Local abnormalities of coagulation and fibrinolysis and alveolar fibrin deposition in sheep with oleic acid-induced lung injury

The Contribution of the Urokinase Plasminogen Activator and the Urokinase Receptor to Pleural and Parenchymal Lung Injury and Repair: A Narrative Review

Pleural and parenchymal lung injury have long been characterized by acute inflammation and pathologic tissue reorganization, when severe. Although transitional matrix deposition is a normal part of the injury response, unresolved fibrin deposition can lead to pleural loculation and scarification of affected areas. Within this review, we present a brief discussion of the fibrinolytic pathway, its components, and their contribution to injury progression. We review how local derangements of fibrinolysis, resulting from increased coagulation and reduced plasminogen activator activity, promote extravascular fibrin deposition. Further, we describe how pleural mesothelial cells contribute to lung scarring via the acquisition of a profibrotic phenotype. We also discuss soluble uPAR, a recently identified biomarker of pleural injury, and its diagnostic value in the grading of pleural effusions. Finally, we provide an in-depth discussion on the clinical importance of single-chain urokinase plasminogen activator (uPA) for the treatment of loculated pleural collections.

Tissue factor pathway inhibitor prevents airway obstruction, respiratory failure and death due to sulfur mustard analog inhalation

Sulfur mustard (SM) inhalation causes airway injury, with enhanced vascular permeability, coagulation, and airway obstruction. The objective of this study was to determine whether recombinant tissue factor pathway inhibitor (TFPI) could inhibit this pathogenic sequence.

METHODS

Rats were exposed to the SM analog 2-chloroethyl ethyl sulfide (CEES) via nose-only aerosol inhalation. One hour later, TFPI (1.5mg/kg) in vehicle, or vehicle alone, was instilled into the trachea. Arterial O2 saturation was monitored using pulse oximetry. Twelve hours after exposure, animals were euthanized and bronchoalveolar lavage fluid (BALF) and plasma were analyzed for prothrombin, thrombin-antithrombin complex (TAT), active plasminogen activator inhibitor-1 (PAI-1) levels, and fluid fibrinolytic capacity. Lung steady-state PAI-1 mRNA was measured by RT-PCR analysis. Airway-capillary leak was estimated by BALF protein and IgM, and by pleural fluid measurement. In additional animals, airway cast formation was assessed by microdissection and immunohistochemical detection of airway fibrin.

RESULTS

Airway obstruction in the form of fibrin-containing casts was evident in central conducting airways of rats receiving CEES. TFPI decreased cast formation, and limited severe hypoxemia. Findings of reduced prothrombin consumption, and lower TAT complexes in BALF, demonstrated that TFPI acted to limit thrombin activation in airways. TFPI, however, did not appreciably affect CEES-induced airway protein leak, PAI-1 mRNA induction, or inhibition of the fibrinolytic activity present in airway surface liquid.

CONCLUSIONS

Intratracheal administration of TFPI limits airway obstruction, improves gas exchange, and prevents mortality in rats with sulfur mustard-analog-induced acute lung injury.

Airway tissue factor-dependent coagulation activity in response to sulfur mustard analog 2-chloroethyl ethyl sulfide

Acute lung injury is a principal cause of morbidity and mortality in response to mustard gas (SM) inhalation. Obstructive, fibrin-containing airway casts have recently been reported in a rat inhalation model employing the SM analog 2-chloroethyl ethyl sulfide (CEES). The present study was designed to identify the mechanism(s) causing activation of the coagulation cascade after CEES-induced airway injury. Here we report that CEES inhalation elevates tissue factor (TF) activity and numbers of detached epithelial cells present in lavage fluid (BALF) from rats after exposure (18 h). In vitro studies using 16HBE cells, or with rat BALF, indicated that detached epithelial cells could convert factor X (FX) to the active form FXa when incubated with factor VII and could elicit rapid clotting of plasma. In addition, immunocytochemical analysis demonstrated elevated cell surface (TF) expression on CEES-exposed 16HBE cells as a function of time. However, total cell TF expression did not increase. Since membrane surfaces bearing TF are important determinants of clot initiation, anticoagulants directed against these entities were tested for ability to limit plasma clotting or FX activation capacity of BALF or culture media. Addition of tifacogin, a TF pathway inhibitor, effectively blocked either activity, demonstrating that the procoagulant actions of CEES were TF pathway dependent. Lactadherin, a protein capable of competing with clotting factors for phospholipid-binding sites, was partially effective in limiting these procoagulant actions. These findings indicate that TF pathway inhibition could be an effective strategy to prevent airway obstruction after SM or CEES inhalation.

Induction of tissue factor by urokinase in lung epithelial cells and in the lungs

RATIONALE

Urokinase-type plasminogen activator (uPA) regulates extracellular proteolysis in lung injury and repair. Although alveolar expression of uPA increases, procoagulant activity predominates.

OBJECTIVES

This study was designed to investigate whether uPA alters the expression of tissue factor (TF), the major initiator of the coagulation cascade, in lung epithelial cells (ECs).

METHODS

Bronchial, primary airway ECs and C57B6 wild-type, uPA-deficient (uPA(-/-)) mice were exposed to phosphate-buffered saline, uPA, or LPS. Immunohistochemistry, protein, cellular, and molecular techniques were used to assess TF expression and activity.

