Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.6.3.44 (P-glycoprotein)
13,344 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. Human intestinal epithelial Caco-2 cells were used to investigate the mechanistic basis of transepithelial secretion of the fluoroquinolone antibiotic ciprofloxacin. 2. Net secretion and cellular uptake of ciprofloxacin (at 0.1 mM) were not subject to competitive inhibition by sulphate, thiosulphate, oxalate, succinate and para-amino hippurate, probenecid (10 mM), taurocholate (100 microM) or bromosulphophthalein (100 microM). Similarly tetraethylammonium and N-'methylnicotinamide (10 mM) were without effect. 3. Net secretion of ciprofloxacin was inhibited by the organic exchange inhibitor 4,4'-diisothiocyanostilbene-2-2'-disulphonic acid (DIDS, 400 microM). 4. Net secretion of ciprofloxacin was partially inhibited by 100 microM verapamil, whilst net secretion of the P-glycoprotein substrate vinblastine was totally abolished under these conditions. Ciprofloxacin secretion was unaltered after preincubation of cells with two anti-P-glycoprotein antibodies (UIC2 and MRK16), which both significantly reduced secretory vinblastine flux (measured in the same cell batch). Ciprofloxacin (3 mM) failed to inhibit vinblastine net secretin in Caco-2 epithelia, and was not itself secreted by the P-glycoprotein expressing and vinblastine secreting dog kidney cell line, MDCK. 5. Net secretion and cellular uptake of ciprofloxacin (at 0.1 mM) were not subject to alterations of either cytosolic or medium pH, or dependent on the presence of medium Na+, Cl- or K+ in the bathing media. 6. The substrate specificity of the ciprofloxacin secretory transport in Caco-2 epithelia is distinct from both the renal organic anion and cation transport. A role for P-glycoprotein in ciprofloxacin secretion may also be excluded. A novel transport mechanism, sensitive to both DIDS and verapamil mediates secretion of ciprofloxacin by human intestinal Caco-2 epithelia.
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PMID:Fluoroquinolone (ciprofloxacin) secretion by human intestinal epithelial (Caco-2) cells. 928 89

P-glycoprotein (Mdr1p) is an ATP-dependent drug efflux pump that is overexpressed in multidrug-resistant cells and some cancers. Mdr1p is also expressed in normal tissues like the kidney, where it can mediate transepithelial drug transport. A human urinary compound that reverses multidrug resistance and blocks [3H]azidopine photolabeling of P-glycoprotein was purified to homogeneity and identified by 1H-NMR and mass spectrometry as the synthetic surfactant nonylphenol ethoxylate (NPE). Multidrug-resistant Chinese hamster ovary (CHO) C5 cells accumulated less [3H]NPE than parental drug-sensitive Aux-B1 cells, and Mdr1p substrates, verapamil and cyclosporin A, increased this surfactant's accumulation in C5 cells. NPE blocked the net transepithelial transport (basolateral to apical) of [3H]cyclosporin A in epithelia formed by Madin-Darby canine kidney (MDCK) cells. Net transepithelial transport (basal to apical) of [3H]NPE was demonstrated in MDCK cells and was inhibited by cyclosporin A. These findings show NPE is a Mdr1p substrate excreted into urine by kidney P-glycoprotein. NPE is a widely used surfactant and a known hormone disrupter that is readily absorbed orally or topically. The current findings indicate the function of kidney Mdr1p may be to eliminate exogenous compounds from the body.
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PMID:Identification of the synthetic surfactant nonylphenol ethoxylate: a P-glycoprotein substrate in human urine. 984 6

