Prostaglandins in bone: bad cop, good cop?

Mechanosignaling in Osteoporosis: When Cells Feel the Force

Bone is a highly mechanosensitive tissue, where mechanical signaling plays a central role in maintaining skeletal homeostasis. Mechanotransduction regulates the balance between bone formation and resorption through coordinated interactions among bone cells. Key mechanosensing structures-including the extracellular/pericellular matrix (ECM/PCM), integrins, ion channels, connexins, and primary cilia, translate mechanical cues into biochemical signals that drive bone adaptation. Disruptions in mechanotransduction are increasingly recognized as an important factor in osteoporosis. Under pathological conditions, impaired mechanical signaling reduces bone formation and accelerates bone resorption, leading to skeletal fragility. Defects in mechanotransduction disrupt key pathways involved in bone metabolism, further exacerbating bone loss. Therefore, targeting mechanotransduction presents a promising pharmacological strategy for osteoporosis treatment. Recent advances have focused on developing drugs that enhance bone mechanosensitivity by modulating key mechanotransduction pathways, including integrins, ion channels, connexins, and Wnt signaling. A deeper understanding of mechanosignaling mechanisms may pave the way for novel therapeutic approaches aimed at restoring bone mass, mechanical integrity, and mechanosensitive bone adaptation.

Bone healing response to systemic bisphosphonate-prostaglandin E2 receptor 4 agonist treatment in female rats with a critical-size femoral segmental defect

Despite the wide body of research into prevention and treatment of nonunion, current bone fracture therapies remain suboptimal in their efficacy. Previous animal studies show that MES-1022, a bone-targeted prodrug that activates the prostaglandin E2 receptor EP4, stimulates bone healing when applied locally in uneventful defects. Here we investigated the healing capacity of systemically administered MES-1022 in a rat femoral critical size segmental defect. Ten-week-old female Sprague-Dawley rats (n = 8/group) underwent a 5 mm osteotomy of the left femoral midshaft, stabilized by a unilateral external fixator. Rats received weekly subcutaneous injections of MES-1022 at 5 mg/kg (MES1022-Hi), 1.7 mg/kg (MES1022-Lo), or Vehicle without a defect site scaffold. Serum bone markers and open field activity were measured pre-osteotomy and throughout the study. Rats were sacrificed after 12 weeks and osteotomized femora were imaged via microcomputed tomography (microCT) followed by histology and immunohistochemistry to assess healing. Complete bridging of the defect occurred in one rat from the MES1022-Hi group and zero from MES1022-Lo and Vehicle groups. However, healing outcomes in both MES-1022 groups for bone volume fraction, bone volume, bridging score, callus tissue composition, callus blood vessel density, P1NP levels, TRAcP-5b levels, and physical activity did not differ from Vehicle. Fracture callus osteoclast density and spleen weight were increased in MES1022-Hi rats relative to Vehicle. Overall, systemic administration of MES-1022 alone may not suffice for treatment of large segmental bone defects. Additional studies are needed to determine whether systemic MES-1022 is a useful therapeutic in conjunction with local scaffolds like bone graft substitutes.

Periodontal response to nonsurgical accelerated orthodontic tooth movement

Tooth movement is a complex process involving the vascularization of the tissues, remodeling of the bone cells, and periodontal ligament fibroblasts under the hormonal and neuronal regulation mechanisms in response to mechanical force application. Therefore, it will inevitably impact periodontal tissues. Prolonged treatment can lead to adverse effects on teeth and periodontal tissues, prompting the development of various methods to reduce the length of orthodontic treatment. These methods are surgical or nonsurgical interventions applied simultaneously within the orthodontic treatment. The main target of nonsurgical approaches is modulating the response of the periodontal tissues to the orthodontic force. They stimulate osteoclasts and osteoclastic bone resorption in a controlled manner to facilitate tooth movement. Among various nonsurgical methods, the most promising clinical results have been achieved with photobiomodulation (PBM) therapy. Clinical data on electric/magnetic stimulation, pharmacologic administrations, and vibration forces indicate the need for further studies to improve their efficiency. This growing field will lead to a paradigm shift as we understand the biological response to these approaches and their adoption in clinical practice. This review will specifically focus on the impact of nonsurgical methods on periodontal tissues, providing a comprehensive understanding of this significant and understudied aspect of orthodontic care.

Application of Mendelian randomization analysis to explore causal associations of aspirin use with bone mineral density and risk of fracture

OBJECTIVE

Previous observational studies on the association between aspirin use, bone mineral density (BMD), and fracture risk have yielded controversial results. This study explored the causal relationship between aspirin use, BMD, and fracture risk using Mendelian randomization (MR).

METHODS

Summary data for aspirin use and BMD of five different body parts (femoral neck, lumbar spine, forearm, heel, and ultra distal forearm) and fractures were obtained from the integrative epidemiology unit open genome-wide association studies database for bidirectional MR analysis. An appropriate model was chosen based on Cochran's Q test, with inverse variance-weighted as the primary method for MR analysis, supplemented by the weighted-median and MR-Egger methods. MR-Egger and MR-PRESSO were used to test for horizontal pleiotropy and exclude significant outliers that could bias the results. Various sensitivity analyses, including leave-one-out analysis, were conducted to ensure the robustness of the findings.

RESULTS

Aspirin use significantly increased lumbar spine BMD (odds ratio [OR] = 4.660; 95% confidence interval [CI]: 1.365-15.906; P = 0.014). No significant causal association was found between aspirin use and fracture risk (beta = 59.951; 95% CI: -265.189-385.091; P = 0.718). No significant reverse causality was observed.

CONCLUSION

This study indicates that aspirin use does not significantly affect fracture risk but has a significant protective effect on lumbar spine BMD, revealing a potential benefit of aspirin against osteoporosis.

FXR Activation Accelerates Early Phase of Osteoblast Differentiation Through COX-2-PGE2-EP4 Axis in BMP-2-Induced Mouse Mesenchymal Stem Cells

Farnesoid X receptor (FXR), a nuclear receptor, is expressed in calvaria and bone marrow stromal cells and plays a role in bone homeostasis. However, the mechanism of FXR-activated osteoblast differentiation remains unclear. In this study, we investigated the regulatory mechanism underlying FXR-activated osteoblast differentiation using bone morphogenetic protein-2 (BMP-2)-induced mouse ST-2 mesenchymal stem cells. We also synthesized a novel FXR agonist, FLG390, and compared its biological effects in osteoblast differentiation with a known FXR agonist, chenodeoxycholic acid (CDCA). As an FXR agonist, FLG390 accelerated osteoblast differentiation to a comparable extent with CDCA, enhancing alkaline phosphatase (ALP) activity and the expression of osteoblast differentiated-related genes such as ALP, collagen type 1 α1 chain (COL1A1), and runt-related transcription factor 2 (RUNX2). FXR activation elevated the expression of cyclooxygenase (COX)-2 and the production of prostaglandin (PG) E2 in the early phase of osteoblast differentiation. A selective COX-2 inhibitor and an antagonist of EP4 receptors, one of PGE2 receptors, partially suppressed FXR-activated osteoblast differentiation. Moreover, treatment with either inhibitor during the first 6 h after initiating osteoblast differentiation repressed FXR-activated osteoblast differentiation to the same extent as did the treatment for 6 d. Therefore, a novel FXR agonist, FLG390, exhibited potency comparable to CDCA. FXR activation promoted the early phase of osteoblast differentiation via the COX-2-PGE2-EP4 axis, representing a potential target for control of bone metabolism.

Sensory nerve EP4 facilitates heterotopic ossification by regulating angiogenesis-coupled bone formation

Objective

Heterotopic ossification (HO) refers to the abnormal development of bone in soft tissue rather than within bone itself. Previous research has shown that sensory nerve prostaglandin E2 receptor 4 (EP4) signaling not only governs pain perception but also influences bone formation. However, the relationship between sensory nerve EP4 and the pathogenesis of HO in the Achilles tendon remains unclear. This study aims to investigate this relationship and the underlying mechanisms.

Methods

We generated sensory nerve EP4-specific knockout mice, with the genotype of Avil-CreEP4fl/fl, was propagated. Transcriptome sequencing and bioinformatics analysis techniques were used to identify the potential molecular pathways involving with sensory nerve EP4. Additionally, a neurectomy mouse model was created by transecting the sciatic nerve transection, to examine the effects and mechanisms of peripheral innervation on HO in vivo. Micro-CT, immunofluorescence (IF), Hematoxylin and Eosin (H&E) Staining, Safranin O-Fast Green staining and western blotting were used to analyze changes in cellular and tissue components.

Results

We here observed an increase in sensory nerve EP4 and H-type vessels during the pathogenesis of HO in both human subjects and mice. Proximal neurectomy through sciatic nerve transection or the targeted knockout of EP4 in sensory nerves hindered angiogenesis-dependent bone formation and the development of HO at the traumatic site of the Achilles tendon. Furthermore, we identified the Efnb2 (Ephrin-B2)/Dll4 (Delta-like ligand 4) axis as a potential downstream element influenced by sensory nerve EP4 in the regulation of HO. Notably, administration of an EP4 inhibitor demonstrated the ability to alleviate HO. Based on these findings, sensory nerve EP4 emerges as an innovative and promising approach for managing HO.

