Role of enzymes mediating thrombosis and thrombolysis in lung disease

D-dimers-"Normal" Levels versus Elevated Levels Due to a Range of Conditions, Including "D-dimeritis," Inflammation, Thromboembolism, Disseminated Intravascular Coagulation, and COVID-19

D-dimers reflect a breakdown product of fibrin. The current narrative review outlines how D-dimers can arise in normal individuals, as well as in patients suffering from a wide range of disease states. D-dimers in normal individuals without evident thrombosis can arise from background fibrinolytic activity in various tissues, including kidney, mammary and salivary glands, which ensures smooth flow of arising fluids where any blood contamination could be immediately lysed. In addition, healthy individuals can also regularly sustain minor injuries, often unbeknown to them, and wound healing follows clot formation in these situations. D-dimers can also arise in anxiety and following exercise, and are also markers of inflammation. Lung inflammation (triggered by microbes or foreign particles) is perhaps also particularly relevant, since the hemostasis system and fibrinolysis help to trap and remove such debris. Lung inflammation in patients with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) may contribute to D-dimer levels additive to thrombosis in patients with COVID-19 (coronavirus disease 2019). Indeed, severe COVID-19 can lead to multiple activation events, including inflammation, primary and secondary hemostasis, and fibrinolysis, all of which may contribute to cumulative D-dimer development. Finally, D-dimer testing has also found a role in the diagnosis and triaging of the so-called (COVID-19) vaccine-induced thrombotic thrombocytopenia.

IKKβ regulates the expression of coagulation and fibrinolysis factors through the NF-κB canonical pathway in LPS-stimulated alveolar epithelial cells type II

Aim: Hypercoagulation and fibrinolysis inhibition in the alveolar cavity are important characteristics in acute respiratory distress syndrome (ARDS). Alveolar epithelial cells type II (AEC II) have been confirmed to have significant role in regulating alveolar hypercoagulation and fibrinolysis inhibition, but the mechanism is unknown. Nuclear factor-κB (NF-κB) signaling pathway has been demonstrated to participate in the pathogenesis of these two abnormalities in ARDS. The purpose of the present study is to explore whether controlling the upstream crucial factor IκB kinase (IKK)β could regulate coagulation and fibrinolysis factors in LPS-stimulated AEC II. Materials and methods: An IKKβ gene regulation model (IKKβ^+/+ and IKKβ^−/−) was prepared using lentiviral vector transfection. The models with wild type cells were all stimulated by lipopolysaccharide (LPS) or saline for 24 h. Expression of the related proteins were determined by western-blotting, ELISA and revere transcription-PCR respectively. Tissue factor (TF) procoagulant activity and nuclear p65 protein level were also detected. Results: IKKβ increased in IKKβ^+/+ cells but decreased in IKKβ^−/− cells. LPS stimulation promoted the expression of p-IκBα, p65, p-p65 and p-IKKβ as well as TF and plasminogen activator inhibitor (PAI)-1, at the mRNA or protein level, and this was significantly enhanced by IKKβ upregulation but weakened by IKKβ downregulation. TF procoagulant activity presented the same changes as the molecules above. ELISAs showed additional increases in the concentrations of as thrombin antithrombin, procollagen III propeptide, thrombomodulin and PAI-1 in IKKβ^+/+ cell supernatant under LPS stimulation, however they decreased in IKKβ^−/−. The level of as antithrombin III however, appeared to show the opposite change to those other factors. Immunofluorescence demonstrated a greatly enhanced expression of p65 in the nucleus by IKKβ upregulation, which was reduced by IKKβ downregulation. Conclusions: IKKβ could regulate the expression and secretion of coagulation and fibrinolysis factors in LPS-stimulated AEC II via the NF-κB p65 signaling pathway. The IKKβ molecule is expected to be a new target for prevention of coagulation and fibrinolysis abnormalities in ARDS.

Enzyme-responsive Drug-delivery Systems

This chapter offers an overview of recent advances in enzyme-responsive materials potentially useful for drug delivery. The systems already developed provide new insights into the chemical design rules and response dynamics achievable by exploiting enzymatic catalysis as selective triggers in controlled release. The first section provides a general introduction about the role of enzymes in diseased states and examples where molecular therapeutics have been developed specifically to interfere with biochemical processes. The parameters to consider in order to develop enzyme-responsive drug-delivery systems are then discussed. Different approaches to design hydrogels, micelles and silica nanocontainers with moieties that can be substrates of enzymes are described with the help of relevant examples that highlight their performance. The research in this area is gaining momentum at a significant pace and it is likely that the first therapeutic enzyme responsive materials will reach the clinic in the next decade.

Epithelial responses to lung injury: role of the extracellular matrix

The key role of extracellular matrices in alveolar epithelial cell (AEC) biology is highlighted by the phenotypes of primary AECs cultured on a soft laminin gel contrasted with that on a stiff, fibronectin matrix. On laminin, AECs maintain an epithelial phenotype, and progenitor cells within this population proliferate. In contrast, on fibronectin, AECs rapidly lose surfactant expression and spread extensively, changes that depend on activation of latent TGF-β1 by engagement of fibronectin-binding integrins. The progenitor subpopulation responding to TGF-β1 undergoes epithelial mesenchymal transition (EMT). Although it remains uncertain to what degree EMT contributes directly to collagen 1 production, signaling pathways critical to EMT are important for repair and fibrosis, implying that EMT is part of the general program of lung repair. EMT reprogramming requires not only Smad signaling but also pY654-β-catenin. Generation of pY654-β-catenin requires assembly of complexes of the integrin α3β1, E-cadherin, and TGF-β1 receptors, and such assembly is a function of cell-cell and cell-matrix contacts. Sequestration of α3β1 or E-cadherin in such contacts prevents complex assembly, TGF-β1 induced pY654-β-catenin generation and EMT. Disruption of these contacts is a signal for the cells to initiate repair. Critical remaining questions center around better definition of direct versus indirect effects of EMT on collagen deposition and the nature of AEC progenitors differentiating during fibrogenesis. Elucidation of specific inhibitors of EMT should further test the question of whether the process is important to fibrosis in vivo and a viable therapeutic target.

