Pathophysiology of bone loss in disuse osteoporosis

Air Pollution and Osteoporosis

PURPOSE OF REVIEW

The purpose of this review is to provide a background of osteoporosis and air pollution, discussing increasing incidence of the disease with exposure to pollutants and the role that inflammation may play in this process.

RECENT FINDINGS

Osteoporosis-related fractures are one of the most pressing challenges for the ageing global population, with significant increases in mortality known to occur after major osteoporotic fractures in the elderly population. Recent studies have established a firm correlative link between areas of high air pollution and increased risk of osteoporosis, particularly alarming given the increasingly urban global population. While the culprit pollutants and molecular mechanisms underlying this phenomenon have not yet been elucidated, initial studies suggest a role for inflammatory cascades in this phenomenon. While much more research is required to identify the most damaging air pollutants and to delineate the specific inflammatory molecular mechanisms, it is clear from the literature that shedding light on these pathways would unveil potential therapeutic targets to treat bone diseases, including osteoporosis. Major deficiencies of current animal models highlight the need for complex human in vitro models such as organ-on-a-chip technology to better understand the impact of air pollution.

Multiscale simulation of the effect of low-intensity pulsed ultrasound on the mechanical properties distribution of osteocytes

Low-intensity pulsed ultrasound (LIPUS) is a potential effective means for the prevention and treatment of disuse osteoporosis. In this paper, the effect of LIPUS exposure on the mechanical properties distribution of the osteocyte system (osteocyte body contains nucleus, osteocyte process, and primary cilia) is simulated. The results demonstrate that the mechanical micro-environment of the osteocyte is significantly improved by ultrasound exposure, and the mean von Mises stress of the osteocyte system increases linearly with the excitation sound pressure amplitude. The mechanical effect of LIPUS on osteocytes is enhanced by the stress amplification mechanism of the primary cilia and osteocyte processes.

Pregnancy and lactation associated osteoporotic vertebral fracture: the neurosurgical perspective through a multicentric study

Pregnancy and lactation-associated osteoporosis is a rare form of osteoporosis occurring during late pregnancy and early lactation, featuring fragility fractures, primarily involving the vertebral bodies and leading to back pain. Its management involves osteoporosis treatment, complicated by potential drug-related dangerous effects on the fetus. Nevertheless, many controversies remain regarding diagnosis, prognosis, and treatment options. Herein, we propose a multicentric case series to provide a comprehensive neurosurgical, gynecological, and endocrinological perspective on the management of pregnancy and lactation-associated osteoporotic vertebral fractures. A multicenter retrospective study was conducted at the Neurosurgical Department of Università degli Studi di Napoli Federico II, the Neurosurgical Unit of Hopitaux Universitaires de Genève, and the Spine and Spinal Cord Surgery Unit of the University Hospital of Udine, collecting data from January 2014 to December 2022. The study has been approved by the ethical committee of each hospital. N = 11 patients with an overall number of 31 fractures were eligible, with a mean age of 36. N = 5 (16%) fractures in 4 patients (36%) developed during pregnancy, and N = 26 (84%) fractures in 7 (64%) patients occurred during lactation. The mean number of fractures per patient was 2,81. In 10 (90%) patients, fractures occurred at the first pregnancy, and 5 (45%) patients had uneventful subsequent pregnancies. The mean clinical signs and symptoms were back pain (92%), followed by loss of height (75%) and kyphosis (4 patients, 35%). One (9,09%) patient underwent in vitro fertilization (IVF), and one patient (9,09%) was receiving hormonal therapy (ethinylestradiol/drosiprenone). 10 out of 11 (90%) patients were treated conservatively, and 6 of them (60%) were managed with an orthosis. One (9,1%) patient underwent surgery for 5-level kyphoplasty. The mean average reduction of pain after one year of follow-up was 6,7 on the visual analogue scale (p-value 0,04). Pregnancy-related osteoporotic vertebral fractures are an emerging issue in developing countries, for which a conservative strategy ensures the best outcomes. The main goal is to improve bone mineral density through calcium and vitamin D supplementation and bone-active drugs as bisphosphonates or teriparatide. Surgery is warranted only in cases of a risk of severe deterioration of neurological functions.

Monthly treatment with romosozumab for 1 year increases bone mineral at the hip, but not the knee, in women with chronic spinal cord injury

Bone loss below the level of neurological lesion is a well-known complication of spinal cord injury (SCI). To date, most research has focused on pharmaceutical intervention using antiresorptives to prevent bone loss during the acute phase of SCI; however, limited research has investigated treatments for established osteoporosis during chronic SCI. Romosozumab, a monoclonal antibody with both antiresorptive and anabolic effects, has demonstrated significant increases in BMD for women with established PMO. Therefore, the purpose of this study was to examine the efficacy of monthly treatment with romosozumab to improve DXA-derived areal BMD at the hip, and CT-derived BMC and strength at the hip and knee in women with chronic SCI and an inability to ambulate. Twelve female participants with chronic SCI were recruited to receive 1 yr of monthly subcutaneous injections of romosozumab (210 mg). DXA and CT scans were taken at baseline, and months 3, 6, and 12 to quantify bone mineral, and finite element (FE) analysis was used to predict bone strength. Longitudinal mixed effects models were employed to determine the impact of treatment on bone properties. After 12 mo of treatment, areal BMD at the lumbar spine and total hip were significantly increased with median changes of 10.2% (IQR: 8.3-15.2%, p<.001) and 4.2% (IQR: 3.4-7.7%, p = .009), respectively. Improvements at the hip were primarily due to increases in trabecular, not cortical, bone and effects were sufficient to significantly increase FE-predicted strength by 20.3% (IQR: 9.5-37.0%, p = .004). Treatment with romosozumab did not lead to any significant improvement in bone mineral at the distal femur or proximal tibia. These findings provide promising results for romosozumab treatment to improve bone mineral and reduce fracture risk at the hip, but not the knee, in women with chronic SCI.

Mechanical protein polycystin-1 directly regulates osteoclastogenesis and bone resorption

Mechanical loading is required for bone homeostasis, but the underlying mechanism is still unclear. Our previous studies revealed that the mechanical protein polycystin-1 (PC1, encoded by Pkd1) is critical for bone formation. However, the role of PC1 in bone resorption is unknown. Here, we found that PC1 directly regulates osteoclastogenesis and bone resorption. The conditional deletion of Pkd1 in the osteoclast lineage resulted in a reduced number of osteoclasts, decreased bone resorption, and increased bone mass. A cohort study of 32,500 patients further revealed that autosomal dominant polycystic kidney disease, which is mainly caused by loss-of-function mutation of the PKD1 gene, is associated with a lower risk of hip fracture than those with other chronic kidney diseases. Moreover, mice with osteoclast-specific knockout of Pkd1 showed complete resistance to unloading-induced bone loss. A mechanistic study revealed that PC1 facilitated TAZ nuclear translocation via the C-terminal tail-TAZ complex and that conditional deletion of Taz in the osteoclast lineage resulted in reduced osteoclastogenesis and increased bone mass. Pharmacological regulation of the PC1-TAZ axis alleviated unloading- and estrogen deficiency- induced bone loss. Thus, the PC1-TAZ axis may be a potential therapeutic target for osteoclast-related osteoporosis.

Deletion of the auxiliary α2δ1 voltage sensitive calcium channel subunit in osteocytes and late-stage osteoblasts impairs femur strength and load-induced bone formation in male mice

Osteocytes sense and respond to mechanical force by controlling the activity of other bone cells. However, the mechanisms by which osteocytes sense mechanical input and transmit biological signals remain unclear. Voltage-sensitive calcium channels (VSCCs) regulate calcium (Ca2+) influx in response to external stimuli. Inhibition or deletion of VSCCs impairs osteogenesis and skeletal responses to mechanical loading. VSCC activity is influenced by its auxiliary subunits, which bind the channel's α1 pore-forming subunit to alter intracellular Ca2+ concentrations. The α2δ1 auxiliary subunit associates with the pore-forming subunit via a glycosylphosphatidylinositol anchor and regulates the channel's calcium-gating kinetics. Knockdown of α2δ1 in osteocytes impairs responses to membrane stretch, and global deletion of α2δ1 in mice results in osteopenia and impaired skeletal responses to loading in vivo. Therefore, we hypothesized that the α2δ1 subunit functions as a mechanotransducer, and its deletion in osteocytes would impair skeletal development and load-induced bone formation. Mice (C57BL/6) with LoxP sequences flanking Cacna2d1, the gene encoding α2δ1, were crossed with mice expressing Cre under the control of the Dmp1 promoter (10 kb). Deletion of α2δ1 in osteocytes and late-stage osteoblasts decreased femoral bone quantity (P < .05) by DXA, reduced relative osteoid surface (P < .05), and altered osteoblast and osteocyte regulatory gene expression (P < .01). Cacna2d1f/f, Cre + male mice displayed decreased femoral strength and lower 10-wk cancellous bone in vivo micro-computed tomography measurements at the proximal tibia (P < .01) compared to controls, whereas Cacna2d1f/f, Cre + female mice showed impaired 20-wk cancellous and cortical bone ex vivo micro-computed tomography measurements (P < .05) vs controls. Deletion of α2δ1 in osteocytes and late-stage osteoblasts suppressed load-induced calcium signaling in vivo and decreased anabolic responses to mechanical loading in male mice, demonstrating decreased mechanosensitivity. Collectively, the α2δ1 auxiliary subunit is essential for the regulation of osteoid-formation, femur strength, and load-induced bone formation in male mice.

