Adrenomedullin reduces VEGF-induced retinal vascular hyperpermeability.

Abstract

Purpose: Purpose:<br /> Diabetic macular edema, caused by the retinal microvascular changes that compromise blood-retinal barrier (BRB), is a major cause of visual dysfunction. Adrenomedullin (AM) is an endogenous peptide first identified as a strong vasodilating molecule. We showed that AM knockout mice (AM-/-) are embryonic lethal with abnormal vascular development and first proved that AM also plays important roles in vascular integrity. AM is also expressed in eyes and upregulated in various eye diseases. However, most of the pathophysiological significance is unknown. In this study, we investigated the effect of AM on retinal vascular hyperpermeability.

Methods: Methods:<br /> AM (10^-7M) or vehicle (control) was administered to wild-type C57BL/6 mice (WT) and Kimba mice using subcutaneous osmotic pumps (0.5μl/h) for 2 weeks. The integrity of the BRB was quantified by Evans blue technique (EB) and Confocal Scanning-Laser Ophthalmoscopy (SLO) in Fluorescein Angiography (FA). Retinal neovascularization and avascular area were evaluated using flat-mount specimens of the mouse retina stained with isolectin B4. Next, using human umbilical vein endothelial cell (HUVEC), AM’s effect on the barrier function was studied by measuring the transendothelial electrical resistance (TEER) and the permeability of FITC-dextran across the endothelial cell monolayer. The expression of tight junction proteins was analyzed by immunohistochemistry and immunoblotting.

Results: Results:<br /> In Kimba mice, which overexpress hVEGF165 in their retinas, BRB breakdown with enhanced vascular permeability was observed. On the other hand, exacerbation of FA leakage grade in Kimba mice was rescued by the exogenous administration of AM. In vitro analysis proved that AM-treatment elevated HUVEC TEER dose-dependently. Moreover, AM reversed VEGF-induced TEER reduction.

Conclusions: Conclusions:<br /> These results suggest that AM attenuates BRB breakdown induced by VEGF165. Our observation may provide a basis for novel therapeutic approach to ocular vascular diseases.