Action of IL-1beta during fracture healing

Angiogenesis unveiled: Insights into its role and mechanisms in cartilage injury

Osteoarthritis (OA) commonly results in compromised mobility and disability, thereby imposing a significant burden on healthcare systems. Cartilage injury is a prevalent pathological manifestation in OA and constitutes a central focus for the development of treatment strategies. Despite the considerable number of studies aimed at delaying this degenerative process, their outcomes remain unvalidated in preclinical settings. Recently, therapeutic strategies focused on angiogenesis have attracted the growing interest from researchers. Thus, we conducted a comprehensive literature review to elucidate the current progress in research and pinpoint research gaps in this domain. Additionally, it provides theoretical guidance for future research endeavors and the development of treatment strategies.

B7-1 and PlGF-1 are two possible new biomarkers to identify fracture-associated trauma patients at higher risk of developing complications: a cohort study

BACKGROUND

Around 10% of fractures lead to complications. With increasing fracture incidences in recent years, this poses a serious burden on the healthcare system, with increasing costs for treatment. In the present study, we aimed to identify potential 'new' blood markers to predict the development of post-surgical complications in trauma patients following a fracture.

METHODS

A total of 292 trauma patients with a complete three-month follow-up were included in this cohort study. Blood samples were obtained from 244 of these patients. Two complication groups were distinguished based on the Clavien-Dindo (CD) classification: CD grade I and CD grade III groups were compared to the controls (CD 0). The Mann-Whitney U test was used to compare the complication groups to the control group.

RESULTS

Analysis of the patients' data revealed that risk factors are dependent on sex. Both, males and females who developed a CD III complication showed elevated blood levels of B7-1 (p = 0.015 and p = 0.018, respectively) and PlGF-1 (p = 0.009 and p = 0.031, respectively), with B7-1 demonstrating greater sensitivity (B7-1: 0.706 (male) and 0.692 (female), PlGF-1: 0.647 (male) and 0.615 (female)). Further analysis of the questionnaires and medical data revealed the importance of additional risk factors. For males (CD 0: 133; CD I: 12; CD III: 18 patients) alcohol consumption was significantly increased for CD I and CD III compared to control with p = 0.009 and p = 0.007, respectively. For females (CD 0: 107; CD I: 10; CD III: 12 patients) a significantly increased average BMI [kg/m2] from 25.5 to 29.7 with CD III was observed, as well as an elevation from one to three comorbidities (p = 0.003).

CONCLUSIONS

These two potential new blood markers hold promise for predicting complication development in trauma patients. Nevertheless, further studies are necessary to evaluate the diagnostic utility of B7-1 and PlGF-1 in predicting complications in trauma patients and consider sex differences before their possible use as routine clinical screening tools.

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.

IL-17RA Signaling in Prx1+ Mesenchymal Cells Influences Fracture Healing in Mice

Fracture healing is a complex series of events that requires a local inflammatory reaction to initiate the reparative process. This inflammatory reaction is important for stimulating the migration and proliferation of mesenchymal progenitor cells from the periosteum and surrounding tissues to form the cartilaginous and bony calluses. The proinflammatory cytokine interleukin (IL)-17 family has gained attention for its potential regenerative effects; however, the requirement of IL-17 signaling within mesenchymal progenitor cells for normal secondary fracture healing remains unknown. The conditional knockout of IL-17 receptor a (Il17ra) in mesenchymal progenitor cells was achieved by crossing Il17raF/F mice with Prx1-cre mice to generate Prx1-cre; Il17raF/F mice. At 3 months of age, mice underwent experimental unilateral mid-diaphyseal femoral fractures and healing was assessed by micro-computed tomography (µCT) and histomorphometric analyses. The effects of IL-17RA signaling on the osteogenic differentiation of fracture-activated periosteal cells was investigated in vitro. Examination of the intact skeleton revealed that the conditional knockout of Il17ra decreased the femoral cortical porosity but did not affect any femoral trabecular microarchitectural indices. After unilateral femoral fractures, Il17ra conditional knockout impacted the cartilage and bone composition of the fracture callus that was most evident early in the healing process (day 7 and 14 post-fracture). Furthermore, the in vitro treatment of fracture-activated periosteal cells with IL-17A inhibited osteogenesis. This study suggests that IL-17RA signaling within Prx1+ mesenchymal progenitor cells can influence the early stages of endochondral ossification during fracture healing.

Advances with Platelet-Rich Plasma for Bone Healing

Despite significant advances in the understanding and delivery of osteosynthesis, fracture non-union remains a challenging clinical problem in orthopaedic surgery. To bridge the gap, basic science characterization of fracture healing provides a platform to identify and target biological strategies to enhance fracture healing. Of immense interest, Platelet-rich plasma (PRP) is a point of care orthobiologic that has been extensively studied in bone and soft tissue healing given its relative ease of translation from the benchtop to the clinic. The aim of this narrative review is to describe and relate pre-clinical in-vitro and in-vivo findings to clinical observations investigating the efficacy of PRP to enhance bone healing for primary fracture management and non-union treatment. A particular emphasis is placed on the heterogeneity of PRP preparation techniques, composition, activation strategies, and delivery. In the context of existing data, the routine use of PRP to enhance primary fracture healing and non-union management cannot be supported. However, it is acknowledged that extensive heterogeneity of PRP treatments in clinical studies adds obscurity; ultimately, refinement (and consensus) of PRP treatments for specific clinical indications, including repetition studies are warranted.

Skeletal-Vascular Interactions in Bone Development, Homeostasis, and Pathological Destruction

Bone is a highly vascularized organ that not only plays multiple roles in supporting the body and organs but also endows the microstructure, enabling distinct cell lineages to reciprocally interact. Recent studies have uncovered relevant roles of the bone vasculature in bone patterning, morphogenesis, homeostasis, and pathological bone destruction, including osteoporosis and tumor metastasis. This review provides an overview of current topics in the interactive molecular events between endothelial cells and bone cells during bone ontogeny and discusses the future direction of this research area to find novel ways to treat bone diseases.

IL-1β contributes to the secretion of sclerostin by osteocytes and targeting sclerostin promotes spinal fusion at early stages

BACKGROUND

Despite extensive research, there is still a need for safe and effective agents to promote spinal fusion. Interleukin (IL)-1β is an important factor which influences the bone repair and remodelling. The purpose of our study was to determine the effect of IL-1β on sclerostin in osteocytes and to explore whether inhibiting the secretion of sclerostin from osteocytes can promote spinal fusion at early stages.

METHODS

Small-interfering RNA was used to suppress the secretion of sclerostin in Ocy454 cells. MC3T3-E1 cells were cocultured with Ocy454 cells. Osteogenic differentiation and mineralisation of MC3T3-E1 cells were evaluated in vitro. SOST knock-out rat generated using the CRISPR-Cas9 system and rat spinal fusion model was used in vivo. The degree of spinal fusion was assessed by manual palpation, radiographic analysis and histological analysis at 2 and 4 weeks.

RESULTS

We found that IL-1β level had a positive association with sclerostin level in vivo. IL-1β promoted the expression and secretion of sclerostin in Ocy454 cells in vitro. Inhibition of IL-1β-induced secretion of sclerostin from Ocy454 cells could promote the osteogenic differentiation and mineralisation of cocultured MC3T3-E1 cells in vitro. The extent of spinal graft fusion was greater in SOST-knockout rats than in wild-type rats at 2 and 4 weeks.

CONCLUSIONS

The results demonstrate that IL-1β contributes to a rise in the level of sclerostin at early stages of bone healing. Suppressing sclerostin may be an important therapeutic target capable of promoting spinal fusion at early stages.

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.

