Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.6.3.44 (P-glycoprotein)
 13,344 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

P-glycoprotein (Pgp) is a trans-membraneous protein that is associated with multidrug resistance (MDR) in human cancer, including hepatocellular carcinomas and leukemias. There is no consensus regarding methods of choice for analysis of Pgp expression, and development of reliable analytical methods is now essential. We have studied the the Pgp expression in human hepatoma and leukemia cell lines using flow cytometry. The aim of the study was to compare binding properties of anti-Pgp antibodies reacting with surface (MRK16, UIC2) and cytoplasmic (C219, JSB-1) epitopes to assess which antibody performed best with respect to fluorescence discrimination. By histogram subtraction the fractions of resistant human hepatoma cells positive for Pgp were 99% (MRK16), 97% (UIC2), 77% (JSB-1), and 51% (C219), demonstrating variations in antibody reactivity. The resolution in detecting decreasing levels of Pgp in hepatoma cells was superior for the externally binding antibodies, showing that there is a correlation between antibody reactivity and fluorescence discrimination. Similar results were obtained for parental and resistant KG1a human leukemia cell lines. The Pgp epitopes remained reactive to the anti-Pgp MAbs after methanol fixation and cryopreservation. By dual parameter flow cytometry it was shown that Pgp expression in viable cells may be assessed together with uptake of epirubicin, which was low in cells expressing high levels of Pgp and vice versa. In conclusion, all tested antibodies proved useful for flow cytometric detection of high levels of Pgp, but the externally binding ones were superior in detection of low and variable levels of Pgp.
 ...
PMID:Binding diversity of antibodies against external and internal epitopes of the multidrug resistance gene product P-glycoprotein. 758 8

P-glycoprotein (P-gp) is a transmembrane glycoprotein responsible for the multidrug resistant (MDR) phenotype in various cancer cells. It has been shown that P-gp transports various kinds of anti-cancer agents as well as hydrophobic chemicals. Although P-gp is also expressed in normal human tissues, such as liver, kidney, and adrenal gland, its function and transporting substrates in these tissues are still unknown. In previous work, we demonstrated that some compounds in human plasma modulate the transporting activity of P-gp. We also found that P-gp is expressed at a high level in the bovine adrenal gland and that this tissue contains large amount of compounds which inhibit the transporting activity of P-gp. We purified such compounds from the adrenal gland by monitoring the ability to enhance the accumulation of [3H]vincristine in MDR cells. Two major compounds were purified and identified as progesterone and pregnenolone by nuclear magnetic resonance (NMR) analysis. Progesterone was the most potent and abundant compound that inhibited the transporting activity of P-gp among the compounds extracted from bovine adrenal gland with methanol. We also found that six authentic progesterone metabolites in the 5 beta-metabolic pathway but none in the 5 alpha-metabolic pathway were able to enhance the accumulation of [3H]vincristine in MDR cells and to inhibit [3H]azidopine photolabeling of P-gp in the adrenal gland. These results indicate that some progesterone metabolites can interact with P-gp and that stereoisomerism around carbon 5 of the progesterone metabolites is important for them to be recognized by P-gp.
 ...
PMID:Progesterone and its metabolites: the potent inhibitors of the transporting activity of P-glycoprotein in the adrenal gland. 790 38

