Distinct Effects of IL-6 Classic and Trans-Signaling in Bone Fracture Healing

Effect of bovine hydroxyapatite composite with secretome under normoxia and hypoxia conditions on inflammatory parameters in massive bone defect of rabbit radius bone

Hydroxyapatite as a scaffold is capable of producing good bone regeneration formation. Incorporating secretome into scaffolds optimizes the bone healing process. The increase in proinflammatory, anti-inflammatory, and growth factors is one of the key factors in bone healing. In this study, we measured the levels of IL-6, IL-10, and FGF-2 to determine the effectiveness of bovine hydroxyapatite with secretome from normoxia and hypoxia on bone healing. This animal study employed a pure experimental research design, utilizing a post-test-only control group design. Bone marrow mesenchymal stem cells from rabbit thigh bones were used to derive secretomes under hypoxic and normoxic conditions. Bovine bone-derived hydroxyapatite (BHA) was treated with secretomes under both conditions. Rabbits' radius bones were implanted with BHA alone, BHA with normoxic secretome, and BHA with hypoxic secretome, then observed for 30 and 60 days. Levels of IL-6, IL-10, and FGF-2 were examined on days 30 and 60. On the 30th day, there was a significant increase in the levels of FGF-2, IL-6, and IL-10, with a dominance of strongly positive levels in BHA alone. However, on the 60th day, the levels of FGF-2, IL-6, and IL-10 started to decrease in all groups, with a dominance of moderately positive levels. Statistical tests showed significant results in all groups on days 30 and 60 (p < .05). Among the three groups, the best levels of growth factors and pro-inflammatory factors, and the lowest levels of anti-inflammatory factors were found in the BHA alone group on evaluation day 30.

Predictive value of serum inflammatory biomarkers in postmenopausal osteoporosis: A cross-sectional study in northwest Iran

The purpose of this study was to compare the inflammatory biomarkers in postmenopausal women with osteoporosis and those with normal bone mineral density (BMD). A total of 850 postmenopausal women aged 50 to 65 were randomly selected for participation in this cross-sectional investigation. 100 women displayed normal BMD, while 101 were diagnosed with osteoporosis, as determined by dual-energy X-ray absorptiometry. Biochemical techniques were used to quantify tumor necrosis factor α (TNF-α) levels, high-sensitivity C-reactive protein (hs-CRP), and interleukin-6. The area under the curve (AUC) for the diagnosis of osteoporosis was calculated using receiver-operator characteristic (ROC) curves. A significant difference was observed between the two groups in terms of age, menopause age, education level, and BMI (p < 0.005). Moreover, TNF-α (p = 0.026) and hs-CRP (p < 0.001) levels were significant differences between two groups. The logistic regression analysis adjusted for the confounders showed that only the elevation of hs-CRP had a significant effect on the risk of osteoporosis (OR (95 % CI):42.41 (12.66-142.3), p < 0.001). ROC analysis demonstrated that at the cut-off point of 0.415, the sensitivity and specificity values of 83.2 % and 82.2 % were obtained, respectively, for hs-CRP. hs-CRP is a valuable test for screening osteoporosis in postmenopausal women due to its accuracy and cost-effectiveness.

Comparing the Immune Response to PEEK as an Implant Material with and without P-15 Peptide as Bone Graft Material in a Rabbit Long Bone Model

P-15 is a 15-amino-acid-long biomimetic peptide widely demonstrated to enhance osteogenesis in vivo. Despite the prevalence of polyether-ether-ketone (PEEK) in interbody device manufacturing, a growing body of evidence suggests it may produce an unfavorable immune response. The purpose of this preliminary study was to characterize the immune response and new bone growth surrounding PEEK implants with and without a P-15 peptide-based osteobiologic. A bilateral femoral defect model was conducted using New Zealand white rabbits. A total of 17 test subjects received one implant in each distal femur, either with or without bone graft material. Animals were allowed to survive to 4 or 8 weeks, at which time the femurs were collected and subjected to micro-computer tomography (microCT) or cytokine analysis. MicroCT analysis included the quantification of bone growth and density surrounding each implant. The cytokine analysis of periprosthetic tissue homogenates included the quantification of interleukins (ILs) and TNF-α expression via ELISA kits. Improvements in bone volume were observed in the P-15 cohort for the regions of interest, 500-136 and 136-0 µm from the implant surface, at 8 weeks post-op. Concentrations of IL-1β, IL-4, and IL-6 cytokines were significantly higher in the P-15 cohort compared to the PEEK cohort at the 4-week timepoint. Significant reductions in the concentrations of IL-4 and IL-6 cytokines from the 4- to 8-week cohort were observed in the P-15 cohort only. The P-15 peptide has the potential to modulate the immune response to implanted materials. We observed improvements in bone growth and a more active micro-environment in the P-15 cohort relative to the PEEK control. This may indicate an earlier transition from the inflammatory to remodeling phase of healing.

Selective inhibition of interleukin 6 receptor decreased inflammatory cytokines and increased proteases in an experimental model of critical calvarial defect

Considering the lack of consensus related to the impact of selective IL-6 receptor inhibition on bone remodeling and the scarcity of reports, especially on large bone defects, this study proposed to evaluate the biological impact of the selective inhibitor of interleukin-6 receptor (tocilizumab) in an experimental model of critical calvarial defect in rats. In this preclinical and in vivo study, 24 male Wistar rats were randomly divided into two groups (n=12/group): defect treated with collagen sponge (CG) and defect treated with collagen sponge associated with 2 mg/kg tocilizumab (TCZ). The defect in the parietal bone was created using an 8-mm diameter trephine drill. After 90 days, the animals were euthanized, and tissue samples (skull caps) were evaluated through micro-CT, histological, immunohistochemistry, cytokines, and RT-qPCR analyses. Tocilizumab reduced mononuclear inflammatory infiltration (P<0.05) and tumor necrosis factor (TNF)-α levels (P<0.01) and down-regulated tissue gene expression of BMP-2 (P<0.001), RUNX-2 (P<0.05), and interleukin (IL)-6 (P<0.05). Moreover, it promoted a stronger immunostaining of cathepsin and RANKL (P<0.05). Micro-CT and histological analyses revealed no impact on general bone formation (P>0.05). The bone cells (osteoblasts, osteoclasts, and osteocytes) in the defect area were similar in both groups (P>0.05). Tocilizumab reduced inflammatory cytokines, decreased osteogenic protein, and increased proteases in a critical bone defect in rats. Ninety days after the local application of tocilizumab in the cranial defect, we did not find a significant formation of bone tissue compared with a collagen sponge.

The double-edged effects of IL-6 in liver regeneration, aging, inflammation, and diseases

Interleukin-6 (IL-6) is a pleiotropic cytokine and exerts its complex biological functions mainly through three different signal modes, called cis-, trans-, and cluster signaling. When IL-6 binds to its membrane or soluble receptors, the co-receptor gp130 is activated to initiate downstream signaling and induce the expression of target genes. In the liver, IL-6 can perform its anti-inflammatory activities to promote hepatocyte reprogramming and liver regeneration. On the contrary, IL-6 also exerts the pro-inflammatory functions to induce liver aging, fibrosis, steatosis, and carcinogenesis. However, understanding the roles and underlying mechanisms of IL-6 in liver physiological and pathological processes is still an ongoing process. So far, therapeutic agents against IL‑6, IL‑6 receptor (IL‑6R), IL-6-sIL-6R complex, or IL-6 downstream signal transducers have been developed, and determined to be effective in the intervention of inflammatory diseases and cancers. In this review, we summarized and highlighted the understanding of the double-edged effects of IL-6 in liver homeostasis, aging, inflammation, and chronic diseases, for better shifting the "negative" functions of IL-6 to the "beneficial" actions, and further discussed the potential therapeutic effects of targeting IL-6 signaling in the clinics.

Interleukin-6 classic and trans-signaling utilize glucose metabolism reprogramming to achieve anti- or pro-inflammatory effects

Interleukin (IL)-6 has anti- and pro-inflammatory functions, controlled by IL-6 classic and trans-signaling, respectively. Differences in the downstream signaling mechanism between IL-6 classic and trans-signaling have not been identified. Here, we report that IL-6 activates glycolysis to regulate the inflammatory response. IL-6 regulates glucose metabolism by forming a complex containing signal-transducing activators of transcription 3 (STAT3), hexokinase 2 (HK2), and voltage-dependent anion channel 1 (VDAC1). The IL-6 classic signaling directs glucose flux to oxidative phosphorylation (OxPhos), while IL-6 trans-signaling directs glucose flux to anaerobic glycolysis. Classic IL-6 signaling promotes STAT3 translocation into mitochondria to interact with pyruvate dehydrogenase kinase-1 (PDK1), leading to pyruvate dehydrogenase α (PDHA) dissociation from PDK1. As a result, PDHA is dephosphorylated, and STAT3 is phosphorylated at Ser727. By contrast, IL-6 trans-signaling promotes the interaction of sirtuin 2 (SIRT2) and lactate dehydrogenase A (LDHA), leading to the dissociation of STAT3 from SIRT2. As a result, LDHA is deacetylated, and STAT3 is acetylated and phosphorylated at Tyr705. IL-6 classic signaling promotes the differentiation of regulatory T cells via the PDK1/STAT3/PDHA axis, whereas IL-6 trans-signaling promotes the differentiation of Th17 cells via the SIRT2/STAT3/LDHA axis. Conclusion: IL-6 classic signaling generates anti-inflammatory functions by shifting energy metabolism to OxPhos, while IL-6 trans-signaling generates pro-inflammatory functions by shifting energy metabolism to anaerobic glycolysis.

