Osteomyelitis Model Research Articles

Development of a pharmacokinetic/pharmacodynamic evaluation model for osteomyelitis and usefulness of tedizolid as an alternative to vancomycin against MRSA osteomyelitis.

This study aimed to develop a suitable osteomyelitis model for pharmacokinetic/pharmacodynamic (PK/PD) evaluation and to investigate the target PK/PD values of vancomycin and tedizolid against methicillin-resistant Staphylococcus aureus (MRSA) osteomyelitis. An osteomyelitis model was established by implanting an MRSA-exposed sterilized suture in the tibia of normal mice and mice with cyclophosphamide-induced neutropenia. The suitability of the osteomyelitis mouse model for PK/PD evaluation was assessed using vancomycin as an indicator. The target PK/PD values for tedizolid were determined using this model. In neutropenic mice, to achieve a static effect and 1 log10 kill against MRSA, the ratios of the area under the free drug concentration-time curve for 24h to the minimum inhibitory concentration (fAUC24/MIC) of vancomycin were 91.29 and 430.03, respectively, confirming the validity of the osteomyelitis model for PK/PD evaluation. In immunocompetent mice, the target fAUC24/MIC values of tedizolid for achieving a static effect and 1 log10 kill against MRSA were 2.40 and 49.20, respectively. Additionally, only a 0.28 log10 kill was achieved in neutropenic mice with 20 times the human equivalent dose of tedizolid. In patients with restored immunity, tedizolid can potentially be used as an alternative to intravenous vancomycin therapy.

METTL3 accelerates staphylococcal protein A (SpA)-induced osteomyelitis progression by regulating m6A methylation-modified miR-320a

Osteomyelitis (OM) is an inflammatory disease of bone infection and destruction characterized by dysregulation of bone homeostasis. Staphylococcus aureus (SA) has been reported to be the most common pathogen causing infectious OM. Recent studies have demonstrated that N6-methyladenosine (m6A) regulators are associated with the development of OM. However, the molecular mechanism of m6A modifications in OM remains unclear. Here, we investigated the function of methyltransferase-like 3 (METTL3)-mediated m6A modification in OM development. In this study, human bone mesenchymal stem cells (hBMSCs) were treated with staphylococcal protein A (SpA), a vital virulence factor of SA, to construct cell models of OM. Firstly, we found that METTL3 was upregulated in OM patients and SpA-induced hBMSCs, and SpA treatment suppressed osteogenic differentiation and induced oxidative stress and inflammatory injury in hBMSCs. Functional experiments showed that METTL3 knockdown alleviated the inhibition of osteogenic differentiation and the promotion of oxidative stress and inflammation in SpA-treated hBMSCs. Furthermore, METTL3-mediated m6A modification upregulated miR-320a expression by promoting pri-miR-320a maturation, and the mitigating effects of METTL3 knockdown on SpA-mediated osteogenic differentiation, oxidative stress and inflammatory responses can be reversed by miR-320 mimic. In addition, we demonstrated that phosphatidylinositol-4, 5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA) was a downstream target of miR-320a, upregulation of PIK3CA alleviated miR-320a-induced inhibition of osteogenic differentiation, and upregulation of oxidative stress and inflammatory responses during SpA infection. Finally, we found that silencing METTL3 alleviated OM development by regulating the miR-320a/PIK3CA axis. Taken together, our data demonstrated that the METTL3/m6A/miR-320a/PIK3CA axis regulated SpA-mediated osteogenic differentiation, oxidative stress, and inflammatory responses in OM, which may provide a new therapeutic strategy for OM patients.

In vivo models of infection: Large animals – Mini review on human-scale one-stage revision in a porcine osteomyelitis model

Animal models are essential for orthopedic infectious research. However, only few models are currently able to capture the complex and multidisciplinary treatment approach for osteomyelitis. To replicate treatment situations in their entirety, large animal models are needed, and the most used species are sheep and pigs. Herein, we review a well-characterized and reproducible porcine model of human-scale one-stage revision of implant-associated osteomyelitis that can be used for robust preclinical testing of operative and post-operative interventions. The pros and cons of the model are discussed in the context of existing literature on large animal revision models.

Local Delivery of Exosomes and Antibiotics in Hydroxyapatite-Based Nanocement for Osteomyelitis Management.

