Candida-induced granulocytic myeloid-derived suppressor cells are protective against polymicrobial sepsis

IMPORTANCE

Polymicrobial intra-abdominal infections are serious clinical infections that can lead to life-threatening sepsis, which is difficult to treat in part due to the complex and dynamic inflammatory responses involved. Our prior studies demonstrated that immunization with low-virulence Candida species can provide strong protection against lethal polymicrobial sepsis challenge in mice. This long-lived protection was found to be mediated by trained Gr-1+ polymorphonuclear leukocytes with features resembling myeloid-derived suppressor cells (MDSCs). Here we definitively characterize these cells as MDSCs and demonstrate that their mechanism of protection involves the abrogation of lethal inflammation, in part through the action of the anti-inflammatory cytokine interleukin (IL)-10. These studies highlight the role of MDSCs and IL-10 in controlling acute lethal inflammation and give support for the utility of trained tolerogenic immune responses in the clinical treatment of sepsis.

Activation of thousands of genes in the lungs and kidneys by sepsis is countered by the selective nuclear blockade

The steady rise of sepsis globally has reached almost 49 million cases in 2017, and 11 million sepsis-related deaths. The genomic response to sepsis comprising multi-system stage of raging microbial inflammation has been reported in the whole blood, while effective treatment is lacking besides anti-microbial therapy and supportive measures. Here we show that, astoundingly, 6,237 significantly expressed genes in sepsis are increased or decreased in the lungs, the site of acute respiratory distress syndrome (ARDS). Moreover, 5,483 significantly expressed genes in sepsis are increased or decreased in the kidneys, the site of acute injury (AKI). This massive genomic response to polymicrobial sepsis is countered by the selective nuclear blockade with the cell-penetrating Nuclear Transport Checkpoint Inhibitor (NTCI). It controlled 3,735 sepsis-induced genes in the lungs and 1,951 sepsis-induced genes in the kidneys. The NTCI also reduced without antimicrobial therapy the bacterial dissemination: 18-fold in the blood, 11-fold in the lungs, and 9-fold in the spleen. This enhancement of bacterial clearance was not significant in the kidneys. Cumulatively, identification of the sepsis-responsive host's genes and their control by the selective nuclear blockade advances a better understanding of the multi-system mechanism of sepsis. Moreover, it spurs much-needed new diagnostic, therapeutic, and preventive approaches.

Rational Design of Stapled Antimicrobial Peptides to Enhance Stability and In Vivo Potency against Polymicrobial Sepsis

In this work, we sought to develop a TP4-based stapled peptide that can be used to counter polymicrobial sepsis. First, we segregated the TP4 sequence into hydrophobic and cationic/hydrophilic zones and substituted the preferred residue, lysine, as the sole cationic amino acid. These modifications minimized the intensity of cationic or hydrophobic characteristics within small segments. Then, we incorporated single or multiple staples into the peptide chain, bracketing the cationic/hydrophilic segments to improve pharmacological suitability. Using this approach, we were able to develop an AMP with low toxicity and notable in vivo efficacy. IMPORTANCE In our in vitro studies, one dual stapled peptide out of the series of candidates (TP4-3: FIIXKKSXGLFKKKAGAXKKKXIKK) showed significant activity, low toxicity, and high stability (in 50% human serum). When tested in cecal ligation and puncture (CLP) mouse models of polymicrobial sepsis, TP4-3 improved survival (87.5% on day 7). Furthermore, TP4-3 enhanced the activity of meropenem against polymicrobial sepsis (100% survival on day 7) compared to meropenem alone (37.5% survival on day 7). Molecules such as TP4-3 may be well suited for a wide variety of clinical applications.

LACTATE IMPAIRS VASCULAR PERMEABILITY BY INHIBITING HSPA12B EXPRESSION VIA GPR81-DEPENDENT SIGNALING IN SEPSIS

ABSTRACT

Introduction: Sepsis impaired vascular integrity results in multiple organ failure. Circulating lactate level is positively correlated with sepsis-induced mortality. We investigated whether lactate plays a role in causing endothelial barrier dysfunction in sepsis. Methods: Polymicrobial sepsis was induced in mice by cecal ligation and puncture (CLP). Lactic acid was injected i.p. (pH 6.8, 0.5 g/kg body weight) 6 h after CLP or sham surgery. To elucidate the role of heat shock protein A12B (HSPA12B), wild-type, HSPA12B-transgenic, and endothelial HSPA12B-deficient mice were subjected to CLP or sham surgery. To suppress lactate signaling, 3OBA (120 μM) was injected i.p. 3 h before surgery. Vascular permeability was evaluated with the Evans blue dye penetration assay. Results: We found that administration of lactate elevated CLP-induced vascular permeability. Vascular endothelial cadherin (VE-cadherin), claudin 5, and zonula occluden 1 (ZO-1) play a crucial role in the maintenance of endothelial cell junction and vascular integrity. Lactate administration significantly decreased VE-cadherin, claudin 5, and ZO-1 expression in the heart of septic mice. Our in vitro data showed that lactate (10 mM) treatment disrupted VE-cadherin, claudin 5, and ZO-1 in endothelial cells. Mechanistically, we observed that lactate promoted VE-cadherin endocytosis by reducing the expression of HSPA12B. Overexpression of HSPA12B prevented lactate-induced VE-cadherin disorganization. G protein-coupled receptor 81 (GPR81) is a specific receptor for lactate. Inhibition of GPR81 with its antagonist 3OBA attenuated vascular permeability and reversed HSPA12B expression in septic mice. Conclusions: The present study demonstrated a novel role of lactate in promoting vascular permeability by decreasing VE-cadherin junctions and tight junctions in endothelial cells. The deleterious effects of lactate in vascular hyperpermeability are mediated via HSPA12B- and GPR81-dependent signaling.

