Therapeutic ionizing radiation induced bone loss: a review of in vivo and in vitro findings

Pilot Study: Short Term Impact of Radiation Therapy on Bone Mineral Density and Bone Metabolism

Despite the risk of complications, high dose radiation therapy is increasingly utilized in the management of selected bone malignancies. In this study, we investigate the impact of moderate to high dose radiation (over 50 Gy) on bone metabolism and structure. Between 2015 and 2018, patients with a primary malignant bone tumor of the sacrum that were either treated with high dose definitive radiation only or a combination of moderate to high dose radiation and surgery were prospectively enrolled at a single institution. Quantitative CTs were performed before and after radiation to determine changes in volumetric bone mineral density (BMD) of the irradiated and non-irradiated spine. Bone histomorphometry was performed on biopsies of the irradiated sacrum and the non-irradiated iliac crest of surgical patients using a quadruple tetracycline labeling protocol. In total, 9 patients were enrolled. Two patients received radiation only (median dose 78.3 Gy) and 7 patients received a combination of preoperative radiation (median dose 50.4 Gy), followed by surgery. Volumetric BMD of the non-irradiated lumbar spine did not change significantly after radiation, while the BMD of the irradiated sacrum did (pre-radiation median: 108.0 mg/cm3 (IQR 91.8-167.1); post-radiation median: 75.3 mg/cm3 (IQR 57.1-110.2); p = 0.010). The cancellous bone of the non-irradiated iliac crest had a stable bone formation rate, while the irradiated sacrum showed a significant decrease in bone formation rate [pre-radiation median: 0.005 mm3/mm2/year (IQR 0.003-0.009), post-radiation median: 0.001 mm3/mm2/year (IQR 0.001-0.001); p = 0.043]. Similar effects were seen in the cancellous and endocortical envelopes. This pilot study shows a decrease of volumetric BMD and bone formation rate after high-dose radiation therapy. Further studies with larger cohorts and other endpoints are needed to get more insight into the effect of radiation on bone. Level of evidence: IV.

CR6-Interacting Factor-1 Promotes Osteoclastogenesis Through the NF-κB Signaling Pathway after Irradiation

Radiation exposure arising from radiotherapy may induce rapid bone loss and an increase in the extent of bone resorption. Reactive oxygen species (ROS) caused by radiation exposure play a crucial role during the process of osteoclastogenesis. However, the pathological mechanisms underlying radiation-induced osteoclastogenesis have yet to be fully elucidated. CR6-interacting factor-1 (Crif1) as a multifunctional protein is involved in regulating multiple biological functions in cells. Here, we investigated the role of Crif1 in radiation-induced osteoclastogenesis and found that radiation exposure induced an increase in the expression level of Crif1 and enhanced osteoclastogenesis in osteoclast progenitors. Crif1 and NF-κB p65 co-localized in the cytoplasm after radiation exposure. Crif1 knockdown did not affect the phosphorylation and total protein levels of extracellular signal-regulated kinases (ERK), c-Jun amino (N)-terminal kinases (JNK), p38, and IκB-α before and after irradiation. However, Crif1 knockdown did lead to the reduced phosphorylation and nuclear translocation of NF-κB p65 after irradiation and resulted in a reduced level of osteoclastogenesis in RAW264.7 cells after irradiation. In vivo studies involving Lyz2Cre;Crif1fl/fl mice possessing the myeloid-specific deletion of Crif1 demonstrated the alleviation of bone loss after irradiation when compared with Crif1fl/fl mice. Our findings demonstrate that Crif1 mediated the phosphorylation and nuclear translocation of NF-κB p65 and promoted osteoclastogenesis via the NF-κB signaling pathway after radiation exposure. Thus, our analysis revealed a specific role for Crif1 in the mediation of radiation-induced bone loss and may provide new insight into potential therapeutic strategies for radiation-induced bone loss.

Long-term pelvic fracture and overall mortality risk after pelvic cancer and pelvic radiation

BACKGROUND

The association of pelvic radiation with pelvic fracture risk has not been examined in prospective cohort settings with comprehensive fracture risk assessment, cancer-free comparison populations, and long-term follow-up. Our objective is to better characterize pelvic fracture and overall mortality risks in postmenopausal women participating in the Women's Health Initiative.

METHODS

A total of 135 743 Women's Health Initiative participants aged 50 to 79 years enrolled from 40 US clinical centers from 1993 to 1998 who had entry Fracture Risk Assessment Tool scores were eligible. Outcomes included pelvic cancer diagnosis, pelvic fracture occurrence, and mortality. Cox proportional hazards regression models were used to examine associations of pelvic cancer and pelvic radiation with pelvic fracture and mortality risk.

