O-016 The distribution and role of M1 and M2 macrophages in healing of aneurysms after platinum coil embolization

Introduction Pro-inflammatory coatings of platinum coils have been used in the treatment of intracranial, saccular aneurysms but failed to reduce recurrence rates. Dysregulation of macrophage polarization, in which pro-inflammatory M1 macrophage population fail to transition to an anti-inflammatory M2 macrophage phenotype, is a characteristic feature of poorly healing wounds. In this study, we aimed to evaluate the distribution of M1 and M2 macrophages and to analyze their association with healing in aneurysms embolized by endovascular coiling. Methods We created 17 elastase-induced aneurysms in female rabbits and subsequently embolized with platinum coils. Aneurysm occlusions were evaluated with angiographic imaging. Aneurysm tissue was harvested at 1, 3, and 6 months for evaluation. Quantification of M1 and M2 macrophage expression was performed by immunofluorescence. Collagen deposition was determined by Masson’s trichrome staining technique. Histologic grading of aneurysms was also performed. Results Angiographic data indicated no significant differences in the geometry of aneurysms between the three treatment-to-sacrifice time groups. M1 macrophage expression in aneurysm tissues was highest at 1 month post-treatment and progressively decreased at 3- and 6 months. Expression of M2 macrophages progressively increased at 3 months and 6 months post-treatment. Collagen deposition was highest at 6 months post-treatment. Our data demonstrated a moderate to weak positive relationship between M2 macrophage expression and collagen deposition and total histologic scores and a strongly positive relationship between M2 macrophage expression and total histologic scores at 6-months post-treatment. Conclusion Our study showed that M2 macrophage expression had a strong positive relationship with total histologic scores at a later stage of healing after endovascular coiling. These findings suggest that interventions aimed at stimulating M2 macrophage expression may improve aneurysm healing after embolization. Disclosures Z. Khashim: None. D. Daying: None. D. Yong Hong: None. S. Herting: None. T. Caracena: None. D. Jakaitis: None. D. Maitland: None. D. F. Kallmes: None. R. Kadirvel: None.