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Alexandra Robciuc, Suvi Ruokonen, Joanna Witos, Antti H Rantamaki, Susanne Wiedmer, Juha M. Holopainen; Toxicity of glaucoma drugs on corneal epithelial cells. Invest. Ophthalmol. Vis. Sci. 2016;57(12):4384. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Glaucoma drugs (GDs) are intended to reduce elevated intraocular pressure and prevent damage to the optic nerve. They are applied topically and increase aqueous humor outflow or reduce aqueous humor production. Majority of the GDs are hydrophobic, similarly to benzalkonium chloride (BAK), and therefore may disturb the organization of the cellular membranes. The aim of our study was to determine the toxicity of the GDs on the ocular surface cells.
The toxicity of clinically efficient doses of latanoprost, timolol maleate, brimonidine tartrate, brinzolamide and pilocarpine hydrochloride was measured at 4, 8, 16 and 24h, using a cell culture of human corneal epithelial cells. The drugs interaction with the plasma membrane was analyzed using the hemolysis assay and capillary electrophoresis. The capacity of the drugs to induce endoplasmic reticulum (ER) stress response was investigated using immunoblotting.
The toxicity assay showed that all GDs affect the viability of the epithelial cells to variable degrees. Early toxicity was measured for pilocarpine 4% and brimonidine 0.1% and 0.15% with 60% cell death at 4h, while pilocarpine 2% and latanoprost 0.005% showed almost 100% toxicity but only after 16h. Timolol 0.5%, as well as pilocarpine 1%, induced 40% cell death at 24h. However, the hemolysis assay was negative for all GDs and capillary electrophoresis confirmed that the GDs interact with the lipid membrane but the interaction is weak and cannot account for the cell death through lysis. Immunoblotting for ER stress markers revealed that the drugs activate the ER stress pathways but only timolol, latanoprost and, to a lower extent, brimonidine have the capacity to induce apoptosis through upregulation of CHOP.
Our study suggests that all GDs affect the viability of the corneal epithelial cells and that the toxicity is determined by their interaction with intracellular components. Topical application implies that GDs need to penetrate the cornea in order to reach their specific targets, consequently, their toxicity could explain, at least in part, their local side effects. These findings support the conclusions from the PESO study, which showed that filtering surgery can be considered as first line of treatment and furthermore suggest that intraocular long-retention implants could be safer to the ocular surface compared to the topical application of anti-glaucoma drugs.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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