RESULTS

After 17.7 years (median) follow-up, 4451 pelvic cancers, 10 139 pelvic fractures, and 33 040 deaths occurred. In multivariable analyses, women with incident pelvic cancer, compared with women who remained pelvic cancer free, had higher pelvic fracture risk (hazard ratio [HR] = 1.26, 95% confidence interval [CI] = 1.11 to 1.43) and higher overall mortality risk (HR = 2.91, 95% CI = 2.77 to 3.05). Women with pelvic cancer treated with pelvic radiation, compared with women with pelvic cancer not treated with pelvic radiation, had higher pelvic fracture risk (HR = 1.98, 95% CI = 1.41 to 2.78) and higher overall mortality after pelvic cancer (HR = 1.32, 95% CI = 1.15 to 1.52).

CONCLUSIONS

Postmenopausal women with pelvic cancer, especially those receiving pelvic radiation, are at higher pelvic fracture risk and higher overall mortality risk. As therapeutic advances have reduced cancer mortality, attention to and interventions for pelvic fracture prevention may be important in pelvic cancer survivors.

Molecular Mechanism of Ferroptosis in Orthopedic Diseases

Ferroptosis is a new iron-dependent programmed cell death process that is directly mediated by the accumulation of lipid peroxides and reactive oxygen species. Numerous studies have shown that ferroptosis is important in regulating the occurrence and development of bone-related diseases, but the underlying mechanisms are not completely clear. Herein, we review the progress of the mechanism of ferroptosis in bone marrow injury, osteoporosis, osteoarthritis, and osteosarcoma and attempt to deeply understand the regulatory targets of ferroptosis, which will open up a new way for the prevention and treatment of orthopedic diseases.

Alteration of osteoclast activity in childhood cancer survivors: Role of iron and of CB2/TRPV1 receptors

Childhood cancer survivors (CCS) are predisposed to the onset of osteoporosis (OP). It is known that iron overload induces osteoclasts (OCs) overactivity and that the iron chelator Deferasirox (DFX) can counteract it. The Cannabinoid Receptor type 2 (CB2) and the transient receptor potential vanilloid type-1 (TRPV1) are potential therapeutic targets for OP. In this study we isolated OCs from peripheral blood of 20 CCS and investigated osteoclast biomarkers expression and iron metabolism evaluating iron release by OCs and the expression of several molecules involved in its regulation. Moreover, we analyzed the effects of CB2 and TRPV1 stimulation in combination with DFX on osteoclast activity and iron metabolism. We observed, for the first time, an osteoclast hyperactivation in CCS suggesting a role for iron in its development. Moreover, we confirmed the well-known role of CB2 and TRPV1 receptors in bone metabolism, suggesting the receptors as possible key biomarkers of bone damage. Moreover, we demonstrated a promising synergism between pharmacological compounds, stimulating CB2 or inhibiting/desensitizing TRPV1 and DFX, in counteracting osteoclast overactivity in CCS to improve their quality of life.

Osteocyte apoptosis, bone marrow adiposity and fibrosis in the irradiated human mandible

Purpose

To assess the effect of radiation therapy on osteocyte apoptosis, osteocyte death, and bone marrow adipocytes in the human mandible and its contribution to the pathophysiology of radiation damage to the mandibular bone.

Methods and Materials

Mandibular cancellous bone biopsies were taken from irradiated patients and nonirradiated controls. Immunohistochemical detection of cleaved caspase-3 was performed to visualize apoptotic osteocytes. The number of apoptotic osteocytes per bone area and per total amount of osteocytes, osteocytes per bone area, and empty lacunae per bone area were counted manually. The percentage fibrotic tissue and adipose tissue per bone marrow area, the percentage bone marrow of total area, and the mean adipocyte diameter (μm) was determined digitally from adjacent Goldner stained sections.

Results

Biopsies of 15 irradiated patients (12 men and 3 women) and 7 nonirradiated controls (5 men and 2 women) were assessed. In the study group a significant increase was seen in the number of empty lacunae, the percentage of adipose tissue of bone marrow area, and the adipocyte diameter. There was no significant difference in bone marrow fibrosis nor apoptotic osteocytes between the irradiated group and the controls.

Conclusions

Irradiation alone does not seem to induce excessive bone marrow fibrosis. The damage to bone mesenchymal stem cells leads to increased marrow adipogenesis and decreased osteoblastogenic potential. Early osteocyte death resulting in avital persisting bone matrix with severely impaired regenerative potential may contribute to the vulnerability of irradiated bone to infection and necrosis.

Ionizing Radiation Activates Mitochondrial Function in Osteoclasts and Causes Bone Loss in Young Adult Male Mice

The damaging effects of ionizing radiation (IR) on bone mass are well-documented in mice and humans and are most likely due to increased osteoclast number and function. However, the mechanisms leading to inappropriate increases in osteoclastic bone resorption are only partially understood. Here, we show that exposure to multiple fractions of low-doses (10 fractions of 0.4 Gy total body irradiation [TBI]/week, i.e., fractionated exposure) and/or a single exposure to the same total dose of 4 Gy TBI causes a decrease in trabecular, but not cortical, bone mass in young adult male mice. This damaging effect was associated with highly activated bone resorption. Both osteoclast differentiation and maturation increased in cultures of bone marrow-derived macrophages from mice exposed to either fractionated or singular TBI. IR also increased the expression and enzymatic activity of mitochondrial deacetylase Sirtuin-3 (Sirt3)-an essential protein for osteoclast mitochondrial activity and bone resorption in the development of osteoporosis. Osteoclast progenitors lacking Sirt3 exposed to IR exhibited impaired resorptive activity. Taken together, targeting impairment of osteoclast mitochondrial activity could be a novel therapeutic strategy for IR-induced bone loss, and Sirt3 is likely a major mediator of this effect.

