Marc J. Schultz

Local activation of coagulation and inhibition of fibrinolysis in the lung during ventilator associated pneumonia

Background: Fibrin deposition is a hallmark of pneumonia. To determine the kinetics of alterations in local coagulation and fibrinolysis in relation to ventilator associated pneumonia (VAP), a single centre prospective study of serial changes in pulmonary and systemic thrombin generation and fibrinolytic activity was conducted in patients at risk for VAP. Methods: Non-directed bronchial lavage (NBL) was performed on alternate days in patients expected to require mechanical ventilation for more than 5 days. A total of 28 patients were studied, nine of whom developed VAP. Results: In patients who developed VAP a significant increase in thrombin generation was observed in the airways, as reflected by a rise in the levels of thrombin-antithrombin complexes in NBL fluid accompanied by increases in soluble tissue factor and factor VIIa concentrations. The diagnosis of VAP was preceded by a decrease in fibrinolytic activity in NBL fluid. Indeed, before VAP was diagnosed clinically, plasminogen activator activity levels in NBL fluid gradually declined, which appeared to be caused by a sharp increase in NBL fluid levels of plasminogen activator inhibitor 1. Conclusion: VAP is characterised by a shift in the local haemostatic balance to the procoagulant side, which precedes the clinical diagnosis of VAP.

Disturbed alveolar fibrin turnover during pneumonia is restricted to the site of infection

Severe infection is associated with profound alterations in the systemic haemostatic balance, with activation of coagulation and suppressed fibrinolysis. Within the alveolar compartment, similar disturbances have been described during pulmonary inflammation. The current authors investigated whether local haemostasis was influenced during ventilator-associated pneumonia (VAP). In five patients with unilateral VAP, bronchoalveolar lavage fluid (BALF) was obtained from both the infected site (as identified on chest radiograph) and the contralateral noninfected lung (with no clinical or radiographic abnormalities). Markers for coagulation and fibrinolysis were compared between infected and noninfected lungs. A total of 10 healthy volunteers and 10 mechanically ventilated patients without pneumonia served as controls. Strong activation of coagulation (high levels of thrombin-antithrombin complexes, soluble tissue factor and factor VIIa) was detected in BALF from infected lungs, compared with that from noninfected lungs and controls. Furthermore, in infected lungs, fibrinolysis was depressed, with high levels of plasminogen activator inhibitor type 1. In conclusion, ventilator-associated pneumonia is characterised by a hypercoagulant state at the site of infection.

Mice Lacking the Multidrug Resistance Protein 1 Are Resistant to Streptococcus pneumoniae-Induced Pneumonia

Leukotrienes (LTs) are considered important for antibacterial defense in the lung. Multidrug resistance protein 1 (mrp1) is a transmembrane protein responsible for the cellular extrusion of LTC4. To determine the role of mrp1 in host defense against pneumonia, mrp1−/− and wild-type mice were intranasally inoculated with Streptococcus pneumoniae. mrp1−/− mice displayed a diminished outgrowth of pneumococci in lungs and a strongly reduced mortality. These findings were related to an effect of mrp1 on LT metabolism, because survival was similar in mrp1−/− and wild-type mice treated with the 5-lipoxygenase-activating protein inhibitor MK-886. Although LTC4 levels remained low in the bronchoalveolar lavage fluid of mrp1−/− mice, LTB4 concentrations were higher than in wild-type mice. These elevated LTB4 concentrations were important for the relative protection of mrp1−/− mice, because the LTB4 antagonist LTB4-dimethyl amide abolished their survival advantage. In vitro experiments suggested that the intracellullar accumulation of LTC4 in mrp1−/− mice results in product inhibition of LTC4-synthase, diminishing substrate competition between LTA4-hydrolase (which yields LTB4) and LTC4-synthase for the available LTA4. We conclude that mrp1−/− mice are resistant against pneumococcal pneumonia by a mechanism that involves increased release of LTB4. These results identify mrp1 as a novel target for adjunctive therapy in pneumonia.

The Role of Interferon-γ in Murine Pneumococcal Pneumonia

mice. In contrast, mice treated with anti–I FN-g did not demonstrate a consistently altered bacterial outgrowth, compared with mice treated with a control antibody. These data suggest that endogenous IFN-g, despite its protective role in defense against intracellular pathogens, does not serve a protective role during pneumococcal pneumonia. Streptococcus pneumoniae is a gram-positive bacterium responsible for .50% of the cases of community-acquired pneumonia. Pneumococcal pneumonia is the fifth leading cause of death worldwide, and, among patients with communityacquired pneumonia who require hospitalization, the mortality rate is as high as 25% [1, 2]. Against this background, and because of the growing resistance of the pneumococcus to antimicrobial therapy, it is important to gain insight into the pathogenesis of pneumococcal pneumonia [3]. Innate defense mechanisms play an important role in the elimination of bacteria from the alveolus. Phagocytic cells, as well as residential NK cells and T cells, participate in this response via the elaboration of chemotactic and regulatory cytokines [4]. Interferon (IFN)‐g is a potent proinflammatory cytokine, produced mainly by antigen-activated T and NK cells. IFN-g exerts several immune regulatory activities, including activation of phagocytes, stimulation of antigen presentation by increasing the expression of class I and II major histocompatibility complex molecules on antigen-presenting cells, orchestration of leukocyteendothelium interactions, and stimulation of the respiratory

