Anion Transport System Research Articles

PM2.5 Exposure Inhibits Transepithelial Anion Short-circuit Current by Downregulating P2Y2 Receptor/CFTR Pathway.

Fine particulate matter (PM2.5) can damage airway epithelial barriers. The anion transport system plays a crucial role in airway epithelial barriers. However, the detrimental effect and mechanism of PM2.5 on the anion transport system are still unclear. In this study, airway epithelial cells and ovalbumin (OVA)-induced asthmatic mice were used. In transwell model, the adenosine triphosphate (ATP)-induced transepithelial anion short-circuit current (Isc) and airway surface liquid (ASL) significantly decreased after PM2.5 exposure. In addition, PM2.5 exposure decreased the expression levels of P2Y2R, CFTR and cytoplasmic free-calcium, but ATP can increase the expressions of these proteins. PM2.5 exposure increased the levels of Th2-related cytokines of bronchoalveolar lavage fluid, lung inflammation, collagen deposition and hyperplasisa of goblet cells. Interestingly, the administration of ATP showed an inhibitory effect on lung inflammation induced by PM2.5. Together, our study reveals that PM2.5 impairs the ATP-induced transepithelial anion Isc through downregulating P2Y2R/CFTR pathway, and this process may participate in aggravating airway hyperresponsiveness and airway inflammation. These findings may provide important insights on PM2.5-mediated airway epithelial injury.

#3386 PROTON-PUMP INHIBITORS AND SERUM CONCENTRATIONS OF UREMIC TOXINS IN PATIENTS WITH CHRONIC KIDNEY DISEASE

Abstract Background and Aims Use of proton-pump inhibitors (PPIs) is common in patients with chronic kidney disease (CKD). PPIs and many uremic toxins (UTs) are eliminated by a kidney tubular organic anion transporter system. In a cross-sectional study, we sought to evaluate the association between PPI prescription and serum concentrations of various UTs. Method We studied a randomly selected subgroup of participants in the CKD-REIN prospective cohort (adult patients with a confirmed diagnosis of CKD and estimated glomerular filtration rate (eGFR) <60ml/min/1.73m²) with available frozen samples collected at baseline. PPI prescription was recorded at baseline. Serum concentrations of 10 UTs were measured using a validated liquid chromatography tandem mass spectrometry technique. Multiple linear regression was performed, with the log UT concentration as the dependent variable. Results Of the 680 included patients [median age: 68 years; median eGFR: 32 ml/min/1.73 m2], 31% had PPI prescriptions at baseline. Patients using PPIs had higher levels of certain UTs in comparison to other patients, including total and free indoxyl sulfate (IS), total and free p-cresylsulfate, total and free p-cresylglucuronide (PCG), phenylacetylglutamine (PAG), free kynurenine, and free hippuric acid. After adjustment for baseline comorbidities, number of co-prescribed drugs and laboratory data including eGFR, associations between PPI prescription and elevated serum concentrations of free and total IS, free and total PCG, and PAG remained significant. Conclusion Our results indicate that PPI prescription is independently associated with serum UT retention. These findings indicate a potential mechanism for side effect of PPIs in CKD patients that will need to be confirmed by longitudinal studies.

Ochratoxin A (OTA) Affect OATPs and PEPTs and Cause RenalDisease

Ochratoxin A (OTA) is a mycotoxin related to the kidneys. There is a consensus that the primary route in which OTAis excreted into the urine is via tubular secretion, possibly through the organic anion transport system. There are somekinds of multipiece organic anion-transporting polypeptides (OATPs), ATP-binding cassettes (ABC) transporters, andtransporters such as organic anion transporters (OATs). These renal transporters are essential in exacerbating OTAinduced nephrotoxicity as OTA penetrates the cell membrane. This work concluded that the renal tubule’s reabsorptionand secretion of OTA might play an essential role in OTA accumulation and nephrotoxicity. Also, it tells us it is essentialto consider the impact of albumin binding on transport in vitro when considering the clearance of OTA in vivo.

Proton-Pump Inhibitors and Serum Concentrations of Uremic Toxins in Patients with Chronic Kidney Disease.