The effect of plasma homocysteine levels on clinical outcomes of patients with acute lung injury/acute respiratory distress syndrome

BACKGROUND

Several reports have shown that homocysteine promotes thrombosis by disturbing the procoagulant-anticoagulant balance, whereas alterations in coagulation and fibrinolysis have been suggested as important pathogenetic and prognostic determinants of mortality in acute lung injury (ALI)/acute respiratory distress syndrome (ARDS). The objective of the study was to evaluate the effect of plasma homocysteine levels on the outcomes of patients with ALI/ARDS.

METHODS

Sixty-nine consecutive ventilated patients with ALI/ARDS were studied. Blood samples were drawn within 3 days of clinical recognition of ARDS. Measurement of plasma homocysteine, vitamin B12, folate, creatinine, protein C and plasminogen-activator inhibitor-1 antigen levels, and genotyping of the methylenetetrahydrofolate reductase gene C677T and A1298C polymorphisms were carried out. The primary outcomes were 28- and 90-day mortality, whereas secondary outcomes included nonpulmonary organ failure-free days, liberation from mechanical ventilation up to day 28, and ventilator-free days during the 28 days after enrollment.

RESULTS

In the multivariable analysis, plasma homocysteine concentration adjusted for age, Acute Physiology and Chronic Health Evaluation II score, methylenetetrahydrofolate reductase C677T and A1298C polymorphisms, and levels of plasminogen-activator inhibitor-1 antigen, protein C, creatinine, vitamin B12, and folate was not found to affect significantly mortality at 28 and 90 days (P = 0.39 and P = 0.83, respectively), days without organ failure besides lungs (P = 0.38), the probability of being free from mechanical ventilation at day 28 (P = 0.63), and days without ventilation assistance (P = 0.73).

CONCLUSION

Our data suggest that increased plasma homocysteine levels, either alone or in synergy with other thrombophilic risk factors, do not seem to adversely affect the prognosis in patients with ALI/ARDS.

Urokinase receptor expression involves tyrosine phosphorylation of phosphoglycerate kinase

The interaction of urokinase-type plasminogen activator (uPA) with its receptor, uPAR, plays a central role in several pathophysiological processes, including cancer. uPA induces its own cell surface receptor expression through stabilization of uPAR mRNA. The mechanism involves binding of a 51 nt uPAR mRNA coding sequence with phosphoglycerate kinase (PGK) to down regulate cell surface uPAR expression. Tyrosine phosphorylation of PGK mediated by uPA treatment enhances uPAR mRNA stabilization. In contrast, inhibition of tyrosine phosphorylation augments PGK binding to uPAR mRNA and attenuates uPA-induced uPAR expression. Mapping the specific peptide region of PGK indicated that its first quarter (amino acids 1-100) interacts with uPAR mRNA. To determine if uPAR expression by uPA is regulated through activation of tyrosine residues of PGK, we mutated the specific tyrosine residue and tested mutant PGK for its ability to interfere with uPAR expression. Inhibition of tyrosine phosphorylation by mutating Y76 residue abolished uPAR expression induced by uPA treatment. These findings collectively demonstrate that Y76 residue present in the first quarter of the PGK molecule is involved in lung epithelial cell surface uPAR expression. This region can effectively mimic the function of a whole PGK molecule in inhibiting tumor cell growth.

A review of pulmonary coagulopathy in acute lung injury, acute respiratory distress syndrome and pneumonia

Enhanced bronchoalveolar coagulation is a hallmark of many acute inflammatory lung diseases such as acute lung injury, acute respiratory distress syndrome and pneumonia. Intervention with natural anticoagulants in these diseases has therefore become a topic of interest. Recently, new data on the role of pulmonary coagulation and inflammation has become available. The aim of this review is to summarize these findings. Furthermore, the results of anticoagulant therapeutic interventions in these disorders are discussed.

The fibrinolytic system and the regulation of lung epithelial cell proteolysis, signaling, and cellular viability

The urokinase-type plasminogen activator (uPA), its receptor (uPAR), and plasminogen activator inhibitor-1 (PAI-1) are key components of the fibrinolytic system and are expressed by lung epithelial cells. uPA, uPAR, and PAI-1 have been strongly implicated in the pathogenesis of acute lung injury (ALI) and pulmonary fibrosis. Recently, it has become clear that regulation of uPA, uPAR, and PAI-1 occurs at the posttranscriptional level of mRNA stability in lung epithelial cells. uPA further mediates its own expression in these cells as well as that of uPAR and PAI-1 through induction of changes in mRNA stability. In addition, uPA-mediated signaling controls the expression of the tumor suppressor protein p53 in lung epithelial cells at the posttranslational level. p53 has recently been shown to be a trans-acting uPA, uPAR, and PAI-1 mRNA-binding protein that regulates the stability of these mRNAs. It is now clear that signaling initiated by uPA mediates dose-dependent regulation of lung epithelial cell apoptosis and likewise involves changes in p53, uPA, uPAR, and PAI-1 expression. These findings demonstrate that the uPA-uPAR-PAI-1 system of lung epithelial cells mediates a broad repertoire of responses that encompass but extend well beyond traditional fibrinolysis, involve newly recognized interactions with p53 that influence the viability of the lung epithelium, and are thereby implicated in the pathogenesis of ALI and its repair.

The pathogenesis of pleural space loculation and fibrosis

PURPOSE OF REVIEW

Organization of parapneumonic effusions may complicate pneumonia, and, annually, thousands of patients require procedures to treat intrapleural loculation and fibrosis. Surgical procedures are often used for the treatment, as fibrinolytic therapy is now not a routine and is undergoing reassessment. Investigation of mechanisms that underlie intrapleural loculation and fibrosis is therefore timely, as are studies on new strategies to medically address these problems with improved efficacy and safety.