MEASUREMENTS AND MAIN RESULTS

uPA enhanced TF mRNA and protein expression, and TF-dependent coagulation in lung ECs. uPA-induced expression of TF involves both increased synthesis and enhanced stabilization of TF mRNA. uPA catalytic activity had little effect on induction of TF. By contrast, deletion of the uPA receptor binding growth factor domain from uPA markedly attenuated the induction of TF, suggesting that uPA receptor binding is sufficient for TF induction. Lung tissues of uPA-deficient mice expressed less TF protein and mRNA compared with wild-type mice. In addition, intratracheal instillation of mouse uPA increased TF mRNA and protein expression and accelerated coagulation in lung tissues. uPA(-/-) mice exposed to LPS failed to induce TF.

CONCLUSIONS

uPA increased TF expression and TF-dependent coagulation in the lungs of mice. We hypothesize that uPA-mediated induction of TF occurs in lung ECs to promote increased fibrin deposition in the airways during acute lung injury.

[Pathophysiology of acute lung injury in severe burn and smoke inhalation injury]

This review article describes the pathophysiological aspects of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS), induced by combined burn and smoke inhalation and examines various therapeutic approaches. The injury results in a fall in arterial oxygenation as a result of airway obstruction, increased pulmonary transvascular fluid flux and loss of hypoxic pulmonary vasoconstriction. The changes in cardiopulmonary function are mediated by reactive oxygen and nitrogen species. Nitric oxide (NO) is generated by both inducible and constitutive isoforms of nitric oxide synthase (NOS). Recently, neuronal NOS emerged as a major component within the pathogenesis of ARDS. NO rapidly combines with the oxygen radical superoxide to form reactive and highly toxic nitrogen species such as peroxynitrite. The control of NO formation involves poly(ADP-ribose) polymerase and its ability to up-regulate the activity of nuclear transcription factors through ribosylation. In addition, present data support a major role of the bronchial circulation in the injury, as blockage of bronchial blood flow will also minimize the pulmonary injury. Current data suggest that cytotoxins and activated cells are formed in the airway and carried to the parenchyma.

Effect of activated protein C on pulmonary blood flow and cytokine production in experimental acute lung injury

OBJECTIVE

In acute lung injury (ALI) activated protein C (APC) may reopen occluded lung vessels and minimize lung inflammation. We aimed at assessing the effect of APC on regional lung perfusion, aerated lung volume, cytokine production and oxygenation in experimental ALI.

DESIGN AND SETTING

Prospective, controlled study in an imaging facility.

PARTICIPANTS

Pigs tracheotomized and mechanically ventilated.

INTERVENTION

Pigs were randomly given intravenously APC (n = 8) or saline (n = 8). Thirty minutes later, ALI was induced by injecting oleic acid.

MEASUREMENTS AND RESULTS

Lung perfusion and aerated lung volume measured with positron emission tomography, plasma cytokines and arterial blood gas were determined just before ALI and 110 and 290 min thereafter. Lung cytokines were measured at the end of the experiment. PaO2 under F I O2 1 was significantly lower in the APC group before lung injury (473+/-129 vs. 578+/-54 mmHg) and 110 min (342+/-138 vs. 446+/-103 mmHg) and 290 min (303+/-171 vs. 547+/-54 mmHg) thereafter (p < 0.05). Lung perfusion nonsignificantly tended to redistribute towards dorsal lung regions with APC. Total aerated lung volume was not different between APC and control before ALI (10.0+/-1.5 vs. 11.0+/-2.5 ml/kg) (p > 0.05) or thereafter. Plasma IL-6 and IL-8 at 110 min were greater with APC (p < 0.05).

CONCLUSIONS

In contrast to studies using other models, pretreatment with APC was associated with worsening oxygenation in the present investigation. This might be due to ventilation-perfusion mismatch, with more perfusion to dependent nonaerated areas.

Recombinant human activated protein C improves pulmonary function in ovine acute lung injury resulting from smoke inhalation and sepsis

OBJECTIVE

To investigate the effects of recombinant human activated protein C (rhAPC) on pulmonary function in acute lung injury (ALI) resulting from smoke inhalation in association with a bacterial challenge.

DESIGN

Prospective, randomized, controlled, experimental animal study with repeated measurements.

SETTING

Investigational intensive care unit at a university hospital.

SUBJECTS

Eighteen sheep (37.2 +/- 1.0 kg) were operatively prepared and randomly allocated to either the sham, control, or rhAPC group (n = 6 each). After a tracheotomy had been performed, ALI was produced in the control and rhAPC group by insufflation of 4 sets of 12 breaths of cotton smoke. Then, a 30 mL suspension of live Pseudomonas aeruginosa bacteria (containing 2-5 x 10(11) colony forming units) was instilled into the lungs according to an established protocol. The sham group received only the vehicle, i.e., 4 sets of 12 breaths of room air and instillation of 30 mL normal saline. The sheep were studied in the awake state for 24 hrs and were ventilated with 100% oxygen. RhAPC (24 mug/kg/hr) was intravenously administered. The infusion was initiated 1 hr post-injury and lasted until the end of the experiment. The animals were resuscitated with Ringer's lactate solution to maintain constant pulmonary artery occlusion pressure.

