The synergistic effects of trolox on arsenic-mediated apoptosis are unique to cancer cells. (A) Normal human PBMCs were isolated from 3 healthy donors using a Ficoll gradient. Colony-forming ability of PBMCs treated with As₂O₃ and trolox was assessed by counting CFU-Es, CFU-GMs, and BFU-Es after 15 days. Results are representative of 3 independent experiments each performed in triplicate. (B) Mouse embryonic fibroblasts were treated with As₂O₃ with or without trolox for 3 days. Apoptosis was detected by PI staining and quantitated by flow cytometry measurement of PI-positive cells. Each bar represents an average of 3 independent samples. Asterisks indicate significant differences from As₂O₃-treated cells (P < .001).