Relationships between Euglobulin Clot Lysis Time and the Plasma Levels of Tissue Plasminogen Activator and Plasminogen Activator Inhibitor 1

Acute and subacute effects of strenuous exercise on platelet aggregation, coagulation and fibrinolysis in patients with stable coronary artery disease

INTRODUCTION

Strenuous exercise may occasionally cause coronary thrombosis with myocardial infarction and sudden cardiac death.

MATERIALS AND METHODS

Patients with stable coronary artery disease (CAD) (n = 164) and healthy individuals (n = 25) performed strenuous exercise on a bicycle ergometer. Blood was drawn at baseline, immediately after exercise and 2 h later. Platelet aggregation was measured with Multiplate® Analyzer. Thrombin generation was determined using a thrombogram and by measuring prothrombin fragment 1 + 2 (F1 + 2). A clot lysis assay was used to investigate fibrinolysis.

RESULTS

From baseline to immediately after exercise, thrombin receptor activating peptide (TRAP)-induced platelet aggregation increased in CAD patients (Δ77 AU × min, 95 % confidence interval (CI): 46;107) and in healthy individuals (Δ153 AU × min, 95%CI: 75;232). Endogenous thrombin potential (ETP) was unaffected by exercise, whilst F1 + 2 increased (Δ17%, 95%CI: 11;24) in CAD patients. Fibrin clot lysis time increased by 9 % (95%CI: 1-17) in CAD patients and by 26 % (95%CI: 8;45) in healthy individuals. When comparing baseline to 2 h post-exercise, TRAP-induced platelet aggregation remained slightly elevated in both CAD patients (Δ53 AU × min, 95%CI: 22;84) and healthy individuals (Δ140 AU × min, 95%CI: 62;219). In contrast, ETP and F1 + 2 decreased in CAD patients (Δ-6 %, 95%CI: -10;-1 and Δ-8 %, 95%CI: -14;-2). Moreover, clot lysis time decreased (Δ-19 %, 95%CI: -27;-11) in patients with CAD and returned to baseline in healthy individuals. All p-values were <0.05.

CONCLUSIONS

Platelet aggregation and F1 + 2 were substantially elevated immediately after exercise in CAD patients, indicating a pro-thrombotic state. After 2 h of recovery, they exhibited a markedly increase in fibrinolysis. Similar results were observed in healthy individuals.

The Fibrinolytic System and Its Measurement: History, Current Uses and Future Directions for Diagnosis and Treatment

The fibrinolytic system is a key player in keeping the haemostatic balance, and changes in fibrinolytic capacity can lead to both bleeding-related and thrombosis-related disorders. Our knowledge of the fibrinolytic system has expanded immensely during the last 75 years. From the first successful use of thrombolysis in myocardial infarction in the 1960s, thrombolytic therapy is now widely implemented and has reformed treatment in vascular medicine, especially ischemic stroke, while antifibrinolytic agents are used routinely in the prevention and treatment of major bleeding worldwide. Despite this, this research field still holds unanswered questions. Accurate and timely laboratory diagnosis of disturbed fibrinolysis in the clinical setting remains a challenge. Furthermore, despite growing evidence that hypofibrinolysis plays a central role in, e.g., sepsis-related coagulopathy, coronary artery disease, and venous thromboembolism, there is currently no approved treatment of hypofibrinolysis in these settings. The present review provides an overview of the fibrinolytic system and history of its discovery; measurement methods; clinical relevance of the fibrinolytic system in diagnosis and treatment; and points to future directions for research.

Assays to quantify fibrinolysis: strengths and limitations. Communication from the International Society on Thrombosis and Haemostasis Scientific and Standardization Committee on fibrinolysis

Fibrinolysis is a series of enzymatic reactions that degrade insoluble fibrin. Plasminogen activators convert the zymogen plasminogen to the active serine protease plasmin, which cleaves and solubilizes crosslinked fibrin clots into fibrin degradation products. The quantity and quality of fibrinolytic enzymes, their respective inhibitors, and clot structure determine overall fibrinolysis. The quantity of protein can be measured by antigen-based assays, and both quantity and quality can be assessed using functional assays. Furthermore, variations of commonly used assays have been reported, which are tailored to address the role(s) of specific fibrinolytic factors and cellular elements (eg, platelets, neutrophils, and red blood cells). Although the concentration and/or activity of a protein can be quantified, how these individual components contribute to the overall fibrinolysis outcome can be challenging to determine. This difficulty is due to temporal changes within and around the thrombi during the clot breakdown, particularly the fibrin matrix structure, and composition. Furthermore, terms such as "fibrinolytic activity/potential," "plasminogen activation," and "plasmin activity" are often used interchangeably despite having different definitions. The purpose of this review is to 1) summarize the assays measuring fibrinolysis activity and potential, 2) facilitate the interpretation of data generated by these assays, and 3) summarize the strengths and limitations of these assays.

Fibrinolytic assays in bleeding of unknown cause: Improvement in diagnostic yield

Introduction

Aim

Methods

Results

Discussion

Fluorescently conjugated annular fibrin clot for multiplexed real-time digestion analysis

Impaired fibrinolysis has long been considered as a risk factor for venous thromboembolism. Fibrin clots formed at physiological concentrations are promising substrates for monitoring fibrinolytic performance as they offer clot microstructures resembling in vivo. Here we introduce a fluorescently labeled fibrin clot lysis assay which leverages a unique annular clot geometry assayed using a microplate reader. A physiologically relevant fibrin clotting formulation was explored to achieve high assay sensitivity while minimizing labeling impact as fluorescence isothiocyanate (FITC)-fibrin(ogen) conjugations significantly affect both fibrin polymerization and fibrinolysis. Clot characteristics were examined using thromboelastography (TEG), turbidity, scanning electron microscopy, and confocal microscopy. Sample fibrinolytic activities at varying plasmin, plasminogen, and tissue plasminogen activator (tPA) concentrations were assessed in the present study and results were compared to an S2251 chromogenic assay. The optimized physiologically relevant clot substrate showed minimal reporter-conjugation impact with nearly physiological clot properties. The assay demonstrated good reproducibility, wide working range, kinetic read ability, low limit of detection, and the capability to distinguish fibrin binding-related lytic performance. In combination with its ease for multiplexing, it also has applications as a convenient platform for assessing patient fibrinolytic potential and screening thrombolytic drug activities in personalized medical applications.

