Different cytotoxic and apoptotic responses of MCF-7 and HT1080 cells to MnO2 nanoparticles are based on similar mode of action.

Manganese (IV) oxide nanoparticles (MnO2 NPs) are increasingly used in numerous applications. Multiple applications of MnO2 NPs, however, increase the human exposure and thus potential risk related to their toxicity. There is little information regarding the toxicity mechanisms of MnO2 NPs in human cells. In this study, we explored the toxic potential of MnO2 NPs in human breast cancer epithelial (MCF-7) and human fibrosarcoma epithelial (HT1080) cells in order to examine whether epithelial cells of different origins showed similar responses. Results demonstrated that MnO2 NPs induced cell viability reduction and membrane damage in both MCF-7 and HT1080 cells in a dose-dependent manner. MnO2 NPs were also found to induce pro-oxidants generation and antioxidants depletion in both cells. We further observed that MnO2 NPs induce apoptosis in both MCF-7 and HT1080 cells evident by altered regulation of apoptotic genes (p53, bax & bcl-2), cell cycle arrest and low mitochondrial membrane potential. Interestingly, we noticed that HT1080 cells were more susceptible to MnO2 NPs exposure than those of MCF-7 cells. This could be due to higher level of MnO2 NPs uptake into HT1080 cells as compared to MCF-7 cells. However, the mechanism of toxicity induced by MnO2 NPs in both MCF-7 and HT1080 cells was highly similar. This study warrants further research to delineate the underlying mechanisms of MnO2 NPs toxicity at in vivo level.