Expression of rat renal cortical OAT1 and OAT3 in response to acute biliary obstruction

Bile Acids and Farnesoid X Receptor in Renal Pathophysiology

BACKGROUND

Bile acids (BAs) act not only as lipids and lipid-soluble vitamin detergents but also function as signaling molecules, participating in diverse physiological processes. The identification of BA receptors in organs beyond the enterohepatic system, such as the farnesoid X receptor (FXR), has initiated inquiries into their organ-specific functions. Among these organs, the kidney prominently expresses FXR.

SUMMARY

This review provides a comprehensive overview of various BA species identified in kidneys and delves into the roles of renal apical and basolateral BA transporters. Furthermore, we explore changes in BAs and their potential implications for various renal diseases, particularly chronic kidney disease. Lastly, we center our discussion on FXR, a key BA receptor in the kidney and a potential therapeutic target for renal diseases, providing current insights into the protective mechanisms associated with FXR agonist treatments.

KEY MESSAGES

Despite the relatively low concentrations of BAs in the kidney, their presence is noteworthy, with rodents and humans exhibiting distinct renal BA compositions. Renal BA transporters efficiently facilitate either reabsorption into systemic circulation or excretion into the urine. However, adaptive changes in BA transporters are evident during cholestasis. Various renal diseases are accompanied by alterations in BA concentrations and FXR expression. Consequently, the activation of FXR in the kidney could be a promising target for mitigating kidney damage.

Influence of the Pringle maneuver during partial hepatectomy on the neuromuscular block induced by intermittent and continuous dosing of rocuronium

PURPOSE

The Pringle maneuver (PM) is a common procedure in hepatectomy that is known to interrupt drug elimination. The purpose of this study was to examine the influence of PM on the duration of action of rocuronium administered by intermittent bolus dosing, the continuous rocuronium infusion dose required for maintenance of a moderate neuromuscular block, and changes in plasma concentrations of rocuronium.

METHODS

Twenty-seven adult patients undergoing partial hepatectomy with PM were enrolled in this study. The duration of action of 0.2 mg/kg rocuronium boluses (DUR), and the continuous rocuronium infusion dose required for maintenance of the height of the first twitch of the train-of-four (T1) at 10-20% of the control value (%T1), respectively, were electromyographically monitored on the adductor digiti minimi muscle. The effects of PM on DUR, %T1, and the plasma concentration of rocuronium were measured.

RESULTS

The DUR was significantly prolonged during PM [mean: 42.2 (SD: 8.0) min, P < 0.001] compared to baseline [29.7 (6.3) min]. It was prolonged even after completion of the PM [46.2 (10.5) min, P < 0.001]. The plasma concentration of rocuronium measured at every reappearance of T1 was comparable between before and during PM. %T1 [15.5 (5.6)%] was significantly depressed after the start of PM [6.5 (3.9)%, P < 0.001], with persistence of the depression even after completion of PM. However, there were no significant changes in the plasma concentration of rocuronium.

CONCLUSIONS

Rocuronium-induced neuromuscular block is significantly augmented during PM. However, the augmentation is not associated with an increase in plasma rocuronium concentration.

Examination of the emerging role of transporters in the assessment of nephrotoxicity

INTRODUCTION

The kidney is vulnerable to various injuries based on its function in the elimination of many xenobiotics, endogenous substances and metabolites. Since transporters are critical for the renal elimination of those substances, it is urgent to understand the emerging role of transporters in nephrotoxicity.

AREAS COVERED

This review summarizes the contribution of major renal transporters to nephrotoxicity induced by some drugs or toxins; addresses the role of transporter-mediated endogenous metabolic disturbances in nephrotoxicity; and discusses the advantages and disadvantages of in vitro models based on transporter expression and function.

EXPERT OPINION

Due to the crucial role of transporters in the renal disposition of xenobiotics and endogenous substances, it is necessary to further elucidate their renal transport mechanisms and pay more attention to the underlying relationship between the transport of endogenous substances and nephrotoxicity. Considering the species differences in the expression and function of transporters, and the low expression of transporters in general cell models, in vitro humanized models, such as humanized 3D organoids, shows significant promise in nephrotoxicity prediction and mechanism study.

Bile Acid-Drug Interaction via Organic Anion-Transporting Polypeptide 4C1 Is a Potential Mechanism of Altered Pharmacokinetics of Renally Excreted Drugs

Patients with liver diseases not only experience the adverse effects of liver-metabolized drugs, but also the unexpected adverse effects of renally excreted drugs. Bile acids alter the expression of renal drug transporters, however, the direct effects of bile acids on drug transport remain unknown. Renal drug transporter organic anion-transporting polypeptide 4C1 (OATP4C1) was reported to be inhibited by chenodeoxycholic acid. Therefore, we predicted that the inhibition of OATP4C1-mediated transport by bile acids might be a potential mechanism for the altered pharmacokinetics of renally excreted drugs. We screened 45 types of bile acids and calculated the IC50, Ki values, and bile acid−drug interaction (BDI) indices of bile acids whose inhibitory effect on OATP4C1 was >50%. From the screening results, lithocholic acid (LCA), glycine-conjugated lithocholic acid (GLCA), and taurine-conjugated lithocholic acid (TLCA) were newly identified as inhibitors of OATP4C1. Since the BDI index of LCA was 0.278, LCA is likely to inhibit OATP4C1-mediated transport in clinical settings. Our findings suggest that dose adjustment of renally excreted drugs may be required in patients with renal failure as well as in patients with hepatic failure. We believe that our findings provide essential information for drug development and safe drug treatment in clinics.

Altered peripheral factors affecting the absorption, distribution, metabolism, and excretion of oral medicines in Alzheimer's disease

Alzheimer's disease (AD) has traditionally been considered solely a neurological condition. Therefore, numerous studies have been conducted to identify the existence of pathophysiological changes affecting the brain and the blood-brain barrier in individuals with AD. Such studies have provided invaluable insight into possible changes to the central nervous system exposure of drugs prescribed to individuals with AD. However, there is now increasing recognition that extra-neurological systems may also be affected in AD, such as the small intestine, liver, and kidneys. Examination of these peripheral pathophysiological changes is now a burgeoning area of scientific research, owing to the potential impact of these changes on the absorption, distribution, metabolism, and excretion (ADME) of drugs used for both AD and other concomitant conditions in this population. The purpose of this review is to identify and summarise available literature reporting alterations to key organs influencing the pharmacokinetics of drugs, with any changes to the small intestine, liver, kidney, and circulatory system on the ADME of drugs described. By assessing studies in both rodent models of AD and samples from humans with AD, this review highlights possible dosage adjustment requirements for both AD and non-AD drugs so as to ensure the achievement of optimum pharmacotherapy in individuals with AD.

The effect of obstructive jaundice on the sensitivity of intravenous anesthetic of remimazolam: study protocol for a controlled multicenter trial

BACKGROUND

It is well known that obstructive jaundice could affect the pharmacodynamics of some anesthetics, and the sensitivity of some anesthetics would increase among icteric patients. Remimazolam is a new ultra-short-acting intravenous benzodiazepine sedative/anesthetic, which is a high-selective and affinity ligand for the benzodiazepine site on the GABAA receptor. However, no study has reported the pharmacodynamics of remimazolam in patients with obstructive jaundice. We hypothesize that obstructive jaundice affects the pharmacodynamics of remimazolam, and the sensitivity of remimazolam increases among icteric patients.

