Diminished bone regeneration after debridement of posttraumatic osteomyelitis is accompanied by altered cytokine levels, elevated B cell activity, and increased osteoclast activity

Chitosan and hyaluronic acid based injectable dual network hydrogels - Mediating antimicrobial and inflammatory modulation to promote healing of infected bone defects

In bone defects, infections lead to excessive inflammation, increased bacterial, and bone lysis, resulting in irregular wounds that hinder new bone regeneration. Injectable bioactive materials with adequate antimicrobial activity and strong osteogenic potential are urgently required to remedy irregular defects, eradicate bacteria, and facilitate the generation of new bone tissue. In this research, injectable dual-network composite hydrogels consisting of sulfated chitosan, oxidized hyaluronic acid, β-sodium glycerophosphate, and CuSr doped mesoporous bioactive glass loaded with bone morphogenetic protein (CuSrMBGBMP-2) were utilized for the first time to treat infectious bone defects. Initially, the hydrogel was injected into the wound at 37 °C with minimal invasion to establish a stable state and prevent hydrogel loss. Subsequently, sulfated chitosan eliminated bacteria at the wound site and facilitated cell proliferation with oxidized hyaluronic acid. Additionally, CuSrMBGBMP-2 strengthened antibacterial properties, regulated inflammatory reactions, promoted angiogenesis and osteogenic differentiation, addressing the deficiency in late-stage osteogenesis. Specifically, the injectable dual-network hydrogel based on chitosan and hyaluronic acid is minimally invasive, offering antibacterial, anti-inflammatory, pro-angiogenic, and bone regeneration properties. Therefore, this hydrogel with injectable dual network properties holds great promise for the treatment of bone infections in the future.

Pharmacological elevation of sphingosine-1-phosphate by S1P lyase inhibition accelerates bone regeneration after post-traumatic osteomyelitis

Posttraumatic osteomyelitis and the ensuing bone defects are a debilitating complication after open fractures with little therapeutic options. We have recently identified potent osteoanabolic effects of sphingosine-1-phosphate (S1P) signalling and have now tested whether it may beneficially affect bone regeneration after infection. We employed pharmacological S1P lyase inhibition by 4-deoxypyrodoxin (DOP) to raise S1P levels in vivo in an unicortical long bone defect model of posttraumatic osteomyelitis in mice. In a translational approach, human bone specimens of clinical osteomyelitis patients were treated in organ culture in vitro with DOP. Bone regeneration was assessed by μCT, histomorphometry, immunohistology and gene expression analysis. The role of S1P receptors was addressed using S1PR3 deficient mice. Here, we present data that DOP treatment markedly enhanced osteogenesis in posttraumatic osteomyelitis. This was accompanied by greatly improved osteoblastogenesis and enhanced angiogenesis in the callus accompanied by osteoclast-mediated bone remodelling. We also identified the target of increased S1P to be the S1PR3 as S1PR3-/- mice showed no improvement of bone regeneration by DOP. In the human bone explants, bone mass significantly increased along with enhanced osteoblastogenesis and angiogenesis. Our data suggest that enhancement of S1P/S1PR3 signalling may be a promising therapeutic target for bone regeneration in posttraumatic osteomyelitis.

Locking the Taylor Spatial Frame - The effect of three additional longitudinal rods on osteotomy site movements

BACKGROUND

In clinical practice, even when the fixator is locked, a noticeable laxity of the construct can be observed. This study was designed to measure the stiffness of the fixator and to analyze the movements of the osteotomy site. Furthermore, the effect of three additional longitudinal rods on the locking of the construct was analyzed.

METHODS

Five synthetic tibia/fixator models (Model A) were tested under rotational torque (40 Nm) and axial compression (700 N). Three additional rigid rods were subsequently mounted, and the tests were repeated (Model B). The movements of the fixator as well as the osteotomy site were registered by a digital optical measurement system. Load- deformation curves, and so stiffness of the models, were calculated and compared.

