KO had elevated plasma levels of TMAO, which is associated with cardiovascular morbidity in chronic kidney disease (CKD). As described in the Remote Sensing and Signaling (RSS) Hypothesis, many of these molecules are involved in interorgan and interorganismal communication, suggesting that uremia is, at least in part, a disorder of RSS.

In renal proximal tubule cells, the organic anion transporters 1 and 3 (OAT1 and OAT3) in the basolateral membrane and the multidrug resistance-associated protein 4 (MRP4) in the apical membrane share substrates and co-operate in renal drug secretion. We hypothesized that recently identified MRP4 inhibitors dantrolene, glafenine, nalidixic acid, and prazosin also interact with human OAT1 and/or OAT3 stably transfected in human embryonic kidney 293 cells. These four drugs were tested as possible inhibitors of p-[3H]aminohippurate (PAH) and [14C]glutarate uptake by OAT1, and of [3H]estrone-3-sulfate (ES) uptake by OAT3. In addition, we explored whether these drugs decrease the equilibrium distribution of radiolabeled PAH, glutarate, or ES, an approach intended to indirectly suggest drug/substrate exchange through OAT1 and OAT3. With OAT3, a dose-dependent inhibition of [3H]ES uptake and a downward shift in [3H]ES equilibrium were observed, indicating that all four drugs bind to OAT3 and may possibly be translocated. In contrast, the interaction with OAT1 was more complex. With [14C]glutarate as substrate, all four drugs inhibited uptake but only glafenine and nalidixic acid shifted glutarate equilibrium. Using [3H]PAH as a substrate of OAT1, nalidixic acid inhibited but dantrolene, glafenine, and prazosin stimulated uptake. Nalidixic acid decreased equilibrium content of [3H]PAH, suggesting that it may possibly be exchanged by OAT1. Taken together, OAT1 and OAT3 interact with the MRP4 inhibitors dantrolene, glafenine, nalidixic acid, and prazosin, indicating overlapping specificities. At OAT1, more than one binding site must be assumed to explain substrate and drug-dependent stimulation and inhibition of transport activity.

Tetrahydrobiopterin (BH4) is a common coenzyme of phenylalanine-, tyrosine-, and tryptophan hydroxylases, alkylglycerol monooxygenase, and NO synthases (NOS). Synthetic BH4 is used medicinally for BH4-responsive phenylketonuria and inherited BH4 deficiency. BH4 supplementation has also drawn attention as a therapy for various NOS-related cardio-vascular diseases, but its use has met with limited success in decreasing BH2, the oxidized form of BH4. An increase in the BH2/BH4 ratio leads to NOS dysfunction. Previous studies revealed that BH4 supplementation caused a rapid urinary loss of BH4 accompanied by an increase in the blood BH2/BH4 ratio and an involvement of probenecid-sensitive but unknown transporters was strongly suggested in these processes. Here we show that OAT1 and OAT3 enabled cells to take up BP (BH4 and/or BH2) in a probenecid-sensitive manner using rat kidney slices and transporter-expressing cell systems, LLC-PK1 cells and Xenopus oocytes. Both OAT1 and OAT3 preferred BH2 and sepiapterin as their substrate roughly 5- to 10-fold more than BH4. Administration of probenecid acutely reduced the urinary exclusion of endogenous BP accompanied by a rise in blood BP in vivo. These results indicated that OAT1 and OAT3 played crucial roles: (1) in determining baseline levels of blood BP by excluding endogenous BP through the urine, (2) in the rapid distribution to organs of exogenous BH4 and the exclusion to urine of a BH4 excess, particularly when BH4 was administered, and (3) in scavenging blood BH2 by cellular uptake as the gateway to the salvage pathway of BH4, which reduces BH2 back to BH4.