RECENT FINDINGS

Contributions made over the past year include basic and translational studies unified by their broad focus on mechanisms by which the pleural compartment undergoes repair. Intrapleural single-chain urokinase was reported to effectively reverse intrapleural loculation when compared with commercially available agents in rabbits with tetracycline-induced pleurodesis. The ability of exogenous sclerosants to produce intrapleural loculation and fibrosis was compared. Overexpression of transforming growth factor beta in the pleural mesothelium promoted subpleural fibrosis, implicating the mesothelial cell in the pathogenesis of this lesion. A new model of pleurodesis in mice was reported, which could facilitate the use of transgenic animals to study the pathogenesis of pleural injury.

SUMMARY

New findings consolidate and extend the view that common mechanisms by which intrapleural organization occurs can be exploited to either generate pleurodesis or effectively reverse intrapleural loculation and fibrosis.

Pharmacotherapy of acute lung injury and the acute respiratory distress syndrome

Acute lung injury and the acute respiratory distress syndrome are common syndromes with a high mortality rate that affect both medical and surgical patients. Better understanding of the pathophysiology of acute lung injury and the acute respiratory distress syndrome and advances in supportive care and mechanical ventilation have led to improved clinical outcomes since the syndrome was first described in 1967. Although several promising pharmacological therapies, including surfactant, nitric oxide, glucocorticoids and lysofylline, have been studied in patients with acute lung injury and the acute respiratory distress syndrome, none of these pharmacological treatments reduced mortality. This article provides an overview of pharmacological therapies of acute lung injury and the acute respiratory distress syndrome tested in clinical trials and current recommendations for their use as well as a discussion of potential future pharmacological therapies including beta(2)-adrenergic agonist therapy, keratinocyte growth factor, and activated protein C.

Regulation of urokinase receptor mRNA stability by hnRNP C in lung epithelial cells

Increased urokinase receptor (uPAR) expression as well as stabilisation of uPAR mRNA contribute to the pathogenesis of lung inflammation and neoplasia. Post-transcriptional regulation of uPAR mRNA involves interaction of both coding and 3'-UTR sequences with regulatory uPAR mRNA binding proteins (Bps). In order to identify novel regulatory interactions, we performed gel mobility shift and UV cross-linking assays and found two distinct uPAR mRNA-protein complexes. We identified a rapidly migrating 40 kDa uPAR mRNABp that selectively bound a 110 nucleotide (nt) fragment of the uPAR mRNA 3'UTR. Chimeric beta-globin/uPAR mRNA containing the 110 nt 40 kDa protein binding fragment destabilised stable beta-globin mRNA with a rate of decay identical to that of chimeric beta-globin/uPAR containing the full uPAR 3'UTR. The 40 kDa uPAR 3'UTR Bp was purified using poly (U) sepharose and identified as heterogeneous nuclear ribonucleoprotein C (hnRNPC). Finally, we confirmed its interaction with the uPAR mRNA 3' UTR by gel mobility supershift assay using an anti-hnRNPC antibody. Direct in vivo interaction of hnRNPC with the uPAR mRNA 3'UTR was demonstrated by immunoprecipitation and combined RT PCR-Southern blotting assay. Co-transfection of hnRNPC cDNA in Beas2B cells reversed destabilisation of chimeric beta-globin/uPAR 3'UTR mRNA and its over-expression also induced uPAR protein and mRNA expression through stabilisation of uPAR mRNA. These observations indicate a novel mechanism of uPAR gene regulation in lung epithelial cells in which cis elements within a 110 nt uPAR mRNA 3'UTR sequence interact with hnRNPC to regulate uPAR mRNA stability.

Pathogenesis of pleural fibrosis

Pleural fibrosis resembles fibrosis in other tissues and can be defined as an excessive deposition of matrix components that results in the destruction of normal pleural tissue architecture and compromised function. Pleural fibrosis may be the consequence of an organised haemorrhagic effusion, tuberculous effusion, empyema or asbestos-related pleurisy and can manifest itself as discrete localised lesions (pleural plaques) or diffuse pleural thickening and fibrosis. Although the pathogenesis is unknown, it is likely that the complex interactions between resident and inflammatory cells, profibrotic mediators and coagulation, and fibrinolytic pathways are integral to pleural remodelling and fibrosis. It is generally considered that the primary target cell for pleural fibrosis is the subpleural fibroblast. However, increasing evidence suggests that mesothelial cells may also play a significant role in the pathogenesis of this condition, both by initiating inflammatory responses and producing matrix components. A greater understanding of the interactions between pleural and inflammatory cells, cytokines and growth factors, and blood derived proteins is required before adequate therapies can be developed to prevent pleural fibrosis from occurring.

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.

Regulation of urokinase receptor expression by phosphoglycerate kinase

Post-transcriptional regulation represents a major mechanism by which eukaryotic gene expression is regulated through cis-trans interactions that serve as signals for rapid alterations of messenger RNA (mRNA) stability. Regulation of urokinase-type plasminogen activator receptor (uPAR) mRNA involves the interaction of a uPAR mRNA coding region sequence with a 50 kD uPAR mRNA binding protein. We purified this protein from human bronchial epithelial (Beas2B) cells and identified it as phosphoglycerate kinase (PGK). We cloned PGK cDNA by polymerase chain reaction and expressed the recombinant PGK protein, which specifically bound the uPAR mRNA coding region by gel mobility shift and Northwestern blotting. We also confirmed a direct interaction of PGK protein with uPAR mRNA by immunoprecipitation. Overexpression of PGK in uPAR-overproducing H157 lung carcinoma cells resulted in decreased cytoplasmic uPAR mRNA and cell surface uPAR protein expression. Reduced uPAR mRNA expression involved decreased stability of the uPAR mRNA. Decline in 3H-thymidine incorporation and migration occurred in H157 cells transfected with PGK cDNA. These results demonstrate that PGK regulates uPAR expression at the post-transcriptional level.

