Melittin Treats Periprosthetic Osteolysis in a Rat Model by Inhibiting the NF-kB Pathway and Regulating the Ratio of Receptor Activator of Nuclear Factor Kappa B Ligand/Osteoprotegerin

BACKGROUND

Aseptic loosening around the prosthesis is a common cause of failure in total joint arthroplasty. Polyethylene wear particles trigger the release of inflammatory factors by macrophages. Key mediators involved in osteoclastogenesis include interleukin-6, tumor necrosis factor-α, receptor activator of nuclear factor kappa B (RANK), RANK ligand (RANKL), and bone protection hormone (Osteoprotegerin [OPG]). The purpose of our experiment was to see whether melittin can slow down the release of inflammatory mediators through the NF-kB pathway, regulate the RANKL/OPG ratio, reduce osteoclast formation, and delay the onset of arthritis in rats.

METHODS

A total of 20 male Sprague-Dawley rats (10 months, Specific Pathogen Free, 350 g ± 20 g) were randomly divided into 5 groups: sham group, model group, melittin concentration 1 group (0.2 mg/kg), concentration 2 group (0.4 mg/kg), and concentration 3 group (0.6 mg/kg). All rats were implanted with TA2 high-purity titanium rods. A drill was used to create a bone canal along the long axis of the femur in the intercondylar notch. The model group and experimental groups were exposed to polyethylene particles, while the sham group did not receive any particles.

RESULTS

The melittin group exhibited significantly increased serum levels of serum P, calcium-phosphorus product, OPG, PINP, PINP/CTX-I, and OPG/RANKKL (P < .05). In the experimental group, micro computed tomography scanning results revealed a decrease in the amount of bone defect around the prosthesis. Immunofluorescence analysis demonstrated a decrease in the expression of IKKα and P65, while the expression of OPG showed an upward trend. Both Hematoxylin-Eosin and Tartrate-Resistant Acid Phosphatase staining revealed less osteoclast and inflammatory cell infiltration in bone resorption pits.

CONCLUSIONS

Our study demonstrates that melittin has the ability to inhibit the NF-kB pathway in a rat model, and reduce the impact of RANKL/OPG, thereby delaying osteoclast activity and alleviating periprosthetic osteolysis.

Nr4a1 enhances Wnt4 transcription to promote mesenchymal stem cell osteogenesis and alleviates inflammation-inhibited bone regeneration

Intense inflammatory response impairs bone marrow mesenchymal stem cell (BMSC)-mediated bone regeneration, with transforming growth factor (TGF)-β1 being the most highly expressed cytokine. However, how to find effective and safe means to improve bone formation impaired by excessive TGF-β1 remains unclear. In this study, we found that the expression of orphan nuclear receptor Nr4a1, an endogenous repressor of TGF-β1, was suppressed directly by TGF-β1-induced Smad3 and indirectly by Hdac4, respectively. Importantly, Nr4a1 overexpression promoted BMSC osteogenesis and reversed TGF-β1-mediated osteogenic inhibition and pro-fibrotic effects. Transcriptomic and histologic analyses confirmed that upregulation of Nr4a1 increased the transcription of Wnt family member 4 (Wnt4) and activated Wnt pathway. Mechanistically, Nr4a1 bound to the promoter of Wnt4 and regulated its expression, thereby enhancing the osteogenic capacity of BMSCs. Moreover, treatment with Nr4a1 gene therapy or Nr4a1 agonist Csn-B could promote ectopic bone formation, defect repair, and fracture healing. Finally, we demonstrated the correlation of NR4A1 with osteogenesis and the activation of the WNT4/β-catenin pathway in human BMSCs and fracture samples. Taken together, these findings uncover the critical role of Nr4a1 in bone formation and alleviation of inflammation-induced bone regeneration disorders, and suggest that Nr4a1 has the potential to be a therapeutic target for accelerating bone healing.

Outcome assessment methods of bioactive and biodegradable materials as pulpotomy agents in primary and permanent teeth: a scoping review

BACKGROUND

Pulpotomy procedures aiming to preserve and regenerate the dentin-pulp complex have recently increased exponentially due to developments in the field of biomaterials and tissue engineering in primary and permanent teeth. Although the number of studies in this domain has increased, there is still scarcity of evidence in the current literature.

OBJECTIVES

(1) Report the methods of outcome assessment of pulpotomy clinical trials in both primary and permanent teeth; (2) Identify the various bioactive agents and biodegradable scaffolds used in pulpotomy clinical trials in both primary and permanent teeth.

MATERIALS AND METHODS

A scoping review of the literature was performed, including a search of primary studies on PubMed, Scopus, Web of Science, ProQuest and Clinicaltrials.gov. A search for controlled trials or randomized controlled trials published between 2012 and 2023 involving primary or permanent teeth receiving partial or full pulpotomy procedures using bioactive/regenerative capping materials was performed.

RESULTS

127 studies out of 1038 articles fulfilled all the inclusion criteria and were included in the current scoping review. More than 90% of the studies assessed clinical and radiographic outcomes. Histological, microbiological, or inflammatory outcomes were measured in only 9.4% of all included studies. Majority of the studies (67.7%) involved primary teeth. 119 studies used non-degradable bioactive cements, while biodegradable scaffolds were used by 32 studies, natural derivates and plant extracts studies were used in only 7 studies. Between 2012 (4 studies) and 2023 (11 studies), there was a general increase in the number of articles published. India, Egypt, Turkey, and Iran were found to have the highest total number of articles published (28, 28,16 and 10 respectively).

CONCLUSIONS

Pulpotomy studies in both primary and permanent teeth relied mainly on subjective clinical and radiographic outcome assessment methods and seldom analyzed pulpal inflammatory status objectively. The use of biodegradable scaffolds for pulpotomy treatments has been increasing with an apparent global distribution of most of these studies in low- to middle-income countries. However, the development of a set of predictable outcome measures as well as long-term evidence from well conducted clinical trials for novel pulpotomy dressing materials are still required.

Navigating Post-Traumatic Osteoporosis: A Comprehensive Review of Epidemiology, Pathophysiology, Diagnosis, Treatment, and Future Directions

Post-traumatic osteoporosis (PTO) presents a significant challenge in clinical practice, characterized by demineralization and decreased skeletal integrity following severe traumatic injuries. This literature review manuscript addresses the knowledge gaps surrounding PTO, encompassing its epidemiology, pathophysiology, risk factors, diagnosis, treatment, prognosis, and future directions. This review emphasizes the complexity of the etiology of PTO, highlighting the dysregulation of biomineralization processes, inflammatory cytokine involvement, hormonal imbalances, glucocorticoid effects, vitamin D deficiency, and disuse osteoporosis. Moreover, it underscores the importance of multidisciplinary approaches for risk mitigation and advocates for improved diagnostic strategies to differentiate PTO from other musculoskeletal pathologies. This manuscript discusses various treatment modalities, including pharmacotherapy, dietary management, and physical rehabilitation, while also acknowledging the limited evidence on their long-term effectiveness and outcomes in PTO patients. Future directions in research are outlined, emphasizing the need for a deeper understanding of the molecular mechanisms underlying PTO and the evaluation of treatment strategies' efficacy. Overall, this review provides a comprehensive overview of PTO and highlights avenues for future investigation to enhance clinical management and patient outcomes.

Exercise and osteoimmunology in bone remodeling

Bones can form the scaffolding of the body, support the organism, coordinate somatic movements, and control mineral homeostasis and hematopoiesis. The immune system plays immune supervisory, defensive, and regulatory roles in the organism, which mainly consists of immune organs (spleen, bone marrow, tonsils, lymph nodes, etc.), immune cells (granulocytes, platelets, lymphocytes, etc.), and immune molecules (immune factors, interferons, interleukins, tumor necrosis factors, etc.). Bone and the immune system have long been considered two distinct fields of study, and the bone marrow, as a shared microenvironment between the bone and the immune system, closely links the two. Osteoimmunology organically combines bone and the immune system, elucidates the role of the immune system in bone, and creatively emphasizes its interdisciplinary characteristics and the function of immune cells and factors in maintaining bone homeostasis, providing new perspectives for skeletal-related field research. In recent years, bone immunology has gradually become a hot spot in the study of bone-related diseases. As a new branch of immunology, bone immunology emphasizes that the immune system can directly or indirectly affect bones through the RANKL/RANK/OPG signaling pathway, IL family, TNF-α, TGF-β, and IFN-γ. These effects are of great significance for understanding inflammatory bone loss caused by various autoimmune or infectious diseases. In addition, as an external environment that plays an important role in immunity and bone, this study pays attention to the role of exercise-mediated bone immunity in bone reconstruction.

Neutrophils in Inflammatory Bone Diseases

PURPOSE OF REVIEW

In this review, we summarize the current evidence that suggests that neutrophils play a key role in facilitating damage to local bone structures.

RECENT FINDINGS

Neutrophil infiltration is a hallmark of inflammatory bone diseases such as rheumatoid arthritis (RA) and periodontitis disease (PD). Both of these human diseases are marked by an imbalance in bone homeostasis, favoring the degradation of local bone which ultimately leads to erosions. Osteoclasts, a multinucleated resident bone cell, are responsible for facilitating the turnover of bone and the bone damage observed in these diseases. The involvement of neutrophils and neutrophil extracellular trap formation have recently been implicated in exacerbating osteoclast function through direct and indirect mechanisms. We highlight a recent finding that NET proteins such as histones and elastase can generate non-canonical, inflammatory osteoclasts, and this process is mediated by post-translational modifications such as citrullination and carbamylation, both of which act as autoantigens in RA. It appears that NETs, autoantibodies, modified proteins, cytokines, and osteoclasts all ultimately contribute to local and permanent bone damage in RA and PD. However, more studies are needed to fully understand the role of neutrophils in inflammatory bone diseases.

