Function and expression of ATP-binding cassette transporters in cultured human Y79 retinoblastoma cells

The aim of this study was to reveal the expression and function of P-glycoprotein and multidrug resistance-associated proteins (MRP), members of the ATP-binding cassette (ABC) superfamily of drug transporters, in cultured human Y79 retinoblastoma cells. ABC transporter mRNA expression was evaluated by conventional reverse transcription-polymerase chain reaction (RT-PCR) and real-time PCR analyses. Cellular accumulation of rhodamine 123 (P-glycoprotein substrate), calcein (MRP substrate), and doxorubicin (P-glycoprotein/MRP substrate) was analyzed by fluorometry. Conventional RT-PCR analysis showed the expression of multidrug resistance 1 (MDR1), MRP1, MRP2 and lung resistance-related protein (LRP) mRNAs. Real-time RT-PCR analysis revealed that the expression levels of the MDR1 and MRP2 genes in Y79 cells were much lower than those in human intestinal cell line Caco-2, while the expression level of MRP1 was higher than that in Caco-2 cells. The accumulation of rhodamine 123 was not enhanced by verapamil or reversin 205, inhibitors of P-glycoprotein, indicating no function of P-glycoprotein in Y79 cells. The accumulation of calcein was significantly increased by various MRP inhibitors including probenecid, indicating that MRP functions in Y79 cells. The accumulation of doxorubicin was increased in the presence of metabolic inhibitors (10 mM 2-deoxyglucose and 5 mM sodium azide). However, most MRP inhibitors such as probenecid and indomethacin did not affect doxorubicin accumulation, while cyclosporin A and taclorimus significantly increased doxorubicin accumulation. These results suggest that MRP, but not P-glycoprotein, functions in Y79 cells, and that the efflux of doxorubicin from Y79 cells may be due to an ATP-dependent transporter, which has not been identified yet.

Effect of Thai plant extracts on P-glycoprotein function and viability in paclitaxel-resistant HepG2 cells

The effects of ethanol extracts from Thai plants on P-glycoprotein (P-gp) function and cell viability were examined using paclitaxel-resistant HepG2 (PR-HepG2) cells. KP018 from Ellipeiopsis cherrevensis and AT80 from Ancistrocladus tectorius increased both rhodamine 123, a typical P-gp substrate, and [(3)H]paclitaxel uptake in PR-HepG2 cells. However, some extracts such as MT80 from Microcos tomentosa increased rhodamine 123, but not [(3)H]paclitaxel, uptake, while MM80 from Micromelum minutum increased only [(3)H]paclitaxel uptake. Thus, the effects of extracts of Thai plants on rhodamine 123 uptake were not necessarily the same as those on [(3)H]paclitaxel uptake. Purified compounds such as bergapten did not affect the uptake of either substrate. KP018, AT80, and MM80 increased [(3)H]paclitaxel uptake and decreased the cell viability in a concentration-dependent manner. Among these extracts, KP018 showed the most potent cytotoxicity. The cytotoxic potency of KP018 on PR-HepG2 cells was similar to that on wild-type HepG2 cells, and was not potentiated by verapamil. At concentrations resulting in no cytotoxicity, AT80 and MM80 potentiated paclitaxel-induced cytotoxicity in PR-HepG2 cells. These results indicate that K018 may be a useful source to search for a new anticancer drug, while AT80 and MM80 may be useful as modulators of P-gp-mediated multidrug resistance in cancer cells.

Role of intestinal efflux transporters in the intestinal absorption of methotrexate in rats

The role of intestinal efflux transporters such as P-glycoprotein (P-gp), breast cancer resistance protein (BCRP) and multidrug resistance-associated proteins (MRPs) in intestinal absorption of methotrexate was examined in rats. In everted intestine, the mucosal efflux of methotrexate after application to serosal side was higher in jejunum than ileum, and the efflux in jejunum was suppressed by pantoprazole, a BCRP inhibitor, and probenecid, an MRP inhibitor, but not by verapamil, a P-gp inhibitor. The mucosal methotrexate efflux in ileum was suppressed by pantoprazole, but not by other inhibitors. On the other hand, the serosal efflux of methotrexate after application to mucosal side was greater in ileum than jejunum, and was suppressed by probenecid. In in-vivo rat studies, the intestinal absorption of methotrexate was significantly higher when methotrexate was administered to ileum than jejunum. Pantoprazole increased methotrexate absorption from jejunum and ileum. Probenecid increased the absorption of methotrexate from jejunum but decreased the absorption from ileum, as evaluated by peak plasma methotrexate levels. In conclusion, BCRP and MRPs are involved in the regional difference in absorption of methotrexate along the intestine, depending on their expression sites.

