PD-1/PD-L1 blockade is a potent adjuvant in treatment of Staphylococcus aureus osteomyelitis in mice

There is no effective therapy for implant-associated Staphylococcus aureus osteomyelitis, a devastating complication after orthopedic surgery. An immune-suppressive profile with up-regulated programmed cell death 1/programmed death ligand 1 (PD-1/PD-L1) was identified based on our transcriptional data (GEO: GSE166522) from a mouse model of S. aureus osteomyelitis. PD-1/PD-L1 expression was up-regulated mainly in F4/80+ macrophages surrounding the abscess in S. aureus-infected bone. Mechanistically, PD-1/PD-L1 activated mitophagy to suppress production of mitochondrial reactive oxygen species (ROS), suppressing the bactericidal function of macrophages. Using neutralizing antibodies for PD-L1 or PD-1, or knockout of PD-L1 adjuvant to gentamicin markedly reduced mitophagy in bone marrow F4/80+ cells, enhanced bacterial clearance in bone tissue and implants, and reduced bone destruction in mice. PD-1/PD-L1 expression was also increased in the bone marrow from individuals with S. aureus osteomyelitis. These findings uncover a so far unknown function of PD-1/PD-L1-mediated mitophagy in suppressing the bactericidal function of bone marrow macrophages.

Structural Analysis of Mitochondrial Dynamics-From Cardiomyocytes to Osteoblasts: A Critical Review

Mitochondria play a crucial role in cell physiology and pathophysiology. In this context, mitochondrial dynamics and, subsequently, mitochondrial ultrastructure have increasingly become hot topics in modern research, with a focus on mitochondrial fission and fusion. Thus, the dynamics of mitochondria in several diseases have been intensively investigated, especially with a view to developing new promising treatment options. However, the majority of recent studies are performed in highly energy-dependent tissues, such as cardiac, hepatic, and neuronal tissues. In contrast, publications on mitochondrial dynamics from the orthopedic or trauma fields are quite rare, even if there are common cellular mechanisms in cardiovascular and bone tissue, especially regarding bone infection. The present report summarizes the spectrum of mitochondrial alterations in the cardiovascular system and compares it to the state of knowledge in the musculoskeletal system. The present paper summarizes recent knowledge regarding mitochondrial dynamics and gives a short, but not exhaustive, overview of its regulation via fission and fusion. Furthermore, the article highlights hypoxia and its accompanying increased mitochondrial fission as a possible link between cardiac ischemia and inflammatory diseases of the bone, such as osteomyelitis. This opens new innovative perspectives not only for the understanding of cellular pathomechanisms in osteomyelitis but also for potential new treatment options.

Comparative efficacy of resorbable fiber wraps loaded with gentamicin sulfate or gallium maltolate in the treatment of osteomyelitis

The high incidence of osteomyelitis associated with critical-sized bone defects raises clinical challenges in fracture healing. Clinical use of antibiotic-loaded bone cement as an adjunct therapy is limited by incompatibility with many antimicrobials, sub-optimal release kinetics, and requirement of surgical removal. Furthermore, overuse of antibiotics can lead to bacterial modifications that increase efflux, decrease binding, or cause inactivation of the antibiotics. Herein, we compared the efficacy of gallium maltolate, a new metal-based antimicrobial, to gentamicin sulfate released from electrospun poly(lactic-co-glycolic) acid (PLGA) wraps in the treatment of osteomyelitis. In vitro evaluation demonstrated sustained release of each antimicrobial up to 14 days. A Kirby Bauer assay indicated that the gentamicin sulfate-loaded wrap inhibited the growth of osteomyelitis-derived isolates, comparable to the gentamicin sulfate powder control. In contrast, the gallium maltolate-loaded wrap did not inhibit bacteria growth. Subsequent microdilution assays indicated a lower than expected sensitivity of the osteomyelitis strain to the gallium maltolate with release concentrations below the threshold for bactericidal activity. A comparison of the selectivity indices indicated that gentamicin sulfate was less toxic and more efficacious than gallium maltolate. A pilot study in a contaminated femoral defect model confirmed that the sustained release of gentamicin sulfate from the electrospun wrap resulted in bacteria density reduction on the surrounding bone, muscle, and hardware below the threshold that impedes healing. Overall, these findings demonstrate the efficacy of a resorbable, antimicrobial wrap that can be used as an adjunct or stand-alone therapy for controlled release of antimicrobials in the treatment of osteomyelitis.

Deficiency of Lipin2 Results in Enhanced NF-κB Signaling and Osteoclast Formation in RAW-D Murine Macrophages

Lipin2 is a phosphatidate phosphatase that plays critical roles in fat homeostasis. Alterations in Lpin2, which encodes lipin2, cause the autoinflammatory bone disorder Majeed syndrome. Lipin2 limits lipopolysaccharide (LPS)-induced inflammatory responses in macrophages. However, little is known about the precise molecular mechanisms underlying its anti-inflammatory function. In this study, we attempted to elucidate the molecular link between the loss of lipin2 function and autoinflammatory bone disorder. Using a Lpin2 knockout murine macrophage cell line, we showed that lipin2 deficiency enhances innate immune responses to LPS stimulation through excessive activation of the NF-κB signaling pathway, partly because of TAK1 signaling upregulation. Lipin2 depletion also enhanced RANKL-mediated osteoclastogenesis and osteoclastic resorption activity accompanied by NFATc1 dephosphorylation and increased nuclear accumulation. These results suggest that lipin2 suppresses the development of autoinflammatory bone disorder by fine-tuning proinflammatory responses and osteoclastogenesis in macrophages. Therefore, this study provides insights into the molecular pathogenesis of monogenic autoinflammatory bone disorders and presents a potential therapeutic intervention.

Identification of Penicillin Binding Protein 4 (PBP4) as a critical factor for Staphylococcus aureus bone invasion during osteomyelitis in mice

Staphylococcus aureus infection of bone is challenging to treat because it colonizes the osteocyte lacuno-canalicular network (OLCN) of cortical bone. To elucidate factors involved in OLCN invasion and identify novel drug targets, we completed a hypothesis-driven screen of 24 S. aureus transposon insertion mutant strains for their ability to propagate through 0.5 μm-sized pores in the Microfluidic Silicon Membrane Canalicular Arrays (μSiM-CA), developed to model S. aureus invasion of the OLCN. This screen identified the uncanonical S. aureus transpeptidase, penicillin binding protein 4 (PBP4), as a necessary gene for S. aureus deformation and propagation through nanopores. In vivo studies revealed that Δpbp4 infected tibiae treated with vancomycin showed a significant 12-fold reduction in bacterial load compared to WT infected tibiae treated with vancomycin (p<0.05). Additionally, Δpbp4 infected tibiae displayed a remarkable decrease in pathogenic bone-loss at the implant site with and without vancomycin therapy. Most importantly, Δpbp4 S. aureus failed to invade and colonize the OLCN despite high bacterial loads on the implant and in adjacent tissues. Together, these results demonstrate that PBP4 is required for S. aureus colonization of the OLCN and suggest that inhibitors may be synergistic with standard of care antibiotics ineffective against bacteria within the OLCN.

Staphylococcus aureus is the most prevalent pathogen in osteomyelitis, and its infection of bone is difficult to cure. S. aureus colonization of the osteocyte lacuno-canalicular network (OLCN) of cortical bone has been identified as a novel pathogenetic mechanism in chronic osteomyelitis. To elucidate factors involved in OLCN invasion, we conducted an in vitro genetic screen that identified pbp4 as a critical gene for S. aureus cell deformation and propagation through nanopores and demonstrated that PBP4 is critical for OLCN colonization in murine osteomyelitis. Thus, PBP4 inhibitors may be novel drugs to treat osteomyelitis in combination with standard of care antibiotics.

MyD88 and IL-1R signaling drive antibacterial immunity and osteoclast-driven bone loss during Staphylococcus aureus osteomyelitis

Staphylococcus aureus is able to infect virtually all organ systems and is a frequently isolated etiologic agent of osteomyelitis, a common and debilitating invasive infection of bone. Treatment of osteomyelitis requires invasive surgical procedures and prolonged antibiotic therapy, yet is frequently unsuccessful due to extensive pathogen-induced bone damage that can limit antibiotic penetration and immune cell influx to the infectious focus. We previously established that S. aureus triggers profound alterations in bone remodeling in a murine model of osteomyelitis, in part through the production of osteolytic toxins. However, staphylococcal strains lacking osteolytic toxins still incite significant bone destruction, suggesting that host immune responses are also major drivers of pathologic bone remodeling during osteomyelitis. The objective of this study was to identify host immune pathways that contribute to antibacterial immunity during S. aureus osteomyelitis, and to define how these immune responses alter bone homeostasis and contribute to bone destruction. We specifically focused on the interleukin-1 receptor (IL-1R) and downstream adapter protein MyD88 given the prominent role of this signaling pathway in both antibacterial immunity and osteo-immunologic crosstalk. We discovered that while IL-1R signaling is necessary for local control of bacterial replication during osteomyelitis, it also contributes to bone loss during infection. Mechanistically, we demonstrate that S. aureus enhances osteoclastogenesis of myeloid precursors in vitro, and increases the abundance of osteoclasts residing on bone surfaces in vivo. This enhanced osteoclast abundance translates to trabecular bone loss, and is dependent on intact IL-1R signaling. Collectively, these data define IL-1R signaling as a critical component of the host response to S. aureus osteomyelitis, but also demonstrate that IL-1R-dependent immune responses trigger collateral bone damage through activation of osteoclast-mediated bone resorption.