Tracheal regeneration and mesenchymal stem cell augmenting potential of natural polyphenol-loaded gelatinmethacryloyl bioadhesive

Hydrogels incorporating natural biopolymer and adhesive substances have extensively been used to develop bioactive drugs and to design cells encapsulating sturdy structure for biomedical applications. However, the conjugation of the adhesive in most hydrogels is insufficient to maintain long-lasting biocompatibility inadequate to accelerate internal organ tissue repair in the essential native cellular microenvironment. The current work elaborates the synthesis of charged choline-catechol ionic liquid (BIL) adhesive and a hydrogel with an electronegative atom rich polyphenol (PU)-laden gelatinmethacryloyl (GelMA) to improve the structural bioactivities for in vivo tracheal repair by inducing swift crosslinking along with durable mechanical and tissue adhesive properties. It was observed that bioactive BIL and PU exhibited potent antioxidant (IC 50 % of 7.91 μg/mL and 24.55 μg/mL) and antibacterial activity against E. coli, P. aeruginosa and S. aureus. The novel integration of photocurable GelMA-BIL-PU revealed outstanding mechanical strength, biodegradability and sustained drug release. The in vitro study showed exceptional cell migration and proliferation in HBECs, while in vivo investigation of the GelMA-BIL-PU hydrogel on a rat's tracheal model revealed remarkable tracheal reconstruction, concurrently reducing tissue inflammation. Furthermore, the optimized GelMA-BIL-PU injectable adhesive bioink blend demonstrated superior MSCs migration and proliferation, which could be a strong candidate for developing stem cell-rich biomaterials to address multiple organ defects.

Trained innate immunity modulates osteoblast and osteoclast differentiation

Macrophages are key regulators in bone repair and regeneration. Recent studies have shown that long-term epigenetic changes and metabolic shifts occur during specific immune training of macrophages that affect their functional state, resulting in heightened (trained) or reduced (tolerant) responses upon exposure to a second stimulus. This is known as innate immune memory. Here, we study the impact of macrophages' memory trait on osteoblast differentiation of human mesenchymal stromal cells (hMSCs) and osteoclast differentiation. An in vitro trained immunity protocol of monocyte-derived macrophages was employed using inactivated Candida albicans and Bacillus Calmette-Guérin (BCG) to induce a 'trained' state and Pam3CSK4 (PAM) and Lipopolysaccharides (LPS) to induce a 'tolerance' state. Macrophages were subsequently cocultured with hMSCs undergoing osteogenic differentiation during either resting (unstimulated) or inflammatory conditions (restimulated with LPS). Alkaline phosphatase activity, mineralization, and cytokine levels (TNF, IL-6, oncostatin M and SDF-1α) were measured. In addition, macrophages underwent osteoclast differentiation. Our findings show that trained and tolerized macrophages induced opposing results. Under resting conditions, BCG-trained macrophages enhanced ALP levels (threefold), while under inflammatory conditions this was found in the LPS-tolerized macrophages (fourfold). Coculture of hMSCs with trained macrophages showed mineralization while tolerized macrophages inhibited the process under both resting and inflammatory conditions. While osteoclast differentiation was not affected in trained-macrophages, this ability was significantly loss in tolerized ones. This study further confirms the intricate cross talk between immune cells and bone cells, highlighting the need to consider this interaction in the development of personalized approaches for bone regenerative medicine.

The impact of age and sex on the inflammatory response during bone fracture healing

Inflammation is thought to be dysregulated with age leading to impaired bone fracture healing. However, broad analyses of inflammatory processes during homeostatic bone aging and during repair are lacking. Here, we assessed changes in inflammatory cell and cytokine profiles in circulation and in bone tissue to identify age- and sex-dependent differences during homeostasis and repair. During homeostatic aging, male mice demonstrated accumulation of CD4+ helper T cells and CD8+ cytotoxic T cells within bone while both pro-inflammatory "M1" and anti-inflammatory "M2" macrophage numbers decreased. Female mice saw no age-associated changes in immune-cell population in homeostatic bone. Concentrations of IL-1β, IL-9, IFNγ, and CCL3/MIP-1α increased with age in both male and female mice, whereas concentrations of IL-2, TNFα, TNFR1, IL-4, and IL-10 increased only in female mice - thus we termed these "age-accumulated" cytokines. There were no notable changes in immune cell populations nor cytokines within circulation during aging. Sex-dependent analysis demonstrated slight changes in immune cell and cytokine levels within bone and circulation, which were lost upon fracture injury. Fracture in young male mice caused a sharp decrease in number of M1 macrophages; however, this was not seen in aged male mice nor in female mice of any age. Injury itself induced a decrease in the number of CD8+ T cells within the local tissue of aged male and of female mice but not of young mice. Cytokine analysis of fractured mice revealed that age-accumulated cytokines quickly dissipated after fracture injury, and did not re-accumulate in newly regenerated tissue. Conversely, CXCL1/KC-GRO, CXCL2/MIP-2, IL-6, and CCL2/MCP-1 acted as "fracture response" cytokines: increasing sharply after fracture, eventually returning to baseline. Collectively, we classify measured cytokines into three groups: (1) age-accumulated cytokines, (2) female-specific age-accumulated cytokines, and (3) fracture response cytokines. These inflammatory molecules represent potential points of intervention to improve fracture healing outcome.

Impact of PEG sensitization on the efficacy of PEG hydrogel-mediated tissue engineering

While poly(ethylene glycol) (PEG) hydrogels are generally regarded as biologically inert blank slates, concerns over PEG immunogenicity are growing, and the implications for tissue engineering are unknown. Here, we investigate these implications by immunizing mice against PEG to stimulate anti-PEG antibody production and evaluating bone defect regeneration after treatment with bone morphogenetic protein-2-loaded PEG hydrogels. Quantitative analysis reveals that PEG sensitization increases bone formation compared to naive controls, whereas histological analysis shows that PEG sensitization induces an abnormally porous bone morphology at the defect site, particularly in males. Furthermore, immune cell recruitment is higher in PEG-sensitized mice administered the PEG-based treatment than their naive counterparts. Interestingly, naive controls that were administered a PEG-based treatment also develop anti-PEG antibodies. Sex differences in bone formation and immune cell recruitment are also apparent. Overall, these findings indicate that anti-PEG immune responses can impact tissue engineering efficacy and highlight the need for further investigation.

Is there a role for N1-N2 neutrophil phenotypes in bone regeneration? A systematic review

PURPOSE

This review aims to provide an overview of the multiple functions of neutrophils, with the recognition of the inflammatory (N1) and regenerative (N2) phenotypes, in relation to fracture healing.

METHODS

A literature search was performed using the PubMed database. The quality of the articles was evaluated using critical appraisal checklists.

RESULTS

Thirty one studies were included in this review. These studies consistently support that neutrophils exert both beneficial and detrimental effects on bone regeneration, influenced by Tumor Necrosis Factor-α (TNF-α), Interleukin 8 (IL-8), mast cells, and macrophages. The N2 phenotype has recently emerged as one promoter of bone healing. The N1 phenotype has progressively been connected with inflammatory neutrophils during fracture healing.

CONCLUSIONS

This review has pinpointed various aspects and mechanisms of neutrophil influence on bone healing. The recognition of N1 and N2 neutrophil phenotypes potentially shed new light on the dynamic shifts taking place within the Fracture Hematoma (FH).

Market Needs and Methodologies Associated with Patient Lipidomic Diagnoses and Analyses

This chapter conducts an in-depth exploration of the impact of musculoskeletal (MSK) disorders and injuries, with a specific emphasis on their consequences within the older population demographic. It underscores the escalating demand for innovative interventions in MSK tissue engineering. The chapter also highlights the fundamental role played by lipid signaling mediators (LSMs) in tissue regeneration, with relevance to bone and muscle recovery. Remarkably, Prostaglandin E2 (PGE2) emerges as a central orchestrator in these regenerative processes. Furthermore, the chapter investigates the complex interplay between bone and muscle tissues, explaining the important influence exerted by LSMs on their growth and differentiation. The targeted modulation of LSM pathways holds substantial promise as a beneficial way for addressing muscle disorders. In addition to these conceptual understandings, the chapter provides a comprehensive overview of methodologies employed in the identification of LSMs, with a specific focus on the Liquid Chromatography-Mass Spectrometry (LC-MS). Furthermore, it introduces a detailed LC MS/MS-based protocol tailored for the detection of PGE2, serving as an invaluable resource for researchers immersed in this dynamic field of study.

Muscle-bone crosstalk via endocrine signals and potential targets for osteosarcopenia-related fracture

Background

Osteosarcopenia is a syndrome coexisting sarcopenia and osteopenia/osteoporosis, with a high fracture risk. Recently, skeletal muscle and bone have been recognized as endocrine organs capable of communication through secreting myokines and osteokines, respectively. With a deeper understanding of the muscle-bone crosstalk, these endocrine signals exhibit an important role in osteosarcopenia development and fracture healing.

Methods

This review summarizes the role of myokines and osteokines in the development and treatment of osteosarcopenia and fracture, and discusses their potential for osteosarcopenia-related fracture treatment.

Results

Several well-defined myokines (myostatin and irisin) and osteokines (RANKL and SOST) are found to not only regulate skeletal muscle and bone metabolism but also influence fracture healing processes. Systemic interventions targeting these biochemical signals has shown promising results in improving the mass and functions of skeletal muscle and bone, as well as accelerating fracture healing processes.