Site-specific bidirectional efflux of 2,4-dinitrophenyl-S-glutathione, a substrate of multidrug resistance-associated proteins, in rat intestine and Caco-2 cells

The site-specific function of multidrug-resistance-associated proteins (MRPs), especially MRP2 and MRP3, was examined in rat intestine and human colon adenocarcinoma (Caco-2) cells. The MRP function was evaluated pharmacokinetically by measuring the efflux transport of 2,4-dinitrophenyl-S-glutathione (DNP-SG), an MRP substrate, after application of 1-chloro-2,4-dinitrobenzene (CDNB), a precursor of DNP-SG. The expression of rat and human MRP2 and MRP3 was analysed by Western blotting. The rat jejunum exhibited a higher apical MRP2 and a lower basolateral MRP3 expression than ileum. In accordance with the expression level, DNP-SG efflux to the mucosal surface was significantly greater in jejunum, while serosal efflux was greater in ileum. Site-specific bidirectional efflux of DNP-SG was also observed in in-vivo studies, in which portal and femoral plasma levels and biliary excretion rate of DNP-SG were significantly higher when CDNB was administered to ileum. Caco-2 cells also showed a bidirectional efflux of DNP-SG. Probenecid, an MRP inhibitor, significantly suppressed the mucosal efflux in jejunum and serosal efflux in ileum. In contrast, probenecid significantly suppressed both apical and basolateral efflux of DNP-SG in Caco-2 cells, though the inhibition was of small magnitude. In conclusion, the efflux of DNP-SG from enterocytes mediated by MRPs exhibited a significant regional difference in rat intestine, indicating possible variability in intestinal bioavailabilities of MRP substrates, depending on their absorption sites along the intestine.

Modulation of intestinal transport of 2,4-dinitrophenyl-S-glutathione, a multidrug resistance-associated protein 2 substrate, by bilirubin treatment in rats

The effect of bilirubin treatment on intestinal transport of 2,4-dinitrophenyl-S-glutathione (DNP-SG), a substrate of multidrug resistance-associated protein 2 (MRP2), after application of 1-chloro-2, 4-dinitrobenzene (CDNB), a precursor of DNP-SG, was examined in rat intestine by the in-vitro everted sac, in-situ re-circulating perfusion, and in-situ loop methods. CDNB was taken up rapidly by jejunum and ileum, and the consequent intestinal efflux of DNP-SG, a glutathione conjugated metabolite of CDNB, was significantly higher in jejunum than in ileum in the in-situ and in-vitro studies. Co-administration of bilirubin (100 μM), as well as probenecid (1 mM) or ciclosporin (100 μM), with CDNB decreased the DNP-SG efflux in jejunum significantly, but not in ileum. The suppression of DNP-SG efflux in jejunum was also observed after intravenous administration of bilirubin (85.5 μmol kg−1), in which plasma bilirubin glucuronide levels were approximately 100 μM. In the in-vitro metabolism study, bilirubin exerted no significant effect on CDNB metabolism in the intestinal S9 fraction (supernatant of 9000 g). These results suggested that the diseased states accompanied with hyperbilirubinaemia might have increased the intestinal absorption, or oral bioavailability, of MRP2 substrates by suppressing MRP2 function at the proximal intestinal region.