// Na Liu 1 , Liuqing Xu 1 , Yingfeng Shi 1 , Lu Fang 1 , Hongwei Gu 1 , Hongrui Wang 1 , Xiaoqiang Ding 2 and Shougang Zhuang 1, 3 1 Department of Nephrology, Shanghai East Hospital, Tongji University School of Medicine, Shanghai 200120, China 2 Division of Nephrology, Zhongshan Hospital, Fudan University, Shanghai 200032, China 3 Department of Medicine, Rhode Island Hospital and Brown University School of Medicine, Providence, RI 02903, USA Correspondence to: Shougang Zhuang, email: szhuang@lifespan.org Xiaoqiang Ding, email: ding.xiaoqiang@zs-hospital.sh.cn Keywords: hyperuricemic nephropathy, ERK1/2, TGF-β/Smad signaling pathway, urate transporters, inflammation Received: November 16, 2016 Accepted: February 20, 2017 Published: April 10, 2017 ABSTRACT The pathogenesis of hyperuricemia-induced chronic kidney disease is largely unknown. In this study, we investigated whether extracellular signal–regulated kinases1/2 (ERK1/2) would contribute to the development of hyperuricemic nephropathy (HN). In a rat model of HN induced by feeding mixture of adenine and potassium oxonate, increased ERK1/2 phosphorylation and severe glomerular sclerosis and renal interstitial fibrosis were evident, in parallel with diminished levels of renal function and increased urine microalbumin excretion. Administration of U0126, which is a selective inhibitor of the ERK1/2 pathway, improved renal function, decreased urine microalbumin and inhibited activation of renal interstitial fibroblasts as well as accumulation of extracellular proteins. U0126 also inhibited hyperuricemia-induced expression of multiple profibrogenic cytokines/chemokines and infiltration of macrophages in the kidney. Furthermore, U0126 treatment suppressed xanthine oxidase, which mediates uric acid production. It also reduced expression of the urate anion exchanger 1, which promotes reabsorption of uric acid, and preserved expression of organic anion transporters 1 and 3, which accelerate uric acid excretion in the kidney of hyperuricemic rats. Finally, U0126 inhibited phosphorylation of Smad3, a key mediator in transforming growth factor (TGF-β) signaling. In cultured renal interstitial fibroblasts, inhibition of ERK1/2 activation by siRNA suppressed uric acid-induced activation of renal interstitial fibroblasts. Collectively, pharmacologic targeting of ERK1/2 can alleviate HN by suppressing TGF-β signaling, reducing inflammation responses, and inhibiting the molecular processes associated with elevation of blood uric acid levels in the body. Thus, ERK1/2 inhibition may be a potential approach for the prevention and treatment of hyperuricemic nephropathy.

Chronic kidney disease (CKD) is a health problem worldwide. Indoxyl sulfate (IS) is a nephro-cardiovascular toxin accumulated in CKD patients and cannot be removed through hemodialysis. The renal excretion of IS was mediated by organic anion transporters (OATs) OAT 1 and OAT 3. Because a number of nonsteroidal anti-inflammatory drugs (NSAIDs) have been reported to inhibit OATs, we hypothesize that NSAIDs might inhibit the renal excretion of IS. Rats were intravenously injected IS with and without diclofenac, ketoprofen or salicylic acid, individually. Blood samples were collected at predetermined time points and the concentrations of IS were determined by HPLC method. The results showed that diclofenac and ketoprofen at 10.0mg/kg significantly decreased the systemic clearance of IS by 71% and 82%, and increased the MRT of IS by 106% and 105%, respectively, whereas salicylic acid did not exhibit significant effects. Cell studies indicated that diclofenac and ketoprofen inhibited the uptake of IS mediated by OAT 1 and OAT 3. In conclusion, diclofenac and ketoprofen inhibited the excretion of IS through inhibition on OAT 1 and OAT 3.

