Plasma and wound fluids from trauma patients suppress neutrophil extracellular respiratory burst

DANGER Signals Activate G -Protein Receptor Kinases Suppressing Neutrophil Function and Predisposing to Infection After Tissue Trauma

OBJECTIVE

Injured tissue predisposes the subject to local and systemic infection. We studied injury-induced immune dysfunction seeking novel means to reverse such predisposition.

BACKGROUND

Injury mobilizes primitive "DANGER signals" [danger-associated molecular patterns (DAMPs)] activating innate immunocyte (neutrophils, PMN) signaling and function. Mitochondrial formyl peptides activate G -protein coupled receptors (GPCR) like formyl peptide receptor-1. Mitochondrial DNA and heme activate toll-like receptors (TLR9 and TLR2/4). GPCR kinases (GRKs) can regulate GPCR activation.

METHODS

We studied human and mouse PMN signaling elicited by mitochondrial DAMPs (GPCR surface expression; protein phosphorylation, or acetylation; Ca 2+ flux) and antimicrobial functions [cytoskeletal reorganization, chemotaxis (CTX), phagocytosis, bacterial killing] in cellular systems and clinical injury samples. Predicted rescue therapies were assessed in cell systems and mouse injury-dependent pneumonia models.

RESULTS

Mitochondrial formyl peptides activate GRK2, internalizing GPCRs and suppressing CTX. Mitochondrial DNA suppresses CTX, phagocytosis, and killing through TLR9 through a novel noncanonical mechanism that lacks GPCR endocytosis. Heme also activates GRK2. GRK2 inhibitors like paroxetine restore functions. GRK2 activation through TLR9 prevented actin reorganization, implicating histone deacetylases (HDACs). Actin polymerization, CTX, bacterial phagocytosis, and killing were also rescued, therefore, by the HDAC inhibitor valproate. Trauma repository PMN showed GRK2 activation and cortactin deacetylation, which varied with severity and was most marked in patients developing infections. Either GRK2 or HDAC inhibition prevented loss of mouse lung bacterial clearance, but only the combination rescued clearance when given postinjury.

CONCLUSIONS

Tissue injury-derived DAMPs suppress antimicrobial immunity through canonical GRK2 activation and a novel TLR-activated GRK2-pathway impairing cytoskeletal organization. Simultaneous GRK2/HDAC inhibition rescues susceptibility to infection after tissue injury.

Visualizing neutrophil extracellular traps in septic equine synovial and peritoneal fluid samples using immunofluorescence microscopy

Septic synovitis and peritonitis are routinely diagnosed in horses based on clinical examination findings and laboratory assessment of synoviocentesis and abdominocentesis samples, respectively. Diagnosis is difficult in some cases because of an overlap in laboratory results for septic and non-septic inflammation. Neutrophil extracellular trap (NET) formation is part of the innate immune response against pathogens. Identifying and quantifying NETs, which have not been explored in clinical samples from horses with septic synovitis and peritonitis, to our knowledge, may be helpful in detecting infectious processes. Our main objective was to determine whether NETs could be visualized in septic equine synovial and peritoneal fluid cytology samples using immunofluorescence with antibodies against citrullinated histone H3 (Cit-H3) and myeloperoxidase (MPO). We analyzed 9 synovial and 4 peritoneal fluid samples. NET percentages were quantified using a simple counting technique, which is suitable for high-quality, well-preserved, and stained cytospin smears. NETs were evident in all septic samples and were absent in a non-septic sample; NETs were better visualized with Cit-H3 than with MPO immunolabeling. Overall, we believe that there is the potential for NETs and associated markers to be used to investigate and understand septic inflammation in horses.

The immune suppressive properties of damage associated molecular patterns in the setting of sterile traumatic injury

Associated with the development of hospital-acquired infections, major traumatic injury results in an immediate and persistent state of systemic immunosuppression, yet the underlying mechanisms are poorly understood. Detected in the circulation in the minutes, days and weeks following injury, damage associated molecular patterns (DAMPs) are a heterogeneous collection of proteins, lipids and DNA renowned for initiating the systemic inflammatory response syndrome. Suggesting additional immunomodulatory roles in the post-trauma immune response, data are emerging implicating DAMPs as potential mediators of post-trauma immune suppression. Discussing the results of in vitro, in vivo and ex vivo studies, the purpose of this review is to summarise the emerging immune tolerising properties of cytosolic, nuclear and mitochondrial-derived DAMPs. Direct inhibition of neutrophil antimicrobial activities, the induction of endotoxin tolerance in monocytes and macrophages, and the recruitment, activation and expansion of myeloid derived suppressor cells and regulatory T cells are examples of some of the immune suppressive properties assigned to DAMPs so far. Crucially, with studies identifying the molecular mechanisms by which DAMPs promote immune suppression, therapeutic strategies that prevent and/or reverse DAMP-induced immunosuppression have been proposed. Approaches currently under consideration include the use of synthetic polymers, or the delivery of plasma proteins, to scavenge circulating DAMPs, or to treat critically-injured patients with antagonists of DAMP receptors. However, as DAMPs share signalling pathways with pathogen associated molecular patterns, and pro-inflammatory responses are essential for tissue regeneration, these approaches need to be carefully considered in order to ensure that modulating DAMP levels and/or their interaction with immune cells does not negatively impact upon anti-microbial defence and the physiological responses of tissue repair and wound healing.

