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

Abstract

PURPOSE. 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. METHODS. 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. RESULTS. 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, Il1b, 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 antiinflammatory LXR/RXR signaling. While inhibiting initial neovascularization, a similar treatment course of dexamethasone did not suppress repeat neovascularization. CONCLUSIONS. 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.

Revascularization after angiogenesis inhibition favors new sprouting over abandoned vessel reuse

“…The persistent vessels remained in the tissue despite a sustained anti-angiogenic milieu, retaining pericyte coverage and an intact, although abnormal, vascular endothelium. Persistent vessels remaining in the tissue are a well-known phenomenon [51], and consistent with the hypothesis of vascular normalization of initial angiogenic vessels following anti-angiogenic treatment [52–54]. Despite this ‘normalization,’ however, we observed abnormalities at the ultrastructural level.…”

Relapse of pathological angiogenesis: functional role of the basement membrane and potential treatment strategies

“…In this model, a month-long period of vascular regression was induced followed by relapse. The relapse of neovascularization was rapid and more aggressive compared to the initial phase of angiogenesis 79 , corroborating observations in tumor studies. Initially, the examination of the regressed corneal vascular bed indicated presence of many ebms with a few persisting blood vessels.…”

“…Recurrence of corneal neovascularization as high as 35% was shown in a prospective interventional case series study following the discontinuation of subconjunctival injections of bevacizumab 77 . Dexamethasone-a corticosteroid-is effective in regressing pathological vessels in the cornea 78 ; however, this treatment was found to be ineffective for regressing recurrent vessels in a cornea model of pathological angiogenesis 79 .…”

“…Some of these pathways include leukocyte extravasation, LPS/IL-1-mediated inhibition of RXR function, ILK signaling, production of nitric oxide and ROS signaling, and innate and adaptive immune responses. Genes such as Il-1β and Cxcl2 were increasingly expressed during relapse than during initial angiogenesis 79 . These findings hint at a potential regulatory basis for the relapse of pathological angiogenesis and a potential memory effect, and some of these pathways can be investigated as targets to inhibit or delay angiogenesis relapse.…”

Discovery of novel L-type voltage-gated calcium channel blockers and application for the prevention of inflammation and angiogenesis

“…gov/pmc/articles/PMC5878206/bin/10456_2018_9594_ MOESM1_ESM.docx). The vessel length from the acquired slit lamp images of the cornea was determined as reported previously [34]. Briefly, the line tool together with the area calculator (ImageJ software, National Institutes of Health, http://rsb.info.nih.gov/ij/index.html) were used to quantify the vascular area as defined by the area of the polygon with vertices demarcated by the limbus and front of neovessels, with the whole area of the polygon determined from the suture position to the limbus and considered as 100%.…”