Effect of silver nitrate solution on corneal epithelial barrier function in rabbits

Some preservatives in eye drops induce corneal epithelial damage. Diquafosol sodium, a dry eye treatment drug released in 2022, contains silver nitrate as a preservative. This study examined the effects of diquafosol sodium ophthalmic solution and silver nitrate solution on the barrier function of corneal epithelial cells in rabbit eyes. The 14 rabbits included in the study were divided into 7 eye drop treatment groups (4 eyes per group): (1) 3% diquafosol (Diquas) without silver nitrate; (2) 3% Diquas LX containing silver nitrate; (3) 3% Diquas LX without silver nitrate; (4) 0.01% silver nitrate; (5) 0.1% silver nitrate; (6) 1% silver nitrate; and (7) saline. Electrical corneal resistance (CR) was measured using a CR-measuring device (CRD) at 30, 60, and 120 minutes after the final instillation, and CR% was calculated. Corneal epithelial damage was evaluated using fluorescein staining 120 minutes after the final instillation.Corneal tissue obtained 120 minutes post-instillation was fixed in 4% paraformaldehyde, permeabilized, and blocked. Zonula occludens-1 protein, which constitutes tight junctions between epithelial cells, was visualized using whole-mount immunohistochemical staining. To examine the expression of ZO-1 in corneal epithelial cells, photographs of the outermost layer of the cornea were taken. CR in the Diquas LX group 1 (containing silver nitrate) reached its peak value (114.2 ± 7.1%) 60 minutes after the final instillation, which was comparable to that in the 0.1% silver nitrate group (117.2 ± 17.6%) and significantly higher than that in the Diquas group 3 (without silver nitrate) (98.8 ± 5.8%; <i>P</i> &lt; 0.05). Zonular occludens-1 protein was localized in a continuous linear pattern at the boundary between epithelial cells in all three Diquas groups. Diquas LX eye drops containing silver nitrate significantly increased CR compared to Diquas eye drops without silver nitrate and improved corneal barrier function. Silver nitrate as a preservative may have contributed to this effect.