Cytokines regulating osteoclast formation and function

In vitro osteoclastogenesis in autoimmune diseases - Strengths and pitfalls of a tool for studying pathological bone resorption and other disease characteristics

Osteoclasts play a critical role in bone pathology frequently associated with autoimmune diseases. Studying the etiopathogenesis of these diseases and their clinical manifestations can involve in vitro osteoclastogenesis, an experimental technique that utilizes osteoclast precursors that are relatively easily accessible from peripheral blood or synovial fluid. However, the increasing number of methodical options to study osteoclastogenesis in vitro poses challenges in translating findings to clinical research and practice. This review compares and critically evaluates previous research work based on in vitro differentiation of human osteoclast precursors originating from patients, which aimed to explain autoimmune pathology in rheumatic and enteropathic diseases. The discussion focuses primarily on methodical differences between the studies, including the origin of osteoclast precursors, culture conditions, and methods for identifying osteoclasts and assessing their activity. Additionally, the review examines the clinical significance of the three most commonly used in vitro approaches: induced osteoclastogenesis, spontaneous osteoclastogenesis, and cell co-culture. By analyzing and integrating the gathered information, this review proposes general connections between different studies, even in cases where their results are seemingly contradictory. The derived conclusions and future directions aim to enhance our understanding of a potential and limitations of in vitro osteoclastogenesis and provide a foundation for discussing novel methods (such as osteoclastogenesis dynamic) and standardized approaches (such as spontaneous osteoclastogenesis) for future use in autoimmune disease research.

Bone Homeostasis and Physiology in Normal and Orthopaedic Disease Conditions

Some of the most common human systemic diseases-both benign and malignant-affect bone regulation, formation, and homeostasis (the cellular balance regulated by osteocytes, osteoblasts, and osteoclasts). This review discusses our current understanding of the molecular components and mechanisms that are responsible for homeostasis and interactions resulting in dysregulation (dysfunction due to the loss of the dynamic equilibrium of bone homeostasis). Knowledge of key pathways in bone biology can improve surgeon understanding, clinical recognition, and treatment of bone homeostasis-related diseases.

Magnetic nanocomplexes coupled with an external magnetic field modulate macrophage phenotype - a non-invasive strategy for bone regeneration

Chronic inflammation is a major cause for the pathogenesis of musculoskeletal diseases such as fragility fracture, and nonunion. Studies have shown that modulating the immune phenotype of macrophages from proinflammatory to prohealing mode can heal recalcitrant bone defects. Current therapeutic strategies predominantly apply biochemical cues, which often lack target specificity and controlling their release kinetics in vivo is challenging spatially and temporally. We show a magnetic iron-oxide nanocomplexes (MNC)-based strategy to resolve chronic inflammation in the context of promoting fracture healing. MNC internalized pro-inflammatory macrophages, when coupled with an external magnetic field, exert an intracellular magnetic force on the cytoskeleton, which promotes a prohealing phenotype switch. Mechanistically, the intracellular magnetic force perturbs actin polymerization, thereby significantly reducing nuclear to cytoplasm redistribution of MRTF-A and HDAC3, major drivers of inflammatory and osteogenic gene expressions. This significantly reduces Nos2 gene expression and subsequently downregulates the inflammatory response, as confirmed by quantitative PCR analysis. These findings are a proof of concept to develop MNC-based resolution-centric therapeutic intervention to direct macrophage phenotype and function towards healing and can be translated either to supplement or replace the currently used anti-inflammatory therapies for fracture healing.

The effect of alginate scaffolds on bone healing in defects formed with drilling model in rat femur diaphysis

Alginate (ALG) is a biocompatible and biodegradable polymer. Mechanical weakness is one of the main problems for the alginate-based scaffolds. Various plasticizer additives or modifications tested to improve the mechanical properties. In the presented study, ALG plasticized with triacetin (TA), and tributyl citrate (TBC) than tested on bone healing. In the presented study, the alginate modified with triacetin or tributyl citrate. In-vitro, and in-vivo efficiency of the scaffolds tested on bone tissue regeneration. Scaffolds fabricated by solvent casting, and physicochemical characterizations performed. Monocytes (THP-1) cultured with scaffolds, and macrophage-released cytokines was determined. In-vivo efficacy of the scaffolds was tested in the rat drill hole model. Alginate and tributyl citrate-modified scaffolds have no cytotoxic effect on osteoblastic cells (MC-3T3). Tributyl citrate modification increased tumor necrosis factor-alpha (TNF-alpha) level but did not increase interleukin -1 beta (IL-1 beta) level. In vivo studies showed that osteoblastic growth was significant in alginate and triacetin-modified scaffolds. However, the best values for osteoclastic activity and osteoid tissue formation seen in the triacetin modification. The results demonstrated that the modified alginate scaffolds were more successful than non-modified alginate scaffolds and can used as long-term bone repairing treatments.

The Effect of Mineralized Plasmatic Matrix and Chitosan on the Healing of Critical-Sized Mandibular Bone Defects in a Rabbit Model

Background: In maxillofacial surgery, critical size mandibular defects remain a challenging issue. There have been numerous attempts to improve mandibular defect healing. Recently, bone tissue engineering has provided many benefits in improving bone healing. Herein, we tried to investigate the effect of Mineralized plasmatic matrix (MPM) and Chitosan to enhance tissue healing and regeneration in mandibular bone defect. Methods: A mandibular bone defect of critical size was created in 45 New Zealand rabbits. There were three groups of rabbits: the MPM group, the Chitosan group, and the control group. Radiographical, histological, and immune histochemical evaluations were performed at 4, 8, and 12 post-operative weeks. Results: The MPM group demonstrated the highest degree of bone formation with uniform radio-opacity nearly like that of adjacent healthy parent tissue. While in the chitosan group, most of the defect area was filled with radio-opaque bone with persistent small radiolucent areas. The control group showed less bone formation than the MPM and chitosan group, with more radiolucent areas. Sections stained with (H&E) demonstrated an increase in osseous tissue formation in both the MPM and chitosan groups. Staining with Masson’s trichrome revealed an increase in fibrous connective tissue proliferation in both the MPM and chitosan groups. In both the MPM and chitosan groups, nuclear factor kappa p65 was downregulated, and matrix metalloproteinase-9 was upregulated. Conclusion: According to the current study, MPM and Chitosan may have beneficial effects on the healing of critical-sized mandibular bone defects.

Increased endoglin levels correlated with angiogenesis-associated angiopoietin-2 in haemophilia patients

INTRODUCTION

Haemophilia is a bleeding disorder that occurs due to the deficiency of coagulation factors, and the angiogenesis process is an important process underlying the pathophysiology of haemophilic arthropathy. The role of the new adipocytokine endoglin (ENG) in patients with haemophilia is not yet known.

AIM

The aim of this study is to evaluate the association between ENG protein and angiogenesis-related cytokines in patients with haemophilia for the first time.

METHODS

Plasma protein levels and mRNA expressions of ENG and various angiogenesis-associated cytokines were compared in blood samples collected from 28 patients with haemophilia A or B and 29 healthy volunteers. The relationship between the cytokines and ENG were determined by correlation analysis.

RESULTS

Plasma ENG levels and angiogenic markers were found to be significantly higher in patients with haemophilia compared to controls. Real-time PCR studies showed that mRNA expressions of ENG, vascular endothelial growth factor A, hypoxia-inducible factor A, and prostaglandin E2 increased in patients with haemophilia. Correlation analysis showed a significant positive correlation between ENG and angiopoietin-2 levels in the haemophilia group. Besides, a significant decrease in annexin-V binding to platelets in haemophilia patients compared to control was found to be related to the bleeding profiles in the patients.