Engineering of immunoinstructive extracellular matrices for enhanced osteoinductivity

The increasing recognition of the contribution of the immune system to activate and prime regeneration implies that tissue engineering strategies and biomaterials design should target regulation of early immunological processes. We previously proposed the cell-based engineering and devitalization of extracellular matrices (ECMs) as a strategy to generate implant materials delivering custom-defined signals. Here, in the context of bone regeneration, we aimed at enhancing the osteoinductivity of such ECMs by enriching their immunomodulatory factors repertoire. Priming with IL1β a cell line overexpressing BMP-2 enabled engineering of ECMs preserving osteoinductive signals and containing larger amounts of angiogenic (VEGF) and pro-inflammatory molecules (IL6, IL8 and MCP1). Upon implantation, these IL1β-induced materials enhanced processes typical of the inflammatory phase (e.g., vascular invasion, osteoclast recruitment and differentiation), leading to 'regenerative' events (e.g., M2 macrophage polarization) and ultimately resulting in faster and more efficient bone formation. These results bear relevance towards the manufacturing of potent off-the-shelf osteoinductive materials and outline the broader paradigm of engineering immunoinstructive implants to enhance tissue regeneration.

Functionalized multidimensional biomaterials for bone microenvironment engineering applications: Focus on osteoimmunomodulation

As bone biology develops, it is gradually recognized that bone regeneration is a pathophysiological process that requires the simultaneous participation of multiple systems. With the introduction of osteoimmunology, the interplay between the immune system and the musculoskeletal diseases has been the conceptual framework for a thorough understanding of both systems and the advancement of osteoimmunomodulaty biomaterials. Various therapeutic strategies which include intervention of the surface characteristics or the local delivery systems with the incorporation of bioactive molecules have been applied to create an ideal bone microenvironment for bone tissue regeneration. Our review systematically summarized the current research that is being undertaken in the field of osteoimmunomodulaty bone biomaterials on a case-by-case basis, aiming to inspire more extensive research and promote clinical conversion.

Modulating macrophage polarization for the enhancement of fracture healing, a systematic review

Background

All fracture repairs start with the innate immune system with the inflammatory response known as the inflammatory stage guided and driven by the secretion of chemokine by the ruptured tissue, followed by the sequential recruitment of neutrophils, monocytes and macrophages. These innate immune cells would infiltrate the fracture site and secrete inflammatory cytokines to stimulate recruitment of more immune cells to arrive at the fracture site coordinating subsequent stages of the repair process. In which, subsidence of pro-inflammatory M1 macrophage and transformation to anti-inflammatory M2 macrophages promotes osteogenesis that marks the start of the anabolic endochondral stage.

Methods

Literature search was performed on Pubmed, Embase, and Web of Science databases (last accessed 15th April 2021) using “macrophage AND fracture”. Review was performed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline.

Results

Eleven pre-clinical animal studies out of 429 articles were included in this systematic review according to our inclusion and exclusion criteria. All of which investigated interventions targeting to modulate the acute inflammatory response and macrophage polarization as evident by various markers in association with fracture healing outcomes.

Conclusion

This systematic review summarizes attempts to modulate the innate immune response with focuses on promoting macrophage polarization from M1 to M2 phenotype targeting the enhancement of fracture injury repair. Methods used to achieve the goal may include applications of damage-associated molecular pattern (DAMP), pathogen-associated molecular pattern (PAMP) or mechanical stimulation that hold high translational potentials for clinical application in the near future.

The promising roles of macrophages in geriatric hip fracture

As aging becomes a global burden, the incidence of hip fracture (HF), which is the most common fracture in the elderly population and can be fatal, is rapidly increasing, and its extremely high fatality rate places significant medical and financial burdens on patients. Fractures trigger a complex set of immune responses, and recent studies have shown that with aging, the immune system shows decreased activity or malfunctions in a process known as immune senescence, leading to disease and death. These phenomena are the reasons why elderly individuals typically exhibit chronically low levels of inflammation and increased rates of infection and chronic disease. Macrophages, which are key players in the inflammatory response, are critical in initiating the inflammatory response, clearing pathogens, controlling the innate and adaptive immune responses and repairing damaged tissues. Tissue-resident macrophages (TRMs) are widely present in tissues and perform immune sentinel and homeostatic functions. TRMs are combinations of macrophages with different functions and phenotypes that can be directly influenced by neighboring cells and the microenvironment. They form a critical component of the first line of defense in all tissues of the body. Immune system disorders caused by aging could affect the biology of macrophages and thus the cascaded immune response after fracture in various ways. In this review, we outline recent studies and discuss the potential link between monocytes and macrophages and their potential roles in HF in elderly individuals.

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

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

Cytokine Profile From the Ligamentum Flavum in Patients with Ossification of the Posterior Longitudinal Ligament in the Cervical Spine

STUDY DESIGN

Histological, immunohistochemical, and suspension array analyses of cytokine expression in human cervical ossification of the posterior longitudinal ligament (OPLL).

OBJECTIVES

The aim of this study was to determine whether changes in the cytokine profile reflect the maturation of chondrocytes and osteoblasts are associated with OPLL development.

SUMMARY OF BACKGROUND DATA

OPLL progresses gradually over a prolonged period and may lead to serious spinal cord complications. However, treatment methods only include conservative therapy for neurological symptoms or surgical decompression, whereas preventive therapy for OPLL remains nonexistent.

METHODS

Ligamentous samples were harvested from 24 patients with OPLL who underwent spinal surgery, and five control samples from cervical spondylotic myelo/radiculopathy patients without OPLL. Tissue sections were used for immunohistochemical studies and primary cells were cultured from the ligamentous samples for cytokine profiling. Using a suspension array system, concentrations of 27 inflammatory cytokines or growth factors were measured to generate the cytokine profiles.

RESULTS

Suspension array and immunoblot analysis revealed significant increments in the levels of interleukin (IL)-6, IL-1α, basic fibroblast growth factor, and RANTES in patients with OPLL. Immunohistochemical analysis further revealed that these factors were present in mesenchymal cells within the degenerative portion of the ligamentous matrix.

CONCLUSION

Our findings suggest that specific changes in the cytokine profile during ossification promote osteoblast differentiation, thereby providing new insights into OPLL pathogenesis. Moreover, this work supports the development of a new therapeutic method for preventing OPLL progression by regulating the cytokine profiles.Level of Evidence: 3.

Effects of osteogenic ambulatory mechanical stimulation on early stages of BMP-2 mediated bone repair

Purpose: Mechanical loading of bone defects through rehabilitation is a promising approach to stimulate repair and reduce nonunion risk; however, little is known about how therapeutic mechanical stimuli modulate early-stage repair before mineralized bone formation. The objective of this study was to investigate the early effects of osteogenic loading on cytokine expression and angiogenesis during the first 3 weeks of BMP-2 mediated segmental bone defect repair.Materials and Methods: A rat model of BMP-2 mediated bone defect repair was subjected to an osteogenic mechanical loading protocol using ambulatory rehabilitation and a compliant, load-sharing fixator with an integrated implantable strain sensor. The effect of fixator load-sharing on local tissue strain, angiogenesis, and cytokine expression was evaluated.Results: Using sensor readings for local measurements of boundary conditions, finite element simulations showed strain became amplified in remaining soft tissue regions between 1 and 3 weeks (Week 3: load-sharing: -1.89 ± 0.35% and load-shielded: -1.38 ± 0.35% vs. Week 1: load-sharing: -1.54 ± 0.17%; load-shielded: -0.76 ± 0.06%). Multivariate analysis of cytokine arrays revealed that load-sharing significantly altered expression profiles in the defect tissue at 2 weeks compared to load-shielded defects. Specifically, loading reduced VEGF (p = 0.052) and increased CXCL5 (LIX) levels. Subsequently, vascular volume in loaded defects was reduced relative to load-shielded defects but similar to intact bone at 3 weeks. Endochondral bone repair was also observed histologically in loaded defects at 3 weeks.Conclusions: Together, these results demonstrate that moderate ambulatory strains previously shown to stimulate bone regeneration significantly alter early angiogenic and cytokine signaling and may promote endochondral ossification.

