Multi-species comparison of the mechanism of biotransformation of MeO-BDEs to OH-BDEs in fish.

Polybrominated diphenyl ethers (PBDEs) and their methoxylated- (MeO-) and hydroxylated- (OH-) analogs are ubiquitously distributed in the environment worldwide. The OH-BDEs have greater potency than PBDEs and can be produced from the transformation of MeO-BDEs. The objectives of the current study were to (1) identify the enzyme(s) that catalyze biotransformation of 6-MeO-BDE-47 to 6-OH-BDE-47 in livers from rainbow trout, and (2) compare biotransformation of 6-MeO-BDE-47 to 6-OH-BDE-47 among rainbow trout, white sturgeon and goldfish. Cytochrome P450 1A (CYP1A) enzymes did not catalyze the biotransformation reaction. However, biotransformation was significantly inhibited by the CYP inhibitors clotrimazole and 1-benzylimidazole but not gestodene. Therefore, the reaction is likely catalyzed by CYP2 enzymes. When biotransformation was compared among species, concentrations of 6-OH-BDE-47 were significantly 3.4- and 9.1-fold greater in microsomes from rainbow trout compared to goldfish or white sturgeon, respectively. Concentrations of 6-OH-BDE-47 in microsomes from goldfish were non-significantly 2.7-fold greater than in sturgeon. The initial rate of biotransformation in microsomes from livers of rainbow trout was significantly 2.0- and 6.2-fold greater than the initial rate of biotransformation in microsomes from livers of goldfish or sturgeon, respectively, while the initial rate in goldfish was significantly 3.1-fold greater than in sturgeon. It is hypothesized that differences in CYP-mediated biotransformation of MeO-BDEs to OH-BDEs could influence concentrations of OH-BDEs in different species of fish.