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Background Silica nanoparticles (SiO2 NPs) are extensively applied in the biomedical field. The increasing medical application of SiO2 NPs has raised concerns about their safety. However, studies on SiO2 NP-induced retinal toxicity are lacking. Methods We investigated the retinal toxicity of SiO2 NPs with different sizes (15 and 50 nm) in vitro and in vivo along with the underlying mechanisms. The cytotoxicity of SiO2 NPs with different sizes was assessed in R28 human retinal precursor cells by determining the ATP content and LDH release. The cell morphologies and nanoparticle distributions in the cells were analyzed by phase-contrast microscopy and transmission electron microscopy, respectively. The mitochondrial membrane potential was examined by confocal laser scanning microscopy. The retinal toxicity induced by SiO2 NPs in vivo was examined by immunohistochemical analysis. To further investigate the mechanism of retinal toxicity induced by SiO2 NPs, reactive oxygen species (ROS) generation, glial cell activation and inflammation were monitored. Results The 15-nm SiO2 NPs were found to have higher cytotoxicity than the larger NPs. Notably, the 15-nm SiO2 NPs induced retinal toxicity in vivo, as demonstrated by increased cell death in the retina, TUNEL-stained retinal cells, retinal ganglion cell degeneration, glial cell activation, and inflammation. In addition, The SiO2 NPs caused oxidative stress, as demonstrated by the increase in the ROS indicator H2DCF-DA. Furthermore, the pretreatment of R28 cells with N-acetylcysteine, an ROS scavenger, attenuated the ROS production and cytotoxicity induced by SiO2 NPs. Conclusions These results provide evidence that SiO2 NPs induce size-dependent retinal toxicity and suggest that glial cell activation and ROS generation contribute to this toxicity. Graphical Abstract

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Retinal ischemia–reperfusion (RIR) injury is involved in the pathogenesis of various vision‐threatening diseases. The overproduction of reactive oxygen species (ROS) is thought to be the main cause of RIR injury. A variety of natural products, including quercetin (Que), exhibit potent antioxidant activity. However, the lack of an efficient delivery system for hydrophobic Que and the presence of various intraocular barriers limit the effective retinal delivery of Que in clinical settings. In this study, we encapsulated Que into ROS‐responsive mitochondria‐targeted liposomes (abbreviated to Que@TPP‐ROS‐Lips) to achieve the sustained delivery of Que to the retina. The intracellular uptake, lysosome escape ability, and mitochondria targeting ability of Que@TPP‐ROS‐Lips were evaluated in R28 retinal cells. Treating R28 cells with Que@TPP‐ROS‐Lips significantly ameliorated the decrease in ATP content, ROS generation, and increase in the release of lactate dehydrogenase in an in vitro oxygen–glucose deprivation (OGD) model of retinal ischemia. In a rat model, the intravitreal injection of Que@TPP‐ROS‐Lips 24 h after inducing retinal ischemia significantly enhanced retinal electrophysiological recovery and reduced neuroinflammation, oxidative stress, and apoptosis. Que@TPP‐ROS‐Lips were taken up by retina for at least 14 days after intravitreal administration. Molecular docking and functional biological experiments revealed that Que targets FOXO3A to inhibit oxidative stress and inflammation. Que@TPP‐ROS‐Lips also partially inhibited the p38 MAPK signaling pathway, which contributes to oxidative stress and inflammation. In conclusion, our new platform for ROS‐responsive and mitochondria‐targeted drug release shows promise for the treatment of RIR injury and promotes the clinical application of hydrophobic natural products.

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