Effects of hexabromocyclododecane and polybrominated diphenyl ethers on mRNA expression in chicken (Gallus domesticus) hepatocytes

Abstract

Hexabromocyclododecane (HBCD) and polybrominated diphenyl ethers (PBDEs) are additive flame retardants used in a wide range of consumer products. Both compounds have been detected in free-living avian species, but toxicological and molecular end points of exposure are limited. An in vitro approach was used to compare concentration-dependent effects of HBCD and the commercial penta-brominated diphenyl ether mixture DE-71 on cytotoxicity and mRNA expression in cultured hepatocytes derived from embryonic chickens. Neither HBCD-α, HBCD-technical mixture (TM), nor DE-71 effected hepatocyte viability at the highest concentrations assessed (30-100 μM). Real-time RT-PCR assays were developed to quantify changes in mRNA abundance of genes associated with chicken xenobiotic-sensing orphan nuclear receptor activation, the thyroid hormone (TH) pathway, and lipid regulation. Exposure to ≥ 1 μM HBCD-α and HBCD-TM resulted in significant upregulation of cytochrome P450 (CYP) 2H1 (fourfold to sevenfold) and CYP3A37 (5- to 30-fold) at 24 and 36 h. In contrast, 30 μM DE-71 caused a twofold increase of CYP2H1 only. UGT1A9 expression was only upregulated by HBCD-α to a maximum of fourfold at ≥ 1 μM. Transthyretin, thyroid hormone-responsive spot 14-α, and liver fatty acid-binding protein were all significantly downregulated (up to sevenfold) for cells exposed to ≥ 1 μM HBCD-α and HBCD-TM. DE-71 also downregulated these three target genes twofold to fivefold at concentrations ≥ 3 μM. Taken together, our results indicate that xenobiotic-metabolizing enzymes and genes associated with the TH pathway and lipid regulation are vulnerable to HBCD and DE-71 administration in cultured avian hepatocytes and might be useful molecular markers of exposure. © The Author 2008. Published by Oxford University Press on behalf of the Society of Toxicology. All rights reserved.