MEASUREMENTS AND MAIN RESULTS

In comparison with nontreatment in controls, the infusion of rhAPC significantly attenuated the fall in Pao2/Fio2 ratio (control group values were 521 +/- 22 at baseline [BL], 72 +/- 5 at 12 hrs, and 74 +/- 7 at 24 hrs, vs. rhAPC group values of 541 +/- 12 at BL, 151 +/- 29 at 12 hours [p < .05 vs. control], and 118 +/- 20 at 24 hrs), and significantly reduced the increase in pulmonary microvascular shunt fraction (Qs/Qt; control group at BL, 0.14 +/- 0.02, and at 24 hrs, 0.65 +/- 0.08; rhAPC group at BL, 0.24 +/- 0.04, and at 24 hrs, 0.45 +/- 0.02 [p < .05 vs. control]) and the increase in peak airway pressure (mbar; control group at BL, 20 +/- 1, and at 24 hrs, 36 +/- 4; rhAPC group at BL, 21 +/- 1, and at 24 hrs, 28 +/- 2 [p < .05 vs. control]). In addition, rhAPC limited the increase in lung 3-nitrotyrosine (after 24 hrs [%]: sham, 7 +/- 2; control, 17 +/- 1; rhAPC, 12 +/- 1 [p < .05 vs. control]), a reliable indicator of tissue injury. However, rhAPC failed to prevent lung edema formation. RhAPC-treated sheep showed no difference in activated clotting time or platelet count but exhibited less fibrin degradation products (1/6 animals) than did controls (4/6 animals).

CONCLUSIONS

Recombinant human activated protein C attenuated ALI after smoke inhalation and bacterial challenge in sheep, without bleeding complications.

Adult respiratory distress syndrome: do selective anticoagulants help?

The adult respiratory distress syndrome (ARDS) is a form of acute lung injury that is characterized by florid extravascular fibrin deposition. Thrombosis in the pulmonary vasculature and disseminated intravascular coagulation have also been observed in association with ARDS. Fibrin deposition does not occur in the normal lung but is virtually universal in acute lung injury induced by disparate insults. A large body of basic and preclinical evidence further implicates abnormalities of pathways of fibrin turnover in the pathogenesis of acute inflammation and fibrotic repair. Coagulation is locally upregulated in the injured lung, while fibrinolytic activity is depressed. These abnormalities occur concurrently and favor alveolar fibrin deposition. The systemic derangements of fibrin turnover in sepsis are similar to those that occur in the injured lung. Recent clinical trials demonstrate that interventions using selective anticoagulation can provide a mortality advantage and that selective anticoagulants differ in their ability to provide clinical benefit. Preclinical trials in primates with sepsis-induced ARDS now indicate that anticoagulant interventions that block the extrinsic coagulation pathway can protect against the development of pulmonary fibrin deposition as well as lung dysfunction and acute inflammation. These observations provide proof of principle that key steps in the coagulation cascade are appropriate therapeutic targets to prevent the development of acute lung injury in ARDS. Ongoing studies and prior publications also support the hypothesis that reversal of the fibrinolytic defect in ARDS could protect against the development of acute lung injury. In all, these studies suggest that fibrin deposition in the injured lung as well as abnormalities of coagulation and fibrinolysis are integral to the pathogenesis of ARDS. The ability of selective anticoagulants to effectively and safely alter clinical outcome in ARDS remains to be determined.

Early elevation of plasma soluble intercellular adhesion molecule-1 in pediatric acute lung injury identifies patients at increased risk of death and prolonged mechanical ventilation

OBJECTIVE

To determine whether soluble intercellular adhesion molecule (sICAM)-1, a biological marker of alveolar epithelial and lung endothelial injury and alveolar macrophage activation, is elevated in the plasma of pediatric patients with acute lung injury and to examine whether elevated plasma sICAM-1 levels correlate with two clinically relevant outcomes, mortality and the duration of mechanical ventilation.

DESIGN

Prospective cohort study.

SETTING

Pediatric intensive care units at an urban children's hospital and a tertiary university medical center.

PATIENTS

Eighty-three pediatric patients with acute lung injury and five intubated controls.

INTERVENTIONS

Plasma sICAM-1 levels were measured on days 1 and 2 of acute lung injury in pediatric patients and on day 1 of mechanical ventilation in control patients.

MEASUREMENTS AND MAIN RESULTS

Plasma sICAM-1 levels were significantly higher in patients with acute lung injury compared with controls (966 +/- 830 vs. 251 +/- 168 ng/mL, p <.05). Levels of sICAM-1 were also significantly higher on days 1 and 2 of acute lung injury in nonsurvivors and in patients requiring prolonged duration of mechanical ventilation. Also, plasma sICAM-1 levels >1000 ng/mL had a high specificity for identifying nonsurvivors of acute lung injury.

CONCLUSIONS

Early elevation of sICAM-1 in the plasma of pediatric patients with acute lung injury is associated with increased risk of death or prolonged duration of mechanical ventilation.

Urokinase-type plasminogen activator potentiates lipopolysaccharide-induced neutrophil activation

Urokinase plasminogen activator (uPA) is a serine protease that catalyzes the conversion of plasminogen to plasmin. Although increased circulating levels of uPA are present in endotoxemia and sepsis, conditions in which activated neutrophils contribute to the development of acute organ dysfunction, the ability of uPA to participate directly in LPS-induced neutrophil activation has not been examined. In the present experiments, we show that uPA can enhance activation of neutrophils exposed to submaximal stimulatory doses of LPS. In particular, uPA increased LPS-induced activation of intracellular signaling pathways, including Akt and c-Jun N-terminal kinase, nuclear translocation of the transcriptional regulatory factor NF-kappa B, and expression of proinflammatory cytokines, including IL-1 beta, macrophage-inflammatory protein-2, and TNF-alpha. There was no effect of uPA on LPS-induced activation of p38 mitogen-activated protein kinase in neutrophils. Transgenic mice unable to produce uPA (uPA(-/-)) were protected from endotoxemia-induced lung injury, as determined by development of lung edema, pulmonary neutrophil accumulation, lung IL-1 beta, macrophage-inflammatory protein-2, and TNF-alpha cytokine levels. These results demonstrate that uPA can potentiate LPS-induced neutrophil responses and also suggest that such effects are sufficiently important in vivo to play a major contributory role in neutrophil-mediated inflammatory responses, such as the development of acute lung injury.