CONCLUSIONS

This study determined that ENG protein may be involved in the formation of angiogenesis in haemophilia patients and its effects may be related to angiogenetic marker angiopoietin-2 in this process. Our findings contribute to the literature during the determination of target proteins in haemophilia treatment.

Polyphenols-loaded electrospun nanofibers in bone tissue engineering and regeneration

Bone is a complex structure with unique cellular and molecular process in its formation. Bone tissue regeneration is a well-organized and routine process at the cellular and molecular level in humans through the activation of biochemical pathways and protein expression. Though many forms of biomaterials have been applied for bone tissue regeneration, electrospun nanofibrous scaffolds have attracted more attention among researchers with their physicochemical properties such as tensile strength, porosity, and biocompatibility. When drugs, antibiotics, or functional nanoparticles are taken as additives to the nanofiber, its efficacy towards the application gets increased. Polyphenol is a versatile green/phytochemical small molecule playing a vital role in several biomedical applications, including bone tissue regeneration. When polyphenols are incorporated as additives to the nanofibrous scaffold, their combined properties enhance cell attachment, proliferation, and differentiation in bone tissue defect. The present review describes bone biology encompassing the composition and function of bone tissue cells and exemplifies the series of biological processes associated with bone tissue regeneration. We have highlighted the molecular mechanism of bioactive polyphenols involved in bone tissue regeneration and specified the advantage of electrospun nanofiber as a wound healing scaffold. As the polyphenols contribute to wound healing with their antioxidant and antimicrobial properties, we have compiled a list of polyphenols studied, thus far, for bone tissue regeneration along with their in vitro and in vivo experimental biological results and salient observations. Finally, we have elaborated on the importance of polyphenol-loaded electrospun nanofiber in bone tissue regeneration and discussed the possible challenges and future directions in this field.

In Vitro Macrophage Immunomodulation by Poly(ε-caprolactone) Based-Coated AZ31 Mg Alloy

Due to its excellent bone-like mechanical properties and non-toxicity, magnesium (Mg) and its alloys have attracted great interest as biomaterials for orthopaedic applications. However, their fast degradation rate in physiological environments leads to an acute inflammatory response, restricting their use as biodegradable metallic implants. Endowing Mg-based biomaterials with immunomodulatory properties can help trigger a desired immune response capable of supporting a favorable healing process. In this study, electrospun poly(ε-caprolactone) (PCL) fibers loaded with coumarin (CM) and/or zinc oxide nanoparticles (ZnO) were used to coat the commercial AZ31 Mg alloy as single and combined formulas, and their effects on the macrophage inflammatory response and osteoclastogenic process were investigated by indirect contact studies. Likewise, the capacity of the analyzed samples to generate reactive oxygen species (ROS) has been investigated. The data obtained by attenuated total reflection Fourier-transform infrared (FTIR-ATR) and X-ray photoelectron spectroscopy (XPS) analyses indicate that AZ31 alloy was perfectly coated with the PCL fibers loaded with CM and ZnO, which had an important influence on tuning the release of the active ingredient. Furthermore, in terms of degradation in phosphate-buffered saline (PBS) solution, the PCL-ZnO- and secondary PCL-CM-ZnO-coated samples exhibited the best corrosion behaviour. The in vitro results showed the PCL-CM-ZnO and, to a lower extent, PCL-ZnO coated sample exhibited the best behaviour in terms of inflammatory response and receptor activator of nuclear factor kappa-B ligand (RANKL)-mediated differentiation of RAW 264.7 macrophages into osteoclasts. Altogether, the results obtained suggest that the coating of Mg alloys with fibrous PCL containing CM and/or ZnO can constitute a feasible strategy for biomedical applications.

Biomarkers of bone disease in persons with haemophilia

INTRODUCTION

Persons with haemophilia (PwH) have abnormally low bone density and increased risk of fractures. We previously demonstrated decreased skeletal health in factor VIII (FVIII)-deficient mice. Thus, we hypothesized factor deficiency is an independent risk factor for decreased skeletal health.

AIM

We seek to identify differences in bone-related cytokine expression among PwH and healthy controls.

METHODS

We evaluated plasma samples from 79 participants with severe FVIII deficiency and 51 age-matched healthy controls. Plasma samples were assessed for RANKL and OPG, cytokines that regulate bone metabolism, and CTX-1, a biomarker for bone resorption, as well as 10 bone-related cytokines.

RESULTS

CTX-1 is higher among samples from FVIII-deficient participants compared to controls (P < .01) but not among participants with recent factor use (within 24 hours of sample collection) (P = .21). Among PwH greater than 16 years of age (PwH ≥ 16), OPG is increased with recent factor use (P < .01) but not without (P = .34). Lower levels of TNF-α (P < .01), interleukin (IL)-12 (P < .01) and IL-10 (P < .001) were found among samples from PwH. Controlling for subject age, IL-12 and IL-10 levels are lower in PwH ≥ 16 (P < .01, P < .001) but not PwH under 16 (PwH < 16) (P > .05). Levels of TNF-α were lower among PwH < 16 only (P < .05). These differences are not observed in participants with recent factor use.

CONCLUSIONS

In PwH, markers of bone metabolism and circulating cytokine levels are abnormal. Recent factor use reverses many of these differences suggesting FVIII replacement ameliorates this pathology. This study suggests bone disease present in PwH is intrinsic to FVIII deficiency.

The Association Between Traumatic Brain Injury and Accelerated Fracture Healing: A Study on the Effects of Growth Factors and Cytokines

Evidence suggests that some systemic and local factors, including cytokines and growth factors in patients with traumatic brain injury (TBI), can play an essential role in accelerating fracture healing. The purpose of this study was to evaluate serum levels of some inflammatory cytokines and growth factors in patients with fracture and TBI as well as healthy subjects. In this study, a total number of 30 patients with a femoral fracture, 30 cases with TBI, 30 patients with TBI and a femoral fracture (fracture + TBI group), and 30 healthy subjects were recruited. The Glasgow Coma Scale (GCS) scores were also determined upon their admission. Then, the serum levels of fibroblast growth factor 2 (FGF-2), transforming growth factor-beta (TGF-β), platelet-derived growth factor (PDGF), bone morphogenetic protein 2 (BMP-2), insulin-like growth factor 1 (IGF-1), interleukin-1 beta (IL-1β), and interleukin-6 (IL-6) were measured via enzyme-linked immunosorbent assay (ELISA) technique, 12 h and 4 weeks after injury and hospital admission. The study results demonstrated that the serum levels of BMP-2, FGF-2, IL-1β, and PDGF in the femoral fracture + TBI group increased significantly over 12 h and after 4 weeks compared with other groups, but the serum levels of IGF-I, IL-6, and TGF-β in this group increased in a significant manner at 12 h compared with other studied groups. The findings also showed that the time to union of a femoral fracture was shorter in the fracture + TBI group than in cases with a femoral fracture alone (p = 0.03). Accordingly, it seems that elevated serum levels of BMP-2, PDGF, FGF-2, and IL-1β may be associated with healing acceleration in fracture + TBI patients. However, further studies are needed to confirm this claim.

