PTH1-34 alleviates radiotherapy-induced local bone loss by improving osteoblast and osteocyte survival

Remineralization Rate of Lytic Lesions of the Spine in Multiple Myeloma Patients Undergoing Radiation Therapy

Study DesignRetrospective cohort study.ObjectiveIn general, Multiple Myeloma (MM) patients are treated with systemic therapy including chemotherapy. Radiation therapy can have an important supportive role in the palliative management of MM-related osteolytic lesions. Our study aims to investigate the degree of radiation-induced remineralization in MM patients to gain a better understanding of its potential impact on bone mineral density and, consequently, fracture prevention. Our primary outcome measure was percent change in bone mineral density measured in Hounsfield Units (Δ% HU) between pre- and post-radiation measurements, compared to non-targeted vertebrae.MethodsWe included 119 patients with MM who underwent radiotherapy of the spine between January 2010 and June 2021 and who had a CT scan of the spine at baseline and between 3-24 months after radiation. A linear mixed effect model tested any differences in remineralization rate per month (βdifference) between targeted and non-targeted vertebrae.ResultsAnalyses of CT scans yielded 565 unique vertebrae (366 targeted and 199 non-targeted vertebrae). In both targeted and non-targeted vertebrae, there was an increase in bone density per month (βoverall = .04; P = .002) with the largest effect being between 9-18 months post-radiation. Radiation did not cause a greater increase in bone density per month compared to non-targeted vertebrae (βdifference = .67; P = .118).ConclusionOur results demonstrate that following radiation, bone density increased over time for both targeted and non-targeted vertebrae. However, no conclusive evidence was found that targeted vertebrae have a higher remineralization rate than non-targeted vertebrae in patients with MM.

Diagnostic and Therapeutic Approaches to Jaw Osteoradionecrosis

Jaw osteoradionecrosis (ORN) is a major complication of head and neck cancer radiotherapy. Treatment complications account for most of the poor outcomes for head and neck cancers and the associated racial health disparities in cancer survivorship. The global incidence of jaw ORN is improving due to pre-radiotherapy patient preparations and improved head and neck cancer radiotherapy protocols. The diagnosis and management of jaw ORN are based on the patient's history and clinical presentation combined with radiological and histopathological tests. Evidence-based jaw ORN therapies focus on preventive, palliative, and surgical principles. However, new and innovative therapeutic approaches based on the cellular and molecular pathophysiological processes of jaw ORN and the jawbone's susceptibility to radiation bone damage are limited. The rationale for this narrative review is to highlight the current diagnostic approaches to jaw ORN and the pathophysiological basis for new therapeutic options for ORN.

AOP Report: Development of an adverse outcome pathway for deposition of energy leading to bone loss

Bone loss, commonly seen in osteoporosis, is a condition that entails a progressive decline of bone mineral density and microarchitecture, often seen in post-menopausal women. Bone loss has also been widely reported in astronauts exposed to a plethora of stressors and in patients with osteoporosis following radiotherapy for cancer. Studies on mechanisms are well documented but the causal connectivity of events to bone loss development remains incompletely understood. Herein, the adverse outcome pathway (AOP) framework was used to organize data and develop a qualitative AOP beginning from deposition of energy (the molecular initiating event) to bone loss (the adverse outcome). This qualitative AOP was developed in collaboration with bone loss research experts to aggregate relevant findings, supporting ongoing efforts to understand and mitigate human system risks associated with radiation exposures. A literature review was conducted to compile and evaluate the state of knowledge based on the modified Bradford Hill criteria. Following review of 2029 studies, an empirically supported AOP was developed, showing the progression to bone loss through many factors affecting the activities of bone-forming osteoblasts and bone-resorbing osteoclasts. The structural, functional, and quantitative basis of each proposed relationship was defined, for inference of causal changes between key events. Current knowledge and its gaps relating to dose-, time- and incidence-concordance across the key events were identified, as well as modulating factors that influence linkages. The new priorities for research informed by the AOP highlight areas for improvement to enable development of a quantitative AOP used to support risk assessment strategies for space travel or cancer radiotherapy.

Cancer treatment-induced bone loss

Cancer treatment-induced bone loss (CTBL) is associated with anti-tumor treatments, including endocrine therapies, chemotherapeutic treatments, radiotherapy, glucocorticoids, and tyrosine kinase inhibitors. Osteoporosis, characterized by the loss of bone mass, can increase the risk of fractures, leading to mortality and long-term disability, even after cancer remission. Cancer and osteoporosis have marked clinical and pathogenetic similarities. Both have a multifactorial etiology, affect the geriatric population, and markedly influence quality of life. Lifestyle management, including calcium and vitamin D supplementation, is recommended but the supporting evidence is limited. Oral and injectable bisphosphonates are effective for osteoporosis and malignant bone disease. Bisphosphonates increase bone mineral density (BMD) in patients with CTBL. Denosumab is also used in the management of CTBL; in clinical trials, it improved BMD and reduced the risk of fracture. Currently, there are no bone anabolic therapies for patients with cancer. Appropriate therapies are necessary to maintain optimal bone health, particularly in patients at heightened risk.

In vivo bioluminescence tomography-guided system for pancreatic cancer radiotherapy research

Recent development of radiotherapy (RT) has heightened the use of radiation in managing pancreatic cancer. Thus, there is a need to investigate pancreatic cancer in a pre-clinical setting to advance our understanding of the role of RT. Widely-used cone-beam CT (CBCT) imaging cannot provide sufficient soft tissue contrast to guide irradiation. The pancreas is also prone to motion. Large collimation is unavoidably used for irradiation, costing normal tissue toxicity. We innovated a bioluminescence tomography (BLT)-guided system to address these needs. We established an orthotopic pancreatic ductal adenocarcinoma (PDAC) mouse model to access BLT. Mice underwent multi-projection and multi-spectral bioluminescence imaging (BLI), followed by CBCT imaging in an animal irradiator for BLT reconstruction and radiation planning. With optimized absorption coefficients, BLT localized PDAC at 1.25 ± 0.19 mm accuracy. To account for BLT localization uncertainties, we expanded the BLT-reconstructed volume with margin to form planning target volume(PTVBLT) for radiation planning, covering 98.7 ± 2.2% of PDAC. The BLT-guided conformal plan can cover 100% of tumors with limited normal tissue involvement across both inter-animal and inter-fraction cases, superior to the 2D BLI-guided conventional plan. BLT offers unique opportunities to localize PDAC for conformal irradiation, minimize normal tissue involvement, and support reproducibility in RT studies.

The mechanism of bone metabolism in a Sprague Dawley rat model of mandibular osteoradionecrosis

Background

Osteoradionecrosis (ORN) is a serious complication of radiotherapy for head and neck cancer. There is currently a lack of data on the dynamic expression of genes related to bone remodeling during the development of mandibular ORN. This study aimed to establish an animal model of ORN in Sprague Dawley (SD) rats, detect the expression of genes related to bone metabolism, observe morphological changes, and clarify the mechanism of ORN.

Methods

A total of 24 male SD rats in group 1 were randomly divided into four groups (n=6/group): group a, normal control; group b, simple tooth extraction; group c, simple radiation; and group d, radiation extraction group. The right mandible of rats in groups c and d was irradiated with a single dose of 35 Gy. The right mandibles were taken from each group for morphological observation 90 days after irradiation. SD rats in group 2 (n=144) were randomly divided into four groups (in similar fashion to group 1 but with groups a', b', c', and d'). Samples were collected at six time points after irradiation. Histopathological changes were observed, and Western blotting (WB) was used to analyze protein expression.

Results

The formation of dead bone and pathological fracture was visible under micro-computed tomography (micro-CT), and tissue biopsy showed late fibrosis repair. In group d', osteogenesis and osteoclasis coexisted in the early irradiation stage. Vascular endothelial growth factor (VEGF) receptor expression was lower in groups c' and d' than in group a'. On day 45, runt-related transcription factor 2 (RUNX2) expression in group d' was lower than that in the other groups. The ratio of receptor activator of nuclear factor-κβ ligand to osteoprotegerin (RANKL:OPG) differed significantly among groups b', c', and d' on the 45th day (d' > c' > b').

Conclusions

Radiation and vascular function damage resulted in the lower expression of VEGF. The first 15 days after radiation was mainly characterized by new bone formation. After 15 days, bone resorption increased. Tooth extraction trauma can aggravate the bone metabolism imbalance and promote ORN occurrence. These findings shed light on the mechanism of ORN.

