Apoptosis in arsenic trioxide-treated Calu-6 lung cells is correlated with the depletion of GSH levels rather than the changes of ROS levels

Arsenic trioxide (ATO) can regulate many biological functions such as apoptosis and differentiation in various cells. We investigated an involvement of ROS such as H₂O₂ and O₂^.-, and GSH in ATO-treated Calu-6 cell death. The levels of intracellular H ₂O₂ were decreased in ATO-treated Calu-6 cells at 72 h. However, the levels of O₂^.- were significantly increased. ATO reduced the intracellular GSH content. Many of the cells having depleted GSH contents were dead, as evidenced by the propidium iodine staining. The activity of CuZn-SOD was strongly down-regulated by ATO at 72 h while the activity of Mn-SOD was weakly up-regulated. The activity of catalase was decreased by ATO. ROS scavengers, Tiron and Trimetazidine did not reduce levels of apoptosis and intracellular O₂^.- in ATO-treated Calu-6 cells. Tempol showing a decrease in intracellular O₂^.- levels reduced the loss of mitochondrial transmembrane potential (ΔΨ_m). Treatment with NAC showing the recovery of GSH depletion and the decreased effect on O₂^.- levels in ATO-treated cells significantly inhibited apoptosis. In addition, BSO significantly increased the depletion of GSH content and apoptosis in ATO-treated cells. Treatment with SOD and catalase significantly reduced the levels of O₂^.- levels in ATO-treated cells, but did not inhibit apoptosis along with non-effect on the recovery of GSH depletion. Taken together, our results suggest that ATO induces apoptosis in Calu-6 cells via the depletion of the intracellular GSH contents rather than the changes of ROS levels.