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

Biophysical properties of alveolar surfactant in drever dogs with hunting associated pulmonary edema

BACKGROUND

A syndrome of acute non-cardiogenic pulmonary edema associated with hunting is prevalent in the drever breed, but etiology of this syndrome is currently unknown. Alveolar surfactant has a critical role in preventing alveolar collapse and edema formation. The aim of this study was to investigate, whether the predisposition to hunting associated pulmonary edema in drever dogs is associated with impaired biophysical properties of alveolar surfactant. Seven privately owned drever dogs with recurrent hunting associated pulmonary edema and seven healthy control dogs of other breeds were included in the study. All affected dogs underwent thorough clinical examinations including echocardiography, laryngeal evaluation, bronchoscopy, and bronchoalveolar lavage (BAL) as well as head, neck and thoracic computed tomography imaging to rule out other cardiorespiratory diseases potentially causing the clinical signs. Alveolar surfactant was isolated from frozen, cell-free supernatants of BAL fluid and biophysical analysis of the samples was completed using a constrained sessile drop surfactometer. Statistical comparisons over consecutive compression expansion cycles were performed using repeated measures ANOVA and comparisons of single values between groups were analyzed using T-test.

RESULTS

There were no significant differences between groups in any of the biophysical outcomes of surfactant analysis. The critical function of surfactant, reducing the surface tension to low values upon compression, was similar between healthy dogs and affected drevers.

CONCLUSIONS

The etiology of hunting associated pulmonary edema in drever dogs is not due to an underlying surfactant dysfunction.

Fibrinogen, Fibrin, and Fibrin Degradation Products in COVID-19

Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) is the highly pathogenic and highly transmissible human coronavirus that is the causative agent for the worldwide COVID-19 pandemic. COVID-19 manifests predominantly as a respiratory illness with symptoms consistent with viral pneumonia, but other organ systems (e.g., kidney, heart, brain) can also become perturbed in COVID-19 patients. Accumulating data suggest that significant activation of the hemostatic system is a common pathological manifestation of SARS-CoV-2 infection. The clotting protein fibrinogen is one of the most abundant plasma proteins. Following activation of coagulation, the central coagulation protease thrombin converts fibrinogen to fibrin monomers, which selfassemble to form a matrix, the primary structural component of the blood clot. Severe COVID-19 is associated with a profound perturbation of circulating fibrinogen, intra- and extravascular fibrin deposition and persistence, and fibrin degradation. Current findings suggest high levels of fibrinogen and the fibrin degradation product D-dimer are biomarkers of poor prognosis in COVID-19. Moreover, emerging studies with in vitro and animal models indicate fibrin(ogen) as an active player in COVID-19 pathogenesis. Here, we review the current literature regarding fibrin(ogen) and COVID-19, including possible pathogenic mechanisms and treatment strategies centered on clotting and fibrin(ogen) function.

COVID-19 coagulopathy - what should we treat?

NEW FINDINGS

What is the topic of this review? Overview of the coagulation abnormalities, including elevated D-dimers widely reported with COVID-19, often labelled as COVID coagulopathy. What advances does it highlight? The review highlights the changes in bronchoalveolar haemostasis due to apoptosis of alveolar cells, which contributes to acute lung injury and acute respiratory distress syndrome; the pathophysiological mechanisms, including endothelial dysfunction and damage responsible for thrombosis of pulmonary microcirculation and potential contribution to the hypoxaemia of COVID-19 acute lung injury; and changes in coagulation proteins responsible for the hypercoagulability and increased risk of thrombosis in other venous and arterial beds. The rationale for anticoagulation and fibrinolytic therapies is detailed, and potential confounders that might have led to less than expected improvement in the various randomised controlled trials are considered.

ABSTRACT

Coronavirus disease 19 (COVID-19) causes acute lung injury with diffuse alveolar damage, alveolar-capillary barrier disruption, thrombin generation and alveolar fibrin deposition. Clinically, hypoxaemia is associated with preserved lung compliance early in the disease, suggesting the lack of excessive fluid accumulation typical of other lung injuries. Notably, autopsy studies demonstrate infection of the endothelium with extensive capillary thrombosis distinct from the embolic thrombi in pulmonary arteries. The inflammatory thrombosis in pulmonary vasculature secondary to endothelial infection and dysfunction appears to contribute to hypoxaemia. This is associated with elevated D-dimers and acquired hypercoagulability with an increased risk of deep vein thrombosis. Hypercoagulability is secondary to elevated plasma tissue factor levels, von Willebrand factor, fibrinogen, reduced ADAMTS-13 with platelet activation and inhibition of fibrinolysis. Multi-platform randomised controlled studies of systemic therapeutic anticoagulation with unfractionated and low molecular mass heparins demonstrated a survival benefit over standard care with full-dose anticoagulation in patients with non-severe disease who require supplemental oxygen, but not in severe disease requiring ventilatory support. Late intervention and the heterogeneous nature of enrolled patients can potentially explain the apparent lack of benefit in severe disease. Improvement in oxygenation has been demonstrated with intravenous fibrinolytics in small studies. Inhaled anticoagulants, thrombolytic agents and non-specific proteolytic drugs in clinical trials for decreasing alveolar fibrin deposition might benefit early disease. Essentially, COVID-19 is a multi-system disorder with pulmonary vascular inflammatory thrombosis that requires an interdisciplinary approach to combination therapies addressing both inflammation and intravascular thrombosis or alveolar fibrin deposits to improve outcomes.

Fusion Expression and Fibrinolytic Activity of rPA/SP-B

BACKGROUND

Pulmonary surfactant dysfunction is an important pathological factor in acute respiratory distress syndrome (ARDS) and pulmonary fibrosis (PF).

OBJECTIVE

In this study, the characteristics of recombinant mature surfactant protein B (SP-B) and reteplase (rPA) fusion protein maintaining good pulmonary surface activity and rPA fibrinolytic activity in acute lung injury cell model were studied.

METHODS

We studied the characteristics of SP-B fusion expression, cloned rPA gene and N-terminal rPA/C-terminal SP-B co-expression gene, and constructed them into eukaryotic expression vector pEZ-M03 to obtain recombinant plasmids pEZ-rPA and pEZ-rPA/SP-B. The recombinant plasmids was transfected into Chinese hamster ovary (CHO) K1 cells and the expression products were analyzed by Western Blot. Lipopolysaccharide (LPS) was used to induce CCL149 (an alveolar epithelial cell line) cell injury model. Fluorescence staining of rPA and rPA/SP-B was carried out with the enhanced green fluorescent protein (eGFP) that comes with pEZ-M03; the cell Raman spectroscopy technique was used to analyze the interaction between rPA/SP-B fusion protein and the phospholipid structure of cell membrane in CCL149 cells. The enzyme activity of rPA in the fusion protein was determined by fibrin-agarose plate method.

RESULTS

The rPA/SP-B fusion protein was successfully expressed. In the CCL149 cell model of acute lung injury (ALI), the green fluorescence of rPA/SP-B is mainly distributed on the CCL149 cell membrane. The rPA/SP-B fusion protein can reduce the disorder of phospholipid molecules and reduce cell membrane damage. The enzyme activity of rPA/SP-B fusion protein was 3.42, and the fusion protein still had good enzyme activity.

CONCLUSION

The recombinant eukaryotic plasmid pEZ-rPA/SP-B is constructed and can be expressed in the eukaryotic system. Studies have shown that rPA/SP-B fusion protein maintains good SP-B lung surface activity and rPA enzyme activity in acute lung injury cell model.

D-Dimers Level as a Possible Marker of Extravascular Fibrinolysis in COVID-19 Patients

BACKGROUND AND OBJECTIVE

Host defence mechanisms to counter virus infection include the activation of the broncho-alveolar haemostasis. Fibrin degradation products secondary to extravascular fibrin breakdown could contribute to the marked increase in D-Dimers during COVID-19. We sought to examine the prognostic value on lung injury of D-Dimers in non-critically ill COVID-19 patients without thrombotic events.

METHODS

This study retrospectively analysed hospitalized COVID-19 patients classified according to a D-Dimers threshold following the COVID-19 associated haemostatic abnormalities (CAHA) classification at baseline and at peak (Stage 1: D-Dimers less than three-fold above normal; Stage 2: D-Dimers three- to six-fold above normal; Stage 3: D-Dimers six-fold above normal). The primary endpoint was the occurrence of critical lung injuries on chest computed tomography. The secondary outcome was the composite of in-hospital death or transfer to the intensive care unit (ICU).

RESULTS

Among the 123 patients included, critical lung injuries were evidenced in 8 (11.9%) patients in Stage 1, 6 (20%) in Stage 2 and 15 (57.7%) in Stage 3 (p = 0.001). D-Dimers staging at peak was an independent predictor of critical lung injuries regardless of the inflammatory burden assessed by CRP levels (OR 2.70, 95% CI (1.50-4.86); p < 0.001) and was significantly associated with increased in-hospital death or ICU transfer (14.9 % in Stage 1, 50.0% in Stage 2 and 57.7% in Stage 3 (p < 0.001)). D-Dimers staging at peak was an independent predictor of in-hospital death or ICU transfer (OR 2.50, CI 95% (1.27-4.93); p = 0.008).

CONCLUSIONS

In the absence of overt thrombotic events, D-Dimers quantification is a relevant marker of critical lung injuries and dismal patient outcome.

