Impact of amorphous SiO₂ nanoparticles on a living organism: Morphological, behavioral, and molecular biology implications

It is generally accepted that silica (SiO₂) is not toxic. But the increasing use of silica nanoparticles (SiO₂NPs) in many different industrial fields has prompted the careful investigation of their toxicity in biological systems. In this report, we describe the effects elicited by SiO₂NPs on animal and cell physiology. Stable and monodisperse amorphous silica nanoparticles, 25 nM in diameter, were administered to living Hydra vulgaris (Cnidaria). The dose-related effects were defined by morphological and behavioral assays. The results revealed an all-or-nothing lethal toxicity with a rather high threshold (35 nM NPs) and a LT50 of 38 h. At sub lethal doses, the morphophysiological effects included: animal morphology alterations, paralysis of the gastric region, disorganization and depletion of tentacle specialized cells, increase of apoptotic and collapsed cells, and reduction of the epithelial cell proliferation rate. Transcriptome analysis (RNAseq) revealed 45 differentially expressed genes, mostly involved in stress response and cuticle renovation. Our results show that Hydra reacts to SiO₂NPs, is able to rebalance the animal homeostasis up to a relatively high doses of SiO₂NPs, and that the physiological modifications are transduced to gene expression modulation.