Peptidoglycan of Staphylococcus aureus causes inflammation and organ injury in the rat*

The role of programmed cell death in organ dysfunction induced by opportunistic pathogens

Sepsis is a life-threatening condition resulting from pathogen infection and characterized by organ dysfunction. Programmed cell death (PCD) during sepsis has been associated with the development of multiple organ dysfunction syndrome (MODS), impacting various physiological systems including respiratory, cardiovascular, renal, neurological, hematological, hepatic, and intestinal systems. It is well-established that pathogen infections lead to immune dysregulation, which subsequently contributes to MODS in sepsis. However, recent evidence suggests that sepsis-related opportunistic pathogens can directly induce organ failure by promoting PCD in parenchymal cells of each affected organ. This study provides an overview of PCD in damaged organ and the induction of PCD in host parenchymal cells by opportunistic pathogens, proposing innovative strategies for preventing organ failure in sepsis.

Lung Organoids—The Ultimate Tool to Dissect Pulmonary Diseases?

Organoids are complex multicellular three-dimensional (3D) in vitro models that are designed to allow accurate studies of the molecular processes and pathologies of human organs. Organoids can be derived from a variety of cell types, such as human primary progenitor cells, pluripotent stem cells, or tumor-derived cells and can be co-cultured with immune or microbial cells to further mimic the tissue niche. Here, we focus on the development of 3D lung organoids and their use as disease models and drug screening tools. We introduce the various experimental approaches used to model complex human diseases and analyze their advantages and disadvantages. We also discuss validation of the organoids and their physiological relevance to the study of lung diseases. Furthermore, we summarize the current use of lung organoids as models of host-pathogen interactions and human lung diseases such as cystic fibrosis, chronic obstructive pulmonary disease, or SARS-CoV-2 infection. Moreover, we discuss the use of lung organoids derived from tumor cells as lung cancer models and their application in personalized cancer medicine research. Finally, we outline the future of research in the field of human induced pluripotent stem cell-derived organoids.

Citral alleviates peptidoglycan-induced inflammation and disruption of barrier functions in porcine intestinal epithelial cells

Peptidoglycan (PGN) is a major polymer in bacterial cell walls and may constrain gut functionality and lower intestinal efficiencies in livestock. Citral has been reported to exhibit antibacterial and anti-inflammatory biological activities, improving the gastrointestinal function of swine. However, the protective effect of citral against PGN-elicited cellular responses and possible underlying mechanisms are unknown. In this study, the porcine jejunal epithelial cell line (IPEC-J2) was challenged with PGN from Staphylococcus aureus (S. aureus) or Bacillus subtilis (B. subtilis) to explore PGN-induced inflammatory responses. Our data showed that the inflammatory response stimulated by PGN from harmful bacteria (S. aureus) was more potent than that from commensal bacteria (B. subtilis) in IPEC-J2 cells. Based on the inflammatory model by PGN from S. aureus, it was demonstrated that PGN could significantly induce inflammatory cytokine production and influence nutrient absorption and barrier function in a dose-dependent manner. However, the PGN-mediated immune responses were remarkably suppressed by citral. In addition, citral significantly attenuated the effect of PGN on the intestine nutrient absorption and barrier function. The expression of TLR2 was strongly induced by PGN stimulation, which was suppressed by citral. All data nominated that citral downregulated PGN-induced inflammation via TLR2-mediated activation of the NF-κB signaling pathway in IPEC-J2 cells. Furthermore, the results also indicate that the PGN degradation through the inclusion of enzymes (e.g., muramidase) as well as the inclusion of citral for attenuating inflammation may improve pig gut health and functionality.

Iron Chelation in Murine Models of Systemic Inflammation Induced by Gram-Positive and Gram-Negative Toxins

Iron is an essential element for various physiological processes, but its levels must remain tightly regulated to avoid cellular damage. Similarly, iron plays a dual role in systemic inflammation, such as with sepsis. Leukocytes utilize iron to produce reactive oxygen species (ROS) to kill bacteria, but pathologically increased iron-catalyzed ROS production in sepsis can lead to damage of host cells, multi-organ failure and death. Temporary reduction in bioavailable iron represents a potential therapeutic target in sepsis. This study investigates the effect of the novel iron chelator, DIBI, in murine models of systemic (hyper-)inflammation: C57BL/6 mice were challenged with toxins from Gram-positive (Staphylococcus aureus: lipoteichoic acid, peptidoglycan) and Gram-negative bacteria (Escherichia coli and Klebsiella pneumoniae: lipopolysaccharide). Intravital microscopy (IVM) was performed to assess immune cell activation and its impact on microvascular blood flow in vivo in the microcirculation of the gut. Plasma inflammatory mediators were measured via multiplex assay, and morphologic change in intestinal tissue was evaluated. DIBI treatment decreased leukocyte (hyper-)activation induced by Gram-positive and Gram-negative toxins. In some cases, it preserved capillary perfusion, reduced plasma inflammatory markers and attenuated tissue damage. These findings support the utility of DIBI as a novel treatment for systemic inflammation, e.g., sepsis.

Effect of bisphenol A on human neutrophils immunophenotype

Neutrophils (PMN) play a key role in eliciting congenital immune response. These cells are equipped with specific receptors that are located on the surface of their cell membrane. These receptors produce various signals which in turn help in the effective functioning of PMN. The activity of these cells may be modified by factors of endo- and exogenous origin, including xenoestrogens such as bisphenol A (BPA). The aim of this study was to evaluate the effect of BPA on the expression of CD11c, CD14, CD15, CD16, CD62L and CD284 compounds on the surface of neutrophils in women and men. The study material included PMN isolated from the whole blood. The cells were incubated in the presence of BPA and/or LPS. Flow cytometry technique was used to evaluate the expression of CD antigens. Studies of these receptors indicate that BPA, at a concentration corresponding to the serum level of this compound in healthy subjects as well as at higher doses, induces changes in the immunophenotype of PMN, which may lead to immunity disorders associated with the dysfunction of these cells. Moreover, the observed effects of xenoestrogen on the expression of CD11c, CD14, CD15, CD16, CD62L and CD284 differentiation markers on these cells are sex-independent.

Lipoteichoic acids as a major virulence factor causing inflammatory responses via Toll-like receptor 2

Lipoteichoic acid (LTA), a major cell wall component of Gram-positive bacteria, is associated with various inflammatory diseases ranging from minor skin diseases to severe sepsis. It is known that LTA is recognized by Toll-like receptor 2 (TLR2), leading to the initiation of innate immune responses and further development of adaptive immunity. However, excessive immune responses may result in the inflammatory sequelae that are involved in severe diseases such as sepsis. Although numerous studies have tried to identify the molecular basis for the pathophysiology of Gram-positive bacterial infection, the exact role of LTA during the infection has not been clearly elucidated. This review provides an overview of LTA structure and host recognition by TLR2 that leads to the activation of innate immune responses. Emphasis is placed on differential immunostimulating activities of LTAs of various Gram-positive bacteria at the molecular level.

Staphylococcus aureus induces IL-8 expression through its lipoproteins in the human intestinal epithelial cell, Caco-2

Staphylococcus aureus can cause the intestinal inflammatory diseases. However, little is known about the molecular mechanism of S. aureus infection in the intestine. In the present study, we investigated whether S. aureus could stimulate human intestinal epithelial cells triggering inflammation. When the human intestinal epithelial cell-line, Caco-2, and the primary colon cells were stimulated with ethanol-inactivated S. aureus, IL-8 expression was induced in a dose-dependent manner. The inactivated S. aureus preferentially stimulated Toll-like receptor (TLR) 2 rather than TLR4. Lipoproteins, lipoteichoic acid (LTA), and peptidoglycan (PGN) are considered as potential TLR2 ligands of S. aureus. Interestingly, S aureus lipoproteins and Pam2CSK4 mimicking Gram-positive bacterial lipoproteins, but not LTA and PGN of S. aureus, significantly induced IL-8 expression in Caco-2 cells. Furthermore, lipoprotein-deficient S. aureus mutant strain failed to induce IL-8 production. Collectively, these results suggest that S. aureus stimulates the human intestinal epithelial cells to induce the chemokine IL-8 production through its lipoproteins, potentially contributing the development of intestinal inflammation.

Early effects of Staphylococcus aureus biofilm secreted products on inflammatory responses of human epithelial keratinocytes

BACKGROUND

Chronic wounds such as diabetic foot ulcers, pressure ulcers, and venous leg ulcers contribute to a considerable amount of mortality in the U.S. annually. The inability of these wounds to heal has now been associated with the presence of microbial biofilms. The aim of this study was to determine if products secreted by S. aureus biofilms play an active role in chronic wounds by promoting inflammation, which is a hallmark of chronic wounds.