Proteomics reveals region-specific hemostatic alterations in response to mechanical ventilation in a preterm lamb model of lung injury

INTRODUCTION

Preterm infants often require assisted ventilation, however ventilation when applied to the immature lung can initiate ventilator-induced lung injury (VILI). The biotrauma which underscores VILI is largely undefined, and is likely to involve vascular injury responses, including hemostasis. We aimed to use a ventilated, preterm lamb model to: (1) characterize regional alterations in hemostatic mediators within the lung and (2) assess the functional impact of protein alterations on hemostasis by analyzing temporal thrombin generation.

MATERIALS AND METHODS

Preterm lambs delivered at 124 to 127 days gestation received 90 min of mechanical ventilation (positive end-expiratory pressure = 8 cm H₂O, V_T = 6-8 ml/kg) and were compared with unventilated control lambs. At study completion, lung tissue was taken from standardized nondependent and gravity-dependent regions, and Orbitrap-mass spectrometry and KEGG were used to identify and map regional alterations in hemostasis pathway members. Temporal alterations in plasma thrombin generation were assessed.

RESULTS

Ventilation was distributed towards the nondependent lung. Significant changes in hemostatic protein abundance, were detected at a two-fold higher rate in the nondependent lung when compared with the gravity-dependent lung. Seven proteins were uniquely altered in non-dependent lung (SERPINA1, MYL12A, RAP1B, RHOA, ITGB1, A2M, GNAI2), compared with a single proteins in gravity-dependent lung (COL1A2). Four proteins were altered in both regions (VTN, FGG, FGA, and ACTB). Tissue protein alterations were mirrored by plasma hypocoagulability at 90-minutes of ventilation.

CONCLUSIONS

We observed regionally specific, hemostatic alterations within the preterm lung together with disturbed fibrinolysis following a short period of mechanical ventilation.

Progressive Lung Injury, Inflammation, and Fibrosis in Rats Following Inhalation of Sulfur Mustard

Sulfur mustard (SM) inhalation causes debilitating pulmonary injury in humans which progresses to fibrosis. Herein, we developed a rat model of SM toxicity which parallels pathological changes in the respiratory tract observed in humans. SM vapor inhalation caused dose (0.2-0.6 mg/kg)-related damage to the respiratory tract within 3 days of exposure. At 0.4-0.6 mg/kg, ulceration of the proximal bronchioles, edema and inflammation were observed, along with a proteinaceous exudate containing inflammatory cells in alveolar regions. Time course studies revealed that the pathologic response was biphasic. Thus, changes observed at 3 days post-SM were reduced at 7-16 days; this was followed by more robust aberrations at 28 days, including epithelial necrosis and hyperplasia in the distal bronchioles, thickened alveolar walls, enlarged vacuolated macrophages, and interstitial fibrosis. Histopathologic changes were correlated with biphasic increases in bronchoalveolar lavage (BAL) cell and protein content and proliferating cell nuclear antigen expression. Proinflammatory proteins receptor for advanced glycation end product (RAGE), high-mobility group box protein (HMGB)-1, and matrix metalloproteinase (MMP)-9 also increased in a biphasic manner following SM inhalation, along with surfactant protein-D (SP-D). Tumor necrosis factor (TNF)-α and inducible nitric oxide synthase (iNOS), inflammatory proteins implicated in mustard lung toxicity, and the proinflammatory/profibrotic protein, galectin (Gal)-3, were upregulated in alveolar macrophages and in bronchiolar regions at 3 and 28 days post-SM. Inflammatory changes in the lung were associated with oxidative stress, as reflected by increased expression of heme oxygenase (HO)-1. These data demonstrate a similar pathologic response to inhaled SM in rats and humans suggesting that this rodent model can be used for mechanistic studies and for the identification of efficacious therapeutics for mitigating toxicity.

The fibrogenic actions of the coagulant and plasminogen activation systems in pulmonary fibrosis

Fibrosis causes irreversible damage to lung structure and function in restrictive lung diseases such as idiopathic pulmonary fibrosis (IPF). Extravascular coagulation involving fibrin formation in the intra-alveolar compartment is postulated to have a pivotal role in the development of pulmonary fibrosis, serving as a provisional matrix for migrating fibroblasts. Furthermore, proteases of the coagulation and plasminogen activation (plasminergic) systems that form and breakdown fibrin respectively directly contribute to pulmonary fibrosis. The coagulants, thrombin and factor Xa (FXa) evoke fibrogenic effects via cleavage of the N-terminus of protease-activated receptors (PARs). Whilst the formation and activity of plasmin, the principle plasminergic mediator is suppressed in the airspaces of patients with IPF, localized increases are likely to occur in the lung interstitium. Plasmin-evoked proteolytic activation of factor XII (FXII), matrix metalloproteases (MMPs) and latent, matrix-bound growth factors such as epidermal growth factor (EGF) indirectly implicate plasmin in pulmonary fibrosis. Another plasminergic protease, urokinase plasminogen activator (uPA) is associated with regions of fibrosis in the remodelled lung of IPF patients and elicits fibrogenic activity via binding its receptor (uPAR). Plasminogen activator inhibitor-1 (PAI-1) formed in the injured alveolar epithelium also contributes to pulmonary fibrosis in a manner that involves vitronectin binding. This review describes the mechanisms by which components of the two systems primarily involved in fibrin homeostasis contribute to interstitial fibrosis, with a particular focus on IPF. Selectively targeting the receptor-mediated mechanisms of coagulant and plasminergic proteases may limit pulmonary fibrosis, without the bleeding complications associated with conventional anti-coagulant and thrombolytic therapies.

Pulmonary Remodeling in Equine Asthma: What Do We Know about Mediators of Inflammation in the Horse?

Equine inflammatory airway disease (IAD) and recurrent airway obstruction (RAO) represent a spectrum of chronic inflammatory disease of the airways in horses resembling human asthma in many aspects. Therefore, both are now described as severity grades of equine asthma. Increasing evidence in horses and humans suggests that local pulmonary inflammation is influenced by systemic inflammatory processes and the other way around. Inflammation, coagulation, and fibrinolysis as well as extracellular remodeling show close interactions. Cytology of bronchoalveolar lavage fluid and tracheal wash is commonly used to evaluate the severity of local inflammation in the lung. Other mediators of inflammation, like interleukins involved in the chemotaxis of neutrophils, have been studied. Chronic obstructive pneumopathies lead to remodeling of bronchial walls and lung parenchyma, ultimately causing fibrosis. Matrix metalloproteinases (MMPs) are discussed as the most important proteolytic enzymes during remodeling in human medicine and increasing evidence exists for the horse as well. A systemic involvement has been shown for severe equine asthma by increased acute phase proteins like serum amyloid A and haptoglobin in peripheral blood during exacerbation. Studies focusing on these and further possible inflammatory markers for chronic respiratory disease in the horse are discussed in this review of the literature.

Biophysical Activity of Impaired Lung Surfactant upon Exposure to Polymer Nanoparticles

Colloidal drug carriers could improve the therapy of numerous airway diseases. However, it remains unclear to what extent nanoscale particulate matter affects the biophysical function of the essential surface-active lining layer of the lungs, especially under predisposed conditions of airway diseases. Accordingly, the current study investigated the impact of defined polymer nanoparticles on impaired lung surfactants. Admixtures of plasma proteins (albumin and fibrinogen) to Curosurf led to a controllable decrease in surface activity (i.e., adsorption and minimal surface tension of >25 and >5 mN/m, respectively), which served as models for dysfunctional lung surfactants. Next, Curosurf preincubated with plasma proteins was challenged with negatively- and positively charged poly(lactide) nanoparticles. Negatively charged nanoparticles significantly perturbed the biophysical function of impaired Curosurf in a dose-dependent manner, most-likely due to a binding of essential surfactant components. By contrast, addition of positively charged nanoparticles led to no further loss of surface activity, but a remarkable depletion of plasma protein content. Once adsorbed to the surface of polymer nanoparticles, plasma proteins were hindered to displace relevant surfactant components from the air/liquid interface. Overall, the current study indicated that, depending on their physicochemical properties, colloidal drug carriers could compromise the biophysical function of impaired lung surfactants. Notably, a positive surface charge represents a parameter for the rationale design of polymer nanomedicines causing negligible adverse events on an impaired surface-active lining layer in the lungs.

Biomarkers in acute lung injury

Acute respiratory distress syndrome (ARDS) and acute lung injury (ALI) result in high permeability pulmonary edema causing hypoxic respiratory failure with high morbidity and mortality. As the population ages, the incidence of ALI is expected to rise. Over the last decade, several studies have identified biomarkers in plasma and bronchoalveolar lavage fluid providing important insights into the mechanisms involved in the pathophysiology of ALI. Several biomarkers have been validated in subjects from the large, multicenter ARDS clinical trials network. Despite these studies, no single or group of biomarkers has made it into routine clinical practice. New high throughput "omics" techniques promise improved understanding of the biologic processes in the pathogenesis in ALI and possibly new biomarkers that predict disease and outcomes. In this article, we review the current knowledge on biomarkers in ALI.

Pulmonary activation of coagulation and inhibition of fibrinolysis after burn injuries and inhalation trauma

BACKGROUND

Pulmonary coagulopathy is intrinsic to pneumonia and other forms of acute lung injury. We hypothesized patients with burn injuries and inhalation trauma to have similar alterations in pulmonary coagulation and fibrinolysis.

