In severely injured and hypoperfused trauma patients, endogenous acute coagulopathy (EAC) is associated with an increased morbidity and mortality. Recent human data correlate this coagulopathy with activation of the protein C pathway. To examine the mechanistic role of protein C in the development of EAC, we used a mouse model of trauma and hemorrhagic shock, characterized by the combination of tissue injury and severe metabolic acidosis. Mice were subjected to one of four treatment groups: 1) C, control; 2) T, trauma (laparotomy); 3) H, hemorrhage (MAP, 35 mmHg × 60 min); 4) TH, trauma + hemorrhage. After 60 min, blood was drawn for analysis. Compared with C mice, the TH mice had a significantly elevated activated partial thromboplastin time (23.3 vs. 34.5 s) and significantly increased levels of activated protein C (aPC; 2.30 vs. 13.58 ng/mL). In contrast, T and H mice did not develop an elevated activated partial thromboplastin time or increased aPC. Selective inhibition of the anticoagulant property of aPC prevented the coagulopathy seen in response to trauma/hemorrhage (23.5 vs. 38.6 s [inhibitory vs. control monoclonal antibody]) with no impact on survival during the shock period. However, complete blockade of both the anticoagulant and cytoprotective functions of aPC caused 100% mortality within 45 min of shock, with histopathology evidence of pulmonary thrombosis and perivascular hemorrhage. These results indicate that our unique mouse model of T/H shock mimics our previous observations in trauma patients and demonstrates that EAC is mediated by the activation of the protein C pathway. In addition, the cytoprotective effect of protein C activation seems to be necessary for survival of the initial shock injury.
Trauma; shock; hemorrhage; hypoperfusion; coagulation; survival
Interleukin (IL)-1β has previously been shown to be among the most biologically active cytokines in the lungs of patients with acute lung injury (ALI). Furthermore, there is experimental evidence that lung vascular permeability increases after short-term exposure to IL-1 protein, although the exact mechanism is unknown. Therefore, the objective of this study was to determine the mechanisms of IL-1β–mediated increase in lung vascular permeability and pulmonary edema following transient overexpression of this cytokine in the lungs by adenoviral gene transfer. Lung vascular permeability increased with intrapulmonary IL-1β production with a maximal effect 7 days after instillation of the adenovirus. Furthermore, inhibition of the αvβ6 integrin and/or transforming growth factor-β attenuated the IL-1β–induced ALI. The results of in vitro studies indicated that IL-1β caused the activation of transforming growth factor-β via RhoA/αvβ6 integrin–dependent mechanisms and the inhibition of the αvβ6 integrin and/or transforming growth factor-β signaling completely blocked the IL-1β–mediated protein permeability across alveolar epithelial cell monolayers. In addition, IL-1β increased protein permeability across lung endothelial cell monolayers via RhoA- and αvβ5 integrin–dependent mechanisms. The final series of in vivo experiments demonstrated that pretreatment with blocking antibodies to both the αvβ5 and αvβ6 integrins had an additive protective effect against IL-1β–induced ALI. In summary, these results demonstrate a critical role for the αvβ5/β6 integrins in mediating the IL-1β–induced ALI and indicate that these integrins could be a potentially attractive therapeutic target in ALI.
lung; cytokines; inflammation; endothelial cells; epithelial cells; rodents
To determine whether early coagulopathy affects the mortality associated with severe civilian pediatric trauma, trauma patients < 18 years of age admitted to a pediatric intensive care unit from 2001 to 2010 were evaluated. Patients with burns, primary asphyxiation, preexisting bleeding diathesis, lack of coagulation studies or transferred from other hospitals > 24 hours after injury were excluded. Age, gender, race, mechanism of injury, initial systolic blood pressure (SBP), Glasgow Coma Scale (GCS) score, Injury Severity Score (ISS), prothrombin time (PT), partial thromboplastin time (PTT), platelet count and International Normalized Ratio (INR) were recorded. An arterial or venous blood gas was performed, if clinically indicated. Coagulopathy was defined as an INR > 1.2. The primary outcome was in-hospital mortality. Secondary outcomes were lengths of ICU and hospital stay. Eight hundred three patients were included in the study. Overall mortality was 13.4%. The incidence of age-adjusted hypotension was 5.4%. Early coagulopathy was observed in 37.9% of patients. High ISS and/or hypotension were associated with early coagulopathy and higher mortality. Early coagulopathy was associated with a modest increase in mortality in pediatric trauma patients without traumatic brain injury (TBI). In contrast, the combination of TBI and early coagulopathy was associated with a four-fold increase in mortality in this patient population. Early coagulopathy is an independent predictor of mortality in civilian pediatric patients with severe trauma. The increase in mortality was particularly significant in patients with TBI either isolated or combined with other injuries, suggesting that a rapid correction of this coagulopathy could substantially decrease the mortality after TBI in pediatric trauma patients.
