Circulating mitochondrial N-formyl peptides contribute to secondary nosocomial infection in patients with septic shock.

Secondary infections typically worsen outcomes of patients recovering from septic shock. Neutrophil [polymorphonuclear leukocytes (PMNs)] migration to secondarily inoculated sites may play a key role in inhibiting progression from local bacterial inoculation to secondary infection. Mitochondrial N-formyl peptide (mtFP) occupancy of formyl peptide receptor-1 (FPR1) has been shown to suppress PMN chemotaxis. Therefore, we studied the association between circulating mtFPs and the development of secondary infection in patients with septic shock. We collected clinical data and plasma samples from patients with septic shock admitted to the intensive care unit for longer than 72 h. Impacts of circulating nicotinamide adenine dinucleotide dehydrogenase subunit-6 (ND6) upon clinical outcomes were analyzed. Next, the role of ND6 in PMN chemotaxis was investigated using isolated human PMNs. Studying plasma samples from 97 patients with septic shock, we found that circulating ND6 levels at admission were independently and highly associated with the development of secondary infection (odds ratio = 30.317, 95% CI: 2.904 to 316.407, P = 0.004) and increased 90-d mortality (odds ratio = 1.572, 95% CI: 1.002 to 2.465, P = 0.049). In ex vivo experiments, ND6 pretreatment suppressed FPR1-mediated PMN chemotactic responses to bacterial peptides in the presence of multiple cytokines and chemokines, despite increased nondirectional PMN movements. Circulating mtFPs appear to contribute to the development of secondary infection and increased mortality in patients with septic shock who survive their early hyperinflammatory phase. The increased susceptibility to secondary infection is probably partly mediated by the suppression of FPR1-mediated PMN chemotaxis to secondary infected sites.

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.

Extracellular mitochondria drive CD8 T cell dysfunction in trauma by upregulating CD39.

RATIONALE: The increased mortality and morbidity seen in critically injured patients appears associated with systemic inflammatory response syndrome (SIRS) and immune dysfunction, which ultimately predisposes to infection. Mitochondria released by injury could generate danger molecules, for example, ATP, which in turn would be rapidly scavenged by ectonucleotidases, expressed on regulatory immune cells. OBJECTIVE: To determine the association between circulating mitochondria, purinergic signalling and immune dysfunction after trauma. METHODS: We tested the impact of hepatocyte-derived free mitochondria on blood-derived and lung-derived CD8 T cells in vitro and in experimental mouse models in vivo. In parallel, immune phenotypic analyses were conducted on blood-derived CD8 T cells obtained from trauma patients. RESULTS: Isolated intact mitochondria are functional and generate ATP ex vivo. Extracellular mitochondria perturb CD8+ T cells in co-culture, inducing select features of immune exhaustion in vitro. These effects are modulated by scavenging ATP, modelled by addition of apyrase in vitro. Injection of intact mitochondria into recipient mice markedly upregulates the ectonucleotidase CD39, and other immune checkpoint markers in circulating CD8+ T cells. We note that mice injected with mitochondria, prior to instilling bacteria into the lung, exhibit more severe lung injury, characterised by elevated neutrophil influx and by changes in CD8+ T cell cytotoxic capacity. Importantly, the development of SIRS in injured humans, is likewise associated with disordered purinergic signalling and CD8 T cell dysfunction. CONCLUSION: These studies in experimental models and in a cohort of trauma patients reveal important associations between extracellular mitochondria, aberrant purinergic signalling and immune dysfunction. These pathogenic factors with immune exhaustion are linked to SIRS and could be targeted therapeutically.

Characterisation of Plasma Mitochondrial DNA, MMP-9 and Neutrophil Elastase in Patients Undergoing Coronary Artery Bypass Grafting: Effects of Tranexamic Acid and Postoperative Pneumonia.

