Cisplatin induces renal expression of P-glycoprotein and canalicular multispecific organic anion transporter

Acquired ABC-transporter overexpression in cancer cells: transcriptional induction or Darwinian selection?

Acquired multidrug resistance (MDR) in tumor diseases has repeatedly been associated with overexpression of ATP-binding cassette transporters (ABC-transporters) such as P-glycoprotein. Both in vitro and in vivo data suggest that these efflux transporters can cause MDR, albeit its actual relevance for clinical chemotherapy unresponsiveness remains uncertain. The overexpression can experimentally be achieved by exposure of tumor cells to cytotoxic drugs. For simplification, the drug-mediated transporter overexpression can be attributed to two opposite mechanisms: First, increased transcription of ABC-transporter genes mediated by nuclear receptors sensing the respective compound. Second, Darwinian selection of sub-clones intrinsically overexpressing drug transporters being capable of extruding the respective drug. To date, there is no definite data indicating which mechanism truly applies or whether there are circumstances promoting either mode of action. This review summarizes experimental evidence for both theories, suggests an algorithm discriminating between these two modes, and finally points out future experimental approaches of research to answer this basic question in cancer pharmacology.

Mutant p53 promotes RCP-dependent chemoresistance coinciding with increased delivery of P-glycoprotein to the plasma membrane

TP53 is the most frequently mutated gene in cancers. Mutations lead to loss of p53 expression or expression of a mutant protein. Mutant p53 proteins commonly lose wild-type function, but can also acquire novel functions in promoting metastasis and chemoresistance. Previously, we uncovered a role for Rab-coupling protein (RCP) in mutant p53-dependent invasion. RCP promotes endosomal recycling and signalling of integrins and receptor tyrosine kinases. In a screen to identify novel RCP-interacting proteins, we discovered P-glycoprotein (P-gp). Thus, we hypothesised that mutant p53 could promote chemoresistance through RCP-dependent recycling of P-gp. The interaction between RCP and P-gp was verified endogenously and loss of RCP or mutant p53 rendered cells more sensitive to cisplatin and etoposide. In mutant p53 cells we detected an RCP-dependent delivery of P-gp to the plasma membrane upon drug treatment and decreased retention of P-gp substrates. A co-localisation of P-gp and RCP was seen in mutant p53 cells, but not in p53-null cells upon chemotherapeutic exposure. In conclusion, mutant p53 expression enhanced co-localisation of P-gp and RCP to allow for rapid delivery of P-gp to the plasma membrane and increased resistance to chemotherapeutics.

P-Glycoprotein/ABCB1 Might Contribute to Morphine/Cisplatin-Induced Hepatotoxicity in Rats

To investigate combined effect of the anticancer drug cisplatin (CP) and the opiate analgesic morphine (MOR) on liver, rats were administered MOR (10 mg/kg/day i.p. for 10 days), with or without CP (7.5 mg/kg i.p. once at day 5 of the study). MOR or CP alone caused deterioration of liver function tests and induced damage to histological architecture of liver. In addition, each drug alone caused hepatic oxidative stress, as evident by significant increase of malondialdehyde and nitric oxide, as well as the significant decrease in GSH, catalase and SOD compared to control. Administration of either MOR or CP also caused liver inflammation, evident by the increase in the pro-inflammatory cytokines; TNF-α and IL-6. In addition, either MOR or CP induced liver apoptosis, as shown by significant increase in expression of the pro-apoptotic marker; caspase 3 compared to control. Either MOR or CP also caused up-regulation of the efflux transporter P-glycoprotein (P-gp). Combining MOR with CP caused deterioration in all parameters tested compared to CP alone. Thus, treatment with MOR worsened CP-induced hepatotoxicity through oxidative stress, inflammation and apoptosis mechanisms. In addition, both drugs contributed to the up-regulation of P-gp, which might be a new mechanism for their hepatotoxic effects.

Renal tubular P-glycoprotein expression is reduced in plasma cell disorders

Background

P-glycoprotein (P-gp) transports many chemicals that vary greatly in their structure and function. It is normally expressed in renal proximal tubular cells. We hypothesized that P-gp expression influences light chain excretion. Therefore, we investigated whether renal tubular P-gp expression is altered in patients with plasma cell disorders.

