Enhancing Bone Neovascularization in Irradiated Distraction Osteogenesis

Introduction: In the setting of bone defects, the injured vasculature and loss of hemodynamic inflow leads to hematoma formation and low oxygen tension which stimulates vascular expansion through the HIf-1α pathway. This pathway upregulates sprouting of type H vessels (CD31hiEmcnhi vessels). We used a irradiated bone model to better characterize the growth of these vessels during distraction osteogenesis. 

Methods: Sprague–Dawley rats were divided into three groups: Distraction Osteogenesis (DO), radiation with DO (xDO), and radiation with DO and DFO implantation (xDODFO). Experimental groups received 35 Gy of radiation. All groups underwent DO. The treatment group received injections into the osteotomy site, every other day, beginning on postoperative day (POD) 4 of DFO. Animals were sacrificed on POD 40 and processed for immunohistochemical analysis. CD31 and Emcn double immunofluorescent staining were performed to evaluate the extent of CD31hiEmcnhi vessel formation. 

Results: There were 6x more type H vessels in DO groups than in xDO groups. Localized DFO significantly increased the abundance of type H vessels of irradiated DO animals compared to xDO by 15x (p 1⁄4 0.00133531). Moreover, the DO and xDODFO groups with higher abundance of type H vessels also demonstrated better angiogenesis and osteogenesis outcomes.

Conclusion: Normal DO demonstrated a significant upregulation of H vessel formation and associated angiogenic-osteogenic coupling. Radiation severely decreased H vessel formation along with an associated significant diminution of new bone formation and nonunion. DFO administration, however, resulted in vascular replenishment and the restoration of high quantities of CD31hiEmcnhi and OPCs, recapitulating the normal process of bony regeneration.