A comparative study of nickel nanoparticle and ionic nickel toxicities in zebrafish: histopathological changes and oxidative stress.

Industry demand for nanomaterials is growing, but metal nanoparticle toxicity is not fully understood. For example, nickel nanoparticles (NiNPs) are used in electric capacitors, and their consumption is increasing, but there have been few reports of their toxicity and environmental effects. To elucidate the toxicological characteristics of NiNPs, we investigated their effects on the histopathology and oxidative states of zebrafish (Danio rerio) and compared the results with those of ionic nickel. Zebrafish exposed to four different concentrations of NiNPs or NiCl2 for 72 hr or 7 days were subjected to histopathological analysis, and tissue samples were subjected to analyses for oxidative stress and gene expression. High concentrations of both NiNPs and NiCl2 caused tissue damage in the gills, digestive tract, and liver. The damage was typically characterized by epithelial degeneration and necrosis in the gills, esophagus, and intestines, as well as by lipid loss and palisade pattern degradation in the liver. The damages to the gills, esophagus, and intestines were more severe after exposure to NiNPs, but exposure to NiCl2 led to more severe liver damage. Exposure to NiNPs increased lipid peroxidation in the skin but decreased it in the liver and intestines; exposure to NiCl2 increased lipid peroxidation in the intestines. Only exposure to NiCl2 changed antioxidative responses, enzymatic antioxidant activities, and metallothionein gene expression. These results indicate that NiNPs, which are highly adsorptive, cause severe damage to the epithelium by physical contact with the cell surface and production of reactive oxygen spices, whereas ionic nickel, which is absorptive, affects cellular antioxidative responses by absorption into the body and delivery to the liver.