Coagulation, fibrinolysis, and fibrin deposition in acute lung injury

OBJECTIVES

To review: a) the role of extravascular fibrin deposition in the pathogenesis of acute lung injury; b) the abnormalities in the coagulation and fibrinolysis pathways that promote fibrin deposition in the acutely injured lung; and c) the pathways that contribute to the regulation of the fibrinolytic system via the lung epithelium, including newly recognized posttranscriptional and urokinase-dependent pathways. Another objective was to determine how novel anticoagulant or fibrinolytic strategies may be used to protect against acute inflammation or accelerated fibrosis in acute lung injury.

DATA SOURCES

Published medical literature.

DATA SUMMARY

Alveolar fibrin deposition is characteristic of diverse forms of acute lung injury. Intravascular thrombosis or disseminated intravascular coagulation can also occur in the acutely injured lung. Extravascular fibrin deposition promotes lung dysfunction and the acute inflammatory response. In addition, transitional fibrin in the alveolar compartment undergoes remodeling leading to accelerated pulmonary fibrosis similar to the events associated with wound healing, or desmoplasia associated with solid neoplasms. In acute lung injury, alveolar fibrin deposition is potentiated by consistent changes in endogenous coagulation and fibrinolytic pathways. Procoagulant activity is increased in conjunction with depression of fibrinolytic activity in the alveolar compartment. Initiation of the procoagulant response occurs as a result of local overexpression of tissue factor associated with factor VII. Depression of fibrinolytic activity occurs as a result of inhibition of urokinase plasminogen activator (uPA) by plasminogen activators, or series inhibition of plasmin by antiplasmins. Locally increased amplification of plasminogen activator inhibitor-1 (PAI-1) is largely responsible for this fibrinolytic defect. Newly described pathways by which lung epithelial cells regulate expression of uPA, its receptor uPAR, and PAI-1 at the posttranscriptional level have been identified. These pathways operate by cis-trans interactions between mRNA binding proteins; regulatory sequences within these mRNAs control their stability. The regulatory mechanisms seem to involve multiple protein-mRNA interactions, and the phosphorylation state of the proteins appears to determine whether complex formation of, or dissociation from, the regulatory sequences occurs. uPA is capable of inducing its own expression in lung epithelial cells as well as that of uPAR and PAI-1-the effects involve posttranscriptional regulatory components. These and related observations have led to the implementation of anticoagulant or fibrinolytic strategies to protect the lung against acute lung injury. The success of new fibrinolytic strategies to block pleural loculation suggests that a similar approach might be used to prevent accelerated pulmonary fibrosis, which can occur in association with many forms of acute lung injury.

CONCLUSIONS

Disordered coagulation and fibrinolysis promote extravascular fibrin deposition in acute lung injury. It is this deposition that characterizes acute lung injury and repair. Expression of uPA, uPAR, and PAI-1 by the lung epithelium, as well as the ability of uPA to induce other components of the fibrinolytic system, involves posttranscriptional regulation. These pathways may contribute to disordered fibrin turnover in the injured lung. The success of anticoagulant or fibrinolytic strategies designed to reverse the abnormalities of local fibrin turnover in acute lung injury supports the inference that abnormalities of coagulation, fibrinolysis, and fibrin deposition have a critical role in the pathogenesis of acute lung injury.

Endothelium and disordered fibrin turnover in the injured lung: newly recognized pathways

OBJECTIVES

To review derangements of pathways of fibrin turnover that promote pathologic fibrin deposition in the acute respiratory distress syndrome and to review the contribution of the endothelium and parenchymal lung cells to the derangements. In addition, to review how these pathways can be exploited in specific clinical circumstances, including sepsis and acute lung injury. Lastly, to review newly recognized posttranscriptional and urokinase-dependent pathways by which the fibrinolytic system is regulated in the lung.

DATA SOURCES

Medical literature published in English from 1966 to present.