GABARAP ameliorates IL-1β-induced inflammatory responses and osteogenic differentiation in bone marrow-derived stromal cells by activating autophagy

Bone mesenchymal stem cells (BMSCs) are the most commonly investigated progenitor cells in bone defect repair and osteoarthritis subchondral bone regeneration; however, these studies are limited by complex inflammatory conditions. In this study, we investigated whether pro-autophagic γ-aminobutyric acid receptor-associated protein (GABARAP) promotes BMSCs proliferation and osteogenic differentiation by modulating autophagy in the presence or absence of interleukin-1 beta (IL-1β) in vitro. The expression levels of all relevant factors were evaluated by qRT-PCR or western blotting where appropriate. BMSCs differentiation were assessed by Alizarin Red, alkaline phosphatase, safranin O, and Oil Red O staining. Furthermore, the interactions between autophagy and osteogenic differentiation were investigated by co-treatment with the autophagy inhibitor 3-methyladenine (3-MA). As the results, we found that treatment with recombinant human His6-GABARAP protein promoted cell proliferation, inhibited apoptosis, and reduced ROS generation by increasing autophagic activity, particularly when co-cultured with IL-1β. Moreover, His6-GABARAP could effectively increase the osteogenic differentiation of BMSCs. The expression levels of inflammatory factors were significantly decreased by His6-GABARAP treatment, whereas its protective effects were attenuated by 3-MA. This study demonstrates that GABARAP maintains BMSCs survival and strengthens their osteogenic differentiation in an inflammatory environment by upregulating mediators of the autophagy pathway.

Changes in macrophage and inflammatory cytokine expressions during fracture healing in an ovariectomized mice model

Background

Macrophages and inflammatory cytokines play important roles in bone fracture healing. However, the expression patterns of macrophages and inflammatory cytokines during fracture healing under the condition of postmenopausal osteoporosis have not been fully revealed.

Methods

Tibia transverse fracture was established 12 weeks after ovariectomy or sham operation in 16-week old female mice. Tibias were harvested before fracture or 1, 3, 5, 7, 14, 21, 28 days after fracture for radiological and histological examinations. M1/M2 inflammatory macrophages, osteal macrophages and gene expressions of tumor necrosis factor-α, interleukin-6, interleukin-1β and macrophage conversion related molecules in the fracture haematoma or callus were also detected.

Results

The processes of fracture healing, especially the phases of endochondral ossification and callus remodeling, were delayed in ovariectomized mice. The expressions of tumor necrosis factor-α and interleukin-6, but not interleukin-1β, in the fracture haematoma or callus were disturbed. Expressions of tumor necrosis factor-α were decreased at 1, 14 and 21 days post-fracture (DPF), and were increased at 3, 5 and 7 DPF. Interleukin-6 expressions at 1, 3 and 21 DPF were significantly increased. We found the decreases in M1 and M2 macrophages at 1 DPF of the initial inflammatory stage. M2 macrophages at 14 DPF of the middle stage and osteal macrophages at 14, 21 and 28 DPF of the middle and late stages of fracture healing were also reduced in ovariectomized mice.

Conclusions

The expressions of macrophages and inflammatory cytokines were impaired in ovariectomized mice, which might contribute partially to poor fracture healing.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-021-04360-z.

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

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

Matrix metalloproteinase (MMP)-degradable tissue engineered periosteum coordinates allograft healing via early stage recruitment and support of host neurovasculature

Despite serving as the clinical "gold standard" treatment for critical size bone defects, decellularized allografts suffer from long-term failure rates of ~60% due to the absence of the periosteum. Stem and osteoprogenitor cells within the periosteum orchestrate autograft healing through host cell recruitment, which initiates the regenerative process. To emulate periosteum-mediated healing, tissue engineering approaches have been utilized with mixed outcomes. While vascularization has been widely established as critical for bone regeneration, innervation was recently identified to be spatiotemporally regulated together with vascularization and similarly indispensable to bone healing. Notwithstanding, there are no known approaches that have focused on periosteal matrix cues to coordinate host vessel and/or axon recruitment. Here, we investigated the influence of hydrogel degradation mechanism, i.e. hydrolytic or enzymatic (cell-dictated), on tissue engineered periosteum (TEP)-modified allograft healing, especially host vessel/nerve recruitment and integration. Matrix metalloproteinase (MMP)-degradable hydrogels supported endothelial cell migration from encapsulated spheroids whereas no migration was observed in hydrolytically degradable hydrogels in vitro, which correlated with increased neurovascularization in vivo. Specifically, ~2.45 and 1.84-fold, and ~3.48 and 2.58-fold greater vessel and nerve densities with high levels of vessel and nerve co-localization was observed using MMP degradable TEP (MMP-TEP) -modified allografts versus unmodified and hydrolytically degradable TEP (Hydro-TEP)-modified allografts, respectively, at 3 weeks post-surgery. MMP-TEP-modified allografts exhibited greater longitudinal graft-localized vascularization and endochondral ossification, along with 4-fold and 2-fold greater maximum torques versus unmodified and Hydro-TEP-modified allografts after 9 weeks, respectively, which was comparable to that of autografts. In summary, our results demonstrated that the MMP-TEP coordinated allograft healing via early stage recruitment and support of host neurovasculature.

The Role of the Immune Microenvironment in Bone Regeneration

Bone is an active tissue, being constantly renewed in healthy individuals with participation of the immune system to a large extent. Any imbalance between the processes of bone formation and bone resorption is linked to various inflammatory bone diseases. The immune system plays an important role in tissue formation and bone resorption. Recently, many studies have demonstrated complex interactions between the immune and skeletal systems. Both of immune cells and cytokines contribute to the regulation of bone homeostasis, and bone cells, including osteoblasts, osteoclasts, osteocytes, also influence the cellular functions of immune cells. These crosstalk mechanisms between the bone and immune system finally emerged, forming a new field of research called osteoimmunology. Therefore, the immune microenvironment is crucial in determining the speed and outcome of bone healing, repair, and regeneration. In this review, we summarise the role of the immune microenvironment in bone regeneration from the aspects of immune cells and immune cytokines. The elucidation of immune mechanisms involved in the process of bone regeneration would provide new therapeutic targets for improving the curative effects of bone injury treatment.

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.

Biomaterials Regulating Bone Hematoma for Osteogenesis

Blood coagulation in tissue healing not only prevents blood loss, but also forms a natural scaffold for tissue repair and regeneration. As blood clot formation is the initial and foremost phase upon bone injury, and the quality of blood clot (hematoma) orchestrates the following inflammatory and cellular processes as well as the subsequent callus formation and bone remodeling process. Inspired by the natural healing hematoma, tissue-engineered biomimic scaffold/hydrogels and blood prefabrication strategies attract significant interests in developing functional bone substitutes. The alteration of the fracture hematoma ca significantly accelerate or impair the overall bone healing process. This review summarizes the impact of biomaterials on blood coagulation and provides evidence on fibrin network structure, growth factors, and biomolecules that contribute to bone healing within the hematoma. The aim is to provide insights into the development of novel implant and bone biomaterials for enhanced osteogenesis. Advances in the understanding of biomaterial characteristics (e.g., morphology, chemistry, wettability, and protein adsorption) and their effect on hematoma properties are highlighted. Emphasizing the importance of the initial healing phase of the hematoma endows the design of advanced biomaterials with the desired regulatory properties for optimal coagulation and hematoma properties, thereby facilitating enhanced osteogenesis and ideal therapeutic effects.

Bone Angiogenesis and Vascular Niche Remodeling in Stress, Aging, and Diseases

The bone marrow (BM) vascular niche microenvironments harbor stem and progenitor cells of various lineages. Bone angiogenesis is distinct and involves tissue-specific signals. The nurturing vascular niches in the BM are complex and heterogenous consisting of distinct vascular and perivascular cell types that provide crucial signals for the maintenance of stem and progenitor cells. Growing evidence suggests that the BM niche is highly sensitive to stress. Aging, inflammation and other stress factors induce changes in BM niche cells and their crosstalk with tissue cells leading to perturbed hematopoiesis, bone angiogenesis and bone formation. Defining vascular niche remodeling under stress conditions will improve our understanding of the BM vascular niche and its role in homeostasis and disease. Therefore, this review provides an overview of the current understanding of the BM vascular niches for hematopoietic stem cells and their malfunction during aging, bone loss diseases, arthritis and metastasis.