Knowledge and awareness assessment of bone loss and fracture risk after spinal cord injury

METHODS

A cross-sectional analysis was conducted on a convenience sample of 138 adults with SCI, who completed a survey regarding knowledge and awareness of post-SCI bone health as part of a larger study. Self-reported demographic information and assessments of bone health knowledge were analyzed.

RESULTS

Approximately 20% (n = 28) of participants had never heard of bone mineral density (BMD), 25% (n = 34) only vaguely remembered that BMD was mentioned during their hospitalization/rehabilitation after SCI, 36% (n = 50) clearly remembered that BMD was mentioned during their hospitalization/rehabilitation, and 17% (n = 24) reported having an individual or group education session on causes and management of low BMD during rehabilitation. Only 30% (n = 42) of participants believed they had adequate knowledge on the subject, while 70% (n = 96) believed their knowledge was inadequate or were unsure. Most participants (73%, n = 101) reported being concerned about the risks of low BMD after SCI and were interested in learning more about prevention (76%, n = 105) and treatment options (78%, n = 108).

CONCLUSIONS

While results suggest that most participants received some information regarding bone health in post-SCI care, over 70% of participants reported wanting more information about bone loss prevention and treatment, indicating bone health education is a patient priority in this population.

The Sequential Therapy in Osteoporosis

Background

Osteoporosis management often involves a sequential treatment approach to optimize patient outcomes and minimize fracture risks. This strategy is tailored to individual patient characteristics, treatment responses, and fracture risk profiles.

Methods

A thorough literature review was systematically executed using prominent databases, including PubMed and EMBASE. The primary aim was to identify original articles and clinical trials evaluating the effectiveness of sequential therapy with anti-osteoporosis drugs, focusing on the period from 1995 to 2023. The analysis encompassed an in-depth examination of osteoporosis drugs, delineating their mechanisms of action, side effects, and current trends as elucidated in the literature.

Results and Discussion

Our study yielded noteworthy insights into the optimal sequencing of pharmacologic agents for the long-term treatment of patients necessitating multiple drugs. Notably, the achievement of optimal improvements in bone mass is observed when commencing treatment with an anabolic medication, followed by the subsequent utilization of an antiresorptive drug. This stands in contrast to initiating therapy with a bisphosphonate, which may potentially diminish outcomes in the post-anabolic intervention period. Furthermore, it has been discerned that caution should be exercised against transitioning from denosumab to PTH homologs due to the adverse effects of heightened bone turnover and sustained weakening of bone structure. Despite the absence of fracture data substantiating the implementation of integrated anabolic/antiresorptive pharmacotherapy, the incorporation of denosumab and teriparatide presents a potential avenue worthy of consideration for individuals at a heightened vulnerability to fragility fractures.

Conclusions

A judiciously implemented sequential treatment strategy in osteoporosis offers a flexible and tailored approach to address diverse clinical scenarios, optimizing fracture prevention and patient outcomes.

Drynaria Naringin alleviated mechanical stress deficiency-caused bone loss deterioration via Rspo1/Lgr4-mediated Wnt/β-catenin signalling pathway

Osteoporosis is a metabolic condition distinguished by the degradation of bone microstructure and mechanical characteristics. Traditional Chinese medicine (TCM) has been employed in China for the treatment of various illnesses. Naringin, an ingredient found in Drynariae TCM, is known to have a significant impact on bone metabolism. For this research, we studied the precise potential effect of Drynaria Naringin on protecting against bone loss caused by stress deficiency. In this study, a tail-suspension (TS) test was performed to establish a mouse model with hind leg bone loss. Some mice received subcutaneous injections of Drynaria Naringin for 30 d. Trabecular bone microarchitecture was evaluated using micro-computed tomography analysis and bone histological analysis. Bone formation and resorption markers were quantified in blood samples from mice or in the supernatant of MC3T3-E1 cells by ELISA analysis, Western blotting, and PCR. Immunofluorescence was utilized to visualize the location of β-catenin. Additionally, siRNA was employed to knockdown-specific genes in the cells. Our findings highlight the efficacy of Drynaria Naringin in protecting against the deterioration of bone loss and promoting bone formation and Rspo1 expression in a mouse model following the TS test. Specifically, in vitro experiments also indicated that Drynaria Naringin may promote osteogenesis through the Wnt/β-catenin signalling pathway. Moreover, our results suggest that Drynaria Naringin upregulates the expression of Rspo1/Lgr4, leading to the promotion of osteogenesis via the Wnt/β-catenin signalling pathway. Therefore, Drynaria Naringin holds potential as a therapeutic medication for osteoporosis. Drynaria Naringin alleviates bone loss deterioration caused by mechanical stress deficiency through the Rspo1/Lgr4-mediated Wnt/β-catenin signalling pathway.

Physiology of sedentary behavior

Sedentary behaviors (SB) are characterized by low energy expenditure while in a sitting or reclining posture. Evidence relevant to understanding the physiology of SB can be derived from studies employing several experimental models: bed rest, immobilization, reduced step count, and reducing/interrupting prolonged SB. We examine the relevant physiological evidence relating to body weight and energy balance, intermediary metabolism, cardiovascular and respiratory systems, the musculoskeletal system, the central nervous system, and immunity and inflammatory responses. Excessive and prolonged SB can lead to insulin resistance, vascular dysfunction, shift in substrate use toward carbohydrate oxidation, shift in muscle fiber from oxidative to glycolytic type, reduced cardiorespiratory fitness, loss of muscle mass and strength and bone mass, and increased total body fat mass and visceral fat depot, blood lipid concentrations, and inflammation. Despite marked differences across individual studies, longer term interventions aimed at reducing/interrupting SB have resulted in small, albeit marginally clinically meaningful, benefits on body weight, waist circumference, percent body fat, fasting glucose, insulin, HbA1c and HDL concentrations, systolic blood pressure, and vascular function in adults and older adults. There is more limited evidence for other health-related outcomes and physiological systems and for children and adolescents. Future research should focus on the investigation of molecular and cellular mechanisms underpinning adaptations to increasing and reducing/interrupting SB and the necessary changes in SB and physical activity to impact physiological systems and overall health in diverse population groups.

Rehabilitation: Neurogenic Bone Loss after Spinal Cord Injury

Osteoporosis is a common skeletal disorder which can severely limit one's ability to complete daily tasks due to the increased risk of bone fractures, reducing quality of life. Spinal cord injury (SCI) can also result in osteoporosis and sarcopenia. Most individuals experience sarcopenia and osteoporosis due to advancing age; however, individuals with SCI experience more rapid and debilitating levels of muscle and bone loss due to neurogenic factors, musculoskeletal disuse, and cellular/molecular events. Thus, preserving and maintaining bone mass after SCI is crucial to decreasing the risk of fragility and fracture in vulnerable SCI populations. Recent studies have provided an improved understanding of the pathophysiology and risk factors related to musculoskeletal loss after SCI. Pharmacological and non-pharmacological therapies have also provided for the reduction in or elimination of neurogenic bone loss after SCI. This review article will discuss the pathophysiology and risk factors of muscle and bone loss after SCI, including the mechanisms that may lead to muscle and bone loss after SCI. This review will also focus on current and future pharmacological and non-pharmacological therapies for reducing or eliminating neurogenic bone loss following SCI.

Heterotypic Cell Culture from Mouse Bone Marrow under Simulated Microgravity: Lessons for Stromal Lineage Functions

Muscle and skeleton structures are considered most susceptible to negative factors of spaceflights, namely microgravity. Three-dimensional clinorotation is a ground-based simulation of microgravity. It provides an opportunity to elucidate the effects of microgravity at the cellular level. The extracellular matrix (ECM) content, transcriptional profiles of genes encoding ECM and remodelling molecules, and secretory profiles were investigated in a heterotypic primary culture of bone marrow cells after 14 days of 3D clinorotation. Simulated microgravity negatively affected stromal lineage cells, responsible for bone tissue formation. This was evidenced by the reduced ECM volume and stromal cell numbers, including multipotent mesenchymal stromal cells (MSCs). ECM genes encoding proteins responsible for matrix stiffness and cell-ECM contacts were downregulated. In a heterotypic population of bone marrow cells, the upregulation of genes encoding ECM degrading molecules and the formation of a paracrine profile that can stimulate ECM degradation, may be mechanisms of osteodegenerative events that develop in real spaceflight.

Zoledronic acid after spinal cord injury mitigates losses in proximal femoral strength independent of ambulation ability

Rapid bone loss can occur after spinal cord injury (SCI) and a standard of care to prevent or treat this phenomenon is an active area of research. Using advanced analysis techniques, this study demonstrates that zoledronic acid, a possible treatment, prevented loss of bone strength at the hip following SCI.