Use of proton-pump inhibitors (PPIs) is common in patients with chronic kidney disease (CKD). PPIs and many uremic toxins (UTs) are eliminated by the kidney's tubular organic anion transporter system. In a cross-sectional study, we sought to evaluate the association between PPI prescription and serum concentrations of various UTs. We studied a randomly selected sub-group of participants in the CKD-REIN cohort (adult patients with a confirmed diagnosis of CKD and estimated glomerular filtration rate (eGFR) < 60 mL/min/1.73 m2) with available frozen samples collected at baseline. PPI prescription was recorded at baseline. Serum concentrations of 10 UTs were measured using a validated liquid chromatography tandem mass spectrometry technique. Multiple linear regression was performed, with the log UT concentration as the dependent variable. Of the 680 included patients (median age: 68 years; median eGFR: 32 mL/min/1.73 m2), 31% had PPI prescriptions at baseline. Patients using PPIs had higher levels of certain UTs in comparison to other patients, including total and free indoxyl sulfate (IS), total and free p-cresylsulfate, total and free p-cresylglucuronide (PCG), phenylacetylglutamine (PAG), free kynurenine, and free hippuric acid. After adjustment for baseline co-morbidities, number of co-prescribed drugs, and laboratory data, including eGFR, associations between PPI prescription and elevated serum concentrations of free and total IS, free and total PCG, and PAG remained significant. Our results indicate that PPI prescription is independently associated with serum UT retention. These findings are interesting to better understand the factors that may modulate serum UT concentration in CKD patients, however, they will need to be confirmed by longitudinal studies.

Bimodal structural tuning of pyrrole-2-carboxamide-based transmembrane ion transport systems.

The pyrrole-2-carboxamide moiety is well known for its presence in various natural products and its use in anion receptor systems. Here we assess the transmembrane anion transport activity of a series of substituted pyrrole-2-carboxamides and show them to be highly tuneable, versatile systems for anion transport by simple variations of pyrrole ring and amide substituents.

Progress and prospects toward supramolecular bioactive ion transporters.

The majority of cellular physiological processes depend on natural ion channels, which are pore-forming membrane-embedded proteins that let ions flow across the cell membranes selectively. This selective movement of ions across the membranes balances the osmolality within and outside the cell. However, mutations in the genes that encode essential membrane transport proteins or structural reorganisation of these proteins can cause life-threatening diseases like cystic fibrosis. Artificial ion transport systems have opened up a way to replace dysfunctional natural ion channels to cure such diseases through channel replacement therapy. Moreover, recent research has also demonstrated the ability of these systems to kill cancer cells, reigniting interest in the field among scientists. Our contributions to the recent progress in the design and development of artificial chloride ion transporters and their effect on biological systems have been discussed in this review. This review would provide current vistas and future directions toward the development of novel ion transporters with improved biocompatibility and desired anti-cancer properties. Additionally, it strongly emphasises stimuli-responsive ion transport systems, which are crucial for obtaining target-specificity and may speed up the application of these systems in clinical therapeutics.

Modulation of transmembrane anion transport of porphyrin boxes by dynamic window size engineering

The development of synthetic transmembrane anion transport systems is of considerable interest, not only for mimicking the functions of natural transmembrane proteins but also for practical applications. We have recently reported a porous organic cage, porphyrin box (PB(8)) having multiple windows surrounded by octyl chains as an iodide selective anion channel. Herein, we report the modulation of transmembrane transport of halides ([Formula: see text], [Formula: see text], and [Formula: see text] by dynamic window size engineering of the cage with different alkyl chain lengths (hexyl PB(6), octyl PB(8) and decyl PB(10)). ‘Apparent’ transport rates were measured by the HPTS fluorescence assay, which shows a gradual decrease in the transport rate upon increasing the length of alkyl chains of PB. We calculate the transport rate per PB in order to make a fair comparison as the ‘apparent’ transport rate is proportional to the number of PBs embedded in the lipid membrane. The transport rate per PB reveals that increasing the length of the alkyl chains of PBs results in a substantial fall in the iodide transport rate while only marginally decreasing the transport rates of bromide and chloride, thereby decreasing the selectivity of iodide transport.

Voriconazole injection may induce delayed methotrexate excretion: a case report and experimental study