Methods

We evaluated renal biopsy specimens from patients with plasma cell disorders (n = 16) and primary focal segmental glomerulosclerosis (the control group, n = 17). Biopsies were stained with an anti-P-gp antibody. Loss of P-gp expression was determined semi-quantitatively. Groups were compared for loss of P-gp expression, and clinical variables.

Results

P-gp expression loss was more severe in patients with plasma cell disorders than it was in those with glomerulonephritis (P = 0.021). In contrast, clinical and histological parameters including serum creatinine, level of urinary protein excretion, and interstitial fibrosis/tubular atrophy grade were not significantly different between the groups. P-gp expression loss increased with age in patients with plasma cell disorders (P = 0.071). This expression loss was not associated with serum creatinine, the level of urinary protein excretion or the interstitial fibrosis/tubular atrophy grade. There was no significant association between the severity of P-gp expression loss with the types and serum levels of light chains, isotypes and serum immunoglobulin levels.

Conclusion

Renal tubular P-gp expression is significantly down-regulated in patients with plasma cell disorders characterized by nephrotic range proteinuria. Additional studies are needed to determine whether reintroduction of renal tubular P-gp expression would mitigate the proximal tubular injury that is caused by free-light chains.

Mitochondria P-glycoprotein confers paclitaxel resistance on ovarian cancer cells

Background: Subcellular expression of P-glycoprotein (P-gp) may play an essential role in multidrug resistance (MDR) in many cancers. However, the mitochondria expression and functional activity of P-gp in ovarian cancer are still unclear. In this study, we isolated mitochondria from A2780 cell line and its paclitaxel-resistant subline A2780T and investigated the expression and function of mitochondria P-gp. Methods: Immunocytochemistry was used to evaluate P-gp expression and subcellular localization in cancer cells. Immunofluorescence and laser confocal microscopy were used to detect the co-localization of P-gp and mitochondria both in ovarian cancer tissues and in cell lines. Western blotting (WB), transmission electron microscopy and JC-1 kit were used to evaluate the purity, integrity and activity of the isolated mitochondria. P-gp expression in the whole cell and the isolated mitochondria was evaluated by WB. Flow cytometry was used to evaluate the efflux function of mitochondria P-gp. Results: P-gp expression was detected at the membrane, cytoplasm and nuclei of the A2780T cells, but not in the A2780 cells. Co-localization of P-gp and mitochondria was observed in the A2780T cell line and ovarian cancer tissues, but not in A2780 cells. The purity, integration and activity of the isolated mitochondria are high. P-gp was highly expressed in the A2780T cells and the isolated mitochondria, but was not found in A2780 cells. Rho123 efflux rate was significantly increased in isolated A2780T mitochondria compared to those in A2780 (43.2% vs 9.6%), but it was partly reversed by cyclosporin A (CsA, a P-gp inhibitor). Conclusion: P-gp is highly expressed in mitochondria of taxol-resistant ovarian cancer cells and ovarian cancer tissues and mediates the drug efflux, which probably protect cancer cells from chemotherapy.

Targeted inhibitors of P-glycoprotein increase chemotherapeutic-induced mortality of multidrug resistant tumor cells

Overexpression of ATP-binding cassette (ABC) transporters is often linked to multidrug resistance (MDR) in cancer chemotherapies. P-glycoprotein (P-gp) is one of the best studied drug transporters associated with MDR. There are currently no approved drugs available for clinical use in cancer chemotherapies to reverse MDR by inhibiting P-glycoprotein. Using computational studies, we previously identified several compounds that inhibit P-gp by targeting its nucleotide binding domain and avoiding its drug binding domains. Several of these compounds showed successful MDR reversal when tested on a drug resistant prostate cancer cell line. Using conventional two-dimensional cell culture of MDR ovarian and prostate cancer cells and three dimensional prostate cancer microtumor spheroids, we demonstrated here that co-administration with chemotherapeutics significantly decreased cell viability and survival as well as cell motility. The P-gp inhibitors were not observed to be toxic on their own. The inhibitors increased cellular retention of chemotherapeutics and reporter compounds known to be transport substrates of P-gp. We also showed that these compounds are not transport substrates of P-gp and that two of the three inhibit P-gp, but not the closely related ABC transporter, ABCG2/BCRP. The results presented suggest that these P-gp inhibitors may be promising leads for future drug development.