METHODS

We performed a prospective study on changes in pulmonary and systemic thrombin generation and fibrinolytic activity in patients with burn injuries and inhalation trauma requiring mechanical ventilation. Nondirected bronchial lavage was performed on alternate days. Patients requiring mechanical ventilation for nonpulmonary reasons who did not meet the North American European Consensus Conference criteria for acute lung injury functioned as control patients.

RESULTS

We studied 13 patients with burn injuries and inhalation trauma and 15 control patients. On admission, patients with burn injuries and inhalation trauma showed a significant increase in thrombin generation in the airways compared with control patients, as reflected by increased lavage fluid levels of thrombin-antithrombin complexes and fibrin degradation products, and decreased lavage fluid levels of activated protein C and antithrombin. Simultaneously, burn patients showed a significant decrease in fibrinolytic activity, as reflected by decreased lavage fluid levels of plasminogen activator activity. Pulmonary coagulopathy persisted throughout the period of mechanical ventilation and was accompanied by similar changes in systemic coagulation and fibrinolysis. There was no significant correlation between changes in coagulation and fibrinolysis and the extent of burn injury.

CONCLUSIONS

Patients with burn injuries and inhalation trauma requiring mechanical ventilation show a distinct and sustained procoagulant and antifibrinolytic shift in the pulmonary compartment. Pulmonary coagulopathy could be an important therapeutic target in these patients.

Safety and tolerability of inhaled heparin in idiopathic pulmonary fibrosis

BACKGROUND

Abnormalities in alveolar coagulation occur in idiopathic pulmonary fibrosis (IPF). Anticoagulants attenuate bleomycin-induced lung fibrosis in animals. In this study, we first examined the pharmacokinetics of inhaled heparin in healthy subjects. Second, we investigated the safety and tolerability of heparin inhalation in IPF patients.

METHODS

Coagulation assays were performed in blood and bronchoalveolar lavage fluid samples from 19 healthy volunteers after inhalation of increasing amounts of unfractionated heparin. The acute effects of heparin inhalation on lung function and exercise capacity and the safety and tolerability of chronic heparin inhalation for 28 days were assessed in 20 IPF patients in an open-label exploratory pilot study.

RESULTS

In healthy subjects, inhalation of 150,000 IU heparin ("filled dose") significantly increased the partial thromboplastin time and anti-factor Xa activity in blood samples indicating the threshold dose. The local alveolar anticoagulant effect was detectable up to 72 h, and the alveolar half-life was estimated at 28 h. In IPF-patients, no acute deleterious effects on pulmonary function, gas exchange, or exercise capacity were noted after inhalation of the threshold dose. During chronic treatment, where one-fourth of the threshold dose was inhaled every 12 h for 28 days to obtain a steady-state anticoagulant activity in the alveolar space approximating the anticoagulant activity observed after threshold dose inhalation, no heparin-related side effects, such as hemoptysis or heparin-induced antibodies and thrombocytopenia, were detected in any patient, and median lung function values, exercise capacity, and quality of life scores appeared largely unaltered. Three adverse and one serious adverse events were noted; however, the relation of these events to the heparin inhalation was assessed as "unlikely" or "no relation" in each case.

CONCLUSIONS

Inhaled heparin appears to be safe and well tolerated in IPF patients. Future clinical trials are required to demonstrate the long-term safety and efficacy of inhaled heparin in IPF.

Up-regulation of the extrinsic coagulation pathway in acute asthma--a case study

INTRODUCTION

In the normal airway, the hemostatic balance is antithrombotic and favors fibrinolysis. Acute asthma is associated with inflammatory cell infiltrate and plasma exudation in the airways. Postmortem specimens following status asthmaticus suggest a role for the activation of the extrinsic coagulation cascade and intraluminal fibrin formation. The authors report a chance observation of fibrin formation in the airways of a patient with moderate asthma 5 days before a severe exacerbation requiring hospital admission.

METHODS

Alpha-2 macroglobulin, an index of plasma leakage, coagulation factors, and D-dimers were measured by enzyme-linked immunosorbent assay (ELISA) in hypertonic saline-induced sputum, as part of a study into airway repair in stable asthma. All subjects were required to have stable symptoms and measures of asthma prior to sampling.

RESULTS

The subject's baseline forced expiratory volume in one second (FEV(1)) was 94% predicted and fraction of exhaled nitric oxide (FeNO) level was 30 ppb prior to sputum induction. Differential sputum cell count revealed an airways neutrophilia (neutrophils 81.1%, eosinophils 0.19%). D-dimers were 70-fold and 22-fold higher than the median value for patients with stable moderate and severe asthma, respectively. Plasma exudation was 42-fold higher than in stable moderate asthma, but on a par with levels found in severe stable asthma, and locally produced coagulation factors may therefore be involved. Levels of fibrinogen, plasminogen, plasminogen activator inhibitor (PAI)-1 and thrombin-activatable fibrinolysis inhibitor (TAFI) were all at least an order of magnitude higher than those seen in stable moderate or severe asthma.

CONCLUSIONS

Acute exacerbation of moderate asthma appears to be associated with a shift to a profibrinogenic, possibly antifibrinolytic, environment in the airways.

Plasminogen Activator Inhibitor I 4G/5G Polymorphism in Neonatal Respiratory Distress Syndrome

Fibrin monomers inhibit surfactant function. 4G/5G insertion/deletion polymorphism plays an important role in the regulation of plasminogen activator inhibitor 1 (PAI-1) gene expression. To examine the genotype distribution of PAI-1 polymorphism in 60 infants with respiratory distress syndrome (RDS) and 53 controls, an allele-specific polymerase chain reaction (PCR) was used. The proportion of 4G/4G, 4G/5G, and 5G/5G genotypes did not differ statistically between the RDS and control groups (P > .05). Having PAI-1 4G/4G genotype polymorphism appears to increase the risk of RDS (odds ratio [OR] =1.5; 95% confidence interval [CI], 0.5-4.3), although it was not statistically significant. No relation was found between the PAI-1 4G/5G polymorphisms and RDS, but there was an increased risk associated with the 4G variant of the PAI-1 gene. We believe that our findings of increased 4G allele of the PAI-1 gene in infants with RDS would also help to clarify the pathogenesis of RDS.

Transforming growth factor-β1 induces expression of human coagulation factor XII via Smad3 and JNK signaling pathways in human lung fibroblasts

Coagulation factor XII (FXII) is a liver-derived serine protease involved in fibrinolysis, coagulation, and inflammation. The regulation of FXII expression is largely unknown. Transforming growth factor-beta1 (TGF-beta1) is a multifunctional cytokine that has been linked to several pathological processes, including tissue fibrosis by modulating procoagulant and fibrinolytic activities. This study investigated whether TGF-beta1 may regulate FXII expression in human lung fibroblasts. Treatment of human lung fibroblasts with TGF-beta1 resulted in a time-dependent increase in FXII production, activation of p44/42, p38, JNK, and Akt, and phosphorylation and translocation into the nucleus of Smad3. However, TGF-beta1-induced FXII expression was repressed only by the JNK inhibitor and JNK and Smad3 antisense oligonucleotides but not by MEK, p38, or phosphoinositide 3-kinase blockers. JNK inhibition had no effect on TGF-beta1-induced Smad3 phosphorylation, association with Smad4, and its translocation into the nucleus but strongly suppressed Smad3-DNA complex formation. FXII promoter analysis revealed that the -299/+1 region was sufficient for TGF-beta1 to induce FXII expression. Sequence analysis of this region detected a potential Smad-binding element at position -272/-269 (SBE-(-272/-269)). Chromatin immunoprecipitation and streptavidin pulldown assays demonstrated TGF-beta1-dependent Smad3 binding to SBE-(-272/-269). Mutation or deletion of SBE-(-272/-269) substantially reduced TGF-beta1-mediated activation of the FXII promoter. Clinical relevance was demonstrated by elevated FXII levels and its co-localization with fibroblasts in the lungs of patients with acute respiratory distress syndrome. Our results show that JNK/Smad3 pathway plays a critical role in TGF-beta1-induced FXII expression in human lung fibroblasts and implicate its possible involvement in pathological conditions characterized by elevated TGF-beta1 levels.

Surfactant phospholipids, surfactant proteins, and inflammatory markers during acute lung injury in children

OBJECTIVE

To explore the pathophysiology of acute lung injury in children.

DESIGN

Prospective cohort study.

SETTING

Regional University Hospital, pediatric intensive care unit.

PATIENTS

Children without a preexisting lung injury who developed acute lung injury and were intubated were eligible for the study. Children without lung injury and intubated for minor surgical procedures acted as controls.

INTERVENTIONS

Bronchoalveolar lavage fluid and blood were collected on days 1 to 4, weekly, and immediately before extubation during acute lung injury. Molecular species compositions of phosphatidylcholine were determined by electrospray ionization mass spectrometry of lipid extracts of bronchoalveolar lavage fluid supernatants. Surfactant proteins A, B, and D and interleukin-8 were measured in bronchoalveolar lavage fluid and plasma by enzyme-linked immunosorbent assay and Western blotting.