Immunohistochemical detection of chemokine receptor 4 expression in chronic osteomyelitis confirms specific uptake in 68Ga-Pentixafor-PET/CT

Previous findings of our group showed the chemokine receptor CXCR4 as a suitable target in PET/CT-imaging of axial bone infections, early postoperative osteomyelitis and periprosthetic infections. The aim of this study was to verify specific uptake of ⁶⁸Ga-Pentixafor in chronic osteomyelitis.

METHODS

29 consecutive patients who underwent ⁶⁸Ga-Pentixafor-PET/CT with clinically suspected osteomyelitis were evaluated retrospectively. Bone tissues of 6 patients were available and evaluated by immunohistochemical staining for CXCR4 and autoradiography with ⁶⁸Ga-Pentixafor. Staining was performed with an anti-CXCR4 antibody. In order to detect lymphocytic infiltration and CXCR4-expressing lymphocytes double immunofluorescence with an anti-CD3 and anti-CXCR4 antibody was performed.

RESULTS

⁶⁸Ga-Pentixafor-PET/ CT was true positive in 16 and true negative in 13 patients. In available bone tissue samples, immunohistochemical staining of CXCR4 expression and autoradiography with ⁶⁸Ga-Pentixafor was highly positive. Double immunofluorescence was able to detect CXCR4-expressing T-lymphocytes within all bone samples while a control sample of noninfected tibial bone was negative for CXCR4.

CONCLUSION

⁶⁸Ga-Pentixafor-PET/CT specifically shows CXCR4-expressing immune cells in chronic osteomyelitis and is therefore a suitable method for imaging chronic infection of the skeleton.Der Chemokinrezeptor CXCR4 konnte in einer Pilotstudie unserer Arbeitsgruppe als geeignete Zielstruktur zur PET/CT-Bildgebung von frühen postoperativen und periprothetischen Osteomyelitiden sowie Osteomyelitiden im Stammskelett identifiziert werden. In dieser Studie haben wir untersucht, ob ⁶⁸Ga-Pentixafor spezifisch CXCR4-exprimierende Entzündungszellen in einer chronischen Osteomyelitis darstellen kann.

METHODEN

Es erfolgte eine retrospektive Auswertung von 29 Patienten mit klinischem Verdacht einer chronischen Osteomyelitis, die mittels ⁶⁸Ga-Pentixafor-PET/CT untersucht wurden. Hiervon lagen uns in 6 Fällen Knochengewebe zur immunhistochemischen und autoradiographischen Evaluation vor. Die Immunhistochemie wurde mit einem anti-CXCR4 Antikörper durchgeführt. Des Weiteren wurden ein anti-CD3 und der anti-CXCR4-Antikörper zur Detektion CXCR4-exprimierender Lymphozyten am Ort der Entzündung mittels Doppel- Immunfluoreszenz verwendet.

ERGEBNISSE

Die ⁶⁸Ga-Pentixafor-PET/CT war bei 16 Patienten richtig positiv und bei 13 Patienten richtig negativ. Die Färbungen der verfügbaren Knochenpräparate waren sowohl in der Immunhistochemie als auch in der Autoradiographie deutlich positiv. In der Immunfluoreszenz konnten zudem CXCR4-exprimierende Lymphozyten am Ort der Entzündung in allen Proben nachgewiesen werden. Die Kontrolle eines Präparats einer nicht infizierten distalen Tibia zeigte dagegen keine CXCR4-oder CD3-Expression.

FAZIT

Mit der ⁶⁸Ga-Pentixafor-PET/CT können spezifisch CXCR4-exprimierende Lymphozyten am Ort der Entzündung nachgewiesen werden. Die ⁶⁸Ga-Pentixafor-PET/CT stellt eine geeignete Methode in der Diagnostik chronischer Osteomyeltiden dar.

Biomimetic 3D in vitro model of biofilm triggered osteomyelitis for investigating hematopoiesis during bone marrow infections

In this work, we define the requirements for a human cell-based osteomyelitis model which overcomes the limitations of state of the art animal models. Osteomyelitis is a severe and difficult to treat infection of the bone that develops rapidly, making it difficult to study in humans. We have developed a 3D in vitro model of the bone marrow, comprising a macroporous material, human hematopoietic stem and progenitor cells (HSPCs) and mesenchymal stromal cells (MSCs). Inclusion of biofilms grown on an implant into the model system allowed us to study the effects of postoperative osteomyelitis-inducing bacteria on the bone marrow. The bacteria influenced the myeloid differentiation of HSPCs as well as MSC cytokine expression and the MSC ability to support HSPC maintenance. In conclusion, we provide a new 3D in vitro model which meets all the requirements for investigating the impact of osteomyelitis.

STATEMENT OF SIGNIFICANCE

Implant-associated osteomyelitis is a persistent bacterial infection of the bone which occurs in many implant patients and can result in functional impairments or even entire loss of the extremity. Nevertheless, surprisingly little is known on the triangle interaction between implant material, bacterial biofilm and affected bone tissue. Closing this gap of knowledge would be crucial for the fundamental understanding of the disease and the development of novel treatment strategies. For this purpose, we developed the first biomaterial-based system that is able to mimic implant-associated osteomyelitis outside of the body, thus, opening the avenue to study this fatal disease in the laboratory.

Implant-Associated Posttraumatic Osteomyelitis: Collateral Damage by Local Host Defense?

Infections following osteosynthesis or total joint replacement, also known as “implant-associated posttraumatic osteomyelitis”, represent a major complication in orthopedic and trauma surgery. While the formation of bacterial biofilms on the implanted osteosynthesis materials is generally accepted as cause of the persistent infection, the molecular mechanisms leading to the progressive and destructive local inflammatory process and eventually to bone degradation, the osteolysis, have not been delineated. Here we provide evidence supporting the hypothesis that it is not the infection per se that causes tissue degradation and osteolysis, but rather the cytotoxic, proteolytic, and proinflammatory effector functions of cells of the host defense, particularly of the infiltrating polymorphonuclear neutrophils.

Application of white blood cell SPECT/CT to predict remission after a 6 or 12 week course of antibiotic treatment for diabetic foot osteomyelitis

AIMS/HYPOTHESIS

Diabetic foot osteomyelitis is a major risk factor for amputation. Medical treatment allows remission in 53-82% of cases. However, the optimal duration of antibiotic therapy remains controversial as a validated marker of osteomyelitis remission is lacking. The aim of this cohort study was to assess prospectively the remission rate of diabetic foot osteomyelitis medically treated using white blood cell (WBC)-single-photon emission computed tomography (SPECT)/computed tomography (CT) as a predictive marker of remission.

METHODS

Individuals with diabetic foot osteomyelitis that was non-surgically treated between April 2014 and December 2015 were included. All participants were treated with antibiotics alone. WBC-SPECT/CT was performed at 6 weeks and antibiotic treatment discontinued if the clinical signs of soft-tissue infection had resolved and there was no abnormal uptake of labelled WBCs. Treatment was otherwise continued for a total of 12 weeks and then discontinued. For these individuals, another WBC-SPECT/CT was performed at 12 weeks. Remission was defined as the absence of recurrence of osteomyelitis at the same location at 1 year.

RESULTS

Forty-five individuals were included; overall remission rate was 84% at 1 year. A 6 week course of antibiotics was used in 23 participants, 22 of whom were in remission at 1 year (96%); a 12 week course was used for 22 participants, 16 of whom were in remission at 1 year (73%). Sensitivity of WBC-SPECT/CT at 12 weeks was 100%, specificity 56%, positive predictive value 46% and negative predictive value 100%.

CONCLUSIONS/INTERPRETATION

The study suggests that WBC-SPECT/CT could predict remission at the end of antibiotic treatment.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02927678.

Targeting osteomyelitis with complete [99mTc]besilesomab and fragmented [99mTc]sulesomab antibodies: kinetic evaluations

BACKGROUND

The aim of this retrospective study was to compare the targeting of "pure" osteomyelitis (i.e., without surrounding soft tissue infection) by directly 99mTc-labelled complete immunoglobulin G (IgG) monoclonal antibody (MAb) ([99mTc]besilesomab) and by directly 99mTc-labelled fragment antigen-binding (FAb) MAb ([99mTc]sulesomab) in relation to their kinetic fate. A total of 73 patients with "pure" osteomyelitis were examined with [99mTc]besilesomab, (Scintimun®, IBA/CIS bio international, Saclay, France; N.=38) and [99mTc]sulesomab (LeukoScan®, Immunomedics Inc., Morris Plains, NJ, USA; N.=35).

METHODS

Kinetic data were deduced from whole-body and single-photon emission computed tomographic scans, performed 10 minutes to 24 hour p.i. (region-of-interest technique [ROI]).

RESULTS

In targeting "pure" osteomyelitis, sensitivities at 1-4 hours were found to be higher for [99mTc]sulesomab (44% and 80% for [99mTc]besilesomab and [99mTc]sulesomab, respectively) but at significantly lower target/background (T/B) ratios than with [99mTc]besilesomab (1.8±0.3 versus 1.4±0.5 for [99mTc]besilesomab and [99mTc]sulesomab respectively; P<0.01). With [99mTc]besilesomab, there was a continuous osteomyelitis uptake over 24 hours, whereas with [99mTc]sulesomab, the maximal uptake occurred mostly within 1-4 hours, with subsequent clearance being slower for antigen-bound activity than for nonspecific background. Hence, diagnosis was possible mostly after 4h with [99mTc]sulesomab but often not before 24 hours with [99mTc]besilesomab, the later increasing significantly (P<0.01) in sensitivity (87% and 84% for [99mTc]besilesomab and [99mTc]sulesomab, respectively).

