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)

We evaluated the effect of water-soluble vitamin E (d-alpha-tocopheryl polyethylene glycol 1000 succinate [TPGS]; Liqui-E) on the oral pharmacokinetics of the cyclosporine, a poorly available (approximately 30%) drug, in healthy volunteers. Ten healthy subjects were given two doses of oral cyclosporine (10mg/kg) separated by a 7-day washout period. Oral TPGS (2.6 IU/kg) was administered concomitantly with one of the cyclosporine doses in a randomized order. A significant increase was observed in area under the blood concentration-time curve (AUC;mean +/ SD) with concomitant TPGS administration (3908 +/- 2601 versus 6296 +/- 5102 ng x hr/ml). Significant decreases were observed in apparent oral clearance (0.24 +/- 0.14 versus 0.15 +/- 0.08 L/hr/kg) and apparent oral steady-state volume of distribution (1.57 +/- 0.95 versus 1.07 +/- 0.73 L/kg). No significant changes were observed in the ratios of metabolites to parent drug AUC values. The comparable relative decreases in apparent oral clearance (38%) and apparent oral steady-state volume of distribution (30%) with TPGS are most likely explained by enhanced absorption, decreased counter transport back into the intestine by P-glycoprotein, or some unknown mechanism by which cyclosporine is protected from metabolism in the gut, thereby increasing bioavailability.
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PMID:The effect of water-soluble vitamin E on cyclosporine pharmacokinetics in healthy volunteers. 865 92

The objectives of this study were (1) to investigate the transporter inhibition activity of three nonionic surfactants on P-glycoprotein, the human intestinal peptide transporter, and the monocarboxylic acid transporter in Caco-2 cell monolayers, and (2) to evaluate the role of membrane fluidity and protein kinase C in surfactant-induced transporter inhibition. All three surfactants inhibited P-glycoprotein (P-gp). Over a range from 0 to 1 mM, Tween 80 and Cremophor EL increased apical-to-basolateral permeability (AP-BL) and decreased basolateral-to-apical (BL-AP) permeability of the P-gp substrate rhodamine 123. Vitamin E TPGS's effect was equally large, but essentially only reduced the BL-AP permeability of rhodamine 123, and did so at a vitamin E TPGS concentration of only 0.025 mM. These P-gp inhibition effects would appear to be related to these excipients' modulation of membrane fluidity, where Tween 80 and Cremophor EL fluidized cell lipid bilayers, while vitamin E TPGS rigidized lipid bilayers. However, among the three surfactants, only Tween 80 inhibited the peptide transporter, as measured by glycyl sarcosine permeability. Likewise, only Cremophor EL inhibited the monocarboxylic acid transporter, as measured by benzoic acid permeability. Nevertheless, at least one of these three surfactants inhibited each P-gp, the human intestinal peptide transporter, and the monocarboxylic acid transporter. A common functional feature of these three surfactants was their ability to modulate fluidity, although results indicate that even strong membrane fluidity modulation alone was not sufficient to reduce transporter activity. N-octyl glucoside, a nonionic surfactant that did not modulate membrane fluidity, did not affect transporter functioning. Protein kinase C inhibitors failed to affect rhodamine 123 and glycyl sarcosine permeability, suggesting protein kinase C inhibition was not the mechanism of transporter inhibition. These results suggest that surfactants can inhibit multiple transporters but that changes in membrane fluidity may not be a generalized mechanism to reduce transporter activity.
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PMID:Effects of nonionic surfactants on membrane transporters in Caco-2 cell monolayers. 1220 53