Contains fulltext : 174845.pdf (Publisher’s version ) (Open Access) The combination of methotrexate with epidermal growth factor receptor (EGFR) recombinant antibody, cetuximab, is currently being investigated in treatment of head and neck carcinoma. As methotrexate is cleared by renal excretion, we studied the effect of cetuximab on renal methotrexate handling. We used human conditionally immortalized proximal tubule epithelial cells overexpressing either organic anion transporter 1 or 3 (ciPTEC-OAT1/ciPTEC-OAT3) to examine OAT1 and OAT3, and the efflux pumps breast cancer resistance protein (BCRP), multidrug resistance protein 4 (MRP4), and P-glycoprotein (P-gp) in methotrexate handling upon EGF or cetuximab treatment. Protein kinase microarrays and knowledge-based pathway analysis were used to predict EGFR-mediated transporter regulation. Cytotoxic effects of methotrexate were evaluated using the dimethylthiazol bromide (MTT) viability assay. Methotrexate inhibited OAT-mediated fluorescein uptake and decreased efflux of Hoechst33342 and glutathione-methylfluorescein (GS-MF), which suggested involvement of OAT1/3, BCRP, and MRP4 in transepithelial transport, respectively. Cetuximab reversed the EGF-increased expression of OAT1 and BCRP as well as their membrane expressions and transport activities, while MRP4 and P-gp were increased. Pathway analysis predicted cetuximab-induced modulation of PKC and PI3K pathways downstream EGFR/ERBB2/PLCg. Pharmacological inhibition of ERK decreased expression of OAT1 and BCRP, while P-gp and MRP4 were increased. AKT inhibition reduced all transporters. Exposure to methotrexate for 24 h led to a decreased viability, an effect that was reversed by cetuximab. In conclusion, cetuximab downregulates OAT1 and BCRP while upregulating P-gp and MRP4 through an EGFR-mediated regulation of PI3K-AKT and MAPKK-ERK pathways. Consequently, cetuximab attenuates methotrexate-induced cytotoxicity, which opens possibilities for further research into nephroprotective comedication therapies.

Organic anion transporter 1 (OAT1) is a polyspecific transport protein located in the basolateral membrane of renal proximal tubule cells. OAT1 plays a pivotal role in drug clearance. Adverse drug reactions (ADR) are observed more frequently in women than in men, especially ADR are higher in women for drugs which are known interactors of OAT1. Sex‐dependent expression of Oat1 has been observed in rodents with a tendency to male‐dominant expression. This study aims at elucidating the transcriptional regulation of human OAT1 and tests the effect of estrogen receptor α (ERα). Promoter activation of OAT1 was assessed by luciferase assays carried out by Opossum kidney (OK) cells, transiently transfected with promoter constructs of human OAT1 and expression vectors for ERα and exposed to 100 nmol/L 17β‐estradiol. Furthermore, a transcription factor array and proteomic analysis was performed to identify estrogen‐induced transcription factors. Human OAT1 was significantly activated by ligand activated ERα. However, activation occurred without a direct interaction of ERα with the OAT1 promoter. Our data rather show an activation of the transcription factors CCAAT‐box‐binding transcription factor (CBF) and heterogeneous nuclear ribonucleoprotein K (HNRNPK) by ERα, which in turn bind and initiate OAT1 promoter activity. Herewith, we provide novel evidence of estrogen‐dependent, transcriptional regulation of polyspecific drug transporters including the estrogen‐induced transcription factors CBF and HNRNPK., We provide novel evidence of estrogen receptor‐dependent, transcriptional regulation of organic anion transporter 1. Human OAT1 promoter was indirectly activated by ERα via the transcription factors CBF and HNRNPK.

Renal drug transporters such as the organic cation transporters (OCTs), organic anion transporters (OATs) and multidrug resistance proteins (MRPs) play an important role in the tubular secretion of many drugs influencing their efficacy and safety. However, only little is known about the distinct protein abundance of these transporters in human kidneys, and about the impact of age and gender as potential factors of inter-subject variability in their expression and function. The aim of this study was to determine the protein abundance of MDR1, MRP1-4, BCRP, OAT1-3, OCT2-3, MATE1, PEPT1/2, and ORCTL2 by liquid chromatography-tandem mass spectrometry-based targeted proteomics in a set of 36 human cortex kidney samples (20 males, 16 females, median age 53 and 55 years, respectively). OAT1 and 3, OCT2 and ORCTL2 were found to be most abundant renal SLC transporters while MDR1, MRP1 and MRP4 were the dominating ABC transporters. Only the expression levels of MDR1 and ORCTL2 were significantly higher abundant in older donors. Moreover, we found several significant correlations between different transporters, which may indicate their functional interplay in renal vectorial transport processes. Our data may contribute to a better understanding of the molecular processes determining renal excretion of drugs.