Conclusion

Our findings demonstrate that the sensory nerve EP4 promotes ectopic bone formation by modulating angiogenesis-associated osteogenesis during HO.

The translational potential of this article

Our results provide a mechanistic rationale for targeting sensory nerve EP4 as a promising candidate for HO therapy.

Differential effects of clopidogrel and/or aspirin on the healing of tooth extraction wound bone tissue

Introduction

A multitude of variables influence the healing of tooth extraction wounds, and delayed or non-healing extraction wounds might complicate later prosthodontic therapy. In this research, we analyzed the effects of systemic clopidogrel and aspirin alone or in combination on the healing of tooth extraction wounds in mice in order to provide experimental evidence for the healing of extraction wounds in patients who are clinically treated with the two medicines.

Methods

7-week-old ICR mice were randomly divided into four groups: control group (CON), clopidogrel group (CLOP), aspirin group (ASP), and clopidogrel combined with aspirin group (CLOP + ASP); left upper first molar was extracted, after which mice in 1 week of adaptive feeding, CLOP/ASP/CLOP + ASP groups were respectively administered with clopidogrel (10 mg/kg/d), aspirin (15 mg/kg/d), clopidogrel (10 mg/kg/d)+aspirin (15 mg/kg/d), and the control group was given an equal amount of 0.9% saline by gavage. Mice in each group were euthanized at 14 and 28 days postoperatively, and the maxilla was extracted. The tissues in the extraction sockets were examined using MicroCT and sectioned for HE staining, Masson staining, and TRAP staining, and immunohistochemistry staining (for TRAP, RANKL and osteoprotegerin).

Results

MicroCT analysis showed that at day 14, BS/BV was significantly lower in CLOP and CLOP + ASP groups compared to control and ASP groups, while BV/TV, Tb.Th was significantly higher. At day 28, BV/TV was significantly higher in the CLOP + ASP group compared to the CLOP group, with p < 0.05 for all results. HE staining and Masson trichrome staining findings revealed that at day 28, the mesenchyme in the bone was further decreased compared to that at day 14, accompanied with tightly arranged and interconnected bone trabeculae. In the quantitative analysis of Masson, the fraction of newly formed collagen was significantly higher in the CLOP group in comparison with that in the CON group (p < 0.05). At day 14, the ASP group had substantially more TRAP-positive cells than the CLOP and CLOP + ASP groups (p < 0.05). In immunohistochemical staining, RANKL expression was found to be significantly higher in the ASP group than those in the other three groups at day 28 (p < 0.05); OPG expression was significantly higher in the CLOP group and the CLOP + ASP group compared with that at day 14, and was higher than that in the ASP group at day 14 and day 28. OPG/RANKL was significantly higher in the CLOP and the CLOP + ASP groups than in the ASP group (p < 0.05).

Conclusion

Clopidogrel alone promotes osteogenesis in the extraction wound, whereas aspirin alone inhibits alveolar bone healing. When the two drugs were combined, the healing effect of the extraction wound was more similar to that of the clopidogrel alone group. These results indicated that clopidogrel could promote the healing of the tooth extraction wound, and neutralize the adverse effect of ASP on osteogenesis when the two drugs were used in combination.

[Local administration of prostaglandins to accelerate the orthodontic movement. A literature review]

Objective

The search to optimize tooth movement and reduce treatment time is of great interest to the orthodontist, as it involves innovating new materials and procedures to achieve the treatment objectives in the short term. The administration of prostaglandins has been studied, and their effect on accelerating tooth movement when administered locally has been proven. The objective of this study was to evaluate the latest achievements concerning the effects of local administration of prostaglandins to accelerate tooth movement for orthodontic purposes.

Methodology

A search was conducted in four databases (PubMed, SciELO, Cochrane, Google Scholar) and three specialized journals (AJODO, Angle Orthodontics, Journal of Clinical Orthodontics) until August 2023. The methodological quality of the studies was analyzed using the PRISMA checklist.

Results

The study had 14 articles. Local administration of prostaglandins accelerates the speed of tooth movement and increases the number of osteoclasts. Evidence of root resorption has been reported concerning high doses of prostaglandins via the submucosal route and a reduction in root resorption by administering prostaglandins with calcium gluconate. Local administration of prostaglandins via the submucosal route produces mild to moderate pain, and inoculation with a local anesthetic is recommended. However, oral administration of the analogous compound Misoprostol does not produce pain or evidence of root resorption.

Conclusions

Sufficient scientific evidence has not been found to support the local administration of prostaglandins as a safe method to accelerate tooth movement in humans.

Magnesium malate-modified calcium phosphate bone cement promotes the repair of vertebral bone defects in minipigs via regulating CGRP

Active artificial bone substitutes are crucial in bone repair and reconstruction. Calcium phosphate bone cement (CPC) is known for its biocompatibility, degradability, and ability to fill various shaped bone defects. However, its low osteoinductive capacity limits bone regeneration applications. Effectively integrating osteoinductive magnesium ions with CPC remains a challenge. Herein, we developed magnesium malate-modified CPC (MCPC). Incorporating 5% magnesium malate significantly enhances the compressive strength of CPC to (6.18 ± 0.49) MPa, reduces setting time and improves disintegration resistance. In vitro, MCPC steadily releases magnesium ions, promoting the proliferation of MC3T3-E1 cells without causing significant apoptosis, proving its biocompatibility. Molecularly, magnesium malate prompts macrophages to release prostaglandin E2 (PGE2) and synergistically stimulates dorsal root ganglion (DRG) neurons to synthesize and release calcitonin gene-related peptide (CGRP). The CGRP released by DRG neurons enhances the expression of the key osteogenic transcription factor Runt-related transcription factor-2 (RUNX2) in MC3T3-E1 cells, promoting osteogenesis. In vivo experiments using minipig vertebral bone defect model showed MCPC significantly increases the bone volume fraction, bone density, new bone formation, and proportion of mature bone in the defect area compared to CPC. Additionally, MCPC group exhibited significantly higher levels of osteogenesis and angiogenesis markers compared to CPC group, with no inflammation or necrosis observed in the hearts, livers, or kidneys, indicating its good biocompatibility. In conclusion, MCPC participates in the repair of bone defects in the complex post-fracture microenvironment through interactions among macrophages, DRG neurons, and osteoblasts. This demonstrates its significant potential for clinical application in bone defect repair.

A narrative review of the effects of vitamin D3 on orthodontic tooth movement: Focus on molecular and cellular mechanisms

Orthodontic tooth movement (OTM) is a critical process in dental alignment, driven by the application of calibrated orthodontic forces. This study delves into the intricate molecular and cellular mechanisms by which vitamin D3 influences OTM. Vitamin D3 is identified as a critical regulator in bone metabolism, enhancing osteoblast activity and bone formation while also modulating osteoclast quantity and RANKL expression, essential for the remodeling of the alveolar bone. The precise mechanisms through which vitamin D3 facilitates these processes are explored, highlighting its potential in accelerating bone remodeling and, consequently, tooth alignment. This comprehensive review underscores vitamin D3's anabolic impact on bone metabolism and its pivotal role in the synthesis and mineralization processes governed by osteoblasts. The findings illuminate vitamin D3's promise in augmenting orthodontic therapy, suggesting its utility in improving treatment efficiency and reducing duration. However, the need for further research into the optimal application of vitamin D3 in orthodontics is emphasized, particularly concerning dosage, timing, and delivery methods.

Skeletal interoception in osteoarthritis

The interoception maintains proper physiological conditions and metabolic homeostasis by releasing regulatory signals after perceving changes in the internal state of the organism. Among its various forms, skeletal interoception specifically regulates the metabolic homeostasis of bones. Osteoarthritis (OA) is a complex joint disorder involving cartilage, subchondral bone, and synovium. The subchondral bone undergoes continuous remodeling to adapt to dynamic joint loads. Recent findings highlight that skeletal interoception mediated by aberrant mechanical loads contributes to pathological remodeling of the subchondral bone, resulting in subchondral bone sclerosis in OA. The skeletal interoception is also a potential mechanism for chronic synovial inflammation in OA. In this review, we offer a general overview of interoception, specifically skeletal interoception, subchondral bone microenviroment and the aberrant subchondral remedeling. We also discuss the role of skeletal interoception in abnormal subchondral bone remodeling and synovial inflammation in OA, as well as the potential prospects and challenges in exploring novel OA therapies that target skeletal interoception.

