Comparison of toxicity of uncoated and coated silver nanoparticles

This study compares toxic effects of uncoated (20, 40, 60 and 80 nm) and OECD (Organization for Economic Co-operation and Development) standard citrate-and polyvinylpyrrolidone (PVP)-coated (10, 50, and 75 nm) silver nanoparticles (Ag-NPs) in J774A.1 macrophage and HT29 epithelial cells. The cells were exposed to different concentrations (silver content) of Ag-NPs for 24 h. Analysis showed that uncoated Ag-NPs, at a concentration of 1 mu g/ml, decreased cell viability by 20-40% and that 20 and 40 nm particles were 10% more cytotoxic than the 60 and 80 nm particles. In exposures to coated Ag-NPs, cell viability dropped at 25 mu g/ml or higher concentrations, and the effects were also size-dependent. PVP-coated particles induced greater cytotoxicity than citrate-coated particles. Changes in sub-cellular architecture were observed in J774A. 1 cells upon exposure to test Ag-NPs. Furthermore, uncoated Ag-NPs (1 mu g/mL) decreased the expression of selected cytokines including TNF-alpha, IL-1 beta, and IL-12 (p70) in J774A. 1 and IL-8 in HT29 cells. In contrast, both citrate-and PVP-coated Ag-NPs increased the expression of these cytokines at higher concentrations (25 mu g/ml), and PVP-coated particles elevated cytokine levels the most. Moreover, while uncoated Ag-NPs resulted in decreased glutathione (GSH) content and increased superoxide dismutase (SOD) activity in test cells in a size-dependent manner at 1 mu g/ml, coated Ag-NPs caused non-significant changes in GSH and SOD, even at the highest test concentrations. Lastly, uncoated (20 and 40 nm) at 1 mu g/ml and coated Ag-NPs (10 nm PVP) at 50 mu g/ml slightly increased the production of reactive oxygen species (ROS). Our data showed that uncoated Ag-NPs are more toxic than coated Ag-NPs. While uncoated Ag-NPs appear to suppress inflammatory responses and enhance oxidative stress in the test cells, coated Ag-NPs induce toxic effects through up-regulation of cytokines. Our findings support the toxicity of Ag-NPs as being size-and coating-dependent while providing additional insight on the health impact of Ag-NPs.