D-dimers are degraded by human neutrophil elastase

Endogenous fibrinolysis-Relevance to clinical thrombosis risk assessment

The development of an obstructive luminal thrombus is pathological and considered a failure of endogenous fibrinolysis. The consequences may be fatal, or result in lasting downstream organ damage. Therefore, assessment of endogenous fibrinolytic status in an individual may identify those at risk of occlusive thrombus formation and provide prognostic information. Arterial thrombi are more platelet rich and more resistant to fibrinolysis than venous thrombi. Several recent studies using global tests of fibrinolysis in patients with acute coronary syndromes (ACS) have shown that despite dual antiplatelet therapy, patients with impaired fibrinolytic status have an increased risk of adverse cardiovascular events, compared with those with effective fibrinolytic function. Such data add significantly to the predictive value of established cardiovascular risk factors and conventional biomarkers. Most data reported have been obtained with the Global Thrombosis Test and the turbidimetric plasma clot lysis assay. A few small studies in patients with ischaemic stroke suggest a similar predictive role of fibrinolytic status assessment in these patients. Studies reporting an association between impaired fibrinolysis and future venous thrombotic events are limited, and in the form of case-control studies. Viscoelastic assays may have a role in the prediction of venous thromboembolic risk. Assays of fibrinolytic function should be used to obtain a more accurate risk of future thrombotic events, particularly in the setting of ACS. The availability of point-of-care tests helps facilitate this and should encourage future studies to assess personalised antithrombotic treatment combinations to optimise fibrinolytic status and reduce thrombosis risk.

COVID-19-associated coagulopathy: An exploration of mechanisms

An ongoing global pandemic of viral pneumonia (coronavirus disease [COVID-19]), due to the virus SARS-CoV-2, has infected millions of people and remains a threat to many more. Most critically ill patients have respiratory failure and there is an international effort to understand mechanisms and predictors of disease severity. Coagulopathy, characterized by elevations in D-dimer and fibrin(ogen) degradation products (FDPs), is associated with critical illness and mortality in patients with COVID-19. Furthermore, increasing reports of microvascular and macrovascular thrombi suggest that hemostatic imbalances may contribute to the pathophysiology of SARS-CoV-2 infection. We review the laboratory and clinical findings of patients with COVID-19-associated coagulopathy, and prior studies of hemostasis in other viral infections and acute respiratory distress syndrome. We hypothesize that an imbalance between coagulation and inflammation may result in a hypercoagulable state. Although thrombosis initiated by the innate immune system is hypothesized to limit SARS-CoV-2 dissemination, aberrant activation of this system can cause endothelial injury resulting in loss of thromboprotective mechanisms, excess thrombin generation, and dysregulation of fibrinolysis and thrombosis. The role various components including neutrophils, neutrophil extracellular traps, activated platelets, microparticles, clotting factors, inflammatory cytokines, and complement play in this process remains an area of active investigation and ongoing clinical trials target these different pathways in COVID-19.

Endogenous Fibrinolysis: An Important Mediator of Thrombus Formation and Cardiovascular Risk

Most acute cardiovascular events are attributable to arterial thrombosis. Plaque rupture or erosion stimulates platelet activation, aggregation, and thrombosis, whilst simultaneously activating enzymatic processes that mediate endogenous fibrinolysis to physiologically maintain vessel patency. Interplay between these pathways determines clinical outcome. If proaggregatory factors predominate, the thrombus may propagate, leading to vessel occlusion. However, if balanced by a healthy fibrinolytic system, thrombosis may not occur or cause lasting occlusion. Despite abundant evidence for the fibrinolytic system regulating thrombosis, it has been overlooked compared with platelet reactivity, partly due to a lack of techniques to measure it. We evaluate evidence for endogenous fibrinolysis in arterial thrombosis and review techniques to assess it, including biomarkers and global assays, such as thromboelastography and the Global Thrombosis Test. Global assays, simultaneously assessing proaggregatory and fibrinolytic pathways, could play a role in risk stratification and in identifying impaired fibrinolysis as a potential target for pharmacological modulation.

Prognostic value of plasma fibrinolysis activation markers in cardiovascular disease

The pivotal role of hypoactive endogenous fibrinolysis in the occurrence of thrombotic cardiovascular events is now well-recognized. To evaluate the diagnostic and prognostic role of impaired fibrinolysis, plasma fibrinolysis markers have been investigated in large prospective studies in both healthy individuals and patients with established coronary disease. Antigen and activity levels of components of the fibrinolytic system were measured by immunoassays, which replaced earlier global fibrinolysis tests. This review covers 45 studies in nearly 50,000 subjects, examining the association between plasma markers of fibrinolysis and coronary artery disease, to establish the usefulness of these markers in predicting future cardiovascular events. The predictive value of plasma levels of tissue-type plasminogen activator, platelet activator inhibitor-1, plasmin-antiplasmin complex, D-dimer, thrombin activatable fibrinolysis inhibitor, and lipoprotein(a) for major adverse cardiac events is highly variable and conflicting, especially after adjusting for conventional risk factors, judging from the published data in the last decade. The value of fibrinolysis activity markers is very limited in aiding diagnosis and risk stratification in the individual patient, on the basis of the weak prognostic values obtained in some studies and the lack of power in others. The physiological limitations of such markers in reflecting endogenous fibrinolysis is discussed. The emerging novel global assays of fibrinolysis will require large-scale clinical trials before their prognostic power or superiority to multiple biomarker measurements can be evaluated.