INTRODUCTION

Bone loss below the level of neurological lesion is a well-known complication of spinal cord injury (SCI), and effective preventive treatment for this phenomenon is an active area of research. Zoledronic acid has demonstrated efficacy to attenuate bone loss at the hip after SCI, but previous studies relied on measurements from dual-energy X-ray absorptiometry. The purpose of this investigation was to more thoroughly characterize changes to bone mineral and strength at the proximal femur in individuals receiving zoledronic acid in the acute SCI stage; we also examined the influence of ambulatory ability on bone outcomes.

METHODS

Participants randomized to either zoledronic acid (n = 29) or placebo (n = 30) received computed tomography (CT) scans and ambulatory assessments at baseline and 6 and 12 months following drug infusion. CT-based finite element (FE) modeling was used to predict changes in proximal femoral strength associated with treatment.

RESULTS

After 12 months, FE-predicted bone strength was reduced by a mean (SD) of 9.6 (17.9)% in the zoledronic acid group versus 24.6 (24.5)% in the placebo group (p = 0.007). These differences in strength were explained by reductions in CT measurements of both trabecular (p < 0.001) and cortical (p ≤ 0.021) bone at the femoral neck and trochanteric region. Ambulation ability influenced select trabecular and cortical parameters, but we were unable to detect an impact on FE-predicted bone strength.

CONCLUSION

These findings demonstrate that treatment with zoledronic acid in acute SCI attenuates losses in proximal femoral strength, which may reduce the risk of hip fractures across patients with varying degrees of ambulatory abilities.

Integration of Metabolomics and Transcriptomics to Reveal the Metabolic Characteristics of Exercise-Improved Bone Mass

(1) Background: Exercise is effective in promoting and maintaining bone mass. The aim of this study was to detect the exercise-induced metabolic changes in bone tissue of zebrafish. (2) Methods: Thirty-eight zebrafish (Danio rerio, six months old) were analyzed. The exercise group (n = 19) received 8 weeks of counter-current swimming training. The control group (n = 19) was not subjected to exercise. Mineralization was quantified, and alkaline phosphatase (Alp) and anti-tartrate acid phosphatase (Trap) activities were estimated (n = 12). The metabolomics (n = 12) and transcriptomics (n = 14) data of bone tissue were used for the integration analyses. (3) Results: The results showed that the exercise training improved the bone mineralization of zebrafish, e.g., the exercise group (5.74 × 104 ± 7.63 × 103) had a higher mean optical density than the control group (5.26 × 104 ± 8.56 × 103, p = 0.046) for the caudal vertebrae. The amount of mineralized matrix in scales of the exercised zebrafish was also higher (0.156 ± 0.012 vs. 0.102 ± 0.003, p = 0.005). Both histological staining and biochemical analysis revealed increased Alp activity (0.81 ± 0.26 vs. 0.76 ± 0.01, p = 0.002) and decreased Trap activity (1.34 ± 0.01 vs. 1.36 ± 0.01, p = 0.005) in the exercise group. A total of 103 different metabolites (DMs, VIP ≥ 1, fold change (FC) ≥ 1.20 or ≤0.83, p < 0.050) were identified. Alanine, aspartate and glutamate metabolism, β-alanine metabolism, pyrimidine metabolism, and pantothenate and CoA biosynthesis were the significantly enriched metabolic pathways (p < 0.050). A total of 35 genes (q ≤ 0.050 (BH), |Log2FC| ≥ 0.5) were coenriched with the 103 DMs in the four identified pathways. Protein–protein interaction network analysis of the 35 genes showed that entpd3, entpd1, and cmpk2 were the core genes. (4) Conclusions: The results of this study suggest that alanine, aspartate and glutamate metabolism, β-alanine metabolism, pyrimidine metabolism, and pantothenate and CoA biosynthesis contributed to exercise-induced improvements in bone mass.

Prevention of osteoporosis in menopausal women: A systematic review of nonpharmacological clinical trials

Osteoporosis is a systemic skeletal disease that is associated with negative physical and psychosocial consequences, so understanding the effective strategies that can be used in the prevention of osteoporosis is especially important. The aim of this study was to integrative review the published interventional of nonpharmacological studies regarding the prevention and treatment of osteoporosis among menopausal women. In this systematic review, databases such as PubMed, PsycInfo, Web of Science (ISI), Scopus, ScienceDirect, EmBase, Cochrane library, Google scholar, and Iranian databases, such as Scientific Information Database and Magiran, were searched. The latest search was performed between "November 2020 and December 2020" separately by two researchers and then double-checked by them. The quality of the included studies was assessed using the Jadad score calculation tool. Twenty eight randomized controlled trials and quasi-experimental studies were included in this current study. The quality assessment indicated that 19 studies had acceptable (good) methodological quality and also 9 studies had weak methodological quality. The main results of this study were classified in three main categories such as exercise or physical activity training (n = 15), educational sessions (n = 11), and other interventions (n = 2). The results of most included studies showed that nonpharmacological strategies such as physical activity and educational interventions are considered as the appropriate actions to prevention of osteoporosis among menopausal women so implementing these strategies can be a good alternative for women with contraindication of hormone therapy or therapeutic treatment.

Bone-Targeting Nanoparticles of a Dendritic (Aspartic acid)3-Functionalized PEG-PLGA Biopolymer Encapsulating Simvastatin for the Treatment of Osteoporosis in Rat Models

Simvastatin (SIM) is a lipid-lowering drug that also promotes bone formation, but its high liver specificity may cause muscle damage, and the low solubility of lipophilic drugs limits the systemic administration of SIM, especially in osteoporosis (OP) studies. In this study, we utilized the bone-targeting moiety of dendritic oligopeptides consisting of three aspartic acid moieties (dAsp3) and amphiphilic polymers (poly(ethylene glycol)-block-poly(lactic-co-glycolic acid); PEG-PLGA) to create dAsp3-PEG-PLGA (APP) nanoparticles (NPs), which can carry SIM to treat OP. An in vivo imaging system showed that gold nanocluster (GNC)-PLGA/APP NPs had a significantly higher accumulation rate in representative bone tissues. In vivo experiments comparing low-dose SIM treatment (0.25 mg/kg per time, 2 times per week) showed that bone-targeting SIM/APP NPs could increase the bone formation effect compared with non-bone-targeting SIM/PP NPs in a local bone loss of hindlimb suspension (disuse) model, but did not demonstrate good bone formation in a postmenopausal (ovariectomized) model of systemic bone loss. The APP NPs could effectively target high mineral levels in bone tissue and were expected to reduce side effects in other organs affected by SIM. However, in vivo OP model testing showed that the same lower dose could not be used to treat different types of OP.

Effect of transcutaneous electrical acupoint stimulation on bone metabolism in patients with immobilisation after foot and ankle fracture surgery: a randomised controlled trial study protocol

INTRODUCTION

Fracture is a disease with a high incidence worldwide. Foot and ankle fractures are common among fractures of the lower extremities. Foot and ankle fractures usually require surgical fixation and a period of fixed treatment, which can lead to decreased bone density. Although transcutaneous electrical acupoint stimulation (TEAS) is widely used for movement system diseases, there is minimal evidence to show the effectiveness of TEAS on patients after surgical fixation of ankle and foot fractures. This trial aims to evaluate whether TEAS can reduce bone loss in patients with immobilisation after ankle and foot fractures.

METHODS AND ANALYSIS

A randomised controlled trial will be conducted in which 60 patients will be randomly divided into two groups: (a) the control group will be treated according to the routine procedures of basic orthopaedics treatment; (b) in the treatment group, bilateral SP36, BL23 and ST36 will be performed on the basis of the control group, and the test will be performed for 30 min every other day for a total of 8 weeks. Bone turnover markers will be used as primary outcome. Secondary outcomes are composed of blood phosphorus, blood calcium and bone mineral density. Treatment safety will be monitored and recorded.

ETHICS AND DISSEMINATION

This trial is approved by the Ethics Committee of Beijing University of Chinese Medicine (2020BZYLL0611) and the Ethics Committee of Beijing Luhe Hospital (2020-LHKY-055-02), and inpatients who meet the following diagnostic and inclusion criteria are eligible to participate in this study.

TRIAL REGISTRATION NUMBER

ChiCTR 2000039944.

Mechanical force-promoted osteoclastic differentiation via periodontal ligament stem cell exosomal protein ANXA3

Exosomes play a critical role in intracellular communication. The biogenesis and function of exosomes are regulated by multiple biochemical factors. In the present study, we find that mechanical force promotes the biogenesis of exosomes derived from periodontal ligament stem cells (PDLSCs) and alters the exosomal proteome profile to induce osteoclastic differentiation. Mechanistically, mechanical force increases the level of exosomal proteins, especially annexin A3 (ANXA3), which facilitates exosome internalization to activate extracellular signal-regulated kinase (ERK), thus inducing osteoclast differentiation. Moreover, the infusion of exosomes derived from PDLSCs into mice promotes mechanical force-induced tooth movement and increases osteoclasts in the periodontal ligament. Collectively, this study demonstrates that mechanical force treatment promotes the biogenesis of exosomes from PDLSCs and increases exosomal protein ANXA3 to facilitate exosome internalization, which activates ERK phosphorylation, thus inducing osteoclast differentiation. Our findings shed light on new mechanisms for how mechanical force regulates the biology of exosomes and bone metabolism.