Urokinase receptor mRNA stability involves tyrosine phosphorylation in lung epithelial cells

Interaction between urokinase-type plasminogen activator (uPA) and its receptor (uPAR) localizes cellular proteolysis and promotes cellular proliferation and migration, effects that may contribute to the pathogenesis of lung inflammation and neoplasia. Enhanced uPAR expression as well as stabilization of uPAR mRNA by transforming growth factor-beta and phorbol myristate acetate (PMA) shares a common mechanism involving phosphorylation and dephosphorylation of a uPAR mRNA-binding protein (uPAR mRNABp). PMA-induced tyrosine phosphorylation of the uPAR mRNABp inhibited the uPAR mRNA-uPAR mRNABp interaction, stabilized uPAR mRNA and enhanced uPAR protein expression. Downregulation of the uPAR mRNA and uPAR mRNABp interaction by PMA and transforming growth factor-beta can be reversed by pretreatment of cells with herbimycin which in turn inhibits expression of uPAR protein via a decrease in uPAR mRNA stability. Our experiments indicate that post-transcriptional regulation of uPAR expression requires activation of tyrosine kinases. Cytokines can regulate uPAR expression of lung-derived epithelial cells at the post-transcriptional level by tyrosine phosphorylation of the uPAR mRNA binding protein and may thereby influence tissue remodeling in lung injury or neoplasia.

Bronchoalveolar coagulation and fibrinolysis in endotoxemia and pneumonia

OBJECTIVES

To review the involvement of coagulation and fibrinolysis in the pathogenesis of acute lung injury during severe infection. To review the cross-talk between coagulation and inflammation that may affect this response.

DATA SOURCES

Published articles on experimental and clinical studies of coagulation and fibrinolysis during infection, inflammation, acute lung injury, and evolving acute respiratory distress syndrome.

CONCLUSIONS

Fibrin deposition is an important feature of pulmonary infection or severe inflammation. The mechanisms that contribute to this fibrin deposition are bronchoalveolar tissue factor-mediated thrombin generation and localized depression of urokinase plasminogen activator-mediated fibrinolysis, caused by the increase of plasminogen activator inhibitors. These effects on pulmonary coagulation and fibrinolysis are regulated by various proinflammatory cytokines. Rather than being a unidirectional relationship, the interaction between inflammation and coagulation involves significant cross-talk. Coagulation and fibrinolytic proteins may have an additional role beyond fibrin turnover and inflammation, e.g., in mechanisms mediating cell recruitment and migration.

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.

Role of protease-activated receptors in airway function: a target for therapeutic intervention?

Protease-activated receptors (PARs) are G-protein-coupled, seven transmembrane domain receptors that act as cellular enzyme sensors. These receptors are activated by the proteolytic cleavage at the amino terminus, enabling interaction between the newly formed "tethered ligand" and the second extracellular loop of the receptor to confer cellular signalling. PARs can also be activated by small peptides that mimic the tethered ligand. In the respiratory tract, PARs may be regulated by endogenous proteases, such as airway trypsin and mast cell tryptase, as well as exogenous proteases, including inhaled aeroallergens such as those from house dust mite faecal pellets. Immunoreactive PARs have been identified in multiple cell types of the respiratory tract, and PAR activation has been reported to stimulate cellular mitogenesis and to promote tissue inflammation. Activation of PARs concurrently stimulates the release of bronchorelaxant and anti-inflammatory mediators, which may serve to induce cytoprotection and to minimise tissue trauma associated with severe chronic airways inflammation. Furthermore, airway inflammatory responses are associated with increased epithelial PAR expression and elevated concentrations of PAR-activating, and PAR-inactivating, proteases in the extracellular space. On this basis, PARs are likely to play a regulatory role in airway homeostasis, and may participate in respiratory inflammatory disorders, such as asthma and chronic obstructive pulmonary disease. Further studies focussing on the effects of newly developed PAR agonists and antagonists in appropriate models of airway inflammation will permit better insight into the role of PARs in respiratory pathophysiology and their potential as therapeutic targets.

Thrombin contributes to bronchoalveolar lavage fluid mitogenicity in lung disease of the premature infant

Chronic lung disease of prematurity (CLD) is a common consequence of neonatal respiratory distress syndrome (RDS) and is characterized by pulmonary fibrosis. Increased thrombin activity in the alveolar compartment is associated with pulmonary fibrosis in adults and animals, and contributes to bronchoalveolar lavage (BAL) fluid mitogenicity for fibroblasts. We hypothesized that BAL fluid from infants who develop CLD contains increased mitogenic activity for lung fibroblasts compared to BAL fluid from resolving RDS, and that increased thrombin levels contribute to this activity. Sequential BAL (postnatal days 2-14) was obtained from 37 premature infants who were ventilated for RDS. Twenty-six infants developed CLD, whereas 11 resolved. BAL fluid mitogenic activity was determined in a proliferation assay, using human fetal lung fibroblasts. The contribution of thrombin to mitogenic activity was determined using the thrombin inhibitor PPACK. Furthermore, thrombin levels in BAL fluid were measured using a specific substrate to detect thrombin activity and by measuring thrombin-antithrombin III complex (TATIII). BAL fluid mitogenic activity was comparable between CLD and RDS (CLD, 33% proliferation on day 2 to 41% on day 14; RDS, 21% on day 2 to 54% on day 7). Thrombin inactivation by PPACK completely inhibited mitogenic activity in BAL samples obtained on days 2 and 4 (CLD, P < 0.001 on days 2 and 4; RDS, P < 0.05 on day 4). From day 7 onwards, inhibition of thrombin only partly reduced (P < 0.05) CLD BAL fluid mitogenic activity, indicating that other mitogenic factors contribute as well. Surprisingly, thrombin activity and TATIII were decreased in BAL fluid from CLD compared with RDS patients on days 2 and 4. In conclusion, our study shows that BAL fluid from infants with and without CLD development is equally mitogenic for lung fibroblasts, and that thrombin is a major mitogen in these samples. This suggests that fibroproliferation may occur early in the lungs from infants with both CLD and RDS, and that thrombin contributes to this.

