Effects of silver nanoparticles on corneal epithelial wound healing

Abstract

Purpose : Silver nanoparticles (AgNPs) are used as an antimicrobial additive in a wide array of applications, including ophthalmic use. However, AgNPs often undergo dissolution resulting in release of silver ions, and subsequent cellular toxicity. The corneal epithelium is a primary exposure site for AgNPs that are administered in or around the eye. Therefore, our objectives were to determine the impact of AgNPs on corneal epithelial cell viability and migration in vitro as well as epithelial wound healing in vivo with a rabbit model.

Methods : Three AgNPs were studied: non-coated AgNP (Ag; 20 nm) and 1% and 10% silver silica (AgSiO₂; <10 nm) at concentrations ranging from 0.05-250 µg/mL. Immortalized human corneal epithelial (hTCEpi) cells were incubated for 24 h with AgNPs and cell viability was assessed with Calcein-AM; 0.1% saponin and distilled water were used as positive and negative controls, respectively. A round wound healing assay with a hTCEpi cell monolayer was performed using concentrations of AgNPs that minimally impacted cell viability. An 8 mm epithelial debridement was made in the right eye of 12 rabbits then 1% AgSiO₂ (10 µg/mL, n=6) or balanced salt solution (BSS, n=6) was administered 4 times a day. Fluorescein stain was performed twice daily to monitor wound area until complete healing occurred. Following euthanasia, autometallography was performed on histologic sections of enucleated globes to determine ocular penetration. One-way ANOVA followed by Dunnett’s multiple-comparison test was used for statistical analysis.

Results : Cell viability was significantly (P<0.001) decreased with Ag at ≥25 µg/mL, 1% AgSiO₂ at ≥12.5 µg/mL and 10% AgSiO₂ at ≥25 µg/ml. Migration of the hTCEpi cells was significantly inhibited (P<0.001) following incubation with 1% or 10% AgSiO₂ at ≥5 µg/mL and Ag at ≥25 µg/mL. Epithelial wound closure did not significantly differ (P=0.97) between rabbits treated with 1% AgSiO₂ (10 µg/mL) or BSS; all rabbits were healed at 92 h post wounding. Autometallography of the right eye demonstrated 1% AgSiO₂ in the corneal stroma, Descemet’s membrane, and on the surface of the iris.

Conclusions : The AgNPs are capable of decreasing corneal epithelial cell viability and migration in a concentration-dependent manner in vitro. However, an in vivo study suggests 1% AgSiO₂ does not impair epithelial wound closure and is capable of penetrating into the cornea and anterior chamber following epithelial debridement.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.