•

Mechanical force promotes the biogenesis of exosomes derived from PDLSCs by RAB27B

•

Mechanical force increases exosomal protein ANXA3 to facilitate exosome internalization

•

ANXA3 activates ERK phosphorylation to induce osteoclast differentiation

•

PDLSC exosomes enhance mechanical force-induced tooth movement

In vivo evaluation of mandibular trabecular and cortical bone quality in psoriasis vulgaris

OBJECTIVE

The aim of this study was to evaluate the effects of psoriasis vulgaris on mandibular structure by calculating fractal dimension (FD) and radiomorphometric indices.

STUDY DESIGN

Panoramic radiographs of 58 patients with psoriasis and 58 healthy participants were assessed. FD was used to analyze trabecular bone architecture in the condyle, angle, and 2 sites in the alveolar bone. Five radiomorphometric indices based on cortical thickness and the mandibular cortical index (MCI) for structure were used to assess cortical bone porosity. Comparisons were made between sites in trabecular and cortical bone. Quantitative and categorical data were statistically analyzed with the significance level at P < .05.

RESULTS

FD was significantly lower in the patients with psoriasis than in the controls in the alveolar bone sites (P ≤ .035). Differences between measurement sites were insignificant in psoriasis (P ≥ .617), but the FD values of some measurement sides in the control group differed significantly (P ≤ .004). All quantitative radiomorphometric indices were significantly lower in patients with psoriasis (P ≤ .034) with significant differences between some sites in both groups. No significant difference was found in MCI frequency distribution between the groups (P = .782).

CONCLUSIONS

Trabecular architecture and cortical thickness were negatively affected in patients with psoriasis, but no differences in cortical porosity were detected between groups.

Lipocalin 2 Influences Bone and Muscle Phenotype in the MDX Mouse Model of Duchenne Muscular Dystrophy

Lipocalin 2 (Lcn2) is an adipokine involved in bone and energy metabolism. Its serum levels correlate with bone mechanical unloading and inflammation, two conditions representing hallmarks of Duchenne Muscular Dystrophy (DMD). Therefore, we investigated the role of Lcn2 in bone loss induced by muscle failure in the MDX mouse model of DMD. We found increased Lcn2 serum levels in MDX mice at 1, 3, 6, and 12 months of age. Consistently, Lcn2 mRNA was higher in MDX versus WT muscles. Immunohistochemistry showed Lcn2 expression in mononuclear cells between muscle fibres and in muscle fibres, thus confirming the gene expression results. We then ablated Lcn2 in MDX mice, breeding them with Lcn2^−/− mice (MDXxLcn2^−/−), resulting in a higher percentage of trabecular volume/total tissue volume compared to MDX mice, likely due to reduced bone resorption. Moreover, MDXxLcn2^−/− mice presented with higher grip strength, increased intact muscle fibres, and reduced serum creatine kinase levels compared to MDX. Consistently, blocking Lcn2 by treating 2-month-old MDX mice with an anti-Lcn2 monoclonal antibody (Lcn2Ab) increased trabecular volume, while reducing osteoclast surface/bone surface compared to MDX mice treated with irrelevant IgG. Grip force was also increased, and diaphragm fibrosis was reduced by the Lcn2Ab. These results suggest that Lcn2 could be a possible therapeutic target to treat DMD-induced bone loss.

Transcriptional responses of skeletal stem/progenitor cells to hindlimb unloading and recovery correlate with localized but not systemic multi-systems impacts

Disuse osteoporosis (DO) results from mechanical unloading of weight-bearing bones and causes structural changes that compromise skeletal integrity, leading to increased fracture risk. Although bone loss in DO results from imbalances in osteoblast vs. osteoclast activity, its effects on skeletal stem/progenitor cells (SSCs) is indeterminate. We modeled DO in mice by 8 and 14 weeks of hindlimb unloading (HU) or 8 weeks of unloading followed by 8 weeks of recovery (HUR) and monitored impacts on animal physiology and behavior, metabolism, marrow adipose tissue (MAT) volume, bone density and micro-architecture, and bone marrow (BM) leptin and tyrosine hydroxylase (TH) protein expression, and correlated multi-systems impacts of HU and HUR with the transcript profiles of Lin^-LEPR⁺ SSCs and mesenchymal stem cells (MSCs) purified from BM. Using this integrative approach, we demonstrate that prolonged HU induces muscle atrophy, progressive bone loss, and MAT accumulation that paralleled increases in BM but not systemic leptin levels, which remained low in lipodystrophic HU mice. HU also induced SSC quiescence and downregulated bone anabolic and neurogenic pathways, which paralleled increases in BM TH expression, but had minimal impacts on MSCs, indicating a lack of HU memory in culture-expanded populations. Although most impacts of HU were reversed by HUR, trabecular micro-architecture remained compromised and time-resolved changes in the SSC transcriptome identified various signaling pathways implicated in bone formation that were unresponsive to HUR. These findings indicate that HU-induced alterations to the SSC transcriptome that persist after reloading may contribute to poor bone recovery.

Durability and delayed treatment effects of zoledronic acid on bone loss after spinal cord injury: a randomized, controlled trial

A single infusion of zoledronic acid (ZOL) after acute spinal cord injury (SCI) attenuates bone loss at the hip (proximal femur) and knee (distal femur and proximal tibia) for at least 6 months. The objective of this study was to examine the effects of timing and frequency of ZOL over 2 years. In this double-blind, placebo-controlled trial, we randomized 60 individuals with acute SCI (<120 days of injury) to receive either ZOL 5-mg infusion (n = 30) or placebo (n = 30). After 12 months, groups were again randomized to receive ZOL or placebo, resulting in four treatment groups for year 2: (i) ZOL both years; (ii) ZOL year 1, placebo year 2; (iii) placebo year 1, ZOL year 2; and (iv) placebo both years. Our primary outcome was bone loss at 12 months; compared to placebo, a single infusion of ZOL attenuated bone loss at the proximal femur, where median changes relative to baseline were -1.7% to -2.2% for ZOL versus -11.3% to -12.8% for placebo (p < 0.001). Similarly, the distal femur and proximal tibia showed changes of -4.7% to -9.6% for ZOL versus -8.9% to -23.0% for placebo (p ≤ 0.042). After 24 months, differences were significant at the proximal femur only (-3.2% to -6.0% for ZOL vs. -16.8% to -21.8% for placebo; p ≤ 0.018). Although not statistically significant, median bone density losses suggested some benefit from two annual infusions compared to a single baseline infusion, as well as from a single infusion 12 months after baseline compared to 2 years of placebo; therefore, further investigation in the 12-month to 24-month treatment window is warranted. No unanticipated adverse events associated with drug treatment were observed. In summary, ZOL 5-mg infusion after acute SCI was well-tolerated and may provide an effective therapeutic approach to prevent bone loss in the first few years following SCI. © 2021 American Society for Bone and Mineral Research (ASBMR).

Resistance to disuse-induced iron overload in Daurian ground squirrels (Spermophilus dauricus) during extended hibernation inactivity

Iron overload occurs in disuse-induced osteoporosis. Hibernators are a natural animal model of resistance to disuse osteoporosis. We hypothesized that hibernators avoid iron overload to resist disuse-induced osteoporosis. Here, the role of iron metabolism in resistance to disuse osteoporosis was investigated by studying differences in iron content and iron metabolism in the femurs and livers of Daurian ground squirrels (Spermophilus dauricus) between the summer active and torpid states. Results showed that the femurs were generally well-maintained during torpor, with no significant differences observed in most bone microstructural parameters, except for a significantly lower (by 40%) trabecular bone connection density. Femur and liver iron concentrations were significantly lower during torpor (by 59% and 49%, respectively). Based on histological staining, livers were iron-negative and femurs showed a reduction in iron-positive area (by 83%) during torpor; The number of osteoblasts and osteoclasts showed no significant differences between the two groups. Most iron metabolism/homeostasis proteins expression levels in the femur and liver showed no significant differences between the two groups, with their stable expression likely preventing iron overload during inactivity. Higher femoral transferrin receptor 1 (TfR1) expression (by 108%) and lower liver ferritin expression (by 45%) were found in torpid squirrels. Lower liver ferritin may be related to the lower iron content, with the elevation in femoral TfR1 potentially related to restoration of bone iron levels. In conclusion, despite long periods of inactivity, iron levels in the femur and liver of squirrels were lower, bone formation and resorption were balanced and no iron overload was observed, as is found under disuse conditions in non-hibernators. Therefore, avoiding iron overload may be a potential mechanism for hibernators to avoid disuse-induced bone loss.