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.

Thrombin-stimulated cell proliferation mediated through activation of Ras/Raf/MEK/MAPK pathway in canine cultured tracheal smooth muscle cells

The elevated level of thrombin has been detected in the airway fluids of asthmatic patients and shown to stimulate cell proliferation in tracheal smooth muscle cells (TSMCs). However, the implication of thrombin in the cell proliferation was not completely understood. In this study, thrombin stimulated [3H]thymidine incorporation and p42/p44 mitogen-activated protein kinase (MAPK) phosphorylation in a time- and concentration-dependent manner in TSMCs. Pretreatment of TSMCs with pertussis toxin (PTX) significantly inhibited [3H]thymidine incorporation and phosphorylation of MAPK induced by thrombin. These responses were attenuated by tyrosine kinase inhibitors genistein and herbimycin A, phosphatidyl inositide (PI)-phospholipase C (PLC) inhibitor U73122, protein kinase C inhibitor GF109203X, removal of Ca2+ by addition of BAPTA/AM plus EGTA, PI 3-kinase inhibitors wortmannin and LY294002, and inhibitor of MEK1/2 PD98059. Furthermore, overexpression of dominant negative mutants, H-Ras-15A and Raf-N4, significantly suppressed p42/p44 MAPK activation induced by thrombin and PDGF-BB, indicating that Ras and Raf may be required for activation of these kinases. These results conclude that the mitogenic effect of thrombin was mediated through the activation of Ras/Raf/MEK/MAPK pathway. Thrombin-mediated MAPK activation was modulated by PI-PLC, Ca2+, PKC, tyrosine kinase, and PI 3-kinase associated with cell proliferation in canine cultured TSMCs.

Urokinase induces expression of its own receptor in Beas2B lung epithelial cells

Interaction between the urokinase-type plasminogen activator (uPA) and its receptor (uPAR) localizes cellular proteolysis and promotes cellular proliferation and migration. The interaction between uPA and uPAR at the surface of epithelial cells thereby contributes to the pathogenesis of lung inflammation and neoplasia. In this study, we sought to determine if uPA itself alters uPAR expression by lung epithelial cells. uPA enhanced uPAR expression as well as (125)I-uPA binding in Beas2B lung epithelial cells in a time- and concentration-dependent manner. The uPA-mediated induction of uPAR is not accomplished through its receptor and requires enzymatic activity. The low molecular weight fragment of uPA, lacking the receptor binding domain, was as potent as intact two-chain uPA in inducing expression of uPAR at the cell surface. Plasmin, the end product of plasminogen activation, did not alter uPA-mediated uPAR expression. Induction of uPAR by uPA represents a novel pathway by which epithelial cells can regulate uPAR-dependent cellular responses that may contribute to stromal remodeling in lung injury or neoplasia.

Long-term inhalation of high-dose nitric oxide increases intraalveolar activation of coagulation system in mice

Inhalation of nitric oxide (NO) is useful for the treatment of patients with pulmonary hypertension. However, the potential toxicity of inhaled NO is still unclear. Coagulation activation plays an important role in lung injury. We assessed the effect of low- and high-dose inhaled NO on the coagulation system in the intraalveolar space of mice. The animals were assigned to five groups (n = 6): [RA] group, mice exposed to fresh air alone; [RA+2 ppm NO] group, fresh air and 2 ppm NO; [RA+40 ppm NO] group, fresh air and 40 ppm NO; [RA+2 ppm NO+O(2)] group, fresh air, 2 ppm NO and O(2); and [RA+40 ppm NO+O(2)] group, fresh air, 40 ppm NO and O(2). Each group was treated for 3 wk. Lung specimens of [RA+40 ppm NO] and [RA+40 ppm NO+O(2)] groups showed significant nitrotyrosine immunoreactivity. BALF concentrations of total protein, thrombin and soluble tissue factor were significantly increased in mice of [RA+40 ppm NO] and [RA+40 ppm NO+O(2)] groups compared with [RA] group. However, BALF concentrations of total protein, thrombin, and soluble tissue factor were not significantly increased in mice of [RA+2 ppm NO] and [RA+2 ppm NO+O(2)] groups compared with [RA] group. Lung tissue factor mRNA expression was higher in the high-dose NO group than in the low-dose NO group. NO donor increased significantly tissue factor activity on alveolar epithelial cells. This study has shown for the first time that long-term inhalation of high, but not low, concentration of NO may activate the clotting system by increasing the lung expression of tissue factor.

Mechanisms of thrombin-induced MAPK activation associated with cell proliferation in human cultured tracheal smooth muscle cells

The elevated level of thrombin has been detected in the airway fluids of asthmatic patients. However, the implication of thrombin in the pathogenesis of bronchial hyperreactivity was not completely understood. Therefore, in this study we investigated the effect of thrombin on cell proliferation and p42/p44 mitogen-activated protein kinase (MAPK) activation in human tracheal smooth muscle cells (TSMCs). Thrombin stimulated [3H]thymidine incorporation and p42/p44 MAPK phosphorylation in a time- and concentration-dependent manner in TSMCs. Pretreatment of TSMCs with pertussis toxin (PTX) significantly inhibited [3H]thymidine incorporation and phosphorylation of MAPK induced by thrombin. These responses were attenuated by tyrosine kinase inhibitors genistein and herbimycin A, phosphatidyl inositide (PI)-phospholipase C (PLC) inhibitor U73122, protein kinase C (PKC) inhibitor GF109203X, removal of Ca(2+) by addition of BAPTA/AM plus EGTA, and PI 3-kinase inhibitors wortmannin and LY294002. In addition, thrombin-induced [3H]-thymidine incorporation and p42/p44 MAPK phosphorylation was completely inhibited by PD98059 (an inhibitor of MEK1/2), indicating that activation of MEK1/2 was required for these responses. Furthermore, overexpression of dominant negative mutants, RasN17 and Raf-301, significantly suppressed p42/p44 MAPK activation induced by thrombin and PDGF-BB, indicating that Ras and Raf may be required for activation of these kinases. These results conclude that the mitogenic effect of thrombin was mediated through the activation of Ras/Raf/MEK/MAPK pathway. Thrombin-mediated MAPK activation was modulated by PI-PLC, Ca(2+), PKC, tyrosine kinase, and PI 3-kinase associated with cell proliferation in cultured human TSMCs.