Ferroptosis in Osteocytes as a Target for Protection Against Postmenopausal Osteoporosis

Ferroptosis is a necrotic form of iron-dependent regulatory cell death. Estrogen withdrawal can interfere with iron metabolism, which is responsible for the pathogenesis of postmenopausal osteoporosis (PMOP). Here, it is demonstrated that estrogen withdrawal induces iron accumulation in the skeleton and the ferroptosis of osteocytes, leading to reduced bone mineral density. Furthermore, the facilitatory effect of ferroptosis of osteocytes is verified in the occurrence and development of postmenopausal osteoporosis is associated with over activated osteoclastogenesis using a direct osteocyte/osteoclast coculture system and glutathione peroxidase 4 (GPX4) knockout ovariectomized mice. In addition, the nuclear factor erythroid derived 2-related factor-2 (Nrf2) signaling pathway is confirmed to be a crucial factor in the ferroptosis of osteocytic cells. Nrf2 regulates the expression of nuclear factor kappa-B ligand (RANKL) by regulating the DNA methylation level of the RANKL promoter mediated by DNA methyltransferase 3a (Dnmt3a), which is as an important mechanism in osteocytic ferroptosis-mediated osteoclastogenesis. Taken together, this data suggests that osteocytic ferroptosis is involved in PMOP and can be targeted to tune bone homeostasis.

Effect of Periodontal Ligament Stem Cells-Derived Conditioned Medium on Gene Expression and Differentiation of Tumor Necrosis Factor-α-Challenged Osteoblasts

OBJECTIVES

 Tumor necrosis factor-α (TNF-α) causes bone resorption in periodontitis. It induces the production of receptor activator of NF-κB ligand (RANKL) from osteoblasts, leading to the disturbance of bone homeostasis through RANKL, RANK, and osteoprotegerin (OPG) axis. This study aimed to explore the effect of periodontal ligament stem cells-derived conditioned medium (PDLSCs-CM) on gene expression related to bone homeostasis and the differentiation of TNF-α-challenged osteoblasts.

MATERIALS AND METHODS

 Human osteoblasts were cultured with 50 ng/mL of TNF-α and 0, 1, 10, and 100 µg/ mL of PDLSCs-CM. Osteoblasts cultured without TNF-α and PDLSCs-CM were served as control. Gene expression of RANKL, OPG, and interleukin-1β (IL-1β) was evaluated by reverse transcription quantitative polymerase chain reaction at 48 hours. The early-stage and late-stage differentiation of TNF-α-challenged osteoblasts without or with PDLSCs-CM was explored by alkaline phosphatase (ALP) activity and alizarin red staining, respectively, at day 1, 3, 6, 9, and 12.

STATISTICAL ANALYSIS

 Mann-Whitney U test was used to analyze the differences in gene expression of TNF-α-challenged osteoblasts at 24 and 48 hours, and Kruskal-Wallis test was used to analyze the effect of PDLSCs-CM on gene expression and ALP activity among all experimental groups using SPSS software version 21.0. Statistical significance was considered with p-value less than 0.05.

RESULTS

 Expression of RANKL, OPG and IL-1β was significantly upregulated in TNF-α-challenged osteoblasts compared to the untreated control. The PDLSCs-CM at 1 and 10 μg/mL downregulated gene expression of TNF-α-challenged osteoblasts compared to the group without PDLSCs-CM, but the difference did not reach statistical significance. The ALP activity was decreased in TNF-α-challenged osteoblasts. The addition of PDLSCs-CM did not alter ALP activity of TNF-α-challenged osteoblasts. Alizarin red staining was comparable in the TNF-α-challenged osteoblasts cultured without or with PDLSCs-CM.

CONCLUSIONS

 The PDLSCs-CM did not alter gene expression involved in bone homeostasis and differentiation of TNF-α-challenged osteoblasts.

Obesity and Skeletal Fragility

Skeletal fracture has recently emerged as a complication of obesity. Given the normal or better than normal bone mineral density (BMD), the skeletal fragility of these patients appears to be a problem of bone quality rather than quantity. Type 2 diabetes mellitus (T2DM), the incidence of which increases with increasing body mass index, is also associated with an increased risk for fractures despite a normal or high BMD. With the additional bone pathology from diabetes itself, patients with both obesity and T2DM could have a worse skeletal profile. Clinically, however, there are no available methods for identifying those who are at higher risk for fractures or preventing fractures in this subgroup of patients. Weight loss, which is the cornerstone in the management of obesity (with or without T2DM), is also associated with an increased risk of bone loss. This review of the literature will focus on the skeletal manifestations associated with obesity, its interrelationship with the bone defects associated with T2DM, and the available approach to the bone health of patients suffering from obesity.

Effect of milk fat globules on growth and metabolism in rats fed an unbalanced diet

We assessed the effects of supplementing milk fat globules (MFG) on the growth and development of the skeleton in rats fed a Western unbalanced diet (UBD). The UBD is high in sugar and fat, low in protein, fiber, and micronutrients, and negatively impacts health. The MFG-a complex lipid-protein assembly secreted into milk-has a unique structure and composition, which differs significantly from isolated and processed dietary ingredients. Rats consuming the UBD exhibited growth retardation and disrupted bone structural and mechanical parameters; these were improved by supplementation with small MFG. The addition of small MFG increased the efficiency of protein utilization for growth, and improved trabecular and cortical bone parameters. Furthermore, consumption of UBD led to a decreased concentration of saturated fatty acids and increased levels of polyunsaturated fatty acids (PUFA), particularly omega-6 PUFA, in the serum, liver, and adipose tissue. The addition of small MFG restored PUFA concentration and the ratio of omega-6 to omega-3 PUFA in bone marrow and adipose tissue. Finally, large but not small MFG supplementation affected the cecal microbiome in rats. Overall, our results suggest that natural structure MFG supplementation can improve metabolism and bone development in rats fed an UBD, with the effects depending on MFG size. Moreover, the benefits of small MFG to bone development and metabolism were not mediated by the microbiome, as the detrimental effects of an UBD on the microbiome were not mitigated by MFG supplementation.

Inflammatory Processes Affecting Bone Health and Repair

PURPOSE OF REVIEW

The purpose of this article is to review the current understanding of inflammatory processes on bone, including direct impacts of inflammatory factors on bone cells, the effect of senescence on inflamed bone, and the critical role of inflammation in bone pain and healing.

RECENT FINDINGS

Advances in osteoimmunology have provided new perspectives on inflammatory bone loss in recent years. Characterization of so-called inflammatory osteoclasts has revealed insights into physiological and pathological bone loss. The identification of inflammation-associated senescent markers in bone cells indicates that therapies that reduce senescent cell burden may reverse bone loss caused by inflammatory processes. Finally, novel studies have refined the role of inflammation in bone healing, including cross talk between nerves and bone cells. Except for the initial stages of fracture healing, inflammation has predominately negative effects on bone and increases fracture risk. Eliminating senescent cells, priming the osteo-immune axis in bone cells, and alleviating pro-inflammatory cytokine burden may ameliorate the negative effects of inflammation on bone.

The influence of inflammation on the characteristics of adipose-derived mesenchymal stem cells (ADMSCs) and tissue repair capability in a hepatic injury mouse model

BACKGROUND

Mesenchymal stem cells (MSCs) are adult stem cells with self-renewal and multi-directional differentiation potential and possess the functions of immunomodulation, regulation of cell growth, and repair of damage. Over recent years, MSCs have been found to regulate the secretion of inflammatory factors and to exert regulatory effects on various lymphocytes in inflammatory states, and on the subsequent repair of tissue damage caused by inflammation. In the present study, we analyzed the effects of tissue inflammation on the characteristics of MSCs.

METHODS

Human fat derived from the infrapatellar fat pad (IPFP) of knees with differing degrees of inflammation was extracted from specimens derived from total knee arthroplasties. HE and immunohistochemical staining was performed to directly observe the evidence and degree of inflammation in human infrapatellar fat pad tissue in order to classify MSCs cells, by their origin, into highly inflamed and lowly inflamed groups, and to study the effect of tissue inflammation on cell acquisition rates via cellular counting data. Flow cytometry assays were performed to investigate the effect of tissue inflammation on MSC surface marker expression. Trilineage differentiation, including osteogenesis, adipogenesis, and chondrogenesis, was performed to assess the effect of tissue inflammation on the ability of MSCs to undergo directed differentiation. The effect of tissue inflammation on the ability of MSCs to proliferate was investigated via clone formation studies. RNA-sequencing was performed to evaluate the transcriptomes of MSCs derived from different areas of inflammation. The effect of tissue inflammation on tissue repair capacity and safety of MSCs was investigated via a murine model of acute liver injury.