BACKGROUND: Postoperative pneumonia is a major cause of morbidity and mortality following cardiac surgery. The inflammatory response to cardiac surgery has been widely studied, but specific mechanisms for postoperative pneumonia have not been determined. Tranexamic acid is renowned for its effect on bleeding but can also modulate inflammatory processes. Cardiac surgery is known to release mitochondrial DAMPs (mtDAMPs) and is linked to postoperative inflammation and atrial fibrillation. We speculated that mtDAMPs might be related to postoperative pneumonia and that this might be modulated by tranexamic acid. METHODS: Forty-one (41) patients from the Aspirin and Tranexamic Acid for Coronary Artery Surgery (ATACAS) trial were studied. Levels of mitochondrial DNA, matrix metallopeptidase 9 (MMP-9) and neutrophil elastase (NE) were determined in plasma preoperatively, at 24 and 72 hours post-surgery and correlated with clinical outcome. RESULTS: mtDNA was significantly elevated postoperatively in the placebo and tranexamic acid (TXA) groups. Neutrophil elastase increased immediately postoperatively and at 24 hours. MMP-9 was elevated in the placebo group early postoperatively and in the TXA group at the immediate postoperative time point and after 24 hours. Six (6) of the 41 (14.6%) patients subsequently developed pneumonia. mtDNA levels were significantly increased at the early postoperative period and the 24-hour time point in patients with pneumonia. CONCLUSIONS: Cardiac surgery releases mtDNA, increases MMP-9 and NE and this was not influenced by TXA. Inflammation postoperatively might be linked to pneumonia since mtDNA was further elevated in these patients. Due to the low number of individuals developing pneumonia, further studies are warranted to clearly identify whether TXA impacts on the inflammatory response in postoperative pneumonia.

Carbon monoxide protects the kidney through the central circadian clock and CD39.

Ischemia reperfusion injury (IRI) is the predominant tissue insult associated with organ transplantation. Treatment with carbon monoxide (CO) modulates the innate immune response associated with IRI and accelerates tissue recovery. The mechanism has been primarily descriptive and ascribed to the ability of CO to influence inflammation, cell death, and repair. In a model of bilateral kidney IRI in mice, we elucidate an intricate relationship between CO and purinergic signaling involving increased CD39 ectonucleotidase expression, decreased expression of Adora1, with concomitant increased expression of Adora2a/2b. This response is linked to a >20-fold increase in expression of the circadian rhythm protein Period 2 (Per2) and a fivefold increase in serum erythropoietin (EPO), both of which contribute to abrogation of kidney IRI. CO is ineffective against IRI in Cd39-/- and Per2-/- mice or in the presence of a neutralizing antibody to EPO. Collectively, these data elucidate a cellular signaling mechanism whereby CO modulates purinergic responses and circadian rhythm to protect against injury. Moreover, these effects involve CD39- and adenosinergic-dependent stabilization of Per2. As CO also increases serum EPO levels in human volunteers, these findings continue to support therapeutic use of CO to treat IRI in association with organ transplantation, stroke, and myocardial infarction.

Multiplexed Plasma Immune Mediator Signatures Can Differentiate Sepsis From NonInfective SIRS: American Surgical Association 2020 Annual Meeting Paper.

OBJECTIVES: Sepsis and sterile both release "danger signals' that induce the systemic inflammatory response syndrome (SIRS). So differentiating infection from SIRS can be challenging. Precision diagnostic assays could limit unnecessary antibiotic use, improving outcomes. METHODS: After surveying human leukocyte cytokine production responses to sterile damage-associated molecular patterns (DAMPs), bacterial pathogen-associated molecular patterns, and bacteria we created a multiplex assay for 31 cytokines. We then studied plasma from patients with bacteremia, septic shock, "severe sepsis," or trauma (ISS ≥15 with circulating DAMPs) as well as controls. Infections were adjudicated based on post-hospitalization review. Plasma was studied in infection and injury using univariate and multivariate means to determine how such multiplex assays could best distinguish infective from noninfective SIRS. RESULTS: Infected patients had high plasma interleukin (IL)-6, IL-1α, and triggering receptor expressed on myeloid cells-1 (TREM-1) compared to controls [false discovery rates (FDR) <0.01, <0.01, <0.0001]. Conversely, injury suppressed many mediators including MDC (FDR <0.0001), TREM-1 (FDR <0.001), IP-10 (FDR <0.01), MCP-3 (FDR <0.05), FLT3L (FDR <0.05), Tweak, (FDR <0.05), GRO-α (FDR <0.05), and ENA-78 (FDR <0.05). In univariate studies, analyte overlap between clinical groups prevented clinical relevance. Multivariate models discriminated injury and infection much better, with the 2-group random-forest model classifying 11/11 injury and 28/29 infection patients correctly in out-of-bag validation. CONCLUSIONS: Circulating cytokines in traumatic SIRS differ markedly from those in health or sepsis. Variability limits the accuracy of single-mediator assays but machine learning based on multiplexed plasma assays revealed distinct patterns in sepsis- and injury-related SIRS. Defining biomarker release patterns that distinguish specific SIRS populations might allow decreased antibiotic use in those clinical situations. Large prospective studies are needed to validate and operationalize this approach.