MEASUREMENTS AND MAIN RESULTS

Eighteen children with acute lung injury were enrolled in the study and compared with eight controls. In children with acute lung injury, there were significant changes in the bronchoalveolar lavage fluid phosphatidylcholine species. Bronchoalveolar lavage fluid dipalmitoyl phosphatidylcholine (PC 16:0/16:0) and palmitoyl-myristoyl phosphatidylcholine (PC 16:0/14:0) significantly deceased during acute lung injury (p < .001 and p < .001, respectively), whereas oleoyl-linoleoyl PC (18:1/18:2), palmitoyl-linoleoyl PC (16:0/18:2) and stearoyl-linoleoyl PC (18:0/18:2) characteristic of plasma PC were significantly increased (p < .05, p < .02, and p < .05 respectively), as well as palmitoyl-oleoyl PC (16:0/18:1), and stearoyl-arachidonoyl PC (18:0/20:4) which are characteristic of cell membranes (p < .02, and p < .02, respectively). There were no significant changes to bronchoalveolar lavage fluid, surfactant protein A or B levels compared with controls during acute lung injury, whereas bronchoalveolar lavage fluid, surfactant protein D, and interleukin-8 levels significantly increased (p < .05 and p < .02, respectively). In plasma during acute lung injury, there were significant increases in surfactant proteins A, B, and D, and interleukin-8 (p < .001, p < .001, p < .05, and p < .001, respectively).

CONCLUSION

Changes to the phosphatidylcholine profile, surfactant proteins, and inflammatory markers of bronchoalveolar lavage fluid and plasma in children with acute lung injury are consistent with an alveolar/blood leakage and inflammatory cell membrane degradation products. These changes are due to alveolar capillary membrane damage and cellular infiltration.

Selective medicated (saline + natural surfactant) bronchoalveolar lavage in unilateral lung contusion. A clinical randomized controlled trial

OBJECTIVE

Open lung and low tidal volume ventilation appear to be a promising ventilation for chest trauma as it can reduce ARDS and improve outcome. Local therapy (e.g. BAL) can be synergic to remove from the lung the debris, mitigate inflammatory cascade and avoid damage spreading to not compromised lung areas.

MATERIALS AND METHODS

44 pulmonary contused patients were randomized to receive broncho-suction and volume controlled low tidal volume ventilation-VCLTVV (Control Group) or the same ventilation plus medicated (saline + surfactant) BAL (Treatment Group). Tidal volume <10 ml/kg, PEEP of 10-12 cm H(2)O and PaO(2) 60-100 mm Hg and PaCO(2) 35-45 mm Hg were used in both groups. BAL was performed using a fiberscope. 4 boluses of 25 ml saline with 2.4 mg/ml of surfactant were introduced into each contused lobe in which, subsequently, 240 mg of surfactant was instilled.

RESULTS

All patients survived. In the Control Group 18 patients developed pneumonia, 5 ARDS and days of intubation were 11.50 (3.83) compared to 5.05 (1.21) of Treatment Group in which OI and PaO(2)/FiO(2) significantly improved from 36 h.

CONCLUSIONS

VCLTVV alone was not able to prevent ARDS and infection in the Control Group as the reduction of intubation. In the Treatment Group, VCLTVV and medicated BAL facilitated the removal of degradated lung material and recruited the contused lung regions, enabling the healing of the lung pathology.

Fibrinogen binding to ICAM-1 promotes EGFR-dependent mucin production in human airway epithelial cells

Mucous hypersecretion is a serious feature of chronic airway diseases such as asthma, chronic obstructive pulmonary disease (COPD), and cystic fibrosis. Although mucins are produced via activation of an EGF receptor (EGFR) signaling cascade, the mechanisms leading to exaggerated mucin production in mucous hypersecretory diseases are unknown. Because expression of ICAM-1 and of the ICAM-1 ligand fibrinogen is increased in the airways of subjects with mucous hypersecretory diseases, we hypothesized that fibrinogen binding to ICAM-1 could increase EGFR-dependent mucin production in human airway (NCI-H292) epithelial cells. Consistent with this hypothesis, we found that an ICAM-1 neutralizing antibody and an ICAM-1(8-22) peptide that binds fibrinogen decreased mucin production induced by the EGFR ligand transforming growth factor (TGF)-alpha dose-dependently. Exogenous fibrinogen and a fibrinogen(117-133) peptide that binds ICAM-1 rescued mucin production in cells treated with the ICAM-1(8-22) peptide. Surprisingly, the ICAM-1(8-22) peptide increased EGFR phosphotyrosine and phospho-ERK1/2 in cells treated with TGF-alpha. The ICAM-1(8-22) peptide-induced increases in EGFR phosphotyrosine and phospho-ERK1/2 were prevented by exogenous fibrinogen, by the fibrinogen(117-133) peptide, and by selective inhibitors of phospholipase C (PLC), protein kinase C (PKC)-alpha/beta, and metalloproteases. These results suggest that fibrinogen binding to ICAM-1 promotes mucin production by decreasing TGF-alpha-induced EGFR and ERK1/2 activation and that the fibrinogen-ICAM-1-dependent decrease in EGFR and ERK1/2 activation occurs via inhibition of an early positive feedback pathway involving PLC- and PKC-alpha/beta-dependent metalloprotease activation and subsequent metalloprotease-dependent EGFR reactivation.

[Value of surfactant replacement therapy in the treatment of acute respiratory distress syndrome]

Acute respiratory distress syndrome (ARDS) is a common, devastating clinical problem arising from a number of conditions, such as pneumonia, trauma or sepsis. Because of its significant mortality and morbidity, ARDS has been in the focus of extensive experimental and clinical research. Since there is little doubt that alterations of the surfactant system contribute to lung dysfunction and the onset of ARDS, several clinical studies examined the therapeutic safety and efficacy of a surfactant replacement therapy. Clinical experience with exogenous surfactant has proven inconsistent as a therapeutic modality for adult patients with ARDS. This is mainly due to a number of confounding factors, e.g. severity of injury at the time of treatment, dosing regimes and delivery methods used in different trials. However, current data suggest that patients with direct ARDS (e.g. pneumonia, aspiration) could benefit from surfactant replacement therapy rather than patients with indirect ARDS (e.g. sepsis, trauma). Although surfactant replacement therapy has been shown to significantly reduce mortality in neonates with ARDS, there has been no large randomised clinical trial showing that exogenous surfactant improves outcome in adults with respiratory failure. Therefore, surfactant therapy cannot be recommended for routine clinical use in adult patients and has to be considered as a last resort treatment.

Pediatric acute lung injury

Among ventilated children, the incidence of acute lung injury (ALI) was 9%; of that latter group 80% developed the acute respiratory distress syndrome (ARDS). The population-based prevalence of pediatric ARDS was 5.5 cases/100.000 inhabitants. Underlying diseases in children were septic shock (34%), respiratory syncytial virus infections (16%), bacterial pneumonia (15%), near-drowning 9%, and others. Mortality ranged from 18% to 27% for ALI (including ALI-non ARDS and ARDS) and from 29% to 50% for ARDS. Mortality was only 3%-11% in children with ALI-non ARDS. As risk factors, oxygenation indices and multi-organ failure have been identified. New insights into the pathophysiology (for example the interplay between intraalveolar coagulation/fibrinolysis and inflammation and the genetic polymorphism for the angiotensin-converting enzyme) offer new therapeutic options. Lung protective mechanical ventilation with optimal lung recruitment is the mainstay of supportive therapy. New therapeutic modalities refer to corticosteroid and surfactant treatment. Well-designed follow up studies are needed.

Adsorption and direct probing of fibrinogen and sodium myristate at the air/water interface

Fibrinogen (FB), a serum protein, is considered a major inhibitor of lung surfactant function at the lining layer of the alveoli. In this study, the adsorption of aqueous bovine FB at the air/water interface was investigated with tensiometry and directly probed for the first time with ellipsometry and infrared reflection adsorption spectroscopy (IRRAS). The tension results show that FB has moderate surface activity. The surface densities of FB were calculated by using two different ellipsometry models to range from 3+/-0.2 to 17+/-2 mg/m2, for 7.5 to 750 ppm of FB in water at 25 degrees C. Although FB at concentrations from 75 to 750 ppm reached about the same steady surface tension value, the surface densities at 750 ppm FB were substantially larger. The same techniques were used for studying aqueous mixtures of 7.5 to 750 ppm FB with 2 mM of sodium myristate (SM) to investigate a possible interaction of the SM with the protein. The behavior of the FB/SM mixtures was found to be close to that of SM alone. The surface tension of the FB/SM mixtures reached values less than 10 mN/m under surface area oscillation at 20 or 80 rpm. These results and the ellipsometry and the IRRAS results indicate that at a concentration of 2 mM SM, FB, up to 750 ppm, does not inhibit the surfactant surface-tension-lowering function. In certain cases the results demonstrate that FB and SM may act cooperatively in lowering the surface tension.

Raised protein levels and altered cellular expression of factor VII activating protease (FSAP) in the lungs of patients with acute respiratory distress syndrome (ARDS)

BACKGROUND

The acute respiratory distress syndrome (ARDS) is characterised by inflammation of the lung parenchyma and changes in alveolar haemostasis with extravascular fibrin deposition. Factor VII activating protease (FSAP) is a recently described serine protease in plasma and tissues known to be involved in haemostasis, cell proliferation and migration.

METHODS

The level of FSAP protein expression was examined by western blotting/ELISA/immunohistochemistry and its activity was investigated by coagulation/fibrinolysis assays in plasma, bronchoalveolar lavage (BAL) fluid and lung tissue of mechanically ventilated patients with early ARDS and compared with patients with cardiogenic pulmonary oedema and healthy controls. Cell culture experiments were performed to assess the influence of different inflammatory stimuli on FSAP expression by various cell populations of the lung.