DATA SUMMARY

Local abnormalities of fibrin turnover in the injured lung recapitulate the systemic changes observed in sepsis. In both circumstances, the procoagulant response is increased, whereas fibrinolytic activity is concurrently depressed. The increased procoagulant activity is related to tissue factor associated with factor VII/VIIa. Fibrinolytic activity in the vasculature is mainly attributable to tissue plasminogen activator, whereas extravascular fibrinolytic activity in the lung is mainly attributable to urokinase plasminogen activator (uPA). Depressed fibrinolytic activity is in large part attributable to plasminogen activator inhibitor-1. In sepsis, activated protein C is also deficient, potentiating the inflammatory response, coagulopathy, and depressed fibrinolysis. Recombinant human activated protein C (drotrecogin alfa [activated]) was successful as an intervention for sepsis in a recent phase 3 clinical trial (PROWESS). Recently, novel posttranscriptional pathways that regulate expression of uPA, its receptor (uPAR), and plasminogen activator inhibitor-1 have been identified. The responsible mechanisms involve cis-trans interactions between newly recognized messenger RNA (mRNA) binding sequences and mRNA binding proteins. A 51 nucleotide mRNA binding sequence within the coding region of uPAR mRNA interacts with a novel 50-kDa mRNA binding protein to destabilize the message. Sequences within the 3' untranslated region of uPA or plasminogen activator inhibitor-1 mRNA interact with 30- and 60-kDa proteins, respectively, to regulate message stability. All of these pathways operate in lung epithelial cells, and endothelial cells regulate uPA expression through a similar pathway. In addition, uPA itself is capable of inducing expression of other components of the fibrinolytic system, including uPAR. This observation defines another feedback loop that could amplify local fibrinolysis and other uPA- or uPAR-mediated cellular responses, including cellular proteolysis, proliferation, and directed cellular migration.

CONCLUSIONS

Novel posttranscriptional pathways regulate expression of uPA, uPAR, and plasminogen activator inhibitor-1. uPA itself is capable of inducing other components of the fibrinolytic system. Some or all of these newly recognized pathways are operative in endothelial and parenchymal lung cells and may influence disordered fibrin turnover in the injured lung.

Tranexamic acid attenuates oleic-acid-induced pulmonary extravasation

OBJECTIVE

Activation of fibrinolysis is implicated in the development of vascular injury in certain lung injuries. It has yet to be reported that activation of plasmin is involved in extravasation caused by oleic acid (OA). We examined whether or not plasmin is involved in pulmonary extravasation by OA.

DESIGN

Prospective trial.

SETTING

University laboratory.

SUBJECTS

A total of 78 guinea pigs (498.9 +/- 10.6 g).

INTERVENTIONS

Evans blue (EB) was administered to anesthetized guinea pigs. Subsequently four protocols were followed: (1) After 1 min, 60 micro l/kg of OA was injected. Perfusion was performed 30, 60 or 90 min after OA injection to wash out intravascular EB. (2) After 1 min, 15, 30 or 60 micro l/kg of OA was injected. (3) Tranexamic acid (TA) (2 g/kg) or saline was administered 30 min before OA (15 micro l/kg) injection. (4) Diphenhydramine hydrochloride (2.9 mg/kg) or saline was administered 7 min before OA (15 micro l/kg) injection.

MEASUREMENT AND RESULTS

Except in protocol 1, the chest cavity was opened 90 min after OA injection. Perfusion was then performed. Airway was separated into four parts from trachea to distal bronchus. EB was extracted from the tissues and measured. OA caused an extravasation throughout airways in a time- and dose-dependent manner. Extravasation was more conspicuous in peripheral tissues. TA significantly attenuated extravasation, while diphenhydramine hydrochloride did not.

CONCLUSIONS

It is suggested that plasmin, but not histamine, is involved in extravasation by OA. Inhibition of plasmin can be an effective strategy for treatment of this kind of lung injury.

Changes in procoagulant and fibrinolytic gene expression during bleomycin-induced lung injury in the mouse

Bleomycin-induced lung injury is an established murine model of human pulmonary fibrosis. Although procoagulant molecules (e.g., tissue factor [TF]) and fibrinolytic components (e.g., urokinase [u-PA] and type 1 plasminogen activator inhibitor [PAI-1]) have been detected in alveolar fluid from injured lungs, the origin of these molecules remains unknown. We therefore examined the expression of procoagulant and fibrinolytic components in relation to the distribution of parenchymal fibrin in bleomycin-injured lungs. Extravascular fibrin localized to the alveolar and extracellular matrix in injured lung tissue. Injured lung tissue extracts contained elevated levels of PAI-1 activity and decreased levels of u-PA activity. Whole lung PAI-1 and TF mRNAs were dramatically induced by lung injury. In situ hybridization of injured lungs revealed that PAI-1, u-PA, and TF mRNAs were induced within the fibrin-rich fibroproliferative lesions, primarily in fibroblast-like and macrophagelike cells, respectively, while TF mRNA was also induced in perilesional alveolar cells. Taken together, these observations suggest that the induction of PAI-1 and TF gene expression plays and important role in the formation and persistence of extracellular fibrin in bleomycin injured murine lungs.

Lung surfactant phospholipids associate with polymerizing fibrin: loss of surface activity

