Cytokines synergistically induce osteoclast differentiation: support by immortalized or normal calvarial cells

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

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

The cGAS-STING Pathway Affects Vertebral Bone but Does Not Promote Intervertebral Disc Cell Senescence or Degeneration

The DNA-sensing cGAS-STING pathway promotes the senescence-associated secretory phenotype (SASP) and mediates type-I interferon inflammatory responses to foreign viral and bacterial DNA as well as self-DNA. Studies of the intervertebral disc in humans and mice demonstrate associations between aging, increased cell senescence, and disc degeneration. Herein we assessed the role of STING in SASP promotion in STING gain- (N153S) and loss-of-function mouse models. N153S mice evidenced elevated circulating levels of proinflammatory markers including IL-1β, IL-6, and TNF-α, showed elevated monocyte and macrophage abundance in the vertebral marrow, and exhibited a mild trabecular and cortical bone phenotype in caudal vertebrae. Interestingly, despite systemic inflammation, the structural integrity of the disc and knee articular joint remained intact, and cells did not show a loss of their phenotype or elevated SASP. Transcriptomic analysis of N153S tissues demonstrated an upregulated immune response by disc cells, which did not closely resemble inflammatory changes in human tissues. Interestingly, STING^-/- mice also showed a mild vertebral bone phenotype, but the absence of STING did not reduce the abundance of SASP markers or improve the age-associated disc phenotype. Overall, the analyses of N153S and STING^-/- mice suggest that the cGAS-STING pathway is not a major contributor to SASP induction and consequent disc aging and degeneration but may play a minor role in the maintenance of trabecular bone in the vertebrae. This work contributes to a growing body of work demonstrating that systemic inflammation is not a key driver of disc degeneration.

IL-1ß, IL-6 and TNF-α expression levels of macrophage cells induced by benzydamine hydrochloride, benzydamine hydrochloride with chitosan, calcium hydroxide and chlorhexidine medicaments: An ELISA study

The aim of the present study was to evaluate IL-1ß, IL-6 and TNF-α expression levels of macrophage cells induced by benzydamine hydrochloride (BNZ), BNZ with chitosan, calcium hydroxide (CH) and chlorhexidine (CHX) medicaments. Half maximal inhibitory concentrations (IC₅₀) were assessed on THP-1, Saos-2, and CRL-2014 cells using MTT assay. THP-1 cells were differentiated into macrophages with phorbol12-myristate13-acetate and activated with lipopolysaccharide. IL-1β, IL-6 and TNF-α levels in supernatants were determined using enzyme-linked immunosorbent assay (ELISA). The data were examined with one-way ANOVA and Tukey's multiple comparison test (p=0.05). At the selected concentrations, the cell viability was higher than 50% for chitosan and CH, whereas CHX presented lower IC₅₀ values than BNZ and BNZ+chitosan. According to ELISA results, the lowest IL-1β, IL-6 and TNF-α values were observed with BNZ+Chitosan 50 µg/mL and BNZ 50 µg/mL. BNZ+chitosan 50 µg/mL combination has revealed promising anti-inflammatory effects. Nevertheless, these findings need to be examined in clinical conditions.

An updated review of the effects of eicosapentaenoic acid- and docosahexaenoic acid-derived resolvins on bone preservation

Resolvins are biosynthesized from omega-3 eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in vivo by means of enzymatic activities, and these factors can attenuate inflammation and promote tissue regeneration. Inflammatory bone disorders can lead to bone loss and thereby be harmful to human health. The link between bone preservation and resolvins has been discussed in some experimental studies. Significant evidence has shown that resolvins benefit bone health and bone preservation by promoting the resolution of inflammation and directly regulating osteoclasts and osteoblasts. Therefore, this review highlights the role and beneficial impact of resolvins derived from EPA and DHA on inflammatory bone disorders, such as rheumatoid arthritis and periodontitis. In addition, the mechanisms by which resolvins exert their beneficial effects on bone preservation have also been summarized based on the available literature.

Cytocompatibility of filling pastes by primary teeth root simulating model

Evaluate the cytocompatibility of Calen^®/ZO, Calcicur^®, Vitapex^®, Endoflas^®, and zinc oxide/eugenol-based (ZOE) root canal pastes (RCP) to human primary osteoblasts (HPO) through a simplified model for primary teeth. The model employed pipette tips filled with 0.037 g of paste, exposed to 185 µL of culture medium for 24 h (n = 6). Release of components was analysed by Proton Nuclear Magnetic Resonance Spectroscopy (¹H-NMR). HPO were exposed to conditioned media for 24 h. Cell viability was assessed by cell density and metabolic activity, and release of interleukin 6 (IL-6), vascular endothelial growth factor (VEGF) and fibroblast growth factor (bFGF) by immunological assay. Physicochemical properties and antimicrobial efficacy were also evaluated. ¹H-NMR spectra analysis showed similarity between ZOE, Endoflas^®, Calcicur^®, and Vitapex^® compared to Calen^®/ZO and positive control, which showed distinct released components. Calen^®/ZO and Calcicur^® exhibited high alkaline pH in all periods and showed similar solubility. Calen^®/ZO, ZOE, and Vitapex^® showed similar flow rate. Calen^®/ZO, Calcicur^®, and Vitapex^® did not exhibit antimicrobial efficacy. Calen^®/ZO presented cytotoxicity (p < 0.05). Pastes did not increase IL-6 release compared to control. Apart from Vitapex^®, all pastes significantly induced VEGF/bFGF release. Interactive effects among released products may affect biological response to filling pastes. Calcicur^®, ZOE, Endoflas^® and Calen^®/ZO presented good to moderate cytocompatibility, with low impact on pro-inflammatory cytokine release and induction of growth factors of interest to tissue repair. This simplified model, specific for the evaluation of the cytocompatibility of RCPs on primary teeth, suggests how these pastes might contribute to bone repair in clinical situations of apical periodontitis in children.

Destroy to Rebuild: The Connection Between Bone Tissue Remodeling and Matrix Metalloproteinases

Bone is a dynamic organ that undergoes constant remodeling, an energetically costly process by which old bone is replaced and localized bone defects are repaired to renew the skeleton over time, thereby maintaining skeletal health. This review provides a general overview of bone’s main players (bone lining cells, osteocytes, osteoclasts, reversal cells, and osteoblasts) that participate in bone remodeling. Placing emphasis on the family of extracellular matrix metalloproteinases (MMPs), we describe how: (i) Convergence of multiple protease families (including MMPs and cysteine proteinases) ensures complexity and robustness of the bone remodeling process, (ii) Enzymatic activity of MMPs affects bone physiology at the molecular and cellular levels and (iii) Either overexpression or deficiency/insufficiency of individual MMPs impairs healthy bone remodeling and systemic metabolism. Today, it is generally accepted that proteolytic activity is required for the degradation of bone tissue in osteoarthritis and osteoporosis. However, it is increasingly evident that inactivating mutations in MMP genes can also lead to bone pathology including osteolysis and metabolic abnormalities such as delayed growth. We argue that there remains a need to rethink the role played by proteases in bone physiology and pathology.