PTH 1-34 reduced apoptosis of MLO-Y4 osteocyte-like cells by activating autophagy and inhibiting ER stress under RPM conditions

Osteocytes, as mechanosensitive cells residing within bone tissue, hold a pivotal role in averting the occurrence and progression of osteoporosis. The apoptosis of osteocytes induced by unloading is one of the contributing factors to osteoporosis, although the underlying molecular mechanisms have not been fully elucidated. PTH 1-34 is known to promote bone formation and inhibit bone loss by targeting osteoblasts and osteocytes. However, it is not known whether PTH 1-34 can inhibit osteocyte apoptosis under unloading conditions and the molecular mechanisms involved. In this study, we employed a Random Positioning Machine (RPM) to emulate unloading conditions and cultured MLO-Y4 osteocyte-like cells, in order to unravel the mechanisms through which PTH 1-34 constrains osteocyte apoptosis amidst unloading circumstances. Our findings revealed that PTH 1-34 activated autophagy while suppressing endoplasmic reticulum stress by curtailing the generation of reactive oxygen species (ROS) in MLO-Y4 osteocyte-like cells during unloading conditions. By shedding light on the osteoporosis triggered by skeletal unloading, this study contributes vital insights that may pave the way for the development of pharmacological interventions.

Cytoprotective Effect of Gallic Acid against Injuries Promoted by Therapeutic Ionizing Radiation in Preosteoblast Cells

Gallic acid (GA) is a powerful antioxidant extracted from plants of the Brazilian Cerrado. Oxidative stress plays an important role in the occurrence of radiation-induced osteonecrosis in patients treated for head and neck cancer. There is a need to develop research aimed at developing complementary therapies to prevent or reverse bone damage. The aim of the present study was to investigate the effect of GA in preosteoblasts exposed to therapeutic ionizing radiation. MC3T3-E1 preosteoblast cells were treated with 10 µM GA and exposed to 6 Gy ionizing radiation. We performed in vitro assays of cell proliferation, oxidative stress analysis by detection of reactive oxygen species, and alkaline phosphatase assay. GA at lower concentrations was able to significantly increase proliferation and inhibit radiation-induced generation of reactive oxygen species in osteoblast precursor cells, despite ionizing radiation-induced injury. Furthermore, GA significantly increased alkaline phosphatase at a dose of 6 Gy. The findings suggested that GA could attenuate ionizing radiation-induced injuries in osteoblast precursor cells. Moreover, in vivo studies are needed to better investigate the role of GA in osteonecrosis, especially in cancer patients undergoing radiotherapy or taking antiresorptive drugs.

Bioinspired synthetic peptide-based biomaterials regenerate bone through biomimicking of extracellular matrix

There have been remarkable advancements in regenerative medicine for bone regeneration, tackling the worldwide health concern of tissue loss. Tissue engineering uses the body's natural capabilities and applies biomaterials and bioactive molecules to replace damaged or lost tissues and restore their functionality. While synthetic ceramics have overcome some challenges associated with allografts and xenografts, they still need essential growth factors and biomolecules. Combining ceramics and bioactive molecules, such as peptides derived from biological motifs of vital proteins, is the most effective approach to achieve optimal bone regeneration. These bioactive peptides induce various cellular processes and modify scaffold properties by mimicking the function of natural osteogenic, angiogenic and antibacterial biomolecules. The present review aims to consolidate the latest and most pertinent information on the advancements in bioactive peptides, including angiogenic, osteogenic, antimicrobial, and self-assembling peptide nanofibers for bone tissue regeneration, elucidating their biological effects and potential clinical implications.

Proton and Carbon Ion Irradiation Changes the Process of Endochondral Ossification in an Ex Vivo Femur Organotypic Culture Model

Particle therapy (PT) that utilizes protons and carbon ions offers a promising way to reduce the side effects of radiation oncology, especially in pediatric patients. To investigate the influence of PT on growing bone, we exposed an organotypic rat ex vivo femur culture model to PT. After irradiation, histological staining, immunohistochemical staining, and gene expression analysis were conducted following 1 or 14 days of in vitro culture (DIV). Our data indicated a significant loss of proliferating chondrocytes at 1 DIV, which was followed by regeneration attempts through chondrocytic cluster formation at 14 DIV. Accelerated levels of mineralization were observed, which correlated with increased proteoglycan production and secretion into the pericellular matrix. Col2α1 expression, which increased during the cultivation period, was significantly inhibited by PT. Additionally, the decrease in ColX expression over time was more pronounced compared to the non-IR control. The chondrogenic markers BMP2, RUNX2, OPG, and the osteogenic marker ALPL, showed a significant reduction in the increase in expression after 14 DIV due to PT treatment. It was noted that carbon ions had a stronger influence than protons. Our bone model demonstrated the occurrence of pathological and regenerative processes induced by PT, thus building on the current understanding of the biological mechanisms of bone.

Radiation Induces Bone Microenvironment Disruption by Activating the STING-TBK1 Pathway

Background and Objectives: Damage to normal bone tissue following therapeutic irradiation (IR) represents a significant concern, as IR-induced bone microenvironment disruption can cause bone loss and create a more favorable environment for tumor metastases. The aim of the present study was to explore the cellular regulatory mechanism of IR-induced bone microenvironment disruption to effectively prevent radiotherapy-associated adverse effects in the future. Materials and Methods: In this study, a mouse model of local IR was established via local irradiation of the left hind limb of BALB/c mice with 12 Gy X-rays, and an in vitro osteocyte (OCY) model was established by exposing osteocyte-like MLO-Y4 cells to 2, 4, and 8 Gy irradiation to analyze multicellular biological injuries and cellular senescence. Small interfering RNA (siRNA) transfection at the cellular level and a selective antagonist intervention C-176 at the animal level were used to explore the potential role of the stimulator of interferon genes (STING) on IR-induced bone microenvironment disruption. Results: The results showed that 12 Gy local IR induces multicellular dysfunction, manifested as ascension of OCYs exfoliation, activation of osteoclastogenesis, degeneration of osteogenesis and fate conversion of adipogenesis, as well as cellular senescence and altered senescence-associated secretory phenotype (SASP) secretion. Furthermore, the expression of STING was significantly elevated, both in the primary OCYs harvested from locally irradiated mice and in vitro irradiated MLO-Y4 cells, accompanied by the markedly upregulated levels of phosphorylated TANK-binding kinase 1 (P-TBK1), RANKL and sclerostin (SOST). STING-siRNA transfection in vitro restored IR-induced upregulated protein expression of P-TBK1 and RANKL, as well as the mRNA expression levels of inflammatory cytokines, such as IL-1α, IL-6 and NF-κB, accompanied by the alleviation of excessive osteoclastogenesis. Finally, administration of the STING inhibitor C-176 mitigated IR-induced activation of osteoclastogenesis and restraint of osteogenesis, ameliorating the IR-induced biological damage of OCYs, consistent with the inhibition of P-TBK1, RANKL and SOST. Conclusions: The STING-P-TBK1 signaling pathway plays a crucial role in the regulation of the secretion of inflammatory cytokines and osteoclastogenesis potential in IR-induced bone microenvironment disruption. The selective STING antagonist can be used to intervene to block the STING pathway and, thereby, repair IR-induced multicellular biological damage and mitigate the imbalance between osteoclastogenesis and osteoblastgenesis.

Enhanced bone regeneration via local low-dose delivery of PTH1-34 in a composite hydrogel

Introducing bone regeneration-promoting factors into scaffold materials to improve the bone induction property is crucial in the fields of bone tissue engineering and regenerative medicine. This study aimed to develop a Sr-HA/PTH_1-34-loaded composite hydrogel system with high biocompatibility. Teriparatide (PTH_1-34) capable of promoting bone regeneration was selected as the bioactive factor. Strontium-substituted hydroxyapatite (Sr-HA) was introduced into the system to absorb PTH_1-34 to promote the bioactivity and delay the release cycle. PTH_1-34-loaded Sr-HA was then mixed with the precursor solution of the hydrogel to prepare the composite hydrogel as bone-repairing material with good biocompatibility and high mechanical strength. The experiments showed that Sr-HA absorbed PTH_1-34 and achieved the slow and effective release of PTH_1-34. In vitro biological experiments showed that the Sr-HA/PTH_1-34-loaded hydrogel system had high biocompatibility, allowing the good growth of cells on the surface. The measurement of alkaline phosphatase activity and osteogenesis gene expression demonstrated that this composite system could promote the differentiation of MC3T3-E1 cells into osteoblasts. In addition, the in vivo cranial bone defect repair experiment confirmed that this composite hydrogel could promote the regeneration of new bones. In summary, Sr-HA/PTH_1-34 composite hydrogel is a highly promising bone repair material.