METHODS

In vitro experiments were conducted to examine changes in gene expression profiles and inflammatory response of human epithelial keratinocytes (HEKa) exposed to products secreted by S. aureus grown in biofilms or products secreted by S. aureus grown planktonically.

RESULTS

After only two hours of exposure, gene expression microarray data showed marked differences in inflammatory, apoptotic, and nitric oxide responses between HEKa cells exposed to S. aureus biofilm conditioned media (BCM) and HEKa cells exposed to S. aureus planktonic conditioned media (PCM). As early as 4 hours post exposure, ELISA results showed significant increases in IL-6, IL-8, TNFα, and CXCL2 production by HEKa cells exposed to BCM compared to HEKa cells exposed to PCM or controls. Nitric oxide assay data also showed significant increases in nitric oxide production by HEKa cells treated with BCM compared to HEKa cells treated with PCM, or controls.

CONCLUSIONS

Taken together, these results support and extend previous findings that indicate products secreted by S. aureus biofilms directly contribute to the chronic inflammation associated with chronic wounds.

Autonomous cure of damaged human intestinal epithelial cells by TLR2 and TLR4-dependent production of IL-22 in response to Spirulina polysaccharides

In order to analyze the damage of human epithelial cells, we used human quasi-normal FPCK-1-1 cells derived from a colonic polyp in a patient with familial adenomatous polyposis as a monolayer, which is co-cultured with peptidoglycan (PGN)-stimulated THP-1 cells. Co-cultured FPCK-1-1 cells showed a decreased transepithelial electrical resistance (TER) and the lower level of claudin-2. When Spirulina complex polysaccharides were added one day before the start of the co-culture, there was no decrease of TER and claudin-2 (early phase damage). In contrast, when Spirulina complex polysaccharides were added to FPCK-1-1 cells after the level of TER had decreased, there was no recovery at the level of claudin-2, though the TER level recovered (late phase damage). The mucosa reconstitution is suggested to be involved in the recovery from the damaged status. Interestingly, autonomous recovery of FPCK-1-1 cells from both the early and late phase damage requires the production of IL-22, because anti-IL-22 antibodies inhibited recovery in these cases. Antibodies against either TLR2 or TLR4 inhibited the production of IL-22 from FPCK-1-1 colon epithelial cells, suggesting that signals through TLR2 and TLR4 are necessary for autonomous recovery of FPCK-1-1 colon epithelial cells by producing IL-22. In conclusion, we have established a useful model for the study of intestinal damage and recovery using human colon epithelial cells and our data suggest that damage to human colon epithelial cells can, at least in part, be recovered by the autonomous production of IL-22 in response to Spirulina complex polysaccharides.

Therapeutic targeting of NOD1 receptors

The nucleotide-binding oligomerization domain 1 (NOD1) protein is an intracellular receptor for breakdown products of peptidoglycan (PGN), an essential bacterial cell wall component. NOD1 responds to γ-D-glutamyl-meso-diaminopimelic acid, which is an epitope unique to PGN structures from all Gram-negative bacteria and certain Gram-positive bacteria. Upon ligand recognition, NOD1 undergoes conformational changes and self-oligomerization mediated by the nucleotide-binding NACHT domains, followed by the recruitment and activation of the serine threonine kinase receptor-interacting protein 2 leading to the activation of NF-κB and MAPK pathways and induction of inflammatory genes. Much of our knowledge is derived from seminal studies using mice deficient in NOD1 and confirming an essential role for NOD1 in the host immune response against gastrointestinal and respiratory pathogens. In addition, recent studies have revealed a role for intracellular NOD1 receptors in the regulation of vascular inflammation and metabolism. This review will discuss our current understanding of intracellular NOD1 receptors in host immunity and chronic inflammatory disorders with a focus on cardiovascular diseases. Although therapeutic advances may have to wait until the complex interplay with pathogens, danger signals, other pattern recognition receptors and overlapping metabolic pathways is further unravelled, the steadily growing body of knowledge suggest that NOD1 antagonism might represent attractive candidate to reduce excessive inflammation associated to intestinal, cardiovascular and metabolic diseases.

Up-regulation of Toll-like receptors 2 and 4 on peripheral monocytes after major abdominal surgical operation

BACKGROUND

This study is to investigate the time-course expression of TLR2 and TLR4 on peripheral monocytes in patients receiving major abdominal surgical operation.

METHODS

Blood samples were obtained from peripheral vein before and after an operation in 30 patients with gastrointestinal or pancreatic surgery. The mRNA expression of TLR2, TLR4, TNF-α and IL-6 on peripheral blood mononuclear cells (PBMC) was analyzed by real-time PCR. The expressions of TLR2, TLR4, HLA-DR, CD80, and CD86 on monocytes were analyzed by flow cytometry. The expressions of TLR2 and TLR4 on monocytes responding to each agonist (zymosan and lipopolysaccharide) were also measured by flow cytometry.

RESULTS

TLR2 and TLR4 mRNA showed significant up-regulation after the completion of the operation when compared with those before the operation. TLR2 expression reached its peak level on day 1 and TLR4 on days 1 and 3. There was no significant difference between pre- and post-operation in the expressions of HLA-DR, CD80 and CD86. Stimulation with zymosan, increased the expression of TLR2 significantly after the operation and reached its highest value on day 3. Similarly, after stimulation with lipopolysaccharide, the expression of TLR4 was also increased and the highest level was observed on day 1. The expression of TNF-α and IL-6 mRNA decreased after completion of the operation and gradually returned to basal level.

CONCLUSIONS

The expressions of TLR2 and TLR4 on monocytes were up-regulated during the early period after a major abdominal surgical operation in patients, which might be related to the activation of innate immunity.

Phenotyping of Nod1/2 double deficient mice and characterization of Nod1/2 in systemic inflammation and associated renal disease

It is indispensable to thoroughly characterize each animal model in order to distinguish between primary and secondary effects of genetic changes. The present study analyzed Nod1 and Nod2 double deficient (Nod1/2 DKO) mice under physiological and inflammatory conditions. Nod1 and Nod2 are members of the Nucleotide-binding domain and Leucine-rich repeat containing Receptor (NLR) family. Several inflammatory disorders, such as Crohn's disease and asthma, are linked to genetic changes in either Nod1 or Nod2. These associations suggest that Nod1 and Nod2 play important roles in regulating the immune system.

Three-month-old wildtype (Wt) and Nod1/2 DKO mice were sacrificed, body and organ weight were determined, and blood was drawn. Except for lower liver weight in Nod1/2 DKO mice, no differences were found in body/organ weight between both strains. Leukocyte count and composition was comparable. No significant changes in analyzed plasma biochemical markers were found. Additionally, intestinal and vascular permeability was determined. Nod1/2 DKO mice show increased susceptibility for intestinal permeability while vascular permeability was not affected. Next we induced septic shock and organ damage by administering LPS+PGN intraperitoneally to Wt and Nod1/2 DKO mice and sacrificed animals after 2 and 24 hours. The systemic inflammatory and metabolic response was comparable between both strains. However, renal response was different as indicated by partly preserved kidney function and tubular epithelial cell damage in Nod1/2 DKO at 24 hours. Remarkably, renal inflammatory mediators Tnfα, KC and Il-10 were significantly increased in Nod1/2 DKO compared with Wt mice at 2 hours.

Systematic analysis of Nod1/2 DKO mice revealed a possible role of Nod1/2 in the development of renal disease during systemic inflammation.

Strain differences in alveolar neutrophil infiltration and macrophage phenotypes in an acute lung inflammation model

Pulmonary infection is a major cause of mortality and morbidity, and the magnitude of the lung inflammatory response correlates with patient survival. Previously, we have shown that neutrophil migration into joints is regulated by arthritis severity quantitative trait loci (QTLs). However, it is unclear whether these QTLs contribute to the regulation of lung inflammation in pneumonias. Therefore, to more clearly define the factors regulating acute inflammatory responses in the lung, we examined two inbred rat strains, DA and F344, that differ in these QTLs and their susceptibility to joint inflammation. Staphylococcal cell wall components lipoteichoic acid (LTA) and peptidoglycan (PGN), administered intratracheally, significantly increased the numbers of neutrophils retrieved in the bronchoalveolar lavage fluid (BALF). F344 had approximately 10-fold more neutrophils in the BALF compared with DA (P < 0.001) and higher BALF concentrations of total protein, tumor necrosis factor-α and macrophage inflammatory protein 2. LTA/PGN administration in DA×F344 congenic strains (Cia3d, Cia4, Cia5a, and Cia6) resulted in inflammation similar to that in DA, demonstrating that the genes responsible for the differences in pulmonary inflammation are not contained within the chromosomal intervals carried by these congenic strains. Alveolar macrophages (AMs) isolated from naïve F344 stimulated in vitro with LTA/PGN produced significantly higher levels of keratinocyte-derived chemokine and macrophage inflammatory protein 2 than alveolar macrophages from DA rats. The differences were related to differential mitogen-activated protein kinase phosphorylation. We conclude that the factors contributing to inflammation can be site and challenge dependent. A better understanding of site-specific inflammation may lead to more effective treatment of acute lung inflammation and injury.

