Vascular smooth muscle cell endovascular therapy stabilizes already developed aneurysms in a model of aortic injury elicited by inflammation and proteolysis

To investigate the efficiency of endovascular smooth muscle cell (VSMC) seeding in promoting healing and stability in already-developed aneurysms obtained by matrix metalloproteases (MMPs)-driven injury. VSMCs are instrumental in arterial healing after injury and are in decreased number in arterial aneurysms. This cellular deficiency may account for poor healing capabilities and ongoing expansion of aneurysms. Aneurysmal aortic xenografts in rats displaying extracellular matrix injury by inflammation and proteolysis were seeded endoluminally with syngeneic VSMCs, with controls receiving culture medium only. Diameter, structure, and the destruction/reconstruction balance were assessed. Eight weeks after endovascular infusion, aneurysmal diameter had increased further, from 3.0 +/- 0.3 mm to 10.9 +/- 6.5 mm (P = 0.009), and medial elastin content had decreased from 36.5 +/- 8.5 to 5.2 +/- 5.5 surface-percent (S%; P = 0.009) in controls, whereas these parameters remained stable in the seeded group (3.0 +/- 0.3 to 2.7 +/- 0.2 mm, P = 0.08; 36.5 +/- 8.4 to 31.6 +/- 9.7 S%, P = 0.22). VSMC seeding was followed by a decrease in mononuclear infiltration. MMP-1, -3, -7, -9, and -12 mRNA contents were sharply decreased in the diseased wall in response to seeding. Tissue inhibitor of metalloproteinase-1, -2, and -3 mRNAs in the intima were increased in a 2 to 10 magnitude in comparison with controls. Gelatin zymography showed the disappearance of MMP-9 activity and reverse zymography a strong increase in tissue inhibitor of metalloproteinase-3 activity in the seeded group. VSMC-seeded aneurysms were rich in collagen and lined with an endothelium instead of a thrombus in controls. VSMCs endovascular seeding restores the healing capabilities of proteolytically injured extracellular matrix in aneurysmal aortas, and stops expansion.