Protective role of melatonin against testicular damage caused by polymicrobial sepsis in adult rats

BACKGROUND

This study aimed to investigate the possible protective effects of melatonin (MEL) against the damage to testicular tissue in rats caused by polymicrobial sepsis as a result of cecal ligation and perforation (CLP).

METHODS

In this study, 21 male Wistar albino rats were used. The rats were randomly divided into three groups (n=7): Sham Control (Group 1), CLP (Group 2), and CLP + MEL (Group 3). Sepsis was created using the CLP method. MEL was administered intraperitoneally in two equal doses of 10 mg/kg at 30 min before and 6 h after perforation. Tissue sections taken from paraffin blocks were stained with hematoxylin and eosin (H and E) and examined histopathologically under a light microscope. Intracellular H2O2 and apoptosis evaluations were carried out using the flow cytometric method.

RESULTS

Sepsis caused a significant reduction in all sperm parameters. There was a significant decrease in sperm density, motility and cell numbers with normal morphology (p<0.05). Intracellular H2O2 level and apoptotic cell percentages increased in sperm cells in the CLP group. MEL treatment was found to significantly reduce sperm abnormalities, testicular damage, intracellular H2O2 levels, and apoptosis.

CONCLUSION

This study showed that melatonin administration could be a potential treatment option to reduce acute testicular tissue damage due to sepsis.

Molecular Methodologies for Improved Polymicrobial Sepsis Diagnosis

Polymicrobial sepsis is associated with worse patient outcomes than monomicrobial sepsis. Routinely used culture-dependent microbiological diagnostic techniques have low sensitivity, often leading to missed identification of all causative organisms. To overcome these limitations, culture-independent methods incorporating advanced molecular technologies have recently been explored. However, contamination, assay inhibition and interference from host DNA are issues that must be addressed before these methods can be relied on for routine clinical use. While the host component of the complex sepsis host–pathogen interplay is well described, less is known about the pathogen’s role, including pathogen–pathogen interactions in polymicrobial sepsis. This review highlights the clinical significance of polymicrobial sepsis and addresses how promising alternative molecular microbiology methods can be improved to detect polymicrobial infections. It also discusses how the application of shotgun metagenomics can be used to uncover pathogen/pathogen interactions in polymicrobial sepsis cases and their potential role in the clinical course of this condition.

Aprepitant: an antiemetic drug, contributes to the prevention of acute lung injury with its anti-inflammatory and antioxidant properties

OBJECTIVES

We investigated, the effects of aprepitant (APRE) on the lung tissues of rats with an experimental polymicrobial sepsis model (CLP: cecal ligation and puncture) biochemically, molecularly and histopathologically.

METHODS

A total of 40 rats were divided into 5 groups with 8 animals in each group. Group 1 (SHAM), control group; Group 2 (CLP), cecal ligation and puncture; Group 3 (CLP + APRE10), rats were administered CLP + 10 mg/kg aprepitant; Group 4 (CLP + APRE20), rats were administered CLP + 20 mg/kg aprepitant; and Group 5 (CLP + APRE40), rats were administered CLP + 40 mg/kg aprepitant. A polymicrobial sepsis model was induced with CLP. After 16 h, lung tissues were taken for examination. Tumour necrosis factor α (TNF-α) and nuclear factor-kappa b (NFK-b) messenger ribonucleic acid (mRNA) expressions were analysed by real-time PCR (RT-PCR), biochemically antioxidant parameters such as superoxide dismutase (SOD) and glutathione (GSH) and oxidant parameters such as malondialdehyde (MDA) and lung damage histopathologically.

KEY FINDINGS AND CONCLUSIONS

The GSH level and SOD activity increased while the MDA level and the expressions of TNF-α and NFK-b were reduced in the groups treated with APRE, especially in the CLP + APRE40 group. The histopathology results supported the molecular and biochemical results.