Conclusion

The regulation of muscle-bone crosstalk via biochemical signals presents a novel and promising strategy for treating osteosarcopenia and fracture by simultaneously enhancing bone and muscle anabolism. We propose that myostatin, irisin, RANKL, and SOST may serve as potential targets to treat fracture patients with osteosarcopenia.

The translational potential of this article

Osteosarcopenia is an emerging geriatric syndrome where sarcopenia and osteoporosis coexist, with high fracture risk, delayed fracture healing, and increased mortality. However, no pharmacological agent is available to treat fracture patients with osteosarcopenia. This review summarizes the role of several myokines and osteokines in the development and treatment of osteosacropenia and fracture, as well as discusses their potential as intervention targets for osteosarcopenia-related fracture, which provides a novel and promising strategy for future osteosarcopenia-related fracture treatment.

Bispecific soluble cytokine receptor-nanobody fusions inhibit Interleukin (IL-)6 trans-signaling and IL-12/23 or tumor necrosis factor (TNF) signaling

At least 0.5% of people in the Western world develop inflammatory bowel disease (IBD). While antibodies that block tumor necrosis factor (TNF) α and Interleukin (IL-)23 have been approved for the treatment of IBD, IL-6 antibodies failed in the phase II clinical trial due to non-tolerable side effects. However, two clinical phase II studies suggest that inhibiting IL-6/soluble IL-6R (sIL-6R)-induced trans-signaling via the cytokine receptor gp130 benefit IBD patients with fewer adverse events. Here we develop inhibitors targeting a combination of IL-6/sIL-6R and TNF or IL-12/IL-23 signaling, named cs130-TNFVHHFc and cs130-IL-12/23VHHFc. Surface plasmon resonance experiments showed that recombinant cs130-TNFVHHFc and cs130-IL-12/23VHHFc bind with high affinity to IL-6/sIL-6R complexes and human TNFα (hTNFα) or IL-12/IL-23, respectively. Immunoprecipitation experiments have verified the higher ordered complex formation of the inhibitors with IL-6/sIL-6R and IL-12. We demonstrated that cs130-TNFVHHFc and cs130-IL-12/23VHHFc block IL-6/sIL-6R trans-signaling-induced proliferation and STAT3 phosphorylation of Ba/F3-gp130 cells, as well as hTNFα- or IL-23-induced signaling, respectively. In conclusion, cs130-TNFVHHFc and cs130-IL-12/23VHHFc represent a class of dimeric and bispecific chimeric cytokine inhibitors that consist of a soluble cytokine receptor fused to anti-cytokine nanobodies.

Integration analysis using bioinformatics and experimental validation on the clinical and biological significance of TSLP in cancers

Thymic stromal lymphopoietin (TSLP) has significantly impacted the development and progression of various neoplastic disorders. To comprehensively evaluate the diverse significance of TSLP in malignant tumors, we first integrative analyze the TSLP expression level in paired and unpaired pan-cancer tissue and cell line, compared against the normal tissue. The correlation between TSLP expression, molecular subtypes, immune subtypes, diagnostic value, and prognostic value in pan-cancer was also investigated. We then explored the impact of TSLP expression on multifaced immune cell infiltration and subsequent clinical outcomes in lung adenocarcinoma (LUAD) patients. and conducted cellular experiments to functionally examine the effect of TSLP on cell proliferation, apoptosis, cell cycle, migration, and invasion in LUAD. The anti-neoplastic mechanism of TSLP was further investigated by qRT-PCR and western blotting. Our findings reveal that TSLP expression is abnormally low in various cancers compared to normal tissue and is associated with different molecular and immune subtypes of cancers. Moreover, ROC and survival analysis results suggest that TSLP expression is correlated with the diagnostic, prognostic, clinical features, and immune cells of LUAD patients. Cell experiments showed that overexpression of TSLP elicited a significant reduction in LUAD cell viability, promoted cell apoptosis, impeded cell cycle progression in the G2/M phase, and inhibited cell migration and invasion. In addition, TSLP inhibited LUAD progression through the JAK1/STAT3 signaling pathway. Therefore, targeting TSLP shows potential as a therapeutic strategy for pan-cancer, particularly for LUAD, and as a biomarker for predicting the prognosis of this malignancy.

Targeting IL-6 trans-signalling: past, present and future prospects

Interleukin-6 (IL-6) is a key immunomodulatory cytokine that affects the pathogenesis of diverse diseases, including autoimmune diseases, chronic inflammatory conditions and cancer. Classical IL-6 signalling involves the binding of IL-6 to the membrane-bound IL-6 receptor α-subunit (hereafter termed 'mIL-6R') and glycoprotein 130 (gp130) signal-transducing subunit. By contrast, in IL-6 trans-signalling, complexes of IL-6 and the soluble form of IL-6 receptor (sIL-6R) signal via membrane-bound gp130. A third mode of IL-6 signalling - known as cluster signalling - involves preformed complexes of membrane-bound IL-6-mIL-6R on one cell activating gp130 subunits on target cells. Antibodies and small molecules have been developed that block all three forms of IL-6 signalling, but in the past decade, IL-6 trans-signalling has emerged as the predominant pathway by which IL-6 promotes disease pathogenesis. The first selective inhibitor of IL-6 trans-signalling, sgp130, has shown therapeutic potential in various preclinical models of disease and olamkicept, a sgp130Fc variant, had promising results in phase II clinical studies for inflammatory bowel disease. Technological developments have already led to next-generation sgp130 variants with increased affinity and selectivity towards IL-6 trans-signalling, along with indirect strategies to block IL-6 trans-signalling. Here, we summarize our current understanding of the biological outcomes of IL-6-mediated signalling and the potential for targeting this pathway in the clinic.

Synthetic Calcium-Phosphate Materials for Bone Grafting

Synthetic bone grafting materials play a significant role in various medical applications involving bone regeneration and repair. Their ability to mimic the properties of natural bone and promote the healing process has contributed to their growing relevance. While calcium-phosphates and their composites with various polymers and biopolymers are widely used in clinical and experimental research, the diverse range of available polymer-based materials poses challenges in selecting the most suitable grafts for successful bone repair. This review aims to address the fundamental issues of bone biology and regeneration while providing a clear perspective on the principles guiding the development of synthetic materials. In this study, we delve into the basic principles underlying the creation of synthetic bone composites and explore the mechanisms of formation for biologically important complexes and structures associated with the various constituent parts of these materials. Additionally, we offer comprehensive information on the application of biologically active substances to enhance the properties and bioactivity of synthetic bone grafting materials. By presenting these insights, our review enables a deeper understanding of the regeneration processes facilitated by the application of synthetic bone composites.

Effect of Expansion Media on Functional Characteristics of Bone Marrow-Derived Mesenchymal Stromal Cells

The therapeutic efficacy of mesenchymal stromal cells (MSCs) has been shown to rely on their immunomodulatory and regenerative properties. In order to obtain sufficient numbers of cells for clinical applications, MSCs have to be expanded ex vivo. Expansion media with xenogeneic-free (XF) growth-promoting supplements like human platelet lysate (PL) or serum- and xenogeneic-free (SF/XF) formulations have been established as safe and efficient, and both groups provide different beneficial qualities. In this study, MSCs were expanded in XF or SF/XF media as well as in mixtures thereof. MSCs cultured in these media were analyzed for phenotypic and functional properties. MSC expansion was optimal with SF/XF conditions when PL was present. Metabolic patterns, consumption of growth factors, and secretome of MSCs differed depending on the type and concentration of supplement. The lactate per glucose yield increased along with a higher proportion of PL. Many factors in the supernatant of cultured MSCs showed distinct patterns depending on the supplement (e.g., FGF-2, TGFβ, and insulin only in PL-expanded MSC, and leptin, sCD40L PDGF-AA only in SF/XF-expanded MSC). This also resulted in changes in cell characteristics like migratory potential. These findings support current approaches where growth media may be utilized for priming MSCs for specific therapeutic applications.

Interleukin 6 promotes BMP9-induced osteoblastic differentiation through Stat3/mTORC1 in mouse embryonic fibroblasts

Interleukin 6 (IL-6) plays a dual role in regulating bone metabolism, although the concrete mechanism is unclear. Bone morphogenetic protein 9 (BMP9) is one of the most potent osteogenic inducers, and a promising alternative for bone tissue engineering. The relationship between IL-6 and BMP9 in osteogenic differentiation remains to be elucidated, and the osteoblastic potential of BMP9 needs to be enhanced to overcome certain shortcomings of BMP9. In this study, we used real-time PCR, western blot, immunofluorescent stain, fetal limb culture and cranial defects repair model to explore the IL-6 role in BMP9-induced osteogenic differentiation in mouse embryonic fibroblasts (MEFs). We found that the rat serum level of IL-6 was increased in the dexamethasone-induced osteoporosis model, and IL-6 expression was detectable in several progenitor cells and MEFs. BMP9 upregulated IL-6 in MEFs, and the BMP9-induced osteoblastic markers were elevated by IL-6, but reduced by IL-6 knockdown. BMP9 and/or IL-6 both activated mTOR, and the IL-6 effect on BMP9-induced osteoblastic markers and bone formation were reduced greatly by mTOR inhibition. Raptor was up-regulated by IL-6 and/or BMP9 specifically, and the osteoblastic markers induced by IL-6 and/or BMP9 were reduced by Raptor knockdown. Meanwhile, Stat-3 was activated by IL-6 and/or BMP9, and the increase of Raptor or osteoblastic markers by IL-6 and/or BMP9 were reduced by Stat-3 inhibition. The Raptor promoter activity was regulated by p-Stat-3. Our finding suggested that IL-6 can promote the BMP9 osteoblastic potential, which may be mediated through activating Stat-3/mTORC1 pathway.

