title: The role of pregnane X receptor in 2-acetylaminofluorene-mediated induction of drug transport and -metabolizing enzymes in mice.
abstract: Activation of the pregnane X receptor (PXR) mediates the induction of several drug transporters and -metabolizing enzymes. In vitro studies have reported that several of these genes are induced after exposure to the hepatocarcinogen, 2-acetylaminofluorene (2-AAF). Thus, we hypothesized that PXR may play a role in the in vivo induction of gene expression by 2-AAF. We examined the expression of the drug-metabolizing enzymes CYP1A2 and CYP3A11 and the drug transporters breast cancer resistance protein (BCRP), MRP2, and OATP2. Wild-type (PXR+/+) and PXR-null (PXR-/-) C57BL/6 mice were injected daily for 7 days with 150 or 300 mg/kg 2-AAF suspended in corn oil (i.p.), whereas the control group received corn oil vehicle. Levels of mRNA isolated from liver were measured by reverse transcription-polymerase chain reaction and normalized to beta-actin. Treatment of PXR+/+ mice resulted in a dose-dependent 2- to 4-fold induction (p<0.001) of MRP2, OATP2, BCRP, CYP3A11, and CYP1A2, but no induction was observed in PXR-/- mice. Induction of PXR mRNA was observed in the 2-AAF-treated PXR+/+ mice. Furthermore, a dose-dependent increase in CYP3A4 promoter construct activity was observed in HepG2 cells cotransfected with human or rat PXR, indicating that 2-AAF does indeed activate PXR. These results suggest that PXR is responsible for 2-AAF-mediated induction of drug efflux transporters and biotransformation enzymes in the liver. Moreover, novel findings demonstrate that PXR plays a role in regulation of the drug efflux transporter, BCRP, in mice.
authors.affiliation: Department of Pharmaceutical Sciences, Leslie Dan Faculty of Pharmacy, University of Toronto, 19 Russell Street, Toronto, Ontario, Canada, M5S 2S2.
authors.forename: Alexander
authors.initials: A
authors.lastname: Anapolsky
authors.forename: Shirley
authors.initials: S
authors.lastname: Teng
authors.forename: Santosh
authors.initials: S
authors.lastname: Dixit
authors.forename: Micheline
authors.initials: M
authors.lastname: Piquette-Miller
mesh_terms: D015073:2-Acetylaminofluorene / Q000494:pharmacology*; D018528:ATP-Binding Cassette Transporters / Q000096:biosynthesis*; D000818:Animals; D001692:Biological Transport; D045744:Cell Line, Tumor; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis*; D004790:Enzyme Induction; D006801:Humans; D008658:Inactivation, Metabolic; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D000077297:Pregnane X Receptor; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000502:physiology*; D011987:Receptors, Steroid / Q000235:genetics / Q000502:physiology*
chemical_list: D018528:ATP-Binding Cassette Transporters; D000077297:Pregnane X Receptor; D018160:Receptors, Cytoplasmic and Nuclear; D011987:Receptors, Steroid; D003577:Cytochrome P-450 Enzyme System; D015073:2-Acetylaminofluorene