Intraalveolar fibrin formation is a hallmark of many acute and chronic lung inflammatory processes. We investigated the influence of fibrin polymerization on biochemical and biophysical properties of a calf lung surfactant extract (CLSE) used for therapy of neonatal distress syndrome. Thrombin-induced coagulation of human fibrinogen (range, 0.04 to 4 mg/ml) in the presence of CLSE (2 mg/ml phospholipids) resulted in progressive loss of surface tension-lowering properties and adsorption facilities of this surfactant preparation; the CLSE-inhibitory capacity of desAABB-fibrin surpassed that of fibrinogen by more than two orders of magnitude. In parallel with the loss of surface activity, association of the predominant surfactant phospholipid dipalmitoylphosphatidylcholine (DPPC) (14C-labeled, admixed to 2 mg/ml CLSE) with polymerizing desAABB-fibrin occurred. A volume of 0.3 mg/ml insoluble fibrin effected a approximately 50% loss, and 0.6 mg/ml a > 90% loss, of DPPC from the aqueous phase. Dioleoylphosphatidylcholine, dipalmitoylphosphatidic acid, stearic acid, palmitic acid, and arachidonic acid, admixed to CLSE as labeled compounds, as well as total CLSE phospholipids were retained in polymerizing desAABB-fibrin with dose-effect curves superimposable to that of DPPC; no fibrin association was noted for 14C-glycerol-3-phosphate. Polymerizing desAA-fibrin, generated by incubation of CLSE-fibrinogen mixtures with arvin, captured DPPC and resulted in loss of surface properties at even lower concentrations, compared with desAABB-fibrin. In contrast, CLSE incubation with preformed desAABB- and desAA-fibrin polymers did not cause substantial phospholipid coupling with the clot material or loss of surface properties. Microtiter plate-immobilized fibrinogen and desAABB- and desAA-fibrinomonomers did not bind CLSE phospholipids enriched with 14C-DPPC.(ABSTRACT TRUNCATED AT 250 WORDS)

Elevated D dimer in the lungs and blood of patients with sarcoidosis

The hypothesis of this study was that D dimer, a specific degradation product of cross-linked fibrin, would be increased in the bronchoalveolar lavage (BAL) fluids of patients with sarcoidosis and that it would be related to other BAL parameters of disease activity. Eight of 10 sarcoidosis patients but none of 18 healthy volunteers had detectable BAL D dimer by enzyme immunoassay. Autoradiography revealed the presence of fibrinogen and D dimer in the BAL fluids from sarcoidosis patients. Bronchoalveolar lavage D dimer levels in sarcoidosis patients correlated with total BAL cells per milliliter, lymphocytes per milliliter, and total protein level, but not macrophages per milliliter. The D dimer in the BAL fluids from sarcoidosis patients did not correlate with D dimer in the blood. Our findings indicate that BAL D dimer parallels directly the lymphocytic alveolitis that characterizes pulmonary sarcoidosis.

Alveolar surfactant and adult respiratory distress syndrome. Pathogenetic role and therapeutic prospects

The adult respiratory distress syndrome (ARDS) is characterized by extended inflammatory processes in the lung microvascular, interstitial, and alveolar compartments, resulting in vasomotor disturbances, plasma leakage, cell injury, and complex gas exchange disturbances. Abnormalities in the alveolar surfactant system have long been implicated in the pathogenetic sequelae of this life-threatening syndrome. This hypothesis is supported by similarities in pulmonary failure between patients with ARDS and preterm babies with infant respiratory distress syndrome, known to be triggered primarily by lack of surfactant material. Mechanisms of surfactant alterations in ARDS include: (a) lack of surface-active compounds (phospholipids, apoproteins) due to reduced generation/release by diseased pneumocytes or to increased loss of material (this feature includes changes in the relative composition of the surfactant phospholipid and/or apoprotein profiles); (b) inhibition of surfactant function by plasma protein leakage (inhibitory potencies of different plasma proteins have been defined); (c) "incorporation" of surfactant phospholipids and apoproteins into polymerizing fibrin upon hyaline membrane formation; and (d) damage/inhibition of surfactant compounds by inflammatory mediators (proteases, oxidants, nonsurfactant lipids). Alterations in alveolar surfactant function may well contribute to a variety of pathophysiological key events encountered in ARDS. These include decrease in compliance, ventilation-perfusion mismatch including shunt flow due to altered gas flow distribution (atelectasis, partial alveolar collapse, small airway collapse), and lung edema formation. Moreover, more speculative at the present time, surfactant abnormalities may add to a reduction in alveolar host defense competence and an upregulation of inflammatory events under conditions of ARDS. Persistent atelectasis of surfactant-deficient and in particular fibrin-loaded alveoli may represent a key event to trigger fibroblast proliferation and fibrosis in late ARDS ("collapse induration"). Overall, the presently available data on surfactant abnormalities in ARDS lend credit to therapeutic trials with transbronchial surfactant administration. In addition to the classical goals of replacement therapy defined for preterm infants (rapid improvement in lung compliance and gas exchange), this approach will have to consider its impact on host defense competence and inflammatory and proliferative processes when applied in adults with respiratory failure.

Tissue factor procoagulant expression by rat alveolar epithelial cells

Fibrin deposition in the alveolar space is characteristic of inflammatory lung injury. The formation of fibrin in the alveolus results from the coagulation of extravasated plasma. The cellular elements that promote intra-alveolar clotting have not been completely defined. We have investigated the capacity of alveolar epithelial cells (AEC) to promote coagulation through the expression of procoagulant activity (PCA) in tissue culture. Using a single-stage coagulation assay, rat AEC monolayers were found to contain 20,750 +/- 4,035 procoagulant units (PCU)/10(6) cells; 10- to 20-fold greater activity than that found in concomitantly isolated alveolar macrophages. The epithelial-derived procoagulant was shown to be tissue factor by a series of assays using clotting factor-deficient human plasmas. Freshly isolated AEC also possessed PCA (2,500 +/- 1,000 PCU/10(6) cells) and expressed a 2.1-kb mRNA that hybridized with a cDNA for murine tissue factor. Using a kinetic turbidometric assay of clot acceleration, PCA was found on the surface of unstimulated epithelial monolayers and could be increased to 170% of control by incubation with phorbol myristate acetate (PMA). This response to PMA was accompanied by a parallel increase in the relative abundance of tissue factor mRNA. AEC shed particulate PCA into the culture media that displayed a specific activity similar to that recovered from alveolar lining fluid. Therefore, by expressing both cell surface and particulate PCA, the alveolar epithelium likely contributes significantly to the modulation of intra-alveolar coagulation.

