Cellular responses induced by silver nanoparticles: In vitro studies

A systematic study on the in vitro interactions of 7–20 nm spherical silver nanoparticles (SNP) with HT-1080 and A431 cells was undertaken as a part of an on-going program in our laboratory to develop a topical antimicrobial agent for the treatment of burn wound infections.Upon exposure to SNP (up to 6.25 μg/mL), morphology of both the cell types remained unaltered. However, at higher concentrations (6.25–50 μg/mL) cells became less polyhedral, more fusiform, shrunken and rounded. IC50 values for HT-1080 and A431 as revealed by XTT assay were 10.6 and 11.6 μg/mL, respectively. When the cells were challenged with ∼1/2 IC50 concentration of SNP (6.25 μg/mL), clear signs of oxidative stress, i.e. decreased GSH (∼2.5-folds in HT-1080, ∼2-folds in A431) and SOD (∼1.6-folds in HT-1080, 3-folds in A431) as well as increased lipid peroxidation (∼2.5-folds in HT-1080, ∼2-folds in A431) were seen. Changes in the levels of catalase and GPx in A431 cells were statistically insignificant in both cell types. DNA fragmentation in SNP-exposed cells suggested apoptosis. When the apoptotic thresholds of SNP were monitored with caspase-3 assay the concentrations required for the onset of apoptosis were found to be much lower (0.78 μg/mL in HT-1080, 1.56 μg/mL in A431) than the necrotic concentration (12.5 μg/mL in both cell types). These results can be used to define a safe range of SNP for the intended application as a topical antimicrobial agent after appropriate in vivo studies.