BACKGROUND:
Despite the success of distraction osteogenesis (DO) in treating craniofacial disease and extremity deformities, distraction protocols are limited by lengthy activation and consolidation phases as well as uncertain healing in certain clinical settings, such as in a previously irradiated tissues. Neovascularisation, or the growth of new blood vessels, plays an important role in formation of new bone and it is a rate limiting process in DO. Using a rat DO model, we investigated whether AMD3100, a partial CXCR4 agonist and mobilizing agent of endothelial progenitor cells (EPCs) involved in new blood vessel formation, would accelerates bony formation in the consolidation phase of DO.
METHODS:
Using our previously described rat distraction model, Sprague Dawley rats aged 8 weeks (n=16) were subjected to unilateral mandibular distraction with 3 day latency, 7 day activation (0.25mm twice daily), and 21 day consolidation phases. From the beginning of the consolidation phase, animals received daily injections of either AMD3100 (10mg/kg) or sterile saline. Circulating endothelial progenitor cell (Sca-1⁺/c-kit⁺) number was quantified using flow cytometry. Animals were sacrificed on postoperative day 31, mandibles were harvested and bony regeneration was assessed radiomorphometrically using micro-CT. CD31 and osteocalcin staining were performed on 6-μm frozen sections of the mandibles to assess for vascular density and osteoblast density, respectively.
RESULTS:
Flow cytometry confirmed an increase in circulating EPCs in response to AMD3100 therapy; peaking with a near 4-fold increase from baseline at treatment day 7, remaining elevated through treatment day 14 and returning to baseline by treatment day 21. Micro-CT demonstrated AMD3100-treated animals had substantially improved bony regeneration compared to sham-treated controls. Immunohistochemistry of the distracted mandibles demonstrated that AMD3100 treatment increased the vascular density showed by CD31 staining (10.76±0.74% vs. 6.59±1.21%, p=0.043). Osteoblast density showed by osteocalcin staining was substantially increased in AMD3100 treated animals compared to sham treated controls (8.93±0.87% vs. 3.94±1.3%, p= 0.032).
CONCLUSIONS:
AMD3100 improves bony regeneration in a rat distraction model as evidenced by increased neovascularization and osteogenesis. This may provide a novel therapy to allow DO to be used in irradiated jaws or other situations known to have impaired bony healing. Furthermore, we may be able to accelerate the rate of bone formation and consolidation, leading to more rapid distraction protocols, diminished patient discomfort and decreased patient morbidity.