Dose-response effect of human equivalent radiation in the murine mandible: Part II. A biomechanical assessment

Intraoperative Optimization of Stromal Vascular Fraction for Remediation of Radiated Fracture Repair: Closing the Gap on Clinical Translation of Cell-Based Therapies

BACKGROUND

Mechanical processing techniques to isolate the stromal vascular fraction (SVF) may optimize clinical translation of cell-based therapeutics. Therefore, the purpose of this study was to develop a technique for intraoperative isolation of SVF for immediate therapeutic use with the primary aim of enhancing bone healing at irradiated fracture sites.

METHODS

Male Lewis rats (n = 29) were divided into groups: fracture, radiation with fracture, and radiation with fracture and SVF implantation. Experimental groups received 35 Gy of targeted radiation. All groups underwent mandibular osteotomy and external fixation. SVF was isolated from inguinal fat pads using Tulip Sizing Transfers, serial filtration, and centrifugation. The resultant cell pellet was implanted at the osteotomy site. After 40 days, bone union and mineralization were evaluated based on gross pathology and micro-computed tomography, respectively, and biomechanical strength testing was performed.

RESULTS

SVF treatment increased union rates after radiation (79% vs 20%). Additionally, SVF improved both bone mineral density (666.2 ± 32.0 vs 312.2 ± 51.7; P = 0.000) and bone volume fraction (0.744 ± 0.072 vs 0.350 ± 0.041; P = 0.000) compared with the irradiated control. In fact, SVF treatment into irradiated fracture sites resulted in bone mineral density and bone volume fraction similar to the bone formed at nonirradiated fracture sites, as there was no significant difference between groups. SVF treatment did not significantly improve biomechanical strength compared with the irradiated control.

CONCLUSIONS

In this study, we developed a novel approach utilizing mechanical methods to enable intraoperative SVF isolation for immediate implantation. SVF demonstrates therapeutic potential for applications in irradiated fracture healing. The results of this study are promising for the long-awaited translation of cell-based therapeutics into the clinical arena.

Pain hypersensitivity, sensorimotor impairment, and decreased muscle force in a novel rat model of radiation-induced peripheral neuropathy

INTRODUCTION

Radiation-induced peripheral neuropathy is a rare, but serious complication often resulting in profound morbidity, life-long disability, and chronic debilitating pain. Unfortunately, this type of peripheral neuropathy is usually progressive, and almost always irreversible. To date, a standardized rat model of radiation-induced peripheral neuropathy has not been established. The purpose of the present study was to examine neuropathic pain, sensorimotor impairment, and muscle force parameters following the administration of a clinically relevant radiation dose in a rat model.

METHODS

Ten rats were randomly assigned to one of two experimental groups: (1) radiation and (2) sham-radiated controls. Radiated animals were given a clinically relevant dose of 35 Gray (Gy) divided into five daily doses of 7 Gy/day. This regimen represents a human equivalent dose of 70 Gy, approximating the same dosage utilized for radiotherapy in oncologic patients. Sham-radiated controls were anesthetized and placed in the radiation apparatus but were not given radiation. All animals were tested for baseline values in both sensorimotor and pain behavioral tests. Sensorimotor testing consisted of the evaluation of walking tracks with the calculation of the Sciatic Functional Index (SFI). Pain-related behavioral measures consisted of mechanical allodynia (von Frey test), cold allodynia (Acetone test), and thermal allodynia (Hargreaves test). Animals were tested serially over an 8-week period. At the study endpoint, electrophysiological and muscle force assessments were completed, and histomorphometric analysis was performed on all sciatic nerves.

RESULTS

Animals that underwent radiation treatment displayed significantly greater pain hypersensitivity to mechanical stimulation as compared to sham radiated controls from weeks 4 to 8 of testing. SFI values indicated sensorimotor impairments in the overground gait of radiated animals as compared to non-radiated animals. Furthermore, radiated animals displayed reduced twitch and tetanic muscle force when compared to sham radiated controls.

CONCLUSIONS

A clinically relevant human equivalent dose of fractionated 35 Gy in rats established significant pain hypersensitivity, impairments in sensorimotor locomotion, and decreased muscle force capacity. This novel rodent model of radiation-induced peripheral neuropathy can be utilized to assess the potential efficacy of therapeutic treatments to either prevent or remediate this clinically debilitating condition.

Effects of different doses of ionizing radiation on alveolar bone repair in post-extraction tooth socket: an experimental study in rats

OBJECTIVE

This study aimed to evaluate the dose-response effects of ionizing radiation (IR) on alveolar bone repair and bone strength after tooth extraction.

MATERIALS AND METHODS

A total of 32 male Wistar rats were used in the study, 28 animals were included in the final analysis, and n = 7 for each experimental group. Mandibular first molars were extracted. After 7 days, the animals were randomly divided into four groups according to single-dose irradiation: NIr, control group; Ir15, irradiated at 15 Gy; Ir20, irradiated at 20 Gy; and Ir30, irradiated at 30 Gy. The tooth extraction sites were subjected to micro-computed tomography (micro-CT), histological, histomorphometric, and biomechanical analyses 14 days after extraction. Data were analyzed using one-way ANOVA followed by Tukey's post hoc test (α = 0.05).

RESULTS

Micro-CT analysis revealed that IR led to lower values of bone volume (BV, in mm3) (0.68 ± 0.08, P < 0.001) and bone volume fraction, ratio of the segmented bone volume to the total volume of the region of interest (BV/TV, in %) (44.1 ± 8.3, P < 0.001) for the Ir30 group compared to the control group. A significantly lower amount of newly formed bone was observed in the Ir30 (P = 0.005) than in the Ir15 group. The histomorphometric results of quantification of bone matrix neoformation and the micro-CT were in agreement, demonstrating greater damage to the Ir30 group. IR30 cells showed a lower percentage of densely packed collagen than control cells. No significant differences were found in the biomechanical parameters.

CONCLUSION

IR affects alveolar bone repair. A dose of 30 Gy reduced the bone healing process owing to a smaller amount of newly formed bone and a lower percentage of densely packed collagen. Therefore, a dose of 30 Gy can be used to successfully establish an animal model of an irradiated mandible that mimics the irradiated clinical conditions.

CLINICAL RELEVANCE

Radiotherapy can lead to severe side effects and tooth extraction is a major risk factor. A proper understanding of the pathological mechanisms of radiation in alveolar bone repair requires the establishment of a suitable animal model of clinical conditions.