Formyl Peptide Receptor-1 Blockade Prevents Receptor Regulation by Mitochondrial Danger-Associated Molecular Patterns and Preserves Neutrophil Function After Trauma.

OBJECTIVES: Trauma predisposes to systemic sterile inflammation (systemic inflammatory response syndrome) as well as infection, but the mechanisms linking injury to infection are poorly understood. Mitochondrial debris contains formyl peptides. These bind formyl peptide receptor-1, trafficking neutrophils to wounds, initiating systemic inflammatory response syndrome, and wound healing. Bacterial formyl peptides, however, also attract neutrophils via formyl peptide receptor-1. Thus, mitochondrial formyl peptides might suppress neutrophils antimicrobial function. Also, formyl peptide receptor-1 blockade used to mitigate systemic inflammatory response syndrome might predispose to sepsis. We examined how mitochondrial formyl peptides impact neutrophils functions contributing to antimicrobial responses and how formyl peptide receptor-1 antagonists affect those functions. DESIGN: Prospective study of human and murine neutrophils and clinical cohort analysis. SETTING: University research laboratory and level 1 trauma center. PATIENTS: Trauma patients, volunteer controls. ANIMAL SUBJECTS: C57Bl/6, formyl peptide receptor-1, and formyl peptide receptor-2 knockout mice. INTERVENTIONS: Human and murine neutrophils functions were activated with autologous mitochondrial debris, mitochondrial formyl peptides, or bacterial formyl peptides followed by chemokines or leukotrienes. The experiments were repeated using formyl peptide receptor-1 antagonist cyclosporin H, "designer" human formyl peptide receptor-1 antagonists (POL7178 and POL7200), or anti-formyl peptide receptor-1 antibodies. Mouse injury/lung infection model was used to evaluate effect of formyl peptide receptor-1 inhibition. MEASUREMENTS AND MAIN RESULTS: Human neutrophils cytosolic calcium, chemotaxis, reactive oxygen species production, and phagocytosis were studied before and after exposure to mitochondrial debris, mitochondrial formyl peptides, and bacterial formyl peptides. Mitochondrial formyl peptide and bacterial formyl peptides had similar effects on neutrophils. Responses to chemokines and leukotrienes were suppressed by prior exposure to formyl peptides. POL7200 and POL7178 were specific antagonists of human formyl peptide receptor-1 and more effective than cyclosporin H or anti-formyl peptide receptor-1 antibodies. Formyl peptides inhibited mouse neutrophils responses to chemokines only if formyl peptide receptor-1 was present. Formyl peptide receptor-1 blockade did not inhibit neutrophils bacterial phagocytosis or reactive oxygen species production. Cyclosporin H increased bacterial clearance in lungs after injury. CONCLUSIONS: Formyl peptides both activate and desensitize neutrophils. Formyl peptide receptor-1 blockade prevents desensitization, potentially both diminishing systemic inflammatory response syndrome and protecting the host against secondary infection after tissue trauma or primary infection.

Mitochondrial DNA in the tumour microenvironment activates neutrophils and is associated with worse outcomes in patients with advanced epithelial ovarian cancer.