BackgroundWe report a case of delayed excretion of methotrexate (MTX) in a pediatric patient on high-dose MTX therapy in response to a change in the concomitant dosage of voriconazole from oral to intravenous. As the intravenous, but not the oral formulation of voriconazole includes sulfobutylether-β-cyclodextrin (SBECD), which has an anionic residue, we hypothesized that SBECD inhibits the renal excretion of anionic compounds.MethodsWe evaluated the inhibitory effects of SBECD on renal excretion of phenolsulfonphthalein (PSP), which is eliminated in urine via organic anion transport systems. PSP was administered intravenously to rats at 2.5 and 25 mg/kg with or without SBECD pretreatment (320 mg/kg).ResultsThe plasma concentration of PSP at the dosage of 2.5 mg/kg were comparable between control and SBECD groups. On the other hand, at 25 mg/kg the elimination of PSP was delayed. The clearance of PSP at the dosage of 25 mg/kg was 9.71 ± 1.65 and 4.13 ± 0.76 mL/min/kg in control and SBECD groups, respectively (p < 0.05). This suggested that SBECD partly inhibits the renal excretion of anionic drugs.ConclusionThe present case report discusses the delayed elimination of MTX in high dose therapy and possible mechanism involving SBECD as an excipient in concomitant drugs. It seems better to avoid choosing injection containing SBECD for patients undergoing HD-MTX treatment. Further studies are needed to confirm the inhibitory effects of SBECD on the renal excretion of MTX, especially in high-dose regimens.

Molecular response and evolution of plant anion transport systems to abiotic stress.

We propose that anion channels are essential players for green plants to respond and adapt to the abiotic stresses associated changing climate via reviewing the literature and analyzing the molecular evolution, comparative genetic analysis, and bioinformatics analysis of the key anion channel gene families. Climate change-induced abiotic stresses including heatwave, elevated CO2, drought, and flooding, had a major impact on plant growth in the last few decades. This scenario could lead to the exposure of plants to various stresses. Anion channels are confirmed as the key factors in plant stress responses, which exist in the green lineage plants. Numerous studies on anion channels have shed light on their protein structure, ion selectivity and permeability, gating characteristics, and regulatory mechanisms, but a great quantity of questions remain poorly understand. Here, we review function of plant anion channels in cell signaling to improve plant response to environmental stresses, focusing on climate change related abiotic stresses. We investigate the molecular response and evolution of plant slow anion channel, aluminum-activated malate transporter, chloride channel, voltage-dependent anion channel, and mechanosensitive-like anion channel in green plant. Furthermore, comparative genetic and bioinformatic analysis reveal the conservation of these anion channel gene families. We also discuss the tissue and stress specific expression, molecular regulation, and signaling transduction of those anion channels. We propose that anion channels are essential players for green plants to adapt in a diverse environment, calling for more fundamental and practical studies on those anion channels towards sustainable food production and ecosystem health in the future.

Exploring Anion-π Interactions and Their Applications in Supramolecular Chemistry.

Noncovalent bond interactions provide primary driving forces for supramolecular processes ranging from molecular recognition to self-assembly of sophisticated abiotic and biological machineries. While hydrogen bonding and π-π interactions are arguably textbook concepts playing indispensable parts in various scientific disciplines, noncovalent anion-π interactions have been emerging as attractive forces between π systems and negatively charged species for just about two decades. At the beginning of this century, three research groups reported independently their computational studies on the interactions between anions and aromatic compounds, proposing attractive anion-π interactions. Since π systems such as aromatic rings are traditionally noted as electron rich entities, anions and π systems would be repulsive to each other if there are any interactions. In stark contrast to the acknowledged cation-π interactions, the seemingly counterintuitive noncovalent anion-π bindings invoked great interest in the following years. Although a plethora of calculations had been published, the lack of experimental evidence cast doubt on the existence of anion-π interactions between anions and charge-neutral aromatic systems.During the same time when anion-π interactions were coined, we were studying the chemistry of novel macrocyclic compounds, namely, heteracalixaromatics, and their applications in supramolecular chemistry. It has been shown that heteracalixaromatics are powerful and versatile macrocyclic hosts to bind various guest species forming interesting assembled structures and organometallic complexes. Being a member of heteracalixaromatics, tetraoxacalix[2]arene[2]triaizne adopts a 1,3-alternate conformational structure yielding a V-shaped cavity or cleft formed by two electron-deficient triazine rings. Advantageously, the macrocycle is able to self-tune the cavity sizes by altering the degrees of conjugation between the bridging oxygen atoms with their bonded aromatic rings in response to the guest species in present, rendering it an ideal tool to explore anion-π interactions. We initiated our study on anion-π interactions using tetraoxacalix[2]arene[2]triazine as a molecular tool with the primary aim to clarify experimentally the uncertainty of whether exclusive anion-π interactions exist between anions and charge-neutral aromatic rings. We provided for the first time concrete evidence substantiating the formation of typical anion-π interaction between the anions and 1,3,5-triazine ring and demonstrated subsequently the generality and binding motifs of anion-π interactions. We have then extended our study to anion-π interaction-directed or -driven anion recognition and selective sensing, transmembrane anion transport, molecular self-assembly, and stimuli-responsive aggregation systems. A number of new generation macrocycles and cages constructed from electron-deficient tetrazine and benzenetriimide segments have also been developed in the meantime, advancing the study of anion-π interactions. This Account summarizes our endeavors to explore nascent anion-π interactions and their applications in supramolecular chemistry. We hope this Account will inspire scientists from various disciplines to explore all aspects of the nascent yet fruitful research area of anion-π interactions.

