Late graft occlusions after coronary artery bypass grafting have been ascribed to neointimal hyperplasia. Given the pivotal role of smooth muscle cells in the pathogenesis of neointimal hyperplasia and the phenotypic heterogeneity of smooth muscle cells across vessels, we hypothesized that differences in long-term graft patency are at least partly related to differences in smooth muscle cell properties. The aim of the present study was to compare the vascular-wall remodeling of human internal thoracic artery, radial artery, and saphenous vein bypass conduits.
We evaluated the intimal thickening of the human graft segments in organ cultures (histopathology, morphometric, and immunofluorescence analyses) and assessed the properties of cultured smooth muscle cells isolated from these vessels in terms of cell proliferation (tritiated thymidine incorporation), migration (modified Boyden chamber), and collagen synthesis (tritiated proline incorporation).
The total vessel-wall growth index and the intimal growth index were significantly higher for saphenous vein rings than for radial artery and internal thoracic artery rings. Immunofluorescence analyses showed predominant involvement of smooth muscle cells in neointimal growth induced by organ culture of saphenous vein rings. Cell proliferation was significantly higher in saphenous vein smooth muscle cells than in radial artery smooth muscle cells and significantly higher in radial artery smooth muscle cells than in internal thoracic artery smooth muscle cells. Migration of smooth muscle cells from saphenous vein grafts was significantly greater than from internal thoracic artery or radial artery grafts. Collagen synthesis was similar in smooth muscle cells from internal thoracic artery, radial artery, and saphenous vein grafts.
Ex vivo vascular-wall remodeling and smooth muscle cell intrinsic growth and migratory properties are dissimilar between arterial and venous grafts and might shed light on reported angiographic patency rates of these grafts.