Hypoxia induces permeability in brain microvessel endothelial cells via VEGF and NO

In this study, an in vitro model of the blood-brain barrier, consisting of porcine brain-derived microvascular endothelial cells (BMEC), was used La e valuate the mechanism of hypoxia-induced hyperpermeability. We show that hy poxia-induced permeability in BMEC was completely abolished by a neutralizi ng antibody to vascular endothelial growth factor (VEGF). In contrast, unde r normoxic conditions, addition of VEGF up to 100 ng/mI did not alter monol ayer barrier function. Treatment with either hypoxia or VEGF under normoxic conditions induced a twofold increase in VEGF binding sites and VEGF recep tor 1 (Flt-1) mRNA expression in BMEC. Hypoxia-induced permeability also wa s prevented by the nitric oxide (NO) synthase inhibitor N-G-monomethyl-L-ar ginine, suggesting that NO is involved in hypoxia-induced permeability chan ges, which was confirmed by measurements of the cGMP level. During normoxia , treatment with VEGF (5 ng/ml) increased permeability as well as cGMP cont ent in the presence of several antioxidants. These results suggest that hyp oxia-induced permeability in vitro is mediated by the VEGF/VEGF receptor sy stem in an autocrine manner and is essentially dependent on reducing condit ions stabilizing the second messenger NO as the mediator of changes in barr ier function of BMEC.