Hypoxia in tumors is generally associated with chemoresistance and radioresistance. However, the correlation between the heterodimeric hypoxia-inducible factor-1 (HIF-1) and the multidrug resistance transporter P-glycoprotein (P-gp) has not been investigated. Herein, we demonstrate that with increasing size of DU-145 prostate multicellular tumor spheroids the pericellular oxygen pressure and the generation of reactive oxygen species decreased, whereas the alpha-subunit of HIF-1 (HIF-1alpha) and P-gp were up-regulated. Furthermore, P-gp was up-regulated under experimental physiological hypoxia and chemical hypoxia induced by either cobalt chloride or desferrioxamine. The pro-oxidants H2O2 and buthionine sulfoximine down-regulated HIF-1alpha and P-gp, whereas up-regulation was achieved with the radical scavengers dehydroascorbate, N-acetylcysteine, and vitamin E. The correlation of HIF-1alpha and P-gp expression was validated by the use of hepatoma tumor spheroids that were either wild type (Hepa1) or mutant (Hepa1C4) for aryl hydrocarbon receptor nuclear translocator (ARNT), i.e., HIF-1beta. Chemical hypoxia robustly increased HIF-1alpha as well as P-gp expression in Hepa1 tumor spheroids, whereas no changes were observed in Hepa1C4 spheroids. Hence, our data demonstrate that expression of P-gp in multicellular tumor spheroids is under the control of HIF-1.
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PMID:Regulation of the multidrug resistance transporter P-glycoprotein in multicellular tumor spheroids by hypoxia-inducible factor (HIF-1) and reactive oxygen species. 1251 19

The potential inhibitory effects of 3 excipients (polyethylene glycol [PEG] 400, Pluronic P85, and vitamin E d-a-tocopheryl polyethylene glycol 1000 succinate [TPGS]) on the P-glycoprotein (P-gp) -mediated efflux of digoxin (DIG) and cytochrome P450 3A (CYP3A) -mediated metabolism of verapamil (VRP) have been examined in an in vitro permeability model. Experiments were conducted utilizing rat jejunal tissue mounted in diffusion chambers and included assessment of the serosal to mucosal (s to m) transport of DIG and the formation of norverapamil (NOR) during the mucosal to serosal transport of VRP, as measures of P-gp efflux and CYP3A metabolism, respectively. The presence of PEG at 1%, 5%, and 20% (wt/vol) reduced both the s to m flux of DIG (by 47%, 57%, and 64%, respectively, when compared to control) and the metabolism of VRP (by 54%, 78%, and 100%) in a concentration-dependent manner. P85 (0.1% wt/vol) significantly reduced s to m DIG flux by 47% and inhibited VRP metabolism by 42%. TPGS had insignificant effects on both metabolism and efflux at a concentration of 0.01% (wt/vol). The P-gp inhibitory effects of PEG and P85 were evident regardless of whether the excipient was added to the mucosal side, the serosal side, or both sides of the tissue. The current data suggest that inclusion of PEG and P85 as solubilizing agents during in vitro permeability assessment may have a significant impact on both drug metabolism and efflux processes. These compounds appear to exert their effects on P-gp primarily via direct transporter inhibition - or indirectly, through effects on buffer osmolarity, membrane fluidity, and/or mitochondrial toxicity and subsequent adenosine triphosphate (ATP) depletion.
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PMID:An in vitro examination of the impact of polyethylene glycol 400, Pluronic P85, and vitamin E d-alpha-tocopheryl polyethylene glycol 1000 succinate on P-glycoprotein efflux and enterocyte-based metabolism in excised rat intestine. 1264 11

R1481 is a sub-type selective muscarinic receptor antagonist with the potential treatment of overactive bladder. R1481 presents two challenges for drug development. The first is the viscous semi-solid nature of the active pharmaceutical ingredient (API). The second challenge is the poor oral bioavailability of this water soluble, metabolically stable compound due to low intestinal permeability, and the P-glycoprotein (P-gp) efflux mechanism. Vitamin E TPGS is reported by others to enhance bioavailability by increasing the solubility of active compounds and by inhibiting P-gp in the intestine. In this report, compatibility of R1481 in Capmul MCM-based formulations with and without vitamin E TPGS is summarized. Review of accelerated stability studies of oral formulations led to the identification of a soft gelatin capsule formulation using neat Capmul MCM as an acceptable formulation for Phase 1 clinical studies. Soft gelatin capsules (5 mg strength) were manufactured with and without the addition of vitamin E TPGS. Clinical data show that vitamin E TPGS does not improve systemic exposure of R1481 in humans.
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PMID:Pre-clinical and clinical evaluation of solution and soft gelatin capsule formulations for a BCS class 3 compound with atypical physicochemical properties. 1529 82

