The wide scale use of ZnO nanoparticles (NPs) in the world consumer market has resulted in likelihood of exposure to human beings. The present study was aimed to assess the in vitro and in vivo interactions of ZnO NPs in the mammalian system and to elucidate the possible mechanism of their toxicity. Our in vitro results using human epidermal cells (A431), primary human epidermal keratinocytes and human liver cells (HepG2) demonstrated that cells exposed to ZnO NPs exhibit a decrease in cell viability which was independent of NP dissolution. ZnO NPs also induced oxidative DNA damage as evidenced by an increase in the Fpg sensitive sites. The reactive oxygen species triggered a decrease in mitochondrial membrane potential and an increase in the ratio of Bax/Bcl2 leading to apoptosis through the intrinsic pathway. In addition, ZnO NPs induced phosphorylation of JNK, P38 and P53ser15. The results from our in vivo studies using a mouse model showed that ZnO NPs induce lipid peroxidation, oxidative DNA damage and apoptosis in liver which further confirmed our in vitro findings. The data from the present study provide valuable insights into the cellular interactions of ZnO NPs and the underlying molecular mechanism of their toxicity. The results also stress the need for a comprehensive environmental health and safety assessment of engineered nanomaterials to ensure safer nanotechnology based products.

The wide scale use of ZnO nanoparticles (NPs) in the world consumer market has resulted in likelihood of exposure to human beings. The present study was aimed to assess the in vitro and in vivo interactions of ZnO NPs in the mammalian system and to elucidate the possible mechanism of their toxicity. Our in vitro results using human epidermal cells (A431), primary human epidermal keratinocytes and human liver cells (HepG2) demonstrated that cells exposed to ZnO NPs exhibit a decrease in cell viability which was independent of NP dissolution. ZnO NPs also induced oxidative DNA damage as evidenced by an increase in the Fpg sensitive sites. The reactive oxygen species triggered a decrease in mitochondrial membrane potential and an increase in the ratio of Bax/Bcl2 leading to apoptosis through the intrinsic pathway. In addition, ZnO NPs induced phosphorylation of JNK, P38 and P53ser15. The results from our in vivo studies using a mouse model showed that ZnO NPs induce lipid peroxidation, oxidative DNA damage and apoptosis in liver which further confirmed our in vitro findings. The data from the present study provide valuable insights into the cellular interactions of ZnO NPs and the underlying molecular mechanism of their toxicity. The results also stress the need for a comprehensive environmental health and safety assessment of engineered nanomaterials to ensure safer nanotechnology based products.