Synthesis of polybrominated diphenyl ethers and their capacity to induce CYP1A by the Ah receptor mediated pathway

Polybrominated diphenyl ethers (PBDEs) have become widely distributed as en vironmental contaminants due to their use as flame retardants. Their struct ural similarity to other halogenated aromatic pollutants has led to specula tion that they might share toxicological properties such as hepatic enzyme induction. In this work we synthesized a number of PBDE congeners, studied their affinity for rat hepatic Ah receptor through competitive binding assa ys, and determined their ability to induce hepatic cytochrome P-450 enzymes by means of EROD (ethoxyresorufin-O-deethylase) assays in human, rat, chic k, and rainbow trout cells. Both pure PBDE congeners and commercial PBDE mi xtures had Ah receptor binding affinities 10(-2)-10(-5) times that of 2,3,7 ,8-tetrachlorodibenzo-p-dioxin. In contrast with polychlorinated biphenyls, Ah receptor binding affinities of PBDEs could not be related to the planar ity of the molecule, possibly because the large size of the bromine atoms e xpands the Ah receptor's binding site. EROD activities of the PBDE congener s followed a similar rank order in all cells. Some congeners, notably PBDE 85, did not follow the usual trend in which strength of Ah receptor binding affinity paralleled P-450 induction potency. Use of the gel retardation as say with a synthetic oligonucleotide indicated that in these cases the liga nded Ah receptor failed to bind to the DNA recognition Sequence.