Radiotherapy-related insufficiency fractures and bone mineral density: what is the connection?

Background

Radiotherapy-related insufficiency fractures (RRIFs) represent a common, burdensome consequence of pelvic radiotherapy. Their underlying mechanisms remain unclear, and data on the effect of osteoporosis are contradictory, with limited studies assessing bone mineral density (BMD) by dual-energy x-ray absorptiometry (DXA).

Methods

BMD by DXA (Hologic) scan and fracture risk following pelvic RRIF were retrospectively assessed in 39 patients (median age 68 years) at a tertiary cancer centre. Patient characteristics and treatment history are presented narratively; correlations were explored using univariate regression analyses.

Results

Additional cancer treatments included chemotherapy (n = 31), surgery (n = 20) and brachytherapy (n = 19). Median interval between initiation of radiotherapy and RRIF was 11 (7.5-20.8) and that between RRIF and DXA 3 was (1-6) months. Three patients had normal BMD, 16 had osteopenia and 16 osteoporosis, following World Health Organization classification. Four patients were <40 years at the time of DXA (all Z-scores > -2). Median 10-year risk for hip and major osteoporotic fracture was 3.1% (1.5-5.7) and 11.5% (7.1-13.8), respectively. Only 33.3% of patients had high fracture risk (hip fracture >4% and/or major osteoporotic >20%), and 31% fell above the intervention threshold per National Osteoporosis Guidelines Group (NOGG) guidance (2017). Higher BMD was predicted by lower pelvic radiotherapy dose (only in L3 and L4), concomitant chemotherapy and higher body mass index.

Conclusion

At the time of RRIF, most patients did not have osteoporosis, some had normal BMD and overall had low fracture risk. Whilst low BMD is a probable risk factor, it is unlikely to be the main mechanism underlying RRIFs, and further studies are required to understand the predictive value of BMD.

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.

Orchestrated delivery of PTH [1-34] followed by zoledronic acid prevents radiotherapy-induced bone loss but does not abrogate marrow damage

Postradiotherapy bone fragility fractures are a frequent late-onset complication in cancer survivors. There is a critical need to develop preventative interventions, and the use of Food and Drug Administration-approved drugs remains an attractive option. Prior data from our lab and others have shown that parathyroid hormone [1-34] mitigates radiotherapy-induced bone loss, but only for the duration of drug delivery. Utilizing a murine hindlimb radiotherapy model, we investigated whether orchestrated delivery of single-dose zoledronic acid could extend these anabolic benefits after cessation of parathyroid hormone delivery. We then explored the potential use of parathyroid hormone as a bone marrow radioprotectant. While the addition of zoledronic acid to parathyroid hormone increased irradiated bone mass, there was no increase in femur bending strength. In this model, the parathyroid hormone was not effective as a marrow radioprotectant, although this could be due to the short course of parathyroid hormone treatment. Marrow repopulation kinetics differed from those in total body irradiation, with hematopoietic stem cell repopulation occurring relatively early at four weeks postirradiation. Furthermore, we found radiation induced a loss of marrow stromal cells and an increase in inflammatory monocytes. Statement of Clinical Significance: Staged delivery of parathyroid hormone and zoledronic acid shows promise as an off-the-shelf intervention to mitigate post-radiotherapy bone damage in cancer patients, but parathyroid hormone is unlikely to function as a broad-spectrum marrow radioprotectant.

Mobile bioluminescence tomography-guided system for pre-clinical radiotherapy research

Due to low imaging contrast, a widely-used cone-beam computed tomography-guided small animal irradiator is less adept at localizing in vivo soft tissue targets. Bioluminescence tomography (BLT), which combines a model of light propagation through tissue with an optimization algorithm, can recover a spatially resolved tomographic volume for an internal bioluminescent source. We built a novel mobile BLT system for a small animal irradiator to localize soft tissue targets for radiation guidance. In this study, we elaborate its configuration and features that are indispensable for accurate image guidance. Phantom and in vivo validations show the BLT system can localize targets with accuracy within 1 mm. With the optimal choice of threshold and margin for target volume, BLT can provide a distinctive opportunity for investigators to perform conformal biology-guided irradiation to malignancy.

High-specificity protection against radiation-induced bone loss by a pulsed electromagnetic field

Radiotherapy increases tumor cure and survival rates; however, radiotherapy-induced bone damage remains a common issue for which effective countermeasures are lacking, especially considering tumor recurrence risks. We report a high-specificity protection technique based on noninvasive electromagnetic field (EMF). A unique pulsed-burst EMF (PEMF) at 15 Hz and 2 mT induces notable Ca²⁺ oscillations with robust Ca²⁺ spikes in osteoblasts in contrast to other waveforms. This waveform parameter substantially inhibits radiotherapy-induced bone loss by specifically modulating osteoblasts without affecting other bone cell types or tumor cells. Mechanistically, primary cilia are identified as major PEMF sensors in osteoblasts, and the differentiated ciliary expression dominates distinct PEMF sensitivity between osteoblasts and tumor cells. PEMF-induced unique Ca²⁺ oscillations depend on interactions between ciliary polycystins-1/2 and endoplasmic reticulum, which activates the Ras/MAPK/AP-1 axis and subsequent DNA repair Ku70 transcription. Our study introduces a previously unidentified method against radiation-induced bone damage in a noninvasive, cost-effective, and highly specific manner.

Acetabular fixation in total hip arthroplasty in the previously irradiated pelvis: a review of basic science and clinical outcomes

Radiation therapy is a common primary, adjuvant, or palliative treatment for many intrapelvic tumors, including primary gastrointestinal, genitourinary, and hematopoietic tumors, as well as metastatic disease to bone. Radiation has well documented microbiologic and clinical effects on bone ranging from radiation osteitis to early degenerative changes of the hip joint and avascular necrosis of the femoral head. Conventional total hip arthroplasty methods have demonstrated high rates of failure in this population, with historical data describing aseptic loosening rates as high as 44-52%, as radiation have been shown to preferentially diminish osteoblast and osteocyte number and function and limit capacity for both cement interdigitation and biologic bony ingrowth. A review of the clinical literature suggests that patients with prior pelvic irradiation are at higher risk for both septic and aseptic loosening of acetabular components, as well as lower postoperative Harris Hip Score (HHS) when compared to historical controls. With limited evidence, trabecular metal shells with multi-screw fixation and cemented polyethene liners, as well as cemented cup-cage constructs both appear to be durable acetabular fixation options, though the indications for each remains elusive. Further prospective data are needed to better characterize this difficult clinical problem.

RadBone: bone toxicity following pelvic radiotherapy - a prospective randomised controlled feasibility study evaluating a musculoskeletal health package in women with gynaecological cancers undergoing pelvic radiotherapy

INTRODUCTION

Patients receiving radiotherapy are at risk of developing radiotherapy-related insufficiency fractures, which are associated with increased morbidity and pose a significant burden to patients' quality of life and to the health system. Therefore, effective preventive techniques are urgently required. The RadBone randomised controlled trial (RCT) aims to determine the feasibility and acceptability of a musculoskeletal health package (MHP) intervention in women undergoing pelvic radiotherapy for gynaecological malignancies and to preliminary explore clinical effectiveness of the intervention.

METHODS AND ANALYSIS

The RadBone RCT will evaluate the addition to standard care of an MHP consisting of a physical assessment of the musculoskeletal health, a 3-month prehabilitation personalised exercise package, as well as an evaluation of the fracture risk and if required the prescription of appropriate bone treatment including calcium, vitamin D and-for high-risk individuals-bisphosphonates. Forty participants will be randomised in each group (MHP or observation) and will be followed for 18 months. The primary outcome of this RCT will be feasibility, including the eligibility, screening and recruitment rate, intervention fidelity and attrition rates; acceptability and health economics. Clinical effectiveness and bone turnover markers will be evaluated as secondary outcomes.

ETHICS AND DISSEMINATION

This study has been approved by the Greater Manchester East Research Ethics Committee (Reference: 20/NW/0410, November 2020). The results will be published in peer-reviewed journals, will be presented in national and international conferences and will be communicated to relevant stakeholders. Moreover, a plain English report will be shared with the study participants, patients' organisations and media.

