The combination of a tumor necrosis factor inhibitor and antibiotic alleviates staphylococcal arthritis and sepsis in mice

Utilization of In Vivo Imaging System to Study Staphylococcal Sepsis and Septic Arthritis Progression in Mouse Model

Staphylococcus aureus [S. aureus] is a leading cause of sepsis and septic arthritis, conditions that pose significant medical challenges due to their high mortality and morbidity. No studies have used an in vivo imaging system [IVIS] to monitor S. aureus sepsis and septic arthritis. Here, we employed a bioluminescent reporter strain of S. aureus, Newman AH5016, administered intravenously to induce sepsis and intra-articularly to induce local septic arthritis in mice. Disease progression was monitored using IVIS to capture bioluminescent signals from kidneys, joints, and whole mice. Cytokines in the blood and joints were measured. The efficacy of cloxacillin treatment was evaluated. In the sepsis model, bioluminescent signals from kidneys, but not from whole mice, were correlated with kidney bacterial load and abscess formation. Ex vivo kidney imaging detected increased bacterial load and abscess formation from day 3 to day 10. Antibiotic treatment significantly reduced kidney signals, correlating with decreased bacterial counts and IL-6 levels, indicating effective infection control. In the local infection model, early-phase bioluminescent signals from joints were correlated with macroscopic arthritis and bacterial burden. Thus, signal detection from kidneys using IVIS is useful for monitoring S. aureus sepsis and assessing antibiotic efficacy, though it may only be effective for early-phase monitoring of local septic arthritis.

Tofacitinib Treatment Suppresses CD4+ T-Cell Activation and Th1 Response, Contributing to Protection against Staphylococcal Toxic Shock

Staphylococcal toxic shock syndrome (STSS) is a rare, yet potentially fatal disease caused by Staphylococcus aureus (S. aureus) enterotoxins, known as superantigens, which trigger an intense immune response. Our previous study demonstrated the protective effect of tofacitinib against murine toxin-induced shock and a beneficial effect against S. aureus sepsis. In the current study, we examined the effects of tofacitinib on T-cell response in peripheral blood using a mouse model of enterotoxin-induced shock. Our data revealed that tofacitinib suppresses the activation of both CD4+ and CD8+ T cells in peripheral blood. Furthermore, both gene and protein levels of Th1 cytokines were downregulated by tofacitinib treatment in mice with enterotoxin-induced shock. Importantly, we demonstrated that CD4+ cells, but not CD8+ cells, are pathogenic in mice with enterotoxin-induced shock. In conclusion, our findings suggest that tofacitinib treatment suppresses CD4+ T-cell activation and Th1 response, thereby aiding in protection against staphylococcal toxic shock in mice. This insight may guide the future development of novel therapies for STSS.

Pathophysiology and Evolving Treatment Options of Septic Arthritis: A Narrative Review

Pyogenic (septic) arthritis is a severe joint infection characterized by the invasion of microorganisms into the synovium, causing inflammation and joint destruction. This review article provides a comprehensive overview of pyogenic arthritis, focusing on etiology, pathogenesis, clinical manifestations, diagnosis, and management strategies. This review explores routes of microbial entry into joints, emphasizing the importance of prompt identification and treatment to prevent irreversible joint damage. Clinical manifestations, such as joint pain, swelling, and limited range of motion, are discussed, along with the challenges in differentiating pyogenic arthritis from other joint disorders. Diagnostic approaches, including joint aspiration and imaging modalities, are critically examined for accuracy in confirming diagnosis. This review also addresses the significance of early intervention through antimicrobial therapy and joint drainage, highlighting the role of multidisciplinary collaboration in optimizing patient outcomes. In summary, the present investigation underscores the complexities of pyogenic arthritis and the need for a comprehensive understanding of pathophysiology for timely and effective management to improve patient prognosis and quality of life.

Exploring the role of bacterial virulence factors and host elements in septic arthritis: insights from animal models for innovative therapies

Septic arthritis, characterized as one of the most aggressive joint diseases, is primarily attributed to Staphylococcus aureus (S. aureus) and often results from hematogenous dissemination. Even with prompt treatment, septic arthritis frequently inflicts irreversible joint damage, leading to sustained joint dysfunction in a significant proportion of patients. Despite the unsatisfactory outcomes, current therapeutic approaches for septic arthritis have remained stagnant for decades. In the clinical context, devising innovative strategies to mitigate joint damage necessitates a profound comprehension of the pivotal disease mechanisms. This entails unraveling how bacterial virulence factors interact with host elements to facilitate bacterial invasion into the joint and identifying the principal drivers of joint damage. Leveraging animal models of septic arthritis emerges as a potent tool to achieve these objectives. This review provides a comprehensive overview of the historical evolution and recent advancements in septic arthritis models. Additionally, we address practical considerations regarding experimental protocols. Furthermore, we delve into the utility of these animal models, such as their contribution to the discovery of novel bacterial virulence factors and host elements that play pivotal roles in the initiation and progression of septic arthritis. Finally, we summarize the latest developments in novel therapeutic strategies against septic arthritis, leveraging insights gained from these unique animal models.

Endogenous blocking of TLR2 along with TNF-α and IL-1β ameliorates the severity of the S. aureus arthritis via modulating STAT3/SOCS3 expressions in tissue resident macrophages

In vivo studies identifying a role of TLR2 in septic arthritis models are lacking. TNF-α played as the most important proinflammatory cytokine, and connected directly to the pathogenesis of bacterial arthritis. IL-1β is another central mediator cytokine in arthritis. It is therefore reasonable to question the role of neutralization of endogenous TNF-α and IL-1β along with TLR2 and associated downstream signaling as crucial mediators in the S. aureus -induced inflammatory arthritis. In reaction to an injury or a pathogen encounter, innate immune cells serve as the initial line of defense. TLR2 mediated entry of S. aureus into macrophage cells initiates an array of inflammatory cascades. After macrophage cell gets activated at the site inflammation, they generate elevated number of cytokines which includes TNF-α, IL-1β. This cytokines signals through STAT1/STAT3 mediated pathways. Thus, aim of this study was to discover how This bone damage could be altered by altering the STAT/STAT3/SOCS3 ratio by blocking TLR2, a particular S. aureus binding site, in conjunction with the use of IL-1 and TNF- antibodies for neutralizing endogenous IL-1β and TNF-α. Additionally, the role of local macrophages in therapy of arthritis was investigated in synovial and Splenic tissue. To comprehend the inflammatory milieu within the system, ROS and other antioxidant enzymes, along with the expression of mTOR in macrophage cells, were also taken into consideration. The detrimental impact of bacterial burden on synovial joints was reduced by simultaneously inhibiting TLR2, TNF-α, and IL-1β. Lowered IFN-γ decreases its sensitivity to STAT1 and lowered IL-6 reduces STAT3 expressions. Whereas, elevated IL-10 enhances SOSC3 expression, which thereby able to limits STAT1/STAT3 inter-conversion. As a result, NF-κB activity was downregulated.

The Impact of Aging and Toll-like Receptor 2 Deficiency on the Clinical Outcomes of Staphylococcus aureus Bacteremia

Staphylococcus aureus (S. aureus) causes a broad range of infections. Toll-like receptor (TLR) 2 senses the S. aureus lipoproteins in S. aureus infections. Aging raises the risk of infection. Our aim was to understand how aging and TLR2 affect the clinical outcomes of S. aureus bacteremia. Four groups of mice (wild type/young, wild type/old, TLR2-/-/young, and TLR2-/-/old) were intravenously infected with S. aureus, and the infection course was followed. Both TLR2 deficiency and aging enhanced the susceptibility to disease. Increased age was the main contributing factor for increased mortality rates and changes in spleen weight, whereas other clinical parameters, such as weight loss and kidney abscess formation, were more TLR2 dependent. Importantly, aging increased mortality rates without relying on TLR2. In vitro, both aging and TLR2 deficiency down-regulated cytokine/chemokine production of immune cells with distinct patterns. In summary, we demonstrate that aging and TLR2 deficiency impair the immune response to S. aureus bacteremia in distinct ways.

Bacterial Lipoproteins Shift Cellular Metabolism to Glycolysis in Macrophages Causing Bone Erosion

Belonging to a group of membrane proteins, bacterial lipoproteins (LPPs) are defined by a unique lipid structure at their N-terminus providing the anchor in the bacterial cell membrane. In Gram-positive bacteria, LPPs play a key role in host immune activation triggered through a Toll-like receptor 2 (TLR2)-mediated action resulting in macrophage stimulation and subsequent tissue damage demonstrated in in vivo experimental models. Yet the physiologic links between LPP activation, cytokine release, and any underlying switches in cellular metabolism remain unclear. In this study, we demonstrate that Staphylococcus aureus Lpl1 not only triggers cytokine production but also confers a shift toward fermentative metabolism in bone marrow-derived macrophages (BMDMs). Lpl1 consists of di- and tri-acylated LPP variants; hence, the synthetic P2C and P3C, mimicking di-and tri-acylated LPPs, were employed to reveal their effect on BMDMs. Compared to P3C, P2C was found to shift the metabolism of BMDMs and the human mature monocytic MonoMac 6 (MM6) cells more profoundly toward the fermentative pathway, as indicated by lactate accumulation, glucose consumption, pH reduction, and oxygen consumption. In vivo, P2C caused more severe joint inflammation, bone erosion, and lactate and malate accumulation than P3C. These observed P2C effects were completely abrogated in monocyte/macrophage-depleted mice. Taken together, these findings now solidly confirm the hypothesized link between LPP exposure, a macrophage metabolic shift toward fermentation, and ensuing bone destruction. IMPORTANCE Osteomyelitis caused by S. aureus is a severe infection of the bone, typically associated with severe bone function impairment, therapeutic failure, high morbidity, invalidity, and occasionally even death. The hallmark of staphylococcal osteomyelitis is the destruction of the cortical bone structures, yet the mechanisms contributing to this pathology are hitherto poorly understood. One bacterial membrane constituent found in all bacteria is bacterial lipoproteins (LPPs). Previously, we have shown that injection of purified S. aureus LPPs into wild-type mouse knee joints caused a TLR2-dependent chronic destructive arthritis but failed to elicit such effect in monocyte/macrophage-depleted mice. This observation stirred our interest in investigating the interaction of LPPs and macrophages and analyzing the underlying physiological mechanisms. This ascertainment of LPP-induced changes in the physiology of macrophages provides an important clue in the understanding of the mechanisms of bone disintegration, opening novel avenues to manage the course of S. aureus disease.