Different modalities of intercellular membrane exchanges mediate cell-to-cell p-glycoprotein transfers in MCF-7 breast cancer cells

Multi-drug resistance (MDR) is a phenomenon by which tumor cells exhibit resistance to a variety of chemically unrelated chemotherapeutic drugs. The classical form of multidrug resistance is connected to overexpression of membrane P-glycoprotein (P-gp), which acts as an energy dependent drug efflux pump. P-glycoprotein expression is known to be controlled by genetic and epigenetic mechanisms. Until now processes of P-gp gene up-regulation and resistant cell selection were considered sufficient to explain the emergence of MDR phenotype within a cell population. Recently, however, "non-genetic" acquisitions of MDR by cell-to-cell P-gp transfers have been pointed out. In the present study we show that intercellular transfers of functional P-gp occur by two different but complementary modalities through donor-recipient cells interactions in the absence of drug selection pressure. P-glycoprotein and drug efflux activity transfers were followed over 7 days by confocal microscopy and flow cytometry in drug-sensitive parental MCF-7 breast cancer cells co-cultured with P-gp overexpressing resistant variants. An early process of remote transfer was established based on the release and binding of P-gp-containing microparticles. Microparticle-mediated transfers were detected after only 4 h of incubation. We also identify an alternative mode of transfer by contact, consisting of cell-to-cell P-gp trafficking by tunneling nanotubes bridging neighboring cells. Our findings supply new mechanistic evidences for the extragenetic emergence of MDR in cancer cells and indicate that new treatment strategies designed to overcome MDR may include inhibition of both microparticles and Tunneling nanotube-mediated intercellular P-gp transfers.

MDR1 and ERCC1 expression predict outcome of patients with locally advanced bladder cancer receiving adjuvant chemotherapy

PURPOSE

The role of adjuvant chemotherapy in patients with locally advanced bladder cancer still remains to be defined. We hypothesized that assessing the gene expression of the chemotherapy response modifiers multidrug resistance gene 1 (MDR1) and excision repair cross-complementing 1 (ERCC1) may help identify the group of patients benefiting from cisplatin-based adjuvant chemotherapy.

EXPERIMENTAL DESIGN

Formalin-fixed paraffin-embedded tumor samples from 108 patients with locally advanced bladder cancer, who had been enrolled in AUO-AB05/95, a phase 3 trial randomizing a maximum of three courses of adjuvant cisplatin and methotrexate (CM) versus methotrexate, vinblastine, epirubicin, and cisplatin (M-VEC), were included in the study. Tumor cells were retrieved by laser-captured microdissection and analyzed for MDR1 and ERCC1 expression using a quantitative real-time reverse transcription-polymerase chain reaction assay. Gene expression levels were correlated with clinical outcomes by multivariate Cox proportional hazards regression analysis.

RESULTS

Expressions of MDR1 and ERCC1 were independently associated with overall progression-free survival (P = .001, relative risk = 2.9 and P = .01, relative risk = 2.24, respectively). The correlation of high MDR1 expression with inferior outcome was stronger in patients receiving M-VEC, whereas ERCC1 analysis performed equally in the CM and M-VEC groups.

CONCLUSIONS

High MDR1 and ERCC1 gene expressions are associated with inferior outcome after cisplatin-based adjuvant chemotherapy for locally advanced bladder cancer. Prospective studies are warranted to define a role for MDR1 and ERCC1 analysis in individualizing multimodality treatment in locally advanced bladder cancer.