RESULTS

FSAP protein level and activity were markedly increased in the plasma and BAL fluid of patients with ARDS with a significant contribution to the increased alveolar procoagulant activity. Immunoreactivity for FSAP was observed in alveolar macrophages, bronchial epithelial and endothelial cells of lungs of patients with ARDS, while in controls the immunoreactivity for FSAP was restricted to alveolar macrophages. Only a low basal level of FSAP expression was detected in these cell populations. However, FSAP-specific mRNA expression was induced by lipopolysaccharide and interleukin-8 in human lung microvascular endothelial cells and in bronchial epithelial cells. FSAP was also found to be taken up by alveolar macrophages and degraded within the lysosomal compartment.

CONCLUSIONS

Increased levels of FSAP and an altered cellular expression pattern are found in the lungs of patients with ARDS. This may represent a novel pathological mechanism which contributes to pulmonary extravascular fibrin deposition and may also modulate inflammation in the acutely injured lung via haemostasis-independent cellular activities of FSAP.

Antithrombin for respiratory distress syndrome in preterm infants

BACKGROUND

Acquired Antithrombin (AT) deficiency is a common and prognostically important finding in sick preterm infants with respiratory distress syndrome (RDS). It has been hypothesised that AT concentrate may improve clinical outcomes in preterm infants with RDS.

OBJECTIVES

To determine whether the administration of AT concentrate decreases mortality in preterm infants with RDS compared with placebo or no treatment.

SEARCH STRATEGY

An electronic literature search in the Cochrane Central Register of Controlled Trials, MEDLINE, and EMBASE in August 2006 was performed. No language restriction was applied. References from identified studies were cross-checked for possible additional studies. Experts in the field and pharmaceutical companies were contacted for unpublished data. Abstracts of the American Society of Pediatric Research and European Society of Pediatric Research meetings (1983-2005) were searched and authors of relevant studies were contacted to obtain additional information.

SELECTION CRITERIA

Randomized controlled trials comparing any dose and duration of AT therapy with placebo or no treatment in preterm infants with RDS.

DATA COLLECTION AND ANALYSIS

Two reviewers independently extracted data from included studies regarding mortality, intraventricular hemorrhage, mechanical ventilation, and other reported events in the clinical course of the patients. Data for similar outcomes were combined where appropriate, using a fixed-effects model in MetaView 4.2 (Update Software).

MAIN RESULTS

Two trials consisting of 182 preterm infants, fulfilled the inclusion criteria. Mean gestational age of patients included was 28 weeks. In one trial, patients had to be intubated and ventilated for RDS to be eligible for the study. In the other trial, RDS was not mentioned as an inclusion criteria, however the vast majority of infants in the study received surfactant. No individual trial showed a significant difference in mortality. One of the trials was stopped early because of an increase in deaths in the AT group. The pooled analysis for mortality within the first week of life showed a typical relative risk of 2.67 (95% CI 0.72-9.83) in favour of the control group. Only the trial that was stopped early followed the infants long enough to report neonatal mortality. This trial reported 7 deaths (11.5%) in the AT group and two deaths (3.3%) in the placebo group within 28 days of life. Secondary outcomes included days of mechanical ventilation and supplemental oxygen which were only reported in 1 trial. Both outcomes were in favour of the control group and statistically significant (p < 0.05).

AUTHORS' CONCLUSIONS

Preterm infants with RDS are unlikely to benefit from AT treatment and may be harmed.

High concentrations of plasminogen activator inhibitor-1 in lungs of preterm infants with respiratory distress syndrome

BACKGROUND

Among preterm infants, respiratory distress syndrome (RDS) is characterized by the presence of intraalveolar fibrin deposition. Fibrin monomers inhibit surfactant function effectively. However, little is known about potential disturbances of intraalveolar fibrinolysis in RDS. We studied levels of major plasminogen activator inhibitor-1 (PAI-1), tissue-type plasminogen activator (tPA), and urokinase-type plasminogen activator (uPA) in lungs of preterm infants with RDS.

METHODS

The antigen levels of PAI-1, tPA, and uPA were measured in 262 samples of tracheal aspirate fluid collected from 37 intubated preterm infants during the first 2 postnatal weeks. To examine the expression of PAI-1, tPA, and uPA in lung tissue, immunohistochemical analyses were performed on autopsy specimens from 7 preterm infants with RDS and 6 newborn infants without pulmonary pathologic conditions.

RESULTS

For infants with an immature surfactant profile, as indicated by lecithin/sphingomyelin ratios in tracheal aspirate fluid of < 10, PAI-1 levels and ratios of PAI-1 to uPA and tPA were significantly higher during postnatal days 1 to 2, compared with infants with lecithin/sphingomyelin ratios of > or = 10. Moreover, infants who subsequently developed bronchopulmonary dysplasia (BPD) (n = 15) had higher PAI-1 levels on days 3 to 4 and days 7 to 8 than did those who survived without BPD. For preterm infants with RDS, immunohistochemical analyses demonstrated increased expression of PAI-1, tPA, and uPA predominantly in alveolar epithelium.

CONCLUSIONS

High concentrations of PAI-1 and an increased ratio of PAI-1 to uPA, with a concurrently less-increased ratio of PAI-1 to tPA, are associated with the severity of RDS among preterm infants during the first postnatal days. Pulmonary inhibition of fibrinolysis is a pathophysiologic feature of RDS and may play a role in the development of BPD.

Bilateral lavage with diluted surfactant improves lung function after unilateral lung contusion in pigs*

OBJECTIVE

This study evaluates the effects of bronchoalveolar lavage with diluted surfactant on unilateral lung contusion-induced lung dysfunction.

DESIGN

Randomized prospective animal study.

SETTING

An animal laboratory.

SUBJECTS

Twenty adult pigs, weighing 25-35 kg.

INTERVENTIONS

Animals were randomly assigned to controls and surfactant treatment. Bilateral lavage with surfactant treatment began 30 mins after unilateral lung contusion. Then 25 mg/kg of body weight diluted Curosurf (5 mg/mL) was applied in a volume of 5 mL/kg of body weight. Observation time was 8 hrs postinjury.

MEASUREMENTS AND MAIN RESULTS

The Pao2/Fio2 ratio fell from 500 to 250 and then recovered gradually in controls and surfactant-treated pigs. After another 4 hrs, the Pao2/Fio2 ratio deteriorated again in controls, but not in surfactant-treated animals. Total compliance fell by 50% after injury but was completely restored by surfactant treatment. Lung contusion increased the median number of neutrophils in bronchoalveolar lavage fluid from 2% to 30% of total cells and peaked >60% at 480 mins in the contused lungs of control pigs. Surfactant-treated pigs had 40% neutrophils at 480 mins without reaching significant difference to controls. The leukocyte neutral proteinase inhibitor increased to 500 ng/mL at 30 mins postinjury in the contused lungs and increased to 2000 ng/mL after surfactant treatment.

CONCLUSIONS

Bilateral bronchoalveolar lavage with diluted surfactant can effectively improve lung function after experimental unilateral lung contusion in pigs.

Extravascular fibrin, plasminogen activator, plasminogen activator inhibitors, and airway hyperresponsiveness

Mechanisms underlying airway hyperresponsiveness are not yet fully elucidated. One of the manifestations of airway inflammation is leakage of diverse plasma proteins into the airway lumen. They include fibrinogen and thrombin. Thrombin cleaves fibrinogen to form fibrin, a major component of thrombi. Fibrin inactivates surfactant. Surfactant on the airway surface maintains airway patency by lowering surface tension. In this study, immunohistochemically detected fibrin was seen along the luminal surface of distal airways in a patient who died of status asthmaticus and in mice with induced allergic airway inflammation. In addition, we observed altered airway fibrinolytic system protein balance consistent with promotion of fibrin deposition in mice with allergic airway inflammation. The airways of mice were exposed to aerosolized fibrinogen, thrombin, or to fibrinogen followed by thrombin. Only fibrinogen followed by thrombin resulted in airway hyperresponsiveness compared with controls. An aerosolized fibrinolytic agent, tissue-type plasminogen activator, significantly diminished airway hyperresponsiveness in mice with allergic airway inflammation. These results are consistent with the hypothesis that leakage of fibrinogen and thrombin and their accumulation on the airway surface can contribute to the pathogenesis of airway hyperresponsiveness.

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.

Prevention of Bleomycin-induced Lung Fibrosis by Aerosolization of Heparin or Urokinase in Rabbits

Bleomycin is a well known fibrogenic agent, provoking an initial adult respiratory distress syndrome-like injury with subsequent strong fibroproliferative response. Severe abnormalities of the alveolar surfactant system, which may be linked to the appearance of alveolar fibrin deposition, have been implicated in the pathogenetic sequence of events. Using a model of standardized aerosol delivery of 1.8 U bleomycin/kg body weight in rabbits, we investigated the influence of repetitive nebulization of heparin or urokinase-type plasminogen activator (u-PA) on the development of lung fibrosis. In an "early" (Days 2-12 postbleomycin) or "late" (Days 14-24 post-bleomycin) treatment protocol, approximately 3,500 U heparin or approximately 6,500 U u-PA was delivered to the bronchoalveolar space. Within four weeks, the bleomycin challenge provoked severe pulmonary fibrosis with reduction of lung compliance, marked increase in soluble collagen (bronchoalveolar lavage fluid) and hydroxyproline content (lung tissue), a typical reticular fibrosis pattern on high-resolution computed tomography, and typical histologic findings. Therapeutic intervention resulted in a far-reaching normalization of compliance, suppression of soluble collagen and hydroxyproline accumulation, and virtual abrogation of the computed tomography scan and histologic features of lung fibrosis, with most prominent effects seen in the early heparin and late u-PA administration. No bleeding complications occurred. These findings strongly support the concept that alveolar fibrin generation is an important event in the development of postbleomycin lung fibrosis. "Compartmentalized" anticoagulation and/or fibrinolysis via inhalational deposition of interventional agents in the alveolar compartment may thus offer a new therapeutic strategy for prevention of fibrosis.

