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AB El-Remessy, MA Behzadian, T Franklin, G Abou-Mohamed, RW Caldwell, RB Caldwell; Peroxynitrite (ONOO-) Increases Vascular Permeability in Experimental Diabetes by a Mechanism Involving Increased Expression of Urokinase Plasminogen Activator Receptor (uPAR) . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1308.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To define the role of ONOO- as mediator of retinal hyperpermeability in experimental diabetes and to examine the molecular mechanisms of this process. Diabetes-induced breakdown of the blood-retinal barrier is positively correlated with increased VEGF expression. VEGF-induced permeability increases have been associated with activation of urokinase plasminogen activator (uPA) and expression of its receptor (uPAR) in bovine retinal endothelial (BRE) cells (Behzadian et al., ARVO 2001). Based on our data showing that high glucose treatment induces ONOO- formation in BRE cells (El-Remessy et al, ARVO 2001), we hypothesized that ONOO- causes retinal vascular hyperpermeability by increasing VEGF expression and that uPAR plays a critical role in the process. Methods: Diabetes was induced in rats by streptozotocin injection. After 2 weeks, BRB permeability was quantified by analyzing extravasation of fluoresceine-labeled albumin. Lipid peroxidation, NOS expression, NOS activity and formation of nitrotyrosine (peroxynitrite end product) were assessed biochemically. Expression of uPAR mRNA and VEGF mRNA was analyzed by real time RT-PCR using a light Cycler and uPAR protein was measured by western blot analysis. Results: Retinal vascular permeability in the diabetic rat retina was increased 2 fold (P<0.01) versus control. This was correlated with significant increases in expression of VEGF and uPAR mRNA. Increases also were observed in uPAR, eNOS and nNOS protein expression as well as in formation of nitric oxide, superoxide anion and their product ONOO-. Treatment of diabetic rats with a NOS inhibitor (L-NAME, 50mg/ kg) or peroxynitrite scavenger (uric acid, 160 mg/kg) blocked the increases in ONOO- formation and prevented the increases in both permeability and uPAR expression. Conclusion: Taken together, these data indicate that early diabetes increases BRB permeability by a mechanism involving the activity of peroxynitrite in promoting expression and activation of uPAR.
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