FINDINGS

Under rotational and axial loadings, Model A was found to be less rigid than Model B (p = 0.034; p = 0.194). Notably, Model A showed a region of laxity around neutral rotational (ΔF = 5 Nm) and axial (ΔF = 16.64 N) loading before a linear deformation trend was measured. Concomitantly, greater osteotomy site movement was measured for Model A than for Model B under full loading (p = 0.05) and within the region of increased laxity (p = 0.042).

INTERPRETATION

The fixator showed an element of laxity around neutral axial and rotational loading, which transferred to the bone and led to a notable amount of osteotomy gap movement. Mounting three additional rods increased the stiffness of the construct and therefore reduced the movement of the osteotomy site.

Graphene oxide/gallium nanoderivative as a multifunctional modulator of osteoblastogenesis and osteoclastogenesis for the synergistic therapy of implant-related bone infection

Currently, implant-associated bacterial infections account for most hospital-acquired infections in patients suffering from bone fractures or defects. Poor osseointegration and aggravated osteolysis remain great challenges for the success of implants in infectious scenarios. Consequently, developing an effective surface modification strategy for implants is urgently needed. Here, a novel nanoplatform (GO/Ga) consisting of graphene oxide (GO) and gallium nanoparticles (GaNPs) was reported, followed by investigations of its in vitro antibacterial activity and potential bacterium inactivation mechanisms, cytocompatibility and regulatory actions on osteoblastogenesis and osteoclastogenesis. In addition, the possible molecular mechanisms underlying the regulatory effects of GO/Ga nanocomposites on osteoblast differentiation and osteoclast formation were clarified. Moreover, an in vivo infectious microenvironment was established in a rat model of implant-related femoral osteomyelitis to determine the therapeutic efficacy and biosafety of GO/Ga nanocomposites. Our results indicate that GO/Ga nanocomposites with excellent antibacterial potency have evident osteogenic potential and inhibitory effects on osteoclast differentiation by modulating the BMP/Smad, MAPK and NF-κB signaling pathways. The in vivo experiments revealed that the administration of GO/Ga nanocomposites significantly inhibited bone infections, reduced osteolysis, promoted osseointegration located in implant-bone interfaces, and resulted in satisfactory biocompatibility. In summary, this synergistic therapeutic system could accelerate the bone healing process in implant-associated infections and can significantly guide the future surface modification of implants used in bacteria-infected environments.

Wnt3a and ASCs are capable of restoring mineralization in staph aureus-infected primary murine osteoblasts

INTRODUCTION

Bone infections are one of the main reasons for impaired bone regeneration and non-union formation. In previous experimental animal studies we could already demonstrate that bone defects due to prior infections showed a markedly reduced healing capacity, which could effectively be enhanced via application of Wnt3a and Adipose-derived stromal cells (ASCs). For a more in-depth analysis, we investigated proliferation and mineralization of cultured osteoblasts infected with staph aureus and sought to investigate effects of Wnt3a and ASCs on infected osteoblasts.

MATERIALS AND METHODS

Primary murine osteoblasts were isolated from calvariae and infected with staph aureus. Infected osteoblasts received treatment via application of recombinant Wnt3a, ASC conditioned medium and were furthermore cocultured with ASCs. Osteoblasts were evaluated by Alamar blue assay for metabolic activity, TUNEL-assay for apoptosis, ALP and Alizarin Red staining for mineralization. In addition, immunoflourescent staining (IF) and qRT-PCR analyses were performed.

RESULTS

Infected osteoblasts showed a markedly reduced ability for mineralization and increased apoptosis, which could be restored to physiological levels by Wnt3a and ASC treatment. Interestingly, metabolic activity of osteoblasts seemed to be unaffected by staph aureus infection. Additional analyses of Wnt-pathway activity revealed effective enhancement of canonical Wnt-pathway activity in Wnt3a-treated osteoblasts.

CONCLUSIONS

In summary, we gained further osteoblast-related insights into pathomechanisms of reduced bone healing capacity upon infections.

