The Effects of Retinoids on Corneal Neovascularization Induced in the Rat

Abstract

Abstract: : Purpose: Retinoids, naturally occurring and synthetic vitamin A analogs, inhibit angiogenesis in various models. In this study, we examined the ability of topical and intraperitoneal (IP) all–trans retinoic acid and topical 9–cis retinoic acid to inhibit corneal neovascularization induced in the rat by silver nitrate cauterization. Methods: Following corneal injury, rats were randomized into four groups and were given either control vehicle or topical or intraperitoneal retinoids for four days. 30µl of topical all–trans retinoic acid was applied four times per day in 0.1% DMSO or 5% DMSO/corn oil vehicle at concentrations of 1, 10, 100, or 1000 µg/ml while 30µl of topical 9–cis retinoic acid was administered four times per day in 5% DMSO/corn oil at concentration of 10, 100, or 1000 µg/ml. IP all–trans retinoic acid in 0.1% DMSO was given once per day at a dose of 1 or 10 mg/kg/day. Upon completion of the treatment period, the rats were perfused with India ink intravenously. The corneas were harvested and mounted on a glass slide. A masked observer utilized computer image analysisto measure the total length of vessels in mm/mm² of corneal area. Results: Topical all–trans retinoic acid in 0.1% DMSO at a concentration of 1000 µg/ml (120 µg/day) demonstrated 12.2 ± 0.86 mm/mm² of corneal neovascularization (P>0.05), while1000 µg/ml of all–trans retinoic acid in 5% DMSO and corn oil suspension had 14.7 ± 0.65 mm/mm² of corneal neovascularization (P>0.05). 1000 µg/ml of 9–cis retinoic acid in 5% DMSO and corn oil suspension also lacked a significant inhibitory response (15.0 ± 0.45 mm/mm², P>0.05). Lower topical concentrations in all treatment groups also lacked an angiostatic response. Finally, IP all–trans retinoic acid in 0.1% DMSO administered at 10 mg/kg/day demonstrated 8.5 ±1.28 mm/mm² of corneal neovascularization (P >0.5). Conclusions:Our results do not support a role for retinoids as therapeutic agents in the treatment for corneal neovascularization induced by the severe injury utilized in this study.

Keywords: retinoids/retinoid binding proteins • neovascularization • cornea: basic science