Interleukin 1 induces multinucleation and bone-resorbing activity of osteoclasts in the absence of osteoblasts/stromal cells

Pathophysiology of bone remodelling cycle: Role of immune system and lipids

Osteoporosis is the most common skeletal disease worldwide, characterized by low bone mineral density, resulting in weaker bones, and an increased risk of fragility fractures. The maintenance of bone mass relies on the precise balance between bone synthesis and resorption. The close relationship between the immune and skeletal systems, called "osteoimmunology", was coined to identify these overlapping "scientific worlds", and its function resides in the evaluation of the mutual effects of the skeletal and immune systems at the molecular and cellular levels, in both physiological and pathological states. Lipids play an essential role in skeletal metabolism and bone health. Indeed, bone marrow and its skeletal components demand a dramatic amount of daily energy to control hematopoietic turnover, acquire and maintain bone mass, and actively being involved in whole-body metabolism. Statins, the main therapeutic agents in lowering plasma cholesterol levels, are able to promote osteoblastogenesis and inhibit osteoclastogenesis. This review is meant to provide an updated overview of the pathophysiology of bone remodelling cycle, focusing on the interplay between bone, immune system and lipids. Novel therapeutic strategies for the management of osteoporosis are also discussed.

IL-1β in Neoplastic Disease and the Role of Its Tumor-Derived Form in the Progression and Treatment of Metastatic Prostate Cancer

Since its discovery, IL-1β has taken center stage as a key mediator of a very broad spectrum of diseases revolving around immuno-mediated and inflammatory events. Predictably, the pleiotropic nature of this cytokine in human pathology has led to the development of targeted therapeutics with multiple treatment indications in the clinic. Following the accumulated findings of IL-1β's central modulatory role in the immune system and the implication of inflammatory pathways in cancer, the use of IL-1β antagonists was first proposed and then also pursued for oncology disorders. However, this approach has consistently relied on the perceived need of interfering with IL-1β synthesized and secreted by immune cells. Herein, we discuss the importance of IL-1β derived from cancer cells which impacts primary tumors, particularly metastatic lesions, separately from and in addition to its more recognized role in immune-mediated inflammatory events. To this end, we focus on the instrumental contribution of IL-1β in the establishment and progression of advanced prostate adenocarcinoma. Special emphasis is placed on the potential role that the standard-of-care treatment strategies for prostate cancer patients have in unleashing IL-1β expression and production at metastatic sites. We conclude by reviewing the therapeutics currently used for blocking IL-1β signaling and propose a rationale for their concomitant use with standard-of-care treatments to improve the clinical outcomes of advanced prostate cancer.

The MCP-3/Ccr3 axis contributes to increased bone mass by affecting osteoblast and osteoclast differentiation

Several CC subfamily chemokines have been reported to regulate bone metabolism by affecting osteoblast or osteoclast differentiation. However, the role of monocyte chemotactic protein 3 (MCP-3), a CC chemokine, in bone remodeling is not well understood. Here, we show that MCP-3 regulates bone remodeling by promoting osteoblast differentiation and inhibiting osteoclast differentiation. In a Ccr3-dependent manner, MCP-3 promoted osteoblast differentiation by stimulating p38 phosphorylation and suppressed osteoclast differentiation by upregulating interferon beta. MCP-3 increased bone morphogenetic protein 2-induced ectopic bone formation, and mice with MCP-3-overexpressing osteoblast precursor cells presented increased bone mass. Moreover, MCP-3 exhibited therapeutic effects by abrogating receptor activator of nuclear factor kappa-B ligand-induced bone loss. Therefore, MCP-3 has therapeutic potential for diseases involving bone loss due to its positive role in osteoblast differentiation and negative role in osteoclast differentiation.

Osteoinduction and osteoimmunology: Emerging concepts

The recognition and importance of immune cells during bone regeneration, including around bone biomaterials, has led to the development of an entire field termed "osteoimmunology," which focuses on the connection and interplay between the skeletal system and immune cells. Most studies have focused on the "osteogenic" capacity of various types of bone biomaterials, and much less focus has been placed on immune cells despite being the first cell type in contact with implantable devices. Thus, the amount of literature generated to date on this topic makes it challenging to extract needed information. This review article serves as a guide highlighting advancements made in the field of osteoimmunology emphasizing the role of the osteoimmunomodulatory properties of biomaterials and their impact on osteoinduction. First, the various immune cell types involved in bone biomaterial integration are discussed, including the prominent role of osteal macrophages (OsteoMacs) during bone regeneration. Thereafter, key biomaterial properties, including topography, wettability, surface charge, and adsorption of cytokines, growth factors, ions, and other bioactive molecules, are discussed in terms of their impact on immune responses. These findings highlight and recognize the importance of the immune system and osteoimmunology, leading to a shift in the traditional models used to understand and evaluate biomaterials for bone regeneration.

Plasmon resonance biosensor for interleukin-1β point-of-care determination: A tool for early periodontitis diagnosis

Among pro-inflammatory cytokines, Interleukin-1β is crucially involved in several inflammatory-based diseases and even cancer. Increased Interleukin-1β levels in oral fluids have been proposed as an early marker of periodontitis, a broadly diffused chronic inflammatory condition of periodontal-supporting tissues, leading eventually to tooth loss. We describe the development of a portable surface-plasmon-resonance-based optical fiber probe suitably coated with an anti-Interleukin-1β antibody monolayer. A pico-nanomolar linear range of determination was obtained in both buffer solution and saliva with a rapid (3 min) incubation and high selectivity in presence of interferents. Higher Interleukin-1β concentration in the saliva of a periodontitis patient compared to a healthy control was determined. These measurements were validated by an automated ELISA system. Our results sustain the potential applicability of the proposed SPR-POF as diagnostic point-of-care device for real-time monitoring of salivary Interleukin-1β, that can support early detection of oral inflammatory-based pathologies and rapid and timely therapeutic decisions.

Equisetum arvense Inhibits Alveolar Bone Destruction in a Rat Model with Lipopolysaccharide (LPS)-Induced Periodontitis

Background and Aims

Equisetum arvense extract (EA) exerts various biological effects, including anti-inflammatory activity. The effect of EA on alveolar bone destruction has not been reported; therefore, we aimed to determine whether EA could inhibit alveolar bone destruction associated with periodontitis in a rat model in which periodontitis was induced using lipopolysaccharide from Escherichia coli (E. coli-LPS).

Methods

Physiological saline or E. coli-LPS or E. coli-LPS/EA mixture was topically administered into the gingival sulcus of the upper molar region of the rats. After 3 days, periodontal tissues of the molar region were collected. Immunohistochemistry was performed for cathepsin K, receptor activator of NF-κB ligand (RANKL), and osteoprotegerin (OPG). The cathepsin K-positive osteoclasts along the alveolar bone margin were counted. EA effects on the expression of the factors regulating osteoclastogenesis in osteoblasts with E. coli-LPS-stimulation were also examined in vitro.

Results

Treatment with EA significantly reduced the number of osteoclasts by decreasing the RANKL-expression and increasing OPG-expression in the periodontal ligament in the treatment group compared to the E. coli-LPS group. The in vitro study showed that the upregulation of p-IκB kinase α and β (p-IKKα/β), p-NF-κB p65, TNF-α, interleukin-6, and RANKL and downregulation of semaphorin 3A (Sema3A), β-catenin, and OPG in the osteoblasts with E. coli-LPS-stimulation improved with EA-treatment.

Conclusion

These findings demonstrated that topical EA suppressed alveolar bone resorption in the rat model with E. coli-LPS-induced periodontitis by maintaining a balance in RANKL/OPG ratio via the pathways of NF-κB, Wnt/β-catenin, and Sema3A/Neuropilin-1. Therefore, EA possesses the potential to prevent bone destruction through inhibiting osteoclastogenesis attributed to cytokine burst under plaque accumulation.