1. In the kidney, a number of transport proteins involved in the secretion of permanently charged organic cations have recently been cloned. To evaluate the possible similarities between intestine and kidney in the handling of organic cations we investigated the transport of 1-methyl-4-phenylpyridinium (MPP+) across monolayers of intestinal Caco-2 cells. MPP+ is a prototypic substrate of the cloned organic cation transporters hOCT1 and hOCT2. 2. In Caco-2 cell monolayers, the basolateral to apical flux of MPP+ was significantly greater than the apical to basolateral flux, consistent with net secretion of MPP+. 3. Net secretion of MPP+ was abolished by addition of either 10 microM cyclosporin A or 100 microM verapamil to the apical membrane. In contrast, secretion of MPP+ was unaffected by addition of either TEA (2 mM) or decynium-22 (2 microM) to either apical or basolateral membranes. These results suggest that MPP+ secretion is mediated primarily by P-glycoprotein located at the apical membrane. We found no evidence of a role for hOCT1 or hOCT2 in the secretion of MPP+. 4. In addition to net secretion of MPP+, we found evidence of a Na(+)-dependent MPP+ uptake mechanism at the apical membrane of Caco-2 cells. 5. Na(+)-dependent MPP+ uptake was sensitive to inhibition by the organic cations; decynium-22 (2 microM), TEA (2 mM) and cimetidine (5 mM) but not by carnitine, guanidine or proline. 6. These results suggest that net secretion of MPP+ across the apical membrane of Caco-2 cells is a function of the relative contributions of MPP+ secretion mediated by P-glycoprotein and MPP+ absorption mediated by a novel Na(+)-dependent transport mechanism.
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PMID:Characterization of MPP+ secretion across human intestinal Caco-2 cell monolayers: role of P-glycoprotein and a novel Na(+)-dependent organic cation transport mechanism. 1071 63

The effect of P-glycoprotein inhibition on the uptake of the HIV type 1 protease inhibitor saquinavir into brain capillary endothelial cells was studied using porcine primary brain capillary endothelial cell monolayers as an in vitro test system. As confirmed by polymerase chain reaction and Western blot analysis, this system functionally expressed class I P-glycoprotein (pgp1A). P-Glycoprotein isoforms pgp1B or pgp1D could not be detected. The uptake of saquinavir into endothelial cells could be described as the result of a diffusional term of uptake and an oppositely directed saturable extrusion process. Net uptake of saquinavir into cultured brain endothelial cells could be increased significantly up to 2-fold by SDZ PSC 833 in a dose-dependent manner, with an IC(50) of 1.13 microM. In addition, the HIV protease inhibitor ritonavir inhibited p-glycoprotein-mediated extrusion of saquinavir with an IC(50) of 0.2 microM, indicating a high affinity of ritonavir for p-glycoprotein. In conclusion, we showed that the HIV protease inhibitor ritonavir is a more potent inhibitor of P-glycoprotein than the multidrug resistance (MDR)-reversing agent SDZ PSC 833. The inclusion of this drug in combination regimens may greatly facilitate brain uptake of HIV protease inhibitors, which is especially important in patients suffering from AIDS dementia complex.
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PMID:HIV protease inhibitor ritonavir: a more potent inhibitor of P-glycoprotein than the cyclosporine analog SDZ PSC 833. 1123 Aug 2

The objective of this work was to study the role of regional intestinal efflux activity of P-glycoprotein (Pgp) in situ in anesthetized rats in limiting the absorption of digoxin. A 10-cm portion of duodenum or jejunum, or 5-cm of colon was perfused single-pass with saline containing [(3)H]digoxin while the appearance of radioactivity in the blood was measured. Verapamil in the perfusate was used as a modulator of Pgp in the intestinal mucosa. Net water absorption, mucosal integrity, and intestinal motility of the isolated segment were monitored, as well as heart rate and blood pressure. Excretion of i.v. administered unlabelled digoxin, 1 mg/kg, into the intestine while perfusing the duodenum-proximal jejunum region, was studied for comparison. At a perfusate concentration of 1 mM, verapamil caused a dramatic increase in [(3)H]digoxin absorption rate from duodenum and jejunum, while the effect in colon was insignificant. At concentrations of 0.1, 1, and 2.5 mM in the duodenal perfusate, verapamil increased the absorption rate of [(3)H]digoxin in a dose-dependent manner. The lowest concentration almost doubled the rate without having any significant effects on the cardiovascular system, intestinal motility, or net absorption of water. The excretion rate of unlabelled digoxin from the blood into the gut lumen was found to be halved in the presence of 0.5 mM verapamil in the perfusate. Absorption rate of [(3)H]digoxin in the rat is likely limited by Pgp-mediated efflux. The data indicate that Pgp plays an important role for digoxin efflux in the small intestine only.
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PMID:The role of P-glycoprotein in limiting intestinal regional absorption of digoxin in rats. 1145 46