The management of bone and joint infections is a formidable challenge in orthopedics and poses a global health concern. While clinical management emphasizes infection prevention and complete eradication, an effective strategy for stabilizing skeletal tissue with adequate soft tissue coverage remains limited. In this study, we have employed a novel approach of using the local delivery of exosomes and antibiotics (rifampicin) using a hydroxyapatite-based nanocement carrier to manage the residual space created during debridement effectively. Additionally, we synthesized a periosteum-guiding antioxidant herbal membrane to leverage the inherent periosteum regeneration capability of the bone, facilitating bone callus repair and natural healing. The synthesized scaffolds were biocompatible and demonstrated potent antibacterial activity in vitro. When evaluated in vivo in the Staphylococcus aureus-induced rat tibial osteomyelitis model, the released drugs successfully cleared the residual bacteria and the released exosome promoted bone healing, resulting in 3-fold increase in bone volume as analyzed via micro-CT analysis. Immunofluorescence staining of periosteum-specific markers also indicated the complete formation of periosteal layers, thus highlighting the complete bone repair.

Silk fibroin/chitosan thiourea hydrogel scaffold with vancomycin and quercetin-loaded PLGA nanoparticles for treating chronic MRSA osteomyelitis in rats

Chronic osteomyelitis presents significant treatment challenges, necessitating an efficient system for infection elimination and bone repair. This study developed a natural hydrogel scaffold using silk fibroin (SF) and chitosan thiourea (CST), incorporating vancomycin (VC) and quercetin (QC) loaded PLGA nanoparticles (NPs) for dual-purpose treatment. SF/CST hydrogel scaffolds exhibited homogeneous porosity and smaller interconnected pore size than pure SF and pure CST hydrogel scaffolds. Optimal PLGA/QC NPs measured 206 nm in size, displayed spherical morphology, had uniform distribution, and achieved 87 % QC loading. The release study showed sustained long-term release of VC and QC from the hydrogel scaffolds for over 20 days. Biocompatibility tests indicated that hydrogel scaffolds promoted osteoblast adhesion without cytotoxicity, with QC-containing scaffolds enhancing osteoblast growth. Antibacterial tests confirmed retained VC activity against methicillin-resistant Staphylococcus aureus (MRSA) in SF/CST. An experimental study assessed the efficacy of the hydrogel scaffolds in a MRSA-infected rat osteomyelitis model. Radiographic scores demonstrated a significant reduction for SF/CST-VC-PLGA/QC NPs compared to control, indicating reduced osteomyelitis effects. Macroscopic evaluations showed notable reductions in gross pathological effects for VC-containing groups. Histopathological assessments revealed significantly lower osteomyelitis scores and higher healing scores in the SF/CST-VC-PLGA/QC NPs, with reduced inflammatory cell infiltration and more organized connective tissue formation. In conclusion, SF/CST-VC-PLGA/QC NPs is an effective dual drug delivery system for osteomyelitis treatment, demonstrating significant antibacterial activity, enhanced bone regeneration, and reduced infection rate.

Drug-Free "Triboelectric Immunotherapy" Activating Immunity for Osteomyelitis Treatment and Recurrence Prevention.

Treatment of osteomyelitis is clinically challenging with low therapeutic efficacy and high risk of recurrence owing to the immunosuppressive microenvironment. Existing therapies are limited by drug concentration and single regulatory effect on the immune network, and emphasize the role of anti-inflammatory effects in reducing osteoclast rather than the role of proinflammatory effects in accelerating infection clearance, which is not conducive to complete bacteria elimination and recurrence prevention. Herein, a direct-current triboelectric nanogenerator (DC-TENG) is established to perform antibacterial effects and modulate immunological properties of infectious microenvironments of osteomyelitis through electrical stimulation, namely triboelectric immunotherapy. Seeing from the results, the triboelectric immunotherapy successfully activates polarization to proinflammatory (M1) macrophages in vitro, accompanied by satisfying direct antibacterial effects. The antibacterial and osteogenic abilities of triboelectric immunotherapy are verified in rat cranial osteomyelitis models. The effects on the polarization and differentiation of immune-related cells in vivo are investigated by establishing in situ tibial osteomyelitis models and immunosurveillance models in C57 mice respectively, indicating the ability of activating immunity and producing immunological memory for in situ infection and secondary recurrence, thus accelerating healing and preventing relapse. This study provides an efficient, long-acting, multifunctional, and wearable triboelectric immunotherapy strategy for drug-free osteomyelitis treatment systems.