Interleukin-18 Impairs the Pulmonary Host Response to Pseudomonas aeruginosa

ABSTRACT Interleukin-18 (IL-18) is a potent cytokine with many different proinflammatory activities. To study the role of IL-18 in the pathogenesis of Pseudomonas pneumonia, IL-18-deficient (IL-18−/−) and wild-type mice were intranasally inoculated with Pseudomonasaeruginosa. IL-18 deficiency was associated with reduced outgrowth of Pseudomonas in the lungs and diminished dissemination of the infection. In addition, pulmonary inflammation (histopathology) and levels of tumor necrosis factor alpha, IL-6, and macrophage inflammatory protein-2 in lungs and plasma were lower in IL-18−/− mice. Consistent with results obtained for IL-18−/− mice, treatment of wild-type mice with a neutralizing IL-18 binding protein-immunoglobulin G Fc fusion construct also attenuated outgrowth of Pseudomonas compared with that for mice treated with a control protein. These results demonstrate that the presence of endogenous IL-18 activity facilitates inflammatory responses in the lung during Pseudomonas pneumonia, concurrently impairing bacterial clearance.

Animal and human models for sepsis.

Several preclinical models for sepsis have been used in the last decades to successfully unravel the pathophysiologic processes during sepsis. Furthermore, these models for sepsis revealed promising immunomodulating agents for the treatment of sepsis. Nevertheless, several clinical trials evaluating the efficacy of these new anti-inflammatory agents in septic patients showed disappointing results. In this article the advantages and disadvantages of different models for sepsis are discussed. Most models for sepsis lack an infectious focus. Importantly, investigations studying the effects of several immunomodulating strategies have demonstrated strikingly opposite results when using models for sepsis lacking an infectious focus and when using models for sepsis with a more natural route of infection. These differences will be discussed in this article. In general, it is advised to use a combination of models to test a new therapeutic agent, before starting a clinical study evaluating this new therapy.

Protein C in pneumonia

Pneumonia is characterised by a disturbed alveolar fibrin turnover which is the net result of activation of coagulation and attenuation of fibrinolysis.1,2 We have recently shown, in patients developing ventilator associated pneumonia (VAP), that suppression of fibrinolysis precedes the clinical diagnosis while procoagulant effects mainly occur afterwards.2 We have extended these findings by investigating the relationship in time between changes in the anticoagulant protein C (PC) pathway and VAP. Levels of PC, activated PC (APC), and soluble thrombomodulin (sTM) were measured in non-directed bronchial lavage fluid collected every other day from critically ill patients during mechanical ventilation. APC was measured with an enzyme capture assay using monoclonal antibody HAPC 1555 and chromogenic substrate Spectrozyme PCa (American Diagnostica, Greenwich, CT, USA);3 PC activity was measured with an amidolytic assay using chromogenic substrate S2366 (Chromogenix, Milan, Italy); and sTM was measured with an ELISA (Diagnostica Stago, Asnieres-sur-Seine, France). Serial data …

Recombinant human tissue factor pathway inhibitor exerts anticoagulant, anti-inflammatory and antimicrobial effects in murine pneumococcal pneumonia

See also Maroney SA, Mast AE. Tissue factor pathway inhibitor and bacterial infection. This issue, pp 119–21.

Natural anticoagulants limit lipopolysaccharide-induced pulmonary coagulation but not inflammation

Pulmonary coagulopathy and hyperinflammation may contribute to an adverse outcome in sepsis. The present study determines the effects of natural inhibitors of coagulation on bronchoalveolar haemostasis and inflammation in a rat model of endotoxaemia. Male Sprague-Dawley rats were randomised to treatment with normal saline, recombinant human activated protein C (APC), plasma-derived antithrombin (AT), recombinant human tissue factor pathway inhibitor (TFPI), heparin or recombinant tissue plasminogen activator (tPA). Rats were intravenously injected with lipopolysaccharide (LPS), which induced a systemic inflammatory response and pulmonary inflammation. Blood and bronchoalveolar lavage were obtained at 4 and 16 h after LPS injection, and markers of coagulation and inflammation were measured. LPS injection caused an increase in the levels of thrombin–AT complexes, whereas plasminogen activator activity was attenuated, both systemically and within the bronchoalveolar compartment. Administration of APC, AT and TFPI significantly limited LPS-induced generation of thrombin–AT complexes in the lungs, and tPA stimulated pulmonary fibrinolytic activity. However, none of the agents had significant effects on the production of pulmonary cytokines, chemokines, neutrophil influx and myeloperoxidase activity. Natural inhibitors of coagulation prevent bronchoalveolar activation of coagulation, but do not induce major alterations of the pulmonary inflammatory response in rat endotoxaemia.

Bronchoalveolar hemostasis in lung injury and acute respiratory distress syndrome

Summary.  Enhanced intrapulmonary fibrin deposition as a result of abnormal broncho‐alveolar fibrin turnover is a hallmark of acute respiratory distress syndrome (ARDS), pneumonia and ventilator‐induced lung injury (VILI), and is important to the pathogenesis of these conditions. The mechanisms that contribute to alveolar coagulopathy are localized tissue factor‐mediated thrombin generation, impaired activity of natural coagulation inhibitors and depression of bronchoalveolar urokinase plasminogen activator‐mediated fibrinolysis, caused by the increase of plasminogen activator inhibitors. There is an intense and bidirectional interaction between coagulation and inflammatory pathways in the bronchoalveolar compartment. Systemic or local administration of anticoagulant agents (including activated protein C, antithrombin and heparin) and profibrinolytic agents (such as plasminogen activators) attenuate pulmonary coagulopathy. Several preclinical studies show additional anti‐inflammatory effects of these therapies in ARDS and pneumonia.