CONCLUSIONS

These results show that the higher sensitivity of [99mTc]sulesomab in osteomyelitis targeting at earlier p.i. times does not rely on an increased antibody uptake but on a more rapid clearance of nonspecific background activity due to faster metabolism and excretion. Intact [99mTc]besilesomab show a slow, continuous uptake, leading to higher T/B at later p.i. times, often beyond the imaging possibilities of 99mTc.

The Efficacy of Boric Acid Used to Treat Experimental Osteomyelitis Caused by Methicillin-Resistant Staphylococcus aureus: an In Vivo Study

We explored the ability of local and systemic applications of boric acid (BA) to reduce the numbers of methicillin-resistant Staphylococcus aureus (MRSA) in a rat model of tibial osteomyelitis (OM), and compared boric acid with vancomycin (V). Implant-associated osteomyelitis was established in 35 rats. After 4 weeks, at which time OM was evident both radiologically and serologically in all animals, the rats were divided into five groups of equal number: group 1, control group (no local application of BA or other medication); group 2, V group; group 3, local BA + V group; group 4, local BA group; and group 5, local + systemic BA group. Serum total antioxidant status, and the levels of tumor necrosis factor (TNF)-α and interleukin (IL)-6, were measured. Pathological changes attributable to bone OM were evaluated using a grading system. Bacterial colony-forming units (CFUs) per gram of bone were counted. The lowest bacterial numbers were evident in group 3, and the bacterial numbers were significantly lower than that of the control group in all four test groups (p < 0.001). Group 3 also had the least severe bone infection (OM score 1.7 ± 1.1, p < 0.05). Upon histological and microbiological evaluation, no significant difference was evident between groups 2 and 3. Total antioxidant levels were significantly different in all treatment groups compared to the control group. Microbiological and histopathological evaluation showed that systemic or local application of BA was effective to treat OM, although supplementary V increased the effectiveness of BA.

Diagnostic value of sinus tract culture versus intraoperative bone culture in patients with chronic osteomyelitis

To compare the organisms isolated from the sinus tract culture and intraoperative bone culture in patients with chronic osteomyelitis. This cross sectional prospective study was conducted from February 2015 to March 2016. Ninety consecutive patients were enrolled in study (n=90). Inclusion criteria were patients with either sex, any age, chronic osteomyelitis having discharging sinus. Sample from sinus tracts and bone were taken through standardized aseptic technique and organism were cultured. There were 62 males and 28 females, male to female ratio 3:1, mean age was 40 years. 23 patients had primary osteomyelitis and 67 had secondary osteomyelitis. 68 patients had orthopaedic implant infections. In 61/90 (67%) patients the same organism was isolated on both sinus tract and intraoperative cultures.In our scenario we found that within the limitations of this study, there was a high ratio of agreement between the sinus tract and intraoperative cultures. We conclude that if used judiciously, sinus tract cultures can yield accurate results in the majority of cases.

Phenol-Soluble Modulins Contribute to Early Sepsis Dissemination Not Late Local USA300-Osteomyelitis Severity in Rabbits

Introduction

In bone and joint infections (BJIs), bacterial toxins are major virulence factors: Panton—Valentine leukocidin (PVL) expression leads to severe local damage, including bone distortion and abscesses, while α-hemolysin (Hla) production is associated with severe sepsis-related mortality. Recently, other toxins, namely phenol-soluble modulins (PSMs) expressed by community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) strain USA300 (LAC WT) were shown to have ex vivo intracellular cytotoxic activity after S. aureus invasion of osteoblasts, but their in vivo contribution in a relatively PVL-sensitive osteomyelitis model remains poorly elucidated.

Materials and Methods

We compared the outcomes of experimental rabbit osteomyelitises induced with pvl⁺hla⁺psms⁺ LAC WT and its isogenic Δpsm derivatives (LAC Δpsmα and LAC Δpsmαβhld) using an inoculum of 3 × 10⁸ CFUs. Mortality, hematogenous spread (blood culture, spleen and kidney), lung and bone involvements were assessed in two groups (non-survivors of severe sepsis and survivors sacrificed on day (D) 14).

Results

Severe sepsis-related mortality tended to be lower for Δpsm derivatives (Kaplan—Meier curves, P = .06). Non-survivors’ bone LAC-Δpsmα (6.9 log₁₀ CFUs/g of bone, P = .04) or -Δpsmαβhld (6.86 log₁₀ CFUs/g of bone, P = .014) densities were significantly higher than LAC WT (6.43 log₁₀ CFUs/g of bone). Conversely, lung Δpsmαβhld CFUs were significantly lower than LAC WT (P = .04). LAC Δpsmα, Δpsmαβhld and WT induced similar bone damage in D14 survivors, with comparable bacterial densities (respectively: 5.89, 5.91, and 6.15 log₁₀ CFUs/g of bone). Meanwhile, pulmonary histological scores of inflammation were significantly higher for LAC Δpsmα- and Δpsmαβhld-infected rabbits compared to LAC WT (P = .04 and .01, respectively) but with comparable lung bacterial densities.

Conclusion

Our experimental results showed that deactivating PSM peptides significantly limited bacterial dissemination from bone during the early phase of infection, but did not affect local severity of USA300 rabbit osteomyelitis.

Genomic Heterogeneity of Methicillin Resistant Staphylococcus aureus Associated with Variation in Severity of Illness among Children with Acute Hematogenous Osteomyelitis

Introduction

The association between severity of illness of children with osteomyelitis caused by Methicillin-resistant Staphylococcus aureus (MRSA) and genomic variation of the causative organism has not been previously investigated. The purpose of this study is to assess genomic heterogeneity among MRSA isolates from children with osteomyelitis who have diverse severity of illness.

Materials and Methods

Children with osteomyelitis were prospectively studied between 2010 and 2011. Severity of illness of the affected children was determined from clinical and laboratory parameters. MRSA isolates were analyzed with next generation sequencing (NGS) and optical mapping. Sequence data was used for multi-locus sequence typing (MLST), phylogenetic analysis by maximum likelihood (PAML), and identification of virulence genes and single nucleotide polymorphisms (SNP) relative to reference strains.

Results

The twelve children studied demonstrated severity of illness scores ranging from 0 (mild) to 9 (severe). All isolates were USA300, ST 8, SCC mec IVa MRSA by MLST. The isolates differed from reference strains by 2 insertions (40 Kb each) and 2 deletions (10 and 25 Kb) but had no rearrangements or copy number variations. There was a higher occurrence of virulence genes among study isolates when compared to the reference strains (p = 0.0124). There were an average of 11 nonsynonymous SNPs per strain. PAML demonstrated heterogeneity of study isolates from each other and from the reference strains.

Discussion

Genomic heterogeneity exists among MRSA isolates causing osteomyelitis among children in a single community. These variations may play a role in the pathogenesis of variation in clinical severity among these children.

Evaluation of the Enterococcus faecalis Biofilm-Associated Virulence Factors AhrC and Eep in Rat Foreign Body Osteomyelitis and In Vitro Biofilm-Associated Antimicrobial Resistance

Enterococcus faecalis can cause healthcare-associated biofilm infections, including those of orthopedic devices. Treatment of enterococcal prosthetic joint infection is difficult, in part, due to biofilm-associated antimicrobial resistance. We previously showed that the E. faecalis OG1RF genes ahrC and eep are in vitro biofilm determinants and virulence factors in animal models of endocarditis and catheter-associated urinary tract infection. In this study, we evaluated the role of these genes in a rat acute foreign body osteomyelitis model and in in vitro biofilm-associated antimicrobial resistance. Osteomyelitis was established for one week following the implantation of stainless steel orthopedic wires inoculated with E. faecalis strains OG1RF, ΩahrC, and ∆eep into the proximal tibiae of rats. The median bacterial loads recovered from bones and wires did not differ significantly between the strains at multiple inoculum concentrations. We hypothesize that factors present at the infection site that affect biofilm formation, such as the presence or absence of shear force, may account for the differences in attenuation in the various animal models we have used to study the ΩahrC and ∆eep strains. No differences among the three strains were observed in the planktonic and biofilm antimicrobial susceptibilities to ampicillin, vancomycin, daptomycin, linezolid, and tetracycline. These findings suggest that neither ahrC nor eep directly contribute to E. faecalis biofilm-associated antimicrobial resistance. Notably, the experimental evidence that the biofilm attachment mutant ΩahrC displays biofilm-associated antimicrobial resistance suggests that surface colonization alone is sufficient for E. faecalis cells to acquire the biofilm antimicrobial resistance phenotype.