Treatment of Periodontal Inflammation in Diabetic Rats with IL-1ra Thermosensitive Hydrogel

Periodontitis is a chronic inflammatory disease that is considered to be the main cause of adult tooth loss. Diabetes mellitus (DM) has a bidirectional relationship with periodontitis. Interleukin-1β (IL-1β) is an important pre-inflammatory factor, which participates in the pathophysiological process of periodontitis and diabetes. The interleukin-1 receptor antagonist (IL-1ra) is a natural inhibitor of IL-1, and the balance between IL-1ra and IL-1β is one of the main factors affecting chronic periodontitis (CP) and diabetes. The purpose of this study is to develop a drug carrier that is safe and nontoxic and can effectively release IL-1ra, which can effectively slow down the inflammation of periodontal tissues with diabetes, and explore the possibility of lowering the blood sugar of this drug carrier. Therefore, in this experiment, a temperature-sensitive hydrogel loaded with IL-1ra was prepared and characterized, and its anti-inflammatory effect in high-sugar environments in vivo and in vitro was evaluated. The results showed that the hydrogel could gel after 5 min at 37 °C, the pore size was 5-70 μm, and the cumulative release of IL-1ra reached 83.23% on the 21st day. Real-time polymerase chain reaction (qRT-PCR) showed that the expression of IL-1β, Interleukin 6 (IL-6), and tumor necrosis factor α (TNF-α) inflammatory factors decreased after the treatment with IL-1ra-loaded thermosensitive hydrogel. Histological evaluation and micro-computed tomography (Micro-CT) showed that IL-1ra-loaded thermosensitive hydrogel could effectively inhibit periodontal inflammation and reduce alveolar bone absorption in rats with diabetic periodontitis. It is worth mentioning that this hydrogel also plays a role in relieving hyperglycemia. Therefore, the temperature-sensitive hydrogel loaded with IL-1ra may be an effective method to treat periodontitis with diabetes.

Fracture-related infection

Musculoskeletal trauma leading to broken and damaged bones and soft tissues can be a life-threating event. Modern orthopaedic trauma surgery, combined with innovation in medical devices, allows many severe injuries to be rapidly repaired and to eventually heal. Unfortunately, one of the persisting complications is fracture-related infection (FRI). In these cases, pathogenic bacteria enter the wound and divert the host responses from a bone-healing course to an inflammatory and antibacterial course that can prevent the bone from healing. FRI can lead to permanent disability, or long courses of therapy lasting from months to years. In the past 5 years, international consensus on a definition of these infections has focused greater attention on FRI, and new guidelines are available for prevention, diagnosis and treatment. Further improvements in understanding the role of perioperative antibiotic prophylaxis and the optimal treatment approach would be transformative for the field. Basic science and engineering innovations will be required to reduce infection rates, with interventions such as more efficient delivery of antibiotics, new antimicrobials, and optimizing host defences among the most likely to improve the care of patients with FRI.

Revisiting the role of IL-1 signaling in the development of apical periodontitis

Apical periodontitis (AP) develops as a result of an immune response to pulpal bacterial infection, and various cytokines are involved in the pathogenesis of AP, with Interleukin (IL)-1 being considered a key cytokine. The role of IL-1 in the pathogenesis of AP has been well studied. It is known that IL-1 expression in periapical lesions correlates closely with the development of AP. IL-1 is a potent bone-resorptive cytokine that induces osteoclast formation and activation. Hence, inhibiting its signaling with IL-1 receptor antagonist (IL-1RA) results in a reduction in periapical lesion size. On the other hand, IL-1 is also a central cytokine that combats bacterial infection by activating innate immune responses. Therefore, a complete loss of IL-1 signaling leads to a failure to limit bacterial dissemination and consequently exacerbates AP. In vivo, IL-1 expression is tightly regulated and its signaling is modulated to optimize the immune response. Obesity causes systemic low-grade chronic inflammation and increases the risk of cardiovascular, renal, and other disorders. In experimentally induced AP, obesity significantly increases periapical bone loss, albeit the underlying mechanism remains unclear. Recent technological innovations have enabled more comprehensive and detailed analyses than previously, leading to new insights into the role of IL-1RA in regulating IL-1 signaling, and modulating apical lesion progression in obesity. In this review, we provide a brief overview of the function of IL-1 in AP development, with special emphasis on the latest findings in normal weight and obese states.

Inflammasomes and the IL-1 Family in Bone Homeostasis and Disease

PURPOSE OF REVIEW

Inflammasomes are multimeric protein structures with crucial roles in host responses against infections and injuries. The importance of inflammasome activation goes beyond host defense as a dysregulated inflammasome and subsequent secretion of IL-1 family members is believed to be involved in the pathogenesis of various diseases, some of which also produce skeletal manifestations. The purpose of this review is to summarize recent developments in the understanding of inflammasome regulation and IL-1 family members in bone physiology and pathology and current therapeutics will be discussed.

RECENT FINDINGS

Small animal models have been vital to help understand how the inflammasome regulates bone dynamics. Animal models with gain or loss of function in various inflammasome components or IL-1 family signaling have illustrated how these systems can impact numerous bone pathologies and have been utilized to test new inflammasome therapeutics. It is increasingly clear that a tightly regulated inflammasome is required not only for host defense but for skeletal homeostasis, as a dysregulated inflammasome is linked to diseases of pathological bone accrual and loss. Given the complexities of inflammasome activation and redundancies in IL-1 activation and secretion, targeting these pathways is at times challenging. Ongoing research into inflammasome-mediated mechanisms will allow the development of new therapeutics for inflammasome/IL-1 diseases.

The Role Of BMPs in the Regulation of Osteoclasts Resorption and Bone Remodeling: From Experimental Models to Clinical Applications

In response to mechanical forces and the aging process, bone in the adult skeleton is continuously remodeled by a process in which old and damaged bone is removed by bone-resorbing osteoclasts and subsequently is replaced by new bone by bone-forming cells, osteoblasts. During this essential process of bone remodeling, osteoclastic resorption is tightly coupled to osteoblastic bone formation. Bone-resorbing cells, multinuclear giant osteoclasts, derive from the monocyte/macrophage hematopoietic lineage and their differentiation is driven by distinct signaling molecules and transcription factors. Critical factors for this process are Macrophage Colony Stimulating Factor (M-CSF) and Receptor Activator Nuclear Factor-κB Ligand (RANKL). Besides their resorption activity, osteoclasts secrete coupling factors which promote recruitment of osteoblast precursors to the bone surface, regulating thus the whole process of bone remodeling. Bone morphogenetic proteins (BMPs), a family of multi-functional growth factors involved in numerous molecular and signaling pathways, have significant role in osteoblast-osteoclast communication and significantly impact bone remodeling. It is well known that BMPs help to maintain healthy bone by stimulating osteoblast mineralization, differentiation and survival. Recently, increasing evidence indicates that BMPs not only help in the anabolic part of bone remodeling process but also significantly influence bone catabolism. The deletion of the BMP receptor type 1A (BMPRIA) in osteoclasts increased osteoblastic bone formation, suggesting that BMPR1A signaling in osteoclasts regulates coupling to osteoblasts by reducing bone-formation activity during bone remodeling. The dual effect of BMPs on bone mineralization and resorption highlights the essential role of BMP signaling in bone homeostasis and they also appear to be involved in pathological processes in inflammatory disorders affecting bones and joints. Certain BMPs (BMP2 and -7) were approved for clinical use; however, increased bone resorption rather than formation were observed in clinical applications, suggesting the role BMPs have in osteoclast activation and subsequent osteolysis. Here, we summarize the current knowledge of BMP signaling in osteoclasts, its role in osteoclast resorption, bone remodeling, and osteoblast–osteoclast coupling. Furthermore, discussion of clinical application of recombinant BMP therapy is based on recent preclinical and clinical studies.

Integrated computational and in vivo models reveal Key Insights into macrophage behavior during bone healing

Myeloid-derived monocyte and macrophages are key cells in the bone that contribute to remodeling and injury repair. However, their temporal polarization status and control of bone-resorbing osteoclasts and bone-forming osteoblasts responses is largely unknown. In this study, we focused on two aspects of monocyte/macrophage dynamics and polarization states over time: 1) the injury-triggered pro- and anti-inflammatory monocytes/macrophages temporal profiles, 2) the contributions of pro- versus anti-inflammatory monocytes/macrophages in coordinating healing response. Bone healing is a complex multicellular dynamic process. While traditional in vitro and in vivo experimentation may capture the behavior of select populations with high resolution, they cannot simultaneously track the behavior of multiple populations. To address this, we have used an integrated coupled ordinary differential equations (ODEs)-based framework describing multiple cellular species to in vivo bone injury data in order to identify and test various hypotheses regarding bone cell populations dynamics. Our approach allowed us to infer several biological insights including, but not limited to,: 1) anti-inflammatory macrophages are key for early osteoclast inhibition and pro-inflammatory macrophage suppression, 2) pro-inflammatory macrophages are involved in osteoclast bone resorptive activity, whereas osteoblasts promote osteoclast differentiation, 3) Pro-inflammatory monocytes/macrophages rise during two expansion waves, which can be explained by the anti-inflammatory macrophages-mediated inhibition phase between the two waves. In addition, we further tested the robustness of the mathematical model by comparing simulation results to an independent experimental dataset. Taken together, this novel comprehensive mathematical framework allowed us to identify biological mechanisms that best recapitulate bone injury data and that explain the coupled cellular population dynamics involved in the process. Furthermore, our hypothesis testing methodology could be used in other contexts to decipher mechanisms in complex multicellular processes.