Antibiotic-eluting scaffolds with responsive dual-release kinetics facilitate bone healing and eliminate S. aureus infection

Osteomyelitis (OM) is a progressive, inflammatory infection of bone caused predominately by Staphylococcus aureus. Herein, we engineered an antibiotic-eluting collagen-hydroxyapatite scaffold capable of eliminating infection and facilitating bone healing. An iterative freeze-drying and chemical crosslinking approach was leveraged to modify antibiotic release kinetics, resulting in a layered dual-release system whereby an initial rapid release of antibiotic to clear infection was followed by a sustained controlled release to prevent reoccurrence of infection. We observed that the presence of microbial collagenase accelerated antibiotic release from the crosslinked layer of the scaffold, indicating that the material is responsive to microbial activity. As exemplar drugs, vancomycin and gentamicin-eluting scaffolds were demonstrated to be bactericidal, and supported osteogenesis in vitro. In a pilot murine model of OM, vancomycin-eluting scaffolds were observed to reduce S. aureus infection within the tibia. Finally, in a rabbit model of chronic OM, gentamicin-eluting scaffolds both facilitated radial bone defect healing and eliminated S. aureus infection. These results show that antibiotic-eluting collagen-hydroxyapatite scaffolds are a one-stage therapy for OM, which when implanted into infected bone defects simultaneously eradicate infection and facilitate bone tissue healing.

Exosomes derived from bone marrow mesenchymal stem cells induce the proliferation and osteogenic differentiation and regulate the inflammatory state in osteomyelitis in vitro model.

Chronic osteomyelitis is a chronic bone infection characterized by progressive osteonecrosis and dead bone formation, which is closely related to persistent infection and chronic inflammation. Exosomes derived from bone marrow-derived mesenchymal stem cells (BMSC) play an important role in bone tissue regeneration and the modulation of inflammatory processes. However, their role and mechanism of action in osteomyelitis have not been reported so far. This paper explores the potential effect of BMSC-derived exosomes on osteomyelitis in vitro model with the aim of providing a theoretical basis for the treatment of osteomyelitis in the future. In this study, exosomes were isolated and extracted from BMSCs and identified. MC3T3-E1 cells were treated with Staphylococcal protein A (SPA) to establish an in vitro model of osteomyelitis. Next, the effects of BMSC-derived exosomes on cell proliferation, apoptosis, angiogenesis, and autophagy in MC3T3-E1 cells treated with SPA were evaluated. Results showed that the proliferation ability of MC3T3-E1 cells increased after co-culture with BMSC-derived exosomes. Moreover, exosomes induced autophagy and osteogenic differentiation in MC3T3-E1 cells. The mRNA and protein levels of factors related to proliferation, differentiation, apoptosis, autophagy, and angiogenesis including β-Catenin, Runx2, Bcl-2, VEGFA, and Beclin-1 upregulated in SPA-treated MC3T3-E1 cells, whereas the levels of inflammatory cytokines including TNF-α, IL-1β, and IL-6 decreased in the supernatant. The results showed that exosomes derived from BMSCs may participate in the attenuation of osteomyelitis by inducing proliferation and osteogenic differentiation and regulating the inflammatory state in bone cells.

Genetic background affects neutrophil activity and determines the severity of autoinflammatory osteomyelitis in mice.

The knowledge about the contribution of the innate immune system to health and disease is expanding. However, to obtain reliable results, it is critical to select appropriate mouse models for in vivo studies. Data on genetic and phenotypic changes associated with different mouse strains can assist in this task. Such data can also facilitate our understanding of how specific polymorphisms and genetic alterations affect gene function, phenotypes, and disease outcomes. Extensive information is available on genetic changes in all major mouse strains. However, comparatively little is known about their impact on immune response and in particular on innate immunity. Here, we analyzed a mouse model of chronic multifocal osteomyelitis (CMO), an autoinflammatory disease driven exclusively by the innate immune system, which is caused by an inactivating mutation in the Pstpip2 gene. We investigated how the genetic background of BALB/c, C57BL/6J, and C57BL/6NCrl strains alters the molecular mechanisms controlling disease progression. While all mice developed the disease, symptoms were significantly milder in BALB/c and partially also in C57BL/6J when compared to C57BL/6NCrl. Disease severity correlated with the number of infiltrating neutrophils and monocytes and with the production of chemokines attracting these cells to the site of inflammation. It also correlated with increased expression of genes associated with autoinflammation, rheumatoid arthritis, neutrophil activation, and degranulation, resulting in altered neutrophil activation in vivo. Together, our data demonstrate striking effects of genetic background on multiple parameters of neutrophil function and activity influencing the onset and course of the CMO disease.