METHODS/DESIGN

The study will be performed as a prospective, controlled, multicenter trial. The study design is a comparison of remimazolam requirements to reach a bispectral index of 50 in patients with obstructive jaundice versus non-jaundiced patients with chronic cholecystitisor intrahepatic bile duct stones. Remimazolam was infused at 6 mg/kg/h until this endpoint was reached.

DISCUSSION

Remimazolam could be suitable for anesthesia of patients with obstructive jaundice, because remimazolam is not biotransformed in the liver. Hyperbilirubinemia has been well-described to have toxic effects on the brain, which causes the increasing of sensitivity to some anesthetics, such as desflurane, isoflurane, and etomidate. Furthermore, remimazolam and etomidate have the same mechanism of action when exerting an anesthetic effect. We aim to demonstrate that obstructive jaundice affects the pharmacodynamics of remimazolam, and the dose of remimazolam when administered to patients with obstructive jaundice should be modified.

TRIAL REGISTRATION

Chinese Clinical Trial Registry ChiCTR2100043585 . Registered on 23 February 2021.

Drug Transporters in the Kidney: Perspectives on Species Differences, Disease Status, and Molecular Docking

The kidneys are a pair of important organs that excretes endogenous waste and exogenous biological agents from the body. Numerous transporters are involved in the excretion process. The levels of these transporters could affect the pharmacokinetics of many drugs, such as organic anion drugs, organic cationic drugs, and peptide drugs. Eleven drug transporters in the kidney (OAT1, OAT3, OATP4C1, OCT2, MDR1, BCRP, MATE1, MATE2-K, OAT4, MRP2, and MRP4) have become necessary research items in the development of innovative drugs. However, the levels of these transporters vary between different species, sex-genders, ages, and disease statuses, which may lead to different pharmacokinetics of drugs. Here, we review the differences of the important transports in the mentioned conditions, in order to help clinicians to improve clinical prescriptions for patients. To predict drug-drug interactions (DDIs) caused by renal drug transporters, the molecular docking method is used for rapid screening of substrates or inhibitors of the drug transporters. Here, we review a large number of natural products that represent potential substrates and/or inhibitors of transporters by the molecular docking method.

Involvement of Organic Anion Transporters in the Pharmacokinetics and Drug Interaction of Rosmarinic Acid

We investigated the involvement of drug transporters in the pharmacokinetics of rosmarinic acid in rats as well as the transporter-mediated drug interaction potential of rosmarinic acid in HEK293 cells overexpressing clinically important solute carrier transporters and also in rats. Intravenously injected rosmarinic acid showed bi-exponential decay and unchanged rosmarinic acid was mainly eliminated by urinary excretion, suggesting the involvement of transporters in its renal excretion. Rosmarinic acid showed organic anion transporter (OAT)1-mediated active transport with a K_m of 26.5 μM and a V_max of 69.0 pmol/min in HEK293 cells overexpressing OAT1, and the plasma concentrations of rosmarinic acid were increased by the co-injection of probenecid because of decreased renal excretion due to OAT1 inhibition. Rosmarinic acid inhibited the transport activities of OAT1, OAT3, organic anion transporting polypeptide (OATP)1B1, and OATP1B3 with IC₅₀ values of 60.6 μM, 1.52 μM, 74.8 μM, and 91.3 μM, respectively, and the inhibitory effect of rosmarinic acid on OAT3 transport activity caused an in vivo pharmacokinetic interaction with furosemide by inhibiting its renal excretion and by increasing its plasma concentration. In conclusion, OAT1 and OAT3 are the major transporters that may regulate the pharmacokinetic properties of rosmarinic acid and may cause herb-drug interactions with rosmarinic acid, although their clinical relevance awaits further evaluation.

The pathogenesis of renal injury in obstructive jaundice: A review of underlying mechanisms, inducible agents and therapeutic strategies

Kidney injury is one of the main complications of obstructive jaundice (OJ) and its pathogenesis has not been clarified. As an independent risk factor for OJ associated with significant morbidity and mortality, it can be mainly divided into two types of morphological injury and functional injury. We called these dysfunctions caused by OJ-induced kidney injury as OJKI. However, the etiology of OJKI is still not fully clear, and research studies on how OJKI becomes a facilitated factor of OJ are limited. This article reviews the underlying pathological mechanism from five aspects, including metabolisms of bile acids, hemodynamic disturbances, oxidative stress, inflammation and the organic transporter system. Some nephrotoxic drugs and measures that can enhance or reduce the renal function with potential intervention in perioperative periods to alleviate the incidence of OJKI were also described. Furthermore, a more in-depth study on the pathogenesis of OJKI from multiple aspects for exploring more targeted treatment measures were further put forward, which may provide new methods for the prevention and treatment of clinical OJKI and improve the prognosis.

Extrahepatic Drug Transporters in Liver Failure: Focus on Kidney and Gastrointestinal Tract

Emerging information suggests that liver pathological states may affect the expression and function of membrane transporters in the gastrointestinal tract and the kidney. Altered status of the transporters could affect drug as well as endogenous compounds handling with subsequent clinical consequences. It seems that changes in intestinal and kidney transporter functions provide the compensatory activity of eliminating endogenous compounds (e.g., bile acids) generated and accumulated due to liver dysfunction. A literature search was conducted on the Ovid and PubMed databases to select relevant in vitro, animal and human studies that have reported expression, protein abundance and function of the gastrointestinal and kidney operating ABC (ATP-binding cassette) transporters and SLC (solute carriers) carriers. The accumulated data suggest that liver failure-associated transporter alterations in the gastrointestinal tract and kidney may affect drug pharmacokinetics. The altered status of drug transporters in those organs in liver dysfunction conditions may provide compensatory activity in handling endogenous compounds, affecting local drug actions as well as drug pharmacokinetics.

Distribution of the organic anion transporters Oat1 and Oat3 between renal membrane microdomains in obstructive jaundice

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.

Proteasome Inhibitors Bortezomib and Carfilzomib Stimulate the Transport Activity of Human Organic Anion Transporter 1

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.

Kinetic analysis of sequential metabolism of triazolam and its extrapolation to humans using an entero-hepatic two-organ microphysiological system

The microphysiological system (MPS) is a promising tool for predicting drug disposition in humans, although limited information is available on the quantitative assessment of sequential drug metabolism in MPS and its extrapolation to humans. In the present study, we first constructed a mechanism-based pharmacokinetic model for triazolam (TRZ) and its metabolites in the entero-hepatic two-organ MPS, composed of intestinal Caco-2 and hepatic HepaRG cells, and attempted to extrapolate the kinetic information obtained with the MPS to the plasma concentration profiles in humans. In the two-organ MPS and HepaRG single culture systems, TRZ was found to be metabolized into α- and 4-hydroxytriazolam and their respective glucuronides. All these metabolites were almost completely reduced in the presence of a CYP3A inhibitor, itraconazole, confirming sequential phase I and II metabolism. Both pharmacokinetic model-dependent and -independent analyses were performed, providing consistent results regarding the metabolic activity of TRZ: clearance of glucuronidation metabolites in the two-organ MPS was higher than that in the single culture system. The plasma concentration profile of TRZ and its two hydroxy metabolites in humans was quantitatively simulated based on the pharmacokinetic model, by incorporating several scaling factors representing quantitative gaps between the MPS and humans. Thus, the present study provided the first quantitative extrapolation of sequential drug metabolism in humans by combining MPS and pharmacokinetic modeling.

