Oxidative stress induced by pure and iron-doped amorphous silica nanoparticles in subtoxic conditions.

Amorphous silica nanoparticles (SiO2-NPs) have found broad applications in industry and are currently intensively studied for potential uses in medical and biomedical fields. Several studies have reported cytotoxic and inflammatory responses induced by SiO2-NPs in different cell types. The present study was designed to examine the association of oxidative stress markers with SiO2-NP induced cytotoxicity in human endothelial cells. We used pure monodisperse amorphous silica nanoparticles of two sizes (16 and 60 nm; S16 and S60) and a positive control, iron-doped nanosilica (16 nm; SFe), to study the generation of hydroxyl radicals (HO·) in cellular-free conditions and oxidative stress in cellular systems. We investigated whether SiO2-NPs could influence intracellular reduced glutathione (GSH) and oxidized glutathione (GSSG) levels, increase lipid peroxidation (malondialdehyde (MDA) and 4-hydroxyalkenal (HAE) concentrations), and up-regulate heme oxygenase-1 (HO-1) mRNA expression in the studied cells. None of the particles, except SFe, produced ROS in cell-free systems. We found significant modifications for all parameters in cells treated with SFe nanoparticles. At cytotoxic doses of S16 (40-50 µg/mL), we detected weak alterations of intracellular glutathione (4 h) and a marked induction of HO-1 mRNA (6 h). Cytotoxic doses of S60 elicited similar responses. Preincubation of cells being exposed to SiO2-NPs with an antioxidant (5 mM N-acetylcysteine, NAC) significantly reduced the cytotoxic activity of S16 and SFe (when exposed up to 25 and 50 µg/mL, respectively) but did not protect cells treated with S60. Preincubation with NAC significantly reduced HO-1 mRNA expression in cells treated with SFe but did not have any effect on HO-1 mRNA level in cell exposed to S16 and S60. Our study demonstrates that the chemical composition of the silica nanoparticles is a dominant factor in inducing oxidative stress.

Influence of size, surface area and microporosity on the in vitro cytotoxic activity of amorphous silica nanoparticles in different cell types.

Identifying the physico-chemical characteristics of nanoparticles (NPs) that drive their toxic activity is the key to conducting hazard assessment and guiding the design of safer nanomaterials. Here we used a set of 17 stable suspensions of monodisperse amorphous silica nanoparticles (SNPs) with selected variations in size (diameter, 2-335 nm), surface area (BET, 16-422 m(2)/g) and microporosity (micropore volume, 0-71 microl/g) to assess with multiple regression analysis the physico-chemical determinants of the cytotoxic activity in four different cell types (J774 macrophages, EAHY926 endothelial cells, 3T3 fibroblasts and human erythrocytes). We found that the response to these SNPs is governed by different physico-chemical parameters which vary with cell type: In J774 macrophages, the cytotoxic activity (WST1 assay) increased with external surface area (alphas method) and decreased with micropore volume (r(2) of the model, 0.797); in EAHY926 and 3T3 cells, the cytotoxic activity of the SNPs (MTT and WST1 assay, respectively) increased with surface roughness and small diameter (r(2), 0.740 and 0.872, respectively); in erythrocytes, the hemolytic activity increased with the diameter of the SNP (r(2), 0.860). We conclude that it is possible to predict with good accuracy the in vitro cytotoxic potential of SNPs on the basis of their physico-chemical characteristics. These determinants are, however, complex and vary with cell type, reflecting the pleiotropic interactions of nanoparticles with biological systems.