Erin E. Page

Stem cells rejuvenate radiation-impaired vasculogenesis in murine distraction osteogenesis.

Background: Radiotherapy is known to be detrimental to bone and soft-tissue repair. Bone marrow stromal cells have been shown to enhance bone regeneration during distraction osteogenesis following radiation therapy. The authors posit that transplanted bone marrow stromal cells will significantly augment the mandibular vascularity devastated by radiation therapy. Methods: Nineteen male Lewis rats were split randomly into three groups: distraction osteogenesis only (n = 5), radiation therapy plus distraction osteogenesis (n = 7), and radiation therapy plus distraction osteogenesis with intraoperative placement of 2 million bone marrow stromal cells (n = 7). A mandibular osteotomy was performed, and an external fixator device was installed. From postoperative days 4 through 12, rats underwent a gradual 5.1-mm distraction followed by a 28-day consolidation period. On postoperative day 40, Microfil was perfused into the vasculature and imaging commenced. Vascular radiomorphometric values were calculated for regions of interest. An analysis of variance with post hoc Tukey or Games-Howell tests was used, dependent on data homogeneity. Results: Stereologic analysis indicated significant remediation in vasculature in the bone marrow stromal cell group compared with the radiation therapy/distraction osteogenesis group. Each of five metrics idicated significant improvements from radiation therapy/distraction osteogenesis to the bone marrow stromal cell group, with no difference between the bone marrow stromal cell group and the distraction osteogenesis group. Conclusions: Bone marrow stromal cells used together with distraction osteogenesis can rejuvenate radiation-impaired vasculogenesis in the mandible, reversing radiation therapy–induced isotropy and creating a robust vascular network. Bone marrow stromal cells may offer clinicians an alternative reconstructive modality that could improve the lifestyle of patients with hypovascular bone.

Vascular analysis as a proxy for mechanostransduction response in an isogenic, irradiated murine model of mandibular distraction osteogenesis.

INTRODUCTION Head and neck cancer is a debilitating and disfiguring disease. Although numerous treatment options exist, an array of debilitating side effects accompany them, causing physiological and social problems. Distraction osteogenesis (DO) can avoid many of the pathologies of current reconstructive strategies; however, due to the deleterious effects of radiation on bone vascularity, DO is generally ineffective. This makes investigating the effects of radiation on neovasculature during DO and creating quantifiable metrics to gauge the success of future therapies vital. The purpose of this study was to develop a novel isogenic rat model of impaired vasculogenesis of the regenerate mandible in order to determine quantifiable metrics of vascular injury and associated damage. METHODS Male Lewis rats were divided into two groups: DO only (n=5) AND Radiation Therapy (XRT)+DO (n=7). Afterwards, a distraction device was surgically implanted into the mandible. Finally, they were distracted a total of 5.1mm. Animals were perfused with a radiopaque casting agent concomitant with euthanasia, and subsequently demineralization, microcomputed tomography, and vascular analysis were performed. RESULTS Vessel volume fraction, vessel thickness, vessel number, and degree of anisotropy were diminished by radiation. Vessel separation was increased by radiation. CONCLUSION The DO group experienced vigorous vessel formation during distraction and neovascularization with a clear, directional progression, while the XRT/DO group saw weak vessel formation during distraction and neovascularization. Further studies are warranted to more deeply examine the impairments in osteogenic mechanotransductive pathways following radiation in the murine mandible. This isogenic model provides quantifiable metrics for future studies requiring a controlled approach to immunogenicity.

Amifostine reduces radiation-induced complications in a murine model of expander-based breast reconstruction.

Background: Immediate expander-based breast reconstruction after mastectomy is a prevalent option for many women with breast cancer. When coupled with adjuvant radiation therapy, however, radiation-induced skin and soft-tissue injury diminish the success of this reconstructive technique. The authors hypothesize that prophylactic administration of the cytoprotectant amifostine will reduce soft-tissue complications from irradiation, aiding expander-based reconstruction. Methods: Sprague-Dawley rats were divided into two groups: operative expander placement (expander group) and operative sham (sham group). Expander specimens received a sublatissimus tissue expander with a 15-cc fill volume; shams underwent identical procedures without expanders. Experimental groups were further divided into control specimens receiving no further intervention, radiation therapy–only specimens receiving human-equivalent irradiation, and amifostine plus radiation therapy specimens receiving both amifostine and human-equivalent irradiation. After a 45-day recovery period, animals were evaluated grossly and with ImageJ analysis for skin and soft-tissue complications. Results: None of the control, radiation therapy–alone, or amifostine plus radiation therapy sham specimens showed skin and soft-tissue complications. For expander animals, significantly fewer amifostine plus radiation therapy specimens [four of 13 (30 percent)] demonstrated skin and soft-tissue complications compared with radiation therapy–alone specimens [nine of 13 (69 percent); p = 0.041]. ImageJ evaluation of expander specimens demonstrated a significant increase in skin and soft-tissue necrosis for radiation therapy–alone specimens (12.94 percent) compared with animals receiving amifostine plus radiation therapy (6.96 percent) (p = 0.019). Conclusions: Amifostine pretreatment significantly reduced skin and soft-tissue complications. These findings demonstrate that amifostine prophylaxis provides protection against radiation-induced skin and soft-tissue injury in a murine model of expander-based breast reconstruction.

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

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.

Abstract 79: deferoxamine in combination with adipose-derived stromal cells rescues mineralization and improves union rate in the treatment of established radiotherapy induced non-unions.

PurPose: Radiotherapy induced non-unions occurring in the head and neck cancer patient population are a devastating morbidity that can cause significant functional deficits, persistent pain and often have a dreadful impact on quality of life. Twenty-three percent of patients with advanced osteoradionecrosis proceed to develop pathologic fractures and associated non-unions. Unfortunately, clinicians have few efficacious treatment options for this catastrophic problem. Previously, we have demonstrated a reproducible non-union rate of approximately 75–80% in a non-treated, rat model of pathologic fracture healing after radiotherapy. Here, we report the utilization of a therapeutic strategy, combining adipose-derived stromal cells (ADSCs) with deferoxamine (DFO) to treat established non-unions in this validated model. Our hypothesis is that ADSCs will act to replenish cellular volume, while DFO will function to augment angiogenesis at the site of the non-union, thereby improving mineralization metrics and union formation after treatment.

Abstract 83: improved biomechanical metrics in the treatment of radiotherapy-induced non-unions with a novel combination therapy.

PurPose: Radiation-induced non-unions are complex morbidities with limited management solutions. In prior studies we have utilized a rat model of mandibular fracture healing after a Human Equivalent Dose of Radiotherapy (HEDR), and have established a reproducible non-union rate of approximately 75–80%. In this study, we sought to combine adipose-derived stem cells (ADSCs) with deferoxamine in order to treat established non-unions in our model. We posit that ADSCs will act as a cellular replacement, while DFO will function to enhance angiogenesis at the non-union site, resulting in improvements in biomechanical metrics after treatment.

Abstract 87: DEFEROXAMINE INDUCES THE RESTORATION OF MINERALIZATION METRICS OF IRRADIATED BONE IN DISTRACTION OSTEOGENESIS

Background: Our laboratory has shown the iron-chelating agent Deferoxamine (DFO) promotes angiogenesis and bone repair in the setting of radiation therapy (XRT) coupled with Distraction Osteogenesis (DO). While these studies demonstrate DFO improves vascular and histologic metrics for irradiated mandibles, clinically impactful effects of DFO on mineralization metrics have never been examined. We hypothesize DFO administration will restore the composition and mineralization of the bony regenerate in an irradiated model of DO.