Inconsistency of Bone Mineral Density Between Femoral Head and Proximal Femur After Femoral Neck Fracture Surgery Indicates Great Possibility of Femoral Head Necrosis

On clinical observation, it was found that the bone mineral density (BMD) of the femoral head and proximal femur was not consistent in some patients with femoral neck fracture after surgery. The current study was performed to explore whether this phenomenon was associated with femoral head necrosis after surgery for femoral neck fracture. Bone mineral density inconsistency is when the difference of the sum of pixel values on both sides of the fracture line has exceeded 30%. Statistical analysis was performed on the clinical characteristics of 271 patients who had received the operation for femoral neck fracture. Chi-square test, Spearman rank correlation, independent sample t test, Kaplan-Meier method, and log-rank test, as well as univariate Cox regression and multivariate Cox regression, were used to analyze the potential relationship among related factors. It was revealed that the incidence of inconsistency in BMD between the femoral head and proximal femur was significantly increased in patients with femoral head necrosis after surgery for femoral neck fracture, and that the consistency was considerably high between BMD inconsistency and femoral head necrosis. The inconsistent BMD occurred 11.1 months earlier than the necrosis of the femoral head. Cox multivariate regression analysis indicated that the inconsistency in BMD between the femoral head and proximal femur after surgery for femoral neck fracture was an independent prognostic factor affecting femoral head necrosis. The inconsistent changes in BMD between the femoral head and proximal femur after surgery for femoral neck fracture indicate a great possibility of femoral head necrosis. [Orthopedics. 2021;44(2):e223-e228.].

Antioxidant Supplementation Does Not Affect Bone Turnover Markers During 60 Days of 6° Head-Down Tilt Bed Rest: Results from an Exploratory Randomized Controlled Trial

BACKGROUND

Immobilization and related oxidative stress are associated with bone loss. Antioxidants like polyphenols, omega-3 fatty acids, vitamins, and micronutrients may mitigate these negative effects on bone metabolism through scavenging of free radicals.

OBJECTIVES

We hypothesized that antioxidant supplementation during 60 days of 6° head-down tilt bed rest (HDBR) would reduce bone resorption and increase bone formation compared to nonsupplemented controls.

METHODS

This exploratory randomized, controlled, single-blind intervention study conducted in a parallel design included 20 healthy male volunteers (age, 34 ± 8 years; weight, 74 ± 6 kg). The study consisted of a 14-day adaptation phase [baseline data collection (BDC)], followed by 60 days of HDBR and a 14-day recovery period (R). In the antioxidant group, volunteers received an antioxidant cocktail (741 mg/d polyphenols, 2.1 g/d omega-3 fatty acids, 168 mg/d vitamin E, and 80 μg/d selenium) with their daily meals. In the control group, volunteers received no supplement. Based on their body weight, all volunteers received an individually tailored and strictly controlled diet, consistent with DRIs. We analyzed biomarkers of calcium homeostasis, bone formation, and bone resorption during BDC, HDBR, and R, as well as for 30 days after the end of HDBR. Data were analyzed by linear mixed models.

RESULTS

The antioxidant supplement did not affect serum calcium, parathyroid hormone, urinary C-telopeptide of type I collagen (CTX), urinary N-telopeptide of type I collagen, serum β-C-telopeptide of type I collagen (β-CTX), bone alkaline phosphatase, aminoterminal propeptide of type I collagen, osteocalcin, or urinary calcium excretion. In both groups, typical bed rest-related changes were observed.

CONCLUSIONS

Supplementation of an antioxidant cocktail to a diet matching the DRIs did not affect bone resorption or formation during 60 days of HDBR in healthy young men. This trial was registered at clinicaltrials.gov as NCT03594799.

Impact of Genetic and Pharmacologic Inhibition of Myostatin in a Murine Model of Osteogenesis Imperfecta

Osteogenesis imperfecta (OI) is a genetic connective tissue disorder characterized by compromised skeletal integrity, altered microarchitecture, and bone fragility. Current OI treatment strategies focus on bone antiresorptives and surgical intervention with limited effectiveness, and thus identifying alternative therapeutic options remains critical. Muscle is an important stimulus for bone formation. Myostatin, a TGF-β superfamily myokine, acts through ActRIIB to negatively regulate muscle growth. Recent studies demonstrated the potential benefit of myostatin inhibition with the soluble ActRIIB fusion protein on skeletal properties, although various OI mouse models exhibited variable skeletal responses. The genetic and clinical heterogeneity associated with OI, the lack of specificity of the ActRIIB decoy molecule for myostatin alone, and adverse events in human clinical trials further the need to clarify myostatin's therapeutic potential and role in skeletal integrity. In this study, we determined musculoskeletal outcomes of genetic myostatin deficiency and postnatal pharmacological myostatin inhibition by a monoclonal anti-myostatin antibody (Regn647) in the G610C mouse, a model of mild-moderate type I/IV human OI. In the postnatal study, 5-week-old wild-type and +/G610C male and female littermates were treated with Regn647 or a control antibody for 11 weeks or for 7 weeks followed by a 4-week treatment holiday. Inhibition of myostatin, whether genetically or pharmacologically, increased muscle mass regardless of OI genotype, although to varying degrees. Genetic myostatin deficiency increased hindlimb muscle weights by 6.9% to 34.4%, whereas pharmacological inhibition increased them by 13.5% to 29.6%. Female +/mstn +/G610C (Dbl.Het) mice tended to have similar trabecular and cortical bone parameters as Wt showing reversal of +/G610C characteristics but with minimal effect of +/mstn occurring in male mice. Pharmacologic myostatin inhibition failed to improve skeletal bone properties of male or female +/G610C mice, although skeletal microarchitectural and biomechanical improvements were observed in male wild-type mice. Four-week treatment holiday did not alter skeletal outcomes. © 2020 American Society for Bone and Mineral Research (ASBMR).

Osteoporosis: Mechanism, Molecular Target and Current Status on Drug Development

CDATA[Osteoporosis is a pathological loss of bone mass due to an imbalance in bone remodeling where osteoclast-mediated bone resorption exceeds osteoblast-mediated bone formation resulting in skeletal fragility and fractures. Anti-resorptive agents, such as bisphosphonates and SERMs, and anabolic drugs that stimulate bone formation, including PTH analogues and sclerostin inhibitors, are current treatments for osteoporosis. Despite their efficacy, severe side effects and loss of potency may limit the long term usage of a single drug. Sequential and combinational use of current drugs, such as switching from an anabolic to an anti-resorptive agent, may provide an alternative approach. Moreover, there are novel drugs being developed against emerging new targets such as Cathepsin K and 17β-HSD2 that may have less side effects. This review will summarize the molecular mechanisms of osteoporosis, current drugs for osteoporosis treatment, and new drug development strategies.

Asymmetric midshaft femur remodeling in an adult male with left sided hip joint ankylosis, Metal Period Nagsabaran, Philippines

OBJECTIVE

This study investigated microstructural changes of the right and left midshaft femur in an archaeological individual afflicted with left-sided hip joint ankylosis to assess whether increased cortical porosity was present as a result of leg disuse.

MATERIALS

The individual is a middle-aged adult male excavated from the Metal Period (∼2000 BP) Nagsabaran, Luzon Island, Philippines.

METHODS

Following standard examination of femur gross anatomy and differential diagnosis of the hip joint fusion, ∼1 cm thick posterior midshaft femur samples were removed for microstructural examination. Using static histomorphometry, bone multi-cellular unit activity from Haversian canal (vascular pore) density, area, and circularity was reconstructed. Spatial positioning of Haversian canals was mapped using Geographic Information Systems software. Phosphate, carbonate, and carbonate:phosphate ratios were obtained using synchrotron-sourced Fourier transform infrared microspectroscopy.

RESULTS

The left femur had greater cortical pore density, with smaller and rounder vascular canals, in addition to lower matrix levels of phosphate and carbonate, when compared to the right femur.

CONCLUSIONS

Our data indicate compromised bone tissue in the left femur, and conform to expected bone functional adaptation paradigms of remodeling responses to pathological and biomechanical changes.

SIGNIFICANCE

The preservation of this individual's hip abnormality created a unique opportunity to evaluate intra-skeletal bone health asymmetry, which may help other researchers evaluate the presence of limb disuse in archaeological samples.

LIMITATIONS

A lack of lower limb data limits our interpretations to femur remodeling only.

SUGGESTIONS FOR FURTHER RESEARCH

Future research efforts should aim to examine the presence of remodeling changes in all bones of the lower limb.

LAYUNIN

Gamit ang buto ng magkabilang pemur ng isang taong natagpuan sa isang archaeological site na may sakit na ankylosis sa kaliwang balakang, pinag-aralan ang iba't-ibang microstructures galing sa gitnang bahagi o midshaft ng pemur upang malaman kung may makikitang mataas na cortical porosity ang buto dahil hindi ito malimit gamitin.

GAMIT

Ang pinag-aaralang buto ay galing sa isang indibidwal na tinatayang middle-age na lalaki na namuhay noong Panahon ng Metal (∼2000 BP) sa Nagsabaran, Cagayan, Republika ng Pilipinas.

PAMAMARAAN

Matapos ang unang pagkilatis sa femur at ang pagkilala ng sakit sa balakang, kumuha ng ∼1 sentimetro ng buto galing sa midshaft ng pemur upang lalong mapag-aralan ang kanyang microstructure. Gamit ang static histomorphometry, napag-aralan ang mga naiwang bakas ng multi-cellular unit activity ayon sa kapal, laki at pagkakabilog ng Haversian canal (vascular pore). Gumamit din ng Geographic Information Systems (GIS) software upang mapag-aralan ang kaugnayan ng posisyon ng Haversian canal. Panghuli, gumamit din ng synchroton-sourced Fourier transform infrared (sFTIR) microspectroscopy upang makuha ang bilang ng phosphate, carbonate, at carbonate:phosphate ratio.