Demonstration of Three Distinct High-Molecular-Weight Complexes between Plasminogen Activator Inhibitor Type 1 and Tissue-Type Plasminogen Activator

BACKGROUND

 Details of the molecular interaction between tissue-type plasminogen activator (tPA) and plasminogen activator inhibitor type-1 (PAI-1) remain unknown.

METHODS AND RESULTS

 Three distinct forms of high-molecular-weight complexes are demonstrated. Two of the forms were detected by mass spectrometry. The high molecular mass detected by MALDI-TOF MS (matrix-assisted laser desorption ionization-time of flight mass spectrometry) was 107,029 Da, which corresponds to the sum of molecular masses of the intact tPA (65,320 Da) and the intact PAI-1 (42,416 Da). The lower molecular mass was 104,367 Da and is proposed to lack the C-terminal bait peptide of PAI-1 (calculated mass: 3,804 Da), which was detected as a 3,808 Da fragment. When the complex was analyzed by SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis), only a single band was observed. However, after treatment by SDS and Triton X-100, two distinct forms of the complex with different mobilities were shown by SDS-PAGE. The higher molecular weight band demonstrated specific tPA activity on fibrin autography, whereas the lower molecular weight band did not. Peptide sequence analysis of these two bands, however, unexpectedly revealed the existence of the C-terminal cleavage peptide in both bands and its amount was less in the upper band. In the upper band, the sequences corresponding to the regions at the interface between two molecules in its Michaelis intermediate were diminished. Thus, these two bands corresponded to distinct nonacyl-enzyme complexes, wherein only the upper band liberated free tPA under the conditions employed.

CONCLUSION

 These data suggest that under physiological conditions a fraction of the tPA-PAI-1 population exists as nonacylated-enzyme inhibitor complex.

Assessment of endogenous fibrinolysis in clinical practice using novel tests: ready for clinical roll-out?

The occurrence of thrombotic complications, which can result in excess mortality and morbidity, represent an imbalance between the pro-thrombotic and fibrinolytic equilibrium. The mainstay treatment of these complications involves the use of antithrombotic agents but despite advances in pharmacotherapy, there remains a significant proportion of patients who continue to remain at risk. Endogenous fibrinolysis is a physiological counter-measure against lasting thrombosis and may be measured using several techniques to identify higher risk patients who may benefit from more aggressive pharmacotherapy. However, the assessment of the fibrinolytic system is not yet accepted into routine clinical practice. In this review, we will revisit the different methods of assessing endogenous fibrinolysis (factorial assays, turbidimetric lysis assays, viscoelastic and the global thrombosis tests), including the strengths, limitations, correlation to clinical outcomes of each method and how we might integrate the assessment of endogenous fibrinolysis into clinical practice in the future.

Fibrinolysis in Acute and Chronic Cardiovascular Disease

The formation of an obstructive thrombus within an artery remains a major cause of mortality and morbidity worldwide. Despite effective inhibition of platelet function by modern antiplatelet therapies, these agents fail to fully eliminate atherothrombotic risk. This may well be related to extensive vascular disease, beyond the protective abilities of the treatment agents used. However, recent evidence suggests that residual vascular risk in those treated with modern antiplatelet therapies is related, at least in part, to impaired fibrin clot lysis. In this review, we attempt to shed more light on the role of hypofibrinolysis in predisposition to arterial vascular events. We provide a brief overview of the coagulation system followed by addressing the role of impaired fibrin clot lysis in acute and chronic vascular conditions, including coronary artery, cerebrovascular, and peripheral vascular disease. We also discuss the role of combined anticoagulant and antiplatelet therapies to reduce the risk of arterial thrombotic events, addressing both efficacy and safety of such an approach. We conclude that impaired fibrin clot lysis appears to contribute to residual thrombosis risk in individuals with arterial disease on antiplatelet therapy, and targeting proteins in the fibrinolytic system represents a viable strategy to improve outcome in this population. Future work is required to refine the antithrombotic approach by modulating pathological abnormalities in the fibrinolytic system and tailoring therapy according to the need of each individual.

Fibrinolysis-resistant carbonylated fibrin detected in thrombi attached to the vascular wall of abdominal aortic aneurysms

In this study, we investigated how carbonylation of fibrinogen by acrolein modified its indispensable function to enhance fibrinolysis after being converted to fibrin and contributed to generating a fibrinolysis-resistant fibrin clot. Acrolein-treated fibrinogen was subjected to tissue plasminogen activator-induced fibrinolysis assay and the effect of lysine residue carbonylation in fibrinogen on fibrinolysis was analyzed. The acrolein-treated fibrinogen-derived fibrin clot appeared more resistant to fibrinolysis and the N-acetyl 3-formyl-3,4-dehydropiperidino (FDP)-Lysine levels in the lysed solution were positively correlated with the duration of clot lysis. The lysine analog 6-amino hexanoic acid (6AHA), which mimics the C-terminal lysine of fibrin, was carbonylated and its enhancing effect on Glu₁-plasminogen activation was evaluated. After incubation with acrolein, 6AHA was converted to N-acetyl FDP-6AHA, losing its ability to enhance Glu₁-plasminogen activation. These results suggest that fibrinogen carbonylation by acrolein to generate N-acetyl FDP-Lysine resulted in the generation of fibrinolysis-resistant fibrin by attenuating the C-terminal lysine-dependent activation of the Glu₁-plasminogen. In abdominal aortic aneurysms, fibrin(ogen) containing the acrolein adduct N-acetyl FDP-Lysine was detected in the vascular wall-attached thrombi. These results suggest that this mechanism is likely involved in the modification of fibrinolysis-resistant thrombi and to their persistence for a long period.