Exploring the Interface between Inflammatory and Therapeutic Glucocorticoid Induced Bone and Muscle Loss

Due to their potent immunomodulatory anti-inflammatory properties, synthetic glucocorticoids (GCs) are widely utilized in the treatment of chronic inflammatory disease. In this review, we examine our current understanding of how chronic inflammation and commonly used therapeutic GCs interact to regulate bone and muscle metabolism. Whilst both inflammation and therapeutic GCs directly promote systemic osteoporosis and muscle wasting, the mechanisms whereby they achieve this are distinct. Importantly, their interactions in vivo are greatly complicated secondary to the directly opposing actions of GCs on a wide array of pro-inflammatory signalling pathways that underpin catabolic and anti-anabolic metabolism. Several clinical studies have attempted to address the net effects of therapeutic glucocorticoids on inflammatory bone loss and muscle wasting using a range of approaches. These have yielded a wide array of results further complicated by the nature of inflammatory disease, underlying the disease management and regimen of GC therapy. Here, we report the latest findings related to these pathway interactions and explore the latest insights from murine models of disease aimed at modelling these processes and delineating the contribution of pre-receptor steroid metabolism. Understanding these processes remains paramount in the effective management of patients with chronic inflammatory disease.

Enzymes and cytokines disease in total hip arthroplasty: promoters of immune loosening

Introducción. Una de las causas más importantes de falla de la prótesis de cadera lo constituye el fenómeno de aflojamiento, el cual se relaciona con la liberación de enzimas mediada por citocinas y produce la lisis del hueso que soporta el implante.Objetivo. Describir los mecanismos de interacción biológica de las moléculas promotoras del aflojamiento de la prótesis total de cadera que con mayor frecuencia están presentes en el proceso.Materiales y métodos. Se realizó una búsqueda de artículos originales y casos clínicos en las bases de datos PubMed y Scopus, sin límite de fecha de publicación, utilizando los términos MeSH “hip prosthesis loosening”, “aseptic loosening”, “cytokines” y “hip arthroplasty failure”. La extracción de datos se hizo mediante la lectura de 250 estudios, de los cuales se seleccionaron 66 para fines de redacción.Resultados. Los autores describen las moléculas más representativas implicadas en el aflojamiento de la prótesis de cadera, además se presentan las interacciones entre ellas.Conclusiones. Enzimas y citocinas han sido ampliamente estudiadas por cuatro décadas, aunque sus mecanismos de interacción son poco conocidos. Los autores proponen un mecanismo de interacción, proceso que podría denominarse “enfermedad de las enzimas y citocinas” o “aflojamiento inmunológico”.

A bispecific antibody that targets IL-6 receptor and IL-17A for the potential therapy of patients with autoimmune and inflammatory diseases

Despite the success of current biological therapeutics for rheumatoid arthritis, these therapies, targeting individual cytokines or pathways, produce beneficial responses in only about half of patients. Therefore, better therapeutics are needed. IL-6 and IL-17A are proinflammatory cytokines in many autoimmune and inflammatory diseases, and several therapeutics have been developed to specifically inhibit them. However, targeting both of these cytokines with a bispecific therapeutic agent could account for their nonoverlapping proinflammatory functions and for the fact that IL-6 and IL-17A act in a positive feedback loop. Here, we present the development of MT-6194, a bispecific antibody targeting both IL-6R and IL-17A that was developed with the FynomAb technology. We also present data from mouse inflammatory disease experiments, indicating that simultaneous inhibition of both IL-6 and IL-17A yields enhanced efficacy compared with inhibition of each cytokine alone.

Ovariectomy-induced bone loss in TNFα and IL6 gene knockout mice is regulated by different mechanisms

We examined the effects of tumor necrosis factor-α (TNFα) and interleukin-6 (IL6) gene knockout in preserving the bone loss induced by ovariectomy (OVX) and the mechanisms involved in bone metabolism. Twenty female wild-type (WT), TNFα-knockout (TNFα^-/-) or IL6-knockout (IL6^-/-) mice aged 12 weeks were sham-operated (SHAM) or subjected to OVX and killed after 4 weeks. Bone mass and skeletal microarchitecture were determined using micro-CT. Bone marrow stromal cells (BMSCs) from all three groups (WT, TNFα^-/- and IL6^-/-) were induced to differentiate into osteoblasts or osteoclasts and treated with 17-β-estradiol. Bone metabolism was assessed by histological analysis, serum analyses and qRT-PCR. OVX successfully induced a high turnover in all mice, but a repair effect was observed in TNFα^-/- and IL6^-/- mice. The ratio of femoral trabecular bone volume to tissue volume, trabecular number and trabecular thickness were significantly decreased in WT mice subjected to OVX, but increased in TNFα^-/- mice (1.62, 1.34, 0.27-fold respectively; P < 0.01) and IL6^-/- mice (1.34, 0.80, 0.22-fold respectively; P < 0.01). Furthermore, we observed a 29.6% increase in the trabecular number in TNFα^-/- mice when compared to the IL6^-/- mice. Both, TNFα^-/- and IL6^-/- BMSCs exhibited decreased numbers of TRAP-positive cells and an increase in ALP-positive cells, with or without E2 treatment (P < 0.05). While the knockout of TNFα or IL6 significantly upregulated mRNA expressions of osteoblast-related genes (Runx2 and Col1a1) and downregulated osteoclast-related mRNA for TRAP, MMP9 and CTSK in vivo and in vitro, TNFα knockout appeared to have roles beyond IL6 knockout in upregulating Col1a1 mRNA expression and downregulating mRNA expressions of WNT-related genes (DKK1 and Sost) and TNF-related activation-induced genes (TRAF6). TNFα seemed to be more potentially invasive in inhibiting bone formation and enhancing TRAF6-mediated osteoclastogenesis than IL6, implying that the regulatory mechanisms of TNFα and IL6 in bone metabolism may be different.

Association of HSP22 with mTOR in osteoblasts: regulation of TNF-α-stimulated IL-6 synthesis

Heat shock protein 22 (HSP22) is ubiquitously expressed in various types of cells including in osteoblasts. We previously reported that tumor necrosis factor (TNF)-α stimulates interleukin (IL)-6 synthesis via p44/p42 MAPK in osteoblast-like MC3T3-E1 cells and that mTOR/p70 S6 kinase (p70 S6K) negatively regulates the IL-6 synthesis. In this study, we investigated the involvement of HSP22 in TNF-α-stimulated-IL-6 synthesis and the underlying mechanism in MC3T3-E1 cells. HSP22 knockdown reduces TNF-α-stimulated release of IL-6. In addition, HSP22 knockdown strengthens TNF-α-induced phosphorylation of p70 S6K but suppresses that of p44/p42 MAPK. HSP22 coimmunoprecipitates with mTOR. HSP22 knockdown increases the basal levels of phosphorylated mTOR. These results strongly suggest that HSP22 interacts with mTOR and regulates TNF-α-induced IL-6 synthesis in osteoblasts.