TRIAL REGISTRATION NUMBER

NCT04555317.

Targeted clearance of p21- but not p16-positive senescent cells prevents radiation-induced osteoporosis and increased marrow adiposity

Cellular senescence, which is a major cause of tissue dysfunction with aging and multiple other conditions, is known to be triggered by p16Ink4a or p21Cip1 , but the relative contributions of each pathway toward inducing senescence are unclear. Here, we directly addressed this issue by first developing and validating a p21-ATTAC mouse with the p21Cip1 promoter driving a "suicide" transgene encoding an inducible caspase-8 which, upon induction, selectively kills p21Cip1 -expressing senescent cells. Next, we used the p21-ATTAC mouse and the established p16-INK-ATTAC mouse to directly compare the contributions of p21Cip1 versus p16Ink4a in driving cellular senescence in a condition where a tissue phenotype (bone loss and increased marrow adiposity) is clearly driven by cellular senescence-specifically, radiation-induced osteoporosis. Using RNA in situ hybridization, we confirmed the reduction in radiation-induced p21Cip1 - or p16Ink4a -driven transcripts following senescent cell clearance in both models. However, only clearance of p21Cip1 +, but not p16Ink4a +, senescent cells prevented both radiation-induced osteoporosis and increased marrow adiposity. Reduction in senescent cells with dysfunctional telomeres following clearance of p21Cip1 +, but not p16Ink4a +, senescent cells also reduced several of the radiation-induced pro-inflammatory senescence-associated secretory phenotype factors. Thus, by directly comparing senescent cell clearance using two parallel genetic models, we demonstrate that radiation-induced osteoporosis is driven predominantly by p21Cip1 - rather than p16Ink4a -mediated cellular senescence. Further, this approach can be used to dissect the contributions of these pathways in other senescence-associated conditions, including aging across tissues.

Transient expansion and myofibroblast conversion of adipogenic lineage precursors mediate bone marrow repair after radiation

Radiation causes a collapse of bone marrow cells and elimination of microvasculature. To understand how bone marrow recovers after radiation, we focused on mesenchymal lineage cells that provide a supportive microenvironment for hematopoiesis and angiogenesis in bone. We recently discovered a nonproliferative subpopulation of marrow adipogenic lineage precursors (MALPs) that express adipogenic markers with no lipid accumulation. Single-cell transcriptomic analysis revealed that MALPs acquire proliferation and myofibroblast features shortly after radiation. Using an adipocyte-specific Adipoq-Cre, we validated that MALPs rapidly and transiently expanded at day 3 after radiation, coinciding with marrow vessel dilation and diminished marrow cellularity. Concurrently, MALPs lost most of their cell processes, became more elongated, and highly expressed myofibroblast-related genes. Radiation activated mTOR signaling in MALPs that is essential for their myofibroblast conversion and subsequent bone marrow recovery at day 14. Ablation of MALPs blocked the recovery of bone marrow vasculature and cellularity, including hematopoietic stem and progenitors. Moreover, VEGFa deficiency in MALPs delayed bone marrow recovery after radiation. Taken together, our research demonstrates a critical role of MALPs in mediating bone marrow repair after radiation injury and sheds light on a cellular target for treating marrow suppression after radiotherapy.

Quantitative Bioluminescence Tomography for In Vivo Volumetric-Guided Radiotherapy

Several groups, including ours, have initiated efforts to develop small-animal irradiators that mimic radiation therapy (RT) for human treatment. The major image modality used to guide irradiation is cone-beam computed tomography (CBCT). While CBCT provides excellent guidance capability, it is less adept at localizing soft tissue targets growing in a low image contrast environment. In contrast, bioluminescence imaging (BLI) provides strong image contrast and thus is an attractive solution for soft tissue targeting. However, commonly used 2D BLI on an animal surface is inadequate to guide irradiation, because optical transport from an internal bioluminescent tumor is highly susceptible to the effects of optical path length and tissue absorption and scattering. Recognition of these limitations led us to integrate 3D bioluminescence tomography (BLT) with the small animal radiation research platform (SARRP). In this chapter, we introduce quantitative BLT (QBLT) with the advanced capabilities of quantifying tumor volume for irradiation guidance. The detail of system components, calibration protocol, and step-by-step procedure to conduct the QBLT-guided irradiation are described.

Irradiation affects the structural, cellular and molecular components of jawbones

PURPOSE

Emerging evidence shows that changes in the bone and its microenvironment following radiotherapy are associated with either an inhibition or a state of low bone formation. Ionizing radiation is damaging to the jawbone as it increases the complication rate due to the development of hypovascular, hypocellular, and hypoxic tissue. This review summarizes and correlates the current knowledge on the effects of irradiation on the bone with an emphasis on jawbone, as these have been a less extensively studied area.

CONCLUSIONS

The stringent regulation of bone formation and bone resorption can be influenced by radiation, causing detrimental effects at structural, cellular, vascular, and molecular levels. It is also associated with a high risk of damage to surrounding healthy tissues and an increased risk of fracture. Technological advances and research on animal models as well as a few human bone tissue studies have provided novel insights into the ways in which bone can be affected by high, low and sublethal dose of radiation. The influence of radiation on bone metabolism, cellular properties, vascularity, collagen, and other factors like inflammation, reactive oxygen species are discussed.

Parathyroid Hormone 1 Receptor Signaling in Dental Mesenchymal Stem Cells: Basic and Clinical Implications

Parathyroid hormone (PTH) and parathyroid hormone-related protein (PTHrP) are two peptides that regulate mineral ion homeostasis, skeletal development, and bone turnover by activating parathyroid hormone 1 receptor (PTH1R). PTH1R signaling is of profound clinical interest for its potential to stimulate bone formation and regeneration. Recent pre-clinical animal studies and clinical trials have investigated the effects of PTH and PTHrP analogs in the orofacial region. Dental mesenchymal stem cells (MSCs) are targets of PTH1R signaling and have long been known as major factors in tissue repair and regeneration. Previous studies have begun to reveal important roles for PTH1R signaling in modulating the proliferation and differentiation of MSCs in the orofacial region. A better understanding of the molecular networks and underlying mechanisms for modulating MSCs in dental diseases will pave the way for the therapeutic applications of PTH and PTHrP in the future. Here we review recent studies involving dental MSCs, focusing on relationships with PTH1R. We also summarize recent basic and clinical observations of PTH and PTHrP treatment to help understand their use in MSCs-based dental and bone regeneration.

Radiotherapy-induced bone deterioration is exacerbated in diabetic rats treated with streptozotocin

Following radiotherapy, patients have decreased bone mass and increased risk of fragility fractures. Diabetes mellitus (DM) is also reported to have detrimental effects on bone architecture and quality. However, no clinical or experimental study has systematically characterized the bone phenotype of the diabetic patients following radiotherapy. After one month of streptozotocin injection, three-month-old male rats were subjected to focal radiotherapy (8 Gy, twice, at days 1 and 3), and then bone mass, microarchitecture, and turnover as well as bone cell activities were evaluated at 2 months post-irradiation. Micro-computed tomography results demonstrated that DM rats exhibited greater deterioration in trabecular bone mass and microarchitecture following irradiation compared with the damage to bone structure induced by DM or radiotherapy. The serum biochemical, bone histomorphometric, and gene expression assays revealed that DM combined with radiotherapy showed lower bone formation rate, osteoblast number on bone surface, and expression of osteoblast-related markers (ALP, Runx2, Osx, and Col-1) compared with DM or irradiation alone. DM plus irradiation also caused higher bone resorption rate, osteoclast number on bone surface, and expression of osteoclast-specific markers (TRAP, cathepsin K, and calcitonin receptor) than DM or irradiation treatment alone. Moreover, lower osteocyte survival and higher expression of Sost and DKK1 genes (two negative modulators of Wnt signaling) were observed in rats with combined DM and radiotherapy. Together, these findings revealed a higher deterioration of the diabetic skeleton following radiotherapy, and emphasized the clinical importance of health maintenance.