The calcium phosphate matrix of FGF-2-apatite composite layers contributes to their biological effects

The purpose of the present study was to fabricate fibroblast growth factor (FGF)-2-apatite composite layers on titanium (Ti) pins in one step at 25 °C using a supersaturated calcium phosphate (CaP) solution, and to evaluate the physicochemical characteristics and biological effects of the coated Ti pins compared with coated Ti pins fabricated at 37 °C. Ti pins were immersed in a supersaturated CaP solution containing 0.5, 1.0, or 2.0 µg/mL FGF-2 at 25 °C for 24 h (25F0.5, 25F1.0, and 25F2.0) or containing 4.0 µg/mL FGF-2 at 37 °C for 48 h (37F4.0). Except for the 25F0.5, the chemical compositions and the mitogenic activity levels of FGF-2 of the composite layers formed by these two methods were similar, except for the Ca/P molar ratio, which was markedly smaller at 25 °C (1.55-1.56±0.01-0.02, p=0.0008-0.0045) than at 37 °C (1.67±0.11). Thus, either the apatite was less mature or the amount of amorphous calcium phosphate was higher in the composite layer formed at 25 °C. In vivo, the pin tract infection rate by visual inspection for 37F4.0 (45%) was lower than that for 25F1.0 (80%, p=0.0213), and the rate of osteomyelitis for 37F4.0 (35%) was lower than that for 25F0.5 (75%, p=0.0341). The extraction torque for 37F4.0 (0.276±0.117 Nm) was higher than that for 25F0.5 (0.192±0.117 Nm, p=0.0142) and that for 25F1.0 (0.176±0.133 Nm, p=0.0079). The invasion rate of S. aureus for 37F4.0 (35%) was lower than that for 25F0.5 (75%, p=0.0110). On the whole, the FGF-2-apatite composite layer formed at 25 °C tended to be less effective at improving fixation strength in the bone-pin interface and resisting pin tract infections. These results suggest that the chemistry of the calcium phosphate matrix that embeds FGF-2, in addition to FGF-2 content and activity, has a significant impact on composite infection resistance and fixation strength.

The potential role of increasing the release of mouse β- defensin-14 in the treatment of osteomyelitis in mice: a primary study

Mammalian β-defensins are small cationic peptides that have been implicated in mediating innate immune defenses against microbial infection. Mouse β-defensin-14 (MBD-14), based on structural and functional similarities, appears to be an ortholog of human β-defensin-3 (HBD-3). Previous studies identified signaling pathway p38 mitogen-activated protein kinase (MAPK) that contributed to the expression of MBD-14 in mouse osteoblasts upon contacted with methicillin-resistance Staphylococcus aureus (MRSA) supernatant, which provided a theoretical basis as a promising therapeutic target in the treatment of intramedullary infection with MRSA in vivo. In this study, the medullary cavities of tibiae were contaminated with MRSA 10(3) colony forming units and different doses of p38 MAPK agonists anisomycin were followed as group III or IV in 30 mice. Fifteen animals that received phosphate- buffered saline served as group II and 15 mice were not contaminated with MRSA and received phosphate-buffered saline served as controls (group I). Follow-up was 7 days. In day 1, day 4 and day 7 postoperatively, infection was evaluated by blood routine, microbiological and histological analyses after sacrifice. All animals of group II developed microbiological and histological signs of infection. Histological signs of infection, white blood counts and cultures of group III and IV showed significantly reduced bacterial growth compared to cultures of group II. Simultaneously, different doses of anisomycin significantly induced the expression of osteoblast-associated genes, including alkaline phosphatase, osteocalcin and collagen type I. In addition, the expression of HBD-3 in human interfacial membranes around infected periprosthetic joint by staphylococcus contaminated was evaluated, and the expression pattern changed with significant induction of HBD-3 in infected periprosthetic joint compared with aseptic loosening under inflammatory conditions. Our primary study indicated that the potential antibacterial role of increased MBD-14 in the osteomyelitis mouse model.

PSTPIP2 deficiency in mice causes osteopenia and increased differentiation of multipotent myeloid precursors into osteoclasts

Missense mutations that reduce or abrogate myeloid cell expression of the F-BAR domain protein, proline serine threonine phosphatase-interacting protein 2 (PSTPIP2), lead to autoinflammatory disease involving extramedullary hematopoiesis, skin and bone lesions. However, little is known about how PSTPIP2 regulates osteoclast development. Here we examined how PSTPIP2 deficiency causes osteopenia and bone lesions, using the mouse PSTPIP2 mutations, cmo, which fails to express PSTPIP2 and Lupo, in which PSTPIP2 is dysfunctional. In both models, serum levels of the pro-osteoclastogenic factor, MIP-1α, were elevated and CSF-1 receptor (CSF-1R)-dependent production of MIP-1α by macrophages was increased. Treatment of cmo mice with a dual specificity CSF-1R and c-Kit inhibitor, PLX3397, decreased circulating MIP-1α and ameliorated the extramedullary hematopoiesis, inflammation, and osteopenia, demonstrating that aberrant myelopoiesis drives disease. Purified osteoclast precursors from PSTPIP2-deficient mice exhibit increased osteoclastogenesis in vitro and were used to probe the structural requirements for PSTPIP2 suppression of osteoclast development. PSTPIP2 tyrosine phosphorylation and a functional F-BAR domain were essential for PSTPIP2 inhibition of TRAP expression and osteoclast precursor fusion, whereas interaction with PEST-type phosphatases was only required for suppression of TRAP expression. Thus, PSTPIP2 acts as a negative feedback regulator of CSF-1R signaling to suppress inflammation and osteoclastogenesis.

New PMMA-based composites for preparing spacer devices in prosthetic infections

Even though the systemic antibiotic therapy is usually applied after prosthetic infections surgical treatments, it is unable to reach the infection site in sufficient concentrations to eradicate bacteria. Delivering antibiotics locally with the use of custom made device (spacer or nail coating) might eradicate or reduce the infection and the risk of recolonization, providing a very high concentration of antibiotic. PMMA-based (Mendec Spine) composites with BaSO(4) were enriched with β-tricalcium phosphate (Porosectan-TCP) or only a slightly higher BaSO(4) concentration (Porosectan-BaSO(4)) to obtain higher porosity. The aim of the study was to evaluate: (i) drug absorption capability and drug release kinetics in vitro soaking them with a combined solution of gentamicin and vancomycin, (ii) their in vitro and in vivo biocompatibility, and finally, (iii) they were tested preliminarily in an experimental model of bone infection. The simultaneous presence of β-TCP and BaSO(4) resulted in the formation of a texture of interconnecting channels with different diameters, from a few microns to several hundred microns, which totally filled the material. The porosity, determined by microcomputed tomography, was significantly higher in both tested plain composites (Porosectan-TCP: +17.3%; Porosectan-BaSO(4): +7.5%) in comparison to control composite material (Mendec Spine). The kinetics of antibiotic release from composites was rapid and complete, producing high drug concentrations for a short period of time. Both composites showed a good level of biocompatibility. The osteomyelitic model confirmed that both composites, soaked in antibiotic solution, were able to cure bone infection. These composites could be useful for preparing devices for prosthetic joint infections treatment also allowing the use of antibiotics solution at required concentrations.

Can procalcitonin predict bone infection in people with diabetes with infected foot ulcers? A pilot study

AIMS

The diagnosis of osteomyelitis is a key step of diabetic foot management. Previous studies showed that procalcitonin (PCT), a novel infection marker, is superior to conventional infection markers in the diagnosis of diabetic foot infection. This study aimed to investigate the serum levels of PCT and other conventional infection markers in diabetic persons with and without osteomyelitis.

METHODS

Twenty-four patients (18 male, mean age: 61.9±10.8 years) with infected foot ulcers were prospectively enrolled. Clinical characteristics of the wounds were noted. Blood samples were obtained for biochemical analysis. Magnetic resonance imaging of the foot was performed in all patients to diagnose osteomyelitis.

RESULTS

Osteomyelitis was found in 13 of 24 (54%) patients. PCT levels were 66.7±43.5 pg/ml in patients with osteomyelitis and 58.6±35.5 pg/ml in patients without osteomyelitis. The difference did not reach statistical significance (p=0.627). Erythrocyte sedimentation rate, but not C-reactive protein and white blood cell count, was found significantly higher in patients with osteomyelitis.

CONCLUSION

In this group of patients, PCT failed to discriminate patients with bone infection. Erythrocyte sedimentation rate can be used as a marker of osteomyelitis in diabetic persons.

Attachment of Staphylococcus aureus is required for activation of nuclear factor kappa B in human osteoblasts

Nuclear factor kappa B (NF-κB) plays a prominent role in the pathogenesis of infectious diseases. Staphylococcus aureus (S. aureus), which can attach to and invade human osteoblasts, is the most common causative agent of osteomyelitis. To determine whether S. aureus can activate NF-κB in human osteoblasts and explore the possible factors of activation in response to infection, we used flow cytometry, enzyme-linked immunosorbent assay, immunoblots, and electrophoretic mobility shift assays to quantify the invasion of bacteria, to measure the interleukin-6 (IL-6) of culture supernatants, and to investigate the IκBα degradation and NF-κB activation in human osteoblasts. Moreover, we explored the possible factors responsible for the activation of NF-κB by preventing S. aureus from physically touching human osteoblasts or inhibiting the invasion of S. aureus into human osteoblasts under co-culture conditions, by incubating proteinase K-treated or ultraviolet-killed S. aureus with human osteoblasts and by treating human osteoblasts with peptidoglycan (PGN) or lipoteichoic acid (LTA). We found that S. aureus induced the IκBα degradation and NF-κB activation, which could regulate IL-6 secretion in the culture supernatants of human osteoblasts in response to infection. In addition, the maximal IκBα degradation and NF-κB activation in human osteoblasts occurred prior to the maximal invasion of S. aureus. It was the attachment not invasion or the secreted soluble factor(s), PGN, LTA of S. aureus, that could induce the IκBα degradation and NF-κB activation in human osteoblasts. These results indicated that S. aureus can activate NF-κB in human osteoblasts and that the attachment of S. aureus is required for this activation in response to infection.