Myeloid-derived monocytes/macrophages are key cells for bone remodeling and injury repair. However, their temporal polarization status and control of bone-resorbing osteoclasts and bone-forming osteoblasts responses is largely unknown. In this study, we focused on two aspects of monocyte/macrophage population dynamics: 1) the injury-triggered pro- and anti-inflammatory monocytes/macrophages temporal profiles, 2) the contributions of pro- versus anti-inflammatory monocytes/macrophages in coordinating healing response. In order to test various hypotheses regarding bone cell populations dynamics, we have integrated a coupled ordinary differential equations-based framework describing multiple cellular species to in vivo bone injury data. Our approach allowed us to infer several biological insights including: 1) anti-inflammatory macrophages are key for early osteoclast inhibition and pro-inflammatory macrophage suppression, 2) pro-inflammatory macrophages are involved in osteoclast bone resorptive activity, whereas osteoblasts promote osteoclast differentiation, 3) Pro-inflammatory monocytes/macrophages rise during two expansion waves, which can be explained by the anti-inflammatory macrophages-mediated inhibition phase between the two waves. Taken together, this mathematical framework allowed us to identify biological mechanisms that recapitulate bone injury data and that explain the coupled cellular population dynamics involved in the process.

Activation and Function of NLRP3 Inflammasome in Bone and Joint-Related Diseases

Inflammation is a pivotal response to a variety of stimuli, and inflammatory molecules such as cytokines have central roles in the pathogenesis of various diseases, including bone and joint diseases. Proinflammatory cytokines are mainly produced by immune cells and mediate inflammatory and innate immune responses. Additionally, proinflammatory cytokines accelerate bone resorption and cartilage destruction, resulting in the destruction of bone and joint tissues. Thus, proinflammatory cytokines are involved in regulating the pathogenesis of bone and joint diseases. Interleukin (IL)-1 is a representative inflammatory cytokine that strongly promotes bone and cartilage destruction, and elucidating the regulation of IL-1 will advance our understanding of the onset and progression of bone and joint diseases. IL-1 has two isoforms, IL-1α and IL-1β. Both isoforms signal through the same IL-1 receptor type 1, but the activation mechanisms are completely different. In particular, IL-1β is tightly regulated by protein complexes termed inflammasomes. Recent research using innovative technologies has led to a series of discoveries about inflammasomes. This review highlights the current understanding of the activation and function of the NLRP3 (NOD-like receptor family, pyrin domain-containing 3) inflammasome in bone and joint diseases.

Body Composition as a Modulator of Bone Health Changes in Patients with Inflammatory Bowel Disease

Background: Bone impairment of multifactorial etiology is a common feature in inflammatory bowel disease (IBD). Body composition parameters, which might be selectively modified in these patients, are important determinants of bone strength. Our aim was to investigate the relationship between components of body composition and bone parameters in IBD patients. Methods: This is a cross-sectional, retrospective study including 80 IBD patients (43 women, 37 men). Lumbar spine (LS), femoral neck (FN) and whole body DXA scans were performed to analyze regional bone mineral density (BMD), as well as body composition, including appendicular skeletal muscle mass index (ASMI), total and visceral fat mass (VAT). Trabecular bone score (TBS) was assessed using iNsight Software. Results: Twenty (25%) IBD patients had inadequate LS-BMD z scores (<=−2DS). Lean mass (LM) was a significant determinant of LS-BMD, after adjusting for age, gender, BMI and fat mass (p < 0.01), while fat mass% remained associated with FN-BMD (p < 0.01). TBS correlated positively with BMI (r = 0.24, p < 0.05), LS-BMD (r = 0.56, p < 0.001), ASMI (r = 0.34, p < 0.001) and negatively with VAT/total fat% (r = −0.27, p < 0.05). Multivariate analysis showed that ASMI, LS-BMD (positively) and VAT/total fat% (negatively) were independently associated with TBS. Conclusions: In IBD patients, skeletal muscle mass and fat percentage and distribution are important factors associated with bone health.

Study on the role of pyroptosis in bone resorption induced by occlusal trauma with or without periodontitis

BACKGROUND AND OBJECTIVE

Occlusal trauma is considered to be a contributing factor to bone loss associated with inflammatory periodontal disease. We hypothesized that pyroptosis, a recently discovered inflammation-induced programmed cell death pathway, plays a role in occlusal trauma.

MATERIALS AND METHODS

The occlusal trauma model was established using a cemented 1-mm elevated computer-aided design and manufacturing (CAD/CAM) metal crown. The periodontitis model was established by periodontal wire ligation with lipopolysaccharide (LPS) injection. The rats were sacrificed at 1, 2, 3, and 4 weeks. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to analyze the expression of pyroptosis-, inflammation-, and osteoclast-related markers. Micro-computed tomography (micro-CT) was used to determine bone morphology parameters. Tissue morphology was evaluated using hematoxylin and eosin staining (H&E). Osteoclasts were identified using tartrate-resistant acid phosphatase (TRAP) staining. The expression and distribution of factors related to pyroptosis and inflammation were evaluated by immunohistochemistry (IHC). The colocalization of dead cells and cysteinyl aspartate-specific proteinase-1 (caspase-1)-positive cells was analyzed by immunofluorescence.

RESULTS

Quantitative real-time polymerase chain reaction and IHC results showed that occlusal trauma induced the expression of pyroptotic factors during the early stages, while occlusal trauma with periodontitis upregulated the expression of pyroptotic factors at the later stages. The results of qRT-PCR, TRAP staining, and micro-CT showed that occlusal trauma with periodontitis increased the production of proinflammatory cytokines, leading to severe bone loss. Glyburide, an NOD-like receptor pyrin domain containing protein 3 (NLRP3)inhibitor, reduced the expression of pyroptosis markers induced by occlusal trauma with periodontitis and reversed bone resorption.

CONCLUSIONS

Pyroptosis was involved in bone loss induced by occlusal trauma with or without periodontitis, while glyburide reversed inflammation and bone resorption.

FAM20C plays a critical role in the development of mouse vertebra

BACKGROUND CONTEXT

Family with sequence similarity 20-member C (FAM20C) is a protein kinase that is responsible for the phosphorylation of many secretory proteins; however, its roles in spine or vertebra development have not be studied.

PURPOSE

The aim of this investigation is to analyze the roles of FAM20C in vertebra development.

STUDY DESIGN/SETTING

A mouse study of the Fam20c gene using conditional knockout to assess the effects of its inactivation on vertebra development.

METHODS

By breeding Sox2-Cre mice with Fam20c^flox/flox mice, Sox2-Cre;Fam20c^flox/flox mice (abbreviated as cKO mice) are created. X-ray radiography, resin-casted scanning electron microscopy, Hematoxylin and Eosin staining, safranin O staining, Goldner's Masson trichrome staining, Von Kossa staining, tartrate-resistant alkaline phosphatase staining, immunohistochemistry staining, Western Immunoblotting and real-time PCR were employed to characterize the vertebrae of cKO mice compared to the normal control mice.

RESULTS

Inactivation of Fam20c in mice results in remarkable spine deformity, severe morphology and mineralization defects, altered levels of osteoblast differentiation markers, reduction of activity of the Wnt/β-catenin signaling pathway and reduced level of osteoclastogenesis in the vertebrae.

CONCLUSIONS

FAM20C plays an essential role in vertebral development; it may regulate vertebral formation through the Wnt/β-catenin signaling pathway.

CLINICAL SIGNIFICANCE

Mutations in the human FAM20C gene are associated with Raine syndrome. The findings of this study provide valuable clues for the clinical management of Raine syndrome regarding spine manifestations in patients.

Macrophage-Osteoclast Associations: Origin, Polarization, and Subgroups

Cellular associations in the bone microenvironment are involved in modulating the balance between bone remodeling and resorption, which is necessary for maintaining a normal bone morphology. Macrophages and osteoclasts are both vital components of the bone marrow. Macrophages can interact with osteoclasts and regulate bone metabolism by secreting a variety of cytokines, which make a significant contribution to the associations. Although, recent studies have fully explored either macrophages or osteoclasts, indicating the significance of these two types of cells. However, it is of high importance to report the latest discoveries on the relationships between these two myeloid-derived cells in the field of osteoimmunology. Therefore, this paper reviews this topic from three novel aspects of the origin, polarization, and subgroups based on the previous work, to provide a reference for future research and treatment of bone-related diseases.