Adipose-Derived Stem Cells Enhance Graft Incorporation and Mineralization in a Murine Model of Irradiated Mandibular Nonvascularized Bone Grafting

BACKGROUND

Nonvascularized bone grafting represents a practical method of mandibular reconstruction. However, the destructive effects of radiotherapy on native bone preclude the use of nonvascularized bone grafts in head and neck cancer patients. Adipose-derived stem cells have been shown to enhance bone healing and regeneration in numerous experimental models. The purpose of this study was to determine the impact of adipose-derived stem cells on nonvascularized bone graft incorporation in a murine model of irradiated mandibular reconstruction.

METHODS

Thirty isogenic rats were randomly divided into 3 groups: nonvascularized bone graft (control), radiation with nonvascularized bone graft (XRT), and radiation with nonvascularized bone graft and adipose-derived stem cells (ASC). Excluding the control group, all rats received a human-equivalent dose of radiation. All groups underwent mandibular reconstruction of a critical-sized defect with a nonvascularized bone graft from the contralateral hemimandible. After a 60-day recovery period, graft incorporation and bone mineralization were compared between groups.

RESULTS

Compared with the control group, the XRT group demonstrated significantly decreased graft incorporation (P = 0.011), bone mineral density (P = 0.005), and bone volume fraction (P = 0.001). Compared with the XRT group, the ASC group achieved a significantly increased graft incorporation (P = 0.006), bone mineral density (P = 0.005), and bone volume fraction (P = 0.013). No significant differences were identified between the control and ASC groups.

CONCLUSIONS

Adipose-derived stem cells enhance nonvascularized bone graft incorporation in the setting of human-equivalent radiation.

Therapeutic Efficacy of Adipose-Derived Stem Cells Versus Bone Marrow Stromal Cells for Irradiated Mandibular Fracture Repair

BACKGROUND

Mesenchymal stem cells have immense potential in applications of bone healing and regeneration. However, few studies have evaluated the therapeutic efficacy of adipose-derived stem cells (ASCs) and bone marrow stromal cells (BMSCs) in irradiated bone. The purpose of this study is to compare the ability of ASCs versus BMSCs to enhance healing outcomes in a murine model of irradiated mandibular fracture repair.

METHODS

Forty-eight isogenic male Lewis rats underwent radiation therapy followed by mandibular osteotomy with intraoperative placement of either ASCs or BMSCs. Animals were killed on postoperative day 40. Mandibles were analyzed for union rate, biomechanical strength, vascularity, and mineralization. Groups were compared at P < 0.05 significance.

RESULTS

The ASC and BMSC groups demonstrated 92% and 75% union rates. Compared with the BMSC group, the ASC group demonstrated a trending increase in maximum load ( P = 0.095) on biomechanical strength analysis and a significant increase in vessel number ( P = 0.001), vessel thickness ( P = 0.035), and vessel volume fraction ( P = 0.007) on micro-computed tomography angiography analysis. No significant differences in bone mineralization were identified on micro-computed tomography analysis.

CONCLUSION

This study demonstrates the superior therapeutic efficacy of ASCs over BMSCs in irradiated fracture healing as evidenced by union rate, vascular morphometry, and a trend in biomechanical strength. We posit that the robust vascular response induced by ASCs better recapitulates the sequence and synchronicity of physiologic bone healing compared with BMSCs, thereby improving the reliability of irradiated fracture repair.

Contemporary biomedical engineering perspective on volitional evolution for human radiotolerance enhancement beyond low-earth orbit

A primary objective of the National Aeronautics and Space Administration (NASA) is expansion of humankind's presence outside low-Earth orbit, culminating in permanent interplanetary travel and habitation. Having no inherent means of physiological detection or protection against ionizing radiation, humans incur capricious risk when journeying beyond low-Earth orbit for long periods. NASA has made large investments to analyze pathologies from space radiation exposure, emphasizing the importance of characterizing radiation's physiological effects. Because natural evolution would require many generations to confer resistance against space radiation, immediately pragmatic approaches should be considered. Volitional evolution, defined as humans steering their own heredity, may inevitably retrofit the genome to mitigate resultant pathologies from space radiation exposure. Recently, uniquely radioprotective genes have been identified, conferring local or systemic radiotolerance when overexpressed in vitro and in vivo. Aiding in this process, the CRISPR/Cas9 technique is an inexpensive and reproducible instrument capable of making limited additions and deletions to the genome. Although cohorts can be identified and engineered to protect against radiation, alternative and supplemental strategies should be seriously considered. Advanced propulsion and mild synthetic torpor are perhaps the most likely to be integrated. Interfacing artificial intelligence with genetic engineering using predefined boundary conditions may enable the computational modeling of otherwise overly complex biological networks. The ethical context and boundaries of introducing genetically pioneered humans are considered.

Intraoperative Stromal Vascular Fraction Therapy Improves Histomorphometric and Vascular Outcomes in Irradiated Mandibular Fracture Repair

BACKGROUND

Cell-based treatments have demonstrated the capacity to enhance reconstructive outcomes in recent decades but are hindered in clinical utility by regulatory hurdles surrounding cell culture. This investigation examines the ability of a noncultured stromal vascular fraction derived from lipoaspirate to enhance bone healing during fracture repair to further the development of translatable cell therapies that may improve outcomes in irradiated reconstruction.

METHODS

Isogenic male Lewis rats were divided into three groups: fracture, irradiated fracture, and irradiated fracture with stromal vascular fraction treatment. Irradiated groups received a fractioned dose of 35 Gy before mandibular osteotomy. Stromal vascular fraction was harvested from the inguinal fat of isogenic donors, centrifuged, and placed intraoperatively into the osteotomy site. All mandibles were evaluated for bony union and vascularity using micro-computed tomography before histologic analysis.

RESULTS

Union rates were significantly improved in the irradiated fracture with stromal vascular fraction treatment group (82 percent) compared to the irradiated fracture group (25 percent) and were not statistically different from the fracture group (100 percent). Stromal vascular fraction therapy significantly improved all metrics of bone vascularization compared to the irradiated fracture group and was not statistically different from fracture. Osteocyte proliferation and mature bone formation were significantly reduced in the irradiated fracture group. Bone cellularity and maturity were restored to nonirradiated levels in the irradiated fracture with stromal vascular fraction treatment group despite preoperative irradiation.

CONCLUSIONS

Vascular and cellular depletion represent principal obstacles in the reconstruction of irradiated bone. This study demonstrates the efficacy of stromal vascular fraction therapy in remediating these damaging effects and provides a promising foundation for future studies aimed at developing noncultured, cell-based therapies for clinical implementation.