Panton-valentine leukocidin enhances the severity of community-associated methicillin-resistant Staphylococcus aureus rabbit osteomyelitis

Background

Extensive spread of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) in the United States, and the concomitant increase in severe invasive staphylococcal infections, including osteomyelitis, in healthy children, has led to renewed interest in Panton-Valentine leukocidin (PVL). However, the pathogenetic role of PVL in staphylococcal infections remains controversial, possibly because it depends on the site of infection.

Methodology/Principal Findings

We compared the course of experimental rabbit osteomyelitis due to the PVL-positive CA-MRSA strain USA 300 (LAC) and its PVL-negative isogenic derivative (LACΔpvl), using a low and a high inoculum (8×10⁵ and 4×10⁸ CFU). With the low inoculum, bone infection was less frequent on day 7 (D7) and day 28 (D28) with LACΔpvl than with LAC (respectively 12/19 and 18/19 animals, p = 0.042). With the high inoculum of both strains, all the animals were infected on D7 and the infection persisted on D28 in almost every case. However, tibial bacterial counts and the serum CRP concentration fell significantly between D7 and D28 with LACΔpvl but not with LAC. Respectively 67% and 60% of LAC-infected rabbits had bone deformation and muscle/joint involvement on D7, compared to 0% and 7% of LACΔpvl-infected rabbits (p = 0.001 and p = 0.005 respectively). Between D0 and D28, the anti-PVL antibody titer increased significantly only with the high inoculum of LAC.

Conclusions/Significance

PVL appears to play a role in the persistence and rapid local extension of rabbit osteomyelitis, in keeping with the greater severity of human bone infections due to PVL-positive S. aureus. The possible therapeutic implications of these findings are discussed.

[Mechanisms of disturbance in regenerative processes in chronic traumatic osteomyelitis]

Analysis of long-term observation and treatment of patients with long bone fractions complicated by chronic traumatic osteomyelitis and relevant literature data made it possible to elucidate general and local mechanisms of disturbance of regenerative processes. Key pathogenetic factors in chronic traumatic osteomyelitis proved to be stress reaction, impaired functional thyroid activity, suppressed immune responsiveness, disturbed bone metabolism, dysbalance of micro- and macroelements, secondary disturbances of peripheral blood flow in the affected limb segment (chronic venous insufficiency), formation of Staphylococcus-dominated microflora in wound discharge, enhanced pathological bone resorption followed by regional osteoporotic changes. It is concluded that the development of pathogenetically-sound treatment modalities based on the above findings will help to avoid undesirable outcomes of chronic traumatic osteomyelitis.

Efficacies of ceftobiprole medocaril and comparators in a rabbit model of osteomyelitis due to methicillin-resistant Staphylococcus aureus

The pharmacokinetics and distribution into bone tissue of ceftobiprole in uninfected New Zealand White rabbits were determined after subcutaneous administration of the prodrug ceftobiprole medocaril. Serum exposure (maximum concentration of the drug in serum, trough concentration, area under the concentration-time curve) to ceftobiprole at 20 and 80 mg/kg was dose proportional, and there was no accumulation of ceftobiprole following repeated (every 6 h [q6h]) injections of the antibiotic. Ceftobiprole titers in the tibial matrix and marrow were 3.2 +/- 1.3 microg/g and 11.2 +/- 6.5 microg/g, respectively, in uninfected animals treated with 20 mg/kg of the antibiotic and 13.4 +/- 7.3 microg/g and 66.3 +/- 43.2 microg/g, respectively, in uninfected animals treated with 80 mg/kg of the antibiotic. No differences in ceftobiprole titers were observed between right and left tibiae for either bone matrix or marrow. The efficacies of 4 weeks of treatment with ceftobiprole (40 mg/kg administered subcutaneously [s.c.] q6h), vancomycin (30 mg/kg administered s.c. q12h), or linezolid (60 mg/kg administered orally q8h) were compared, using a rabbit model of methicillin-resistant Staphylococcus aureus tibial osteomyelitis. After treatment with ceftobiprole, the bacterial titers in all infected left tibiae from evaluable rabbits were below the level of detection, whereas only 73% of infected left tibiae from vancomycin- or linezolid-treated animals had bacterial titers below the level of detection; the mean titers of ceftobiprole were 3 to 5 times higher in infected left tibiae than in uninfected right tibiae. These results indicate that ceftobiprole provided effective parenteral treatment of osteomyelitis in this rabbit model.

Chronic recurrent multifocal osteomyelitis: a concise review and genetic update

Chronic recurrent multifocal osteomyelitis is an autoinflammatory disorder characterized by bone pain and fever, a course of exacerbations and remissions, and a frequent association with other inflammatory conditions. Because its etiology is largely unknown, the diagnosis is still based on clinical criteria; treatment is empiric and not always successful. The diagnosis is supported by the presence of osteolytic lesions with surrounding sclerosis apparent on radiographs, and silent asymptomatic lesions frequently appear on nuclear scans. The histologic findings in bone biopsies are nonspecific, showing inflammatory changes with granulocytic infiltration. Several observations suggest the contribution of genetic factors to the etiology of chronic recurrent multifocal osteomyelitis. Indeed, mutations in LPIN2 cause a syndromic form of chronic recurrent multifocal osteomyelitis known as Majeed syndrome, while mutations in pstpip2 cause a murine form of the disorder. The roles played by LPIN2 and the human homolog of pstpip2, PSTPIP2, in the etiology of chronic recurrent multifocal osteomyelitis are uncertain but are currently being investigated. We emphasize the need to validate diagnostic clinical criteria and develop new pathogenesis-based targeted therapy.

The Value of Quantitative Uptake of 99mTc-MDP and 99mTc-HMPAO White Blood Cells in Detecting Osteomyelitis in Violated Peripheral Bones

Our objective in this study was to evaluate whether measurement of quantitative uptake of (99m)Tc-methylene diphosphate (MDP) and (99m)Tc-hexamethylpropyleneamine oxime (HMPAO) white blood cells (WBCs) is useful in detecting osteomyelitis in peripheral bony lesions.

METHODS

Twenty-four patients (12 men and 12 women; age range, 25-72 y) were referred for imaging because of clinically suspected osteomyelitis. They had a traumatic fracture (n = 10), knee prosthesis (n = 5), hip prosthesis (n = 2), diabetic foot (n = 4), or chronic osteomyelitis (n = 3). Three-phase bone scanning and (99m)Tc-HMPAO WBC studies were performed on all patients within the same week. Regions of interest were drawn over the abnormal bony sites and the contralateral normal sites, and the abnormal-to-normal uptake ratios (A/N ratios) were obtained for both studies.

RESULTS

All patients had abnormal findings on 3-phase bone scanning, whereas 17 (71%) had abnormal findings on (99m)Tc-HMPAO WBC studies, of which 15 were confirmed to be true-positive. In those 15 patients, the mean A/N ratios for (99m)Tc-MDP and (99m)Tc-HMPAO WBC were 3.0 +/- 1.6 (range, 1.3-6.2) and 1.8 +/- 0.3 (range, 1.4-2.2), respectively. In the other 9 patients, whose scan results were clinically confirmed to be true-negative, the mean A/N ratios for (99m)Tc-MDP and (99m)Tc-HMPAO WBC were 2.1 +/- 1.2 and 1.2 +/- 0.2, respectively. In the group with a (99m)Tc-MDP A/N ratio greater than 2 (n = 15), 87% (13/15) had a high (99m)Tc-HMPAO WBC A/N ratio (>1.5), including 2 that were false-positive. In the remaining 2 patients, one with chronic osteomyelitis and the other with a recent hip prosthesis, (99m)Tc-HMPAO WBC ratios were normal. In the group with a bone A/N ratio of less than 2 (n = 9), only 4 patients (44%) were true-positive for acute osteomyelitis.

CONCLUSION

(99m)Tc-MDP bone scanning alone, with an A/N ratio of more than 2, is useful in detecting osteomyelitis in violated bone except in the case of a recent hip prosthesis or chronic osteomyelitis.

RANKL and cathepsin K in diffuse sclerosing osteomyelitis of the mandible

BACKGROUND

Diffuse sclerosing osteomyelitis (DSO) of the mandible is characterized by mixed bone resorption and formation.

METHODS

Immunohistopathology of DSO in the clinically acute and subacute phases was compared with healthy bone.

RESULTS

Receptor activator of nuclear factor kappaB ligand (RANKL) was found in DSO lesions. When it was used in vitro to stimulate monocytes, cathepsin K expression was observed in mononuclear prefusion precursors and in multinuclear giant cells. Similarly, exacerbations of DSO were characterized by RANKL and induction of cathepsin K in mononuclear precursor cells, which subsequently seem to differentiate into osteoclasts or foreign body giant cells. The proportion of bone to soft tissue increased with the duration of disease.

CONCLUSIONS

RANKL-driven osteoclastogenesis and acidic cysteine endoproteinase cathepsin K seem to play important roles in DSO as osteoclast-mediated bone resorption may represent the primary disease process later followed by new bone formation.