A preliminary investigation of short-term cytokine expression in gingival crevicular fluid secondary to high-level orthodontic forces and the associated root resorption: case series analytical study

BACKGROUND

Orthodontically induced iatrogenic root resorption (OIIRR) is an unavoidable inflammatory process. Several factors claimed to be related to the severity of OIIRR. Orthodontic forces cause micro-trauma to the periodontal ligament and activate a cascade of cellular events associated with local periodontal inflammation. The purpose of this split-mouth study were (1) to investigate the changes in cytokine profile in the gingival crevicular fluid (GCF) secondary to heavy orthodontic forces and (2) to compare the cytokine expression between participants showing high and low root resorption.

METHODS

Eight participants requiring maxillary first premolar extractions involved in this study. The teeth on the tested side (TS) received 225 g of controlled buccal tipping force for 28 days, while the contralateral teeth act as a control (CS). GCF was collected from both TS and CS teeth at 0 h (prior to application of force) and 3 h, 1 day, 3 days, 7 days and 28 days after the application of force, and analysed with multiplex bead immunoassay to determine the cytokine levels.

RESULTS

Statistically significant temporal increase was found in the TS teeth for tumour necrosis factor alpha (TNF-α) at 3 h and 28 days (p = 0.01). Interleukin 7 (IL-7) significantly peaked at the 28th day. Comparing cytokine profile for participants with high and low root resorption (>0.35 and <0.15 mm3, respectively), the levels of GM-CSF was significantly greater in low root resorption cases (p < 0.05). The amounts of root resorption which craters on mesial, distal surfaces and middle third region were significant in the TS teeth (p < 0.05).

CONCLUSIONS

IL-7 and TNF-α (pro-resorptive cytokine) increased significantly secondary to a high-level of orthodontic force application. Significantly high levels of granulocyte macrophage colony-stimulating factor (anti-resorptive cytokine) were detected in mild root resorption cases secondary to high-level orthodontic force application. A future long-term randomised clinical trial with larger sample taking in consideration gender, age and growth pattern distribution would be recommended.

Markers in blood and saliva for prediction of orthodontically induced inflammatory root resorption: a retrospective case controlled-study

BACKGROUND

Hormonal and enzymatic factors may render certain individuals more susceptible to orthodontically induced inflammatory root resorption (OIIRR). The objectives of this study are (1) to identify biochemical key markers in blood and saliva that may be correlated to the trend of extensive OIIRR and (2) to utilise these markers to predict a susceptible patient-receiving orthodontic treatment.

METHODS

Nine patients (mean age 23 + 2.9 years) who had moderate to severe OIIRR that assessed via orthopantomograms and met the inclusion criteria were classified as the root resorption group (RRG). Blood chemistry was evaluated using the collection of fasting blood and unstimulated saliva samples. Multiplex enzyme-linked immunosorbent assay (ELISA) arrays were used to screen blood and saliva samples for human cytokines, chemokines and several key enzymes that may play a role in root resorption following orthodontic force application. Biochemical findings from 16 matching subjects were used as the control (CG) for comparative measurements.

RESULTS

Patients with moderate to severe OIIRR showed a significant increase in salivary cytokines including interleukin (IL) 7, IL-10, IL-12p70 and interferon-gamma (IFN-γ) level as well as a significant decrease in IL-4 level. Osteocalcin and procollagen type I N-terminal peptide (P1NP) appeared to be the only blood factors that showed a significant difference, more in the CG than the RRG.

CONCLUSIONS

Saliva might be a more valuable way of measuring changes in cytokine expression than blood secondary to orthodontic treatment. Although the increased expression of pro-inflammatory and anti-inflammatory cytokines may be determinants in the development of moderate to severe OIIRR, cytokine expression may be affected by several potential inflammations in another part of the body. Future research could investigate the cause/effect relationship of different cytokines, in a larger group of patients and at different time intervals, using digital subtraction radiography techniques and microfluidic biosensors.

Epigenetic mechanisms of myeloid differentiation in the tumor microenvironment

Myeloid cells are extremely plastic as they respond and terminally differentiate into a plethora of functional types, in the blood or tissues, in response to a variety of growth factors, cytokines and pathogenic molecules. This plasticity is also manifested by the subversion of normal differentiation into the aberrant generation of a variety of tolerogenic myeloid cells in the tumoral microenvironment, where a variety of factors are released. Epigenetic mechanisms are in great part responsible for the plasticity of myeloid cells both under physiological and tumoral conditions. The development of compounds that inhibit epigenetic enzymes provides novel therapeutic opportunities to intercept the crosstalk between cancer cells and host myeloid cells. Here, we summarize our current knowledge on the myeloid cell types generated in the cancer environment, the factors and epigenetic enzymes participating in these processes and propose a number of potential targets for future pharmacological use.

Obesity is a concern for bone health with aging

Accumulating evidence supports a complex relationship between adiposity and osteoporosis in overweight/obese individuals, with local interactions and endocrine regulation by adipose tissue on bone metabolism and fracture risk in elderly populations. This review was conducted to summarize existing evidence to test the hypothesis that obesity is a risk factor for bone health in aging individuals. Mechanisms by which obesity adversely affects bone health are believed to be multiple, such as an alteration of bone-regulating hormones, inflammation, oxidative stress, the endocannabinoid system, that affect bone cell metabolism are discussed. In addition, evidence on the effect of fat mass and distribution on bone mass and quality is reviewed together with findings relating energy and fat intake with bone health. In summary, studies indicate that the positive effects of body weight on bone mineral density cannot counteract the detrimental effects of obesity on bone quality. However, the exact mechanism underlying bone deterioration in the obese is not clear yet and further research is required to elucidate the effect of adipose depots on bone and fracture risk in the obese population.

Activation status of γδ T cells dictates their effect on osteoclast generation and bone resorption

γδ T cells, a small subset of T cell population (5–10%), forms a bridge between innate and adaptive immunity. Although the role of γδ T cells in infectious diseases and antitumor immunity is well investigated, their role in bone biology needs to be explored. Aminobisphosphonates are used as a standard treatment modality for bone related disorders and are potent activators of γδ T cells. In the present study, we have compared the effect of “activated” and “freshly isolated” γδ T cells on osteoclast generation and function. We have shown that “activated” (αCD3/CD28 + rhIL2 or BrHPP + rhIL2 stimulated) γδ T cells inhibit osteoclastogenesis, while “freshly isolated” γδ T cells enhance osteoclast generation and function. Upon stimulation with phosphoantigen (BrHPP), “freshly isolated” γδ T cells were also able to suppress osteoclast generation and function. Cytokine profiles of these cells revealed that, “freshly isolated” γδ T cells secrete higher amounts of IL6 (pro-osteoclastogenic), while “activated” γδ T cells secrete high IFNγ levels (anti-osteoclastogenic). Neutralization of IFNγ and IL6 reversed the “inhibitory” or “stimulatory” effect of γδ T cells on osteoclastogenesis. In conclusion, we have shown that, activation status and dynamics of IL6 and IFNγ secretion dictate pro and anti-osteoclastogenic role of γδ T cells.