RESULTS

The results of cell count data indicate that a high degree of tissue inflammation significantly decreases the acquisition rate of MSCs, and the proportion of CD34+ and CD146+ cells. The results of our trilineage differentiation assay show that a higher degree of inflammation decreases osteogenic differentiation and enhances adipogenic and chondrogenic differentiation of MSCs. However, these differences were not statistically significant. Clone formation assays indicate that the degree of tissue inflammation at the MSC source does not significantly affect the proliferative capacity of MSCs. The transcriptomes of MSCs remain relatively stable in fat pad tissues derived from both highly and lowly inflamed samples. The results of acute liver injury investigations in mice indicate that MSCs of high and low inflammatory tissue origin have no significant difference in their tissue repair capability.

CONCLUSIONS

High tissue inflammation at the source of MSCs reduces the acquisition rate of MSCs and the percentage of CD34+ and CD146+ cells acquisition. However, source tissue inflammation may not significantly affect trilineage differentiation potential and proliferative capacity of MSCs. Also, MSCs obtained from differing source degrees of inflammation retain stable and similar transcriptomic profile and are both safe and efficacious for tissue repair/regeneration without detectable differences.

Osteoprotective Role of the Mir338 Cluster Ablation during Periodontitis

Periodontitis is a chronic inflammatory disease that compromises the integrity of the supporting tissues of the teeth and leads to the loss of the alveolar bone. The Mir338 cluster has been proven to be a potential target for the treatment of osteoporosis and is also enriched in gingival tissues with periodontitis; however, its role in periodontitis remains unknown. Here, we aimed to use periodontitis as a model to expand our understanding of the Mir338 cluster in osteoimmunology and propose a new target to protect against bone loss during periodontitis progression. Significant enrichment of the Mir338 cluster was validated in gingival tissues from patients with chronic periodontitis and a ligature-induced periodontitis mouse model. In vivo, attenuation of alveolar bone loss after 7 d of ligature was observed in the Mir338 cluster knockout (KO) mice. Interestingly, immunofluorescence and RNA sequencing showed that ablation of the Mir338 cluster reduced osteoclast formation and elevated the inflammatory response, with enrichment of IFN-γ and JAK-STAT signaling pathways. Ablation of the Mir338 cluster also skewed macrophages toward the M1 phenotype and inhibited osteoclastogenesis via Stat1 in vitro and in vivo. Furthermore, the local administration of miR-338-3p antagomir prevented alveolar bone loss from periodontitis. In conclusion, the Mir338 cluster balanced M1 macrophage polarization and osteoclastogenesis and could serve as a novel therapeutic target against periodontitis-related alveolar bone loss.

Occurrence of radiopaque and mixed lesions at periapical region in patients with rheumatoid arthritis and ankylosing spondylitis: a retrospective study

BACKGROUND

Rheumatoid arthritis (RA) and ankylosing spondylitis (AS) have different effects on bones, cartilage and joints, sometimes destroying the spine and joints, and other times causing new bone formation. This study aimed to evaluate the effects of RA and AS on the types (radiolucent, radiopaque and mixed) of periapical lesions in jaw bones.

METHODS

This study included 708 individuals (97 with AS, 327 with RA and 284 healthy controls (C)) and a total of 17,118 teeth (AS: 2,442; RA: 7,638; C: 7,038). The number of teeth, extracted teeth and teeth with root canal treatment and the presence of radiopaque, radiolucent and mixed periapical lesions were recorded from dental panoramic radiographs. Kruskal-Wallis and chi-square tests were used for statistical analysis.

RESULTS

The frequency of radiopaque lesions in the AS and RA groups was similar (p > 0.05) and significantly higher than in the C group (p < 0.05) (AS: 13.4%; RA: 6.1%; C: 2%). Mixed lesions (AS: 3.1%; RA: 4.0%; C: 0.4%) were statistically significantly higher for the RA group compared to the C group (p < 0.05), while the AS-C and AS-RA groups were similar (p > 0.05). There was no significant difference in terms of radiolucent lesions among groups (p > 0.05).

CONCLUSION

Radiopaque apical lesions were frequent in RA and AS patients, while mixed lesions were significantly higher in RA patients.

Multimorbidity in rheumatoid arthritis: common mechanistic links and impact and challenges in routine clinical practice

Early identification and management of multimorbidity in patients with rheumatic and musculoskeletal diseases (RMDs), such as RA, is an integral, but often neglected, aspect of care. The prevalence and incidence of conditions such as osteoporosis, cardiovascular disease, pulmonary disease and malignancies, often co-existing with RA, continues to have significant implications for the management of this patient group. Multimorbidity in RMDs can be associated with inflammatory disease activity and target organ damage. Lifestyle factors, such as smoking and inactivity, further contribute to the burden of disease. Inflammation is the underlying factor, not just in RA but also many comorbidities. The current framework of a treat-to-target approach focuses on achieving early remission and inflammatory activity suppression. We describe how the comorbidity burden in people with RMDs impacts on disease outcome and treatment response. The importance of addressing comorbidity at an early stage and adopting a patient centred approach is critical in modern practice.

Bone Involvement in Rheumatoid Arthritis and Spondyloartritis: An Updated Review

Several rheumatologic diseases are primarily distinguished by their involvement of bone tissue, which not only serves as a mere target of the condition but often plays a pivotal role in its pathogenesis. This scenario is particularly prominent in chronic inflammatory arthritis such as rheumatoid arthritis (RA) and spondyloarthritis (SpA). Given the immunological and systemic nature of these diseases, in this review, we report an overview of the pathogenic mechanisms underlying specific bone involvement, focusing on the complex interactions that occur between bone tissue's own cells and the molecular and cellular actors of the immune system, a recent and fascinating field of interest defined as osteoimmunology. Specifically, we comprehensively elaborate on the distinct pathogenic mechanisms of bone erosion seen in both rheumatoid arthritis and spondyloarthritis, as well as the characteristic process of aberrant bone formation observed in spondyloarthritis. Lastly, chronic inflammatory arthritis leads to systemic bone involvement, resulting in systemic bone loss and consequent osteoporosis, along with increased skeletal fragility.

Myeloid Cells As a Promising Target for Brain-Bone Degenerative Diseases from a Metabolic Point of View

Brain and bone degenerative diseases such as Alzheimer's disease and osteoporosis are common in the aging population and lack efficient pharmacotherapies. Myeloid cells are a diverse group of mononuclear cells that plays important roles in development, immune defense, and tissue homeostasis. Aging drastically alters the expansion and function of myeloid cells, which might be a common pathogenesis of the brain-bone degenerative diseases. From this perspective, the role of myeloid cells in brain-bone degenerative diseases is discussed, with a particular focus on metabolic alterations in myeloid cells. Furthermore, targeting myeloid cells through metabolic regulation via drugs such as metformin and melatonin is proposed as a potential therapy for the clinical treatment of brain-bone diseases.

Melatonin and bone-related diseases: an updated mechanistic overview of current evidence and future prospects

PURPOSE

Bone diseases account for an enormous cost burden on health systems. Bone disorders are considered as age-dependent diseases. The aging of world population has encouraged scientists to further explore the most effective preventive modalities and therapeutic strategies to overcome and reduce the high cost of bone disorders. Herein, we review the current evidence of melatonin's therapeutic effects on bone-related diseases.

METHODS

This review summarized evidences from in vitro, in vivo, and clinical studies regarding the effects of melatonin on bone-related diseases, with a focus on the molecular mechanisms. Electronically, Scopus and MEDLINE®/PubMed databases were searched for articles published on melatonin and bone-related diseases from inception to June 2023.

RESULTS

The findings demonstrated that melatonin has beneficial effect in bone- and cartilage-related disorders such as osteoporosis, bone fracture healing, osteoarthritis, and rheumatoid arthritis, in addition to the control of sleep and circadian rhythms.

CONCLUSION

A number of animal and clinical studies have indicated that various biological effects of melatonin may suggest this molecule as an effective therapeutic agent for controlling, diminishing, or suppressing bone-related disorders. Therefore, further clinical studies are required to clarify whether melatonin can be effective in patients with bone-related diseases.

Hydraulic calcium silicate-based root canal sealers mitigate proinflammatory cytokine synthesis and promote osteogenesis in vitro

Background/purpose

The mineralized tissue-inductive ability and anti-inflammatory properties of hydraulic calcium silicate-based (HCSB) sealers have not been fully elucidated. This study aimed to evaluate the effects of the HCSB sealers Bio-C sealer (BioC), Well-Root ST (WST), and EndoSequence BC sealer (BC), on osteoblastic differentiation/mineralization and proinflammatory cytokine synthesis by macrophages.

Materials and methods

Diluted extracts of set sealers or calcium chloride solutions of approximately equivalent Ca2+ concentrations were applied to a mouse osteoblastic cell line (Kusa-A1 cells) and lipopolysaccharide-stimulated mouse macrophage cell line (RAW264.7 cells). Expressions of osteoblastic markers in Kusa-A1 cells and proinflammatory cytokines in RAW264.7 cells were evaluated by reverse transcription-quantitative polymerase chain reaction and enzyme-linked immunosorbent assays. Mineralized nodules were detected by Alizarin red S staining. Cell proliferation was assessed by WST-8 assay and cell attachment on set sealers was examined by scanning electron microscopy.

Results

The three sealer extracts significantly upregulated osteocalcin and osteopontin mRNA, and promoted significant mineralized nodule formation in Kusa-A1 cells. The three sealer extracts significantly downregulated the mRNA expressions of interleukin (IL)-1α, IL-1β, IL-6, and tumor necrosis factor (TNF)-α and protein levels of IL-6 and TNF-α in RAW264.7 cells. Calcium chloride solutions induced osteoblastic differentiation/mineralization. AH Plus Jet (a control sealer) extract did not. The three HCSB sealers did not interfere with the growth and attachment of Kusa-A1 cells.