Transcriptional regulation of the interleukin-1beta promoter via fibrinogen engagement of the CD18 integrin receptor

Fibrinogen, with or without its conversion to fibrin, in the extravascular spaces of injured and inflamed lung tissues is thought to promote inflammatory responses that can eventually lead to pulmonary fibrosis. One of these responses likely involves the elaboration of the proinflammatory cytokine interleukin (IL)- 1beta. We reported that both fibrinogen and fibrin stimulated production of IL-1beta message and protein by binding to CD18 integrin receptors on normal human monocytes (J. Immunol., 1995;154:1879-1887). The purpose of the current work was to extend our previous observations by characterizing the transcriptional regulation of fibrinogen-induced IL-1beta expression. Our model was the human monocytic cell line U937 transfected with the human IL-1beta promoter connected to reporter genes. We found that fibrinogen induced the IL-1beta promoter and that induction could be blocked by anti-CD18 antibody. Transfection with deletion constructs of the promoter and DNA electrophoresis mobility gel shift assays suggested that sequences containing activator protein (AP)-1, cyclic adenosine monophosphate response element (CRE), and nuclear factor (NF)-kappaB cis-acting motifs regulate IL-1beta gene expression by fibrinogen. In combination with competitive cotransfection studies using consensus oligonucleotides mimicking these motifs, we conclude that transactivation of an NF-kappaB-like sequence is necessary for induction of the IL-1beta gene, that activation of CRE may repress induction of the gene, and that AP-1 potentially modulates induction and repression of the gene induced by fibrinogen. This study begins to define the molecular mechanisms by which fibrin(ogen) promotes and regulates expression of the IL-1beta gene and further substantiates a role for fibrin(ogen) in tissue injury and inflammation.

Heterogeneity of procoagulant activity and cytokine release in subpopulations of alveolar macrophages and monocytes

We have studied the expression of tissue factor (TF) and fibrinopeptide A (FPA) generation as well as the release capacity of TNF-alpha, IL-1beta, and IL-6 in density-defined subpopulations of alveolar macrophages (AM) and monocytes (Mo). TF was equally expressed on all AM subpopulations and Mo, while the FPA-forming capacity was at the same level in low density AM as in Mo and was significantly (P < 0.05) higher in low density AM than in high density AM. The lipopolysaccharide (LPS)-induced release of TNF-alpha was higher (P < 0.05) in high density AM than in low density AM and in Mo. IL-1beta release was undetectable in unstimulated AM and in LPS-stimulated low density AM, while the LPS-induced IL-1beta release in high density AM was low compared to the levels demonstrated in Mo. LPS-stimulated IL-6 release was not distinctively different in the AM subpopulations and Mo. The presented study showed that FPA generation and LPS-stimulated TNF-alpha release were dependent on the density (i.e., maturity) of AM. This implies that a skewed distribution of AM subpopulations induced by disease processes may profoundly influence the inflammatory reactions, including extravascular activation of coagulation.

Differential effects of anti-cytokine treatment on bronchoalveolar hemostasis in endotoxemic chimpanzees

Activation and inhibition of coagulation and fibrinolysis was analyzed in bronchoalveolar lavage (BAL) fluids obtained from endotoxin-challenged chimpanzees. The mediatory role of tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) on endotoxin-induced changes in bronchoalveolar coagulation and fibrinolysis was investigated in experiments in which the infusion of endotoxin was combined with the administration of monoclonal anti-TNF-alpha or anti-IL-6 antibodies. Endotoxin infusion elicited a marked increase in bronchoalveolar thrombin generation as measured by levels of prothrombin activation fragment F1+2 and thrombin-antithrombin complexes. Markers for intrinsic pathway activation were not detectable, suggesting that the thrombin generation was mediated by the tissue factor-dependent route. Levels of antithrombin were low before the injection of endotoxin and not detectable hereafter. The administration of anti-IL-6 antibody completely abolished the endotoxin-induced activation of bronchoalveolar coagulation, whereas treatment with anti-TNF-alpha antibody only partly inhibited this effect. Bronchoalveolar fibrinolytic activity, due to urokinase-type plasminogen activator (u-PA), was significantly depressed after endotoxin injection, mainly due to a striking increase in plasminogen activator inhibitor-2 levels in BAL fluid. The endotoxin-induced effects on bronchoalveolar fibrinolysis could be blocked by the simultaneous administration of anti- TNF-alpha antibodies. We conclude that endotoxemia results in the activation of bronchoalveolar coagulation, which is apparently mediated by the tissue factor route of coagulation activation and which may be amplified by consumption of antithrombin III. Bronchoalveolar fibrinolytic activity is significantly abolished by increased levels of mainly PAI-2 after the injection of endotoxin. The endotoxin-induced effects on bronchoalveolar coagulation appears to be mediated by IL-6, whereas TNF-alpha seems to be the pivotal mediator of the endotoxin-induced depression of bronchoalveolar fibrinolysis.