Linking skeletal muscle aging with osteoporosis by lamin A/C deficiency

The nuclear lamina protein lamin A/C is a key component of the nuclear envelope. Mutations in the lamin A/C gene (LMNA) are identified in patients with various types of laminopathy-containing diseases, which have features of accelerated aging and osteoporosis. However, the underlying mechanisms for laminopathy-associated osteoporosis remain largely unclear. Here, we provide evidence that loss of lamin A/C in skeletal muscles, but not osteoblast (OB)-lineage cells, results in not only muscle aging-like deficit but also trabecular bone loss, a feature of osteoporosis. The latter is due in large part to elevated bone resorption. Further cellular studies show an increase of osteoclast (OC) differentiation in cocultures of bone marrow macrophages/monocytes (BMMs) and OBs after treatment with the conditioned medium (CM) from lamin A/C-deficient muscle cells. Antibody array screening analysis of the CM proteins identifies interleukin (IL)-6, whose expression is markedly increased in lamin A/C-deficient muscles. Inhibition of IL-6 by its blocking antibody in BMM-OB cocultures diminishes the increase of osteoclastogenesis. Knockout (KO) of IL-6 in muscle lamin A/C-KO mice diminishes the deficits in trabecular bone mass but not muscle. Further mechanistic studies reveal an elevation of cellular senescence marked by senescence-associated beta-galactosidase (SA-β-gal), p16Ink4a, and p53 in lamin A/C-deficient muscles and C2C12 muscle cells, and the p16Ink4a may induce senescence-associated secretory phenotype (SASP) and IL-6 expression. Taken together, these results suggest a critical role for skeletal muscle lamin A/C to prevent cellular senescence, IL-6 expression, hyperosteoclastogenesis, and trabecular bone loss, uncovering a pathological mechanism underlying the link between muscle aging/senescence and osteoporosis.

Influence of infliximab therapy on bone healing post-dental extraction in rats

OBJECTIVE

TNF-α, which acts directly on osteoclastogenesis, may modify bone turnover. Thus, the objective of this study was to evaluate the influence of infliximab on extraction socket healing.

MATERIAL AND METHODS

Eighty-four Wistar rats were randomized into two groups (infliximab EV 5 mg / kg or saline EV 1 ml / kg) and submitted to lower first molar extraction protocol. The animals were sacrificed 1, 3, 7, 14, 21 and 28 days after surgery. The jaws were subjected to radiographic, histomorphometric, histochemical (picrosirius red) and immunohistochemical (TNF-α, RANKL and OPG) analysis.

RESULTS

No differences were observed between the groups in surgical difficulty parameters: mass of teeth, number of root fractures and surgical time. Lower area filling with bone as well as increased amounts of remaining cicatricial tissue were observed in the infliximab group at 14 days (p < 0.001). Lower scores for polymorphonuclear neutrophils were seen at 3 (p < 0.01) and 7 days (p < 0.001), lower mononuclear counts at 7 days (p < 0.01) and lower osteoclast counts at 7 and 14 days (p < 0.01 and p < 0.001, respectively). Additionally, reduced TNF-α, RANKL and OPG immunoreactivity were observed, especially at 7 days (p < 0.05).

CONCLUSION

TNF-α inhibitor may alter the bone repair capacity after tooth extraction, especially in the initial repair periods, by lower expression of TNF α, RANKL and OPG. Thus, additional caution may be needed in patients who use this class of medication after dental extraction.

Exiting the limbo of perimortem trauma: A brief review of microscopic markers of hemorrhaging and early healing signs in bone

The assessment and interpretation of the timing of skeletal trauma can be of extreme difficulty in post-mortem specimens, especially because of post-mortem processes and taphonomic events. The chronological diagnosis of bone trauma, consisting usually in the gross distinction between antemortem, perimortem and post-mortem, is based almost uniquely on macroscopic and morphologic parameters in the anthropological field. However, both the interference of taphonomy and the scarce persistence of specific features indicating vitality (meaning etymologically "produced in life") and/or some very early bone healing reactions, make it extremely difficult. In this perspective, it is important not only to distinguish between peri and post-mortem lesions, but also to interpret perimortem lesions with respect to vitality and time elapsed since the trauma which may change the course of the investigations. And techniques of forensic pathology applied to forensic anthropology can come in extremely handy. If any traces of vital blood extravasation, haemorrhage, hematoma, inflammation, and biomarkers of early healing reaction are found in the bone tissue of a skeletal lesion (regardless the state of preservation of the body), then can they be used as a diagnostic tool or marker of vitality for that lesion? In these terms, vital reactions like bleeding or any early sign of bone healing can be the only evidence for demonstrating that a traumatic event was prior the death. Nevertheless, very little information, or research for that matter, is available in literature concerning persistence and detectability of vitality markers during the bone decomposition process. A fundamental point for properly determining the vitality of a fracture and estimating the post-traumatic time interval in skeletal lesions is the physio-pathological picture of the very initial healing process. This article attempts to provide a review of the physiopathological current knowledge available and applicable to osteology.

Daily oligofructose-enriched inulin intake impacts bone turnover markers but not the cytokine profile in pediatric patients with celiac disease on a gluten-free diet: Results of a randomised, placebo-controlled pilot study

BACKGROUND

Bone metabolism disturbances are commonly observed in patients with newly diagnosed celiac disease (CD). The only available treatment for CD-the intake of a gluten-free diet (GFD)-has been found to be insufficient in effectively improving bone health in some patients. Therefore, there is an urgent need to modify the GFD so as to allow for the provision of all the necessary nutrients and improved absorption. Prebiotics intake reportedly improves the absorption of bone-related vitamin D and calcium as well as bone metabolism. The effect of prebiotic intake on bone health in CD patients has not been studied yet. This study aimed to evaluate the effect of oligofructose-enriched inulin intake on bone metabolism and immune response in children with CD on a GFD.

METHODS

A total of 34 children with CD were randomised into two groups receiving 10 g of oligofructose-enriched inulin (Synergy 1) or a placebo (maltodextrin) for three months, together with a strict GFD. The children's bone metabolism marker levels and cytokine profiles were analysed before and after the intervention.

RESULTS

After supplementation, the concentration of osteocalcin increased significantly in children receiving Synergy 1, while the concentration of bone alkaline phosphatase increased in both groups, independent of supplementation. After the intervention, the level of pyridinoline increased significantly in the placebo group, resulting in a concentration that was two times higher than that in the Synergy 1 group, in which it remained stable. Moreover, the plasma concentrations of N-terminal telopeptides of type I collagen decreased in both the groups, whereas the tartrate-resistant acid phosphatase 5b level increased particularly in the Synergy 1 group. The intervention did not lead to immunological response changes.

CONCLUSIONS

The proposed supplementation beneficially altered bone metabolism, through increased bone formation rates and decreased bone resorption process rates. Supplementation of GFD with prebiotic oligofructose-enriched inulin may be a promising auxiliary therapy for bone metabolism improvements in children with CD.

Isolation and Generation of Osteoclasts

This chapter describes the isolation, culture, and staining of osteoclasts. The key advantages of this assay are that it allows direct measurement of osteoclast number, bone resorption, as well as yielding good quantities of osteoclasts at defined stages of formation for molecular analysis. An additional focus of this chapter will be the generation of osteoclasts from less conventional animal species and cell lines.

Sexual Dimorphism in Immunity to Oral Bacterial Diseases: Intersection of Neutrophil and Osteoclast Pathobiology

Sex is a biological variable that affects immune responses to bacterial and other types of infectious agents. Males and females are known to have differential oral bacterial disease burden in periodontal and endodontic disease. Understanding that there is a contribution from both sex and gender to these oral diseases, we discuss in this review recent sex-based findings that provide a pathobiological basis for differences observed between males and females. Sexual dimorphism of immune responses with respect to neutrophil trafficking and osteoclast differentiation and formation is presented as a plausible mechanism to explain the sexual differences. We also emphasize that sex, as a biological variable, should be considered in these types of oral immunologic studies.

