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Improvement of Corneal Barrier Function by the P2Y₂ Agonist INS365 in a Rat Dry Eye Model

From Santen Pharmaceutical Co., Ltd., Nara Research and Development Center, Japan.

PURPOSE. Because purinoceptor P2Y₂ receptor agonists elicit increases in net Cl, fluid transport, and glycoprotein release onto the ocular surface, they are candidates for treatment of dry eye syndrome. Accordingly, the effects of such an agonist INS365 on these parameters were characterized in a rat dry eye model.

METHODS. An SD rat dry eye model was used in which exorbital lacrimal gland extirpation decreased the Schirmer test score by at least 50%. After 8 weeks, when significant increases occurred in corneal epithelial permeability, INS365-containing eye drops were applied six times daily for the next 4 weeks at concentrations from 0.03% to 3.0%. Corneal barrier function was evaluated based on measurements with a modified anterior fluorometer of fluorescein penetrance at 1, 2, and 4 weeks after initial application. After INS365 application, the periodic acid–Schiff reagent (PAS)–stained area was evaluated in histologic sections of the tarsal and bulbar conjunctiva.

RESULTS. Ten minutes after INS365 eye drop application at doses of either 3.0% or 8.5%, a 1.5-fold transient increase in tear fluid secretion occurred in both the control and dry eye model animals. These transient increases nearly returned to baseline after 60 minutes. Furthermore, after 5 minutes, 1.0% INS365 was sufficient to cause a maximal transient decrease in the PAS-stained area of more than 30%, which thereafter recovered toward the initial level. Beginning at 2 weeks and continuing for an additional 2 weeks, maximal declines in dye penetrance of approximately 50% occurred with doses of INS365 as low as 1%. Such improvement in corneal epithelial resistance was accompanied by complete restoration of the PAS-stained area to the level seen in the control animal.

CONCLUSIONS. In a rat dry eye model, the P2Y₂ agonist INS365 was found to improve surface health, based on increases in tear fluid secretion, corneal epithelial resistance, and release of glycoprotein-containing moieties from goblet cells. These effects suggest that INS365 is a potential therapeutic agent for use in the treatment of dry eye syndrome.

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