Protein C anticoagulant system in patients with interstitial lung disease

Excessive procoagulant activity in the alveolar space may play a relevant role in the pathogenesis of pulmonary fibrosis. Hypercoagulability results from the disruption of the balance between the procoagulant and anticoagulant factors. The aim of this study was to assess the levels of molecular markers of the anticoagulant protein C (PC) pathway in the bronchoalveolar lavage fluid (BALF) and plasma of 11 patients with idiopathic pulmonary fibrosis (IPF), 14 with sarcoidosis and 16 with collagen vascular disease (CVD)-associated interstitial lung disease (CVD-ILD). Six healthy nonsmoking volunteers served as control subjects. BALF concentrations of the marker of clotting activation, thrombin- antithrombin III complex (TAT), in patients with sarcoidosis and CVD-ILD were significantly greater than those in control subjects. PC levels in BALF were markedly higher in patients with IPF (610 +/- 150 ng/ml), sarcoidosis (680 +/- 170 ng/ml), and CVD-ILD (1,580 +/- 600 ng/ml) than in control subjects (230 +/- 140 ng/ml). BALF concentrations of activated PC-PC inhibitor (APC-PCI) complex were significantly decreased in IPF (0.46 +/- 0.16 ng/ml), sarcoidosis (0. 43 +/- 0.11 ng/ml), and CVD-ILD (0.50 +/- 0.15 ng/ml) patients as compared with control subjects (1.08 +/- 0.23 ng/ml). APC-PCI/PC ratios were significantly lower in patients with IPF (2.70 +/- 1.74 ng/microg), sarcoidosis (1.94 +/- 0.82 ng/microg), and CVD-ILD (1.89 +/- 0.68 ng/microg) than in control subjects (15.91 +/- 8.45 ng/microg). Plasma levels of APC- PCI and the APC-PCI/PC ratio were also significantly decreased in patients with CVD-ILD as compared with control subjects. Overall, these findings suggest that decreased PC activation with increased procoagulant activity occurs in patients with ILD.

Plasminogen activators, integrins, and the coordinated regulation of cell adhesion and migration

Cellular migration is critically dependent on an interplay between forces of attachment and detachment. Recent studies show that the serine protease urokinase and its major inhibitor and receptor regulate the adhesive properties of integrins, at least in part through initiation of cellular signals. These new functions for an old protease system imply intricate connections between proteolysis and adhesion that operate at the cell surface to regulate migration.

Increased neutrophil elastase, persistent intravascular coagulation, and decreased fibrinolytic activity in patients with posttraumatic acute respiratory distress syndrome

BACKGROUND

To investigate the role of plasma neutrophil elastase (elastase-alpha1-proteinase inhibitor complex), plasminogen activator inhibitor-1 (PAI-1), and disseminated intravascular coagulation (DIC) in patients with posttraumatic acute respiratory distress syndrome (ARDS) and to explore the time course of the changes of these factors after trauma, we performed a prospective case-control study.

METHODS

The study subjects consisted of 41 trauma patients, 5 with ARDS, 7 at risk for but not developing the syndrome, and 29 control patients without or with no risk for ARDS. Plasma neutrophil elastase, PAI-1 activity, and PAI-1 antigen concentration were measured on the day of the injury and on days 1, 3, and 5 after admission. DIC was measured on the basis of the DIC score. The results of these measurements and demographic data were compared among the three groups.

RESULTS

Neutrophil elastase, PAI-1 activity, and PAI-1 antigen concentration for the ARDS patients continued to be markedly high until the fifth day of admission, and the values on the fifth day were significantly higher than those of the other two groups. All patients with ARDS developed DIC. A decrease in the DIC score was found for the control patients and also for the patients at risk for ARDS; however, for the patients with ARDS, the DIC score did not improve during the study period (p = 0.5809).

CONCLUSION

We provide precise information on the time course of neutrophil elastase, PAI-1, and DIC in trauma patients with ARDS and those at risk of developing this syndrome. Neutrophil activation and persistent intravascular coagulation as well as impaired fibrinolysis may play a role in the pathogenesis of posttraumatic ARDS.

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.

Plasminogen activators and their inhibitors in non-small cell lung cancer. Low content of type 2 plasminogen activator inhibitor associated with tumor dissemination

BACKGROUND

Evidence suggests that plasminogen activators and their inhibitors play an important role in tumor spread.

METHODS

In this study, we measured the antigen levels of urokinase (u-PA), tissue plasminogen activator (t-PA), type 1 plasminogen activator inhibitor (PAI-1), and type 2 plasminogen activator inhibitor (PAI-2), and cancer tissue (19 adenocarcinomas and 19 squamous cell carcinomas) and normal lung tissue.

RESULTS

u-PA, PAI-1, and PAI-2 antigen levels in cancer tissue were significantly higher than those in normal tissue (P < 0.001 in u-PA and PAI-1; P < 0.005 in PAI-2), whereas t-PA antigen levels in cancer tissue were significantly lower than those in normal tissue (P < 0.005). In case with lymph node involvement (LN+ cases), PAI-2 antigen levels were significantly lower than those in cases without lymph node involvement (LN- cases) (P < 0.02), whereas there was no difference in either u-PA or PAI-1 antigen levels between these two groups. Furthermore, u-PA antigen levels showed a significant positive correlation with PAI-2 antigen levels in LN- cases (r = 0.696; P < 0.005), although there was no correlation between these two parameters in LN+ cases.

CONCLUSIONS

The antigen levels of u-PA, PAI-1, and PAI-2 in cancer tissue were significantly higher than those in normal tissue, and lower content of PAI-2 was associated with lymph node metastasis.

Immunohistochemical study of tumor cell-associated plasminogen activators and plasminogen activator inhibitors in lung carcinomas

STUDY OBJECTIVE

To compare the expression of plasminogen activators (PA) and plasminogen activator inhibitors (PAI) in normal lung mucosa and lung carcinomas.

DESIGN

Immunohistochemical localization of urokinase-type PA (uPA), tissue-type PA (tPA), type 1 PAI (PAI-1), and type 2 PAI (PAI-2) in four normal lung biopsy specimens and in four adenocarcinomas (AC), four squamous carcinomas (SC), two large-cell carcinomas (LCC), and ten small-cell carcinomas (SCC) biopsy specimens. Qualitative immunostaining scoring system.