Increased Expression of Renal Drug Transporters in a Mouse Model of Familial Alzheimer's Disease

It is well established that the expression and function of drug transporters at the blood-brain barrier are altered in Alzheimer's disease (AD). However, we recently demonstrated in a mouse model of AD that the expression of key drug transporters and metabolizing enzymes was modified in peripheral organs, such as the small intestine and liver, suggesting that systemic drug absorption may be altered in AD. The purpose of this study was to determine whether the expression of drug transporters in the kidneys differed between 8- to 9-month-old wild-type mice and APPswe/PSEN1dE9 (APP/PS1) transgenic mice, a mouse model of familial AD, using a quantitative targeted absolute proteomics approach. The protein expression of the drug transporters-multidrug resistance-associated protein 2, organic anion transporter 3, and organic cation transporter 2-was upregulated 1.6-, 1.3-, and 1.4-fold, respectively, in kidneys from APP/PS1 mice relative to wild-type mice. These results suggest that in addition to modified oral absorption of certain drugs, it is possible that the renal excretion of drugs that are multidrug resistance-associated protein 2, organic anion transporter 3, and organic cation transporter 2 substrates could be altered in AD. These changes could affect the interpretation of studies conducted during drug development using this mouse model of AD and potentially impact dosage regimens of such drugs prescribed in this patient population.

Renal Drug Transporters and Drug Interactions

Transporters in proximal renal tubules contribute to the disposition of numerous drugs. Furthermore, the molecular mechanisms of tubular secretion have been progressively elucidated during the past decades. Organic anions tend to be secreted by the transport proteins OAT1, OAT3 and OATP4C1 on the basolateral side of tubular cells, and multidrug resistance protein (MRP) 2, MRP4, OATP1A2 and breast cancer resistance protein (BCRP) on the apical side. Organic cations are secreted by organic cation transporter (OCT) 2 on the basolateral side, and multidrug and toxic compound extrusion (MATE) proteins MATE1, MATE2/2-K, P-glycoprotein, organic cation and carnitine transporter (OCTN) 1 and OCTN2 on the apical side. Significant drug-drug interactions (DDIs) may affect any of these transporters, altering the clearance and, consequently, the efficacy and/or toxicity of substrate drugs. Interactions at the level of basolateral transporters typically decrease the clearance of the victim drug, causing higher systemic exposure. Interactions at the apical level can also lower drug clearance, but may be associated with higher renal toxicity, due to intracellular accumulation. Whereas the importance of glomerular filtration in drug disposition is largely appreciated among clinicians, DDIs involving renal transporters are less well recognized. This review summarizes current knowledge on the roles, quantitative importance and clinical relevance of these transporters in drug therapy. It proposes an approach based on substrate-inhibitor associations for predicting potential tubular-based DDIs and preventing their adverse consequences. We provide a comprehensive list of known drug interactions with renally-expressed transporters. While many of these interactions have limited clinical consequences, some involving high-risk drugs (e.g. methotrexate) definitely deserve the attention of prescribers.

Interactions of 172 plant extracts with human organic anion transporter 1 (SLC22A6) and 3 (SLC22A8): a study on herb-drug interactions

Background

Herb-drug interactions (HDIs) resulting from concomitant use of herbal products with clinical drugs may cause adverse reactions. Organic anion transporter 1 (OAT1) and 3 (OAT3) are highly expressed in the kidney and play a key role in the renal elimination of substrate drugs. So far, little is known about the herbal extracts that could modulate OAT1 and OAT3 activities.

Methods

HEK293 cells stably expressing human OAT1 (HEK-OAT1) and OAT3 (HEK-OAT3) were established and characterized. One hundred seventy-two extracts from 37 medicinal and economic plants were prepared. An initial concentration of 5 µg/ml for each extract was used to evaluate their effects on 6-carboxylfluorescein (6-CF) uptake in HEK-OAT1 and HEK-OAT3 cells. Concentration-dependent inhibition studies were conducted for those extracts with more than 50% inhibition to OAT1 and OAT3. The extract of Juncus effusus, a well-known traditional Chinese medicine, was assessed for its effect on the in vivo pharmacokinetic parameters of furosemide, a diuretic drug which is a known substrate of both OAT1 and OAT3.

Results

More than 30% of the plant extracts at the concentration of 5 µg/ml showed strong inhibitory effect on the 6-CF uptake mediated by OAT1 (61 extracts) and OAT3 (55 extracts). Among them, three extracts for OAT1 and fourteen extracts for OAT3 were identified as strong inhibitors with IC₅₀ values being <5 µg/ml. Juncus effusus showed a strong inhibition to OAT3 in vitro, and markedly altered the in vivo pharmacokinetic parameters of furosemide in rats.

Conclusion

The present study identified the potential interactions of medicinal and economic plants with human OAT1 and OAT3, which is helpful to predict and to avoid potential OAT1- and OAT3-mediated HDIs.

Furosemide Pharmacokinetics in Adult Rats become Abnormal with an Adverse Intrauterine Environment and Modulated by a Post-Weaning High-Fat Diet

Adult individuals born with intrauterine growth restriction (IUGR) have physiological maladaptations that significantly increase risk of chronic disease. We suggested that such abnormalities in organ function would alter pharmacokinetics throughout life, exacerbated by environmental mismatch. Pregnant and lactating rats were fed either a purified control diet (18% protein) or low-protein diet (9% protein) to produce IUGR offspring. Offspring were weaned onto either laboratory chow (11% fat) or high-fat diet (45% fat). Adult offspring (5 months old) were dosed with furosemide (10 mg/kg i.p.) and serum and urine collected. The overall exposure profile in IUGR males was significantly reduced due to a ~35% increase in both clearance and volume of distribution. Females appeared resistant to the IUGR phenotype. The effects of the high-fat diet trended in the opposite direction to that of IUGR, with increased drug exposure due to decreases in both clearance (31% males, 46% females) and volume of distribution (24% males, 44% females), with a 10% longer half-life in both genders. The alterations in furosemide pharmacokinetics and pharmacodynamics were explained by changes in the expression of renal organic anion transporters 1 and 3, and sodium-potassium-chloride cotransporter-2. In summary, this study suggests that IUGR and diet interact to produce subpopulations with similar body-weights but dissimilar pharmacokinetic profiles; this underlines the limitation of one-size-fits-all dosing which does not account for physiological differences in body composition resulting from IUGR and diet.

Expression of renal Oat5 and NaDC1 transporters in rats with acute biliary obstruction

AIM: To examine renal expression of organic anion transporter 5 (Oat5) and sodium-dicarboxylate cotransporter 1 (NaDC1), and excretion of citrate in rats with acute extrahepatic cholestasis.