Gelatin-based nanoparticles and antibiotics: a new therapeutic approach for osteomyelitis?

The result of infection of bone with microorganisms is osteomyelitis and septic arthritis. Methicillin-resistant Staphylococcus aureus (MRSA) is responsible for most of its cases (more than 50%). Since MRSA is resistant to many treatments, it is accompanied by high costs and numerous complications, necessitating more effective new treatments. Recently, development of gelatin nanoparticles have attracted the attention of scientists of biomedicine to itself, and have been utilized as a delivery vehicle for antibiotics because of their biocompatibility, biodegradability, and cost-effectiveness. Promising results have been reported with gelatin modification and combinations with chemical agents. Although these findings have been suggested that gelatin has the potential to be a suitable option for continuous release of antibiotics in osteomyelitis and septic arthritis treatment, they still have not become routine in clinical practices. The most deliver antibiotic using gelatin-derived composites is vancomycin which is showed the good efficacy. To date, a number of pre-clinical studies evaluated the utility of gelatin-based composites in the management of osteomyelitis. Gelatin-based composites were found to have satisfactory performance in the control of infection, as well as the promotion of bone defect repair in chronic osteomyelitis models. This review summarized the available evidence which provides a new insight into gelatin-derived composites with controlled release of antibiotics.

Staphylococcus aureus infection initiates hypoxia-mediated STIP1 homology and U-box containing protein 1 upregulation to trigger osteomyelitis

Although little is known about the regulatory mechanisms underlying the pathogenesis of osteomyelitis caused by Staphylococcus aureus (S. aureus), hypoxia-inducible factor-1α (HIF-1α) and STIP1 homology and U-box containing protein 1 (STUB1) have been found to be up-regulated in both S. aureus infected MC3T3-E1 cells and in patients with osteomyelitis. HIF-1α directly targets STUB1 to induce its expression. In MC3T3-E1 cells infected with S. aureus, silencing HIF-1α and STUB1 and administering the hypoxia inhibitor IDF-11774 consistently increased the expression of OSX and RUNX2, as well as the levels of alizarin Red S and alkaline phosphatase activity. In a mouse model of osteomyelitis, S. aureus infection elevated HIF-1α expression and serum STUB1 levels. Interleukin (IL)-6, IL-1β, and C-reactive protein levels in serum were reduced after treatment with the hypoxia inhibitor IDF-11774. Following an infection with S. aureus, hypoxia was activated to cause STUB1 overexpression by directly targeting HIF-1α, ultimately causing osteomyelitis symptoms such as osteogenesis and mineralization defected and increased inflammation. This study presents a novel signaling cascade in the pathogenesis of osteomyelitis involving hypoxia/HIF-1α/STUB1. This signaling cascade may be a target for therapeutic interventions.

RANKL-mediated osteoclast formation is required for bone loss in a murine model of Staphylococcus aureus osteomyelitis

Staphylococcus aureus osteomyelitis leads to extensive bone destruction. Osteoclasts are bone resorbing cells that are often increased in bone infected with S. aureus. The cytokine RANKL is essential for osteoclast formation under physiological conditions but in vitro evidence suggests that inflammatory cytokines may by-pass the requirement for RANKL. The goal of this study was to determine whether RANKL-dependent osteoclast formation is essential for the bone loss that occurs in a murine model of S. aureus osteomyelitis. To this end, humanized-RANKL mice were infected by direct inoculation of S. aureus into a unicortical defect in the femur. Mice were treated with vehicle or denosumab, a human monoclonal antibody that inhibits RANKL, both before and during a 14-day infection period. The severe cortical bone destruction caused by infection was completely prevented by denosumab administration even though the bacterial burden in the femur was not affected. Osteoclasts were abundant near the inoculation site in vehicle-treated mice but absent in denosumab-treated mice. In situ hybridization demonstrated that S. aureus infection potently stimulated RANKL expression in bone marrow stromal cells. The extensive reactive bone formation that occurs in this osteomyelitis model was also reduced by denosumab administration. Lastly, there was a notable lack of osteoblasts near the infection site suggesting that the normal coupling of bone formation to bone resorption was disrupted by S. aureus infection. These results demonstrate that RANKL-mediated osteoclast formation is required for the bone loss that occurs in S. aureus infection and suggest that disruption of the coupling of bone formation to bone resorption may also contribute to bone loss in this condition.

