Endogenous cell therapy improves bone healing.

BACKGROUND: Although bone repair is often a relatively rapid and efficient process, many bone defects do not heal. Because an adequate blood supply is essential for new bone formation, we hypothesized that augmenting new blood vessel formation by increasing the number of circulating vasculogenic progenitor cells (PCs) with AMD3100 and enhancing their trafficking to the site of injury with recombinant human parathyroid hormone (rhPTH) will improve healing. METHODS: Critical-sized 3-mm cranial defects were trephined into the right parietal bone of C57BLKS/J 6 mice (N = 120). The mice were divided into 4 equal groups (n = 30 for each). The first group received daily subcutaneous injections of AMD3100 (5 mg/kg). The second group received daily subcutaneous injections of rhPTH (5 mg/kg). The third group received both AMD3100 and rhPTH. The fourth group received subcutaneous injections of saline. Circulating vasculogenic PC numbers, new blood vessel formation, and bony regeneration were assessed. Progenitor cell adhesion, migration, and tubule formation were assessed in the presence of rhPTH and AMD3100. RESULTS: Flow cytometry demonstrated that combination therapy significantly increased the number of circulating PCs compared with all other groups. In vitro, AMD3100-treated PCs had significantly increased adhesion migration, and tubule formation was assessed in the presence of rhPTH. Combination therapy significantly improved new blood vessel formation in those with cranial defect compared with all other groups. Finally, bony regeneration was significantly increased in the combination therapy group compared with all other groups. CONCLUSIONS: The combination of a PC-mobilizing and traffic-enhancing agent improved bony regeneration of calvarial defects in mice.