Fig. 5

ZnO NPs trigger autophagic cell death. a The pan-caspase inhibitor zVAD-fmk failed to protect cells from ZnO NP-induced toxicity. b The PI3K inhibitor wortmannin partially protected from ZnO NP-triggered cell death. Cells were preincubated with zVAD-fmk and wortmannin prior to exposure to ZnO NPs. The metabolic activity (indicative of cell viability) was determined using the Alamar blue assay after 24 h. Data shown are mean values ± S.D. (n = 3). ****p < 0.0001, (significant difference between control and treatments); ###p < 0.001 (significant difference between the respective treatments). c–e Confocal micrographs of RAW-Difluo™ mLC3 cells exposed for 24 h to ZnO NPs. c control, d ZnO NPs (7.5 µg/mL), and e ZnO NPs (15 µg/mL). For results on CuO NPs using the same autophagy assay, refer to Additional file 1