Apoptosis of HUVECs after exposure to silica nanoparticles for 24 h.
(A) Apoptotic and necrotic populations of cells double-stained with PI- and FITC-labled Annexin V were depicted by flow cytometry. FITC negative and PI negative were designated as live cells in the lower left quadrant; FITC positive and PI negative as apoptotic cells in the upper left quadrant; FITC positive and PI positive as necrotic cells in the upper right quadrant; and FITC negative and PI positive as large nuclear fragments in the lower right quadrant. (B) HUVECs exposure to silica nanoparticles caused increase of both necrosis and apoptosis rate. The apoptosis rate was much lower than the necrosis rate. Data are expressed as means ± S.D. from three independent experiments (*p<0.05).