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)

Epithelial cells of the small intestine are responsible for the resorption of different food components as well as potentially toxic agents such as benzo[a]pyrene (B[a]P), a particular contaminant of charcoal-grilled meat. This study was undertaken to investigate any functional relationship between the metabolism of B[a]P and the unidirectional transport of metabolites back into the intestinal lumen mediated by ATP-binding cassette (ABC) transport proteins. The human intestinal Caco-2 cell line was used. In addition, mdr1- and mrp2-transfected MDCK cells were employed to characterize the possible role of these ABC transport proteins in the polarized transport. After incubations of Caco-2 cells with B[a]P, HPLC analysis revealed that the primary metabolites of B[a]P were B[a]P-1-sulfate and B[a]P-3-sulfate. Other metabolites, such as B[a]P-3-glucuronide, B[a]P-9,10-diol, or B[a]P-3,6-quinone, could be detected only in small amounts. The transport experiments using Transwell chambers clearly showed that B[a]P-1- and B[a]P-3-sulfate were actively transported toward the apical (luminal) region. This transport increased after induction of CYP1A1/CYP1B1 (Phase 1)-metabolism, although a decrease was observed during concomitant inhibition. Inhibition studies using chemical inhibitors of P-glycoprotein, MRPs, showed no effects. A comparison between the transport of B[a]P-1- and B[a]P-3-sulfate in wild-type and mrp2-transfected MDCKII cells revealed no differences at all. The results indicate that B[a]P is metabolized by Caco-2 cells mainly to B[a]P-1- and B[a]P-3-sulfate, which are subject to an apically directed transport. Furthermore ABC transport proteins P-glycoprotein, MRP1, and MRP2 are not involved in this polarized B[a]P-sulfate secretion.
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PMID:Interaction between metabolism and transport of benzo[a]pyrene and its metabolites in enterocytes. 1238 8

Epithelial cells of the gastrointestinal tract are challenged by exposure to many potentially toxic agents including the well-known food contaminant benzo[a]pyrene (B[a]P). They are equipped with a variety of Phase 1- and Phase 2-enzymes that are able to metabolize B[a]P. Furthermore, transmembranous ABC-transport proteins are expressed at the apical pole of these cells. The aim of this study was to investigate whether [14C]B[a]P or products of the metabolism are transported by intestinal cells back into the gut lumen. The intestinal Caco-2 cell line was used as a metabolism and transport model. Experiments with Caco-2 monolayers in the Transwell-system revealed that radiolabeled substance is transported towards the apical (luminal) region. This transport was characterized as active and increased after induction of cytochromes P450 1A1 and 1B1 by beta-naphthoflavone. On the other hand, transport was decreased with the concomitant inhibition of Phase 1-metabolism. TLC-analysis revealed that the primary metabolites of B[a]P found in the supernatant were very polar; other metabolites of less polarity could only be detected in trace amounts. These results indicate that B[a]P is metabolized by Caco-2 cells to highly polar metabolites resulting from biphasic metabolism and that these polar metabolites are subject to an apically directed transport. Chemical inhibition studies showed that P-glycoprotein and MRP1 or 2 were not involved in this polarized B[a]P-metabolite secretion.
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PMID:Human intestinal Caco-2 cells display active transport of benzo[a]pyrene metabolites. 1245 61