Overcoming Nuclear Winter: The Cutting-edge Science of Bone Healing and Regeneration in Irradiated Fields

Background:

The incidence of cancer worldwide is expected to be more than 22 million annually by 2030. Approximately half of these patients will likely require radiation therapy. Although radiotherapy has been shown to improve disease control and increase survivorship, it also results in damage to adjacent healthy tissues, including the bone, which can lead to devastating skeletal complications, such as nonunion, pathologic fractures, and osteoradionecrosis. Pathologic fractures and osteoradionecrosis are ominous complications that can result in large bone and soft tissue defects requiring complex reconstruction. Current clinical management strategies for these conditions are suboptimal and dubious at best. The gold standard in treatment of severe radiation injury is free tissue transfer; however, this requires a large operation that is limited to select candidates.

Methods:

With the goal to expand current treatment options and to assuage the devastating sequelae of radiation injury on surrounding normal tissue, our laboratory has performed years of translational studies aimed at remediating bone healing and regeneration in irradiated fields. Three therapeutics (amifostine, deferoxamine, and adipose-derived stem cells) have demonstrated great promise in promoting healing and regeneration of irradiated bone.

Results:

Amifostine confers prophylactic protection, whereas deferoxamine and adipose-derived stem cells function to remediate postradiation associated injury.

Conclusions:

These prospective therapeutics exploit a mechanism attributed to increasing angiogenesis and ultimately function to protect or restore cellularity, normal cellular function, osteogenesis, and bone healing to nonirradiated metrics. These discoveries may offer innovative treatment alternatives to free tissue transfer with the added benefit of potentially preventing and treating osteoradionecrosis and pathologic fractures

Noncultured Minimally Processed Adipose-Derived Stem Cells Improve Radiated Fracture Healing

Adipose-derived stem cells mitigate deleterious effects of radiation on bone and enhance radiated fracture healing by replacing damaged cells and stimulating angiogenesis. However, adipose-derived stem cell harvest and delivery techniques must be refined to comply with the US Food and Drug Administration restrictions on implantation of cultured cells into human subjects prior to clinical translation. The purpose of this study is to demonstrate the preservation of efficacy of adipose-derived stem cells to remediate the injurious effects of radiation on fracture healing utilizing a novel harvest and delivery technique that avoids the need for cell culture. Forty-four Lewis rats were divided into 4 groups: fracture control (Fx), radiated fracture control (XFx), radiated fracture treated with cultured adipose-derived stem cells (ASC), and radiated fracture treated with noncultured minimally processed adipose-derived stem cells (MP-ASC). Excluding the Fx group, all rats received a fractionated human-equivalent dose of radiation. All groups underwent mandibular osteotomy with external fixation. Following sacrifice on postoperative day 40, union rate, mineralization, and biomechanical strength were compared between groups at P < 0.05 significance. Compared with Fx controls, the XFx group demonstrated decreased union rate (100% vs 20%), bone volume fraction (P = 0.003), and ultimate load (P < 0.001). Compared with XFx controls, the MP-ASC group tripled the union rate (20% vs 60%) and demonstrated statistically significant increases in both bone volume fraction (P = 0.005) and ultimate load (P = 0.025). Compared with the MP-ASC group, the ASC group showed increased union rate (60% vs 100%) and no significant difference in bone volume fraction (P = 0.936) and ultimate load (P = 0.202). Noncultured minimally processed adipose-derived stem cells demonstrate the capacity to improve irradiated fracture healing without the need for cell proliferation in culture. Further refinement of the cell harvest and delivery techniques demonstrated in this report will enhance the ability of noncultured minimally processed adipose-derived stem cells to improve union rate and bone quality, thereby optimizing clinical translation.

Development of a Rat Model of Mandibular Irradiation Sequelae for Preclinical Studies of Bone Repair

Repairing mandibular bone defects after radiotherapy of the upper aerodigestive tract is clinically challenging. Although bone tissue engineering has recently generated a number of innovative treatment approaches for osteoradionecrosis (ORN), these modalities must be evaluated preclinically in a relevant, reproducible, animal model. The objective of this study was to evaluate a novel rat model of mandibular irradiation sequelae, with a focus on the adverse effects of radiotherapy on bone structure, intraosseous vascularization, and bone regeneration. Rats were irradiated with a single 80 Gy dose to the jaws. Three weeks after irradiation, mandibular bone defects of different sizes (0, 1, 3, or 5 mm) were produced in each hemimandible. Five weeks after the surgical procedure, the animals were euthanized. Explanted mandibular samples were qualitatively and quantitatively assessed for bone formation, bone structure, and intraosseous vascular volume by using micro-computed tomography, scanning electron microscopy, and histology. Twenty irradiated hemimandibles and 20 nonirradiated hemimandibles were included in the study. The bone and vessel volumes were significantly lower in the irradiated group. The extent of bone remodeling was inversely related to the defect size. In the irradiated group, scanning electron microscopy revealed a large number of polycyclic gaps consistent with periosteocytic lysis (described as being pathognomonic for ORN). This feature was correlated with elevated osteoclastic activity in a histological assessment. In the irradiated areas, the critical-sized defect was 3 mm. Hence, our rat model of mandibular irradiation sequelae showed hypovascularization and osteopenia. Impact statement Repairing mandibular bone defects after radiotherapy of the upper aerodigestive tract is clinically challenging. Novel tissue engineering approaches for healing irradiated bone must first be assessed in animal models. The current rat model of mandibular irradiation sequelae is based on tooth extraction after radiotherapy. However, the mucosal sequelae of radiotherapy often prevent the retention of tissue-engineered biomaterials within the bone defect. We used a submandibular approach to create a new rat model of mandibular irradiation sequelae, which enables the stable retention of biomaterials within the bone defect and should thus facilitate the assessment of bone regeneration.