Recognition of Plasminogen Activator Inhibitor Type 1 as the Primary Regulator of Fibrinolysis

The fibrinolytic system consists of a balance between rates of plasminogen activation and fibrin degradation, both of which are finely regulated by spatio-temporal mechanisms. Three distinct inhibitors of the fibrinolytic system that differently regulate these two steps are plasminogen activator inhibitor type-1 (PAI-1), α2-antiplasmin, and thrombin activatable fibrinolysis inhibitor (TAFI). In this review, we focus on the mechanisms by which PAI-1 governs total fibrinolytic activity to provide its essential role in many hemostatic disorders, including fibrinolytic shutdown after trauma. PAI-1 is a member of the serine protease inhibitor (SERPIN) superfamily and inhibits the protease activities of plasminogen activators (PAs) by forming complexes with PAs, thereby regulating fibrinolysis. The major PA in the vasculature is tissue-type PA (tPA) which is secreted from vascular endothelial cells (VECs) as an active enzyme and is retained on the surface of VECs. PAI-1, existing in molar excess to tPA in plasma, regulates the amount of free active tPA in plasma and on the surface of VECs by forming a tPA-PAI-1 complex. Thus, high plasma levels of PAI-1 are directly related to attenuated fibrinolysis and increased risk for thrombosis. Since plasma PAI-1 levels are highly elevated under a variety of pathological conditions, including infection and inflammation, the fibrinolytic potential in plasma and on VECs is readily suppressed to induce fibrinolytic shutdown. A congenital deficiency of PAI-1 in humans, in turn, leads to life-threatening bleeding. These considerations support the contention that PAI-1 is the primary regulator of the initial step of fibrinolysis and governs total fibrinolytic activity.

Development and application of global assays of hyper- and hypofibrinolysis

Numerous methods for evaluation of global fibrinolytic activity in whole blood or plasma have been proposed, with the majority based on tissue-type plasminogen activator (t-PA) addition to initiate fibrinolysis. We propose that such an approach is useful to reveal hypofibrinolysis, but t-PA concentrations should be kept to a minimum. In this paper, we describe a low-concentration t-PA plasma turbidity assay to evaluate several congenital factor deficiencies, including plasminogen activator inhibitor-1 (PAI-1) and plasminogen deficiency, as well as hemophilia A and B. In addition, we demonstrate a threshold dependency on endogenous PAI-1 levels. To assess endogenous hyperfibrinolysis, we suggest that assays that avoid t-PA addition are preferable, with assays based on euglobulin fractionation remaining a viable choice. We describe a euglobulin fraction clot lysis time (ECLT) assay with spectrophotometric readout and other modifications, and evaluate it as a tool to measure hyperfibrinolysis in inherited clotting factor deficiency states. We demonstrate that the ECLT is predominantly driven by residual amounts of PAI-1, t-PA, and α2-antiplasmin. These assays should be further evaluated for the detection of hypo- or hyperfibrinolysis in acquired thrombotic or hemorrhagic disorders.

Regulation of plasminogen activation on cell surfaces and fibrin

The fibrinolytic system dissolves fibrin and maintains vascular patency. Recent advances in imaging analyses allowed visualization of the spatiotemporal regulatory mechanism of fibrinolysis, as well as its regulation by other plasma hemostasis cofactors. Vascular endothelial cells (VECs) retain tissue-type plasminogen activator (tPA) after secretion and maintain high plasminogen (plg) activation potential on their surfaces. As in plasma, the serpin, plasminogen activator inhibitor type 1 (PAI-1), regulates fibrinolytic potential via inhibition of the VEC surface-bound plg activator, tPA. Once fibrin is formed, plg activation by tPA is initiated and effectively amplified on the surface of fibrin, and fibrin is rapidly degraded. The specific binding of plg and tPA to lytic edges of partly degraded fibrin via newly generated C-terminal lysine residues, which amplifies fibrin digestion, is a central aspect of this pathophysiological mechanism. Thrombomodulin (TM) plays a role in the attenuation of plg binding on fibrin and the associated fibrinolysis, which is reversed by a carboxypeptidase B inhibitor. This suggests that the plasma procarboxypeptidase B, thrombin-activatable fibrinolysis inhibitor (TAFI), which is activated by thrombin bound to TM on VECs, is a critical aspect of the regulation of plg activation on VECs and subsequent fibrinolysis. Platelets also contain PAI-1, TAFI, TM, and the fibrin cross-linking enzyme, factor (F) XIIIa, and either secrete or expose these agents upon activation in order to regulate fibrinolysis. In this review, the native machinery of plg activation and fibrinolysis, as well as their spatiotemporal regulatory mechanisms, as revealed by imaging analyses, are discussed.

Measuring fibrinolysis: from research to routine diagnostic assays

Development and standardization of fibrinolysis methods have progressed more slowly than coagulation testing and routine high-throughput screening tests for fibrinolysis are still lacking. In laboratory research, a variety of approaches are available and are applied to understand the regulation of fibrinolysis and its contribution to the hemostatic balance. Fibrinolysis in normal blood is slow to develop. For practical purposes plasminogen activators can be added to clotting plasma, or euglobulin prepared to reduce endogenous inhibitors, but results are complicated by these manipulations. Observational studies to identify a 'fibrinolysis deficit' have concluded that excess fibrinolysis inhibitors, plasminogen activator inhibitor 1 (PAI-1) or thrombin-activatable fibrinolysis inhibitor (TAFI), zymogen or active enzyme, may be associated with an increased risk of thrombosis. However, results are not always consistent and problems of adequate standardization are evident with these inhibitors and also for measurement of fibrin degradation products (D-dimer). Few methods are available to investigate fibrinolysis under flow, or in whole blood, but viscoelastic methods (VMs) such as ROTEM and TEG do permit the contribution of cells, and importantly platelets, to be explored. VMs are used to diagnose clinical hyperfibrinolysis, which is associated with high mortality. There is a debate on the usefulness of VMs as a point-of-care test method, particularly in trauma. Despite the difficulties of many fibrinolysis methods, research on the fibrinolysis system, taking in wider interactions with hemostasis proteins, is progressing so that in future we may have more complete models and better diagnostic methods and therapeutics.

