Sulodexide prevents activation of the PLA2/COX-2/VEGF inflammatory pathway in human retinal endothelial cells by blocking the effect of AGE/RAGE

Diabetic retinopathy is characterized by the breakdown of endothelial blood-retinal barrier. We tested the hypothesis that sulodexide (SDX), a highly purified glycosaminoglycan composed of 80% iduronylglycosaminoglycan sulfate and 20% dermatan sulfate, protects human retinal endothelial cells (HREC) from high glucose (HG)-induced damage, through the suppression of inflammatory ERK/cPLA2/COX-2/PGE2 pathway, by blocking the effect of advanced glycation end-products (AGEs). HREC were treated with HG (25 mM) or AGEs (glycated-BSA, 2 mg/ml) for 48 h, with or without SDX (60 μg/ml) or aflibercept (AFL, 40 μg/ml), a VEGF-trap. SDX protected HREC from HG-induced damage (MTT and LDH release) and preserved their blood-retinal barrier-like properties (Trans Endothelial Electrical Resistance and junction proteins, claudin-5, VE-cadherin and occludin, immunofluorescence and immunoblot) as well as their angiogenic potential (Tube Formation Assay). Both HG and AGEs increased phosphoERK and phospho-cPLA2, an effect counteracted by SDX and, less efficiently, by AFL. Both HG and exogenous VEGF (80 ng/ml) increased PGE2 release, an effect partially reverted by SDX for HG and by AFL for VEGF. Analysis of NFκB activity revealed that HG increased the abundance of p65 in the nuclear fraction (nuclear translocation), an effect entirely reverted by SDX, but only partially by AFL. SDX, AFL and SDX + AFL protected HREC even when added 24 h after HG. These data show that SDX protects HREC from HG damage and suggest that it counteracts the activation of ERK/cPLA2/COX-2/PGE2 pathway by reducing AGE-related signaling and downstream NFκB activity. This mechanism, partially distinct from VEGF blockade, may contribute to the therapeutic effect of SDX.