BACKGROUND: Advanced cancer causes necrosis and releases damage-associated molecular patterns (DAMPs). Mitochondrial DAMPs activate neutrophils, including generation of neutrophil extracellular traps (NETs), which are injurious, thrombogenic, and implicated in metastasis. We hypothesised that extracellular mitochondrial DNA (mtDNA) in ascites from patients with epithelial ovarian cancer (EOC) would correlate with worse outcomes. METHODS: Banked ascites supernatants from patients with newly diagnosed advanced EOC were analysed for mtDNA, neutrophil elastase, and activation of healthy donor neutrophils and platelets. TCGA was mined for expression of SELP and ELANE. RESULTS: The highest quartile of ascites mtDNA correlated with reduced progression-free survival (PFS) and a higher likelihood of disease progression within 12-months following primary surgery (n = 68, log-rank, p = 0.0178). NETs were detected in resected tumours. Ascites supernatants chemoattracted neutrophils, induced NETs, and activated platelets. Ascites exposure rendered neutrophils suppressive, based on abrogation of ex vivo stimulated T cell proliferation. Increased SELP mRNA expression correlated with worse overall survival (n = 302, Cox model, p = 0.02). CONCLUSION: In this single-centre retrospective analysis, ascites mtDNA correlated with worse PFS in advanced EOC. Mitochondrial and other DAMPs in ascites may activate neutrophil and platelet responses that facilitate metastasis and obstruct anti-tumour immunity. These pathways are potential prognostic markers and therapeutic targets.

Mitochondrial DAMPs Are Released During Cardiopulmonary Bypass Surgery and Are Associated With Postoperative Atrial Fibrillation.

BACKGROUND: Atrial fibrillation (AF) is the most frequent complication of surgery performed on cardiopulmonary bypass (CPB) and recent work associates CPB with postoperative inflammation. We have shown that all tissue injury releases mitochondrial damage associated molecular patterns (mtDAMPs) including mitochondrial DNA (mtDNA). This can act as a direct, early activator of neutrophils (PMN), eliciting a systemic inflammatory response syndrome (SIRS) while suppressing PMN function. Neutrophil Extracellular Traps (NETs) are crucial to host defence. They carry out NETosis wherein webs of granule proteins and chromatin trap and kill bacteria. We hypothesised that surgery performed on CPB releases mtDAMPs into the circulation. Molecular patterns thus mobilised during CPB might then participate in the pathogenesis of SIRS and predict postoperative complications like AF [1]. METHODS: We prospectively studied 16 patients undergoing elective operations on CPB. Blood was sampled preoperatively, at the end of CPB and on days 1-2 postoperatively. Plasma samples were analysed for mtDNA. Neutrophil IL-6 gene expression was studied to assess induction of SIRS. Neutrophils were also assayed for the presence of neutrophil extracellular traps (NETs/NETosis). These biologic findings were then correlated to clinical data and compared in patients with and without postoperative AF (POAF). RESULTS: Mitochondrial DNA was significantly elevated following CPB (six-fold increase post-CPB, p=0.008 and five-fold increase days 1-2, p=0.02). Patients with POAF showed greater increases in mtDNA post-CPB than those without. Postoperative AF was seen in all patients with a ≥2-fold increase of mtDNA (p=0.037 vs. <2-fold). Neutrophil IL-6 gene transcription increased postoperatively demonstrating SIRS that was greatest days 1-2 (p=0.039). Neutrophil extracellular trap (NET) formation was markedly suppressed in the post-CPB state. CONCLUSION: Mitochondrial DNA is released by CPB surgery and is associated with POAF. IL-6 gene expression increases after CPB, demonstrating the evolution of postoperative SIRS. Lastly, cardiac surgery on CPB also suppressed PMN NETosis. Taken together, our data suggest that mtDNA released during surgery on CPB, may be involved in the pathogenesis of SIRS and related postoperative inflammatory events like POAF and infections. Mitochondrial DNA may therefore prove to be an early biomarker for postoperative complications with the degree of association to be determined in appropriately sized studies. If mtDNA is directly involved in cardiac inflammation, mtDNA-induced toll-like receptor-9 (TLR9) signalling could also be targeted therapeutically.

Circulating mitochondrial DAMPs cause inflammatory responses to injury.