Implantable hyaluronic acid-deferoxamine conjugate prevents nonunions through stimulation of neovascularization

Approximately 6.3 million fractures occur in the U.S. annually, with 5–10% resulting in debilitating nonunions. A major limitation to achieving successful bony union is impaired neovascularization. To augment fracture healing, we designed an implantable drug delivery technology containing the angiogenic stimulant, deferoxamine (DFO). DFO activates new blood vessel formation through iron chelation and upregulation of the HIF-1α pathway. However, due to its short half-life and rapid clearance, maintaining DFO at the callus site during peak fracture angiogenesis has remained challenging. To overcome these limitations, we composed an implantable formulation of DFO conjugated to hyaluronic acid (HA). This compound immobilizes DFO within the fracture callus throughout the angiogenic window, making it a high-capacity iron sponge that amplifies blood vessel formation and prevents nonunions. We investigated implanted HA-DFO’s capacity to facilitate fracture healing in the irradiated rat mandible, a model whereby nonunions routinely develop secondary to obliteration of vascularity. HA-DFO implantation significantly improved radiomorphometrics and metrics of biomechanical strength. In addition, HA-DFO treated mandibles exhibited a remarkable 91% bone union rate, representing a 3.5-fold improvement over non-treated/irradiated controls (20% bone union rate). Collectively, our work proposes a unique methodology for the targeted delivery of DFO to fracture sites in order to facilitate neovascularization. If these findings are successfully translated into clinical practice, millions of patients will benefit from the prevention of nonunions.

Radioprotection With Amifostine Enhances Bone Strength and Regeneration and Bony Union in a Rat Model of Mandibular Distraction Osteogenesis

BACKGROUND

Using distraction osteogenesis (DO) to regenerate robust endogenous bone could greatly enhance postoncologic reconstruction of head and neck cancer. However, radiation (XRT) corrosive effects still preclude DO's immense potential. We posit that adjunctive pretreatment with the radioprotectant amifostine (AMF) can optimize wound healing and allow for successful DO with quantifiable enhancements in bony union and strength despite previous surgical bed irradiation.

METHODS

Two groups of murine left hemimandibles were exposed to a human equivalent radiation dosage fractionated over 5 daily doses of 7 Gy. AMF-XRT-DO (n = 30) received AMF before radiation, whereas XRT-DO (n = 22) was untreated. All animals underwent left hemimandibular osteotomy and external fixator placement, followed by distraction to a 5.1-mm gap. Left hemimandibles were harvested and mechanically tested for parameters of strength, yield, and breaking load.

RESULTS

Radiation-related complications such as severe alopecia were significantly increased in XRT-DO compared with the AMF-treated group (P = 0.001), whereas infection and death were comparable (P = 0.318). Upon dissection, bony defects were grossly visible in XRT-DO distraction gap compared with AMF-XRT-DO, which exhibited significantly more complete unions (P = 0.004). Those results were significantly increased in the specimens prophylactically treated with AMF (yield: 39.41 N vs 21.78 N, P = 0.023; breaking load: 61.74 N vs 34.77 N, P = 0.044; respectively).

CONCLUSIONS

Our study revealed that AMF enhances biomechanical strength, regeneration, and bony union after radiation in a murine model of DO. The use of prophylactic AMF in combination with DO offers the promise of an alternative reconstructive option for patients afflicted with head and neck cancer.

Meloxicam as a Radiation-Protective Agent on Mandibles of Irradiated Rats

This study evaluated the action of ionizing radiation and the possible radioprotective effect of the non-steroidal anti-inflammatory drug meloxicam on the bone physiology of rat mandibles by assessing the alveolar socket healing and bone strength. Forty male Wistar rats were divided in 4 groups (n=10): control (CG), irradiated (IG), meloxicam (MG), meloxicam irradiated (MIG). A dose of 0.2 mg/kg meloxicam was administered to MG and MIG. After this, IG and MIG were irradiated with 15 Gy radiation dose in the mandible. Forty days after the above procedures, the mandibular first molars were extracted and the animals were killed after 15 or 30 days (n=5). Micro-computed tomography and bending test were used to evaluate alveolar socket healing and bone strength, respectively. At 15 days, bone volume, bone volume fraction and trabecular thickness were higher in the CG and MG than in the IG and MIG; and trabecular separation was higher in the IG compared with the others. At 30 days, there was a difference only in trabecular separation, which was higher in IG than in CG and MG, and MIG did not differ from the others. Bone strength was lower in IG compared with CG and MG, and MIG did not differ from the others. In conclusion, the ionizing radiation affected the bone physiology of rat mandibles, delaying the alveolar socket healing and reducing the bone strength. Moreover, the meloxicam had a positive effect on the trabecular separation in alveolar socket healing and on the bone strength.

Amifostine Treatment Mitigates the Damaging Effects of Radiation on Distraction Osteogenesis in the Murine Mandible

According to the American Society of Clinical Oncology, in 2012, more than 53,000 new cases of head and neck cancers (HNCs) were reported in the United States alone and nearly 12,000 deaths occurred relating to HNC. Although radiotherapy (XRT) has increased survival, the adverse effects can be unrelenting and their management is rarely remedial. Current treatment dictates surgical mandibular reconstruction using free tissue transfer. These complex operations entail extended hospitalizations and attendant complications often lead to delays in initiation of adjuvant therapy, jeopardizing prognosis as well as quality of life. The creation of new bone by distraction osteogenesis (DO) generates a replacement of deficient tissue from local substrate and could have immense potential therapeutic ramifications. Radiotherapy drastically impairs bone healing, precluding its use as a reconstructive method for HNC. We posit that the deleterious effects of XRT on bone formation could be pharmacologically mitigated. To test this hypothesis, we used a rodent model of DO and treated with amifostine, a radioprotectant, to assuage the XRT-induced injury on new bone formation. Amifostine had a profound salutary effect on bone regeneration, allowing the successful implementation of DO as a reconstructive technique. The optimization of bone regeneration in the irradiated mandible has immense potential for translation from the bench to the bedside, providing improved therapeutic options for patients subjected to XRT.

Axially vascularized tissue-engineered bone constructs retain their in vivo angiogenic and osteogenic capacity after high-dose irradiation

In order to introduce bone tissue engineering to the field of oncological reconstruction, we are investigating for the first time the effect of various doses of ionizing irradiation on axially vascularized bone constructs. Synthetic bone constructs were created and implanted in 32 Lewis rats. Each construct was axially vascularized through an arteriovenous loop made by direct anastomosis of the saphenous vessels. After 2 weeks, the animals received ionizing irradiation of 9 Gy, 12 Gy and 15 Gy, and were accordingly classified to groups I, II and III, respectively. Group IV was not irradiated and acted as a control. Tissue generation, vascularity, cellular proliferation and apoptosis were investigated either 2 or 5 weeks after irradiation through micro-computed tomography, histomorphometry and real-time polymerase chain reaction (PCR). At 2 weeks after irradiation, tissue generation and central vascularity were significantly lower and apoptosis was significantly higher in groups II and III than group IV, but without signs of necrosis. Cellular proliferation was significantly lower in groups I and II. After 5 weeks, the irradiated groups showed improvement in all parameters in relation to the control group, indicating a retained capacity for angiogenesis after irradiation. PCR results confirmed the expression of osteogenesis-related genes in all irradiated groups. Dense collagen was detected 5 weeks after irradiation, and one construct showed discrete islands of bone indicating a retained osteogenic capacity after irradiation. This demonstrates for the first time that axial vascularization was capable of supporting a synthetic bone construct after a high dose of irradiation that is comparable to adjuvant radiotherapy. Copyright © 2016 John Wiley & Sons, Ltd.