Adipose-Derived Stem Cell: "Treat or Trick"

Stem cells have been widely used for treating disease due to the various benefits they offer in the curing process. Several treatments using stem cells have undergone clinical trials, such as cell-based therapies for heart disease, sickle cell disease, thalassemia, etc. Adipose-derived stem cells are some of the many mesenchymal stem cells that exist in our body that can be harvested from the abdomen, thighs, etc. Adipose tissue is easy to harvest, and its stem cells can be obtained in higher volumes compared to stem cells harvested from bone marrow, for which a more invasive technique is required with a smaller volume obtained. Many scientists have expressed interest in investigating the role of adipose-derived stem cells in treating disease since their use was first described. This is due to these stem cells' ability to differentiate into multiple lineages and secrete a variety of growth factors and proteins. Previous studies have found that the hormones, cytokines, and growth factors contained in adipose tissue play major roles in the metabolic regulation of adipose tissue, as well as in energy balance and whole-body homeostasis through their endocrine, autocrine, and paracrine functions. These are thought to be important contributors to the process of tissue repair and regeneration. However, it remains unclear how effective and safe ADSCs are in treating diseases. The research that has been carried out to date is in order to investigate the impact of ADSCs in disease treatment, as described in this review, to highlight its "trick or treat" effect in medical treatment.

Local Wnt3a treatment restores bone regeneration in large osseous defects after surgical debridement of osteomyelitis

Impaired bone homeostasis caused by osteomyelitis provokes serious variations in the bone remodeling process, thereby involving multiple inflammatory cytokines to activate bone healing. We have previously established a mouse model for post-traumatic osteomyelitis and studied bone regeneration after sufficient debridement. Moreover, we could further characterize the postinfectious inflammatory state of bony defects after debridement with elevated osteoclasts and decreased bone formation despite the absence of bacteria. In this study, we investigated the positive effects of Wnt-pathway modulation on bone regeneration in our previous established mouse model. This was achieved by local application of Wnt3a, a recombinant activator of the canonical Wnt-pathway. Application of Wnt3a could enhance new bone formation, which was verified by histological and μ-CT analysis. Moreover, histology and western blots revealed enhanced osteoblastogenesis and downregulated osteoclasts in a RANKL-dependent manner. Further analysis of Wnt-pathway showed downregulation after bone infections were reconstituted by application of Wnt3a. Interestingly, Wnt-inhibitory proteins Dickkopf 1 (DKK1), sclerostin, and secreted frizzled protein 1 (sFRP1) were upregulated simultaneously to Wnt-pathway activation, indicating a negative feedback for active form of Beta-catenin. In this study, we could demonstrate enhanced bone formation in defects caused by post-traumatic osteomyelitis after Wnt3a application. KEY MESSAGES: Osteomyelitis decreases bone regeneration Wnt3a restores bone healing after infection Canonical Wnt-pathway activation with negative feedback.

A thermo-sensitive injectable hydroxypropyl chitin hydrogel for sustained salmon calcitonin release with enhanced osteogenesis and hypocalcemic effects

Pharmacotherapy towards hypercalcemia treatment mainly caused by osteoporosis and bone tumor is an effective method to regulate in vivo calcium equilibrium. As a clinical therapeutic peptide, salmon calcitonin (sCT) is considered as a quick-acting medicine but it is limited by the short half-life. To address this challenge, we designed an injectable thermo-sensitive hydrogel based on hydroxypropyl chitin (HPCH) and incorporated the complex of sCT and hyaluronic acid (HA) (sCT-HA) with high association efficiency up to 96.84 ± 7.25%. This composite hydrogel showed a tunable biodegradable property. In vitro sCT release profiles revealed that this hydrogel can achieve long-term sustained sCT release (28 days) with considerable structure stability. The cellular study illustrated outstanding compatibility and osteoconductive potential of this multi-component hydrogel according to the higher ALP activity (2.10-fold), calcium expression (2.30-fold) and extracellular calcium deposition (1.10-fold) compared to that of the sCT group. In vivo sCT release confirmed that this hydrogel system realized sustained sCT release and a continuous hypocalcemic effect for as long as 28 days, and there were no inflammation and immune responses according to the histological evaluations (H&E and IgG staining). These findings demonstrate that this osteoconductive hydrogel system can provide a promising method for therapy of bone related disease.

