Parathyroid hormone therapy mollifies radiation-induced biomechanical degradation in murine distraction osteogenesis

Postradiation Fractures after Combined Modality Treatment in Extremity Soft Tissue Sarcomas

Soft tissue sarcoma (STS) of the extremities is typically treated with limb-sparing surgery and radiation therapy; with this treatment approach, high local control rates can be achieved. However, postradiation bone fractures, fractures occurring in the prior radiation field with minimal or no trauma, are a serious late complication that occurs in 2–22% of patients who receive surgery and radiation for STS. Multiple risk factors for sustaining a postradiation fracture exist, including high radiation dose, female sex, periosteal stripping, older age, femur location, and chemotherapy administration. The treatment of these pathological fractures can be difficult, with complications including delayed union, nonunion, and infection posing particular challenges. Here, we review the mechanisms, risk factors, and treatment challenges associated with postradiation fractures in STS patients.

Teriparatide therapy for severe, refractory osteoradionecrosis of the jaw

Although osteoradionecrosis (ORN) is a serious complication of craniofacial radiotherapy, the current management methods remain suboptimal. Teriparatide (TPTD), a recombinant human parathyroid hormone (1-34), has shown beneficial effects on osseous regeneration in medication-related osteonecrosis of the jaw or periodontitis. However, TPTD therapy in irradiated bones has not been indicated yet because of the theoretical risk of osteosarcoma seen in rat models. Hence, we first report here two patients with tongue cancer with late-emerging ORN who were successfully treated with TPTD for 4-6 months with serum calcium and vitamin D supplementation. In contrast to the usual progress of ORN, the bone defect regenerated well and bone turnover markers including serum C-terminal telopeptide of type 1 collagen and osteocalcin were restored with TPTD therapy. Our experience might suggest that TPTD therapy with careful monitoring can provide an effective treatment option for patients with ORN in select refractory cases, with the benefits outweighing the potential risks.

Significant Differences in the Bone of an Isogenic Inbred Versus Nonisogenic Outbred Murine Mandible: A Study in Rigor and Reproducibility

Inattention to differences between animal strains is a potential cause of irreproducibility of basic science investigations. Accordingly, the authors' laboratory sought to ensure that cross-comparisons of results generated from studies of mandibular physiology utilizing the Sprague Dawley and Lewis rat strains are valid. The authors specifically investigated baseline histomorphometrics, bone mineral density, and biomechanical strength of the unaltered endogenous mandibles of the inbred, isogenic Lewis rat, and the outbred, nonisogenic Sprague Dawley rat to determine if they are indeed equal. The authors hypothesized that little difference would be found within these metrics.The authors' study utilized 20 male Lewis and Sprague Dawley rats, which underwent no manipulation other than final dissection and analysis. Ten rats from each strain underwent bone mineral density and biomechanical strength analysis. The remaining rats underwent histological analysis. Descriptive and bivariate statistics were computed and the P value was set at 0.05.Lewis rats had a significantly greater number of empty lacunae. Sprague Dawley rats exhibited a significantly greater ratio of bone volume-to-total volume, bone mineral density, tissue mineral density, bone volume fraction, and total mineral content. No differences were found during biomechanical testing.This study demonstrates that differences exist between the Lewis and Sprague Dawley rat within unaltered baseline mandibular tissue. However, these differences appear to have limited functional impact, as demonstrated by similar biomechanical strength metrics. Other specific differences not addressed in this manuscript may exist. However, the authors believe that researchers may confidently cross-compare results between the 2 strains, while taking into account the differences found within this study.

Role of parathyroid hormone in regeneration of irradiated bone in a murine model of mandibular distraction osteogenesis

BACKGROUND

The purpose of this study was to measure the histologic and histomorphometric effects of parathyroid hormone (PTH) treatment on irradiated bone undergoing distraction osteogenesis (DO).

METHODS

Thirty-four rats were divided into 3 groups. The control group underwent DO and the radiation control group underwent radiotherapy (RT) before DO. The PTH group underwent RT and received PTH during DO. Quantitative histology and histomorphometry were performed.

RESULTS

RT resulted in a depletion of osteocytes and increase in empty lacunae. Treatment with PTH resulted in an increase in osteocyte counts and decrease in empty lacunae (p < .05), restoring osteocytes to levels seen in nonradiated bone (p = .121). RT decreased bone volume to tissue volume (BV-TV) ratio and increased osteoid volume to tissue volume (OV-TV) ratio, signifying increased immature bone formation. PTH treatment restored OV-TV ratio to that observed in nonradiated bone.

CONCLUSION

PTH treatment of irradiated bone enhanced bone regeneration and restored osteocyte counts and OV-TV ratio to levels comparable to nonradiated bone. © 2016 Wiley Periodicals, Inc. Head Neck 39: 464-470, 2017.

Parathyroid Hormone (1-34) Transiently Protects Against Radiation-Induced Bone Fragility

Radiation therapy for soft tissue sarcoma or tumor metastases is frequently associated with damage to the underlying bone. Using a mouse model of limited field hindlimb irradiation, we assessed the ability of parathyroid hormone (1-34) fragment (PTH) delivery to prevent radiation-associated bone damage, including loss of mechanical strength, trabecular architecture, cortical bone volume, and mineral density. Female BALB/cJ mice received four consecutive doses of 5 Gy to a single hindlimb, accompanied by daily injections of either PTH or saline (vehicle) for 8 weeks, and were followed for 26 weeks. Treatment with PTH maintained the mechanical strength of irradiated femurs in axial compression for the first eight weeks of the study, and the apparent strength of irradiated femurs in PTH-treated mice was greater than that of naïve bones during this time. PTH similarly protected against radiation-accelerated resorption of trabecular bone and transient decrease in mid-diaphyseal cortical bone volume, although this benefit was maintained only for the duration of PTH delivery. Overall, PTH conferred protection against radiation-induced fragility and morphologic changes by increasing the quantity of bone, but only during the period of administration. Following cessation of PTH delivery, bone strength and trabecular volume fraction rapidly decreased. These data suggest that PTH does not negate the longer-term potential for osteoclastic bone resorption, and therefore, finite-duration treatment with PTH alone may not be sufficient to prevent late onset radiotherapy-induced bone fragility.

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.