Expression and kinetics of induced procoagulant activity in bovine pulmonary alveolar macrophages

Leukocytes, especially macrophages, are important cellular mediators of fibrin deposition and removal at tissue sites of inflammation. Pulmonary fibrin deposition is a prominent feature of bovine acute lung injury; therefore, we studied the resting and stimulated procoagulant responses of bovine pulmonary alveolar macrophages (PAM) and peripheral blood neutrophils (PMN). Freshly isolated normal PAM and PMN expressed negligible procoagulant activity. PAM stimulated with endotoxin lipopolysaccharide (LPS), 4 beta-phorbol 12-myristate 13-acetate (PMA) and bovine recombinant interleukin-1 beta (rBIL-1 beta) exhibited protein synthesis- and dose-dependent enhancement of procoagulant activity in 8-h cultures. Bovine recombinant granulocyte macrophage-colony stimulating factor (rBGM-CSF) and recombinant human gamma-interferon (rHIFN-gamma) did not induce procoagulant activity. The kinetics of LPS- and PMA-enhanced PAM procoagulant activity differed: LPS-induced enhancement developed earlier and more rapidly than PMA-induced enhancement. Pasteurella haemolytica LPS was more potent than Escherichia coli LPS in enhancing PAM procoagulant activity, while dexamethasone decreased both baseline and LPS- or PMA-stimulated activity by approximately 50%. PAM procoagulant activity resulted from tissue factor expression. Bovine PMN produced negligible procoagulant activity when stimulated, and are thus unlikely to be major contributors to procoagulant activity in bovine lung. Activity inhibitory to bovine tissue factor was present in both calf and adult sera, and was partly dependent on the presence of factor X for activity. Rapid induction of bovine PAM procoagulant activity by inflammatory mediators, and subsequent resistance to degradation, may thus combine to promote an alveolar microenvironment permissive to fibrin deposition in bovine acute lung injury.

Procoagulant activity in bronchoalveolar lavage of severely traumatized patients--relation to the development of acute respiratory distress

In a prospective study in severely traumatized patients, procoagulant activity (PCA) was determined in bronchoalveolar lavage fluids (BAL). Bronchoscopy with lavage was serially performed during the first 15 days after injury (in total 148 samples of 25 patients). PCA was measured as recalcification times in the absence or presence of excess phosphatidylethanolamine and translated into procoagulant unit equivalents using standard thromboplastin. The data were correlated to the extent of respiratory failure in the injured patients and were compared to PCA in 29 lavage samples obtained from 10 healthy control subjects. A several-fold increase in BAL PCA was noted in all trauma victims, evident already within the first 24 h after injury. A progressive rise in PCA occurred from the 4th posttraumatic day and was highly significantly more pronounced in patients developing serious respiratory failure than in those with only mild pulmonary dysfunction. Significant correlations were noted between PCA increase and alveolar protein-leakage, granulocyte-influx and surfactant alterations, however with correlation coefficients not surpassing 0.55. We conclude that a marked increase in procoagulant activity occurs in severely injured patients, which may favour alveolar fibrin deposition and is related to the development of acute respiratory failure.

Secretion of plasminogen activator inhibitor by normal rat pleural leukocytes in culture

The normal balance between coagulation and fibrinolysis in the pleural cavity is poorly understood despite the critical role of the pleura in the movement of the lungs. To determine the fibrinolytic activity and the interaction between plasminogen activators and their inhibitors in the normal pleural space, we tested normal rat pleural leukocytes, principally macrophages and mast cells, and their supernatants, for activity in an [125I]fibrin degradation assay. It was found that pleural leukocytes did not release plasminogen activator, but the leukocytes and their supernatants inhibited the plasminogen-dependent fibrinolysis caused by both alveolar leukocytes and mesothelial cells. Further experiments demonstrated that pleural leukocytes produce a protein inhibitor primarily against urokinase-induced fibrinolysis in culture and that macrophages are the main source of the inhibitor. The lysate of mast cell-enriched population exhibited high plasminogen activator activity while no such activity could be determined in macrophage-enriched lysate. These data show that normal rat pleural leukocytes contain plasminogen activator inside the cells and synthesize a urokinase-type plasminogen activator inhibitor in culture that may be important in the fibrinolysis/coagulation balance in the pleural space.

Endotoxin-mediated bovine alveolar macrophage procoagulant induction is dependent on protein kinase C activation

The induction of pulmonary alveolar macrophage (PAM) tissue factor-dependent procoagulant activity is central to the deposition of inflammatory fibrin in the pulmonary alveolus. The presence of enhanced tissue factor activity is often associated with pulmonary fibrin deposition, an important pathogenetic event that can delay resolution of pulmonary inflammation and promote the induction of pulmonary fibrosis. Since tissue factor synthesis induction and activation pathways are potential therapeutic targets for modulation of alveolar macrophage tissue factor (procoagulant) activity, we examined the pathways through which endotoxin lipopolysaccharide (LPS) induces bovine PAM tissue factor-dependent procoagulant activity. PAM procoagulant activity was markedly enhanced to 10 times the levels of freshly isolated PAM after 8 h of culture in the presence of either the protein kinase C (PKC) agonist phorbol 12-myristate 13-acetate (PMA) or LPS. Both LPS-(P less than 0.002) and PMA-induced activity (P less than 0.007) was completely ablated by the PKC inhibitor 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H 7,100 microM) but was unaffected by the cyclic nucleotide-dependent protein kinase inhibitor N-(2-guanidinoethyl)-5-isoquinolinesulfonamide (HA-1004, 100 microM). The arachidonate cyclooxygenase pathway inhibitor phenylbutazone (10(-4) M) had modest effects that were not statistically significant. The unstimulated increase of procoagulant activity in 8-h cultures was unaffected by the same inhibitory modulations.(ABSTRACT TRUNCATED AT 250 WORDS)

