Title: Targeting Neuroinflammation: A Novel Approach to Treating Vasospasm following Subarachnoid Hemorrhage-

Abstract

Background: Cerebral vasospasm (CV) can contribute significant morbidity for subarachnoid hemorrhage (SAH) patients. A key unknown is how CV induction is triggered following SAH. Methods: c57/bl6 wild type and c57/bl6 IL-6 female knockout (KO) mice were utilized with groups: saline injected, SAH, SAH + IL-6 blockade, SAH IL-6 KO, SAH IL-6 KO + IL-6 administration. For SAH, 50m blood was collected from tail puncture and administered into basal cisterns. IL-6 blockade was given at various time points. Various markers of neuroinflammation were measured with western blot and immunohistochemistry. Cerebral blood flow was also measured. Vasospasm was measured via cardiac injection of india-ink/gelatin. Turning test and Garcia’s modified SAH score were utilized. P<0.05 was considered significant. Results: IL-6 expression peaked 3 days following SAH (p<0.05). Human IL-6 was increased in aneurysmal blood (p<0.05). Receptor upregulation was periventricular and perivascular. A significant increase in BBB markers endothelin 1 and occludin were noted following SAH but reduced with IL-6 blockade (p<0.01). CV occurred 5 days post SAH but was absent in IL-6 KO mice and mitigated with IL-6 blockade (p<0.05). IL-6 blockade, and IL-6 KO mitigated effects of SAH on cerebral blood flow (p<0.05). SAH mice had impaired performance on turn test and poor Modified Garcia Scores compared to saline and IL-6 blockade. A distinct microglia phenotype was noted day 5 in the SAH group (overlap coefficients r=0.96 and r=0.94) for Arg1 and iNOS, which was altered by IL-6 blockade. Day 7, a significant increase in toll-like receptor 4 and Stat3 were noted. This was mitigated by IL-6 blockade and IL-6 KO, which also reduced Caspase 3 (p<0.05). Ventricular dilation and increased tunel positivity were noted day 9 but resolved by IL-6 blockade (p<0.05). Conclusion: correlation between IL-6 and CV has been well documented. We show that a mechanistic connection exists via the inflammatory response, and IL-6 blockade provides benefit in reducing CV and its consequences.