Mechanisms of Toxicity of Amorphous Silica Nanoparticles on Human Lung Submucosal Cells in Vitro: Protective Effects of Fisetin

There is growing evidence that amorphous silica nanoparticles (SiO₂-NP) can cause an inflammatory response in the lung. We studied in vitro the effects of exposing human lung submucosal cells to SiO₂-NP of various sizes (10, 150, and 500 nm) for 2-24 h. Cell survival, reactive oxygen species (ROS), malondialdehyde (MDA) levels, cytokine production, inflammatory gene expression, and genotoxicity were measured after exposure of Calu-3 cells to 10SiO₂-NP in the presence or absence of the flavanoid fisetin and an antioxidant enzyme catalase. The exposure of Calu-3 cells to 10SiO₂-NP resulted in (1) increased cytotoxicity and cell death in a time- and concentration-dependent manner, with a lethal concentration (LC₅₀) of 9.7 μg/mL after 24 h; (2) enhanced gene expression of interleukin (IL)-6, IL-8, and matrix metalloproteinase-9; (3) a significant correlation between increases in MDA and cytotoxicity at 18 h; (4) ROS production; (5) IL-6 and IL-8 release; and (6) up-regulation of the pro-apoptotic genes, p53 and caspase-3. Cell death and inflammatory reactions were attenuated by fisetin and catalase. We observed that 150- and 500SiO₂-NP exerted no toxic effects on Calu-3 cells. In conclusion, the nanotoxicity of amorphous 10SiO₂-NP on submucosal cells is associated with inflammation, the release of ROS leading to apoptosis, and decreased cell survival. The nanotoxic effects of 10SiO₂-NP can be decreased by fisetin and catalase treatment, implicating oxidative stress in this injury.