Bioinformatic analysis of protein structure-function relationships: case study of leukocyte elastase (ELA2) missense mutations

Cyclic and congenital neutropenia are caused by mutations in the human neutrophil elastase (HNE) gene (ELA2), leading to an immunodeficiency characterized by decreased or oscillating levels of neutrophils in the blood. The HNE mutations presumably cause loss of enzyme activity, consequently leading to compromised immune system function. To understand the structural basis for the disease, we implemented methods from bioinformatics to analyze all the known HNE missense mutations at both the sequence and structural level. Our results demonstrate that the 32 different mutations have diverse effects on HNE structure and function, affecting structural disorder and aggregation tendencies, stability maintaining contacts, and electrostatic properties. A large proportion of the mutations are located at conserved amino acids, which are usually essential in determining protein structure and function. The majority of the disease-causing HNE missense mutations lead to major structural changes and loss of stability in the protein. A few mutations also affect functional residues, leading into decreased catalytic activity or altered ligand binding. Our analysis reveals the putative effects of all known missense mutations in HNE, thus allowing the structural basis of cyclic and congenital neutropenia to be elucidated. We have employed and analyzed a set of some 30 different methods for predicting the effects of amino acid substitutions. We present results and experience from the analysis of the applicability of these methods in the analysis of numerous genes, proteins, and diseases to reveal protein structure-function relationships and disease genotype-phenotype correlations.

Urinary trypsin inhibitor reduces C-X-C chemokine production in rat liver ischemia/reperfusion

BACKGROUND AND AIM

Protease inhibitors attenuate ischemia/reperfusion injury. However, the underlying mechanisms by which protease inhibitors prevent reperfusion injury remain obscure. Neutrophils play an important role in reperfusion injury. We studied the effects of urinary trypsin inhibitor (UTI) on production of the C-X-C chemokine, cytokine-induced neutrophil chemoattractant (CINC), by Kupffer cells during ischemia/reperfusion of the liver.

METHODS

Liver ischemia was induced in rats by occlusion of the portal vein for 30 min. UTI (50,000 U/kg) was injected intravenously 5 min before vascular clamping. Serum CINC concentrations were measured by enzyme-linked immunosorbent assay. Levels of CINC mRNA in the liver were determined by Northern blot analysis. We also examined the inhibitory effects of UTI on in vitro CINC production by peritoneal macrophages in response to neutrophil elastase (NE).

RESULTS

Serum CINC concentrations increased and peaked 6 h after reperfusion. However, pretreatment of animals with UTI blunted this increase in CINC and significantly reduced CINC mRNA levels in the liver after ischemia/reperfusion. UTI also decreased neutrophil accumulation in the liver 24 h after reperfusion. In vitro CINC production by Kupffer cells from rats pretreated with UTI 3 h after ischemia/reperfusion was significantly decreased compared to those from untreated animals. UTI reduced NE activity in vitro in a dose-dependent manner, and UTI significantly reduced in vitro CINC production by peritoneal macrophages stimulated with NE.

CONCLUSION

UTI reduces the production of CINC by Kupffer cells stimulated with NE, attenuating ischemia/reperfusion injury of the liver.

Neutrophil elastase and oxygen radicals enhance monocyte chemoattractant protein- expression after ischemia/reperfusion in rat liver

BACKGROUND

The monocyte chemoattractant protein-1 (MCP-1) is produced during reperfusion injury and induces tissue factor that is the initiator of the clotting cascade. Neutrophil elastase is a crucial mediator of inflammatory tissue damage. Activation of the coagulation system stimulates cytokine production by activated leukocytes. We investigated the effects of neutrophil elastase and oxygen radicals generated by hypoxia associated with microthrombus formation on MCP-1 expression after ischemia/reperfusion in rat liver.

METHODS

In vitro MCP-1 production by macrophages after stimulation with human neutrophil elastase (HNE) or oxygen radicals generated by hypoxanthine and xanthine oxidase was examined. Liver ischemia was induced in rats by occluding the portal vein for 30 min. An inhibitor of human neutrophil elastase (ONO-5046*Na, 10 mg/kg) and antithrombin III (AT-III, 250 U/kg) were injected i.v. 5 min before vascular clamping. Serum concentrations of MCP-1 were measured by enzyme-linked immunosorbent assay.

RESULTS

Human neutrophil elastase or oxygen radicals significantly enhanced in vitro MCP-1 production by macrophage. Serum MCP-1 concentrations reached a peak at 6 hr after reperfusion and then gradually decreased. However, pretreatment of animals with AT-III or ONO-5046*Na alone resulted in significantly smaller increases in serum concentrations of MCP-1 after reperfusion. Pretreatment with both ONO-5046*Na and AT-III produced additive effects. The combined treatment with ONO-5046*Na and AT-III significantly reduced MCP-1 mRNA in liver after ischemia/reperfusion.