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.

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.

The role of senolytics in osteoporosis and other skeletal pathologies

The skeletal system undergoes irreversible structural deterioration with aging, leading to increased fracture risk and detrimental changes in mobility, posture, and gait. This state of low bone mass and microarchitectural changes, diagnosed as osteoporosis, affects millions of individuals worldwide and has high clinical and economic burdens. Recently, pre-clinical studies have linked the onset of age-related bone loss with an accumulation of senescent cells in the bone microenvironment. These senescent cells appear to be causal to age-related bone loss, as targeted clearance of these cells leads to improved bone mass and microarchitecture in old mice. Additionally, other pathologies leading to bone loss that result from DNA damage, such as cancer treatments, have shown improvements after clearance of senescent cells. The development of new therapies that clear senescent cells, termed "senolytics", is currently underway and may allow for the modulation of bone loss that results from states of high senescent cell burden, such as aging.

MicroRNA-26 regulates the expression of CTGF after exposure to ionizing radiation

Radiation-induced fibrosis (RIF) is a serious complication that occurs after irradiation and which is caused by the deposition of extracellular matrix (ECM) proteins such as collagen. However, the underlying mechanisms, including the expression of the cytokines, that promote the RIF process, are not yet fully understood. MicroRNAs (miRNAs) have recently been suggested to act as post-transcriptional repressors for many genes; however, their role in the process of RIF remains to be elucidated. Our previous study showed that ionizing radiation increased the type I collagen expression through the activation of transforming growth factor (TGF)-β, while miR-29 repressed this increase. This study aimed to investigate the mechanisms by which the expression of connective tissue growth factor (CTGF), a downstream mediator of TGF-β, is controlled by miRNAs post-transcriptionally after exposure to ionizing radiation. The expression of CTGF in NIH-3T3 cells and mouse embryonic fibroblasts was increased by ionizing radiation. However, this increase was suppressed with a specific inhibitor of TGF-β receptor. Among the predictable miRNAs that target the CTGF gene, the expression of miR-26a was downregulated after exposure to ionizing radiation and this regulation was negatively mediated by TGF-β signaling. miR-26a negatively regulated the CTGF expression at the post-transcriptional level; however, ionizing radiation suppressed this negative regulation. In addition, the overexpression of miR-26a inhibited the expression of CTGF and type I collagen after irradiation. In conclusion, miR-26a modulates the expression of CTGF via TGF-β signaling in irradiated fibroblasts. The results suggest the potential application of miR-26a in the treatment of RIF.

The need for a dose constraint in hip prosthesis to minimize later hip dysfunction. A retrospective analysis of relevant cases

Results from a single-institution study support the need of a dose constraint for patients who have previously undergone hip replacement surgery. Our study provides evidence that a dose above 30 Gy to the area of hip prosthesis is significantly correlated with later hip arthroplasty dysfunction as measured by the Harris Hip Score. As total hip arthroplasty becomes more and more common, it is urgent to further look into radiation therapy treatment parameters that can be modified to improve the quality of life of patients who receive pelvic irradiation after hip arthroplasty. Further prospective studies are needed to extract safe conclusions.

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.

Radiation induces primary osteocyte senescence phenotype and affects osteoclastogenesis in vitro

Irradiation-induced bone remodeling imbalances arise as a consequence of the dysregulation of bone formation and resorption. Due to the abundance of osteocytes, their long life and their dual-regulatory effects on both osteoblast and osteoclast function, they serve as critical coordinators of bone remolding. In the present study, femur and tibia-derived primary osteocytes were cultured and irradiated to observe the functional changes and the cellular senescence phenotype in vitro. Irradiation directly reduced cell viability, affected the crucial dendritic morphology and altered the expression of functional proteins, including upregulation of receptor activator of nuclear factor-κB ligand and sclerostin, and downregulation of osteoprotegerin. Irradiated osteocytes were shown to exhibit notable DNA damage, which resulted in the initiation of a typical cellular senescence phenotype. Furthermore, it was found that irradiation-induced prematurely senescent osteocytes stimulate molecular secretion, referred to as senescence-associated secretory phenotype (SASP), which may be involved in modulation of the bone microenvironment, including the promotion of osteoclastogenesis. Taken together, the results showed that irradiation triggered osteocyte senescence and the acquisition of an associated secretory phenotype. This further resulted in an imbalance of bone remodeling through senescent influence on proliferation, morphology and marker protein production, but also indirectly via a paracrine pathway through SASP secretion. The results of the present study may highlight the potential of SASP-targeted interventions for the management of radiation-induced bone loss.