Long-term Consequences of Traumatic Brain Injury in Bone Metabolism

Traumatic brain injury (TBI) leads to long-term cognitive, behavioral, affective deficits, and increase neurodegenerative diseases. It is only in recent years that there is growing awareness that TBI even in its milder form poses long-term health consequences to not only the brain but to other organ systems. Also, the concept that hormonal signals and neural circuits that originate in the hypothalamus play key roles in regulating skeletal system is gaining recognition based on recent mouse genetic studies. Accordingly, many TBI patients have also presented with hormonal dysfunction, increased skeletal fragility, and increased risk of skeletal diseases. Research from animal models suggests that TBI may exacerbate the activation and inactivation of molecular pathways leading to changes in both osteogenesis and bone destruction. TBI has also been found to induce the formation of heterotopic ossification and increased callus formation at sites of muscle or fracture injury through increased vascularization and activation of systemic factors. Recent studies also suggest that the disruption of endocrine factors and neuropeptides caused by TBI may induce adverse skeletal effects. This review will discuss the long-term consequences of TBI on the skeletal system and TBI-induced signaling pathways that contribute to the formation of ectopic bone, altered fracture healing, and reduced bone mass.

Excessive Activation of TLR4/NF-κB Interactively Suppresses the Canonical Wnt/β-catenin Pathway and Induces SANFH in SD Rats

Nuclear factor-kappa B (NF-κB) interactively affects the Wnt/β-catenin pathway and is closely related to different diseases. However, such crosstalk effect in steroid-associated necrosis of femoral head (SANFH) has not been fully explored and evaluated. In this study, early-stage SANFH was induced by two doses of lipopolysaccharide (LPS, 2 mg/kg/day) and three doses of methylprednisolone (MPS, 40 mg/kg/day). LPS and pyrrolidine dithiocarbamate (PDTC) were administered to activate the TLR4/NF-κB pathway and selectively block the activation of NF-κB, respectively. Results showed that PDTC treatment significantly reduced NF-κB expression, diminished inflammation, and effectively decreased bone resorption processes (osteoclastogenesis, adipogenesis, and apoptosis), which were evidently reinforced after osteonecrosis induction. Moreover, PDTC remarkably increased the interfered Wnt/β-catenin pathway and elevated bone formation processes (osteogenesis and angiogenesis). Ultimately, PDTC treatment effectively reduced the incidence of SANFH. Therefore, the excessive activation of TLR4/NF-κB may interactively suppress the Wnt/β-catenin pathway and induce SANFH. Hence, we propose NF-κB-targeted treatment as a novel therapeutic strategy for SANFH.

Macrophages and bone inflammation

Bone metabolism is tightly regulated by the immune system. Accelerated bone destruction is observed in many bone diseases, such as rheumatoid arthritis, fracture, and particle-induced osteolysis. These pathological conditions are associated with inflammatory responses, suggesting the contribution of inflammation to bone destruction. Macrophages are heterogeneous immune cells and are polarized into the proinflammatory M1 and antiinflammatory M2 phenotypes in different microenvironments. The cytokines produced by macrophages depend on the macrophage activation and polarization. Macrophages and macrophage-derived cytokines are important to bone loss in inflammatory bone disease. Recent studies have shown that macrophages can be detected in bone tissue and interact with bone cells. The interplay between macrophages and bone cells is critical to bone formation and repair. In this article, we focus on the role of macrophages in inflammatory bone diseases, as well as discuss the latest studies about macrophages and bone formation, which will provide new insights into the therapeutic strategy for bone disease.

Systemic Inflammatory Mediators and Bone Homeostasis in Intestinal Failure

BACKGROUND

A proinflammatory state has been described in patients with intestinal failure. The prevalence of metabolic bone disease in this group is considerable. It is not known whether this proinflammatory state is related to bone parameters, though bone disease is recognized as a proinflammatory process in postmenopausal women. The purpose of this study was to examine whether inflammation was related to bone disease.

METHODS

Eight patients with parenteral nutrition (PN)-dependent intestinal failure but no recent infections or immunosuppressive medications had serum assayed for interleukin-6 (IL-6), tumor necrosis factor (TNF)-alpha, and its receptors (TNFR-I and TNFR-II), C-reactive protein, and whole blood for lymphocyte proliferation. Routine clinical laboratory measures of vitamin D, parathyroid hormone, serum calcium, and phosphorus within 3 months of the inflammatory measures were compared by Pearson's correlation to the inflammatory measures.

RESULTS

Mean values for calcium, phosphorus, and albumin were normal, but 25-hydroxy vitamin D was reduced and parathyroid hormone and alkaline phosphatase elevated. Serum total calcium was negatively related to TNFR-II, TNF-alpha and positively to T-helper cells. Longer PN dependence was associated with inflammation and negatively with T-helper cells.

CONCLUSIONS

These preliminary findings are hypothesis generating only but support an association of low calcium and longer duration of PN with inflammation in patients with intestinal failure. Whether the inflammation results from vitamin D deficiency or the vitamin D deficiency develops secondary to excessive use of activated vitamin D to modulate inflammation from some other cause, such as a component of PN or repeated infectious challenge, requires further study.

Sex-based differential regulation of bacterial-induced bone resorption

BACKGROUND AND OBJECTIVE

Periodontal disease pathogenesis is comprised of the complex inflammatory immune response to oral bacterial dysbiosis. Like other inflammatory diseases, there is sexual dimorphism evident in periodontal diseases. During periodontitis, inflammatory chemokines direct neutrophils to migrate to the site of infection to neutralize the pathogen. Interestingly, these same chemokines are also involved in regulating pathogen-induced osteoclast formation. Previous reports show differences in bone turnover and lymphocyte recruitment between sexes. We hypothesize that chemokine expression is differentially regulated by sex and thus results in differential osteoclast formation.

MATERIAL AND METHODS

Male and female mice were utilized to isolate neutrophils based on expression of Ly6G-specific, as well as defined osteoclast progenitors. Cells were stimulated with lipopolysaccharide (LPS; 100 ng/mL) then analyzed for neutrophil infiltration and gene expression. Defined osteoclast progenitors were primed: macrophage-colony stimulating factor (25 ng/mL), receptor activator of NF-κB ligand (50 ng/mL), then stimulated with LPS. Osteoclasts were enumerated via TRAP stain and mRNA isolated for gene expression analysis via quantitative polymerase chain reaction.

RESULTS

In response to LPS, male neutrophils in vitro respond with increased chemokine expression and significantly more osteoclast formed in response to LPS compared to females.

CONCLUSIONS

Findings support observations in humans regarding a sexual dimorphism in oral bacterial infections of alveolar bone loss. Males have a strong inflammatory response to bacterial infection, resulting in increased inflammatory microenvironment, reduced pathogenic bacteria clearance and increased osteoclast-driven bone loss in response to differential expression of key chemokines.