Adipose-Derived Stromal Cells Are Capable of Restoring Bone Regeneration After Post-Traumatic Osteomyelitis and Modulate B-Cell Response

Bone infections are a frequent cause for large bony defects with a reduced healing capacity. In previous findings, we could already show diminished healing capacity after bone infections, despite the absence of the causing agent, Staphylococcus aureus. Moreover, these bony defects showed reduced osteoblastogenesis and increased osteoclastogenesis, meaning elevated bone resorption ongoing with an elevated B‐cell activity. To overcome the negative effects of this postinfectious inflammatory state, we tried to use the regenerative capacity of mesenchymal stem cells derived from adipose tissue (adipose‐derived stem cells [ASCs]) to improve bone regeneration and moreover were curious about immunomodulation of applicated stem cells in this setting. Therefore, we used our established murine animal model and applicated ASCs locally after sufficient debridement of infected bones. Bone regeneration and resorption as well as immunological markers were investigated via histology, immunohistochemistry, Western blot, and fluorescence‐activated cell scanning (FACS) analysis and μ‐computed tomography (CT) analysis. Interestingly, ASCs were able to restore bone healing via elevation of osteoblastogenesis and downregulation of osteoclasts. Surprisingly, stem cells showed an impact on the innate immune system, downregulating B‐cell population. In summary, these data provide a fascinating new and innovative approach, supporting bone healing after bacterial infections and moreover gain insights into the complex ceremony of stem cell interaction in terms of bone infection and regeneration. stem cells translational medicine2019;8:1084–1091

Lysostaphin and BMP-2 co-delivery reduces S. aureus infection and regenerates critical-sized segmental bone defects

Staphylococcus aureus is the most common pathogen associated with bacterial infections in orthopedic procedures. Infections often lead to implant failure and subsequent removal, motivating the development of bifunctional materials that both promote repair and prevent failure due to infection. Lysostaphin is an anti-staphylococcal enzyme resulting in bacterial lysis and biofilm reduction. Lysostaphin use is limited by the lack of effective delivery methods to provide sustained, high doses of enzyme to infection sites. We engineered a BMP-2-loaded lysostaphin-delivering hydrogel that simultaneously prevents S. aureus infection and repairs nonhealing segmental bone defects in the murine radius. Lysostaphin-delivering hydrogels eradicated S. aureus infection and resulted in mechanically competent bone. Cytokine and immune cell profiling demonstrated that lysostaphin-delivering hydrogels restored the local inflammatory environment to that of a sterile injury. These results show that BMP-2-loaded lysostaphin-delivering hydrogel therapy effectively eliminates S. aureus infection while simultaneously regenerating functional bone resulting in defect healing.

Dual-functional 3D-printed composite scaffold for inhibiting bacterial infection and promoting bone regeneration in infected bone defect models

Infection is one of the pivotal causes of nonunion in large bone defect after trauma or tumor resection. Three-dimensional (3D) composite scaffold with multifunctional-therapeutic properties offer many advantages over allogenic or xenogenic bone grafting for the restoration of challenging infected bone defects. In the previous study, we demonstrated that quaternized chitosan (HACC)-grafted polylactide-co-glycolide (PLGA)/hydroxyapatite (HA) scaffold (PLGA/HA/HACC) via 3D-printing technique exhibited significantly improved antimicrobial and osteoconductive property in vitro, together with good biocompatibility in vivo. Hence, the present study further investigated whether such an innovative bone substitute could effectively inhibit the bacterial biofilm formation and promote bone regeneration in vivo. To evaluate the bone repairing effects of the 3D-printed scaffolds on infected cortical and cancellous bone defects scenarios, eighty female Sprague Dawley rats and thirty-six female New Zealand white rabbits were used to establish infected femoral shaft defect and condyle defect model, respectively. X-ray, micro-CT, microbiological and histopathological analyses were used to assess the anti-infection and bone repairing potential of the dual-functional porous scaffolds. We observed that HACC-grafted PLGA/HA scaffolds exhibited significantly enhanced anti-infection and bone regeneration capability in different infected bone defect models. In addition, the degradation rate of the scaffolds appeared to be closely related to the progress of infection, influencing the bone repairing potential of the scaffolds in infected bone defects models. In general, this investigation is of great significance as it demonstrates promising applications of the 3D-printed dual-functional PLGA/HA/HACC scaffold for repairing different types of bone defect under infection.