The clinical relevance of multidrug resistance (MDR)-related proteins in childhood acute lymphoblastic leukemia (ALL) is largely unknown. The diversity of techniques, fixation methods, storage of cells (fresh or cryopreserved) etc, may contribute to discrepancies observed between several studies. We therefore optimized the detection of P-glycoprotein (P-gp), MDR-associated protein (MRP) and lung resistance-related protein (LRP) by immunocytochemistry and flow cytometry in childhood ALL cells. Thirteen fixation methods were compared using six antibodies in both immunocytochemistry and flow cytometry. The optimal fixation for P-gp (C219, MRK16), MRP (MRPr1) and LRP (LRP56) was a mixture of 2% (v/v) formaldehyde solution and acetone incubated for only 10 s at room temperature (FAc). For MRP recognized by MRPm6, the optimal fixation condition was acetone for 5 min at room temperature in immunocytochemistry, and methanol for 15 min at -20 degrees C in flow cytometry. P-gp staining by 4E3 was strongly antibody batch-dependent; on cytospins FAc fixation was optimal, but inconclusive data were obtained by flow cytometry. The optimized fixation conditions on fresh samples revealed a day-to-day variation in staining (both increasing and decreasing) in one third of the immunocytochemical tests. In flow cytometry the day-to-day variation in the fluorescence index was -1 +/- 22%. In both techniques, staining was comparable between fresh and cryopreserved cells. We recommend the use of the above mentioned fixation methods in order to study the clinical relevance of P-gp, MRP and LRP in childhood ALL.
 ...
PMID:Optimal immunocytochemical and flow cytometric detection of P-gp, MRP and LRP in childhood acute lymphoblastic leukemia. 920 95

The presence in orange juice of compounds that specifically inhibit the P-glycoprotein (P-gp) drug efflux transporter, but not the cytochrome P450 (CYP) isozyme CYP3A4, was investigated. The uptake of [(3)H]vinblastine, a substrate of P-gp, by Caco-2 cells was measured. An ethyl acetate extract of orange juice did not affect the initial uptake rate of [(3)H]vinblastine but significantly increased the steady-state uptake, as did cyclosporin A (20 microM), an inhibitor of P-gp. No significant effect on the uptake of 3-O-[(3)H]methylglucose or [(14)C]phenylalanine by Caco-2 cells was found, compared with the control. When the extract was separated on a Cosmosil column, the eluate with 70% methanol showed the most potent ability to increase [(3)H]vinblastine uptake. Additional separation of the 70% methanol eluate on a silica gel column with hexane-acetone (3:1) gave 3,3',4',5,6,7,8-heptamethoxyflavone (HMF) and 4',5,6,7,8-pentamethoxyflavone (tangeretin). HMF, tangeretin, and 3',4',5,6,7,8-hexamethoxyflavone (nobiletin), another methoxyflavone contained in orange juice, all increased the steady-state uptake of [(3)H]vinblastine by Caco-2 cells in a concentration-dependent manner. The order of potency of these compounds at the concentration of 50 microM was tangeretin > HMF > nobiletin. None of these methoxyflavones inhibited 6beta-hydroxylation of testosterone catalyzed by CYP3A4. The ethyl acetate extract of orange juice and these methoxyflavones also increased steady-state [(3)H]vinblastine uptake by LLC-GA5-COL300 cells (a cell line transfected with human MDR1 cDNA). We conclude that these methoxyflavones enhanced vinblastine uptake by specifically inhibiting drug efflux via P-gp. They may have potential as agents for reversing multidrug resistance or for recovering the bioavailability of certain drugs.
 ...
PMID:Polymethoxylated flavones in orange juice are inhibitors of P-glycoprotein but not cytochrome P450 3A4. 1073 74