Role of mitogen-activated protein kinases in peptidoglycan-induced expression of inducible nitric oxide synthase and nitric oxide in mouse peritoneal macrophages: extracellular signal-related kinase, a negative regulator

The expression of inducible nitric oxide synthase (iNOS) and the production of nitric oxide (NO) are important host defense mechanisms against pathogens in mononuclear phagocytes. The objectives of this study were to examine the roles of mitogen-activated protein kinases (MAPKs) and transcription factors (nuclear factor-κB [NF-κB] and activating protein 1 [AP-1]) in peptidoglycan (PGN)-induced iNOS expression and NO production in macrophages. PGN is a cell wall component of Gram-positive bacteria that stimulates inflammatory responses both ex vivo and in vivo. PGN stimulates the activation of all three classes of MAPKs, extracellular signal-related kinase (ERK), c-Jun N-terminal kinase (JNK), and p38(mapk) in macrophages, albeit with differential activation kinetics. Using a selective inhibitor of JNK (SP600125) and JNK1/2 small interfering RNA (siRNA) knocked-down macrophages, it was observed that PGN-induced iNOS and NO expression is significantly inhibited. This suggested that JNK MAPK plays an essential role in PGN-induced iNOS expression and NO production. In contrast, inhibition of the ERK pathway using PD98059 dose dependently enhanced PGN-induced iNOS expression and NO production. PGN-induced ERK activation was attenuated in ERK1/2 siRNA knocked-down macrophages; however, NO and iNOS expression were significantly enhanced. An electrophoretic mobility shift assay showed that SP600125 inhibited PGN-induced NF-κB and AP-1 activation, whereas inhibition of the ERK pathway enhanced NF-κB activation, but with no effect on AP-1. These results indicate that the JNK MAPK positively regulate PGN-induced iNOS and NO expression by activating NF-κB and AP-1 transcription factors, whereas the ERK pathway plays a negative regulatory role via affecting NF-κB activity.

Regulation of heme oxygenase-1 gene by peptidoglycan involves the interaction of Elk-1 and C/EBPalpha to increase expression

Heme oxygenase (HO)-1 is a cytoprotective enzyme with anti-inflammatory properties. HO-1 is induced during a systemic inflammatory response, and expression of HO-1 is beneficial during sepsis of a Gram-positive source. Systemic infection from Gram-positive organisms has emerged as an important cause of sepsis, with Staphylococcus aureus as a common etiology. An important mediator of Gram-positive infections is peptidoglycan (PGN), a cell wall component of these organisms. Here, we demonstrate that HO-1 played an important, protective role in vivo, as mice deficient in HO-1 were very sensitive to the lethal effects of PGN derived from S. aureus. PGN induced HO-1 protein and mRNA levels, and this regulation occurred at the level of gene transcription. The PGN-responsive region of the HO-1 promoter (from -117 to -66 bp) contains a functional EBS, and Ets proteins are known to be involved in the regulation of inflammatory responses. We showed previously that Ets factors (activators Ets-2 and Ets-1 and repressor Elk-3) regulate HO-1 expression by Gram-negative endotoxin. However, during exposure to a Gram-positive stimulus in the present study, Elk-1 was a potent activator of HO-1 in conjunction with PGN. The ability of Elk-1 to induce HO-1 promoter activity was independent of direct DNA binding, but rather occurred by interacting with the CCAAT/enhancer-binding protein-alpha (C/EBPalpha), which binds to DNA. Moreover, silencing of C/EBPalpha in macrophages prevented induction of HO-1 promoter activity by either Elk-1 or PGN. These data provide further insight into the regulation and function of HO-1 by a mediator of Gram-positive bacteria.

Staphylococcal surgical site infections

Staphylococcus aureus is the leading cause of surgical site infections (SSI) in the United States. In particular, SSI caused by methicillin-resistant Staphylococcus aureus (MRSA) has emerged as a devastating complication, leading to increased mortality rates, increased length of hospitalization, and increased costs. Proven strategies for prevention of SSI caused by S aureus include addressing modifiable risk factors and correct choice and timing of antimicrobial prophylaxis. Other strategies, including decolonization and the use of vancomycin, remain controversial.

MAP Kinase Phosphatase-1 and Septic Shock

Mitogen-activated protein (MAP)(§) kinase cascades are crucial signal transduction pathways in the biosynthesis of proinflammatory cytokines. MAP kinase phosphatase (MKP)-1, an archetypal member of the MKP family, plays a pivotal role in the feedback control of p38 and JNK. In vitro studies using cultured macrophages have provided strong evidence for a critical role of MKP-1 in the restraint of pro-inflammatory cytokine biosynthesis. Recently, a number of studies conducted using MKP-1 knockout mice have verified the importance of MKP-1 in the regulation of p38 and JNK and in the regulation of pro-inflammatory cytokine synthesis. Upon lipopolysaccharide challenge MKP-1 knockout mice produced dramatically greater amounts of inflammatory cytokines, developed severe hypotension, and multi-organ failure, and exhibited a remarkable increase in mortality. These studies demonstrate that MKP-1 is an essential feedback regulator of the innate immune response, and that it plays a critical role in preventing septic shock and multi-organ dysfunction during pathogenic infection.

Regulation of gene expression of hepatic drug metabolizing enzymes and transporters by the Toll-like receptor 2 ligand, lipoteichoic acid

Expression of hepatic drug metabolizing enzymes (DMEs) is altered in infection and inflammation. However, the role of Gram+ve bacterial components and their receptor, Toll-like receptor (TLR) 2 in regulation of hepatic DMEs is unknown. Gene expression of DMEs is regulated by members of the nuclear receptor superfamily (PXR, CAR and RXRalpha). The TLR2 ligand, lipoteichoic acid (LTA) reduced RNA levels of CAR and its target genes, Cyp2b10, Cyp2a4 and Sultn in mouse liver ( approximately 60-80% reduction). Hepatic genes regulated by PXR and CAR, Cyp3a11 and Mrp2 were moderately reduced by LTA, along with approximately 50% reduction of PXR RNA and nuclear protein levels of RXRalpha. The effects of LTA were significantly attenuated by pre-treatment with the Kupffer cell inhibitor, gadolinium chloride, indicating that Kupffer cells contribute to LTA-mediated down-regulation of hepatic genes. These results indicate that treatment with Gram+ve bacterial components preferentially down-regulate CAR and its target genes in the liver.

Staphylococcus aureus isolated from a horse in a sudden death condition in Kassala state, eastern Sudan

In this study, Staphylococcus aureus was isolated from a draught horse presented to Kassala Veterinary Research Laboratory (KVRL) for investigation and diagnosis. The affected animal was previously treated with Gentamycin and Tetracycline before submitted to this laboratory, but the animal was not cure. Thereafter, the animal was attended to the laboratory; it was suffering from inguinal abscess and some clinical signs. Clinical and laboratory examinations were carried out however, the animal was suddenly fallen and died immediately. Then post-mortem, bacteriological and histopathological examinations were done. S. aureus was isolated as pure culture from the lungs and peritoneum of the necropsied animal. This isolate showed highly sensitivity to Erythromycin and Clindamycin and it was resistant to Penicillin, Cloxacillin, Cefotaxime, Co-Trimoxazole, Cephalexin and Tetracycline. It was concluded from this study, the shock resulted from S. aureus was the causative agent of the death in this case.

