Targeted metabolome analysis of the dog brain exposed to PCBs suggests inhibition of oxidative phosphorylation by hydroxylated PCBs

Abstract

Canis lupus familiaris (domestic dog) possess a high capacity to metabolize higher-chlorinated polychlorinated biphenyls (PCBs) to thyroid hormone (TH)-like hydroxylated PCB metabolites (OH-PCBs). As a result, the brain could be at high risk of toxicity caused by OH-PCBs. To evaluate the effect of OH-PCBs on dog brain, we analyzed OH-PCB levels in the brain and the metabolome of the frontal cortex following exposure to a mixture of PCBs (CB18, 28, 70, 77, 99, 101, 118, 138, 153, 180, 187, and 202). 4-OH-CB202 and 4-OH-CB107 were major OH-PCBs in the brain of PCB-exposed dogs. These OH-PCBs were associated with metabolites involved in urea cycle, proline-related compounds, and purine, pyrimidine, glutathione, and amino-acid metabolism in dog brain. Moreover, adenosine triphosphate levels in the PCBs exposure group were significantly lower than in the control group. These results suggest that OH-PCB exposure is associated with a disruption in TH homeostasis, generation of reactive oxygen species, and/or disruption of oxidative phosphorylation (OXPHOS) in brain cells. Among them, OXPHOS disturbance could be associated with both disruptions in cellular amino-acid metabolism and urea cycle. Therefore, an OXPHOS activity assay was performed to evaluate the disruption of OXPHOS by OH-PCBs. The results indicated that 4-OH-CB107 inhibits the function of Complexes III, IV, and V of the electron transport chain, suggesting that 4-OH-CB107 inhibit these complexes in OXPHOS. The neurotoxic effects of PCB exposure may be mediated through mitochondrial toxicity of OH-PCBs in the brain.

Keywords: Brain; Dog; Hydroxylated PCBs; Metabolome; OXPHOS; Urea cycle.