Sphingolipid-Induced Bone Regulation and Its Emerging Role in Dysfunction Due to Disease and Infection

The human skeleton is a metabolically active system that is constantly regenerating via the tightly regulated and highly coordinated processes of bone resorption and formation. Emerging evidence reveals fascinating new insights into the role of sphingolipids, including sphingomyelin, sphingosine, ceramide, and sphingosine-1-phosphate, in bone homeostasis. Sphingolipids are a major class of highly bioactive lipids able to activate distinct protein targets including, lipases, phosphatases, and kinases, thereby conferring distinct cellular functions beyond energy metabolism. Lipids are known to contribute to the progression of chronic inflammation, and notably, an increase in bone marrow adiposity parallel to elevated bone loss is observed in most pathological bone conditions, including aging, rheumatoid arthritis, osteoarthritis, and osteomyelitis. Of the numerous classes of lipids that form, sphingolipids are considered among the most deleterious. This review highlights the important primary role of sphingolipids in bone homeostasis and how dysregulation of these bioactive metabolites appears central to many chronic bone-related diseases. Further, their contribution to the invasion, virulence, and colonization of both viral and bacterial host cell infections is also discussed. Many unmet clinical needs remain, and data to date suggest the future use of sphingolipid-targeted therapy to regulate bone dysfunction due to a variety of diseases or infection are highly promising. However, deciphering the biochemical and molecular mechanisms of this diverse and extremely complex sphingolipidome, both in terms of bone health and disease, is considered the next frontier in the field.

The combined use of anti-peptic agents is associated with an increased risk of osteoporotic fracture: a nationwide case-control study

BACKGROUND/AIMS

Long-term use of acid suppressants such as proton pump inhibitors (PPIs) and histamine 2 receptor antagonist (H2RA) has been associated with the risk of osteoporotic fracture. Acid suppressants and muco-protective agents (MPAs) are often used together as anti-ulcer agents. We evaluated the association between the risk of osteoporotic fracture and the combined use of these anti-peptic agents.

METHODS

A population-based case-control study was conducted by analyzing the Korean National Health Insurance Data from 2014 to 2020. Patients who had been prescribed anti-peptic agents, such as PPI, H2RA, or MPA, were included. Considering the incidence of osteoporotic fractures, the case group (n = 14,704) and control group (n = 58,816) were classified by 1:4 matching based on age and sex.

RESULTS

The use of all types of anti-peptic agents was associated with an increased risk of osteoporotic fractures (PPI: hazard osteoratio [HR], 1.31; H2RA: HR, 1.44; and MPA: HR, 1.33; all p < 0.001). Compared to PPI alone, the combined use of "PPI and H2RA" (HR, 1.58; p = 0.010) as well as "PPI, H2RA, and MPA" (HR, 1.71; p = 0.001) was associated with an increased risk of osteoporotic fracture. However, compared with PPI alone, "MPA and PPI or H2RA" was not associated with an increased risk of osteoporotic fracture.

CONCLUSION

This study found that the combined use of "PPI and H2RA" was associated with a higher risk of osteoporotic fractures. In cases where deemed necessary, the physicians may initially consider prescribing the combination use of MPA.

Crosstalk Between the Neuroendocrine System and Bone Homeostasis

The homeostasis of bone microenvironment is the foundation of bone health and comprises 2 concerted events: bone formation by osteoblasts and bone resorption by osteoclasts. In the early 21st century, leptin, an adipocytes-derived hormone, was found to affect bone homeostasis through hypothalamic relay and the sympathetic nervous system, involving neurotransmitters like serotonin and norepinephrine. This discovery has provided a new perspective regarding the synergistic effects of endocrine and nervous systems on skeletal homeostasis. Since then, more studies have been conducted, gradually uncovering the complex neuroendocrine regulation underlying bone homeostasis. Intriguingly, bone is also considered as an endocrine organ that can produce regulatory factors that in turn exert effects on neuroendocrine activities. After decades of exploration into bone regulation mechanisms, separate bioactive factors have been extensively investigated, whereas few studies have systematically shown a global view of bone homeostasis regulation. Therefore, we summarized the previously studied regulatory patterns from the nervous system and endocrine system to bone. This review will provide readers with a panoramic view of the intimate relationship between the neuroendocrine system and bone, compensating for the current understanding of the regulation patterns of bone homeostasis, and probably developing new therapeutic strategies for its related disorders.

Osteoimmunology: Interactions With the Immune System in Spinal Fusion

Spinal fusion is important for the clinical success of patients undergoing surgery, and the immune system plays an increasingly recognized role. Osteoimmunology is the study of the interactions between the immune system and bone. Inflammation impacts the osteogenic, osteoconductive, and osteoinductive properties of bone grafts and substitutes and ultimately influences the success of spinal fusion. Macrophages have emerged as important cells for coordinating the immune response following spinal fusion surgery, and macrophage-derived cytokines impact each phase of bone graft healing. This review explores the cellular and molecular immune processes that regulate bone homeostasis and healing during spinal fusion.

Biomechanics in the onset and severity of spondyloarthritis: a force to be reckoned with

Increasing evidence suggests that there is a pivotal role for physical force (mechanotransduction) in the initiation and/or the perpetuation of spondyloarthritis; the review contained herein examines that evidence. Furthermore, we know that damage and inflammation can limit spinal mobility, but is there a cycle created by altered spinal mobility leading to additional damage and inflammation?Over the past several years, mechanotransduction, the mechanism by which mechanical perturbation influences gene expression and cellular behaviour, has recently gained popularity because of emerging data from both animal models and human studies of the pathogenesis of ankylosing spondylitis (AS). In this review, we provide evidence towards an appreciation of the unsolved paradigm of how biomechanical forces may play a role in the initiation and propagation of AS.

Do Clinical Parameters Reflect Local Bone Metabolism in Heterotopic Ossification After Septic or Aseptic THA?

BACKGROUND

Heterotopic ossification (HO) is a common complication after THA. Although current research primarily focuses on treatment and prevention, little is known about the local bone metabolism of HO and clinical contributing factors.

QUESTIONS/PURPOSES

We aimed to assess bone remodeling processes in HO using histomorphometry, focusing on the effects of inflammation and prior NSAID treatment. Specifically, we asked: (1) Are HO specimens taken from patients with periprosthetic joint infection (PJI) more likely to exhibit active bone modeling and remodeling than specimens taken at the time of revision from patients without infection? (2) Do clinical or inflammatory serum and synovial parameters reflect the microstructure of and remodeling in both HO entities? (3) Is NSAID treatment before revision surgery associated with altered local bone mineralization or remodeling properties?

METHODS

Between June 2021 and May 2022, we screened 395 patients undergoing revision THA at two tertiary centers in Germany. Of those, we considered all patients with radiographic HO as potentially eligible. Based on that, 21% (83 of 395) were eligible; a further 43 were excluded because of an inability to remove the implant intraoperatively (16 patients), insufficient material (11), comorbidities with a major effect on bone metabolism (10), or bone-specific drugs (six), leaving 10% (40) for analysis in this retrospective, comparative study. HO specimens were collected during aseptic (25 patients: 18 male, seven female, mean age 70 ± 11 years, mean BMI 29 ± 4 kg/m 2 ) and septic (15 patients: 11 male, four female, mean age 69 ± 9 years, mean BMI 32 ± 9 kg/m 2 ) revision THA at a mean of 6 ± 7 years after primary implantation and a mean age of 70 ± 9 years at revision. Septic origin (PJI) was diagnosed based on the 2018 International Consensus Meeting criteria, through a preoperative assessment of serum and synovial parameters. To specify the local bone microstructure, ossification, and cellular bone turnover, we analyzed HO specimens using micro-CT and histomorphometry on undecalcified sections. Data were compared with those of controls, taken from femoral neck trabecular bone (10 patients: five female, five male, mean age 75 ± 6 years, mean BMI 28 ± 4 kg/m 2 ) and osteophytes (10 patients: five female, five male, mean age 70 ± 10 years, mean BMI 29 ± 7 kg/m 2 ). The time between primary implantation and revision (time in situ), HO severity based on the Brooker classification, and serum and synovial markers were correlated with HO microstructure and parameters of cellular bone turnover. In a subgroup of specimens of patients with NSAID treatment before revision, osteoid and bone turnover indices were evaluated and compared a matched cohort of specimens from patients without prior NSAID treatment.