STATEMENT OF SIGNIFICANCE

Currently, it is clinically urgent to exploit bone substitutes with potential of bacterial inhibition and bone regeneration. However, bone scaffolds with relatively low risks of bacterial resistance and tissue toxicity used for combating infected bone defects remain to be developed. We have reported that quaternized chitosan (HACC)-grafted 3D-printed PLGA/HA composite scaffold had enhanced in vitro antimicrobial and osteoconductive property, and well cytocompatibility in our published study. This continuing study further confirmed that HACC-grafted PLGA/HA scaffolds exhibited significantly enhanced anti-infection and bone regeneration efficacy in both cortical bone defect in rat and cancellous bone defect in rabbit under infection. Meanwhile, we also found that the degradation rate of the scaffolds seemed to be closely related to the progress of infection, influencing the bone repairing potential of the scaffolds in infected bone defects models. In conclusion, this study provides significant opportunities to develop a 3D-printed bone scaffold with dual functions used for infected bone defects in future plastic and orthopaedic surgery.

Innate Immunity to Staphylococcus aureus: Evolving Paradigms in Soft Tissue and Invasive Infections

Staphylococcus aureus causes a wide range of diseases that together embody a significant public health burden. Aided by metabolic flexibility and a large virulence repertoire, S. aureus has the remarkable ability to hematogenously disseminate and infect various tissues, including skin, lung, heart, and bone, among others. The hallmark lesions of invasive staphylococcal infections, abscesses, simultaneously denote the powerful innate immune responses to tissue invasion as well as the ability of staphylococci to persist within these lesions. In this article, we review the innate immune responses to S. aureus during infection of skin and bone, which serve as paradigms for soft tissue and bone disease, respectively.

Immunoprecipitation high performance liquid chromatographic analysis of healing process in chronic suppurative osteomyelitis of the jaw

PURPOSE

Chronic suppurative osteomyelitis (CSO) of the jaw is one of the most difficult infectious diseases to manage, because it causes progressive bony destruction and is associated with bacterial inhabitation of the sequestra. A combination of antibiotic therapy and surgical debridement is often used to treat CSO. Nevertheless, various systemic conditions can lead to life-threatening complications.

METHODS

The present study aimed to explore the wound healing progress in 16 cases of CSO through protein expression analysis of postoperative exudates (POE) that were collected 6 h, 1 day, and 2 days after saucerization and/or decortication. A bony lesion was removed during surgery and then examined pathologically, and the CSO POE was examined by immunoprecipitation thus high performance chromatography (IP-HPLC). The POE at 6 h was used as a comparative control.

RESULTS

Histologically the CSO lesion showed a necrotic granulomatous lesion heavily infiltrated with polymorphonuclear leukocytes, macrophages, and plasma cells, admixed with multiple sequestra inhabited by bacterial colonies. The IP-HPLC analysis displayed a slight increase in innate immunity-related proteins, i.e., NFkB, TNFα, IL-1, IL-6, IL-28, and LL-37, but a gradual decrease of bacteria-related inflammatory proteins, i.e., IL-8, IL-12, CD31, CD68, and lysozyme. The angiogenesis-related proteins, i.e., VEGF-A and VEGF-C, were slightly decreased but TGF-β1 and bFGF were markedly increased on day 2. The osteogenesis-related proteins, i.e., OPG and ALP, were slightly increased, while the osteoclastogenesis-related protein, RANKL was slightly decreased compared to the control.

CONCLUSION

These findings indicate that the infected CSO undergoes a rapid wound healing process with active osteogenesis and a gradual decrease in bacteria-related inflammation, predicting a favorable prognosis after surgery. Moreover, IP-HPLC can be useful in monitoring the POE and wound healing processes during the postoperative period.