METHODS: Obstructive jaundice was induced in rats by double ligation and division of the common bile duct (BDL group). Controls underwent sham operation that consisted of exposure, but not ligation, of the common bile duct (Sham group). Studies were performed 21 h after surgery. During this period, animals were maintained in metabolic cages in order to collect urine. The urinary volume was determined by gravimetry. The day of the experiment, blood samples were withdrawn and used to measure total and direct bilirubin as indicative parameters of hepatic function. Serum and urine samples were used for biochemical determinations. Immunoblotting for Oat5 and NaDC1 were performed in renal homogenates and brush border membranes from Sham and BDL rats. Immunohistochemistry studies were performed in kidneys from both experimental groups. Total RNA was extracted from rat renal tissue in order to perform reverse transcription polymerase chain reaction. Another set of experimental animals were used to evaluate medullar renal blood flow (mRBF) using fluorescent microspheres.

RESULTS: Total and direct bilirubin levels were significantly higher in BDL animals, attesting to the adequacy of biliary obstruction. An important increase in mRBF was determined in BDL group (Sham: 0.53 ± 0.12 mL/min per 100 g body weight vs BDL: 1.58 ± 0.24 mL/min per 100 g body weight, P < 0.05). An increase in the urinary volume was observed in BDL animals. An important decrease in urinary levels of citrate was seen in BDL group. Besides, a decrease in urinary citrate excretion (Sham: 0.53 ± 0.11 g/g creatinine vs BDL: 0.07 ± 0.02 g/g creatinine, P < 0.05) and an increase in urinary excretion of H⁺ (Sham: 0.082 ± 0.03 μmol/g creatinine vs BDL: 0.21 ± 0.04 μmol/g creatinine, P < 0.05) were observed in BDL animals. We found upregulations of both proteins Oat5 and NaDC1 in brush border membranes where they are functional. Immunohistochemistry technique corroborated these results for both proteins. No modifications were observed in Oat5 mRNA and in NaDC1 mRNA levels in kidney from BDL group as compared with Sham ones.

CONCLUSION: Citrate excretion is decreased in BDL rats, at least in part, because of the higher NaDC1 expression. Using the outward gradient of citrate generated by NaDC1, Oat5 can reabsorb/eliminate different organic anions of pathophysiological importance.

Renal xenobiotic transporter expression is altered in multiple experimental models of nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease is the most common chronic liver disease, which can progress to nonalcoholic steatohepatitis (NASH). Previous investigations demonstrated alterations in the expression and activity of hepatic drug transporters in NASH. Moreover, studies using rodent models of cholestasis suggest that compensatory changes in kidney transporter expression occur to facilitate renal excretion during states of hepatic stress; however, little information is currently known regarding extrahepatic regulation of drug transporters in NASH. The purpose of the current study was to investigate the possibility of renal drug transporter regulation in NASH across multiple experimental rodent models. Both rat and mouse NASH models were used in this investigation and include: the methionine and choline-deficient (MCD) diet, atherogenic diet, fa/fa rat, ob/ob and db/db mice. Histologic and pathologic evaluations confirmed that the MCD and atherogenic rats as well as the ob/ob and db/db mice all developed NASH. In contrast, the fa/fa rats did not develop NASH but did develop extensive renal injury compared with the other models. Renal mRNA and protein analyses of xenobiotic transporters suggest that compensatory changes occur in NASH to favor increased xenobiotic secretion. Specifically, both apical efflux and basolateral uptake transporters are induced, whereas apical uptake transporter expression is repressed. These results suggest that NASH may alter the expression and potentially function of renal drug transporters, thereby impacting drug elimination mechanisms in the kidney.

Evaluation of the transporter-mediated herb-drug interaction potential of DA-9801, a standardized dioscorea extract for diabetic neuropathy, in human in vitro and rat in vivo

Background

Drug transporters play important roles in the absorption, distribution, and elimination of drugs and thereby, modulate drug efficacy and toxicity. With a growing use of poly pharmacy, concurrent administration of herbal extracts that modulate transporter activities with drugs can cause serious adverse reactions. Therefore, prediction and evaluation of drug-drug interaction potential is important in the clinic and in the drug development process. DA-9801, comprising a mixed extract of Dioscoreae rhizoma and Dioscorea nipponica Makino, is a new standardized extract currently being evaluated for diabetic peripheral neuropathy in a phase II clinical study.

Method

The inhibitory effects of DA-9801 on the transport functions of organic cation transporter (OCT)1, OCT2, organic anion transporter (OAT)1, OAT3, organic anion transporting polypeptide (OATP)1B1, OATP1B3, P-glycoprotein (P-gp), and breast cancer resistance protein (BCRP) were investigated in HEK293 or LLC-PK1 cells. The effects of DA-9801 on the pharmacokinetics of relevant substrate drugs of these transporters were also examined in vivo in rats.

Results

DA-9801 inhibited the in vitro transport activities of OCT1, OCT2, OAT3, and OATP1B1, with IC₅₀ values of 106, 174, 48.1, and 273 μg/mL, respectively, while the other transporters were not inhibited by 300 μg/mL DA-9801. To investigate whether this inhibitory effect of DA-9801 on OCT1, OCT2, and OAT3 could change the pharmacokinetics of their substrates in vivo, we measured the pharmacokinetics of cimetidine, a substrate for OCT1, OCT2, and OAT3, and of furosemide, a substrate for OAT1 and OAT3, by co-administration of DA-9801 at a single oral dose of 1,000 mg/kg. Pre-dose of DA-9801 5 min or 2 h prior to cimetidine administration decreased the C_max of cimetidine in rats. However, DA-9801 did not affect the elimination parameters such as half-life, clearance, or amount excreted in the urine, suggesting that it did not inhibit elimination process of cimetidine, which is governed by OCT1, OCT2, and OAT3. Moreover, DA-9801 did not affect the pharmacokinetic characteristics of furosemide, as evidenced by its unchanged pharmacokinetic parameters.

Conclusion

Inhibitory effects of DA-9801 on OCT1, OCT2, and OAT3 observed in vitro may not necessarily translate into in vivo herb-drug interactions in rats even at its maximum effective dose.

Drug disposition alterations in liver disease: extrahepatic effects in cholestasis and nonalcoholic steatohepatitis

INTRODUCTION

The pharmacokinetics (PK) of drugs and xenobiotics, namely pharmaceuticals, is influenced by a host of factors that include genetics, physiological factors and environmental stressors. The importance of disease on the disposition of xenobiotics has been increasingly recognized among medical professionals for alterations in key enzymes and membrane transporters that influence drug disposition and contribute to the development of adverse drug reactions.

AREAS COVERED

This review will survey pertinent literature of how liver disease alters the PKs of drugs and other xenobiotics. The focus will be on nonalcoholic steatohepatitis as well as cholestatic liver diseases. A review of basic pharmacokinetic principles, with a special emphasis on xenobiotic metabolizing enzymes and membrane transporters, will be provided. Specifically, examples of how genetic alterations affect metabolism and excretion, respectively, will be highlighted. Lastly, the idea of 'extrahepatic' regulation will be explored, citing examples of how disease manifestation in the liver may affect drug disposition in distal sites, such as the kidney.

EXPERT OPINION

An expert opinion will be provided highlighting the definite need for data in understanding extrahepatic regulation of membrane transporters in the presence of liver disease and its potential to dramatically alter the PK and toxicokinetic profile of numerous drugs and xenobiotics.