Steroid resistance is a major problem in the management of patients with inflammatory bowel disease. In Crohn disease, poor response to corticosteroids has been related to increased expression of the drug efflux pump, P-glycoprotein. However, it has not been investigated thoroughly whether corticosteroids commonly used for drug therapy in inflammatory bowel disease are substrates of P-glycoprotein. We tested the hypothesis that budesonide and prednisone are substrates of P-glycoprotein thereby possibly contributing to variable therapeutic effects. Polarized, basal to apical transport of [3H]budesonide and [3H]prednisone was studied in monolayers of L-MDR1 cells (LLC-PK1 cells stably transfected with human MDR1 cDNA) and Caco-2 cells, both of which express P-glycoprotein in their apical membrane. Drug transport was measured during 4 hours at substrate concentrations of 5 microM. Net transport rates and permeability coefficients were calculated. Inhibition of P-glycoprotein-mediated transport across Caco-2 monolayers was determined after addition of the P-glycoprotein inhibitor PSC-833. The net transport rate from the basolateral to the apical side was significantly higher in L-MDR1 than in LLC-PK1 cells for both budesonide and prednisone. Apparent permeability coefficients of budesonide and prednisone reflected polarized transport from basal to apical. PSC-833 inhibited the polarized transport of both corticosteroids. In conclusion, budesonide and prednisone were identified as substrates of the intestinal drug efflux pump, P-glycoprotein. Therefore, drug secretion via P-glyco-protein into gut lumen might play a more important role in pharmacokinetics and pharmacodynamics of these corticosteroids than currently appreciated in gastroenterological practice.
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PMID:Identification of budesonide and prednisone as substrates of the intestinal drug efflux pump P-glycoprotein. 1547 18

Intestinal induction of Pgp is known to limit the oral availability of certain drug compounds and give rise to detrimental drug-drug interactions. We have investigated the induction of P-glycoprotein (Pgp; MDR1) activity in a human intestinal epithelial cell line (T84) following pre-exposure to a panel of drug compounds, reported to be Pgp substrates, inhibitors or inducers. Human MDR1-transfected MDCKII epithelial monolayers were used to assess Pgp substrate interactions and inhibition of digoxin secretion by the selected drug compounds. The T84 cell line was used to assess induction of Pgp-mediated digoxin secretion following pre-exposure to the same compounds. Changes in gene expression (MDR1, MRP2, PXR and CAR) were determined by quantitative RT-PCR. Net transepithelial digoxin secretion was increased (1.3 fold, n=6, P<0.05) following pre-exposure to the PXR activator hyperforin (100nM, 72h), as was MDR1 mRNA expression (3.0 fold, n=4, P<0.05). A number of Pgp substrates (quinidine, amprenavir, irinotecan, topotecan, atorvastatin and erythromycin) induced net digoxin secretion, as did the non-Pgp substrate artemisinin. Various non-Pgp substrates demonstrated inhibition of digoxin secretion (verapamil, mifepristone, clotrimazole, mevastatin, diltiazem and isradipine) but did not induce Pgp-mediated digoxin secretion. Of the compounds that increased Pgp secretion, quinidine, topotecan, atorvastatin and amprenavir pre-exposure also elevated MDR1 mRNA levels, whereas erythromycin, irinotecan and artemisinin displayed no change in transcript levels. This indicates possible post-translational regulation of digoxin secretion. Finally, a strong correlation between drug modulation of MRP2 and PXR mRNA expression levels was evident.
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PMID:Induction of P-glycoprotein expression and function in human intestinal epithelial cells (T84). 1870 21