Gene expression of S100a8/a9 predicts Staphylococcus aureus-induced septic arthritis in mice

Septic arthritis is the most aggressive joint disease associated with high morbidity and mortality. The interplay of the host immune system with the invading pathogens impacts the pathophysiology of septic arthritis. Early antibiotic treatment is crucial for a better prognosis to save the patients from severe bone damage and later joint dysfunction. To date, there are no specific predictive biomarkers for septic arthritis. Transcriptome sequencing analysis identified S100a8/a9 genes to be highly expressed in septic arthritis compared to non-septic arthritis at the early course of infection in an Staphylococcus aureus septic arthritis mouse model. Importantly, downregulation of S100a8/a9 mRNA expression at the early course of infection was noticed in mice infected with the S. aureus Sortase A/B mutant strain totally lacking arthritogenic capacity compared with the mice infected with parental S. aureus arthritogenic strain. The mice infected intra-articularly with the S. aureus arthritogenic strain significantly increased S100a8/a9 protein expression levels in joints over time. Intriguingly, the synthetic bacterial lipopeptide Pam2CSK4 was more potent than Pam3CSK4 in inducing S100a8/a9 release upon intra-articular injection of these lipopeptides into the mouse knee joints. Such an effect was dependent on the presence of monocytes/macrophages. In conclusion, S100a8/a9 gene expression may serve as a potential biomarker to predict septic arthritis, enabling the development of more effective treatment strategies.

Tumour Necrosis Factor-α, Chemokines, and Leukocyte Infiltrate Are Biomarkers for Pathology in the Brains of Venezuelan Equine Encephalitis (VEEV)-Infected Mice

Venezuelan equine encephalitis virus (VEEV) is a disease typically confined to South and Central America, whereby human disease is characterised by a transient systemic infection and occasionally severe encephalitis, which is associated with lethality. Using an established mouse model of VEEV infection, the encephalitic aspects of the disease were analysed to identify biomarkers associated with inflammation. Sequential sampling of lethally challenged mice (infected subcutaneously) confirmed a rapid onset systemic infection with subsequent spread to the brain within 24 h of the challenge. Changes in inflammatory biomarkers (TNF-α, CCL-2, and CCL-5) and CD45+ cell counts were found to correlate strongly to pathology (R>0.9) and present previously unproven biomarkers for disease severity in the model, more so than viral titre. The greatest level of pathology was observed within the olfactory bulb and midbrain/thalamus. The virus was distributed throughout the brain/encephalon, often in areas not associated with pathology. The principal component analysis identified five principal factors across two independent experiments, with the first two describing almost half of the data: (1) confirmation of a systemic Th1-biased inflammatory response to VEEV infection, and (2) a clear correlation between specific inflammation of the brain and clinical signs of disease. Targeting strongly associated biomarkers of deleterious inflammation may ameliorate or even eliminate the encephalitic syndrome of this disease.

Simultaneous neutralization of TGF-β and IL-6 attenuates Staphylococcus aureus-induced arthritic inflammation through differential modulation of splenic and synovial macrophages

Septic arthritis is a joint disease caused by Staphylococcus aureus. Different macrophage populations contribute in various ways to control blood-borne infections and induce inflammatory responses. Macrophage tissue-resident niche is necessary for the suppression of chronic inflammation and may contribute to the pathogenesis of septic arthritis. Thus, to obtain a resolution of the disease and restoration of synovial homeostasis, it needs the activation of macrophages that further regulate the inflammatory consequences. The aim of this study was to find out the mechanism by which neutralization of transforming growth factor-beta (TGF-β) and/or interleukin (IL)-6 after induction of septic arthritis could alter the specific macrophage responses in spleen and synovial joints via different cytokines (osteoprotegerin (OPG), osteopontin (OPN), IL-10, IL-12 and CXCL8) cross-talking, and how the response could be modulated by reactive oxygen species vs antioxidant enzyme activities. Dual neutralization of TGF-β and IL-6 is notably effective in eliciting splenic and synovial tissue-resident macrophage responses. Synovial macrophage-derived IL-10 can elicit protection against septic arthritis via regulating receptor-activated nuclear factor Kappa-B ligand (RANKL)/OPG interaction. They also reduced oxidative stress by increasing the activity of antioxidant enzymes including SOD and catalase. Histopathological analysis revealed that dual neutralization of TGF-β and IL-6 prevented bone destruction and osteoclastic activity in septic arthritis by promoting the differential functional response of the splenic and synovial macrophages. Additionally, the macrophage-derived IL-10 can elicit protection against S. aureus-induced septic arthritis via regulating RANKL/OPG interaction. Further studies on STAT3 and STAT4 are needed for the understanding of such cross-talking in resident macrophages of arthritic mice.

Staphylococcus aureus lipoproteins in infectious diseases

Infections with the Gram-positive bacterial pathogen Staphylococcus aureus remain a major challenge for the healthcare system and demand new treatment options. The increasing antibiotic resistance of S. aureus poses additional challenges, consequently inflicting a huge strain in the society due to enormous healthcare costs. S. aureus expresses multiple molecules, including bacterial lipoproteins (Lpps), which play a role not only in immune response but also in disease pathogenesis. S. aureus Lpps, the predominant ligands of TLR2, are important for bacterial survival as they maintain the metabolic activity of the bacteria. Moreover, Lpps possess many diverse properties that are of vital importance for the bacteria. They also contribute to host cell invasion but so far their role in different staphylococcal infections has not been fully defined. In this review, we summarize the current knowledge about S. aureus Lpps and their distinct roles in various infectious disease animal models, such as septic arthritis, sepsis, and skin and soft tissue infections. The molecular and cellular response of the host to S. aureus Lpp exposure is also a primary focus.

Phenol-soluble modulin α and β display divergent roles in mice with staphylococcal septic arthritis

Phenol-soluble modulin α (PSMα) is identified as potent virulence factors in Staphylococcus aureus (S. aureus) infections. Very little is known about the role of PSMβ which belongs to the same toxin family. Here we compared the role of PSMs in S. aureus-induced septic arthritis in a murine model using three isogenic S. aureus strains differing in the expression of PSMs (Newman, Δpsmα, and Δpsmβ). The effects of PSMs on neutrophil NADPH-oxidase activity were determined in vitro. We show that the PSMα activates neutrophils via the formyl peptide receptor (FPR) 2 and reduces their NADPH-oxidase activity in response to the phorbol ester PMA. Despite being a poor neutrophil activator, PSMβ has the ability to reduce the neutrophil activating effect of PSMα and to partly reverse the effect of PSMα on the neutrophil response to PMA. Mice infected with S. aureus lacking PSMα had better weight development and lower bacterial burden in the kidneys compared to mice infected with the parental strain, whereas mice infected with bacteria lacking PSMβ strain developed more severe septic arthritis accompanied with higher IL-6 and KC. We conclude that PSMα and PSMβ play distinct roles in septic arthritis: PSMα aggravates systemic infection, whereas PSMβ protects arthritis development.

Phenol-soluble modulin α and β display divergent roles in staphylococcal infection and its associated septic arthritis - whereas PSMα is a virulence factor for neutrophils that worsens infection, PSMβ protects from the development of septic arthritis.

Commensal Bacteria Augment Staphylococcus aureus septic Arthritis in a Dose-Dependent Manner

Background

Septic arthritis is considered one of the most dangerous joints diseases and is mainly caused by the Gram-positive bacterium Staphylococcus aureus (S. aureus). Human skin commensals are known to augment S. aureus infections. The aim of this study was to investigate if human commensals could augment S. aureus-induced septic arthritis.

Method

NMRI mice were inoculated with S. aureus alone or with a mixture of S. aureus together with either of the human commensal Staphylococcus epidermidis (S. epidermidis) or Streptococcus mitis (S. mitis). The clinical, radiological and histopathological changes due to septic arthritis were observed. Furthermore, the serum levels of chemokines and cytokines were assessed.

Results

Mice inoculated with a mixture of S. aureus and S. epidermidis or S. mitis developed more severe and frequent clinical arthritis compared to mice inoculated with S. aureus alone. This finding was verified pathologically and radiologically. Furthermore, the ability of mice to clear invading bacteria in the joints but not in kidneys was hampered by the bacterial mixture compared to S. aureus alone. Serum levels of monocyte chemoattractant protein 1 were elevated at the early phase of disease in the mice infected with bacterial mixture compared with ones infected with S. aureus alone. Finally, the augmentation effect in septic arthritis development by S. epidermidis was bacterial dose-dependent.