RESULTS

Patients with aseptic and septic HO presented with a higher bone volume (BV/TV; aseptic: 0.41 ± 0.15, mean difference 0.20 [95% CI 0.07 to 0.32]; septic: 0.43 ± 0.15, mean difference 0.22 [95% CI 0.08 to 0.36]; femoral neck: 0.21 ± 0.04; both p < 0.001), lower bone mineral density (aseptic: 809 ± 66 mg HA/cm 3 , mean difference -91 mg HA/cm 3 [95% CI -144 to -38]; septic: 789 ± 44 mg HA/cm 3 , mean difference -111 mg HA/cm 3 [95% CI -169 to -53]; femoral neck: 899 ± 20 mg HA/cm 3 ; both p < 0.001), and ongoing bone modeling with endochondral ossification and a higher proportion of woven, immature bone (aseptic: 25% ± 17%, mean difference 25% [95% CI 9% to 41%]; septic: 37% ± 23%, mean difference 36% [95% CI 19% to 54%]; femoral neck: 0.4% ± 0.5%; both p < 0.001) compared with femoral neck specimens. Moreover, bone surfaces were characterized by increased osteoblast and osteoclast indices in both aseptic and septic HO, although a higher density of osteocytes was detected exclusively in septic HO (aseptic: 158 ± 56 1/mm 2 versus septic: 272 ± 48 1/mm 2 , mean difference 114 1/mm 2 [95% CI 65 to 162]; p < 0.001). Compared with osteophytes, microstructure and turnover indices were largely similar in HO. The Brooker class was not associated with any local bone metabolism parameters. The time in situ was negatively associated with bone turnover in aseptic HO specimens (osteoblast surface per bone surface: r = -0.46; p = 0.01; osteoclast surface per bone surface: r = -0.56; p = 0.003). Serum or synovial inflammatory markers were not correlated with local bone turnover in septic HO. Specimens of patients with NSAID treatment before revision surgery had a higher osteoid thickness (10.1 ± 2.1 µm versus 5.5 ± 2.6 µm, mean difference -4.7 µm [95% CI -7.4 to -2.0]; p = 0.001), but there was no difference in other osteoid, structural, or cellular parameters.

CONCLUSION

Aseptic and septic HO share phenotypic characteristics in terms of the sustained increase in bone metabolism, although differences in osteocyte and adipocyte numbers suggest distinct homeostatic mechanisms. These results suggest persistent bone modeling or remodeling, with osteoblast and osteoclast indices showing a moderate decline with the time in situ in aseptic HO. Future studies should use longitudinal study designs to correlate our findings with clinical outcomes (such as HO growth or recurrence). In addition, the molecular mechanisms of bone cell involvement during HO formation and growth should be further investigated, which may allow specific therapeutic and preventive interventions.

CLINICAL RELEVANCE

To our knowledge, our study is the first to systematically investigate histomorphometric bone metabolism parameters in patients with HO after THA, providing a clinical reference for evaluating modeling and remodeling activity. Routine clinical, serum, and synovial markers are not useful for inferring local bone metabolism.

Untargeted plasma metabolome identifies biomarkers in patients with extracranial arteriovenous malformations

Objective: This study aimed to investigate the plasma metabolic profile of patients with extracranial arteriovenous malformations (AVM). Method: Plasma samples were collected from 32 AVM patients and 30 healthy controls (HC). Ultra-high performance liquid chromatography-mass spectrometry (UHPLC-MS) was employed to analyze the metabolic profiles of both groups. Metabolic pathway enrichment analysis was performed through Kyoto Encyclopedia of Genes and Genomes (KEGG) database and MetaboAnalyst. Additionally, machine learning algorithms such as Least Absolute Shrinkage and Selection Operator (LASSO) and random forest (RF) were conducted to screen characteristic metabolites. The effectiveness of the serum biomarkers for AVM was evaluated using a receiver-operating characteristics (ROC) curve. Result: In total, 184 differential metabolites were screened in this study, with 110 metabolites in positive ion mode and 74 metabolites in negative mode. Lipids and lipid-like molecules were the predominant metabolites detected in both positive and negative ion modes. Several significant metabolic pathways were enriched in AVMs, including lipid metabolism, amino acid metabolism, carbohydrate metabolism, and protein translation. Through machine learning algorithms, nine metabolites were identify as characteristic metabolites, including hydroxy-proline, L-2-Amino-4-methylenepentanedioic acid, piperettine, 20-hydroxy-PGF2a, 2,2,4,4-tetramethyl-6-(1-oxobutyl)-1,3,5-cyclohexanetrione, DL-tryptophan, 9-oxoODE, alpha-Linolenic acid, and dihydrojasmonic acid. Conclusion: Patients with extracranial AVMs exhibited significantly altered metabolic patterns compared to healthy controls, which could be identified using plasma metabolomics. These findings suggest that metabolomic profiling can aid in the understanding of AVM pathophysiology and potentially inform clinical diagnosis and treatment.

Primary hypertrophic osteoarthropathy: genetics, clinical features and management

Primary hypertrophic osteoarthropathy (PHO) is a genetic disorder mainly characterized by clubbing fingers, pachydermia and periostosis. Mutations in the HPGD or SLCO2A1 gene lead to impaired prostaglandin E2 (PGE2) degradation, thus elevating PGE2 levels. The identification of the causative genes has provided a better understanding of the underlying mechanisms. PHO can be divided into three subtypes according to its pathogenic gene and inheritance patterns. The onset age, sex ratio and clinical features differ among subtypes. The synthesis and signaling pathways of PGE2 are outlined in this review. Cyclooxygenase-2 (COX-2) is the key enzyme that acts as the rate-limiting step for prostaglandin production, thus COX-2 inhibitors have been used to treat this disease. Although this treatment showed effective results, it has side effects that restrain its use. Here, we reviewed the genetics, clinical features, differential diagnosis and current treatment options of PHO according to our many years of clinical research on the disease. We also discussed probable treatment that may be an option in the future.

Nonsteroidal Anti-inflammatory Drugs in the Acute Post-operative Period Are Associated With an Increased Incidence of Pseudarthrosis, Hardware Failure, and Revision Surgery Following Single-level Spinal Fusion

STUDY DESIGN

Retrospective study.

SUMMARY OF BACKGROUND DATA

Research has shown that the use of NSAIDs and COX-2 inhibitors increases the risk of pseudoarthrosis following spinal fusion surgery. Pseudoarthrosis can lead to complications such as chronic pain and the need for additional surgeries.

OBJECTIVE

The purpose of this study was to examine the relationship between NSAID and COX-2 inhibitor use and pseudarthrosis, hardware complications, and revision surgeries in patients undergoing posterior spinal instrumentation and fusion.

METHODS

We queried the PearlDiver database using CPT and ICD-10 codes to identify patients between the ages of 50 and 85 who underwent posterior spinal instrumentation between 2016 and 2019 and experienced pseudarthrosis, hardware failure, or revision surgery. Information regarding age, Charlson Comorbidity Index, tobacco use, osteoporosis, and obesity were extracted from the database along with COX-2 or NSAID use during the first 6-week post-surgery period. Logistic regression was used to identify associations while adjusting for confounders.

RESULTS

There were 178,758 patients included in the cohort; 9,586 experienced pseudarthrosis (5.36%), 2828 (1.58%) experienced hardware failure, and 10,457 (5.85%) patients underwent revision fusion surgery. Of these patients 23,602 (13.2%) filled NSAID and 5278 (2.95%) filled COX-2 prescriptions. A significantly higher proportion of patients using NSAIDs experienced pseudarthrosis, hardware failure, and revision surgery compared to patients not taking NSAIDs. COX-2 inhibitors were also associated with a significantly higher rate of pseudarthrosis, hardware failure, and revision surgery. Postoperative ketorolac use was not associated with these complications. Regression models demonstrated that both NSAIDs and COX-2 inhibitors were associated with statistically higher pseudarthrosis, hardware failure, and revision surgery rates.

CONCLUSIONS

Both NSAID and COX-2 inhibitor use in the early post-surgical period may be associated with increased rates of pseudarthrosis, hardware failure, and revision surgery in patients undergoing posterior spinal instrumentation and fusion.

Pathophysiological mechanism of acute bone loss after fracture

BACKGROUND

Acute bone loss after fracture is associated with various effects on the complete recovery process and a risk of secondary fractures among patients. Studies have reported similarities in pathophysiological mechanisms involved in acute bone loss after fractures and osteoporosis. However, given the silence nature of bone loss and bone metabolism complexities, the actual underlying pathophysiological mechanisms have yet to be fully elucidated.

AIM OF REVIEW

To elaborate the latest findings in basic research with a focus on acute bone loss after fracture. To briefly highlight potential therapeutic targets and current representative drugs. To arouse researchers' attention and discussion on acute bone loss after fracture.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Bone loss after fracture is associated with immobilization, mechanical unloading, blood supply damage, sympathetic nerve regulation, and crosstalk between musculoskeletals among other factors. Current treatment strategies rely on regulation of osteoblasts and osteoclasts, therefore, there is a need to elucidate on the underlying mechanisms of acute bone loss after fractures to inform the development of efficacious and safe drugs. In addition, attention should be paid towards ensuring long-term skeletal health.