Transcriptomic characteristics analysis of bone from chronic osteomyelitis

To explore the molecular mechanism of chronic osteomyelitis and to clarify the role of MAPK signal pathway in the pathogenesis of chronic osteomyelitis, by collecting and analyzing the transcriptional information of bone tissue in patients with chronic osteomyelitis. Four cases of traumatic osteomyelitis in limbs from June 2019 to June 2020 were selected, and the samples of necrotic osteonecrosis from chronic osteomyelitis (necrotic group), and normal bone tissue (control group) were collected. Transcriptome information was collected by Illumina Hiseq Xten high throughput sequencing platform, and the gene expression in bone tissue was calculated by FPKM. The differentially expressed genes were screened by comparing the transcripts of the Necrotic group and control group. Genes were enriched by GO and KEGG. MAP3K7 and NFATC1 were selected as differential targets in the verification experiments, by using rat osteomyelitis animal model and immunohistochemical analysis. A total of 5548 differentially expressed genes were obtained by high throughput sequencing by comparing the necrotic group and control group, including 2701 up-regulated and 2847 down-regulated genes. The genes enriched in MAPK pathway and osteoclast differentiation pathway were screened, the common genes expressed in both MAPK and osteoclast differentiation pathway were (inhibitor of nuclear factor κ subunit Beta, IκBKβ), (mitogen-activated protein kinase 7, MAP3K7), (nuclear factor of activated t cells 1, NFATC1) and (nuclear factor Kappa B subunit 2, NFκB2). In rat osteomyelitis model, MAP3K7 and NFATC1 were highly expressed in bone marrow and injured bone tissue. Based on the transcriptome analysis, the MAPK signaling and osteoclast differentiation pathways were closely related to chronic osteomyelitis, and the key genes IκBKβ, MAP3K7, NFATC1, NFκB2 might be new targets for clinical diagnosis and therapy of chronic osteomyelitis.

In situ generating CO gas for destroying bacterial biofilms

The resistance and impermeability of bacterial biofilms lead to incurable infections. Interference with bacterial respiration is the key to the eradication of bacterial biofilm, but breaking the deep-tissue biofilm barrier to disrupt bacterial respiration still lacks effective means. Here, we report a hydrogel microsphere that disrupts bacterial respiration, supports in situ production of carbon monoxide gas (CO) to enhance the oxygen-depleted environment of biofilms and disrupts the bacterial respiratory chain, eliminating the bacterial biofilm ecotone (BRDMs). Under the specific interaction of α-helical structure and bacterial biofilm, BRDMs rapidly anchored and accumulated on the surface of bacterial biofilm within 8 h. Meanwhile, 8.64 μM CO gas was released in situ under an oxidative stress environment to deeply penetrate the biofilm and continuously destroy bacterial terminal oxidase, block bacterial respiration and finally disintegrate the biofilm. In a model of osteomyelitis, BRDMs disrupt the ecotopic colonization of MRSA biofilms in deep tissues, reduce inflammation, restore internal environmental homeostasis and accelerate tissue regeneration. BRDMs could be designed to remove drug-resistant biofilms from a wide range of deep tissues.

Bacterial micro-aggregates as inoculum in animal models of implant-associated infections