18F FDG-PET imaging in musculoskeletal infection

(18)F Fluorodeoxyglucose-positron emission tomography (FDG-PET) has become an encouraging imaging modality in musculoskeletal infection. This application has an incremental value in the assessment of both acute and chronic infection and has shown to be more accurate in detecting chronic osteomyelitis than conventional radionuclide imaging. Whether FDG-PET has the potential to replace conventional scintigraphy completely depends on a number of factors, including cost and availability. Conventional radionuclide studies have represented imaging methods of choice in the diagnosis of implant-associated infection in patients with trauma so far. However, nonspecific tissue uptake of imaging agents and limited spatial resolution restrict their usefulness. Magnetic resonance imaging (MRI) and computed tomography (CT) image quality is degraded in the presence of metallic implants due to susceptibility and beam-hardening artifacts, respectively. Although its role is still evolving, FDG-PET imaging will have increased importance in patients with metallic implants used for trauma surgery because FDG uptake is not hampered by metallic artifacts. In contrast to patients with metallic implants, PET may not be as useful in the diagnosis of infection in patients with failed total joint replacements. In this situation, combined 111Indium-labeled leucocyte/(99m)Tc-sulfur colloid marrow imaging still remains the gold standard. This article reviews the currently available literature on FDG-PET and PET/CT in the diagnosis of musculoskeletal infection.

Penetration of moxifloxacin into bone in patients undergoing total knee arthroplasty

OBJECTIVES

To investigate plasma and bone moxifloxacin concentrations following oral administration of a single or double dose of the drug, in order to consider its potential role in the treatment of osteomyelitis.

PATIENTS AND METHODS

Thirty consecutive patients undergoing total knee arthroplasty were recruited. Three groups, of ten patients each, were formed: group A received moxifloxacin 400 mg orally 2 h (range 1.5-2.5) preoperatively, group B received moxifloxacin 400 mg orally 4 h (range 3.5-4.5) preoperatively and group C received moxifloxacin 400 mg orally 14 h preoperatively, followed by a second dose 2 h (range 1.5-2.5) preoperatively. During surgery, at the time of bone removal, a blood sample and aliquots of cortical and cancellous bone were collected and moxifloxacin concentrations were measured by HPLC.

RESULTS

Mean plasma, cancellous bone and cortical bone concentrations were, respectively: 3.45, 1.89 and 1.43 mg/L for group A; 3.73, 1.81 and 1.56 mg/L for group B; and 6.26, 2.97 and 2.54 mg/L for group C.

CONCLUSIONS

These data show a good penetration of moxifloxacin into both cancellous and cortical bone, with concentrations, after double dosing, exceeding the MIC90 for most pathogens involved in osteomyelitis and the clinic susceptibility breakpoint for Mycobacterium tuberculosis.

Osteoblasts produce monocyte chemoattractant protein-1 in a murine model of Staphylococcus aureus osteomyelitis and infected human bone tissue

Incidences of osteomyelitis caused by Staphylococcus aureus have increased dramatically in recent years, in part, due to the appearance of community-acquired antibiotic-resistant strains. Therefore, understanding the pathogenesis of this organism has become imperative. Recently, we have described the surprising ability of bone-forming osteoblasts to secrete a number of important immune mediators when exposed to S. aureus in vitro. In the present study, we provide the first evidence for the in vivo production of the pivotal inflammatory chemokine, monocyte chemoattractant protein-1 (MCP-1), by osteoblasts during S. aureus-associated bone infection. Quantitative real-time PCR was employed to determine levels of mRNA encoding MCP-1 in vivo using a mouse model that closely resembles the pathology of trauma-induced staphylococcal osteomyelitis. Expression of this inflammatory chemokine and osteoblast-specific markers was investigated by confocal laser scanning microscopy in bone tissue from organ cultures of neonatal mouse calvaria and from the in vivo mouse model. Furthermore, the clinical relevancy of these findings was investigated by performing similar studies on infected human bone tissue from patients with S. aureus-associated osteomyelitis. Here, we confirm that expression of mRNA encoding MCP-1 is elevated in bacterially infected murine bone tissue. Importantly, we show that these increases translate into marked elevations in the expression of MCP-1 protein that co-localizes with osteoblast markers in infected bone tissue. Such increases could not be attributed solely to mechanical damage as a similar response was observed in infected but otherwise undamaged organ cultures. Finally, we have demonstrated the in vivo production of MCP-1 by osteoblasts in bone specimens from patients with S. aureus-associated osteomyelitis. As such, these studies demonstrate that bacterial challenge of osteoblasts during bone diseases such as staphylococcal osteomyelitis induces cells to produce a key inflammatory chemokine that can direct appropriate host responses or may contribute to progressive inflammatory damage.

Measurement of oxygen partial pressure in the mandibular bone using a polarographic fine needle probe

In this study, the oxygen partial pressure in the cancellous bone substance of the mandible was measured for the first time with a polarographic fine needle probe. This has so far only been established in soft tissue. The aim was to prove and to test the feasibility in principle of this method of measurement in order to ascertain the normal values for the O2 partial pressure in healthy bone. These values were afterwards compared with the results of measurements in areas of different pathological bone conditions in order to assess the clinical suitability of the method for "mapping" during mandibular resection. Measurements of oxygen partial pressure were made in a total of 42 patients (16 women, 26 men). Of these, 12 patients with clinically normal bones served as a control group. Seventeen patients had osteoradionecrosis following radiation treatment, and 13 patients presented with chronic osteomyelitis of the mandible. All measurements were carried out with a polarographic fine needle probe applied to the cancellous bone substance. The statistical analysis included a comparison of the mean values of the oxygen partial pressures measured. No statistical correlation between oxygen partial pressure and pH and hemoglobin values could be detected. The average oxygen partial pressure in the healthy mandibular bone was 71.4 mmHg. In non-healthy bone, the value fell to an average of 30.6 mmHg (osteoradionecrosis 32.3 mmHg, chronic osteomyelitis of the mandibular bone 28.4 mmHg). Statistically, the differences in the group values ascertained were highly significant (P < 0.005). The data found show that this method can be successfully used to detect poorly perfused bone. The values are reproducible and reflect the clinical situation. In the long term, the method appears to be a suitable diagnostic tool for assessing the oxygen supply in bone in studying various clinical problems related to bone surgery.

Comparison of 18F-FDG and 68Ga PET imaging in the assessment of experimental osteomyelitis due to Staphylococcus aureus

PURPOSE

Although positron emission tomography (PET) using 2-[18F]fluoro-2-deoxy-D-glucose (18F-FDG) is a promising imaging modality for bone infections, the technique may still give false-positive results due to unspecific uptake in healing bone. This experimental study compared 18F-FDG and 68Ga in PET imaging of osteomyelitis and normal bone healing.

METHODS

A diffuse osteomyelitis model of the tibia was applied in the rat (n=50). Two weeks after operation, PET imaging with 18F-FDG and 68Ga was performed, followed by peripheral quantitative computed tomography (pQCT) and radiography. Osteomyelitis was verified by quantitative bacteriology. In addition to in vivo imaging, ex vivo measurements of tissue radioactivity were performed to verify uptake of the tracers.

RESULTS

Compared with controls with normal bone healing, the osteomyelitic tibias showed increased SUV ratios (i.e. radioactivity ratios between the operated and non-operated sides) for both 18F-FDG (1.74+/-0.37) and 68Ga (1.62+/-0.28) (P<0.001). Ex vivo measurements also showed increased tracer accumulation in the infected bone (P=0.003 for 18F-FDG and P<0.001 for 68Ga). The intensity of 68Ga uptake reflected pathological changes of osteomyelitic bones measured by pQCT. The uptake of 18F-FDG, however, did not show as close a correlation with the anatomical changes. The healing bones without infection exhibited slightly elevated uptake of 18F-FDG (SUV ratio 1.16+/-0.06), but 68Ga did not accumulate in the healing bone, as judged on the basis of both in vivo imaging (SUV ratio 1.02+/-0.05) and ex vivo measurements (SUV 0.92+/-0.21) (P=0.003 and P=0.022 compared with 18F-FDG uptake, respectively).

CONCLUSION

This study suggests the feasibility of 68Ga PET imaging of bone infections. However, further studies are needed to clarify the value of 68Ga PET for clinical purposes.

Comparative 18F-FDG PET of experimental Staphylococcus aureus osteomyelitis and normal bone healing

PET using (18)F-FDG is a promising imaging modality for bone infections, based on intensive consumption of glucose by mononuclear cells and granulocytes. The method may have limitations in distinguishing uncomplicated bone healing from osteomyelitis. Bone healing involves an inflammatory phase that represents a highly activated state of cell metabolism and glucose consumption, mimicking infection on PET images. This laboratory study of a standardized model was designed to compare the (18)F-FDG PET characteristics of normal bone healing with those of local osteomyelitis.

METHODS

A localized osteomyelitis model of the rabbit tibia was created by modifying a previously reported canine model. In the osteomyelitic group (n = 8), a standardized metaphyseal defect of the proximal right tibia was surgically created and filled with a block of orthopedic bone cement, followed by injection of a predetermined amount (0.1 mL) of Staphylococcus aureus (strain 52/52A/80, 1 x 10(5)/mL) into the space around the cement. The control group of animals with normal bone healing (n = 8) underwent the same procedure, but the bacterial injection was replaced by a sterile saline injection. The bone cement was surgically removed during debridement at 2 wk. Osteomyelitis was confirmed with positive bacterial cultures during the debridement and 6 wk later at the time of sacrifice. (18)F-FDG PET and peripheral quantitative CT were performed 3 and 6 wk after the debridement. The presence of osteomyelitic bone changes on plain radiographs was classified according to a previously published system.