Injury causes a systemic inflammatory response syndrome (SIRS) that is clinically much like sepsis. Microbial pathogen-associated molecular patterns (PAMPs) activate innate immunocytes through pattern recognition receptors. Similarly, cellular injury can release endogenous 'damage'-associated molecular patterns (DAMPs) that activate innate immunity. Mitochondria are evolutionary endosymbionts that were derived from bacteria and so might bear bacterial molecular motifs. Here we show that injury releases mitochondrial DAMPs (MTDs) into the circulation with functionally important immune consequences. MTDs include formyl peptides and mitochondrial DNA. These activate human polymorphonuclear neutrophils (PMNs) through formyl peptide receptor-1 and Toll-like receptor (TLR) 9, respectively. MTDs promote PMN Ca(2+) flux and phosphorylation of mitogen-activated protein (MAP) kinases, thus leading to PMN migration and degranulation in vitro and in vivo. Circulating MTDs can elicit neutrophil-mediated organ injury. Cellular disruption by trauma releases mitochondrial DAMPs with evolutionarily conserved similarities to bacterial PAMPs into the circulation. These signal through innate immune pathways identical to those activated in sepsis to create a sepsis-like state. The release of such mitochondrial 'enemies within' by cellular injury is a key link between trauma, inflammation and SIRS.

NADPH oxidase and Nrf2 regulate gastric aspiration-induced inflammation and acute lung injury.

Recruitment of neutrophils and release of reactive oxygen species are considered to be major pathogenic components driving acute lung injury (ALI). However, NADPH oxidase, the major source of reactive oxygen species in activated phagocytes, can paradoxically limit inflammation and injury. We hypothesized that NADPH oxidase protects against ALI by limiting neutrophilic inflammation and activating Nrf2, a transcriptional factor that induces antioxidative and cytoprotective pathways. Our objective was to delineate the roles of NADPH oxidase and Nrf2 in modulating acute lung inflammation and injury in clinically relevant models of acute gastric aspiration injury, a major cause of ALI. Acid aspiration caused increased ALI (as assessed by bronchoalveolar lavage fluid albumin concentration) in both NADPH oxidase-deficient mice and Nrf2(-/-) mice compared with wild-type mice. NADPH oxidase reduced airway neutrophil accumulation, but Nrf2 decreased ALI without affecting neutrophil recovery. Acid injury resulted in a 120-fold increase in mitochondrial DNA, a proinflammatory and injurious product of cellular necrosis, in cell-free bronchoalveolar lavage fluid. Pharmacologic activation of Nrf2 by the triterpenoid 1-[2-cyano-3-,12-dioxooleana-1,9 (11)-dien-28-oyl]imidazole limited aspiration-induced ALI in wild-type mice and reduced endothelial cell injury caused by mitochondrial extract-primed human neutrophils, leading to the conclusion that NADPH oxidase and Nrf2 have coordinated, but distinct, functions in modulating inflammation and injury. These results also point to Nrf2 as a therapeutic target to limit ALI by attenuating neutrophil-induced cellular injury.

Heme: The Lord of the Iron Ring.

Heme is an iron-protoporphyrin complex with an essential physiologic function for all cells, especially for those in which heme is a key prosthetic group of proteins such as hemoglobin, myoglobin, and cytochromes of the mitochondria. However, it is also known that heme can participate in pro-oxidant and pro-inflammatory responses, leading to cytotoxicity in various tissues and organs such as the kidney, brain, heart, liver, and in immune cells. Indeed, heme, released as a result of tissue damage, can stimulate local and remote inflammatory reactions. These can initiate innate immune responses that, if left uncontrolled, can compound primary injuries and promote organ failure. In contrast, a cadre of heme receptors are arrayed on the plasma membrane that is designed either for heme import into the cell, or for the purpose of activating specific signaling pathways. Thus, free heme can serve either as a deleterious molecule, or one that can traffic and initiate highly specific cellular responses that are teleologically important for survival. Herein, we review heme metabolism and signaling pathways, including heme synthesis, degradation, and scavenging. We will focus on trauma and inflammatory diseases, including traumatic brain injury, trauma-related sepsis, cancer, and cardiovascular diseases where current work suggests that heme may be most important.

Cytomegalovirus durably primes neutrophil oxidative burst.