Interaction of five anthraquinones from rhubarb with human organic anion transporter 1 (SLC22A6) and 3 (SLC22A8) and drug-drug interaction in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Rhubarb is a well-known traditional Chinese medicine and has been used in China for thousands of years. Anthraquinone derivatives including rhein, emodin, aloe-emodin, chrysophanol and physcion are the important components in rhubarb.

MATERIALS AND METHODS

Here we studied the interaction of five anthraquinone derivatives with human renal organic anion transporter 1 (hOAT1) and hOAT3 stably expressed in cells, and interaction of rhein or rhubarb extract (RE) with furosemide (FS, substrate of OATs) in rats.

RESULTS

Uptake of 6-carboxyl fluorescein via hOAT1 and fluorescein via hOAT3 were markedly inhibited by rhein, emodin and aloe-emodin, and slightly inhibited by chrysophanol and physcion. The estimated IC₅₀ values for rhein, emodin, aloe-emodin and probenecid (typical inhibitor of hOAT1 and hOAT3) were 0.23, 0.61, 2.29 and 18.34 μM for hOAT1, and 0.08, 1.22, 5.37 and 5.83 μM for hOAT3, respectively. Furthermore, the data from the cellular accumulation assay indicated that these five compounds were not substrates of hOAT1 or hOAT3. Pharmacokinetic interaction between rhein and FS in rats showed that area under the curve (AUC₀-t) for FS was increased by 65% when coadministrated with rhein. RE was also used to interact with FS in rats and results showed that AUC₀-t of FS was increased by 32% and by 52% when coadministrated with single-dose or multiple-dose of RE, respectively.

CONCLUSIONS

These findings suggested that five anthraquinones inhibited hOAT1 and hOAT3, but these compounds were not transported by hOAT1 or hOAT3. Furthermore, rhein or RE, might cause drug-drug interaction when coadministrated with substrates of OAT1 or OAT3 in vivo.

Protein expression of kidney and liver bilitranslocase in rats exposed to mercuric chloride--a potential tissular biomarker of toxicity

Bilitranslocase (BTL) is a plasma membrane carrier that transports organic anions of physiological and pharmacological interest. It is expressed in basolateral plasma membrane of kidney and liver. BTL has been recently described as a marker of transition from normal tissue to its neoplastic transformation in human kidney. Inorganic mercury is a major environmental contaminant that produces many toxic effects. Previous reports have described an interaction between BTL and mercuric ions. This study was designed to evaluate the renal and hepatic expression of BTL in rats exposed to a nephrotoxic and hepatotoxic dose of HgCl2. Male rats were treated with a single injection of HgCl2 at a dose of 4mg/kg body wt, i.p. (HgCl2 group). Control rats received the vehicle alone (Control group). Studies were carried out 18h after injection. Afterwards, the kidneys and livers were excised and processed for histopathological studies or immunoblot (homogenates and crude membranes) techniques. In rats treated with HgCl2, immunoblotting showed a significant decrease in the abundance of BTL in homogenates and plasma membranes from kidney and liver. BTL decrease of expression might reflect the grade of damage in renal tubule cells and in hepatocytes. Thus, BTL might be postulated as a new biomarker of tissue toxicity induced by mercury.

Influence of obstructive jaundice on pharmacodynamics of rocuronium

BACKGROUND

Anesthetics are variable in patients with obstructive jaundice. The minimum alveolar concentration awake of desflurane is reduced in patients with obstructive jaundice, while it has no effect on pharmacodynamics and pharmacokinetics of propofol. In this study, we investigated the influence of obstructive jaundice on the pharmacodynamics and blood concentration of rocuronium.

METHODS

Included in this study were 26 control patients and 27 patients with obstructive jaundice. Neuromuscular block of rocuronium was monitored by acceleromyography. Onset time, spontaneous recovery of the height of twitch first (T1) to 25% of the final T1 value (Duration 25%, Dur 25%), recovery index (RI), and spontaneous recovery of train-of-four (TOF) ratios to 70% were measured. The plasma rocuronium concentrations were determined by high performance liquid chromatography using berberine as an internal standard.

RESULTS

There was no significant difference in onset time between the two groups. The Dur 25%, the recovery index and the time of recovery of the TOF ratios to 70% were all prolonged in the obstructive jaundice group compared with the control group. The plasma concentration of rocuronium at 60, 90 and 120 min after bolus administration was significantly higher in the obstructive jaundice group.

CONCLUSIONS

The neuromuscular blockade by rocuronium is prolonged in obstructive jaundice patients, and therefore precautions should be taken in case of postoperative residual neuromuscular block. The possible reason is impedance of rocuronium excretion due to biliary obstruction and increased plasma unbound rocuronium because of free bilirubin competing with it for albumin binding.

Expression and function of renal and hepatic organic anion transporters in extrahepatic cholestasis

Obstructive jaundice occurs in patients suffering from cholelithiasis and from neoplasms affecting the pancreas and the common bile duct. The absorption, distribution and elimination of drugs are impaired during this pathology. Prolonged cholestasis may alter both liver and kidney function. Lactam antibiotics, diuretics, non-steroidal anti-inflammatory drugs, several antiviral drugs as well as endogenous compounds are classified as organic anions. The hepatic and renal organic anion transport pathways play a key role in the pharmacokinetics of these compounds. It has been demonstrated that acute extrahepatic cholestasis is associated with increased renal elimination of organic anions. The present work describes the molecular mechanisms involved in the regulation of the expression and function of the renal and hepatic organic anion transporters in extrahepatic cholestasis, such as multidrug resistance-associated protein 2, organic anion transporting polypeptide 1, organic anion transporter 3, bilitranslocase, bromosulfophthalein/bilirubin binding protein, organic anion transporter 1 and sodium dependent bile salt transporter. The modulation in the expression of renal organic anion transporters constitutes a compensatory mechanism to overcome the hepatic dysfunction in the elimination of organic anions.

Endocrine and metabolic regulation of renal drug transporters

Renal xenobiotic transporters are important determinants of urinary secretion and reabsorption of chemicals. In addition to glomerular filtration, these processes are key to the overall renal clearance of a diverse array of drugs and toxins. Alterations in kidney transporter levels and function can influence the efficacy and toxicity of chemicals. Studies in experimental animals have revealed distinct patterns of renal transporter expression in response to sex hormones, pregnancy, and growth hormone. Likewise, a number of disease states including diabetes, obesity, and cholestasis alter the expression of kidney transporters. The goal of this review is to provide an overview of the major xenobiotic transporters expressed in the kidneys and an understanding of metabolic conditions and hormonal factors that regulate their expression and function.