Immunomodulatory Effect of Doxycycline Ameliorates Systemic and Pulmonary Inflammation in a Murine Polymicrobial Sepsis Model

Acute lung injury is an inflammatory condition developed after severe sepsis in response to excessive secretion of pro-inflammatory cytokines. Doxycycline is widely reported to possess immunomodulatory activity through inhibition of various inflammatory pathways. Considering the broad spectrum of anti-inflammatory activity, protective effect of doxycycline was evaluated in clinically relevant murine polymicrobial sepsis model induced by caecal ligation and puncture (CLP). In this model, sepsis is accompanied with infection and therefore ceftriaxone at sub-protective dose was combined to retard the bacterial growth. Three hours after CLP challenge, mice were administered vehicle, ceftriaxone (100 mg/kg subcutaneously) alone and in combination with immunomodulatory dose of doxycycline (50 mg/kg, intraperitoneal) and survival were monitored for 5 days. Bacterial count in blood and peritoneal fluid along with cytokines [interleukin (IL)-6, IL-1β, tumour necrosis factor (TNF)-α] and myeloperoxidase (MPO) in plasma and lung homogenate were measured at 18 h post-CLP. Plasma glutathione (GSH) was also determined. Doxycycline in presence of ceftriaxone improved survival of septic mice by significantly reducing the plasma and lung pro-inflammatory cytokines and MPO levels. It also increased plasma GSH levels. Doxycycline did not improve antibacterial effect of ceftriaxone in combination, suggesting that the protective effect of doxycycline was due to its immunomodulatory activity. Doxycycline in the presence of ceftriaxone demonstrated improved survival of septic mice by modulating the immune response.

Divergent Effects of the N-Methyl-D-Aspartate Receptor Antagonist Kynurenic Acid and the Synthetic Analog SZR-72 on Microcirculatory and Mitochondrial Dysfunction in Experimental Sepsis

Introduction: Sepsis is a dysregulated host response to infection with macro- and microhemodynamic deterioration. Kynurenic acid (KYNA) is a metabolite of the kynurenine pathway of tryptophan catabolism with pleiotropic cell-protective effects under pro-inflammatory conditions. Our aim was to investigate whether exogenously administered KYNA or the synthetic analog SZR-72 affects the microcirculation and mitochondrial function in a clinically relevant rodent model of intraabdominal sepsis.

Methods: Male Sprague–Dawley rats (n = 8/group) were subjected to fecal peritonitis (0.6 g kg⁻¹ feces ip) or a sham operation. Septic animals were treated with sterile saline or received ip KYNA or SZR-72 (160 μmol kg⁻¹ each) 16 and 22 h after induction. Invasive monitoring was performed on anesthetized animals to evaluate respiratory, cardiovascular, renal, hepatic and metabolic dysfunctions (PaO₂/FiO₂ ratio, mean arterial pressure, urea, AST/ALT ratio and lactate levels, respectively) based on the Rat Organ Failure Assessment (ROFA) score. The ratio of perfused vessels (PPV) of the ileal serosa was quantified with the intravital imaging technique. Complex I- and II-linked (CI; CII) oxidative phosphorylation capacities (OXPHOS) and mitochondrial membrane potential (ΔΨmt) were evaluated by High-Resolution FluoRespirometry (O2k, Oroboros, Austria) in liver biopsies. Plasma endothelin-1 (ET-1), IL-6, intestinal nitrotyrosine (NT) and xanthine oxidoreductase (XOR) activities were measured as inflammatory markers.

Results: Sepsis was characterized by an increased ROFA score (5.3 ± 1.3 vs. 1.3 ± 0.7), increased ET-1, IL-6, NT and XOR levels, and decreased serosal PPV (65 ± 12% vs. 87 ± 7%), ΔΨmt and CI–CII-linked OXPHOS (73 ± 16 vs. 158 ± 14, and 189 ± 67 vs. 328 ± 81, respectively) as compared to controls. Both KYNA and SZR-72 reduced systemic inflammatory activation; KYNA treatment decreased serosal perfusion heterogeneity, restored PPV (85 ± 11%) and complex II-linked OXPHOS (307 ± 38), whereas SZR-72 improved both CI- and CII-linked OXPHOS (CI: 117 ± 18; CII: 445 ± 107) without effects on PPV 24 h after sepsis induction.

Conclusion: Treatment with SZR-72 directly modulates mitochondrial respiration, leading to improved conversion of ADP to ATP, while administration of KYNA restores microcirculatory dysfunction. The results suggest that microcirculatory and mitochondrial resuscitation with KYNA or the synthetic analog SZR-72 might be an appropriate supportive tool in sepsis therapy.

Microbial Exposure Enhances Immunity to Pathogens Recognized by TLR2 but Increases Susceptibility to Cytokine Storm through TLR4 Sensitization

Microbial exposures can define an individual's basal immune state. Cohousing specific pathogen-free (SPF) mice with pet store mice, which harbor numerous infectious microbes, results in global changes to the immune system, including increased circulating phagocytes and elevated inflammatory cytokines. How these differences in the basal immune state influence the acute response to systemic infection is unclear. Cohoused mice exhibit enhanced protection from virulent Listeria monocytogenes (LM) infection, but increased morbidity and mortality to polymicrobial sepsis. Cohoused mice have more TLR2⁺ and TLR4⁺ phagocytes, enhancing recognition of microbes through pattern-recognition receptors. However, the response to a TLR2 ligand is muted in cohoused mice, whereas the response to a TLR4 ligand is greatly amplified, suggesting a basis for the distinct response to Listeria monocytogenes and sepsis. Our data illustrate how microbial exposure can enhance the immune response to unrelated challenges but also increase the risk of immunopathology from a severe cytokine storm.

