title: Technical pentabromodiphenyl ether and hexabromocyclododecane as activators of the pregnane-X-receptor (PXR).
abstract: Technical pentabrominated diphenyl ether (pentaBDE mix) is a mixture of polybrominated diphenyl ethers (PBDEs) which has been widely used as a flame retardant. Since its ban in several countries it has been replaced by other brominated flame retardants such as hexabromocyclododecane (HBCD). Both certain PBDE congeners and HBCD are present in environmental and human samples reflecting their persistent and bioaccumulative properties. PentaBDE mix and HBCD have recently been found to induce cytochrome P450 (CYP) 3 enzymes in rat liver. In this study we tested both technical pentaBDE mix and HBCD for their potency to induce CYP3A enzymes in rat hepatocytes in primary culture, and in rat H4IIE and human HepG2 hepatoma cells. In rat hepatocytes, HBCD was a more effective CYP3A1 inducer than pentaBDE mix, being less effective, however, than the prototype inducer dexamethasone. In human HepG2 cells, both compounds and the prototype inducer rifampicin were about equally effective. In contrast, in HepG2 cells, HBCD failed to induce luciferin-PFBE dealkylase, a common catalytic activity of a number of CYP3A enzymes, possibly reflecting enzyme inhibition. A significant induction of catalytic activity was observed in rat hepatocytes with both compounds. Analysis of a XREM-driven reporter gene activity in transfected cells confirmed that both compounds act as agonists of the human and rat pregnane-X-receptor, which was detectable in all cell types used.
authors.affiliation: Food Chemistry and Toxicology, University of Kaiserslautern, Erwin-Schroedinger-Strasse 52, D-67663 Kaiserslautern, Germany.
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Fery
authors.forename: Inga
authors.initials: I
authors.lastname: Buschauer
authors.forename: Christian
authors.initials: C
authors.lastname: Salzig
authors.forename: Patrick
authors.initials: P
authors.lastname: Lang
authors.forename: Dieter
authors.initials: D
authors.lastname: Schrenk
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002384:Catalysis; D002467:Cell Nucleus / Q000187:drug effects / Q000201:enzymology; D002478:Cells, Cultured; D051544:Cytochrome P-450 CYP3A / Q000096:biosynthesis / Q000235:genetics; D004790:Enzyme Induction / Q000187:drug effects; D005411:Flame Retardants / Q000633:toxicity*; D055768:Halogenated Diphenyl Ethers / Q000633:toxicity*; D022781:Hepatocytes / Q000187:drug effects / Q000201:enzymology; D006801:Humans; D006842:Hydrocarbons, Brominated / Q000633:toxicity*; D007202:Indicators and Reagents; D000077297:Pregnane X Receptor; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D051381:Rats; D011987:Receptors, Steroid / Q000819:agonists*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012727:Sex Characteristics; D014162:Transfection
chemical_list: D005411:Flame Retardants; D055768:Halogenated Diphenyl Ethers; D006842:Hydrocarbons, Brominated; D007202:Indicators and Reagents; D000077297:Pregnane X Receptor; D012333:RNA, Messenger; D011987:Receptors, Steroid; C089796:hexabromocyclododecane; C086401:pentabromodiphenyl ether; D051544:Cytochrome P-450 CYP3A