Anti-Inflammatory and Antioxidant Properties of Carvacrol and Magnolol, in Periodontal Disease and Diabetes Mellitus

Periodontal disease and diabetes mellitus are two pathologies that are extremely widespread worldwide and share the feature of chronic inflammation. Carvacrol is a phenolic monoterpenoid, produced by a variety of herbs, the most well-known of which is Origanum vulgare. Magnolol is a traditional polyphenolic compound isolated from the stem bark of Magnolia officinalis, mainly used in Chinese medicine. The purpose of this paper is to review the therapeutic properties of these bioactive compounds, in the treatment of periodontitis and diabetes. Based on our search strategy we conducted a literature search in the PubMed and Google Scholar databases to identify studies. A total of one hundred eighty-four papers were included in the current review. The results show that carvacrol and magnolol have anti-inflammatory, antioxidant, antimicrobial, anti-osteoclastic, and anti-diabetic properties that benefit both pathologies. Knowledge of the multiple activities of carvacrol and magnolol can assist with the development of new treatment strategies, and the design of clinical animal and human trials will maximize the potential benefits of these extracts in subjects suffering from periodontitis or diabetes.

Extracellular vesicles derived from the periodontal pathogen Filifactor alocis induce systemic bone loss through Toll-like receptor 2

Periodontitis is an inflammatory disease induced by local infection in tooth-supporting tissue. Periodontitis is associated with systemic bone diseases, but little is known about the mechanism of the causal effect of periodontitis on systemic bone resorption. Bacteria-derived extracellular vesicles (EVs) act as natural carriers of virulence factors that are responsible for systemic inflammation. In this study, we investigated the role of EVs derived from Filifactor alocis, a Gram-positive, anaerobic periodontal pathogen, in systemic bone loss and osteoclast differentiation. F. alocis EVs accumulated in the long bones of mice after intraperitoneal administration. These EVs induced proinflammatory cytokines, osteoclastogenesis, and bone resorption via Toll-like receptor 2 (TLR2). The phase separation of F. alocis EVs showed that amphiphilic molecules were responsible for the induced bone resorption and osteoclastogenesis. The osteoclastogenic effects of F. alocis EVs were reduced by lipoprotein lipase. Proteomic analysis of the amphiphilic molecules identified seven lipoproteins. Our results indicate that lipoprotein-like molecules in F. alocis EVs may contribute to systemic bone loss via TLR2.

Lack of 5-lipoxygenase in intramembranous and endochondral 129Sv mice skeleton and intramembranous healing

OBJECTIVE

To analyze the lack of 5-lipoxygenase (5LO) on dental socket healing and post-natal phenotype of intramembranous and endochondral bones.

DESIGN

Wild type (WT) 129/SvEv (n = 20) and 5LO knockout (5LOKO) (n = 20) male mice underwent tooth extraction of the upper right incisor and were euthanized after 7, 14, and 30 day time points for the evaluation of dental socket healing and histological phenotyping of intramembranous (IM) and endochondral (EC) bones. Microscopic analysis of alveolar sockets included histopathological description, histomorphometry, and immunohistochemistry for 5LO, cyclooxygenase 2 (COX2), and tartrate resistant acid phosphatase (TRAP).

RESULTS

Histological phenotyping revealed thicker cortical bone in EC bones (femur and vertebra) of 5LOKO mice compared to WTs, with no differences in collagenous content. Although dental socket healing was similarly observed in both groups, WT mice revealed increased numbers of COX-2+ and 5LO+ cells during bone maturing stage, with a decrease of TRAP+ cells at day 30. On the other hand, an increased quantity of fibroblasts was observed at day 7 in 5LOKO group, as well as increased inflammatory infiltrate and significantly decreased TRAP+ cells at final stages of alveolar socket healing in comparison to WTs.

CONCLUSIONS

The lack of 5LO in 5LOKO mice resulted in thicker cortical of EC, but not of IM post natal bones. Furthermore, genetic deletion of 5LO in the 5LOKO mice directly affected the inflammatory response during socket healing, influencing initial and late phases of bone repair in a model of post-tooth extraction in 129Sv WT and 5LOKO mice.

The role of renin angiotensin system in the pathophysiology of rheumatoid arthritis

BACKGROUND

In rheumatoid arthritis (RA) and osteoarthritis (OA), chronic inflammatory processes lead to progresive joint destruction. The renin-angiotensin system (RAS) is involved in the pathogenesis of RA and OA. The aim of this mini-review article is to summarize evidence on the role of RAS in RA and OA.

METHODS

A non-systematic search in Pubmed included terms as "rheumatoid arthritis", "renin angiotensin system", "osteopenia", "RANKL", "DKK-1", "MMP", "inflammation", "angiogenesis", "local renin-angiotensin system", "angiotensin converting enzyme", "AT2 receptor", "Ang-(1-7)", "VEGF", "angiotensine receptor blocker", "angiotensin converting enzyme inhibitors", "renin inhibitors".

RESULTS

Both RAS axes, the classical one, formed by angiotensin converting enzyme (ACE), angiotensin (Ang) II and AT1 receptor (AT1R) and the counter-regulatory one, composed by ACE2, Ang-(1-7) and the Mas receptor, modulate inflammation and tissue damage. Ang II activates pro-inflammatory mediators and oxidative stress. Conversely, Ang-(1-7) exerts anti-inflammatory actions, decreasing cytokine release, leukocyte attraction, density of vessels, tissue damage and fibrosis. Angiogenesis facilitates inflammatory cells invasion, while osteopenia causes joint dysfunction. Up-regulated osteoclastogenisis and down-regulated osteoblastogeneses were associaed with the activation of the classical RAS axis. Three different pathways, RANKL, DKK-1 and MMPs are enhanced by classical RAS activation. The treatment of RA included methotrexate and corticosteroids, which can cause side effects. Studies with angiotensin receptor blockers (ARBs), angiotensin converting enzyme inhibitors (ACEi) and renin inhibitors have been conducted in experimental and clinical RA with promising results.

CONCLUSION

The classical RAS activation is an important mechanism in RA pathogenesis and the benefit of ARB and ACEi administration should be further investigated.

Myeloproliferative Disorders and its Effect on Bone Homeostasis: The Role of Megakaryocytes

Myeloproliferative Neoplasms (MPNs) are a heterogeneous group of chronic hematological diseases that arise from the clonal expansion of abnormal hematopoietic stem cells, of which Polycythemia Vera (PV), Essential Thrombocythemia (ET), and Primary Myelofibrosis (PMF) have been extensively reviewed in context of clonal expansion, fibrosis and other phenotypes. Here, we review current knowledge on the influence of different forms of MPN on bone health. Studies implicated various degrees of effect of different forms of MPN on bone density, and on osteoblast proliferation and differentiation, using murine models and human data. The majority of studies show that bone volume is generally increased in PMF patients, whereas it is slightly decreased or not altered in ET and PV patients, although possible differences between male and female phenotypes were not fully explored in most MPN forms. Osteosclerosis seen in PMF patients is a serious complication that can lead to bone marrow failure, and the loss of bone reported in some ET and PV patients can lead to osteoporotic fractures. Some MPN forms are associated with increased number of megakaryocytes (MKs), and several of the MK-associated factors in MPN are known to affect bone development. Here, we review known mechanisms involved in these processes, with focus on the role of MKs and secreted factors. Understanding MPN-associated changes in bone health could improve early intervention and treatment of this side effect of the pathology.

In Vivo Tumorigenesis, Osteolytic Sarcomas, and Tumorigenic Cell Lines from Transgenic Mice Expressing the Human T-Lymphotropic Virus Type 1 (HTLV-1) Tax Viral Oncogene

Human T-lymphotropic virus type 1 (HTLV-1) causes adult T-cell leukemia, a disease commonly associated with hypercalcemia and osteolysis. There is no effective treatment for HTLV-1, and the osteolytic mechanisms are not fully understood. Mice expressing the HTLV-1 oncogene Tax, driven by the human granzyme B promoter (Tax+), develop osteolytic tumors. To investigate the progression of the bone-invasive malignancies, wild-type, Tax+, and Tax+/interferon-γ-/- mice were assessed using necropsy, histologic examination, IHC analysis, flow cytometry, and advanced imaging. Tax+ and Tax+/interferon-γ-/- malignancies of the ear, tail, and foot comprised poorly differentiated, round to spindle-shaped cells with prominent neutrophilic infiltrates. Tail tumors originated from muscle, nerve, and/or tendon sheaths, with frequent invasion into adjacent bone. F4/80+ and anti-mouse CD11b (Mac-1)+ histiocytic cells predominated within the tumors. Three Tax+/interferon-γ-/- cell lines were generated for in vivo allografts, in vitro gene expression and bone resorption assays. Two cell lines were of monocyte/macrophage origin, and tumors formed in vivo in all three. Differences in Pthrp, Il6, Il1a, Il1b, and Csf3 expression in vitro were correlated with differences in in vivo plasma calcium levels, tumor growth, metastasis, and neutrophilic inflammation. Tax+ mouse tumors were classified as bone-invasive histiocytic sarcomas. The cell lines are ideal for further examination of the role of HTLV-1 Tax in osteolytic tumor formation and the development of hypercalcemia and tumor-associated inflammation.

