Titanium dioxide nanoparticles induce apoptosis through ROS-Ca 2+ -p38/AKT/mTOR pathway in TM4 cells

Titanium dioxide nanoparticles (TiO NPs) can cause apoptosis in TM4 cells; however, the underlying mechanism has not been entirely elucidated. The purpose of this study was to investigate the effects of TiO NPs on ROS, Ca level, p38/AKT/mTOR pathway, and apoptosis in TM4 cells and to evaluate the role of Ca in p38/AKT/mTOR pathway and apoptosis. After exposure to different concentrations (0, 50, 100, 150, and 200 μg/mL) of TiO NPs for 24 h, cell viability, ROS, Ca level, Ca -ATPase activity, p38/AKT/mTOR pathway-related proteins, apoptosis rate, and apoptosis-related proteins (Bax, Bcl-2, Caspase 3, Caspase 9, and p53) were detected. The ROS scavenger NAC was used to determine the effect of ROS on Ca level. The Ca chelator BAPTA-AM was used to evaluate the role of Ca in p38/AKT/mTOR pathway and apoptosis. TiO NPs significantly inhibited cell viability, increased ROS level, and elevated Ca level while suppressing Ca -ATPase activity. TiO NPs regulated the p38/AKT/mTOR pathway via increasing p-p38 level and decreasing p-AKT and p-mTOR levels. TiO NPs significantly enhanced the apoptosis. NAC attenuated Ca overload and reduction in Ca -ATPase activity caused by TiO NPs. BAPTA-AM alleviated TiO NPs-induced abnormal expression of p38/AKT/mTOR pathway-related proteins. BAPTA-AM assuaged the apoptosis caused by TiO NPs. Altogether, this study revealed that TiO NPs elevated intracellular Ca level through ROS accumulation. Subsequently, the heightened intracellular Ca level was observed to exert regulation over the p38/AKT/mTOR pathway, ultimately culminating in apoptosis. These results provides a complementary understanding to the mechanism of TiO NPs-induced apoptosis in TM4 cells.