RESULTS

Before surgery, the standardized uptake values of (18)F-FDG did not differ markedly between the right and left tibias. In the control animals, uncomplicated bone healing was associated with a temporary increase in (18)F-FDG uptake at 3 wk (P = 0.007), but it returned almost to normal by 6 wk. In the experimental animals, localized osteomyelitis resulted in an intense continuous uptake of (18)F-FDG, which was higher than that of healing and intact bones at 3 wk (P = 0.014 and P < 0.001, respectively) and at 6 wk (P < 0.001).

CONCLUSION

(18)F-FDG PET seems to be an efficient tool in the differentiation of uneventful bone healing from bone healing complicated by localized osteomyelitis.

Polymorphonuclear neutrophils in posttraumatic osteomyelitis: cells recovered from the inflamed site lack chemotactic activity but generate superoxides

The pathogenesis of posttraumatic osteomyelitis, one of the major complications after orthopedic surgery, is not yet understood. Formation of bacterial biofilms on the implant is presumed, conferring resistance to antibiotic therapy and probably also to the host defense mechanisms. In that context, the polymorphonuclear neutrophils (PMN) having infiltrated the infected site were recovered and characterized phenotypically and functionally. Loss of CD62L and upregulation of CD14 were seen, as was expression of CD83. Expression of the latter is dependent on de novo protein synthesis and thus is indicative of an extended life span and a transdifferentiation of the PMN at the infected site. The infiltrated PMN had lost their chemotactic activity, whereas the capacity to produce superoxides was preserved and in some patients even enhanced. In vitro experiments done in parallel showed that long-term culture with interferon-gamma resulted in similar alterations of PMN: loss of chemotactic activity, whereas other functions of PMN, such generation of superoxides and phagocytosis of opsonized bacteria, were preserved or even enhanced. The loss of the migratory capacity of PMN having already emigrated from the blood vessel to the infected site is not expected to affect the host defense negatively. Assuming, however, that bacteria are organized as a biofilm and that infiltration into this biofilm is required for phagocytosis of the bacteria, our data could to some extent explain why despite being activated, the PMN are not able to control the infection. By releasing their cytotoxic, proteolytic, and collagenolytic potential, PMN might instead contribute to tissue destruction and eventually to osteolysis.

Osteoblasts express the inflammatory cytokine interleukin-6 in a murine model of Staphylococcus aureus osteomyelitis and infected human bone tissue

Staphylococcus aureus is the single most common cause of osteomyelitis in humans. Incidences of osteomyelitis caused by S. aureus have increased dramatically in recent years, in part due to the appearance of community-acquired antibiotic resistant strains. Therefore, understanding the pathogenesis of this organism has become imperative. Recently, we have described the surprising ability of bone-forming osteoblasts to secrete a number of important immune mediators when exposed to S. aureus in vitro. In the present study, we provide the first evidence for the in vivo production of such molecules by osteoblasts during bacterial infection of bone. These studies demonstrate the expression of the key inflammatory cytokine interleukin-6 by osteoblasts in organ cultures of neonatal mouse calvaria, and in vivo using a mouse model that closely resembles the pathology of trauma-induced staphylococcal osteomyelitis, as determined by confocal microscopic analysis. Importantly, we have established the clinical relevancy of these findings in infected human bone tissue from patients with S. aureus-associated osteomyelitis. As such, these studies demonstrate that bacterial challenge of osteoblasts during bone diseases, such as osteomyelitis, induces cells to produce inflammatory molecules that can direct appropriate host responses or contribute to progressive inflammatory damage.

Regulation of monocyte chemokine and MMP-9 secretion by proinflammatory cytokines in tuberculous osteomyelitis

Tuberculous osteomyelitis causes bony destruction as a result of interactions among the pathogen, resident bone cells, and influxing leukocytes. Recruitment of monocytes and T cells is critical for antimycobacterial granuloma formation, but little is known about mechanisms regulating this in bone. We investigated the role of tumor necrosis factor alpha (TNF-alpha) and interleukin (IL)-1, key cytokines in granuloma formation, in networks involving human osteoblasts and monocytes. Experiments focused on CXC ligand (CXCL)8, CCL2, and matrix metalloproteinase (MMP)-9, human monocyte-derived mediators involved in control of leukocyte influx. TNF-alpha but not IL-1 has a key role stimulating CXCL8 secretion in Mycobacterium tuberculosis-infected human osteoblast MG-63 cells. Conditioned medium from M. tuberculosis-infected osteoblasts (COBTB) drives CXCL8 and some CCL2 gene expression and secretion from primary human monocytes. IL-1 receptor antagonist and to a lesser extent anti-TNF-alpha inhibited COBTB-induced CXCL8 secretion (P<0.01) but did not affect gene expression. IL-1 blockade had a comparatively lesser effect on CCL2 secretion, whereas anti-TNF decreased CCL2 concentrations from 7840 +/- 140 to 360 +/- 80 pg/ml/4 x 10(5) cells. Neither proinflammatory mediator affects MMP-9 secretion from COBTB-stimulated human monocytes. In summary, in a paracrine network, M. tuberculosis-infected osteoblasts drive high-level CXCL8, comparatively less CCL2, but do not alter MMP-9 secretion from uninfected human monocytes. This network is, in part, regulated by IL-1 and TNF-alpha.

Bone gentamicin concentration after intra-articular injection or regional intravenous perfusion in the horse

OBJECTIVE

To compare intra-articular (IA) and bone gentamicin concentrations achieved after intra-articular administration or regional intravenous perfusion (RIP).

STUDY DESIGN

Experimental study.

ANIMALS

Twelve healthy adult horses.

METHODS

Horses were assigned to 2 treatment groups (n = 6/group): Group 1, 1 g gentamicin administered simultaneously in both left and right metacarpophalangeal joints and group 2, 1 g gentamicin administered simultaneously in both left and right lateral palmar veins. Serum, synovial fluid, and bone biopsy specimens were collected. Gentamicin concentrations were determined by fluorescence polarization immunoassay. Bone, synovial fluid, and serum gentamicin concentrations were compared over time and between groups using 2-way ANOVA. Significance of all tests were evaluated at P <.05.

RESULTS

IA metacarpophalangeal joint administration resulted in higher concentration of gentamicin in synovial fluid than RIP administration. Synovial fluid concentration remained above minimum inhibitory concentration (MIC) for common pathogens for over 24 hours with IA and RIP administration. Bone gentamicin concentration remained above MIC for 8 hours with both methods; there was no significant difference in gentamicin concentration in bone with either method. Neither IA nor RIP administration had a significant effect on serum concentration of gentamicin.

CONCLUSIONS

In normal horses, there is no difference in bone gentamicin concentration obtained with IA or RIP administration.

CLINICAL RELEVANCE

Based on MIC for common equine pathogens, administration of gentamicin intra-articularly or by regional intravenous perfusion should be useful for treatment of osteomyelitis.

Nuclear medicine and infection detection: the relative effectiveness of imaging with 111In-oxine-, 99mTc-HMPAO-, and 99mTc-stannous fluoride colloid-labeled leukocytes and with 67Ga-citrate

With a current annual mortality rate of around 35% worldwide, infection remains a significant concern, and the diagnosis and localization of infectious foci is an important health issue. As an established infection-imaging modality, nuclear medicine plays a vital health-care role in the diagnosis and subsequent effective treatment of this condition. Despite the development of several newer radiopharmaceuticals, (67)Ga and leukocyte imaging procedures have maintained their established place for infection. Several techniques in nuclear medicine significantly aid infection diagnosis, including imaging with (111)In-oxine-, (99m)Tc-hexamethylpropyleneamine oxime-, and (99m)Tc-stannous fluoride colloid-labeled leukocytes and with (67)Ga-citrate. Each radiopharmaceutical has specific advantages and disadvantages that make it suitable to diagnose different infectious processes (e.g., soft-tissue sepsis, inflammatory bowel disease, osteomyelitis, occult fever, fever of unknown origin, and infections commonly found in immunocompromised patients). After finishing this article, the reader should be able to identify the properties of an ideal radiopharmaceutical for infection imaging, list a range of available infection-imaging radiopharmaceuticals, compare the relative results of a range of radiopharmaceuticals used internationally to detect infection in the body, understand several common infectious processes that can be diagnosed using nuclear medicine techniques, and select an appropriate radiopharmaceutical to image a range of infectious processes.

Expression of VEGF and MMP-9 in giant cell tumor of bone and other osteolytic lesions

This study aims to investigate the expression of vascular endothelial growth factor (VEGF) and matrix metalloproteinase-9 (MMP-9) in giant cell tumor of bone (GCT) and other osteolytic lesions in bone. By using semi-quantitative RT-PCR, we showed that three major isoforms of VEGF (121, 165 and 189) were expressed in GCTs, with isoform 121 being the most abundant. The expression levels of VEGF and MMP-9 mRNA were significantly higher in advanced GCTs (stage II/III) than in stage I GCTs. We further elucidated the cellular localization of VEGF and MMP-9 gene transcripts in GCT and other osteolytic lesions using an in situ hybridization assay. The results showed that stromal tumor cells and osteoclast-like giant cells of GCT, fibrous stromal cells in anuerysmal bone cysts and fibrous dysplasia, and Langerhans-type giant cells as well as histocytes in eosinophillic granuloma, were all strongly positive for VEGF and MMP-9 mRNA expression. In a prospective study, we performed VEGF and MMP-9 immuno-staining on paraffin sections of pathological tissues harvested from 48 patients (14 GCT, 10 anuerysmal bone cysts, 10 eosinophillic granuloma, 4 fibrous dysplasia, 2 simple bone cyst, 2 osteomyelitis and 6 patients with fractured femoral head as control). The results showed that the differences in VEGF and MMP-9 expression between Stage I and other advanced Stages (II, III and recurrent) were highly significant (p<0.001), with advanced stages showing a higher mean expression. The difference between recurrent and Stage II and III lesions, was also statistically significant (p=0.03 for VEGF, and p=0.01 for MMP-9 expression), with recurrent lesions showing a higher mean expression of both VEGF and MMP-9. In conclusion, VEGF and MMP-9 expression in osteolytic lesions of bone co-relates well with the extent of bone destruction and local recurrence. Their expression may therefore provide some prognostic indication of the possible aggressive behavior of the underlying pathology.