Nanoparticulation of poorly water soluble drugs using a wet-mill process and physicochemical properties of the nanopowders

In order to improve the dissolution and oral absorption properties of poorly water soluble drugs such as omeprazole, albendazole and danazol, various dispersing agents were added to prepare nanopowder formulations using an ULTRA APEX MILL, which is a wet-mill instrument, and their physicochemical properties were evaluated. Using Pluronic F-108 or F-68 as dispersing agents, slurries containing drug particles having nanometer size were obtained for all model drugs tested. Omeprazole, a heat labile drug, was not degraded by wet-milling and the omeprazole nanoparticles in a milled slurry did not aggregate for 24 h after wet-milling. After lyophilization of these milled slurries containing drug nanoparticles, fine solid white nanopowders were obtained. Scanning electron microscopy (SEM) suggested that the model drugs were milled into nanometer size. X-ray powder diffraction (XRPD) patterns and Differential Scanning Calorimetry (DSC) curves confirmed that all milled drug nanopowders were crystalline, although milling of albendazole nanopowder transformed it to another crystal form. Wet-milling using an ULTRA APEX MILL offers a highly effective approach to produce stable drug nanopowders and is a very useful tool for bioavailability enhancement of poorly water soluble and heat labile drugs.

Low-affinity transport of FITC-albumin in alveolar type II epithelial cell line RLE-6TN

FITC-albumin uptake by cultured alveolar type II epithelial cells, RLE-6TN, is mediated by high- and low-affinity transport systems. In this study, characteristics of the low-affinity transport system were evaluated. The uptake of FITC-albumin was time and temperature dependent and was inhibited by metabolic inhibitors and bafilomycin A1. Confocal laser scanning microscopic analysis showed punctate localization of the fluorescence in the cells, which was partly localized in lysosomes. FITC-albumin taken up by the cells gradually degraded over time, as shown by fluoroimage analyzer after SDS-PAGE. The uptake of FITC-albumin by RLE-6TN cells was not inhibited by caveolae-mediated endocytosis inhibitors such as nystatin, but was inhibited by clathrin-mediated endocytosis inhibitors such as phenylarsine oxide. The uptake was also inhibited by potassium depletion and hypertonicity, conditions known to inhibit clathrin-mediated endocytosis. In addition, macropinocytosis inhibitors such as 5-(N-ethyl-N-isopropyl) amiloride inhibited the uptake. These results indicate that the low-affinity transport of FITC-albumin in RLE-6TN cells is at least in part mediated by clathrin-mediated endocytosis, but not by caveolae-mediated endocytosis. Possible involvement of macropinocytosis was also suggested.

Transport of prostaglandin E1 across rat erythrocyte membrane

In this study erythrocyte transport of prostaglandin E1 (PGE1) was investigated by employing inside-out membrane vesicles prepared from rat erythrocytes. The uptake of [3H]PGE1 in the presence of ATP was significantly higher than that of AMP, suggesting the involvement of an ATP-dependent efflux system in PGE1 transport across the erythrocyte membrane. Coincubation of glutathione with ATP further stimulated the uptake of [3H]PGE1. The uptake of [3H]PGE1 in the presence of ATP and glutathione was temperature-sensitive, and various eicosanoids including PGE2 and PGF2alpha decreased the uptake. Multidrug resistance-associated protein (MRP) 4 substrates/inhibitors including methotrexate, indomethacin, taurocholic acid and indocyanine green significantly inhibited [3H]PGE1 uptake. Western blot analysis revealed that Mrp4 is expressed in rat erythrocyte membrane. These results suggest that the release of PGE1 from the erythrocyte into the blood circulation may be mediated by ATP-dependent efflux pump(s) such as Mrp4.

Comparison of Albumin Uptake in Rat Alveolar Type II and Type I-like Epithelial Cells in Primary Culture

PURPOSE

To elucidate and compare the activity and mechanism of albumin uptake in primary cultured alveolar type II and type I-like epithelial cells.

MATERIALS AND METHODS

Type II epithelial cells isolated from rat lungs were cultured for 2 days at 5 x 10(6) cells/35-mm dish or for 6 days at 2 x 10(6) cells/35-mm dish. The mRNA expression of marker genes and FITC-albumin uptake were examined.

