Schroeder, Dana

Introduction: Numerous endovascular tools exist for the treatment of intracranial aneurysms with an increased use of flow-diverting devices in recent years. However, the biological mechanisms leading to aneurysm healing or potential complications such as delayed aneurysm ruptures after flow-diverter treatment are not yet well established. We used RNA-sequencing technology to identify genes relevant for biological impact of coils and flow-diverters in elastase-induced saccular aneurysms in rabbits and to identify genes and pathways of potential clinical interest. Methods: Elastase-induced saccular aneurysms were created at the origin of the right common carotid artery. Aneurysms were treated with coils (n=5) or flow-diverters (Pipeline Embolic Device, Covidien, CA) (n=4). Untreated aneurysms (n=6) were used as controls. Messenger RNA and microRNA were isolated from the aneurysms at 4 weeks following treatment. RNA samples were processed using RNA-seq technology. RNA-seq results were analyzed by using the Ingenuity Pathway Analysis tool. Results: Using RNA sequencing for coiled versus non-treated aneurysms, 464 genes were found to be differentially expressed with 58 genes down regulated and 406 genes up regulated. Using the same criteria for the flow-diverter treated aneurysms, 177 genes were found to be differentially expressed with 8 genes down regulated and 169 genes up regulated. Comparing coiled versus flow-diverter treated aneurysms, 13 genes were significantly differentially expressed with 8 down regulated and 5 up regulated genes. Genes identified with the highest interest for aneurysms healing were fibroblast growth factor-23, matrix metalloproteinases (MMP)-1, Scinderin and Basigin (implicated in MMP-2 and MMP-9 regulation). Pathway analysis associated these genes with inflammatory response, cellular migration, and coagulation, among other functions. Conclusions: RNA-sequencing analysis of rabbit aneurysms revealed differential regulation of some key pathways, including inflammation and cellular migration that could explain the different biological mechanisms implicated in aneurysms healing either after coiling or flow-diverter treatments and could explain potential device-related complications.

Purpose Long-term occlusion of coiled aneurysms frequently fails, probably because of poor intrasaccular healing and inadequate endothelialization across the aneurysm neck. The purpose of this study was to determine if attachment of autologous mesenchymal stem cells (MSCs) to platinum coils would improve the healing response in an elastase-induced aneurysm model in rabbits. Materials and methods With approval from the institutional animal care and use committee, aneurysms were created in rabbits and embolized with control platinum coils (Axium; Medtronic) (n=6) or coils seeded ex vivo with autologous adipose-tissue MSCs (n=7). Aneurysmal occlusion after embolization was evaluated at 1 month with angiography. Histological samples were analyzed by gross imaging and graded on the basis of neck and dome healing on H&E staining. Fibrosis was evaluated using a ratio of the total area presenting collagen. Endothelialization of the neck was quantitatively analyzed using CD31 immunohistochemistry. χ2 and Student's t-test were used to compare groups. Results Healing score (11.5 vs 8.0, p=0.019), fibrosis ratio (10.3 vs 0.13, p=0.006) and endothelialization (902 262 μm2 vs 31 810 μm2, p=0.041) were significantly greater in the MSC group. The MSC group showed marked cellular proliferation and thrombus organization, with a continuous membrane bridging the neck of the aneurysm. Angiographic stable or progressive occlusion rate was significantly lower in the MSC group (0.00, 95% CI 0.00 to 0.41) compared with controls (0.67, 95% CI 0.22 to 0.96) (p=0.02). Conclusions Autologous MSCs attached to platinum coils significantly improve histological healing, as they result in improved neck endothelialization and collagen matrix formation within the aneurysm sac.

The dual-layer Woven EndoBridge (WEB) device (WEB II) is designed to improve the performance of the first-generation WEB device. This study was performed to evaluate the acute and chronic performance of WEB II for aneurysm occlusion in an elastase-induced aneurysm model in rabbits. We implanted WEB II devices in 36 elastase-induced aneurysms and followed up for one, three, six, and 12 months. Degree of aneurysm occlusion at follow-up was graded on the Web Occlusion Scale (WOS): Grade A, complete aneurysm occlusion; Grade B, complete occlusion with recess filling; Grade C, residual neck filling; and Grade D, residual aneurysm filling. Hematoxylin and eosin staining was performed for histological assessment of aneurysm healing. Grades A, B, C, and D aneurysm occlusion at one-month follow-up were noted in three (17%), three (17%), eight (44%), and four (22%) of 18 cases, respectively. At the three-month time point Grades A, B, C, and D were shown in two (33%), two (33%), one (17%), and one (17%) aneurysms. Six months after treatment, one (17%), two (33%), two (33%), and one (17%) cases demonstrated Grades A, B, C, and D occlusion. At the 12-month time point, Grades B, C, and D were shown in three (50%), two (33%), and one (17%) aneurysms. Histologic evaluation showed progressive thrombus organization within aneurysm lumen from one to 12 months. These results indicated that the WEB II device can achieve high rates of aneurysm occlusion over time in experimental aneurysms.