Diclofenac, a NSAID, delays fracture healing in aged mice

Nonsteroidal anti-inflammatory drugs (NSAIDs), such as diclofenac, belong to the most prescribed analgesic medication after traumatic injuries. However, there is accumulating evidence that NSAIDs impair fracture healing. Because bone regeneration in aged patients is subject to significant changes in cell differentiation and proliferation as well as a markedly altered pharmacological action of drugs, we herein analyzed the effects of diclofenac on bone healing in aged mice using a stable closed femoral facture model. Thirty-three mice (male n = 14, female n = 19) received a daily intraperitoneal injection of diclofenac (5 mg/kg body weight). Vehicle-treated mice (n = 29; male n = 13, female n = 16) served as controls. Fractured mice femora were analyzed by means of X-ray, biomechanics, micro computed tomography (μCT), histology and Western blotting. Biomechanical analyses revealed a significantly reduced bending stiffness in diclofenac-treated animals at 5 weeks after fracture when compared to vehicle-treated controls. Moreover, the callus tissue in diclofenac-treated aged animals exhibited a significantly reduced amount of bone tissue and higher amounts of fibrous tissue. Further histological analyses demonstrated less lamellar bone after diclofenac treatment, indicating a delay in callus remodeling. This was associated with a decreased number of osteoclasts and an increased expression of osteoprotegerin (OPG) during the early phase of fracture healing. These findings indicate that diclofenac delays fracture healing in aged mice by affecting osteogenic growth factor expression and bone formation as well as osteoclast activity and callus remodeling.

β-TCP/S53P4 Scaffolds Obtained by Gel Casting: Synthesis, Properties, and Biomedical Applications

The objective of this study was to investigate the osteogenic and antimicrobial effect of bioactive glass S53P4 incorporated into β-tricalcium phosphate (β-TCP) scaffolds in vitro and the bone neoformation in vivo. β-TCP and β-TCP/S53P4 scaffolds were prepared by the gel casting method. Samples were morphologically and physically characterized through X-ray diffraction (XRD) and scanning electron microscope (SEM). In vitro tests were performed using MG63 cells. American Type Culture Collection reference strains were used to determine the scaffold's antimicrobial potential. Defects were created in the tibia of New Zealand rabbits and filled with experimental scaffolds. The incorporation of S53P4 bioglass promotes significant changes in the crystalline phases formed and in the morphology of the surface of the scaffolds. The β-TCP/S53P4 scaffolds did not demonstrate an in vitro cytotoxic effect, presented similar alkaline phosphatase activity, and induced a significantly higher protein amount when compared to β-TCP. The expression of Itg β1 in the β-TCP scaffold was higher than in the β-TCP/S53P4, and there was higher expression of Col-1 in the β-TCP/S53P4 group. Higher bone formation and antimicrobial activity were observed in the β-TCP/S53P4 group. The results confirm the osteogenic capacity of β-TCP ceramics and suggest that, after bioactive glass S53P4 incorporation, it can prevent microbial infections, demonstrating to be an excellent biomaterial for application in bone tissue engineering.

Bone and Cytokine Markers Associated With Bone Disease in Systemic Mastocytosis

BACKGROUND

Mastocytosis encompasses a heterogeneous group of diseases characterized by tissue accumulation of clonal mast cells, which frequently includes bone involvement. Several cytokines have been shown to play a role in the pathogenesis of bone mass loss in systemic mastocytosis (SM), but their role in SM-associated osteosclerosis remains unknown.

OBJECTIVE

To investigate the potential association between cytokine and bone remodeling markers with bone disease in SM, aiming at identifying biomarker profiles associated with bone loss and/or osteosclerosis.

METHODS

A total of 120 adult patients with SM, divided into 3 age and sex-matched groups according to their bone status were studied: (1) healthy bone (n = 46), (2) significant bone loss (n = 47), and (3) diffuse bone sclerosis (n = 27). Plasma levels of cytokines and serum baseline tryptase and bone turnover marker levels were measured at diagnosis.

RESULTS

Bone loss was associated with significantly higher levels of serum baseline tryptase (P = .01), IFN-γ (P = .05), IL-1β (P = .05), and IL-6 (P = .05) versus those found in patients with healthy bone. In contrast, patients with diffuse bone sclerosis showed significantly higher levels of serum baseline tryptase (P < .001), C-terminal telopeptide (P < .001), amino-terminal propeptide of type I procollagen (P < .001), osteocalcin (P < .001), bone alkaline phosphatase (P < .001), osteopontin (P < .01), and the C-C Motif Chemokine Ligand 5/RANTES chemokine (P = .01), together with lower IFN-γ (P = .03) and RANK-ligand (P = .04) plasma levels versus healthy bone cases.

CONCLUSIONS

SM with bone mass loss is associated with a proinflammatory cytokine profile in plasma, whereas diffuse bone sclerosis shows increased serum/plasma levels of biomarkers related to bone formation and turnover, in association with an immunosuppressive cytokine secretion profile.

Functional Role of Phospholipase D in Bone Metabolism

Phospholipase D (PLD) proteins are major enzymes that regulate various cellular functions, such as cell growth, cell migration, membrane trafficking, and cytoskeletal dynamics. As they are responsible for such important biological functions, PLD proteins have been considered promising therapeutic targets for various diseases, including cancer and vascular and neurological diseases. Intriguingly, emerging evidence indicates that PLD1 and PLD2, 2 major mammalian PLD isoenzymes, are the key regulators of bone remodeling; this suggests that these isozymes could be used as potential therapeutic targets for bone diseases, such as osteoporosis and rheumatoid arthritis. PLD1 or PLD2 deficiency in mice can lead to decreased bone mass and dysregulated bone homeostasis. Although both mutant mice exhibit similar skeletal phenotypes, PLD1 and PLD2 play distinct and nonredundant roles in bone cell function. This review summarizes the physiological roles of PLD1 and PLD2 in bone metabolism, focusing on recent findings of the biological functions and action mechanisms of PLD1 and PLD2 in bone cells.

Connexin 43 hemichannels and prostaglandin E2 release in anabolic function of the skeletal tissue to mechanical stimulation

Bone adapts to changes in the physical environment by modulating remodeling through bone resorption and formation to maintain optimal bone mass. As the most abundant connexin subtype in bone tissue, connexin 43 (Cx43)-forming hemichannels are highly responsive to mechanical stimulation by permitting the exchange of small molecules (<1.2 kDa) between bone cells and the extracellular environment. Upon mechanical stimulation, Cx43 hemichannels facilitate the release of prostaglandins E2 (PGE2), a vital bone anabolic factor from osteocytes. Although most bone cells are involved in mechanosensing, osteocytes are the principal mechanosensitive cells, and PGE2 biosynthesis is greatly enhanced by mechanical stimulation. Mechanical stimulation-induced PGE2 released from osteocytic Cx43 hemichannels acts as autocrine effects that promote β-catenin nuclear accumulation, Cx43 expression, gap junction function, and protects osteocytes against glucocorticoid-induced osteoporosis in cultured osteocytes. In vivo, Cx43 hemichannels with PGE2 release promote bone formation and anabolism in response to mechanical loading. This review summarizes current in vitro and in vivo understanding of Cx43 hemichannels and extracellular PGE2 release, and their roles in bone function and mechanical responses. Cx43 hemichannels could be a significant potential new therapeutic target for treating bone loss and osteoporosis.

Oxylipin-PPARγ-initiated adipocyte senescence propagates secondary senescence in the bone marrow

The chronic use of glucocorticoids decreases bone mass and quality and increases bone-marrow adiposity, but the underlying mechanisms remain unclear. Here, we show that bone-marrow adipocyte (BMAd) lineage cells in adult mice undergo rapid cellular senescence upon glucocorticoid treatment. The senescent BMAds acquire a senescence-associated secretory phenotype, which spreads senescence in bone and bone marrow. Mechanistically, glucocorticoids increase the synthesis of oxylipins, such as 15d-PGJ2, for peroxisome proliferator-activated receptor gamma (PPARγ) activation. PPARγ stimulates the expression of key senescence genes and also promotes oxylipin synthesis in BMAds, forming a positive feedback loop. Transplanting senescent BMAds into the bone marrow of healthy mice is sufficient to induce the secondary spread of senescent cells and bone-loss phenotypes, whereas transplanting BMAds harboring a p16INK4a deletion did not show such effects. Thus, glucocorticoid treatment induces a lipid metabolic circuit that robustly triggers the senescence of BMAd lineage cells that, in turn, act as the mediators of glucocorticoid-induced bone deterioration.

Aspirin prevents estrogen deficiency-induced bone loss by inhibiting osteoclastogenesis and promoting osteogenesis

BACKGROUND

Aspirin is a commonly used antipyretic, analgesic, and anti-inflammatory drug. Numerous researches have demonstrated that aspirin exerts multiple biological effects on bone metabolism. However, its spatiotemporal roles remain controversial according to the specific therapeutic doses used for different clinical conditions, and the detailed mechanisms have not been fully elucidated. Hence, in the present study, we aimed to identify the dual effects of different aspirin dosages on osteoclastic activity and osteoblastic bone formation in vitro and in vivo.

METHODS

The effects of varying doses of aspirin on osteoclast and osteoblast differentiation were evaluated in vitro. The underlying molecular mechanisms were detected using quantitative real-time polymerase chain reaction, western blotting, and immunofluorescence techniques. An ovariectomized rat osteoporosis model was used to assess the bone-protective effects of aspirin in vivo.