Muramyl dipeptide enhances the response to endotoxin to cause multiple organ injury in the anesthetized rat

Nucleotide oligomerization domain (NOD) proteins recognize peptidoglycan fragments, resulting in up-regulation of transcription factors, and may enhance the inflammatory response to infection. Specifically, NOD2 has been shown to sense muramyl dipeptide (MDP), which is released during bacterial cell growth and replication. Activation of NOD2 by MDP enhances the inflammatory response caused by LPS (endotoxin). Here, we investigated the effects of MDP on the organ injury/dysfunction caused by systemic administration of a low dose of LPS. Male Wistar rats were coadministered with either MDP (1 - 10 mg kg(-1), i.v.) or vehicle (0.5 mL kg(-1) saline, i.v.), and a low dose of LPS (1 mg kg(-1), i.v.) or vehicle (1 mL kg(-1), saline, i.v.). MAP and heart rate were continuously monitored for 6 h. Markers of organ dysfunction/injury, plasma cytokine levels, and lung myeloperoxidase activity were measured 6 h after MDP and LPS coadministration. In a separate study, MDP (3 or 10 mg kg(-1), i.v.) or vehicle (0.5 mL kg(-1) saline, i.v.) was administered 24 h before LPS infusion. When compared with animals receiving low-dose LPS alone, coadministration of MDP (10 mg kg(-1), i.v.) and LPS, or administration of MDP (10 mg kg(-1), i.v.) 24 h before LPS resulted in a significant increase in the degree of organ injury, cytokine release, and lung injury caused by LPS alone. Thus, our results demonstrate that the two bacterial wall components MDP and LPS work in concert to cause multiple organ injury and systemic inflammation. We hope that our results stimulate other studies designed to evaluate the effects of NOD ligands in animal models of inflammation.

Increased surface toll-like receptor 2 expression in superantigen shock

OBJECTIVE

Examination of the interaction between gram-positive bacterial superantigens and toll-like receptor 2 (TLR2) in health and critical illness.

DESIGN

Laboratory ex vivo model and prospective clinical, cohort study.

SETTING

Two research laboratories in university hospitals and two intensive care units.

SUBJECTS/PATIENTS

Laboratory study was performed in transfected HeLa cells and primary human monocytes from healthy volunteers. Clinical study used cells from 20 healthy controls and 45 critically ill patients with circulatory shock.

INTERVENTIONS

HeLa cells and purified monocytes were exposed to purified superantigens or isogenic bacterial supernatants and readout obtained by cytokine enzyme-linked immunosorbent assay, flow cytometry, and quantitative real-time polymerase chain reaction. Peripheral blood mononuclear cells from patients with circulatory shock were compared with controls using flow cytometry and measurement of cytokines after ligand exposure.

MEASUREMENTS AND MAIN RESULTS

Superantigens were unable to signal through ligation by TLR2. However, TLR2 was up-regulated on the surface of primary human monocytes, without detectable TLR2 messenger RNA neosynthesis, by a range of superantigens and superantigen-containing Streptococcus pyogenes supernatants, although not by isogenic superantigen-negative strains. Superantigen mutant constructs with disrupted major histocompatibility complex class II-binding sites did not support TLR2 up-regulation. TLR2 up-regulation was associated with an increase in the proinflammatory response to TLR2 ligands only at high ligand concentrations. TLR2 was up-regulated in a small subset of patients with severe S. pyogenes sepsis but not in patients with any other category of septic or circulatory shock; responses to TLR2 ligands were reduced in all categories of critically ill patient, however.

CONCLUSIONS

Superantigens up-regulate monocyte surface TLR2 expression through major histocompatibility complex class II signaling. Enhanced surface TLR2 expression may be a specific feature of patients with S. pyogenes-induced shock. Importantly, intensity of TLR2 signaling is not necessarily coupled to TLR2 expression when ligand concentrations are low or after onset of critical illness.

Activation of cytokine synthesis by systemic infusions of lipopolysaccharide and peptidoglycan in a porcine model in vivo and in vitro

BACKGROUND

The incidence of gram-positive and mixed bacterial infections in surgical patients has increased, and there has been an alarming rise in the number of drug-resistant bacteria. Peptidoglycan (PepG) is a cell wall component of gram-positive bacteria that stimulates inflammatory responses both ex vivo and in vivo. The systemic effects of PepG on inflammation have not been studied in a large animal model.

METHODS

Anesthetized pigs were subjected to 8-h continuous intravenous infusions of lipopolysaccharide (LPS) (4 mcg/kg/h), PepG (40 mcg/kg/h), LPS plus PepG, or saline. The concentrations of tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, IL-6, IL-8, and IL-10 were measured in the plasma prior to infusion (time 0) and thereafter every second hour until the end of the experiments. Heparinized whole blood samples drawn at time 0 and after a 6-h infusion of LPS or PepG were incubated ex vivo with PepG (10 mcg/mL), LPS (10 ng/mL), or a combination of PepG and LPS to study the immunologic consequences of systemic inflammation. Concentrations of TNF-alpha, IL-8, and IL-1beta were measured in the supernatant liquids.

RESULTS

In vivo, there was transient upregulation of TNF-alpha after infusion of LPS, PepG, or the combination. Interleukin-6 and IL-8 were upregulated by LPS but not by PepG. In vitro studies of whole blood obtained at time 0 revealed a synergistic effect of LPS and PepG on the release of TNF-alpha. Incubation of whole blood obtained after 6 h of infusion of LPS or PepG revealed tolerance and cross-tolerance between the two bacterial components in the induction of TNF-alpha, IL-8, and IL-1beta.

CONCLUSIONS

Peptidoglycan is a potent inducer of TNF-alpha in this large animal model. Peptidoglycan and LPS synergized to increase the formation of the proinflammatory cytokine TNF-alpha. The study demonstrates for the first time the development of tolerance and cross-tolerance between LPS and PepG in a large animal model. These phenomena could be of importance for the signs and symptoms of sepsis.

Peptidoglycan-mediated IL-8 expression in human alveolar type II epithelial cells requires lipid raft formation and MAPK activation

Staphylococcus aureus, a major sepsis-causing Gram-positive bacterium, invades pulmonary epithelial cells and causes lung diseases. In the lung, alveolar type II epithelial cells play an important role in innate immunity by secreting chemokines and antimicrobial peptides upon bacterial infection whereas type I cells mainly function in gas-exchange. In this study, we investigated the ability of S. aureus peptidoglycan (PGN) to induce expression of a chemokine, IL-8, in a human alveolar type II epithelial cell line, A549. PGN induces IL-8 mRNA and protein expression in a dose- and time-dependent manner. Supplementation of soluble CD14 further enhanced the PGN-induced IL-8 expression. Interestingly, PGN-induced IL-8 expression was inhibited by nystatin, a specific inhibitor for lipid rafts, but not by chlorpromazine, a specific inhibitor for clathrin-coated pits. Furthermore, PGN-induced IL-8 expression was attenuated by inhibitors for MAP kinases such as ERK, p38 kinase, and JNK/SAPK, whereas no inhibitory effect was observed by inhibitors for reactive oxygen species or protein kinase C. Electrophoretic mobility shift assay demonstrates that PGN increased the DNA binding of the transcription factors, AP-1 and NF-kappaB while minimally, NF-IL6, all of which are involved in the transcription of IL-8. Taken together, these results suggest that PGN induces IL-8 expression in a CD14-enhanced manner in human alveolar type II epithelial cells, through the formation of lipid rafts and the activation of MAP kinases, which ultimately leads to activation of AP-1, NF-kappaB, and NF-IL6.

Knockout of Mkp-1 enhances the host inflammatory responses to gram-positive bacteria

MAPK phosphatase (MKP)-1 is an archetypal member of the dual specificity protein phosphatase family that dephosphorylates MAPK. We have previously demonstrated that MKP-1 acts as a negative regulator of p38 and JNK in immortalized macrophages after stimulation with peptidoglycan isolated from Gram-positive bacteria. To define the physiological function of MKP-1 during Gram-positive bacterial infection, we studied the innate immune responses to Gram-positive bacteria using Mkp-1 knockout (KO) mice. We found that Mkp-1(-/-) macrophages exhibited prolonged activation of p38 and JNK, but not of ERK, following exposure to either peptidoglycan or lipoteichoic acid. Compared with wild-type (WT) macrophages, Mkp-1(-/-) macrophages produced more proinflammatory cytokines such as TNF-alpha and IL-6. Moreover, after challenge with peptidoglycan, lipoteichoic acid, live or heat-killed Staphylococcus aureus bacteria, Mkp-1 KO mice also mounted a more robust production of cytokines and chemokines, including TNF-alpha, IL-6, IL-10, and MIP-1alpha, than did WT mice. Accordingly, Mkp-1 KO mice also exhibited greater NO production, more robust neutrophil infiltration, and more severe organ damage than did WT mice. Surprisingly, WT and Mkp-1 KO mice exhibited no significant difference in either bacterial load or survival rates when infected with live S. aureus. However, in response to challenge with heat-killed S. aureus, Mkp-1 KO mice exhibited a substantially higher mortality rate compared with WT mice. Our studies indicate that MKP-1 plays a critical role in the inflammatory response to Gram-positive bacterial infection. MKP-1 serves to limit the inflammatory reaction by inactivating JNK and p38, thus preventing multiorgan failure caused by exaggerated inflammatory responses.

