In the present study, toxicity of commercial zinc oxide nanoparticles (ZnO NPs) was studied on the bacterium Pseudomonas sp., human promyelocytic leukemia (HL-60) cells, and peripheral blood mononuclear cells (PBMC). The toxicity was assessed by measuring growth, cell viability, and protein expression in bacterial cell. The bacterial growth and viability decreased with increasing concentrations of ZnO NP. Three major proteins, ribosomal protein L1 and L9 along with alkyl hydroperoxides reductase, were upregulated by 1.5-, 1.7-, and 2.0-fold, respectively, after ZnO NP exposure. The results indicated oxidative stress as the leading cause of toxic effect in bacteria. In HL-60 cells, cytotoxic and genotoxic effects along with antioxidant enzyme activity and reactive oxygen species (ROS) generation were studied upon ZnO NP treatment. ZnO NP exhibited dose-dependent increase in cell death after 24-h exposure. The DNA-damaging potential of ZnO NP in HL-60 cells was maximum at 0.05 mg/L concentration. Comet assay showed 70-80% increase in tail DNA at 0.025 to 0.05 mg/L ZnO NP concentration. A significant increase of 1.6-, 1.4-, and 2.0-fold in ROS level was observed after 12 h. Genotoxic potential of ZnO NPs was also demonstrated in PBMC through DNA fragmentation. Thus, ZnO NP, besides being an essential element having antibacterial activity, also showed toxicity towards human cells (HL-60 and PBMC).
Keywords: Cytotoxicity; DNA damage; MTT; Protein expression; ROS; ZnO NP.