CONCLUSIONS

MCP-1 production by macrophages is stimulated by neutrophil elastase and oxygen radicals generated by hypoxia, probably due to microthrombus formation after ischemia/reperfusion of the rat liver.

Human homozygous type I plasminogen deficiency and ligneous conjunctivitis

On the basis of a questionnaire sent to the ophthalmology departments of hospitals throughout Germany, 10 patients with ligneous conjunctivitis or pseudomembranous disease, ranging in age from 1 to 71 years were identified. All 10 patients had severely reduced plasminogen levels. Genetic analysis revealed homozygous type I plasminogen deficiency (which had not previously been described in humans) in 7 patients and compound heterozygous plasminogen deficiency in 1 patient. Clear differentiation was not possible in 2 patients. Most of the parents had heterozygous plasminogen deficiency. None of the patients had experienced any episodes of thrombosis. Additionally, the following observations were made: 1) Levels of polymorphonuclear (PMN)-elastase protein were markedly elevated in 6 of 6 patients and 10 of 11 parents tested, and levels were higher in homozygotes than in heterozygotes. 2) Hereditary factor XII deficiency was found in 3 of 6 patients tested. 3) C1-inhibitor was elevated in 2 of 4 patients, prekallikrein was elevated in 1 of 4 patients, and plasminogen activator inhibitor type 1 was elevated in 1 of 4 patients. Infusions of lys-plasminogen concentrate induced pronounced fibrinolytic activity as indicated by high levels of D-dimer, increases in plasmin-antiplasmin complex and decreases in polymorphonuclear elastase. C1-inhibitor, prekallikrein and PAI-1 normalized after repeated infusions of lys-plasminogen. In contrast to dysplasminogenemia, severe type I plasminogen deficiency might be seen as a problem of extravascular space, in particular of the mucous membranes, possibly triggered by mechanically induced or inflammatory lesions of the vessels supplying the tissue.

Degradation of fibrinogen and cross-linked fibrin by human neutrophil elastase generates D-like fragments detected by ELISA but not latex D-dimer test

Recently, we observed that D-dimers are degraded by human neutrophil elastase (HNE) into two D-like fragments, reacting with the monoclonal antibody in an ELISA D-dimer test but not reacting with the corresponding latex D-dimer test. To investigate this in more detail, we studied the degradation of cross-linked fibrin and fibrinogen by plasmin and HNE to see if this resulted in D-fragments or D-like fragments. Degradation of fibrinogen, both by plasmin and HNE, resulted in D- and D-like fragments, respectively, detected by the ELISA D-dimer test. Degradation of cross-linked fibrin by plasmin and HNE also resulted in D- and D-like fragments, which were detected by the ELISA method. Intact D-dimers detected by the latex D-dimer test were only observed after degradation of cross-linked fibrin with plasmin. We conclude that during lysis of cross-linked fibrin as well as fibrinogen by plasmin and HNE, D-fragments, and D-like fragments, detected by the ELISA D-dimer test, are formed. Only during degradation of cross-linked fibrin by plasmin, intact D-dimers, detected by latex D-dimer test, are formed. The ELISA D-dimer test may therefore be used to detect fibrin and fibrinogen degradation products generated by the combined action of plasmin and HNE in sepsis and other conditions with increased HNE activity, while the latex D-dimer test may be used to detect plasmin derived intact D-dimers.

Discrepancy between latex and ELISA D-dimer values in sepsis may be caused by human neutrophil elastase

We have recently shown that D-dimers are degraded by human neutrophil elastase (HNE) in vitro, causing rapid decrease in the D-dimer levels measured by a Latex test, but not with an ELISA test employing the same monoclonal antibody against D-dimer. To see if such discrepant D-dimer concentrations occurred in patients with high HNE concentration, we examined 80 plasma samples from 8 patients with sepsis with a Latex and an ELISA test and calculated the ratio between the D-dimer values obtained with the two tests. Twenty healthy pregnant and twenty pre-eclamptic patients, who are known to have raised D-dimer but low HNE concentrations, were chosen as controls. HNE levels were estimated by determining the HNE-alpha 1-proteinase inhibitor complex (HNE-A1PI) concentration. HNE-A1PI concentration was increased in sepsis patients compared with pre-eclamptic patients (p < 0.0005) and healthy pregnant women (p < 0.0005). In sepsis patients, the D-dimer results were skewed towards lower ratios between Latex and ELISA values compared to pre-eclamptic patients (p = 0.008) and healthy pregnant women (p = 0.0001). In plasma samples from patients with the largest discrepancy between Latex and ELISA D-dimer values, Western blotting with immunostaining indicated degradation of D-dimers to D-like fragments similar to those observed following degradation of cross-linked fibrin by HNE in vitro. We conclude that in sepsis patients there is a marked discrepancy between Latex and ELISA D-dimer values that may be caused by HNE. In such patients Latex D-dimer assays may cause severe underestimation of fibrinolysis.