The role of myofibroblasts in the development of osteoradionecrosis in a newly established rabbit model

This study aimed to establish a proper animal model of osteoradionecrosis of jaws (ORNJ) and to observe preliminarily the characteristics of myofibroblasts, the key effector cell of fibrosis, in ORNJ. Rabbit mandibles were irradiated at three different doses based on a human equivalent radiation schedule, and examined by gross manifestation, single-photon emission computed tomography (SPECT), micro-computed tomography, sequential fluorochrome labeling, and histology. Immunohistochemistry staining of α-SMA was applied to detect the existence of myofibroblasts. The exposed necrotic bone, which is the main indication of ORNJ, started to be observed at all rabbits at 9 Gy. With the radiation dose increasing, the microarchitecture of the irradiated mandibles was more destroyed, the metabolism and mineralization of the irradiated mandibles diminished, the osteocytes number decreased, and more mature bones were substituted by fibrosis in the irradiated mandibles. In addition, as the radiation dose increased, the myofibroblast number increased and collected around the separated sequestrum, which indicated that myofibroblasts might relate to the pathogenesis of ORNJ. In summary, a clinically translational ORNJ model was successfully established in our study, and the role of myofibroblasts in the pathogenesis of ORNJ is described for the first time.

Translational treatment paradigm for managing non-unions secondary to radiation injury utilizing adipose derived stem cells and angiogenic therapy

BACKGROUND

Bony non-unions arising in the aftermath of collateral radiation injury are commonly managed with vascularized free tissue transfers. Unfortunately, these procedures are invasive and fraught with attendant morbidities. This study investigated a novel, alternative treatment paradigm utilizing adipose-derived stem cells (ASCs) combined with angiogenic deferoxamine (DFO) in the rat mandible.

METHODS

Rats were exposed to a bioequivalent dose of radiation and mandibular osteotomy. Those exhibiting non-unions were subsequently treated with surgical debridement alone or debridement plus combination therapy. Radiographic and biomechanical outcomes were assessed after healing.

RESULTS

Significant increases in biomechanical strength and radiographic metrics were observed in response to combination therapy (p < .05). Importantly, combined therapy enabled a 65% reduction in persisting non-unions when compared to debridement alone.

CONCLUSION

We support the continued investigation of this promising combination therapy in its potential translation for the management of radiation-induced bony pathology. © 2015 Wiley Periodicals, Inc. Head Neck 38: E837-E843, 2016.

Dose-response effect of human equivalent radiation in the mandible

BACKGROUND

Despite widespread use of adjuvant irradiation for head and neck cancer, the extent of damage to the underlying bone is not fully understood but is associated with pathologic fractures, nonunion, and osteoradionecrosis. The authors' laboratory previously demonstrated that radiation significantly impedes new bone formation in the murine mandible. We hypothesize that the detrimental effects of human equivalent radiation on the murine mandible results in a dose-dependent degradation in traditional micro-computed tomography (micro-CT) metrics.

METHODS

Fifteen male Sprague-Dawley rats were randomized into 3 radiation dosage groups: low (5.91 Gy), middle (7 Gy), and high (8.89 Gy), delivered in 5 daily fractions. These dosages approximated 75%, 100%, and 150%, respectively, of the biologically equivalent dose that the human mandible receives during radiation treatment. Hemimandibles were harvested 56 days after radiation and scanned using micro-CT. Bone mineral density, tissue mineral density, and bone volume fraction were measured along with microdensitometry measurements.

RESULTS

Animals demonstrated dose-dependent adverse effects of mucositis, alopecia, weight loss, and mandibular atrophy with increasing radiation. Traditional micro-CT parameters were not sensitive enough to demonstrate statistically significant differences between the radiated groups; however, microdensitometry analysis showed clear differences between radiated groups and statistically significant changes between radiated and nonradiated groups.

CONCLUSIONS

The authors report dose-dependent and clinically significant adverse effects of fractionated human equivalent radiation to the murine mandible. The authors further report the limited capacity of traditional micro-CT metrics to adequately capture key changes in bone composition and present microdensitometric histogram analysis to demonstrate significant radiation-induced changes in mineralization patterns.

Raman spectroscopy delineates radiation-induced injury and partial rescue by amifostine in bone: a murine mandibular model

Despite its therapeutic role in head and neck cancer, radiation administration degrades the biomechanical properties of bone and can lead to pathologic fracture and osteoradionecrosis. Our laboratories have previously demonstrated that prophylactic amifostine administration preserves the biomechanical properties of irradiated bone and that Raman spectroscopy accurately evaluates bone composition ex vivo. As such, we hypothesize that Raman spectroscopy can offer insight into the temporal and mechanical effects of both irradiation and amifostine administration on bone to potentially predict and even prevent radiation-induced injury. Male Sprague-Dawley rats (350-400 g) were randomized into control, radiation exposure (XRT), and amifostine pre-treatment/radiation exposure groups (AMF-XRT). Irradiated animals received fractionated 70 Gy radiation to the left hemi-mandible, while AMF-XRT animals received amifostine just prior to radiation. Hemi-mandibles were harvested at 18 weeks after radiation, analyzed via Raman spectroscopy, and compared with specimens previously harvested at 8 weeks after radiation. Mineral (ρ958) and collagen (ρ1665) depolarization ratios were significantly lower in XRT specimens than in AMF-XRT and control specimens at both 8 and 18 weeks. amifostine administration resulted in a full return of mineral and collagen depolarization ratios to normal levels at 18 weeks. Raman spectroscopy demonstrates radiation-induced damage to the chemical composition and ultrastructure of bone while amifostine prophylaxis results in a recovery towards normal, native mineral and collagen composition and orientation. These findings have the potential to impact on clinical evaluations and interventions by preventing or detecting radiation-induced injury in patients requiring radiotherapy as part of a treatment regimen.