Therapeutic potential of iron chelators on osteoporosis and their cellular mechanisms

Iron is an essential trace element in the metabolism of almost all living organisms. Iron overload can disrupt bone homeostasis by significant inhibition of osteogenic differentiation and stimulation of osteoclastogenesis, consequently leading to osteoporosis. Iron accumulation is also involved in the osteoporosis induced by multiple factors, such as estrogen deficiency, ionizing radiation, and mechanical unloading. Iron chelators are first developed for treating iron overloaded disorders. However, growing evidence suggests that iron chelators can be potentially used for the treatment of bone loss. In this review, we focus on the therapeutic effects of iron chelators on bone loss. Iron chelators have therapeutic effects not only on iron overload induced osteoporosis, but also on osteoporosis induced by estrogen deficiency, ionizing radiation, and mechanical unloading, and in Alzheimer's disease-associated osteoporotic deficits. Iron chelators differently affect the cellular behaviors of bone cells. For osteoblast lineage cells (bone mesenchymal stem cells and osteoblasts), iron chelation stimulates osteogenic differentiation. Conversely, iron chelation significantly inhibits osteoclast differentiation. These different responses may be associated with the different needs of iron during differentiation. Fibroblast growth factor 23, angiogenesis, and antioxidant capability are also involved in the osteoprotective effects of iron chelators.

CircRNA-016901 silencing attenuates irradiation-induced injury in bone mesenchymal stem cells via regulating the miR-1249-5p/HIPK2 axis

Currently, bone marrow transplantation remains the basic treatment for various hematological tumors and irradiation is one of the most important pretreatment methods. However, irradiation pretreatment may result in damage to bone mesenchymal stem cells (BMSCs). The present study aimed to investigate the effect of circular RNA-016901 (circ-016901) on the injury of irradiation-induced BMSCs and the underlying mechanism. The expression levels of circ-016901, microRNA-1249-5p (miR-1249-5p) and homeodomain interacting protein kinase 2 (HIPK2) in irradiation-induced mouse BMSCs at various irradiation doses were detected via reverse transcription-quantitative PCR (RT-qPCR). The effect of circ-016901 on cell proliferation was examined using Cell Counting Kit-8 assays following silencing or overexpression of circ-016901. Cell apoptosis was detected by flow cytometry and caspase-3/7 activity. The expression of autophagy-related markers, including Beclin-1 and LC3-II/I, was detected at the mRNA and protein levels by RT-qPCR and western blotting, respectively. Irradiation treatment upregulated the expression of circ-016901 and HIPK2 and downregulated miR-1249-5p expression. The expression levels of LC3-II/I and Beclin-1 in BMSCs were downregulated in a dose-dependent manner. Silencing of circ-016901 promoted proliferation of irradiation-induced BMSCs and attenuated irradiation-induced apoptosis. Moreover, silencing of circ-016901 elevated the expressions of LC3-II/I and Beclin-1 in irradiation-induced BMSCs. Similar results were obtained with miR-1249-5p overexpression and HIPK2 silencing. These results demonstrated that circ-016901 silencing attenuated injury in irradiation-induced mouse BMSCs by regulating the miR-1249-5p/HIPK2 axis, providing a novel target for future research on the mechanism of radiation resistance in BMSCs.

Intraperitoneal injection of Desferal® alleviated the age-related bone loss and senescence of bone marrow stromal cells in rats

Background

Age-related bone loss plays a vital role in the development of osteoporosis and osteoporotic fracture. Bone marrow stromal cell (BMSC) senescence is highly associated with osteoporosis and limits the application of BMSCs in regenerative medicine. Hypoxia is an essential component for maintaining the normal physiology of BMSCs. We have reported that activation of hypoxia-induced factor by deletion of von Hippel-Lindau gene in osteochondral progenitor cells protected mice from aging-induced bone loss. However, whether pharmacologically manipulation of hypoxic niche would attenuate age-related bone loss and dysfunction of BMSCs is not well understood.

Methods

Twelve-month-old Sprague-Dawley rats were used as an aged model and were intraperitoneally injected with Desferal® (20, 60 mg/kg weight or vehicle), three times a week for a continuous 8-week period. Two-month-old young rats were set as a reference. After 8 weeks, micro-CT and HE staining were performed to determine the effect of Desferal® on bone loss. In order to investigate the effects of Desferal® on BMSC senescence, 12-month-old rats were treated with high-dose Desferal® (60 mg/kg weight) daily for 10 days. BMSCs were isolated and evaluated using CCK-8 assay, colony-forming cell assay, cell differentiation assay, laser confocal for reactive oxygen species (ROS) level, senescence-associated β-galactosidase (SA-β-gal) staining, and molecular expression test for stemness/senescence-associated genes.

Results

Micro-CT and HE staining showed that high-dose Desferal® significantly prevented bone loss in aged rats. Compared with vehicle group, the ex vivo experiments showed that short-term Desferal® administration could promote the potential of BMSC growth (proliferation and colony formation ability) and improve the rebalance of osteogenic and adipogenic differentiation, as well as rejuvenate senescent BMSCs (ROS level and SA-β-gal staining) and revise the expression of stemness/senescence-associated genes. The potential of BMSCs from 12M-H-Desferal® group at least partly revised to the level close to 2-month-old group.