Can Neutrophils Prevent Nosocomial Pneumonia after Serious Injury?

Nosocomial pneumonia is a leading cause of critical illness and mortality among seriously injured trauma patients. However, the link between injury and the development of nosocomial pneumonia is still not well recognized. Our work strongly suggests that mitochondrial damage-associated molecular patterns (mtDAMPs), especially mitochondrial formyl peptides (mtFPs) released by tissue injury, play a significant role in developing nosocomial pneumonia after a serious injury. Polymorphonuclear leukocytes (neutrophils, PMN) migrate toward the injury site by detecting mtFPs through formyl peptide receptor 1 (FPR1) to fight/contain bacterial infection and clean up debris. Activation of FPR1 by mtFPs enables PMN to reach the injury site; however, at the same time it leads to homo- and heterologous desensitization/internalization of chemokine receptors. Thus, PMN are not responsive to secondary infections, including those from bacteria-infected lungs. This may enable a progression of bacterial growth in the lungs and nosocomial pneumonia. We propose that the intratracheal application of exogenously isolated PMN may prevent pneumonia coupled with a serious injury.

ROLE OF PEPTIDYLARGININE DEIMINASE AND NEUTROPHIL EXTRACELLULAR TRAPS IN INJURIES: FUTURE NOVEL DIAGNOSTICS AND THERAPEUTIC TARGETS

ABSTRACT

Injuries lead to an early systemic inflammatory state with innate immune system activation. Neutrophil extracellular traps (NETs) are a complex of chromatin and proteins released from the activated neutrophils. Although initially described as a response to bacterial infections, NETs have also been identified in the sterile postinjury inflammatory state. Peptidylarginine deiminases (PADs) are a group of isoenzymes that catalyze the conversion of arginine to citrulline, termed citrullination or deimination. PAD2 and PAD4 have been demonstrated to play a role in NET formation through citrullinated histone 3. PAD2 and PAD4 have a variety of substrates with variable organ distribution. Preclinical and clinical studies have evaluated the role of PADs and NETs in major trauma, hemorrhage, burns, and traumatic brain injury. Neutrophil extracellular trap formation and PAD activation have been shown to contribute to the postinjury inflammatory state leading to a detrimental effect on organ systems. This review describes our current understanding of the role of PAD and NET formation following injury and burn. This is a new field of study, and the emerging data appear promising for the future development of targeted biomarkers and therapies in trauma.

Evaluating the effect of montelukast tablets on respiratory complications in patients following blunt chest wall trauma: A double-blind, randomized clinical trial

PURPOSE

Patients with multiple traumas are at high risk of developing respiratory complications, including pneumonia and acute respiratory distress syndrome. Many pulmonary complications are associated with systemic inflammation and pulmonary neutrophilic infiltration. Leukotriene-receptor antagonists are anti-inflammatory and anti-oxidant drugs subsiding airway inflammation. The present study investigates the effectiveness of montelukast in reducing pulmonary complications among trauma patients.

METHODS

This randomized, double-blind, placebo-control trial was conducted in patients with multiple blunt traumas and evidence of lung contusion detected via CT scan. We excluded patients if they met at least one of the following conditions: <16 years old, history of cardiopulmonary diseases or positive history of montelukast-induced hypersensitivity reactions. Patients were allocated to the treatment (10 mg of montelukast) or placebo group using permuted block randomization method. The primary measured outcome was the volume of pulmonary contusion at the end of the trial. The secondary outcomes were intensive care unit and hospital length of stay, ventilation days, multi-organ failure, and the in-hospital mortality rate.

RESULTS

In total, 65 eligible patients (treatment = 31, placebo = 34) were included for the final analysis. The treatment group had more pulmonary contusion volume (mean (SD), mm³) at the right (68726.97 (93656.54) vs. 59730.27 (76551)) and the left side (67501.71 (91514) vs. 46502.21 (80604.21)), higher initial C-reactive peptide level (12.16 (10.58) vs. 10.85 (17.9)) compared to the placebo group, but the differences were not statistically significant (p > 0.05). At the end of the study, the mean (SD) of pulmonary contusion volume (mm³) (right side = 116748.74 (361705.12), left side = 64522.03 (117266.2)) of the treatment group were comparable to that of the placebo group (right side = 40051.26 (64081.56), left side = 25929.12 (47417.13), p = 0.228 and 0.082, respectively). Moreover, both groups have statistically similar hospital (mean (SD), days) (10.87 (9.83) vs. 13.05 (10.12)) and intensive care unit length of stays (mean (SD), days) (7.16 (8.15) vs. 7.82 (7.48)). Of note, the frequency of the in-hospital complications (treatment vs. control group) including acute respiratory distress syndrome (12.9% vs. 8.8%, p = 0.71), pneumonia (19.4% vs. 17.6%, p = 0.85), multi-organ failure (12.9% vs. 17.6%, p = 0.58) and the mortality rate (22.6% vs. 14.7%, p = 0.41) were comparable between the groups.

CONCLUSION

Administrating montelukast has no preventive or therapeutic effects on lung contusion or its complications.

Emerging Paradigms in the Prevention of Surgical Site Infection: The Patient Microbiome and Antimicrobial Resistance

This article summarizes new scientific evidence on the pathogenesis of surgical site infection, including the roles of the patient microbiome and antimicrobial resistance, and reviews changes in guidelines and clinical practices for prevention.