Drug transport by Organic Anion Transporters (OATs)

Common to all so far functionally characterized Organic Anion Transporters (OATs) is their broad substrate specificity and their ability to exchange extracellular against intracellular organic anions. Many OATs occur in renal proximal tubules, the site of active drug secretion. Exceptions are murine Oat6 (nasal epithelium), human OAT7 (liver), and rat Oat8 (renal collecting ducts). In human kidneys, OAT1, OAT2, and OAT3 are localized in the basolateral membrane, and OAT4, OAT10, and URAT1 in the apical cell membrane of proximal tubule cells, respectively. In rats and mice, Oat1 and Oat3 are located basolaterally, and Oat2, Oat5, Oat9, Oat10, and Urat1 apically. Several classes of drugs interact with human OAT1-3, including ACE inhibitors, angiotensin II receptor antagonists, diuretics, HMG CoA reductase inhibitors, β-lactam antibiotics, antineoplastic and antiviral drugs, and uricosuric drugs. For most drugs, interaction was demonstrated in vitro by inhibition of OAT-mediated transport of model substrates; for some drugs, transport by OATs was directly proven. Based on IC₅₀ values reported in the literature, OAT1 and OAT3 show comparable affinities for diuretics, cephalosporins, and nonsteroidal anti-inflammatory drugs whereas OAT2 has a lower affinity to most of these compounds. Drug-drug interactions at OAT1 and OAT3 may retard renal drug secretion and cause untoward effects. OAT4, OAT10, and URAT1 in the apical membrane contribute to proximal tubular urate absorption, and OAT10 to nicotinate absorption. OAT4 is in addition able to release drugs, e.g. diuretics, into the tubule lumen.

Effect of JBP485 on obstructive jaundice is related to regulation of renal Oat1, Oat3 and Mrp2 expression in ANIT-treated rats

The objective was to determine whether protective effects of JBP485 on biliary obstruction induced by alpha-naphthylisothiocyanate (ANIT) are mediated by the organic anion transporters Oat1, Oat3 and the multidrug resistance-associated protein Mrp2. The ANIT-induced increases in bilirubin (BIL), alanine aminotransferase (ALT) and aspartate transaminase (AST) in rat serum were inhibited significantly by oral administration of JBP485. The plasma concentration of JBP485 which is the substrate of Oat1 and Oat3 determined by LC-MS/MS was markedly increased after intravenous administration in ANIT-treated rats, whereas cumulative urinary excretion of JBP485 in vivo and the uptake of JBP485 in kidney slices were decreased remarkably. RT-PCR and Western blot showed the decreased expression of Oat1 and Oat3, increased expression of Mrp2 in ANIT-induced rats, meanwhile, the expression levels of Mrp2 and Oat1 were up-regulated after administration of JBP485. The up-regulation of Mrp2 and Oat1 was associated with a concomitant increase in urinary BIL after treatment with JBP485 in ANIT-treated rats. The mechanism for JBP485 to restore liver function might be related to improvement of the expression and function for Oat1 and Mrp2 as well as facilitation of urinary excretion for hepatoxic substance.

Mammalian MATE (SLC47A) transport proteins: impact on efflux of endogenous substrates and xenobiotics

Multidrug and toxin extrusion proteins (MATEs; SLC47A) are mammalian transporters being predominately expressed in the brush-border membrane of proximal tubule epithelial cells in the kidney and the canalicular membrane of hepatocytes. Functionally, MATEs act as efflux transporters for organic compounds, thereby mediating the elimination process. Two isoforms, MATE1 and 2, have been identified, and, so far, only a limited number of substrates, including clinically used drugs such as metformin and cimetidine, are known. A knockout mouse model has been established, as well, and is a valuable tool for further systematic pharmacokinetic analyses. In this review, we summarize the progress in MATE research on structural, molecular, functional, and pathophysiological aspects. Consequences of genetic variants for pharmacokinetic alterations and drug therapy are discussed.

In vitro and in vivo evidence of the importance of organic anion transporters (OATs) in drug therapy

Organic anion transporters 1-10 (OAT1-10) and the urate transporter 1 (URAT1) belong to the SLC22A gene family and accept a huge variety of chemically unrelated endogenous and exogenous organic anions including many frequently described drugs. OAT1 and OAT3 are located in the basolateral membrane of renal proximal tubule cells and are responsible for drug uptake from the blood into the cells. OAT4 in the apical membrane of human proximal tubule cells is related to drug exit into the lumen and to uptake of estrone sulfate and urate from the lumen into the cell. URAT1 is the major urate-absorbing transporter in the apical membrane and is a target for uricosuric drugs. OAT10, also located in the luminal membrane, transports nicotinate with high affinity and interacts with drugs. Major extrarenal locations of OATs include the blood-brain barrier for OAT3, the placenta for OAT4, the nasal epithelium for OAT6, and the liver for OAT2 and OAT7. For all transporters we provide information on cloning, tissue distribution, factors influencing OAT abundance, interaction with endogenous compounds and different drug classes, drug/drug interactions and, if known, single nucleotide polymorphisms.

Elevated systemic elimination of cimetidine in rats with acute biliary obstruction: the role of renal organic cation transporter OCT2

Renal tubular secretion of cationic drugs is dominated by two classes of organic cation transporters, OCT2/SLC22A2 and MATE1/SLC47A1, localized to the basolateral and brush-border membranes of the renal tubular epithelial cells, respectively. However, little is known about the expression and function of these transporters in acute cholestasis. Systemic clearance of cimetidine was significantly higher in rats with bile duct ligation (BDL) for 24 hours than in sham-operated rats, with no significant changes in the volume of distribution between the groups. In addition, net tubular secretory clearance of cimetidine was significantly higher in the BDL rats compared with the sham rats, with no significant changes in the glomerular filtration rate. Moreover, the renal tissue-to-plasma concentration ratio of cimetidine was elevated in BDL rats, although the renal tissue-to-urine clearance ratio of cimetidine was not different between the two groups. The expression level of basolateral organic cation transporter rOCT2 protein in the kidney cortex was markedly higher in BDL rats than that in the sham rats, but that of H+/organic cation antiporter rMATE1 protein in the brush-border membranes was not significantly different between the two groups. These results demonstrate that the renal tubular secretion of cimetidine was increased by acute cholestasis, and this increase was attributable to elevated expression levels of rOCT2 but not of rMATE1 in the rat.

Organic anion transporters: discovery, pharmacology, regulation and roles in pathophysiology

Our understanding of the mechanisms behind inter- and intra-patient variability in drug response is inadequate. Advances in the cytochrome P450 drug metabolizing enzyme field have been remarkable, but those in the drug transporter field have trailed behind. Currently, however, interest in carrier-mediated disposition of pharmacotherapeutics is on a substantial uprise. This is exemplified by the 2006 FDA guidance statement directed to the pharmaceutical industry. The guidance recommended that industry ascertain whether novel drug entities interact with transporters. This suggestion likely stems from the observation that several novel cloned transporters contribute significantly to the disposition of various approved drugs. Many drugs bear anionic functional groups, and thus interact with organic anion transporters (OATs). Collectively, these transporters are nearly ubiquitously expressed in barrier epithelia. Moreover, several reports indicate that OATs are subject to diverse forms of regulation, much like drug metabolizing enzymes and receptors. Thus, critical to furthering our understanding of patient- and condition-specific responses to pharmacotherapy is the complete characterization of OAT interactions with drugs and regulatory factors. This review provides the reader with a comprehensive account of the function and substrate profile of cloned OATs. In addition, a major focus of this review is on the regulation of OATs including the impact of transcriptional and epigenetic factors, phosphorylation, hormones and gender.

