Purpose: Acidic fibroblast growth factor (aFGF) is a potent mitogen for vascular and other mesenchymal cells in vitro that can induce angiogenesis in vivo. Although heparin has no mitogenic potential of its own, it is an important aFGF cofactor in vitro and may also be capable of stimulating angiogenesis. Because the development of a collateral vasculature in response to ischemia appears to be dependent on angiogenesis, we compared the abilities of aFGF with or without heparin and heparin alone to accelerate angiogenesis in a rat hind limb ischemia model.
Methods: Daily subcutaneous injections of saline solution (1 ml), heparin (0.05 mg), or human recombinant aFGF with or without heparin (1 microgram aFGF, 0.05 mg heparin) were administered into the hind limb region distal to the point of unilateral femoral artery ligation in the rat for the 10 days immediately after vascular occlusion. Angiogenicity was determined by histologic assessment of treatment outcomes.
Results: Histologic assessment of the number of vessels per microscopic field 10 days after vascular ligation in the fibrofatty tissues distal to the ligation point had the following results: saline solution, 10 +/- 4 vessels; heparin, 13 +/- 4 vessels (p < 0.05 vs saline solution); aFGF, 26 +/- 8 vessels; and aFGF/heparin 36 +/- 8 vessels (aFGF, aFGF/ heparin, p < 0.001 vs saline solution). Similar increases in vascularization were also noted in the skeletal muscle tissues distal to the vascular ligation point. Immunohistochemical analysis for the presence of proliferating cell nuclear antigen, a marker for mitogenic activity, demonstrated corresponding increases in proliferating cell nuclear antigen labeling for each of the treatment groups, expressed as a percentage of total vascular cell nuclei, as follows: saline solution, 7% +/- 2%; heparin, 21% +/- 8% (p < 0.05 vs saline solution); aFGF, 67% +/- 9%; and aFGF/heparin, 83% +/- 5% (aFGF, aFGF/heparin, p < 0.001 vs saline solution).
Conclusions: The increased vascularization and mitogenic activity demonstrated by these respective studies suggest that angiogenesis is significantly accelerated by the administration of heparin alone and is accelerated to a greater extent by the administration of aFGF with or without heparin. The aFGF/heparin regimen may represent an optimal means of augmenting collateral vessel growth to relieve ischemia in the clinical setting.