Is it time to rethink the inoculum of animal models of implant-associated infections (IAI)? Traditionally, animal models of IAI are based on inoculation with metabolically active overnight cultures of planktonic bacteria or pre-grown surface-attached biofilms. However, such inoculums do not mimic the clinical initiation of IAI. Therefore, the present study aimed to develop a clinically relevant inoculum of low metabolic micro-aggregated bacteria. The porcine Staphylococcus aureus strain S54F9 was cultured in Tryptone Soya Broth (TSB) for seven days to facilitate the formation of low metabolic micro-aggregates. Subsequently, the aggregated culture underwent filtration using cell strainers of different pore sizes to separate micro-aggregates. Light microscopy was used to evaluate the aggregate formation and size in the different fractions, while isothermal microcalorimetry was used to disclose a low metabolic activity. The micro-aggregate fraction obtained with filter size 5–15 μm (actual measured mean size 32 μm) was used as inoculum in a porcine implant-associated osteomyelitis (IAO) model and compared to a standard overnight planktonic inoculum and a sham inoculum of 0.9 % saline. The micro-aggregate and planktonic inoculums caused IAO with the re-isolation of S. aureus from soft tissues, bones, and implants. However, compared to their planktonic counterpart, neither of the micro-aggregate inoculated animals showed signs of osteomyelitis, i.e., sequester, osteolysis, and pus at gross inspection. Furthermore, inoculation with low metabolic micro-aggregates resulted in a strong healing response with pronounced osteoid formation, comparable to sham animals. In conclusion, the formation and separation of low metabolic bacterial micro-aggregates into various size fractions is possible, however, planktonic bacteria were still seen in all size fractions. Inoculation with micro-aggregates caused a less-aggressive osteomyelitis i.e. combination of infected tissue and strong healing response. Therefore, the use of low metabolic micro-aggregates could be a relevant inoculum for animal models of less-aggressive and thereby slower developing IAI and add in to our understanding of the host-implant-bacteria interactions in slow-onset low-grade infections.

A Self-Transformed N-Chlorinated ε-Polylysine Coating Endows Titanium Implants with Programmed Integration of Robust Antibacterial and Pro-Osteogenic Abilities

Implant-associated infection and poor osseointegration are the main causes of orthopedic implantation failure. For a long-term successful implantation, simultaneously introducing prevention of infection and promotion of osteogenesis into implants is highly desired but remains a grand challenge. Inspired by the human immune mechanism of tissue repair under bacterial infection, we propose a self-transformed strategy for the modification of titanium with porous N-chlorinated ε-polylysine coating (Ti-PL-NCl) through pore-making, surface grafting and chlorination. The as-prepared Ti-PL-NCl exhibits an excellent antibacterial activity against S. aureus and E. coli in the presence of N-chloramine in the early stage, with an antibacterial rate as high as 95.8% and 99.4%, respectively. With the consumption of oxidative chlorine, the N─Cl groups of Ti-PL-NCl are transformed into N─H groups with moderate antibacterial yet strong pro-osteogenic abilities. The self-transformed N-chlorinated ε-polylysine coating enables Ti-PL-NCl to achieve long-lasting antibacterial activity as well as enhanced pro-osteogenesis, thus providing adaptive bioactivities for bone-implant integration. Rat implant-associated osteomyelitis model confirms that Ti-PL-NCl has excellent efficacy of infection prevention and osseointegration promotion. This work may provide a new paradigm of designing multifunctional implants to achieve long-term successful implantation.

Cytosolic nucleic acid sensors stimulate protective bone cell responses to Staphylococcus aureus

Abstract Staphylococcus aureus is the causative agent of osteomyelitis, an inflammatory infection of the bone. Despite available treatments, S. aureus invasion of resident bone cells limits antibiotic effectiveness and provides a protective niche for viable bacteria contributing to recurrent and persistent infections. Previously, we have demonstrated a significant increase in proinflammatory cytokines, chemokines, and osteoclastogenic factors in an in vivo model of localized Staphylococcal osteomyelitis. Interestingly, we also observed a significant production of type I IFNs in infected femurs compared to the contralateral control. It is now appreciated that resident bone cells express a variety of pattern recognition receptors for identification of pathogens and stimulation of immune responses. Here, we demonstrate that S. aureus infected osteoblasts produce significant increases in both mRNA encoding type I IFNs and protein. Our data demonstrates that cytosolic nucleic acids sensors, including the RNA sensor RIG-I and the DNA sensor cGAS, are upregulated by osteoblasts and initiate osteoblast responses to S. aureus challenge. Notably, S. aureus viability is necessary for stimulation of osteoblast production of type I IFNs. Furthermore, our data indicate that IFN-β serves to restrict intracellular S. aureus burden. Our ongoing studies seek to investigate the therapeutic potential of augmenting these protective bone cell responses in a murine model of Staphylococcal osteomyelitis.

Engineering Photothermal Catalytic CO2 Nanoreactor for Osteomyelitis Treatment by In Situ CO Generation.