RESULTA

Napag-alaman na ang kaliwang pemur ay mayroong higit na maraming cortical pores, maliit at mabilog na vascular canals, at mababang bilang ng phosphate, carbonate kung ihahambing sa kanang pemur.

KONKLUSYON

Ayon sa aming datos, ang kaliwang pemur ay umaayon sa mga katangian ng isang butong may sakit. Sumunod din ito sa inaasahang bone functional adaptation paradigms of remodeling ng buto dahil may sakit at hindi nagamit.

KAHALAGAHAN

Dahil maganda ang pagkakalibing ng buto ng balakang, nagkaroon ng pagkakataong makilatis ang kalusugan ng sinaunang-tao sa pamamagitan ng pag-aaral ng kalusugan ng buto. Dagdag pa, makakatulong din ito upang malaman kung ibang mananaliksik ang pag-aaral ng ibang butong hindi nagagamit mula sa archaeological site.

LIMITASYON

Dahil walang nakuhang ibang buto mula sa binti at paa, ang pemur lang ang naimbestigahan.

MUNGKAHI PARA SA MGA SUSUNOD NA PAG-AARAL

Kung magkakaroon ng pagkakataon sa susunod, dapat maimbistigahan ang lahat ng buto ng binti (lower limb).

Severe bone microarchitecture deterioration in a family with hereditary neuropathy: evidence of the key role of the mechanostat

In this report, we present three cases of individuals from the same family with a diagnosis of CMT with severe tibia bone microarchitecture deterioration assessed by HR-pQCT. Charcot-Marie-Tooth disease (CMT) or hereditary neuropathy involves both motor and sensory nerves. Falls are often the first manifestation in these patients and represent an important risk factor for fracture. The reduction of mechanical input on bone inhibits bone formation by osteoblasts and accelerates bone resorption by osteoclasts, leading to disuse osteoporosis. We report three cases of individuals from the same family with a diagnosis of CMT with severe tibia bone microarchitecture deterioration assessed by high-resolution peripheral quantitative computed tomography (HR-pQCT). This affectation was exclusive to the tibia; the radius remained undamaged, showing the consequences of the lack of mobility and mechanical stimulation. Physical activity and rehabilitation, in addition to adequate calcium and vitamin D supplementation, may play an essential role in the management of this disease.

A Procedure to Define Customized Musculoskeletal Models for the Analysis of the Crutch-Orthosis-Assisted Gait of Spinal Cord Injured Subjects

Subjects suffering from spinal cord injury with lower extremity impairment generally use a wheelchair to move. However, some of them are capable of walking with the help of orthoses and crutches. Standing up and walking regularly have huge benefits for the general health state of these subjects, since it reduces the negative consequences of sedentarism. Therefore, achieving adherence to assisted gait is important, but there is a risk of abandoning due to several issues such as pain, fatigue, or very low speed, which can make the subject return to solely use the wheelchair. Musculoskeletal models can provide estimations of muscular forces and activations, which in turn enable to calculate magnitudes such as joint reactions, energetic cost, and bone stress and strain. These magnitudes can serve to evaluate the impact of assisted gait in the subject's health and to assess the likelihood of adherence. Moreover, they can be used as indicators to compare different assistive devices for a particular subject. As every spinal cord-injured (SCI) subject represents a different case, a procedure to define customized musculoskeletal models for the crutch-orthosis-assisted gait of SCI subjects is proposed in this paper. Issues such as selection of muscles and integration of models of trunk, upper and lower extremities, and assistive devices (crutches and orthoses) are addressed. An inverse-dynamics-based physiological static optimization method that takes into account muscle dynamics at low computational cost is applied to obtain estimates of muscle forces and joint reactions. The method is experimentally validated by electromyography in a case study.

The Central Role of Osteocytes in the Four Adaptive Pathways of Bone's Mechanostat

We review evidence supporting an updated mechanostat model in bone that highlights the central role of osteocytes within bone's four mechanoadaptive pathways: 1) formation modeling and 2) targeted remodeling, which occur with heightened mechanical loading, 3) resorption modeling, and 4) disuse-mediated remodeling, which occur with disuse. These four pathways regulate whole-bone stiffness in response to changing mechanical demands.

The Interventional Effects of Tubson-2 Decoction on Ovariectomized Rats as Determined by a Combination of Network Pharmacology and Metabolomics

Post-menopausal osteoporosis (PMOP) is associated with estrogen deficiency and worldwide, is becoming increasingly more prevalent in aging women. Various anti-PMOP drugs have been developed to reduce the burden of PMOP; generally, these drugs are efficacious, but with some adverse side effects. Tubson-2 decoction (TBD), a popular traditional Mongolian medicine, has been used to treat PMOP for centuries. However, the precise mechanisms underlying the action of TBD on PMOP have yet to be fully elucidated. Herein, we combined network pharmacology with untargeted metabolomics to identify the key targets and metabolic pathways associated with the interventional effects of TBD on ovariectomized (OVX) rats. Furthermore, we investigated the bone histomorphometry of eight different groups of rats to evaluate the therapeutic effect of TBD. First, we established a TBD-target/PMOP network via network pharmacology; this network identified three key protein targets-vitamin D receptor (VDR), cytochrome P450 19A1 (CYP19A1), and 11β-hydroxysteroid dehydrogenase type 1 (HSD11B1). Morphological analysis showed that severe impairment of the bone micro-architecture in OVX rats could be improved by TBD administration. The TBD-treated rats had a significantly lower bone surface-to-tissue volume (BS/TV) and a significantly smaller trabecular separation (Tb·Sp.) (P<0.05) than the OVX rats; in contrast, bone volume fraction (BVF), trabecular thickness (Tb·Th.), trabecular number (Tb·N.), and bone mineral density (BMD) were significantly higher in the TBD-treated rats (P<0.05). Multivariate and univariate analysis showed that OVX resulted in significant alterations in the concentrations of 105 metabolites and 11 metabolic pathways (P<0.05); in addition, 26 potential biomarkers were identified to investigate the progression of PMOP. Network pharmacology showed that major alterations in vitamin B6 metabolism were associated with the VDR target. Next, we validated the three crucial targets (VDR [P<0.01], HSD11B1 [P<0.01], and CYP19A1 [P<0.05]) by enzyme-linked immunosorbent assays (ELISAs) and demonstrated that the levels of these targets were elevated in the OVX group but reduced in the TBD-treatment group. Collectively, our results suggest that the interventional effects of TBD on OVX rats are likely to be associated with the down regulation of VDR. Our findings enhance our molecular understanding of the interventional effects of TBD on PMOP and will allow us to develop further TBD studies.

Metabolomics profiling reveals Echinops latifolius Tausch improves the trabecular micro-architecture of ovariectomized rats mainly via intervening amino acids and glycerophospholipids metabolism

ETHNOPHARMACOLOGICAL RELEVANCE

Echinops latifolius Tausch (ELT) is traditional Mongolian medicine in China, and often used to against osteoporosis, strengthen tendons and bones, clear bones heat.

AIM OF THE STUDY

To study efficacy of ELT on ovariectomized (OVX) rats and underly metabolic pathways related to trabecular micro-architecture changing of OVX.

MATERIALS AND METHODS

Three-month-old female Wistar rats were randomly divided into 4 groups (n = 6) including normal group (without surgery), sham group (bilateral laparotomy), OVX group (bilateral ovariectomy), and ELT-treated groups (ELT-treated after bilateral ovariectomy). The effects of ELT on trabecular micro-architecture and biochemical markers of OVX rat were investigated by dual-energy X-ray absorptiometry machine and Enzyme-linked immunosorbent assay (ELISA), respectively. Untargeted metabolomics strategy was applied to discover the potential biomarkers and related metabolic pathways involving the progression of OVX-induced osteoporosis.

RESULTS

The trabecular micro-architecture and biochemical markers of OVX rats were improved by ELT. We found 36 potential biomarkers and 21 related metabolic pathways were involved in progression of OVX-induced osteoporosis. Amino acids metabolism and glycerophospholipids metabolism were mainly intervened in ELT treatment on ovariectomized rats. The disordered amino acids and glycerophospholipids metabolism closely related to the imbalance between bone resorption and formation were reversed by administration of ELT, indicating that the influences of ELT on OVX rats' trabecular micro-architecture may possible be associated with intervening amino acids and glycerophospholipids metabolism.

CONCLUSIONS

This approach may provide the metabolomic perspective to link metabolic alterations and anti-osteoporosis action of ELT, to further explain how ELT works in postmenopausal patients with bone loss.

