Death and cell cycle progression are differently conditioned by the AgNP size in osteoblast-like cells

Silver nanoparticles (AgNPs) are useful to a wide range of consumer's and medical products, due to their antimicrobial and anti-inflammatory activities. AgNPs have been used to prevent the microbial colonization, therefore decreasing the risk of infection, on implantable devices, tumor prostheses, bone cement and surgical instruments. However, the putative toxicity of AgNPs to bone cells is still poorly understood. Therefore, this study aimed to contribute to enlighten the role of ionic silver release of small sized NPs on the biological outcomes of bone cells, in particular to what concerns to induction of cytotoxic and genotoxic effects. To achieve that goal osteoblast-like MG-63 cells were exposed to well characterized PVP coated AgNPs of two different primary sizes (10nm and 20nm) and evaluated after 24 and 48h. Our results showed that, the smaller sized AgNPs (10nm) are more reactive and prone to form large aggregates, being therefore mandatory to provide a careful characterization of the particles, before the toxicity assessment. We also demonstrate that for short period exposures (up to 48h) ionic silver (from AgNO₃) is more toxic than the corresponding dose of AgNP. However, when assessing longer term exposures by the clonogenic assay, we demonstrated the inverse effect, the AgNPs turn out being more toxic, completely inhibiting plate efficiency. Therefore, AgNPs toxicity cannot be attributed to the dissociated Ag⁺ alone. Also, when comparing size-dependent effects, we demonstrate that AgNP20 were found to induce a cell cycle arrest at G0/G1 and apoptosis, while AgNP10 did not induce a cytostatic effect, but rather induced necrosis. Finally, combining the chemical and toxicological profiles of both AgNP sizes, we hypothesize that the size dependent AgNP toxicity may be associated in part with the NPs interference with the cell membranes and consequent uptake/adsorption processes.