Local activation of the coagulation and fibrinolysis systems in lung disease

Extravascular coagulation and fibrinolysis is an integral part of inflammatory reactions. Disordered expression of procoagulant and profibrinolytic factors by mononuclear phagocytes of the lung (i.e. lung alveolar macrophages (LAM) and interstitial macrophages) may have important bearings on inflammatory lung tissue destruction and repair. Based on this hypothesis we have measured the presence of trigger molecules and activation products of the coagulation and fibrinolytic system in cell-free bronchoalveolar lavage fluid and in bronchoalveolar cells. Patient groups with chronic obstructive disease (COLD) (n = 76), idiopathic pulmonary fibrosis (IPF) (n = 29), sarcoidosis (n = 22), lung cancer (n = 36), pneumonia (n = 39), acquired immunodeficiency syndrome (AIDS) (n = 17) and a control group (n = 60) were studied by bronchoalveolar lavage (BAL). In all patient groups tissue thromboplastin (TPL) and fibrinopeptide A (FPA) were significantly increased compared to controls. Plasminogen activator (PA) activity was significantly lower in patients than in normals, and usually associated with high levels of antifibrinolytic activity. The level of PA inhibitor (PAI-2) was not significantly higher in any patient group compared to controls. The sensitivity of the method for fibrin degradation products (FDP) analysis was not high enough to detect FDP in BAL fluid of control individuals, whereas such products could be demonstrated in 25-53% of patients in various categories. We conclude that disordered expression of procoagulant and plasminogen activator activities in bronchoalveolar lavage fluid may reflect a milieu that favours accumulation of fibrin in inflammatory lung tissue and form the basis for the development of pulmonary fibrosis.

Local abnormalities in coagulation and fibrinolytic pathways predispose to alveolar fibrin deposition in the adult respiratory distress syndrome

To determine the possible mechanism(s) promoting alveolar fibrin deposition in the adult respiratory distress syndrome (ARDS), we investigated the initiation and regulation of both fibrinolysis and coagulation from patients with ARDS (n = 14), at risk for ARDS (n = 5), and with interstitial lung diseases (ILD) (n = 8), and normal healthy individuals (n = 13). Bronchoalveolar lavage (BAL) extrinsic pathway inhibitor activity was increased in ARDS BAL compared with patients at risk for ARDS (P = 0.0146) or normal controls (P = 0.0013) but tissue factor-factor VII procoagulant activity was significantly increased in ARDS BAL compared with all other groups (P less than 0.001). Fibrinolytic activity was not detectable in BAL of 10 of the 14 patients with ARDS and low levels of activity were found in BAL of the other four ARDS patients. Depressed fibrinolysis in ARDS BAL was not due to local insufficiency of plasminogen; rather, there was inhibition of both plasmin and plasminogen activator. Plasminogen activator inhibitor 1 was variably detected and low levels of plasminogen activator inhibitor 2 were found in two ARDS BAL samples, but plasminogen activator inhibitor 2 was otherwise undetectable. ARDS BAL antiplasmin activity was, in part, due to alpha 2-antiplasmin. We conclude that abnormalities that result in enhanced coagulation and depressed fibrinolysis, thereby predisposing to alveolar fibrin deposition, occur in the alveolar lining fluids from patients with ARDS.

Local abnormalities of coagulation and fibrinolytic pathways that promote alveolar fibrin deposition in the lungs of baboons with diffuse alveolar damage

Because alveolar fibrin is a prominent histologic feature of diffuse lung injury in baboons, we hypothesized that local abnormalities of pathways of fibrin turnover would favor fibrin deposition in the alveolar space. To test this hypothesis, procoagulant and fibrinolytic activities were characterized in serial bronchoalveolar lavage (BAL) of baboons with evolving diffuse alveolar damage (DAD) induced by exposure to 100% O2. BAL procoagulant activity, characterized mainly as the tissue factor-Factor VII complex, was markedly increased after induction of DAD. Extrinsic pathway inhibitor was likewise increased in BAL during evolving DAD but was insufficient to control coagulation. Urokinase-like fibrinolytic activity was usually detectable in baseline BAL but was undetectable after 7 d of O2. DAD BAL contained significantly increased plasminogen levels, plasmin inhibitor activity sufficient to neutralize all plasmin produced by BAL plasminogen activator found in control BAL and detectable plasminogen activator inhibitor-1. Antiplasmin activity was due, in part, to increased alpha 2-antiplasmin. These changes correlated with quantitatively increased alveolar fibrin deposition demonstrated by histologic and morphometric analyses. Multiple abnormalities of pathways of fibrin turnover occur concurrently in the alveolar compartment of the lungs of baboons with DAD, which collectively predispose to diffuse alveolar fibrin deposition.