The extent of apoptosis was evaluated by using Annexin V/PI staining and flow cytometry as described previously [53] . In brief, 1610 6 cells were washed once in 16PBS and were stained with Annexin V-FITC and PI (2 mg/mL) according to manufacturer's instructions. Samples were acquired on a FACScan flow cytometer (Becton Dickinson, San Jose, CA) and analyzed with the WinMDI 2.8 software program.