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RAGE-Mediated Suppression of Interleukin-10 Results in Enhanced Mortality in a Murine Model of Acinetobacter baumannii Sepsis.

ABSTRACT: The receptor for advanced glycation end products (RAGE) is a pattern recognition receptor capable of recognizing multiple pathogen-associated and danger-associated molecular patterns that contributes to the initiation and potentiation of inflammation in many disease processes. During infection, RAGE functions to either exacerbate disease severity or enhance pathogen clearance depending on the pathogen studied. Acinetobacter baumannii is an opportunistic human pathogen capable of causing severe infections, including pneumonia and sepsis, in impaired hosts. The role of RAGE signaling in response to opportunistic bacterial infections is largely unknown. In murine models of A. baumannii pneumonia, RAGE signaling alters neither inflammation nor bacterial clearance. In contrast, RAGE-/- mice systemically infected with A. baumannii exhibit increased survival and reduced bacterial burdens in the liver and spleen. The increased survival of RAGE-/- mice is associated with increased circulating levels of the anti-inflammatory cytokine interleukin-10 (IL-10). Neutralization of IL-10 in RAGE-/- mice results in decreased survival during systemic A. baumannii infection that mirrors that of wild-type (WT) mice, and exogenous IL-10 administration to WT mice enhances survival in this model. These findings demonstrate the role for RAGE-dependent IL-10 suppression as a key modulator of mortality from Gram-negative sepsis.

SUBMITTER: Noto MJ

PROVIDER: S-EPMC5328494 | biostudies-other | 2017 Mar

REPOSITORIES: biostudies-other

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Project description:Immune response stimulation to prevent infection progression may be an adjuvant to antimicrobial treatment. Lysophosphatidylcholine (LPC) is an immunomodulator involved in immune cell recruitment and activation. In this study, we aimed to evaluate the efficacy of LPC in combination with colistin, tigecycline, or imipenem in experimental murine models of peritoneal sepsis and pneumonia. We used Acinetobacter baumannii strain Ab9, which is susceptible to colistin, tigecycline, and imipenem, and multidrug-resistant strain Ab186, which is susceptible to colistin and resistant to tigecycline and imipenem. Pharmacokinetic and pharmacodynamic parameters for colistin, tigecycline, and imipenem and the 100% minimal lethal dose (MLD100) were determined for both strains. The therapeutic efficacies of LPC, colistin (60 mg/kg of body weight/day), tigecycline (10 mg/kg/day), and imipenem (180 mg/kg/day), alone or in combination, were assessed against Ab9 and Ab186 at the MLD100 in murine peritoneal sepsis and pneumonia models. The levels of pro- and anti-inflammatory cytokines, i.e., tumor necrosis factor alpha (TNF-?) and interleukin-10 (IL-10), were determined by enzyme-linked immunosorbent assay (ELISA) for the same experimental models after inoculating mice with the MLD of both strains. LPC in combination with colistin, tigecycline, or imipenem markedly enhanced the bacterial clearance of Ab9 and Ab186 from the spleen and lungs and reduced bacteremia and mouse mortality rates (P < 0.05) compared with those for colistin, tigecycline, and imipenem monotherapies. Moreover, at 4 h post-bacterial infection, Ab9 induced higher TNF-? and lower IL-10 levels than those with Ab186 (4 ?g/ml versus 3 ?g/ml [P < 0.05] and 2 ?g/ml versus 3.4 ?g/ml [P < 0.05], respectively). LPC treatment combined with colistin, tigecycline, or imipenem modestly reduced the severity of infection by A. baumannii strains with different resistance phenotypes compared to LPC monotherapy in both experimental models.

