ROLE OF ENDOTHELIUM IN GRAFT INTIMAL HYPERPLASIA

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The long-term objective of this proposal is to understand the role of the endothelium in intimal hyperplasia of vascular grafts. An endothelial cell (EC) lining on a prosthetic graft is considered since it has been shown to reduce graft thrombogenicity and platelet activation, as well as improve the short-term patency of small caliber grafts. HOwever, EC have potentially undesirable functions, such as the production of smooth muscle cell (SMC) mitogens which may induce excessive proliferation of cells in the subendothelial tissue. In fact, intimal hyperplasia is often most severe in graft regions that are firs endothelialized, in the areas adjacent to the anastomoses. Furthermore, our preliminary studies have suggested that EC seeded onto grafts produce a platelet-derived growth factor-like protein (PDGFc) at very high rates. This growth factor stimulates the proliferation of cultured SMC and is thought to be involved in atherosclerotic lesion development. Experiments in this proposal will test the hypothesis that EC o expanded polytetrafluoroethylene (ePTFE) grafts produce mitogens, including PDGFc, which are responsible for increased SMC proliferation causing subendothelial intimal hyperplasia. We further propose that this activation of EC to produce SMC mitogens may be regulated by alteration of the physical and biochemical properties of the graft substrate, or by changes in the humoral environment. To test these hypotheses, the production of EC-derived growth factors on EC seeded ePTFE prostheses will be related to the degree of graft endothelialization in canine studies extending up to 6 months. At intermediate stages of endothelialization, the graft will be removed, and PDGFc production will be measured and compared to that of adjacent vessels and to cultured cells. Since SMC and macrophages under certain conditions also produce PDGFc, the graft cells responsible for PDGFc production will be identified by in situ hybridization using PDGF A-chain and B-chain cDNA probes. In addition, EC and SMC will be cultured separately and PDGFc production measured in vitro. To determine the effects of substrate on total mitogen and PDGFc production, growth factor secretin in vitro and in vivo will be studied on modified substrates. Furthermore, since fish oils have been shown to reduce graft intimal hyperplasia, and more recently to inhibit PDGFc production in vitro, the effect of these oils on production of growth factors by EC on seeded grafts will be studied. If the proposed studies show that growth factor production by cells on vascular grafts remains high, even after achievement of a stable endothelial lining, then development of means of inhibiting mitogen production may be necessary to control development of anastomotic intimal hyperplasia.