Conclusion

The commensal bacteria dose-dependently augment S. aureus-induced septic arthritis in a mouse model of septic arthritis.

Mini Review Therapeutic Strategies Targeting for Biofilm and Bone Infections

Bone infection results in a complex inflammatory response and bone destruction. A broad spectrum of bacterial species has been involved for jaw osteomyelitis, hematogenous osteomyelitis, vertebral osteomyelitis or diabetes mellitus, such as Staphylococcus aureus (S. aureus), coagulase-negative Staphylococcus species, and aerobic gram-negative bacilli. S. aureus is the major pathogenic bacterium for osteomyelitis, which results in a complex inflammatory response and bone destruction. Although various antibiotics have been applied for bone infection, the emergence of drug resistance and biofilm formation significantly decrease the effectiveness of those agents. In combination with gram-positive aerobes, gram-negative aerobes and anaerobes functionally equivalent pathogroups interact synergistically, developing as pathogenic biofilms and causing recurrent infections. The adhesion of biofilms to bone promotes bone destruction and protects bacteria from antimicrobial agent stress and host immune system infiltration. Moreover, bone is characterized by low permeability and reduced blood flow, further hindering the therapeutic effect for bone infections. To minimize systemic toxicity and enhance antibacterial effectiveness, therapeutic strategies targeting on biofilm and bone infection can serve as a promising modality. Herein, we focus on biofilm and bone infection eradication with targeting therapeutic strategies. We summarize recent targeting moieties on biofilm and bone infection with peptide-, nucleic acid-, bacteriophage-, CaP- and turnover homeostasis-based strategies. The antibacterial and antibiofilm mechanisms of those therapeutic strategies include increasing antibacterial agents’ accumulation by bone specific affinity, specific recognition of phage-bacteria, inhibition biofilm formation in transcription level. As chronic inflammation induced by infection can trigger osteoclast activation and inhibit osteoblast functioning, we additionally expand the potential applications of turnover homeostasis-based therapeutic strategies on biofilm or infection related immunity homeostasis for host-bacteria. Based on this review, we expect to provide useful insights of targeting therapeutic efficacy for biofilm and bone infection eradication.

Lipoproteins Cause Bone Resorption in a Mouse Model of Staphylococcus aureus Septic Arthritis

Septic arthritis, most often caused by Staphylococcus aureus, is a rapidly progressive and destructive joint disease with substantial mortality and morbidity. Staphylococcus aureus lipoproteins (Lpps) are known to induce arthritis and bone destruction. Here, we aimed to investigate the bone resorptive effect of S. aureus Lpps in a murine arthritis model by intra-articular injection of purified S. aureus Lpps, synthetic lipopeptides, and live S. aureus strains. Analyses of the bone mineral density (BMD) of the distal femur bone were performed. Intra-articular injection of both live S. aureus and purified S. aureus Lpps were shown to significantly decrease total- and trabecular BMD. Liquid chromatography–mass spectrometry analyses revealed that the Lpps expressed by S. aureus SA113 strain contain both diacyl and triacyl lipid moieties. Interestingly, synthetic diacylated lipopeptide, Pam₂CSK₄, was more potent in inducing bone resorption than synthetic triacylated lipopeptide, Pam₃CSK₄. Modified lipoproteins lacking the lipid moiety were deprived of their bone resorptive abilities. Monocyte depletion by clodronate liposomes fully abrogated the bone resorptive capacity of S. aureus lipoproteins. Our data suggest that S. aureus Lpps induce bone resorption in locally-induced murine arthritis, an effect mediated by their lipid-moiety through monocytes/macrophages.

Fibrin(ogen) engagement of S. aureus promotes the host antimicrobial response and suppression of microbe dissemination following peritoneal infection

The blood-clotting protein fibrin(ogen) plays a critical role in host defense against invading pathogens, particularly against peritoneal infection by the Gram-positive microbe Staphylococcus aureus. Here, we tested the hypothesis that direct binding between fibrin(ogen) and S. aureus is a component of the primary host antimicrobial response mechanism and prevention of secondary microbe dissemination from the peritoneal cavity. To establish a model system, we showed that fibrinogen isolated from Fibγ^Δ5 mice, which express a mutant form lacking the final 5 amino acids of the fibrinogen γ chain (termed fibrinogenγ^Δ5), did not support S. aureus adherence when immobilized and clumping when in suspension. In contrast, purified wildtype fibrinogen supported robust adhesion and clumping that was largely dependent on S. aureus expression of the receptor clumping factor A (ClfA). Following peritoneal infection with S. aureus USA300, Fibγ^Δ5 mice displayed worse survival compared to WT mice coupled to reduced bacterial killing within the peritoneal cavity and increased dissemination of the microbes into circulation and distant organs. The failure of acute bacterial killing, but not enhanced dissemination, was partially recapitulated by mice infected with S. aureus USA300 lacking ClfA. Fibrin polymer formation and coagulation transglutaminase Factor XIII each contributed to killing of the microbes within the peritoneal cavity, but only elimination of polymer formation enhanced systemic dissemination. Host macrophage depletion or selective elimination of the fibrin(ogen) β2-integrin binding motif both compromised local bacterial killing and enhanced S. aureus systemic dissemination, suggesting fibrin polymer formation in and of itself was not sufficient to retain S. aureus within the peritoneal cavity. Collectively, these findings suggest that following peritoneal infection, the binding of S. aureus to stabilized fibrin matrices promotes a local, macrophage-mediated antimicrobial response essential for prevention of microbe dissemination and downstream host mortality.

The Gram-positive bacterium Staphylococcus aureus (S. aureus) produces a number of soluble and surface-associated proteins that bind the host coagulation protein fibrinogen. The contribution of fibrinogen-S. aureus binding through the fibrinogen receptor clumping factor A (ClfA) in peritoneal infection has not been defined. Elimination of the binding motif on fibrinogen for ClfA or deletion of ClfA from S. aureus significantly reduced S. aureus-fibrinogen binding and bacterial clumping in solution. In a mouse model of peritonitis, loss of these activities resulted in diminished bacterial killing, increased bacterial dissemination, and worsened host survival. Although fibrin polymer formation and fibrin(ogen)-macrophage binding are mechanistically linked to the local antimicrobial response, fibrin formation in and of itself is not sufficient to suppress microbe dissemination. These discoveries have identified important components of the fibrin(ogen)-dependent host antimicrobial response against S. aureus, providing further understanding of this physiological response to infection which could uncover potential therapeutic strategies for peritonitis patients.

Neutralization of IL-17 and treatment with IL-2 protects septic arthritis by regulating free radical production and antioxidant enzymes in Th17 and Tregs: An immunomodulatory TLR2 versus TNFR response

Septic arthritis is a destructive joint disease caused by Staphylococcus aureus. Synovial inflammation involved Th17 proliferation and down regulation of Treg population, thus resolution of inflammation targeting IL-17 may be important to control arthritis. Endogenous inhibition of IL-17 to regulate arthritic inflammation correlating with Th17/Treg cells TLR2 and TNFRs are not done. The role of SOD, CAT and GRx in relation to ROS production during arthritis along with expression of TLR2, TNFR1/TNFR2 in Th17/Treg cells of mice treated with IL-17A Ab/ IL-2 were studied. Increased ROS, reduced antioxidant enzyme activity was found in Th17 cells of SA infected mice whereas Treg cells of IL-17A Ab/ IL-2 treated group showed opposite effects. Neutralization of IL-17 after arthritis cause decreased TNFR1 and increased TNFR2 expression in Treg cells. Thus, neutralization of IL-17 or IL-2 treatment regulates septic arthritis by enhancing anti-inflammatory properties of Treg via antioxidant balance and modulating TLR2/TNFR response.

Inhibition of the lipoxin A4 and resolvin D1 receptor impairs host response to acute lung injury caused by pneumococcal pneumonia in mice

Resolution of the acute respiratory distress syndrome (ARDS) from pneumonia requires repair of the injured lung endothelium and alveolar epithelium, removal of neutrophils from the distal airspaces of the lung, and clearance of the pathogen. Previous studies have demonstrated the importance of specialized proresolving mediators (SPMs) in the regulation of host responses during inflammation. Although ARDS is commonly caused by Streptococcus pneumoniae, the role of lipoxin A4 (LXA4) and resolvin D1 (RvD1) in pneumococcal pneumonia is not well understood. In the present experimental study, we tested the hypothesis that endogenous SPMs play a role in the resolution of lung injury in a clinically relevant model of bacterial pneumonia. Blockade of formyl peptide receptor 2 (ALX/FPR2), the receptor for LXA4 and RvD1, with the peptide WRW4 resulted in more pulmonary edema, greater protein accumulation in the air spaces, and increased bacteria accumulation in the air spaces and the blood. Inhibition of this receptor was also associated with decreased levels of proinflammatory cytokines. Even in the presence of antibiotic treatment, WRW4 inhibited the resolution of lung injury. In summary, these experiments demonstrated two novel findings: LXA4 and RvD1 contribute to the resolution of lung injury due to pneumococcal pneumonia, and the mechanism of their benefit likely includes augmenting bacterial clearance and reducing pulmonary edema via the restoration of lung alveolar-capillary barrier permeability.

