The Alterations Of ES Expression In Ischemic Brain Tissue And The Influences Of Angiogenic Factors On The Cerebral Ischemia

Objective: The CNS is particularly vulnerable to ischemia and acquires sufficient blood supply. Angiogenesis, the sprouting of new capillaries from pre-existing vessels, is a crucial force for protecting ischemic brain tissue through to increase brain tissue perfusion and improve functional outcome after cerebral ischemia. The endogenous angiogenic response is the result of the balance between pro-angiogenic factors and antiangiogenic factors. In the present study, we measure the endostain (a strong anti-angiogenic factor) and vascular endothelial growth factor (VEGF) levels in the brain tissue of rabbits following cerebral ischemia induced by middle cerebral artery occlusion (MCAO), investigate the effects of NO donor L-arginine and exogenous VEGF on angiogenesis and apoptosis of brain cells, and evaluate whether NO and VEGF may interact to promote angiogenesis in an ischemic brain.Materials and Methods: Eighty New Zealand white rabbits were randomly assigned according to the experimental objective. Animal were anesthetized with sodium pentobarbital (30mg/kg, i.v.), fixed in a special rabbit operating table. Rabbit models of focal cerebral ischemia were performed according to the method described by O'Brien et al. with a minor modification. The middle cerebral artery (MCA) was exposed at its origin through left orbital approach. A small wire hook was inserted under the unilateral MCA, and then the MCA was blocked by the bipolar electric coagulation and cut at its origin. Systemic administration of L-arginine was given to rabbit with middle cerebral artery occlusion and VEGF (165) was infused into right lateral ventricular of the animals (0.5μg/Kg) in 1 hour after MCAO. Control animals received vehicle only. The expression of VEGF and endostation were measured by enzyme-linked immunosorbent assay (ELISA), fluorescent RT-PCR and immunohistochemistry, respectively. In situ hybridization was used to characterize the expression of endostatin mRNA. Brain microvascular density (MVD) was assessed with CD34 immunohistochemistry. Change of apoptotic cells was evaluated by flow cytometer and brain edema was determined by measuring brain water content.Results: Both the protein (P<0.01) and mRNA (P<0.05) of endostatin increased significantly in the ischemic brain tissues after MCAO compared with the control group. VEGF production increased in the brain after cerebral ischemia (P<0.05). There was significantly enhancement in MVD of brain tissue in animal treated with VEGF compared to controls (P<0.01) in 5 day after cerebral ischemia, but brain water content also significantly increased in VEGF-treated animals compared to controls (P<0.05). The apoptosis ratio of brain cells in L-arginine treated group was significantly reduced (P<0.01) and brain MVD was significantly increased (P<0.01). Furthermore, systemic administration of L-arginine to rabbits with middle cerebral artery occlusion significantly enhanced VEGF mRNA expression (P<0.05), and diminished water levels of ischemic brain tissue.Conclusion: Angiogenesis may play an important role in neuroprotection after cerebral ischemia. Therefore, targeting the formation of new blood vessels is regarded as a promising strategy in cerebral ischemia therapy. However, angiogenesis is a complex process, including a complicated mechanism which is modulated by many pro-angiogenic factors and anti-angiogenic factors. The study is the first report that cerebral ischemia not only induces VEGF expression but also leads to an up-regulation of endostatin in the brain. The up-regulation of endostatin may serve as a deleterious mechanism for ischemic injury through blocking angiogenesis. The exogenous VEGF and L-arginine can promote angiogenesis in ischemic brain tissue and play important roles in neuroprotection for focal cerebral ischemia. The exogenous NO enhances VEGF expression and alleviates brain edema and suggests combination treatment with NO donor and VEGF may have synergistic effects on neuropretection after cerebra ischemia.