Repeat Corneal Neovascularization is Characterized by More Aggressive Inflammation and Vessel Invasion Than in the Initial Phase.

Abstract

Treatment of corneal neovascularization can lead to vessel regression and recovery of corneal transparency. Here, we examined the response of the cornea to a repeated stimulus after initial vessel regression comparing the second wave of neovascularization with the first. Corneal neovascularization was induced by surgical suture placement in the rat cornea for 7 days, followed by suture removal and a 30-day regression period. Corneas were then re-sutured and examined for an additional 4 days. Longitudinal slit-lamp imaging, in vivo confocal microscopy, and microarray analysis of global gene expression was conducted to assess the inflammatory and neovascularization response. Inhibitory effect of topical dexamethasone for repeat neovascularization was assessed. After initial robust neovascularization, 30 days of regression resulted in the recovery of corneal transparency; however, a population of barely functional persistent vessels remained at the microscopic level. Upon re-stimulation, inflammatory cell invasion, persistent vessel dilation, vascular invasion, and gene expression of Vegfa, Il1β, Il6, Ccl2, Ccl3, and Cxcl2 all doubled relative to initial neovascularization. Repeat neovascularization occurred twice as rapidly as initially, with activation of nitric oxide and reactive oxygen species, matrix metalloproteinase, and leukocyte extravasation signaling pathways, and suppression of anti-inflammatory LXR/RXR signaling. While inhibiting initial neovascularization, a similar treatment course of dexamethasone did not suppress repeat neovascularization. Persistent vessels remaining after the initial resolution of neovascularization can rapidly reactivate to facilitate more aggressive inflammation and repeat neovascularization, highlighting the importance of achieving and confirming complete vessel regression after an initial episode of corneal neovascularization.