Simulated Galactic Cosmic Rays Modify Mitochondrial Metabolism in Osteoclasts, Increase Osteoclastogenesis and Cause Trabecular Bone Loss in Mice

Space is a high-stress environment. One major risk factor for the astronauts when they leave the Earth's magnetic field is exposure to ionizing radiation from galactic cosmic rays (GCR). Several adverse changes occur in mammalian anatomy and physiology in space, including bone loss. In this study, we assessed the effects of simplified GCR exposure on skeletal health in vivo. Three months following exposure to 0.5 Gy total body simulated GCR, blood, bone marrow and tissue were collected from 9 months old male mice. The key findings from our cell and tissue analysis are (1) GCR induced femoral trabecular bone loss in adult mice but had no effect on spinal trabecular bone. (2) GCR increased circulating osteoclast differentiation markers and osteoclast formation but did not alter new bone formation or osteoblast differentiation. (3) Steady-state levels of mitochondrial reactive oxygen species, mitochondrial and non-mitochondrial respiration were increased without any changes in mitochondrial mass in pre-osteoclasts after GCR exposure. (4) Alterations in substrate utilization following GCR exposure in pre-osteoclasts suggested a metabolic rewiring of mitochondria. Taken together, targeting radiation-mediated mitochondrial metabolic reprogramming of osteoclasts could be speculated as a viable therapeutic strategy for space travel induced bone loss.

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.

Preclinical models for investigating how bone marrow adipocytes influence bone and hematopoietic cellularity

Laboratory mice are a crucial preclinical model system for investigating bone marrow adipocyte (BMAd)-bone and BMAd-hematopoiesis interactions. In this review, we evaluate the suitability of mice to model common human diseases related to osteopenia or hematopoietic disorders, point out consistencies and discrepancies among different studies, and provide insights into model selection. Species, age, sex, skeletal site, and treatment protocol should all be considered when designing future studies.

The combined effects of simulated microgravity and X-ray radiation on MC3T3-E1 cells and rat femurs

Microgravity is well-known to induce Osteopenia. However, the combined effects of microgravity and radiation that commonly exist in space have not been broadly elucidated. This research investigates the combined effects on MC3T3-E1 cells and rat femurs. In MC3T3-E1 cells, simulated microgravity and X-ray radiation, alone or combination, show decreased cell activity, increased apoptosis rates by flow cytometric analysis, and decreased Runx2 and increased Caspase-3 mRNA and protein expressions. In rat femurs, simulated microgravity and X-ray radiation, alone or combination, show increased bone loss by micro-CT test and Masson staining, decreased serum BALP levels and Runx2 mRNA expressions, and increased serum CTX-1 levels and Caspase-3 mRNA expressions. The strongest effect is observed in the combined group in MC3T3-E1 cells and rat femurs. These findings suggest that the combination of microgravity and radiation exacerbates the effects of either treatment alone on MC3T3-E1 cells and rat femurs.

In vivo bioluminescence tomography-guided radiation research platform for pancreatic cancer: an initial study using subcutaneous and orthotopic pancreatic tumor models

Genetically engineered mouse model(GEMM) that develops pancreatic ductal adenocarcinoma(PDAC) offers an experimental system to advance our understanding of radiotherapy(RT) for pancreatic cancer. Cone beam CT(CBCT)-guided small animal radiation research platform(SARRP) has been developed to mimic the RT used for human. However, we recognized that CBCT is inadequate to localize the PDAC growing in low image contrast environment. We innovated bioluminescence tomography(BLT) to guide SARRP irradiation for in vivo PDAC. Before working on the complex PDAC-GEMM, we first validated our BLT target localization using subcutaneous and orthotopic pancreatic tumor models. Our BLT process involves the animal transport between the BLT system and SARRP. We inserted a titanium wire into the orthotopic tumor as the fiducial marker to track the tumor location and to validate the BLT reconstruction accuracy. Our data shows that with careful animal handling, minimum disturbance for target position was introduced during our BLT imaging procedure(<0.5mm). However, from longitudinal 2D bioluminescence image(BLI) study, the day-to-day location variation for an abdominal tumor can be significant. We also showed that the 2D BLI in single projection setting cannot accurately capture the abdominal tumor location. It renders that 3D BLT with multiple-projection is needed to quantify the tumor volume and location for precise radiation research. Our initial results show the BLT can retrieve the location at 2mm accuracy for both tumor models, and the tumor volume can be delineated within 25% accuracy. The study for the subcutaneous and orthotopic models will provide us valuable knowledge for BLT-guided PDAC-GEMM radiation research.

Osteocyte apoptosis: the roles and key molecular mechanisms in resorption-related bone diseases

Vital osteocytes have been well known to function as an important orchestrator in the preservation of robustness and fidelity of the bone remodeling process. Nevertheless, some key pathological factors, such as sex steroid deficiency and excess glucocorticoids, and so on, are implicated in inducing a bulk of apoptotic osteocytes, subsequently resulting in resorption-related bone loss. As much, osteocyte apoptosis, under homeostatic conditions, is in an optimal state of balance tightly controlled by pro- and anti-apoptotic mechanism pathways. Importantly, there exist many essential signaling proteins in the process of osteocyte apoptosis, which has a crucial role in maintaining a homeostatic environment. While increasing in vitro and in vivo studies have established, in part, key signaling pathways and cross-talk mechanism on osteocyte apoptosis, intrinsic and complex mechanism underlying osteocyte apoptosis occurs in various states of pathologies remains ill-defined. In this review, we discuss not only essential pro- and anti-apoptotic signaling pathways and key biomarkers involved in these key mechanisms under different pathological agents, but also the pivotal role of apoptotic osteocytes in osteoclastogenesis-triggered bone loss, hopefully shedding new light on the attractive and proper actions of pharmacotherapeutics of targeting apoptosis and ensuing resorption-related bone diseases such as osteoporosis and fragility fractures.

The Influence of Radiation on Bone and Bone Cells-Differential Effects on Osteoclasts and Osteoblasts

The bone is a complex organ that is dependent on a tight regulation between bone formation by osteoblasts (OBs) and bone resorption by osteoclasts (OCs). These processes can be influenced by environmental factors such as ionizing radiation (IR). In cancer therapy, IR is applied in high doses, leading to detrimental effects on bone, whereas radiation therapy with low doses of IR is applied for chronic degenerative and inflammatory diseases, with a positive impact especially on bone homeostasis. Moreover, the effects of IR are of particular interest in space travel, as astronauts suffer from bone loss due to space radiation and microgravity. This review summarizes the current state of knowledge on the effects of IR on bone with a special focus on the influence on OCs and OBs, as these cells are essential in bone remodeling. In addition, the influence of IR on the bone microenvironment is discussed. In summary, the effects of IR on bone and bone remodeling cells strongly depend on the applied radiation dose, as differential results are provided from in vivo as well as in vitro studies with varying doses of IR. Furthermore, the isolated effects of IR on a single cell type are difficult to determine, as the bone cells and bone microenvironment are building a tightly regulated network, influencing on one another. Therefore, future research is necessary in order to elucidate the influence of different bone cells on the overall radiation-induced effects on bone.

Targeted Reduction of Senescent Cell Burden Alleviates Focal Radiotherapy-Related Bone Loss

Clinical radiotherapy treats life-threatening cancers, but the radiation often affects neighboring normal tissues including bone. Acute effects of ionizing radiation include oxidative stress, DNA damage, and cellular apoptosis. We show in this study that a large proportion of bone marrow cells, osteoblasts, and matrix-embedded osteocytes recover from these insults only to attain a senescent profile. Bone analyses of senescence-associated genes, senescence-associated beta-galactosidase (SA-β-gal) activity, and presence of telomere dysfunction-induced foci (TIF) at 1, 7, 14, 21, and 42 days post-focal radiation treatment (FRT) in C57BL/6 male mice confirmed the development of senescent cells and the senescence-associated secretory phenotype (SASP). Accumulation of senescent cells and SASP markers were correlated with a significant reduction in bone architecture at 42 days post-FRT. To test if senolytic drugs, which clear senescent cells, alleviate FRT-related bone damage, we administered the senolytic agents, dasatinib (D), quercetin (Q), fisetin (F), and a cocktail of D and Q (D+Q). We found moderate alleviation of radiation-induced bone damage with D and Q as stand-alone compounds, but no such improvement was seen with F. However, the senolytic cocktail of D+Q reduced senescent cell burden as assessed by TIF⁺ osteoblasts and osteocytes, markers of senescence (p16 ^Ink4a and p21), and key SASP factors, resulting in significant recovery in the bone architecture of radiated femurs. In summary, this study provides proof of concept that senescent cells play a role in radiotherapy-associated bone damage, and that reduction in senescent cell burden by senolytic agents is a potential therapeutic option for alleviating radiotherapy-related bone deterioration. © 2020 American Society for Bone and Mineral Research.

