Oxidative Stress Pathway Mechanisms Induced by Four Individual Heavy Metals (As, Hg, Cd and Pb) and Their Quaternary on MCF-7 Breast Cancer Cells

Cell death induced by the production of reactive oxygen species (ROS) has largely been associated with the activation of oxidative stress pathway; however, the direct mechanism(s) involved are unknown. This study evaluates the oxidative stress pathways by which four heavy metals (As, Hg, Cd and Pb) administered singly and as a quaternary mixture induce cytotoxic effects on MCF-7 breast cancer cells, in the presence and absence of cellular antioxidant, glutathione (GSH). Cells were exposed to 21.7 µg/ml of the individual metals and the mixture and assayed after 5 hr. Cellular levels of nonspecific ROS, superoxide anion (O2•), mitochondria membrane potential (MMP), and GSH were assayed using flow cytometry-FACScalibur equipped with cell quest pro for data collection. Results showed that, in the presence of cellular GSH, As and Pb induced cytotoxicity by reducing the MMP while Cd, and Hg were cytotoxic by the production of mostly superoxide anions and nonspecific ROS. The mixture exhibited cytotoxicity by decreasing the cellular MMP as well as producing ROS and O2•. When the synthesis of cellular glutathione was inhibited, all five treatments damaged the mitochondria membrane and depleted basal GSH. In addition to depleting the basal GSH and causing damage to the mitochondria membrane, Cd, As, and Pb also elicited the production of ROS.