Development and validation of a high throughput whole blood thrombolysis plate assay

The objective of this work was to develop a high throughput assay for testing in vitro the thrombolytic activity using citrated whole blood samples, and to overcome the limitations of currently available techniques. We successfully developed a method that involves forming halo shaped, tissue factor induced, whole blood clots in 96 well plates, and then precisely measuring the thrombolysis process with a spectrophotometer plate reader. We here describe the implementation of this novel method, which we refer to as halo assay, and its validation with plasmin, urokinase and tissue plasminogen activator at different doses. The resulting data is a highly detailed thrombolysis profile, allowing comparison of different fibrinolytic agents. The time point analysis allows kinetic data to be collected and calculated to determine key parameters such as the activation time and the rate of fibrinolysis. We also assessed the capacity of the model to study the effect of clot maturation time on the fibrinolytic rate, an aspect of thrombosis rather unexplored with currently available methods, but of increasing importance in drug development. This novel thrombolysis assay could be an extremely useful research tool; to study the complex process of thrombolysis, and a valuable translational clinical tool; as a screening device to rapidly identify hypo- or hyper-fibrinolysis.

Fibrinolysis status in the Budd-Chiari syndrome in China

Pathogenesis and clinical characteristics of the Budd-Chiari syndrome (BCS) in Asia are somewhat different from the ones observed in Western countries. Obstruction of the inferior vena cava (IVC) or of the hepatic veins is caused to a greater extent by membranous webs than by thrombosis. Impaired fibrinolysis has been found in European patients with BCS, but its status in Chinese patients with this condition is still unknown. To explore the characteristics of fibrinolysis in BCS patients in this country, we measured the euglobulin lysis time (ELT) for overall fibrinolysis and the plasma levels of five fibrinolytic components in 65 Chinese patients with BCS and 43 healthy controls. In patients, ELTs were slightly shorter than in controls (mean, 293 vs. 357 min, P < 0.02), tissue type plasminogen activator levels were higher than in controls (mean, 239 vs. 185 pg/ml, P < 0.01), and plasminogen activator inhibitor 1 levels were lower than in controls (mean, 1.43 vs. 1.73 ng/ml, P < 0.001). To explore BCS in more detail, we subgrouped the cases according to age, type of venous occlusion, Child-Pugh score, and thrombosis. As a result of this analysis, we found that young patients (age <30 years) had a longer ELT (mean, 440 min) than the older patient groups (30 ≤ age ≤ 44, 45 ≤ age ≤ 54, age>54 years; mean ELT = 242, 198, and 289 min, respectively, all P < 0.05). The independent hepatic vein occlusion subgroup showed a longer ELT (mean, 367 min) than the combined hepatic vein and IVC or the independent IVC occlusion subgroup (mean ELT = 233 and 260 min, both P < 0.05). ELT did not show significant differences between Child-Pugh class A and B subgroups (mean, 267 vs. 333 min, P > 0.05). ELT in the subgroup without thrombosis was shorter than in controls (mean, 288 vs. 358 min, P < 0.05), and in the subgroup with thrombosis, it was also slightly shorter than in controls, without reaching statistical significance (mean, 306 vs. 358 min, P > 0.05). By and large, overall fibrinolytic potential was slightly increased in Chinese patients with BCS in this study, but fibrinolysis differed according to its baseline characteristics. Compared with the one seen in BCS patients from Western countries, BCS in China exhibits certain special changes in fibrinolysis and we were able to explain some of these changes.

Protective effect of composite earthworm powder against diabetic complications via increased fibrinolytic function and improvement of lipid metabolism in ZDF rats

Thrombosis is the leading cause of mortality globally. It is not only a complication but also a risk factor for progression of diabetes. However, alternative oral therapies and prophylaxis with less adverse effect for thrombosis have not been well studied. In this study, composite powder containing earthworm (CEP) was used and its fibrinolytic activity was measured. CEP was found to have a high urokinase-type plasminogen activator like activity in an in vitro assay. It also had significantly shortened euglobulin clot lysis time (ECLT) at 4 and 24 h after ingestion in Sprague Dawley rats. Zucker Diabetic Fatty rats were used to assess the effect of CEP on diabetes and diabetic nephropathy. After 10 weeks of feeding, CEP significantly shortened ECLT and attenuated HbA1c, hepatic lipid accumulation, and urinary albumin excretion and improved glomerular mesangial matrix score. Therefore, CEP may have beneficial effects on diabetes and diabetic nephropathy.

Bidirectional functions of thrombin on fibrinolysis: Evidence of thrombin-dependent enhancement of fibrinolysis provided by spontaneous plasma clot lysis

Besides procoagulant activity, thrombin exhibits anticoagulant and profibrinolytic activities. We demonstrated that the euglobulin clot lysis time (ECLT) was shortened by endogenously generated thrombin as a result of the inactivation of plasminogen activator inhibitor type 1 (PAI-1). In contrast, thrombin suppressed fibrinolytic activity through the activation of thrombin activatable fibrinolysis inhibitor (TAFI). Here, using three different clot lysis assays of the ECLT, the tissue plasminogen activator supplemented plasma clot lysis time (tPA-PCLT) and the spontaneous plasma clot lysis time (s-PCLT), we analyzed how the coagulation process modifies fibrinolysis. The ECLT was shortened by exogenously supplemented thrombin in a dose-dependent manner in the absence of calcium ion (Ca(++)), whereas this shortening was not observed in the presence of Ca(++) where endogenous prothrombin was effectively activated to thrombin. This shortening was also not observed for the tPA-PCLT, in which tPA is supplemented in excess and PAI-1 activity is mostly lost. On the contrary, thrombin dose-dependently prolonged the tPA-PCLT, which was mostly abolished by inhibitors of carboxypeptidase and activated FXIII, suggesting that the prolongation is TAFI- and Factor XIII-dependent. The s-PCLT was shortened when thrombin generation was boosted by supplementing tissue factor and phosphatidylserine together with Ca(++), which was more apparent in the presence of inhibitors of activated FXIII and activated TAFI. Thus, thrombin appeared to express its enhancing effect on fibrinolysis even in plasma, in addition to its inhibiting effect. These bidirectional functions of thrombin on fibrinolysis seem to take place on demand under different environments to maintain adequate vascular blood flow.

A case of late stent thrombosis following platelet transfusion in a patient with aplastic anemia

Aplastic anemia is a condition in which the bone marrow fails to produce adequate numbers of peripheral blood elements. The incidences of atherosclerosis and myocardial infarction in patients with congenital coagulation disorders and chronic thrombocytopenia are very low. In this paper, a case of late stent thrombosis within a drug-eluting stent occurring after platelet transfusion in a patient with aplastic anemia is presented. The authors' observations emphasize the risks of platelet transfusion and the authors' support withholding such a treatment unless vitally indicated, in patients with coronary artery stent implantation and even in those on dual antiplatelet therapy.