Single cell transcriptomics identifies a unique adipose lineage cell population that regulates bone marrow environment

Bone marrow mesenchymal lineage cells are a heterogeneous cell population involved in bone homeostasis and diseases such as osteoporosis. While it is long postulated that they originate from mesenchymal stem cells, the true identity of progenitors and their in vivo bifurcated differentiation routes into osteoblasts and adipocytes remain poorly understood. Here, by employing large scale single cell transcriptome analysis, we computationally defined mesenchymal progenitors at different stages and delineated their bi-lineage differentiation paths in young, adult and aging mice. One identified subpopulation is a unique cell type that expresses adipocyte markers but contains no lipid droplets. As non-proliferative precursors for adipocytes, they exist abundantly as pericytes and stromal cells that form a ubiquitous 3D network inside the marrow cavity. Functionally they play critical roles in maintaining marrow vasculature and suppressing bone formation. Therefore, we name them marrow adipogenic lineage precursors (MALPs) and conclude that they are a newly identified component of marrow adipose tissue.

Phenomenon of osteocyte lacunar mineralization: indicator of former osteocyte death and a novel marker of impaired bone quality?

An increasing number of patients worldwide suffer from bone fractures that occur after low intensity trauma. Such fragility fractures are usually associated with advanced age and osteoporosis but also with long-term immobilization, corticosteroid therapy, diabetes mellitus, and other endocrine disorders. It is important to understand the skeletal origins of increased bone fragility in these conditions for preventive and therapeutic strategies to combat one of the most common health problems of the aged population. This review summarizes current knowledge pertaining to the phenomenon of micropetrosis (osteocyte lacunar mineralization). As an indicator of former osteocyte death, micropetrosis is more common in aged bone and osteoporotic bone. Considering that the number of mineralized osteocyte lacunae per bone area can distinguish healthy, untreated osteoporotic and bisphosphonate-treated osteoporotic patients, it could be regarded as a novel structural marker of impaired bone quality. Further research is needed to clarify the mechanism of lacunar mineralization and to explore whether it could be an additional target for preventing or treating bone fragility related to aging and various endocrine diseases.

H-type blood vessels participate in alveolar bone remodeling during murine tooth extraction healing

OBJECTIVES

We aimed to investigate whether skeletal-specific H-type blood vessels exist in alveolar bone and how they function in alveolar bone remodeling.

MATERIALS AND METHODS

H-type vessels with high expression of CD31 and Endomucin (CD31^hi Emcn^hi ) were immunostained in alveolar bone. Abundance and age-related changes in CD31^hi Emcn^hi endothelial cells (H-ECs) were detected by flow cytometry. Osteoprogenitors association with H-type vessels and bone mass were detected in tooth extraction model of alveolar bone remodeling by immunohistofluorescence and micro-CT, respectively. Transcription and expression of H-EC feature genes during in vitro Notch inhibition were measured by RT-qPCR and immunocytofluorescence.

RESULTS

We verified that H-type vessels existed in alveolar bone, the abundance of which was highest at infancy age, then decreased but maintained a constant level during aging. In tooth extraction model, H-ECs significantly increased with concomitant perivascular accumulation of Runx2⁺ osteoprogenitors and gradually augmentation of bone mass. Notch inhibition of in vitro cultured H-ECs resulted in decreased expression levels of Emcn and hes1, but not Pecam1 or Kdr genes, with decreased expression levels of H-EC numbers, accordingly.

CONCLUSIONS

The present study suggests that H-type vessels promote osteogenesis during alveolar bone remodeling. Notch signaling pathway regulates expression of Emcn and possibly determines fate and functions of alveolar H-ECs.

Bench to Bedside: Animal Models of Radiation Induced Musculoskeletal Toxicity

Ionizing radiation is a critical aspect of current cancer therapy. While classically mature bone was thought to be relatively radio-resistant, more recent data have shown this to not be the case. Radiation therapy (RT)-induced bone loss leading to fracture is a source of substantial morbidity. The mechanisms of RT likely involve multiple pathways, including changes in angiogenesis and bone vasculature, osteoblast damage/suppression, and increased osteoclast activity. The majority of bone loss appears to occur rapidly after exposure to ionizing RT, with significant changes in cortical thickness being detectable on computed tomography (CT) within three to four months. Additionally, there is a dose–response relationship. Cortical thinning is especially notable in areas of bone that receive >40 gray (Gy). Methods to mitigate toxicity due to RT-induced bone loss is an area of active investigation. There is an accruing clinical trial investigating the use of risderonate, a bisphosphonate, to prevent rib bone loss in patients undergoing lung stereotactic body radiation therapy (SBRT). Additionally, several other promising therapeutic/preventative approaches are being explored in preclinical studies, including parathyroid hormone (PTH), amifostine, and mechanical loading of irradiated bones.

Megakaryocytes promote bone formation through coupling osteogenesis with angiogenesis by secreting TGF-β1

Rationale: The hematopoietic system and skeletal system have a close relationship, and megakaryocytes (MKs) may be involved in maintaining bone homeostasis. However, the exact role and underlying mechanism of MKs in bone formation during steady-state and stress conditions are still unclear.

Methods: We first evaluated the bone phenotype with MKs deficiency in bone marrow by using c-Mpl-deficient mice and MKs-conditionally deleted mice. Then, osteoblasts (OBs) proliferation and differentiation and CD31^hiEmcn^hi tube formation were assessed. The expression of growth factors related to bone formation in MKs was detected by RNA-sequencing and enzyme-linked immunosorbent assays (ELISAs). Mice with specific depletion of TGF-β1 in MKs were used to further verify the effect of MKs on osteogenesis and angiogenesis. Finally, MKs treatment of irradiation-induced bone injury was tested in a mouse model.

Results: We found that MKs deficiency significantly impaired bone formation. Further investigations revealed that MKs could promote OBs proliferation and differentiation, as well as CD31^hiEmcn^hi vessels formation, by secreting high levels of TGF-β1. Consistent with these findings, mice with specific depletion of TGF-β1 in MKs displayed significantly decreased bone mass and strength. Importantly, treatment with MKs or thrombopoietin (TPO) substantially attenuated radioactive bone injury in mice by directly or indirectly increasing the level of TGF-β1 in bone marrow. MKs-derived TGF-β1 was also involved in suppressing apoptosis and promoting DNA damage repair in OBs after irradiation exposure.

Conclusions: Our findings demonstrate that MKs contribute to bone formation through coupling osteogenesis with angiogenesis by secreting TGF-β1, which may offer a potential therapeutic strategy for the treatment of irradiation-induced osteoporosis.

Reporting Guidelines, Review of Methodological Standards, and Challenges Toward Harmonization in Bone Marrow Adiposity Research. Report of the Methodologies Working Group of the International Bone Marrow Adiposity Society

The interest in bone marrow adiposity (BMA) has increased over the last decade due to its association with, and potential role, in a range of diseases (osteoporosis, diabetes, anorexia, cancer) as well as treatments (corticosteroid, radiation, chemotherapy, thiazolidinediones). However, to advance the field of BMA research, standardization of methods is desirable to increase comparability of study outcomes and foster collaboration. Therefore, at the 2017 annual BMA meeting, the International Bone Marrow Adiposity Society (BMAS) founded a working group to evaluate methodologies in BMA research. All BMAS members could volunteer to participate. The working group members, who are all active preclinical or clinical BMA researchers, searched the literature for articles investigating BMA and discussed the results during personal and telephone conferences. According to the consensus opinion, both based on the review of the literature and on expert opinion, we describe existing methodologies and discuss the challenges and future directions for (1) histomorphometry of bone marrow adipocytes, (2) ex vivo BMA imaging, (3) in vivo BMA imaging, (4) cell isolation, culture, differentiation and in vitro modulation of primary bone marrow adipocytes and bone marrow stromal cell precursors, (5) lineage tracing and in vivo BMA modulation, and (6) BMA biobanking. We identify as accepted standards in BMA research: manual histomorphometry and osmium tetroxide 3D contrast-enhanced μCT for ex vivo quantification, specific MRI sequences (WFI and H-MRS) for in vivo studies, and RT-qPCR with a minimal four gene panel or lipid-based assays for in vitro quantification of bone marrow adipogenesis. Emerging techniques are described which may soon come to complement or substitute these gold standards. Known confounding factors and minimal reporting standards are presented, and their use is encouraged to facilitate comparison across studies. In conclusion, specific BMA methodologies have been developed. However, important challenges remain. In particular, we advocate for the harmonization of methodologies, the precise reporting of known confounding factors, and the identification of methods to modulate BMA independently from other tissues. Wider use of existing animal models with impaired BMA production (e.g., Pfrt^-/-, Kit^W/W-v) and development of specific BMA deletion models would be highly desirable for this purpose.