RESULTS

Aspirin dose-dependently suppressed RANKL-induced osteoclasts differentiation and bone resorption in vitro and reduced the expression of osteoclastic marker genes, including TRAP, cathepsin K, and CTR. Further molecular analysis revealed that aspirin impaired the RANKL-induced NF-κB and MAPK signaling pathways and prevented the nuclear translocation of the NF-κB p65 subunit. Low-dose aspirin promoted osteogenic differentiation, whereas these effects were attenuated when high-dose aspirin was administered. Both low and high doses of aspirin prevented bone loss in an ovariectomized rat osteoporosis model in vivo.

CONCLUSION

Aspirin inhibits RANKL-induced osteoclastogenesis and promotes osteogenesis in a dual regulatory manner, thus preventing bone loss in vivo. These data indicate that aspirin has potential applications in the prevention and treatment of osteopenia.

The role of non-steroidal anti-inflammatory drugs as adjuncts to periodontal treatment and in periodontal regeneration

Periodontitis is the sixth most prevalent chronic disease globally and places significant burdens on societies and economies worldwide. Behavioral modification, risk factor control, coupled with cause-related therapy have been the "gold standard" treatment for managing periodontitis. Given that host inflammatory and immunological responses play critical roles in the pathogenesis of periodontitis and impact treatment responses, several adjunctive strategies aimed at modulating host responses and improving the results of periodontal therapy and maintenance have been proposed. Of the many pharmacological host modulators, we focused on non-steroidal anti-inflammatory drugs (NSAIDs), due to their long history and extensive use in relieving inflammation and pain and reducing platelet aggregation. NSAIDs have been routinely indicated for treating rheumatic fever and osteoarthritis and utilized for the prevention of cardiovascular events. Although several efforts have been made to incorporate NSAIDs into the treatment of periodontitis, their effects on periodontal health remain poorly characterized, and concerns over the risk-benefit ratio were also raised. Moreover, there is emerging evidence highlighting the potential of NSAIDs, especially aspirin, for use in periodontal regeneration. This review summarizes and discusses the use of NSAIDs in various aspects of periodontal therapy and regeneration, demonstrating that the benefits of NSAIDs as adjuncts to conventional periodontal therapy remain controversial. More recent evidence suggests a promising role for NSAIDs in periodontal tissue engineering and regeneration.

Cystic Fibrosis Bone Disease: The Interplay between CFTR Dysfunction and Chronic Inflammation

Cystic fibrosis is a monogenic disease with a multisystemic phenotype, ranging from predisposition to chronic lung infection and inflammation to reduced bone mass. The exact mechanisms unbalancing the maintenance of an optimal bone mass in cystic fibrosis patients remain unknown. Multiple factors may contribute to severe bone mass reduction that, in turn, have devastating consequences in the patients' quality of life and longevity. Here, we will review the existing evidence linking the CFTR dysfunction and cell-intrinsic bone defects. Additionally, we will also address how the proinflammatory environment due to CFTR dysfunction in immune cells and chronic infection impairs the maintenance of an adequate bone mass in CF patients.

Hallmarks of peripheral nerve function in bone regeneration

Skeletal tissue is highly innervated. Although different types of nerves have been recently identified in the bone, the crosstalk between bone and nerves remains unclear. In this review, we outline the role of the peripheral nervous system (PNS) in bone regeneration following injury. We first introduce the conserved role of nerves in tissue regeneration in species ranging from amphibians to mammals. We then present the distribution of the PNS in the skeletal system under physiological conditions, fractures, or regeneration. Furthermore, we summarize the ways in which the PNS communicates with bone-lineage cells, the vasculature, and immune cells in the bone microenvironment. Based on this comprehensive and timely review, we conclude that the PNS regulates bone regeneration through neuropeptides or neurotransmitters and cells in the peripheral nerves. An in-depth understanding of the roles of peripheral nerves in bone regeneration will inform the development of new strategies based on bone-nerve crosstalk in promoting bone repair and regeneration.

HSP70 inhibitors upregulate prostaglandin E1-induced synthesis of interleukin-6 in osteoblasts

Interleukin-6 (IL-6) is a pro-inflammatory and bone-resorptive cytokine that also regulates bone formation. We previously showed that prostaglandin E1 (PGE1) induces the synthesis of IL-6 by activating p44/p42 mitogen-activated protein kinase (MAPK), stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK), and p38 MAPK in osteoblast-like MC3T3-E1 cells. In the present study, we investigated whether heat shock protein 70 (HSP70), a molecular chaperone that coordinates protein folding and homeostasis, affects PGE1-stimulated IL-6 synthesis in MC3T3-E1 cells through the MAPK activation. The osteoblast-like MC3T3-E1 cells were treated with HSP70 inhibitors-VER-155008 and YM-08-, PD98059, SB203580 or SP600125 and then stimulated with PGE1. IL-6 synthesis was evaluated using an IL-6 enzyme-linked immunosorbent assay kit. IL-6 mRNA expression was measured by real-time RT-PCR. The phosphorylation of p38 MAPK was evaluated by Western blotting. We found that VER-155008, an HSP70 inhibitor, enhanced the PGE1-stimulated IL-6 release and IL-6 mRNA expression. YM-08, another HSP70 inhibitor, also enhanced PGE1-stimulated IL-6 release. PD98059, a p44/p42 MAPK inhibitor, and SP600125, a SAPK/JNK inhibitor, upregulated PGE1-stimulated IL-6 release. On the other hand, SB203580, a p38 MAPK inhibitor, suppressed PGE1-stimulated IL-6 release. YM-08 stimulated the PGE1-induced phosphorylation of p38 MAPK. SB203580 suppressed the amplification by YM-08 of the PGE1-stimulated IL-6 release. Our results suggest that HSP70 inhibitors upregulate the PGE1-stimulated IL-6 synthesis through p38 MAPK in osteoblasts and therefore affect bone remodeling.

Skeletal interoception in bone homeostasis and pain

Accumulating evidence indicates that interoception maintains proper physiological status and orchestrates metabolic homeostasis by regulating feeding behaviors, glucose balance, and lipid metabolism. Continuous skeletal remodeling consumes a tremendous amount of energy to provide skeletal scaffolding, support muscle movement, store vital minerals, and maintain a niche for hematopoiesis, which are processes that also contribute to overall metabolic balance. Although skeletal innervation has been described for centuries, recent work has shown that skeletal metabolism is tightly regulated by the nervous system and that skeletal interoception regulates bone homeostasis. Here, we provide a general discussion of interoception and its effects on the skeleton and whole-body metabolism. We also discuss skeletal interoception-mediated regulation in the context of pathological conditions and skeletal pain as well as future challenges to our understanding of these process and how they can be leveraged for more effective therapy.

Low dose aspirin associated with greater bone mineral density in older adults

The use of low-dose aspirin in older adults is increasing as is the prevalence of osteoporosis. Aspirin has been shown in numerous studies to affect bone metabolism. However, there is no clear link between low-dose aspirin use and bone mineral density (BMD). This study examined differences in bone mineral density between low-dose aspirin users and non-aspirin users in adults aged 50-80 years. We conducted a cross-sectional study of 15,560 participants who participated in the National Health and Nutrition Examination Survey (NHANES) 2017-March 2020. We used a multivariate logistic regression model to evaluate the relationship between low-dose aspirin and femoral neck BMD, femoral total BMD, intertrochanteric BMD, and the first lumbar vertebra BMD (L1 BMD) in patients aged 50 to 80 years. A total of 1208 (Group 1: femoral neck BMD, total femur BMD, and intertrochanter BMD) and 1228 (Group 2: L1 BMD) adults were included in this study. In both group 1 and group 2, BMD was higher in the low-dose aspirin group than in the non-aspirin group (Total femur BMD β = 0.019, 95% CI 0.004-0.034; Femoral neck BMD β = 0.017, 95% CI 0.002-0.032; Intertrochanter BMD β = 0.025, 95% CI 0.007-0.043; L1 BMD β = 0.026, 95% CI 0.006-0.046). In subgroup analyses stratified by gender, this positive association existed in both gender after adjusting for confounders. On subgroup analyses stratified by age, this positive association existed in three different age groups after adjusting for confounders. To test whether the effect of low-dose aspirin on BMD was affected by gender and age, the interaction P value was greater than 0.05. These findings from a human study looking into the relationship between low-dose aspirin use and BMD suggest that regular low-dose aspirin may be associated with a higher BMD. The association between low-dose aspirin and BMD did not differ by age group or gender.