Fibrinolysis-inhibitory capacity of clot-embedded surfactant is enhanced by SP-B and SP-C

Incorporation of pulmonary surfactant into fibrin inhibits its plasmic degradation. In the present study we investigated the influence of surfactant proteins (SP)-A, SP-B, and SP-C on the fibrinolysis-inhibitory capacity of surfactant phospholipids. Plasmin-induced fibrinolysis was quantified by means of a (125)I-fibrin plate assay, and surfactant incorporation into polymerizing fibrin was analyzed by measuring the incorporation of (3)H-labeled L-alpha-dipalmitoylphosphatidylcholine into the insoluble clot material. Incorporation of a calf lung surfactant extract (Alveofact) and an organic extract of natural rabbit large surfactant aggregates (LSA) into a fibrin clot revealed a stronger inhibitory effect on plasmic cleavage of this clot than a synthetic phospholipid mixture (PLX) and unprocessed LSA. Reconstitution of PLX with SP-B and SP-C increased, whereas reconstitution with SP-A decreased, the fibrinolysis-inhibitory capacity of the phospholipids. The SP-B effect was paralleled by an increased incorporation of phospholipids into fibrin. We conclude that the inhibitory effect of surfactant incorporation into polymerizing fibrin on its susceptibility to plasmic cleavage is enhanced by SP-B and SP-C but reduced by SP-A. In the case of SP-B, increased phospholipid incorporation may underlie this finding.

Heparin nebulization attenuates acute lung injury in sepsis following smoke inhalation in sheep

Pseudomonas pneumonia is a common complication of smoke inhalation injury. Airway casts formed from clotted mucous occur frequently in this condition. A recent report shows that intravenous heparin improves oxygenation and reduces lung damage in a sheep model of smoke inhalation. We hypothesized that nebulized heparin could be an effective means of reducing cast formation. Female sheep (n = 19) were surgically prepared for a study of acute lung injury (ALI). After a tracheotomy, 48 breaths of cotton smoke (<40 degrees C) were inflated into the airway. Afterwards, live Pseudomonas aeruginosa (5 x 10(11) CFU) was instilled into the lung. All sheep were mechanically ventilated with 100% O2 and were divided into four groups: a heparin-nebulized group (n = 5; animals received aerosolized heparin [10,000 I.U.] 1 h after the bacterial instillation and subsequently every 4 h thereafter), an intravenous heparin group (n = 5,300 U/kg/23 h, infusion was started 1 h after the injury), a saline-nebulization group (n = 5; animals received inhaled nebulized saline), and a sham injury group (n = 4, treated in the same fashion, but no injury). The animals were sacrificed after 24 h of mechanical ventilation, and lung samples were harvested. Sheep exposed to lung injury presented with typical hyperdynamic cardiovascular changes and a corresponding drop in PaO2. These changes were significantly attenuated in the heparin groups. Histological changes consisting of cellular infiltrates, lung edema, congestion, and cast formation were reduced by heparin. These data suggest that nebulized inhaled heparin is a beneficial therapy for sepsis-induced ALI.

An ELISA technique for quantification of surfactant apoprotein (SP)-C in bronchoalveolar lavage fluid

Pulmonary surfactant apoprotein C (SP-C) is a small, unique peptide that contributes to the reduction of alveolar surface tension. Due to the extreme hydrophobic nature of this peptide it was hitherto not possible to quantify SP-C in biological samples by immunological techniques. Using a newly developed polyclonal antibody raised against recombinant human SP-C in rabbits, we now describe an enzyme-linked immunosorbent assay (ELISA) to quantitate SP-C in bronchoalveolar lavage fluid (BALF). Solid phase binding of the hydrophobic SP-C was achieved by transfer of the standard or BALF samples (diluted in 80% isopropanol, pH 3.5) to polystyrene microtiter plates. Sequential treatment with trifluoroethanol and methanol (2x) was employed to improve antigen presentation and to minimize the influence of phospholipids. With this assay, SP-C from human, rabbit, porcine, and bovine surfactant was detectable. No cross-reactivity of the antibody to human SP-A and monomeric and dimeric SP-B was encountered. Total serum proteins did not affect ELISA signals, as evident from spiking experiments. The detection limit of the ELISA ranged below 3 ng/ml, and intra- and interassay coefficients of variation were 3.5% (n = 16) and 5.3% (n = 6), respectively. Serial dilutions of BALF showed good linearity, and excellent recovery rates were obtained upon spiking of human BALF. A mean value of 579.5 +/- 45.9 ng/ml (mean +/- SEM) SP-C was found in BALF samples of human healthy volunteers (n = 22), corresponding to 26.61 +/- 1.91 microg SP-C/mg total phospholipids (PL). SP-C levels were significantly lower in BALF of patients with acute respiratory distress syndrome (ARDS) (286.9 +/- 19.8 ng/ml [p < 0.001]; 13.92 +/- 1.93 microg SP-C/mg PL [p < 0.001], n = 48). We conclude that SP-C may be quantified with high specificity, reproducibility, and sensitivity in bronchoalveolar lavage samples by the presently described ELISA technique and that SP-C levels are significantly decreased in ARDS.

Surfactant alteration and replacement in acute respiratory distress syndrome

The acute respiratory distress syndrome (ARDS) is a frequent, life-threatening disease in which a marked increase in alveolar surface tension has been repeatedly observed. It is caused by factors including a lack of surface-active compounds, changes in the phospholipid, fatty acid, neutral lipid, and surfactant apoprotein composition, imbalance of the extracellular surfactant subtype distribution, inhibition of surfactant function by plasma protein leakage, incorporation of surfactant phospholipids and apoproteins into polymerizing fibrin, and damage/inhibition of surfactant compounds by inflammatory mediators. There is now good evidence that these surfactant abnormalities promote alveolar instability and collapse and, consequently, loss of compliance and the profound gas exchange abnormalities seen in ARDS. An acute improvement of gas exchange properties together with a far-reaching restoration of surfactant properties was encountered in recently performed pilot studies. Here we summarize what is known about the kind and severity of surfactant changes occurring in ARDS, the contribution of these changes to lung failure, and the role of surfactant administration for therapy of ARDS.

Conebulization of surfactant and urokinase restores gas exchange in perfused lungs with alveolar fibrin formation

Alveolar fibrin generation has been suggested to possess strong surfactant-inhibitory potency. In perfused rabbit lungs, fibrin formation in the alveolar space was induced by sequential ultrasonic aerosolization of fibrinogen and thrombin, and the efficacy of rescue administration of surfactant and urokinase was investigated. Ventilation-perfusion (VA/Q) distribution was assessed by the multiple inert gas elimination technique. Aerosolization of fibrinogen (approximately 20 mg/kg body wt) increased shunt flow to approximately 7%. Sequential nebulization of fibrinogen and thrombin (1.3 U/kg body wt) caused alveolar fibrin deposition, documented immunohistologically, and provoked marked shunt flow, progressing to approximately 22% at the end of the experiments. The hemodynamics were virtually unchanged. Rescue aerosolization of natural bovine surfactant (15 mg/kg body wt) or urokinase-type plasminogen activator (4,500 U/kg body wt), undertaken after fibrin formation, improved gas exchange but progressive shunt flow still occurred (efficacy, surfactant > urokinase). In contrast, conebulization of surfactant and urokinase reversed shunt flow to approximately 7%, with an increased appearance of normal VA/Q matching. We conclude that alveolar fibrin formation is a potent surfactant-inhibitory mechanism in intact lungs, provoking severe VA/Q mismatch with a predominance of shunt flow, and that rescue aerosolization of surfactant plus urokinase may offer restoration of gas exchange under these conditions.

Surfactant components modulate fibroblast apoptosis and type I collagen and collagenase-1 expression

During lung injury, fibroblasts migrate into the alveolar spaces where they can be exposed to pulmonary surfactant. We examined the effects of Survanta and surfactant protein A (SP-A) on fibroblast growth and apoptosis and on type I collagen, collagenase-1, and tissue inhibitor of metalloproteinase (TIMP)-1 expression. Lung fibroblasts were treated with 100, 500, and 1,000 microg/ml of Survanta; 10, 50, and 100 microg/ml of SP-A; and 500 microg/ml of Survanta plus 50 microg/ml of SP-A. Growth rate was evaluated by a formazan-based chromogenic assay, apoptosis was evaluated by DNA end labeling and ELISA, and collagen, collagenase-1, and TIMP-1 were evaluated by Northern blotting. Survanta provoked fibroblast apoptosis, induced collagenase-1 expression, and decreased type I collagen affecting mRNA stability approximately 10-fold as assessed with the use of actinomycin D. Collagen synthesis and collagenase activity paralleled the gene expression results. SP-A increased collagen expression approximately 2-fold and had no effect on collagenase-1, TIMP-1, or growth rate. When fibroblasts were exposed to a combination of Survanta plus SP-A, the effects of Survanta were partially reversed. These findings suggest that surfactant lipids may protect against intraluminal fibrogenesis by inducing fibroblast apoptosis and decreasing collagen accumulation.