Cytomegalovirus (CMV) is a ubiquitous herpes virus that infects most humans, thereafter persisting lifelong in tissues of the host. It is a known pathogen in immunosuppressed patients, but its impact on immunocompetent hosts remains less understood. Recent data have shown that CMV leaves a significant and long-lasting imprint in host immunity that may confer some protection against subsequent bacterial infection. Such innate immune activation may come at a cost, however, with potential to cause immunopathology. Neutrophils are central to many models of immunopathology, and while acute CMV infection is known to influence neutrophil biology, the impact of chronic CMV infection on neutrophil function remains unreported. Using our murine model of CMV infection and latency, we show that chronic CMV causes persistent enhancement of neutrophil oxidative burst well after resolution of acute infection. Moreover, this in vivo priming of marrow neutrophils is associated with enhanced formyl peptide receptor expression, and ultimately constitutive c-Jun N-terminal kinase phosphorylation and enhanced CD14 expression in/on circulating neutrophils. Finally, we show that neutrophil priming is dependent on viral load, suggesting that naturally infected human hosts will show variability in CMV-related neutrophil priming. Altogether, these findings represent a previously unrecognized and potentially important impact of chronic CMV infection on neutrophil responsiveness in immunocompetent hosts.

Neutrophil heterogeneity and emergence of a distinct population of CD11b/CD18-activated low-density neutrophils after trauma.

INTRODUCTION: Multiple large clinical trauma trials have documented an increased susceptibility to infection after injury. Although neutrophils (polymorphonuclear leukocytes [PMNs]) were historically considered a homogeneous cell type, we hypothesized that injury could alter neutrophil heterogeneity and predispose to dysfunction. To explore whether trauma modifies PMN heterogeneity, we performed an observational mass-spectrometry-based cytometry study on total leukocytes and low-density PMNs found in the peripheral blood mononuclear cell fraction of leukocytes from healthy controls and trauma patients. METHODS: A total of 74 samples from 12 trauma patients, each sampled at 1 or more time points, and matched controls were fractionated and profiled by mass-spectrometry-based cytometry using a panel of 44 distinct markers. After deconvolution and conservative gating on neutrophils, data were analyzed using Seurat, followed by clustering of principal components. RESULTS: Eleven distinct neutrophil populations were resolved in control and trauma neutrophils based on differential protein surface marker expression. Trauma markedly altered the basal heterogeneity of neutrophil subgroups seen in the control samples, with loss of a dominant population of resting neutrophils marked by high expression of C3AR and low levels of CD63, CD64, and CD177 (cluster 1), and expansion of two alternative neutrophil populations, one of which is marked by high expression of CD177 with suppression of CD10, CD16, C3AR, CD63, and CD64 (cluster 6). Remarkably, following trauma, a substantially larger percentage of neutrophils sediment in the monocyte fraction. These low-density neutrophils bear markers of functional exhaustion and form a unique trauma-induced population (cluster 9) with markedly upregulated expression of active surface adhesion molecules (activated CD11b/CD18), with suppression of nearly all other surface markers, including receptors for formyl peptides, leukotrienes, chemokines, and complement. CONCLUSION: Circulating neutrophils demonstrate considerable evidence of functional heterogeneity that is markedly altered by trauma. Trauma induces evolution of a novel, exhausted, low-density neutrophil population with immunosuppressive features.

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

BACKGROUND: Trauma increases susceptibility to secondary bacterial infections. The events suppressing antimicrobial immunity are unclear. Polymorphonuclear neutrophils (PMNs) migrate toward bacteria using chemotaxis, trap them in extracellular neutrophil extracellular traps, and kill them using respiratory burst (RB). We hypothesized that plasma and wound fluids from trauma patients alter PMN function. METHODS: Volunteer PMNs were incubated in plasma or wound fluids from trauma patients (days 0 and 1, days 2 and 3), and their functions were compared with PMNs incubated in volunteer plasma. Chemotaxis was assessed in transwells. Luminometry assessed total and intracellular RB responses to receptor-dependent and independent stimulants. Neutrophil extracellular trap formation was assessed using elastase assays. The role of tissue necrosis in creating functionally suppressive systemic PMN environments was assessed using a novel pig model where PMNs were incubated in uninjured pig plasma or plasma from pigs undergoing intraperitoneal instillation of liver slurry. RESULTS: Both plasma and wound fluids from trauma patients markedly suppress total PMN RB. Intracellular RB is unchanged, implicating suppression of extracellular RB. Wound fluids are more suppressive than plasma. Biofluids suppressed RB maximally early after injury and their effects decayed with time. Chemotaxis and neutrophil extracellular trap formation were suppressed by biofluids similarly. Lastly, plasma from pigs undergoing abdominal liver slurry instillation suppressed PMN RB, paralleling suppression by human trauma biofluids. CONCLUSION: Trauma plasma and wound fluids suppress RB and other key PMNs antimicrobial functions. Circulating suppressive signals can be derived from injured or necrotic tissue at wound sites, suggesting a key mechanism by which tissue injuries can put the host at risk for infection.