Macrophage GIT1 Contributes to Bone Regeneration by Regulating Inflammatory Responses in an ERK/NRF2-Dependent Way

Despite the best treatment, approximately 10% of fractures still face undesirable repair. Recently, many studies have focused on the importance of macrophages in bone repair; however, the cellular mechanisms by which they work are not yet fully understood. In this study, we explored the functions of macrophage G-protein-coupled receptor interacting protein 1 (GIT1) in healing a tibial monocortical defect model. Using GIT1^flox/flox Lyz2-Cre (GIT1 CKO) mice, we observed that a GIT1 deficiency in the macrophages led to an exacerbation of interleukin 1β (IL1β) production, more M1-like macrophage infiltration, and impaired intramembranous ossification in vivo. The results of in vitro assays further indicated that the macrophage GIT1 plays a critical role in several cellular processes in response to lipopolysaccharide (LPS), such as anti-oxidation, IL1β production alleviation, and glycolysis control. Although GIT1 has been recognized as a scaffold protein, our data clarified that GIT1-mediated extracellular-signal-regulated kinase (ERK) phosphorylation could activate nuclear factor (erythroid-derived 2)-like 2 (NRF2) in macrophages after LPS treatment. Moreover, we demonstrated that macrophage GIT1-activated ERK/NRF2 negatively regulates the 6-phosphofructo-2-kinase/fructose-2, 6-biphosphatase 3 (PFKFB3), facilitating the decrease of glycolysis. Our findings uncovered a previously unrecognized role of GIT1 in regulating ERK/NRF2 in macrophages to control the inflammatory response, suggesting that macrophage GIT1 could be a potential target to improve bone regeneration. © 2020 The Authors. Journal of Bone and Mineral Research published by American Society for Bone and Mineral Research..

Macrophage subtype and cytokine expression characterization during the acute inflammatory phase of mouse bone fracture repair

Fracture repair is a complex process requiring heterotypic interactions between osteogenic cells and immune cells. Recent evidence indicates that macrophages are critically involved in fracture repair. Polarized macrophage populations differentially promote and regulate inflammation in other tissues, but little is known about the various macrophage subtypes and their signaling activities following a bone fracture. The authors hypothesized that classically activated (M1 subtype) and alternatively activated (M2 subtype) macrophages are active during the early repair process to initiate and regulate the inflammatory response. To test our hypothesis, bone marrow was collected from intact femurs (naïve group), contralateral and fractured femurs of mice on days 0, 1, 2, 4, and 7 postfracture. Macrophages were isolated from the bone marrow and macrophage subtypes were identified using flow cytometry with antibodies to F4/80, MHC II, CD86, CD11c, and CD40. Bone marrow cytokine levels were measured using xMAP. Flow cytometry revealed dynamic changes in M1 subtype (F4/80+/MHC II+/CD86+), M2 subtype (F4/80+/MHC II-/CD86-), and dendritic cell (DCs; MHCII+/CD11c+/CD40+) populations following fracture as compared to naïve controls. M1 subtype levels were correlated with IL-1α, IL-1ß, IL-2, IL-17, Eotaxin, and MCP-1, while DCs were correlated with IL-6, G-CSF, LIF, KC, and VEGF-A. The results indicate that M1 and M2 subtypes and DCs are recruited to the fracture site early during the repair process and consequently may work in tandem to regulate the inflammatory response required to recruit osteogenic cells needed for later stages of repair.

Inflammatory response in postmenopausal osteoporotic fracture healing

A balanced inflammatory response is important for successful fracture healing. The response of osteoporotic fracture healing is deranged and an altered inflammatory response can be one underlying cause. The objectives of this review were to compare the inflammatory responses between normal and osteoporotic fractures and to examine the potential effects on different healing outcomes. A systematic literature search was conducted with relevant keywords in PubMed, Embase, and Web of Science independently. Original preclinical studies and clinical studies involving the investigation of inflammatory response in fracture healing in ovariectomized (OVX) animals or osteoporotic/elderly patients with available full text and written in English were included. In total, 14 articles were selected. Various inflammatory factors were reported; of those tumour necrosis factor-α (TNF-α) and interleukin (IL)-6 are two commonly studied markers. Preclinical studies showed that OVX animals generally demonstrated higher systemic inflammatory response and poorer healing outcomes compared to normal controls (SHAM). However, it is inconclusive if the local inflammatory response is higher or lower in OVX animals. As for clinical studies, they mainly examine the temporal changes of the inflammatory stage or perform comparison between osteoporotic/fragility fracture patients and normal subjects without fracture. Our review of these studies emphasizes the lack of understanding that inflammation plays in the altered fracture healing response of osteoporotic/elderly patients. Taken together, it is clear that additional studies, preclinical and clinical, are required to dissect the regulatory role of inflammatory response in osteoporotic fracture healing.

Cite this article: Bone Joint Res 2020;9(7):368–385.

IL-1β promotes osteogenic differentiation of mouse bone marrow mesenchymal stem cells via the BMP/Smad pathway within a certain concentration range

Inflammatory factors play an important role in the process of fracture healing. The influence of interleukin (IL)-1β, a key inflammatory factory, on new bone formation has been controversial. The aim of the present study was to investigate whether IL-1β affects the osteogenic differentiation of mouse bone marrow mesenchymal stem cells (MBMMSCs), and examined its effective concentration range and molecular mechanism of action. MBMMSC proliferation in the presence of IL-1β was observed using a Cell-Counting Kit-8 assay, and the effect of IL-1β on MBMMSC apoptosis was examined via flow cytometry. Alkaline phosphatase assay, Alizarin Red staining and quantitative assays were performed to evaluate the osteogenic differentiation of MBMMSCs. The expression levels of osteogenic differentiation markers were detected using reverse transcription-quantitative PCR (RT-qPCR). It was demonstrated that within a concentration range of 0.01-1 ng/ml, IL-1β promoted osteogenic differentiation of MBMMSCs and did not induce apoptosis. Furthermore, RT-qPCR results indicated that IL-1β increased osteogenic gene expression within this concentration range. Moreover, Western blotting results identified that the bone morphogenetic protein/Smad (BMP/Smad) signaling pathway was significantly activated by IL-1β under osteogenic conditions. Therefore, the present results suggested that within a certain concentration range, IL-1β promoted osteogenic differentiation and function of MBMMSCs via the BMP/Smad signaling pathway.

Expression and Role of IL-1β Signaling in Chondrocytes Associated with Retinoid Signaling during Fracture Healing

The process of fracture healing consists of an inflammatory reaction and cartilage and bone tissue reconstruction. The inflammatory cytokine interleukin-1β (IL-1β) signal is an important major factor in fracture healing, whereas its relevance to retinoid receptor (an RAR inverse agonist, which promotes endochondral bone formation) remains unclear. Herein, we investigated the expressions of IL-1β and retinoic acid receptor gamma (RARγ) in a rat fracture model and the effects of IL-1β in the presence of one of several RAR inverse agonists on chondrocytes. An immunohistochemical analysis revealed that IL-1β and RARγ were expressed in chondrocytes at the fracture site in the rat ribs on day 7 post-fracture. In chondrogenic ATDC5 cells, IL-1β decreases the levels of aggrecan and type II collagen but significantly increased the metalloproteinase-13 (Mmp13) mRNA by real-time reverse transcription-polymerase chain reaction (RT-PCR) analysis. An RAR inverse agonist (AGN194310) inhibited IL-1β-stimulated Mmp13 and Ccn2 mRNA in a dose-dependent manner. Phosphorylated extracellular signal regulated-kinases (pERK1/2) and p-p38 mitogen-activated protein kinase (MAPK) were increased time-dependently by IL-1β treatment, and the IL-1β-induced p-p38 MAPK was inhibited by AGN194310. Experimental p38 inhibition led to a drop in the IL-1β-stimulated expressions of Mmp13 and Ccn2 mRNA. MMP13, CCN2, and p-p38 MAPK were expressed in hypertrophic chondrocytes near the invaded vascular endothelial cells. As a whole, these results point to role of the IL-1β via p38 MAPK as important signaling in the regulation of the endochondral bone formation in fracture healing, and to the actions of RAR inverse agonists as potentially relevant modulators of this process.