Regulation of hepatic ABCC transporters by xenobiotics and in disease states

The subfamily of ABCC transporters consists of 13 members in mammals, including the multidrug resistance-associated proteins (MRPs), sulfonylurea receptors (SURs), and the cystic fibrosis transmembrane conductance regulator (CFTR). These proteins play roles in chemical detoxification, disposition, and normal cell physiology. ABCC transporters are expressed differentially in the liver and are regulated at the transcription and translation level. Their expression and function are also controlled by post-translational modification and membrane-trafficking events. These processes are tightly regulated. Information about alterations in the expression of hepatobiliary ABCC transporters could provide important insights into the pathogenesis of diseases and disposition of xenobiotics. In this review, we describe the regulation of hepatic ABCC transporters in humans and rodents by a variety of xenobiotics, under disease states and in genetically modified animal models deficient in transcription factors, transporters, and cell-signaling molecules.

Role of glutathione in the regulation of Cisplatin resistance in cancer chemotherapy

Three mechanisms have been proposed for the role of glutathione (GSH) in regulating cisplatin (CDDP) sensitivities that affects its ultimate cell-killing ability: (i) GSH may serve as a cofactor in facilitating multidrug resistance protein 2- (MRP2-) mediated CDDP efflux in mammalian cells, since MRP2-transfected cells were shown to confer CDDP resistance; (ii) GSH may serve as a redox-regulating cytoprotector based on the observations that many CDDP-resistant cells overexpress GSH and γ-glutamylcysteine synthesis (γ-GCS), the rate-limiting enzyme for GSH biosynthesis; (iii) GSH may function as a copper (Cu) chelator. Elevated GSH expression depletes the cellular bioavailable Cu pool, resulting in upregulation of the high-affinity Cu transporter (hCtr1) which is also a CDDP transporter. This has been demonstrated that overexpression of GSH by transfection with γ-GCS conferred sensitization to CDDP toxicity. This review describes how these three models were developed and critically reviews their importance to overall CDDP cytotoxicity in cancer cell treatments.

A mathematical feasibility argument for the use of aptamers in chemotherapy and imaging

A challenge for drug design is to create molecules with optimal functions that also partition efficiently into the appropriate in vivo compartment(s). This is particularly true in cancer treatments because cancer cells upregulate their expression of multidrug resistance transporters, which necessitates a higher concentration of extracellular drug to promote sufficiently high intracellular concentrations for cell killing. Pharmacokinetics can be improved by ancillary molecules, such as cyclodextrins, that increase the effective concentrations of hydrophobic drugs in the blood by providing hydrophobic binding pockets. However, the extent to which the extracellular concentration of drug can be increased is limited. A second approach, different from the 'push' mechanism just discussed, is a 'pull' mechanism by which the effective intracellular concentrations of a drug is increased by a molecule with an affinity for the drug that is located inside the cell. Here we propose and give a proof in principle that intracellular RNA aptamers might perform this function. The mathematical model considers the following: Suppose I denotes a drug (inhibitor) that must be distributed spatially throughout a cell, but that tends to remain outside the cell due the transport properties of the cell membrane. Suppose that E, an enzyme that binds to I, is expressed by the cell and remains in the cell. It may be that the equilibrium E+I[right arrow over left arrow]{k(-1)k(1)}P is not sufficiently far enough to the right to drive enough free inhibitor into the cell to completely inhibit the enzyme. Here we evaluate the use of an intracellular aptamer with affinity for the inhibitor (I) to increase the efficiency of inhibitor transport across the cell membrane and thus drive the above equilibrium further to the right than would ordinarily be the case. We show that this outcome will occur if: (1) the aptamer neither binds too tightly nor too weakly to the inhibitor than the enzyme and (2) the aptamer is much more diffusible in the cell cytoplasm than the enzyme. Thus, we propose and show by simulation that an intracellular aptamer can be enlisted for an integrated approach to increasing inhibitor effectiveness and imaging aptamer-expressing cells.