An Integrated Pharmacological, Structural, and Genetic Analysis of Extracellular Versus Intracellular ROS Production in Neutrophils.

The neutrophil NADPH oxidase produces both intracellular and extracellular reactive oxygen species (ROS). Although oxidase activity is essential for microbial killing, and ROS can act as signaling molecules in the inflammatory process, excessive extracellular ROS directly contributes to inflammatory tissue damage, as well as to cancer progression and immune dysregulation in the tumor microenvironment. How specific signaling pathways contribute to ROS localization is unclear. Here we used a systems pharmacology approach to identify the specific Class I PI3-K isoform p110ß, and PLD1, but not PLD2, as critical regulators of extracellular, but not intracellular ROS production in primary neutrophils. Combined crystallographic and molecular dynamics analysis of the PX domain of the oxidase component p47phox, which binds the lipid products of PI 3-K and PLD, was used to clarify the membrane-binding mechanism and guide the design of mutant mice whose p47phox is unable to bind 3-phosphorylated inositol phospholipids. Neutrophils from these K43A mutant animals were specifically deficient in extracellular, but not intracellular, ROS production, and showed increased dependency on signaling through the remaining PLD1 arm. These findings identify the PX domain of p47phox as a critical integrator of PLD1 and p110ß signaling for extracellular ROS production, and as a potential therapeutic target for modulating tissue damage and extracellular signaling during inflammation.

Recombinant activated factor VII safety in trauma patients: results from the CONTROL trial.

BACKGROUND: Safety data on recombinant activated factor VII (rFVIIa, NovoSeven; Novo Nordisk A/S, Bagsværd, Denmark) in actively hemorrhaging trauma patients are limited. We present detailed safety data from a large multicenter, randomized, placebo-controlled phase III study (the CONTROL trial). METHODS: Data from 560 patients were analyzed. Subjects were monitored for adverse events (AEs) after rFVIIa or placebo administration. Incidences, timing, and presence of risk factors were reported by site investigators, supported by external study monitors and overseen by an independent Data Monitoring Committee. RESULTS: There were no differences in overall mortality, organ system failure, or AEs, serious AEs, or medical events of special interest. Arterial and venous thromboembolic (TE) events and their risk factors were similar in both groups. The greatest risk factor for TE events was a chest injury requiring mechanical ventilation >3 days (86%). There were four site investigator-reported myocardial infarctions in the rFVIIa group of which only one met diagnostic criteria preestablished by the Data Monitoring Committee. There were no reported myocardial infarctions in the placebo group. Troponins were increased in 30% of all patients. The rate of acute respiratory distress syndrome was lower in the rFVIIa (3.0%) than in the placebo (7.2%) group (p = 0.022). CONCLUSIONS: This represents the largest placebo-controlled dataset of rFVIIa use in trauma patients to date. In this prospective study of critically bleeding trauma patients, rFVIIa use was associated with an imbalance of investigator-reported Acute myocardial infarction/non-ST segment elevation myocardial infarction (AMI/NSTEMI), but was not associated with an increased risk for other AEs, including TE complications.

Role of Mitochondria-Derived Danger Signals Released After Injury in Systemic Inflammation and Sepsis.

Significance: Sepsis is a major public health concern, with high mortality and morbidity, especially among patients undergoing trauma. It is characterized by a systemic inflammatory response syndrome (SIRS) occurring in response to infection. Although classically associated with pathogens, many patients with SIRS do not have infection. The variability of the disease course cannot be fully explained by our current understanding of its pathogenesis. Thus, other factors are likely to play key roles in the development and progression of SIRS/sepsis. Recent Advances: Circulating levels of damage-associated molecular patterns (DAMPs) seem to correlate with SIRS/sepsis morbidity and mortality. Of the known DAMPs, those of mitochondrial (mt) origin have been of particular interest, since their DNA (mtDNA) and formyl peptides (mtFPs) resemble bacterial DNA and peptides, and hence, when released, may be recognized as "danger signals." Critical Issues: mtDAMPs released after tissue injury trigger immune responses similar to those induced by pathogens. Thus, they can result in systemic inflammation and organ damage, similar to that observed in SIRS/sepsis. We will discuss recent findings on the roles of mtDAMPs, particularly regarding the less recognized mtFPs, in the activation of inflammatory responses and development of SIRS/sepsis. Future Directions: There are no established methods to predict the course of SIRS/sepsis, but clinical studies reveal that plasma levels of mtDAMPs may correlate with the outcome of the disease. We propose that non-pathogen-initiated, mtDAMPs-induced SIRS/sepsis events need further studies aimed at early clinical recognition and better treatment of this disease.