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Freshly isolated (unstimulated) γδ T cells enhance osteoclastogenesis.

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Activated γδ T cells inhibit osteoclast generation and function.

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Activated γδ T cells secrete high IFNγ, while freshly isolated secrete high IL6.

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Dynamics of IL6/IFNγ explains pro- and anti-osteoclastogenic effect of γδ T cells.

The Breast Cancer to Bone (B2B) Metastases Research Program: a multi-disciplinary investigation of bone metastases from breast cancer

Background

Bone is the most common site of breast cancer distant metastasis, affecting 50–70 % of patients who develop metastatic disease. Despite decades of informative research, the effective prevention, prediction and treatment of these lesions remains elusive. The Breast Cancer to Bone (B2B) Metastases Research Program consists of a prospective cohort of incident breast cancer patients and four sub-projects that are investigating priority areas in breast cancer bone metastases. These include the impact of lifestyle factors and inflammation on risk of bone metastases, the gene expression features of the primary tumour, the potential role for metabolomics in early detection of bone metastatic disease and the signalling pathways that drive the metastatic lesions in the bone.

Methods/Design

The B2B Research Program is enrolling a prospective cohort of 600 newly diagnosed, incident, stage I-IIIc breast cancer survivors in Alberta, Canada over a five year period. At baseline, pre-treatment/surgery blood samples are collected and detailed epidemiologic data is collected by in-person interview and self-administered questionnaires. Additional self-administered questionnaires and blood samples are completed at specified follow-up intervals (24, 48 and 72 months). Vital status is obtained prior to each follow-up through record linkages with the Alberta Cancer Registry. Recurrences are identified through medical chart abstractions. Each of the four projects applies specific methods and analyses to assess the impact of serum vitamin D and cytokine concentrations, tumour transcript and protein expression, serum metabolomic profiles and in vitro cell signalling on breast cancer bone metastases.

Discussion

The B2B Research Program will address key issues in breast cancer bone metastases including the association between lifestyle factors (particularly a comprehensive assessment of vitamin D status) inflammation and bone metastases, the significance or primary tumour gene expression in tissue tropism, the potential of metabolomic profiles for risk assessment and early detection and the signalling pathways controlling the metastatic tumour microenvironment. There is substantial synergy between the four projects and it is hoped that this integrated program of research will advance our understanding of key aspects of bone metastases from breast cancer to improve the prevention, prediction, detection, and treatment of these lesions.

Cytokine-mediated bone destruction in rheumatoid arthritis

Bone homeostasis, which involves formation and resorption, is an important process for maintaining adequate bone mass in humans. Rheumatoid arthritis (RA) is an autoimmune disease characterized by inflammation and bone loss, leading to joint destruction and deformity, and is a representative disease of disrupted bone homeostasis. The bone loss and joint destruction are mediated by immunological insults by proinflammatory cytokines and various immune cells. The connection between bone and immunity has been intensely studied and comprises the emerging field of osteoimmunology. Osteoimmunology is an interdisciplinary science investigating the interplay between the skeletal and the immune systems. The main contributors in osteoimmunology are the bone effector cells, such as osteoclasts or osteoblasts, and the immune cells, particularly lymphocytes and monocytes. Physiologically, osteoclasts originate from immune cells, and immune cells regulate osteoblasts and vice versa. Pathological conditions such as RA might affect these interactions, thereby altering bone homeostasis, resulting in the unfavorable outcome of bone destruction. In this review, we describe the osteoclastogenic roles of the proinflammatory cytokines and immune cells that are important in the pathophysiology of RA.

Pro-inflammatory cytokine release and cell growth inhibition in primary human oral cells after exposure to endodontic sealer

AIM

To assay the toxicity of the single-methacrylate-based sealer urethane dimethacrylate (UDMA) (EndoRez) in terms of cell growth and pro-inflammatory cytokines release, in expanded ex vivo human dental pulp stem cells (hDPSCs), human periodontal ligament stem cells (hPDLSCs), human gingival fibroblasts (hGFs) and human osteoblasts (hOSTs).

METHODOLOGY

Dental pulp and periodontal ligament stem cells, osteoblasts and fibroblasts were derived from five young donors. After in vitro isolation, hDPSCs, hPDLSCs, hGFs and hOSTs were seeded to resin-based sealers for 24, 48, 72 h up to 1 week. The morphological features and the cell growth and the release of pro-inflammatory interleukin (IL)6, IL8, IL12 and tumour necrosis factor (TNF) α were analysed. Differences in cell growth and in interleukin secretion were analysed for statistical significance with two-way anova tests for multiple comparisons.

RESULTS

Exposure to endodontic sealer based on UDMA resulted in a 50% decrease in survival oral cells at 24 h of incubation. No evident morphological changes were present in cell cultures examined. After 48 h, 72 h and 1-week culture time, a progressive cell growth was evident. A significant up-regulation of IL6, IL8, IL12 and TNFα cytokines in cells in contact with the dental sealer compared to the control was observed.

CONCLUSION

In vitro, EndoRez interacted with primary human hDPSCs, hPDLSCs, hGFs and hOSTs causing damage to biological system evidenced through cell growth inhibition and up-regulation of IL6, IL8, IL12 and TNFα proinflammatory mediators.

Titanium and zirconia particle-induced pro-inflammatory gene expression in cultured macrophages and osteolysis, inflammatory hyperalgesia and edema in vivo

AIMS

The biological reaction to wear debris is critical to the osteolysis underlying aseptic loosening of joint prosthetic implants. In an attempt to reduce aseptic loosening, ceramics have been introduced. This study was designed to evaluate, compare and correlate the expression of Toll-like receptors (TLRs), their intracellular adaptors and proinflammatory cytokines in cultured macrophages challenged with titanium or zirconia particles, as well as particle-induced osteolysis in calvaria and hyperalgesia and edema in hind paw.

MAIN METHODS

TLRs and their adaptors were evaluated at the mRNA level by RT-PCR, and cytokine expression was evaluated at the mRNA and protein levels. Osteolysis and hyperalgesia and edema were evaluated in vivo, in calvaria and hind paw, respectively.

KEY FINDINGS

Cultured macrophages challenged with zirconia or titanium particles expressed increased mRNA for TLRs 2, 3, 4 and 9, and their adaptors MyD88, TRIF and NF-κB and cytokines TNF-α, IL-1β and IL-6, which were also increased at protein level. Quantitative differences are evident and, in general, zirconia particle-induced pro-inflammatory gene expression was lower than that induced by titanium particles. In in vivo experiments, exposition to titanium or zirconia particles induced osteolysis in calvaria and hyperalgesia and edema in hind paw; however those induced by zirconia particles were significantly lower. There is a strong and positive correlation between the expressions of mRNA for TLR4, NF-κB, TNF-α, IL-1β and IL-6.

SIGNIFICANCE

Collectively, our data suggest that zirconia ceramic particles are less bioactive than titanium particles.