RESULTS

The cells cultured for 2 days exhibited cuboidal type II epithelial morphology with lamellar bodies inside the cells, while the cells cultured for 6 days exhibited squamous type I epithelial morphology. These morphological characteristics were consistent with the changes in mRNA expression pattern of marker genes. FITC-albumin uptake in both cells was temperature-dependent and was inhibited by metabolic inhibitors and bafilomycin A1. The rate of uptake was much higher in type II cells than type I-like cells. In both cells, FITC-albumin uptake was inhibited by clathrin mediated-endocytosis inhibitors, but not by caveolae mediated-endocytosis inhibitors.

CONCLUSIONS

These findings indicate that albumin in alveolar lining fluid is internalized into type II and type I epithelial cells via clathrin-mediated endocytosis, and the rate of albumin uptake is higher in type II cells than type I cells.

Modulation of function of multidrug resistance associated-proteins by Kaempferia parviflora extracts and their components

In this study, the effects of extracts and flavone derivatives from the rhizome of Kaempferia parviflora on multidrug resistance associated-proteins (MRP)-mediated transport in A549 cells were examined. The cells employed express MRP1 and MRP2, but not P-glycoprotein. The cellular accumulation of calcein, an MRP substrate, was significantly increased by various MRP inhibitors without being affected by verapamil, a typical P-glycoprotein inhibitor. Ethanol and aqueous extracts from K. parviflora rhizome increased the accumulation of calcein and doxorubicin in A549 cells in a concentration-dependent manner. The inhibitory potency of the ethanol extract for MRP function was greater than that of the aqueous extract. Among six flavone derivatives isolated from K. parviflora rhizome, 5,7-dimethoxyflavone exhibited a maximal stimulatory effect on the accumulation of doxorubicin in A549 cells. The accumulation of doxorubicin was increased by four flavone derivatives without 5-hydroxy group, but not by the other two flavone derivatives with 5-hydroxy group. In addition, 5,7-dimethoxyflavone and 3,5,7,3',4'-pentamethoxyflavone decreased resistance to doxorubicin in A549 cells. These findings indicate that extracts and flavone derivatives from the rhizome of K. parviflora suppress MRP function, and therefore may be useful as modulators of multidrug resistance in cancer cells.

Effects of Kaempferia parviflora extracts and their flavone constituents on P-glycoprotein function

The purpose of this study was to examine the effects of extracts and flavone derivatives from the rhizome of Kaempferia parviflora on P-glycoprotein (P-gp)-mediated transport in LLC-GA5-COL150, a transfectant cell line of a porcine kidney epithelial cell line LLC-PK1 with human MDR1 cDNA. Ethanol extract obtained from Kaempferia parviflora rhizome significantly increased the accumulation of rhodamine 123 and daunorubicin, P-gp substrates, in LLC-GA5-COL150 cells, but not in LLC-PK1 cells. The aqueous extract also increased the accumulation in LLC-GA5-COL150 cells with lower potency than the ethanol extract. The effects of flavone derivatives isolated from the rhizome of Kaempferia parviflora on P-gp function were examined. Among six flavones tested, 3,5,7,3',4'-pentamethoxyflavone most potently increased the accumulation of rhodamine 123 and daunorubicin in LLC-GA5-COL150 cells in a concentration-dependent manner. In addition, 5,7-dimethoxyflavone to lesser degree increased rhodamine 123 accumulation in LLC-GA5-COL150 cells. In contrast, the other four flavone derivatives had no significant effect on the accumulation of rhodamine 123 in LLC-GA5-COL150 cells in a concentration range tested. These results indicate that extracts and flavone derivatives from the rhizome of Kaempferia parviflora can inhibit P-gp function, which may be useful for overcoming P-gp-mediated multidrug resistance and improving the oral bioavailability of anticancer agents.