Alveolar fibrin formation caused by enhanced procoagulant and depressed fibrinolytic capacities in severe pneumonia. Comparison with the acute respiratory distress syndrome

Changes in the alveolar hemostatic balance in severe pneumonia were compared with those in the acute respiratory distress syndrome (ARDS). Analysis was performed in bronchoalveolar lavage fluids (BALF) of patients with ARDS triggered by nonpulmonary underlying events in the absence of lung infection (ARDS; n = 25), pneumonia demanding mechanical ventilation (PNEU-vent; n = 114), spontaneously breathing patients with pneumonia (PNEU-spon; n = 40), and ARDS in combination with lung infection (ARDS+PNEU; n = 43); comparison with healthy control subjects (n = 35) was performed. In all groups of patients, BALF total procoagulant activity was increased by nearly two orders of magnitude, being largely attributable to the tissue factor pathway of coagulation. Concomitantly, markedly reduced overall fibrinolytic capacity (fibrin plate assay) was noted in the lavage fluids of all patients. BALF levels of urokinase-type plasminogen activator were significantly reduced throughout, whereas the lavage concentrations of tissue-type plasminogen activator did not differ from those in control subjects. In addition, markedly enhanced levels of plasminogen activator- inhibitor I and alpha(2)-antiplasmin were noted in ARDS, ARDS+PNEU, and PNEU-vent, but not in PNEU-spon. In all groups of patients, the changes in the lavage enzymatic activities were paralleled by manifold increased BALF concentrations of fibrinopeptide A and D-dimer, reflecting in vivo coagulation processes. Within the overall number of patients with pneumonia, changes in the alveolar hemostatic balance were more prominent in alveolar and interstitial pneumonia than in bronchopneumonia. Acute inflammatory lung injury, whether triggered by nonpulmonary systemic events or primary lung infection, is thus consistently characterized by both enhanced procoagulant and depressed fibrinolytic activities in the alveolar lining layer, with the appearance of fibrin formation in this compartment. Profile and extent of changes in severe pneumonia demanding respirator therapy are virtually identical to those in ARDS, whereas somewhat less prominent alterations of the alveolar hemostatic balance are noted in spontaneously breathing patients with pneumonia.

Cleavage of surfactant-incorporating fibrin by different fibrinolytic agents. Kinetics of lysis and rescue of surface activity

Incorporation of surfactant into polymerizing fibrin causes loss of surface activity and marked retardation of clot lysis by plasmin (Günther and colleagues, Am. J. Physiol. 1994;267:L618-L624). We compared the efficacy of tissue-type plasminogen activator (t-PA), urokinase-type plasminogen activator (u-PA), activated anisoylated streptokinase-plasminogen activator complex (APSAC), and plasmin to dissolve surfactant-incorporating fibrin. Alveofact was employed as a natural surfactant source, and plasminogen was coincorporated into the fibrin matrix at a physiologic ratio to fibrin. Fibrinolysis was quantified by the release of tracer from (125)I-labeled fibrin, and the pattern of split products was characterized by sodium dodecyl sulfate polyacrylamide gel electrophoresis. In addition, we investigated the fibrinolysis-related restoration of surface activity by measurement in the pulsating bubble surfactometer. Concentrations of all fibrinolytic agents were chosen to effect approximately 40% lysis of clot material in the absence of surfactant (control). When incorporated into the fibrin matrix, but not when admixed after clot formation, surfactant inhibited the cleavage of fibrin by all fibrinolytic agents in a dose-dependent manner. Interestingly, t-PA and u-PA were significantly less inhibited than was plasmin or APSAC. The pattern of arising fibrin scission products was identical for all fibrinolytic approaches and was independent of surfactant incorporation. Adsorption and minimum surface tension-lowering properties of Alveofact were almost completely lost upon incorporation into fibrin, but surface activity was fully restored upon sustained clot lysis with all fibrinolytic agents. We conclude that the fibrinolytic capacity of all agents investigated is markedly inhibited by surfactant incorporation in fibrin, but this inhibition is significantly less pronounced in the agents employing preincorporated plasminogen (t-PA and u-PA), as compared with plasmin and APSAC. The plasminogen activators may thus proffer to "rescue" pulmonary surfactant function by induction of fibrinolysis in the alveolar compartment.

Local effect of lung contusion on lung surfactant composition in multiple trauma patients

OBJECTIVE

The aim of this study was to investigate the direct influence of lung contusion on pulmonary surfactant in multiple trauma patients.

DESIGN

Prospective, nonrandomized study.

SETTING

University hospital, trauma intensive care unit.

PATIENTS

Eighteen multiple trauma patients with unilateral lung contusions and Injury Severity Scores >19 were studied prospectively.

INTERVENTIONS

Bronchoalveolar lavage was performed daily until either day 7 or extubation. Samples from the side of lung contusion (n = 62) and the contralateral, uninjured side (n = 62) were obtained at the same time in 14 patients. Total phospholipids, total phospholipid classes, and surfactant apoprotein A were quantified. Additionally, surfactant function was measured with a pulsating bubble surfactometer in four patients. All data are presented as mean +/- SEM. Statistical analyses were performed using programs of SPSS for Windows 6.1.3 (SPSS Inc., Chicago, IL) (Student's t-test; p < .05).

MEASUREMENTS AND MAIN RESULTS

Total phospholipids were significantly increased on the side of lung contusion (contusion side, 40+/-7 microg/mL; contralateral side, 21+/-3 microg/mL; p = .004). The percentage contents of phosphatidylcholine (contusion side, 87.1%+/-1.0%; contralateral side, 84.3%+/-1.0%; p = .04) and sphingomyelin (contusion side, 2.9%+/-0.3%; contralateral side, 1.9%+/-0.2%; p = .004) were significantly higher. In contrast, the percentage content of phosphatidylglycerol was significantly decreased (contusion side, 4.1%+/-0.1%; contralateral side, 6.9%+/-0.6%; p = .001). No alterations were found for the relative contents of phosphatidylethanolamine (contusion side, 2.4%+/-0.2%; contralateral side, 2.2%+/-0.2%; p = .47), phosphatidylinositol (contusion side, 3.5%+/-0.4%; contralateral side, 4.6%+/-0.5%; p = .06), and surfactant apoprotein A (contusion side, 7177+/-1404 ng/mL; contralateral side, 4513+/-787 ng/mL, p = .10). There was no statistical difference for minimal surface tension measured with the pulsating bubble surfactometer after 5 mins of oscillation (contusion side, 29.5+/-2.3 mN/m; contralateral side, 23.7+/-2.1 mN/m; p = .08).

CONCLUSIONS

Direct damage of lung parenchyma by lung contusion alters the composition of surfactant. No additional changes in surfactant function were observed that would argue in favor of functional compensation.

Inhibition of factor XIIIa-mediated incorporation of fibronectin into fibrin by pulmonary surfactant

Intra-alveolar deposition of exudated plasma proteins is a hallmark of acute and chronic inflammatory lung diseases. In particular, fibrin and fibronectin may provide a primary matrix for fibrotic lung remodeling in the alveolar compartment. The present study was undertaken to explore the effect of two surfactant preparations on the incorporation of fibronectin into fibrin. We observed that surfactant phospholipids are associated with insoluble fibrin, factor XIIIa-cross-linked fibrin, and cross-linked fibrin with incorporated fibronectin. Factor XIIIa-mediated binding of fibronectin to fibrin was noticeably altered in the presence of surfactant. Coincubation with two different commercially available surfactants but not with dipalmitoylphosphatidylcholine alone resulted in a reduction of fibronectin incorporation into fibrin clots by approximately one-third. This effect was not dependent on the calcium concentration. We conclude that 1) factor XIIIa-cross-linked fibrin-fibronectin is able to incorporate surfactant phospholipids in amounts comparable to fibrin clots without fibronectin and 2) the binding of fibronectin to fibrin is partially inhibited in the presence of pulmonary surfactant.

Heparin improves gas exchange during experimental acute lung injury in newborn piglets

Although intrapulmonary fibrin deposition is a pathognomonic feature of acute lung injury, it remains uncertain whether thrombin inhibitors affect clinically important outcomes. We hypothesized that both heparin and antithrombin (AT) concentrate improve gas exchange during experimental respiratory distress syndrome. We also tested whether combination therapy is more beneficial than monotherapy. Forty-eight newborn piglets were randomized within 12 litters to one of four groups in a factorial design: (1) AT; (2) heparin; (3) AT plus heparin; (4) untreated control animals. After lung lavage and 4 h of barovolutrauma, mechanical ventilation was continued for 24 h during which ventilator pressures and inspired oxygen were adjusted to maintain normal blood gases. The arterial/ alveolar oxygen tension ratio (a/A ratio) and the ventilator efficiency index (VEI) at 18 and 24 h were compared by repeated measures analysis of variance (ANOVA). In contrast to our hypothesis, only heparin improved gas exchange, and we found little evidence of an interaction with AT. The a/A ratio was 0.48 +/- 0.27 (mean +/- SD) in the presence of heparin versus 0.33 +/- 0.26 in its absence; p = 0.01. Corresponding VEI was 0.30 +/- 0.12 versus 0.25 +/- 0.14; p = 0.04. Hyaline membrane formation was also decreased in heparin-treated animals (p = 0.02).