Reversibility of marrow adipose accumulation and reduction of trabecular bone in the epiphysis of the proximal tibia

Mechanical stimuli play an important role in the homeostasis of trabecular bone and marrow adipose tissue, particularly for the weight-bearing skeleton. Prolonged immobilization and disuse have been shown to reduce trabecular bone content and increase marrow adipose tissue in the bones of lower limb joints such as the knee. However, details on the temporal response of this relationship to prolonged immobilization and its reversibility is limited. Forty rats had one knee immobilized at 45° of flexion for 2, 4, 8, or 16 weeks and subsequently remobilized for 0 or 8 weeks. The contralateral knees were used as controls. Histomorphometric measures of trabecular bone and marrow adipose tissue (MAT) areas were conducted in the epiphysis of the proximal tibia. Knee immobilization for 4, 8, and 16 weeks significantly reduced trabecular bone area by -0.125, -0.139, and -0.161 mm²/mm², respectively, with corresponding 95 % CIs of [-0.012, -0.239], [-0.006, -0.273], and [-0.101, -0.221]. MAT area significantly increased at 2 and 16 weeks by +0.008 and +0.027 mm²/mm², respectively, with 95 % CIs of [0.014, 0.002] and [0.039, 0.016]. Remobilization for 8 weeks restored trabecular bone area compared to the contralateral knee and the magnitude of change was significantly greater for 8 and 16 weeks of immobilization with effect sizes of 1.69 and 1.86, respectively. The difference in MAT area between immobilized and contralateral knees were eliminated with remobilization. These results characterize the temporal response of trabecular bone and MAT in the epiphysis of the proximal tibia to joint immobilization and remobilization.

Hibernating bear serum hinders osteoclastogenesis in-vitro

Bears do not suffer from osteoporosis during hibernation, which is associated with long-term inactivity, lack of food intake, and cold exposure. However, the mechanisms involved in bone loss prevention have scarcely been elucidated in bears. We investigated the effect of serum from hibernating Japanese black bears (Ursus thibetanus japonicus) on differentiation of peripheral blood mononuclear cells (PBMCs) to osteoclasts (OCs). PBMCs collected from 3 bears were separately cultured with 10% serum of 4 active and 4 hibernating bears (each individual serum type was assessed separately by a bear PBMCs), and differentiation were induced by treatment with macrophage colony stimulating factor (M-CSF) and receptor activator of NF-kB ligand (RANKL). PBMCs that were cultured with the active bear serum containing medium (ABSM) differentiated to multi-nucleated OCs, and were positive for TRAP stain. However, cells supplemented with hibernating bear serum containing medium (HBSM) failed to form OCs, and showed significantly lower TRAP stain (p < 0.001). On the other hand, HBSM induced proliferation of adipose derived mesenchymal stem cells (ADSCs) similarly to ABSM (p > 0.05), indicating no difference on cell growth. It was revealed that osteoclastogenesis of PBMCs is hindered by HBSM, implying an underlying mechanism for the suppressed bone resorption during hibernation in bears. In addition, this study for the first time showed the formation of bears’ OCs in-vitro.

Enhanced osteogenesis and therapy of osteoporosis using simvastatin loaded hybrid system

Postmenopausal osteoporosis is a common chronic dynamic bone disorder, caused by estrogen deficiency. To address this issue, we constructed a controlled drug-release system composed of poly (N-isopropylacrylamide) brush modified mesoporous hydroxyapatite (MHA-SIM-P) loaded with simvastatin (SIM) using an ovariectomised (OVX) rat model. Quantitative alkaline phosphatase activity assay, alizarin red staining and RT-PCR were tested to evaluate the osteogenic ability in vitro. The results showed that the MHA-SIM-P nanoparticles significantly improved the osteogenic differentiation of OVX bone marrow stromal cells (BMSCs) in vitro. In osteoporotic animal model, the therapeutic efficiency for bone defect was evaluated by μCT analysis, tartrate-resistant acid phosphatase, haematoxylin and eosin staining, which showed improved bone formation and less osteoclastic response in OVX rats after surgery for 3 and 6 weeks. This polymer brush modified MHA system provided a sustained release system of hydrophobic SIM to inhibit osteoporosis together with MHA nanoparticle promoting the osteogenesis. Thus, this novel strategy exhibited great potential for promoting osteogenic ability and treating local osteoporotic defects.

Functional Block of Interleukin-6 Reduces a Bone Pain Marker but Not Bone Loss in Hindlimb-Unloaded Mice

Interleukin-6 (IL-6) is widely accepted to stimulate osteoclasts. Our aim in this study was to examine whether the inhibitory effect of IL-6 on bone loss and skeletal pain associated with osteoporosis in hindlimb-unloaded (HU) mice in comparison with bisphosphonate. Eight-week-old male ddY mice were tail suspended for 2 weeks. Starting immediately after reload, vehicle (HU group), alendronate (HU-ALN group), or anti-IL-6 receptor antibody (HU-IL-6i group) was injected subcutaneously. After a 2-week treatment, pain-related behavior was examined using von Frey filaments. The bilateral distal femoral and proximal tibial metaphyses were analyzed three-dimensionally with micro-computed tomography. Calcitonin gene-related peptide (CGRP) expressions in dorsal root ganglion (DRG) neurons innervating the hindlimbs were examined using immunohistochemistry. HU mice with tail suspension developed bone loss. The HU mice showed mechanical hyperalgesia in the hindlimbs and increased CGRP immunoreactive neurons in the L3-5 DRG. Treatment with IL-6i and ALN prevented HU-induced mechanical hyperalgesia and upregulation of CGRP expressions in DRG neurons. Furthermore, ALN but not IL-6i prevented HU-induced bone loss. In summary, treatment with IL-6i prevented mechanical hyperalgesia in hindlimbs and suppressed CGRP expressions in DRG neurons of osteoporotic models. The novelty of this research suggests that IL-6 is one of the causes of immobility-induced osteoporotic pain regardless improvement of bone loss.

Signalling molecule transport analysis in lacunar-canalicular system

Mechanical loading-induced fluid flow in lacunar-canalicular space (LCS) of bone excites osteocyte cells to release signalling molecules which initiate osteo-activities. Theoretical models considered canaliculi as a uniform and symmetrical space/channel in bone. However, experimental studies reported that canalicular walls are irregular and curvy resulting in inhomogeneous fluid motion which may influence the molecular transport. Therefore, a new mathematical model of LCS with curvy canalicular walls is developed to characterize cantilever bending-induced canalicular flow behaviour in terms of pore-pressure, fluid velocity, and streamlines. The model also analyses the mobility of signalling molecules involved in bone mechanotransduction as a function of loading frequency and permeability of LCS. Inhomogeneous flow is observed at higher loading frequency which amplifies mechanotransduction; nevertheless, it also promotes trapping of signalling molecules. The effects of shape and size of signalling molecules on transport behaviour are also studied. Trivially, signalling molecules larger in size and weight move slower as compared to molecules small in size and weight which validates the findings of the present study. The outcomes will ultimately be useful in designing better biomechanical exercise in combination with pharmaceutical agents to improve the bone health.

Global and site-specific analysis of bone in a rat model of spinal cord injury-induced osteoporosis

Micro-Computed Tomography bone analysis is the gold standard method for assessing trabecular and cortical bone microarchitecture in small animal bones. This technique reports morphometric parameters as averages over selected volumes of interest (VOIs). This study proposes the introduction of an additional global 2D morphometric step into the analysis process, that provides a survey of the underlying morphometric variation present throughout both trabecular and cortical bone. The visualisation of these morphometric distributions provides a systematic approach to VOI selection that provides rationale and adds confidence to subsequent 3D morphometric analysis. To test the applicability and value of this methodological addition it was applied to the distal femur of a rat model of spinal cord injury (SCI)-induced osteoporosis. The 2D morphometric variation of both trabecular and cortical bone was quantified as a function of bone length. SCI-induced osteoporosis was localised in i) trabecular bone, where metaphyseal bone was more severely affected than epiphyseal bone, and there was a significant reduction in Distal Femoral Trabecular Extent, a new parameter defined here that quantifies how far trabecular bone penetrates in to the marrow cavity, ii) cortical bone, where diaphyseal bone underwent significant lowering of both cortical area and thickness, while distal-metaphyseal bone did not. Theses site-specific changes were validated, further elucidated and compared with follow-up conventional 3D analysis. The techniques applied here are equally applicable to other long bones (tibia, humerus, radius, ulna), other types of imaging modality and other types of experimental design including the effects of rehabilitation, aging, loading, gene knockout and pharmacological intervention.

•

2D morphological surveying identifies regions warranting further 3D investigation.

•

Trabecular microarchitecture site-specifically varies in the distal femur.

•

SCI-induced osteoporosis changes metaphyseal more than epiphyseal trabecular bone.

•

SCI-induced osteoporosis reduced the extent of metaphyseal trabecular bone.

The NATO project: nanoparticle-based countermeasures for microgravity-induced osteoporosis

Recent advances in nanotechnology applied to medicine and regenerative medicine have an enormous and unexploited potential for future space and terrestrial medical applications. The Nanoparticles and Osteoporosis (NATO) project aimed to develop innovative countermeasures for secondary osteoporosis affecting astronauts after prolonged periods in space microgravity. Calcium- and Strontium-containing hydroxyapatite nanoparticles (nCa-HAP and nSr-HAP, respectively) were previously developed and chemically characterized. This study constitutes the first investigation of the effect of the exogenous addition of nCa-HAP and nSr-HAP on bone remodeling in gravity (1 g), Random Positioning Machine (RPM) and onboard International Space Station (ISS) using human bone marrow mesenchymal stem cells (hBMMSCs). In 1 g conditions, nSr-HAP accelerated and improved the commitment of cells to differentiate towards osteoblasts, as shown by the augmented alkaline phosphatase (ALP) activity and the up-regulation of the expression of bone marker genes, supporting the increased extracellular bone matrix deposition and mineralization. The nSr-HAP treatment exerted a protective effect on the microgravity-induced reduction of ALP activity in RPM samples, and a promoting effect on the deposition of hydroxyapatite crystals in either ISS or 1 g samples. The results indicate the exogenous addition of nSr-HAP could be potentially used to deliver Sr to bone tissue and promote its regeneration, as component of bone substitute synthetic materials and additive for pharmaceutical preparation or food supplementary for systemic distribution.