Profibrinolytic effect of Enzamin, an extract of metabolic products from Bacillus subtilis AK and Lactobacillus

Fibrinolytic system impairment contributes to the development of thrombotic disease such as cardiovascular disease and stroke. Therefore, an agent that increases fibrinolytic activity may be useful for the prevention of these diseases. In this study, to explore novel profibrinolytic agents, we examined the profibrinolytic effect of Enzamin, an extract of metabolic products from Bacillus subtilis AK and Lactobacillus in vitro and in vivo. Enzamin directly enhanced plasmin activity generated by tissue-type plasminogen activator (t-PA) by twofold but not by urokinase-type plasminogen activator (u-PA) in vitro, which was measured employing both the chromogenic substrate H-D: -Val-Leu-Lys-pNA (S-2251) and fibrin plate. Enzamin also increased plasmin activity generated by t-PA in the cell lysate and culture medium of endothelial cells, measured by fibrin zymography. Furthermore, the oral administration of a 1% concentration of Enzamin increased plasmin activity generated by t-PA by 1.7-fold but not by u-PA in the euglobulin fraction of mouse plasma. In conclusion, Enzamin has a unique ability to enhance the fibrinolytic activity through an increase in endogenous plasmin activity generated by t-PA released from endothelial cells, and may be a beneficial supplement for the prevention of thrombotic episodes.

Effects of imidapril therapy on endogenous fibrinolysis in patients with recent myocardial infarction

BACKGROUND

Treatment with an angiotensin-converting enzyme (ACE) inhibitor in patients with myocardial infarction has been shown to modify endogenous fibrinolysis.

HYPOTHESIS

We investigated the effects of the ACE inhibitor imidapril on endogenous fibrinolysis in association with the serum ACE activity.

METHODS

In a randomized, double-blind, placebo-controlled study beginning 4 weeks after uncomplicated myocardial infarction, 15 patients received imidapril (5 mg daily) (imidapril group) and another 15 received placebo therapy (placebo group) for 4 weeks. Blood sampling was performed before the start of administration and on Days 3, 7, and 28 after the start of administration. Serum ACE activity and plasma fibrinolytic variables [plasminogen activator inhibitor (PAI) activity, plasminogen activator inhibitor type 1 (PAI-1) antigen level, and tissue type plasminogen activator (TPA) antigen level] were measured.

RESULTS

There was no difference between the imidapril and placebo groups in serum ACE activity or plasma fibrinolytic variables before administration. Serum ACE activity decreased significantly on Days 3, 7, and 28 in the imidapril group. The decrease of PAI activity and PAI-1 antigen levels was significantly less on Days 7 and 28, but not on Day 3. The TPA antigen level in the imidapril group was unchanged. None of the parameters in the placebo group was changed.

CONCLUSION

The ACE inhibitor imidapril modified fibrinolysis, but the effects occurred after the inhibition of serum ACE activity.

Unique secretory dynamics of tissue plasminogen activator and its modulation by plasminogen activator inhibitor-1 in vascular endothelial cells

We analyzed the secretory dynamics of tissue plasminogen activator (tPA) in EA.hy926 cells, an established vascular endothelial cell (VEC) line producing GFP-tagged tPA, using total internal reflection-fluorescence (TIR-F) microscopy. tPA-GFP was detected in small granules in EA.hy926 cells, the distribution of which was indistinguishable from intrinsically expressed tPA. Its secretory dynamics were unique, with prolonged (> 5 minutes) retention of the tPA-GFP on the cell surface, appearing as fluorescent spots in two-thirds of the exocytosis events. The rapid disappearance (mostly by 250 ms) of a domain-deletion mutant of tPA-GFP possessing only the signal peptide and catalytic domain indicates that the amino-terminal heavy chain of tPA-GFP is essential for binding to the membrane surface. The addition of PAI-1 dose-dependently facilitated the dissociation of membrane-retained tPA and increased the amounts of tPA-PAI-1 high-molecular-weight complexes in the medium. Accordingly, suppression of PAI-1 synthesis in EA.hy926 cells by siRNA prolonged the dissociation of tPA-GFP, whereas a catalytically inactive mutant of tPA-GFP not forming complexes with PAI-1 remained on the membrane even after PAI-1 treatment. Our results provide new insights into the relationship between exocytosed, membrane-retained tPA and PAI-1, which would modulate cell surface-associated fibrinolytic potential.

Risk factors for osteonecrosis of the femoral head in patients with sickle cell disease

The mechanisms involved in the pathogenesis of osteonecrosis of the femoral head in sickle cell disease are not fully known. The aim of this study was to identify risk factors for osteonecrosis of the femoral head among sickle cell disease patients. Clinical (frequency of painful crises and hospitalisation) and laboratory parameters (euglobulin clot lysis time, haematocrit, platelet count, and leucocyte count) of 25 consecutive patients with avascular necrosis of the femoral head from sickle cell disease were compared with those of 26 age- and sex-matched sickle cell disease patients without avascular necrosis. The group with avascular necrosis of the femoral head (mean age 23.7+/-4.9 years) had a significantly higher rate of painful crises (p = 0.03) and hospitalisations per year (p = 0.002) than the group without avascular necrosis (mean age 21.6+/-5.2 years). The group with avascular necrosis also had a significantly higher euglobulin clot lysis time than the group without avascular necrosis (p = 0.001). In conclusion, it appears that not all patients with sickle cell disease have impaired fibrinolytic activity. The aetiology of avascular necrosis in sickle cell disease is multifactorial.