Conclusions

The current study suggested that Desferal®, an iron-chelating agent, could alleviate age-related bone loss in middle-aged rats. Meanwhile, we found that short-term intraperitoneal injection of Desferal® partly rejuvenate BMSCs from aged rats. Overall, we demonstrated a novel role of Desferal® in rejuvenating aged BMSCs and preventing age-related bone loss.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-020-02112-9.

LncRNA HOTAIR promotes the growth and metastasis of gastric cancer by sponging miR-1277-5p and upregulating COL5A1

BACKGROUND

Emerging studies have shown that HOTAIR acts as an oncogene in gastric cancer (GC). However, its role in the extracellular matrix and in tumor immune infiltration remains unknown.

METHODS

HOTAIR and COL5A1 levels were analyzed by bioinformatics analysis and validated by qRT-PCR, western blotting and immunohistochemistry assays. The regulatory relationships between components of the HOTAIR/miR-1277-5p/COL5A1 axis and the role of this axis in GC were predicted by bioinformatics analysis, and validated by in vitro and in vivo experiments. The correlation between COL5A1 and GC immune infiltration was assessed by bioinformatics analysis and a COL5A1-based predictive nomogram was established using the Stomach Adenocarcinoma dataset from The Cancer Genome Atlas.

RESULTS

We found that HOTAIR and COL5A1 were overexpressed in GC compared to normal controls, which predicted poor prognosis. The regulatory relationship of the HOTAIR/miR-1277-5p/COL5A1 axis in GC was demonstrated, and HOTAIR and COL5A1 were found to promote GC growth while miR-1277-5p exerted the reverse effects. In addition, COL5A1 was negatively associated with tumor purity but positively associated with immune infiltration, which suggested that COL5A1-mediated GC growth may be partially mediated by the regulation of immune infiltration. Additionally, the established COL5A1-based nomogram showed that COL5A1 can serve as a prognostic biomarker in GC.

CONCLUSIONS

HOTAIR regulates GC growth by sponging miR-1277-5p and upregulating COL5A1, and COL5A1-mediated GC cell proliferation may be mediated by effects on the tumor microenvironment, which provides novel targets for GC treatment.

Osteocyte Cellular Senescence

PURPOSE OF REVIEW

Senescent cells are now known to accumulate in multiple tissues with aging and through their inflammation (the senescence-associated secretory phenotype, SASP) contribute to aging and chronic diseases. Here, we review the roles of senescent osteocytes in the context of bone loss.

RECENT FINDINGS

Numerous studies have established that senescent osteocytes accumulate in the bone microenvironment with aging in mice and in humans. Moreover, at least in mice, elimination of senescent cells results in attenuation of age-related bone loss. Osteocyte senescence also occurs in response to other cellular stressors, including radiotherapy, chemotherapy, and metabolic dysfunction, where it appears to mediate skeletal deterioration. Osteocyte senescence is linked to bone loss associated with aging and other conditions. Senescent osteocytes are potential therapeutic targets to alleviate skeletal dysfunction. Additional studies better defining the underlying mechanisms as well as translating these exciting findings from mouse models to humans are needed.

Bone Health Management After Hematopoietic Cell Transplantation: An Expert Panel Opinion from the American Society for Transplantation and Cellular Therapy

Bone health disturbances commonly occur after hematopoietic cell transplantation (HCT) with loss of bone mineral density (BMD) and avascular necrosis (AVN) foremost among them. BMD loss is related to pretransplantation chemotherapy and radiation exposure and immunosuppressive therapy for graft-versus-host-disease (GVHD) and results from deficiencies in growth or gonadal hormones, disturbances in calcium and vitamin D homeostasis, as well as osteoblast and osteoclast dysfunction. Although the pathophysiology of AVN remains unclear, high-dose glucocorticoid exposure is the most frequent association. Various societal treatment guidelines for osteoporosis exist, but the focus is mainly on menopausal-associated osteoporosis. HCT survivors comprise a distinct population with unique comorbidities, making general approaches to bone health management inappropriate in some cases. To address a core set of 16 frequently asked questions (FAQs) relevant to bone health in HCT, the American Society of Transplant and Cellular Therapy Committee on Practice Guidelines convened a panel of experts in HCT, adult and pediatric endocrinology, orthopedics, and oral medicine. Owing to a lack of relevant prospective controlled clinical trials that specifically address bone health in HCT, the answers to the FAQs rely on evidence derived from retrospective HCT studies, results extrapolated from prospective studies in non-HCT settings, relevant societal guidelines, and expert panel opinion. Given the heterogenous comorbidities and needs of individual HCT recipients, answers to FAQs in this article should be considered general recommendations, with good medical practice and judgment ultimately dictating care of individual patients. Readers are referred to the Supplementary Material for answers to additional FAQs that did not make the core set.