International audience; The beta-lactam penicillin antibiotic cloxacillin (CLX) presents wide inter-individual pharmacokinetics variability. To better understand its molecular basis, the precise identification of the detoxifying actors involved in CLX disposition and elimination would be useful, notably with respect to renal secretion known to play a notable role in CLX elimination. The present study was consequently designed to analyze the interactions of CLX with the solute carrier transporters organic anion transporter (OAT) 1 and OAT3, implicated in tubular secretion through mediating drug entry at the basolateral pole of renal proximal cells. CLX was first shown to block OAT1 and OAT3 activity in cultured OAT-overexpressing HEK293 cells. Half maximal inhibitory concentration (IC50) value for OAT3 (13 mu m) was however much lower than that for OAT1 (560 mu m); clinical inhibition of OAT activity and drug-drug interactions may consequently be predicted for OAT3, but not OAT1. OAT3, unlike OAT1, was next shown to mediate CLX uptake in OAT-overexpressing HEK293 cells. Kinetic parameters for this OAT3-mediated transport of CLX (K-m = 10.7 mu m) were consistent with a possible in vivo saturation of this process for high CLX plasma concentrations. OAT3 is consequently likely to play a pivotal role in renal CLX secretion and consequently in total renal CLX elimination, owing to the low plasma unbound fraction of the antibiotic. OAT3 genetic polymorphisms as well as co-administered drugs inhibiting in vivo OAT3 activity may therefore be considered as potential sources of CLX pharmacokinetics variability.

With the internationally growing popularity of traditional Chinese medicine (TCM), TCM-induced nephropathy has attracted public attention. Minimizing this toxicity is an important issue for future research. Typical nephrotoxic TCM drugs such as Aristolochic acid, Tripterygium wilfordii Hook. f, Rheum officinale Baill, and cinnabar mainly damage renal proximal tubules or cause interstitial nephritis. Transporters in renal proximal tubule are believed to be critical in the disposition of xenobiotics. In this review, we provide information on the alteration of renal transporters by nephrotoxic TCMs, which may be helpful for understanding the nephrotoxic mechanism of TCMs and reducing adverse effects. Studies have proven that when administering nephrotoxic TCMs, the expression or function of renal transporters is altered, especially organic anion transporter 1 and 3. The alteration of these transporters may enhance the accumulation of toxic drugs or the dysfunction of endogenous toxins and subsequently sensitize the kidney to injury. Transporters-related drug combination and clinical biomarkers supervision to avoid the risk of future toxicity are proposed.

Significance Here, we report that the kidney has an effective sensing and signaling mechanism to balance microbial metabolite levels in the human body. Using healthy volunteers and in vivo and in vitro assays, we show that the kidney responds to elevated endogenous metabolite levels and stimulates organic anion secretion by AhR and EGFR signaling, controlled by miR-223 and reactive oxygen species. This remote sensing function aids body homeostasis and has important implications for the identification of novel therapeutic targets to preserve kidney function in patients., Membrane transporters and receptors are responsible for balancing nutrient and metabolite levels to aid body homeostasis. Here, we report that proximal tubule cells in kidneys sense elevated endogenous, gut microbiome-derived, metabolite levels through EGF receptors and downstream signaling to induce their secretion by up-regulating the organic anion transporter-1 (OAT1). Remote metabolite sensing and signaling was observed in kidneys from healthy volunteers and rats in vivo, leading to induced OAT1 expression and increased removal of indoxyl sulfate, a prototypical microbiome-derived metabolite and uremic toxin. Using 2D and 3D human proximal tubule cell models, we show that indoxyl sulfate induces OAT1 via AhR and EGFR signaling, controlled by miR-223. Concomitantly produced reactive oxygen species (ROS) control OAT1 activity and are balanced by the glutathione pathway, as confirmed by cellular metabolomic profiling. Collectively, we demonstrate remote metabolite sensing and signaling as an effective OAT1 regulation mechanism to maintain plasma metabolite levels by controlling their secretion.

