Significance of nitric oxide and peroxynitrite in permeability changes of the retinal microvascular endothelial cell monolayer induced by vascular endothelial growth factor

Reactive oxygen species (ROS) play an important role in signaling pathways stimulated by growth factors in vascular cells. We investigated whether vas cular endothelial growth factor (VEGF), which is upregulated in diabetic re tinopathy and atherosclerosis, is able to enhance production of ROS, and if so, whether ROS modulate endothelial permeability. ROS levels in bovine re tinal microvascular endothelial cells (BMEC) were measured by the oxidation of 2',7'-dichlorodihydrofluorescein (DCHF), and permeability was examined by monitoring the passage of albumin through BMEC monolayers. VEGF stimulat ed oxidation of DCHF in BMEC, an effect which was inhibited by superoxide d ismutase (SOD) and the nitric oxide (NO) synthase inhibitor, N-G-nitro-L-ar ginine methyl ester (L-NAME), but not by D-NAME. Urate, a scavenger of pero xynitrite, attenuated the VEGF-induced oxidation of DCHF. VEGF elicited a s ignificant increase in the macromolecule permeability of BMEC monolayers wi th in 30 min. SOD did not modify the basal or the VEGF-stimulated hyperperm eability, but the combination of SOD and VEGF induced a transient reduction in permeability after 10 min. L-NAME, but not D-NAME, enhanced VEGF-induce d hyperpermeability without affecting basal values. Urate did not modify th e VEGF-induced changes in permeability. In conclusion, VEGF stimulates oxid ation of DCHF, which most likely represents peroxynitrite formation, and in duces an increase in permeability of BMEC monolayers. Activation of NO synt hase seems to counteract this stimulatory effect of VEGF on endothelial per meability. Copyright(C) 1999 S. Karger AG. Basel.