Extracellular ATP and its derivatives provide spatiotemporal guidance for bone adaptation to wide spectrum of physical forces

ATP is a ubiquitous intracellular molecule critical for cellular bioenergetics. ATP is released in response to mechanical stimulation through vesicular release, small tears in cellular plasma membranes, or when cells are destroyed by traumatic forces. Extracellular ATP is degraded by ecto-ATPases to form ADP and eventually adenosine. ATP, ADP, and adenosine signal through purinergic receptors, including seven P2X ATP-gated cation channels, seven G-protein coupled P2Y receptors responsive to ATP and ADP, and four P1 receptors stimulated by adenosine. The goal of this review is to build a conceptual model of the role of different components of this complex system in coordinating cellular responses that are appropriate to the degree of mechanical stimulation, cell proximity to the location of mechanical injury, and time from the event. We propose that route and amount of ATP release depend on the scale of mechanical forces, ranging from vesicular release of small ATP boluses upon membrane deformation, to leakage of ATP through resealable plasma membrane tears, to spillage of cellular content due to destructive forces. Correspondingly, different P2 receptors responsive to ATP will be activated according to their affinity at the site of mechanical stimulation. ATP is a small molecule that readily diffuses through the environment, bringing the signal to the surrounding cells. ATP is also degraded to ADP which can stimulate a distinct set of P2 receptors. We propose that depending on the magnitude of mechanical forces and distance from the site of their application, ATP/ADP profiles will be different, allowing the relay of information about tissue level injury and proximity. Lastly, ADP is degraded to adenosine acting via its P1 receptors. The presence of large amounts of adenosine without ATP, indicates that an active source of ATP release is no longer present, initiating the transition to the recovery phase. This model consolidates the knowledge regarding the individual components of the purinergic system into a conceptual framework of choreographed responses to physical forces.

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Cellular bioenergetic molecule ATP is released when cell is mechanically stimulated.

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ATP release is proportional to the amount of cellular damage.

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ATP diffusion and transformation to ADP indicates the proximity to the damage.

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Purinergic receptors form a network choreographing cell response to physical forces.

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Complete transformation of ATP to adenosine initiates the recovery phase.

Peripheral nerves in the tibial subchondral bone : the role of pain and homeostasis in osteoarthritis

Osteoarthritis (OA) is a highly prevalent degenerative joint disorder characterized by joint pain and physical disability. Aberrant subchondral bone induces pathological changes and is a major source of pain in OA. In the subchondral bone, which is highly innervated, nerves have dual roles in pain sensation and bone homeostasis regulation. The interaction between peripheral nerves and target cells in the subchondral bone, and the interplay between the sensory and sympathetic nervous systems, allow peripheral nerves to regulate subchondral bone homeostasis. Alterations in peripheral innervation and local transmitters are closely related to changes in nociception and subchondral bone homeostasis, and affect the progression of OA. Recent literature has substantially expanded our understanding of the physiological and pathological distribution and function of specific subtypes of neurones in bone. This review summarizes the types and distribution of nerves detected in the tibial subchondral bone, their cellular and molecular interactions with bone cells that regulate subchondral bone homeostasis, and their role in OA pain. A comprehensive understanding and further investigation of the functions of peripheral innervation in the subchondral bone will help to develop novel therapeutic approaches to effectively prevent OA, and alleviate OA pain.

Cite this article: Bone Joint Res 2022;11(7):439–452.

Stimulation of Osteoclast Formation by Oncostatin M and the Role of WNT16 as a Negative Feedback Regulator

Oncostatin M (OSM), which belongs to the IL-6 family of cytokines, is the most potent and effective stimulator of osteoclast formation in this family, as assessed by different in vitro assays. Osteoclastogenesis induced by the IL-6 type of cytokines is mediated by the induction and paracrine stimulation of the osteoclastogenic cytokine receptor activator of nuclear factor κ-B ligand (RANKL), expressed on osteoblast cell membranes and targeting the receptor activator of nuclear factor κ-B (RANK) on osteoclast progenitor cells. The potent effect of OSM on osteoclastogenesis is due to an unusually robust induction of RANKL in osteoblasts through the OSM receptor (OSMR), mediated by a JAK-STAT/MAPK signaling pathway and by unique recruitment of the adapter protein Shc1 to the OSMR. Gene deletion of Osmr in mice results in decreased numbers of osteoclasts and enhanced trabecular bone caused by increased trabecular thickness, indicating that OSM may play a role in physiological regulation of bone remodeling. However, increased amounts of OSM, either through administration of recombinant protein or of adenoviral vectors expressing Osm, results in enhanced bone mass due to increased bone formation without any clear sign of increased osteoclast numbers, a finding which can be reconciled by cell culture experiments demonstrating that OSM can induce osteoblast differentiation and stimulate mineralization of bone nodules in such cultures. Thus, in vitro studies and gene deletion experiments show that OSM is a stimulator of osteoclast formation, whereas administration of OSM to mice shows that OSM is not a strong stimulator of osteoclastogenesis in vivo when administered to adult animals. These observations could be explained by our recent finding showing that OSM is a potent stimulator of the osteoclastogenesis inhibitor WNT16, acting in a negative feedback loop to reduce OSM-induced osteoclast formation.

Pharmacological antagonism of EP2 receptor does not modify basal cardiovascular and respiratory function, blood cell counts, and bone morphology in animal models

The EP2 receptor has emerged as a therapeutic target with exacerbating role in disease pathology for a variety of peripheral and central nervous system disorders. We and others have recently demonstrated beneficial effects of EP2 antagonists in preclinical models of neuroinflammation and peripheral inflammation. However, it was earlier reported that mice with global EP2 knockout (KO) display adverse phenotypes on fertility and blood pressure. Other studies indicated that EP2 activation with an agonist has a beneficial effect of healing fractured bone in animal models. These results impeded the development of EP2 antagonists, and EP2 antagonism as therapeutic strategy. To determine whether treatment with EP2 antagonist mimics the adverse phenotypes of the EP2 global KO mouse, we tested two EP2 antagonists TG11-77. HCl and TG6-10-1 in mice and rats while they are on normal or high-salt diet, and by two different administration protocols (acute and chronic). There were no adverse effects of the antagonists on systolic and diastolic blood pressure, heart rate, respiratory function in mice and rats regardless of rodents being on a regular or high salt diet. Furthermore, chronic exposure to TG11-77. HCl produced no adverse effects on blood cell counts, bone-volume and bone-mineral density in mice. Our findings argue against adverse effects on cardiovascular and respiratory systems, blood counts and bone structure in healthy rodents from the use of small molecule reversible antagonists for EP2, in contrast to the genetic ablation model. This study paves the way for advancing therapeutic applications of EP2 antagonists against diseases involving EP2 dysfunction.

The Osteogenesis Imperfecta Type V Mutant BRIL/IFITM5 Promotes Transcriptional Activation of MEF2, NFATc, and NR4A in Osteoblasts

BRIL (bone restricted ifitm-like; also known as IFITM5) is a transmembrane protein expressed in osteoblasts. Although its role in skeletal development and homeostasis is unknown, mutations in BRIL result in rare dominant forms of osteogenesis imperfecta. The pathogenic mechanism has been proposed to be a gain-of or neomorphic function. To understand the function of BRIL and its OI type V mutant (MALEP BRIL) and whether they could activate signaling pathways in osteoblasts, we performed a luciferase reporter assay screen based on the activity of 26 transcription factors. When overexpressed in MC3T3-E1 and MLO-A5 cells, the MALEP BRIL activated the reporters dependent on MEF2, NFATc, and NR4A significantly more. Additional co-transfection experiments with MEF2C and NFATc1 and a number of their modulators (HDAC4, calcineurin, RCAN, FK506) confirmed the additive or synergistic activation of the pathways by MALEP, and suggested a coordinated regulation involving calcineurin. Endogenous levels of Nr4a members, as well as Ptgs2, were upregulated by MALEP BRIL. Y2H and co-immunoprecipitation indicated that BRIL interacted with CAML, but its contribution as the most upstream stimulator of the Ca²⁺-calcineurin-MEF2/NFATc cascade was not confirmed convincingly. Altogether the data presented provide the first ever readout to monitor for BRIL activity and suggest a potential gain-of-function causative effect for MALEP BRIL in OI type V, leading to perturbed signaling events and gene expression.

A Review of Aceclofenac: Analgesic and Anti-Inflammatory Effects on Musculoskeletal Disorders

Aceclofenac is an oral non-steroidal anti-inflammatory drug (NSAID) with anti-inflammatory and analgesic properties. Although there are some differences in the authorized indications between countries, aceclofenac is mainly recommended for the treatment of inflammatory and painful processes, such as low back pain (LBP), scapulohumeral periarthritis, extraarticular rheumatism, odontalgia, and osteoarthritis (OA), rheumatoid arthritis (RA), and ankylosing spondylitis (AS). The analgesic properties and tolerability profile of aceclofenac in musculoskeletal disorders are reviewed, focusing on relevant and recent studies. The efficacy and safety comparison of aceclofenac with other analgesics and anti-inflammatory agents in OA, AS, RA, and LBP is described. Relevant studies were identified following a literature search of PubMed using the terms "aceclofenac" and "clinical trials" published from 1 Jan 1992 to 1 Jan 2020. Aceclofenac is at least as effective as other NSAIDs in reducing pain and/or improving functional capacity in chronic pain conditions (OA, AS, RA, and LBP). It is generally well tolerated and appears to have a more favorable GI profile than other NSAIDs. Thus, current evidence indicates that aceclofenac is a useful option for the management of pain and inflammation across a wide range of painful conditions.