Prophylactic administration of Amifostine protects vessel thickness in the setting of irradiated bone

Although often beneficial in the treatment of head and neck cancer (HNC), radiation therapy (XRT) leads to the depletion of vascular supply and eventually decreased perfusion of the tissue. Specifically, previous studies have demonstrated the depletion of vessel volume fraction (VVF) and vessel thickness (VT) associated with XRT. Amifostine (AMF) provides protection from the detrimental effects of radiation damage, allowing for reliable post-irradiation fracture healing in the murine mandible. The purpose of this study is to investigate the prophylactic ability of AMF to protect the vascular network in an irradiated field. Sprague-Dawley rats (n = 17) were divided into 3 groups: control (C, n = 5), radiated (XRT, n = 7), and radiated mandibles treated with Amifostine (AMF XRT, n = 5). Both groups receiving radiation underwent a previously established, human equivalent dose of XRT totaling 35 Gy, equally fractionated over 5 days. The AMF XRT group received a weight dependent (0.5 mg AMF/5 g body weight) subcutaneous injection of AMF 45 min prior to XRT. Following a 56-day recovery period, mandibles were perfused, dissected, and imaged with μCT. ANOVA was used for comparisons between groups and p < 0.05 was considered statistically significant. Stereologic analysis demonstrated a significant and quantifiable restoration of VT in AMF treated mandibles as compared to those treated with radiation alone (0.061 ± 0.011 mm versus 0.042 ± 0.004 mm, p = 0.027). Interestingly, further analysis demonstrated no significant difference in VT between control mandibles and those treated with AMF (0.067 ± 0.016 mm versus 0.061 ± 0.011 mm, p = 0.633). AMF treatment also showed an increase in VVF, however those results were not statistically significant from VVF values demonstrated by the XRT group. Our data support the contention that AMF therapy acts prophylactically to protect vessel thickness. Based on these findings, we support the continued investigation of this treatment paradigm in its potential translation for the prevention of vascular depletion after radiotherapy.

New approach for the treatment of osteoradionecrosis with pentoxifylline and tocopherol

Osteoradionecrosis (ORN) of the jaw is a significant complication of radiotherapy for oral cavity cancer. In addition to antibiotic medication, treatment options such as hyperbaric oxygen therapy, surgical approaches, and combined therapy with pentoxifylline and tocopherol have been recently introduced. In this review article, we will discuss the definition and classifications of osteoradionecrosis, its etiology and pathophysiology, previous treatment options, oral and maxillofacial complications of radiotherapy, basic information on pentoxifylline and tocopherol, recent reports of pentoxifylline and tocopherol combined therapy, and, finally, ORN-induced animal models and future approaches.

Targeting angiogenesis as a therapeutic means to reinforce osteocyte survival and prevent nonunions in the aftermath of radiotherapy

BACKGROUND

Radiotherapy (XRT) exerts detrimental collateral effects on bone tissue through mechanisms of vascular damage and impediments to osteocytes, ultimately predisposing patients to the debilitating problems of late pathologic fractures and nonunions. We posit that angiogenic therapy will reverse these pathologic effects in a rat model of radiated fracture healing.

METHODS

Three groups of rats underwent mandibular osteotomy. Radiated groups received a fractionated 35-Gy dose before surgery. The deferoxamine (DFO) group received local injections postoperatively. A 40-day healing period was allowed before histology. Analysis of variance (ANOVA; p < .05) was used for group comparisons.

RESULTS

Radiated fractures revealed a significantly decreased osteocyte count and corresponding increase in empty lacunae when compared to nonradiated fractures (p = .001). With the addition of DFO, these differences were not appreciated. Further, a 42% increase in bony unions was observed after DFO therapy.

CONCLUSION

Targeting angiogenesis is a useful means for promoting osteocyte survival and preventing bone pathology after XRT.

Prophylactic amifostine preserves the biomechanical properties of irradiated bone in the murine mandible

BACKGROUND

The authors have previously demonstrated that amifostine prophylaxis mitigates the pernicious effects of radiation in settings of fracture repair and distraction osteogenesis. Expanding on these studies, the authors examined the biomechanical properties of uninjured bone exposed to both radiation and amifostine. The authors hypothesize that radiation will degrade the biomechanical properties of native bone, and further hypothesize that prophylactic amifostine will preserve biomechanical properties to levels of normal bone and protect against radiation-induced morbidities.

METHODS

Rats were randomized into control, irradiated, and amifostine pretreatment plus radiation (amifostine-pretreated) groups. Irradiated animals received a fractionated dosing schedule of 35 Gy, with amifostine-pretreated animals receiving amifostine before irradiation. Hemimandibles were harvested at 8 and 18 weeks for biomechanical testing and micro-computed tomographic analysis.

RESULTS

At 8 weeks, irradiated specimens displayed elevations above controls for all biomechanical properties. At 18 weeks, the biomechanical properties of irradiated specimens degraded in comparison with controls; at both time points, amifostine-pretreated specimens were maintained at levels comparable to controls. There was a significant decrease in tissue mineral density from 8- to 18-week irradiated specimens, whereas no such change existed for control and amifostine-pretreated specimens.

CONCLUSIONS

The authors' findings demonstrate paradoxical and transient elevations in the initial biomechanical properties of irradiated specimens that were not sustained through the later study time point. Amifostine pretreatment, however, provided uninterrupted preservation of the biomechanical properties of normal, native bone at both time points. This supports the contention that amifostine is capable of providing continuous protection to bone against the untoward effects of radiation therapy.

Amifostine protects vascularity and improves union in a model of irradiated mandibular fracture healing

BACKGROUND

Pathologic fractures of the mandible can be devastating to cancer patients and are due in large part to the pernicious effects of irradiation on bone vascularity. The authors' aim was to ascertain whether amifostine, a radioprotective drug, will preserve vascularity and improve bone healing in a murine model of irradiated mandibular fracture repair.

METHODS

Rats were randomized into three groups: nonirradiated fracture (n = 9), irradiation/fracture (n = 5), and amifostine/irradiation/fracture (n = 7). Animals in the irradiation groups underwent a human equivalent dose of radiation directed at the left hemimandible. Animals treated in the amifostine group received amifostine concomitantly with radiation. All animals underwent unilateral left mandibular osteotomy with external fixation set to a 2.1-mm fracture gap. Fracture healing was allowed for 40 days before perfusion with Microfil. Vascular radiomorphometrics were quantified with micro-computed tomography.

RESULTS

When compared with the irradiated/fractured group, amifostine treatment more than doubled the rate of fracture unions to 57 percent. Amifostine treatment also resulted in an increase in vessel number (123 percent; p < 0.05) and a corresponding decrease in vessel separation (55.5 percent; p < 0.05) there was no statistical difference in the vascularity metrics between the amifostine/irradiation/fracture group and the nonirradiated/fracture group.