Histone deacetylase 3 supports endochondral bone formation by controlling cytokine signaling and matrix remodeling

Histone deacetylase (HDAC) inhibitors are efficacious epigenetic-based therapies for some cancers and neurological disorders; however, each of these drugs inhibits multiple HDACs and has detrimental effects on the skeleton. To better understand how HDAC inhibitors affect endochondral bone formation, we conditionally deleted one of their targets, Hdac3, pre- and postnatally in type II collagen α1 (Col2α1)-expressing chondrocytes. Embryonic deletion was lethal, but postnatal deletion of Hdac3 delayed secondary ossification center formation, altered maturation of growth plate chondrocytes, and increased osteoclast activity in the primary spongiosa. HDAC3-deficient chondrocytes exhibited increased expression of cytokine and matrix-degrading genes (Il-6, Mmp3, Mmp13, and Saa3) and a reduced abundance of genes related to extracellular matrix production, bone development, and ossification (Acan, Col2a1, Ihh, and Col10a1). Histone acetylation increased at and near genes that had increased expression. The acetylation and activation of nuclear factor κB (NF-κB) were also increased in HDAC3-deficient chondrocytes. Increased cytokine signaling promoted autocrine activation of Janus kinase (JAK)-signal transducer and activator of transcription (STAT) and NF-κB pathways to suppress chondrocyte maturation, as well as paracrine activation of osteoclasts and bone resorption. Blockade of interleukin-6 (IL-6)-JAK-STAT signaling, NF-κB signaling, and bromodomain extraterminal proteins, which recognize acetylated lysines and promote transcriptional elongation, significantly reduced Il-6 and Mmp13 expression in HDAC3-deficient chondrocytes and secondary activation in osteoclasts. The JAK inhibitor ruxolitinib also reduced osteoclast activity in Hdac3 conditional knockout mice. Thus, HDAC3 controls the temporal and spatial expression of tissue-remodeling genes and inflammatory responses in chondrocytes to ensure proper endochondral ossification during development.

Repetitive reduction lead to significant elevated IL-6 and decreased IL-10 levels in femoral osteotomies: A quantitative analysis of a robot-assisted reduction process in a rat model

INTRODUCTION

The field of robot-assisted fracture reduction has been developed by several research groups over more than one decade by now, with the main goals of increasing the fracture reduction accuracy. However, the influence of different reduction paths to patients' physiology is not fully known yet. The aim of our study was to compare the impacts of a robot-assisted direct reduction path versus an artificially prolonged reduction path by measuring the cytokine responses in an in vivo rat model.

MATERIALS AND METHODS

Thirty-six male CD(©) rats were assigned into three groups with an external fixator and osteotomy on the left femur. Seven days later, the robot was attached and one group was reduced in a single attempt, while the other group underwent 10 attempts by the robot. The third group was the control group without reduction. Before, and as well as 6, 24 and 48h after the reduction process blood samples were collected. IL-1, IL-6, IL-10, IL-17, and MCP-1 concentrations where analysed via ELISA or cytometric bead assay. Muscle biopsies in the osteotomy area were collected 48h after the reduction process for histological analyses. Statistical significance was set at p≤0.05.

RESULTS

Analysis of the cytokines showed that the pro-inflammatory cytokine IL-6 of the Ten-Attempts reduction group significantly increased 6h after reduction compared to the control group. IL-6 further showed markedly elevated levels 6h after surgery in the Ten-Attempts reduction group compared to the Single-Attempt reduction group. On the anti-inflammatory side, IL-10 showed a significant decrease in the Ten-Attempts reduction group 6h after reduction compared to the Single-Attempt reduction and control group. Muscle biopsies showed a significant increase of pathological changes in both reduction groups and an increase in the severity of bleedings of the Ten-Attempts reduction group compared to the Single-Attempt reduction and control group.

CONCLUSION

A direct and gentle reduction procedure as feasible by the aid of a robot is preferable over a prolonged reduction in terms of cytokine response and tissue changes.

Serum CX3CL1/fractalkine concentrations are positively associated with disease severity in postmenopausal osteoporotic patients

BACKGROUND

The chemokine (C-X3-C motif) ligand 1 (CX3CL1), also called fractalkine (FKN), has recently been reported to be involved in osteoclastogenic process and pathological bone destruction.

OBJECTIVE

This study aimed to investigate the link between serum CX3CL1/FKN levels with disease progression of postmenopausal osteoporotic patients.

METHODS

A total of 53 women with postmenopausal osteoporosis (PMOP group), 51 postmenopausal non-osteoporotic female patients (PMNOP group) and 50 premenopausal non-osteoporotic healthy women of childbearing age (control group) were enrolled in the study. The bone mineral density (BMD) for all subjects was determined via dual-energy X-ray absorptiometry of the lumbar spine, femoral neck, internal trochanter, total hip, greater trochanter and Ward's triangle. The levels of FKN in the serum were examined using the enzyme-linked immunosorbent assay method. The serum bone resorption markers TRACP-5b, NTX levels, inflammation markers IL-1β and IL-6 as well as oestrogen-2(E2) were also detected in all participants. The visual analogue scores (VAS) and Oswestry Disability Index (ODI) for low back pain were recorded in PMOP females for evaluation of osteoporotic pain and function.

RESULTS

FKN levels were significantly higher in postmenopausal osteoporotic patients compared with postmenopausal non-osteoporotic females (139.8 ± 44.3 pg/mL VS 116.5 ± 23.1 pg/mL, p < 0.05) and healthy controls (139.8 ± 44.3 pg/mL VS 109.7 ± 19.4 pg/mL, p < 0.05). Serum FKN concentrations were negatively associated with BMD at femoral neck (r = -0.394, p = 0.004), total hip(r = -0.374, p = 0.006), internal trochanter(r = -0.340, p = 0.013), greater trochanter(r = -0.376, p = 0.006), Ward's triangle(r = -0.343, p = 0.012), L1-L4 lumbar spine(r = -0.339, p = 0.013) and positively associated with VAS (r = 0.321, p = 0.019) and ODI (r = 0.377, p = 0.005) scores, bone turnover makers (TRACP-5b:r = 0.341, p = 0.012; NTX:r = 0.364, p = 0.007)as well as inflammation markers (IL-1β: r = 0.396, p = 0.003; IL-6:r = 0.355, p = 0.009) in postmenopausal osteoporotic patients.

CONCLUSIONS

Serum FKN may serve as a novel biomarker for assessing disease progression and a new potential therapeutic target for anti-resorptive treatment in osteoporosis patients.

Inflammation, fracture and bone repair

The reconstitution of lost bone is a subject that is germane to many orthopedic conditions including fractures and non-unions, infection, inflammatory arthritis, osteoporosis, osteonecrosis, metabolic bone disease, tumors, and periprosthetic particle-associated osteolysis. In this regard, the processes of acute and chronic inflammation play an integral role. Acute inflammation is initiated by endogenous or exogenous adverse stimuli, and can become chronic in nature if not resolved by normal homeostatic mechanisms. Dysregulated inflammation leads to increased bone resorption and suppressed bone formation. Crosstalk among inflammatory cells (polymorphonuclear leukocytes and cells of the monocyte-macrophage-osteoclast lineage) and cells related to bone healing (cells of the mesenchymal stem cell-osteoblast lineage and vascular lineage) is essential to the formation, repair and remodeling of bone. In this review, the authors provide a comprehensive summary of the literature related to inflammation and bone repair. Special emphasis is placed on the underlying cellular and molecular mechanisms, and potential interventions that can favorably modulate the outcome of clinical conditions that involve bone repair.

ARTD1 regulates osteoclastogenesis and bone homeostasis by dampening NF-κB-dependent transcription of IL-1β

While ADP-ribosyltransferase diphtheria toxin-like 1 (ARTD1, formerly PARP1) and its enzymatic activity have been shown to be important for reprogramming and differentiation of cells, such as during adipogenesis, their role and mechanism in regulating osteoclastogenesis and bone homeostasis are largely unknown. Here, in cell culture-based RANKL-induced osteoclastogenesis models, we show that silencing of ARTD1 or inhibition of its enzymatic activity enhances osteoclast differentiation and function. As a consequence of ARTD1 silencing or inhibition, the recruitment of p65/RelA to the IL-1β promoter, which is associated with transcriptionally active histone marks, IL-1β expression and inflammasome-dependent secretion of IL-1β are enhanced. This subsequently promotes sustained induction of the transcription factor Nfatc1/A and osteoclastogenesis in an autocrine manner via the IL-1 receptor. In vivo, Artd1-deficient mice display significantly decreased bone mass as a consequence of increased osteoclast differentiation. Accordingly, the expression of osteoclast markers is enhanced in mutant compared to wild-type mice. Together, these results indicate that ARTD1 controls osteoclast development and bone remodelling via its enzymatic activity by modulating the epigenetic marks surrounding the IL-1β promoter and expression of IL-1β and subsequently also Nfatc1/A.