IL-1Ra gene transfer potentiates BMP2-mediated bone healing by redirecting osteogenesis toward endochondral ossification

An estimated 100,000 patients each year in the United States suffer severe disability from bone defects that fail to heal, a condition where bone-regenerative therapies could provide substantial clinical benefits. Although recombinant human bone morphogenetic protein-2 (rhBMP2) is an osteogenic growth factor that is clinically approved for this purpose, it is only effective when used at exceedingly high doses that incur substantial costs, induce severe inflammation, produce adverse side effects, and form morphologically abnormal bone. Using a validated rat femoral segmental defect model, we show that bone formed in response to clinically relevant doses of rhBMP2 is accompanied by elevated expression of interleukin-1 (IL-1). Local delivery of cDNA encoding the IL-1 receptor antagonist (IL-1Ra) achieved bridging of segmental, critical size defects in bone with a 90% lower dose of rhBMP2. Unlike use of high-dose rhBMP2, bone formation in the presence of IL-1Ra occurred via the native process of endochondral ossification, resulting in improved quality without sacrificing the mechanical properties of the regenerated bone. Our results demonstrate that local immunomodulation may permit effective use of growth factors at lower doses to recapitulate more precisely the native biology of healing, leading to higher-quality tissue regeneration.

Longitudinal Profiling of Plasma Cytokines and Its Association With Postoperative Delirium in Elderly Patients Undergoing Major Lower Limb Surgery: A Prospective Observational Study

BACKGROUND

Surgery is accompanied by a systemic inflammatory response that may presage delirium in susceptible individuals. Little is known about the trajectory of plasma proinflammatory cytokines and their potential associations with postoperative delirium (POD). The current study longitudinally assessed both pro and anti-inflammatory plasma cytokine response and development of POD in older surgical patients to investigate associations with individual and/or clusters of cytokines that may indicate pathogenic mechanisms.

METHODS

A prospective longitudinal study sought to enroll patients >60 years old who were scheduled for major lower limb surgery under general anesthesia. Blood was obtained preoperatively and postoperatively from day 1 through postoperative day 4 for measurement of plasma interleukin-1β (IL-1β), IL-2, IL-4, IL-6, soluble IL-6 receptor (sIL-6R), IL-10, and tumor necrosis factor-α (TNF-α). Participants were assessed for POD twice daily for 4 days using the confusion assessment method. Trajectory of postoperative changes in plasma cytokines was determined by a group-based trajectory modeling analysis that was informed by distinct cytokines identified by time-dependent Cox regression model.

RESULTS

One hundred eighty-eight patients were assessed for eligibility of whom 129 underwent major surgery and 126 had complete datasets for final analysis. POD was diagnosed in 31 of 126 patients (24.6%). Time-dependent Cox regression model identified that higher IL-6 and sIL-6R levels were associated with higher risk of developing POD. A two-cluster model (stable lower and fluctuating higher levels) was considered to be the most statistically appropriate model for IL-6 and sIL-6R trajectory. More participants with fluctuating higher IL-6 were delirious (73.3% vs 18.0%, P = .001) as were those with fluctuating higher sIL-6R (81.3% vs 16.4%, P = .001).

CONCLUSIONS

As higher IL-6 and sIL-6R levels were significantly associated with higher risk of POD and the combination is required for IL-6 trans-signaling, it is possible that activation of this pathway may be associated with POD. Furthermore, it will be important to determine whether high levels of the combination of IL-6 and sIL-6R can be an early biomarker for the subsequent development of POD.

Dissecting Interleukin-6 Classic and Trans-signaling in Inflammation and Cancer

Interleukin-6 (IL-6) is a cytokine synthesized by many cells in the human body. IL-6 binds to a membrane-bound receptor (IL-6R), which is only present on hepatocytes, some epithelial cells, and some leukocytes. The complex of IL-6 and IL-6R binds to the ubiquitously expressed receptor subunit gp130, which forms a homodimer and thereby initiates intracellular signaling, e.g., the JAK/STAT and MAPK pathways. Proteases can cleave the membrane-bound IL-6R from the cell surface and generate a soluble IL-6R (sIL-6R), which retains its ability to bind IL-6. The IL-6/sIL-6R complex associates with gp130 and induces signaling even on cells which do not express the IL-6R. This paradigm has been called IL-6 trans-signaling, whereas signaling via the membrane-bound IL-6R is referred to as classic signaling. We have generated several molecular tools to differentiate between both pathways and to analyze the consequences of cellular IL-6 signaling in vivo. One of these tools is soluble gp130Fc, which selectively inhibits IL-6 trans-signaling. This protein under the WHO name Olamkicept has successfully undergone phase II clinical trials in patients with autoimmune diseases. Here, in this chapter, we describe several molecular tools to differentiate between IL-6 classic and trans-signaling and to analyze the consequences of cellular IL-6 signaling in vivo.

Fracture Healing in the Setting of Endocrine Diseases, Aging, and Cellular Senescence

More than 2.1 million age-related fractures occur in the United States annually, resulting in an immense socioeconomic burden. Importantly, the age-related deterioration of bone structure is associated with impaired bone healing. Fracture healing is a dynamic process which can be divided into four stages. While the initial hematoma generates an inflammatory environment in which mesenchymal stem cells and macrophages orchestrate the framework for repair, angiogenesis and cartilage formation mark the second healing period. In the central region, endochondral ossification favors soft callus development while next to the fractured bony ends, intramembranous ossification directly forms woven bone. The third stage is characterized by removal and calcification of the endochondral cartilage. Finally, the chronic remodeling phase concludes the healing process. Impaired fracture healing due to aging is related to detrimental changes at the cellular level. Macrophages, osteocytes, and chondrocytes express markers of senescence, leading to reduced self-renewal and proliferative capacity. A prolonged phase of "inflammaging" results in an extended remodeling phase, characterized by a senescent microenvironment and deteriorating healing capacity. Although there is evidence that in the setting of injury, at least in some tissues, senescent cells may play a beneficial role in facilitating tissue repair, recent data demonstrate that clearing senescent cells enhances fracture repair. In this review, we summarize the physiological as well as pathological processes during fracture healing in endocrine disease and aging in order to establish a broad understanding of the biomechanical as well as molecular mechanisms involved in bone repair.

The Effect of Anti-rheumatic Drugs on the Skeleton

The therapeutic armamentarium for rheumatoid arthritis has increased substantially over the last 20 years. Historically antirheumatic treatment was started late in the disease course and frequently included prolonged high-dose glucocorticoid treatment which was associated with accelerated generalised bone loss and increased vertebral and non-vertebral fracture risk. Newer biologic and targeted synthetic treatments and a combination of conventional synthetic DMARDs prevent accelerated systemic bone loss and may even allow repair of cortical bone erosions. Emerging data also gives new insight on the impact of long-term conventional synthetic DMARDs on bone health and fracture risk and highlights the need for ongoing studies for better understanding of "established therapeutics". An interesting new antirheumatic treatment effect is the potential of erosion repair with the use of biologic DMARDs and janus kinase inhibitors. Although several newer anti-rheumatic drugs seem to have favorable effects on bone mineral density in RA patients, these effects are modest and do not seem to influence the fracture risk thus far. We summarize recent developments and findings of the impact of anti-rheumatic treatments on localized and systemic bone integrity and health.

Local immune cell contributions to fracture healing in aged individuals - A novel role for interleukin 22

With increasing age, the risk of bone fractures increases while regenerative capacity decreases. This variation in healing potential appears to be linked to adaptive immunity, but the underlying mechanism is still unknown. This study sheds light on immunoaging/inflammaging, which impacts regenerative processes in aging individuals. In an aged preclinical model system, different levels of immunoaging were analyzed to identify key factors that connect immunoaged/inflammaged conditions with bone formation after long bone fracture. Immunological facets, progenitor cells, the microbiome, and confounders were monitored locally at the injury site and systemically in relation to healing outcomes in 12-month-old mice with distinct individual levels of immunoaging. Bone tissue formation during healing was delayed in the immunoaged group and could be associated with significant changes in cytokine levels. A prolonged and amplified pro-inflammatory reaction was caused by upregulated immune cell activation markers, increased chemokine receptor availability and a lack of inhibitory signaling. In immunoaged mice, interleukin-22 was identified as a core cell signaling protein that played a central role in delayed healing. Therapeutic neutralization of IL-22 reversed this specific immunoaging-related disturbed healing. Immunoaging was found to be an influencing factor of decreased regenerative capacity in aged individuals. Furthermore, a novel therapeutic strategy of neutralizing IL-22 may successfully rejuvenate healing in individuals with advanced immune experiences.