Hydrochlorothiazide (HCTZ) is the most widely used thiazide diuretic for the treatment of hypertension either alone or in combination with other antihypertensives. HCTZ is mainly cleared by the kidney via tubular secretion, but the underlying molecular mechanisms are unclear. Using cells stably expressing major renal organic anion and cation transporters [human organic anion transporter 1 (hOAT1), human organic anion transporter 3 (hOAT3), human organic cation transporter 2 (hOCT2), human multidrug and toxin extrusion 1 (hMATE1), and human multidrug and toxin extrusion 2-K (hMATE2-K)], we found that HCTZ interacted with both organic cation and anion transporters. Uptake experiments further showed that HCTZ is transported by hOAT1, hOAT3, hOCT2, and hMATE2-K but not by hMATE1. Detailed kinetic analysis coupled with quantification of membrane transporter proteins by targeted proteomics revealed that HCTZ is an excellent substrate for hOAT1 and hOAT3. The apparent affinities ( Km) for hOAT1 and hOAT3 were 112 ± 8 and 134 ± 13 μM, respectively, and the calculated turnover numbers ( kcat) were 2.48 and 0.79 s−1, respectively. On the other hand, hOCT2 and hMATE2-K showed much lower affinity for HCTZ. The calculated transport efficiency ( kcat/ Km) at the single transporter level followed the rank order of hOAT1> hOAT3 > hOCT2 and hMATE2-K, suggesting a major role of organic anion transporters in tubular secretion of HCTZ. In vitro inhibition experiments further suggested that HCTZ is not a clinically relevant inhibitor for hOAT1 or hOAT3. However, strong in vivo inhibitors of hOAT1/3 may alter renal secretion of HCTZ. Together, our study elucidated the molecular mechanisms underlying renal handling of HCTZ and revealed potential pathways involved in the disposition and drug-drug interactions for this important antihypertensive drug in the kidney.

The effect of dotinurad [(3,5-dichloro-4-hydroxyphenyl)(1,1-dioxo-1,2-dihydro-3H-1λ6-1,3-benzothiazol-3-yl)methanone] was compared with that of commercially available uricosuric agents—namely, benzbromarone, lesinurad, and probenecid. Its effect on urate secretion transporters was evaluated using probe substrates for respective transporters. Dotinurad, benzbromarone, lesinurad, and probenecid inhibited urate transporter 1 (URAT1) with IC50 values of 0.0372, 0.190, 30.0, and 165 μM, respectively. Dotinurad weakly inhibited ATP-binding cassette subfamily G member 2 (ABCG2), organic anion transporter 1 (OAT1), and OAT3, with IC50 values of 4.16, 4.08, and 1.32 μM, respectively, indicating higher selectivity for URAT1. The hypouricemic effects of dotinurad and benzbromarone were evaluated in Cebus monkeys. Dotinurad, at doses of 1–30 mg/kg, concomitantly decreased plasma urate levels and increased fractional excretion of urate (FEUA) in a dose-dependent manner. On the contrary, benzbromarone, at a dose of 30 mg/kg, showed a modest effect on plasma urate levels. The inhibitory effect of dotinurad on urate secretion transporters was evaluated in Sprague-Dawley rats, with sulfasalazine and adefovir as probe substrates of ABCG2 and OAT1, respectively. Drugs, including febuxostat as a reference ABCG2 inhibitor, were administered orally before sulfasalazine or adefovir administration. Dotinurad had no effect on urate secretion transporters in vivo, whereas benzbromarone, lesinurad, probenecid, and febuxostat increased the plasma concentrations of probe substrates. These results suggested dotinurad is characterized as a selective urate reabsorption inhibitor (SURI), which is defined as a potent URAT1 inhibitor with minimal effect on urate secretion transporters, including ABCG2 and OAT1/3, because of its high efficacy in decreasing plasma urate levels compared with that of other uricosuric agents. SIGNIFICANCE STATEMENT Our study on the inhibitory effects on urate transport showed that dotinurad had higher selectivity for urate transporter 1 (URAT1) versus ATP-binding cassette subfamily G member 2 (ABCG2) and organic anion transporter (OAT) 1/3 compared to other uricosuric agents. In Cebus monkeys, dotinurad decreased plasma urate levels and increased fractional excretion of urate in a dose-dependent manner. To determine the inhibitory effect of dotinurad on urate secretion transporters, we studied the movement of substrates of ABCG2 and OAT1 in rats. Dotinurad had no effect on these transporters, whereas the other uricosuric agents increased the plasma concentrations of the substrates. These results suggested dotinurad as a potent and selective urate reabsorption inhibitor is characterized by increased efficacy with decreasing plasma urate levels.

