Superior performance of thrombomodulin coated small caliber ePTFE grafts

Abstract

Introduction: The performance of synthetic bypass grafts to tibial level outflow arteries is greatly limited by early thrombosis and intimal hyperplasia. In addition to its anticoagulant effect, thrombomodulin (TM), an endogenous thrombin inhibitor, also displays anti-proliferative and anti-migratory effects on vascular smooth muscle cells. In this study, we coated small caliber expanded polytetrafluoroethylene (ePTFE) grafts with TM to examine its effect on patency and intimal hyperplasia. Methods: 4 mm diameter ePTFE grafts were pretreated with the cross-linking agent 1-ethyl-3-(3-diamethylaminopropyl)-carbodiimide and then incubated with either 40μg (0.1 μg/μl) TM or buffer control at 4o C overnight. Either coated or uncoated grafts were then surgically implanted into the common carotid arteries of male pigs (32–47 kg) as an interposition graft. Grafts were then harvested at 1 week post-implantation and analyzed grossly and histologically for patency and intimal hyperplasia. Samples were also analyzed by scanning (SEM) and transmission (TEM) electron microscopy and immunohistochemistry for the presence of TM on the graft surface at explantation. Results: Successful coating of ePTFE with soluble TM was confirmed using SEM and TEM and protein C activation assays prior to implantation. At 1 week following implantation, 5 of 6 uncoated grafts thrombosed while 5 of 6 TM coated grafts remained patent (P = 0.01). In addition, endothelialization was evident histologically on the TM coated grafts and absent in control grafts. No difference was observed in degree of intimal hyperplasia at 1 week with minimal hyperplasia in either group at this early time point. SEM, TEM and immunohistochemical staining demonstrated the presence of TM remaining on the surface of the explanted coated grafts (open circles). Conclusion: Thrombomodulin can be durably coated onto ePTFE with TM remaining on the graft under arterial flow conditions. TM appears to promote endothelial growth and provides an anti-thrombotic surface to reduce early graft thrombosis.