Radiation alters osteoclastogenesis by regulating the cytoskeleton and lytic enzymes in RAW 264.7 cells and mouse bone marrow-derived macrophages

PURPOSE

The aim of the present study was to investigate the duality of irradiation effect on osteoclastogenesis, particularly on the cytoskeleton and expression of lytic enzymes in osteoclast precursors. Therefore, the present study may serve as a useful reference for the prevention and treatment of radiation-induced bone loss in the clinic.

MATERIALS AND METHODS

Two typical osteoclast precursors, murine RAW 264.7 macrophage cells and mouse bone marrow-derived macrophages (BMMs), were exposed to radiation in the order of 0.25-8 Gy, and the effects on cell viability, TRAP activity and bone resorption were subsequently investigated. Furthermore, changes in the cytoskeleton, cell apoptosis, and expression of lytic enzymes in osteoclasts were examined to elucidate the molecular mechanism of the duality of irradiation on osteoclastogenesis.

RESULTS

Morphological changes and impaired viability were observed in RAW 264.7 cells and BMMs treated with 1-8 Gy irradiation with or without RANKL. However, the cell fusion tendency of osteoclasts was enhanced after 2 Gy irradiation, and an increased number of fused giant osteoclasts and enhanced F-actin ring formation were observed. Consistently, the bone resorption activity and the enzyme expression of TRAP, cathepsin K, matrix metalloproteinase 9, activator protein 1, and Caspase 9 were increased following irradiation with 2 Gy. Furthermore, intracellular ROS production and apoptosis of osteoclast precursors were increased.

CONCLUSIONS

Irradiation with 2 Gy inhibited the viability of osteoclast precursors, but increased osteoclastogenesis by enhancing cell fusion and increasing the secretion of lytic enzymes, which may be an important mechanism of radiation-induced bone loss.

Ionizing Radiation Exacerbates the Bone Loss Induced by Iron Overload in Mice

Patients with radiotherapy are at significant risks of bone loss and fracture. On the other hand, osteoporosis often occurs in disorders characterized by iron overload. Either ionizing radiation (IR) or iron overload alone has detrimental effects on bone metabolism, but their combined effects are not well defined. In this study, we evaluated the effects of IR on bone loss in an iron-overload mouse model induced by intraperitoneal injection of ferric ammonium citrate (FAC). In the present study, we found that IR additively aggravated iron overload induced by FAC injections. Iron overload stimulated hepcidin synthesis, while IR had an inhibitory effect and even inhibited the stimulatory effects of iron overload. Micro-CT analysis demonstrated that the loss of bone mineral density and bone volume, and the deterioration of bone microarchitecture were greatest in combined treatment group. Iron altered the responses of bone cells to IR. Iron enhanced the responses of osteoclasts to IR with elevated osteoclast differentiation, but did not affect osteoblast differentiation. Our study indicates that IR and iron in combination lead to a more severe impact on the bone homeostasis when compared with their respective effects. IR aggravated iron overload induced bone loss by heightened bone resorption relative to formation. The addictive effects may be associated with the exacerbated iron accumulation and osteoclast differentiation.

Bone microarchitecture and turnover in the irradiated human mandible

OBJECTIVES

The aim of this study was to assess the microarchitecture and turnover in irradiated cancellous mandibular bone and the relation with radiation dose, to elucidate the effects of radiotherapy on the mandible.

PATIENTS AND METHODS

Mandibular cancellous bone biopsies were taken from irradiated patients and controls. Micro-CT scanning was performed to analyze microstructural bone parameters. Bone turnover was assessed by histomorphometry. Local radiation dose at the biopsy site (Dmax) was estimated from radiotherapy plans.

RESULTS

Twenty-seven irradiated patients and 35 controls were included. Osteoid volume (Osteoid Volume/Bone Volume, OV/BV) [0.066/0.168 (median/interquartile range (IQR), OV/BV; %), P < 0.001], osteoid surface (Osteoid Surface/Bone Surface, OS/BS) [0.772/2.17 (median/IQR, OS/BS; %), P < 0.001] and osteoclasts number (Osteoclasts per millimetre bone surface, Ocl/mmBS; mm²) [0.026/0.123 (median/IQR, Ocl/mmBS; mm²), P < 0.001] were decreased; trabecular number (Tb.N) was lower [1.63/0.63 (median/IQR, Tb.N; 1/mm^-1), P = 0.012] and trabecular separation (Tb.Sp) [0.626/0.24 (median/IQR, Tb.Sp; μm), P = 0.038] was higher in irradiated mandibular bone. With higher Dmax, trabecular number increases (Spearman's correlation R = 0.470, P = 0.018) and trabecular separation decreases (Spearman's correlation R = -0.526, P = 0.007). Bone mineral density (BMD, milligrams hydroxyappetite per cubic centimetre, mgHA/cm³) [1016/99 (median/IQR, BMD; mgHA/cm³), P = 0.03] and trabecular separation [0.739/0.21 (median/IQR, Tb.Sp; μm), P = 0.005] are higher whereas connectivity density (Conn Dens) [3.94/6.71 (median/IQR, Conn Dens), P = 0.047] and trabecular number [1.48/0.44 (median/IQR, Tb.N; 1/mm^-1), P = 0.002] are lower in Dmax ≤50 Gy compared to controls.