Conclusion

BioC, WST, and BC were biocompatible, upregulated osteoblastic differentiation/mineralization, and downregulated proinflammatory cytokine expression. Ca2+ released from HCSB sealers might be involved, at least in part, in the induction of osteoblastic differentiation/mineralization.

Betulinic Acid Attenuates Osteoarthritis via Limiting NLRP3 Inflammasome Activation to Decrease Interleukin-1β Maturation and Secretion

Introduction

Osteoarthritis (OA) is the most common degenerative joint disorder. Prior studies revealed that activation of NLRP3 inflammasome could promote the activation and secretion of interleukin-1β (IL-1β), which has an adverse effect on the progression of OA. Betulinic acid (BA) is a compound extract of birch, whether it can protect against OA and the mechanisms involved are still unknown.

Materials and Methods

In vivo experiments, using gait analysis, ELISA, micro-CT, and scanning electron microscopy (SEM), histological staining, immunohistological (IHC) and immunofluorescence (IF) staining, and atomic force microscopy (AFM) to assess OA progression after intraperitoneal injection of 5 and 15 mg/kg BA in an OA mouse model. In vitro experiments, caspase-1, IL-1β, and the N-terminal fragment of gasdermin D (GSDMD-NT) were measured in bone marrow-derived macrophages (BMDMs) by using ELISA, western blot, and immunofluorescence staining.

Results

We demonstrated that OA progression can be postponed with intraperitoneal injection of 5 and 15 mg/kg BA in an OA mouse model. Specifically, BA postponed DMM-induced cartilage deterioration, alleviated subchondral bone sclerosis, and relieved synovial inflammation. In vitro studies, the activated NLRP3 inflammasome produces mature IL-1β by facilitating the cleavage of pro-IL-1β, and BA could inhibit the activation of NLRP3 inflammasome in BMDMs.

Conclusions

Taken together, our analyses revealed that BA attenuates OA via limiting NLRP3 inflammasome activation to decrease the IL-1β maturation and secretion.

Effect of Targeted Cytokine Inhibition on Progression of Post-Traumatic Osteoarthritis Following Intra-Articular Fracture

Intra-articular fractures (IAF) result in significant and prolonged inflammation, increasing the chances of developing post-traumatic osteoarthritis (PTOA). Interleukin-one beta (IL-1β) and Tumor Necrosis Factor-alpha (TNF-α) are key inflammatory factors shown to be involved in osteochondral degradation following IAF. As such, use of targeted biologics such as Infliximab (INX), a TNF-α inhibitor, and Anakinra (ANR), an interleukin-one (IL-1) receptor antagonist (IL1RA), may protect against PTOA by damping the inflammatory response to IAF and reducing osteochondral degradation. To test this hypothesis, IAFs were induced in the hindlimb knee joints of rats treated with INX at 10 mg/kg/day, ANR at 100 g/kg/day, or saline (vehicle control) by subcutaneous infusion for a period of two weeks and healing was evaluated at 8-weeks post injury. Serum and synovial fluid (SF) were analyzed for soluble factors. In-vivo microcomputed tomography (µCT) scans assessed bone mineral density and bone morphometry measurements. Cationic CA4+ agent assessed articular cartilage composition via ex vivo µCT. Scoring according to the Osteoarthritis Research Society International (OARSI) guidelines was performed on stained histologic tibia sections at the 56-day endpoint on a 0-6 scale. Systemically, ANR reduced many pro-inflammatory cytokines and reduced osteochondral degradation markers Cross Linked C-Telopeptide Of Type II (CTXII, p < 0.05) and tartrate-resistant acid phosphatase (TRAP, p < 0.05). ANR treatment resulted in increased chemokines; macrophage-chemotractant protein-1 (MCP-1), MPC-3, macrophage inhibitory protein 2 (MIP2) with a concomitant decrease in proinflammatory interleukin-17A (IL17A) at 14 days post-injury within the SF. Microcomputed tomography (µCT) at 56 days post-injury revealed ANR Treatment decreased epiphyseal degree of anisotropy (DA) (p < 0.05) relative to saline. No differences were found with OARSI scoring but contrast-enhanced µCT revealed a reduction in glycosaminoglycan content with ANR treatment. These findings suggest targeted cytokine inhibition, specifically IL-1 signaling, as a monotherapy has minimal utility for improving IAF healing outcomes but may have utility for promoting a more permissive inflammatory environment that would allow more potent disease modifying osteoarthritis drugs to mitigate the progression of PTOA after IAF.

Post-Operative Greater Tuberosity Resorption or Malreduction Is Associated with Poor Prognostic Outcomes in Patients with Proximal Humeral Fractures Treated Operatively-A Single-Center Retrospective Cohort Study

(1) Background: Proximal humerus fractures can be a debilitating condition if not properly treated. These fracture patterns are varied and differ in every patient. Functional outcomes may be determined by the integrity of the shoulder girdle involving the rotator cuff insertion. The post-operative resorption or malreduction of the greater tuberosity (GT) is an important factor contributing to the poor functional outcome of a patient. Thus, we intend to evaluate the cause-and-effect relationship between GT complications and clinical prognosis and outcomes. (2) Methods: A single-center retrospective comparative study was performed to evaluate the functional outcomes of patients undergoing operative fixation for this injury. A total of 387 consecutive cases treated operatively from 2019-2021 were included for analysis. (3) Results: 94 cases fulfilled our criteria for analysis. A matched-group comparison of 19 patients each was performed to compare demographics, post-operative fracture characteristics and clinical outcomes. (4) Conclusions: The resorption or malreduction of the GT contributes greatly to the prognostic outcome in patients treated with open reduction and internal fixation (ORIF) surgery. In our demographic study, obesity is another contributing factor affecting the parameters of post-operative reduction in proximal humerus fractures. Appropriate surgical planning and post-operative multidisciplinary care must be taken into consideration to attain a satisfactory prognostic outcome.

Association between Adiposity and Bone Mineral Density in Adults: Insights from a National Survey Analysis

Adiposity and bone mineral density (BMD) are closely associated. The aim of this research was to investigate the association between BMD and adiposity measures in adults, including gynoid percent fat (GPF), android percent fat (APF), total percent fat (TPF), visceral adipose tissue percent (VAT%), and total lean mass percent (TLM%). Participants (n = 11,615) aged 18 years and older were analyzed using data from the National Health and Nutrition Examination Survey (NHANES) spanning from 1999 to 2018. Associations between BMD and adiposity measures were investigated, and potential differences based on gender and age were explored. Significant negative associations were observed among TPF, APF, GPF, VAT%, and BMD in the fully adjusted models, while TLM% and BMD were positively associated. Stratifying by age and sex, TPF, GPF, and VAT% consistently demonstrated a negative correlation with BMD. In the young adult group, a TPF of 38.2% eliminated the negative correlation between BMD and TPF. Male BMD exhibited an inverted U-shaped relationship with APF, peaking at 35.6%, while a similar pattern was observed for the middle-aged group BMD and APF, with a peak at 31.7%. This large-sample research found a significant negative association between adiposity measures and BMD, providing valuable revelations regarding the intricate connection between adiposity and bone health.

Prolonged release of an antimicrobial peptide GL13K-loaded thermosensitive hydrogel on a titanium surface improves its antibacterial and anti-inflammatory properties

The application of titanium in the orthopedic and dental fields is associated with bacterial infection and chronic inflammation, especially in the early stages after its implantation. In the present study, we investigated the antibacterial and anti-inflammatory activities of a titanium surface that was immobilized in a thermosensitive PLGA-PEG-PLGA hydrogel containing the antimicrobial peptide GL13K. The FTIR results confirmed the successful loading of GL13K. The degradation of the hydrogel and release of GL13K persisted for two weeks. The modified titanium surface exhibited a significant inhibitory effect on Porphyromonas gingivalis in contact with its surface, as well as an inhibitory effect on P.g in the surrounding environment by releasing GL13K antimicrobial peptides. The modified titanium surfaces were biocompatible with RAW264.7. Furthermore, the expression of pro-inflammatory cytokines IL-1β, TNF-α and iNOS was down-regulated, whereas anti-inflammatory cytokines Arg-1, IL-10 and VEGF-A were up-regulated on the modified titanium surfaces on days 3 and 5. This effect was attributed to the polarization of macrophages from the M1 to M2 phenotype, which was confirmed by the detection of macrophage M1/M2 biomarkers via immunofluorescence staining and flow cytometry. Thus, the thermosensitive PLGA-PEG-PLGA hydrogel release system carrying the antimicrobial peptide GL13K on a titanium surface exhibited antibacterial and anti-inflammatory properties and promoted macrophage polarization from the M1 to M2 phenotype, which may help create a favourable niche for bone formation under infective condition.