The role of IL-6 on apical periodontitis: a systematic review

The aim of this review was to examine current knowledge of the role of interleukin-6 (IL-6) in apical periodontitis (AP) pathogenesis as an inflammatory or pro-inflammatory cytokine. It also looked at whether IL-6 could serve as a measure for differential diagnosis or as a biomarker that can further predict the progression of bone resorption. A systematic review relating to AP and IL-6 was made via PubMed, BIOSIS, Cochrane, EMBASE and Web of Science databases using keywords and controlled vocabulary. Two independent reviewers first screened titles and abstracts and then the full texts. The reference lists of the identified publications were examined for additional titles. Eighteen papers were studied in total. In vitro studies (n = 6) revealed that IL-6 is present in AP, and its levels are proportional to the size of the periapical lesions. Neutrophils and macrophages resident in these lesions can produce IL-6 in vitro after a bacterial stimulus. Animal studies (n = 5) showed that IL-6 is present in AP and that osteoblasts can produce IL-6 in vivo. On the other hand, two studies using IL-6 knockout mice revealed larger periapical lesions when compared with control groups, demonstrating IL-6's role as an anti-inflammatory cytokine. In human studies (n = 7), IL-6 was identified in AP, and its levels were higher in symptomatic, epithelialized and large lesions than in asymptomatic and small lesions. These data lead to the conclusion that IL-6 may play a pro-inflammatory role, increasing its levels and reabsorbing bone in the presence of infections. When IL-6 is not present, other cytokines such as IL-1 and TNF-α induce bone resorption. Further studies about the relationship between AP development and the cytokine network must be performed to establish the exact role of each cytokine in the inflammatory process.

Interrelationship of circulating matrix metalloproteinase-9, TNF-α, and OPG/RANK/RANKL systems in COPD patients with osteoporosis

Previous studies have shown that matrix metalloproteinase-9 (MMP-9) and its cognate inhibitor TIMP-1, inflammatory cytokine TNF-α, and the OPG/RANK/RANKL system may each play individual roles in the pathogenesis of osteoporosis in patients with COPD. In the present study, we investigated the interrelationships of these factors in male COPD patients with and without osteoporosis. The serum levels of MMP-9, MMP-9/TIMP-1 ratio, TNF-α, RANKL, OPG, and the RANKL/OPG ratio were higher in COPD patients with osteoporosis than in individuals with normal or low bone mineral density (BMD) (N = 30, all P < 0.05 or < 0.01). The lung function FEV1%Pre and the BMD of the lumbar spine and femoral neck were found to be negatively correlated with MMP-9 serum level (r = -0.36, P < 0.05, r = -0.58, P < 0.001, and r = -0.62, P < 0.01, respectively), RANKL serum level (r = -0.21, P < 0.05, and r = -0.25, P < 0.05, and r = -0.26, P < 0.05, respectively), and RANKL/OPG ratio (r = -0.23, P < 0.05, r = -0.33, P < 0.05, and r = -0.38, P < 0.05, respectively). However, they had no correlation with TIMP-1, TNF-α, OPG, or RANK. The MMP-9 serum level was found to be positively correlated with TNF-α level (r = 0.35, P < 0.05) and RANKL/OPG ratio (r = 0.27, P < 0.05) but not associated with RANKL. These results suggest that MMP-9, TNF-α, and the OPG/RANK/RANKL system may be closely interrelated and may play interactive roles in pathogenesis of osteoporosis in COPD.

Effect of dietary legumes on bone-specific gene expression in ovariectomized rats

In previous studies, we found that the consumption of legumes decreased bone turnover in ovariectomized rats. The purpose of the present study is to determine whether the protective effects on bone mineral density (BMD) and the microarchitecture of a diet containing legumes are comparable. In addition, we aim to determine their protective actions in bones by studying bone specific gene expression. Forty-two Sprague-Dawley rats are being divided into six groups during the 12 week study: 1) rats that underwent sham operations (Sham), 2) ovariectomized rats fed an AIN-93M diet (OVX), 3) ovariectomized rats fed an AIN-93M diet with soybeans (OVX-S), 4) ovariectomized rats fed an AIN-93M diet with mung beans (OVX-M), 5) ovariectomized rats fed an AIN-93M diet with cowpeas (OVX-C), and 6) ovariectomized rats fed an AIN-93M diet with azuki beans (OVX-A). Consumption of legumes significantly increased BMD of the spine and femur and bone volume of the femur compared to the OVX. Serum calcium and phosphate ratio, osteocalcin, expression of osteoprotegerin (OPG), and the receptor activator of nuclear factor κB ligand (RANKL) ratio increased significantly, while urinary excretion of calcium and deoxypyridinoline and expression of TNF-α and IL-6 were significantly reduced in OVX rats fed legumes, compared to OVX rats that were not fed legumes. This study demonstrates that consumption of legumes has a beneficial effect on bone through modulation of OPG and RANKL expression in ovariectomized rats and that legume consumption can help compensate for an estrogen-deficiency by preventing bone loss induced by ovarian hormone deficiency.

[Principles of tribological analysis of endoprostheses]

For the tribological characterization of artificial joints, various experimental methods are currently available. However, the in vitro test conditions applied are only comparable in a limited way and transferability to the in vivo situation is also restricted. This is due to the different wear simulation concepts used and partly insufficient simulation of clinical worst case situations. In the present paper current scientific methods and procedures for tribological testing of artificial joints are presented. In addition, the biological effects of wear products are described enabling clinicians to challenge tribological studies and to facilitate specific interpretation of scientific results taking the clinical situation into account.

Osteoimmunology and the influence of pro-inflammatory cytokines on osteoclasts

Bone and immune system are functionally interconnected. Immune and bone cells derive from same progenitors in the bone marrow, they share a common microenvironment and are being influenced by similar mediators. The evidence on increased bone resorption associated with inappropriate activation of T cells such as during inflammation, is well established. However, the molecular mechanisms beyond this clinical observation have begun to be intensively studied with the advancement of osteoimmunology. Now days, we have firm evidence on the influence of numerous proinflammatory cytokines on bone cells, with the majority of data focused on osteoclasts, the bone resorbing cells. It has been shown that some proinflammatory cytokines could possess osteoclastogenic and/or anti-osteoclastogenic properties and can target osteoclasts directly or via receptor activator of nuclear factor κB (RANK)/RANK ligand(RANKL)/osteoprotegerin (OPG) system. Several studies have reported opposing data regarding (anti)osteoclastogenic properties of these cytokines.

Therefore, the first part of this review is summarizing current evidence on the influence of pro-inflammatory cytokines on osteoclasts and thus on bone resorption. In the second part, the evidence on the role of pro-inflammatory cytokines in osteoporosis and osteoarthritis is reviewed to show that unravelling the mechanisms beyond such complex bone diseases, is almost impossible without considering skeletal and immune systems as an indivisible integrated system.