Renal xenobiotic transporters are differentially expressed in mice following cisplatin treatment

The goal of this study was to identify alterations in mRNA and protein expression of various xenobiotic transport proteins in mouse kidney during cisplatin-induced acute renal failure. For this purpose, male C57BL/6J mice received a single dose of cisplatin (18 mg/kg, i.p.) or vehicle. Four days later, tissues were collected for assessment of plasma BUN, histopathological analysis of renal lesions, and mRNA and Western blot analysis of renal transporters including organic anion and cation transporters (Oat, Oct), organic anion transporting polypeptides (Oatp), multidrug resistance-associated proteins (Mrp), multidrug resistance proteins (Mdr), breast cancer resistance protein (Bcrp) and multidrug and toxin extrusion proteins (Mate). Cisplatin treatment caused necrosis of renal proximal tubules along with elevated plasma BUN and renal kidney injury molecule-1 mRNA expression. Cisplatin-induced renal injury increased mRNA and protein levels of the efflux transporters Mrp2, Mrp4, Mrp5, Mdr1a and Mdr1b. Uptake transporters Oatp2a1 and Oatp2b1 mRNA were also up-regulated following cisplatin. By contrast, expression of Oat1, Oat2, Oct2 and Oatp1a1 mRNA was reduced in cisplatin-treated mice. Expression of several uptake and efflux transporters was unchanged in cisplatin-treated mice. Apical staining of Mrp2 and Mrp4 proteins was enhanced in proximal tubules from cisplatin-treated mice. Collectively, these expression patterns suggest coordinated regulation of uptake and efflux pathways during cisplatin-induced renal injury. Reduced expression of basolateral and apical uptake transporters along with enhanced transcription of export transporters likely represents an adaptation to lower intracellular accumulation of chemicals, prevent their reabsorption and enhance urinary clearance.

P-glycoprotein induction and tumor cell-kill dynamics in response to differential doxorubicin dosing strategies: a theoretical pharmacodynamic model

PURPOSE

The objectives of this work were 1) to develop a theoretical pharmacodynamic model that captures dynamic changes resulting from drug/therapy mediated P-glycoprotein (P-gp) induction and 2) to compare the pharmacodynamic outcomes of several doxorubicin (DOX) dosing schemes through simulations.

METHODS

We developed a theoretical model that included a pharmacokinetic (PK) model for intracellular DOX-mediated P-gp induction and a pharmacodynamic (PD) model using a threshold trigger function for tumor cell-kill. In this model, both the level of P-gp induction and rate of tumor cell death were modulated by intracellular DOX concentration. Most model parameters were obtained from literature sources, and a few were either fixed or reasonably estimated.

RESULTS

Comparative dosing simulations showed that a 10-week constant infusion in which a tumor cell population was continuously exposed to the drug did not produce the best PD profile. On the other hand, dosing schemes where the cell population was initially challenged with a high dose, followed by intermittent dosing, generated the best PD profile. The favorable outcome of the latter dosing schemes was correlated with the lowest expression of P-gp in terms of area under the curve (AUC) during treatment period.

CONCLUSIONS

The simulations led us to conclude that drug resistance, particularly resistance caused by P-gp overexpression, induced during chemotherapy may, in part, be circumvented by designing optimal dosing strategies that minimize P-gp induction.

Restored expression and activity of organic ion transporters rOAT1, rOAT3 and rOCT2 after hyperuricemia in the rat kidney

We previously reported that in hyperuricemic rats, renal impairment occurred and organic ion transport activity decreased, accompanied with a specific decrease in the expression of rat organic anion transporters, rOAT1 and rOAT3, and organic cation transporter, rOCT2. In the present study, we investigated the reversibility of the organic ion transport activity and expression of organic ion transporters (slc22a) during recovery from hyperuricemia. Hyperuricemia was induced by the administration of a chow containing uric acid and oxonic acid, an inhibitor of uric acid metabolism. Four days after discontinuance of the chow, the plasma uric acid concentration returned to the normal level, and renal functions such as creatinine clearance and BUN levels were restored, although the recovery of tubulointerstitial injury was varied in sites of the kidney. Basolateral uptake of p-aminohippurate (PAH) and tetraethylammonium (TEA), and both protein and mRNA levels of rOAT1, rOAT3 and rOCT2 in the kidney gradually improved during 14 days of recovery from hyperuricemia. Basolateral PAH transport showed a higher correlation with the protein level of rOAT1 (r(2)=0.80) than rOAT3 (r(2)=0.34), whereas basolateral TEA transport showed a strong correlation with rOCT2 protein (r(2)=0.91). The plasma testosterone concentration, which is a dominant factor in the regulation of rOCT2, was gradually restored during the recovery from hyperuricemia, but the correlation between the plasma testosterone level and rOCT2 protein expression in the kidney was not significant. These results suggest that the regulation of organic ion transporters, rOAT1, rOAT3 and rOCT2, by hyperuricemia is reversible, and the organic ion transport activity restores according to the expression levels of these transporters.