Mast Cells Drive Systemic Inflammation and Compromised Bone Repair After Trauma

There is evidence that mast cells contribute to inflammation induced by hemorrhagic shock, severe tissue injury or sepsis. Mast cells are highly responsive to alarm signals generated after trauma, and release many inflammatory mediators including interleukin-6, a key mediator of posttraumatic inflammation. An overwhelming posttraumatic inflammation causes compromised bone healing; however, the underlying cellular and molecular mechanisms are poorly understood. Recently, we found that mast cells trigger local and systemic inflammation after isolated fracture leading to uneventful bone repair. Here, we investigated whether mast cells critically contribute to trauma-induced compromised bone healing. Male Mcpt5-Cre⁺ R-DTA mice, which lack connective tissue type mast cells, and their mast cell-competent Cre^- littermates underwent a femur fracture with/without thoracic trauma. Posttraumatic systemic and local inflammation and bone repair were assessed 3 h and 21 d post injury. Both, the systemic and pulmonary inflammation was significantly increased in mast cell-competent mice upon combined trauma compared to isolated fracture. In mast cell-deficient mice, the increase of inflammatory mediators in the circulation induced by the severe trauma was abolished. In the bronchoalveolar lavage fluid, the trauma-induced increase of inflammatory cytokines was not reduced, but the neutrophil invasion into the lungs was significantly diminished in the absence of mast cells. Locally in the fracture hematoma, mast cell-competent mice displayed reduced inflammatory mediator concentrations after combined trauma compared to isolated fracture, which was abolished in mast cell-deficient mice. Notably, while combined trauma resulted in compromised bone repair in mast cell-competent mice, indicated by significantly reduced bone and increased cartilage fracture callus contents, this was abolished in Mcpt5-Cre⁺ R-DTA mice. Therefore, mast cells contribute to trauma-induced compromised bone repair and could be a potential target for new treatment options to improve fracture healing in multiply injured patients.

Microstructure, mechanical properties and osseointegration ability of Ta-20Zr alloy used as dental implant material

The aim of this study was to evaluate the application prospect of a tantalum (Ta) and zirconium (Zr) alloy as a dental implant material. The Ta-20Zr (wt.%) alloy was prepared by powder metallurgy, and its microstructure and mechanical properties were analyzed by standard techniques. The effect of Ta-20Zr alloy on inflammation, bone remodeling and osseointegration was analyzed in rat and rabbit models by biochemical, histological and imaging tests. The Ta-20Zr alloy showed excellent mechanical compatibility with the bone tissue on account of similar elastic modulus (49.2 GPa), thereby avoiding the 'stress shielding effect'. Furthermore, Ta-20Zr alloy enhanced the inflammatory response by promoting secretion of interleukin-6 (IL-6) and IL-10, and facilitated the balance between the M1/M2 macrophage phenotypes. Finally, Ta-20Zr also showed excellent osseointegration and osteogenic ability without any systemic side effects, making it an ideal dental implant material.

Expression of inflammatory cytokines in mesenchymal stem cells derived from proximal humerus fractures

BACKGROUND

Mesenchymal stem cells (MSCs) are an excellent treatment option for a wide variety of orthopaedic conditions. This study aimed to establish if bone marrow MSCs obtained from proximal humerus fractures can be an alternative source for obtaining primary cultures of human MSCs.

METHODS

Human bone marrow was obtained during osteosynthesis surgeries on closed proximal humerus fractures within 48 hours of injury. MSCs were harvested using the Ficoll gradient separation protocol and in vitro cultured until the third passage. Then, the cells were immunophenotyped by flow cytometry using stem cell specific surface markers. The cells were also induced to differentiate into osteoblasts and adipocytes for the characterization and confirmation of MSCs. The production of cytokines interleukin (IL)-1β, IL-6, IL-8, IL-10, tumor necrosis factor α (TNF-α), and interferon γ (IFN-γ) was assessed using enzyme-linked immunosorbent assay (ELISA) in the supernatant of the cultures after 3, 5 or 7 days.

RESULTS

Immunophenotyping showed high expression of the stem cell surface markers CD73, CD90, and CD105 and negative or very low expression of CD34, CD45, CD11b, CD19, and human leukocyte antigen (HLA)-DR. The bone marrow derived MSCs were able to differentiate into osteoblasts and adipocytes. The quantification of secreted cytokines revealed that IL-8 was the most produced cytokine, followed by IL-6 and IL-10 at similar quantities and lower levels of IL-1β. TNF-α and IFN-γ were not detected.

CONCLUSIONS

Proximal humerus fractures can be an alternative source for the collection of bone marrow MSCs. The cytokine production of these cells is very similar to the production profile of fracture haematomas previously reported and may be used for improving bone repair.

Macrophage-like Cells Are Responsive to Titania Nanotube Intertube Spacing-An In Vitro Study

With the introduction of a new interdisciplinary field, osteoimmunology, today, it is well acknowledged that biomaterial-induced inflammation is modulated by immune cells, primarily macrophages, and can be controlled by nanotopographical cues. Recent studies have investigated the effect of surface properties in modulating the immune reaction, and literature data indicate that various surface cues can dictate both the immune response and bone tissue repair. In this context, the purpose of the present study was to investigate the effects of titanium dioxide nanotube (TNT) interspacing on the response of the macrophage-like cell line RAW 264.7. The cells were maintained in contact with the surfaces of flat titanium (Ti) and anodic TNTs with an intertube spacing of 20 nm (TNT20) and 80 nm (TNT80), under standard or pro-inflammatory conditions. The results revealed that nanotube interspacing can influence macrophage response in terms of cell survival and proliferation, cellular morphology and polarization, cytokine/chemokine expression, and foreign body reaction. While the nanostructured topography did not tune the macrophages' differentiation into osteoclasts, this behavior was significantly reduced as compared to flat Ti surface. Overall, this study provides a new insight into how nanotubes' morphological features, particularly intertube spacing, could affect macrophage behavior.

An intron SNP rs2069837 in IL-6 is associated with osteonecrosis of the femoral head development

Background

Genetic polymorphisms play a crucial role in the development of osteonecrosis of the femoral head (ONFH). This study mainly explored the association of IL-6 variants and ONFH susceptibility among the Chinese Han population.

Methods

Two variants (rs2069837, and rs13306435) in the IL-6 gene were identified and genotyped from 566 patients with ONFH and 566 healthy controls. The associations between IL-6 polymorphisms and ONFH susceptibility were assessed using odds ratio (OR) and 95% confidence interval (95% CI) via logistic regression. The potential function of these two variants was predicted by the HaploReg online database.

Results

The results of the overall analysis revealed that IL-6 rs2069837 was correlated with decreased risk of ONFH among the Chinese Han population (p < 0.05). In stratified analysis, rs2069837 also reduced the susceptibility to ONFH in older people (> 51 years), males, nonsmokers, and nondrinkers (p < 0.05). However, no associations between rs13306435 and ONFH susceptibility were observed (p > 0.05).

Conclusions

To sum up, we suggested that rs2069837 G>A polymorphism in the IL-6 gene was significantly associated with a decreased risk of ONFH among the Chinese Hans. These findings underscored the crucial role of IL-6 rs2069837 in the occurrence of ONFH.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12920-021-01142-3.

Incretins Enhance PGF2α-Induced Synthesis of IL-6 and Osteoprotegerin in Osteoblasts

Incretins including glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1), which are secreted from the small intestine after oral food ingestion, are currently well-known to stimulate insulin secretion from pancreatic β-cells and used for the treatment of type 2 diabetes mellitus. We have previously reported that prostaglandin F_2α (PGF_2α) stimulates the synthesis of interleukin-6 (IL-6) and osteoprotegerin in osteoblast-like MC3T3-E1 cells, and that IL-6 and osteoprotegerin release are mediated through the p44/p42 mitogen-activated protein (MAP) kinase, p38 MAP kinase or stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) pathways. In the present study, we investigated the effects of incretins including GLP-1 and GIP, on the PGF_2α-induced synthesis of IL-6 and osteoprotegerin and examined the detailed mechanism in osteoblast-like MC3T3-E1 cells. We found that GIP and GLP-1 significantly stimulated the PGF_2α-induced synthesis of IL-6 in osteoblast-like MC3T3-E1 cells. In addition, GIP and GLP-1 significantly enhanced the PGF_2α-induced mRNA expression levels of IL-6. On the other hand, GIP and GLP-1 markedly stimulated the PGF_2α-induced synthesis of osteoprotegerin. However, the phosphorylation of p44/p42 MAP kinase, p38 MAP kinase, or JNK induced by PGF_2α was not affected by GIP or GLP-1. Therefore, these results strongly suggest that incretins enhance the PGF_2α-induced synthesis of IL-6 and osteoprotegerin in osteoblast-like MC3T3-E1 cells. However, these syntheses are not mediated through p44/p42 MAP kinase, p38 MAP kinase, or JNK pathways.