Adipose-Derived Mesenchymal Stem Cells Prevent Systemic Bone Loss in Collagen-Induced Arthritis

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic inflammatory synovitis leading to joint destruction and systemic bone loss. The inflammation-induced bone loss is mediated by increased osteoclast formation and function. Current antirheumatic therapies primarily target suppression of inflammatory cascade with limited or no success in controlling progression of bone destruction. Mesenchymal stem cells (MSCs) by virtue of their tissue repair and immunomodulatory properties have shown promising results in various autoimmune and degenerative diseases. However, the role of MSCs in prevention of bone destruction in RA is not yet understood. In this study, we investigated the effect of adipose-derived MSCs (ASCs) on in vitro formation of bone-resorbing osteoclasts and pathological bone loss in the mouse collagen-induced arthritis (CIA) model of RA. We observed that ASCs significantly inhibited receptor activator of NF-κB ligand (RANKL)-induced osteoclastogenesis in both a contact-dependent and -independent manner. Additionally, ASCs inhibited RANKL-induced osteoclastogenesis in the presence of proinflammatory cytokines such as TNF-α, IL-17, and IL-1β. Furthermore, treatment with ASCs at the onset of CIA significantly reduced clinical symptoms and joint pathology. Interestingly, ASCs protected periarticular and systemic bone loss in CIA mice by maintaining trabecular bone structure. We further observed that treatment with ASCs reduced osteoclast precursors in bone marrow, resulting in decreased osteoclastogenesis. Moreover, ASCs suppressed autoimmune T cell responses and increased the percentages of peripheral regulatory T and B cells. Thus, we provide strong evidence that ASCs ameliorate inflammation-induced systemic bone loss in CIA mice by reducing osteoclast precursors and promoting immune tolerance.

Impaired Fracture Healing after Hemorrhagic Shock

Impaired fracture healing can occur in severely injured patients with hemorrhagic shock due to decreased soft tissue perfusion after trauma. We investigated the effects of fracture healing in a standardized pressure controlled hemorrhagic shock model in mice, to test the hypothesis that bleeding is relevant in the bone healing response. Male C57/BL6 mice were subjected to a closed femoral shaft fracture stabilized by intramedullary nailing. One group was additionally subjected to pressure controlled hemorrhagic shock (HS, mean arterial pressure (MAP) of 35 mmHg for 90 minutes). Serum cytokines (IL-6, KC, MCP-1, and TNF-α) were analyzed 6 hours after shock. Fracture healing was assessed 21 days after fracture. Hemorrhagic shock is associated with a significant increase in serum inflammatory cytokines in the early phase. Histologic analysis demonstrated a significantly decreased number of osteoclasts, a decrease in bone quality, and more cartilage islands after hemorrhagic shock. μCT analysis showed a trend towards decreased bone tissue mineral density in the HS group. Mechanical testing revealed no difference in tensile failure. Our results suggest a delay in fracture healing after hemorrhagic shock. This may be due to significantly diminished osteoclast recruitment. The exact mechanisms should be studied further, particularly during earlier stages of fracture healing.

Improved fracture healing in patients with concomitant traumatic brain injury: proven or not?

Over the last 3 decades, scientific evidence advocates an association between traumatic brain injury (TBI) and accelerated fracture healing. Multiple clinical and preclinical studies have shown an enhanced callus formation and an increased callus volume in patients, respectively, rats with concomitant TBI. Over time, different substances (cytokines, hormones, etc.) were in focus to elucidate the relationship between TBI and fracture healing. Until now, the mechanism behind this relationship is not fully clarified and a consensus on which substance plays the key role could not be attained in the literature. In this review, we will give an overview of current concepts and opinions on this topic published in the last decade and both clinical and pathophysiological theories will be discussed.

Phosphorus-insufficient maternal milk is associated with ectopic expression of collagen I and female-specific bony changes in infant mouse cartilages

Excessive phosphorus intake causes diseases such as hyperphosphatemia and hypocalcaemia, but the effect of dietary insufficiency of phosphorus is unclear. Here, we explored the effect of phosphorus dietary insufficiency on tissue growth and maintenance by using C57BL/6J mice fed a low phosphorus diet, which contained 18.5% of the phosphorus of a normal diet. We demonstrated that the phosphorus content in the maternal milk of mother mice was significantly reduced due to the consumption of a low phosphorus diet, which further resulted in bone deformation in infant mice in a female-specific manner. Polarizing microscopic analysis of low-phosphorus milk (LPM)-induced bone deformation resulted in unusually formed crystals inside cartilage. Furthermore, immunohistochemical analysis revealed ectopic expression of collagen I in the region where crystals were ectopically formed. Electron microscopic analysis showed morphological features similar to bone tissues. Immunochemical analysis demonstrated that the amount of interleukin-6 (IL-6), a cytokine known to trigger osteoclast formation, was significantly reduced in the maternal milk of mice fed the low-phosphorus diet. Our results suggest that phosphorus intake from maternal milk is involved in infant cartilage formation.

Bone marrow stromal cells derived MCP-1 reverses the inhibitory effects of multiple myeloma cells on osteoclastogenesis by upregulating the RANK expression

Multiple myeloma (MM) cells are responsible for aberrant osteoclast (OC) activation. However, when cocultured monocytes, but not OC precursors, with MM cells, we made a novel observation that MM cells inhibited receptor activator of nuclear factor κB ligand (RANKL)-induced increase of OC differentiation, OC gene expression, signaling pathways and bone resorption activity. Our results showed that MM cells produced multiple inhibitory cytokines of osteoclastogenesis, such as IL-10, which activated STAT3 signaling and induce OC inhibition. However, cocultures of bone marrow stromal cells (BMSCs) reversed MM-induced OC inhibition. We found that MM cells increased production of MCP-1 from BMSCs and BMSC-derived MCP-1 enhanced OC formation. Mechanistic studies showed that IL-10 downregulated RANK expression in monocytes and thus, inhibited RANKL-induced OC formation. In contrast, MCP-1 upregulated RANK expression and thus, enhanced OC formation. Overall, our studies for the first time demonstrated that MM cell have inhibitory effects on osteoclastogenesis by producing inhibitory cytokines. Our results further indicate that activation of osteoclastogenesis in bone marrow requests the crosstalk of MM cells, BMSCs and their produced cytokines. Thus, our studies provide evidences that targeting bone marrow microenvironmental cells and/or cytokines may be a new approach to treating MM bone destruction.

Differentiation of osteoprogenitor cells is affected by trauma-haemorrhage

INTRODUCTION

In multiple trauma patients an increased incidence of delayed healing and non-union has been observed. The exact mechanisms underlying this delayed fracture healing are still not fully understood.

MATERIAL AND METHODS

40 male C57BL/6N-mice underwent standardized midline laparotomy and pressure-controlled haemorrhage (TH) or implantation of catheters without blood loss (sham procedure). Animals were sacrificed 24h or 72 h later. Osteoprogenitor cells derived from bone marrow were isolated and differentiated into osteoblasts for 20 days and osteoclasts for 7 days. Osteoblast mineralization and osteoclast numbers were determined, and gene expression of Alpl, Bglap, Opg, Rankl was measured in osteoblast cell culture, as well as gene expression of Rank, Ctsk and Nfatc1 was determined in osteoclast cell culture. Furthermore, plasma Opg, Rankl and TRAP were measured.

