Matrix metalloproteinase-9 may play a role in recanalization and recurrence after therapeutic embolization of aneurysms or arteries.

Purpose: Matrix metalloproteinase (MMP)-9 plays various roles in vascular healing and angiogenesis. This study was conducted to determine if MMP-9 is involved in healing or recanalization after therapeutic occlusion of arteries or aneurysms.

Materials And Methods: Angiographic and pathologic changes were investigated in canine bilateral venous pouch carotid aneurysms embolized with gelatin sponges with or without previous endothelial denudation, a procedure that can prevent recanalization. To assess a potential role of MMP-9, messenger RNA (mRNA) and protein were compared in denuded and nondenuded aneurysms 4, 7, and 14 days after embolization. To assess if MMP-9 is essential to arterial recanalization, transmyocardial angiography and pathologic findings were compared 14 days after carotid occlusion with platinum coils in MMP-9-knockout and wild-type mice.

Results: Denudation of the endothelial lining led to improved angiographic results at 3 weeks (P < .001). Neointimal closure of the aneurysm neck was more complete in denuded versus nondenuded aneurysms. Denudation was followed by a decrease in MMP-9 mRNA (86%, P < .05) and protein (30%, P < .05) 7 days after embolization and a decrease in von Willebrand factor compared with nondenuded aneurysms. MMP-9 immunostaining of axial sections from embolized aneurysms confirmed MMP-9-positive endothelialized clefts, which were absent in denuded aneurysms. Transmyocardial angiography and pathologic examination showed recanalization of one of nine coiled carotid arteries of MMP-9-knockout mice, compared with five of seven controls (P = .035).

Conclusions: MMP-9 may play a role in recanalization of arteries after coil occlusion and in recurrences after sponge embolization of aneurysms.