The ectopic F(O)F(1) ATP synthase of rat liver is modulated in acute cholestasis by the inhibitor protein IF1

Rat liver plasma membranes contain F(O)F(1) complexes (ecto-F(O)F(1)) displaying a similar molecular weight to the mitochondrial F(O)F(1) ATP synthase, as evidenced by Blue Native PAGE. Their ATPase activity was stably reduced in short-term extra-hepatic cholestasis. Immunoblotting and immunoprecipitation analyses demonstrated that the reduction in activity was not due to a decreased expression of ecto-F(O)F(1) complexes, but to an increased level of an inhibitory protein, ecto-IF(1), bound to ecto-F(O)F(1). Since cholestasis down regulates the hepatic uptake of HDL-cholesterol, and ecto-F(O)F(1) has been shown to mediate SR-BI-independent hepatic uptake of HDL-cholesterol, these findings provide support to the hypothesis that ecto-F(O)F(1) contributes to the fine control of reverse cholesterol transport, in parallel with SR-BI. No activity change of the mitochondrial F(O)F(1) ATP synthase (m-F(O)F(1)), or any variation of its association with m-IF(1) was observed in cholestasis, indicating that ecto-IF(1) expression level is modulated independently from that of ecto-F(O)F(1), m-IF(1) and m-F(O)F(1).

Expression and function of Oat1 and Oat3 in rat kidney exposed to mercuric chloride

This study was designed to evaluate the expression and function of the organic anion transporters, Oat1 and Oat3, in rats exposed to a nephrotoxic dose of HgCl(2). Oat1 protein expression increased in renal homogenates and decreased in renal basolateral membranes from HgCl(2) rats, while Oat3 protein abundance decreased in both kidney homogenates and basolateral membranes. The lower protein levels of Oat1 and Oat3 in basolateral membranes explain the lower uptake capacity for p-aminohippurate (in vitro assays) and the diminution of the systemic clearance of this organic anion (in vivo studies) observed in treated rats. Since both transporters mediate mercury access to the renal cells, their down-regulation in basolateral membranes might be a defensive mechanism developed by the cell to protect itself against mercury injury. The pharmacological modulation of the expression and/or the function of Oat1 and Oat3 might be an effective therapeutic strategy for reducing the nephrotoxicity of mercury.

Characterization of the mechanisms involved in the increased renal elimination of bromosulfophthalein during cholestasis: involvement of Oatp1

The kidneys and liver are the major routes for organic anion elimination. We have recently shown that acute obstructive jaundice is associated with increased systemic and renal elimination of two organic anions, p-aminohippurate and furosemide, principally excreted through urine. This study examined probable adaptive mechanisms involved in renal elimination of bromosulfophthalein (BSP), a prototypical organic anion principally excreted in bile, in rats with acute obstructive jaundice. Male Wistar rats underwent bile duct ligation (BDL rats). Pair-fed sham-operated rats served as controls. BSP renal clearance was performed by conventional techniques. Renal organic anion-transporting polypeptide 1 (Oatp1) expression was evaluated by immunoblotting and IHC. Excreted, filtered, and secreted loads of BSP were all higher in BDL rats compared with Sham rats. The higher BSP filtered load resulted from the increase in plasma BSP concentration in BDL rats, because glomerular filtration rate showed no difference with the Sham group. The increase in the secreted load might be explained by the higher expression of Oatp1 observed in apical membranes from kidneys of BDL animals. This likely adaptation to hepatic injury, specifically in biliary components elimination, might explain, at least in part, the huge increase in BSP renal excretion observed in this experimental model.

Renal elimination of organic anions in cholestasis

The disposition of most drugs is highly dependent on specialized transporters. OAT1 and OAT3 are two organic anion transporters expressed in the basolateral membrane of renal proximal tubule cells, identified as contributors to xenobiotic and endogenous organic anion secretion. It is well known that cholestasis may cause renal damage. Impairment of kidney function produces modifications in the renal elimination of drugs. Recent studies have demonstrated that the renal abundance of OAT1 and OAT3 plays an important role in the renal elimination of organic anions in the presence of extrahepatic cholestasis. Time elapsed after obstructive cholestasis has an important impact on the regulation of both types of organic anion transporters. The renal expression of OAT1 and OAT3 should be taken into account in order to improve pharmacotherapeutic efficacy and to prevent drug toxicity during the onset of this hepatic disease.

Oat5 and NaDC1 protein abundance in kidney and urine after renal ischemic reperfusion injury

The aim of this study was to evaluate the abundance of the organic anion transporter 5 (Oat5) and the sodium-dicarboxylate cotransporter 1 (NaDC1) in kidney and urine after renal ischemic reperfusion injury. Renal injury was induced in male Wistar rats by occlusion of both renal pedicles for 0 (Group Sham), 5 (Group I5R60), or 60 (Group I60R60) min. The studies were performed after 60 min of reperfusion. The expression of Oat5 and NaDC1 was evaluated by IHC and Western blotting. Oat5 and NaDC1 abundance and alkaline phosphatase activity (AP) were assayed in urine. A decreased expression in renal homogenates and apical membranes and an increase in urinary excretion of Oat5 and NaDC1 were observed in I60R60 rats, as well as alterations of other widely used parameters for renal dysfunction and injury (plasma creatinine, urinary AP activity, kidney weight, histological lesions). In contrast, in the I5R60 group, only an increase in urinary excretion of Oat5 and mild histopathological damage was detected. This is the first study on Oat5 and NaDC1 detection in urine. These results suggest that urinary excretion of Oat5 might be an early indicator of renal dysfunction, which is useful for detection of even minor alterations in renal structural and functional integrity.

Adaptive responses of renal organic anion transporter 3 (OAT3) during cholestasis

During cholestasis, bile acids are mainly excreted into the urine, but adaptive renal responses to cholestasis, especially molecular mechanisms for renal secretion of bile acids, have not been well understood. Organic anion transporters (OAT1 and OAT3) are responsible for membrane transport of anionic compounds at the renal basolateral membranes. In the present study, we investigated the pathophysiological roles of OAT1 and OAT3 in terms of renal handling of bile acids. The Eisai hyperbilirubinemic rats (EHBR), mutant rats without multidrug resistance-associated protein 2, showed higher serum and urinary concentrations of bile acids, compared with Sprague-Dawley (SD) rats (wild type). The protein expression level of rat OAT3 was significantly increased in EHBR compared with SD rats, whereas the expression of rat OAT1 was unchanged. The transport activities of rat and human OAT3, but not OAT1, were markedly inhibited by various bile acids such as chenodeoxycholic acid and cholic acid. Cholic acid, glycocholic acid, and taurocholic acid, which mainly increased during cholestasis, are transported by OAT3. The plasma concentration of beta-lactam antibiotic cefotiam, a specific substrate for OAT3, was more increased in EHBR than in SD rats despite upregulation of OAT3 protein. This may be due to the competitive inhibition of cefotiam transport by bile acids via OAT3. In conclusion, the present study clearly demonstrated that OAT3 is responsible for renal secretion of bile acids during cholestasis and that the pharmacokinetic profile of OAT3 substrates may be affected by cholestasis.