The aims of this study were to carry out a thorough quality control setup for essential Caco-2 cell characteristics in P-glycoprotein (P-gp) inhibition studies and to explore if Aloe vera juice (AVJ) inhibits the bidirectional transport of the P-gp substrate digoxin (30 nm). Seven AVJ concentrations (0.00001-1.0 mg/mL), anticipated to cover a clinically relevant range, were tested and digoxin apparent permeability coefficients (Papp), net Papp values (Papp(Net)) and net flux values (J(Net)) were calculated. Relevant validation parameters for P-gp inhibition studies in Caco-2 cells are suggested to include, as a minimum, an assay linearity test with and without a known P-gp inhibitor, cell cytotoxicity testing (MTT-test) for substrates and inhibitors, and cell integrity testing by TEER and mannitol transport measurements. The question is also raised whether a minimum effect of a reference P-gp inhibitor as verapamil should be demanded. Cell cytotoxicity was seen for digoxin at concentrations >or=3 microM and for AVJ at 10 mg/mL. AVJ did not inhibit the P-gp transport of digoxin in any of the concentrations tested. This indicates that AVJ is no inhibitor of the P-gp mediated transport of digoxin in vitro if AVJ is present in clinically relevant concentrations.
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PMID:Caco-2 cell methodology and inhibition of the P-glycoprotein transport of digoxin by Aloe vera juice. 1900 53

Cellular accumulation and intracellular distribution of the anthracycline epirubicin (EPI) were studied by flow cytometry and confocal laser scan microscopy in resistant (HB8065/R) and sensitive (HB8065/S) human hepatoma cells. Using peroxidase immunohistochemistry HB8065/R cells were shown to express the multidrug efflux transporter P-glycoprotein (Pgp). Net drug accumulation was detectable in both cell types within seconds of treatment, and the intracellular drug level increased to a plateau after 15 min in HB8065/R cells and after 90 min to a 4.2 times higher level in HB8065/S cells. A 50% growth inhibition (GI50) was obtained in HB8065/R cells with 46 times as high EPI dose as in HB8065/S cells. Verapamil (VPL) increased the cellular accumulation of EPI and decreased the growth inhibition in HB8065/R cells. The cellular pharmacokinetics and cytotoxicity of EPI in HB8065/R cells reflect the increased levels of Pgp compared to HB8065/S cells.
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PMID:Pharmacokinetics and cytotoxicity of epirubicin (epi) in drug-resistant human hepatoma-cells (hb8065). 2156 42

Lilly Laboratories cell porcine kidney 1 (LLC-PK1) cells transfected with human P-glycoprotein (LLC-PK1-P-gp) are widely used in transport assays to identify drug candidates that function as substrates of this efflux transporter. Endogenous transporters expressed in LLC-PK1 cells may complicate the interpretation of findings from P-gp-mediated transport assays. We investigated the impact of porcine breast cancer resistance protein (Bcrp) in P-gp-mediated transport assays in LLC-PK1 cells. Porcine Bcrp mRNA was detected in both LLC-PK1 wildtype (WT) and LLC-PK1-P-gp cells by quantitative RT-PCR. To investigate the activity and impact of porcine Bcrp, we conducted transport assays using 6 typical BCRP substrates in LLC-PK1 cells. Efflux ratios (ER) of the 6 BCRP substrates in LLC-PK1 WT cells were >2, and were reduced in the presence of the BCRP inhibitor Ko143. The efflux activities of the 6 BCRP substrates were confirmed using MDCKII cells transfected with human BCRP. Net ERs of prazosin and fluvastatin, dual substrates of P-gp and BCRP, determined by dividing ERs in LLC-PK1-P-gp cells by those in LLC-PK1 WT cells, were <2, but increased to >2 in the presence of Ko143. These results indicated that endogenous Bcrp in LLC-PK1 cells was involved in the transport of BCRP substrates and may interfere with the identification of P-gp substrates.
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PMID:The Impact of Endogenous Breast Cancer Resistance Protein on Human P-Glycoprotein-Mediated Transport Assays Using LLC-PK1 Cells Transfected With Human P-Glycoprotein. 3033 64


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