Prediction of polybrominated diphenyl ethers (PBDEs) as potential substrates of various human CYP enzymes and laboratory test of BDE-99 for its metabolism-activated mutagenicity

Polybrominated diphenyl ethers (PBDEs) are persistent organic pollutants, of which BDE-47 could be activated by human cytochrome P450s (CYPs) for chromosome-damaging effects. However, the metabolic activation and mutagenicity of other PBDEs remain unknown. In this study, 14 representative PBDEs were analyzed by molecular docking as potential substrates for several human CYPs. The results showed negative free energies for each pair of binding, however, different CYPs demonstrated largely varied frequencies of binding conformations favoring a substrate potential: CYP2E1, 3A4, and 2B6 being suitable for all/most compounds. Using BDE-99 (5 ∼ 40 μM) as a model compound (exposing for 2 cell cycles), it did not induce micronucleus in a human hepatoma HepG2 cell line, however, positive result was observed in C3A cells (derived from HepG2 but with enhanced expression of CYPs). Pretreatment of HepG2 cells with each of bisphenol A (1 μM, inducer of CYPs) and CITCO (10 μM, inducer of CYP2B6) led to micronucleus formation by BDE-99, while the effect of BDE-99 in C3A cells was abolished by 1-aminobenzotriazole (60 μM, inhibitor of CYPs). In a V79-derived cell line genetically engineered for expressing human CYP2B6 BDE-99 induced micronucleus, while it was negative in V79-Mz and its derivatives expressing several other human CYPs. The micronuclei formed in HepG2 cells pretreated with BPA and CITCO were free of centromere protein B immunofluorescence staining. Finally, BDE-99 weakly induced PIG-A gene mutations in C3A, while negative in HepG2 cells. In conclusion, our study suggest that BDE-99 may be activated by human CYP2B6 for chromosome-breaking effects.