Rheumatoid Arthritis in the View of Osteoimmunology

Rheumatoid arthritis is characterized by synovial inflammation and irreversible bone erosions, both highlighting the immense reciprocal relationship between the immune and bone systems, designed osteoimmunology two decades ago. Osteoclast-mediated resorption at the interface between synovium and bone is responsible for the articular bone erosions. The main triggers of this local bone resorption are autoantibodies directed against citrullinated proteins, as well as pro-inflammatory cytokines and the receptor activator of nuclear factor-κB ligand, that regulate both the formation and activity of the osteoclast, as well as immune cell functions. In addition, local bone loss is due to the suppression of osteoblast-mediated bone formation and repair by inflammatory cytokines. Similarly, inflammation affects systemic bone remodeling in rheumatoid arthritis with the net increase in bone resorption, leading to systemic osteoporosis. This review summarizes the substantial progress that has been made in understanding the pathophysiology of systemic and local bone loss in rheumatoid arthritis.

Receptor Activator of Nuclear Factor kappa-B Ligand is Not Regulated During Chronic Osteomyelitis in Pigs

Bone loss is a major complication of osteomyelitis and from numerous in-vitro studies, it has been concluded that the bone lysis is caused by elevated expression of the receptor activator of nuclear factor κB ligand (RANKL), leading to increased osteoclast activity. However, we failed to find any relationship between bone loss and osseous RANKL expression in a porcine model of acute and chronic implant-associated osteomyelitis (IAO) due to Staphylococcus aureus or in chronic osteomyelitis lesions in slaughter pigs. Surprisingly, we found that the expression of RANKL was reduced during chronic bone infections. This is in line with the few studies conducted on human samples. A significant bone loss was observed in IAO lesions and in lesions from slaughter pigs, but with no indication of osteoclast involvement using histochemistry, immunohistochemistry for RANKL, receptor activator of nuclear factor kappa-B, osteoprotegerin and cathepsin K, and high-throughput quantitative real-time polymerase chain reaction on bone tissue from osteomyelitic lesions. A strong inflammatory response was seen in the infected animals and, therefore, we propose proteolytic enzymes induced by inflammation to be a major component of the bone loss. Furthermore, we found a significant upregulation of the IL26 gene in infected animals, which can inhibit RANKL-induced osteoclastogenesis, but has no homologue in mice. This finding emphasises that neither murine models nor in-vitro studies can mirror human disease development completely. The present study emphasises that the interactions between microorganisms, the immune system and bone cells in osteomyelitis are too complex to be accurately represented by an in-vitro model.

Role of interleukin-1 and inflammasomes in oral disease

BACKGROUND

Inflammation promotes immune cell infiltration into tissues and induces production of pro-inflammatory cytokines that mediate innate immune responses. Acute or temporary inflammation results in the required repair of the inflamed tissues. However, chronic inflammation leads to pathogenesis of inflammatory conditions such as periodontal disease. In periodontal tissues, pro-inflammatory cytokines mediate inflammatory responses and accelerate the bone-resorbing activity of osteoclasts, resulting in destruction of alveolar bone. Levels of interleukin-1 (IL-1), a major pro-inflammatory cytokine that strongly promotes osteoclastic activity, are elevated in oral tissues of patients with periodontitis. Therefore, elucidation of the mechanisms underlying IL-1 production will enhance our understanding of the pathogenesis of periodontal disease.

HIGHLIGHT

IL-1 has two isoforms: IL-1α and IL-1β. Both isoforms bind to the same IL-1 receptor and have identical biological activity. Unlike that of IL-1α, the IL-1β precursor is not bioactive. To induce its bioactivity, the IL-1β precursor is cleaved by caspase-1, whose activation is mediated by multiprotein complexes termed inflammasomes. Thus, IL-1β maturation and activity are strictly regulated by inflammasomes. This review highlights the current understanding of the molecular mechanisms underlying IL-1 production and the related inflammasome activity.

CONCLUSION

Inhibition of IL-1 production or the inflammasomes via their regulatory mechanisms may facilitate prevention or treatment of periodontal disease and other inflammatory diseases.

Increase in the Number of Bone Marrow Osteoclast Precursors at Different Skeletal Sites, Particularly in Long Bone and Jaw Marrow in Mice Lacking IL-1RA

Recently, it was shown that interleukin-1β (IL-1β) has diverse stimulatory effects on different murine long bone marrow osteoclast precursors (OCPs) in vitro. In this study, interleukin-1 receptor antagonist deficient (Il1rn^-/-) and wild-type (WT) mice were compared to investigate the effects of enhanced IL-1 signaling on the composition of OCPs in long bone, calvaria, vertebra, and jaw. Bone marrow cells were isolated from these sites and the percentage of early blast (CD31^hi Ly-6C^-), myeloid blast (CD31⁺ Ly-6C⁺), and monocyte (CD31^- Ly-6C^hi) OCPs was assessed by flow cytometry. At the time-point of cell isolation, Il1rn^-/- mice showed no inflammation or bone destruction yet as determined by histology and microcomputed tomography. However, Il1rn^-/- mice had an approximately two-fold higher percentage of OCPs in long bone and jaw marrow compared to WT. Conversely, vertebrae and calvaria marrow contained a similar composition of OCPs in both strains. Bone marrow cells were cultured with macrophage colony stimulating factor (M-CSF) and receptor of NfκB ligand (RANKL) on bone slices to assess osteoclastogenesis and on calcium phosphate-coated plates to analyze mineral dissolution. Deletion of Il1rn increased osteoclastogenesis from long bone, calvaria, and jaw marrows, and all Il1rn^-/- cultures showed increased mineral dissolution compared to WT. However, osteoclast markers increased exclusively in Il1rn^-/- osteoclasts from long bone and jaw. Collectively, these findings indicate that a lack of IL-1RA increases the numbers of OCPs in vivo, particularly in long bone and jaw, where rheumatoid arthritis and periodontitis develop. Thus, increased bone loss at these sites may be triggered by a larger pool of OCPs due to the disruption of IL-1 inhibitors.

Relevance of Caspase-1 and Nlrp3 Inflammasome on Inflammatory Bone Resorption in A Murine Model of Periodontitis

This study investigates the role of NLRP3 inflammasome and its main effector Caspase-1 in inflammation and alveolar bone resorption associated with periodontitis. Heat-killed Aggregatibacter actinomycetemcomitans (Aa) was injected 3x/week (4 weeks) into gingival tissues of wild-type (WT), Nlrp3-KO and Caspase1-KO mice. Bone resorption was measured by µCT and osteoclast number was determined by tartrate-resistant acid phosphatase (TRAP) staining. Inflammation was assessed histologically (H/E staining and immunofluorescence of CD45 and Ly6G). In vitro studies determined the influence of Nlrp3 and Caspase-1 in Rankl-induced osteoclast differentiation and activity and on LPS-induced expression of inflammation-associated genes. Bone resorption was significantly reduced in Casp1-KO but not in Nlrp3-KO mice. Casp1-KO mice had increased in osteoclast numbers, whereas the inflammatory infiltrate or on gene expression were similar to those of WT and Nlrp3-KO mice. Strikingly, osteoclasts differentiated from Nlrp3-deficient macrophages had increased resorbing activity in vitro. LPS-induced expression of Il-10, Il-12 and Tnf-α was significantly reduced in Nlrp3- and Casp1-deficient macrophages. As an inceptive study, these results suggest that Nlrp3 inflammasome does not play a significant role in inflammation and bone resorption in vivo and that Caspase-1 has a pro-resorptive role in experimental periodontal disease.