Pediatric trauma; Coagulopathy; Traumatic brain injury; Tissue hypoperfusion; Mortality
Antibiotics-induced release of the pore-forming virulence factor pneumolysin (PLY) in patients with pneumococcal pneumonia results in its presence days after lungs are sterile and is a major factor responsible for the induction of permeability edema. Here we sought to identify major mechanisms mediating PLY-induced endothelial dysfunction. We evaluated PLY-induced endothelial hyperpermeability in human lung microvascular endothelial cells (HL-MVECs) and human lung pulmonary artery endothelial cells in vitro and in mice instilled intratracheally with PLY. PLY increases permeability in endothelial monolayers by reducing stable and dynamic microtubule content and modulating VE-cadherin expression. These events, dependent upon an increased calcium influx, are preceded by protein kinase C (PKC)-α activation, perturbation of the RhoA/Rac1 balance, and an increase in myosin light chain phosphorylation. At later time points, PLY treatment increases the expression and activity of arginase in HL-MVECs. Arginase inhibition abrogates and suppresses PLY-induced endothelial barrier dysfunction by restoring NO generation. Consequently, a specific PKC-α inhibitor and the TNF-derived tonoplast intrinsic protein peptide, which blunts PLY-induced PKC-α activation, are able to prevent activation of arginase in HL-MVECs and to reduce PLY-induced endothelial hyperpermeability in mice. Arginase I (AI)+/−/arginase II (AII)−/− C57BL/6 mice, displaying a significantly reduced arginase I expression in the lungs, are significantly less sensitive to PLY-induced capillary leak than their wild-type or AI+/+/AII−/− counterparts, indicating an important role for arginase I in PLY-induced endothelial hyperpermeability. These results identify PKC-α and arginase I as potential upstream and downstream therapeutic targets in PLY-induced pulmonary endothelial dysfunction.
PKC; arginase; pneumococcus; pneumolysin; TNF
High mobility group box 1 (HMGB1) protein is a danger-signaling molecule, known to activate an inflammatory response via TLR4 and RAGE. HMGB1 can be either actively secreted or passively released from damaged alveolar epithelial cells. Previous studies have shown that IL-1β, a critical mediator acute lung injury in humans that is activated by HMGB1, enhances alveolar epithelial repair, although the mechanisms are not fully understood. Herein, we tested the hypothesis that HMGB1 released by wounded alveolar epithelial cells would increase primary rat and human alveolar type II cell monolayer wound repair via an IL-1β-dependent activation of TGF-β1. HMGB1 induced in primary cultures of rat alveolar epithelial cells results in the release of IL-1β that caused the activation of TGF-β1 via a p38 MAPK-, RhoA- and αvβ6 integrin-dependent mechanism. Furthermore, active TGF-β1 accelerated the wound closure of primary rat epithelial cell monolayers via a PI3 kinase α-dependent mechanism. In conclusion, this study demonstrates that HMGB1 released by wounded epithelial cell monolayers, accelerates wound closure in the distal lung epithelium via the IL-1β-mediated αvβ6-dependent activation of TGF-β1, and thus could play an important role in the resolution of acute lung injury by promoting repair of the injured alveolar epithelium.
The receptor for advanced glycation endproducts (RAGE) recognizes a variety of ligands that play an important role in the posttraumatic inflammatory response. However, whether soluble RAGE (sRAGE) is released early after trauma-hemorrhage in humans and whether such a release is associated with the development of an inflammatory response and coagulopathy is not known and therefore constitutes the aim of the present study.