Hepatocellular transport in acquired cholestasis: new insights into functional, regulatory and therapeutic aspects

The recent overwhelming advances in molecular and cell biology have added enormously to our understanding of the physiological processes involved in bile formation and, by extension, to our comprehension of the consequences of their alteration in cholestatic hepatopathies. The present review addresses in detail this new information by summarizing a number of recent experimental findings on the structural, functional and regulatory aspects of hepatocellular transporter function in acquired cholestasis. This comprises (i) a short overview of the physiological mechanisms of bile secretion, including the nature of the transporters involved and their role in bile formation; (ii) the changes induced by nuclear receptors and hepatocyte-enriched transcription factors in the constitutive expression of hepatocellular transporters in cholestasis, either explaining the primary biliary failure or resulting from a secondary adaptive response; (iii) the post-transcriptional changes in transporter function and localization in cholestasis, including a description of the subcellular structures putatively engaged in the endocytic internalization of canalicular transporters and the involvement of signalling cascades in this effect; and (iv) a discussion on how this new information has contributed to the understanding of the mechanism by which anticholestatic agents exert their beneficial effects, or the manner in which it has helped the design of new successful therapeutic approaches to cholestatic liver diseases.

Elimination of organic anions in response to an early stage of renal ischemia-reperfusion in the rat: role of basolateral plasma membrane transporters and cortical renal blood flow

BACKGROUND/AIMS

The knowledge of molecular mechanisms determining drug pharmacokinetics in pathological states is relevant for the development of new therapeutic approaches. This study was undertaken to evaluate the cortical renal blood flow (cRBF) and the renal protein expression of the organic anion transporters (OAT1 and OAT3) in association with the elimination of organic anions in an early stage of renal ischemia-reperfusion.

METHODS

Ischemic acute renal failure (ARF) was induced in adult male Wistar rats by occlusion of both renal pedicles during 60 min, followed by 60 min of reperfusion (ARF group). Pair-fed sham-operated rats served as controls. The renal protein expression of OAT1 and OAT3 was evaluated by immunohistochemistry techniques and by Western blotting in renal cortex homogenates and in basolateral plasma membranes. A pharmacokinetic study of p-aminohippurate (PAH, a prototypical organic anion) was performed. cRBF was determined using fluorescent microspheres.

RESULTS

ARF rats displayed a significant decrease in systemic clearance and in renal excretion of PAH. OAT1 and OAT3 protein abundance showed a statistically significant reduction both in homogenates and in basolateral plasma membranes from ARF rats. Immunohistochemical studies confirmed the changes in the cortical renal expression of these transporters. ARF animals also showed a decrease in cRBF.

CONCLUSIONS

The decrease in PAH elimination observed in an early stage of renal ischemia-reperfusion in male Wistar rats might be explained by the sum of the lower OAT1 and OAT3 expression in renal basolateral plasma membranes plus the decrease in cRBF. These findings might have significant implications in the development of novel pharmacological strategies to be applied in the initial stages of ischemic ARF.

Hepatocyte nuclear factor-4{alpha} regulates the human organic anion transporter 1 gene in the kidney

Human organic anion transporter 1 (OAT1, SLC22A6), which is localized to the basolateral membranes of renal tubular epithelial cells, plays a critical role in the excretion of anionic compounds. OAT1 is regulated by various pathophysiological conditions, but little is known about the molecular mechanisms regulating the expression of OAT1. In the present study, we investigated the transcriptional regulation of OAT1 and found that hepatocyte nuclear factor (HNF)-4alpha markedly transactivated the OAT1 promoter. A deletion analysis of the OAT1 promoter suggested that the regions spanning -1191 to -700 base pairs (bp) and -140 to -79 bp were essential for the transactivation by HNF-4alpha. These regions contained a direct repeat separated by two nucleotides (DR-2), which is one of the consensus sequences binding to HNF-4alpha, and an inverted repeat separated by eight nucleotides (IR-8), which was recently identified as a novel element for HNF-4alpha, respectively. An electrophoretic mobility shift assay showed that HNF-4alpha bound to DR-2 and IR-8 under the conditions of HNF-4alpha overexpression. Furthermore, under normal conditions, HNF-4alpha bound to IR-8, and a mutation in IR-8 markedly reduced the OAT1 promoter activity, indicating that HNF-4alpha regulates the basal transcription of OAT1 via IR-8. This paper reports the first characterization of the human OAT1 promoter and the first gene in the kidney whose promoter activity is regulated by HNF-4alpha.

Adaptive response to increased bile acids: induction of MDR1 gene expression and P-glycoprotein activity in renal epithelial cells

Cholestatic liver disease and increased serum bile acid concentrations are known to trigger various adaptive responses including the induction of hepatic, intestinal and renal bile acid transport proteins, but renal P-glycoprotein (Pgp, multidrug resistance protein 1, MDR1) remained uninvestigated in this context. We show that treatment of Madin Darby canine kidney (MDCK) cells with pathophysiologically relevant concentrations of chenodeoxycholic acid (CDCA; 100 microM) for 12 h induces MDR1 transcript levels in vitro more than twofold. CDCA and deoxycholic acid pre-treatment for 24-96 h (100 microM) also increased Pgp activity measured as rhodamine efflux, while cholic acid and taurocholic acid were not effective in concentrations up to 600 microM. CDCA pre-treatment (100 microM, 72 h) also resulted in a doubling of rhodamine123 secretion across an epithelium-like monolayer grown on Transwell filters and decreased the sensitivity towards the kidney toxic drugs cyclosporine A and paclitaxel. These findings predict physiologically as well as pharmacologically relevant consequences of liver disease for Pgp substrate transport and toxicity in the kidneys.

Organic anion transporter family: current knowledge

Organic anion transporters (OATs) play an essential role in the elimination of numerous endogenous and exogenous organic anions from the body. The renal OATs contribute to the excretion of many drugs and their metabolites that are important in clinical medicine. Several families of multispecific organic anion and cation transporters, including OAT family transporters, have recently been identified by molecular cloning. The OAT family consists of six isoforms (OAT1 - 4, URAT1, and rodent Oat5) and they are all expressed in the kidney, while some are also expressed in the liver, brain, and placenta. The OAT family represents mainly the renal secretory and reabsorptive pathway for organic anions and is also involved in the distribution of organic anions in the body, drug-drug interactions, and toxicity of anionic substances such as nephrotoxic drugs and uremic toxins. In this review, current knowledge of and recent progress in the understanding of several aspects of OAT family members are discussed.

Renal elimination of p-aminohippurate (PAH) in response to three days of biliary obstruction in the rat. The role of OAT1 and OAT3

Pharmacokinetic studies of the drugs administered to subjects with mechanical cholestasis are scarce. The purpose of the present study was to examine the effects of bile duct ligation of 3 days (peak of elevation of serum bile acids and bilirubin) on the systemic and renal PAH clearance and on the expression of cortical renal OAT1 and OAT3 in a rat model. PAH is the prototypical substrate of the renal organic anion transport system. Male Wistar rats underwent a bile duct ligation (BDL rats). Pair-fed sham-operated rats served as controls. BDL rats displayed a significantly lower systemic PAH clearance. Renal studies revealed a reduction in the renal clearance and in the excreted and secreted load of PAH in BDL rats. The OAT1 protein expression in kidney homogenates was not modified, but it decreased in the basolateral membranes from BDL rats. In contrast, OAT3 abundance in both kidney cortex homogenates and in basolateral membranes increased by 3 days after the ligation. Immunocytochemical studies (light microscopic and confocal immunofluorescence microscopic analyses) confirmed the changes in the renal expression of these transport proteins. The present study demonstrates the key role of OAT1 expression in the impaired elimination of PAH after 3 days of obstructive cholestasis.