CONCLUSIONS

Amifostine prophylaxis during radiation maintains mandibular vascularity at levels observed in nonirradiated fracture specimens, corresponding to improved unions. These results set the stage for clinical exploration of this targeted therapy alone and in combination with other treatments, to mitigate the effects of irradiation on bone healing and fracture repair.

Deferoxamine administration delivers translational optimization of distraction osteogenesis in the irradiated mandible

BACKGROUND

The authors' laboratory has previously demonstrated that deferoxamine promotes angiogenesis and bone repair in the setting of radiation therapy coupled with distraction osteogenesis. However, clinically relevant effects of deferoxamine administration on union rate and micro-computed tomographic and biomechanical parameters are unknown. The authors posit that administration of deferoxamine will increase union rate, mineralization, and strength of the regenerate in an irradiated distraction osteogenesis model.

METHODS

Sprague-Dawley rats were randomized into three groups: distraction osteogenesis-control, distraction osteogenesis-radiation therapy, and distraction osteogenesis-radiation therapy-deferoxamine. All animals underwent an osteotomy and distraction osteogenesis across a 5.1-mm distraction gap. Irradiated animals received 35-Gy human-equivalent radiation therapy 2 weeks before surgery, and deferoxamine was injected postoperatively in the regenerate site of treatment animals. Animals were killed on postoperative day 40, and mandibles were harvested to determine rates of bony union and micro-computed tomographic and biomechanical parameters.

RESULTS

Compared with irradiated mandibles, deferoxamine-treated mandibles exhibited a higher union rate (11 percent versus 92 percent, respectively). Across micro-computed tomographic and biomechanical parameters, significant diminutions were observed with administration of radiation therapy, whereas deferoxamine therapy resulted in significant restoration to levels of controls, with select metrics exhibiting significant increases even beyond controls.

CONCLUSIONS

The authors' data confirm that deferoxamine restores clinically relevant metrics of bony union and micro-computed tomographic and biomechanical parameters in a model of irradiated distraction osteogenesis in the murine mandible. Their findings support a potential use for deferoxamine in treatment protocols to allow predictable and reliable use of distraction osteogenesis as a viable reconstructive option in patients with head and neck cancer.

The effect of Amifostine prophylaxis on bone densitometry, biomechanical strength and union in mandibular pathologic fracture repair

BACKGROUND

Pathologic fractures (Fx) of the mandibles are severely debilitating consequences of radiation (XRT) in the treatment of craniofacial malignancy. We have previously demonstrated Amifostine's effect (AMF) in the remediation of radiation-induced cellular damage. We posit that AMF prophylaxis will preserve bone strength and drastically reverse radiotherapy-induced non-union in a murine mandibular model of pathologic fracture repair.

MATERIALS AND METHODS

Twenty-nine rats were randomized into 3 groups: Fx, XRT/Fx, and AMF/XRT/Fx. A fractionated human equivalent dose of radiation was delivered to the left hemimandibles of XRT/Fx and AMF/XRT/Fx. AMF/XRT/Fx was pre-treated with AMF. All groups underwent left mandibular osteotomy with external fixation and setting of a 2.1mm fracture gap post-operatively. Utilizing micro-computed tomography and biomechanical testing, the healed fracture was evaluated for strength.

RESULTS

All radiomorphometrics and biomechanical properties were significantly diminished in XRT/Fx compared to both Fx and AMF/XRT/Fx. No difference was demonstrated between Fx and AMF/XRT/Fx in both outcomes.

CONCLUSION

Our investigation establishes the significant and substantial capability of AMF prophylaxis to preserve and enhance bone union, quality and strength in the setting of human equivalent radiotherapy. Such novel discoveries establish the true potential to utilize pharmacotherapy to prevent and improve the treatment outcomes of radiation-induced late pathologic fractures.

Deferoxamine restores callus size, mineralization, and mechanical strength in fracture healing after radiotherapy

BACKGROUND

Therapeutic augmentation of fracture-site angiogenesis with deferoxamine has proven to increase vascularity, callus size, and mineralization in long-bone fracture models. The authors posit that the addition of deferoxamine would enhance pathologic fracture healing in the setting of radiotherapy in a model where nonunions are the most common outcome.

METHODS

Thirty-five Sprague-Dawley rats were divided into three groups. Fracture, irradiated fracture, and irradiated fracture plus deferoxamine. The irradiated fracture and irradiated fracture plus deferoxamine groups received a human equivalent dose of radiotherapy [7 Gy/day for 5 days, (35 Gy)] 2 weeks before mandibular osteotomy and external fixation. The irradiated fracture plus deferoxamine group received injections of deferoxamine into the fracture callus after surgery. After a 40-day healing period, mandibles were dissected, clinically assessed for bony union, imaged with micro-computed tomography, and tension tested to failure.

RESULTS

Compared with irradiated fractures, metrics of callus size, mineralization, and strength in deferoxamine-treated mandibles were significantly increased. These metrics were restored to a level demonstrating no statistical difference from control fractures. In addition, the authors observed an increased rate of achieving bony unions in the irradiated fracture plus deferoxamine-treated group when compared with irradiated fracture (67 percent and 20 percent, respectively).

CONCLUSIONS

The authors' data demonstrate nearly total restoration of callus size, mineralization, and biomechanical strength, and a threefold increase in the rate of union with the use of deferoxamine. The authors' results suggest that the administration of deferoxamine may have the potential for clinical translation as a new treatment paradigm for radiation-induced pathologic fractures.

Stem cell therapy remediates reconstruction of the craniofacial skeleton after radiation therapy

This study utilized transplanted bone marrow stromal cells (BMSCs) as a cellular replacement therapy to remedy radiation-induced injury and restore impaired new bone formation during distraction osteogenesis (DO). BMSC therapy brought about the successful generation of new bone and significantly improved both the rate and quality of a bony union of irradiated, distracted [X-ray radiation therapy (XRT)/DO] murine mandibles to the level of nonirradiated DO animals. The bone mineral density and bone volume fraction were also significantly improved by the BMSC replacement therapy showing no difference when compared to nonirradiated animals. Finally, a biomechanical analysis examining the yield, failure load, and ultimate load also demonstrated a significantly improved structural integrity in BMSC-treated XRT/DO mandibles over XRT/DO alone. These results indicate that administration of BMSCs intraoperatively to a radiated distraction gap can function as an adequate stimulant to rescue the ability for irradiated bone to undergo DO and produce a healed regenerate of a vastly superior quality and strength. We believe that the fundamental information on the optimization of bone regeneration in the irradiated mandible provided by this work has immense potential to be translated from the bench to the bedside to lead to improved therapeutic options for patients suffering from the disastrous sequelae of radiation therapy.