Vibration of osteoblastic cells using a novel motion-control platform does not acutely alter cytosolic calcium, but desensitizes subsequent responses to extracellular ATP

Low-magnitude high-frequency mechanical vibration induces biological responses in many tissues. Like many cell types, osteoblasts respond rapidly to certain forms of mechanostimulation, such as fluid shear, with transient elevation in the concentration of cytosolic free calcium ([Ca²⁺ ]_i ). However, it is not known whether vibration of osteoblastic cells also induces acute elevation in [Ca²⁺ ]_i . To address this question, we built a platform for vibrating live cells that is compatible with microscopy and microspectrofluorometry, enabling us to observe immediate responses of cells to low-magnitude high-frequency vibrations. The horizontal vibration system was mounted on an inverted microscope, and its mechanical performance was evaluated using optical tracking and accelerometry. The platform was driven by a sinusoidal signal at 20-500 Hz, producing peak accelerations from 0.1 to 1 g. Accelerometer-derived displacements matched those observed optically within 10%. We then used this system to investigate the effect of acceleration on [Ca²⁺ ]_i in rodent osteoblastic cells. Cells were loaded with fura-2, and [Ca²⁺ ]_i was monitored using microspectrofluorometry and fluorescence ratio imaging. No acute changes in [Ca²⁺ ]_i or cell morphology were detected in response to vibration over the range of frequencies and accelerations studied. However, vibration did attenuate Ca²⁺ transients generated subsequently by extracellular ATP, which activates P2 purinoceptors and has been implicated in mechanical signaling in bone. In summary, we developed and validated a motion-control system capable of precisely delivering vibrations to live cells during real-time microscopy. Vibration did not elicit acute elevation of [Ca²⁺ ]_i , but did desensitize responses to later stimulation with ATP.

Mir-494 inhibits osteoblast differentiation by regulating BMP signaling in simulated microgravity

Although the BMPR-SMAD-RUNX2 signaling pathway plays widely recognized roles in BMP-induced osteogenesis, factors regulating this pathway remain to be defined. In this study, we used simulated microgravity models, which represent mechanical unloading conditions, to detect miRNAs that function in osteoblast differentiation. We found that miR-494 was persistently increased in C2C12 cells subjected to clinorotation conditions and in osteoblasts isolated from tail-suspended rats. Experiments showed that the overexpression of miR-494 correlated with a marked reduction in osteoblast differentiation genes and a decrease in osteogenesis in BMP2-induced osteogenetic differentiation. In contrast, the inhibition of miR-494 promoted BMP2-induced osteogenesis and partially rescued osteoblast differentiation disorder under simulated microgravity conditions. Mechanism studies revealed that miR-494 directly targeted BMPR2 and RUNX2, both of which play vital roles in the BMPR-SMAD-RUNX2 signaling pathway. More importantly, we demonstrated a positive feedback loop between miR-494 and MYOD, a critical transcription factor for myogenesis, indicating that miR-494 may participate in deciding cell fate of the multipotent mesenchymal stem cells (MSCs). Collectively, our study reveals an important role for miR-494 in regulating osteogenesis, the identification of which not only clarifies a regulator of BMP2-induced osteoblast differentiation, but also offers a possible strategy for preventing bone loss under microgravity conditions.

Recent Progress in Space Physiology and Aging

Astronauts coming back from long-term space missions present with different health problems potentially affecting mission performance, involving all functional systems and organs and closely resembling those found in the elderly. This review points out the most recent advances in the literature in areas of expertise in which specific research groups were particularly creative, and as they relate to aging and to possible benefits on Earth for disabled people. The update of new findings and approaches in space research refers especially to neuro-immuno-endocrine-metabolic interactions, optic nerve edema, motion sickness and muscle-tendon-bone interplay and aims at providing the curious - and even possibly naïve young researchers – with a source of inspiration and of creative ideas for translational research.

Paravertebral injection of botulinum toxin-A reduces lumbar vertebral bone quality

Aging has been associated with decreases in muscle strength and bone quality. In older patients, paravertebral muscle atrophy tends to coincide with vertebral osteoporosis. The purpose of this study was to investigate the effects of a paravertebral injection of botulinum toxin-A (BTX) on paravertebral muscle atrophy and lumbar vertebral bone quality. Forty 16-week-old female SD rats were randomly divided into four groups: (1) a control group (CNT); (2) a resection of erector spinae muscles group (RESM); (3) a botulinum toxin-A group (BTX), treated with 5U BTX by local injection into the paravertebral muscles bilaterally; and (4) a positive control group (OVX), treated by bilateral ovariectomy. Rats were sacrificed at 12 weeks post-surgery, and the lumbar vertebrae (L3-L6) were collected. Micro-CT scans showed that rats in the three experimental groups-particularly the OVX rats-had fewer trabeculae and trabecular connections than rats in the CNT group. BMD was significantly lower in rats in the OVX, RESM, and BTX groups than in the CNT group (p < 0.01). Vertebral compression testing revealed significantly lower maximum load, energy absorption, maximum stress, and elastic modulus values in the three experimental groups compared with the CNT group (p < 0.01); these parameters were lowest in the OVX group (p < 0.05). Our results demonstrate that local BTX injection causes sufficient muscle atrophy and dysfunction to result in local lumbar vertebral bone loss and quality deterioration in a model of paravertebral muscle atrophy. Clinical Significance: The muscular tissues surrounding the lumbar vertebrae should be preserved during clinical surgery to avoid loss of bone quality and mass in the adjacent bone. Maintaining paravertebral muscle strength is an important consideration for patients with early osteoporosis. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2664-2670, 2018.

Overexpression of DNMT1 leads to hypermethylation of H19 promoter and inhibition of Erk signaling pathway in disuse osteoporosis

Disuse osteoporosis (DOP) is a common complication of the lack of mechanical loading. The precise mechanism underlying DOP remains unknown, although epigenetic modifications may be a major cause. Recently, cumulative research has revealed that DNA methyltransferase (DNMT) proteins can catalyze the conversion of cytosine to 5-methylcytosine (5mC), altering the epigenetic state of DNA. Here, we report that DNMT1 expression and lncRNA-H19 methylation are upregulated in the femoral tissues of DOP rats, accompanied with inhibited Erk signaling pathway. Overexpression of DNMT1 in UMR-106 cells mimics 5mC enrichment in the H19 promoter, inhibition of Erk signaling and impairment of osteogenesis, which can be rescued by 5'-aza-deoxycytidine (5'-Aza) treatment. Moreover, local intramedullary injection of Dnmt1 siRNA (siDNMT1) in Sprague-Dawley (SD) rats abrogated disuse lncRNA-H19 (H19) downregulation, Erk signaling inhibition, histopathological changes, and bone microstructure declines in the distal femur in vivo. Therefore, our data identify for the first time a new signaling cascade in DOP: mechanical unloading causes upregulation of DNMT1 and hypermethylation of H19 promoter, which subsequently leads to downregulation of lncRNA-H19 and inhibition of the ERK signaling, suggesting a new potential therapeutic target.

The bone remodelling cycle

The bone remodelling cycle replaces old and damaged bone and is a highly regulated, lifelong process essential for preserving bone integrity and maintaining mineral homeostasis. During the bone remodelling cycle, osteoclastic resorption is tightly coupled to osteoblastic bone formation. The remodelling cycle occurs within the basic multicellular unit and comprises five co-ordinated steps; activation, resorption, reversal, formation and termination. These steps occur simultaneously but asynchronously at multiple different locations within the skeleton. Study of rare human bone disease and animal models have helped to elucidate the cellular and molecular mechanisms that regulate the bone remodelling cycle. The key signalling pathways controlling osteoclastic bone resorption and osteoblastic bone formation are receptor activator of nuclear factor-κB (RANK)/RANK ligand/osteoprotegerin and canonical Wnt signalling. Cytokines, growth factors and prostaglandins act as paracrine regulators of the cycle, whereas endocrine regulators include parathyroid hormone, vitamin D, calcitonin, growth hormone, glucocorticoids, sex hormones, and thyroid hormone. Disruption of the bone remodelling cycle and any resulting imbalance between bone resorption and formation leads to metabolic bone disease, most commonly osteoporosis. The advances in understanding the cellular and molecular mechanisms underlying bone remodelling have also provided targets for pharmacological interventions which include antiresorptive and anabolic therapies. This review will describe the remodelling process and its regulation, discuss osteoporosis and summarize the commonest pharmacological interventions used in its management.