Bacteria and Host Interplay in Staphylococcus aureus Septic Arthritis and Sepsis

Staphylococcus aureus (S. aureus) infections are a major healthcare challenge and new treatment alternatives are needed. S. aureus septic arthritis, a debilitating joint disease, causes permanent joint dysfunction in almost 50% of the patients. S. aureus bacteremia is associated with higher mortalities than bacteremia caused by most other microbes and can develop to severe sepsis and death. The key to new therapies is understanding the interplay between bacterial virulence factors and host immune response, which decides the disease outcome. S. aureus produces numerous virulence factors that facilitate bacterial dissemination, invasion into joint cavity, and cause septic arthritis. Monocytes, activated by several components of S. aureus such as lipoproteins, are responsible for bone destructions. In S. aureus sepsis, cytokine storm induced by S. aureus components leads to the hyperinflammatory status, DIC, multiple organ failure, and later death. The immune suppressive therapies at the very early time point might be protective. However, the timing of treatment is crucial, as late treatment may aggravate the immune paralysis and lead to uncontrolled infection and death.

Ibudilast Mitigates Delayed Bone Healing Caused by Lipopolysaccharide by Altering Osteoblast and Osteoclast Activity

Bacterial infection in orthopedic surgery is challenging because cell wall components released after bactericidal treatment can alter osteoblast and osteoclast activity and impair fracture stability. However, the precise effects and mechanisms whereby cell wall components impair bone healing are unclear. In this study, we characterized the effects of lipopolysaccharide (LPS) on bone healing and osteoclast and osteoblast activity in vitro and in vivo and evaluated the effects of ibudilast, an antagonist of toll-like receptor 4 (TLR4), on LPS-induced changes. In particular, micro-computed tomography was used to reconstruct femoral morphology and analyze callus bone content in a femoral defect mouse model. In the sham-treated group, significant bone bridge and cancellous bone formation were observed after surgery, however, LPS treatment delayed bone bridge and cancellous bone formation. LPS inhibited osteogenic factor-induced MC3T3-E1 cell differentiation, alkaline phosphatase (ALP) levels, calcium deposition, and osteopontin secretion and increased the activity of osteoclast-associated molecules, including cathepsin K and tartrate-resistant acid phosphatase in vitro. Finally, ibudilast blocked the LPS-induced inhibition of osteoblast activation and activation of osteoclast in vitro and attenuated LPS-induced delayed callus bone formation in vivo. Our results provide a basis for the development of a novel strategy for the treatment of bone infection.

Hydrocortisone decreases lethality and inflammatory cytokine and nitric oxide production in rats challenged with B. anthracis cell wall peptidoglycan

Background

Lethal B. anthracis infection produces high proinflammatory peptidoglycan (PGN) burdens in hosts. We investigated whether the lethality and inflammation anthrax PGN can produce are related.

Methods

At 6 h before and the start of 24 h anthrax PGN infusions, rats (n = 198) were treated with diluent (controls) or one of three IV-doses of either hydrocortisone (125, 12.5 or 1.25 mg/kg) or TNF-soluble receptor (TNFsr; 2000, 1000 or 333 μg/kg), non-selective and selective anti-inflammatory agents, respectively.

Results

Compared to controls, hydrocortisone 125 and 12.5 mg/kg each decreased 7-day lethality (p ≤ 0.004). Hydrocortisone 125 mg/kg decreased IL-1β, IL-6, TNFα, MCP, MIP-1α, MIP-2, RANTES and nitric oxide (NO) blood levels at 4 and 24 h after starting PGN (except MCP at 24 h). Each decrease was significant at 4 h (except MIP-1α that was significant at 24 h) (p ≤ 0.05). Similarly, hydrocortisone 12.5 mg/kg decreased each measure at 4, 24 and 48 h (except TNFα at 24 h and MIP-1α at 24 and 48 h and NO at 48 h). Decreases were significant for IL-6 and NO at 4 h and RANTES at 48 h (p ≤ 0.05). Hydrocortisone 1.25 mg/kg had non-significant effects. Each TNFsr dose decreased lethality but non-significantly. However, when doses were analyzed together, TNFsr decreased lethality in a potential trend (p = 0.16) and IL-6 and NO significantly at 4 h (p = 0.05).

Conclusions

Peptidoglycan-stimulated host inflammation may contribute to B. anthracis lethality.

The Expression of von Willebrand Factor-Binding Protein Determines Joint-Invading Capacity of Staphylococcus aureus, a Core Mechanism of Septic Arthritis

Septic arthritis, one of the most dangerous joint diseases, is predominantly caused by Staphylococcus aureus In contrast, coagulase-negative staphylococci are rarely found in septic arthritis. We hypothesize that coagulases released by S. aureus, including coagulase (Coa) and von Willebrand factor-binding protein (vWbp), play potent roles in the induction of septic arthritis. Four isogenic S. aureus strains differing in expression of coagulases (wild-type [WT] Newman, Δcoa, Δvwb, and Δcoa Δvwb) were used to induce septic arthritis in both wild-type and von Willebrand factor (vWF)-deficient mice. Septic arthritis severity was greatly reduced when wild-type mice were infected with the Δcoa Δvwb and Δvwb variants compared to WT or Δcoa strains, suggesting that vWbp rather than Coa is a major virulence factor in S. aureus septic arthritis. vWF-deficient mice were more susceptible to bone damage in septic arthritis, especially when the Δvwb strain was used. Importantly, no difference in arthritis severity between the Δvwb and WT strains was observed in vWF-deficient mice. Collectively, we conclude that vWbp production by S. aureus enhances staphylococcal septic arthritis.IMPORTANCE Septic arthritis remains one of the most dangerous joint diseases with a rapidly progressive disease character. Despite advances in the use of antibiotics, permanent reductions in joint function due to joint deformation and deleterious contractures occur in up to 50% of patients with septic arthritis. So far, it is still largely unknown how S. aureus initiates and establishes joint infection. Here, we demonstrate that von Willebrand factor-binding protein expressed by S. aureus facilitates the initiation of septic arthritis. Such effect might be mediated through its interaction with a host factor (von Willebrand factor). Our finding contributes significantly to the full understanding of septic arthritis etiology and will pave the way for new therapeutic modalities for this devastating disease.

Rationalized inhibition of mixed lineage kinase 3 and CD70 enhances life span and antitumor efficacy of CD8+ T cells

BACKGROUND

The mitogen-activated protein kinases (MAPKs) are important for T cell survival and their effector function. Mixed lineage kinase 3 (MLK3) (MAP3K11) is an upstream regulator of MAP kinases and emerging as a potential candidate for targeted cancer therapy; yet, its role in T cell survival and effector function is not known.

METHODS

T cell phenotypes, apoptosis and intracellular cytokine expressions were analyzed by flow cytometry. The apoptosis-associated gene expressions in CD8+CD38+ T cells were measured using RT2 PCR array. In vivo effect of combined blockade of MLK3 and CD70 was analyzed in 4T1 tumor model in immunocompetent mice. The serum level of tumor necrosis factor-α (TNFα) was quantified by enzyme-linked immunosorbent assay.

RESULTS

We report that genetic loss or pharmacological inhibition of MLK3 induces CD70-TNFα-TNFRSF1a axis-mediated apoptosis in CD8+ T cells. The genetic loss of MLK3 decreases CD8+ T cell population, whereas CD4+ T cells are partially increased under basal condition. Moreover, the loss of MLK3 induces CD70-mediated apoptosis in CD8+ T cells but not in CD4+ T cells. Among the activated CD8+ T cell phenotypes, CD8+CD38+ T cell population shows more than five fold increase in apoptosis due to loss of MLK3, and the expression of TNFRSF1a is significantly higher in CD8+CD38+ T cells. In addition, we observed that CD70 is an upstream regulator of TNFα-TNFRSF1a axis and necessary for induction of apoptosis in CD8+ T cells. Importantly, blockade of CD70 attenuates apoptosis and enhances effector function of CD8+ T cells from MLK3-/- mice. In immune-competent breast cancer mouse model, pharmacological inhibition of MLK3 along with CD70 increased tumor infiltration of cytotoxic CD8+ T cells, leading to reduction in tumor burden largely via mitochondrial apoptosis.

CONCLUSION

Together, these results demonstrate that MLK3 plays an important role in CD8+ T cell survival and effector function and MLK3-CD70 axis could serve as a potential target in cancer.

Interleukin-1β and tumor necrosis factor are essential in controlling an experimental orthopedic implant-associated infection

Orthopedic implant-associated infection (OIAI) is a major complication that leads to implant failure. In preclinical models of Staphylococcus aureus OIAI, osteomyelitis and septic arthritis, interleukin-1α (IL-1α), IL-1β, and tumor necrosis factor (TNF) are induced, but whether they have interactive or distinctive roles in host defense are unclear. Herein, a S. aureus OIAI model was performed in mice deficient in IL-1α, IL-1β, or TNF. Mice deficient in IL-1β or TNF (to a lesser extent) but not IL-1α had increased bacterial burden at the site of the OIAI throughout the 28-day experiment. IL-1β and TNF had a combined and critical role in host defense as mice deficient in both IL-1R and TNF (IL-1R/TNF-deficient mice) had a 40% mortality rate, which was associated with markedly increased bacterial burden at the site of the OIAI infection. Finally, IL-1α- and IL-1β-deficient mice had impaired neutrophil recruitment whereas IL-1β-, TNF-, and IL-1R/TNF-deficient mice all had impaired recruitment of both neutrophils and monocytes. Therefore, IL-1β and TNF contributed to host defense against S. aureus OIAI and neutrophil recruitment was primarily mediated by IL-1β and monocyte recruitment was mediated by both IL-1β and TNF.

