Figure 3: Effect of arsenic trioxide on early apoptosis. Arsenic trioxide induced apoptosis in A549 cells. Propidium iodide (PI) is represented by FL1-H on the x-axis, and annexin V-FITC is represented by FL2-H on the y-axis. Viable cells are found in the lower left quadrant (annexin V and PI negative), apoptotic cells are found in the upper left quadrant (annexin V positive and PI negative), dead cells are found in the upper right quadrant (annexin V and PI positive), and damaged cells are found in the lower right quadrant (annexin V negative and PI positive). Annexin V conjugated with propidium iodide (PI) revealed dead cells as represented in upper right quadrants (A-D). Data from the Annexin V FITC flow cytometry analysis of ATO 48 hr exposure revealed that the dead cells were significantly different (*) compared to the control (E) using the one-way ANOVA analysis (p < 0.05).