<i>In vitro</i> inflammatory and cytotoxic responses of human alveolar cells to amorphous silica nanoparticles exposure

Silicon dioxide nanoparticles (SiO₂NPs) are widely used to manufacture products for human consumption. However, their large-scale use in many fields poses risks to industrial workers. In this study, we investigated the cytotoxic and inflammatory potential of SiO₂NPs in the human cell line A549, representing the human alveolar epithelium. The NPs were characterized using energy-dispersive x-ray spectroscopy coupled with scanning electron microscopy, x-ray diffraction, transmission electron microscopy, dispersion, and dynamic light scattering. The effects on A549 cells were monitored by cell adhesion and proliferation using electrical impedance, as well as cell viability, apoptosis, necrosis, and secretion of multiple inflammatory mediators. SiO₂NPs did not alter the adhesion and proliferation of A549 cells but led to cell death by apoptosis at the highest concentrations tested. SiO₂NP impacted the secretion of pro-inflammatory (tumor necrosis factor-<i>α</i>, interleukin (IL)-8, monocyte chemoattractant protein-1, eotaxin, regulated upon activation, normal T cell expressed and secreted, vascular growth factor, granulocyte-macrophage colony-stimulating factor, and granulocyte-colony stimulating factor) and anti-inflammatory (IL-1ra and IL-10) mediators. These results indicate that, even with little impact on cell viability, SiO₂NPs can represent a silent danger, owing to their influence on inflammatory mediator secretion and unbalanced local homeostasis.