Identification of an IL-1 receptor mutation driving autoinflammation directs IL-1-targeted drug design

The interleukin 1 (IL-1) pathway signals through IL-1 receptor type 1 (IL-1R1) and emerges as a central mediator for systemic inflammation. Aberrant IL-1 signaling leads to a range of autoinflammatory diseases. Here, we identified a de novo missense variant in IL-1R1 (p.Lys131Glu) in a patient with chronic recurrent multifocal osteomyelitis (CRMO). Patient PBMCs showed strong inflammatory signatures, particularly in monocytes and neutrophils. The p.Lys131Glu substitution affected a critical positively charged amino acid, which disrupted the binding of the antagonist ligand, IL-1Ra, but not IL-1α or IL-1β. This resulted in unopposed IL-1 signaling. Mice with a homologous mutation exhibited similar hyperinflammation and greater susceptibility to collagen antibody-induced arthritis, accompanied with pathological osteoclastogenesis. Leveraging the biology of the mutation, we designed an IL-1 therapeutic, which traps IL-1β and IL-1α, but not IL-1Ra. Collectively, this work provides molecular insights and a potential drug for improved potency and specificity in treating IL-1-driven diseases.

Shared inflammatory pathways of rheumatoid arthritis and atherosclerotic cardiovascular disease

The association between chronic inflammation and increased risk of cardiovascular disease in rheumatoid arthritis (RA) is well established. In the general population, inflammation is an established independent risk factor for cardiovascular disease, and much interest is placed on controlling inflammation to reduce cardiovascular events. As inflammation encompasses numerous pathways, the development of targeted therapies in RA provides an opportunity to understand the downstream effect of inhibiting specific pathways on cardiovascular risk. Data from these studies can inform cardiovascular risk management in patients with RA, and in the general population. This Review focuses on pro-inflammatory pathways targeted by existing therapies in RA and with mechanistic data from the general population on cardiovascular risk. Specifically, the discussions include the IL-1, IL-6 and TNF pathways, as well as the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) signalling pathway, and the role of these pathways in RA pathogenesis in the joint alongside the development of atherosclerotic cardiovascular disease. Overall, some robust data support inhibition of IL-1 and IL-6 in decreasing the risk of cardiovascular disease, with growing data supporting IL-6 inhibition in both patients with RA and the general population to reduce the risk of cardiovascular disease.

Calotropis procera latex protein reduces inflammation and bone loss in ligature-induced period ontitis in male rats

OBJECTIVE

Calotropis procera latex protein (CpLP) is a popular anti-inflammatory and therefore we aimed to study its effects on inflammatory bone loss.

DESIGN

Male Wistar rats were subjected to a ligature of molars. Groups of rats received intraperitoneally CpLP (0.3 mg/kg, 1 mg/kg, or 3 mg/kg) or saline (0.9% NaCl) one hour before ligature and then daily up to 11 days, compared to naïve. Gingiva was evaluated by myeloperoxidase activity and interleukin-1 beta (IL-1β) expression by ELISA. Bone resorption was evaluated in the region between the cement-enamel junction and the alveolar bone crest. The histology considered alveolar bone resorption and cementum integrity, leukocyte infiltration, and attachment level, followed by immunohistochemistry bone markers between 1^st and 2^nd molars. Systemically, the weight of the body and organs, and a leukogram were performed.

RESULTS

The periodontitis significantly increased myeloperoxidase activity and the IL-1β level. The increased bone resorption was histologically corroborated by periodontal destruction, leukocyte influx, and attachment loss, as well as the increasing receptor activator of the nuclear factor-kappa B ligand (RANKL)/osteoprotegerin (OPG) ratio, and Tartrate-resistant acid phosphatase (TRAP)+ cells when compared to naïve. CpLP significantly reduced myeloperoxidase activity, level of IL-1β, alveolar bone resorption, periodontal destruction, leukocyte influx, and attachment loss. The CpLp also reduced the RANKL/OPG ratio and TRAP+ cells, when compared with the saline group, and did not affect the systemic parameters.

CONCLUSIONS

CpLP exhibited a periodontal protective effect by reducing inflammation and restricting osteoclastic alveolar bone resorption in this rat model.

Molecular Basis beyond Interrelated Bone Resorption/Regeneration in Periodontal Diseases: A Concise Review

Periodontitis is the sixth most common chronic inflammatory disease, destroying the tissues supporting the teeth. There are three distinct stages in periodontitis: infection, inflammation, and tissue destruction, where each stage has its own characteristics and hence its line of treatment. Illuminating the underlying mechanisms of alveolar bone loss is vital in the treatment of periodontitis to allow for subsequent reconstruction of the periodontium. Bone cells, including osteoclasts, osteoblasts, and bone marrow stromal cells, classically were thought to control bone destruction in periodontitis. Lately, osteocytes were found to assist in inflammation-related bone remodeling besides being able to initiate physiological bone remodeling. Furthermore, mesenchymal stem cells (MSCs) either transplanted or homed exhibit highly immunosuppressive properties, such as preventing monocytes/hematopoietic precursor differentiation and downregulating excessive release of inflammatory cytokines. In the early stages of bone regeneration, an acute inflammatory response is critical for the recruitment of MSCs, controlling their migration, and their differentiation. Later during bone remodeling, the interaction and balance between proinflammatory and anti-inflammatory cytokines could regulate MSC properties, resulting in either bone formation or bone resorption. This narrative review elaborates on the important interactions between inflammatory stimuli during periodontal diseases, bone cells, MSCs, and subsequent bone regeneration or bone resorption. Understanding these concepts will open up new possibilities for promoting bone regeneration and hindering bone loss caused by periodontal diseases.

Reduced bone formation and increased bone resorption drive bone loss in Eimeria infected broilers

Coccidiosis is an economically significant disease in the global poultry industry, but little is known about the mechanisms of bone defects caused by coccidiosis; thus, the study focused on effects of coccidiosis on the bone homeostasis of young broiler chickens. A total of 480 male Cobb500 broilers were randomly allocated into four treatment groups, including an uninfected control consuming diet ad libitum, two infected groups were orally gavaged with two different concentrations of sporulated Eimeria oocysts, and an uninfected pair-fed group fed the same amount of feed as the high Eimeria-infected group consumed. Growth performance and feed intake were recorded, and samples were collected on 6 days post infection. Results indicated that coccidiosis increased systemic oxidative status and elevated immune response in bone marrow, suppressing bone growth rate (P < 0.05) and increasing bone resorption (P < 0.05) which led to lower bone mineral density (P < 0.05) and mineral content (P < 0.05) under Eimeria infection. With the same amount of feed intake, the uninfected pair-fed group showed a distinguished bone formation rate and bone resorption level compared with the Eimeria infected groups. In conclusion, inflammatory immune response and oxidative stress in broilers after Eimeria infection were closely associated with altered bone homeostasis, highlighting the role of inflammation and oxidative stress in broiler bone homeostasis during coccidiosis.

The Ethanol Extracts of Osmanthus fragrans Leaves Ameliorate the Bone Loss via the Inhibition of Osteoclastogenesis in Osteoporosis

The aim of this study was to evaluate the anti-osteoporosis effects of Osmanthus fragrans leaf ethanol extract (OFLEE) in bone marrow-derived macrophages (BMM) and animals with osteoporosis. OFLEE not only suppressed tartrate-resistant acid phosphatase (TRAP)-positive cells with multiple nuclei but also decreased TRAP activity in BMM treated with macrophage colony stimulating factor (M-CSF) and receptor activator of nuclear factor-κB (NF-κB) ligand (RANKL). The formation of F-actin rings and the expression and activation of matrix metalloproteinases were decreased by OFLEE in BMM treated with M-CSF and RANKL. OFLEE suppressed M-CSF- and RANKL-induced osteoclastogenesis by inhibiting NF-κB phosphorylation, tumor necrosis factor receptor-associated factor 6, c-fos, the nuclear factor of activated T-cells, cytoplasmic 1, and cathepsin K in BMM. OFLEE downregulated reactive oxygen species, cyclooxygenase-2, inducible nitric oxide synthase, prostaglandin E₂, tumor necrosis factor α, interleukin (IL)-1β, IL-6, IL-17, and RANKL in BMM treated with M-CSF and RANKL. Oral administration of OFLEE suppressed osteoporotic bone loss without hepatotoxicity in ovariectomy-induced osteoporosis animals. Our findings suggest that OFLEE, with anti-inflammatory effects, prevents osteoporotic bone loss through the suppression of osteoclastic differentiation in BMM and animals with osteoporosis.

Increased UHMWPE Particle-Induced Osteolysis in Fetuin-A-Deficient Mice

Particle-induced osteolysis is a major cause of aseptic prosthetic loosening. Implant wear particles stimulate tissue macrophages inducing an aseptic inflammatory reaction, which ultimately results in bone loss. Fetuin-A is a key regulator of calcified matrix metabolism and an acute phase protein. We studied the influence of fetuin-A on particle-induced osteolysis in an established mouse model using fetuin-A-deficient mice. Ten fetuin-A-deficient (Ahsg−/−) mice and ten wild-type animals (Ahsg+/+) were assigned to test group receiving ultra-high molecular weight polyethylene (UHMWPE) particle implantation or to control group (sham surgery). After 14 days, bone metabolism parameters RANKL, osteoprotegerin (OPG), osteocalcin (OC), alkaline phosphatase (ALP), calcium, phosphate, and desoxypyridinoline (DPD) were examined. Bone volume was determined by microcomputed tomography (μCT); osteolytic regions and osteoclasts were histomorphometrically analyzed. After particle treatment, bone resorption was significantly increased in Ahsg−/− mice compared with corresponding Ahsg+/+ wild-type mice (p = 0.007). Eroded surface areas in Ahsg−/− mice were significantly increased (p = 0.002) compared with Ahsg+/+ mice, as well as the number of osteoclasts compared with control (p = 0.039). Fetuin-A deficiency revealed increased OPG (p = 0.002), and decreased levels of DPD (p = 0.038), OC (p = 0.036), ALP (p < 0.001), and Ca (p = 0.001) compared with wild-type animals. Under osteolytic conditions in Ahsg−/− mice, OPG was increased (p = 0.013), ALP (p = 0.015) and DPD (p = 0.012) were decreased compared with the Ahsg+/+ group. Osteolytic conditions lead to greater bone loss in fetuin-A-deficient mice compared with wild-type mice. Reduced fetuin-A serum levels may be a risk factor for particle-induced osteolysis while the protective effect of fetuin-A might be a future pathway for prophylaxis and treatment.