One hundred sixty eight patients were studied as part of a prospective cohort study of severe trauma patients admitted to a single Level 1 Trauma center. Blood was drawn within 10 minutes of arrival to the Emergency Department (ED) before the administration of any fluid resuscitation. sRAGE, TNF-a, IL-6, von Willebrand Factor (vWF), Angiopoietin-2 (Ang-2), Prothrombin time, (PT), prothrombin fragments 1+2 (PF1+2), soluble thrombomodulin (sTM), protein C (PC), plasminogen activator inhibitor-1 (PAI-1), and D-Dimers (fibrin degradation products) were measured using standard techniques. Base deficit was used as a measure of tissue hypoperfusion. Measurements were compared to outcome measures obtained from the electronic medical record and trauma registry.
Plasma levels of sRAGE were increased within 30 minutes after severe trauma in humans and correlated with the severity of injury, early posttraumatic coagulopathy and hyperfibrinolysis as well as with endothelial cell activation (angiopoietin-1 and complement). Furthermore, we found that there was a significant relationship between plasma levels of sRAGE and the development of acute renal failure. This relationship was not quite significant for patients who developed acute lung injury (p=.11), although patients with less than 26 ventilator-free days had significantly higher plasma levels of sRAGE than those with more than 26 ventilator-free days. Finally, there was no relationship between plasma levels of sRAGE and mortality rate in trauma patients.
The results of this study demonstrate that the release of sRAGE in the bloodstream of trauma patients requires severe injury and is associated with coagulation abnormalities and endothelial cell and complement activation.
sRAGE; Trauma; Coagulopathy; Protein C; Complement
Elevated plasma and bronchoalveolar lavage fluid plasminogen activator inhibitor 1 (PAI-1) levels are associated with adverse clinical outcome in patients with pneumonia caused by Pseudomonas aeruginosa. However, whether PAI-1 plays a pathogenic role in the breakdown of the alveolar–capillary barrier caused by P aeruginosa is unknown.
The role of PAI-1 in pulmonary host defence and survival during P aeruginosa pneumonia in mice was tested. The in vitro mechanisms by which P aeruginosa causes PAI-1 gene and protein expression in lung endothelial and epithelial cells were also examined.
Methods and results
PAI-1 null and wild-type mice that were pretreated with the PAI-1 inhibitor Tiplaxtinin had a significantly lower increase in lung vascular permeability than wild-type littermates after the airspace instillation of 1 × 107 colony-forming units (CFU) of P aeruginosa bacteria. Furthermore, P aeruginosa in vitro induced the expression of the PAI-1 gene and protein in a TLR4/p38/RhoA/NF-κB (Toll-like receptor 4/p38/RhoA/nuclear factor-κB) manner in lung endothelial and alveolar epithelial cells. However, in vivo disruption of PAI-1 signalling was associated with higher mortality at 24 h (p<0.03) and higher bacterial burden in the lungs secondary to decreased neutrophil migration into the distal airspace in response to P aeruginosa.
The results indicate that PAI-1 is a critical mediator that controls the development of the early lung inflammation that is required for the activation of the later innate immune response necessary for the eradication of P aeruginosa from the distal airspaces of the lung.
Rationale: Cigarette smoking has been demonstrated in laboratory studies to have effects on lung epithelial and endothelial function similar to those observed in acute lung injury (ALI). However, the association between active and passive cigarette smoke exposure and susceptibility to ALI has not been prospectively studied.
Objectives: We hypothesized that both active and passive cigarette smoke exposure would be associated with increased susceptibility to ALI after severe blunt trauma.
Methods: We measured levels of cotinine, a metabolite of nicotine and validated biomarker of tobacco use, in plasma samples obtained immediately on arrival at the emergency department from 144 adult subjects after severe blunt trauma. Patients were then followed for the development of ALI.
Measurements and Main Results: Increasing quartiles of plasma cotinine were associated with the development of ALI (odds ratio [OR] for developing ALI in highest cotinine quartile, 3.25; 95% confidence interval [CI], 1.22–8.68; P = 0.017 for trend across quartiles). Moderate to heavy passive smoke exposure was associated with nearly the same odds of developing ALI as active smoking (OR for moderate to heavy passive smoking compared with no exposure or low level exposure, 3.03; 95% CI, 1.15–8.04; OR for active smoking, 2.77; 95% CI, 1.28–5.99). This association persisted after adjusting for other predictors of ALI, including Injury Severity Score and alcohol abuse.