Tofacitinib treatment aggravates Staphylococcus aureus septic arthritis, but attenuates sepsis and enterotoxin induced shock in mice

Tofacitinib, a janus kinase inhibitor, is a novel immunosuppressive drug for treatment of rheumatoid arthritis (RA). Septic arthritis (SA) and sepsis caused by Staphylococcus aureus (S. aureus), for which RA patients are at risk, are infections with high mortality. The aim of this study was to investigate the effect of tofacitinib on S. aureus infections using mouse models. In vitro tofacitinib treated mouse splenocytes were stimulated with S. aureus derived stimuli. Mice pre-treated with tofacitinib were inoculated intravenously with either arthritogenic- or septic doses of S. aureus. Arthritis severity and mortality were compared between groups. Additionally, pre-treated mice were challenged with staphylococcal toxin TSST-1 to induce shock. Tofacitinib inhibited splenocyte proliferation and IFN-γ production in response to TSST-1 and dead S. aureus. In SA, tofacitinib treatment aggravated arthritis with more severe bone erosions. However, in sepsis, treated mice displayed significantly prolonged survival compared to controls. Similarly, in staphylococcal enterotoxin-induced shock tofacitinib pre-treatment, but not late treatment dramatically reduced mortality, which was accompanied by decreased levels of TNF-α and IFN-γ. Our findings show that tofacitinib treatment increase susceptibility of SA in mice, but has a positive effect on survival in S. aureus-induced sepsis and a strong protective effect in toxin-induced shock.

Neutralization of TNF-α and IL-1β Regulates CXCL8 Production through CXCL8/CXCR1 Axis in Macrophages during Staphylococcus aureus Infection

Anti-cytokine therapy is widely acknowledged as an anti-inflammatory technique to treat varied infectious diseases. TNF-α and IL-1β are major cytokines that regulate every aspect of the inflammatory process. However, the effects of single or dual cytokine neutralization on S. aureus mediated CXCL8 secretion and CXCR1 expression in murine peritoneal macrophages remained noninvestigated. Thus we aimed to explore the effects of kinetic-dose dependent neutralization of TNF-α and IL-1β using specific anti-cytokine antibodies and its influential impact on the CXCL8/CXCR1 axis at different stages of S. aureus (30, 60, and 90 min) infection. The murine peritoneal macrophages were isolated and infected with viable S. aureus followed by subsequent addition of anti-TNF-α and anti-IL-1β into the medium. The treated cells were centrifuged and lysate and supernatant collected for various experiments. The ROS generation was measured and cytokine production was estimated by ELISA. The expression of TNFR1, IL-1R, CXCR1, signaling molecules (NF-κB and JNK) were evaluated by Western blot. The role of single or dual cytokine neutralization on intracellular bacterial phagocytosis had also been analyzed by confocal microscopy. Dual cytokine neutralization significantly suppressed ROS, cytokines, CXCL8 secretion, and intracellular bacterial count compared to single cytokine neutralization and it was more apparent at 90 min post S. aureus infection. There was a drastic reduction in TNFR1, IL-1R, and CXCR1 expression on macrophage surface due to reduced expression of downstream signaling molecules, NF-κB and JNK. Hence dual cytokine neutralization was more effectual compared to single cytokine neutralization in the downregulation of S. aureus induced CXCR1 expression.

[Recombinant short TNF-BD protein from smallpox virus is pharmacologically active in an experimental septic shock model]

Tumor necrosis factor (TNF) is one among the key cytokines that mediate the immune system to protect humans against viral infections. Throughout evolution, anthropogenic Variola virus (VARV) has developed effective mechanisms to overcome human defense reactions. The viral genome encodes soluble proteins imitating the structure of cellular cytokine receptors. These proteins compete with cellular receptors for cytokine binding, thus blocking the antiviral immune response. In particular, the G2R gene of VARV encodes the TNF decoy receptor, VARV-CrmB protein. This protein consists of N-ended TNF-biding (TNF-BD) and C-ended chemokine binding (Ch-BD) domains. Recombinant VARV-CrmB protein has been produced in insect cells using molecular cloning methods and its TNF neutralizing activity has been shown in vitro and in vivo. To decrease the immunogenicity of this protein, a recombinant plasmid coding for shortened TNF-BD protein of VARV in Escherichia coli cells has been constructed. Using the method of immobilized metal affinity chromatography, recombinant TNF-BD protein corresponding to the TNF-biding domain of VARV-CrmB protein was purified from E. coli cells. The therapeutic potential of TNF-BD was studied using an experimental model of LPS-induced septic shock. After septic shock induction, several doses of recombinant TNF-BD were injected and the mortality of experimental animals was observed during 7 days. All mice not injected with TNF-BD had been dead by day 3 of the experiment, but 30, 40 and 60 % of the experimental animals, who received different TNF-BD doses, survived in a dose-dependent manner. Data obtained demonstrate that recombinant TNF-BD protein is pharmacologically active in the experimental model of LPS-induced septic shock.

Mice Lacking γδ T Cells Exhibit Impaired Clearance of Pseudomonas aeruginosa Lung Infection and Excessive Production of Inflammatory Cytokines

Pseudomonas aeruginosa is an opportunistic pathogen that causes chronic and life-threatening infections in immunocompromised patients. A better understanding of the role that innate immunity plays in the control of P. aeruginosa infection is crucial for therapeutic development. Specifically, the role of unconventional immune cells like γδ T cells in the clearance of P. aeruginosa lung infection is not yet well characterized.

Pseudomonas aeruginosa is an opportunistic pathogen that causes chronic and life-threatening infections in immunocompromised patients. A better understanding of the role that innate immunity plays in the control of P. aeruginosa infection is crucial for therapeutic development. Specifically, the role of unconventional immune cells like γδ T cells in the clearance of P. aeruginosa lung infection is not yet well characterized. In this study, the role of γδ T cells was examined in an acute mouse model of P. aeruginosa lung infection. In the absence of γδ T cells, mice displayed impaired bacterial clearance and decreased survival, outcomes which were associated with delayed neutrophil recruitment and impaired recruitment of other immune cells (macrophages, T cells, natural killer cells, and natural killer T [NKT] cells) into the airways. Despite reduced NKT cell recruitment in the airways of mice lacking γδ T cells, NKT cell-deficient mice exhibited wild-type level control of P. aeruginosa infection. Proinflammatory cytokines were also altered in γδ T cell-deficient mice, with increased production of interleukin-1β, interleukin-6, and tumor necrosis factor. γδ T cells did not appear to contribute significantly to the production of interleukin-17A or the chemokines CXCL1 and CXCL2. Importantly, host survival could be improved by inhibiting tumor necrosis factor signaling with the soluble receptor construct etanercept in γδ cell-deficient mice. These findings demonstrate that γδ T cells play a protective role in coordinating the host response to P. aeruginosa lung infection, both in contributing to early immune cell recruitment and by limiting inflammation.

The role of Staphylococcus aureus lipoproteins in hematogenous septic arthritis

Permanent joint dysfunction is a devastating complication in patients with septic arthritis. Staphylococcus aureus (S. aureus) lipoproteins (Lpp), the predominant ligands for TLR2, are known to be arthritogenic and induce bone destruction when introduced directly into the joint. Here, we aim to investigate the importance of S. aureus Lpp and TLR2 in a hematogenous septic arthritis model, which is the most common route of infection in humans. C57BL/6 wild-type and TLR2 deficient mice were intravenously inoculated with S. aureus Newman parental strain or its lipoprotein-deficient Δlgt mutant strain. The clinical course of septic arthritis, radiological changes, and serum levels of cytokines and chemokines, were assessed. Newman strain induced more severe and frequent clinical septic polyarthritis compared to its Δlgt mutant in TLR2 deficient mice, but not in wild-type controls. Bone destruction, however, did not differ between groups. Lpp expression was associated with higher mortality, weight loss as well as impaired bacterial clearance in mouse kidneys independent of TLR2. Furthermore, Lpp expression induced increased systemic pro-inflammatory cytokine and neutrophil chemokine release. Staphylococcal Lpp are potent virulence factors in S. aureus systemic infection independent of host TLR2 signalling. However, they have a limited impact on bone erosion in hematogenous staphylococcal septic arthritis.

Evaluation of the effect of intraperitoneal etanercept administration on oxidative stress and inflammation indicators in the kidney and blood of experimental sepsis-induced rats

INTRODUCTION:

Sepsis is an important cause of mortality and morbidity, and inflammatory response and oxidative stress play major roles underlying its pathophysiology. Here, we evaluated the effect of intraperitoneal etanercept administration on oxidative stress and inflammation indicators in the kidney and blood of experimental sepsis-induced rats.

METHODS:

Twenty-eight adult Sprague Dawley rats were classified into Control (Group 1), Sepsis (Group 2), Sepsis+Cefazolin (Group 3), and Sepsis+Cefazolin+Etanercept (Group 4) groups. Kidney tissue and serum samples were obtained for biochemical and histopathological investigations and examined for the C reactive protein (CRP), tumor necrosis factor-alpha (TNF-α), triggering receptor expressed on myeloid cells (TREM), and malondialdehyde (MDA) levels.