Induction of proteins involved in multidrug resistance (P-glycoprotein, MRP1, MRP2, LRP) and of CYP 3A4 by rifampicin in LLC-PK1 cells

P-glycoprotein, multidrug resistance-related proteins (MRPs) and lung resistance-related protein (LRP) are involved in multidrug resistance in tumor cells but are also expressed in normal tissues. In the LLC-PK(1) tubular renal cell line, a 15-day treatment with 25 microM rifampicin significantly increased the mRNA levels of P-glycoprotein, MRP1, MRP2, LRP and cytochrome P450 3A4 (CYP 3A4). Western blot analysis confirmed a moderate increase in the expression of P-glycoprotein and MRP2, but not MRP1 also at the protein level. The intracellular uptake of doxorubicin was significantly lower in rifampicin pretreated cells. A pretreatment with 6-[82S,4R,6E)-4-methyl-2-(methylamino)-3-oxo-6-octenoic acid]cyclosporin D, valspodar (PSC 833), a specific inhibitor of P-glycoprotein, with (3-(3-(2-(7-chloro-2-quinidinyl)ethenyl-phenyl)((3-diimethyl amino-3oxo propyl)thio)methyl)thio)propanoic acid, sodium salt (MK-571), a specific inhibitor of MRP1, and with verapamil, that inhibits both proteins, significantly increased doxorubicin cell accumulation in rifampicin pretread cells. In rifampicin treated cells cultured on porous membranes, doxorubicin showed a polarized transport, that was reduced by a pretreatment with PSC 833. A chronic treatment with rifampicin induces the expression of transport proteins and of CYP 3A4 and could therefore alter the renal elimination kinetics of drugs that are their substrates.

Decreased activity of basolateral organic ion transports in hyperuricemic rat kidney: roles of organic ion transporters, rOAT1, rOAT3 and rOCT2

We investigated organic anion and cation transport activity and the expression of several organic ion transporters in hyperuricemic rat kidney. Feeding oxonic acid, an inhibitor of uric acid metabolism, and uric acid for 10 days significantly increased plasma uric acid level. Plasma creatinine and blood urea nitrogen concentrations also increased in hyperuricemic rats, indicating impaired renal function. The accumulation of organic anions, p-aminohippurate (PAH) and methotrexate, and cations, tetraethylammonium (TEA) and cimetidine, into renal slices was markedly decreased, suggesting decreased transport activity for organic anions and cations at the basolateral membrane in the kidney. The expression levels of basolateral organic anion transporters rOAT1 and rOAT3, and organic cation transporter, rOCT2, significantly decreased in hyperuricemic rat kidney as assessed by mRNA and protein levels. In contrast, the expression of rOCT1 was unaltered by hyperuricemia at both mRNA and protein levels. Moreover, the mRNA expression of kidney-specific organic anion transporters, OAT-K1 and OAT-K2, and organic anion transporting polypeptide (oatp) 1, which localize at the brush-border membrane in the kidney, was unchanged in hyperuricemic rats. In conclusion, we showed decreased basolateral organic anion and cation transport activity, accompanied by a specific decrease in rOAT1, rOAT3 and rOCT2 expression in hyperuricemic rat kidney. These phenomena partly contribute to the changed renal disposition of organic anions and cations in hyperuricemia.