Conclusions: Both moderate to heavy passive smoking and active smoking are independently associated with the development of ALI after severe blunt trauma. This finding has important implications both for public health and for understanding the pathogenesis of ALI.
cigarette smoking; acute lung injury; acute respiratory distress syndrome; cotinine; secondhand smoke exposure
Activation of the stress protein response (SPR) inhibits iNOS-dependent release of NO from alveolar macrophages by blocking the activation of the STAT1 pathway in response to IFN-γ, a major cytokine present in the airspace of patients with acute lung injury. Inhibition of STAT1 phosphorylation after heat stress was associated with detergent insolubilization of the STAT1 protein and its proteasomal degradation which was reversed with the pretreatment of cells with glycerol, a chemical chaperone that reduces the extent of heat-induced protein denaturation. This early effect of SPR is the result of the disruption of the Hsp90 binding to the STAT1 protein. Our results also demonstrated that a late effect of SPR activation involves the regulation of iNOS function by inducible Hsp70 (Hsp70i). The STAT1 signaling pathway recovered function within 12 hours post-SPR activation and synthesis of the iNOS protein, however, NO production did not occur until 72 hours later. Inhibiting Hsp70i expression after heat stress recovered iNOS function whereas overexpressing Hsp70i in the absence of heat stress inhibited iNOS function. In summary, heat stress-induced transient inhibition of STAT1 following its dissociation from Hsp90, and the later transient inhibition of iNOS activity by inducible Hsp70, represent novel mechanisms by which the activation of the stress protein response inhibits the IFN-γ signaling pathway in alveolar macrophages. Since Hsp90 inhibitors have been shown to be safe in humans, these results also highlight a potential clinical application for this class of drugs in modulating NO signaling during the early phase of acute lung injury.
Lung; Chaperones; Macrophages; Heat Shock; Signal Transduction
Pseudomonas aeruginosa is an opportunistic pathogen that can cause severe pneumonia associated with airspace flooding with protein-rich edema in critically ill patients. The type III secretion system is a major virulence factor and contributes to dissemination of P. aeruginosa. However, it is still unknown which particular bacterial toxin and which cellular pathways are responsible for the increase in lung endothelial permeability induced by P. aeruginosa. Thus, the first objective of this study was to determine the mechanisms by which this species causes an increase in lung endothelial permeability. The results showed that ExoS and ExoT, two of the four known P. aeruginosa type III cytotoxins, were primarily responsible for bacterium-induced increases in protein permeability across the lung endothelium via an inhibition of Rac1 and an activation of the RhoA signaling pathway. In addition, inhibition of the αvβ5 integrin, a central regulator of lung vascular permeability, prevented these P. aeruginosa–mediated increases in albumin flux due to endothelial permeability. Finally, prior activation of the stress protein response or adenoviral gene transfer of the inducible heat shock protein Hsp72 also inhibited the damaging effects of P. aeruginosa on the barrier function of lung endothelium. Taken together, these results demonstrate the critical role of the RhoA/αvβ5 integrin pathway in mediating P. aeruginosa–induced lung vascular permeability. In addition, activation of the stress protein response with pharmacologic inhibitors of Hsp90 may protect lungs against P. aeruginosa–induced permeability changes.
lung; Pseudomonas aeruginosa; endothelial cells; integrin; heat shock response
High mobility group box nuclear protein 1 (HMGB1) is a DNA nuclear binding protein that has recently been shown to be an early trigger of sterile inflammation in animal models of trauma-hemorrhage via the activation of the Toll-like-receptor 4 (TLR4) and the receptor for the advanced glycation endproducts (RAGE). However, whether HMGB1 is released early after trauma hemorrhage in humans and is associated with the development of an inflammatory response and coagulopathy is not known and therefore constitutes the aim of the present study.
