Topical Modulation of Interleukin-1 Activity in Corneal Neovascularization

PURPOSE: To determine whether inflammatory corneal neovascularization (CNV) is associated with interleukin-1 (IL-1) activity and if so, to assess the efficacy of topical interleukin-1 receptor antagonist (IL-1ra) to suppress CNV. METHODS: Inflammatory CNV was induced on day 0 by placement of paracentral intrastromal sutures in BALB/c murine eyes. Quantification of IL-1alpha and -beta cytokine levels was done by a sandwich enzyme-linked immunosorbent assay (ELISA) on the supernatants of incubated corneas excised at specified time points after induction of CNV (n = 6 per time point studied). To study suppression of CNV by IL-1ra, animals were divided into treatment subgroups that received topical 20 mg/ml of IL-1ra mixed in 0.2% sodium hyaluronate (n = 28) or placebo (vehicle) alone (n = 22) 3 times daily during days 0-35. Other groups of animals received placebo for 1 (n = 10) or 2 (n = 14) weeks before being switched and retained on IL-1ra. Neovascularization was assessed biomicroscopically and graded by using a standardized scheme. RESULTS: Induction of CNV stimulus was associated with a significant surge in the expression of both IL-1alpha (p < 0.001) and IL-1beta (p < 0.001) as early as 2 h after the stimulus, which peaked at 24 h, before decreasing substantially in the case of IL-1beta and returning to basal levels by day 7. Topical application of IL-1ra led to a significant suppression of CNV for the duration of therapy only if initiated early after induction of the neovascular stimulus. Initiation of therapy 1 week after CNV induction was associated only with a transient suppression in the angiogenic response. CONCLUSION: Our data strongly implicate IL-1 as a critical mediator in the early phase of CNV and suggest that IL-1ra can be an effective modality in suppressing CNV if initiated sufficiently early after the inflammatory neovascular stimulus.