Yunnan Baiyao diminishes lipopolysaccharide-induced inflammation in osteoclasts

Yunnan Baiyao (YNBY) has been refined for hundreds of years and has become a treasure of proprietary Chinese medicine that has significant curative effects in the field of hemostasis, blood circulation, and callus. In past years, YNBY has been demonstrated to play an anti-inflammatory role in bone-related diseases, such as rheumatoid arthritis and osteoporosis. However, the osteoclasts are multinucleated giant cells that resorb bone and participate in the occurrence, development, and progression of these bone-related diseases. Previous studies have reported that the inflammatory function is closely associated with arachidonic acid (AA) metabolism, as well as some inflammatory-related pathways, including the nuclear factor кB (NF-кB), mitogen-activated protein kinase (MAPK), and Wnt5a pathways. Therefore, we speculated that the anti-inflammatory effect of YNBY might be associated with the NF-кB, MAPK, and Wnt5a pathways. In order to further excavate the anti-inflammatory roles of YNBY, lipopolysaccharide (LPS) with an optimal concentration of 1,000 pg/ml was used to induce inflammation in osteoclasts. Our results showed that YNBY with a time- and dose-dependent method decreased the concentration of pro-inflammatory cytokines and the expression levels of cyclooxygenase-1 (COX-1), COX-2, 5-lipoxygenase, and prostaglandin E2. Moreover, it was found that COX-2 was the target gene regulated by YNBY. Finally, using NF-кB and MAPK pathway inhibitors or miRNA101b (involved in the Wnt5a pathway) in tandem with YNBY and the results exhibited that these groups caused a reduction in COX-1 and COX-2 expression, indicating that the anti-inflammatory function of YNBY might directly affect the NF-кB, MAPK, and Wnt5a pathways. PRACTICAL APPLICATIONS: Yunnan Baiyao (YNBY) is mainly extracted from precious Chinese medicines such as Panax notoginseng, borneol, musk, and yam and has a wide range of clinical applications. It is not only used to treat various types of traumatic injuries, but also used for upper gastrointestinal bleeding and wound ulcers, neonatal umbilitis, recurrent oral ulcers, esophagitis, bacterial dysentery, and so on. Although the detailed mechanism of action is not clear at present, it is believed that this is related to its anti-inflammatory, hemostatic, and immune-enhancing effects. Many bone-related diseases, such as rheumatoid arthritis and osteoporosis, are regarded to be intimately related to the inflammatory reaction. Thus, this study aimed to explore the underlying mechanisms of YNBY at anti-inflammatory roles. And our results suggested that YNBY directly affected the inflammatory cytokines and AA metabolic products which referred to the NF-кB, MAPK, and Wnt5a pathways, as well as AA metabolism, respectively. Hence, the practical applications of YNBY are the anti-inflammatory effects used to treat for bone-related diseases.

Autoinflammatory Disorders with Perinatal Onset

Autoinflammatory disorders are rare genetic defects that result in inflammation in the absence of an infectious or autoimmune disease. Although very rare, these disorders can occur in the perinatal period, and recognizing their presentation is important because there are often long-term complications and effective targeted therapies for these disorders. Most of these disorders present with rash, fevers, and laboratory evidence of inflammation. Importantly, these disorders can now be separated into their pathophysiologic mechanisms of action, which can also guide therapies. The article reviews the different mechanisms of autoinflammatory disorders and highlights those disorders that can present in the newborn period.

The inflammatory response to bone infection - a review based on animal models and human patients

Bone infections are difficult to diagnose and treat, especially when a prosthetic joint replacement or implant is involved. Bone loss is a major complication of osteomyelitis, but the mechanism behind has mainly been investigated in cell cultures and has not been confirmed in human settings. Inflammation is important in initiating an appropriate immune response to invading pathogens. However, many of the signaling molecules used by the immune system can also modulate bone remodeling and contribute to bone resorption during osteomyelitis. Our current knowledge of the inflammatory response relies heavily on animal models as research based on human samples is scarce. Staphylococcus aureus is one of the most common causes of bone infections and is the pathogen of choice in animal models. The regulation of inflammatory genes during prosthetic joint infections and implant-associated osteomyelitis has only been studied in rodent models. It is important to consider the validity of an animal model when results are extrapolated to humans, and both bone composition and the immune system of pigs has been shown to be more similar to humans, than to rodents. Here in vivo studies on the inflammatory response to prosthetic joint infections and implant-associated osteomyelitis are reviewed.

Cytokines and Bone: Osteoimmunology

Cytokines and hematopoietic growth factors have traditionally been thought of as regulators of the development and function of immune and blood cells. However, an ever-expanding number of these factors have been discovered to have major effects on bone cells and the development of the skeleton in health and disease (Table 1). In addition, several cytokines have been directly linked to the development of osteoporosis in both animal models and in patients. In order to understand the mechanisms regulating bone cells and how this may be dysregulated in disease states, it is necessary to appreciate the diverse effects that cytokines and inflammation have on osteoblasts, osteoclasts, and bone mass. This chapter provides a broad overview of this topic with extensive references so that, if desired, readers can access specific references to delve into individual topics in greater detail.

Specific RANK Cytoplasmic Motifs Drive Osteoclastogenesis

Upon receptor activator of NF-κB ligand (RANKL) binding, RANK promotes osteoclast formation through the recruitment of tumor necrosis factor (TNF) receptor-associated factors (TRAFs). In vitro assays identified two RANK intracellular motifs that bind TRAFs: PVQEET^560-565 (Motif 2) and PVQEQG^604-609 (Motif 3), which potently mediate osteoclast formation in vitro. To validate the in vitro findings, we have generated knock-in (KI) mice harboring inactivating mutations in RANK Motifs 2 and 3. Homozygous KI (RANK^KI/KI ) mice are born at the predicted Mendelian frequency and normal in tooth eruption. However, RANK^KI/KI mice exhibit significantly more trabecular bone mass than age- and sex-matched heterozygous KI (RANK^+/KI ) and wild-type (RANK^+/+ ) counterparts. Bone marrow macrophages (BMMs) from RANK^KI/KI mice do not form osteoclasts when they are stimulated with macrophage colony-stimulating factor (M-CSF) and RANKL in vitro. RANKL is able to activate the NF-κB, ERK, p38, and JNK pathways in RANK^KI/KI BMMs, but it cannot stimulate c-Fos or NFATc1 in the RANK^KI/KI cells. Previously, we showed that RANK signaling plays an important role in Porphyromonas gingivalis (Pg)-mediated osteoclast formation by committing BMMs into the osteoclast lineage. Here, we show that RANKL-primed RANK^KI/KI BMMs are unable to differentiate into osteoclasts in response to Pg stimulation, indicating that the two RANK motifs are required for Pg-induced osteoclastogenesis. Mechanistically, RANK Motifs 2 and 3 facilitate Pg-induced osteoclastogenesis by stimulating c-Fos and NFATc1 expression during the RANKL pretreatment phase as well as rendering c-Fos and NFATc1 genes responsive to subsequent Pg stimulation. Cell-penetrating peptides (CPPs) conjugated with RANK segments containing Motif 2 or 3 block RANKL- and Pg-mediated osteoclastogenesis. The CPP conjugates abrogate RANKL-stimulated c-Fos and NFATc1 expression but do not affect RANKL-induced activation of NF-κB, ERK, p38, JNK, or Akt signaling pathway. Taken together, our current findings demonstrate that RANK Motifs 2 and 3 play pivotal roles in osteoclast formation in vivo and mediate Pg-induced osteoclastogenesis in vitro.

Water extract of Cnidii Rhizoma suppresses RANKL-induced osteoclastogenesis in RAW 264.7 cell by inhibiting NFATc1/c-Fos signaling and prevents ovariectomized bone loss in SD-rat

Background

Cnidii Rhizoma is the dried root stem of Cnidium officinale Makino. Cnidii Rhizoma (CR) has been used to treat menstrual irregularity, menstrual pain, and menopause in Korea. However, the effects and mechanisms of CR on RANKL-induced osteoclastogenesis pathway remain to be elucidated. In this study, we investigated the effects of CR on the inhibition of bone resorption of osteoclast and its mechanism RANK signaling pathway.

Methods

The anti-osteoclastogenesis of water extract of CR was measured using RAW 264.7 cell. Tartrate-resistant acid phosphatase (TRAP) assay, pit assay, reverse transcription polymerase chain reaction (RT-PCR) and western blot were performed. Moreover, the effects of CR were determined with an in vivo model using ovariectomized (OVX) rats.

Results

CR extract suppressed osteoclastogenesis, its activity and bone resorption activity through decreasing gene of osteoclast-related such as nuclear factor of activated T-cells, cytoplasmic 1 (NFATc1), c-Fos, etc. Moreover, CR extract prevented the bone loss in OVX rats.

Conclusion

These results show that CR has a positive effect on menopausal osteoporosis by suppressing osteoclastogenesis.

Electronic supplementary material

The online version of this article (10.1186/s12906-019-2611-8) contains supplementary material, which is available to authorized users.