Oral and systemic administration of beta-glucan protects against lipopolysaccharide-induced shock and organ injury in rats

beta-Glucans are glucose polymers with a variety of stimulatory effects on the immune system. The objective of this study was to determine the effect of prophylactic oral administration of soluble Saccharomyces cerevisiae-derived beta-1,3/1,6-glucan (SBG) on the outcome of experimental endotoxaemia and shock-associated organ injury. Male Wistar rats were pretreated with SBG orally (SBGpo, 20 mg/kg/day) for 14 days, subcutaneously (SBGsc, 2 mg/kg/day) for 3 days, or vehicle (placebo). Rats were anaesthetized and subjected to endotoxaemia by intravenous infusion of Escherichia coli lipopolysaccharide (LPS) (6 mg/kg) or saline infusion (sham). We observed significant levels of plasma beta-glucan in the SBGpo group (P<0 x 5), although the SBGsc group had levels approximately 40-fold higher despite a 10-fold lower dose. SBG prophylaxis caused enhanced blood pressure recovery following LPS-induced blood pressure collapse. Oral treatment with SBG attenuated the LPS-induced rise in plasma creatinine levels (P<0 x 05), indicating protection against renal injury. SBG also attenuated the plasma levels of aspartate aminotransferase and alanine aminotransferase (SBGpo, P<0 x 01; SBGsc, P<0 x 01), indicating protection against LPS-induced hepatic injury. A moderate increase in baseline interleukin (IL)-1beta levels was observed in the SBGsc group (P< 0 x 05). In the LPS-challenged rats, plasma levels of proinflammatory cytokines was moderately reduced in both SBG-treated groups compared to placebo. SBG treatment, particularly oral administration, had a striking effect on the haemodynamics of LPS-treated rats, although only a minute fraction of the orally administered beta-glucan translocated to the circulation. Enhanced organ perfusion may thus be responsible for the attenuated levels of indicators of kidney and liver injury seen in SBG-treated rats.

ALTERATIONS IN INFLAMMATORY CAPACITY AND TLR EXPRESSION ON MONOCYTES AND NEUTROPHILS AFTER CARDIOPULMONARY BYPASS

Cardiopulmonary bypass (CPB) is associated with immune paresis, which predisposes to the development of postoperative sepsis. The aims of this study were to characterize the ex vivo cytokine responses to bacterial cell wall components in whole blood from patients undergoing CPB and to determine whether altered leukocyte expression of Toll-like receptors (TLRs) is involved in immune paresis after CPB. We recruited 6 patients undergoing routine cardiac surgery with CPB. Preoperatively, at the end of CPB and 20 h later, blood was obtained, anticoagulated, and leukocyte surface expression of CD14, TLR2, and TLR4 was quantified by flow cytometry. In addition, blood was incubated at 37 degrees C in the presence of peptidoglycan (PepG) and/or lipopolysaccharide (LPS), and plasma cytokines were measured by enzyme immunoassay. At the end of CPB, ex vivo production of tumor necrosis factor alpha, interleukin (IL) 1beta, IL-8, and IL-10 in response to PepG or LPS was virtually abolished (P < 0.05). The following day, there was recovery of all cytokine responses to PepG. Tumor necrosis factor alpha and IL-1beta responses to LPS partially recovered, whereas IL-8 and IL-10 responses recovered. At the end of CPB, there was more than 50% reduction in neutrophil TLR2 and TLR4 expression (P < 0.05), with recovery to baseline the following day. There was a 29% reduction in monocyte TLR4 expression at the end of CPB (P < 0.05) and more than 120% increase in monocyte TLR2 and 4 expression the following day (P < 0.05). In conclusion, reduced ex vivo production of cytokines cannot be fully accounted for by downregulation of TLR expression, although receptor upregulation may contribute to the later recovery of responsiveness.

Glycogen synthase kinase 3beta as a target for the therapy of shock and inflammation

After the discovery that glycogen synthase kinase (GSK) 3beta plays a fundamental role in the regulation of the activity of nuclear factor kappaB, a number of studies have investigated the effects of this protein kinase in the regulation of the inflammatory process. The GSK-3beta inhibition, using genetically modified cells and chemically different pharmacological inhibitors, affects the regulation of various inflammatory mediators in vitro and in vivo. Insulin, an endogenous inhibitor of GSK-3 in the pathway leading to the regulation of glycogen synthase activity, has recently been clinically used in the therapy for septic shock. The beneficial anti-inflammatory effects of insulin in preclinical and clinical studies could possibly be due, at least in part, to the inhibition of GSK-3 and not directly correlated to the regulation of blood glucose. We describe the latest studies describing the effects of GSK-3 inhibition as potential target of the therapy for diseases associated with inflammation, ischemia/reperfusion, and shock.

Staphylococcus aureus peptidoglycan impairs fracture healing: an experimental study in rats

Staphylococcus aureus is the common organism causing musculoskeletal infections. Staphylococcus aureus peptidoglycan (SaPG) has been identified to increase the acute inflammatory response to wounding, increase reparative granulation tissue, and improve healing. The healing of bone fractures is a balanced process of granulation tissue that is calcified to obtain increasing stability. By increasing reparative collagen accumulation, however, SaPG may induce a shift towards immature fibrous callus production. Therefore, it was our hypothesis that SaPG would impair bone healing after fracture. In three groups, each of nine rats, a mid-diaphyseal osteotomy/fracture of the femoral bone was performed and then nailed. In one group of animals, SaPG was applied locally at the fracture site, and in another group SaPG was applied intraperitoneally (systemically). Control littermate received saline. The animals were sacrificed after 6 weeks, and the mechanical characteristics of the healing osteotomies were evaluated. We found that application of SaPG locally induced a hypertrophic and immature callus as evaluated by callus production, by bone mineral content and density, and by bending moment and rigidity. In the rats given SaPG intraperitoneally, bone healing went uneventful compared to the control rats. Collectively, these data show that SaPG induces an alteration in the normal bone healing response towards a less calcified callus production.

Anti-inflammatory properties of enamel matrix derivative in human blood

BACKGROUND AND OBJECTIVE

Enamel matrix derivative (EMD), extracted from porcine tooth buds, has been shown to promote periodontal healing in patients with severe periodontitis. This involves modulation of the inflammatory response followed by the onset of periodontal regeneration. Based on these observations, we examined the ability of EMD to modulate the release of a pro-inflammatory cytokine [tumor necrosis factor (TNF)-alpha], an anti-inflammatory cytokine (interleukin-10) and a chemokine (interleukin- 8) in whole human blood challenged by bacterial cell wall components.

MATERIAL AND METHODS

Whole blood from healthy donors was challenged by lipopolysaccharide or peptidoglycan and incubated with different concentrations of EMD or a cAMP analogue 8-(4-chlorophenyl)thio-cAMP (8-CPT-cAMP). TNF-alpha, interleukin-8 and interleukin-10 were analysed from plasma by enzyme-linked immunosorbent assay (ELISA) while cAMP levels of peripheral blood mononuclear cell lysates were analysed by enzyme immunoassay (EIA).

RESULTS

We found that EMD attenuated the release of TNF-alpha and interleukin-8 in whole blood from healthy donors challenged by lipopolysaccharide or peptidoglycan, while the release of interleukin-10 was unchanged. Enamel matrix derivative also produced a four-fold increase in the cAMP levels of peripheral blood mononuclear cell lysates. Like EMD, 8-CPT-cAMP attenuated the formation of TNF-alpha, but not of interleukin-10, in blood challenged by lipopolysaccharide.

CONCLUSION

Enamel matrix derivative limits the release of pro-inflammatory cytokines induced by lipopolysaccharide or peptidoglycan in human blood, suggesting that it has anti-inflammatory properties. We propose that this effect of EMD is, at least partly, secondary to an increase in the intracellular levels of cAMP in peripheral blood mononuclear cells.