Effect of teriparatide on early sinus graft healing in the ovariectomized rabbit

OBJECTIVES

The purpose of this study was to determine the effect of administering intermittent parathyroid hormone 1-34 [teriparatide, (PTH)] on the maxillary sinus lift and bone grafting in osteoporotic rabbits induced by ovariectomy and glucocorticoid.

MATERIALS AND METHODS

Ovariectomies were performed on 20 female New Zealand white rabbits that were randomly divided into two groups: (a) the PTH group (n = 10), in which 10 μg kg^-1  day^-1 PTH was injected subcutaneously 5 days a week for 5 weeks (from 1 week before until 4 weeks after sinus surgery), and (b) the saline group (n = 10), in which saline substituted PTH at the same dose, mode of administration, and duration. Bone grafting with bovine bone mineral was augmented into 13 sinuses, and bone grafts and implants were simultaneously performed in seven sinuses, in both groups. Animals were sacrificed at 4 weeks after surgery. To determine whether PTH was an effective treatment for osteoporosis, we measured the bone mineral density (BMD) of the right femur using micro-computed tomography and performed radiographic and histometric analyses of the maxillary sinus surgery site. The Mann-Whitney test was used for statistical analysis.

RESULTS

It was found that BMD increased in the femur, whereas none of the radiographic and histometric parameters differed significantly between the groups in the sinus, while there were large interindividual variations within groups.

CONCLUSIONS

These findings suggest that intermittent PTH does not promote new bone formation in the augmented maxillary sinus of ovariectomized rabbits.

Evaluation of longitudinal time-lapsed in vivo micro-CT for monitoring fracture healing in mouse femur defect models

Longitudinal in vivo micro-computed tomography (micro-CT) is of interest to non-invasively capture the healing process of individual animals in preclinical fracture healing studies. However, it is not known whether longitudinal imaging itself has an impact on callus formation and remodeling. In this study, a scan group received weekly micro-CT measurements (week 0-6), whereas controls were only scanned post-operatively and at week 5 and 6. Registration of consecutive scans using a branching scheme (bridged vs. unbridged defect) combined with a two-threshold approach enabled assessment of localized bone turnover and mineralization kinetics relevant for monitoring callus remodeling. Weekly micro-CT application did not significantly change any of the assessed callus parameters in the defect and periosteal volumes. This was supported by histomorphometry showing only small amounts of cartilage residuals in both groups, indicating progression towards the end of the healing period. Also, immunohistochemical staining of Sclerostin, previously associated with mediating adverse radiation effects on bone, did not reveal differences between groups. The established longitudinal in vivo micro-CT-based approach allows monitoring of healing phases in mouse femur defect models without significant effects of anesthesia, handling and radiation on callus properties. Therefore, this study supports application of longitudinal in vivo micro-CT for healing-phase-specific monitoring of fracture repair in mice.

Effects of ionizing radiation on woven bone: influence on the osteocyte lacunar network, collagen maturation, and microarchitecture

OBJECTIVES

Evaluate the effects of ionizing radiation on microarchitecture, the osteocyte lacunar network, and collagen maturity in a bone repair site.

MATERIALS AND METHODS

Bone defects were created on tibias of 20 New Zealand rabbits. After 2 weeks, the animals were randomly divided into (n = 10) NoIr (nonirradiated group) and Ir (irradiated group). In the Ir, the animals received single-dose irradiation of 30 Gy on the tibia and were euthanized after 2 weeks. Bone microarchitecture parameters were analyzed by using micro-CT, and the osteocyte lacunar network, bone matrix, and collagen maturation by histomorphometric analysis. The data were analyzed using unpaired Student's t test (α = 0.05).

RESULTS

Trabecular thickness in Ir was lower than that in NoIr (P = 0.028). No difference was found for bone volume fraction and bone area. Lacunae filled with osteocytes were more numerous (P < 0.0001) in NoIr (2.6 ± 0.6) than in Ir (1.97 ± 0.53). Empty lacunae were more prevalent (P < 0.003) in Ir (0.14 ± 0.10) than in NoIr (0.1 ± 0.1). The mean osteocyte lacunae size was higher (P < 0.01) in Ir (15.4 ± 4.41) than in NoIr (12.7 ± 3.7). Picrosirius red analysis showed more (P < 0.05) mature collagen in NoIr (29.0 ± 5.3) than in Ir (23.4 ± 4.5). Immature collagen quantification revealed no difference between groups.

CONCLUSIONS

Ionizing radiation compromised bone formation and an impairment in bone repair in irradiated woven bone was observed.

CLINICAL RELEVANCE

Before radiotherapy, patients usually need surgical intervention, which may be better performed, if clinicians understand the repair process in irradiated bone, using novel approaches for treating these individuals.

In Vivo Bioluminescence Tomography Center of Mass-Guided Conformal Irradiation

PURPOSE

The cone-beam computed tomography (CBCT)-guided small animal radiation research platform (SARRP) has provided unique opportunities to test radiobiologic hypotheses. However, CBCT is less adept to localize soft tissue targets growing in a low imaging contrast environment. Three-dimensional bioluminescence tomography (BLT) provides strong image contrast and thus offers an attractive solution. We introduced a novel and efficient BLT-guided conformal radiation therapy and demonstrated it in an orthotopic glioblastoma (GBM) model.

METHODS AND MATERIALS

A multispectral BLT system was integrated with SARRP for radiation therapy (RT) guidance. GBM growth curve was first established by contrast CBCT/magnetic resonance imaging (MRI) to derive equivalent sphere as approximated gross target volume (aGTV). For BLT, mice were subject to multispectral bioluminescence imaging, followed by SARRP CBCT imaging and optical reconstruction. The CBCT image was acquired to generate anatomic mesh for the reconstruction and RT planning. To ensure high accuracy of the BLT-reconstructed center of mass (CoM) for target localization, we optimized the optical absorption coefficients μ_a by minimizing the distance between the CoMs of BLT reconstruction and contrast CBCT/MRI-delineated GBM volume. The aGTV combined with the uncertainties of BLT CoM localization and target volume determination was used to generate estimated target volume (ETV). For conformal irradiation procedure, the GBM was first localized by the predetermined ETV centered at BLT-reconstructed CoM, followed by SARRP radiation. The irradiation accuracy was qualitatively confirmed by pathologic staining.

RESULTS

Deviation between CoMs of BLT reconstruction and contrast CBCT/MRI-imaged GBM is approximately 1 mm. Our derived ETV centered at BLT-reconstructed CoM covers >95% of the tumor volume. Using the second-week GBM as an example, the ETV-based BLT-guided irradiation can cover 95.4% ± 4.7% tumor volume at prescribed dose. The pathologic staining demonstrated the BLT-guided irradiated area overlapped well with the GBM location.

CONCLUSIONS

The BLT-guided RT enables 3-dimensional conformal radiation for important orthotopic tumor models, which provides investigators a new preclinical research capability.

Nonvascularized Bone Graft Reconstruction of the Irradiated Murine Mandible: An Analogue of Clinical Head and Neck Cancer Treatment

Nonvascularized bone grafts (NBGs) represent a practical method of mandibular reconstruction that is precluded in head and neck cancer patients by the destructive effects of radiotherapy. Advances in tissue-engineering may restore NBGs as a viable surgical technique, but expeditious translation demands a small-animal model that approximates clinical practice. This study establishes a murine model of irradiated mandibular reconstruction using a segmental iliac crest NBG for the investigation of imperative bone healing strategies. Twenty-seven male isogenic Lewis rats were divided into 2 groups; control bone graft and irradiated bone graft (XBG). Additional Lewis rats served as graft donors. The XBG group was administered a fractionated dose of 35Gy. All rats underwent reconstruction of a segmental, critical-sized defect of the left hemi-mandible with a 5 mm NBG from the iliac crest, secured by a custom radiolucent plate. Following a 60-day recovery period, hemi-mandibles were evaluated for bony union, bone mineralization, and biomechanical strength (P < 0.05). Bony union rates were significantly reduced in the XBG group (42%) compared with controls (80%). Mandibles in the XBG group further demonstrated substantial radiation injury through significant reductions in all metrics of bone mineralization and biomechanical strength. These observations are consistent with the clinical sequelae of radiotherapy that limit NBGs to nonirradiated patients. This investigation provides a clinically relevant, quantitative model in which innovations in tissue engineering may be evaluated in the setting of radiotherapy to ultimately provide the advantages of NBGs to head and neck cancer patients and reconstructive surgeons.