The Role of Mast Cells in Bone Metabolism and Bone Disorders

Mast cells (MCs) are important sensor and effector cells of the immune system that are involved in many physiological and pathological conditions. Increasing evidence suggests that they also play an important role in bone metabolism and bone disorders. MCs are located in the bone marrow and secrete a wide spectrum of mediators, which can be rapidly released upon activation of mature MCs following their differentiation in mucosal or connective tissues. Many of these mediators can exert osteocatabolic effects by promoting osteoclast formation [e.g., histamine, tumor necrosis factor (TNF), interleukin-6 (IL-6)] and/or by inhibiting osteoblast activity (e.g., IL-1, TNF). By contrast, MCs could potentially act in an osteoprotective manner by stimulating osteoblasts (e.g., transforming growth factor-β) or reducing osteoclastogenesis (e.g., IL-12, interferon-γ). Experimental studies investigating MC functions in physiological bone turnover using MC-deficient mouse lines give contradictory results, reporting delayed or increased bone turnover or no influence depending on the mouse model used. By contrast, the involvement of MCs in various pathological conditions affecting bone is evident. MCs may contribute to the pathogenesis of primary and secondary osteoporosis as well as inflammatory disorders, including rheumatoid arthritis and osteoarthritis, because increased numbers of MCs were found in patients suffering from these diseases. The clinical observations could be largely confirmed in experimental studies using MC-deficient mouse models, which also provide mechanistic insights. MCs also regulate bone healing after fracture by influencing the inflammatory response toward the fracture, vascularization, bone formation, and callus remodeling by osteoclasts. This review summarizes the current view and understanding of the role of MCs on bone in both physiological and pathological conditions.

Modulation of the Inflammatory Response and Bone Healing

The optimal treatment for complex fractures and large bone defects is an important unsolved issue in orthopedics and related specialties. Approximately 5-10% of fractures fail to heal and develop non-unions. Bone healing can be characterized by three partially overlapping phases: the inflammatory phase, the repair phase, and the remodeling phase. Eventual healing is highly dependent on the initial inflammatory phase, which is affected by both the local and systemic responses to the injurious stimulus. Furthermore, immune cells and mesenchymal stromal cells (MSCs) participate in critical inter-cellular communication or crosstalk to modulate bone healing. Deficiencies in this inter-cellular exchange, inhibition of the natural processes of acute inflammation, and its resolution, or chronic inflammation due to a persistent adverse stimulus can lead to impaired fracture healing. Thus, an initial and optimal transient stage of acute inflammation is one of the key factors for successful, robust bone healing. Recent studies demonstrated the therapeutic potential of immunomodulation for bone healing by the preconditioning of MSCs to empower their immunosuppressive properties. Preconditioned MSCs (also known as "primed/ licensed/ activated" MSCs) are cultured first with pro-inflammatory cytokines (e.g., TNFα and IL17A) or exposed to hypoxic conditions to mimic the inflammatory environment prior to their intended application. Another approach of immunomodulation for bone healing is the resolution of inflammation with anti-inflammatory cytokines such as IL4, IL10, and IL13. In this review, we summarize the principles of inflammation and bone healing and provide an update on cellular interactions and immunomodulation for optimal bone healing.

Osteoimmunology: Inflammatory osteolysis and regeneration of the alveolar bone

AIM

Osteoimmunology covers the cellular and molecular mechanisms responsible for inflammatory osteolysis that culminates in the degradation of alveolar bone. Osteoimmunology also focuses on the interplay of immune cells with bone cells during bone remodelling and regeneration. The aim of this review was to provide insights into how osteoimmunology affects alveolar bone health and disease.

METHOD

This review is based on a narrative approach to assemble mouse models that provide insights into the cellular and molecular mechanisms causing inflammatory osteolysis and on the impact of immune cells on alveolar bone regeneration.

RESULTS

Mouse models have revealed the molecular pathways by which microbial and other factors activate immune cells that initiate an inflammatory response. The inflammation-induced alveolar bone loss occurs with the concomitant suppression of bone formation. Mouse models also showed that immune cells contribute to the resolution of inflammation and bone regeneration, even though studies with a focus on alveolar socket healing are rare.

CONCLUSIONS

Considering that osteoimmunology is evolutionarily conserved, osteolysis removes the cause of inflammation by provoking tooth loss. The impact of immune cells on bone regeneration is presumably a way to reinitiate the developmental mechanisms of intramembranous and endochondral bone formation.

Keel Fracture Causes Stress and Inflammatory Responses and Inhibits the Expression of the Orexin System in Laying Hens

Simple Summary

Keel fracture is an important health and welfare problem in laying hens in all production systems. Previous studies have shown that keel fracture can influence hens’ behavior, reduce production performances, and cause pain in laying hens. Additionally, keel fracture also affects their feed intake. However, it is not clear whether the keel fracture induces stress, inflammation, or influences the orexin systems in laying hens. Orexin, also called hypocretin, is associated with the regulation of feed intake, energy homeostasis, and metabolism in poultry animals. Therefore, this study aimed to investigate the effects of keel fracture on stress and inflammatory responses and the activity of the orexin system of laying hens. Our results indicate that keel fracture not only induced stress and inflammatory responses, but inhibited the activity of the orexin system in laying hens. This study provides insights into the adverse effects of keel fracture on laying hens.

Abstract

Keel fracture has negative effects on the health and welfare of laying hens. We investigated effects of keel fracture on stress, inflammation, and the orexin system in laying hens. Ninety 17-week-old Lohmann white laying hens were palpated and euthanatized at 42 weeks old, and marked as normal keel (NK)/fractured keel (FK) from absence/presence of keel fracture. Serum, brain, liver, and abdominal-muscle samples were collected from 10 NK and 10 FK hens to determine the stress and inflammatory responses and the activity of orexin systems by corticosterone content, expression of heat shock proteins (TNF-α 60, 70, 90), and inflammatory factors (tumor necrosis factor (TNF)-α, nuclear factor-kappa Bp65 (NF-κBp65), inducible nitric oxide synthase (iNOS), prostaglandin E synthases (PTGEs), cyclooxygenase-2 (COX-2), interleukin-1β (IL-1β)), orexin (ORX), and orexin-receptor 1/2 (ORXR1/ORXR2). The FK hens had higher serum corticosterone content, Hsps, and inflammatory factor mRNA expression levels than NK hens, although levels of iNOS in the liver and TNF-α in the muscle were similar. Protein levels of Hsp70 and Hsp90 in the brain and liver, iNOS and COX-2 in the liver, NF-κBp65, iNOS, and COX-2 in the brain of FK hens were increased compared with NK hens. Furthermore, FK hens had lower mRNA expression of ORX, ORXR1, and ORXR2 than NK hens. Therefore, keel fracture causes stress and inflammation, and inhibits the expression of the orexin system in laying hens.

Extracellular Matrices to Modulate the Innate Immune Response and Enhance Bone Healing

Extracellular matrices (ECMs) have emerged as promising off-the-shelf products to induce bone regeneration, with the capacity not only to activate osteoprogenitors, but also to influence the immune response. ECMs generated starting from living cells such as mesenchymal stromal cells (MSCs) have the potential to combine advantages of native tissue-derived ECMs (e.g., physiological presentation of multiple regulatory factors) with those of synthetic ECMs (e.g., customization and reproducibility of composition). MSC-derived ECMs could be tailored by enrichment not only in osteogenic cytokines, but also in immunomodulatory factors, to skew the innate immune response toward regenerative processes. After reviewing the different immunoregulatory properties of ECM components, here we propose different approaches to engineer ECMs enriched in factors capable to regulate macrophage polarization, recruit host immune and mesenchymal cells, and stimulate the synthesis of other immunoinstructive cytokines. Finally, we offer a perspective on the possible evolution of the paradigm based on biological and chemico-physical design considerations, and the use of gene editing approaches.