Mechanical ventilation induces inflammation, lung injury, and extra-pulmonary organ dysfunction in experimental pneumonia

Mechanical ventilation (MV) is frequently employed for the management of critically ill patients with respiratory failure. A major complication of mechanical ventilation (MV) is the development of ventilator-associated pneumonia (VAP), in which Staphylococcus aureus is a prominent pathogen. Moreover, previous studies suggest that MV may be an important cofactor in the development of acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS). S. aureus pulmonary infection was induced in spontaneously breathing mice (C57Bl/6) or mechanically ventilated mice to determine whether MV contributes to the development of ALI and/or systemic inflammation. The combination of MV and bacteria significantly increased the influx of neutrophils into bronchoalveolar lavage fluid (BALF), augmented pulmonary production of the proinflammatory cytokines KC, MIP-2, TNF-alpha, and IL-6, and increased alveolar-capillary permeability to proteins. MV also induced proinflammatory cytokine expression in peripheral blood, associated with extrapulmonary hepatic and renal dysfunction. Surprisingly, bacterial clearance in the lungs and extrapulmonary bacterial dissemination was not affected by MV. These data indicate that MV exacerbates both pulmonary and systemic inflammation in response to bacteria and contributes to the pathogenesis of both ALI and the multiple organ dysfunction syndrome, without necessarily affecting bacterial clearance or extra-pulmonary bacterial dissemination.

Cytokine responses to CpG DNA in human leukocytes

Previous studies have implicated a role of bacterial DNA, containing unmethylated cytosine-phosphate-guanosine (CpG) motifs, in the initiation of systemic inflammation. This is based on the ability of CpG-DNA to act in synergy with lipopolysaccharide (LPS) to trigger tumor necrosis factor alpha (TNFalpha) production in murine monocytes and to enhance LPS toxicity in rodents. In this study we investigated the capacity of CpG-DNA to trigger and modulate cytokine responses in human leukocytes. A human blood assay, as well as isolated cultures of monocytes and neutrophils, was exposed to the synthetic oligodeoxynucleotides (ODNs) CpG ODN (2006) and GpC ODN (2006-GC), alone or in combination with peptidoglycan or LPS. Plasma or supernatants were isolated and analyzed for TNFalpha, interleukin-1 beta (IL-1beta), IL-6 and IL-8 by ELISA. In the blood, 2006 (but not 2006-GC) induced the release of TNFalpha (P < 0.05) and possibly IL-1beta and IL-6. IL-8 was induced in a CpG-independent manner. When co-administered with peptidoglycan, both ODNs enhanced the release of cytokines, but not consistently CpG dependent. When co-administered with LPS, only IL-8 values were enhanced, whereas IL-6 was suppressed at early time points. In monocyte and neutrophil cultures, CpG dependent induction of cytokine release was not observed. However, both ODNs inhibited LPS-induced IL-6. In conclusion, the capacity of CpG DNA to trigger the release of TNFalpha and to enhance LPS-induced release of this cytokine is confirmed in human whole blood, but not in adherent human monocytes. Most effects of the ODNs on cytokine release in human leukocytes were CpG independent.

Activation of the liver X receptor protects against hepatic injury in endotoxemia by suppressing Kupffer cell activation

Recent reports have demonstrated that liver X receptors (LXRs) of the nuclear receptor family have anti-inflammatory effects on macrophages. Here we examine whether activation of LXR by the synthetic agonist GW3965 can ameliorate the liver injury/dysfunction caused by endotoxins in the rat. Male Wistar rats received GW3965 (0.3 mg/kg) or vehicle (50% dimethyl sulfoxide) 30 min before coadministration of lipopolysaccharide (LPS, 5 mg/kg i.v.) and peptidoglycan (1 mg/kg i.v.). Treatment with GW3965 attenuated the increase in the plasma levels of alanine aminotransferase and bilirubin (markers of liver injury/dysfunction) as well as the focal hepatocyte necrosis (histology) caused by coadministration of LPS and peptidoglycan. This protective effect of GW3965 treatment was associated with reduced infiltration of mast cells in the liver (histopathology) and reduced gene expression of the chemokines eotaxins 1 and 2, whereas MIP-2 mRNA levels were not affected. Plasma levels of tumor necrosis factor alpha and prostaglandin E2 were significantly attenuated by GW3965, whereas plasma interleukins 6 and 10 were not altered. High expression of LXRalpha mRNA was observed in Kupffer cell cultures, suggesting that Kupffer cells are targets of GW3965. Subsequent in vitro studies in Kupffer cells demonstrated that exposure to GW3965 attenuated the LPS-induced release of tumor necrosis factor alpha and prostaglandin E2 in a dose-dependent manner. In conclusion, this study demonstrates that activation of LXR by GW3965 protects against liver injury and dysfunction in a rat model of endotoxemia, in part by exerting an anti-inflammatory effect on Kupffer cells.

Mediator Responses in Surgical Infections

BACKGROUND

Surgical infections, and sepsis in particular, are characterized by extensive release of mediators. Our laboratories have been interested in understanding how these substances contribute to morbidity and mortality during various stages of surgical infections in order to develop new and more effective therapeutics and treatment strategies.

METHODS

In a series of in vitro studies, human plasma was exposed to lipopolysaccharide (LPS), and whole blood was treated with peptidoglycan from Staphylococcus aureus. The activity of peptidoglycan also was studied in the rat, and LPS infusion was tested in dog and pig models. In a clinical study, the relation of serum LPS to multiple organ dysfunction and failure was studied in patients in the surgical intensive care unit.

RESULTS

Exposure of plasma to LPS led to formation of bradykinin, activation of the plasma kallikrein-kinin system, and reduction of kallikrein inhibitor capacity. The coagulation, fibrinolysis, and complement cascades were activated. Peptidoglycan caused rapid release of tumor necrosis factor-alpha, interleukin-1beta, and interleukin-6 from macrophages and activation of the genes encoding pro-inflammatory and anti-inflammatory cytokines. In the rat, peptidoglycan induced cytokine release, caused liver and kidney dysfunction, and induced matrix metalloproteinase-9 (MMP-9) activity in the liver and lung. In the dog and pig, LPS caused substantial activation of plasma proteases. Clinically, a finding of LPS in the plasma was associated with multiple organ dysfunction and failure. These patients also revealed substantial activation of the plasma cascade systems, as well as systemic cytokine release.

CONCLUSION

On the basis of these observations, we developed a monitoring system to recognize early signs of infection.

Lysophosphatidylcholine reduces the organ injury and dysfunction in rodent models of gram-negative and gram-positive shock

1. Lysophosphatidylcholine (LPC) modulates the inflammatory response and reduces mortality in animal models of sepsis. Here, we investigate the effects of LPC from synthetic (sLPC) and natural, soy bean derived LPC, (nLPC) sources on the organ injury/dysfunction caused by systemic administration of lipopolysaccharide (LPS) or peptidoglycan (PepG) and lipoteichoic acid (LTA). 2. Rats were subjected to (i) endotoxaemia (LPS 6 mg kg(-1) i.v.) and treated with sLPC (1-100 mg kg(-1)), (ii) endotoxaemia and treated with nLPC (10 mg kg(-1)) or (iii) gram-positive shock (PepG 10 mg kg(-1) and LTA 3 mg kg(-1) i.v.) and treated with sLPC (10 mg kg(-1)). 3. Endotoxaemia or gram-positive shock for 6 h resulted in increases in serum makers of renal dysfunction and liver, pancreatic and neuromuscular injury. 4. Administration of sLPC, at 1 or 2 h after LPS, dose dependently (1-10 mg kg(-1)) reduced the organ injury/dysfunction. High doses of sLPC (30 and 100 mg kg(-1)) were shown to be detrimental in endotoxaemia. sLPC also afforded protection against the organ injury/dysfunction caused by gram-positive shock. nLPC was found to be protective in endotoxaemic animals. 5. The beneficial effects of sLPC were associated with an attenuation in circulating levels of interleukin-1beta (IL-1beta). 6. In conclusion, LPC dose and time dependently reduces the organ injury and circulating IL-1beta levels caused by gram-negative or gram-positive shock in the rat. Thus, we speculate that appropriate doses of LPC may be useful in reducing the degree of organ injury and dysfunction associated with shock of various aetiologies.

Peptidoglycan--an endotoxin in its own right?