RESULTS:

The levels of TNF-α, TREM, and MDA in serum and kidney samples were significantly higher in rats from sepsis group than in rats from control group (p < 0.05). Group 3 showed a significant reduction in serum levels of TNF-α, CRP, and TREM as compared with Group 2 (p < 0.05). Serum TNF-α, CRP, TREM, and MDA levels and kidney TNF-α and TREM levels were significantly lower in Group 4 than in Group 2 (p < 0.05). Serum TNF-α and TREM levels in Group 4 were significantly lower than those in Group 3, and histopathological scores were significantly lower in Group 3 and Group 4 than in Group 2 (p < 0.05). Histopathological scores of Group 4 were significantly lower than those of Group 3 (p < 0.05).

CONCLUSIONS:

Etanercept, a TNF-α inhibitor, may ameliorate sepsis-induced oxidative stress, inflammation, and histopathological damage.

Synovial Fluid Interleukin-16 Contributes to Osteoclast Activation and Bone Loss through the JNK/NFATc1 Signaling Cascade in Patients with Periprosthetic Joint Infection

Because of lipopolysaccharide (LPS)-mediated effects on osteoclast differentiation and bone loss, periprosthetic joint infection (PJI) caused by Gram-negative bacteria increases the risk of aseptic loosening after reimplantation. Synovial fluid interleukin-16 (IL-16) expression was higher in patients with PJI than in patients without joint infection. Thus, we explored the effects of IL-16 on bone. We investigated whether IL-16 modulates osteoclast or osteoblast differentiation in vitro. An LPS-induced bone loss mice model was used to explore the possible advantages of IL-16 inhibition for the prevention of bone loss. IL-16 directly activated p38 and c-Jun N-terminal kinase (JNK)/mitogen-activated protein kinase (MAPK) signaling and increased osteoclast activation markers, including tartrate-resistant acid phosphatase (TRAP), cathepsin K, and nuclear factor of activated T cells 1 (NFATc1). IL-16 directly caused monocytes to differentiate into TRAP-positive osteoclast-like cells through NFATc1 activation dependent on JNK/MAPK signaling. Moreover, IL-16 did not alter alkaline phosphatase activity or calcium deposition during osteoblastic differentiation. Finally, IL-16 inhibition prevented LPS-induced trabecular bone loss and osteoclast activation in vivo. IL-16 directly increased osteoclast activation through the JNK/NFATc1 pathway. IL-16 inhibition could represent a new strategy for treating infection-associated bone loss.

Pre-treatment with IL2 gene therapy alleviates Staphylococcus aureus arthritis in mice

BACKGROUND

Staphylococcus aureus (S. aureus) arthritis is one of the most detrimental joint diseases known and leads to severe joint destruction within days. We hypothesized that the provision of auxiliary immunoregulation via an expanded compartment of T regulatory cells (Tregs) could dampen detrimental aspects of the host immune response whilst preserving its protective nature. Administration of low-dose interleukin 2 (IL2) preferentially expands Tregs, and is being studied as a treatment choice in several autoimmune conditions. We aimed to evaluate the role of IL2 and Tregs in septic arthritis using a well-established mouse model of haematogenously spred S. aureus arthritis.

METHODS

C57BL/6 or NMRI mice we intravenously (iv) injected with a defined dose of S. aureus LS-1 or Newman and the role of IL2 and Tregs were assessed by the following approaches: IL2 was endogenously delivered by intraperitoneal injection of a recombinant adeno-associated virus vector (rAAV) before iv S. aureus inoculation; Tregs were depleted before and during S. aureus arthritis using antiCD25 antibodies; Tregs were adoptively transferred before induction of S. aureus arthritis and finally, recombinant IL2 was used as a treatment starting day 3 after S. aureus injection. Studied outcomes included survival, weight change, bacterial clearance, and joint damage.

RESULTS

Expansion of Tregs induced by IL2 gene therapy prior to disease onset does not compromise host resistance to S. aureus infection, as the increased proportions of Tregs reduced the arthritis severity as well as the systemic inflammatory response, while simultaneously preserving the host's ability to clear the infection.

CONCLUSIONS

Pre-treatment with IL2 gene therapy dampens detrimental immune responses but preserves appropriate host defense, which alleviates S. aureus septic arthritis in a mouse model.

Potential anti-arthritic and anti-inflammatory effects of TNF-α processing inhibitor-1 (TAPI-1): A new approach to the treatment of S. aureus arthritis

Treatment of septic arthritis has become more challenging due to the rise of multidrug resistant strains of Staphylococcus aureus (S. aureus) in recent years. Failure of antibiotic therapies has compelled to initiate the search for new alternatives. This study aimed to unveil the potential anti-arthritic effects of TAPI-1 (TNF-α processing inhibitor-1), an inhibitor that inhibits TACE (TNF-α converting enzyme) mediated release of soluble TNF-α and its receptors along with attenuation of other inflammatory and joint destructive factors responsible for the progression of arthritis. Male Swiss albino mice were inoculated with live S. aureus (5 × 10⁶ cells/mouse) for the development of septic arthritis. TAPI-1 was administered intraperitoneally (10 mg/kg body weight) post S. aureus infection at regular intervals. Throughout the experiment, the severity of arthritis was obtained to be significantly low after TAPI-1 administration. Arthritis index and histopathology confirmed effectiveness of TAPI-1 in mitigating inflammation induced paw swelling and less bone-cartilage destruction in the arthritic knee joints. Lower levels of soluble tumor necrosis factor alpha (sTNF-α) and soluble tumor necrosis factor alpha receptor-1 (sTNFR-1) were detected in the TAPI-1 treated group suggesting TAPI-1 mediated blocking of TACE with subsequent inhibition of TNF-α signalling. Treatment with TAPI-1 lowered the levels of reactive species; matrix metalloproteinase-2 (MMP-2), receptor activator of nuclear factor kappa-B ligand (RANKL) and osteopontin (OPN) denoting less matrix degradation and less osteoclastic bone resorption. Together, this experimental work authenticates TAPI-1 as an alternative therapeutic intervention for the treatment of S. aureus arthritis.

A novel mouse model for septic arthritis induced by Pseudomonas aeruginosa

Septic arthritis is one of the most aggressive joint diseases. Although caused predominantly by S. aureus, Gram-negative bacteria, Pseudomonas aeruginosa among them, account for a significant percentage of the causal agents of septic arthritis. However, septic arthritis caused by P. aeruginosa has not been studied thus far, due to lack of an animal model. NMRI mice were inoculated with different doses of P. aeruginosa. The clinical course of septic arthritis and radiological changes of joints were examined. Furthermore, the host molecular and cellular mechanisms involved in P. aeruginosa-induced septic arthritis were investigated. Inoculation of mice with P. aeruginosa caused septic arthritis in a dose-dependent manner. Neutrophil depletion led to higher mortality and more severe joint destruction (p < 0.01). In contrast, monocyte depletion resulted in higher mortality (p < 0.05) but similar arthritis severity compared to controls. Mice depleted of CD4+ T-cells inoculated with P. aeruginosa displayed less severe bone damage (p < 0.05). For the first time, a mouse model for P. aeruginosa septic arthritis is presented. Our data demonstrate that neutrophils play a protective role in P. aeruginosa septic arthritis. Monocytes/macrophages, on the other hand, are only essential in preventing P. aeruginosa-induced mortality. Finally, CD4+ T-cells are pathogenic in P. aeruginosa septic arthritis.

Anti-TNF-α therapy alters the gut microbiota in proteoglycan-induced ankylosing spondylitis in mice

Ankylosing spondylitis is a chronic, progressive disease, and its treatment is relevant to the gut microbiota. Anti-tumor necrosis factor-alpha (anti-TNF-α) therapy alters the gut microbiota in many diseases, including inflammatory bowel disease. However, little is known about the effect of TNF-α blocker treatment on the gut microbiota in ankylosing spondylitis. Herein, the effect of a TNF-α blocker on the gut microbiota in proteoglycan-induced arthritis was investigated. Proteoglycan-induced mice were treated with an rhTNFR:Fc solution of etanercept (5 µg/g) for 4 weeks. rhTNFR:Fc treatment attenuated the arthritis incidence and severity of arthritis in the proteoglycan-induced mice and decreased inflammation in the ankle joints and ameliorated ileal tissue destruction. Moreover, high gut permeability occurred, and zonula occludens-1 and occludin protein levels were reduced in proteoglycan-induced mice. These levels were significantly restored by the administration of rhTNFR:Fc. The serum TNF-α and IL-17 levels were also decreased. In addition, flora analysis via 16S rDNA high-throughput sequencing revealed that rhTNFR:Fc treatment restored the gut microbiota composition to a composition similar to that in control mice. In conclusion, anti-TNF-α therapy attenuated proteoglycan-induced arthritis progression and modulated the gut microbiota and intestinal barrier function. These results provide new insights for anti-TNF-α therapy strategies via regulating the gut microbiota in ankylosing spondylitis.

Periprosthetic Joint Infection Caused by Gram-Positive Versus Gram-Negative Bacteria: Lipopolysaccharide, but not Lipoteichoic Acid, Exerts Adverse Osteoclast-Mediated Effects on the Bone

Periprosthetic joint infection (PJI)-the most common cause of knee arthroplasty failure-may result from Gram-positive (GP) or Gram-negative (GN) bacterial infections. The question as to whether PJI due to GP or GN bacteria can lead to different rates of aseptic loosening after reimplantation remains open. We have investigated this issue through a retrospective review of clinical records obtained from 320 patients with bacterial PJI. The results revealed that, compared with GP infections, GN infections were associated with an increased risk of aseptic loosening. In animal studies, mice underwent intrafemoral injection of lipopolysaccharide (LPS) from GN bacteria or lipoteichoic acid (LTA) from GP bacteria. We demonstrate that LPS-but not LTA-reduced both the number of trabeculae and the bone mineral density in mice. In addition, LPS-treated mice exhibited a reduced body weight, higher serum osteocalcin levels, and an increased number of osteoclasts. LPS accelerated monocyte differentiation into osteoclast-like cells, whereas LTA did not. Finally, ibudilast-a toll-like receptor (TLR)-4 antagonist-was found to inhibit LPS-induced bone loss and osteoclast activation in mice. Taken together, our data indicate that PJI caused by GN bacteria portends a higher risk of aseptic loosening after reimplantation, mainly because of LPS-mediated effects on osteoclast differentiation.