Ageing affects the proliferation and mineralization of rat dental pulp stem cells under inflammatory conditions

AIM

To comparatively evaluate changes in the proliferation and mineralization abilities of dental pulp stem cells (DPSCs) from juvenile and adult rats in a lipopolysaccharide (LPS)-induced inflammatory microenvironment to provide a theoretical basis for the age-related differences observed in DPSCs during repair of inflammatory injuries.

METHODOLOGY

DPSCs were isolated from juvenile (JDPSCs) and adult rats (ADPSCs), and senescence-associated β-galactosidase staining was used to compare senescence between JDPSCs and ADPSCs. Effects of LPS on JDPSCs and ADPSCs proliferation were investigated by cell counting kit-8 assays and flow cytometry. Alizarin red staining, quantitative reverse transcription polymerase chain reaction and Western blot assay were used to examine the effects of LPS on mineralization-related genes and proteins in JDPSCs and ADPSCs. Immunohistochemistry was used to compare interleukin-1β (IL-1β) and osteocalcin (OCN) expression in the pulpitis model. Unpaired Student's t-tests and one-way anova were used for statistical analysis.

RESULTS

DPSCs were isolated from juvenile and adult rat dental pulp tissues. At low concentrations (0.1-1 μg mL^-1 ), LPS significantly promoted the proliferation of JDPSCs (P < 0.01) and ADPSCs (P < 0.01 or P < 0.05), with the effect being stronger in JDPSCs than in ADPSCs. In addition, mineralized nodules and the expression of mineralization-related genes (OCN, DSPP, ALP, BSP) increased significantly after stimulation with LPS (0.5 μg mL^-1 ) in JDPSCs and ADPSCs (P < 0.01 or P < 0.05), and JDPSCs displayed a more obvious increase than ADPSCs. Western blots revealed OCN and ALP expression levels in JDPSCs treated with LPS were significantly upregulated (P < 0.05); meanwhile, ALP expression in ADPSCs increased slightly but significantly (P < 0.05), and OCN expression was not affected. Finally, IL-1β expression was significantly higher (P < 0.05) and OCN expression was significantly lower (P < 0.05) in the inflamed dental pulp of adult rats than in juvenile rats.

CONCLUSIONS

A certain degree of inflammatory stimulation promoted the proliferation and mineralization of DPSCs; however, this effect declined with age. The DPSCs of adult donors in an inflammatory microenvironment have a weaker repair ability than that of juvenile donors, who are better candidates for tissues damage repair.

Postoperative Serum Levels of Interleukin-1β (IL-1β), Interleukin-17 (IL-17), and Tumor Necrosis Factor-α (TNF-α) in Patients Following Hip Replacement Surgery for Traumatic Fractured Femoral Neck: A Retrospective Study

Background

This study aimed to investigate the clinical significance of postoperative serum levels of interleukin-1β (IL-1β), interleukin-17 (IL-17), and tumor necrosis factor-α (TNF-α) in patients who required hip replacement surgery for traumatic fractured neck of femur.

Material/Methods

A retrospective study included 180 patients who had hip replacement surgery for traumatic fractured neck of femur and a control group of 100 patients. Differences between the two groups were compared for serum levels of IL-1β, IL-17, and TNF-α, and the Harris Hip Score (HHS) (maximum 100 points) using Pearson’s correlation.

Results

Serum levels of IL-1β, IL-17, and TNF-α in the control group were significantly lower than those in the study group (P<0.05). According to the HHS, there were 53 patients in the excellent group, 65 patients in the good group, 43 patients in the fair group and 19 patients in the poor group. Postoperative indicator analysis showed significant differences in IL-1β, IL-17, and TNF-α levels between the four groups (P<0.05). Clinical indicators increased from the excellent group to the poor group, with significant differences between the four groups (P<0.05). Postoperative levels of IL-1β, IL-17, and TNF-α were significantly decreased (P<0.05). Pearson’s correlation analysis showed a significant correlation with the clinical indicators (P<0.05).

Conclusions

In patients with hip replacement surgery for traumatic fractured neck of femur, measurement of postoperative serum levels of IL-1β, IL-17, and TNF-α were shown to be potential prognostic indicators.

Low-Intensity Pulsed Ultrasound Prevents Development of Bisphosphonate-Related Osteonecrosis of the Jaw-Like Pathophysiology in a Rat Model

We developed a rat model of bisphosphonate-related osteonecrosis of the jaw (BRONJ) by removing a maxillary molar tooth (M1) from ovariectomized rats after treatment with alendronate. To mimic periodontitis, some of the rats were administered Porphyromonas gingivalis (p. gingivalis) at the M1 site every 2 to 3 d for 2 wk. Rats pretreated with alendronate plus p. gingivalis showed delayed healing of socket epithelia, periosteal reaction of alveolar bone formation and lower bone mineral density in the alveolus above adjacent M2 teeth. These abnormalities were prevented by tooth socket exposure to 20 min/d low-intensity pulsed ultrasound (LIPUS), which restored diminished expression of RANKL, Bcl-2, IL-6, Hsp70, NF-κB and TNF-α messenger ribonucleic acids in remote bone marrow, suggesting LIPUS prevented development of BRONJ-like pathophysiology in rat by inducing systemic responses for regeneration, in addition to accelerating local healing. Non-invasive treatment by LIPUS, as well as low-level laser therapy, may be useful for medication-related osteonecrosis of the jaw patients.

Suppression of NLRP3 inflammasome improves alveolar bone defect healing in diabetic rats

Background

Excessive inflammatory response under hyperglycemia can impair alveolar bone defect healing under diabetic conditions. NLRP3 (NACHT [nucleotide-binding oligomerization], LRR [leucine-rich repeat], and PYD [pyrin domain] domains-containing protein 3) inflammasome has been considered to play a crucial role in the inflammatory response, but its correlation with the impaired alveolar bone repair in diabetes still remains unclarified. The objective of the current study is to investigate the effect of NLRP3 inflammasome inhibition by a lentiviral short hairpin RNA (shRNA) targeting NLRP3 on alveolar bone defect healing in diabetic rats.

Methods

Diabetes was induced in rats by high-fat diet and streptozotocin injection, and alveolar bone defects in both maxillae were created by surgery. Then, the lentiviral shRNA targeting NLRP3 was applied in the defect. Eight weeks after surgery, the alveolar bone regeneration was examined using hematoxylin and eosin (H&E) staining, and the gene expression in the bone healing site was detected using quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) analysis and western blot analysis.

Results

H&E staining showed that treatment with lentiviral shRNA targeting NLRP3 could increase the bone regeneration score in the alveolar bone defect of diabetic rats. Additionally, qRT-PCR analysis and western blot analysis of the bone defect demonstrated that this shRNA inhibited the expression of NLRP3, apoptosis-associated speck-like protein containing a CARD, caspase-1, and proinflammatory cytokine interleukin-1β and increased the expression of osteogenic markers Runt-related transcription factor 2 and osteocalcin.

Conclusions

Our findings suggested that inhibition of NLRP3 inflammasome could improve alveolar bone defect healing in diabetic rats. The beneficial effect may correlate with reduced proinflammatory cytokine production and increased osteogenic gene expression in hyperglycemia.

Electronic supplementary material

The online version of this article (10.1186/s13018-019-1215-9) contains supplementary material, which is available to authorized users.

Effects of inflammatory cytokines on bone/cartilage repair

Many inflammatory factors can affect cell behaviors and work as a form of inter-regulatory networks through the inflammatory pathway. Inflammatory cytokines are critical for triggering bone regeneration after fracture or bone injury. Also, inflammatory cytokines play an important role in cartilage repair. The synergistic or antagonistic effects of both proinflammatory and anti-inflammatory cytokines have a great influence on fracture healing. This review discusses key inflammatory cytokines and signaling pathways involved in bone or cartilage repair.

