Endothelial Protection of Vasoactive Intestinal Peptide Enhances Angiogenesis Mediated by eNOS Pathway Following Focal Cerebral Ischemia in Rats

In the present study, we investigated the effects of vasoactive intestinal peptide (VIP) on angiogenesis after cerebral ischemia and the mechanism underlying such effects. After a 2 h middle cerebral artery occlusion, the rats were intracerebroventricularly treated using VIP. Functional outcome was studied with the neurological severity score. Apoptosis of rat brain microvascular endothelial cells and angiogenesis were assessed via immunohistochemistry. In addition, Western blotting was carried out to examine the expression of B-cell leukemia-2 (Bcl-2) and Bcl-2-associated X protein (Bax) as well as the levels of endothelial nitric oxide synthase (eNOS) and phosphorylation of eNOS (p-eNOS) in the brain. In ischemic rats, treatment with VIP significantly (P < 0.05) reduced the neurological severity score, and increased the numbers of BrdU positive endothelial cells in enlarged cerebral vessels and CD34 positive capillary density. The angiogenic effect of VIP was attenuated by L-NAME, a non-selective NOS inhibitor. The protein levels of p-eNOS were significantly (P < 0.05) increased in VIP-treated rats. VIP treatment significantly (P < 0.05) decreased the numbers of TUNEL positive endothelial cells, up-regulated the expression of Bcl-2 and inhibited the expression of Bax. The results of the present study suggest that treatment with VIP enhances angiogenesis mediated by eNOS pathway, contributing to improvement in functional outcome in ischemic rats. The proangiogenic action of VIP may be associated with protection against brain microvascular endothelial cells injury by regulating Bcl-2 and Bax expression.