Inhibition And Mechanism Of Intravitreal Cyclooxygenase-2 Inhibitor On Choroidal Neovascularization In A Laser-induced Rat Model

Background:Choroidal neovascularization(CNV) is known to cause major vision loss in many ophthalmic conditions. The most common diseases associated with CNV are age related macular degeneration(AMD), angioid streaks(AS), pathological myopia and presumed ocular histoplasmosis syndrome(POHS). Newly formed vessels generated from the choriocapillaris infiltrate through Bruch's membrane, leading to the formation of a neovascular submacular membrane subretinal space. CNV vessels are fragile and leaky, leading to hemorrhage or exudation, which injures photoreceptor cells. Further, these proliferative vessels induce the formation of fibrovascular scarring, which results in irreversible damage to retinal function and can lead to blindness. CNV results from a local imbalance between pro- and antiangiogenic growth factors. Vascular endothelial growth factor(VEGF), a major pro-angiogenic growth factor, stimulates the proliferation of endothelial cells and increasing their permeability by the induction of fenestrations. Inducible cyclooxygenase, or COX-2, has been shown to modulate the expression of the VEGF ligand and its receptors, and this enzyme isoform has been implicated as an important proangiogenic protein in human and experimental cancers. Cyclooxygenase-2 (COX-2) expresses in CNVs from AMD patients and in the laser-induced CNV in mice. And the selective inhibitors of COX-2 can suppress CNV, but there is no definite result. A selective cyclooxygenase-2 inhibitor, celecoxib, is the only NSAID approved by the Food and Drug Administration for the treatment of familial adenomatous polyposis(FAP) patients. Therefore, the study whether intravitreal celecoxib can suppress choroidal neovascularization in a laser-induced rat model and the mechanism can help us better understand the mechanisms of CNV and find a new way for treatment of the CNV-related disorders.Objective: To observe the inhibition of intravitreal celecoxib on experimental choroidal neovascularization induced by photocoagulation in BN rats and investigate the mechanism.Methods: The experimental choroidal neovascularization was induced by 532 nm laser photocoagulation in BN rat. As soon as photocoagulation, 6 rats were randomly divided into two groups: Medication administration group(n=3) of intravitreous injection with 10μl celecoxib(1mg/ml) and control group(n=3) of intravitreous injection with 10μl PBS(0.01M). The thickness and the area of CNV were qualified by HE(n=3) and choroidal flatmount(n=3) at day 14 after photocoagulation. 33 rats were randomly divided into five groups: control group(6 rats), photocoagulation 1d group(6 rats), photocoagulation 3d group(6 rats), photocoagulation 7d group(9 rats), photocoagulation 14d group(6 rats). The location of COX-2 and VEGF in CNV were detected by immunohistochemistry at day 7 after photocoagulation(n=3). The expression of COX-2 and VEGF was examined by Western Blotting(n=3) and RT-PCR(n=3) in control and at day 1, 3, 7, 14 after photocoagulation. As soon as photocoagulation, 12 rats were randomly divided into two groups: Medication administration group (n=6) and control group(n=6). The expression of COX-2 and VEGF was examined by Western Blotting(n=3) and RT-PCR(n=3) at day 7 after photocoagulation.Results: Compared to the control group, The thickness and the area of CNV in medication administration group were significantly decreased at day 14 after photocoagulation(P<0.01). The protein of COX-2 and VEGF were collocated in vascular endothelial cells and some stromal cells in CNV. The expression of COX-2 was prior to the expression of VEGF. Compared to the control group, the expression of COX-2 and VEGF were significantly increased in 3 to 7 days(P<0.01). In the medication administration group, the expression of VEGF was significantly decreased(P<0.05), but mRNA of COX-2 was not decreased at day 7 after photocoagulation(P>0.05).Conclusion: Celecoxib significantly inhibits the thickness and the area of CNV by intravitreous injection. The COX-2 was increased in the early stage of experimental choroidal neovascularization induced by 532 nm laser photocoagulation in BN rats. COX-2 may plays an important role in the pathogenesis of CNV by regulating VEGF.