Characterization of prostaglandin E1 transport in rat renal brush-border membrane

Transport of prostaglandin E(1) (PGE(1)) was investigated in rat renal brush-border membrane vesicles. The uptake of [(3)H]PGE(1) was sensitive to osmosis and temperature. This uptake was saturable and mediated by high-affinity (K(m)=2.1 microM)/low-capacity (V(max)=17.4 pmol/mg protein/30 sec) and low-affinity (K(m)=526.5 microM)/high-capacity (V(max)=1,032.5 pmol/mg protein/30 sec) transport systems. [(3)H]PGE(1) uptake was Na(+)-independent and inhibited by various eicosanoids including PGE(2) and PGF(2alpha). Bromcresol green and sulfobromophthalein, potent inhibitors of prostaglandin transporter (PGT), significantly decreased [(3)H]PGE(1) uptake. Uptake was also inhibited by indomethacin and probenecid, which reportedly have little effect on PGT. Benzylpenicillin and taurocholate decreased the uptake of [(3)H]PGE(1). Like p-[(14)C]aminohippurate (PAH) uptake by vesicles, the uptake of [(3)H]PGE(1) was stimulated by an inside-positive membrane potential, created by applying an inward K(+) gradient and valinomycin. However, the uptake of [(3)H]PGE(1) was not inhibited by PAH, suggesting that PAH and PGE(1) are transported by separate transport systems. [(3)H]PGE(1) uptake was not stimulated by outwardly directed gradients of Cl(-) nor unlabeled PGE(1), indicating that an anion exchanger may not be involved in PGE(1) transport. These findings suggest that the transport of PGE(1) in rat renal brush-border membrane is mediated by specific transport system(s), at least in part, by a potential-sensitive transport system.

Function of multidrug resistance-associated protein 2 in acute hepatic failure rats

The function of multidrug resistance-associated protein 2 (Mrp2) in the intestine and liver, as well as intestinal Mrp2 expression, was analyzed in CCl(4)-induced acute hepatic failure rats with hyperbilirubinemia. The plasma level of bilirubin glucuronides, endogenous Mrp2-substrates, was 26 microM at 24 h after CCl(4) treatment. Mrp2 protein levels in jejunum decreased to 41% of control level. Mrp2-mediated efflux of 2,4-dinitrophenyl-S-glutathione (DNP-GSH), an Mrp2-substrate, in jejunum decreased to 31% of control in vitro, and was almost completely suppressed in vivo to the same level as that in the presence of probenecid, an Mrp2-inhibitor. Biliary excretion of DNP-GSH was suppressed to the same level as that inhibited by intravenous probenecid. The suppression of Mrp2 and the increased plasma bilirubin glucuronides recovered within 24 h thereafter. These results suggest that hyperbilirubinemia in disease states may be related to the systemic suppression of Mrp2 function.

Interaction of valproic acid and carbapenem antibiotics with multidrug resistance-associated proteins in rat erythrocyte membranes

We recently reported that the decrease in plasma valproic acid (VPA) level by carbapenem antibiotics (CPs) may partly be due to the increased erythrocyte distribution of VPA. In order to clarify the mechanisms underlying altered VPA distribution in erythrocytes, we examined the role of multidrug resistance-associated proteins (Mrps). The uptake of 2,4-dinitrophenyl-S-glutathione (DNP-SG), a substrate of Mrps, by inside-out vesicles (IOVs) prepared from rat erythrocytes was an ATP-dependent, active process. DNP-SG uptake was mediated by high- and low-affinity transport systems, and was inhibited by various Mrp inhibitors such as probenecid and indomethacin. Glutathione stimulated only the high-affinity transport system. VPA inhibited the low-affinity transport of DNP-SG, while panipenem, a CP, inhibited both high- and low-affinity transport. ATP-dependent, Mrp-mediated transport of methotrexate, another Mrp substrate, in IOVs was also observed, and VPA and various CPs inhibited the transport. The uptake of [(3)H]VPA was examined, and found to be ATP-dependent. ATP-dependent uptake of [(3)H]VPA was inhibited by Mrp inhibitors and panipenem, while the inhibition was not observed in the absence of ATP. These results indicate that VPA and CPs interact with Mrp-mediated transport in erythrocyte membranes, and VPA itself is transported by Mrps, which is inhibited by panipenem. Thus, the increased erythrocyte distribution of VPA by CPs observed under in vivo conditions may partly be explained by their interaction with Mrps in erythrocyte membranes.