Gadoxetic disodium-enhanced MRI to characterize T1 relaxation values and expression level of organic anion transporters and multidrug resistance protein on hepatocyte surface membrane of normal C57BL/6 mice

Objective: The characteristics of T1 relaxation values and the expression levels of organic anion transport system (OATP) and multidrug resistance protein carrier (MRP) on hepatocyte surface membrane were quantitatively studied to evaluate liver function in normal C57BL/6 mice with gadoxetic disodium-enhanced MRI. Methods: Ten 6-weeks-old, normal C57BL/6 mice were included in this study. Gadoxetic disodium- enhanced MRI examination was performed. Longitudinal relaxation time images before and 20 min after contrast injection (hepatobiliary-specific phase) were acquired. T1-relaxation time, T1 relaxation time decline rate (△T) and rapid initial enhancement slope percentage in the first-pass study of the liver parenchyma before and after administration of gadoxetate disodium were measured. Liver parenchyma specimens were detected by Western blotting and the values ​​of OATP1, MRP2, and MRP3 were recorded. Statistical results were expressed in mean. Results: The mean T1 relaxation time of 10 normal C57BL/6 mice before and after enhancement was 659.13 ± 24.07, and 408.87 ± 27.21 ms. The mean T1 relaxation time decline rate and rapid initial enhancement slope percentage in the first-pass study was 37.12% ± 4.95% and 4.14% ± 0.96% ms. Furthermore, the mean value of OATP1, MRP2 and MRP3 were 29 952.1 ± 11 475.2, 34 376.4 ± 33 228.4 and 357 308.9 ± 64 646.5. Conclusion: T1-relaxation values, T1 relaxation time decline rate and rapid initial enhancement slope percentage in the first-pass study before and after gadoxetic disodium-enhanced MRI were determined in normal C57BL/6 mice as well as quantitative values of OATP1, MRP2 and MRP3 at the molecular level on the hepatocyte surface membrane were helpful for liver injury model with control study.

Guard Cell Membrane Anion Transport Systems and Their Regulatory Components: An Elaborate Mechanism Controlling Stress-Induced Stomatal Closure.

When plants are exposed to drastic environmental changes such as drought, salt or bacterial invasion, rapid stomatal movement confers tolerance to these stresses. This process involves a variety of guard cell expressed ion channels and their complex regulation network. Inward K+ channels mainly function in stomatal opening. On the other hand, guard cell anion channels play a crucial role in the closing of stomata, which is vital in terms of preventing water loss and bacterial entrance. Massive progress has been made on the research of these anion channels in the last decade. In this review, we focus on the function and regulation of Arabidopsis guard cell anion channels. Starting from SLAC1, a main contributor of stomatal closure, members of SLAHs (SLAC1 homologues), AtNRTs (Nitrate transporters), AtALMTs (Aluminum-activated malate transporters), ABC transporters, AtCLCs (Chloride channels), DTXs (Detoxification efflux carriers), SULTRs (Sulfate transporters), and their regulator components are reviewed. These membrane transport systems are the keys to maintaining cellular ion homeostasis against fluctuating external circumstances.

Improvement of Anion Transport Systems by Modulation of Chalcogen Interactions: The influence of solvent.

A series of potential anion transporters, dithieno[3,2-b;2',3'-d]thiophenes (DTT), involving anion-chalcogen interactions have been studied by analyzing the interaction energy, geometry, and charge transfer. It was found that gas phase calculations show very negative interaction energies with short anion-chalcogen distances, but when solvent effects are considered, the interaction energy values decreased drastically concomitantly with an elongation on the interatomic distances. To enhance the chalcogen interaction between the DTT derivatives and the anion, increasing the anion transporter capacity, bisisothioazole moiety was considered; i.e., the σ-hole of the chalcogen atom was modulated by substitution of the adjacent carbon by a nitrogen atom in the S-C axis, increasing the depth of the σ-hole and therefore the interaction between the chalcogen and anion. Finally, different anions were analyzed within the complexes, finding that F- and NO3- would be the best candidates to form complexes and possibly displace other anions such as Cl- or Br-.