Studies aimed at dissecting the complex pathophysiology of sepsis with multiple organ failure have traditionally focused on lipopolysaccharide of gram-negative bacteria, which is widely regarded as the classical endotoxin. However, gram-positive sepsis now accounts for up to 50% of all cases, calling for a shift of focus. Peptidoglycan (PepG) is the major cell wall component of gram-positive bacteria and has been increasingly recognized as an important proinflammatory molecule. During gram-positive infections, PepG reaches the circulation by bacterial breakdown or translocation from the intestine. Administration of PepG induces all the classical features of infectious illness and endotoxemia and may cause systemic inflammation with organ failure in animal models. Its potency, however, is crucially dependent on various features of its complex structure. PepG interacts with the innate immune system through receptors mainly expressed on monocytes/macrophages but may induce inflammatory changes in other cell types as well. Among the most extensively studied receptor systems are the nucleotide-binding oligomerization domains, the toll-like receptors, and the PepG recognition proteins. Based on the current available literature, we would like to propose that PepG must be regarded as an endotoxin in its own right and to encourage further work in the field of PepG signaling.

Virulence determinants in Staphylococcus aureus and their involvement in clinical syndromes

Staphylococcus aureus is a major human pathogen responsible for a variety of toxin-mediated and suppurative diseases. About 50 staphylococcal virulence factors have been described to date. In this review, we examine the clinical implications of key staphylococcal virulence factors in toxin-mediated diseases, septic shock, and severe focal infections such as arthritis, infective endocarditis, pneumonia acquired during mechanical ventilation, and necrotizing pneumonia. Staphylococcal pathogenicity is sometimes due principally to a single virulence factor, as in toxic shock syndrome and necrotizing pneumonia. In contrast, several virulence factors are involved in other staphylococcal disease, such as septic shock. A better knowledge of the mechanism of action of each virulence factor involved in the different staphylococcal diseases could open the way to the use of specific inhibitors in the clinical setting.

The etiology of sepsis: turned inside out

The sepsis syndrome is thought to occur when microbial products activate Toll-like receptors stimulating widespread inflammation, in turn causing organ failure, shock and death. However, recent discoveries reveal that: (i) not only microbial substances but also endogenous molecules can trigger Toll-like receptors; (ii) Toll-like receptor-4, the endotoxin receptor, is constitutively suppressed; and (iii) the first step in sepsis could be the release of Toll-like receptor-4 from suppression. These discoveries suggest that endotoxin might not always initiate the sepsis syndrome and they explain why anti-endotoxin therapies fail. The discoveries also suggest new therapeutic targets - endogenous agonists and Toll-like receptor regulators - for treatment of sepsis.

Peptidoglycan of Staphylococcus aureus upregulates monocyte expression of CD14, Toll-like receptor 2 (TLR2), and TLR4 in human blood: possible implications for priming of lipopolysaccharide signaling

Previous studies have indicated that peptidoglycan (PepG) from gram-positive bacteria can exert a priming effect on the innate immune response to lipopolysaccharide (LPS) from gram-negative bacteria. Here, we hypothesized that this priming effect may be preceded by enhanced expression of monocyte CD14, Toll-like receptor 2 (TLR2), and TLR4. In an ex vivo whole human blood model, we observed a substantial synergy between LPS and PepG in the release of tumor necrosis factor alpha and interleukin-1beta (IL-1beta) over the 24-h experimental period, whereas the effect on IL-8 and IL-10 release was more time dependent. The priming effect of PepG on cytokine release was preceded by a rapid upregulation of CD14, TLR2, and TLR4 expression on monocytes: at 3 hours there was a twofold increase in CD14 expression (P < 0.03), a fivefold increase in TLR2 expression (P < 0.03), and a twofold increase in TLR4 expression (P < 0.03). CD14 and TLR2 remained upregulated throughout the experimental period following exposure to PepG (P < 0.05). Only a transient upregulation of these monocyte receptors was observed following treatment with LPS or LPS plus PepG. In conclusion, the synergistic effect of LPS and PepG on cytokine release is preceded by a reciprocal upregulation of TLR2 and TLR4 by both bacterial cell wall components.

GSK-3beta inhibitors attenuate the organ injury/dysfunction caused by endotoxemia in the rat

OBJECTIVE

Serine-threonine protein kinase glycogen synthase kinase (GSK)-3 is involved in regulation of many cell functions, but its role in regulation of inflammatory response is unknown. Here we investigate the effects of GSK-3beta inhibition on organ injury/dysfunction caused by lipopolysaccharide or coadministration of lipopolysaccharide and peptidoglycan in the rat.

DESIGN

Prospective, randomized study.

SETTING

University-based research laboratory.

SUBJECTS

Ninety-nine anesthetized male Wistar rats.

INTERVENTIONS

Study 1: Rats received either intravenous Escherichia coli lipopolysaccharide (6 mg/kg) or vehicle (1 mL/kg; saline). Study 2: Rats received either intravenous E. coli lipopolysaccharide (1 mg/kg) and Staphylococcus aureus peptidoglycan (0.3 mg/kg) or vehicle. The potent and selective GSK-3beta inhibitors TDZD-8 (1 mg/kg intravenously), SB216763 (0.6 mg/kg intravenously), and SB415286 (1 mg/kg intravenously) or vehicle (10% dimethyl sulfoxide) was administered 30 mins before lipopolysaccharide or lipopolysaccharide and peptidoglycan.

MEASUREMENTS AND MAIN RESULTS

Endotoxemia resulted in increases in the serum levels of creatinine (indicator of renal dysfunction), aspartate aminotransferase, alanine aminotransferase (markers for hepatocellular injury), lipase (indicator of pancreatic injury), and creatine kinase (indicator of neuromuscular injury). Coadministration of lipopolysaccharide and peptidoglycan resulted in hepatocellular injury and renal dysfunction. All GSK-3beta inhibitors attenuated the organ injury/dysfunction caused by lipopolysaccharide or lipopolysaccharide and peptidoglycan. GSK-3beta inhibition reduced the Ser536 phosphorylation of nuclear factor-kappaB subunit p65 and the messenger RNA expression of nuclear factor-kappaB-dependent proinflammatory mediators but had no effect on the nuclear factor-kappaB/DNA binding activity in the lung. GSK-3beta inhibition reduced the increase in nuclear factor-kappaB p65 activity caused by interleukin-1 in human embryonic kidney cells in vitro.

CONCLUSIONS

The potent and selective GSK-3beta inhibitors TDZD-8, SB216763, and SB415286 reduced the organ injury/dysfunction caused by lipopolysaccharide or lipopolysaccharide and peptidoglycan in the rat. We propose that GSK-3beta inhibition may be useful in the therapy of the organ injury/dysfunction associated with sepsis, shock, and other diseases associated with local or systemic inflammation.

PEPTIDOGLYCAN OF STAPHYLOCCUS AUREUS INDUCES ENHANCED LEVELS OF MATRIX METALLOPROTEINASE-9 IN HUMAN BLOOD ORIGINATING FROM NEUTROPHILS

Enhanced plasma levels of matrix metalloproteinase 9 (MMP-9) detected in patients with severe sepsis are thought to contribute to the development of organ dysfunction in endotoxemia. We have recently reported that peptidoglycan, the major wall component of gram-positive bacteria, increases MMP-9 levels in lung and liver and organ injury in the rat. Thus far, it is unclear whether MMP-9 is part of the septic response to peptidoglycan in human blood. The aim of the present study was to examine the regulation of MMP-9 by peptidoglycan in human leukocytes. The addition of peptidoglycan to whole human blood caused enhanced levels of MMP-9 after 1 h of incubation (306 vs. 75 ng/mL, P < or = 0.05) and onward, as measured by enzyme-linked immunoabsorbant assay. In neutrophil cultures, MMP-9 values increased significantly after 30 min of incubation with peptidoglycan (242 vs. 121 ng/mL, P < or = 0.05), whereas muramyl dipeptide had no effect. In contrast, adherent monocytes released insignificant amounts of MMP-9. To examine whether the released MMP-9 resulted from de novo synthesis, intracellular and secreted MMP-9 was measured during stimulation of neutrophils. The total MMP-9 values (the sum of intracellular and secreted MMP-9) before and after stimulation were mainly unaltered. The enhanced MMP-9 levels induced by peptidoglycan was attenuated by inhibitors of p38 mitogen-activated protein kinases (MAPK), (SB202190, 25 microM) and ERK1/2 (PD98059, 25 microM) and inhibitors of Src Tyrosine kinase (PP2, 5 microM) and PI3-K (LY294002, 25 microM).

Diagnostic and predictive value of the silkworm larvae plasma test for postoperative infection following gastrointestinal surgery

OBJECTIVE

To determine whether the silkworm larvae plasma (SLP) test is a reliable diagnostic marker of infection in patients with infectious complications following gastrointestinal surgery.

DESIGN

Prospective study.

SETTING

Department of Surgery, University Hospital, Shiga University of Medical Science.