RESULTS

Mineralization capacity of osteoblasts was unchanged after TH, but Alpl gene expression after 23 days was significantly decreased compared to sham. Osteoclast number of group TH 8 days was significantly decreased compared to sham. Furthermore, gene expression of Ctsk and Nfatc1 were increased in group TH 10 days compared to group TH 8 days. Plasma Opg concentration was significantly elevated and Rankl concentrations were significantly declined in TH groups compared to sham groups after 24h and 72 h.

CONCLUSION

TH results in a diminished osteoclast number after 8 days, whereas differentiation of osteoblasts seems to be unaffected. The reduction of osteoclast number seems to be mediated through the Rankl-Opg-signalling pathway. However, further studies in models including a fractured extremity with a longer observation period are needed to identify the relevance of the Rankl-Opg- pathway in delayed fracture healing after TH and to focus on possible therapeutic interventions.

Analysis of the host transcriptome from demyelinating spinal cord of murine coronavirus-infected mice

Persistent infection of the mouse central nervous system (CNS) with mouse hepatitis virus (MHV) induces a demyelinating disease pathologically similar to multiple sclerosis and is therefore used as a model system. There is little information regarding the host factors that correlate with and contribute to MHV-induced demyelination. Here, we detail the genes and pathways associated with MHV-induced demyelinating disease in the spinal cord. High-throughput sequencing of the host transcriptome revealed that demyelination is accompanied by numerous transcriptional changes indicative of immune infiltration as well as changes in the cytokine milieu and lipid metabolism. We found evidence that a Th1-biased cytokine/chemokine response and eicosanoid-derived inflammation accompany persistent MHV infection and that antigen presentation is ongoing. Interestingly, increased expression of genes involved in lipid transport, processing, and catabolism, including some with known roles in neurodegenerative diseases, coincided with demyelination. Lastly, expression of several genes involved in osteoclast or bone-resident macrophage function, most notably TREM2 and DAP12, was upregulated in persistently infected mouse spinal cord. This study highlights the complexity of the host antiviral response, which accompany MHV-induced demyelination, and further supports previous findings that MHV-induced demyelination is immune-mediated. Interestingly, these data suggest a parallel between bone reabsorption by osteoclasts and myelin debris clearance by microglia in the bone and the CNS, respectively. To our knowledge, this is the first report of using an RNA-seq approach to study the host CNS response to persistent viral infection.

The prevalence of disordered eating and possible health consequences in adolescent female tennis players from Rio de Janeiro, Brazil

The aim of this study was to estimate the prevalence of disordered eating and possible health consequences in adolescent female tennis players. This cross-sectional controlled study investigated the pubertal development (Tanner stages); body composition (dual energy X-ray absorptiometry-DXA); dietary intake (food record); presence of disordered eating (EAT-26, BITE and BSQ); menstrual status (questionnaire) and bone mineral density (DXA). The Female Athlete Triad (FAT) was divided into two severity stages. The study included 45 adolescents (24 athletes and 21 controls) at some pubertal developmental stage. The athletes exhibited better body composition profiles. We found that 91.7%, 33.3% and 25% of athletes and 71.4%, 9.5% and 33.3% of controls met criteria for disordered eating and/or low energy availability, menstrual irregularities and low bone mass, respectively. A greater percentage of athletes than controls presented with 1 and 2 FAT components (stage I), and 4.2% presented with the full syndrome. In conclusion, tennis players appear to present with more severe disorders than controls and should be monitored to avoid damage to their performance and health.

M-CSF potently augments RANKL-induced resorption activation in mature human osteoclasts. PLoS One. 2011;6:e21462. [PMID: 21738673 PMCID: PMC3126821 DOI: 10.1371/journal.pone.0021462]

Macrophage-CSF (M-CSF) is critical for osteoclast (OC) differentiation and is reported to enhance mature OC survival and motility. However, its role in the regulation of bone resorption, the main function of OCs, has not been well characterised. To address this we analysed short-term cultures of fully differentiated OCs derived from human colony forming unit-granulocyte macrophages (CFU-GM). When cultured on dentine, OC survival was enhanced by M-CSF but more effectively by receptor activator of NFκB ligand (RANKL). Resorption was entirely dependent on the presence of RANKL. Co-treatment with M-CSF augmented RANKL-induced resorption in a concentration-dependent manner with a (200-300%) stimulation at 25 ng/mL, an effect observed within 4-6 h. M-CSF co-treatment also increased number of resorption pits and F-actin sealing zones, but not the number of OCs or pit size, indicating stimulation of the proportion of OCs activated. M-CSF facilitated RANKL-induced activation of c-fos and extracellular signal-regulated kinase (ERK) 1/2 phosphorylation, but not NFκB nor nuclear factor of activated T-cells, cytoplasmic-1 (NFATc1). The mitogen-activated protein kinase kinase (MEK) 1 inhibitor PD98059 partially blocked augmentation of resorption by M-CSF. Our results reveal a previously unidentified role of M-CSF as a potent stimulator of mature OC resorbing activity, possibly mediated via ERK upstream of c-fos.

The biology of fracture healing

The biology of fracture healing is a complex biological process that follows specific regenerative patterns and involves changes in the expression of several thousand genes. Although there is still much to be learned to fully comprehend the pathways of bone regeneration, the over-all pathways of both the anatomical and biochemical events have been thoroughly investigated. These efforts have provided a general understanding of how fracture healing occurs. Following the initial trauma, bone heals by either direct intramembranous or indirect fracture healing, which consists of both intramembranous and endochondral bone formation. The most common pathway is indirect healing, since direct bone healing requires an anatomical reduction and rigidly stable conditions, commonly only obtained by open reduction and internal fixation. However, when such conditions are achieved, the direct healing cascade allows the bone structure to immediately regenerate anatomical lamellar bone and the Haversian systems without any remodelling steps necessary. In all other non-stable conditions, bone healing follows a specific biological pathway. It involves an acute inflammatory response including the production and release of several important molecules, and the recruitment of mesenchymal stem cells in order to generate a primary cartilaginous callus. This primary callus later undergoes revascularisation and calcification, and is finally remodelled to fully restore a normal bone structure. In this article we summarise the basic biology of fracture healing.

Diverse effects of Porphyromonas gingivalis on human osteoclast formation

Porphyromonas gingivalis is associated with periodontitis, a chronic inflammatory disease of the tooth-supporting tissues. A major clinical symptom is alveolar bone loss due to excessive resorption by osteoclasts. P. gingivalis may influence osteoclast formation in diverse ways; by interacting directly with osteoclast precursors that likely originate from peripheral blood, or indirectly by activating gingival fibroblasts, cells that can support osteoclast formation. In the present study we investigated these possibilities. Conditioned medium from viable or dead P. gingivalis, or from gingival fibroblasts challenged with viable or dead P. gingivalis were added to human mononuclear osteoclast precursors. After 21 days of culture the number of multinucleated (≥3 nuclei) tartrate resistant acid phosphatase (TRACP)-positive cells was determined as a measure for osteoclast formation. Conditioned medium from viable P. gingivalis, and from fibroblasts with viable P. gingivalis stimulated osteoclast formation (1.6-fold increase p < 0.05). Conditioned medium from dead bacteria had no effect on osteoclast formation, whereas conditioned medium from fibroblasts with dead bacteria stimulated formation (1.4-fold increase, p < 0.05). Inhibition of P. gingivalis LPS activity by Polymyxin B reduced the stimulatory effect of conditioned medium. Interestingly, when RANKL and M-CSF were added to cultures, conditioned media inhibited osteoclast formation (0.6-0.7-fold decrease, p < 0.05). Our results indicate that P. gingivalis influences osteoclast formation in vitro in different ways. Directly, by bacterial factors, likely LPS, or indirectly, by cytokines produced by gingival fibroblasts in response to P. gingivalis. Depending on the presence of RANKL and M-CSF, the effect of P. gingivalis is either stimulatory or inhibitory.