Mast Cells Trigger Disturbed Bone Healing in Osteoporotic Mice

Mast cells are important tissue-resident sensor and effector immune cells but also play a major role in osteoporosis development. Mast cells are increased in numbers in the bone marrow of postmenopausal osteoporotic patients, and mast cell-deficient mice are protected from ovariectomy (OVX)-induced bone loss. In this study, we showed that mast cell-deficient Mcpt5-Cre R-DTA mice were protected from OVX-induced disturbed fracture healing, indicating a critical role for mast cells in the pathomechanisms of impaired bone repair under estrogen-deficient conditions. We revealed that mast cells trigger the fracture-induced inflammatory response by releasing inflammatory mediators, including interleukin-6, midkine (Mdk), and C-X-C motif chemokine ligand 10 (CXCL10), and promote neutrophil infiltration into the fracture site in OVX mice. Furthermore, mast cells were responsible for reduced osteoblast and increased osteoclast activities in OVX mice callus, as well as increased receptor activator of NF-κB ligand serum levels in OVX mice. Additional in vitro studies with human cells showed that mast cells stimulate osteoclastogenesis by releasing the osteoclastogenic mediators Mdk and CXCL10 in an estrogen-dependent manner, which was mediated via the estrogen receptor alpha on mast cells. In conclusion, mast cells negatively affect the healing of bone fractures under estrogen-deficient conditions. Hence, targeting mast cells might provide a therapeutic strategy to improve disturbed bone repair in postmenopausal osteoporosis. © 2021 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Myeloid cell-derived catecholamines influence bone turnover and regeneration in mice

Catecholamine signaling is known to influence bone tissue as reuptake of norepinephrine released from sympathetic nerves into bone cells declines with age leading to osteoporosis. Further, β-adrenoceptor-blockers like propranolol provoke osteoprotective effects in osteoporotic patients. However, besides systemic adrenal and sympathetic catecholamine production, it is also known that myeloid cells can synthesize catecholamines, especially under inflammatory conditions. To investigate the effects of catecholamines produced by CD11b⁺ myeloid cells on bone turnover and regeneration, a mouse line with specific knockout of tyrosine hydroxylase, the rate-limiting enzyme of catecholamine synthesis, in CD11b⁺ myeloid cells (TH^flox/flox/CD11b-Cre⁺, referred to as TH^CD11b-Cre) was generated. For bone phenotyping, male mice were sacrificed at eight and twelve weeks of age and harvested bones were subjected to bone length measurement, micro-computed tomography, fluorescence-activated cell sorting of the bone marrow, gene expression analysis, histology and immunohistochemistry. Support for an age-dependent influence of myeloid cell-derived catecholamines on bone homeostasis is provided by the fact that twelve-week-old, but not eight-week-old TH^CD11b-Cre mice, developed an osteopenic phenotype and showed increased numbers of neutrophils and T lymphocytes in the bone marrow, while CCL2, IL-6, IL-4 and IL-10 mRNA expression was reduced in sorted myeloid bone marrow cells. To investigate the influence of myeloid cell-derived catecholamines on fracture healing, mice received a diaphyseal femur osteotomy. Three days post-fracture, immunohistochemistry revealed an increased number of macrophages, neutrophils and cytotoxic T lymphocytes in the fracture hematoma of TH^CD11b-Cre mice. Micro-computed tomography on day 21 showed a decreased tissue mineral density, a reduced bone volume and less trabeculae in the fracture callus indicating delayed fracture healing, probably due to the increased presence of inflammatory cells in TH^CD11b-Cre mice. This indicates a crucial role of myeloid cell-derived catecholamines in immune cell-bone cell crosstalk and during fracture healing.

Relevance of Cellular Redox Homeostasis for Vital Functions of Human Dental Pulp Cells

Odontogenic MSCs are vulnerable to LPS-triggered bacterial infections, and they respond by secreting inflammatory mediators, such as IL-6, and with mineralization. Since both processes might be prone to a disturbance of the redox homeostasis, the oxidative stress influence on vital functions of human dental pulp cells (HPCs) was investigated. With these aims, a model of LPS-stimulated primary HPCs was established, and anti- and pro-oxidant substances were administered up to 21 days to measure inflammation and mineralization parameters. LPS-stimulated HPCs retained mineralization potential, which was decreased with the antioxidants NAC and fisetin and the pro-oxidant BSO. The expression of surface markers related to odontogenic commitment was influenced accordingly but counteracted by the enhanced expression of BMP2 and ALP at the transcriptional level. LPS triggers an early IL-6 production in non-odontogenic conditions, while it can be measured only after 15 days in the presence of the differentiation medium. The present study shows that HPCs functions causally depend on a tightly regulated cellular redox balance. Our data demonstrate a redox control of pulp MSC odontogenic commitment along with a potential association between an IL-6 late secretion and mineralization. These findings lay the groundwork for investigations on the molecular role of IL-6 in dental hard tissue metabolism.

Butyrate Inhibits Osteoclast Activity In Vitro and Regulates Systemic Inflammation and Bone Healing in a Murine Osteotomy Model Compared to Antibiotic-Treated Mice

Short-chain fatty acids (SCFAs) produced by the gut microbiota have previously been demonstrated to play a role in numerous chronic inflammatory diseases and to be key mediators in the gut-bone signaling axis. However, the role of SCFAs in bone fracture healing and its impact on systemic inflammation during the regeneration process has not been extensively investigated yet. The aim of this study was to first determine the effects of the SCFA butyrate on key cells involved in fracture healing in vitro, namely, osteoclasts and mesenchymal stromal cells (MSCs), and second, to assess if butyrate supplementation or antibiotic therapy impacts bone healing, systemic immune status, and inflammation levels in a murine osteotomy model. Butyrate significantly reduced osteoclast formation and resorption activity in a dose-dependent manner and displayed a trend for increased calcium deposits in MSC cultures. Numerous genes associated with osteoclast differentiation were differentially expressed in osteoclast precursor cells upon butyrate exposure. In vivo, antibiotic-treated mice showed reduced SCFA levels in the cecum, as well as a distinct gut microbiome composition. Furthermore, circulating proinflammatory TNFα, IL-17a, and IL-17f levels, and bone preserving osteoprotegerin (OPG), were increased in antibiotic-treated mice compared to controls. Antibiotic-treated mice also displayed a trend towards delayed bone healing as revealed by reduced mineral apposition at the defect site and higher circulating levels of the bone turnover marker PINP. Butyrate supplementation resulted in a lower abundance of monocyte/macrophages in the bone marrow, as well as reduced circulating proinflammatory IL-6 levels compared to antibiotic- and control-treated mice. In conclusion, this study supports our hypothesis that SCFAs, in particular butyrate, are important contributors to successful bone healing by modulating key cells involved in fracture healing as well as systemic inflammation and immune responses.

Selective Inhibition of IL-6 Trans-Signaling Has No Beneficial Effect on the Posttraumatic Cytokine Release after Multiple Trauma in Mice

While improvements in pre-hospital and in-hospital care allow more multiple trauma patients to advance to intensive care, the incidence of posttraumatic multiple organ dysfunction syndrome (MODS) is on the rise. Herein, the influence of a selective IL-6 trans-signaling inhibition on posttraumatic cytokine levels was investigated as an approach to prevent MODS caused by a dysbalanced posttraumatic immune reaction. Therefore, the artificial IL-6 trans-signaling inhibitor sgp130Fc was deployed in a murine multiple trauma model (femoral fracture plus bilateral chest trauma). The traumatized mice were treated with sgp130Fc (FP) and compared to untreated mice (WT) and IL-6 receptor knockout mice (RKO), which received the same traumas. The overall trauma mortality was 4.4%. Microscopic pulmonary changes were apparent after multiple trauma and after isolated bilateral chest trauma. Elevated IL-6, MCP-3 and RANTES plasma levels were measured after trauma, indicating a successful induction of a systemic inflammatory reaction. Significantly reduced IL-6 and RANTES plasma levels were visible in RKO compared to WT. Only a little effect was visible in FP compared to WT. Comparable cytokine levels in WT and FP indicate neither a protective nor an adverse effect of sgp130Fc on the cytokine release after femoral fracture and bilateral chest trauma.

Blocking only the bad side of IL-6 in inflammation and cancer

Interleukin-6 (IL-6) is considered an inflammatory cytokine, which is involved not only in most inflammatory states but it also plays a prominent role in inflammation associated cancers. The response of cells to the cytokine strictly depends on the presence of the IL-6 receptor (IL-6R),which presents IL-6 to the signal transducing receptor subunit gp130, which is expressed on all cells of the body. The expression of IL-6R is limited to some cells, which are therefore IL-6 target cells. The IL-6R can be cleaved by proteases and the thus generated soluble IL-6R (sIL-6R) still binds the ligand IL-6. The complex of IL-6 and sIL-6R can bind to gp130 on any cell, induce dimerization of gp130 and intracellular signaling. This process has been named IL-6 trans-signaling. A fusion protein of soluble gp130 with the constant portion of human IgG1 (sgp130Fc) turned out to be a potent and specific inhibitor of IL-6 trans-signaling. In many animal models of human diseases the significance of IL-6 trans-signaling has been analyzed. It turned out that the activities of IL-6 mediated by the sIL-6R are the pro-inflammatory activities of the cytokine whereas activities of IL-6 mediated by the membrane-bound IL-6R are rather protective and regenerative. The sgp130Fc protein has recently been developed into a biologic. The possible consequences of a specific IL-6 trans-signaling blockade is discussed in the light of the recent successfully concluded phase II clinical trials in patients with inflammatory bowel disease.

Initial displacement of the intra-articular surface after articular fracture correlates with PTA in C57BL/6 mice but not "superhealer" MRL/MpJ mice

Posttraumatic arthritis (PTA) occurs commonly after articular fracture and may arise, in part, from joint surface incongruity after injury. MRL/MpJ (MRL) "super-healer" mice are protected from PTA compared to C57BL/6 (B6) mice following articular fracture. However, the relationship between the initial displacement of the articular surface, biologic response, and susceptibility to PTA after fracture remains unclear. The objective of this study was to assess whether joint incongruity after articular fracture, as measured by in vivo micro-computed tomography (microCT), could predict pathomechanisms of PTA in mice. B6 and MRL mice (n = 12/strain) received a closed articular fracture (fx) of the left tibial plateau. Articular incongruity was quantified as bone surface deviations (BSD) for each in vivo microCT scan obtained from pre-fx to 8 weeks post-fx, followed by histologic assessment of arthritis. Serum concentrations of bone formation (PINP) and bone resorption (CTX-I) biomarkers were quantified longitudinally. Both strains showed increases in surface incongruity over time, as measured by increases in BSD. In B6 mice, acute surface incongruity was significantly correlated to the severity of PTA (R ²  = 0.988; p = .0006), but not in MRL mice (R ²  = 0.224; p = .220). PINP concentrations significantly decreased immediately post-fx in B6 mice (p = .023) but not in MRL mice, indicating higher bone synthesis in MRL mice. MRL/MpJ mice demonstrate a unique biologic response to articular fracture such that the observed articular bone surface displacement does not correlate with the severity of subsequent PTA. Clinical Relevance: Identifying therapies to enhance acute biologic repair following articular fracture may mitigate the risk of articular surface displacement for PTA.

