We previously described the behaviour of different cobalt forms, i.e., cobalt nanoparticles (CoNP), cobalt microparticles (CoMP) and cobalt ions (Co(2+)), in culture medium (dissolution, interaction with medium components, bioavailability) as well as their uptake and intracellular distribution in Balb/3T3 mouse fibroblasts (Sabbioni, Nanotoxicology, 2012). Here, we assess the cytotoxicity and morphological transformation of CoNP compared not only to Co(2+), but also to CoMP and to released Co products. Cytotoxicity reached maximum at 4-h exposure, with ranking CoMP > CoNP > Co(2+). However, if we consider toxicity as a function of intracellular Co, toxicity of the ionic forms seems to prevail over the particles. Co forms other than Co(2+) released from particles had toxicity intermediate between particles and ions. Alterations in concentrations of essential elements (Cu, Mg, Zn) in cells exposed to Co particles may contribute to toxicity. Both CoMP and CoNP (but not Co(2+) and other released Co forms) induced morphological transformation (CoMP > CoNP). This was dependent on reactive oxygen species production and lipid peroxidation, as indicated by inhibition of type III foci with ascorbic acid. The present results suggest that the previously demonstrated massive mitochondrial and nuclear Co internalisation and DNA adduct formation by CoMP and CoNP (Sabbioni, Nanotoxicology, 2012) induce toxicity and transformation. On the contrary, the role of ions released by particles in culture medium is negligible. Thus, both the chemical and the physical properties of Co particles contribute to cytotoxicity and morphological transformation.
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