D-Malate decreases renal content of α-ketoglutarate, a driving force of organic anion transporters OAT1 and OAT3, resulting in inhibited tubular secretion of phenolsulfonphthalein, in rats.

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 60min 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 8.60ml/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.

Carcinogenicity of chromium and chemoprevention: a brief update.

Chromium has two main valence states: hexavalent chromium (Cr[VI]) and trivalent chromium (Cr[III]). Cr(VI), a well-established human carcinogen, can enter cells by way of a sulfate/phosphate anion-transport system, and then be reduced to lower-valence intermediates consisting of pentavalent chromium (Cr[V]), tetravalent chromium (Cr[IV]) or Cr(III) via cellular reductants. These intermediates may directly or indirectly result in DNA damage or DNA–protein cross-links. Although Cr(III) complexes cannot pass easily through cell membranes, they have the ability to accumulate around cells to induce cell-surface morphological alteration and result in cell-membrane lipid injuries via disruption of cellular functions and integrity, and finally to cause DNA damage. In recent years, more research, including in vitro, in vivo, and epidemiological studies, has been conducted to evaluate the genotoxicity/carcinogenicity induced by Cr(VI) and/or Cr(III) compounds. At the same time, various therapeutic agents, especially antioxidants, have been explored through in vitro and in vivo studies for preventing chromium-induced genotoxicity/carcinogenesis. This review aims to provide a brief update on the carcinogenicity of Cr(VI) and Cr(III) and chemoprevention with different antioxidants.

Roles of organic anion transporters (OATs) in renal proximal tubules and their localization.

Organic anions (OAs) are secreted in renal proximal tubules in two steps. In the first step, OAs are transported from the blood through basolateral membranes into proximal tubular cells. The prototypical substrate for renal organic anion transport systems, para-aminohippurate (PAH), is transported across basolateral membranes of proximal tubular cells via OAT1 (SLC22A6) and OAT3 (SLC22A8) against an electrochemical gradient in exchange for intracellular dicarboxylates. In the second step, OAs exit into urine through apical membranes of proximal tubules. This step is thought to be performed by multidrug efflux transporters and a voltage-driven organic anion transporter. However, the molecular nature and precise functional properties of these efflux systems are largely unknown. Recently, we characterized an orphan transporter known as human type I sodium-phosphate transporter 4, hNPT4 (SLC17A3), using the Xenopus oocyte expression system. hNPT4 acts as a voltage-driven efflux transporter ("human OATv1") for several OAs such as PAH, estrone sulfate, diuretic drugs, and urate. Here, we describe a model for an OA secretory pathway in renal tubular cells in which OAs exit cells and enter the tubular lumen via hOATv1 (hNPT4). Additionally, hOATv1 functions as a common renal secretory pathway for both urate and drugs, indicating that hOATv1 may be a leak pathway for excess urate that is reabsorbed via apical URAT1 to control the intracellular urate levels. Therefore, we propose a molecular mechanism for the induction of hyperuricemia by diuretics: the diuretics enter proximal tubular cells via basolateral OAT1 and/or OAT3 and may then interfere with the NPT4-mediated apical urate efflux in the renal proximal tubule.

Selenium-containing organic nanoparticles as silent precursors for ultra-sensitive thiol-responsive transmembrane anion transport.

An anion transporter with a selenoxide group was able to form nanoparticles in water, whose activity was fully turned off due to the aggregation effect. The formed nanoparticles have a uniform size and can be readily dispersed in water at high concentrations. Turn-on of the nanoparticles by reducing molecules is proposed to be a combined process, including the reduction of selenoxide to selenide, disassembly of the nanoparticles and location of the transporter to the lipid membrane. Accordingly, a special acceleration phase can be observed in the turn-on kinetic curves. Since turn-on of the nanoparticles is quantitatively related to the amount of reductant, the nanoparticles can be activated in a step-by-step manner. Due to the sensibility of this system to thiols, cysteine can be detected at low nanomolar concentrations. This ultra-sensitive thiol-responsive transmembrane anion transport system is quite promising in biological applications.

The pharmacokinetics of high-dose methotrexate in people living with HIV on antiretroviral therapy.