Influences of the IL-6 cytokine family on bone structure and function

The IL-6 family of cytokines comprises a large group of cytokines that all act via the formation of a signaling complex that includes the glycoprotein 130 (gp130) receptor. Despite this, many of these cytokines have unique roles that regulate the activity of bone forming osteoblasts, bone resorbing osteoclasts, bone-resident osteocytes, and cartilage cells (chondrocytes). These include specific functions in craniofacial development, longitudinal bone growth, and the maintenance of trabecular and cortical bone structure, and have been implicated in musculoskeletal pathologies such as craniosynostosis, osteoporosis, rheumatoid arthritis, osteoarthritis, and heterotopic ossifications. This review will work systematically through each member of this family and provide an overview and an update on the expression patterns and functions of each of these cytokines in the skeleton, as well as their negative feedback pathways, particularly suppressor of cytokine signaling 3 (SOCS3). The specific cytokines described are interleukin 6 (IL-6), interleukin 11 (IL-11), oncostatin M (OSM), leukemia inhibitory factor (LIF), cardiotrophin 1 (CT-1), ciliary neurotrophic factor (CNTF), cardiotrophin-like cytokine factor 1 (CLCF1), neuropoietin, humanin and interleukin 27 (IL-27).

Composite Coating of Graphene Oxide/TiO2 Nanotubes/HHC-36 Antibacterial Peptide Construction and an Exploration of Its Bacteriostat and Osteogenesis Effects

Graphene oxide (GO), a kind of polymer, is often selected as a controlled released agent, whereas titanium dioxide (TiO2) nanotubes are commonly used as a drug-coated carrier. This study was conducted to develop methods for manufacturing the GO/TiO2/HHC-36 composite coating and exploring its bacteriostat and osteogenesis properties. The GO/TiO2 nanotubes were prepared by electrochemical methods and HHC-36 was then adsorbed to GO/TiO2to obtain GO/TiO2/HHC-36. Sustained release of HHC-36 was analyzed and the antibacterial effect was examined by the inhibition zone test. The biocompatibility and osteogenesis in vitro of GO/TiO2/HHC-36 were explored. Finally, the osteogenesic property of the composite coating was investigated in a rat femoral defect model in vivo. GO/TiO2/HHC-36 was successfully prepared and had good controlled released performance in vitro. The inhibit zone size of S. aureus was 2.1 mm and that of E. coli was 3.0 mm. GO/TiO2/HHC-36 showed good biocompatibility with mesenchymal stem cells (MSCs) and promoted their adhesion, migration, and differentiation. In addition, the secretion of alkaline phosphatase, collagen, mineralized matrix and osteoblast-related nutrient factors of MSCs was increased after treatment with GO/TiO2/HHC-36. Furthermore, GO/TiO2/HHC-36 also stimulated endotheliocytes to secrete VEGF, leading to angiogenesis. Finally, implantation of GO/TiO2/HHC-36 in the rat femur defect model resulted in MSC migration and increased expression of osteoblast related proteins. The composite coating with controlled released of HHC-36 showed distinct antibacterial properties and promoted osteogenesis in vitro and in vivo.

Network Pharmacological Study of Achyranthis bidentatae Radix Effect on Bone Trauma

Purpose

Bone trauma is a clinical condition that afflicts the majority of the world's population. For the management of bone trauma, the underlying mechanisms of the drugs effective for bone healing are deemed necessary. Achyranthis bidentatae Radix (ABR) is a popular alternative medicine recommended in the treatment of bone trauma and injury, yet its mechanism of action persists to be vague. This study was conducted for the evaluation of the mode of action of ABR through network pharmacology in treating bone trauma.

Methods

An extensive survey of published works led to the development of a drug-target database, after which multiple protein targets for bone trauma were discerned. The protein-protein interaction network was developed by utilizing the STITCH database and gene ontology (GO) enrichment analysis using Cytoscape and ClueGO. Moreover, docking studies were performed for revealing the affinity of various ingredients with IL6.

Results

The extensive literature survey yielded the presence of 176 components in ABR, and 151 potential targets were acquired. Scrutinization of these targets revealed that 21 potential targets were found to be associated with bone trauma. Out of which, some remarkable targets such as IL6, MAPK14, MAPK8, SRC, PTGS2, and MMP2 were observed to be associated in the functional interaction of ABR. According to docking results, several ingredients of ABR such as Baicalien, Copistine, Epiberberine, Kaempferol, and Palmatine have the lowest docking scores (range between -6 and -7).

Conclusions

The results of the study elucidated that ABR can positively be utilized for the management of bone trauma, which can be mediated by multiple molecular mechanisms such as ERBB2 signaling pathway, positive regulation of oxidoreductase activity, JNK cascade pathway, multicellular organism metabolic process, T cell costimulation, and the positive regulation of MAPK activity. The findings also suggest that several ingredients of ABR such as Baicalien, Copistine, Epiberberine, Kaempferol, and Palmatine have good affinity with IL6, suggesting the promising potential of ABR in treating bone trauma, likely through IL6.

Systemic and local cardiac inflammation after experimental long bone fracture, traumatic brain injury and combined trauma in mice

Background

Trauma is the leading cause of death and disability worldwide, especially in the young population. Cardiac injuries are an independent predictor for a poor overall outcome after trauma. The aim of the present study was to analyze systemic inflammation as well as local cardiac inflammation after experimental limb-, neuro- and combined trauma in mice.

Methods

Male C57BL/6 mice received either a closed tibia fracture (Fx), isolated traumatic brain injury (TBI) or a combination of both (Fx ​+ ​TBI). Control animals underwent sham procedure. After 6 and 24 ​h, systemic levels of inflammatory mediators were analyzed, respectively. Locally, cardiac inflammation and cardiac structural alterations were investigated in left ventricular tissue of mice 6 and 24 ​h after trauma.

Results

Mice showed enhanced systemic inflammation after combined trauma, which was manifested by increased levels of KC, MCP-1 and G-CSF. Locally, mice exhibited increased expression of inflammatory cytokines (IL-1β, TNF) in heart tissue, which was probably mediated via toll-like receptor (TLR) signaling. Furthermore, mice demonstrated a redistribution of connexin 43 in cardiac tissue, which appeared predominantly after combined trauma. Besides inflammation and structural cardiac alterations, expression of glucose transporter 4 (GLUT4) mRNA was increased in the heart early after TBI and after combination of TBI and limb fracture, indicating a modification of energy metabolism. Early after combination of TBI and tibia fracture, nitrosative stress was increased, manifested by elevation of nitrotyrosine in cardiac tissue. Finally, mice showed a trend of increased systemic levels of cardiac troponin I and heart-fatty acid binding protein (HFABP) after combined trauma, which was associated with a significant decrease of troponin I and HFABP mRNA expression in cardiac tissue after TBI and combination of TBI and limb fracture.

Conclusion

Mice exhibited early cardiac alterations as well as alterations in cardiac glucose transporter expression, indicating a modification of energy metabolism, which might be linked to increased systemic- and local cardiac inflammation after limb-, neuro- and combined trauma. These cardiac alterations might predispose individuals for secondary cardiac damage after trauma that might compromise cardiac function after TBI and long bone fracture.

Translational potential statement

Injuries to the head and extremities frequently occur after severe trauma. In our study, we analyzed the effects of closed tibia fracture, isolated TBI, and the combination of both injuries with regard to the development of post-traumatic secondary cardiac injuries.

Intact Glucocorticoid Receptor Dimerization Is Deleterious in Trauma-Induced Impaired Fracture Healing

Following severe trauma, fracture healing is impaired because of overwhelming systemic and local inflammation. Glucocorticoids (GCs), acting via the glucocorticoid receptor (GR), influence fracture healing by modulating the trauma-induced immune response. GR dimerization-dependent gene regulation is essential for the anti-inflammatory effects of GCs. Therefore, we investigated in a murine trauma model of combined femur fracture and thoracic trauma, whether effective GR dimerization influences the pathomechanisms of trauma-induced compromised fracture healing. To this end, we used mice with decreased GR dimerization ability (GR^dim). The healing process was analyzed by cytokine/chemokine multiplex analysis, flow cytometry, gene-expression analysis, histomorphometry, micro-computed tomography, and biomechanical testing. GR^dim mice did not display a systemic or local hyper-inflammation upon combined fracture and thorax trauma. Strikingly, we discovered that GR^dim mice were protected from fracture healing impairment induced by the additional thorax trauma. Collectively and in contrast to previous studies describing the beneficial effects of intact GR dimerization in inflammatory models, we report here an adverse role of intact GR dimerization in trauma-induced compromised fracture healing.