Circadian clock molecules CLOCK and CRYs modulate fibrinolytic activity by regulating the PAI-1 gene expression

Disruptions of circadian rhythms are associated with the development of many disorders. However, whether a disruption of the circadian clock can cause anomalies of the hemostatic balance remains unknown. The present study examines coagulation and fibrinolytic activities in circadian clock mutants, a homozygous Clock mutant and Cry1/Cry2 double knockout (Cry1/2-deficient) mice. The euglobulin clot lysis time (ELT) showed circadian variations that peaked at 21:00 (early night) in wild-type mice, suggesting that fibrinolytic activity is lowest at this time. The ELT was continuously reduced in Clock mutants, while the ELT was significantly increased and did not differ between day and night (9:00 and 21:00) in Cry1/2-deficient mice. The prothrombin time (PT) and activated partial prothrombin time (APTT) were constant in all genotypes. To identify which factors cause the loss of ELT rhythm, we measured fibrinolytic parameters in Clock mutant and Cry1/2-deficient mice. The robust circadian fluctuation of plasma plasminogen activator inhibitor 1 (PAI-1) that peaked at early night was damped to trough levels in Clock mutant mice. On the other hand, PAI-1 levels in Cry1/2-deficient mice remained equivalent to the peak levels of those in wild-type mice at both 9:00 and 21:00. Circadian changes in plasma PAI-1 levels seemed to be regulated at the level of gene expression, because the plasma PAI-1 levels in Clock mutant and Cry1/2-deficient mice were closely correlated with the level of PAI-1 mRNA transcript in these mice. Plasma plasminogen and hepatic mRNA levels were not rhythmic in wild-type mice, and continuously higher in Clock mutant than in wild-type or Cry1/2-deficient mice. In contrast, the activity and mRNA levels of tissue type plasminogen activator (t-PA), plasma levels and mRNA levels of plasminogen, and plasma levels of alpha2 plasmin inhibitor (alpha2PI) in all genotypes were constant throughout the day. Coagulation parameters such as factor VII, factor X, prothrombin and fibrinogen remained constant throughout the day, and were not affected by clock gene mutations. These results suggest that circadian clock molecules play an important role in hemostatic balance by regulating the fibrinolytic systems.

C-reactive protein decreases tissue plasminogen activator activity in human aortic endothelial cells: evidence that C-reactive protein is a procoagulant

OBJECTIVE

C-reactive protein (CRP) can promote atherothrombosis by decreasing endothelial nitric oxide synthase and prostacyclin, and by stimulating both plasminogen activator inhibitor-1 in endothelial cells and tissue factor in mononuclear cells. Plasminogen activator-1, a marker of fibrinolysis, is the primary inhibitor of tissue plasminogen activator (tPA). Thus, we tested the effect of CRP on tPA in human aortic endothelial cells.

METHODS AND RESULTS

Incubation of human aortic endothelial cells with CRP (> or =12.5 microg/mL) significantly decreased tPA antigen and activity. Adenyl cyclase inhibitors, an endothelin receptor antagonist, superoxide dismutase, and a nitric oxide donor failed to reverse the effect of CRP on tPA. CRP increased interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha. Neutralization of both IL-1beta and TNFalpha reversed the inhibition of tPA by CRP. Furthermore, in volunteers that have high CRP levels, euglobulin clot lysis time was significantly increased compared with those that have low CRP levels, providing further evidence that high CRP levels are associated with a procoagulant state.

CONCLUSIONS

CRP inhibits tPA activity via generation of proinflammatory cytokines (IL-1beta and TNFalpha). This study provides additional novel data that CRP is a procoagulant and has implications for atherothrombosis.

Resolution of Budd-Chiari syndrome due to activation of endogenous fibrinolysis that may be induced by weight reduction

We describe a 45-year-old female with polycythemia vera and Leiden factor V mutation, who suffered the subacute form of Budd-Chiari syndrome and was treated with anticoagulants and diuretics. Surprisingly, after 3 months clinical signs of Budd-Chiari syndrome resolved; venography disclosed the resolution of thrombosis in the vena cava inferior and hepatic veins. This was associated with considerable increase of endogenous fibrinolytic activity, documented by a substantial change in the euglobulin clot lysis time, and a decrease of plasminogen activator inhibitor antigen and activity. During the disease the patient followed a diet and significantly reduced her body weight. Putting all data together it could be speculated that weight reduction (along with anticoagulants) considerably activated endogenous fibrinolysis, resulting in spontaneous resolution of Budd-Chiari syndrome. The validity of this explanation should be explored in a larger clinical study.

Synthesis and Thrombolytic Activity of Carboline‐3‐carboxylic Acid Modified Metabolites of Ala‐Arg‐Pro‐Ala‐Lys

From the metabolism of H-Ala-Arg-Pro-Ala-Lys-OH, four metabolites, H-Pro-Ala-Lys-OH, H-Arg-Pro-Ala-Lys-OH, H-Ala-Arg-Pro-OH, and H-Ala-Arg-Pro-Ala-OH were identified. In order to find a new lead compound of thrombolytic peptide, 3S-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid was introduced to the N- and C-terminal of the metabolites by use of the common coupling strategy. Under this condition, the pseudopeptides (5a-d and 7a-d) were obtained with a good yield. The thrombolytic activities of 3S-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid containing oligopeptides were evaluated in vitro and in vivo. The result indicated that the thrombolytic activity of the pseudopeptide depended on the sequence and the modification pattern of the metabolites, and only when 3S-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid was introduced into the C-terminal of H-Pro-Ala-Lys-OH or H-Arg-Pro-Ala-Lys-OH, the desirable thrombolytic activity was retained and enhanced significantly.

The composition and sequence specificity of Pro-Ala-Lys-OH for the thrombolytic activities of P6A and related oligopeptides

The in vitro and in vivo thrombolytic activities of Ala-Arg-Pro-Ala-Lys-OH, its analogs and the related peptides were assayed. The results indicate that when (5)Lys of Ala-Arg-Pro-Ala-Lys-OH is changed into (5)Arg, and (3)Lys of Pro-Ala-Lys-OH is changed into (3)Arg the thrombolytic activities are collapsed; when Pro-Ala-Lys-OH is changed into Ala-Pro-Lys-OH, and Ala-Arg-Pro-Ala-Lys-OH is changed into Ala-Arg-Ala-Pro-Lys-OH the thrombolytic activities are also collapsed; when (5)Lys of Ala-Arg-Pro-Ala-Lys-OH is changed into (5)nLeu the thrombolytic activities are again collapsed. All of the results indicate that for the thrombolytic activities of Ala-Arg-Pro-Ala-Lys-OH and the related peptides Pro-Ala-Lys-OH exhibits either amino acid composition specificity or sequence specificity. The composition and sequence specificity of Pro-Ala-Lys-OH reflects its rule as the pharmacophore of P6A and the related peptides.

