Human CYP2A6, CYP2B6, AND CYP2E1 Atropselectively Metabolize Polychlorinated Biphenyls to Hydroxylated Metabolites

Exposure to chiral polychlorinated biphenyls (PCBs) has been associated with neurodevelopmental disorders. Their hydroxylated metabolites (OH-PCBs) are also potentially toxic to the developing human brain; however, the formation of OH-PCBs by human cytochrome P450 (P450) isoforms is poorly investigated. To address this knowledge gap, we investigated the atropselective biotransformation of 2,2',3,4',6-pentachlorobiphenyl (PCB 91), 2,2',3,5',6-pentachlorobiphenyl (PCB 95), 2,2',3,3',4,6'-hexachlorobiphenyl (PCB 132), and 2,2',3,3',6,6'-hexachlorobiphenyl (PCB 136) by different human P450 isoforms. In silico predictions with ADMET Predictor and MetaDrug software suggested a role of CYP1A2, CYP2A6, CYP2B6, CYP2E1, and CYP3A4 in the metabolism of chiral PCBs. Metabolism studies with recombinant human enzymes demonstrated that CYP2A6 and CYP2B6 oxidized PCB 91 and PCB 132 in the meta position and that CYP2A6 oxidized PCB 95 and PCB 136 in the para position. CYP2B6 played only a minor role in the metabolism of PCB 95 and PCB 136 and formed meta-hydroxylated metabolites. Traces of para-hydroxylated PCB metabolites were detected in incubations with CYP2E1. No hydroxylated metabolites were present in incubations with CYP1A2 or CYP3A4. Atropselective analysis revealed P450 isoform-dependent and congener-specific atropselective enrichment of OH-PCB metabolites. These findings suggest that CYP2A6 and CYP2B6 play an important role in the oxidation of neurotoxic PCBs to chiral OH-PCBs in humans.