Relationship between diet-related inflammation and bone health under different levels of body mass index

BACKGROUND

Osteoporosis is a major public health problem. Dietary inflammatory preference and body mass index (BMI) are emerging factors that tends to affect bone health. There is limited evidence regarding the joint influence of BMI and dietary status on the bone health. This study aimed to investigate the relationship between dietary inflammatory index (DII) and bone health among adults under different levels of BMI utilizing the National Health and Nutrition Examination Survey (NHANES).

METHODS

Data were collected from 2005-2010, 2013-2014 to 2017-2018 in NHANES. In total, 10,521 participants who aged ≥ 20 years and had complete data for dietary intake interview, bone mineral density (BMD) and bone mineral content (BMC) were included. DII was performed to evaluate the dietary inflammatory potential based on dietary intake interview. We evaluated bone health by femoral neck BMD and BMC measured by dual energy X-ray absorptiometry. Weighted multivariable linear regression and BMI-stratified subgroup analysis were performed.

RESULTS

The average DII score for 10,521 participants was 1.24 ± 0.04, mean femoral neck BMD was 0.82 ± 0.00 g/cm² and mean BMC was 4.37 ± 0.01 g. In the fully adjusted model, there was a negative correlation between DII with BMD (β = - 0.016, P < 0.001) and BMC (β = - 0.011, P < 0.001) in the most anti-inflammatory diet. Using BMI-stratified subgroup analysis, this correlation became more evident in both the overweight (BMD: β = - 0.024, P < 0.001; BMC: β = - 0.058, P = 0.042) and obese groups (BMD: β = - 0.015, P = 0.049; BMC: β = - 0.009, P = 0.042), while this correlation was opposite in DII tertile 2 (middle DII score) in the underweight group (BMD: β = 0.047, P = 0.038; BMC: β = 0.274, P = 0.010).

CONCLUSION

Relationship between higher consumption of pro-inflammatory and increased risk of lower BMD and BMC was only existed in overweight and obese participants.

IL-1 Generated by Oral Squamous Cell Carcinoma Stimulates Tumor-Induced and RANKL-Induced Osteoclastogenesis: A Possible Mechanism of Bone Resorption Induced by the Infiltration of Oral Squamous Cell Carcinoma

We previously observed a novel osteoclastogenesis system that is induced by oral squamous cell carcinoma (OSCC) cells, which target osteoclast precursor cells (OPC) without upregulation of the master transcriptional factor of osteoclastogenesis, NFATc1. Here, we analyzed inflammatory cytokines that were preferentially expressed in one of the osteoclastogenic OSCC cell lines, namely NEM, compared with the subclone that had lost its osteoclastogenic properties. Based on a gene expression microarray and a protein array analyses, IL-1, IL-6, IL-8, and CXCL1 were chosen as candidates responsible for tumor-induced osteoclastogenesis. From the results of the in vitro osteoclastogenesis assay using OPCs cultured with OSCC cells or their culture supernatants, IL-1 was selected as a stimulator of both OSCC-induced and RANKL-induced osteoclastogenesis. The IL-1 receptor antagonist significantly attenuated osteoclastogenesis induced by NEM cells. The stimulatory effects of IL-1 for OSCC-induced and RANKL-induced osteoclastogenesis were effectively attenuated with cannabidiol and denosumab, respectively. These results suggest that IL-1 secreted from OSCC cells stimulates not only tumor-induced osteoclastogenesis targeting OPCs but also physiological RANKL-induced osteoclastogenesis, and this may be the biological mechanism of bone resorption induced by the infiltration of OSCC. These results also suggest that IL-1 inhibitors are candidates for therapeutic agents against bone resorption induced by OSCC.

Potential Association of Osteoporosis and Not Osteoporotic Fractures in Patients with Gout: A Longitudinal Follow-Up Study

Health issues associated with gout and increased occurrence of osteoporosis or fractures have been raised; however, the results are elusive. Herein, we explored the possible link between gout and incident osteoporosis/osteoporotic fractures based on long-term follow-up nationwide data. This study enrolled 16,305 patients with gout and 65,220 controls who were matched by propensity score at a 1:4 ratio on the basis of sex, age, income, and residence from the Korean National Health Insurance Service-Health Screening Cohort database (2002−2015). A Cox proportional hazard model was employed to identify the relevance between gout and incident osteoporosis/fractures, following adjustment for various covariates. In the follow-up period, osteoporosis developed in 761 individuals with gout and 2805 controls (incidence rates: 8.0 and 7.3/1000 person-years, respectively), and each osteoporotic fracture in the distal radius (2.8 vs. 2.7/1000 person-years), hip (1.3 vs. 1.3/1000 person-years), and spine (4.5 vs. 4.5/1000 person-years) occurred in gout and control groups, respectively. After adjustment, the gout group presented an 11% higher development of osteoporosis (95% confidence interval = 1.02−1.20) than the controls (p = 0.011). Subgroup analyses maintained the augment of incident osteoporosis in sufferers with gout, particularly in either men or <60 years. However, no such relevance was identified between gout and incident osteoporotic fractures at any site. In conclusion, gout may result in a slightly elevated likelihood of developing osteoporosis, and not osteoporotic fractures, in the Korean population.

Dual-functional composite scaffolds for inhibiting infection and promoting bone regeneration

The treatment of infected bone defects is an intractable problem in orthopedics. It comprises two critical parts, namely that of infection control and bone defect repair. According to these two core tasks during treatment, the ideal approach of simultaneously controlling infection and repairing bone defects is promising treatment strategy. Several engineered biomaterials and drug delivery systems with dual functions of anti-bacterial action and ostogenesis-promotion have been developed and demonstrated excellent therapeutic effects. Compared with the conventional treatment method, the dual-functional composite scaffold can provide one-stage treatment avoiding multiple surgeries, thereby remarkably simplifying the treatment process and reducing the treatment time, overcoming the disadvantages of conventional bone transplantation. In this review, the impaired bone repair ability and its specific mechanisms in the microenvironment of pathogen infection and excessive inflammation were analyzed, providing a theoretical basis for the treatment of infectious bone defects. Furthermore, we discussed the composite dual-functional scaffold composed of a combination of antibacterial and osteogenic material. Finally, a series of advanced drug delivery systems with antibacterial and bone-promoting capabilities were summarized and discussed. This review provides a comprehensive understanding for the microenvironment of infectious bone defects and leading-edge design strategies for the antibacterial and bone-promoting dual-function scaffold, thus providing clinically significant treatment methods for infectious bone defects.

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Antibacterial and bone-promoting dual-function scaffolds are ideal strategies for treatment of infectious bone defects.

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The effect of infection on bone repair was summarized in detail from four important aspects.

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A variety of dual-function scaffolds based on antibacterial and osteogenic materials were discussed.

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Dual-function drug delivery systems promoting repair of infectious bone defects by locally releasing functional agents.

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Leading-edge design strategies, challenges and prospects for dual-functional biomaterials were provided.

Ameliorative Effect of Tocotrienols on Perimenopausal-Associated Osteoporosis-A Review

Osteoporosis, or bone loss, is a disease that affects many women globally. As life expectancy increases, the risk of osteoporosis in women also increases, too, and this will create a burden on the healthcare and economic sectors of a country. Osteoporosis was once thought to be a disease that would occur only after menopause. However, many studies have shown that osteoporosis may develop even in the perimenopausal stage. Due to the erratic levels of estrogen and progesterone during the perimenopausal stage, studies suggest that women are exposed to the risk of developing osteoporosis even at this stage. The erratic hormonal changes result in the production of proinflammatory mediators and cause oxidative stress, which leads to the progressive loss of bone-building activities. Tocotrienols, members of vitamin E, have many health-promoting properties. Due to their powerful anti-oxidative and anti-inflammatory properties, tocotrienols have shown positive anti-osteoporotic properties in post-menopausal studies. Hence, we propose here that tocotrienols could also possibly alleviate perimenopausal osteoporosis by discussing in this review the connection between inflammatory mediators produced during perimenopause and the risk of osteoporosis. Tocotrienols could potentially be an anti-osteoporotic agent, but due to their low bioavailability, they have not been as effective as they could be. Several approaches have been evaluated to overcome this issue, as presented in this review. As the anti-osteoporotic effects of tocotrienols were mostly studied in post-menopausal models, we hope that this review could pave the way for more research to be done to evaluate their effect on peri-menopausal models so as to reduce the risk of osteoporosis from an earlier stage.