1. The presence of inhibitors of drug efflux transporters, such as P-glycoprotein (P-gp), in grapefruit juice (GFJ) was confirmed based on the uptake of [(3)H]-vinblastine (VBL) by Caco-2 cells. 2. The uptake of [(3)H]-VBL by Caco-2 cells was significantly increased by the ethyl acetate extract of GFJ as well as by cyclosporin A. The extract was separated on a Cosmosil column and the eluate with 60% methanol increased [(3)H]-VBL uptake, while the activity to inhibit CYP3A4 was greatest in the 70 and 80% eluates. 3. These results show that the major inhibitor of efflux transport of VBL is different from that of CYP3A4. 4. Further separation of the 60% methanol eluate afforded dihydroxybergamottin (DHBG). Both ethyl acetate extract of GFJ and DHBG increased steady-state [(3)H]-VBL uptake by LLC-GA5-COL300 cells. Besides DHBG, other furanocoumarins contained in GFJ, such as bergamottin, FC726, bergaptol and bergapten, increased the steady-state uptake of [(3)H]-VBL by Caco-2 cells. 5. The order of inhibitory potency of these compounds was FC726>DHBG>bergamottin>bergapten>bergaptol . While, the IC(50) values for inhibition of CYP3A4 were 0.075, 0.45, 1.0, 1.0 and >20 microM, respectively. Bergaptol specifically inhibited VBL efflux. 6. DHBG was thus identified as a candidate for inhibitors of VBL transport, together with other furanocoumarins. Moreover, partly involvement of the P-gp inhibition was suggested. 7. Therefore, the inhibition of efflux transport of drugs as well as of drug metabolism by CYP3A4 could be an important cause of drug-GFJ interaction.
 ...
PMID:Effect of furanocoumarin derivatives in grapefruit juice on the uptake of vinblastine by Caco-2 cells and on the activity of cytochrome P450 3A4. 1090 78

P-glycoprotein (P-gp) acts as an active efflux mechanism for a large number of cytostatics and seems to be involved in the frequent failure of cancer chemotherapy. The molecular events of substrate recognition and transport still are not understood completely. We show here that the percentage of P-gp epitopes available for labeling with UIC2 monoclonal antibody is increased significantly after methanol permeabilization/fixation of cells. At the same time, binding of the MRK16 and 4E3 anti-P-gp antibodies is changed only moderately. Confocal microscopical images of UIC2-PE-labeled cells show that the epitopes becoming available after fixation are situated mainly in the plasma membrane. Thus, only a minority of P-gp molecules are accessible for UIC2 in the cell membrane of live cells, and methanol treatment can expose a large pool of previously plasma membrane-embedded, cryptic UIC2 epitopes. The UIC2-reactive P-gp molecules do not appear to be sequestered spatially, as suggested by the high fluorescence resonance energy transfer efficiency measured between the fluorescently labeled competing UIC2 and MRK16 antibodies, suggestive of P-gp dimerization and oligomerization on live cells.
 ...
PMID:Conformational heterogeneity of P-glycoprotein. 1112 83

1. Chronic use of Saint John's wort (SJW) has been shown to lower the bioavailability for a variety of co-administered drugs including indinavir, cyclosporin, and digoxin. Decreases in intestinal absorption through induction of the multidrug resistance transporter, P-glycoprotein (P-gp), may explain decreased bioavailability. 2. The present study characterized the response of P-gp to chronic and acute exposure of SJW and hypericin (HYP, a presumed active moiety within SJW) in an in vitro system. Experiments were performed with 3 to 300 microg ml(-1) of methanol-extracted SJW and 0.03 to 3 microM HYP, representing low to high estimates of intestinal concentrations. 3. In induction experiments, LS-180 intestinal carcinoma cells were exposed for 3 days to SJW, HYP, vehicle or a positive control (ritonavir). P-gp was quantified using Western blot analysis. P-gp expression was strongly induced by SJW (400% increase at 300 microg ml(-1)) and by HYP (700% at 3 microM) in a dose-dependent fashion. Cells chronically treated with SJW had decreased accumulation of rhodamine 123, a P-gp substrate, that was reversed with acute verapamil, a P-gp inhibitor. Fluorescence microscopy of intact cells validated these findings. In Caco-2 cell monolayers, SJW and HYP caused moderate inhibition of P-gp-attributed transport at the maximum concentrations tested. 4. SJW and HYP significantly induced P-gp expression at low, clinically relevant concentrations. Similar effects occurring in vivo may explain the decreased bioavailability of P-gp substrate drugs when co-administered with SJW.
 ...
PMID:Saint John's wort: an in vitro analysis of P-glycoprotein induction due to extended exposure. 1173 35