The YIN and YANG of lipoproteins in developing and preventing infectious arthritis by Staphylococcus aureus

Rapid bone destruction often leads to permanent joint dysfunction in patients with septic arthritis, which is mainly caused by Staphylococcus aureus (S. aureus). Staphylococcal cell wall components are known to induce joint inflammation and bone destruction. Here, we show that a single intra-articular injection of S. aureus lipoproteins (Lpps) into mouse knee joints induced chronic destructive macroscopic arthritis through TLR2. Arthritis was characterized by rapid infiltration of neutrophils and monocytes. The arthritogenic effect was mediated mainly by macrophages/monocytes and partially via TNF-α but not by neutrophils. Surprisingly, a S. aureus mutant lacking Lpp diacylglyceryl transferase (lgt) caused more severe joint inflammation, which coincided with higher bacterial loads of the lgt mutant in local joints than those of its parental strain. Coinjection of pathogenic S. aureus LS-1 with staphylococcal Lpps into mouse knee joints caused improved bacterial elimination and diminished bone erosion. The protective effect of the Lpps was mediated by their lipid moiety and was fully dependent on TLR2 and neutrophils. The blocking of CXCR2 on neutrophils resulted in total abrogation of the protective effect of the Lpps. Our data demonstrate that S. aureus Lpps elicit innate immune responses, resulting in a double-edged effect. On the one hand, staphylococcal Lpps boost septic arthritis. On the other hand, Lpps act as adjuvants and activate innate immunity, which could be useful for combating infections with multiple drug-resistant strains.

Rapid bone destruction often leads to permanent joint dysfunction in septic arthritis, which is mainly caused by S. aureus. Despite advances in the use of antibiotics, permanent reductions in joint function occur in up to 50% of patients, who may also need joint replacement surgery. Additional challenge is posed by increasing antibiotic resistance of S. aureus, causing significant clinical and economic consequences. Although the outcome is poor, the current treatments for septic arthritis remain unchanged since many decades. It is largely unknown which bacterial factors cause aggressive joint damage. Here, we show that a single intra-articular injection of S. aureus lipoproteins (Lpps) into mouse knee joints induced chronic destructive macroscopic arthritis, and the monocytes/macrophages were the main culprit. However, coinjection of pathogenic S. aureus with Lpps into mouse knee joints attenuated the disease. The protective effect of Lpps was mediated by their lipid moiety, TLR2 on the host cells, neutrophil chemokine release, and consequent neutrophil recruitment. Our finding might be used as a novel concept in the treatment of multidrug-resistant bacterial infections.

Dual neutralization of TNFR-2 and MMP-2 regulates the severity of S. aureus induced septic arthritis correlating alteration in the level of interferon gamma and interleukin-10 in terms of TNFR2 blocking

Severity of S. aureus septic arthritis is correlated to prolonged inflammation by inflammatory cytokines like TNF-α, IL-1β, and IL-6 even after successful elimination of bacteria. Role of TNF-α via TNFR2 is not well established in this aspect. IFN-γ induces TNF-α release from the macrophages augmenting the inflammatory arthritis. IL-10 modulates the levels of pro-inflammatory cytokines promoting resolution of inflammation. TNF-α-TNFR2 signaling upregulates both of these cytokines. Higher level of MMP-2 induction by inflammatory cytokines during arthritis promotes tissue destruction. Whether dual neutralization of TNFR-2 and MMP-2 regulates the severity of S. aureus arthritis by modulating local and systemic cytokine milieu mainly due to TNFR-2 blocking was an obvious question. Here, we attempted the effects of neutralization of MMP-2 and TNFR2 on S. aureus arthritis and its impact on pro-inflammatory cytokines and some other parameters related to tissue destruction. Reduction in arthritis index was noticed in infected mice treated with both MMP-2 inhibitor and TNFR2 antibody. Lowest levels of inflammatory cytokines, iNOS, RANKL, NF-κb, JNK kinase, ROS, and MPO, and lysozyme activity were observed in combined neutralization group at 9 and 15 dpi, but at 3 dpi, most of the above parameters remained elevated due to TNFR2 neutralization. Diminished IL-10 and IFN-γ levels as a result of TNFR2 neutralization at early and later phase of infection respectively might be responsible for these contrasting effects. Overall, it can be suggested that administration of MMP-2 inhibitor and TNFR2 antibody in combination is protective against the inflammation and tissue destruction associated with S. aureus infection during the arthritic episode.

Drug Repositioning to Alleviate Systemic Inflammatory Response Syndrome Caused by Gram-Negative Bacterial Outer Membrane Vesicles

Sepsis is characterized by systemic inflammatory response syndrome (SIRS) accompanied with infection. Gram-negative bacteria can evoke sepsis by activating the host immune system, such as the release of IL-6 and TNF-α, through their virulence factors. Outer membrane vesicles (OMVs), nanosized bilayered proteolipids derived from Gram-negative bacteria, harbor various virulence factors and are shown to induce SIRS. Here, drugs are repositioned to alleviate SIRS caused by Gram-negative bacterial OMVs. Using novel OMV-based drug screening systems, a total of 178 commercially available drugs are primarily screened, and a total of 18 repositioned drug candidates are found to effectively block IL-6 and TNF-α production from OMV-stimulated macrophages. After excluding the compounds which are previously known to intervene sepsis or which show cytotoxicity to macrophages, the compounds which show dose-dependency in inhibiting the release of IL-6 and TNF-α by the OMV-stimulated macrophages in vitro and which reduce OMV-induced SIRS in vivo are selected. Salbutamol, a β2 adrenergic receptor agonist, is selected as a novel candidate to alleviate OMV-induced SIRS. This study sheds light on using Gram-negative bacterial OMVs in exploring novel candidate compounds to alleviate inflammatory diseases including sepsis.

Antibiotics with Interleukin-15 Inhibition Reduce Joint Inflammation and Bone Erosions but Not Cartilage Destruction in Staphylococcus aureus-Induced Arthritis

Staphylococcus aureus-induced arthritis causes rapid joint destruction, often leading to disabling joint damage despite antibiotics. We have previously shown that interleukin-15 (IL-15) inhibition without antibiotics is beneficial in S. aureus-induced arthritis. We therefore hypothesized that the inhibition of IL-15, in combination with antibiotics, might represent a useful therapy that would reduce inflammation and joint destruction but preserve the host's ability to clear the infection. Female wild-type C57BL/6 mice were intravenously inoculated with the toxic shock syndrome toxin 1 (TSST-1)-producing LS-1 strain of S. aureus with 0.8 × 10⁸ CFU S. aureus LS-1/mouse. Three days later, treatment consisting of cloxacillin, followed by flucloxacillin, together with either anti-IL-15 antibodies (aIL-15ab) or control antibodies, was started. Studied outcomes included survival, weight change, bacterial clearance, and joint damage. The addition of aIL-15ab to antibiotics in S. aureus-induced arthritis reduced synovitis and bone erosions compared to controls. The number of bone-resorbing osteoclasts in the joints was reduced, whereas cartilage destruction was not significantly altered. Importantly, the combination therapy did not adversely affect the clinical outcome of S. aureus-induced arthritis, such as survival or weight change, or compromise the host's ability to clear the infection. Since the clinical outcome of S. aureus-induced arthritis was not affected, the addition of aIL-15ab to antibiotics ought to be safe. Taken together, the combination of aIL-15ab and antibiotics is a beneficial, but not optimal, treatment of S. aureus-induced arthritis since it reduces synovitis and bone erosions but has a limited effect on cartilage destruction.

Neutralization of MMP-2 and TNFR1 Regulates the Severity of S. aureus-Induced Septic Arthritis by Differential Alteration of Local and Systemic Proinflammatory Cytokines in Mice

Despite advancement in the field of antibiotics septic arthritis remains a serious concern till date. Staphylococcus aureus is the most common bacterium that causes septic arthritis. Severity of this disease is directly correlated with chronic inflammation induced by proinflammatory cytokines like TNF-α, interleukin (IL)-1β, IL-6, and induction of matrix metalloproteinases (MMPs) including MMP-2. The objective of our study was to evaluate the role of MMP-2 and tumor necrosis factor receptor 1 (TNFR1) in the pathogenesis of S. aureus infection-induced septic arthritis. Mice were infected with live S. aureus (5 × 10⁶ cells/ml) followed by administration of MMP-2 inhibitor and TNFR1 antibody. Arthritis index showed highest reduction in severity of arthritis in mice treated with both MMP-2 inhibitor and TNFR1 antibody after infection. Combined neutralization of MMP-2 and TNFR1 led to marked diminution in bacterial count in the combined group. Lowest levels of pro inflammatory cytokines like TNF-α, IL-1β, IL-6, and IFN-γ were observed in both serum and synovial tissues indicating maximum protection in S. aureus arthritis during combination treatment. Increment in the level of IL-10 in the combination group could be positively correlated with the recovery of arthritis. Similarly, expressions of COX-2 and iNOS, markers of acute inflammation were also significantly reduced in the combination group due to resolution of inflammation. Levels of O2^.- and NO also showed a significant fall in case of the group treated with MMP-2 inhibitor and TNFR1 antibody both. Neutralization of both MMP-2 and TNFR1 caused rapid decline in recruitment of neutrophil and macrophages in the synovial tissues as evident from reduced MPO and MCP-1 levels, respectively, compared to other groups. Overall, it can be suggested that administration of MMP-2 inhibitor and TNFR1 antibody in combination is protective against the severity of inflammation and cartilage destruction associated with S. aureus infection-induced septic arthritis by altering the levels of cytokines.