RESULTS

tPA and uPA immunostaining scores from all specimens were statistically similar. The cellular staining for uPA and tPA was generally constant (normal epithelial layers, AC cells, SC cells) except for LCC cells (inconstant uPA staining, p < 10(-3). Both PAIs were detected in cells of the normal epithelial layer. The four carcinoma cell types stained for PAI in a statistically different pattern (p < 10(-3)). Cells of the peripheral cords of SCC were inconstantly PAI-1 and PAI-2 positive (p < 10(-3)). LCC were PAI-2 negative and inconstantly stained for PAI-1. SCC cells were PAI-1 and PAI-2 negative.

CONCLUSION

Lung carcinomas of worst clinical prognosis no longer express PAI reactivity. The imbalance of the plasminogen activation pathway may favor the spreading of the more invasive histologic types of bronchogenic carcinomas.

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.

Lung capillary endothelial cells produce and secrete urokinase-type plasminogen activator

Bovine lung capillary endothelial cells (BLuEC) were isolated, and their ability to produce plasminogen activator (PA) in vitro was demonstrated. BLuEC secreted more than 10 times as much as urokinase-type PA (u-PA) as did bovine aortic, hepatic capillary and adrenal capillary endothelial cells, and lung fibroblasts. BLuEC secreted u-PA on both sides of the cell layer, the luminal surface, and the basic surface attached to the basement membrane. u-PA mRNA was detected in BLuEC by Northern blotting, but not in endothelial cells from other tissues and fibroblasts. These results suggest that BLuEC may contribute not only to the patency of lung vessels but also to the maintenance of alveolar functions through the production and secretion of u-PA.

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.

Procoagulant activity in bronchoalveolar fluids: no relationship with tissue factor pathway inhibitor activity

Abnormalities in local coagulation may explain alveolar fibrin deposition which often accompanies human lung injuries. The purpose of this study was to investigate the generation of procoagulant activity (PCA) and tissue factor pathway inhibitor (TFPI) in selected bronchoalveolar lavage fluids (BAL) from controls (n = 7) and from patients with interstitial lung diseases (n = 9), Pneumocystis carinii (PCP) pneumonia (n = 11) and bacterial pneumonia (n = 8). As compared with controls a significant increase of PCA was observed in the three groups with lung diseases. PCA in BAL from patients with untreated interstitial lung diseases (PC Units mean of 162 +/- 48) was significantly higher than PCA of treated patients (PC Units 36 +/- 10; p less than 0.05). Increases of PCA paralleled protein levels in BAL and the protein/albumin ratios were comparable in the four groups. TFPI was significantly increased in PCP (p less than 0.02) and bacterial pneumonia (p less than 0.03), but only marginally increased in interstitial lung diseases when compared with controls. No correlation was found between TFPI and PCA in any of the four groups. These data indicate that increased procoagulant activity observed in various lung diseases is not counterbalanced by TFPI.

Immunohistochemical localization of coagulation, fibrinolytic and antifibrinolytic markers in adenocarcinoma of the lung

Extravascular coagulation and fibrinolysis are intimately involved in and modulate cancer cell growth, invasion and metastasis. Samples from resection specimens of patients with primary lung cancer (adenocarcinomas) were tested with monoclonal (MAb) and polyclonal (PAb) antibodies against various factors of the coagulation or fibrinolysis systems, or against antigens of inflammatory or proliferating cells. MAb Ki-67 specific to nuclear antigens of proliferating cells showed a distinct but variable staining of cell nuclei throughout the tumor tissue. Nests of tumor tissue stained with cytokeratin-specific antibodies (PKK1), whereas other parts were negative. Fibrin(ogen) and fibronectin were found throughout the tumor tissue stroma and in the alveolar lining, and the most densely stained areas were at the transition zone between normal and tumor tissue. Fibrinolytic system components like tissue plasminogen activators (t-PA), and urokinase (u-PA), and their inhibitors PAI-1 and PAI-2 were all studied. All specimens were negative for t-PA (except endothelial linings), whereas urokinase-specific antibodies stained loosely packed tumor cells and macrophages within the tumor stromal tissue and alveolar septa. Both PAI-1 and PAI-2 were most prominently expressed within interstitial and alveolar macrophages. A weaker staining of tumor tissue cells was demonstrated. Inflammatory cells like macrophages and T lymphocytes were located in aggregates or diffusely spread within tumor stromal tissue. The inflammatory reaction was most intense at the border between normal lung and tumor tissue.

Characteristics of alveolar macrophages in an animal model of resolving pulmonary inflammation

Little is known about the functions of alveolar macrophages during the later resolving phases of pulmonary inflammation. We have used an animal model of resolving pulmonary inflammation to obtain inflammatory macrophages (IMs) and have compared several IM functions with those of resident macrophages (RMs). IMs were frequently peroxidase positive and contained large amounts of myeloperoxidase activity. IMs also contained significant amounts of a serine protease type of elastase. The procoagulant activity of IMs was less than that of RMs, and IMs exhibited increased plasminogen activator activity when incubated on fibrin matrices. IMs also degraded fibrin directly, without plasminogen, and this activity was due to two different enzymes of molecular weights 39 and 63 kD that were present in IM granules and plasma membranes. These results suggest that, in vivo, IMs take up PMN enzymes and alter their procoagulant and fibrinolytic activity to maximize fibrin removal. These IM functions may be important for successful resolution of inflammatory injury.

Asbestos exposure results in increased lung procoagulant activity in vivo and in vitro

Enhanced fibrin deposition is a common histologic finding in fibrotic lung disorders including asbestosis and may be an important mechanism by which fibroblast proliferation is modulated. Asbestos-induced activation of lung interstitial cells may result in enhanced expression of procoagulant activity which contributes to the inflammatory response resulting in subsequent fibrin deposition. The current study examines procoagulant activity in bronchoalveolar lavage fluid from patients with clinically diagnosed asbestosis, patients with asbestos exposure without asbestosis, and normal, control subjects. Results indicated that asbestos exposure resulted in increased lung procoagulant expression in vivo, and furthermore, suggested that both endothelial cells and alveolar macrophages represented lung parenchymal cells which may contribute to this activity. This imbalance in coagulation homeostasis may be important in the regulation of fibrotic responses observed in asbestosis.