Elucidating\nthe Metabolism of Chiral PCB95 in Wildtype\nand Transgenic Mouse Models with Altered Cytochrome P450 Enzymes Using\nIntestinal Content Screening

Polychlorinated biphenyls (PCBs), such as 2,2′,3,5′,6-pentachlorobiphenyl\n(PCB95), are persistent organic pollutants associated with adverse\nhealth outcomes, including developmental neurotoxicity. PCB95 is a\nchiral neurotoxic PCB congener atropselectively metabolized to potentially\nneurotoxic metabolites in vivo. However, the metabolic pathways of\nmost PCB congeners, including PCB95, remain unknown. To address this\nknowledge gap, we analyzed the intestinal contents of mice exposed\nto PCB95 to elucidate the PCB95 metabolism pathway and assess if genetic\nmanipulation of hepatic drug-metabolizing enzymes affects PCB95 metabolism.\nOur study exposed male and female wildtype (WT), <i>Cyp2abfgs</i>-null (KO), and CYP2A6-transgenic/<i>Cyp2abfgs-null</i> (KI) mice orally to 1.0 mg/kg body weight of PCB95. Intestinal content\nwas collected 24 h after PCB administration. aS-PCB95 was enriched\nin all intestinal content samples, irrespective of sex and genotype.\nGas chromatography–tandem mass spectrometry (GC–MS/MS)\nanalyses identified 5 mono- (OH-PCB95) and 4 dihydroxylated PCB (diOH-PCB95)\nmetabolites. Liquid chromatography–high-resolution mass spectrometry\n(LC–HRMS) identified 15 polar hydroxylated, methoxylated, and\nsulfated PCB95 metabolites, including 3 dechlorinated metabolites.\nA sex difference in the relative OH-PCB95 levels was observed only\nfor KO in the LC–HRMS analysis. Genotype-dependent differences\nwere observed for female, but not male, mice, with OH-PCB95 levels\nin female KO (F<sub>KO</sub>) mice tending to be lower than those\nin female WT (F<sub>WT</sub>) and KI (F<sub>KI</sub>) mice. Based\non the GC–MS/MS analysis, these differences are due to the\nunknown PCB95 metabolites, X1-95 and Y1-95. These findings demonstrate\nthat combining GC–MS/MS analyses and LC–HRMS subject\nscreening of the intestinal content of PCB95-exposed mice can significantly\nadvance our understanding of PCB95 metabolism in vivo.