A sensitive high-performance liquid chromatographic (HPLC) method was developed for the determination of paclitaxel in micro-samples of rat plasma in order to study the mechanism of enhanced systemic exposure of paclitaxel co-administered with P-glycoprotein inhibitors. The assay involved solid-phase extraction procedures using 2'-methylpaclitaxel as the internal standard. Chromatographic separations were achieved using a ZORBAX ODS C18 column and mobile phase consisting of acetonitrile, methanol and ammonium acetate buffer (10 mM, pH 5.0) (48.5:16.5:35) pumped at 0.8 ml/min. The effluents were measured for UV absorption at 227 nm, with retention times of 8.5 and 11.0 min for paclitaxel and 2'-methylpaclitaxel, respectively. The chromatographic separation was excellent, with no endogenous interference. The standard curves showed a good linearity (r=0.9994) over the concentration ranges of 10-1,000 ng/ml. At 1,000 ng/ml, the absolute recoveries of paclitaxel and 2'-methylpaclitaxel are 89 and 90%, respectively. The intra- and inter-day variabilities of paclitaxel were both less than 15%. This validated method for the assay of paclitaxel in micro-sample rat plasma made it feasible to study the pharmacokinetics of the drug in a single rat.
 ...
PMID:Quantitation of paclitaxel in micro-sample rat plasma by a sensitive reversed-phase HPLC assay. 1260 67

To evaluate the intestinal permeability of poorly water-soluble compounds, it is of importance to completely dissolve them in a medium and to avoid precipitation during experiments. This study was undertaken to find an agent possessing a high-solubilizing capacity and exhibiting minimal modulating impact on membrane integrity and absorption systems such as passive diffusion and carrier-mediated permeation. Phenytoin dissolution was compared in the presence of seven solubilizing agents at concentrations of 1, 2, or 5% using a centrifugation method. The capacity to dissolve phenytoin was great in beta-cyclodextrin (beta-CD) and hydroxypropyl beta-cyclodextrin, followed by Tween 80. Those of methanol, dimethyl sulfoxide, dimethyl acetoamide, and polyethylene glycol 400 were much lower than expected. One percent beta-CD did not alter the absorption of fluorescein isothiocyanate-dextran 4,000 or the release of protein and lactate dehydrogenase into in situ loop contents, suggesting that 1% beta-CD had no significant impact on the integrity of the intestinal membrane. One percent beta-CD also did not alter the absorption of caffeine, ceftibuten, or rhodamine 123 from in situ jejunal loops, indicating no interference with passive diffusion and active transports mediated by a peptide transporter and P-glycoprotein. In conclusion, 1% beta-CD is a suitable solubilizing agent for evaluating in situ intestinal absorption of poorly water-soluble compounds.
 ...
PMID:Beta-cyclodextrin as a suitable solubilizing agent for in situ absorption study of poorly water-soluble drugs. 1526 50

Extracts of bitter melon, soybean, dokudami and welsh onion by 40% methanol increased the accumulation of rhodamine-123 by Caco-2 cells, suggesting that these extracts inhibited P-glycoprotein (P-gp). The extract of bitter melon was separated in a tC18 cartridge column and the eluate from 80% acetonitrile most markedly increased the [(3)H]-daunomycin accumulation by Caco-2 cells. The inhibitory compounds in the bitter melon fraction were isolated by HPLC with Pegasil C4 and Pegasil ODS columns. The HPLC fraction having the highest activity was analyzed by (1)H-NMR and FAB-MS, and the active compound was identified as 1-monopalmitin. The inhibitory activities of 1-monopalmitin and its related compounds suggested that the inhibition of P-gp activity was not dependent on the degree of unsaturation of fatty acid in the monoglyceride, but on the chain length. It was also suggested that the monoglyceride structure played an important role in the inhibition of P-gp activity. Monoglycerides could therefore alter the pharmacokinetics of drugs by inhibiting the P-gp-mediated efflux.
 ...
PMID:Inhibitory effect of a bitter melon extract on the P-glycoprotein activity in intestinal Caco-2 cells. 1535 76


1 2 3 4 Next >>