Faculty Bibliography

BACKGROUND: : Distraction osteogenesis has revolutionized the treatment of craniofacial deformities, but it is limited by lengthy consolidation periods and tenuous healing in certain clinical settings, such as irradiated tissue. In this study, the authors aim to investigate whether increasing neovascularization by progenitor cell mobilization accelerates bone formation during distraction. METHODS: : Sprague-Dawley rats aged 8 weeks (n = 36) were subjected to unilateral mandibular distraction with 3-day latency, 7-day activation (0.25 mm twice daily), and 21-day consolidation periods. From the beginning of the consolidation period, animals received daily injections of either AMD3100 (bone marrow progenitor cell mobilizing agent) or sterile saline. Animals were euthanized on postoperative day 31; mandibles were harvested; and bone regeneration was assessed using micro-computed tomography, immunohistochemistry, bone morphogenetic protein-2 enzyme-linked immunosorbent assay, and mechanical testing. RESULTS: : Immunohistochemistry demonstrated that AMD3100 treatment increased vascular density and bone formation. Micro-computed tomography and dual-emission x-ray absorptiometry demonstrated that AMD3100-treated animals had improved bone generation compared with sham-treated controls. Greater force was required on three-point testing to break AMD3100-treated bone. Bone morphogenetic protein-2 expression was up-regulated with AMD3100. Interestingly, the nondistracted contralateral hemimandibles treated with AMD3100 were also stronger than sham-treated counterparts. CONCLUSIONS: : Progenitor cell mobilization improves bone regeneration in a rat distraction model. Furthermore, because this effect is seen in healthy bone and in ischemic bone healing during distraction, the mechanism is not merely related to oxygenation, but could be a phenomenon of fluid flow

BACKGROUND: : Although bone repair is a relatively efficient process, a significant portion of patients fail to heal their fractures. Because adequate blood supply is essential to osteogenesis, the authors hypothesize that augmenting neovascularization by increasing the number of circulating progenitor cells will improve bony healing. METHODS: : Bilateral full-thickness defects were created in the parietal bones of C57 wild-type mice. Intraperitoneal AMD3100 (n = 33) or sterile saline (n = 33) was administered daily beginning on postoperative day 3 and continuing through day 18. Circulating progenitor cell number was quantified by fluorescence-activated cell sorting. Bone regeneration was assessed with micro-computed tomography. Immunofluorescent CD31 and osteocalcin staining was performed to assess for vascularity and osteoblast density. RESULTS: : AMD3100 treatment increased circulating progenitor cell levels and significantly improved bone regeneration. Calvarial defects of AMD3100-treated mice demonstrated increased vascularity and osteoblast density. CONCLUSIONS: : Improved bone regeneration in this model was associated with elevated circulating progenitor cell number and subsequently improved neovascularization and osteogenesis. These findings highlight the importance of circulating progenitor cells in bone healing and may provide a novel therapy for bone regeneration

Prolyl hydroxylase domain 2 (PHD2) has been implicated in several pathways of cell signaling, most notably in its regulation of hypoxia-inducible factor (HIF)-1alpha stability. In normoxia, PHD2 hydroxylates proline residues on HIF-1alpha, rendering it inactive. However, in hypoxia, PHD2 is inactive, HIF-1alpha is stabilized and downstream effectors such as vascular endothelial growth factor and fibroblast growth factor-2 are produced to promote angiogenesis. In the present study we utilize RNA interference to PHD2 to promote therapeutic angiogenesis in a diabetic wound model, presumably by the stabilization of HIF-1alpha. Stented wounds were created on the dorsum of diabetic Lepr db/db mice. Mice were treated with PHD2 small interfering RNA (siRNA) or nonsense siRNA. Wounds were measured photometrically on days 0-28. Wounds were harvested for histology, protein, and RNA analysis. Diabetic wounds treated with siRNA closed within 21+/-1.2 days; sham-treated closed in 28+/-1.5 days. By day 7, Western blot revealed near complete suppression of PHD protein and corresponding increased HIF-1alpha. Angiogenic mediators vascular endothelial growth factor and fibroblast growth factor-2 were elevated, corresponding to increased CD31 staining in the treated groups. siRNA-mediated silencing of PHD2 increases HIF-1alpha and several mediators of angiogenesis. This corresponded to improved time to closure in diabetic wounds compared with sham-treated wounds. These findings suggest that impaired wound healing in diabetes can be ameliorated with therapeutic angiogenesis

BACKGROUND: Although different cranioplasty storage methods are currently in use, no study has prospectively compared these methods. The authors compare freezing and subcutaneous storage methods in a rat model. METHODS: Trephine defects (10 mm) were created in 45 Sprague-Dawley rats. The cranial bone grafts were stored in an autologous subcutaneous pocket (n = 15), frozen at -80 degrees C (n = 15), immediately analyzed (n = 12), or immediately replanted into the defect (n = 3). After 10 days of storage, the subcutaneous or frozen grafts were either replanted (subcutaneous, n = 3; frozen, n = 3) or analyzed (subcutaneous, n = 12; frozen, n = 12). Grafts underwent histologic analysis, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, alkaline phosphatase assay, mechanical testing, and micro-computed tomographic imaging. RESULTS: After 10 days of storage, physiologic assays demonstrated a significant decrease in cellular functionality (e.g., alkaline phosphatase assay concentration: fresh, 18.8 +/- 0.77 mM/mg; subcutaneous, 12.2 +/- 0.63 mM/mg; frozen, 8.07 +/- 1.1 mM/mg; p < 0.012 for all comparisons). Mechanical integrity (maximal load) of fresh grafts was greatest (fresh, 9.26 +/- 0.29 N; subcutaneous, 6.27 +/- 0.64 N; frozen, 4.65 +/- 0.29 N; fresh compared with frozen, p < 0.001; fresh compared with subcutaneous, p = 0.006). Replantation of subcutaneously stored and frozen grafts resulted in limited bony union and considerable resorption after 12 weeks; in contrast, replanted fresh grafts demonstrated bony union and little resorption. CONCLUSIONS: Current preservation methods for interval cranioplasty do not maintain bone graft viability. Subcutaneous storage appears to provide a small advantage compared with freezing.