An investigation into human vein graft intimal hyperplasia.

The most common cause of vein bypass graft failure in the postoperative period of 1 month to 1 year is stenosis, which occurs in up to 30% of arterial reconstructions. This thesis investigates the intimal hyperplasia underlying such lesions using a laboratory model. The first chapter reviews the current literature regarding vein graft stenoses and is followed in Chapter 2 by a brief introduction to tissue and organ culture and their usefulness as investigative research tools. Before embarking on a study of a pathological condition, Chapter 3 studies the structure of the "normal" long saphenous vein in patients undergoing arterial surgery. A degree of intimal thickening was identified in the majority of the veins in this population, the possible causes of which are discussed. The fourth chapter describes and validates an organ culture of human saphenous vein to study the vascular biology of vein graft intimal hyperplasia. Since smooth muscle cell proliferation is a pivotal event in the development of such lesions, a reliable and reproducible method of assessing proliferation was required and is described in Chapter 5. Chapter 6 investigates the effect of endothelial denudation on the development of intimal thickening, and an organ coculture study described in Chapter 7 positively identifies a soluble paracrine mediator produced by the endothelium which can promote intimal hyperplasia. The following chapters utilise variations of the coculture method to further define the precise role played by the endothelium. Chapter 8 demonstrates that isolated, cultured endothelial cells do not promote intimal thickening in denuded veins, suggesting that the normal anatomical location of endothelial cells overlying smooth muscle cells in the vein wall may be important. Chapter 9 therefore describes the development of a method to reseed endothelial cells onto denuded vein segments in order to observe whether the development of intimal hyperplasia can be restored. This proved not to be the case, possibly because the process of culturing had phenotypically altered the endothelial cells, thereby rendering them incapable of producing their paracrine factor. However, a number of other hypotheses and methods by which they could be investigated, are also discussed. The main drawback of human saphenous vein organ culture is that it is a no-flow system. There is considerable evidence in the literature to show that haemodynamics modify the normal and pathological structure and function of blood vessels. Chapter 10 therefore describes the development of an in vitro flow model of saphenous vein graft intimal hyperplasia in an attempt to model the in vivo situation more closely. The final chapter summarises the data presented in this thesis, draws conclusions, and examines prospects for future research in this field.