A placebo-controlled randomized trial of antithrombin therapy in neonatal respiratory distress syndrome

Neonatal respiratory distress syndrome (RDS) is associated with decreased plasma activity of antithrombin (AT) and increased formation of thrombin. We tested whether AT reduces thrombin formation, improves gas exchange, and decreases the duration of mechanical ventilation and supplemental oxygen. One hundred twenty-two infants were randomized to pasteurized AT concentrate or to placebo. Two ml/kg (equivalent to 100 IU AT/kg) were followed by 1 ml/kg (50 IU/kg) every 6 h for 48 h. Outcome measures included plasma AT activity, thrombin-AT (TAT) complex, prothrombin fragment (F1+2), the ratio of arterial to alveolar oxygen pressure [(a/A)PO2], and the ventilator efficiency index (VEI). In the AT group (n = 61), mean (SD) birth weight was 1,198 (301) g, mean (SD) gestational age (GA) was 28.3 (2.0) wk, 54% were male. In the placebo group (n = 61), mean (SD) birth weight was 1,201 (315) g, mean (SD) GA was 28.8 (2. 3) wk, 51% were male. In treated infants, AT activity was raised to means of 1.69 and 2.25 U/ml at 24 and 48 h, respectively. Corresponding means in control infants were 0.37 and 0.44 U/ml (p < 0.0001). F1+2, but not TAT, was significantly reduced by AT (p = 0. 004). VEI and (a/A)PO2 were similar in both groups throughout the first week of life. Median days receiving mechanical ventilation were 7.1 (AT) versus 4.8 (placebo), p = 0.0014. Median days receiving supplemental oxygen were 7.9 (AT) versus 5.5 (placebo), p < 0.0001. There were seven (11.5%) deaths in the AT group and three (4.9%) deaths in the placebo group. We conclude that treatment with AT cannot be recommended in premature infants with RDS.

Effect of lung contusion on surfactant composition in multiple-trauma patients

OBJECTIVE

The aim of this study was to investigate alterations of the surfactant system in multiple-trauma patients (MTP) with lung contusion and the influence of single- or multiple-organ dysfunction syndrome (OF/MOF) on the surfactant system.

SETTING

University hospital, trauma-intensive care unit.

DESIGN

Prospective, nonrandomized study.

METHODS

MTP with an Injury Severity Score > 19 points have been recorded prospectively since 1992. Bronchoalveolar lavages were obtained daily either until day 14 or extubation. Three groups of MTP were compared: noL: MTP, no lung contusion (n = 14); LuCo-: MTP, lung contusion, no OF/MOF (n = 17); LuCo+: MTP, lung contusion, with OF/MOF (n = 10). Also, surfactant samples of 11 healthy volunteers (Con) were investigated and compared with MTP. All data were presented as mean +/- SEM. Statistical analysis were performed using programs of SPSS 6.0.1. (univariate ANOVA, Fisher's Exact Test, p < = 0.05).

RESULTS

There were no differences in sex and age. Injury Severity Score was significantly impaired in group LuCo+ (44 +/- 4), compared with groups noL (31 +/- 3) and LuCo- (34 +/- 3). Group noL showed no statistical differences for lung function, total protein, and total phospholipid content of the bronchoalveolar lavage compared with group LuCo-. Furthermore, the relative content of phosphatidylcholine and phosphatidylglycerol in total phospholipids and surfactant-associated protein A were not significantly altered compared with group LuCo-. Lung function in group LuCo+ was significantly impaired and led to hypoxemia on the day of trauma. Total protein content and total phospholipids were significantly elevated in group LuCo+ compared with groups noL and LuCo- on the first day. Also, the relative content of phosphatidylcholine was significantly increased in group LuCo+ up to day 4, compared with groups noL and LuCo-. In comparison with groups noL and LuCo-, a significant decrease of the relative content of phosphatidylglycerol was obtained in group LuCo+ up to day 7. The surfactant-associated protein A was increased in group LuCo+ during the whole observation time, compared with the other groups.

CONCLUSIONS

Multiple trauma leads to alterations in the surfactant system. The composition of surfactant was not further influenced by lung contusion alone. Only MTP with OF/MOF during the intensive care unit treatment showed significant alterations in surfactant composition and a decrease in lung function.

Comparative effects of some serum components and proteolytic products of fibrinogen on surface tension-lowering abilities of beractant and a synthetic peptide containing surfactant KL4

The serum components of C-reactive protein, lysophosphati-dylcholine, fibrinogen, and fibrinogen proteolytic products have been shown to reduce surface tension-lowering abilities of lung surfactant. The inhibitory effects of these serum components were compared among four different surfactants: natural lung surfactant, a phospholipid mixture that had no surfactant proteins, KL4 surfactant which has a synthetic surfactant protein B (SP-B)-like peptide, and beractant (BER) which has both SP-B and SP-C. The pulsating bubble surfactometer was used to measure the surface tension of these surfactants after the addition of inhibitors. Inhibition of BER and KL4 surfactant was observed with some serum components within 1 min of pulsation, but was reversed after 3 min of pulsation for KL4 surfactant and to a lesser extent with BER. The surface tension of phospholipid mixture alone was significantly increased and did not improve with further pulsations. Natural lung surfactant was least inhibited and was affected only at very high fibrinogen concentrations (5 mg/mL). At identical concentrations of these inhibitors, KL4 surfactant was inhibited less compared with BER. We conclude that the response of a lung surfactant to inhibitory agents may depend on the presence or absence of surfactant-related protein(s) in the surfactant and the concentration of exogenous surfactant used. KL4 surfactant, which has a synthetic peptide in lieu of SP-B, resists inhibition to these serum components more than BER at similar phospholipid concentrations.

Thrombin inhibitors reduce intrapulmonary accumulation of fibrinogen and procoagulant activity of bronchoalveolar lavage fluid during acute lung injury induced by pulmonary overdistention in newborn piglets

We determined whether antithrombin (AT III) or hirudin (a specific thrombin inhibitor) reduce both the accumulation of fibrinogen in lung parenchyma and the procoagulant activity of bronchoalveolar lavage (BAL) fluid during acute lung injury induced by pulmonary overdistention. Newborn piglets were randomized to six-hourly infusions of AT III concentrate, a continuous infusion of recombinant hirudin, or no anticoagulant therapy. All animals were subjected to 24 h of identical mechanical ventilation at high peak pressures (3.9 kPa or 40 cm H2O). Tidal volumes were raised to a mean of 69 mL/kg in all three groups. Mean AT III levels in supplemented piglets (n = 22) were increased to 1.46 (SD 0.24) U/mL at 24 h, compared with 0.67 (SD 0.16) U/mL in controls (n = 23). The median activated partial thromboplastin time in animals receiving hirudin (n = 18) was prolonged to 53 s versus 34 s in untreated animals. The intrapulmonary accumulation of i.v. administered 125I-fibrinogen was reduced by AT III concentrate or hirudin, compared with untreated littermates (p = 0.003). The procoagulant activity of BAL fluid was also decreased by both thrombin inhibitors (p = 0.001). Intrapulmonary accumulation of fibrinogen and the procoagulant activity of BAL fluid were reduced by AT III or hirudin during lung injury caused by pulmonary overdistention. Future investigations should determine whether tangible clinical benefits result from this reduced potential for fibrin deposition in the injured lung.

Plasminogen activator activity in preterm infants with respiratory distress syndrome: relationship to the development of bronchopulmonary dysplasia

Respiratory distress syndrome (RDS) is characterized by the presence of fibrin-rich exudates in the alveoli. Fibrin and its degradation products may play an important role in the pathogenesis of bronchopulmonary dysplasia (BPD). The purpose of this study was to test the hypothesis that preterm neonates with RDS have depressed alveolar fibrinolytic activity and that those with RDS progressing to BPD have an even greater impairment in alveolar fibrinolysis. Serial tracheal aspirate (TA) samples from intubated neonates--9 control and 46 with RDS--were analyzed for fibrinolytic activity. In neonates with RDS, 26 resolved, 18 progressed to BPD, and 2 died before 28 d. Plasminogen activator (PA) and its inhibitor (PAI) were identified in TA by reverse fibrin autography and immunoblotting. Net PA/plasmin activity in TA was significantly depressed on d 1 of life in patients with self-resolved RDS (median = 20.85 ng/mL, p < 0.05) and RDS progressing to BPD (median = 4.97 ng/mL, p < 0.001) compared with control patients (median = 87.1 ng/mL). In addition, neonates progressing to BPD had significantly lower PA/plasmin activity on day one of life compared with neonates with self-resolved RDS (p < 0.001). ELISA for specific PA and PAI were not significantly different. We speculate that depressed fibrinolytic activity may place preterm neonates at risk for RDS and that the degree of this depression may predict the progression to BPD. In infants < or = 30 wk of gestation at birth with RDS, a PA/plasmin activity < or = 10.0 ng/mL on the 1st d of life had a positive predictive value of 80% (12/15) and a negative predictive value of 82% (9/11) for the progression to BPD.