The use of adult adipose-derived stem cells in the creation of a tissue engineered vascular bypass graft

Abstract

Even with the advent of the emerging field of endovascular surgery to correct complications of peripheral and cardiovascular disease, bypass of occluded vessels remains an important surgical technique. According to the American Heart Association, 448,000 inpatient bypass procedures were performed in the United States. Additionally, 8,000,000 Americans present with peripheral arterial disease. Moreover, by 2020 the AHA reports more than 700,000 Americans will have a need for kidney dialysis with a requirement for percutaneous, arterovenous access. Autologous vascular tissue remains the gold standard conduit for arterial bypass providing an effective and versatile substitute for use in these life enhancing and saving procedures. Unfortunately, it has been reported that up to 40% of patients lack adequate tissue for successful surgery. In the absence of autologous tissue, surgeons rely on alternative conduits such as prosthetic grafts. When compared to autologous tissue, the results of coronary artery bypass, lower extremity bypass, and vascular access using prosthetic grafts yield significantly lower patency rates and increased frequency of infection indicating a clear need for improved alternatives. The leading field of Tissue Engineering and Regenerative Medicine aims to provide the understanding, methods, and technology required to generate a solution to this important concern.^ The goal of this proposal was to design, create, and evaluate a tissue-engineered vascular bypass graft utilizing adipose-derived stem cells (ASC) seeded onto a natural conduit of decellularized venous tissue. Initial data demonstrated that adipose-derived stem cells can be easily obtained in large quantity and when cultured in the presence of endothelial cell growth factor and stimulated with shear stress, express markers of the endothelial phenotype. However, these cells were lost when seeded on the lumen of a decellularized venous scaffold and exposed to physiologic shear stress. To prevent detachment, the luminal surface was coated with fibronectin prior to ASC seeding. The construct was then pre-conditioned to shear stress utilizing a novel method. Linear shear conditioning and subsequent up-regulation of integrin expression resulted in ASC retention on the venous scaffold. A further limitation of the use of ASC was lack of nitric oxide synthase expression. To address this issue, ASC differentiation towards the endothelial phenotype was advanced through adenoviral transfection with endothelial nitric oxide synthase. The transfection of the stem cells elicited the production of significant concentrations of bioactive nitric oxide gas. Finally, to assess the utility of the tissue engineered graft they were implanted as aortic interposition grafts within a rabbit model. Compared with nonseeded decellularized vein grafts, tissue engineered grafts were protected against thrombosis and intimal hyperplasia. Taken together, the results of this investigation present clear success in the pursuit of our goal.