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

Titanium dioxide nanoparticles (TiO 2 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 2 NPs on ROS, Ca 2+ level, p38/AKT/mTOR pathway, and apoptosis in TM4 cells and to evaluate the role of Ca 2+ in p38/AKT/mTOR pathway and apoptosis. After exposure to different concentrations (0, 50, 100, 150, and 200 μg/mL) of TiO 2 NPs for 24 h, cell viability, ROS, Ca 2+ level, Ca 2+ -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 2+ level. The Ca 2+ chelator BAPTA-AM was used to evaluate the role of Ca 2+ in p38/AKT/mTOR pathway and apoptosis. TiO 2 NPs significantly inhibited cell viability, increased ROS level, and elevated Ca 2+ level while suppressing Ca 2+ -ATPase activity. TiO 2 NPs regulated the p38/AKT/mTOR pathway via increasing p-p38 level and decreasing p-AKT and p-mTOR levels. TiO 2 NPs significantly enhanced the apoptosis. NAC attenuated Ca 2+ overload and reduction in Ca 2+ -ATPase activity caused by TiO 2 NPs. BAPTA-AM alleviated TiO 2 NPs-induced abnormal expression of p38/AKT/mTOR pathway-related proteins. BAPTA-AM assuaged the apoptosis caused by TiO 2 NPs. Altogether, this study revealed that TiO 2 NPs elevated intracellular Ca 2+ level through ROS accumulation. Subsequently, the heightened intracellular Ca 2+ 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 2 NPs-induced apoptosis in TM4 cells.