RvE1 Attenuates Polymicrobial Sepsis-Induced Cardiac Dysfunction and Enhances Bacterial Clearance

The development of cardiac dysfunction caused by microbial infection predicts high mortality in sepsis patients. Specialized pro-resolving mediators (SPMs) mediate resolution of inflammation in many inflammatory diseases, and are differentially expressed in plasma of sepsis patients. Here, we investigated whether the levels of SPMs are altered in the murine septic heart following polymicrobial sepsis-induced cardiac dysfunction. Ten weeks-old male C57BL/6 mice were subjected to polymicrobial sepsis induced by cecal ligation and puncture (CLP), which is a clinically relevant sepsis model receiving analgesics, antibiotics, and fluid resuscitation. CLP caused a significant systolic dysfunction assessed by echocardiography. The hearts were subjected to LC-MS/MS based lipid mediator profiling. Many SPMs were significantly reduced in septic hearts, among which RvE1 had a ~93-fold reduction. Treatment of CLP mice with synthetic RvE1 (1 μg/mouse i.v.) at 1 h after CLP increased peritoneal macrophages number, particularly MHC II^- macrophages. RvE1 reduced pro-inflammatory gene expression (interleukin-1β, interleukin-6, and CCL2) in lipopolysaccharide-stimulated bone marrow-derived macrophages (BMDMs) in vitro. RvE1 attenuated cardiac dysfunction in septic mice and increased cardiac phosphorylated Akt; decreased cardiac phosphorylated IκB kinase α/β, nuclear translocation of the NF-κB subunit p65, extracellular signal-regulated kinase 1/2, and c-Jun amino-terminal kinases 1/2. Most notably, RvE1 treatment reduced peritoneal bacterial load and promoted phagocytosis activity of BMDMs. In conclusion, cardiac SPMs, particularly RvE1, are substantially reduced in mice with polymicrobial sepsis. Delayed therapeutic administration of RvE1 to mice with polymicrobial sepsis attenuates the cardiac dysfunction through modulating immuno-inflammatory responses. In addition to the above effects, the ability to enhance bacterial clearance makes RvE1 an ideal therapeutic to reduce the sequalae of polymicrobial sepsis.

Oxidation-Specific Epitopes (OSEs) Dominate the B Cell Response in Murine Polymicrobial Sepsis

In murine abdominal sepsis by colon ascendens stent peritonitis (CASP), a strong increase in serum IgM and IgG antibodies was observed, which reached maximum values 14 days following sepsis induction. The specificity of this antibody response was studied in serum and at the single cell level using a broad panel of bacterial, sepsis-unrelated as well as self-antigens. Whereas an antibacterial IgM/IgG response was rarely observed, studies at the single-cell level revealed that IgM antibodies, in particular, were largely polyreactive. Interestingly, at least 16% of the IgM mAbs and 20% of the IgG mAbs derived from post-septic mice showed specificity for oxidation-specific epitopes (OSEs), which are known targets of the innate/adaptive immune response. This identifies those self-antigens as the main target of B cell responses in sepsis.

Agaricus brasiliensis Mushroom Protects Against Sepsis by Alleviating Oxidative and Inflammatory Response

Sepsis is characterized by the host's dysregulated immune response to an infection followed by a potentially fatal organ dysfunction. Although there have been some advances in the treatment of sepsis, mainly focused on broad-spectrum antibiotics, mortality rates remain high, urging for the search of new therapies. Oxidative stress is one of the main features of septic patients, so antioxidants can be a good alternative treatment. Agaricus brasiliensis is a nutraceutical rich in bioactive compounds such as polyphenols and polysaccharides, exhibiting antioxidant, antitumor, and immunomodulatory activities. Here, we investigated the immunomodulatory and antioxidant effects of A. brasilensis aqueous extract in the cecal ligation and puncture (CLP) sepsis model. Our data showed that aqueous extract of A. brasiliensis reduced systemic inflammatory response and improved bacteria clearance and mice survival. In addition, A brasiliensis decreased the oxidative stress markers in serum, peritoneal cavity, heart and liver of septic animals, as well as ROS production (in vitro and in vivo) and tert-Butyl hydroperoxide-induced DNA damage in peripheral blood mononuclear cells from healthy donors in vitro. In conclusion, the aqueous extract of A. brasiliensis was able to increase the survival of septic animals by a mechanism involving immunomodulatory and antioxidant protective effects.