Expression of multiple drug resistant (MDR) phenotype and over-expression of P-glycoprotein (P-gp) in the human hepatocellular carcinoma (HCC) cell clone P1(0.5), derived from the PLC/PRF/5 cell line (P5), are associated with strong resistance to oxidative stress and a significant (p < 0.01) increase in intracellular vitamin E content as compared with the parental cell line. This study evaluates the role of vitamin E in conferring resistance to drugs and oxidative stress in P1(0.5) cells. Parental drug-sensitive cells, P5, were incubated in alpha-tocopherol succinate (alpha-TS, 5 microM for 24 h) enriched medium to increase intracellular vitamin E content to levels comparable to those observed in P1(0.5) cells at basal conditions. Susceptibility to lipid peroxidation and oxidative DNA damage were assessed by measuring the concentration of thiobarbituric-reactive substances (TBARS) and 8-hydroxy-2'-deoxyguanosine (8-OHdG) at basal and after experimental conditions. Cell capacity to form colonies and resistance to doxorubicin were also studied. P5 cells, treated with alpha-TS, became resistant to ADP-Fe3+ and to ionizing radiation-induced lipid peroxidation as P1(0.5) cells. Exposure to ADP-Fe3+ or ionizing radiation increased TBARS and the 8-OHdG content in the P5 cells, while vitamin E enrichment abolished these effects. Irradiation doses at 5 cGy increased TBARS and 8-OHdG. They also inhibited cell capacity to form colonies in the untreated P5 cells. Incubation with alpha-TS fully reverted this effect and significantly (p < 0.01) reduced the inhibitory effect of cell proliferation induced by irradiation doses at >500 cGy. Resistance to doxorubicin was not affected by alpha-TS. These observations demonstrate the role of vitamin E in conferring protection from lipid peroxidation, ionizing radiation and oxidative DNA damage on the human HCC cell line. They also rule out any role of P-gp over-expression as being responsible for these observations in cells with MDR phenotype expression.
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PMID:Vitamin E protects DNA from oxidative damage in human hepatocellular carcinoma cell lines. 1545 40

In this study improvement in the bioavailability of carbamazepine (CBZ) prepared as solid dispersions by conventional solvent evaporation and supercritical fluid (SCF) processing methods was assessed, along with the elucidation of the mechanism of improved absorption. Solid dispersions of CBZ in polyethylene glycol (PEG) with either Gelucire 44/14 or vitamin E-TPGS (TPGS) were evaluated by intrinsic dissolution. Directional transport through Caco-2 cell monolayers was determined in the presence and absence of TPGS. Cell viability in presence of various concentrations of amphiphilic carriers was seen. In vivo oral bioavailability was determined in rats. The apparent intrinsic dissolution rates (IDR) of both conventional- and SCF-CBZ/PEG 8000/TPGS solid dispersions were increased by 13- and 10.6-fold, respectively, relative to neat CBZ. CBZ was not a substrate of P-glycoprotein. Higher CBZ permeability was seen in presence of 0.1% TPGS. Cell viability studies showed significant cytotoxicity only at or above 0.1% amphiphilic carrier. Supercritical treated formulation (without amphiphilic carrier) displayed oral bioavailability on par with those conventional solid dispersions augmented with amphiphilic carriers. An in vitro-in vivo correlation was seen between IDR and the AUC of the various CBZ solid dispersions. Bioavailability of CBZ was more a function of dissolution as opposed to membrane effects. Although bioavailability from SCF processed dispersions was better than conventionally processed counterparts (except for one formulation containing Gelucire 44/14), an interaction of processing method and inclusion of an amphiphilic carrier, rather by one factor alone contributed to optimal absorption, thus giving contradictory results for Gelucire 44/14 and TPGS formulations.
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PMID:In vitro-in vivo evaluation of supercritical processed solid dispersions: permeability and viability assessment in Caco-2 cells. 1546 28