Mesenchymal stem cell transplantation in polytrauma: Evaluation of bone and liver healing response in an experimental rat model

PURPOSE

Trauma is the most common cause of death of young people in the world. As known, mesenchymal stem cells (MSCs) accelerate tissue regeneration mechanisms. In our study, we aimed to investigate the effects of MSCs transplantation on the healing of liver and bone tissue by considering trauma secondary inflammatory responses.

METHODS

56 adult Wistar-albino rats were divided into two groups: the polytrauma (liver and bone) (n = 28), and the liver trauma group (n = 28). At 36 h and 5th day after surgery, both rats with polytrauma and with isolated liver injury received either intravenous (IV) or intraperitoneal (IP) injections of MSCs (one million cells per kg body weight). Untreated groups received IV and IP saline injections. At day 21 after surgery, liver, tibia and fibula of the subjects were excised and evaluated for histopathologic and histomorphometric examination. Additionally, whole blood count (white blood cells, hemoglobin and platelets), C-reactive protein (CRP), glucose, alanine aminotransferase (ALT), aspartate aminotransferase (AST), albumin, blood gas, and trauma markers interleukin-1B (IL-1B), interleukin-6 (IL-6), and tumor necrosis factor alpha (TNF alpha) levels were investigated.

RESULTS

In general, MSC transplantations were well tolerated by the subjects. It was found that ALT, CRP, albumin were significantly lower in rats which received MSCs (p < 0.001). Inflammation of the liver and bone tissue in the MSC-injected rats were significantly lower than that of the untreated groups.

CONCLUSIONS

Herewith we have shown that MSC infusion in posttraumatic rats leads to less aggressive and more effective consequences on liver and bone tissue healing. Human MSC treatment for trauma is still in early stages of development; thus standard protocols, and patient inclusion criteria should be established beforehand clinical trials.

Cellular biology of fracture healing

The biology of bone healing is a rapidly developing science. Advances in transgenic and gene-targeted mice have enabled tissue and cell-specific investigations of skeletal regeneration. As an example, only recently has it been recognized that chondrocytes convert to osteoblasts during healing bone, and only several years prior, seminal publications reported definitively that the primary tissues contributing bone forming cells during regeneration were the periosteum and endosteum. While genetically modified animals offer incredible insights into the temporal and spatial importance of various gene products, the complexity and rapidity of healing-coupled with the heterogeneity of animal models-renders studies of regenerative biology challenging. Herein, cells that play a key role in bone healing will be reviewed and extracellular mediators regulating their behavior discussed. We will focus on recent studies that explore novel roles of inflammation in bone healing, and the origins and fates of various cells in the fracture environment. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

The Bidirectional Interactions Between Inflammation and Coagulation in Fracture Hematoma

IMPACT STATEMENT

The review leads to better understanding of the interrelation between inflammation mediators and coagulation factors in the early fracture hematoma, and their influences on hematoma formation in the beginning of fracture healing. Furthermore, development of therapies aimed at simultaneous modulation of both coagulation factors and inflammation factors that affect hematoma structure, rather than specific factors, may be most promising.

Immunohistochemical evaluation after Sr-enriched biphasic ceramic implantation in rabbits femoral neck: comparison of seven different bone conditions

Strontium (Sr) has shown effectiveness for stimulating bone remodeling. Nevertheless, the exact therapeutic values are not established yet. Authors hypothesized that local application of Sr-enriched ceramics would enhance bone remodeling in constant osteoporosis of rabbits' femoral neck bone. Seven different bone conditions were analyzed: ten healthy rabbits composed a control group, while other twenty underwent ovariectomy and were divided into three groups. Bone defect was filled with hydroxyapatite 30% (HAP) and tricalcium phosphate 70% (TCP) granules in 7 rabbits, 5% of Sr-enriched HAP/TCP granules in 7, but sham defect was left unfilled in 6 rabbits. Bone samples were obtained from operated and non-operated legs 12 weeks after surgery and analyzed by histomorphometry and immunohistochemistry (IMH). Mean trabecular bone area in control group was 0.393 mm2, in HAP/TCP - 0.226 mm2, in HAP/TCP/Sr - 0.234 mm2 and after sham surgery - 0.242 mm2. IMH revealed that HAP/TCP/Sr induced most noticeable increase of nuclear factor kappa beta 105 (NFkB 105), osteoprotegerin (OPG), osteocalcin (OC), bone morphogenetic protein 2/4 (BMP 2/4), collagen type 1α (COL-1α), interleukin 1 (IL-1) with comparison to intact leg; NFkB 105 and OPG rather than pure HAP/TCP or sham bone. We concluded that Sr-enriched biomaterials induce higher potential to improve bone regeneration than pure bioceramics in constant osteoporosis of femoral neck bone. Further studies on bigger osteoporotic animals using Sr-substituted orthopedic implants for femoral neck fixation should be performed to confirm valuable role in local treatment of osteoporotic femoral neck fractures in humans.

Human Spinal Bone Dust as a Potential Local Autograft: In Vitro Potent Anabolic Effect on Human Osteoblasts

STUDY DESIGN

In vitro Study.

OBJECTIVE

To evaluate the effect that factors released from human posterior spinal bone dust have on primary human osteoblast growth and maturation.

SUMMARY OF BACKGROUND DATA

Bone dust, created during spinal fusion surgeries, has the potential to be used as an autologous bone graft by providing a source of viable autologous osteoblasts and mesenchymal stem cells with osteogenic potential. Till date, no information is available on whether bone dust also provides a source of anabolic factors with the potential to enhance osteoblast proliferation and maturation, which would enhance its therapeutic potential.

METHODS

Bone dust was collected from consenting patients undergoing elective posterior spinal fusion surgeries, and primary human osteoblasts were cultured from patients undergoing elective hip or knee arthroplasty. Growth factors and cytokines released by bone dust were quantified using enzyme-linked immunosorbent assay. Primary human osteoblast proliferation and gene expression in response to bone dust were assessed using H-thymidine incorporation and real-time polymerase chain reaction, respectively.

RESULTS

Human bone dust released anabolic cytokines (IL-1β and IL-6) and growth factors (TGF-β, VEGF, FGF-Basic, and PDGF-BB) in increasing concentrations over a 7-day period. In vitro, the anabolic factors released by bone dust increased osteoblast proliferation by 7-fold, compared with osteoblasts cultured alone. In addition, the factors released from bone dust up-regulated a number of osteoblastic genes integral to osteoblast differentiation, maturation, and angiogenesis.

CONCLUSION

This study is the first to demonstrate that human posterior spinal bone dust released anabolic factors that potently enhance osteoblast proliferation and the expression of genes that favor bone healing and bone union. As bone dust is anabolic and its harvest is fast, simple, and safe to perform, spinal surgeons should be encouraged to 'recycle' bone dust and harness the regenerative potential of this free autologous bone graft.

LEVEL OF EVIDENCE

N/A.

Inflammation, mesenchymal stem cells and bone regeneration

Achieving satisfactory reconstruction of bone remains an important goal in orthopedic and dental conditions such as bone trauma, osteoporosis, arthritis, osteonecrosis, and periodontitis. Appropriate temporal and spatial differentiation of mesenchymal stem cells (MSCs) is essential for postnatal bone regeneration. Additionally, an acute inflammatory response is crucial at the onset of bone repair, while an adaptive immune response has important implications during late bone remodeling. Various reports have indicated bidirectional interactions between MSCs and inflammatory cells or molecules. For example, inflammatory cells can recruit MSCs, direct their migration and differentiation, so as to exert anabolic effects on bone repair. Furthermore, both pro-inflammatory and anti-inflammatory cytokines can regulate MSCs properties and subsequent bone regeneration. MSCs have demonstrated highly immunosuppressive functions, such as inhibiting the differentiation of monocytes/hematopoietic precursors and suppressing the secretion of pro-inflammatory cytokines. This review emphasizes the important interactions between inflammatory stimuli, MSCs, and bone regeneration as well as the underlying regulatory mechanisms. Better understanding of these principles will provide new opportunities for promoting bone regeneration and the treatment of bone loss associated with immunological diseases.

