Dexamethasone treatment and ICAM-1 deficiency impair VEGF-induced angiogenesis in adult brain

BACKGROUND: Infusion of exogenous vascular endothelial growth factor (VEGF) into adult brain at doses above 60 ng/day induces dramatic angiogenesis accompanied by vascular leak and inflammation. Blood vessels formed by this treatment are dilated and tortuous, exhibiting a pathological morphology. Pathological VEGF-induced angiogenesis is preceded by vascular leak and inflammation, which have been proposed to mediate subsequent angiogenesis. METHODS: To test this hypothesis, we infused VEGF into the brains of adult rats to induce pathological angiogenesis. Some of these rats were treated with dexamethasone, a potent anti-inflammatory glucocorticoid, to inhibit inflammation and edema. RESULTS: We demonstrate that inhibition of inflammation by treatment with dexamethasone significantly attenuated VEGF-induced pathological angiogenesis. To present converging evidence that inflammation may be important in this angiogenic process, we also demonstrate that mice genetically deficient in the inflammatory mediator intercellular adhesion molecule-1 have attenuated VEGF-induced angiogenesis. These same mice showed normal amounts of physiological angiogenesis in response to enriched environments, however, suggesting that a generalized reduction in vascular plasticity could not account for their poor angiogenic response to VEGF. CONCLUSIONS: Taken together, the data from these experiments suggest that the inflammation which occurs before or during VEGF-induced pathological brain angiogenesis plays a contributory role in the pathological angiogenic process.