Photocatalytic carbon dioxide (CO2) reduction is an effective method for in vivo carbon monoxide (CO) generation for antibacterial use. However, the available strategies mainly focus on utilizing visible-light-responsive photocatalysts to achieve CO generation. The limited penetration capability of visible light hinders CO generation in deep-seated tissues. Herein, a photothermal CO2 catalyst (abbreviated as NNBCs) to achieve an efficient hyperthermic effect and in situ CO generation is rationally developed, to simultaneously suppress bacterial proliferation and relieve inflammatory responses. The NNBCs are modified with a special polyethylene glycol and further embellished by bicarbonate (BC) decoration via ferric ion-mediated coordination. Upon exposure to 1064nm laser irradiation, the NNBCs facilitated efficient photothermal conversion and in situ CO generation through photothermal CO2 catalysis. Specifically, the photothermal effect accelerated the decomposition of BC to produce CO2 for photothermal catalytic CO production. Benefiting from the hyperthermic effect and in situ CO production, in vivo assessments using an osteomyelitis model confirmed that NNBCs can simultaneously inhibit bacterial proliferation and attenuate the photothermal effect-associated pro-inflammatory response. This study represents the first attempt to develop high-performance photothermal CO2 nanocatalysts to achieve in situ CO generation for the concurrent inhibition of bacterial growth and attenuation of inflammatory responses.

In situ formed antibacterial hydrogel with collagenase-responsive activity for prevention of MRSA-induced osteomyelitis

Osteomyelitis caused by methicillin-resistant Staphylococcus aureus (MRSA) is a challenging and life-threatening disease due to its long duration and deep site of occurrence. Herein, we design an in situ formed antibacterial hydrogel with collagenase-respontive activity for the prevention of MRSA-induced osteomyelitis. This hydrogel is constructed by chemical bonding between a 4-arm polyethylene glycol maleimide (4-Arm-PEG-Mal), an N-terminal maleimidated antimicrobial peptide (Mal-AMP) and a collagenase-cleavable peptide with two thiol groups (HS-VPM-SH). Collagenase-induced hydrogel cleavage confers on-demand delivery of the antimicrobial peptide, thereby enhancing the combating activity against MRSA in an infected environment. The designed hydrogel, namely AMP/VPM/PEG hydrogel, can be formed rapidly in situ under physiological conditions due to the rapid bonding between the maleimide and thiol groups. In the in vivo rat osteomyelitis model, the AMP/VPM/PEG hydrogel can be administered by simply injecting the 4-Arm-PEG-Mal and peptide solutions with a 26G needle, which is a minimally invasive method. In vivo evaluation further demonstrates that AMP/VPM/PEG hydrogel can successfully prevent MRSA-induced osteomyelitis. This work provides a minimally invasive approach for intramedullary delivery of antimicrobial peptides on-demand and may provide a viable strategy for the osteomyelitis prevention in clinic.

Eradication of Staphylococcus aureus in Implant-Associated Osteomyelitis by an Injectable In Situ-Forming Depot Antibiotics Delivery System.

Bone infections with Staphylococcus aureus are notoriously difficult to treat and have high recurrence rates. Local antibiotic delivery systems hold the potential to achieve high in situ antibiotic concentrations, which are otherwise challenging to achieve via systemic administration. Existing solutions have been shown to confer suboptimal drug release and distribution. Here we present and evaluate an injectable in situ-forming depot system termed CarboCell. The CarboCell technology provides sustained and tuneable release of local high-dose antibiotics. CarboCell formulations of levofloxacin or clindamycin with or without antimicrobial adjuvants cis-2-decenoic acid or cis-11-methyl-2-dodecenoic acid were tested in experimental rodent and porcine implant-associated osteomyelitis models. In the porcine models, debridement and treatment with CarboCell-formulated antibiotics was carried out without systemic antibiotic administration. The bacterial burden was determined by quantitative bacteriology. CarboCell formulations eliminated S. aureus in infected implant rat models. In the translational implant-associated pig model, surgical debridement and injection of clindamycin-releasing CarboCell formulations resulted in pathogen-free bone tissues and implants in 9 of 12 and full eradication in 5 of 12 pigs. Sustained release of antimicrobial agents mediated by the CarboCell technology demonstrated promising therapeutic efficacy in challenging translational models and may be beneficial in combination with the current standard of care.