Project description:BackgroundSepsis is a serious syndrome that is caused by an unbalanced host inflammatory response to an infection. The cytokine network plays a pivotal role in the orchestration of inflammatory response during sepsis. IL-26 is an emerging proinflammatory member of the IL-10 cytokine family with multifaceted actions in inflammatory disorders. However, its role in the pathogenesis of sepsis remains unknown.MethodsSerum IL-26 level was measured and analyzed in 52 septic patients sampled on the day of intensive care unit (ICU) admission, 18 non-septic ICU patient controls, and 30 healthy volunteers. In addition, the effects of recombinant human IL-26 on host inflammatory response in cecal ligation and puncture (CLP)-induced polymicrobial sepsis were determined.ResultsOn the day of ICU admission, the patients with sepsis showed a significant increase in serum IL-26 levels compared with ICU patient controls and healthy volunteers, and the serum IL-26 levels were related to the severity of sepsis. Nonsurvivors of septic patients displayed significantly higher serum IL-26 levels compared with survivors. A high serum IL-26 level on ICU admission was associated with 28-day mortality, and IL-26 was found to be an independent predictor of 28-day mortality in septic patients by logistic regression analysis. Furthermore, administration of recombinant human IL-26 increased lethality in CLP-induced polymicrobial sepsis. Despite a lower bacterial load, septic mice treated with recombinant IL-26 had higher concentrations of IL-1β, IL-4, IL-6, IL-10, IL-17A, TNF-α, CXCL1, and CCL2 in peritoneal lavage fluid and blood and demonstrated more severe multiple organ injury (including lung, liver and kidney) as indicated by clinical chemistry and histopathology. Furthermore, septic mice treated with recombinant human IL-26 showed an increased neutrophil recruitment to the peritoneal cavity.ConclusionsSeptic patients had elevated serum IL-26 levels, which may correlate with disease severity and mortality. In experimental sepsis, we demonstrated a previously unrecognized role of IL-26 in increasing lethality despite promoting antibacterial host responses.

Project description:Patients recovering from traumatic injuries or surgery often require weeks to months of hospitalization, increasing the risk for wound and surgical site infections caused by ESKAPE pathogens, which include A. baumannii (the ESKAPE pathogens are Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species). As new therapies are being developed to counter A. baumannii infections, animal models are also needed to evaluate potential treatments. Here, we present an excisional, murine wound model in which a diminutive inoculum of a clinically relevant, multidrug-resistant A. baumannii isolate can proliferate, form biofilms, and be effectively treated with antibiotics. The model requires a temporary, cyclophosphamide-induced neutropenia to establish an infection that can persist. A 6-mm-diameter, full-thickness wound was created in the skin overlying the thoracic spine, and after the wound bed was inoculated, it was covered with a dressing for 7 days. Uninoculated control wounds healed within 13 days, whereas infected, placebo-treated wounds remained unclosed beyond 21 days. Treated and untreated wounds were assessed with multiple quantitative and qualitative techniques that included gross pathology, weight loss and recovery, wound closure, bacterial burden, 16S rRNA community profiling, histopathology, peptide nucleic acid-fluorescence in situ hybridization, and scanning electron microscopy assessment of biofilms. The range of differences that we are able to identify with these measures in antibiotic- versus placebo-treated animals provides a clear window within which novel antimicrobial therapies can be assessed. The model can be used to evaluate antimicrobials for their ability to reduce specific pathogen loads in wounded tissues and clear biofilms. Ultimately, the mouse model approach allows for highly powered studies and serves as an initial multifaceted in vivo assessment prior to testing in larger animals.

Project description:BackgroundInterestingly, Acinetobacter baumannii presents an enhanced capacity to form biofilms (also named pellicles) at the air-liquid interface as compared to the other Acinetobacter species. This characteristic questions the contribution of this phenotype to an increased risk of clinical infections by this pathogen.Methodology/principal findingsBy a proteomic approach using 2-D gel electrophoresis-LC-MS/MS mass spectrometry, we compared the membrane protein patterns of A. baumannii 77, a pellicle-forming clinical isolate, grown in planktonic and in sessile modes. We identified 52 proteins with a differential expression, including 32 up-regulated and 20 down-regulated in the pellicle state. Several proteins, differentially expressed during pellicle development, were of particular interest. We determined the over-expression of four siderophore iron uptake systems including the acinetobactin and enterobactin receptors and confirmed that the development of this type of biofilm is promoted by ferric ions. Two over-expressed proteins, CarO and an OprD-homologue, putative carbapenem-resistance associated porins, would be involved in the transport of specific compounds, like ornithine, a biosynthesis precursor of a siderophore from the hydroxamate family. We evidenced the overexpression of a lipase and a transporter of LCFA that may be involved in the recycling of lipids inside the pellicle matrix. Finally, we demonstrated both by proteomic and by AFM studies that this particular type of biofilm required multiple pili systems to maintain this cohesive structure at the air-liquid interface; two of these systems have never been described in A. baumannii.Conclusions/significanceOur study demonstrated that several proteins, overexpressed at a late state of pellicle development, could be potentially involved in virulence processes. Therefore, regarding the number of potential virulence factors that are over-expressed in this growth mode, the pellicle-forming clinical isolates should be kept under survey.

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RAGE-Mediated Suppression of Interleukin-10 Results in Enhanced Mortality in a Murine Model of Acinetobacter baumannii Sepsis.

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