Cytokines and bone-related factors in systemically healthy patients with chronic periodontitis and patients with type 2 diabetes and chronic periodontitis

BACKGROUND

This study compares the levels of cytokines and bone-related factors in the gingival crevicular fluid (GCF) of systemically healthy patients with chronic periodontitis (CP); and better-controlled, and poorly controlled patients with type 2 diabetes and CP.

METHODS

Thirty-seven patients with type 2 diabetes and CP and 20 systemically healthy patients with CP were enrolled in this study. The patients with diabetes mellitus were categorized as better-controlled (n = 17; HbA(1c) levels ≤8%) or poorly controlled (n = 20; glycated hemoglobin values >8%). Levels of tumor necrosis factor-α, interleukin (IL)-4, interferon (IFN)-γ, IL-23, IL-17, soluble receptor activator of nuclear factor-kappa B ligand (sRANKL), and osteoprotegerin (OPG) in GCF of diseased sites were analyzed by enzyme-linked immunosorbent assay.

RESULTS

Type 2 diabetes mellitus, as a whole, upregulates the levels of OPG, sRANKL, IFN-γ, IL-17, and IL-23 and downregulates the production of IL-4 in sites with CP (P <0.05). Better-controlled individuals exhibited the highest levels of IFN-γ, whereas poorly controlled patients presented the highest levels of IL-17 (P <0.05). There were no differences in the levels of tumor necrosis factor-α, OPG, and IL-23 among systemically healthy, better-controlled, and poorly controlled patients with diabetes (P >0.05).

CONCLUSIONS

Increased levels of proinflammatory cytokines and RANKL were observed in the GCF of patients with type 2 diabetes with CP, compared to patients without diabetes. In addition, poor or good glycemic status seems to modulate osteo-immunoinflammatory mediators in a different manner.

Estrogen enhances the functions of CD4(+)CD25(+)Foxp3(+) regulatory T cells that suppress osteoclast differentiation and bone resorption in vitro

Cross-talk has been shown to occur between the immune system and bone metabolism pathways. In the present study, we investigated the impact of CD4(+)CD25(+)Foxp3(+) regulatory T (Treg) cells on osteoclastogenesis and bone resorption. Treg cells that were isolated and purified from peripheral blood mononuclear cells (PBMCs) of healthy adults inhibited both the differentiation of osteoclasts (OCs) from human embryo bone marrow cells (BMCs) and the pit formation in a dose-dependent manner. In cell cocultures, the production levels of both interleukin-10 (IL-10) and transforming growth factor-beta 1 (TGF-β1) were proportionally upregulated as the ratio of Treg cells to BMCs was increased, and the inhibition of OC differentiation and bone resorption by Treg cells was completely reversed by anti-IL-10 and anti-TGF-β1 antibodies. Treatment of BMC and Treg cell cocultures with 17β-estradiol (E2) at concentrations between 10⁻⁷ and 10⁻⁹ mol/l suppressed OC differentiation and bone resorption more efficiently than it did in cultures of BMCs alone; this enhanced suppression occurred via the stimulation of Treg cell IL-10 and TGF-β1 expression. These data suggest that Treg cells suppress OC differentiation and bone resorption by secreting IL-10 and TGF-β1. E2 enhances the suppressive effects of Treg cells on OC differentiation and bone resorption by stimulating IL-10 and TGF-β1 secretion from these cells. Therefore, Treg cell-derived IL-10 and TGF-β1 are likely involved in the regulation of E2 on bone metabolism and represent potential therapeutic targets for the treatment of postmenopausal osteoporosis (PMO).

Celiac disease and pediatric type 1 diabetes: diagnostic and treatment dilemmas

Despite the advent of sensitive and specific serologic testing, routine screening for celiac disease (CD) in diabetic populations may not be universal practice, and many clinicians struggle to find the optimal approach to managing CD in pediatric Type 1 diabetes (T1D) patients. While some clinicians advocate screening for CD in all patients with T1D, others are unsure whether this is warranted. The diagnosis of patients who present with symptomatic CD, including malabsorption and obvious pathology upon biopsy, remains straightforward, with improvements noted on a gluten-free diet. Many patients identified by screening, however, tend to be asymptomatic. Evidence is inconclusive as to whether the benefits of screening and potentially treating asymptomatic individuals outweigh the harms of managing a population already burdened with a serious illness. This review focuses on current knowledge of CD in children and youth with T1D, highlighting important elements of the disease's pathophysiology, epidemiology, clinical presentation, and diagnostic challenges.

Matrix Metalloproteinase Activity in the Stromal Cell of Giant Cell Tumor of Bone

Giant cell tumor of bone (GCT) is a destructive and potentially metastatic bone tumour in which the characteristic giant cells have classically been considered the culprits in bone destruction. However, the neoplastic element of the tumour consists of propagative osteoblast-like stromal cells that may play a role in bone resorption. The objectives of this study were to determine the expression and activity of the gelatinases, matrix metalloproteinase (MMP)-2 and -9, in GCT stromal cells, and to determine if these cells have bone-resorbing capabilities. We performed immunohistochemistry on clinical specimens, and real-time polymerase chain reaction (PCR) and zymography on cell lysates and conditioned media from cultured clinical GCT specimens in order to evaluate the expression and activity of MMP-2 and-9 in GCT stromal cells. Our results support the fact that GCT stromal cells express MMP-2 and MMP-9 and are capable of gelatin degradation in vitro. These cells may therefore play a role in bone destruction in GCT.

Interferon regulatory factor-8 regulates bone metabolism by suppressing osteoclastogenesis

Bone metabolism results from a balance between osteoclast-driven bone resorption and osteoblast-mediated bone formation. Diseases such as periodontitis and rheumatoid arthritis are characterized by increased bone destruction due to enhanced osteoclastogenesis. Here we report that interferon regulatory factor-8 (IRF-8), a transcription factor expressed in immune cells, is a key regulatory molecule for osteoclastogenesis. IRF-8 expression in osteoclast precursors was downregulated during the initial phase of osteoclast differentiation induced by receptor activator of nuclear factor-kappaB ligand (RANKL), which is encoded by the Tnfsf11 gene. Mice deficient in Irf8 showed severe osteoporosis, owing to increased numbers of osteoclasts, and also showed enhanced bone destruction after lipopolysaccharide (LPS) administration. Irf8-/- osteoclast precursors underwent increased osteoclastogenesis in response to RANKL and tumor necrosis factor-alpha (TNF-alpha). IRF-8 suppressed osteoclastogenesis by inhibiting the function and expression of nuclear factor of activated T cells c1 (NFATc1). Our results show that IRF-8 inhibits osteoclast formation under physiological and pathological conditions and suggest a model where downregulation of inhibitory factors such as IRF-8 contributes to RANKL-mediated osteoclastogenesis.

Modulation of the inflammatory response for enhanced bone tissue regeneration

Proinflammatory cytokines are infamous for their catabolic effects on tissues and joints in both inflammatory diseases and following the implantation of biomedical devices. However, recent studies indicate that many of these same molecules are critical for triggering tissue regeneration following injury. This review will discuss the role of inflammatory signals in regulating bone regeneration and the impact of both immunomodulatory and antiinflammatory pharmacologic agents on fracture healing, to demonstrate the importance of incorporating rational control of inflammation into the design of tissue engineering strategies.