Polychlorinated biphenyl (PCB)-induced oxidative stress mediates cytotoxicity in human breast and prostate epithelial cells

This thesis describes studies that are designed to investigates the hypothesis that mitochondrial production of reactive oxygen species (O₂^*- and H₂O₂) cause oxidative stress during PCB exposure and this increased production of ROS contributes to the biological effects of PCBs on cell proliferation in human breast and prostate epithelial cells. Exponentially growing non-malignant human breast epithelial cells (MCF-10A) and non-malignant human prostate epithelial cells (RWPE-1) were treated with selected PCBs and their metabolites (PCB3, 77, 153, Aroclor and 4ClBQ). Results showed that PCBs and their metabolites could significantly inhibit MCF-10A and RWPE-1 cell growth as well as inducing clonogenic cell killing. These PCBs were also found to increase steady-state levels of mitochondrial O₂^*- and H₂O₂. Furthermore, the same PCBs were also found to induce alterations in SOD activities in MCF-10A and RWPE-1 cells. 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 MCF-10A and RWPE-1 cells from PCB-induced toxicity even when added following PCB exposure. Similar experiments were also accomplished using airborne PCBs treated RWPE-1 cells. 4-OH-PCB11, a metabolite of airborne PCB 11 is shown to lead to steady-state increases in superoxide and hydroperoxides in exponentially growing RWPE-1 human nonmalignant prostate epithelial cells. This increased level of ROS was accompanied by the inhibition of cell growth and clonogenic cell killing. Furthermore treatment of cells with antioxidants one hour following exposure to 4-OH-PCB11 was able to significantly diminish the toxicity in human prostate epithelial cells. These results strongly supported the hypothesis that exposure to PCBs or their metabolites can induce the cytotoxicity and alterations in cellular proliferation as well as causing oxidative stress in exponentially growing human breast and prostate epithelial cells. More importantly, the data also provide clear evidence that antioxidant manipulations after PCB exposure are capable of protecting human cells against PCB-induced cytotoxicity. Based on these observations, the long term goal of this work is to develop a mechanism based biochemical rationale for the development of pharmaceutical manipulations to protect humans from PCB intoxication.