PATIENTS

One hundred and twelve adult patients undergoing gastrointestinal surgery

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Thirty-nine of 112 patients developed infectious complications (infected group). Seven patients with sepsis (severely infected group) and 32 patients without sepsis (minor infected group) were observed. The operation time, blood loss, and age were significantly greater in both infected groups than in the noninfected group. The systemic inflammatory response syndrome score on postoperative day (POD) 1 and POD7 was highest in the severely infected group. The increase in C-reactive protein on POD3 and POD7 was significantly higher in both infected groups than in the noninfected group. White blood cell counts on POD7 were elevated significantly higher in the severely infected group than in the other groups. Immediately after surgery, SLP activity significantly increased compared with presurgery in all groups and was significantly higher in the minor and severely infected groups than in the noninfected group. The increased SLP activity returned to preoperative levels in the minor and noninfected groups; however, SLP activity in the severely infected groups remained high throughout the observational period. The most significant factor and time point that predicted infectious complications were the SLP test on POD1; sensitivity 66.7%, specificity 90.4%, positive and negative predictive values 78.8% and 83.5%. The area under the receiver operating characteristic curve for the SLP test was 0.813 +/- 0.046.

CONCLUSIONS

The SLP test appears to be a useful marker of diagnosis and prediction of infectious complications following gastrointestinal surgery. Moreover, the SLP test may be able to evaluate not only the existence but also the severity of infection in surgical patients.

Lipopolysaccharide and lipoteichoic acid induce different innate immune responses in bovine mammary epithelial cells

The objective of the present study was to characterize the innate immune responses induced by in vitro stimulation of bovine primary mammary epithelial cells (bMEC) using gram-negative lipopolysaccharide (LPS) and gram-positive lipoteichoic acid (LTA) bacterial cell wall components. Quantitative real-time PCR (qRT-PCR) was employed to examine the mRNA expression of a panel of 22 cytokines, chemokines, beta-defensins and components of the Toll-Like Receptor signaling pathway. Stimulation of bMEC with LPS for 24h elicited a marked increase in mRNA expression for IL-1beta, IL-8, TNFalpha, CXCL6 and beta-defensin while members of the Toll-Like Receptor pathway, although present, were largely unaffected. Surprisingly, stimulation of these cells with LTA for 24 h did not significantly alter the expression of these genes. A time course of the expression of IL-1beta, IL-8, TNFalpha, CXCL6 and beta-defensin was subsequently performed. The mRNA levels of all genes increased rapidly after stimulation for 2-4 h with both LPS and LTA but only the former treatment resulted in sustained responses. In contrast, the increased gene expression for LTA stimulated cells returned to resting levels after 8-16 h with the exception of beta-defensin, which remained up-regulated. The limited and unsustained cytokine response to LTA may explain why mastitis caused by gram-positive bacteria has greater potential for chronic intra-mammary infection than gram-negative infection. It was concluded that bovine mammary epithelial cells have a strong but differential capacity to mount innate immune responses to bacterial cell wall components.

A free radical scavenger, edaravone (MCI-186), diminishes intestinal neutrophil lipid peroxidation and bacterial translocation in a rat hemorrhagic shock model*

OBJECTIVE

To investigate the effects of edaravone, a novel free radical scavenger, on bacterial translocation induced by hemorrhagic shock.

DESIGN

Prospective, randomized, unblinded animal study.

SETTING

Surgical research laboratories of Shiga University of Medical Science.

SUBJECTS

Male specific-pathogen-free Sprague-Dawley rats.

INTERVENTIONS

The rats were randomly divided into three groups: conventional saline treatment, edaravone treatment, and sham shock induction. The saline and edaravone groups were subjected to hemorrhagic shock (mean arterial pressure of 30 mm Hg, for 30 or 60 mins). Rats were killed 30 or 60 mins after shock induction. Mesenteric lymph nodes were cultured for determination of bacterial translocation. Systemic plasma silkworm larvae plasma test, which can detect peptidoglycan and beta-glucan, and endotoxin tests were performed. Immunohistochemistry for 4-hydroxy-2-nonenal (4-HNE) was used to assess lipid peroxidation after shock.

MEASUREMENTS AND MAIN RESULTS

The incidence and magnitude of hemorrhagic-shock-induced bacterial translocation to mesenteric lymph nodes were reduced by edaravone. Hemorrhagic-shock-induced increase of plasma silkworm larvae plasma test was also reduced by edaravone. Immunohistochemistry for 4-HNE showed many 4-HNE-positive cells in the lamina propria of the ileum 60 mins after hemorrhagic shock. Double immunohistochemistry revealed that many of these 4-HNE-positive cells were also myeloperoxidase positive. Moreover, the percentage of double-labeled cells with 4-HNE and myeloperoxidase in myeloperoxidase-positive cells was significantly lower in the edaravone group than in the saline group.

CONCLUSIONS

The present findings suggest that lipid peroxidation of intestinal neutrophils is involved in bacterial translocation during hemorrhagic shock and that edaravone is potentially useful in diminishing bacterial translocation after hemorrhagic shock.

The function of mitogen-activated protein kinase phosphatase-1 in peptidoglycan-stimulated macrophages

Mitogen-activated protein (MAP) kinases play a pivotal role in the macrophages in the production of proinflammatory cytokines triggered by lipopolysaccharides. However, their function in the responses of macrophages to Gram-positive bacteria is poorly understood. Even less is known about the attenuation of MAP kinase signaling in macrophages exposed to Gram-positive bacteria. In the present study, we have investigated the regulation of MAP kinases and the role of MAP kinase phosphatase (MKP)-1 in the production of pro-inflammatory cytokines using murine RAW264.7 and primary peritoneal macrophages after peptidoglycan stimulation. Treatment of macrophages with peptidoglycan resulted in a transient activation of JNK, p38, and extracellular signal-regulated kinase. Most interestingly, MKP-1 expression was potently induced by peptidoglycan, and this induction was concurrent with MAP kinase dephosphorylation. Triptolide, a diterpenoid triepoxide, potently blocked the induction of MKP-1 by peptidoglycan and prolonged the activation of JNK and p38. Overexpression of MKP-1 substantially attenuated the production of tumor necrosis factor (TNF)-alpha induced by peptidoglycan, whereas knockdown of MKP-1 by small interfering RNA substantially increased the production of both TNF-alpha and interleukin-1 beta. Finally, we found that in primary murine peritoneal macrophages, MKP-1 induction following peptidoglycan stimulation also coincided with inactivation of JNK and p38. Blockade of MKP-1 induction resulted in a sustained activation of both JNK and p38 in primary macrophages. Our results reveal that MKP-1 critically regulates the expression of TNF-alpha and interleukin-1 beta in RAW264.7 cells and further suggest a central role for this phosphatase in controlling the inflammatory responses of primary macrophages to Gram-positive bacterial infection.

PEPTIDOGLYCAN OF S. AUREUS CAUSES INCREASED LEVELS OF MATRIX METALLOPROTEINASES IN THE RAT

Matrix metalloproteinases (MMPs) have been suggested to contribute to the organ injury in septic patients. We recently demonstrated that peptidoglycan (PepG) of S. aureus causes organ injury in the rat. A possible role for MMPs in the septic response to PepG is unknown. In the present study, we have examined whether the release of MMP-9 (gelatinase B) and MMP-2 (gelatinase A) is induced by PepG in the anesthetized rat. Male Wistar rats were injected intravenously with PepG (10 mg/kg), LPS (1 mg/kg), or a combination of LPS and PepG (1 mg/kg of each). After 1 or 3 h, liver, lung, and plasma were harvested. MMP-9 and MMP-2 levels were analyzed in organ homogenates and in plasma samples by zymography. MMP-9 levels were significantly increased in the lung within 1 h after injection of PepG, LPS, or combined treatment, compared with sham animals (P < or = 0.05). In the liver and plasma, MMP-9 was clearly increased by PepG or LPS at both 1 and 3 h compared with sham animals (P < or = 0.05). Considerable basal amounts of MMP-2 protein were seen in the liver and in plasma. In the lung, MMP-2 levels were elevated by combined LPS/PepG at 1 h and by LPS at 3 h (P < or = 0.05). In contrast, MMP-2 activity in the liver was significantly reduced by bacterial products. In the plasma, no major alterations of MMP-2 levels were observed. Our data show that PepG of S. aureus causes a rapid elevation of MMP-9 protein in the liver, lung, and blood of the rat. Based on these and previous data, we hypothesize that the release of MMP-9 in lung, liver, and blood is part of the septic host response to systemic PepG.