One hundred sixty eight patients were studied as part of a prospective cohort study of severe trauma patients admitted to a single Level 1 Trauma center. Blood was drawn within 10 minutes of arrival to the emergency room before the administration of any fluid resuscitation. HMGB1, tumor necrosis factor (TNF)-α, interleukin (IL)-6, von Willebrand Factor (vWF), angiopoietin-2 (Ang-2), Prothrombin time (PT), prothrombin fragments 1+2 (PF1+2), soluble thrombomodulin (sTM), protein C (PC), plasminogen activator inhibitor-1 (PAI-1), tissue plasminogen activator (tPA) and D-Dimers were measured using standard techniques. Base deficit was used as a measure of tissue hypoperfusion. Measurements were compared to outcome measures obtained from the electronic medical record and trauma registry.
Plasma levels of HMGB1 were increased within 30 minutes after severe trauma in humans and correlated with the severity of injury, tissue hypoperfusion, early posttraumatic coagulopathy and hyperfibrinolysis as well with a systemic inflammatory response and activation of complement. Non-survivors had significantly higher plasma levels of HMGB1 than survivors. Finally, patients who later developed organ injury, (acute lung injury and acute renal failure) had also significantly higher plasma levels of HMGB1 early after trauma.
The results of this study demonstrate for the first time that HMGB1 is released into the bloodstream early after severe trauma in humans. The release of HMGB1 requires severe injury and tissue hypoperfusion, and is associated with posttraumatic coagulation abnormalities, activation of complement and severe systemic inflammatory response.
Previous studies have shown that heat shock protein 72 (Hsp72) is found in the extracellular space (eHsp72) and that eHsp72 has potent immunomodulatory effects. However, whether eHsp72 is present in the distal air spaces and whether eHsp72 could modulate removal of alveolar edema is unknown. The first objective was to determine whether Hsp72 is released within air spaces and whether Hsp72 levels in pulmonary edema fluid would correlate with the capacity of the alveolar epithelium to remove alveolar edema fluid in patients with ALI/ARDS. Patients with hydrostatic edema served as controls. The second objective was to determine whether activation of the stress protein response (SPR) caused the release of Hsp72 into the extracellular space in vivo and in vitro and to determine whether SPR activation and/or eHsp72 itself would prevent the IL-1β-mediated inhibition of the vectorial fluid transport across alveolar type II cells. We found that eHsp72 was present in plasma and pulmonary edema fluid of ALI patients and that eHsp72 was significantly higher in pulmonary edema fluid from patients with preserved alveolar epithelial fluid clearance. Furthermore, SPR activation in vivo in mice and in vitro in lung endothelial, epithelial, and macrophage cells caused intracellular expression and extracellular release of Hsp72. Finally, SPR activation, but not eHsp72 itself, prevented the decrease in alveolar epithelial ion transport induced by exposure to IL-1β. Thus SPR may protect the alveolar epithelium against oxidative stress associated with experimental ALI, and eHsp72 may serve as a marker of SPR activation in the distal air spaces of patients with ALI.
pulmonary edema; alveolar fluid clearance; heat shock response; respiratory distress syndrome; heat shock protein 70
Increased lung vascular permeability is an important contributor to respiratory failure in acute lung injury (ALI). We found that a function-blocking antibody against the integrin αvβ5 prevented development of lung vascular permeability in two different models of ALI: ischemia-reperfusion in rats (mediated by vascular endothelial growth factor [VEGF]) and ventilation-induced lung injury (VILI) in mice (mediated, at least in part, by transforming growth factor-β [TGF-β]). Knockout mice homozygous for a null mutation of the integrin β5 subunit were also protected from lung vascular permeability in VILI. In pulmonary endothelial cells, both the genetic absence and blocking of αvβ5 prevented increases in monolayer permeability induced by VEGF, TGF-β, and thrombin. Furthermore, actin stress fiber formation induced by each of these agonists was attenuated by blocking αvβ5, suggesting that αvβ5 regulates induced pulmonary endothelial permeability by facilitating interactions with the actin cytoskeleton. These results identify integrin αvβ5 as a central regulator of increased pulmonary vascular permeability and a potentially attractive therapeutic target in ALI.
integrin αvβ5; lung vascular permeability; pulmonary endothelial barrier function
We have shown that injury to alveolar epithelial type I cells may account, in part, for damage to the air-blood barrier of the lung in a rat model of Staphylococcus aureus pneumonia. We have also shown that alpha-toxin is an important cause of damage to the air-blood barrier; however, our data suggest that the toxin is not acting directly on alveolar type I cells.