New Insights to the Crosstalk between Vascular and Bone Tissue in Chronic Kidney Disease-Mineral and Bone Disorder

Vasculature plays a key role in bone development and the maintenance of bone tissue throughout life. The two organ systems are not only linked in normal physiology, but also in pathophysiological conditions. The chronic kidney disease–mineral and bone disorder (CKD-MBD) is still the most serious complication to CKD, resulting in increased morbidity and mortality. Current treatment therapies aimed at the phosphate retention and parathyroid hormone disturbances fail to reduce the high cardiovascular mortality in CKD patients, underlining the importance of other factors in the complex syndrome. This review will focus on vascular disease and its interplay with bone disorders in CKD. It will present the very late data showing a direct effect of vascular calcification on bone metabolism, indicating a vascular-bone tissue crosstalk in CKD. The calcified vasculature not only suffers from the systemic effects of CKD but seems to be an active player in the CKD-MBD syndrome impairing bone metabolism and might be a novel target for treatment and prevention.

Components and Mechanisms of Nuclear Mechanotransduction

The cell nucleus is best known as the container of the genome. Its envelope provides a barrier for passive macromolecule diffusion, which enhances the control of gene expression. As its largest and stiffest organelle, the nucleus also defines the minimal space requirements of a cell. Internal or external pressures that deform a cell to its physical limits cause a corresponding nuclear deformation. Evidence is consolidating that the nucleus, in addition to its genetic functions, serves as a physical sensing device for critical cell body deformation. Nuclear mechanotransduction allows cells to adapt their acute behaviors, mechanical stability, paracrine signaling, and fate to their physical surroundings. This review summarizes the basic chemical and mechanical properties of nuclear components, and how these properties are thought to be utilized for mechanosensing.

Skeleton interoception regulates bone and fat metabolism through hypothalamic neuroendocrine NPY

The central nervous system regulates activity of peripheral organs through interoception. In our previous study, we have demonstrated that PGE2/EP4 skeleton interception regulate bone homeostasis. Here, we show that ascending skeleton interoceptive signaling downregulates expression of hypothalamic neuropeptide Y (NPY) and induce lipolysis of adipose tissue for osteoblastic bone formation. Specifically, the ascending skeleton interoceptive signaling induces expression of small heterodimer partner-interacting leucine zipper protein (SMILE) in the hypothalamus. SMILE binds to pCREB as a transcriptional heterodimer on Npy promoters to inhibit NPY expression. Knockout of EP4 in sensory nerve increases expression of NPY causing bone catabolism and fat anabolism. Importantly, inhibition of NPY Y1 receptor (Y1R) accelerated oxidation of free fatty acids in osteoblasts and rescued bone loss in AvilCre:Ptger4fl/fl mice. Thus, downregulation of hypothalamic NPY expression lipolyzes free fatty acids for anabolic bone formation through a neuroendocrine descending interoceptive regulation.

Components and Mechanisms of Nuclear Mechanotransduction

The cell nucleus is best known as the container of the genome. Its envelope provides a barrier for passive macromolecule diffusion, which enhances the control of gene expression. As its largest and stiffest organelle, the nucleus also defines the minimal space requirements of a cell. Internal or external pressures that deform a cell to its physical limits cause a corresponding nuclear deformation. Evidence is consolidating that the nucleus, in addition to its genetic functions, serves as a physical sensing device for critical cell body deformation. Nuclear mechanotransduction allows cells to adapt their acute behaviors, mechanical stability, paracrine signaling, and fate to their physical surroundings. This review summarizes the basic chemical and mechanical properties of nuclear components, and how these properties are thought to be utilized for mechanosensing. Expected final online publication date for the Annual Review of Cell and Developmental Biology, Volume 37 is October 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Parathyroid hormone and its related peptides in bone metabolism

Parathyroid hormone (PTH) is an 84-amino-acid peptide hormone that is secreted by the parathyroid gland. It has different administration modes in bone tissue through which it promotes bone formation (intermittent administration) and bone resorption (continuous administration) and has great potential for application in sbone defect repair. PTH regulates bone metabolism by binding to PTH1R. PTH plays an osteogenic role by acting directly on mesenchymal stem cells, cells with an osteoblastic lineage, osteocytes, and T cells. It also participates as an osteoclast by indirectly acting on osteoclast precursor cells and osteoclasts and directly acting on T cells. In these cells, PTH activates the Wnt signaling, cAMP/PKA, cAMP/PKC, and RANKL/RANK/OPG pathways and other signaling pathways. Although PTH(1-34), also known as teriparatide, has been used clinically, it still has some disadvantages. Developing improved PTH-related peptides is a potential solution to teriparatide's shortcomings. The action mechanism of these PTH-related peptides is not exactly the same as that of PTH. Thus, the mechanisms of PTH and PTH-related peptides in bone metabolism were reviewed in this paper.

Pleiotropic Effects of Acetylsalicylic Acid after Coronary Artery Bypass Grafting-Beyond Platelet Inhibition

Acetylsalicylic acid (ASA) is one of the most frequently used medications worldwide. Yet, the main indications for ASA are the atherosclerosis-based cardiovascular diseases, including coronary artery disease (CAD). Despite the increasing number of percutaneous procedures to treat CAD, coronary artery bypass grafting (CABG) remains the treatment of choice in patients with multivessel CAD and intermediate or high anatomical lesion complexity. Taking into account that CABG is a potent activator of inflammation, ASA is an important part in the postoperative therapy, not only due to ASA antiplatelet action, but also as an anti-inflammatory agent. Additional benefits of ASA after CABG include anticancerogenic, hypotensive, antiproliferative, anti-osteoporotic, and neuroprotective effects, which are especially important in patients after CABG, prone to hypertension, graft occlusion, atherosclerosis progression, and cognitive impairment. Here, we discuss the pleiotropic effects of ASA after CABG and provide insights into the mechanisms underlying the benefits of treatment with ASA, beyond platelet inhibition. Since some of ASA pleiotropic effects seem to increase the risk of bleeding, it could be considered a starting point to investigate whether the increase of the intensity of the treatment with ASA after CABG is beneficial for the CABG group of patients.

The Role of Inflammation in Breast and Prostate Cancer Metastasis to Bone

Tumor metastasis to bone is a common event in multiple forms of malignancy. Inflammation holds essential functions in homeostasis as a defense mechanism against infections and is a strategy to repair injured tissue and to adapt to stress conditions. However, exaggerated and/or persistent (chronic) inflammation may eventually become maladaptive and evoke diseases such as autoimmunity, diabetes, inflammatory tissue damage, fibrosis, and cancer. In fact, inflammation is now considered a hallmark of malignancy with prognostic relevance. Emerging studies have revealed a central involvement of inflammation in several steps of the metastatic cascade of bone-homing tumor cells through supporting their survival, migration, invasion, and growth. The mechanisms by which inflammation favors these steps involve activation of epithelial-to-mesenchymal transition (EMT), chemokine-mediated homing of tumor cells, local activation of osteoclastogenesis, and a positive feedback amplification of the protumorigenic inflammation loop between tumor and resident cells. In this review, we summarize established and evolving concepts of inflammation-driven tumorigenesis, with a special focus on bone metastasis.

Acetaminophen reduces osteoprotegerin synthesis stimulated by PGE2 and PGF2α in osteoblasts: attenuation of SAPK/JNK but not p38 MAPK or p44/p42 MAPK

Acetaminophen is one of the most widely used analgesic and antipyretic medicines, whose long-period use has reportedly been associated with an increased risk of bone fracture. However, the mechanism underlying this undesired effect remains to be investigated. The homeostatic control of bone tissue depends on the interaction between osteoblasts and osteoclasts. Osteoprotegerin produced by osteoblasts is known to play an essential role in suppressing osteoclast induction. We have previously reported that prostaglandin (PG) E₂ and PGF_2α induce osteoprotegerin synthesis through p38 mitogen-activated protein kinase (MAPK), p44/p42 MAPK and stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) in osteoblast-like MC3T3-E1 cells. In the present study, we investigated the effects of acetaminophen on the osteoprotegerin synthesis induced by PGE₂ and PGF_2α in MC3T3-E1 cells. Acetaminophen significantly suppressed the osteoprotegerin release stimulated by PGE₂ and PGF_2α. The PGE₂-induced expression of osteoprotegerin mRNA was also reduced by acetaminophen. Acetaminophen markedly downregulated the phosphorylation of SAPK/JNK stimulated by PGE₂ and PGF_2α, but not those of p38 MAPK or p44/p42 MAPK. SP600125, an inhibitor of SAPK/JNK, suppressed the levels of PGE₂- and PGF_2α-upregulated osteoprotegerin mRNA expression. Taken together, these results strongly suggest that acetaminophen reduces the PGE₂- and PGF_2α-stimulated synthesis of osteoprotegerin in osteoblasts, and that the suppressive effect is exerted via attenuation of SAPK/JNK. These findings provide a molecular basis for the possible effect of acetaminophen on bone tissue metabolism.