Endothelial HSPA12B Exerts Protection Against Sepsis-Induced Severe Cardiomyopathy via Suppression of Adhesion Molecule Expression by miR-126

Heat shock protein A12B (HSPA12B) is predominately expressed in endothelial cells (ECs) and has been reported to protect against cardiac dysfunction from endotoxemia or myocardial infarction. This study investigated the mechanisms by which endothelial HSPA12B protects polymicrobial sepsis–induced cardiomyopathy. Wild-type (WT) and endothelial HSPA12B knockout (HSPA12B^–/–) mice were subjected to polymicrobial sepsis induced by cecal ligation and puncture (CLP). Cecal ligation and puncture sepsis accelerated mortality and caused severe cardiac dysfunction in HSPA12B^–/– mice compared with WT septic mice. The levels of adhesion molecules and the infiltrated immune cells in the myocardium of HSPA12B^–/– septic mice were markedly greater than in WT septic mice. The levels of microRNA-126 (miR-126), which targets adhesion molecules, in serum exosomes from HSPA12B^–/– septic mice were significantly lower than in WT septic mice. Transfection of ECs with adenovirus expressing HSPA12B significantly increased miR-126 levels. Increased miR-126 levels in ECs prevented LPS-stimulated expression of adhesion molecules. In vivo delivery of miR-126 carried by exosomes into the myocardium of HSPA12B^–/– mice significantly attenuated CLP sepsis increased levels of adhesion molecules, and improved CLP sepsis–induced cardiac dysfunction. The data suggest that HSPA12B protects against sepsis-induced severe cardiomyopathy via regulating miR-126 expression which targets adhesion molecules, thus decreasing the accumulation of immune cells in the myocardium.

A probable case of catastrophic antiphospholipid syndrome: Should high-dose steroids be given in the setting of polymicrobial sepsis?

In this clinical vignette, we present a case of a 59-year-old woman with catastrophic antiphospholipid syndrome likely triggered by polymicrobial sepsis. The diagnostic criteria and clinical manifestations of catastrophic antiphospholipid syndrome are reviewed. We also compare diagnostic criteria and clinical manifestations with other clinical entities in the differential diagnosis, including thrombotic thrombocytopenic purpura-hemolytic-uremic syndrome, disseminated intravascular coagulation, sepsis, and inflammatory bowel disease. Catastrophic antiphospholipid syndrome is a rare, but lethal condition, and treatment recommendations are based on expert consensus and analyses of the international Catastrophic Antiphospholipid Syndrome Registry. Current management guidelines recommend triple therapy, with anticoagulation, glucocorticoids, and plasma exchange or intravenous immunoglobulins. This case brings this rare clinical entity to the attention of clinicians and emphasizes the need for more research to understand the best management. It also raises the question of whether high-dose steroids should be continued for treatment of catastrophic antiphospholipid syndrome in the setting of a severe sepsis.

Azithromycin in Combination with Ceftriaxone Reduces Systemic Inflammation and Provides Survival Benefit in a Murine Model of Polymicrobial Sepsis

Sepsis is a life-threatening systemic inflammatory condition triggered as a result of an excessive host immune response to infection. In the past, immunomodulators have demonstrated a protective effect in sepsis. Azithromycin (a macrolide antibiotic) has immunomodulatory activity and was therefore evaluated in combination with ceftriaxone in a clinically relevant murine model of sepsis induced by cecal ligation and puncture (CLP). First, mice underwent CLP and 3 h later were administered the vehicle or a subprotective dose of ceftriaxone (100 mg/kg of body weight subcutaneously) alone or in combination with an immunomodulatory dose of azithromycin (100 mg/kg intraperitoneally). Survival was monitored for 5 days. In order to assess the immunomodulatory activity, parameters such as plasma and lung cytokine (interleukin-6 [IL-6], IL-1β, tumor necrosis factor alpha) concentrations, the plasma glutathione (GSH) concentration, plasma and lung myeloperoxidase (MPO) concentrations, body temperature, blood glucose concentration, and total white blood cell count, along with the bacterial load in blood, peritoneal lavage fluid, and lung homogenate, were measured 18 h after CLP challenge. Azithromycin in the presence of ceftriaxone significantly improved the survival of CLP-challenged mice. Further, the combination attenuated the elevated levels of inflammatory cytokines and MPO in plasma and lung tissue and increased the body temperature and blood glucose and GSH concentrations, which were otherwise markedly decreased in CLP-challenged mice. Ceftriaxone produced a significant reduction in the bacterial load, while coadministration of azithromycin did not produce a further reduction. Therefore, the survival benefit offered by azithromycin was due to immunomodulation and not its antibacterial action. The findings of this study indicate that azithromycin, in conjunction with appropriate antibacterial agents, could provide clinical benefits in sepsis.