Expression of the multidrug resistance (MDR) transporter P-glycoprotein (P-gp) has been demonstrated to be regulated by hypoxia-inducible factor-1alpha (HIF-1alpha) and inhibited by intracellular reactive oxygen species (ROS). Herein, P-gp and HIF-1alpha expression were investigated in multicellular prostate tumor spheroids overexpressing the ROS-generating enzyme Nox-1 in comparison to the mother cell line DU-145. In Nox-1-overexpressing tumor spheroids (DU-145Nox1) generation of ROS as well as expression of Nox-1 was significantly increased as compared to DU-145 tumor spheroids. ROS generation was significantly inhibited in the presence of the NADPH-oxidase antagonists diphenylen-iodonium chloride (DPI) and 4-(2-aminoethyl)benzenesulfonyl fluoride (AEBSF). Albeit growth kinetic of DU-145Nox1 tumor spheroids was decreased as compared to DU-145 spheroids, elevated expression of Ki-67 was observed indicating increased cell cycle activity. In DU-145Nox1 tumor spheroids, expression of HIF-1alpha as well as P-gp was significantly decreased as compared to DU-145 spheroids, which resulted in an increased retention of the anticancer agent doxorubicin. Pretreatment with the free radical scavengers vitamin E and vitamin C increased the expression of P-gp as well as HIF-1alpha in Nox-1-overexpressing cells, whereas no effect of free radical scavengers was observed on mdr-1 mRNA expression. In summary, the data of the present study demonstrate that the development of P-gp-mediated MDR is abolished under conditions of elevated ROS levels, suggesting that the MDR phenotype can be circumvented by modest increase of intracellular ROS generation.
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PMID:Reactive oxygen species-linked regulation of the multidrug resistance transporter P-glycoprotein in Nox-1 overexpressing prostate tumor spheroids. 1608 77

D-alpha-tocopheryl poly(ethylene glycol) 1000 succinate (TPGS 1000) is a widely used form of vitamin E. TPGS 1000 is comprised of a hydrophilic polar (water-soluble) head and a lipophilic (water-insoluble) alkyl tail. TPGS 1000 has been used as a solubilizer, an emulsifier and as a vehicle for lipid-based drug delivery formulations. Most recently, TPGS 1000 has been recognized as an effective oral absorption enhancer. An enhancing effect is consistent with a surfactant-induced inhibition of P-glycoprotein (P-gp), and perhaps other drug transporter proteins; however, the exact inhibition mechanism(s) remain unclear. Therefore, in an attempt to generate additional knowledge, we have synthesized and tested various TPGS analogs containing different PEG chain length (TPGS 200/238/400/600/1000/2000/3400/3500/4000/6000). These results demonstrate a relationship between TPGS PEG chain length and influence on rhodamine 123 (RHO) transport in Caco-2 monolayers, a relationship which may be illustrated using a Weibull distribution.
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PMID:Influence of vitamin E TPGS poly(ethylene glycol) chain length on apical efflux transporters in Caco-2 cell monolayers. 1641 30

Breast cancer resistance protein (BCRP/ABCG2) plays an important role in drug disposition. To examine whether some currently used excipients could inhibit its function, we measured the uptake of [(3)H]mitoxantrone in BCRP-, P-glycoprotein (P-gp)- or green fluorescent protein (GFP)-expressing cells, in the presence or absence of 15 kinds of currently used excipients. Of 15 excipients, five (Cremophor EL, Tween 20, Span 20, Pluronic P85 and Brij 30) increased the uptake of [(3)H]mitoxantrone in BCRP-expressing cells. On the other hand, ten (Cremophor EL, Cremophor RH40, Tween 20, Tween 80, Span 20, Pluronic P85, vitamin E TPGS, Brij 30, Myrj 52 and Gelucire 44/14) significantly increased uptake in P-gp-expressing cells. No significant effects on intracellular ATP levels were observed following treatments with the excipients that inhibited BCRP function. Taken together, this study demonstrated that some excipients might be potent BCRP inhibitors, and there may be differences in the effects of excipients on the functions of BCRP and P-gp.
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PMID:Effect of excipients on breast cancer resistance protein substrate uptake activity. 1790 Jul 39


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