Comparison of fibrinolytic activity in the femoral vein and the right atrium

Local fibrinolytic activity in leg veins has not been completely explored. Since the blood in the right atrium is a mixture of venous blood supplied from the whole body, the fibrinolytic activity in the right atrium may be used as a reference value to which local values can be compared in order to identify local hyperfibrinolysis or hypofibrinolysis. We compared fibrinolytic parameters [tissue-type plasminogen activator (t-PA), plasminogen activator inhibitor (PAI-1), euglobulin clot lysis time] measured in the femoral vein with those in the right atrium. The blood samples were obtained during right heart catheterization of 51 patients. No differences in t-PA antigen [9.6 ng/ml (6.6-11.9 ng/ml) versus 8.1 ng/ml (6.7-11.3 ng/ml)] [median (interquartile range)] and PAI-1 antigen [9.3 ng/ml (7.1-16.0 ng/ml) versus 8.4 ng/ml (5.5-14.3 ng/ml)] levels were found, whereas t-PA activity was significantly higher [183 IU/ml (39-1097 IU/ml) versus 92 IU/ml (5-680 IU/ml), P < 0.05], PAI-1 activity significantly lower [7.2 IU/ml (5.1-10.2 IU/ml) versus 7.9 IU/ml (5.8-10.3 IU/ml), P < 0.05], and the euglobulin clot lysis time was significantly shorter [6.2 1000/min (4.8-10.0 1000/min) versus 5.5 1000/min (4.1-9.1 1000/min), P < 0.05] in the femoral vein compared with the right atrium. In conclusion, our results show that local fibrinolytic activity in the femoral vein is higher than in the right atrium, and thus demonstrate that increased local fibrinolysis is present in leg veins.

Activated protein C attenuates coagulation-associated over-expression of fibrinolytic activity by suppressing the thrombin-dependent inactivation of PAI-1

Several activated coagulation factors have been reported to enhance fibrinolysis by neutralizing plasminogen activator inhibitor type 1 (PAI-1) activity. We evaluated the physiological relevance of this mechanism using the euglobulin clot lysis time (ECLT) assay in the presence and absence of Ca2+, which is controlled by PAI-1 and mimics physiological thrombolysis. We found that the ECLT (18.5 +/- 0.6 h) was shortened by Ca2+ (5 mm) (6.6 +/- 0.1 h). A significant difference was observed in thrombin generation by the presence of Ca2+ in the euglobulin fraction. Prothrombin was almost fully converted to thrombin within 15 min in the presence of Ca2+, whereas essentially no conversion was observed without Ca2+. The presence of activated protein C (aPC) suppressed thrombin generation, and attenuated the shortening of ECLT in a dose-dependent manner, an effect enhanced by phospholipid and protein S. In the absence of Ca2+, aPC did not prolong the ECLT. After addition of biotin-labeled recombinant PAI-1 to the euglobulin fraction, PAI-1 was cleaved to lower molecular weight forms only in the presence of Ca2+. This cleavage did not occur in the presence of aPC, suggesting that thrombin was the catalyst for PAI-1 cleavage. The cleavage and inactivation of PAI-1 by generated thrombin is proposed to be responsible for the shortening of ECLT by Ca2+ and for coagulation-associated over-expression of fibrinolysis. Under such conditions, aPC appeared to suppress thrombin generation and to normalize highly activated fibrinolysis.

Identification, synthesis and bioassay for the metabolites of P6A

The metabolites Ala-Arg-Pro-Ala-OH, Ala-Arg-Pro-OH, Arg-Pro-Ala-Lys-OH and Pro-Ala-Lys-OH were identified by HPLC/ESI/MS from the in vivo blood of Ala-Arg-Pro-Ala-Lys-OH (P6A) received mice. The in vitro incubation of P6A in the blood of mice the same metabolites were also found by use of the Prep LC System. The protective intermediates of these metabolites were prepared via the solution method using the stepwise synthesis in 77.4, 90, 88, and 80% yield, respectively. After deprotection with catalytic hydrogenation the intermediates were converted into the corresponding sequences Arg-Pro-Ala-Lys-OH, Pro-Ala-Lys-OH, Ala-Arg-Pro-Ala-OH, and Ala-Arg-Pro-OH in 90, 95, 85% and 86% yield, respectively. In the thrombolysis in vivo assay the synthetic Ala-Arg-Pro-Ala-OH, and Ala-Arg-Pro-OH exhibited no activity. On the other hand the thrombolytic activity of Arg-Pro-Ala-Lys-OH was comparable to P6A, and an enhanced thrombolytic activity was observed for Pro-Ala-Lys-OH. In the in vitro fibrinolytic lysis tests the approximate results were obtained and an enhanced activity was also observed for Pro-Ala-Lys-OH. In the euglobulin clot lysis time tests P6A, Arg-Pro-Ala-Lys-OH and Pro-Ala-Lys-OH gave significantly shorter time than that given by UK, demonstrating their fast action.

A new euglobulin clot lysis assay for global fibrinolysis

Plasma fibrinolytic activity has been measured by the euglobulin clot lysis time (ELT) since the late 1950s. The euglobulin clot lysis assay (ECLA) method has been modified using a computerized kinetic spectrophotometric microtiter plate reader and measures optical density changes of recalcified euglobulin fraction of plasma samples over time. This method has been applied to normal healthy adults, children, pregnant women and newborn infants, which represent physiologic extremes of the ELT. The ECLA method adds measurements of maximum absorbance (Max Abs), area under the curve (AUC) and mean velocity to the standard clot lysis time. The resulting curves are unique to this method and have been analyzed and compared in order to establish normal ranges. Fibrinogen levels, plasminogen activator inhibitor-1 (PAI-1) antigen, PAI-1 activity and thrombin activatable fibrinolytic inhibitor (TAFI) antigen levels were measured in each individual of the four groups. Each protein measured within each study group except TAFI correlated with the lysis time, maximum absorbance and area under the curve. Considering all four groups together, PAI correlates most highly with lysis time, fibrinogen correlates the highest with Max Abs; fibrinogen and PAI-1 antigen have equally high correlations to AUC. Area under the curve is highly correlated with all coagulation parameters measured; the most significant contributor is fibrinogen. These observations are interesting, but at this time, it cannot be said that any of the test parameters are better than lysis time in distinguishing between these normal physiologic states.