CONCLUSIONS

Radiotherapy dramatically impairs bone turnover in the mandible. Deterioration in microarchitecture only affects bone irradiated with a Dmax of <50 Gy. The 50 Gy value seems to be a critical threshold to where the effects of the radiation is more detrimental.

The osteoprotective effects of artemisinin compounds and the possible mechanisms associated with intracellular iron: A review of in vivo and in vitro studies

Osteoporosis is a progressive systemic disease characterized by low bone mineral density and deterioration of bone microarchitecture. The current therapies are effective to prevent further bone loss and fractures but they are accompanied by undesirable side effects and cost issues. The discovery of Chinese herbal medicines with osteoprotective effects provides alternative treatments to prevent bone loss without causing severe side effects. Artemisinin (ARS) and its related compounds have been clinically used as antimalarial agents. Interestingly, their bioactivity is not limited to antimalarial treatment. Experimental evidences indicate that ARS compounds are a potential type of therapeutic alternative medicine for bone loss induced by accelerated osteoclastic bone resorption. The present review intends to summarize the current understandings of ARS compounds and their molecular mechanisms of actions in preventing bone loss. ARS compounds selectively inhibit osteoclast differentiation by downregulation of pathways involved in receptor activator of nuclear factor kappa-B ligand (RANKL) -induced osteoclastogenesis, and have no effect on osteogenic differentiation of osteoblasts. The exact mechanism of activation and action of these anti-resorption effects are not fully elucidated. Considering the characteristic of high levels of intracellular iron in osteoclasts, ARS compounds may inhibit osteoclast differentiation via mechanisms associated with intracellular iron, including the cleavage of endoperoxide bridge, oxidative damage and ferroptosis. The anti-resorptive effects of ARS compounds need to be further investigated in bone loss models caused by different factors, and to be under clinical development.

Irradiation-induced senescence of bone marrow mesenchymal stem cells aggravates osteogenic differentiation dysfunction via paracrine signaling

The role of cellular senescence induced by radiation in bone loss has attracted much attention. As one of the common complications of anticancer radiotherapy, irradiation-induced bone deterioration is common and clinically significant, but the pathological mechanism has not been elucidated. This study was performed to explore the cellular senescence and senescence-associated secretory phenotype (SASP) induction of bone marrow-derived mesenchymal stem cells (BMSCs) by irradiation and its role in osteogenic differentiation dysfunction. It was observed that irradiated BMSCs lost typical fibroblast-like morphology, exhibited suppressed viability and differentiation potential accompanied with senescence phenotypes, including an increase in senescence-associated β-galactosidase (SA-β-gal) staining-positive cells, and upregulated senescence-related genes p53/p21, whereas no changes happened to p16. Additionally, DNA damage γ-H2AX foci, G0/G1 phase of cell cycle arrest, and cellular and mitochondrial reactive oxygen species (ROS) increased in an irradiation dose-dependent manner. Meanwhile, the JAK1/STAT3 pathway was activated and accompanied by an increase in SASP secretion, such as IL-6, IL-8, and matrix metalloproteinase-9 (MMP9), whereas 0.8 μM JAK1 inhibitor (JAKi) treatment effectively inhibited the JAK pathway and SASP production. Furthermore, conditioned medium (CM) from irradiation-induced senescent (IRIS) BMSCs exhibited a markedly reduced ability in osteogenic differentiation and marker gene expression of osteoblasts, whereas CM with JAKi intervention may effectively improve these deterioration effects. In conclusion, irradiation could provoke BMSC senescence and SASP secretion and further aggravate osteogenic differentiation dysfunction via paracrine signaling, whereas SASP targeting may be a possible intervention strategy for alleviating irradiation-induced bone loss.

Radiotherapy in Fibrodysplasia Ossificans Progressiva: A Case Report and Systematic Review of the Literature

Fibrodysplasia ossificans progressiva (FOP) is an autosomal dominant disease, characterized by the formation of heterotopic ossification (HO) in muscles, ligaments, and tendons. Flare-ups, an inflammatory process that often precedes the formation of HO, can occur spontaneously, but trauma is also a common trigger. It is not known whether radiotherapy, especially in higher doses, might cause sufficient trauma or inflammation to trigger a flare-up and subsequent HO in FOP patients. We report the case of a patient undergoing radiotherapy for the treatment of a 1-cm-wide basal cell carcinoma (BCC) of the lower lip. In addition, we present a systematic review of the available literature. Our patient received 54 Gy in 18 fractions with orthovoltage therapy, resulting in a clinical complete response of the tumor. Six months after treatment, there were no signs of HO either clinically or on [¹⁸F]NaF PET/CT. The systematic review identified 11 publications describing either radiation treatment in FOP or radiation therapy as a cause of HO in non-FOP patients. Six case reports described the use of radiation in FOP patients for various reasons, including one with a high-dose treatment of a lip BCC using superficial X-ray therapy. The remaining five studies described the use of low-dose radiotherapy to prevent or treat either an FOP flare-up or HO formation. None of these cases showed worsening of disease that could be attributed to the use of radiation therapy. Radiation induced HO in non-FOP patients was rare and occurred in five studies. The largest of these studies suggested that HO was induced after treatment with high doses, resulting in more widespread evidence of tissue damage, potentially being the end result of this damage. In conclusion, available reports suggest no contraindication to radiotherapy in FOP patients; although the number of cases was small, systematic toxicity reports often were not available, and none of the reports described high-dose, high-energy radiation treatment at locations such as muscle and joint regions.