Sphingosine 1-Phosphate- and C-C Chemokine Receptor 2-Dependent Activation of CD4+ Plasmacytoid Dendritic Cells in the Bone Marrow Contributes to Signs of Sepsis-Induced Immunosuppression

Sepsis is the dysregulated response of the host to systemic, mostly bacterial infection, and is associated with an enhanced susceptibility to life-threatening opportunistic infections. During polymicrobial sepsis, dendritic cells (DCs) secrete enhanced levels of interleukin (IL) 10 due to an altered differentiation in the bone marrow and contribute to the development of immunosuppression. We investigated the origin of the altered DC differentiation using murine cecal ligation and puncture (CLP), a model for human polymicrobial sepsis. Bone marrow cells (BMC) were isolated after sham or CLP operation, the cellular composition was analyzed, and bone marrow-derived DCs (BMDCs) were generated in vitro. From 24 h on after CLP, BMC gave rise to BMDC that released enhanced levels of IL-10. In parallel, a population of CD11c^hiMHCII⁺CD4⁺ DCs expanded in the bone marrow in a MyD88-dependent manner. Prior depletion of the CD11c^hiMHCII⁺CD4⁺ DCs from BMC in vitro reversed the increased IL-10 secretion of subsequently differentiating BMDC. The expansion of the CD11c^hiMHCII⁺CD4⁺ DC population in the bone marrow after CLP required the function of sphingosine 1-phosphate receptors and C-C chemokine receptor (CCR) 2, the receptor for C-C chemokine ligand (CCL) 2, but was not associated with monocyte mobilization. CD11c^hiMHCII⁺CD4⁺ DCs were identified as plasmacytoid DCs (pDCs) that had acquired an activated phenotype according to their increased expression of MHC class II and CD86. A redistribution of CD4⁺ pDCs from MHC class II⁻ to MHC class II⁺ cells concomitant with enhanced expression of CD11c finally led to the rise in the number of CD11c^hiMHCII⁺CD4⁺ DCs. Enhanced levels of CCL2 were found in the bone marrow of septic mice and the inhibition of CCR2 dampened the expression of CD86 on CD4⁺ pDCs after CLP in vitro. Depletion of pDCs reversed the bias of splenic DCs toward increased IL-10 synthesis after CLP in vivo. Thus, during polymicrobial sepsis, CD4⁺ pDCs are activated in the bone marrow and induce functional reprogramming of differentiating BMDC toward an immunosuppressive phenotype.

Celecoxib Enhances the Efficacy of Low-Dose Antibiotic Treatment against Polymicrobial Sepsis in Mice and Clinical Isolates of ESKAPE Pathogens

Treatment of multidrug resistant bacterial infections has been a great challenge globally. Previous studies including our study have highlighted the use of celecoxib, a non-steroidal anti-inflammatory drug in combination with antibiotic has decreased the minimal inhibitory concentration to limit Staphylococcus aureus infection. However, the efficacy of this combinatorial treatment against various pathogenic bacteria is not determined. Therefore, we have evaluated the potential use of celecoxib in combination with low doses of antibiotic in limiting Gram-positive and Gram-negative bacteria in vivo in murine polymicrobial sepsis developed by cecum ligation and puncture (CLP) method and against clinically isolated human ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species). The in vivo results clearly demonstrated a significant reduction in the bacterial load in different organs and in the inflammatory markers such as COX-2 and NF-κB via activation of SIRT1 in mice treated with imipenem, a choice of antibiotic for polymicrobial sepsis treatment. Combinatorial treatment of ampicillin and celecoxib was effective on clinical isolates of ESKAPE pathogens, 45% of tested clinical isolates showed more than 50% reduction in the colony forming units when compared to ampicillin alone. In conclusion, this non-traditional treatment strategy might be effective in clinic to reduce the dose of antibiotic to treat drug-resistant bacterial infections.

Reduced Expression of SARM in Mouse Spleen during Polymicrobial Sepsis

Objective Immune dysfunction, including prominent apoptosis of immune cells and decreased functioning of the remaining immune cells, plays a central role in the pathogenesis of sepsis. Sterile α and HEAT/armadillo motif-containing protein (SARM) is implicated in the regulation of immune cell apoptosis. This study aimed to elucidate SARM contributes to sepsis-induced immune cell death and immunosuppression. Methods A mouse model of polymicrobial sepsis was generated by cecum ligation and puncture (CLP). SARM gene and protein expression, caspase 3 cleavage and intracellular ATP production were measured in the mouse spleens. Results CLP-induced polymicrobial sepsis specifically attenuated both the gene and protein expression of SARM in the spleens. Moreover, the attenuation of SARM expression synchronized with splenocyte apoptosis, as evidenced by increased caspase 3 cleavage and ATP depletion. Conclusions These findings suggest that SARM is a potential regulator of sepsis-induced splenocyte apoptosis.