[The study of the antioxidant enzymes in erythrocytes in lung diseases]

The activity of antioxidative enzymes Cu, Zn-superoxidedismutase (SOD) and catalase as well as content of glutathione and activity of its metabolism enzymes--glutathione reductase (GR) and glutathione peroxidase (GP) were studied in red blood cells of 82 patients: with chronic obstructive pulmonary diseases (COPD, n = 26), chest osteomyelitis (n = 12), malignant (n = 21) and benign (n = 23) pulmonary lesions. Red blood cells from 26 donors served as a control. Enzymes of glutathione and catalase metabolism in the red cells inhibited their activity in all the above pulmonary diseases vs those of the controls: GR activity in COPD and chest osteomyelitis decreased by 40% and more, lung tumors--by 32-36%. GP activity--by 24-27%, 14-19%, respectively. Catalase activity in pulmonary diseases was suppressed by 38-45%. SOD activity in chest osteomyelitis and pulmonary tumors is lower by 37-40% while in COPD is higher by 36%. Activation of SOD in red cells in COPD may be regarded as a compensatory-adaptive response to excessive accumulation of free oxygen radicals in alveoli in COPD.

[The significance of lipid peroxides for prediction of traumatic mandibular osteomyelitis]

68 patients with mandible's fractures were observed. There was studied the importance of peroxygenation of lipids and antioxydation system for prognosing and diagnosing of posttraumatic osteomyelitis of mandible. It was established that the intensifies of peroxygenation of lipids increased and the level of antioxydation system decreased in cases of mandible's fractures. The patients having posttraumatic osteomyelitis afterwards had the more changes in concentration of peroxygenation of lipids.

Inhibitory effect of roxithromycin on the local levels of bone-resorbing cytokines in an experimental model of murine osteomyelitis

OBJECTIVES

The purpose of this study was to evaluate the inhibitory effect of roxithromycin on the production of interleukin (IL)-1beta, IL-6 and tumour necrosis factor-alpha (TNF-alpha) in a murine tibial osteomyelitis model using Staphylococcus aureus.

METHODS

Cytokine levels in supernatants derived from bone homogenates were measured by enzyme-linked immunosorbent assay for 28 days, after oral administration of roxithromycin at 5 mg/kg/day.

RESULTS

There was no significant difference in IL-6 levels between a group receiving roxithromycin administration and a group not receiving roxithromycin. IL-1beta and TNF-alpha levels were significantly lower for the administration group after 7-14 days and after 21-28 days, respectively. However, a significant difference in bacterial counts in bone between the groups was not observed.

CONCLUSION

These results indicate that roxithromycin suppresses the local expression of IL-1beta and TNF-alpha, and may exhibit an anti-inflammatory effect in this osteomyelitis model.

Local levels of interleukin-1beta, -4, -6 and tumor necrosis factor alpha in an experimental model of murine osteomyelitis due to staphylococcus aureus

The purpose of this study is to evaluate local levels of interleukin-1 beta (IL-1 beta), -4 (IL-4), -6 (IL-6), and tumour necrosis factor-alpha (TNF-alpha), in a model of murine osteomyelitis due to Staphylococcus aureus. Cytokine levels in supernatants derived from bone homogenates were determined by enzyme-linked immunosorbent assay, for 28 days following the direct implantation of murine tibiae with S.aureus. Levels of IL-1 beta and IL-6 in infected bone were elevated in the early post-infection period and then decreased. In contrast, TNF-alpha levels remained elevated 3 to 28 days post-infection, while IL-4 levels were elevated late in the course of infection. The histopathology of infected bone showed predominant infiltration of inflammatory cells and bone resorption 3 to 7 days after infection, and bone resorption and adjacent areas of formation 14 to 28 days after infection. These results suggest that the elevated IL-1 beta and IL-6 levels induced by infection may be related to bone damage mainly in the early phase of infection, and that TNF-alpha and IL-4 may at least in part be associated with histopathological changes, including both bone resorption and formation in the later phase of this osteomyelitis model.

The co-expression of CD117 (c-kit) and osteocalcin in activated bone marrow stem cells in different diseases

It is still difficult to identify a potential stem cell in the bone marrow which can give rise to haematopoiesis and mesenchymal cells. In the past, the stem cells for both tissues were considered to be from different stem cell pools, but it has been shown recently in vitro and in vivo that there is an unexpected plasticity at least among early haemopoietic progenitors which can give rise also to mesenchymal tissue. In an attempt to identify stem cells in the bone marrow, which are common precursors to both lineages, we observed that fibroblast-like periosteal cells changed their morphology towards an osteoblastic differentiation with a more cuboidal or triangular morphology especially close to metastatic infiltrates. As a marker for haemopoietic progenitors, we used an antibody against the tyrosine kinase receptor c-kit (CD117) and an anti-osteocalcin antibody to stain mesenchymal cells with a osteoblastic potential. Normal bone marrow specimens only showed a discrete expression pattern of CD117 and osteocalcin, but periosteal stem cells, which strongly co-express the applied haemopoietic and mesenchymal markers, were found particularly in the bone marrow of patients with infiltrates of malignant lymphoma or metastasis from prostate or breast cancer. The evaluation of bone marrow specimens from patients with an aplastic syndrome or myelodysplastic syndrome showed a more heterogenous expression pattern. Our results show that a stem cell candidate common to haematopoiesis and mesenchymal progeny can be detected in bone marrow specimens after activation, as demonstrated by the co-expression of CD117 and osteocalcin, which also seems to be associated with haematological diseases or metastatic infiltration in the bone marrow.

18-fluorodeoxyglucose positron emission tomographic imaging in the detection and monitoring of infection and inflammation

During the past decade, 18-fluorodeoxyglucose (FDG) positron emission tomography (PET) has rapidly evolved from a pure research modality to a clinical necessity. FDG-PET was introduced to determine the state of brain function in physiologic and pathologic states. Its use as a powerful tool to diagnose, stage, and monitor patients with a variety of malignancies has been truly revolutionary. However, FDG is a nonspecific tracer and it has been found to accumulate at sites of infection and inflammation. It is becoming evident that PET imaging will play a major role in the treatement of patients with suspected infection and inflammation. PET has been shown to be particularly valuable in the evaluation of chronic osteomyelitis, infected prostheses, sarcoidosis, fever of unknown origin, and acquired immunodeficiency syndrome. Because of its ability to quantitate the rate of FDG uptake, PET may prove to be a powerful modality for the monitoring of disease activity and response to therapy. Novel PET tracers are being tested for imaging infection and inflammation that may further enhance the role of this technique in the appropriate clinical setting. PET imaging to detect and characterize infection and inflammation may become a major clinical indication in the day-to-day practice of medicine.

Effect of hyperbaric oxygen exposure on oxygen tension within the medullary canal in the rabbit tibial osteomyelitis model

The effect on intramedullary oxygen tension of 100% oxygen exposure at 1, 2, 2.4, and 3 atm pressure was studied in 12 New Zealand white rabbits with chronic right tibial osteomyelitis. The model, modified from that described by others, incorporates a multipuncture silastic closure plug placed transcortically in the proximal tibial metaphysis through which platinum needle, polarographic electrode oxygen tension determinations can be made without repeat surgical exposure. In 40% of the control, left, noninfected tibial metaphyses the baseline oxygen tension with the animals breathing room air at sea level was suboptimal for leukocyte bacterial killing. This oxygen tension was depressed further in the infected right tibia. Medullary canal oxygen tension increased in response to hyperbaric oxygen exposure in both the infected and noninfected tibiae. Whereas the amount of the oxygen tension increase varied with the presence of infection and depth of dive, neither the time for oxygen tension to plateau nor the time required for return to baseline tension after completion of hyperbaric oxygen exposure varied with the presence of infection or depth of dive. After completion of hyperbaric oxygen exposure, the oxygen tension within the medullary canal returned to baseline within 15 min.

Collagen and fibronectin binding in experimental staphylococcal osteomyelitis

A new mouse model of locally induced osteomyelitis was used to study the importance for pathogenicity of the specific binding ability of Staphylococcus aureus to collagen and fibronectin. This method appears to be convenient, reproducible, and suitable for large-scale experiments. In contrast to previous studies in experimental arthritis and endocarditis models, no difference in infection rates was found between the strains deficient in binding to collagen compared with the corresponding adherence-proficient strains. However, fibronectin binding ability in this model, in contrast to the endocarditis model, is thought to enhance the microorganisms' capacity to establish an infection. Infections caused by the fibronectin-binding strain also are thought to be clinically more aggressive than those caused by the nonbinding strain. Specific adherence mechanisms are thought to be operative in the pathogenesis of biomaterial associated osteomyelitis, and an improved understanding of such mechanisms may have an important prophylactic and therapeutic impact.