Inhibition of titanium particle-induced inflammation by the proteasome inhibitor bortezomib in murine macrophage-like RAW 264.7 cells

Wear particle-induced inflammatory osteolysis is the major cause of aseptic loosening after total joint replacement. The predominant cell type within periprosthetic tissues is macrophages. We investigate the anti-inflammatory effects of the proteasome inhibitor bortezomib (Bzb) on murine macrophage-like RAW 264.7 cells stimulated with titanium (Ti) particles. RAW 264.7 cells were cultured with 1 nM Bzb and 0.1 mg/ml Ti particles for 48 h; cells without Ti and Bzb or without Bzb were used as negative and loading controls. Results showed that the expression of inflammatory cytokines (TNF-α, IL-1β, IL-6, and IL-10), chemokines [monocyte chemoattractant protein-1 (MCP-1), macrophage inflammatory protein-1 alpha (MIP-1α)], and inflammatory enzymes [inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2)] increased in RAW 264.7 cells cultured with Ti. Bzb treatment significantly reduced the expression of TNF-α, IL-1β, IL-6, MCP-1, MIP-1α, iNOS, and COX-2 and induced the expression of IL-10 in a time-dependent manner. These results suggest that Bzb inhibits Ti-induced inflammation in macrophages, and provide a promising therapeutic target for treating or preventing aseptic loosening.

Alterations in the Synthesis of IL-1β, TNF-α, IL-6, and Their Downstream Targets RANKL and OPG by Mouse Calvarial Osteoblasts In vitro: Inhibition of Bone Resorption by Cyclic Mechanical Strain

Mechanical strain is an important determinant of bone mass and architecture, and the aim of this investigation was to further understand the role of the cell-cell signaling molecules, IL-1β, TNF-α, and IL-6 in the mechanobiology of bone. Mouse calvarial osteoblasts in monolayer culture were subjected to a cyclic out-of-plane deformation of 0.69% for 6 s, every 90 s for 2-48 h, and the levels of each cytokine plus their downstream targets RANKL and OPG measured in culture supernatants by ELISAs. Mouse osteoblasts constitutively synthesized IL-1β, TNF-α, and IL-6, the production of which was significantly up-regulated in all three by cyclic mechanical strain. RANKL and OPG were also constitutively synthesized; mechanical deformation however, resulted in a down-regulation of RANKL and an up-regulation OPG synthesis. We next tested whether the immunoreactive RANKL and OPG were biologically active in an isolated osteoclast resorption pit assay - this showed that culture supernatants from mechanically deformed cells significantly inhibited osteoclast-mediated resorptive activity across the 48 h time-course. These findings are counterintuitive, because IL-1β, TNF-α, and IL-6 have well-established reputations as bone resorptive agents. Nevertheless, they are pleiotropic molecules with multiple biological activities, underlining the complexity of the biological response of osteoblasts to mechanical deformation, and the need to understand cell-cell signaling in terms of cytokine networks. It is also important to recognize that osteoblasts cultured in vitro are deprived of the mechanical stimuli to which they are exposed in vivo - in other words, the cells are in a physiological default state that in the intact skeleton leads to decreased bone strains below the critical threshold required to maintain normal bone structure.

Differences in proliferation, differentiation, and cytokine production by bone cells seeded on titanium-nitride and cobalt-chromium-molybdenum surfaces

Titanium-nitride coating is used to improve cobalt-chromium-molybdenum implant survival in total knee arthroplasty, but its effect on osteoconduction is unknown. Chromium and cobalt ions negatively affect the growth and metabolism of cultured osteoblasts while enhancing osteoclastogenic cytokine production. Therefore, it was hypothesized that a titanium-nitride surface would enhance osteoblast proliferation and/or differentiation and reduce osteoclastogenic cytokine production compared with a cobalt-chromium-molybdenum surface. MC3T3-E1 osteoblasts showed increased proliferation and decreased differentiation on titanium-nitride, while cytokine interleukin-6 production was higher on porous cobalt-chromium-molybdenum (p < 0.05), though interleukin-1β was occasionally detected on both surfaces. These findings suggest improved osteoconduction on titanium-nitride compared with cobalt-chromium-molybdenum surface.

An overview of the regulation of bone remodelling at the cellular level

OBJECTIVES

To review the current literature on the regulation of bone remodelling at the cellular level.

DESIGN AND METHODS

The cellular activities of the cells in the basic multicellular unit (BMU) were evaluated.

RESULTS

Bone remodelling requires an intimate cross-talk between osteoclasts and osteoblasts and is tightly coordinated by regulatory proteins that interact through complex autocrine/paracrine mechanisms. Osteocytes, bone lining cells, osteomacs, and vascular endothelial cells also regulate bone remodelling in the BMU via cell signalling networks of ligand-receptor complexes. In addition, through secreted and membrane-bound factors in the bone microenvironment, T and B lymphocytes mediate bone homeostasis in osteoimmunology.

CONCLUSIONS

Osteoporosis and other bone diseases occur because multicellular communication within the BMU is disrupted. Understanding the cellular and molecular basis of bone remodelling and the discovery of novel paracrine or coupling factors, such as RANKL, sclerostin, EGFL6 and semaphorin 4D, will lay the foundation for drug development against bone diseases.

Disturbance of the OPG/RANK/RANKL pathway and systemic inflammation in COPD patients with emphysema and osteoporosis

BACKGROUND

Osteoporosis is one of the systemic features of COPD. A correlation between the emphysema phenotype of COPD and reduced bone mineral density (BMD) is suggested by some studies, however, the mechanisms underlying this relationship are unclear. Experimental studies indicate that IL-1β, IL-6 and TNF-α may play important roles in the etiology of both osteoporosis and emphysema. The OPG/RANK/RANKL system is an important regulator of bone metabolism, and participates in the development of post-menopausal osteoporosis. Whether the OPG/RANK/RANKL pathway is involved in the pathogenesis of osteoporosis in COPD has not been studied.

METHODS

Eighty male patients (current or former smokers) completed a chest CT scan, pulmonary function test, dual x-ray absorptiometry measurements and questionnaires. Among these subjects, thirty patients with normal BMD and thirty patients with low BMD were selected randomly for measurement of IL-1β, IL-6, TNF-α (flow cytometry) and OPG/RANK/RANKL (ELISA). Twenty age-matched healthy volunteers were recruited as controls.

RESULTS

Among these eighty patients, thirty-six had normal BMD and forty-four had low BMD. Age, BMI and CAT score showed significant differences between these two COPD groups (p < 0.05). The low-attenuation area (LAA%) in the lungs of COPD patients was negatively correlated with lumbar vertebral BMD (r = 0.741; p < 0.0001). Forward logistic regression analysis showed that only LAA% (p = 0.005) and BMI (p = 0.009) were selected as explanatory variables. The level of IL-1β was significantly higher in the COPD patients as compared to the normal controls (p < 0.05), but the difference between the two COPD groups did not reach significance. The levels of IL-6 and TNF-α among the three groups were significantly different (p < 0.05). The level of RANKL and the RANKL/OPG ratio were significantly higher in COPD patients with low BMD compared to those with normal BMD and the normal controls (p < 0.05), and correlated negatively with lumbar vertebral BMD, but positively with LAA%.