Kaempferol and Chrysin Synergies to Improve Septic Mice Survival

Previously, we reported the role of synergy between two flavonoids—namely, chrysin and kaempferol—in inhibiting the secretion of a few major proinflammatory mediators such as tumor necrosis factor-alpha (TNF-α), prostaglandin E₂ (PGE₂), and nitric oxide (NO) from lipopolysaccharide (LPS)-induced RAW 264.7 cells. The present study aims to evaluate the effects of this combination on a murine model of polymicrobial sepsis induced by cecal ligation and puncture (CLP). Severe sepsis was induced in male ICR mice (n = 7) via the CLP procedure. The effects of chrysin and kaempferol combination treatment on septic mice were investigated using a 7-day survival study. The levels of key proinflammatory mediators and markers—such as aspartate aminotransferase (AST), TNF-α, and NO—in the sera samples of the septic mice were determined via ELISA and fluorescence determination at different time point intervals post-CLP challenge. Liver tissue samples from septic mice were harvested to measure myeloperoxidase (MPO) levels using a spectrophotometer. Moreover, intraperitoneal fluid (IPF) bacterial clearance and total leukocyte count were also assessed to detect any antibacterial effects exerted by chrysin and kaempferol, individually and in combination. Kaempferol treatment improved the survival rate of CLP-challenged mice by up to 16%. During this treatment, kaempferol expressed antibacterial, antiapoptotic and antioxidant activities through the attenuation of bacterial forming units, AST and NO levels, and increased polymorphonuclear leukocyte (PMN) count in the IPF. On the other hand, the chrysin treatment significantly reduced serum TNF-α levels. However, it failed to significantly improve the survival rate of the CLP-challenged mice. Subsequently, the kaempferol/chrysin combination treatment significantly improved the overall 7-day survival rate by 2-fold—up to 29%. Kaempferol and chrysin revealed some synergistic effects by acting individually upon multiple pathophysiological factors involved during sepsis. Although the kaempferol/chrysin combination did not exhibit significant antibacterial effects, it did exhibit anti-inflammatory and antioxidant activities, which translate to significant improvement in the survival rate of septic animals. These findings suggest the potential application of this combination treatment as a beneficial adjuvant supplement strategy in sepsis control.

The role of myeloid differentiation factor 88 on mitochondrial dysfunction of peritoneal leukocytes during polymicrobial sepsis

OBJECTIVE

To investigate the role of myeloid differentiation factor 88 (MyD88) on mitochondrial dysfunction of peritoneal leukocytes during polymicrobial sepsis.

MATERIAL AND METHODS

Polymicrobial peritonitis, a clinically relevant mouse model of sepsis, was generated by cecum ligation and puncture (CLP) in both male C57BL/6J wild-type (WT) and MyD88 knockout (MyD88(-/-)) mice. Twenty-four hours after surgeries, peritoneal leukocytes were collected and four parameters of mitochondrial function, including total intracellular and mitochondrial ROS burst, mitochondrial membrane depolarization and ATP depletion, were measured by flow cytometry or ATP assay, and then compared.

RESULTS

Polymicrobial sepsis led to a marked mitochondrial dysfunction of peritoneal leukocytes with total intracellular and mitochondrial ROS overproduction, decreased mitochondrial membrane potential and reduced intracellular ATP production. In comparison, there was no significant difference in the extent of mitochondrial dysfunction of peritoneal leukocytes between WT and MyD88(-/-) septic mice.

CONCLUSIONS

MyD88 may be not sufficient to regulate mitochondrial dysfunction of peritoneal leukocytes during polymicrobial sepsis.

Fish Oil-Based Fat Emulsion Reduces Acute Kidney Injury and Inflammatory Response in Antibiotic-Treated Polymicrobial Septic Mice

Acute kidney injury (AKI) is a common complication in sepsis. This study compared the effects of a fish oil-based with a mixed oil fat emulsion on remote renal injury in an antibiotic-treated septic murine model. Mice were randomly assigned to a normal control (NC) group and three septic groups. Sepsis was induced by cecal ligation and puncture (CLP). The antibiotic was injected intraperitoneally (IP) after CLP and then daily till the time of sacrifice. Three hours after antibiotic treatment, one of the septic groups was injected IP with a fish oil-based emulsion (FO), while the other two groups were given either a mixed oil emulsion (MO) or saline (SC). The septic groups were further divided into two separate time groups, with blood and kidneys samples collected at 24 h or 72 h post-CLP. The results showed that sepsis leads to the activation of neutrophils, T helper (Th)1/Th-2/Th-17 and Treg cells (p < 0.05). Plasma NGAL and mRNA expressions of renal MyD88 and TLR4 were also enhanced (p < 0.05). Compared to the SC group, the group given the fish oil-based emulsion had decreased plasma NGAL by 22% and Treg by 33%. Furthermore, renal gene expressions of MyD88 and TLR4 reduced by 46% and 62%, respectively, whereas heat shock protein 70 and peroxisome proliferator-activated receptor-γ increased by 158% and 69%, respectively (p < 0.05), at Day 3 after CLP. These results suggest that administration of a fish oil-based emulsion has favorable effects, maintaining blood T cell percentage, downregulating Treg expression, attenuating systemic and local inflammation and offering renal protection under conditions of antibiotic-treated polymicrobial sepsis.