Deferoxamine inhibits iron-uptake stimulated osteoclast differentiation by suppressing electron transport chain and MAPKs signaling

Iron overload causes osteoporosis by enhancing osteoclastic bone resorption. During differentiation, osteoclasts demand high energy and contain abundant mitochondria. In mitochondria, iron is used for the synthesis of Fe-S clusters to support mitochondria biogenesis and electron transport chain. Moreover, mitochondrial reactive oxygen species (ROS) play an important role in osteoclastogenesis. Activation of MAPKs (ERK1/2, JNK, and p38) by ROS is essential and contribute to osteoclast differentiation. How iron chelation impairs electron transport chain and ROS dependent MAPKs activation during osteoclast differentiation is unknown. This study aimed to determine the direct effects of iron chelation on osteoclast differentiation, electron transport chain and MAPKs activation. In the present study, we found that when iron chelator, deferoxamine (DFO), was added, a dose-dependent inhibition of osteoclast differentiation and bone resorption was observed. Supplementation of transferrin-bound iron recovered osteoclastogenesis. Iron chelation resulted in a marked decrease in ferritin level, and increased expression of transferrin receptor 1 and ferroportin. As an iron chelator, DFO negatively affected mitochondrial function through decreasing activities of all the complexes. Expressions of mitochondrial subunits encoded both by mitochondrial and nuclear DNA were decreased. DFO augmented production of mitochondrial ROS, but inhibited the phosphorylation of ERK1/2, JNK, and p38, even in the presence of hydrogen peroxide. These results suggest that iron chelation directly inhibits iron-uptake stimulated osteoclast differentiation and suppresses electron transport chain. Iron chelation negatively regulates MAPKs activation, and this negative regulation is independent on ROS stimulation.

Lowering iron level protects against bone loss in focally irradiated and contralateral femurs through distinct mechanisms

Radiation therapy leads to increased risk of late-onset fragility and bone fracture due to the loss of bone mass. On the other hand, iron overloading causes osteoporosis by enhancing bone resorption. It has been shown that total body irradiation increases iron level, but whether the systemic bone loss is related to the changes in iron level and hepcidin regulation following bone irradiation remains unknown. To investigate the potential link between them, we first created an animal model of radiation-induced systemic bone loss by targeting the mid-shaft femur with a single 2 Gy dose of X-rays. We found that mid-shaft femur focal irradiation led to structural deterioration in the distal region of the trabecular bone with increased osteoclasts surface and expressions of bone resorption markers in both irradiated and contralateral femurs relative to non-irradiated controls. Following irradiation, reduced hepcidin activity of the liver contributed to elevated iron levels in the serum and liver. By injecting hepcidin or deferoxamine (an iron chelator) to reduce iron level, deterioration of trabecular bone microarchitecture in irradiated mice was abrogated. The ability of iron chelation to inhibit radiation-induced osteoclast differentiation was observed in vitro as well. We further showed that ionizing radiation (IR) directly stimulated osteoclast differentiation and bone resorption in bone marrow cells isolated not from contralateral femurs but from directly irradiated femurs. These results suggest that increased iron levels after focal radiation is at least one of the main reasons for systemic bone loss. Furthermore, bone loss in directly irradiated bones is not only due to the elevated iron level, but also from increased osteoclast differentiation. In contrast, the bone loss in the contralateral femurs is mainly due to the elevated iron level induced by IR alone. These novel findings provide proof-of-principle evidence for the use of iron chelation or hepcidin as therapeutic treatments for IR-induced osteoporosis.

Effects of Iron Overload and Oxidative Damage on the Musculoskeletal System in the Space Environment: Data from Spaceflights and Ground-Based Simulation Models

The space environment chiefly includes microgravity and radiation, which seriously threatens the health of astronauts. Bone loss and muscle atrophy are the two most significant changes in mammals after long-term residency in space. In this review, we summarized current understanding of the effects of microgravity and radiation on the musculoskeletal system and discussed the corresponding mechanisms that are related to iron overload and oxidative damage. Furthermore, we enumerated some countermeasures that have a therapeutic potential for bone loss and muscle atrophy through using iron chelators and antioxidants. Future studies for better understanding the mechanism of iron and redox homeostasis imbalance induced by the space environment and developing the countermeasures against iron overload and oxidative damage consequently may facilitate human to travel more safely in space.