Raman spectroscopy demonstrates Amifostine induced preservation of bone mineralization patterns in the irradiated murine mandible

PURPOSE

Adjuvant radiotherapy in the management of head and neck cancer remains severely debilitating. Fortunately, newly developed agents aimed at decreasing radiation-induced damage have shown great promise. Amifostine (AMF) is a compound, which confers radio-protection to the exposed normal tissues, such as bone. Our intent is to utilize Raman spectroscopy to demonstrate how AMF preserves the mineral composition of the murine mandible following human equivalent radiation.

METHODS

Sprague Dawley rats were randomized into 3 experimental groups: control (n=5), XRT (n=5), and AMF-XRT (n=5). Both XRT and AMF groups underwent bioequivalent radiation of 70Gy in 5 fractions to the left hemimandible. AMF-XRT received Amifostine prior to radiation. Fifty-six days post-radiation, the hemimandibles were harvested, and Raman spectra were taken in the region of interest spanning 2mm behind the last molar. Bone mineral and matrix-specific Raman bands were analyzed using one-way ANOVA, with statistical significance at p<0.05.

RESULTS

The full-width at half-maximum of the primary phosphate band (FWHM) and the ratio of carbonate/phosphate intensities demonstrated significant differences between AMF-XRT versus XRT (p<0.01) and XRT versus control (p<0.01). There was no difference between AMF-XRT and control (p>0.05) in both Raman metrics. Computer-aided spectral subtraction further confirmed these results where AMF-XRT was spectrally similar to the control. Interestingly, the collagen cross-link ratio did not differ between XRT and AMF-XRT (p<0.01) but was significantly different from the control (p<0.01).

CONCLUSION

Our novel findings demonstrate that AMF prophylaxis maintains and protects bone mineral quality in the setting of radiation. Raman spectroscopy is an emerging and exceptionally attractive clinical translational technology to investigate and monitor both the destructive effects of radiation and the therapeutic remediation of AMF on the structural, physical and chemical qualities of bone.

Quantitative histologic evidence of amifostine-induced cytoprotection in an irradiated murine model of mandibular distraction osteogenesis

BACKGROUND

Head and neck cancer management requires adjuvant radiotherapy. The authors have previously demonstrated the damaging effect of a human equivalent dose of radiation on a murine mandibular model of distraction osteogenesis. Using quantitative histomorphometry, the authors' specific aim was to objectively measure amifostine radioprotection of the cellular integrity and tissue quality of an irradiated and distracted regenerate.

METHODS

Sprague-Dawley rats were assigned randomly into two groups: radiotherapy/distraction osteogenesis and amifostine/radiotherapy/distraction osteogenesis, which received amifostine before radiotherapy. Both groups received a fractionated human equivalent dose of radiation prior to left mandibular osteotomy with fixator placement. Distraction to 5.1 mm was followed by a 28-day consolidation period. Quantitative histomorphometry was performed on left hemimandibles for osteocytes, empty lacunae, bone volume-to-tissue volume ratio, and osteoid volume-to-tissue volume ratio.

RESULTS

Amifostine/radiotherapy/distraction osteogenesis exhibited bony bridging as opposed to radiotherapy/distraction osteogenesis fibrous unions. Quantitative histomorphometry analysis revealed statistically significant higher osteocyte count and bone volume-to-tissue volume ratio in amifostine-treated mandibles compared with irradiated mandibles. There was a corresponding decrease in empty lacunae and the ratio of osteoid volume-to-tissue volume between both groups.

CONCLUSIONS

The authors have successfully established the significant osseous cytoprotective and histoprotective capacity of amifostine for distraction osteogenesis in the face of radiotherapy. The amifostine-sparing effect on bone cellularity correlated with increased bony unions and elimination of fibrous union. The authors posit that the demonstration of similar efficacy of amifostine in the clinic may allow the successful implementation of distraction osteogenesis as a viable reconstructive option for head and neck cancer in the future.

Localized deferoxamine injection augments vascularity and improves bony union in pathologic fracture healing after radiotherapy

BACKGROUND

Medically based efforts and alternative treatment strategies to prevent or remediate the corrosive effects of radiotherapy on pathologic fracture healing have failed to produce clear and convincing evidence of success. Establishing an effective pharmacologic option to prevent or treat the development of non-unions in this setting could have immense therapeutic potential. Experimental studies have shown that deferoxamine (DFO), an iron-chelating agent, bolsters vascularity and subsequently enhances normal fracture healing when injected locally into a fracture callus in long bone animal models. Since radiotherapy is known to impede angiogenesis, we hypothesized that the pharmacologic addition of DFO would serve to mitigate the effects of radiotherapy on new vessel formation in vitro and in vivo.

MATERIALS AND METHODS

In vitro investigation of angiogenesis was conducted utilizing HUVEC cells in Matrigel. Endothelial tubule formation assays were divided into four groups: Control, Radiated, Radiated+Low-Dose DFO and Radiated+High-Dose DFO. Tubule formation was quantified microscopically and video recorded for the four groups simultaneously during the experiment. In vivo, three groups of Sprague-Dawley rats underwent external fixator placement and fracture osteotomy of the left mandible. Two groups received pre-operative fractionated radiotherapy, and one of these groups was treated with DFO after fracture repair. After 40 days, the animals were perfused and imaged with micro-CT to calculate vascular radiomorphometrics.

RESULTS

In vitro, endothelial tubule formation assays demonstrated that DFO mitigated the deleterious effects of radiation on angiogenesis. Further, high-dose DFO cultures appeared to organize within 2h of incubation and achieved a robust network that was visibly superior to all other experimental groups in an accelerated fashion. In vivo, animals subjected to a human equivalent dose of radiotherapy (HEDR) and left mandibular fracture demonstrated quantifiably diminished μCT metrics of vascular density, as well as a 75% incidence of associated non-unions. The addition of DFO in this setting markedly improved vascularity as demonstrated with 3D angiographic modeling. In addition, we observed an increased incidence of bony unions in the DFO treated group when compared to radiated fractures without treatment (67% vs. 25% respectively).

CONCLUSION

Our data suggest that selectively targeting angiogenesis with localized DFO injections is sufficient to remediate the associated severe vascular diminution resulting from a HEDR. Perhaps the most consequential and clinically relevant finding was the ability to reduce the incidence of non-unions in a model where fracture healing was not routinely observed.