Gadolinium chloride modulates bradykinin-induced pulmonary vasoconstriction and hypoxic pulmonary vasoconstriction during polymicrobial abdominal sepsis in rats

BACKGROUND

Macrophages importantly contribute to sepsis-induced lung injury. As their impact on pulmonary endothelial injury and dysregulation of hypoxic pulmonary vasoconstriction (HPV) remains unclear, we assessed pulmonary endothelial dysfunction and HPV by macrophage inhibition via gadolinium chloride (GC) pre-treatment in rats with peritonitis (cecal ligation and puncture [CLP]).

METHODS

The following four study groups were made: Group I: SHAM and group II: SHAM + GC (pre-treatment with NaCl 0.9% or GC 14 mg/kg body weight (b.w.) intravenously 24 hours prior to sham laparotomy); group III: CLP and group IV: CLP + GC (pre-treatment with NaCl 0.9% or GC 14 mg/kg b.w. 24 hours prior to induction of peritonitis). Exhaled nitric oxide (exNO), bradykinin-induced pulmonary vasoconstriction (=surrogate marker of endothelial dysfunction) and HPV were investigated in isolated and perfused lungs (n = 40). Using the same protocol wet to dry lung weight ratio and myeloperoxidase (MPO) activity were investigated in separate rats (n = 28). In additional rats (n = 12) of groups III and IV nitrite levels in alveolar macrophages (AM) were measured.

RESULTS

In sepsis, GC pre-treatment significantly attenuated exNO levels, AM-derived nitrite levels, lung MPO activity, and restored blunted HPV, but severely enhanced endothelial dysfunction in healthy and septic animals.

CONCLUSION

Macrophages exhibit a controversial role in sepsis-induced lung injury. The GC-induced restoration of inflammation parameters to sham levels is clearly limited by the negative impact on CLP-induced endothelial injury in this setting. The exact link between the GC-associated modulation of the NO pathway demonstrated and septic lung injury needs to be determined in future studies.

Super-low dose endotoxin pre-conditioning exacerbates sepsis mortality

Sepsis mortality varies dramatically in individuals of variable immune conditions, with poorly defined mechanisms. This phenomenon complements the hypothesis that innate immunity may adopt rudimentary memory, as demonstrated in vitro with endotoxin priming and tolerance in cultured monocytes. However, previous in vivo studies only examined the protective effect of endotoxin tolerance in the context of sepsis. In sharp contrast, we report herein that pre-conditioning with super-low or low dose endotoxin lipopolysaccharide (LPS) cause strikingly opposite survival outcomes. Mice pre-conditioned with super-low dose LPS experienced severe tissue damage, inflammation, increased bacterial load in circulation, and elevated mortality when they were subjected to cecal-ligation and puncture (CLP). This is in contrast to the well-reported protective phenomenon with CLP mice pre-conditioned with low dose LPS. Mechanistically, we demonstrated that super-low and low dose LPS differentially modulate the formation of neutrophil extracellular trap (NET) in neutrophils. Instead of increased ERK activation and NET formation in neutrophils pre-conditioned with low dose LPS, we observed significantly reduced ERK activation and compromised NET generation in neutrophils pre-conditioned with super-low dose LPS. Collectively, our findings reveal a mechanism potentially responsible for the dynamic programming of innate immunity in vivo as it relates to sepsis risks.

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Super-low dose endotoxin pre-conditioning exacerbates, while higher dose endotoxin alleviates sepsis mortality.

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Super-low dose endotoxin reduces, while higher dose endotoxin facilitates neutrophil extracellular trap (NET) formation.

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Super-low dose endotoxin suppresses, while higher dose endotoxin induces ERK activation required for NET formation.

Role of extracellular histones in the cardiomyopathy of sepsis

The purpose of this study was to define the relationship in polymicrobial sepsis (in adult male C57BL/6 mice) between heart dysfunction and the appearance in plasma of extracellular histones. Procedures included induction of sepsis by cecal ligation and puncture and measurement of heart function using echocardiogram/Doppler parameters. We assessed the ability of histones to cause disequilibrium in the redox status and intracellular [Ca(2+)]i levels in cardiomyocytes (CMs) (from mice and rats). We also studied the ability of histones to disturb both functional and electrical responses of hearts perfused with histones. Main findings revealed that extracellular histones appearing in septic plasma required C5a receptors, polymorphonuclear leukocytes (PMNs), and the Nacht-, LRR-, and PYD-domains-containing protein 3 (NLRP3) inflammasome. In vitro exposure of CMs to histones caused loss of homeostasis of the redox system and in [Ca(2+)]i, as well as defects in mitochondrial function. Perfusion of hearts with histones caused electrical and functional dysfunction. Finally, in vivo neutralization of histones in septic mice markedly reduced the parameters of heart dysfunction. Histones caused dysfunction in hearts during polymicrobial sepsis. These events could be attenuated by histone neutralization, suggesting that histones may be targets in the setting of sepsis to reduce cardiac dysfunction.