Monocyte exocytosis of mitochondrial danger-associated molecular patterns in sepsis suppresses neutrophil chemotaxis.

BACKGROUND: Trauma and sepsis both increase the risk for secondary infections. Injury mobilizes mitochondrial (MT) danger-associated molecular patterns (mtDAMPs) directly from cellular necrosis. It is unknown, however, whether sepsis can cause active MT release and whether mtDAMPs released by sepsis might affect innate immunity. METHODS: Mitochondrial release from human monocytes (Mo) was studied after LPS stimulation using electron microscopy and using fluorescent video-microscopy of adherent Mo using Mito-Tracker Green (MTG) dye. Release of MTG+ microparticles was studied using flow cytometry after bacterial stimulation by size exclusion chromatography of supernatants with polymerase chain reaction (PCR) for mitochondrial DNA (mtDNA). Human neutrophil (PMN), chemotaxis, and respiratory burst were studied after PMN incubation with mtDNA. RESULTS: LPS caused Mo to release mtDAMPs. Electron microscopy showed microparticles containing MT. mtDNA was present both in microvesicles and exosomes as shown by PCR of the relevant size exclusion chromatography bands. In functional studies, PMN incubation with mtDNA suppressed chemotaxis in a dose-dependent manner, which was reversed by chloroquine, suggesting an endosomal, toll-like receptor-9-dependent mechanism. In contrast, PMN respiratory burst was unaffected by mtDNA. CONCLUSION: In addition to passive release of mtDAMPs by traumatic cellular disruption, inflammatory and infectious stimuli cause active mtDAMP release via microparticles. mtDNA thus released can have effects on PMN that may suppress antimicrobial function. mtDAMP-mediated "feed-forward" mechanisms may modulate immune responses and potentially be generalizable to other forms of inflammation. Where they cause immune dysfunction the effects can be mitigated if the pathways by which the mtDAMPs act are defined. In this case, the endosomal inhibitor chloroquine is benign and well tolerated. Thus, it may warrant study as a prophylactic antiinfective after injury or prior sepsis.

Direct Airway Instillation of Neutrophils Overcomes Chemotactic Deficits Induced by Injury.

BACKGROUND: Trauma induces neutrophil migration toward injury sites, both initiating wound healing and protecting against local bacterial infection. We have previously shown that mitochondrial formyl peptides (mtFPs) released by injured tissues act as chemoattractants by ligating neutrophil (PMN) formyl peptide receptor 1 (FPR1). But this process can also internalize multiple neutrophil chemoattractant receptors and thus might limit neutrophil migration to the lung in response to bacteria. Our objective was to better understand susceptibility to pneumonia after injury and thus find ways to reverse it. METHODS AND RESULTS: We modeled the alveolar chemotactic environment in pulmonary infections by incubating Staphylococcus aureus or Escherichia coli with peripheral blood mononuclear cells. Survey of the chemotactic mediators in the resultant conditioned media (CM) showed multiple potent chemoattractants. Pretreating PMN with mtFPs to mimic injury potently reduced net migration toward CM and this net effect was mostly reversed by an FPR1 antagonist. Using an established mouse model of injury-dependent lung infection, we then showed simple instillation of exogenous unstimulated human neutrophils into the airway resulted in bacterial clearance from the lung. CONCLUSION: Injury-derived mtFPs suppress global PMN localization into complex chemotactic environments like infected alveoli. Transplantation of naive exogenous human neutrophils into the airway circumvents that pathologic process and prevents development of post-traumatic pneumonia without injury noted to the recipients.