Molecular aspects of renal anionic drug transport

Multiple organic anion transporters in the proximal tubule of the kidney are involved in the secretion of drugs, toxic compounds, and their metabolites. Many of these compounds are potentially hazardous on accumulation, and it is therefore not surprising that the proximal tubule is also an important target for toxicity. In the past few years, considerable progress has been made in the cloning of these transporters and their functional characterization following heterologous expression. Members of the organic anion transporter (OAT), organic anion transporting polypeptide (OATP), multidrug resistance protein (MRP), sodium-phosphate transporter (NPT), and peptide transporter (PEPT) families have been identified in the kidney. In this review, we summarize our current knowledge on their localization, molecular and functional characteristics, and substrate and inhibitor specificity. A major challenge for the future will be to understand how these transporters work in concert to accomplish the renal secretion of specific anionic substrates.

Increased renal expression of bilirubin glucuronide transporters in a rat model of obstructive jaundice

Regulation of bilirubin glucuronide transporters during hyperbilirubinemia in hepatic and extrahepatic tissues is not completely clear. In the present study, we evaluated the regulation of the bilirubin glucuronide transporters, multidrug resistance-associated proteins (MRP)2 and 3, in rats with obstructive jaundice. Bile duct ligation (BDL) or sham operation was performed in Wistar rats. Liver and kidneys were removed 1, 3, and 5 days after BDL (n = 4, in each group). Serum and urine were collected to measure bilirubin levels just before animal killing. MRP2 And MRP3 mRNA expressions were determined by real-time RT-PCR. Protein expression of MRP2 and MRP3 was determined by Western blotting. Renal MRP2 function was evaluated by para-aminohippurate (PAH) clearance. The effect of conjugated bilirubin, unconjugated bilirubin, human bile, and sulfate-conjugated bile acid on MRP2 gene expression was also evaluated in renal and hepatocyte cell lines. Serum bilirubin and urinary bilirubin excretion increased significantly after BDL. In the liver, the mRNA expression of MRP2 decreased 59, 86, and 82%, and its protein expression decreased 25, 74, and 93% compared with sham-operated animals after 24, 72, and 120 h of BDL, respectively. In contrast, the liver expression of MRP3 mRNA increased 138, 2,137, and 3,295%, and its protein expression increased 560, 634, and 612% compared with sham-operated animals after 24, 72, and 120 h of BDL, respectively. On the other hand, in the kidneys, the mRNA expression of MRP2 increased 162, 73, and 21%, and its protein expression increased 387, 558, and 472% compared with sham-operated animals after 24, 72, and 120 h of BDL, respectively. PAH clearance was significantly increased after BDL. The mRNA expression of MRP2 increased in renal proximal tubular epithelial cells after treatment with conjugated bilirubin, sulfate-conjugated bile acid or human bile. Upregulation of MRP2 in the kidneys and MRP3 in the liver may be a compensatory mechanism to improve bilirubin clearance during obstructive jaundice.

Two apical multidrug transporters, P-gp and MRP2, are differently altered in chronic renal failure

Tubular function is altered in chronic renal failure (CRF). Whether drug secretion by renal tubules is modified in CRF is questioned because of frequent accumulation of various toxins in CRF. This function mainly involves ATP-dependent drug transporters, particularly P-glycoprotein (P-gp) and multidrug resistance-associated protein (MRP) 2, both present in apical membrane of epithelial cells. The present study was aimed at determining the changes in P-gp and MRP2 expression induced by experimental CRF in kidney and liver. The relationship between MRP2 and glutathione metabolism changes was examined because MRP2 transports GSSG and glutathione conjugates. Rats underwent either 80% subtotal nephrectomy (Nx) or sham operation, and determinations were performed 3 and 6 wk later. CRF induced a 70--200% rise in protein and mRNA expression of MRP2 after 3 and 6 wk post-Nx in remnant kidney and after 6 wk in liver. However, P-gp expression was unchanged by CRF. Relative to whole kidney mass, total MRP2 levels decreased by only 27% in Nx rats whereas total P-gp levels were reduced by 60%. Renal GSSG and total glutathione levels were increased by 30% in Nx rats, but glutathione-S-transferase (GST) activity was normal; liver GSSG levels and GST activity were reduced in Nx rats. In conclusion, CRF resulted in specific overexpression of MRP2 in kidney and liver. This could be an adaptative response to some elevated circulating toxins. The later MRP2 induction and different glutathione changes in liver compared with kidney suggest different mechanisms for MRP2 induction and/or action in these two tissues.