Abstract 441: Cerebral Vasospasm Depends On Rac-1 Mediated Oxidative Stress

Abstract

Subarachnoid hemorrhage is one of the most common events related to hypertensive crisis. The cerebral vasospasm is the complication of subarachnoid hemorrhage that causes more frequently death. Experimental evidences describe a direct relationship between hemolysed blood and vasospasm. Understand the molecular basis of vasospasm could help to reduce the mortality in patients with cerebrovascular damage. To clarify this aim, carotid and basilary arteries of rats were mounted on pressure myography and perfused at 100 mmHg. The vessels were placed in intracerebral fluid and entire (eb) or hemolysed blood (hb) was added. Our results showed that the eb did not modify the diameter of the vessel. Meanwhile, hb caused a clear vasoconstriction (max vasoconstriction: 10±1 vs 430±15, p<0.01). Previous studies have hypothesized that oxidative stress could be involved in the cerebral vasospasm. So, the vessels were incubated with Tyron, an antioxidant agent. Our data demonstrated that the administration of Tyron reduced the vasoconstriction induced by hb (max vasoconstriction: 205±7 vs 410±12, p<0.01) without influencing the effect of eb, suggesting an involvement of oxidative stress in the vascular response. Moreover, using lucigenin assay we found an increase in oxidative stress directly in the vessel treated with hb. One of the most important source of oxidative stress is the NADPH oxidase which needs Rac-1 to be activated. Our results demonstrated that the hb, and not the eb, was able to activate Rac-1 in the vessel, evaluated by Rac-1/PAK complex. To clearly define the role of Rac-1 in the vasoconstriction induced by hb, the vessels were transfected with an adenoviral vector containing Rac-1 dominant negative or an empty adenoviral vector. In this experimental condition, the vascular response induced by the hb was significantly blunted as compared to vessels treated with the empty adenovirus (max vasoconstriction: 180±7 vs 390±17, p<0.01). Our results demonstrate that the vasoconstriction induced by the hb is induced by Rac-1-mediated oxidative stress. Thus, Rac-1 could represent the target of novel therapeutic strategies to reduce the cerebral vasospasm and so the mortality in patients with subarachnoid hemorrhage.