Neutralization of TNFR-1 and TNFR-2 modulates S. aureus induced septic arthritis by regulating the levels of pro inflammatory and anti inflammatory cytokines during the progression of the disease

Staphylococcal septic arthritis remains a serious medical concern due to rapid and sustained production of inflammatory cytokines that leads to progressive and irreversible joint destruction with high mortality rate in patients despite adequate antibiotics treatment. TNF-α signalling via TNFR-1 contributes to arthritic destruction by aggravating inflammation. Impact of TNFR-2 signalling is not well established in this aspect. Hence the objective of our study was to evaluate the role of dual neutralization TNFR-1 and TNFR-2 in the pathogenesis of S. aureus infection induced septic arthritis. Mice were infected with live S. aureus (5 × 10⁶ cells/ml) followed by administration of TNFR-1and TNFR-2 neutralizing antibody. To measure arthritis index and osteoclastogenesis, histology result in joint tissue and TRAP staining images of arthritis joints have been performed respectively. Maximum reduction in the joint and paw swelling was observed in infected mice treated with both TNFR-1 and TNFR-2 antibody. NF-κB signalling was found to be mainly regulated by TNFR-1 whereas TNFR-2 significantly modulated JNK pathway. Lowest levels of inflammatory cytokines like TNF-α, IL-1β, IL-6, and IFN-γ were observed in both serum and synovial tissues signifying maximum protection in S. aureus arthritis during combination treatment. However IFN-γ and IL-10 levels were significantly altered by TNFR-2 neutralization that indicates both pro and anti inflammatory role of TNFR-2 respectively. Highest decrement in ROS concentration, iNOS expression with least MPO and lysozyme activity was detected in case of combined neutralization. During the early phase of infection all the aforesaid inflammatory parameters remained elevated due to lack of IL-10 as a result of TNFR-2 neutralization as IL-10 negatively modulates pro inflammatory cytokines. Increase in inflammatory cytokines during early phase might also be responsible for decreased bacterial count in TNFR-2 neutralized groups. Thus it can be suggested that combined administration of TNFR-1 and TNFR-2 antibody has a beneficial effect against the severity of S. aureus induced arthritis.

CXCR2 is critical for bacterial control and development of joint damage and pain in Staphylococcus aureus-induced septic arthritis in mouse

Staphylococcus aureus is the main pathogen associated with septic arthritis. Upon infection, neutrophils are quickly recruited to the joint by different chemoattractants, especially CXCR1/2 binding chemokines. Although their excessive accumulation is associated with intense pain and permanent articular damage, neutrophils have an important function in controlling bacterial burden. This work aimed to study the role of CXCR2 in the control of infection, hypernociception and tissue damage in S. aureus-induced septic arthritis in mice. The kinetics of neutrophil recruitment correlated with the bacterial load recovered from inflamed joint after intra-articular injection of S. aureus. Treatment of mice from the start of infection with the non-competitive antagonist of CXCR1/2, DF2156A, reduced neutrophil accumulation, cytokine production in the tissue, joint hypernociception and articular damage. However, early DF2156A treatment increased the bacterial load locally. CXCR2 was important for neutrophil activation and clearance of bacteria in vitro and in vivo. Start of treatment with DF2156A 3 days after infection prevented increase in bacterial load and reduced the hypernociception in the following days, but did not improve tissue damage. In conclusion, treatment with DF2156A seems be effective in controlling tissue inflammation and dysfunction but its effects are highly dependent on the timing of the treatment start.

Implications of designing a bromelain loaded enteric nanoformulation on its stability and anti-inflammatory potential upon oral administration

The objective of the present investigation was to develop an enteric nano-formulation of bromelain to improve its stability and anti-inflammatory potential. Bromelain loaded nanoparticles (Br-NPs) were developed using a Eudragit L 100 polymer by a double emulsion solvent evaporation method to obtain gastro-resistant properties. Br-NPs were characterized for particle size (248.89 ± 22.76 nm), zeta potential (-27.34 ± 2.17 mV), entrapment efficiency (85.42 ± 5.34%), surface morphology (spherical) and in vitro release profile. Infrared spectroscopy confirmed the entrapment of bromelain while thermal and pXRD analysis concomitantly corroborated the reduced crystallinity of bromelain in nanoparticles. Formulations showed gastro-resistant behavior at gastric pH and sustained bromelain release up to 10 h in phosphate buffer at pH 6.8 and followed Higuchi square root release kinetics. The optimized lyophilized formulation ensured 2 year shelf-life at room temperature. In vivo studies revealed significantly improved performance of entrapped bromelain in inhibiting carrageenan induced paw edema by mitigating leucocyte migration and release of nitric oxide, TNFα and IL-1β in paw compared to bromelain solution. In conclusion, enteric Br-NPs could be a viable drug delivery system for effective oral bromelain delivery in inflammatory conditions.

Infliximab alleviates the mortality, mesenteric hypoperfusion, aortic dysfunction, and multiple organ damage in septic rats

Tumor necrosis factor-alpha (TNF-α) is a pivotal mediator that triggers inflammatory process, oxidative stress, and multiple organ injury in sepsis. We investigated the effects of infliximab on survival, mesenteric artery blood flow (MBF), vascular reactivity, and oxidative and inflammatory injuries in cecal ligation and puncture (CLP)-induced sepsis. Wistar rats were divided into Sham, CLP, Sham+infliximab, and CLP+infliximab subgroups. Twenty-four hours before the operations, rats were injected intraperitoneally with infliximab (7 mg/kg) or vehicle (saline; 1 mL/kg). Twenty hours after the operations, MBF and phenylephrine responses of isolated aortic rings were measured. Tissue damages were examined biochemically and histopathologically. Furthermore, survival rates were monitored throughout 96 h. Infliximab improved survival, mesenteric perfusion, and aortic function after CLP. Increases of serum AST, ALT, LDH, BUN, Cr, and inflammatory cytokines (tumor necrosis factor-alpha, interleukin-1 beta, and interleukin-6) induced by CLP were blocked by infliximab. Infliximab prevented malondialdehyde elevations in septic liver, lung, spleen, and kidney tissues, as well as glutathione reductions in septic liver, spleen, and kidney tissues. Protective effects of infliximab on multiple organ damage were also observed histopathologically. Infliximab showed protective effects in sepsis due to its improvement effects on mesenteric perfusion, aortic function, and its anti-inflammatory and antioxidative effects.

[Effects of recombinant fusion protein interleukin-18 on expression of immune-inflammatory factors in mice infected with Staphylococcus aureus]

OBJECTIVE

To observe the effects of recombinant fusion protein interleukin (IL)-18 on the expression of immune-inflammatory factors in the mice infected with Staphylococcus aureus (SA), and to investigate the mechanism of action of IL-18 in defense of SA infection in vivo.

METHODS

A total of 40 specific pathogen-free female BLAB/c mice were randomly divided into four groups: control, SA infection, immunized, and intervention. A mouse model of SA infection was established by nasal inoculation with SA liquid. The immunized group and the intervention group were intranasally given IL-18 before SA modeling, and then the SA infection group and the intervention group received the nasal inoculation with SA liquid; the control group was treated with phosphate buffered saline instead. The levels of IL-4, interferon (IFN)-γ, tumor necrosis factor (TNF), granulocyte colony-stimulating factor (G-CSF), IgM in the serum and bronchoalveolar lavage fluid (BALF) of mice were measured by enzyme-linked immunosorbent assay. The expression of macrophage inflammatory protein (MIP)-1α mRNA and MIP-2β mRNA in the lung tissue of mice were determined by real-time fluorescent quantitative PCR.

RESULTS

Compared with the control group, the SA infection group and the immunized group had significantly higher levels of IL-4, G-CSF, and IgM in the serum and BALF and expression of MIP-1α mRNA and MIP-2β mRNA in the lung tissue (P<0.05); the SA infection group had a significantly lower level of IFN-γ and a significantly higher level of TNF in the serum and BALF (P<0.05); the immunized group had a significantly higher level of IFN-γ in the serum and BALF (P<0.05). Compared with the SA infection group, the intervention group had significantly higher levels of IL-4, IFN-γ, G-CSF, and IgM in the serum and BALF and expression of MIP-1α mRNA in the lung tissue. In contrast, the intervention group showed a significantly lower level of TNF in the serum and BALF and expression of MIP-2β mRNA in the lung tissue (P<0.05). All the above indicators in the intervention group were significantly higher than those in the control group (P<0.05), except the serum level of IFN-γ.

CONCLUSIONS

In the mice infected with SA, the recombinant fusion protein IL-18 by mucosal immunity can affect inflammatory factors in the serum and BALF and the expression of MIP-1α mRNA and MIP-2β mRNA in the lung tissue to promote the anti-infective immune response and enhance the ability to clear pathogens.