MyD88 and IL-1R signaling drive antibacterial immunity and osteoclast-driven bone loss during Staphylococcus aureus osteomyelitis

Staphylococcus aureus is able to infect virtually all organ systems and is a frequently isolated etiologic agent of osteomyelitis, a common and debilitating invasive infection of bone. Treatment of osteomyelitis requires invasive surgical procedures and prolonged antibiotic therapy, yet is frequently unsuccessful due to extensive pathogen-induced bone damage that can limit antibiotic penetration and immune cell influx to the infectious focus. We previously established that S. aureus triggers profound alterations in bone remodeling in a murine model of osteomyelitis, in part through the production of osteolytic toxins. However, staphylococcal strains lacking osteolytic toxins still incite significant bone destruction, suggesting that host immune responses are also major drivers of pathologic bone remodeling during osteomyelitis. The objective of this study was to identify host immune pathways that contribute to antibacterial immunity during S. aureus osteomyelitis, and to define how these immune responses alter bone homeostasis and contribute to bone destruction. We specifically focused on the interleukin-1 receptor (IL-1R) and downstream adapter protein MyD88 given the prominent role of this signaling pathway in both antibacterial immunity and osteo-immunologic crosstalk. We discovered that while IL-1R signaling is necessary for local control of bacterial replication during osteomyelitis, it also contributes to bone loss during infection. Mechanistically, we demonstrate that S. aureus enhances osteoclastogenesis of myeloid precursors in vitro, and increases the abundance of osteoclasts residing on bone surfaces in vivo. This enhanced osteoclast abundance translates to trabecular bone loss, and is dependent on intact IL-1R signaling. Collectively, these data define IL-1R signaling as a critical component of the host response to S. aureus osteomyelitis, but also demonstrate that IL-1R-dependent immune responses trigger collateral bone damage through activation of osteoclast-mediated bone resorption.

Glycogen synthase kinase-3 inhibitor as a multi-targeting anti-rheumatoid drug

Rheumatoid arthritis (RA) is a chronic inflammatory joint disease that causes swelling, bone erosion, and joint disorder. Patients with RA therefore suffer from pain and physiological disability, and have a decreased quality of life. During the progression of RA, many different types of cells and inflammatory factors influence each other with an important role. A better understanding of the pathology of RA should therefore lead to the development of effective anti-rheumatoid drugs, such as the anti-TNFα antibody. Glycogen synthase kinase-3 (GSK-3) is a cytoplasmic serine/threonine protein kinase that is involved in a large number of key cellular processes and is dysregulated in a wide variety of diseases, including inflammation and osteoporosis. The accumulated evidence has suggested that GSK-3 could be involved in multiple steps in the progression of RA. In the present review, the mechanisms of the pathogenesis of RA are summarized, and recent developments and potential new drugs targeting GSK-3 are discussed.

Increased bone mass in a mouse model with low fat mass

Mice with impaired acute inflammatory responses within adipose tissue display reduced diet-induced fat mass gain associated with glucose intolerance and systemic inflammation. Therefore, acute adipose tissue inflammation is needed for a healthy expansion of adipose tissue. Because inflammatory disorders are associated with bone loss, we hypothesized that impaired acute adipose tissue inflammation leading to increased systemic inflammation results in a lower bone mass. To test this hypothesis, we used mice overexpressing an adenoviral protein complex, the receptor internalization and degradation (RID) complex that inhibits proinflammatory signaling, under the control of the aP2 promotor (RID tg mice), resulting in suppressed inflammatory signaling in adipocytes. As expected, RID tg mice had lower high-fat diet-induced weight and fat mass gain and higher systemic inflammation than littermate wild-type control mice. Contrary to our hypothesis, RID tg mice had increased bone mass in long bones and vertebrae, affecting trabecular and cortical parameters, as well as improved humeral biomechanical properties. We did not find any differences in bone formation or resorption parameters as determined by histology or enzyme immunoassay. However, bone marrow adiposity, often negatively associated with bone mass, was decreased in male RID tg mice as determined by histological analysis of tibia. In conclusion, mice with reduced fat mass due to impaired adipose tissue inflammation have increased bone mass.

Hyperbaric oxygen therapy ameliorates osteonecrosis in patients by modulating inflammation and oxidative stress

Early stages of avascular necrosis of the femoral head (AVNFH) can be conservatively treated with hyperbaric oxygen therapy (HBOT). This study investigated how HBOT modulates inflammatory markers and reactive oxygen species (ROS) in patients with AVNFH. Twenty-three male patients were treated with two cycles of HBOT, 30 sessions each with a 30 days break between cycles. Each session consisted of 90 minutes of 100% inspired oxygen at 2.5 absolute atmospheres of pressure. Plasma levels of tumor necrosis factor alfa (TNF-α), interleukin 6 (IL-6), interleukin 1 beta (IL-1β) and ROS production were measured before treatment (T0), after 15 and 30 HBOT sessions (T1 and T2), after the 30-day break (T3), and after 60 sessions (T4). Results showed a significant reduction in TNF-α and IL-6 plasma levels over time. This decrease in inflammatory markers mirrored observed reductions in bone marrow edema and reductions in patient self-reported pain.

Magnolol Inhibits Osteoclast Differentiation via Suppression of RANKL Expression

Magnolol, a compound from the traditional Korean herb Magnolia sp., has been exhaustively investigated as a therapeutic agent against several diseases including systemic and local inflammation. We examined the effects of magnolol on osteoclastic differentiation associated with inflammation. Magnolol markedly reduced interleukin (IL)-1-induced osteoclast formation in co-cultures of murine osteoblasts and bone marrow cells, whereas it had no effect on receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclast formation in bone marrow macrophage cultures. In osteoblasts, magnolol markedly inhibited both the up-regulation of RANKL expression and the production of prostaglandin E₂ (PGE₂) in response to IL-1 treatment. Addition of exogenous PGE₂ reversed the inhibitory effects of magnolol on IL-1-induced RANKL expression in osteoblasts and osteoclast formation in co-cultures. Magnolol inhibited IL-1-induced PGE₂ production, at least in part by suppressing cyclooxygenase-2 (COX-2) expression. Taken together, these results demonstrate that magnolol inhibits IL-1-induced RANKL expression in osteoblasts through suppression of COX-2 expression and PGE₂ production, resulting in inhibition of osteoclast differentiation in co-cultures.

Effects of loxoprofen on the apical root resorption during orthodontic tooth movement in rats

Studies have revealed that severe apical root resorption during tooth movement is caused by the noninfective inflammatory reaction of apical root tissues. We hypothesized that loxoprofen can suppress apical root resorption during tooth movement. Cyclic tensile force (CTF) of 10 kPa was applied to the human pulp cells for 48 hours by the Flexcell Strain Unit. Loxoprofen (10 and 100 μM) was added to the culture cells, and expression of cyclooxygenase (COX)-1, COX-2, interleukin (IL)-1β, receptor activator of nuclear factor kappa-B ligand (RANKL), tumor necrosis factor (TNF)-α, and macrophage colony-stimulating factor (M-CSF) were examined. To determine the effects of loxoprofen sodium on apical root reabsorption during tooth movement, the upper first molars of 7-week-old rats were subjected to mesial movement by 10g force for 30 days with or without the oral administration of loxoprofen. Gene expression and protein concentration of COX-1, COX-2, IL-1β, TNF-α, RANKL and M-CSF were significantly higher in the CTF group than in the control group. However, these levels were decreased by loxoprofen administration. After orthodontic tooth movement, the expression of IL-1β, TNF-α, RANKL and M-CSF decreased in the loxoprofen group than in the control group by immunohistochemical staining. In comparison to control group, less number of odontoclasts and a decrease in the amount of apical root resorption was observed in the loxoprofen group. Many osteoclasts became visible on the pressure side of the alveolar bone in the both groups, and the amount of tooth movement did not show a significant difference. These findings demonstrate that severe apical root resorption may be suppressed by loxoprofen administration, without a disturbance of tooth movement.

Anti-HMGB1 Neutralizing Antibody Attenuates Periodontal Inflammation and Bone Resorption in a Murine Periodontitis Model

High mobility group box 1 (HMGB1) is a non-histone DNA-binding protein that is secreted into the extracellular milieu in response to inflammatory stimuli. The secreted HMGB1 mediates various inflammatory diseases, including periodontitis; however, the underlying mechanisms of HMGB1-induced periodontal inflammation are not completely understood. Here, we examined whether anti-HMGB1 neutralizing antibody inhibits periodontal progression and investigated the molecular pathology of HMGB1 in vitro and in vivo. In vitro analysis indicated that HMGB1, granulocyte-macrophage colony-stimulating factor (GM-CSF), and interleukin-1β (IL-1β) were secreted in response to tumor necrosis factor-α (TNF-α) stimuli in human gingival epithelial cells (HGECs) and human monocytic leukemia cells (THP-1) treated with phorbol myristate acetate. Increased levels of GM-CSF and IL-1β were observed in the conditioned media from TNF-α-stimulated HGECs and THP-1 in vitro Simultaneous stimulation with TNF-α and anti-HMGB1 antibody significantly decreased TNF-α-induced inflammatory cytokine secretion. Experimental periodontitis was induced in mice using Porphyromonas gingivalis-soaked ligatures. The extracellular translocation was confirmed in gingival epithelia in the periodontitis model mice by immunofluorescence analysis. Systemic administration of anti-HMGB1 neutralizing antibody significantly inhibited translocation of HMGB1. The anti-HMGB1 antibody inhibited periodontal inflammation, expression of IL-1β and C-X-C motif chemokine ligand 1 (CXCL1), migration of neutrophils, and bone resorption, shown by bioluminescence imaging of myeloperoxidase activity, quantitative reverse transcription-PCR (RT-PCR), and micro-computed tomography analysis. These findings indicate that HMGB1 is secreted in response to inflammatory stimuli caused by periodontal infection, which is crucial for the initiation of periodontitis, and the anti-HMGB1 antibody attenuates the secretion of a series of inflammatory cytokines, consequently suppressing the progression of periodontitis.