Several defence mechanisms, such as cytochrome P450 1A (CYP1A) enzymes and P-glycoprotein (Pgp), may influence the intracellular concentration and consequently the toxicity of xenobiotics. The parallel expression of CYP1A and Pgp has been investigated in mammals and, to a lesser extent in fish, in search for evidence of co-ordinated responses to xenobiotic exposure. The aryl hydrocarbon receptor (AHR) agonists are well known CYP1A inducers but some of them resulted not to have a uniquely defined action on Pgp levels in mammalian and fish species. To the best of our knowledge, no detailed studies have been carried out so far on amphibians Xenopus laevis. For this reason, in this work, the time dependent responses of the hepatic CYP1A and Pgp, to the prototypical CYP1A inducers, benzo(a)pyrene (B(a)P), 3-methylcholanthrene (3MC) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in X. laevis have been assessed at the protein level and compared. The responsiveness of Xenopus intestinal Pgp to these compounds has also been analysed, as the epithelial cells lining the lumen of intestine represent another preferential site of Pgp expression. In addition, since the thyroid hormone has been demonstrated to down regulate the mdr gene during Xenopus development and in primary culture of Xenopus intestinal epithelial cells, the effects of 3,3',5-triiodo-L-thyronine (T(3)) on CYP1A and Pgp protein levels have been investigated in adult organisms. Western blot evidenced that a single injection of B(a)P (100 mg/kg), 3MC (20 mg/kg), and TCDD (3 microg/kg) elicited a statistically significant induction of hepatic CYP1A at all time points considered (72, 120 and 168 h) which decreased in time. The same trend of liver CYP1A induction was observed in T(3) treated Xenopus (15 microg/kg). Unlike CYP1A induction, the modulation of hepatic and intestinal Pgp expression exhibits an heterogeneous pattern. The basal levels of hepatic and intestinal Pgp were not statistically significant affected by treatments. In particular, the hepatic Pgp levels seem not to be induced by TCDD and T(3) at all times considered in comparison to control. For the first time the modulation of CYP1A and Pgp levels by B(a)P, 3MC and in particular by TCDD and T(3) in Xenopus has been demonstrated and the results herewith indicate that the two target defence mechanisms respond to AHR agonists in a dissimilar way in terms of proteins induction in Xenopus. Moreover, these data suggest additional experiments in order to clarify the complex mechanism, which adjusts the parallel expression of CYP1A and Pgp in Xenopus.
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PMID:Differential modulation of cytochrome P-450 1A and P-glycoprotein expression by aryl hydrocarbon receptor agonists and thyroid hormone in Xenopus laevis liver and intestine. 1265 91

Seasonal variations of six mussel (Mytilus galloprovincialis) biomarkers at two sites in the Mediterranean Sea were compared with physiological indices (condition, growth and gonad maturation), environmental parameters (temperature, salinity and turbidity), and chemical contamination levels. The basal levels of acetylcholinesterase (AChE), DNA adducts, benzo[a]pyrene hydroxylase (BPH), heat-shock proteins (HSP70), metallothioneins (MT) and P-glycoprotein (P-gp)-mediated multixenobiotic resistance (MXR) were estimated as early warning signals in caged mussels sampled at Carteau (native site) and La Fourcade (transplantation site) over a 2-year period. The Carteau and La Fourcade mussels have specific chemical contamination profiles but a similar range of values. For example, both are highly contaminated by heavy metals (201 and 258.4 mg kg(-1) dw, respectively) and considered as moderately impacted for polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs). However, contamination levels at Carteau are twice as high for PAHs (101.5 mg g(-1) dw) and PCBs (90.2 mg g(-1) dw) than La Fourcade. The seasonal contamination trend at Carteau showed six-fold higher levels of pyrolytic pollutants in winter. Although few tissue lesions were detected in individuals studied at either site, greater parasitic infestation was observed at Carteau. The results of findings from the two Mediterranean pilot studies support the adaptability of transplanted mussels to be used as biomarkers and to establish physiological endpoints for chemical contaminant exposure.
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PMID:Seasonal variations of a battery of biomarkers and physiological indices for the mussel Mytilus galloprovincialis transplanted into the northwest Mediterranean Sea. 1553 49

The main exposure pathway of benzo[a]pyrene (Bap) for humans is considered to be via the daily diet. The purpose of this study was to investigate the effect of BaP on the intestinal transport of chemicals mediated by P-glycoprotein (P-gp). The intestinal epithelial membrane transport of rhodamine-123 (Rho-123), a substrate of P-gp, was examined using a monolayer of the human Caco-2 cell line grown in transwells. In the monolayer exposed to Bap for 72 h before transport experiments, the ratio of the apparent permeability coefficients (P(app)) of Rho-123 efflux increased compared to that of the control. The permeability of rhodamine-B (Rho-B), not a substrate of P-gp, showed no difference between the monolayers. Treatment with quinidine or cyclosporine A, which are P-gp inhibitors, decreased the P(app) of Rho-123 to the same degree in both monolayers. The transport of Rho-123 was not influenced by the presence of Bap. Thus, Bap seemed not to act directly on the efflux activity of P-gp and be a binding site competitor of Rho-123. In the Caco-2 cells that enhanced the efflux of Rho-123 by the treatment with Bap, an increase in mRNA expression of MDR 1 (P-gp) was confirmed compared to that of control by RT-PCR. Furthermore, Western blot analysis using a monoclonal antibody, C219, demonstrated the increase of P-gp in Caco-2 cells exposed to Bap, compared with controls. It was inferred that Bap exposure induced the expression of P-gp, which led to the observed increase in efflux transport of Rho-123. The possibility was suggested that Bap might affect the disposition of medicines by increasing P-gp expression.
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PMID:Effect of benzo[a]pyrene on P-glycoprotein-mediated transport in Caco-2 cell monolayer. 1664 97

