Endothelial cell aging detection by means of atomic force spectroscopy

Endothelial cell aging is related to changes not only in cell phenotype, such as luminal changes, intimal and medial thickening, and increased vascular stiffness, but encompasses different cell responses to various substances including drugs or nanomaterials. In the present work, time- and dose-dependent elasticity changes evoked by silver nanoparticles in endothelial cells in early (below 15) passages were analyzed. Silver nanoparticle concentrations of 3, 3.6, and 16 mu g/mL were selected for elasticity measurements for long incubation (24 hours) and of 1 and 3 mu g/mL for monitoring dynamic elasticity changes of 1-, 3-, and 6-hour incubations. Surprisingly, a significant reduction in the cells elasticity modulus at lower number of passages exposed to silver nanoparticles used at 3 mu g/mL for 24 hours was demonstrated. These results are in contrast to those obtained for endothelial cells in late (33-43) passages that may result from cellular aging in response to nanosilver. Furthermore, for short incubation times (1 and 3 hours), SNP-induced significant increase in the cell elasticity modulus was detected. In current work, we also attempted to answer the question whether the changes in cell elasticity were induced by the silver nanoparticles stabilized with polyvinyl pyrrolidone or by stabilizer itself. Elasticity measurements were supplemented by observations made with transmission electron microscopy and scanning electron microscopy, which confirmed the presence of silver nanoparticles inside the cells and on the cell membrane. Additionally, activation of reactive oxygen species was detected for cells exposed to SNPs for 1 and 3 hours, which was accompanied by increased cell elasticity modulus suggesting a possible mechanism of observed phenomenon.