The effect of local application of recombinant human basic fibroblast growth factor (rhbFGF) on fracture repair was examined using normal rats and streptozotocin-diabetic rats with impaired repairing ability. Immediately after fracturing the fibula, rhbFGF was applied by a single injection to the fracture site. Application of rhbFGF increased the volume and mineral content of callus in a dose-dependent manner in both normal and diabetic rats, and callus formation of diabetic rats was stimulated to levels similar to those in nontreated normal rats. The marked effect of rhbFGF on fracture repair was associated with an improvement in the mechanical properties of the healing fibula in both normal and diabetic rats. Immunohistochemical staining showed that endogenous bFGF was widely distributed in normal rats 1 and 3 weeks after fracture, especially in the soft callus and periosteum, whereas much less bFGF was detected in diabetic rats. Insulin treatment of diabetic rats restored the immunostaining for bFGF. These results demonstrate that bFGF is expressed during the early stage of fracture repair, and that the impaired fracture-repairing ability in diabetic rats is associated with reduced expression of bFGF at the fracture site. A single application of bFGF immediately after fracture not only facilitates the repair process in normal rats, but also recovers the impaired repairing ability in diabetic rats. These results suggest that local application of bFGF may facilitate bone union in patients with impaired as well as normal repairing ability.

The effects of a single local injection of recombinant human fibroblast growth factor-2 on the healing of segmental bone defects were evaluated in rabbits. One month after the external fixator originally designed for this experiment was installed in the tibia of the rabbit, a 3-mm bone defect was created by an osteotomy in the middle of the tibia and 0, 50, 100, 200, or 400 microg of fibroblast growth factor-2 in 100 microl of saline solution was injected into the defect. Injection of the growth factor increased the volume and mineral content of newly made bone at the defect in a dose-dependent manner with significant effects at concentrations of 100 microg or greater. These significant effects were observed at 5 weeks and later. One hundred micrograms of the growth factor increased the volume and mineral content of newly made bone by 95 and 36%, respectively, at 5 weeks. These results indicate that a single local injection of fibroblast growth factor-2 stimulates the healing of segmental defects. We speculate that such an injection could be clinically useful for the healing of fractures even when the fracture gap is rather large.

One of the greatest needs in the clinical bone field is a bioactive agent to stimulate bone formation. We previously reported that fibroblast growth factor-2 (FGF-2) exhibited strong anabolic actions on bone formation in models of rodents and dogs. Aiming at a clinical application, this study was undertaken to clarify the effect of a single local application of recombinant human FGF-2 on fracture healing in nonhuman primates. After a fracture was created at the midshaft of the right ulna of animals and stabilized with an intramedullary nail, gelatin hydrogel alone (n = 10) or gelatin hydrogel containing 200 microg FGF-2 (n = 10) was injected into the fracture site. Although 4 of 10 animals treated with the vehicle alone remained in a nonunion state even after 10 weeks, bone union was complete at 6 weeks in all 10 animals treated with FGF-2. Significant differences in bone mineral content and density at the fracture site between the vehicle and FGF-2 groups were seen at 6 weeks and thereafter. FGF-2 also increased the mechanical property of the fracture site. We conclude that FGF-2 accelerates fracture healing and prevents nonunion in primates, and therefore propose that it is a potent bone anabolic agent for clinical use.

No abstract

The effect on intraosseous bone formation of a single local injection of recombinant human basic fibroblast growth factor into the distal femur was examined in normal and ovariectomized rabbits. In normal rabbits, basic fibroblast growth factor increased bone mineral density around the injected site in a dose-dependent manner at 4 weeks, with significant effects at concentrations of 400 micrograms and greater. Doses of 400 and 1,600 micrograms of basic fibroblast growth factor increased bone mineral density by 8 and 9%, respectively, compared with the opposite control femur. Histological examination showed that basic fibroblast growth factor (400 micrograms) induced the proliferation or recruitment of undifferentiated mesenchymal cells around the existing trabeculae at 3 days after the injection. For the first 2 weeks, osteoid formation was strongly stimulated, and this was followed by mineral apposition for another 2 weeks, at which time the femurs were harvested. Consequently, basic fibroblast growth factor stimulated intraosseous bone formation at 4 weeks. We speculate that the direct action of basic fibroblast growth factor on bone formation may be to stimulate proliferation or recruitment of minimally differentiated mesenchymal cells and to initiate the cascade of events in later stages of bone formation. In ovariectomized rabbits, basic fibroblast growth factor (400 micrograms) also increased bone mineral density, histomorphometrical bone formation markers, and trabecular connectivity to levels similar to those in rabbits who had received sham operations.