The previous studies from our laboratory reported that benzo(a)pyrene (Bap) influenced efflux transport of rhodamine 123 (Rho-123) by induction of P-glycoprotein (P-gp) in Caco-2 cells. The present study investigated whether induction of P-gp and the enhanced efflux transport of Rho-123 were caused by benzo(e)pyrene (Bep), which has a structure similar to Bap, but is not a carcinogenic compound. In Caco-2 monolayer exposed to 50 microM Bep for 72 h, the ratio of the apparent permeability coefficient (P(app)) of Rho-123 efflux increased significantly compared to that of the control monolayer. Similarly, a significant increase in expression of MDR1 mRNA and of P-gp at the protein level were detected by RT-PCR and by Western blot analysis, respectively, in Caco-2 cells exposed to Bep, compared to that of the control. Caco-2 cells exposed to Bep showed oxidative stress that was detected by fluorescence microscopy using aminophenyl fluorescein. However, the oxidative stress was weaker compared with that of Bap. The cellular GSH content was decreased to 80% or 59% of control cells, respectively, in Caco-2 cells exposed to either Bep or Bap. Our results further show that Bep or Bap-induced P-gp in Caco-2 cells might have been the result of oxidative stress rather than DNA damage.
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PMID:Effects of benzo(e)pyrene and benzo(a)pyrene on P-glycoprotein-mediated transport in Caco-2 cell monolayer: a comparative approach. 1740 18

Imazalil (IMA) is a widely used imidazole-antifungal pesticide and, therefore, a food contaminant. This compound is also used as a drug (enilconazole). As intestine is the first site of exposure to ingested drugs and pollutants, we have investigated the effects of IMA, at realistic intestinal concentrations, on xenobiotic-metabolizing enzymes and efflux pumps by using Caco-2 cells, as a validated in vitro model of the human intestinal absorptive epithelium. For comparison, other conazole fungicides, i.e. ketoconazole, propiconazole and tebuconazole, were also studied. IMA induced cytochrome P450 (CYP) 1A1 activity to the same extent as benzo(a)pyrene (B(a)P) or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), in a dose- and time-dependent manner. Cell-free aryl hydrocarbon receptor (AhR) binding assay and reporter gene assay suggested that IMA is not an AhR-ligand, implying that IMA-mediated induction should involve an AhR-independent pathway. Moreover, IMA strongly inhibited the CYP3A4 activity in 1,25-vitamin D(3)-induced Caco-2 cells. The other fungicides had weak or nil effects on CYP activities. Study of the apical efflux pump activities revealed that ketoconazole inhibited both P-glycoprotein (Pgp) and multidrug resistance-associated protein 2 (MRP-2) or breast cancer resistance protein (BCRP), whereas IMA and other fungicides did not. Our results imply that coingestion of IMA-contaminated food and CYP3A4- or CYP1A1-metabolizable drugs or chemicals could lead to drug bioavailability modulation or toxicological interactions, with possible adverse effects for human health.
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PMID:CYP1A1 induction and CYP3A4 inhibition by the fungicide imazalil in the human intestinal Caco-2 cells-comparison with other conazole pesticides. 1907 Jun 57