Cytokine-mediated immunomodulation of osteoclastogenesis

Cytokines are an important set of proteins regulating bone homeostasis. In inflammation induced bone resorption, cytokines, such as RANKL, TNF-α, M-CSF, are indispensable for the differentiation and activation of resorption-driving osteoclasts, the process we know as osteoclastogenesis. On the other hand, immune system produces a number of regulatory cytokines, including IL-4, IL-10 and IFNs, and limits excessive activation of osteoclastogenesis and bone loss during inflammation. These unique properties make cytokines powerful targets as rheostat to maintain bone homeostasis and for potential immunotherapies of inflammatory bone diseases. In this review, we summarize recent advances in cytokine-mediated regulation of osteoclastogenesis and provide insights of potential translational impact of bench-side research into clinical treatment of bone disease.

Risk factors for future osteoporosis in perimenopausal Japanese women

OBJECTIVE

The aims of this study were to investigate trends in bone mineral density (BMD) loss and related factors in early postmenopausal women in Japan, identify risk factors for future osteoporosis, and predict osteoporosis before it occurs.

METHODS

The study population consisted of women who were 50 to 54 years old at the time of the survey in 2002 or 2006. The study included a questionnaire and physical measurement findings (BMD, height, body weight [WT], body mass index [BMI], and handgrip strength). One hundred sixty-seven women continued to participate in the study and had BMD measurements at the 9- or 10-year follow-up of the Japanese Population-based Osteoporosis study. Statistical analyses were performed using Pearson correlation to examine each factor of physical measurement and BMD for lumbar spine (LS) and femoral neck (FN). The receiver operating characteristic curve of this data was also predictive of osteoporosis in 2011 for 2002 data; BMD at the age of 50 to 54 years was then used to predict the likelihood of being diagnosed with osteoporosis 9 and 10 years later.

RESULTS

At the baseline in 2002 and 2006, WT, BMI, height, and handgrip strength were positively correlated with BMD. The optimal cutoff values for BMD in 2006 to predict osteoporosis in 2016 were LS less than 0.834 g/cm 2 and FN less than 0.702 g/cm 2 . These data were also predictive of osteoporosis in 2011 for 2002 data; applying this to the 2002 data, LS/FN had a sensitivity of 92%/100%, a specificity of 87%/81%, a positive predictive value of 55%/48%, and a negative predictive value of 98%/100%. The larger WT and BMI also resulted in a greater decrease in BMD of FN after 9 or 10 years.

CONCLUSIONS

We have identified a cutoff value for BMD to predict future osteoporosis in menopausal women and found a negative correlation between WT and BMI in menopausal women and changes in BMD of the FN over the next 10 years.

Autophagy Plays Multiple Roles in the Soft-Tissue Healing and Osseointegration in Dental Implant Surgery-A Narrative Review

Dental endo-osseous implants have become a widely used treatment for replacing missing teeth. Dental implants are placed into a surgically created osteotomy in alveolar bone, the healing of the soft tissue lesion and the osseointegration of the implant being key elements to long-term success. Autophagy is considered the major intracellular degradation system, playing important roles in various cellular processes involved in dental implant integration. The aim of this review is an exploration of autophagy roles in the main cell types involved in the healing and remodeling of soft tissue lesions and implant osseointegration, post-implant surgery. We have focused on the autophagy pathway in macrophages, endothelial cells; osteoclasts, osteoblasts; fibroblasts, myofibroblasts and keratinocytes. In macrophages, autophagy modulates innate and adaptive immune responses playing a key role in osteo-immunity. Autophagy induction in endothelial cells promotes apoptosis resistance, cell survival, and protection against oxidative stress damage. The autophagic machinery is also involved in transporting stromal vesicles containing mineralization-related factors to the extracellular matrix and regulating osteoblasts' functions. Alveolar bone remodeling is achieved by immune cells differentiation into osteoclasts; autophagy plays an important and active role in this process. Autophagy downregulation in fibroblasts induces apoptosis, leading to better wound healing by improving excessive deposition of extracellular matrix and inhibiting fibrosis progression. Autophagy seems to be a dual actor on the scene of dental implant surgery, imposing further research in order to completely reveal its positive features which may be essential for clinical efficacy.

Rheumatoid arthritis and osteoimmunology: The adverse impact of a deregulated immune system on bone metabolism

The term osteoimmunology describes an interdisciplinary research field that links the investigation of osteology (bone cells) with immunology. The crosstalk between innate and adaptive immune cells and cells involved in bone remodeling, mainly bone-resorbing osteoclasts and bone-forming osteoblasts, becomes particularly obvious in the inflammatory autoimmune disease rheumatoid arthritis (RA). Besides striking inflammation of the joints, RA causes bone loss, leading to joint damage and disabilities as well as generalized osteoporosis. Mechanistically, RA-associated immune cells (macrophages, T cells, B cells etc.) produce high levels of pro-inflammatory cytokines, receptor activator of nuclear factor κB ligand (RANKL) and autoantibodies that promote bone degradation and at the same time counteract new bone formation. Today, antirheumatic therapy effectively ceases joint inflammation and arrests bone erosion. However, the repair of established bone lesions still presents a challenging task and requires improved treatment options. In this review, we outline the knowledge gained over the past years about the immunopathogenesis of RA and the impact of a dysregulated immune system on bone metabolism.

Risk factors for osteoporosis and fractures in rheumatoid arthritis

People with rheumatoid arthritis (RA) have both disease-specific risk factors for osteoporosis and fractures in addition to those that affect the general population. Disease specific risks include directly pathogenic auto-antibodies, chronic exposure to systemic inflammation, and joint damage causing early disability. Risk factors that affect the general population which may have a higher prevalence in RA include smoking, calcium and vitamin D deficiency as well as hypogonadism. Additionally, chronic exposure to glucocorticoids results in reduced bone mineral density and body composition changes which can further increase fracture risk. In this review we discuss these risk-factors for osteoporosis as well as factors that may impact fall and fracture risk in people with RA.

A Review of Signaling Transduction Mechanisms in Osteoclastogenesis Regulation by Autophagy, Inflammation, and Immunity

Osteoclastogenesis is an ongoing rigorous course that includes osteoclast precursors fusion and bone resorption executed by degradative enzymes. Osteoclastogenesis is controlled by endogenous signaling and/or regulators or affected by exogenous conditions and can also be controlled both internally and externally. More evidence indicates that autophagy, inflammation, and immunity are closely related to osteoclastogenesis and involve multiple intracellular organelles (e.g., lysosomes and autophagosomes) and certain inflammatory or immunological factors. Based on the literature on osteoclastogenesis induced by different regulatory aspects, emerging basic cross-studies have reported the emerging disquisitive orientation for osteoclast differentiation and function. In this review, we summarize the partial potential therapeutic targets for osteoclast differentiation and function, including the signaling pathways and various cellular processes.

Intestinal Inflammation Promotes MDL-1+ Osteoclast Precursor Expansion to Trigger Osteoclastogenesis and Bone Loss

BACKGROUND & AIMS

Inflammatory bowel disease (IBD) is characterized by severe gastrointestinal inflammation, but many patients experience extra-intestinal disease. Bone loss is one common extra-intestinal manifestation of IBD that occurs through dysregulated interactions between osteoclasts and osteoblasts. Systemic inflammation has been postulated to contribute to bone loss, but the specific pathologic mechanisms have not yet been fully elucidated. We hypothesized that intestinal inflammation leads to bone loss through increased abundance and altered function of osteoclast progenitors.

METHODS

We used chemical, T cell driven, and infectious models of intestinal inflammation to determine the impact of intestinal inflammation on bone volume, the skeletal cytokine environment, and the cellular changes to pre-osteoclast populations within bone marrow. Additionally, we evaluated the potential for monoclonal antibody treatment against an inflammation-induced osteoclast co-receptor, myeloid DNAX activation protein 12-associating lectin-1 (MDL-1) to reduce bone loss during colitis.

RESULTS

We observed significant bone loss across all models of intestinal inflammation. Bone loss was associated with an increase in pro-osteoclastogenic cytokines within the bone and an expansion of a specific Cd11b^-/loLy6C^hi osteoclast precursor (OCP) population. Intestinal inflammation led to altered OCP expression of surface receptors involved in osteoclast differentiation and function, including the pro-osteoclastogenic co-receptor MDL-1. OCPs isolated from mice with intestinal inflammation demonstrated enhanced osteoclast differentiation ex vivo compared to controls, which was abrogated by anti-MDL-1 antibody treatment. Importantly, in vivo anti-MDL-1 antibody treatment ameliorated bone loss during intestinal inflammation.

CONCLUSIONS

Collectively, these data implicate the pathologic expansion and altered function of OCPs expressing MDL-1 in bone loss during IBD.