CONCLUSIONS

Radiographic emphysema is correlated with low BMD in current and former smokers with COPD. IL-1β, IL-6, TNF-α, and the osteoporosis-related protein system OPG/RANK/RANKL may have some synergetic effects on emphysema and bone loss in COPD.

Impaired bone formation and osteopenia in heterozygous β(IVSII-654) knockin thalassemic mice

β-thalassemia caused by the C→T mutation at nucleotide 654 of the intron 2 (β(IVSII-654)) results in aberrant splicing of β-globin RNA, leading to an almost absence of β-globin synthesis. Although trabecular and cortical bone loss was previously reported in β-thalassemic mice with deletion of β-globin gene, the microscopic changes in trabecular structure in β(IVSII-654) thalassemic mice remained elusive. Here, we investigated the macroscopic and microscopic bone changes in 12-week-old β(IVSII-654) knockin thalassemic mice by dual-energy X-ray absorptiometry (DXA) and histomorphometric analysis, respectively. DXA revealed a decrease in bone mineral density in the lumbar vertebrae and tibial metaphysis, but not in the femoral diaphysis, suggesting that β(IVSII-654) thalassemia predominantly led to osteopenia at the trabecular site, but not the cortical site. Further histomorphometric analysis of the tibial secondary spongiosa showed that trabecular bone volume was significantly decreased with the expansion of marrow cavity. Decreases in osteoblast surface, osteoid surface, mineral apposition rate, mineralizing surface, and mineralized volume were also observed. Moreover, trabecular bone resorption was markedly enhanced as indicated by increases in the osteoclast surface and eroded surface. It could be concluded that β(IVSII-654) thalassemia impaired bone formation and enhanced bone resorption, thereby leading to osteopenia especially at the trabecular sites, such as the tibial metaphysis.

Osteoporosis in diabetes mellitus: Possible cellular and molecular mechanisms

Osteoporosis, a global age-related health problem in both male and female elderly, insidiously deteriorates the microstructure of bone, particularly at trabecular sites, such as vertebrae, ribs and hips, culminating in fragility fractures, pain and disability. Although osteoporosis is normally associated with senescence and estrogen deficiency, diabetes mellitus (DM), especially type 1 DM, also contributes to and/or aggravates bone loss in osteoporotic patients. This topic highlight article focuses on DM-induced osteoporosis and DM/osteoporosis comorbidity, covering alterations in bone metabolism as well as factors regulating bone growth under diabetic conditions including, insulin, insulin-like growth factor-1 and angiogenesis. Cellular and molecular mechanisms of DM-related bone loss are also discussed. This information provides a foundation for the better understanding of diabetic complications and for development of early screening and prevention of osteoporosis in diabetic patients.

Steady and oscillatory fluid flows produce a similar osteogenic phenotype

Mechanical loading induces positive changes in the skeleton due to direct effects on bone cells, which may include regulation of transcription factors that support osteoblast differentiation and function. Flow effects on osteoblast transcription factors have generally been evaluated after short exposures. In this work, we assayed flow effects on osteogenic genes at early and late time points in a preosteoblast (CIMC-4) cell line and evaluated both steady and oscillatory flows. Four hours of steady unidirectional flow decreased the level of RANKL mRNA 53 ± 7% below that of nonflowed cells, but increases in Runx2 and osterix mRNA (44 ± 22% and 129 ± 12%, respectively) were significant only after 12-19 h of continuous flow. Late flow effects on RANKL and osterix were also induced by an intermittent flow-rest protocol (four cycles of 1 h on/1 h off + overnight rest). Four hours of oscillatory flow decreased RANKL mRNA at this early time point (63 ± 2%) but did not alter either osterix or Runx2. When oscillatory flow was delivered using the intermittent flow-rest protocol, Runx2 and osterix mRNA increased significantly (85 ± 19% and 161 ± 22%, respectively). Both β-catenin and ERK1/2, known to be involved in RANKL regulation, were rapidly activated by steady flow. Inhibition of flow-activated ERK1/2 prevented the increase in osterix mRNA but not Runx2; Runx2 phosphorylation was increased by flow, an effect which likely contributes to osterix induction. This work shows that both steady and oscillatory fluid flows can support enhancement of an osteogenic phenotype.

Prolactin alters the mRNA expression of osteoblast-derived osteoclastogenic factors in osteoblast-like UMR106 cells

Prolactin (PRL) is known to participate in the lactation-induced maternal bone loss, presumably by inducing the release of receptor activator of nuclear factor-κB ligand (RANKL), a potent osteoclastogenic factor from osteoblasts. Since maternal bone resorption was too massive to be solely explained by RANKL and osteoclasts did not express PRL receptors (PRLR), the involvement of some other osteoblast-derived osteoclastogenic modulators was anticipated. Herein, the authors used quantitative real-time PCR to investigate the mRNA expressions of various osteoclastogenic factors in osteoblast-like UMR106 cells directly exposed to PRL for 48 h. These cells were found to express PRLR and respond to 300 ng/ml PRL by increasing RANKL mRNA expression. This PRL concentration (comparable to plasma PRL levels in lactation) also induced the upregulation of monocyte chemoattractant protein (MCP)-1, cyclooxygenase (Cox)-2, and ephrin-B1, whereas a higher concentration (500 ng/ml) was required to upregulate tumor necrosis factor (TNF)-α and interleukin (IL)-1. However, 100-500 ng/ml PRL affected neither the cell proliferation, the cell viability nor the mRNA expressions of macrophage colony-stimulating factor, IL-6, ephrin type-B receptor 4 and ephrin-B2. In conclusion, besides RANKL overexpression, PRL upregulated the expressions of other osteoclastogenic modulators, i.e., MCP-1, Cox-2, TNF-α, IL-1, and ephrin-B1, thus, further explaining how PRL induced bone loss in lactating mothers.

Dietary alpha lipoic acid supplementation prevents synovial inflammation and bone destruction in collagen-induced arthritic mice

Rheumatoid arthritis (RA) is a chronic inflammatory disorder characterized by chronic inflammation and joint destruction. In this study, we investigated whether dietary supplementation with alpha lipoic acid (ALA) suppresses collagen-induced arthritis (CIA) in mice. Mice were randomly divided into three groups: (1) a control CIA group was fed a normal diet, (2) a CIA group was fed a 0.1% ALA diet (average ALA intake of 160 mg/kg/day), and (3) a CIA group was fed a 0.5% ALA diet (average ALA intake of 800 mg/kg/day). The ALA-fed mice showed a decreased incidence and severity of arthritis compared to the normal diet group. Radiographic findings revealed a dramatic decrease in bone destruction, and histological findings showed extensively suppressed pathological changes in the ALA-fed mice. The ALA-fed mice exhibited inhibited generation of tartrate resistant acid phosphatase (TRAP)-positive osteoclasts in vivo. Additionally, ALA-fed mice reduced production of various proinflammatory cytokines and the soluble receptor activator of NF-κB ligand (sRANKL) in the joint tissues and the sera. In conclusion, dietary supplementation with ALA attenuated inflammatory responses and bone destruction in CIA mice.