Purpose Clinical outcomes for lymphoma in people living with HIV (PLWH) are similar to those in the general public. However, a number of concerns remain including pharmacological interactions between cytotoxic chemotherapy and antiretroviral therapy (ARVs). Much attention has focussed on pharmacokinetic interactions attributable to effects on hepatic microsomal enzymes, but not on competition for the renal organic anion transport system. High-dose (3 g/m2) intravenous methotrexate (MTX) is part a of (R)-CODOX-M/IVAC chemotherapy regimen for HIV-associated Burkitt/Burkitt-like lymphoma (BL/BLL). We investigated MTX pharmacokinetics and evaluated the effects of renal function (eGFR), age and use of different classes of ARVs.MethodsForty-three PLWH treated with ARVs and (R)-CODOX-M/IVAC are included in the analysis. Plasma MTX concentration was measured (ARK TM MTX assay, VITROS® 5600) daily after administration until levels were <0.04/mmol/L. MTX elimination half-life was correlated with age, renal function and antiretroviral regimen.ResultsOne hundred and fifty timed plasma MTX levels were collected. The median MTX elimination half-life was 21.7 h (range 9.4–204.4). MTX elimination half-life was not influenced by age (p = 0.71), eGFR (p = 0.67) or use of non-nucleoside reverse transcriptase inhibitors (NNRTIs) or integrase inhibitors (p = 0.15). Similarly, different NRTI backbones did not affect MTX elimination kinetics (p = 0.68), despite the potential overlapping competition for active renal tubular transporters between MTX and tenofovir.ConclusionAlthough there is potential competition for active renal tubular transporters between MTX and tenofovir, no prolongation of MTX half-life was observed. These findings are reassuring to clinicians managing patients with dual diagnoses.

Lithium Interferes with the Urinary Excretion of Phenolsulfonphthalein in Rats: Involvement of a Reduced Content of α-Ketoglutarate, the Driving Force for Organic Anion Transporters OAT1 and OAT3, in the Kidney Cortex

Aims: Lithium is effective in the treatment for bipolar disorder and is known to influence renal functions. The purpose of this study was to examine the effects of lithium on the renal organic anion transport system. Methods: Pharmacokinetic experiments using rats and Western blotting were conducted. Results: Until 60 min after the intravenous injection of phenolsulfonphthalein, a typical substrate of the renal organic anion transporters, as a bolus, 41.2% of the dose was recovered in the urine, and the infusion of lithium chloride dose-dependently interfered with its renal excretion. No significant changes were observed in the expression levels of rat organic anion transporters rOAT1 and rOAT3, and the content of α-ketoglutarate, the driving force for both transporters, was significantly decreased in the kidney cortex of rats administered lithium. Conclusion: These findings represented the dysfunction of the renal organic anion transport system in rats by lithium. As the mechanism, the reduced driving force for rOAT1 and rOAT3 was suggested to be involved at least in part.

A renal-like organic anion transport system in the ciliary epithelium of the bovine and human eye.

The purpose of this study was to determine the direction of organic anion (OA) transport across the ciliary body and the transport proteins that may contribute. Transport of several OAs across the bovine ciliary body was examined using ciliary body sections mounted in Ussing chambers and a perfused eye preparation. Microarray, reverse-transcription polymerase chain reaction (RT-PCR), immunoblotting, and immunohistochemistry were used to examine OA transporter expression in human ocular tissues. Microarray analysis showed that many OA transporters common to other barrier epithelia are expressed in ocular tissues. mRNA (RT-PCR) and protein (immunoblotting) for OAT1, OAT3, NaDC3, and MRP4 were detected in extracts of the human ciliary body from several donors. OAT1 and OAT3 localized to basolateral membranes of nonpigmented epithelial cells and MRP4 to basolateral membranes of pigmented cells in the human eye. Para-aminohippurate (PAH) and estrone-3-sulfate transport across the bovine ciliary body in the Ussing chambers was greater in the aqueous humor-to-blood direction than in the blood-to-aqueous humor direction, and active. There was little net directional movement of cidofovir. Probenecid (0.1 mM) or novobiocin (0.1 mM) added to the aqueous humor side of the tissue, or MK571 (5-(3-(2-(7-chloroquinolin-2-yl)ethenyl)phenyl)-8-dimethylcarbamyl-4,6-dithiaoctanoic acid; 0.1 mM) added to the blood side significantly reduced net active PAH transport. The rate of 6-carboxyfluorescein elimination from the aqueous humor of the perfused eye was reduced 80% when novobiocin (0.1 mM) was present in the aqueous humor. These data indicate that the ciliary body expresses a variety of OA transporters, including those common to the kidney. They are likely involved in clearing potentially harmful endobiotic and xenobiotic OAs from the eye.