Interleukin-6 (IL-6) deficiency enhances intramembranous osteogenesis following stress fracture in mice

Interleukin-6 (IL-6) is highly upregulated in response to skeletal injury, suggesting it plays a role in the inflammatory phase of fracture repair. However, the impact of IL-6 on successful repair remains incompletely defined. Therefore, we investigated the role of IL-6 in two models of fracture repair (full fracture and stress fracture) using 12-week old IL-6 global knockout mice (IL-6 KO) and wild type (WT) littermate controls. Callus morphology and mineral density 14 days after full femur fracture did not differ between IL-6 knockout mice and controls. In contrast, IL-6 KO mice had an enhanced bone response 7 days after ulnar stress fracture compared to WT, with increased total callus volume (p = 0.020) and callus bone volume (p = 0.045). IL-6 KO did not alter the recruitment of immune cells (Gr-1 or F4/80 positive) to the stress fracture callus. IL-6 KO also did not alter the number of osteoclasts in the stress fracture callus. Using RNA-seq, we identified differentially expressed genes in stress fracture vs. contralateral control ulnae, and observed that IL-6 KO resulted in only modest alterations to the gene expression response to stress fracture (SFx). Wnt1 was more highly upregulated in IL-6 KO SFx callus at both day 1 (fold change 12.5 in KO vs. 5.7 in WT) and day 3 (fold change 4.7 in KO vs. 1.9 in WT). Finally, using tibial compression to induce bone formation without bone injury, we found that IL-6 KO directly impacted osteoblast function, increasing the propensity for woven bone formation. In summary, we report that IL-6 knockout enhanced formation of callus and bone following stress fracture injury, likely through direct action on the osteoblast's ability to produce woven bone. This suggests a novel role of IL-6 as a suppressor of intramembranous bone formation.

Assessing causal relationship from gut microbiota to heel bone mineral density

Recent studies have demonstrated the important role played by gut microbiota in regulating bone development, but the evidence of such causal relationship is still sparse in human population. The aim of this study is to assess the causal relationship from gut microbiota to bone development and to identify specific causal bacteria taxa via a Mendelian randomization (MR) approach. A genome-wide association study (GWAS) summary statistic based two-sample MR analysis was performed. Summary statistics of microbiome GWAS (MGWAS) in 1126 twin pairs of the TwinsUK study was used as discovery sample, and the MGWAS in 984 Dutch participants from the LifeLines-DEEP cohort was used as replication sample. Estimated heel bone mineral density (eBMD) GWAS in 426,824 participants from the UK biobank (UKB) cohort was used as outcome. Bacteria were grouped into taxa features at both order and family levels. In the discovery sample, a total of 25 bacteria features including 9 orders and 16 families were analyzed. Fourteen features (5 orders + 9 families) were nominally significant, including 5 orders (Bacteroidales, Clostridiales, Lactobacillales, Pasteurellales and Verrucomicrobiales) and 9 families (Bacteroidaceae, Clostridiaceae, Lachnospiraceae, Mogibacteriaceae, Pasteurellaceae, Porphyromonadaceae, Streptococcaceae, Verrucomicrobiaceae and Veillonellaceae). One order Clostridiales and its child taxon, family Lachnospiraceae, were successfully replicated in the replication sample (Clostridiales P_discovery = 3.32 × 10^-3P_replication = 7.29 × 10^-3; Lachnospiraceae P_discovery = 0.03 P_replication = 7.29 × 10^-3). Our findings provided evidence of causal relationship from microbiota to bone development, as well as identified specific bacteria taxa that regulated bone mass variation, thus providing new insights into the microbiota mediated bone development mechanism.

The Role of gp130 Cytokines in Tuberculosis

Protective immune responses to Mycobacterium tuberculosis (Mtb) infection substantially depend on a delicate balance within cytokine networks. Thus, immunosuppressive therapy by cytokine blockers, as successfully used in the management of various chronic inflammatory diseases, is often connected with an increased risk for tuberculosis (TB) reactivation. Hence, identification of alternative therapeutics which allow the treatment of inflammatory diseases without compromising anti-mycobacterial immunity remains an important issue. On the other hand, in the context of novel therapeutic approaches for the management of TB, host-directed adjunct therapies, which combine administration of antibiotics with immunomodulatory drugs, play an increasingly important role, particularly to reduce the duration of treatment. In both respects, cytokines/cytokine receptors related to the common receptor subunit gp130 may serve as promising target candidates. Within the gp130 cytokine family, interleukin (IL)-6, IL-11 and IL-27 are most explored in the context of TB. This review summarizes the differential roles of these cytokines in protection and immunopathology during Mtb infection and discusses potential therapeutic implementations with respect to the aforementioned approaches.

Tocilizumab, a Potent Interleukin-6 Receptor Inhibitor, Decreases Bone Resorption and Increases the Rate of Bacterial Infection After Tooth Extraction in Rats

PURPOSE

Our objective was to evaluate the influence of pretreatment with tocilizumab (TCZ) in bone healing after tooth extraction in rats.

METHODS

Wistar male rats were equally divided into sham (ie, nonoperated), saline (both treated with 0.1 ml/kg saline), and six TCZ groups treated with 1, 2, 4, 8, 16, and 32 mg/kg TCZ (TCZ1 to TCZ32, respectively). Twenty-four hours after administration of vehicle or TCZ, exodontia of the first lower left molar was performed, and the animals were euthanized three days later for hematological analysis and organ (liver, spleen, and kidney mass indexes, and histological evaluation), gingiva (myeloperoxidase [MPO] assay), and mandible (radiographic, histomorphometric analysis, and IL-6 immunostaining) evaluation. Analysis of variance/Bonferroni test (statistical significance, P < .05) was performed using GraphPad Prism version 5.0 (GraphPad Inc, San Diego, CA, USA).

RESULTS

There was no difference in radiographic results; however, leukopenia (P = .039) and neutropenia (P < .001) were statistically significant in the TCZ16 and TCZ32 groups. Weight loss (P < .001) and reduced liver index (P = .001) were significantly dose-dependent; however, no histological alterations were observed in the other organs. Osteoclast counts were reduced in groups TCZ4 to TCZ32 (P < .001), and IL-6 immunostaining increased in the TCZ8 to TCZ32 groups (P < .001). Alveolar infection rates increased in groups TCZ4 to TCZ32 (P < .001), and MPO had a biphasic response, exhibiting a reduction in groups TCZ2 and TCZ4, and an increase in group TCZ32 (P = .004).

CONCLUSION

TCZ-induced immunosuppression led to a reduction in osteoclast function, an increase in alveolar infection, and compensatory neutrophil infiltration.

Akkermansia muciniphila promotes type H vessel formation and bone fracture healing by reducing gut permeability and inflammation

Improving revascularization is one of the major measures in fracture treatment. Moderate local inflammation triggers angiogenesis, whereas systemic inflammation hampers angiogenesis. Previous studies showed that Akkermansia muciniphila, a gut probiotic, ameliorates systemic inflammation by tightening the intestinal barrier. In this study, fractured mice intragastrically administrated with A. muciniphila were found to display better fracture healing than mice treated with vehicle. Notably, more preosteclasts positive for platelet-derived growth factor-BB (PDGF-BB) were induced by A. muciniphila at 2 weeks post fracture, coinciding with increased formation of type H vessels, a specific vessel subtype that couples angiogenesis and osteogenesis, and can be stimulated by PDGF-BB. Moreover, A. muciniphila treatment significantly reduced gut permeability and inflammation at the early stage. Dextran sulfate sodium (DSS) was used to disrupt the gut barrier to determine its role in fracture healing and whether A. muciniphila still can stimulate bone fracture healing. As expected, A. muciniphila evidently improved gut barrier, reduced inflammation and restored the impaired bone healing and angiogenesis in DSS-treated mice. Our results suggest that A. muciniphila reduces intestinal permeability and alleviates inflammation, which probably induces more PDGF-BB+ preosteoclasts and type H vessel formation in callus, thereby promoting fracture healing. This study provides the evidence for the involvement of type H vessels in fracture healing and suggests the potential of A. muciniphila as a promising strategy for bone healing.This article has an associated First Person interview with the first author of the paper.

Duloxetine strengthens osteoblast activation by prostaglandin E1: Upregulation of p38 MAP kinase

Duloxetine, a serotonin-norepinephrine reuptake inhibitor, is currently recommended as a useful medicine to chronic pain including low back pain. However, as the analogy of classical selective serotonin reuptake inhibitors, there is a concern to deteriorate osteoporosis with remaining to clarify the exact mechanism of duloxetine in bone metabolism. We have previously reported that prostaglandin E1 (PGE1) induces the synthesis of both osteoprotegerin (OPG) and interleukin-6 (IL-6), essential regulators of bone metabolism, in osteoblast-like MC3T3-E1 cells. Based upon them, we herein investigated the mechanism whereby the effect of duloxetine on the synthesis of OPG and IL-6 induced by PGE1 in these cells. Duloxetine enhanced the release from MC3T3-E1 cells of both OPG and IL-6 stimulated by PGE1. However, reboxetine, a selective and specific inhibitor of norepinephrine reuptake, failed to affect the PGE1-induced release of OPG or IL-6. Oppositely, fluvoxamine and sertraline, agents belonging to the class of selective serotonin reuptake inhibitor, upregulated the PGE1-stimulated release of both OPG and IL-6. Duloxetine amplified the expression of OPG mRNA and IL-6 mRNA stimulated by PGE1. Duloxetine strengthened the PGE1-induced p38 MAP kinase phosphorylation, which was amplified by fluvoxamine as well. SB203880, an inhibitor of p38 MAP kinase, suppressed the amplifying effects by duloxetine or fluvoxamine on the PGE1-stimulated release of OPG and IL-6. These results strongly suggest that duloxetine could strengthen osteoblast activation by PGE1 through the upregulation of p38 MAP kinase, leading to increasing the synthesis of OPG and IL-6.