Ethnopharmacological relevance The major terpene lactones of ginkgo biloba extract (GBE) include ginkgolide A, B, C and bilobalide are used for the protection of cardiovascular, cerebrovascular and neurodegenerative diseases. Terpene lactones are orally bioavailable and predominantly eliminated via the renal pathway. However, information on the transporters involved in the pharmacokinetics (PK) and renal excretion of terpene lactones is limited. Aim of the study The objective of this study is to assess the role of OAT1/3 which are important transporters in the human kidney in the PK and renal excretion ginkgolide A, B, C and bilobalide. Materials and methods Uptake of ginkgolide A, B, C and bilobalide in Madin-Darby Canine Kidney (MDCK) and human embryonic kidney 293 (HEK293) cells overexpressing OAT1 or OAT3, respectively were studied. To verify the result from in vitro cell models, the studies on PK, kidney accumulation and urinary excretion of ginkgolide A, B, C and bilobalide were carried out in rats. Results The result showed that ginkgolide A, B, C and bilobalide are low-affinity substrates of OAT1/3. Following co-administration with probenecid, a typical inhibitor of OAT1/3, the rat plasma concentrations of ginkgolide A, B, C and bilobalide increased significantly. AUC showed a significant increase in the probenecid-treated rats compared to control rats (893.48 vs. 1123.85, 314.91 vs. 505.74, and 2724.97 vs. 3096.40 μg/L*h for ginkgolide A, B and bilobalide, respectively), while the clearance of these compounds significantly decreased. The accumulation of ginkgolide A, B and bilobalide in the kidney of the probenecid-treated rats was reduced by 1.8, 2.4, and 1.5-fold, respectively; further reducing the cumulative urinary recovery of these compounds. Conclusion The findings indicated that ginkgolide A, B and bilobalide are excreted via OAT1/3-mediated transport in the kidney and OAT1/3 inhibitor significantly influence the PK ginkgolides and bilobalide.

Acute kidney injury (AKI) is a high frequent and common complication following acute myocardial infarction (AMI). This study examined and identified the effect of AMI-induced AKI on organic anion transporter 1 (Oat1) and Oat3 transport using clinical setting of pre-renal AKI in vivo. Cardiac ischaemia (CI) and cardiac ischaemia and reperfusion (CIR) were induced in rats by 30-min left anterior descending coronary artery occlusion and 30-min occlusion followed by 120-min reperfusion, respectively. Renal hemodynamic parameters, mitochondrial function and Oat1/Oat3 expression and function were determined along with biochemical markers. Results showed that CI markedly reduced renal blood flow and pressure by approximately 40%, while these parameters were recovered during reperfusion. CI and CIR progressively attenuated renal function and induced oxidative stress by increasing plasma BUN, creatinine and malondialdehyde levels. Correspondingly, SOD, GPx, CAT mRNAs were decreased, while TNFα, IL1β, COX2, iNOS, NOX2, NOX4, and xanthine oxidase were increased. Mitochondrial dysfunction as indicated by increasing ROS, membrane depolarisation, swelling and caspase3 activation were shown. Early significant detection of AKI; KIM1, IL18, was found. All of which deteriorated para-aminohippurate transport by down-regulating Oat1 during sudden ischaemia. This consequent blunted the trafficking rate of Oat1/Oat3 transport via down-regulating PKCζ/Akt and up-regulating PKCα/NFκB during CI and CIR. Thus, this promising study indicates that CI and CIR abruptly impaired renal Oat1 and regulatory proteins of Oat1/Oat3, which supports dysregulation of remote sensing and signalling and inter-organ/organismal communication. Oat1, therefore, could potentially worsen AKI and might be a potential therapeutic target for early reversal of such injury.

Andrographolide, a major bioactive compound isolated from Andrographis paniculata (Burm. F.) Nees, was evaluated for its effects on the hOAT1 membrane transporter. Substrate determination and inhibition of hOAT1-mediated uptake transport assay was carried out using recombinant CHO-hOAT1 cells. The results showed that the uptake ratio of andrographolide was less than 2.0 at all concentrations tested, indicating that andrographolide is not a hOAT1 substrate. Andrographolide has no significant effects on the p-aminohippuric acid uptake and on the mRNA and protein expression of hOAT1. In conclusion, andrographolide may not pose a drug-herb interaction risk related to hOAT1.