Role of oxidative stress in the apoptosis induction by NPs in 16HBE 14o- cells. Flow cytometry analysis after 4 hours of NP exposure (20 μg.cm-2) with or without PEG-catalase after 30 minutes of pretreatment with 1000 I U PEG-catalase A) DNA fragmentation (% of cells in the sub-G1 peak) B) loss of mitochondrial membrane potential (% of cells with low CMXRos staining) C) caspase activation (% of vibrant positive cells). Data are represented as mean ± SD (n = 3). Representative result of three independent experiments. * statistically different from control p < 0.05 (two tailed). # statistically different from particle treated group without catalase p < 0.05 (two tailed).