A major complication of diabetes is amputation of the lower limb due to arterial disease. The resulting vascular insufficiency is created by the narrowing or complete blockage of arteries. Although some vascular branches or collateralization is normally present proximal to the diseased tissue (especially in longterm chronic ischemic tissue), vascularization and blood flow is often poor and incomplete (Yarom, 1992). The most direct way to reduce this risk is to increase the blood flow to the ischemic site.
The aim of this study is to determine whether the local administration of a potent and specific angiogenic synthetic peptide derived from the laminin A chain, SIKVAV (Ser-Ile-Lys-Val-Ala-Val), enhances collateralization of the muscle tissue in a ischemic lower limb rat model. Normally vessels in the adult body are well regulated and do not grow or form new networks. However, under some conditions, for example in response to tumor growth, these vessels are induced to branch and grow to support the expansion of the tumor mass. Information derived from diverse vascular model systems, many involving tumor cells, have resulted in the identification of several angiogenic compounds, such as acid and basic fibroblast growth factor (FGF) and vascular endothelial growth factor (VEGF); however, in vivo some of these compounds were found to be sensitive to proteolysis, thus unstable. The principal investigator has examined the six amino acid peptide SIKVAV and shown that it can be synthesized in large quantities, is extremely angiogenic in tissue culture and in models of angiogenesis in vivo, and has a long halflife. We will use SIKVAV to stimulate collateralization in the lower limb after chronic occlusion of the femoral artery and revascularization will be enhanced by placing a slow release pellet containing the peptide over the diseased area. We will then examine blood flow to skeletal muscle using latex beads, and vascular casts to determine the degree of vascularization to the tissue. To better understand the process of induced neovascularization by several forms of this peptide we will examine directly the biological effect(s) of several forms of SIKVAV in vitro using cultured human umbilical vein endothelial cells. Furthermore we will examine tissue sections of the lower limb by in situ hybridization at different times during the study to determine if the expression of other angiogenic factors (FGF, VEGF, IL1a) are induced by SIKVAV. The ultimate long-range goal will be development of a pharmacological treatment using this peptide directed at increasing new vessels in areas of ischemia. Such treatment would allow improved peripheral vascularization and perhaps result in survival of limbs otherwise destined for amputation.
