Nonporous silica nanoparticles (SiNPs) have potential as promising carriers for ophthalmic drugs. However, the in vivo safety of ocular topical SiNPs remains unclear. This study investigated the in vivo safety of oral and ocular topical applications of 100 nm-sized SiNPs in Sprague-Dawley rats. The rats were divided into the following four groups: low-dose oral administration (total 100 mg/kg of SiNPs mixed with food for one week), high-dose oral administration (total 1000 mg/kg of SiNPs mixed with food for one week), ocular topical administration (10 mg/ml concentration, one drop, applied to the right eyes four times a day for one month), or a negative control (no SiNP treatment). The rats were observed for 12 weeks to investigate any signs of general or ocular toxicity. During the observation period, no differences were observed in the body weights, food and water intakes, behaviors and abnormal symptoms of the four groups. No animal deaths occurred. After 12 weeks, hematologic, blood biochemical parameters and ophthalmic examinations revealed no abnormal findings in any of the animals. The lack of toxicity of the SiNPs was further verified in autopsy findings of brain, liver, lung, spleen, heart, kidneys, intestine, eyeballs, and ovaries or testes.

Nonporous silica nanoparticles (SiNPs) are promising drug carrier platforms for intraocular drug delivery. In this study, we investigated the safety of three different sizes of SiNPs (50, 100, and 150 nm) in a human corneal endothelial cell (HCEC) line, B4G12. The HCECs were exposed to different concentrations (0, 25, 50, and 100 µg/ml) of three sizes of SiNPs for up to 48 h. Cellular viability, autophagy, lactate dehydrogenase (LDH) assay, and mammalian target of rapamycin (mTOR) pathway activation were evaluated. Intracellular distribution of the SiNPs was evaluated with transmission electron microscopy (TEM). TEM revealed that the SiNPs were up-taken by the HCECs inside cytoplasmic vacuoles. No mitochondrial structural damage was observed. Both cellular viability and LDH level remained unchanged with up to 100 µg/mL of SiNP treatment. Autophagy showed a significant dose-dependent activation with 50, 100, and 150 nm SiNPs. However, the mTOR activation remained unchanged. Human corneal tissue culture with 100 µg/ml concentrations of SiNPs for 72 h revealed no significant endothelial toxicity. In vivo corneal safety of the SiNPs (0.05 ml intracameral injection, 200 mg/ml concentration) was also verified in rabbit models. These findings suggested that 50, 100, and 150 nm SiNPs did not induce acute significant cytotoxicity in corneal endothelial cells at concentrations up to 100 µg/mL. However, long-term toxicity of SiNPs remains unknown.

Although the wound healing effects of nitric oxide (NO) are known, the mechanism by which NO modulates corneal wound healing remains unclear. In this study, we investigated the effect of exogenous NO donor (NaNO₂) on corneal wound healing. We found that NaNO₂(0.1 μM to 100 μM) increased human corneal epithelial cell (HCEC) viability and migration. It also modulated the phosphorylation of mitogen-activated protein kinases (MAPKs) in a time- dependent manner in those HCECs. Further, p38 MAPK phosphorylation increased at 6 h and normalized at 24 h, while the phosphorylation of extracellular signal regulated kinase (ERK) was increased both at 6 h and 24 h. Topical treatment with NaNO₂(10 μM) enhanced corneal epithelial healing and decreased corneal opacity in murine corneal alkali burn model by modulating inflammatory cytokines. Our findings suggest that NO increased HCEC proliferation and migration via time-dependent MAPK activation and eventually enhanced corneal recovery from the alkali burn.

The retina plays a key role in human vision. It is composed of cells that are essential for vision signal generation. Thus far, conventional medications have been ineffective for treating retinal diseases because of the intrinsic blood–retinal barrier. Nanoparticles (NPs) are promising effective platforms for ocular drug delivery. However, nanotoxicity in the retinal tissue has not received much attention. This study used R28 cells (a retinal precursor cell line that originated from rats) to investigate the safety of two commonly used types of NPs: silica nanoparticles (SiO₂NPs, 100 nm) and titanium dioxide nanoparticles (TiO₂NPs, 100 nm). Cellular viability and reactive oxygen species generation were measured after 24, 48, and 72 h of exposure to each NP. Cellular autophagy and the mTOR pathways were evaluated. The retinal toxicity of the NPs was investigated in vivo in rat models. Both types of NPs were found to induce significant dose-dependent toxicity on the R28 cells. A significant elevation of reactive oxygen species generation was also observed. Increased autophagy and decreased mTOR phosphorylation were observed after SiO₂NPs and TiO₂NPs exposure. The diffuse apoptosis of the retinal cellular layers was detected after intravitreal injection.

Objective: To investigate the toxicity of cetalkonium chloride (CKC) on primary cultured human corneal epithelial cells (HCECs). Methods: HCECs were subjected to various concentrations (0.03125 × 10⁻⁴ to 2.0 × 10⁻⁴% (w/v)) of CKC for durations ranging from 24 to 72 h. Cell viability was evaluated using the CCK-8 kit along with live and dead cell staining. Intracellular reactive oxygen species (ROS) levels were measured 20 min following CKC exposure. Observations of changes in cell morphology, cytoplasmic actin filaments, and mitochondrial distribution were conducted using immunocytochemistry and MitoTracker assays. Protein expression levels related to cell survival pathways, including mTOR, ERK, Akt, Bcl-xL, and BAX, were examined via Western blot analysis. Results: CKC exhibited dose-dependent toxicity in HCECs. Exposure to CKC concentrations below 0.125 × 10⁻⁴% resulted in no significant decrease in HCEC viability for up to 72 h. Conversely, exposure to CKC at concentrations of 1.0 × 10⁻⁴% or higher led to significantly decreased HCEC viability. Following exposure to higher concentrations of CKC, elevated levels of intracellular ROS and LDH release were observed. This toxicity was further characterized by decreased levels of phosphorylated mTOR, phosphorylated Akt, phosphorylated ERK, and Bcl-xL, as well as an increase in BAX expression. As the CKC concentration increased, HCECs decreased in size, and mitochondria displayed a loss of characteristic punctate staining. Conclusions: Our findings indicated that exposure to CKC caused significant toxicity in HCECs, which varied with concentration and duration of exposure. This toxicity was associated with an increase in ROS, mitochondrial alterations, and a decline in activity of the cell survival pathways.