Abstract W P253: Repeated Remote Ischemic Conditioning (RIC) after Intracerebral Hemorrhage Regulates Macrophage Polarization and CD36 Expression to Promote Hematoma Resolution

Abstract

Background: RIC-therapy during sub-arachnoid hemorrhage in humans was found well tolerated. We tested the hypothesis that repeated daily RIC-therapy would improve post-ICH outcomes in mice. Methods: ICH was induced by collagenase injection into the brain of CD1 male mice (4-mo old). Mice were randomized for either once daily RIC-therapy or related sham-procedure starting 2-hours post-ICH until sacrifice. RIC-therapy post-ICH was also tested in mice pre-treated with clodronate-liposome consequently deficient in macrophage population. Laser speckle imager (LSCI) was used to detect changes in peripheral ischemia resulting from space occupying hematoma. SWI/ FLASH (T2*W) MRI was used to estimate hematoma size. Behavioral outcomes were assessed by focal deficit score and beam walk challenge. Hemoglobin content in the brain tissue by spectrophotometry, macrophage polarization with CD36 expression in peripheral blood by flowcytometry, and histopathological analyses in the brain, were also performed. Statistical significance was determined at p<0.05. Results: Even after 5-days post-ICH, peripheral cerebral ischemia was evident, which was significantly attenuated by RIC-therapy due to reduced hematoma size. Effect of RIC-therapy on hematoma resolution was abolished in the clodronate-liposome treated mice. Higher focal deficit score and impaired fine motor coordination were significantly evident in ICH mice, which was attenuated by RIC-therapy. Post-ICH increased hemoglobin content at day 5 was significantly reduced by RIC-therapy. Interestingly, repeated RIC-therapy promoted macrophage polarization towards M2 (anti-inflammatory) phenotype with increased CD36 expression. At 2-weeks post ICH, cresyl violet and Luxol-Fast blue staining showed significantly increased cell death and white matter degeneration (WMD), respectively, in the ICH mice. RIC-therapy after ICH significantly reduced the cell death and WMD in a 2-weeks follow up. Conclusion: Human subjects deficient in CD36 have impaired capability of hematoma resolution. Long-term RIC-therapy might be helpful in spontaneous hematoma resolution via increased M2-type macrophage and CD36 expression.