Role of hypoxia in growth factor responses: differential effects of basic fibroblast growth factor and...

Both recombinant basic fibroblast growth factor and platelet-derived growth factor-BB homodimer are potent inducers of new tissue generation in models of normal dermal repair. However, their therapeutic targets include chronic wounds, which are frequently characterized by local tissue hypoxia. To explore the potential of recombinant basic fibroblast growth factor and platelet-derived growth factor-BB homodimer to stimulate more clinically relevant repair, we created an ischemic dermal wound on the rabbit ear by ligating two of the arteries which feed the ear. Both recombinant basic fibroblast growth factor and platelet-derived growth factor-BB homodimer stimulated marked neovascularization of the wound (p < 0.0001), but only recombinant platelet-derived growth factor-BB homodimer accelerated and augmented granulation tissue formation (p = 0.01) and reepithelialization. This study is the first demonstration of a direct angiogenic effect of recombinant platelet-derived growth factor-BB homodimer in vivo. India ink perfusion coupled with endothelial cell-specific histochemistry showed that nearly all the neovessels in all wounds were functional, indicating rapid capillary morphogenesis. In the nonischemic (normal) rabbit ear, recombinant basic fibroblast growth factor and platelet-derived growth factor-BB homodimer accelerated healing comparably, as expected. Higher doses of recombinant basic fibroblast growth factor also failed to elicit stimulatory effects in ischemic wounds. These results indicate that differential responsiveness to growth factors is related to local tissue hypoxia, angiogenesis alone is an insufficient stimulus for repair. These data also suggest new therapeutic approaches for the treatment of chronic wounds.