Titanium induced production of chemokines CCL17/TARC and CCL22/MDC in human osteoclasts and osteoblasts

There is increasing evidence that titanium (Ti(IV)) ions are released from orthopedic implants and play a role in aseptic loosening. This study aimed to investigate whether titanium induces expression of chemokines and cytokines that are important in osteoclastogenesis in human osteoclasts and osteoblasts. Incubation of those cells with 1 muM Ti(IV) significantly upregulated expression of CCL17/TARC and CCL22/MDC, RANK-L, M-CSF and pro-inflammatory cytokines as determined by quantitative real-time PCR and ELISA assays. Additionally, flow cytometry was used to show Ti(IV) related increased expression of CCR4, the cognate receptor for CCL17 and CCL22 in challenged osteoclast precursors. These results strongly suggest that Ti(IV) ions play a role in the recruitment of osteoclast precursors to the bone-implant interface by increasing CCL17 and CCL22 expression and by upregulating their cognate receptor. Moreover the increased expression of RANK-L and M-CSF by osteoblasts together with increased levels of pro-inflammatory cytokines may enhance osteoclast differentiation and activity, and subsequently contribute to the pathomechanism of aseptic loosening.

Characterisation of the osteoclastogenic potential of human osteoblastic and fibroblastic conditioned media

Although M-CSF and RANKL are sufficient to promote in vitro osteoclastogenesis, in vivo this is a complex process which requires the action of many signalling molecules and cellular crosstalks. In this work, isolated or combined conditioned media, obtained from human adult skin fibroblast and bone marrow cells, were tested for their osteoclastogenic potential, through an indirect co-culture system, in the absence of recombinant M-CSF and RANKL. Osteoclastogenesis was assessed on human peripheral blood mononuclear cells (PBMC) and CD14+ cell cultures by quantification of total protein content, tartrate-resistant acid phosphatase (TRAP) activity, presence of multinucleated cells positive for TRAP, RT-PCR of TRAP, CATK, CA2, c-myc and c-src and presence of multinucleated cells displaying actin rings, vitronectin and calcitonin receptors. Cultures supplemented with M-CSF and RANKL were used as positive controls. It was observed that the conditioned medium from dexamethasone osteogenic-induced bone marrow cell cultures displayed the highest osteoclastogenic potential, with similar behaviour to that observed in the presence of both M-CSF and RANKL. Comparatively, fibroblastic conditioned medium elicited a slightly lower osteoclastogenic response. Combination of both conditioned media resulted in a significant increase of TRAP activity. On the other hand, conditioned medium from non-osteogenic-induced bone marrow cell cultures presented the lowest osteoclastogenic potential. These results were observed for both PBMC and CD14+ cell cultures, suggesting that fibroblast and osteoblast cells are able to modulate osteoclastogenesis in the absence of physical cell-cell interactions. In addition, osteoclastogenic potential of bone marrow cells increases with their osteoblastic differentiation.

Decrease in particle-induced osteolysis in ovariectomized mice

Postmenopausal osteoporosis is a common disorder that results from increased osteoclastic activity caused by estrogen deficiency. Whether postmenopausal bone remodeling can alter the response to particulate debris is unknown. The purpose of this study was to evaluate the bone response to polyethylene particles in an ovariectomized murine model. Polyethylene particles were implanted onto the calvaria of seven control mice and seven ovariectomized (OVX) mice, as compared with calvaria from sham-operated and OVX mice. Calvaria were harvested after 14 days. Skulls were analyzed with a high-resolution micro-CT and by histomorphometry after staining with Stevenel blue and picrofuschine, and for tartrate-specific alkaline phosphatase. As assessed by micro-CT, particle implantation induced a significant decrease in bone thickness in control mice, while bone thickness remained stable in OVX mice. In particle-implanted animals, the osteoclast number was 2.84 +/- 0.3 in control mice and 1.74 +/- 0.22 in OVX mice. Mean bone loss was -12% +/- 1.9% in control mice and -4.7% +/- 1.7% in OVX animals. The reduction of osteolytic response suggests that ovariectomy may have a protective role against particle-induced bone resorption.

Titanium IV ions induced human osteoclast differentiation and enhanced bone resorption in vitro

There is increasing evidence that titanium (Ti) ions are released from orthopedic implants, with concentrations in the range of 1 microM in tissue and blood, and may play a role in aseptic loosening of orthopedic implants. This study investigated whether Ti(IV) ions induce differentiation of monocytic osteoclast precursors into osteo-resorptive multinucleated cells and influence the activation and function of in vitro generated osteoclasts. Human monocytes and in vitro generated osteoclasts were exposed to 1 microM Ti(IV) ions for 10 days. Thereafter, osteoclast differentiation, activation, and function were evaluated. Transcription of specific osteoclastic genes was measured using quantitative reverse transcription polymerase chain reactions, which showed increased expression of tartrate-resistant acid phosphatase (TRAP) in approximately 20% of Ti(IV)-treated monocytes. Detection and quantification of intracellular TRAP activity using ELF97 as a fluorescent substrate revealed a significant increase of TRAP-positive cells in Ti(IV)-treated monocytes. Additionally, as demonstrated on dentin slide cultures, Ti(IV)-treated monocytes became functional bone resorbing cells, significantly increasing their osteo-resorptive activity to similar levels as osteoclasts in vitro. These results suggest that Ti(IV) ions released by biocorrosion from orthopedic implants induce differentiation of monocytes toward mature, functional osteoclasts, which may well contribute the pathomechanism of aseptic loosening.

Co-Cr-Mo alloy particles induce tumor necrosis factor alpha production in MLO-Y4 osteocytes: a role for osteocytes in particle-induced inflammation

Wear debris-induced osteolysis is purportedly the limiting problem affecting the long term results of joint arthroplasty. Pathogenic effects of wear debris in peri-implant cells such as macrophages, osteoblasts and osteoclasts have been well studied. In contrast, the effects of wear debris on osteocytes, which make up over 90% of all bone cells, remain unknown. We hypothesized that metal implant debris can induce the pro-inflammatory response in osteocytes. This study demonstrated the effects of cobalt-chromium-molybdenum alloy (Co-Cr-Mo) particles on a well-characterized MLO-Y4 osteocyte cell line. Co-Cr-Mo alloy particle treatment significantly (p<0.05) up-regulated tumor necrosis factor alpha (TNFalpha) gene expression after 3 and 6 h and TNFalpha protein production after 24 h, but down-regulated interleukin-6 (IL-6) gene expression after 6 h. Co-Cr-Mo alloy particle treatment also induced osteocyte apoptosis after 24 h. This apoptotic effect was partially (40%) dependent on TNFalpha. Therefore, our results suggest that osteocytes play a role in particle-induced inflammation and bone resorption following total joint arthroplasty by inducing pro-inflammatory cytokines and inducing osteocyte apoptosis.