Reproducibility and Radiation Effect of High-Resolution In Vivo Micro Computed Tomography Imaging of the Mouse Lumbar Vertebra and Long Bone

A moderate radiation dose, in vivo µCT scanning protocol was developed and validated for long-term monitoring of multiple skeletal sites (femur, tibia, vertebra) in mice. A customized, 3D printed mouse holder was designed and utilized to minimize error associated with animal repositioning, resulting in good to excellent reproducibility in most cortical and trabecular bone microarchitecture and density parameters except for connectivity density. Repeated in vivo µCT scans of mice were performed at the right distal femur and the 4th lumbar vertebra every 3 weeks until euthanized at 9 weeks after the baseline scan. Comparing to the non-radiated counterparts, no radiation effect was found on trabecular bone volume fraction, osteoblast and osteoblast number/surface, or bone formation rate at any skeletal site. However, trabecular number, thickness, and separation, and structure model index were sensitive to ionizing radiation associated with the µCT scans, resulting in subtle but significant changes over multiple scans. Although the extent of radiation damage on most trabecular bone microarchitecture measures are comparable or far less than the age-related changes during the monitoring period, additional considerations need to be taken to minimize the confounding radiation factors when designing experiments using in vivo µCT imaging for long-term monitoring of mouse bone.

Increased risk of pelvic fracture after radiotherapy in rectal cancer survivors: A propensity matched study

To determine whether radiotherapy (RT) can increase pelvic fracture risk in rectal cancer survivors. Rectal cancer patients who underwent curative surgery between 1996 and 2011 in Taiwan were retrospectively studied using the National Health Insurance Research Database (NHIRD) of Taiwan. ICD‐9 Codes 808, 805.4‐805.7, 806.4‐806.7, and 820 (including pelvic, sacrum, lumbar, and femoral neck fracture) were defined as pelvic fracture. Propensity scores for RT, age, and sex were used to perform one‐to‐one matches between the RT and non‐RT group. Risks of pelvic and arm fractures were compared by multivariable Cox regression. Of the 32 689 patients, 7807 (23.9%) received RT, and 1616 suffered from a pelvic fracture (incidence rate: 1.17/100 person‐years). The median time to pelvic fracture was 2.47 years. After matching, 6952 patients each in the RT and non‐RT groups were analyzed. RT was associated with an increased risk of pelvic fractures in the multivariable Cox model (hazard ratio (HR): 1.246, 95% confidence interval (CI): 1.037‐1.495, P = 0.019) but not with arm fractures (HR: 1.013, 95% CI: 0.814‐1.259, P = 0.911). Subgroup analyses revealed that RT was associated with a higher pelvic fracture rate in women (HR: 1.431, 95% CI: 1.117‐1.834) but not in men, and the interaction between sex and RT was significant (P = 0.03). The HR of pelvic fracture increased 2‐4 years after RT (HR: 1.707, 95% CI: 1.150‐2.534, P = 0.008). An increased risk of pelvic fracture is noted in rectal cancer survivors, especially women, who receive RT.

Periosteal Mesenchymal Progenitor Dysfunction and Extraskeletally-Derived Fibrosis Contribute to Atrophic Fracture Nonunion

Atrophic nonunion represents an extremely challenging clinical dilemma for both physicians and fracture patients alike, but its underlying mechanisms are still largely unknown. Here, we established a mouse model that recapitulates clinical atrophic nonunion through the administration of focal radiation to the long bone midshaft 2 weeks before a closed, semistabilized, transverse fracture. Strikingly, fractures in previously irradiated bone showed no bony bridging with a 100% nonunion rate. Radiation triggered distinct repair responses, separated by the fracture line: a less robust callus formation at the proximal side (close to the knee) and bony atrophy at the distal side (close to the ankle) characterized by sustained fibrotic cells and type I collagen-rich matrix. These fibrotic cells, similar to human nonunion samples, lacked osteogenic and chondrogenic differentiation and exhibited impaired blood vessel infiltration. Mechanistically, focal radiation reduced the numbers of periosteal mesenchymal progenitors and blood vessels and blunted injury-induced proliferation of mesenchymal progenitors shortly after fracture, with greater damage particularly at the distal side. In culture, radiation drastically suppressed proliferation of periosteal mesenchymal progenitors. Radiation did not affect hypoxia-induced periosteal cell chondrogenesis but greatly reduced osteogenic differentiation. Lineage tracing using multiple reporter mouse models revealed that mesenchymal progenitors within the bone marrow or along the periosteal bone surface did not contribute to nonunion fibrosis. Therefore, we conclude that atrophic nonunion fractures are caused by severe damage to the periosteal mesenchymal progenitors and are accompanied by an extraskeletal, fibro-cellular response. In addition, we present this radiation-induced periosteal damage model as a new, clinically relevant tool to study the biologic basis of therapies for atrophic nonunion. © 2018 American Society for Bone and Mineral Research.

Potential role of senescence in radiation-induced damage of the aged skeleton

Human aging-related changes are exacerbated in cases of disease and cancer, and conversely aging is a catalyst for the occurrence of disease and multimorbidity. For example, old age is the most significant risk factor for cancer and among people who suffer from cancer, >60% are above the age of 65. Oxidative stress and DNA damage, leading to genomic instability and telomere dysfunction, are prevalent in aging and radiation-induced damage and are major cellular events that lead to senescence. Human exposures from nuclear fallout, cosmic radiation and clinical radiotherapy (RT) are some common sources of irradiation that affect bone tissue. RT has been used to treat malignant tumors for over a century, but the effects of radiation damage on tumor-adjacent normal tissue has largely been overlooked. There is an increase in the percent survivorship among patients post-RT, and it is in older survivors where the deleterious synergy between aging and radiation exposure conspires to promote tissue deterioration and dysfunction which then negatively impacts their quality of life. Thus, an aging skeleton is already pre-disposed to architectural deterioration, which is further worsened by radiation-induced bone damage. Effects of senescence and the senescence associated secretory phenotype (SASP) have been implicated in age-associated bone loss, but their roles in radiation-associated bone damage are still elusive. RT is used in treatment for a variety of cancers and in different anatomical locations, the sequelae of which include long-term morbidity and lifelong discomfort. Therefore, consideration of the growing evidence that implicates the role of senescence in radiation-induced bone damage argues in favor of exploiting current senotherapeutic approaches as a possible prevention or treatment.

Metformin Alleviates the Bone Loss Induced by Ketogenic Diet: An In Vivo Study in Mice

Metformin (Met), an anti-diabetes drug, has also shown therapeutic effects for ovariectomy-induced (OVX) osteoporosis. However, similar effects against bone loss induced by a ketogenic diet (KD) have not been tested. This study was aimed to evaluate the microarchitectures and biomechanics of KD-induced osteoporosis with and without administration of Met, and compare the effect of Met on bone loss induced by KD with OVX. Forty female C57BL/6J mice were randomly divided into Sham, OVX, OVX + Met (100 mg/kg/day), KD (3:1 ratio of fat to carbohydrate and protein), and KD + Met (100 mg/kg/day) groups. After 12 weeks, the bone mass and biomechanics were measured in distal cancellous bone and in mid-shaft cortical bone of the femur. The activities of serum alkaline phosphatase (ALP) and tartrate-resistant acid phosphatase (TRAP), together with immunohistochemistry staining of osteocalcin (OCN) and TRAP, were evaluated. Both OVX and KD induced significant bone loss and compromised biomechanical properties in the cancellous bone, but no effect was found in cortical bone. The administration of Met increased the cancellous bone volume fraction (BV/TV) from 3.78 to 5.23% following the OVX and from 4.04 to 6.33% following the KD, it also enhanced the compressive stiffness from 47 to 160 N/mm following the OVX and from 35 to 340 N/mm with the KD. Met effectively increased serum ALP in the KD group while decreased serum TRAP in the OVX group, but up-regulated expression of OCN and down-regulated expression of TRAP in both OVX and KD groups. The present study demonstrated that Met effectively attenuated the cancellous bone loss induced by KD and maintained the biomechanical properties of long bones, providing evidence for Met as a treatment of by KD-induced osteoporosis in teenage skeleton.