title: Regulation of P-glycoprotein by orphan nuclear receptors in human brain microvessel endothelial cells.
abstract: In mammalian systems, pregnane X receptor (PXR) and constitutive androstane receptor (CAR) have been recognized as xenobiotic-sensors which can up-regulate the functional expression of drug transporters, such as P-glycoprotein (P-gp). In the brain, an increase in P-gp expression can further limit drug permeability across the blood-brain barrier (BBB) and potentially reduce CNS pharmacotherapy efficacy. At present, the involvement of human PXR (hPXR) and CAR (hCAR) in the regulation of P-gp expression at the human BBB is unknown. In this study, we investigate the role of hPXR and hCAR in the regulation of P-gp expression using a human cerebral microvessel endothelial cell culture system. We demonstrate that activation of hPXR and hCAR by their respective ligands leads to P-gp induction at both mRNA and protein levels, while pharmacological inhibitors of hPXR and hCAR prevent ligand-mediated P-gp induction. Ligand-induced nuclear translocation of hPXR is observed, although such effect could not be demonstrated for hCAR. Furthermore, down-regulation of hPXR and hCAR proteins using small-interfering RNA decreased P-gp expression. Our findings provide first evidence for P-gp regulation by hPXR and hCAR at the human BBB and suggest insights on how to achieve selective P-gp regulation at this site.
authors.affiliation: Department of Pharmaceutical Sciences, Leslie Dan Faculty of Pharmacy, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Gary N Y
authors.initials: GN
authors.lastname: Chan
authors.forename: Md Tozammel
authors.initials: MT
authors.lastname: Hoque
authors.forename: Carolyn L
authors.initials: CL
authors.lastname: Cummins
authors.forename: Reina
authors.initials: R
authors.lastname: Bendayan
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000818:Animals; D001812:Blood-Brain Barrier / Q000166:cytology / Q000502:physiology; D001921:Brain / Q000098:blood supply / Q000166:cytology / Q000378:metabolism*; D002461:Cell Line, Transformed; D002478:Cells, Cultured; D000090702:Constitutive Androstane Receptor; D042783:Endothelial Cells / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D056945:Hep G2 Cells; D006801:Humans; D008024:Ligands; D055806:Microvessels / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D057093:Orphan Nuclear Receptors / Q000502:physiology*; D000077297:Pregnane X Receptor; D012333:RNA, Messenger / Q000502:physiology; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors / Q000502:physiology*; D011987:Receptors, Steroid / Q000037:antagonists & inhibitors / Q000502:physiology*
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000090702:Constitutive Androstane Receptor; D008024:Ligands; D057093:Orphan Nuclear Receptors; D000077297:Pregnane X Receptor; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D011987:Receptors, Steroid