P-glycoprotein (Pgp) participates in the export of numerous toxins, drugs, and physiological compounds. To examine the involvement of Pgp in smoke-induced oral cell insult, the effects of extracts of the mainstream tobacco smoke (TS) on Pgp were studied in an oral epidermal carcinoma cell line, OECM-1. TS was first extracted with cyclohexane (CTS) and the residues were further extracted with isopropanol (ITS). For comparison, cells were exposed to CTS and ITS at the concentrations according to their relative extraction yield. ITS but not CTS decreased the efflux of a Pgp substrate, rhodamine (Rh) 123, in a concentration- and time-dependent manner. The efflux was also decreased by co-exposure to CTS and ITS. However, immunoblot analysis revealed that the protein level of Pgp was not affected by ITS. Naphthalene, mainly detected in the ITS, decreased Rh 123 efflux. However, the efflux activity was not affected by benzo(a)pyrene and nicotine, which were present in the CTS and both extracts, respectively. Co-exposure to CTS in combination with ITS, naphthalene, or verapamil enhanced cell insult compared to single exposure. These results demonstrated that smoke and its constituent, naphthalene, diminished Pgp-mediated efflux. The reduction in Pgp function could be a stimulatory factor of TS-induced oral cell insult.
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PMID:Suppressive effect of tobacco smoke extracts on oral P-glycoprotein function and its impact in smoke-induced insult to oral epidermal cells. 1913 10

Benzo(a)pyrene (BP) is the best studied polycyclic aromatic hydrocarbon, classified as carcinogenic to humans. The carcinogenic metabolite, benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide (BPDE), binds covalently to DNA. The key enzyme in this metabolic reaction is CYP1A1, which has also been found in placenta and human trophoblastic cells. By using human placental perfusion we confirmed that BP added to the maternal circulation in concentrations of 0.1 and 1 microM reaches fetal compartment but somewhat slower than the freely diffusible reference substance antipyrine. A well-known P-glycoprotein (ABCB1/P-gp) antagonist verapamil did not affect the transfer more than it did in the case of antipyrine, indicating that ABCB1/P-gp does not have a role in BP transfer. In one of the two placentas perfused for 6 h with the higher concentration of BP (1 microM) BPDE specific DNA adducts were found in placental tissue after the perfusion, but not before. The ability of human trophoblastic cells to activate BP to BPDE-DNA adducts was confirmed in human trophoblastic BeWo cells. This study shows that maternal exposure to BP leads to the exposure of the fetus to BP and/or its metabolites and that placenta itself can activate BP to DNA adducts.
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PMID:Placental transfer and DNA binding of benzo(a)pyrene in human placental perfusion. 2046 50

Fish bioaccumulate a variety of contaminants and act as an exposure portal to the human consumer. Surfactants, known pharmaceutically to alter membrane permeability, change drug bioavailability and attenuate transporter function are also found in contaminant mixtures in the aquatic environment. The overall objective of this study was to determine if the surfactant C-12 linear alkylbenzene sulfonate (LAS) at environmentally relevant concentrations, alters the disposition and enhances bioaccumulation of co-exposed dietary xenobiotics in the catfish. Included for study were the carcinogen benzo(a)pyrene (BaP), pharmaceutical, ivermectin (IVM), and P-glycoprotein (P-gp) substrate rhodamine 123 (Rho-123), each exhibiting different dispositional footprints. Rho-123 transport into bile and membrane fluidity was examined in isolated perfused livers from control and LAS exposed catfish. Mass balance residue assessments were performed on catfish following in vivo exposure for 12 days to LAS in water at 0, 100 or 300 microg/L with 6 days of (3)H-IVM or (3)H-BaP gavage treatments. LAS at 1, 5 and 20 microM in the perfused liver, significantly decreased the transport of Rho-123 (1 microM) into bile by 18.6, 38.1 and 66.7%, respectively. Fluorescence anisotropy measurements demonstrated a 29.7% increase in fluidity at the (1 microM, 348 microg/L) LAS concentration. In vivo mass balance studies indicated that waterborne LAS (100 and 300 microg/L) increased the dietary dose remaining in fish by 39% and 78% for (3)H-IVM and 50 and 157% for (3)H-BaP. LAS at environmentally relevant concentrations altered the bioavailability and disposition of dietary xenobiotics in the catfish. Co-exposure with LAS increases xenobiotic bioaccumulation, potential toxicity of mixture components to the fish and the potential for residue transfer from fish to the consumer.
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PMID:Enhanced bioaccumulation of dietary contaminants in catfish with exposure to the waterborne surfactant linear alkylbenzene sulfonate. 2054 17


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