The key role of proinflammatory cytokines, matrix proteins, RANKL/OPG and Wnt/β-catenin in bone healing of hip arthroplasty patients

INTRODUCTION

We still lack understanding of why some implants fail while most remain stable after decades of use. Proinflammatory cytokines, matrix proteins and bone regulating cytokines of the RANKL/OPG (receptor activator of nuclear factor kappa B ligand/osteoprotegerin) and Wnt/β-catenin pathways are mandatory for normal bone repair but their spatial and temporal role in the healing of primary total hip arthroplasties (THA) has not been previously shown.

MATERIALS AND METHODS

Twenty-four osteoarthritis patients with one-sided well-fixed primary THA were prospectively monitored during 18years (18Y) with repeated blood samples, clinical variables and radiographs. Eighty-one healthy donors divided in three age- and gender-matched groups and twenty osteoarthritis patients awaiting THA and serving as control of the validity of stored plasma in THA patients, were included. Plasma was analyzed for C-reactive protein (CRP), interleukin (IL)-6, IL-8, IL-1β, tumor necrosis factor (TNF)-α, osteopontin (OPN), secreted protein acidic and rich in cysteine (SPARC/osteonectin), osteocalcin (OC), bone specific alkaline phosphatase (BALP), N-terminal propeptide of collagen type I (P1NP), RANKL, OPG, the Wnt agonistic ligands (Wnt)-1 and Wnt-3a, and the Wnt antagonists sclerostin, Dickkopf (Dkk)-1, Dkk-3, Dkk-4, secreted frizzled related protein (sFRP)-1, sFRP-3 and Wnt inhibitory factor-1 (Wif-1).

RESULTS

Inflammatory mediators in arthroplasty patients (CRP, IL-6, OPN) increased significantly on day one after surgery vs preoperative value (PR) and healthy subjects and returned to baseline at 6W. TNF-α did not change relative preoperative level or healthy subjects. SPARC and OC increased in a biphasic fashion with the primary phase beginning shortly after surgery and lasting 3M (SPARC) and 2Y (OC) while the secondary phase peaked at 1Y (SPARC) and 13Y (OC), with both returning to basal level at 15Y. BALP peaked at 3M after surgery with a return to basal level at 2Y followed by a continuous increase from 5Y until 18Y. P1NP increased immediately after surgery and returned to basal level at 6W followed by a new peak at 10Y returning to basal at 13Y. IL-8 and IL-1β peaked at 5Y post-THA and returned to basal level at 10Y. RANKL/OPG and Wnt/β-catenin remained at preoperative levels until 5Y post-THA when a sustained increase in OPG level, paralleled by a sustained decrease in sclerostin, started and lasted until 18Y. Despite a strong increase by RANKL at 13Y, the OPG/RANKL-ratio remained high between 5Y and 18Y. Dkk-1 and sFRP-1 remained at basal level until 5Y followed by a peak at 7Y and a return to basal level at 15Y. Similarly, RANKL increased after 5Y, peaked at 13Y and returned to basal levels at 18Y, thus coinciding with Wnt-1. In contrast, Wnt3a, Dkk-3, Dkk-4, sFRP-3 and Wif-1 did not differ from preoperative levels or healthy subjects during the course of the follow-up.

CONCLUSION

The primary peak of proinflammatory cytokines involved in the initiation of bone healing after trauma is in line with previous results. The primary phase of increased matrix proteins, P1NP and BALP paralleled by RANKL, OPG and Wnt/β-catenin remaining at preoperative level until 5Y, support a strong formation of mineralized matrix and to a lesser degree bone during this phase. The secondary proinflammatory peak at 5Y is likely a trigger of coupled bone remodeling and neosynthesis as it is followed by increased levels of the bone anabolic turnover marker, BALP, and mediators of the RANKL/OPG and Wnt/β-catenin pathways. A continuous increase by OPG level and the bone turnover marker, BALP, lasting from 5Y until 18Y and paralleled by a similar decrease in sclerostin level support their being key regulators of bone anabolism, whereas the transient and opposed activities of RANKL, Wnt-1, Dkk-1 and sFRP-1 serve as fine tuning tools during the coupled remodeling phase.

Immunological characterization of the early human fracture hematoma

The initial inflammatory phase of fracture healing is of great importance for the clinical outcome. We aimed to develop a detailed time-dependent analysis of the initial fracture hematoma. We analyzed the composition of immune cell subpopulations by flow cytometry and the concentration of cytokines and chemokines by bioplex in 42 samples from human fractures of long bones <72 h post-trauma. The early human fracture hematoma is characterized by maturation of granulocytes and migration of monocytes/macrophages and hematopoietic stem cells. Both T helper cells and cytotoxic T cells proliferate within the fracture hematoma and/or migrate to the fracture site. Humoral immunity characteristics comprise high concentration of pro-inflammatory cytokines such as IL-6, IL-8, IFNγ and TNFα, but also elevated concentration of anti-inflammatory cytokines, e.g., IL-1 receptor antagonist and IL-10. Furthermore, we found that cells of the fracture hematoma represent a source for key chemokines. Even under the bioenergetically restricted conditions that exist in the initial fracture hematoma, immune cells are not only present, but also survive, mature, function and migrate. They secrete a cytokine/chemokine cocktail that contributes to the onset of regeneration. We hypothesize that this specific microenvironment of the initial fracture hematoma is among the crucial factors that determine fracture healing.

Nanotopography-based strategy for the precise manipulation of osteoimmunomodulation in bone regeneration

Immune cells play vital roles in regulating bone dynamics. Successful bone regeneration requires a favourable osteo-immune environment. The high plasticity and diversity of immune cells make it possible to manipulate the osteo-immune response of immune cells, thus modulating the osteoimmune environment and regulating bone regeneration. With the advancement in nanotechnology, nanotopographies with different controlled surface properties can be fabricated. On tuning the surface properties, the osteo-immune response can be precisely modulated. This highly tunable characteristic and immunomodulatory effects make nanotopography a promising strategy to precisely manipulate osteoimmunomdulation for bone tissue engineering applications. This review first summarises the effects of the immune response during bone healing to show the importance of regulating the immune response for the bone response. The plasticity of immune cells is then reviewed to provide rationales for manipulation of the osteoimmune response. Subsequently, we highlight the current types of nanotopographies applied in bone biomaterials and their fabrication techniques, and explain how these nanotopographies modulate the immune response and the possible underlying mechanisms. The effects of immune cells on nanotopography-mediated osteogenesis are emphasized, and we propose the concept of "nano-osteoimmunomodulation" to provide a valuable strategy for the development of nanotopographies with osteoimmunomodulatory properties that can precisely regulate bone dynamics.

The cytokines and micro-environment of fracture haematoma: Current evidence

Fracture haematoma formation is the first and foremost important stage of fracture healing. It orchestrates the inflammatory and cellular processes leading to the formation of callus and the restoration of the continuity of the bone. Evidence suggests that blocking this initial stage could lead to an impairment of the overall bone healing process. This review aims to analyse the existing evidence of molecular contributions to bone healing within fracture haematoma and to determine the potential to modify the molecular response to fracture in the haematoma with the aim of improving union times. A comprehensive search of literature documenting fracture haematoma cytokine content was performed. Suitable papers according to prespecified criteria were identified and analysed according to Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines. A total of 89 manuscripts formed the basis of this analysis. Low oxygen tension, high acidity, and high calcium characterised initially the fracture haematoma micro-environment. In addition, a number of cytokines have been measured with concentrations significantly higher than those found in peripheral circulation. Growth factors have also been isolated, with an observed increase in bone morphogenetic proteins, platelet-derived growth factor, and transforming growth factor. Although molecular modification of fracture haematoma has been attempted, more research is required to determine a suitable biological response modifier leading to therapeutic effects. The cytokine content of fracture haematoma gives insight into processes occurring in the initial stages of fracture healing. Manipulation of signalling molecules represents a promising pathway to target future therapies aiming to upregulate the osteogenesis.