The degree of peri-implant osteolysis induced by PEEK, CoCrMo, and HXLPE wear particles: a study based on a porous Ti6Al4V implant in a rabbit model

Background

Polyether-ether-ketone (PEEK), cobalt-chromium-molybdenum (CoCrMo), and highly cross-linked polyethylene (HXLPE) are biomaterials used in orthopedic implants; their wear particles are considered to induce peri-implant osteolysis. We examined whether different particle types induce the same degree of peri-implant osteolysis.

Methods

Forty female rabbits were randomly divided into four groups—the control group (n = 10), which received implantation operation and sham operation at 1 month postoperation; three experimental groups (n = 10 in each group), which received implantation operation along with administration of 0.1 mL of particle suspension (approximately 1.0 × 10⁸ PEEK, CoCrMo, or HXLPE wear particles) into the knee joint at 1 month postoperation. All rabbits were sacrificed at 2 months postoperation. The synovium was removed and histologically assessed. The distal femurs with the implants were analyzed via micro-computed tomography (CT) and hard tissue biopsy.

Results

The average size of almost 90% of the particles was < 5 μm, indicating no significant difference in the three particle types. IL-1β, IL-8, TNFα, RANKL, and MCP-1 expression in PEEK and CoCrMo groups was high, while that in the HXLPE group was low. The bone density (BD) and bone volume/total volume (BV/TV) of the porous structures (part of the implants in all groups) in experimental groups did not decrease markedly (p > 0.05), while BD in the peripheral regions in experimental groups decreased markedly compared to control groups (p < 0.05). BV/TV in the peripheral regions was significantly decreased in PEEK and CoCrMo groups when compared to control group (p < 0.05), while no significant difference was noted between HXLPE and control groups (p > 0.05). The changes in BV observed in the hard tissue sections were consistent with those noted in the micro-CT findings.

Conclusion

PEEK, CoCrMo, and HXLPE wear particles (approximately having the same size and doses) induce peri-implant osteolysis to a different degree: HXLPE particles induce peri-implant osteolysis to a mild degree, while PEEK and CoCrMo particles caused significant peri-implant osteolysis. In case of a porous implant, osteolysis occurred primarily in the peripheral region, rather than in the porous structures. Our findings would be helpful for implant designers to choose friction pairs in orthopedic components.

IL-1β Induces Pathologically Activated Osteoclasts Bearing Extremely High Levels of Resorbing Activity: A Possible Pathological Subpopulation of Osteoclasts, Accompanied by Suppressed Expression of Kindlin-3 and Talin-1

As osteoclasts have the central roles in normal bone remodeling, it is ideal to regulate only the osteoclasts performing pathological bone destruction without affecting normal osteoclasts. Based on a hypothesis that pathological osteoclasts form under the pathological microenvironment of the bone tissues, we here set up optimum culture conditions to examine the entity of pathologically activated osteoclasts (PAOCs). Through searching various inflammatory cytokines and their combinations, we found the highest resorbing activity of osteoclasts when osteoclasts were formed in the presence of M-CSF, receptor activator of NF-κB ligand, and IL-1β. We have postulated that these osteoclasts are PAOCs. Analysis using confocal laser microscopy revealed that PAOCs showed extremely high proton secretion detected by the acid-sensitive fluorescence probe Rh-PM and bone resorption activity compared with normal osteoclasts. PAOCs showed unique morphology bearing high thickness and high motility with motile cellular processes in comparison with normal osteoclasts. We further examined the expression of Kindlin-3 and Talin-1, essential molecules for activating integrin β-chains. Although normal osteoclasts express high levels of Kindlin-3 and Talin-1, expression of these molecules was markedly suppressed in PAOCs, suggesting the abnormality in the adhesion property. When whole membrane surface of mature osteoclasts was biotinylated and analyzed, the IL-1β-induced cell surface protein was detected. PAOCs could form a subpopulation of osteoclasts possibly different from normal osteoclasts. PAOC-specific molecules could be an ideal target for regulating pathological bone destruction.

Chronological differential effects of pro-inflammatory cytokines on RANKL-induced osteoclast differentiation of canine bone marrow-derived macrophages

The aim of this study was to investigate osteoclastogenic properties of inflammatory cytokines at different time-points of osteoclastogenesis. Bone marrow-derived macrophages from five healthy dogs were stimulated with the macrophage colony-stimulating factor, receptor activator of nuclear factor-κB ligand and inflammatory cytokines such as interleukin (IL)-1β, tumor necrosis factor (TNF)-α and IL-17. Osteoclasts (OC) formation and function were enhanced with TNF-α regardless of temporal differences. But in contrast, IL-1β suppressed the osteoclastogenesis at early phase of the process while upregulating at the late phase. Furthermore, differentiation of OC precursors into OC was suppressed at high concentrations of IL-17. Collectively, the results revealed that suppressing TNF-α would be a promising strategy to inhibit inflammation-associated bone destruction in dogs.

Molecular Pathogenesis and Diagnostic Imaging of Metastatic Jaw Tumors

Metastasis is the spread of malignant cells from a primary tumor to distant sites through lymphatics or blood vessels. Malignant lesions metastasizing to the oral and perioral region are a rarity indeed. Malignant lesions could metastasize to both soft tissue of oral cavity and the hard tissues of the jaws and recent meta-analysis showed that metastasis is more common in the jaws than oral soft tissues because of rich vascular supply. The incidence is very low when compared to the incidence of primary oral cancers; nevertheless, one has to include in the diagnostic workup, metastatic malignant lesions, when an irregular ill-defined radiolucency or radiodensity with ragged edges in noted. It could be a challenging task for a diagnostician, in cases with the presence and location of the primary tumor is unknown. Advanced oral imaging technologies and biochemical markers play a vital role in diagnosing such lesions.

Multinucleated Giant Cells: Good Guys or Bad Guys?

Multinucleated giant cells (MNGCs) are a special class of giant cell formed by the fusion of monocytes/macrophages abundantly found in human tissues. While historically their role around certain classes of biomaterials have been directly linked to a foreign body reaction leading to material rejection, recent accumulating evidence has put into question their role around certain classes of bone biomaterials. It was once thought that specifically in bone tissues, all giant cells were considered osteoclasts characterized by their ability to resorb and replace bone grafts with newly formed native bone. More recently, however, a special subclass of bone biomaterials has been found bordered by large MNGCs virtually incapable of resorbing bone substitutes even years after their implantation yet surrounded by stable bone. Interestingly, research from the field of cardiovascular disease has further shown how a shift in macrophage polarization from M1 "tissue-inflammatory" macrophages toward M2 "wound-healing" macrophages in atherosclerotic plaque may lead to MNGC formation and ectopic calcification of arteries. Despite the growing observation that MNGC formation occurs around certain bone biomaterials, their role in these tissues remains extremely poorly understood and characterized. In summary, four central aspects of this review are discussed with a focus on (1) the role of MNGCs in bone/tissue biology, and their ability to induce vascularization/new bone formation, their role around, (2) bone substitutes for bone augmentation, (3) dental implants, as well as (4) during peri-implant infection. The authors express the necessity to no longer refer to MNGCs as "good" or "bad" cells, but instead point toward the necessity to more specifically characterize them scientifically and appropriately as M1-MNGC and M2-MNGC accordingly. Future research investigating the factors influencing their polarization as a "center of control" is also likely to act as a key factor in the progression/resolution of various diseases.

Postmenopausal osteoporosis in rheumatoid arthritis: The estrogen deficiency-immune mechanisms link

Rheumatoid arthritis (RA) is characterized, among other factors, by systemic bone loss, reaching ~50% prevalence of osteoporosis in postmenopausal women. This is roughly a doubled prevalence in comparison with age-matched non-RA women. Postmenopausal RA women are more likely to be sero-positive for the anti-citrullinated peptide antibody (ACPA). Our extensive review of recent scientific literature enabled us to propose several mechanisms as responsible for the accelerated bone loss in ACPA(+) RA postmenopausal women. Menopause-associated estrogen deficiency plays a major role in these pathological mechanisms, as follows.