Silica nanoparticles induce endoplasmic reticulum stress response, oxidative stress and activate the mitogen-activated protein kinase (MAPK) signaling pathway.

Application of silica nanoparticles (SiO-NPs) may result in human exposure. Here we investigate unexplored modes of action by which SiO-NPs with average size of 225 nm act on human hepatoma cells (Huh7). We focused on the endoplasmic (ER) stress response and on mitogen-activated protein kinase (MAPK) signaling pathways. Both pathways were induced. ER stress and the associated three unfolded protein response (UPR) pathways were activated as demonstrated by significant inductions of and and a moderate but significant induction of at 0.05 and 0.5 mg/ml. In addition to activation of interferon stimulated genes , , and were up-regulated. As a consequence of ER stress, the pro-inflammatory cytokine TNFα and PP2Ac were induced following exposure to 0.05 mg/ml SiO-NPs. Additionally, this occurred at 0.005 mg/ml SiO-NPs for TNFα at 24 h. This in turn led to a strong transcriptional induction of MAP-kinases and its target genes , and . A strong transcriptional down-regulation of the proapoptotic gene occurred at 0.05 and 0.5 mg/ml SiO-NP. Exposure of Huh7 cells to the anti-oxidant N-acetyl cysteine reduced transcriptional induction of ER stress markers demonstrating a link between the induction of oxidative stress and ER stress. Our study demonstrates that SiO-NPs lead to strong ER stress and UPR induction, oxidative stress, activation of MAPK signaling and down-regulation of . All of these activated pathways, which are analyzed here for the first time in detail, inhibit apoptosis and induce cell proliferation, which may contribute to a hepatotoxic, inflammatory and tumorigenic action of SiO-NPs.