Chronic in vitro shear stress stimulates endothelial cell retention on prosthetic vascular grafts and reduces subsequent in vivo neointimal thickness

Objective: The absence of endothelial cells at the luminal surface of a pro sthetic vascular graft potentiates thrombosis and neointimal hyperplasia, w hich are common causes of graft failure in humans. This study tested the hy pothesis that pretreatment with chronic in vitro shear stress enhances subs equent endothelial cell retention on vascular grafts implanted in vivo. Methods: Cultured endothelial cells derived from Fischer 344 rat aorta mere seeded onto the luminal surface of 1.5-mm internal diameter polyurethane v ascular grafts. The seeded grafts were treated for 3 days with 1 dyne/cm(2) shear stress and then for an additional 3 days with 1 or 25 dyne/cm(2) she ar stress in vitro. The grafts then were implanted as aortic interposition grafts into syngeneic rats in vivo. Grafts that were similarly seeded with endothelial cells but not treated with shear stress and grafts that were no t seeded with endothelial cells served as controls. The surgical hemostasis time was monitored. Endothelial cell identity, density, and graft patency rate were evaluated 24 hours after implantation. Endothelial cell identity in vivo was confirmed with cells transduced in vitro with beta-galactosidas e complementary DNA in a replication-deficient adenoviral vector. Histologi c, scanning electron microscopic, and immunohistochemical analyses were per formed 1 week and 3 months after implantation to establish cell identity an d to measure neointimal thickness. Results: The pretreatment with 25 dyne/cm(2)-but not with 0 or 1 dyne/cm(2) -shear stress resulted in the retention of fully confluent endothelial cell monolayers on the grafts 24 hours after implantation in vivo. Retention of seeded endothelial cells was confirmed by the observation that beta-galact osidase transduced cells were retained as a monolayer 24 hours after implan tation in who. In the grafts with adherent endothelial cells that were pret reated with shear stress, immediate graft thrombosis was inhibited and surg ical hemostasis time was significantly prolonged. Confluent intimal endothe lial cell monolayers also were present 1 week and 3 months after implantati on. However, 1 week after implantation, macrophage infiltration was observe d beneath the luminal cell monolayer. Three months after the implantation i n who, subendothelial neointimal cells that contained alpha-smooth muscle a ctin were present. The thickness of this neointima averaged 41 +/- 12 mu m and 60 +/- 23 mu m in endothelial cell-seeded grafts that were pre treated with 25 dyne/cm(2) shear stress and 1 dyne/cm(2) shear stress, respectively and 158 +/- 46 mu m in grafts that were not seeded with endothelial cells. Conclusion: The effect of chronic shear stress on the enhancement of endoth elial cell retention in vitro can be exploited to fully endothelialize synt hetic vascular grafts, which reduces immediate in vivo graft thrombosis and subsequent neointimal thickness.