Interleukin-1 receptor antagonist enhances the therapeutic efficacy of a low dose of rhBMP-2 in a weight-bearing rat femoral defect model

In the clinical treatment of fractures, rhBMP-2 administration is associated with a well-established profile of side-effects, including osteolysis and ectopic bone formation, which are driven by pro-inflammatory processes triggered by the use of high doses. Immunomodulatory strategies could minimize the incidence of side-effects by enabling the use of lower, and safer, rhBMP-2 doses. This study investigated whether interleukin-1 receptor antagonist (IL-1Ra) can enhance the therapeutic efficacy of a low dose of rhBMP-2 in a weight-bearing femoral fracture healing model. Exogenous IL-1Ra, in combination with rhBMP-2, was delivered using a collagen-hydroxyapatite scaffold (CHA) to attenuate IL-1β produced in response to fracture. Femoral defects were treated with CHA scaffolds alone, or loaded with IL-1Ra (2.5 µg), rhBMP-2 (1 µg), IL-1Ra (2.5 µg) in combination with rhBMP-2 (1 µg). Bone healing was assessed over 14 weeks in comparison to control groups, empty defect, and a higher dose of rhBMP-2 (5 µg), which were recently demonstrated to lead to non-union, and successful bridging of the defect, respectively. The combination of IL-1Ra and rhBMP-2 led to significantly faster early bone formation, at both week 4 and 6, compared to a low dose of rhBMP-2 alone. By 14 weeks, the combination of IL-1Ra and a rhBMP-2 promoted full bridging of femurs, which were 3-fold more mechanically reliable compared to the femurs treated with a low dose of rhBMP-2 alone. Taken together, this study demonstrates that IL-1Ra can significantly enhance femoral bone healing when used in combination with a low dose of rhBMP-2. STATEMENT OF SIGNIFICANCE: Enabling the use of lower and safer doses of rhBMP-2, a potent inducer of bone formation, is of clinical relevance in orthopaedic medicine. In this study, the immunomodulatory interleukin-1 receptor antagonist (IL-1Ra) was investigated for its capacity to enhance the therapeutic efficacy of rhBMP-2 when used at lower doses in a weight-bearing femoral fracture healing model. The combination of IL-1Ra and rhBMP-2 led to significantly faster early bone formation, and resulted in more mechanically reliable healed femurs, compared to a low dose of rhBMP-2 alone. This demonstrates for the first time in a rat long bone healing model that IL-1Ra can significantly enhance bone healing when used in combination with a low dose of rhBMP-2.

Involvement of NF-κB/NLRP3 axis in the progression of aseptic loosening of total joint arthroplasties: a review of molecular mechanisms

Particulate wear debris can trigger pro-inflammatory bone resorption and result in aseptic loosening. This complication remains major postoperative discomforts and complications for patients who underwent total joint arthroplasty. Recent studies have indicated that wear debris-induced aseptic loosening is associated with the overproduction of pro-inflammatory cytokines. The activation of osteoclasts as a result of inflammatory responses is associated with osteolysis. Moreover, stimulation of inflammatory signaling pathways such as the NF-κB/NLRP3 axis results in the production of pro-inflammatory cytokines. In this review, we first summarized the potential inflammatory mechanisms of wear particle-induced peri-implant osteolysis. Then, the therapeutic approaches, e.g., biological inhibitors, herbal products, and stem cells or their derivatives, with the ability to suppress the inflammatory responses, mainly NF-κB/NLRP3 signaling pathways, were discussed. Based on the results, activation of macrophages following inflammatory stimuli, overproduction of pro-inflammatory cytokines, and subsequent differentiation of osteoclasts in the presence of wear particles lead to bone resorption. The activation of NF-κB/NLRP3 signaling pathways within the macrophages stimulates the production of pro-inflammatory cytokines, e.g., IL-1β, IL-6, and TNF-α. According to in vitro and in vivo studies, novel therapeutics significantly promoted osteogenesis, suppressed osteoclastogenesis, and diminished particle-mediated bone resorption. Conclusively, these findings offer that suppressing pro-inflammatory cytokines by regulating both NF-κB and NLRP3 inflammasome represents a novel approach to attenuate wear-particle-related osteolytic diseases.

Increasing trend of radiographic features of knee osteoarthritis in rheumatoid arthritis patients before total knee arthroplasty

To investigate the trend and factors related to the occurrence of osteoarthritis (OA)-like features on knee radiographs of rheumatoid arthritis (RA) patients undergoing total knee arthroplasty (TKA) in the recent decades. To classify antero-posterior knee radiographs into 'RA' and 'OA-like RA' groups, a deep learning model was developed by training the network using knee radiographs of end-stage arthropathy in RA patients obtained during 2002-2005 and in primary OA patients obtained during 2007-2009. We used this model to categorize 796 knee radiographs, which were recorded in RA patients before TKA during 2006-2020, into 'OA-like RA' and 'RA' groups. The annual ratio of 'OA-like RA' was investigated. Moreover, univariate and multivariate analyses were performed to identify the factors associated with the classification as OA-like RA using clinical data from 240 patients. The percentage of 'OA-like RA' had significant increasing trend from 20.9% in 2006 to 67.7% in 2020. Higher body mass index, use of biologics, and lower level of C-reactive protein were identified as independent factors for 'OA-like RA'. An increasing trend of knee radiographs with OA-like features was observed in RA patients in the recent decades, which might be attributed to recent advances in pharmacotherapy.

SARS-CoV-2 infection induces inflammatory bone loss in golden Syrian hamsters

Extrapulmonary complications of different organ systems have been increasingly recognized in patients with severe or chronic Coronavirus Disease 2019 (COVID-19). However, limited information on the skeletal complications of COVID-19 is known, even though inflammatory diseases of the respiratory tract have been known to perturb bone metabolism and cause pathological bone loss. In this study, we characterize the effects of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection on bone metabolism in an established golden Syrian hamster model for COVID-19. SARS-CoV-2 causes significant multifocal loss of bone trabeculae in the long bones and lumbar vertebrae of all infected hamsters. Moreover, we show that the bone loss is associated with SARS-CoV-2-induced cytokine dysregulation, as the circulating pro-inflammatory cytokines not only upregulate osteoclastic differentiation in bone tissues, but also trigger an amplified pro-inflammatory cascade in the skeletal tissues to augment their pro-osteoclastogenesis effect. Our findings suggest that pathological bone loss may be a neglected complication which warrants more extensive investigations during the long-term follow-up of COVID-19 patients. The benefits of potential prophylactic and therapeutic interventions against pathological bone loss should be further evaluated.

Although extrapulmonary complications of different organ systems are recognized in patients with severe COVID19 effects are less well studied. Here, Qiao et al. characterize the pathogenesis of SARS-CoV-2 on bone metabolism in Syrian hamster and find that bone loss is associated with virus-mediated cytokine dysregulation.

Pathological Osteoclasts and Precursor Macrophages in Inflammatory Arthritis

Macrophages comprise a variety of subsets with diverse biological functions, including inflammation, tissue repair, regeneration, and fibrosis. In the bone marrow, macrophages differentiate into multinucleated osteoclasts, which have a unique bone-destroying capacity and play key roles in physiological bone remodelling. In contrast, osteoclasts are also involved in inflammatory bone erosion in arthritis and it has been unclear whether the osteoclasts in different tissue settings arise from similar monocytoid precursors and share similar phenotypes. Rapid progresses in the sequencing technologies have provided many important insights regarding the heterogeneity of different types of osteoclasts. The application of single-cell RNA sequencing (scRNA-seq) to the osteoclast precursor-containing macrophages enabled to identify the specific subpopulation differentiating into pathological mature osteoclasts in joints. Furthermore, an intravital imaging technology using two-photon microscopy has succeeded in visualizing the real-time dynamics of immune cells in the synovial microenvironment. These technologies together contributed to characterize the unique macrophages in the inflamed synovium, termed “arthritis-associated osteoclastogenic macrophages (AtoMs)”, causing the pathological bone destruction in inflammatory arthritis. Here, we review and discuss how novel technologies help to better understand the role of macrophages in inflammatory arthritis, especially focusing of osteoclastogenesis at the pannus-bone interface.

Deletion of IL-17ra in osteoclast precursors increases bone mass by decreasing osteoclast precursor abundance

Metabolic bone diseases, such as osteoporosis, typically reflect an increase in the number and activity of bone-resorbing osteoclasts that result in a loss of bone mass. Inflammatory mediators have been identified as drivers of both osteoclast formation and activity. The IL-17 family of inflammatory cytokines has gained attention as important contributors to both bone formation and resorption. The majority of IL-17 cytokines signal through receptor complexes containing IL-17a receptor (IL-17ra); however, the role of IL-17ra signaling in osteoclasts remains elusive. In this study, we conditionally deleted Il17ra in osteoclast precursors using LysM-Cre and evaluated the phenotypes of skeletally mature male and female conditional knockout and control mice. The conditional knockout mice displayed an increase in trabecular bone microarchitecture in both the appendicular and axial skeleton. Assessment of osteoclast formation in vitro revealed that deletion of Il17ra decreased osteoclast number, which was confirmed in vivo using histomorphometry. This phenotype was likely driven by a lower abundance of osteoclast precursors in IL-17ra conditional knockout mice. This study suggests that IL-17ra signaling in preosteoclasts can contribute to osteoclast formation and subsequent bone loss.

Substance P, A Promising Therapeutic Target in Musculoskeletal Disorders

A large number of studies have focused on the role of substance P (SP) and the neurokinin-1 receptor (NK1R) in the pathogenesis of a variety of medical conditions. This review provides an overview of the role of the SP-NK1R pathway in the pathogenesis of musculoskeletal disorders and the evidence for its role as a therapeutic target for these disorders, which are major public health problems in most countries. To summarize, the brief involvement of SP may affect tendon healing in an acute injury setting. SP combined with an adequate conjugate can be a regenerative therapeutic option in osteoarthritis. The NK1R antagonist is a promising agent for tendinopathy, rheumatoid arthritis, and osteoarthritis. Research on the SP-NK1R pathway will be helpful for developing novel drugs for osteoporosis.