POLYCHLORINATED BIPHENYL (PCB)-INDUCED OXIDATIVE STRESS AND CYTOTOXICITY CAN BE MITIGATED BY ANTIOXIDANTS FOLLOWING EXPOSURE

摘要

PCBs and PCB metabolites have been suggested to cause cytotoxicity by inducing oxidative stress but the effectiveness of antioxidant intervention following exposure is not established. Exponentially growing MCF-10A human breast and RWPE-1 human prostate epithelial cells continuously exposed for 5 days to 3 μM PCBs [Aroclor 1254, PCB153, and the 2-(4-chlorophenyl)-1,4-benzoquinone metabolite of PCB3 (4ClBQ)] were found to exhibit growth inhibition and clonogenic cell killing, with 4ClBQ having the most pronounced effects. These PCBs were also found to increase steady-state levels intracellular O2^·− and H2O2 (as determined by dihydroethidium, MitoSOX^™red and 5-(and-6)-carboxy-2′,7′-dichlorodihydrofluorescein diacetate oxidation). These PCBs also caused 1.5- to 5.0-fold increases in MnSOD activity in MCF-10A cells and 2.5- to 5-fold increases in CuZnSOD activity in RWPE-1 cells. Measurement of MitoSOX^™red oxidation with confocal microscopy coupled with co-localization of MitoTracker green in MCF-10A and RWPE-1 cells, supported the hypothesis that PCBs caused increased steady-state levels of O2^·− in mitochondria. Finally, treatment with either N-acetyl-cysteine (NAC), or the combination of polyethylene glycol (PEG) conjugated CuZnSOD and PEG-catalase added 1 hour after PCBs, significantly protected these cells from PCB toxicity. These results support the hypothesis that exposure of exponentially growing human breast and prostate epithelial cells to PCBs causes increased steady-state levels of intracellular O2^·− and H2O2, induction of MnSOD or CuZnSOD activities, as well as clonogenic cell killing that could be inhibited by a clinically relevant thiol antioxidant, NAC, as well as by catalase and superoxide dismutase following PCB exposure.