Cellular effects of nickel and nickel oxide nanoparticles : focus on mechanisms related to carcinogenicity

Abstract

There has been a rapid increase in the production and usage of nanomaterials during the last decade and therefore it is of great importance to properly investigate safety of these materials. This thesis specifically focuses on nickel (Ni) and nickel oxide (NiO) nanoparticles (NPs). Ni metal particles have been classified by the International Agency for Research on Cancer as possibly carcinogenic to humans, Group 2B, while Ni compounds are classified in Group 1 i.e. carcinogenic to humans. There has been no specific classification for Ni containing nanoparticles yet and the risks or mechanisms of carcinogenicity are not fully elucidated. Human exposure to Ni containing nanoparticles can occur in occupational settings such as through nickel containing dust or through manufacturing of Ni NPs. The overall aim of this thesis was to increase the knowledge about the mechanisms underlying the carcinogenicity of Ni and Ni compounds as well as to particularly elucidate if Ni in the form of NPs (Ni and NiO) act via different mechanisms compared to those of soluble nickel (NiCl2).

In study I different models were employed to investigate genotoxicity and underlying mechanisms. Stronger genotoxic effects were observed for Ni and NiO NPs compared to NiCl2 and oxidative stress was identified as an important mechanism for genotoxicity rather than direct DNA binding. In general, mutagenic effects were low however a significant increase was observed at one concentration of NiO. In study II genotoxicity and the involvement of calcium as a possible underlying mechanism was investigated. Chromosomal damage was induced by Ni and NiO NPs as well as NiCl2 but cellular uptake was only observed for Ni and NiO NPs. A mechanism dependent on calcium and iron was identified for cyto- and genotoxicity. In study III inflammation and secondary genotoxicity was investigated by using macrophages and lung cells in a co-culture model as well as use of a conditioned media approach. Release of inflammatory cytokines from macrophages, exposed to Ni and NiO NPs, was found and evidence of secondary genotoxicity was observed. However it is still unclear what factors are responsible for these observations. In study IV the ability of Ni and NiO NPs as well as NiCl2 to induce markers related to epithelial to mesenchymal transition (EMT) and a stem cell like phenotype was studied. Induction of both EMT and stem cell markers as well as cellular invasion/migration was found. Little to no differences was observed between the Ni and NiO NPs and soluble Ni.

In conclusion both primary and secondary genotoxicity was observed following exposure to Ni and NiO NPs as well as mechanisms related to EMT and a stem cell like phenotype. NiO NPs were most potent in generating intracellular ROS and inducing DNA strand breaks. Ni and NiO NPs was shown to be taken up by the cells while ionic Ni was not (or limited) which lead to the hypothesis that Ni might act via mechanisms related to extracellular factors or interaction with cell membranes/receptors. The studies in this thesis have contributed to the knowledge in the field of different mechanisms related to carcinogenicity of Ni and NiO NPs.