Arsenic trioxide (ATO) affects many biological functions such as cell proliferation, apoptosis, differentiation and angiogenesis in various cells. We investigated the in vitro effects of ATO as a reactive oxygen species (ROS) generator or a glutathione (GSH) depletor on apoptosis in HeLa cells. ATO decreased the viability of HeLa cells in a dose-dependent manner with an IC50 of approximately 5-6 µM. ATO triggered apoptosis, which is accompanied by the loss of mitochondrial transmembrane potential (ΔΨm). Intracellular general ROS levels in HeLa cells were increased or decreased depending on the concentration of ATO. Particularly, the levels of O2·- were increased by ATO. In addition, we detected a decreased GSH content in ATO-treated cells. The GSH-depleted cells mainly showed propidium iodine-positive staining, indicating that the majority of the cells were dead. Diethyldithiocarbamate (DDC; an inhibitor of Cu,Zn-SOD) induced apoptosis and the loss of mitochondrial transmembrane potential (ΔΔΨm) in HeLa control cells. DDC intensified apoptosis, the loss of mitochondrial transmembrane potential, increased levels of O22·- and GSH depletion in ATO-treated cells. L-buthionine sulfoximine (BSO; an inhibitor of GSH synthesis) did not induce apoptosis in HeLa control cells, but increased levels of apoptosis, O22·- and GSH depletion in ATO-treated cells. In conclusion, the changes in intracellular GSH levels rather than ROS levels are tightly related to the enhancement of ATO-induced apoptosis in HeLa cells by DDC or BSO.

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