PAI-1 in human hypertension: relation to hypertensive groups

BACKGROUND

Although the renin-angiotensin system and insulin resistance (IR) have been identified as major regulators of plasminogen activator inhibitor type-1 (PAI-1), their roles in hypertensive subjects is not clearly defined.

METHODS

We examined the effect of dietary salt restriction on PAI-1 levels in 239 hypertensive subjects from three centers. Subjects were placed on a 200 and 10 mmol/day sodium diets for 1-week periods. Plasma renin activity (PRA) and PAI-1 levels were measured on the last day of both diets and fasting insulin, glucose, and aldosterone (ALDO) levels, only on the low salt diet.

RESULTS

Sodium restriction increased PAI-1 levels from 32.1 +/- 2.5 ng/mL to 39.8 +/- 3.2 ng/mL (P = .009). There was a strong positive correlation between PAI-1 levels and PRA (r = 0.228, P = .0004), IR (r = 0.222, P = .001), triglycerides (r = 0.275, P < .001), and ALDO (P = .018 for linear trend). The patients were divided into low renin (low IR and ALDO levels), nonmodulators (normal PRA, high IR, and low ALDO levels), and modulators (normal PRA, intermediate IR, and normal ALDO levels) groups to assess the relative contribution of each factor to PAI-1 levels. Modulators had significantly (P = .019) higher PAI-1 levels compared to the low renin and nonmodulators who had similar PAI-1 levels.

CONCLUSIONS

Plasma renin activity, IR, and ALDO all correlate with PAI-1 levels in the hypertensive subjects. However, the data suggest that ALDO may be an important factor contributing to the variability of PAI-1 levels in individual hypertensive subjects.

Effect of a synthetic carboxy-terminal peptide of alpha(2)-antiplasmin on urokinase-induced fibrinolysis

alpha(2)-Antiplasmin (alpha(2)AP) interferes with the binding of plasminogen to fibrin because lysine residues in its carboxy-terminal region compete with those in fibrin, presumably the same way that free lysine or epsilon-aminocaproic acid (EACA) inhibits plasminogen binding to fibrin. While this overall process causes an inhibition of fibrinolysis, the converse was observed with a 26-residue synthetic peptide (AP26) corresponding to the carboxy-terminal region of alpha(2)AP. The AP26 peptide, in fact, accelerated urokinase-induced lysis of (1) fully crosslinked fibrin with complete gamma-dimer and alpha-polymer formation; (2) partially crosslinked fibrin that had undergone only gamma-dimerization; and (3) noncrosslinked fibrin. The AP26 peptide also inhibited factor XIIIa-catalyzed crosslinking of fibrin alpha-chains, and this also accelerated lysis of fibrin. EACA had no effect. In the presence of noncrosslinked fibrin, AP26 promoted plasminogen activation by urokinase and fibrinolysis. EACA only slightly increased the rate of plasminogen activation, and as expected, it inhibited fibrinolysis. Since AP26 peptide enhanced the lysis of partially crosslinked and noncrosslinked fibrin, our results indicate that inhibition of factor XIIIa-catalyzed alpha-polymer formation by AP26, although associated with accelerated fibrinolysis, is not the primary mechanism. Instead, our data support the conclusion that AP26 enhances the conversion of plasminogen to plasmin approximately 5-fold, probably by inducing a conformational change in plasminogen structure just as occurs with low concentrations of lysine or EACA. At higher concentrations, however, AP26 apparently does not approach the avidity or affinity of lysine or EACA for the kringle structures of plasminogen or plasmin so that their binding to fibrin is blocked. Whether AP26 alone, or as part of another molecule, could have potential for enhancing thrombolysis will require further study.

Plasma fibrinogen level is an important determinant of prolonged euglobulin clot lysis time in hemodialysis patients

The euglobulin clot lysis time (ECLT), a traditional measure of plasminogen activation, directly depends on plasma fibrinogen (FBG) level. This fact was neglected in studies concluding that prolonged ECLT in chronic hemodialysis (HD) patients pointed exclusively to impaired fibrinolysis. We studied the relations between ECLT and plasma FBG levels in HD patients in relation to certain hepatic and inflammatory markers. Median ECLT of 320 minutes (range, 150 to 620 minutes) and plasma FBG of 306 mg/dL (range, 171 to 553 mg/dL) were higher in 75 HD patients than in 60 healthy controls (Mann-Whitney p < 0.0001). There were positive associations between these parameters both in the patients (Spearman p = 0.273, p = 0.018) and the controls (p = 0.672, p < 0.0001). The FBG-corrected ECLT (plasma FBG/ECLT) (in mg/[min x dL]) in the patients (0.92 [range, 0.47 to 2.43]) was not different (p = 0.065) from that in the controls (1.08 [0.58 to 1.67]). In the patients, serum alanine aminotransferase inversely correlated with ECLT (p = -0.306, p = 0.008) and FBG (p = -0.310, p = 0.007), whereas serum C-reactive protein was associated positively with these variables (p = 0.383, p = 0.0007; p = 0.477, p < 0.0001, respectively). The FBG-corrected ECLT was not related to either marker. In conclusion, increased plasma FBG level, a continuum between liver dysfunction and stimulation by chronic inflammation, is an important determinant of prolonged ECLT in HD patients. The FBG-corrected ECLT value suggests that baseline activation of fibrinolysis is normal in these patients, and that this simple index could be useful in its laboratory assessment.

Elevation of plasma free PAI-1 levels as an integrated endothelial response to severe burns

To clarify the role of plasminogen activator inhibitor type 1 (PAI-1) in postburn hypercoagulation, we assayed the plasma levels of tissue-type plasminogen activator (t-PA) antigen, total PAI-1 antigen, and total t-PA-PAI-1 complex in 15 burned patients. The total body surface area of the burn injury ranged from 30 to 80%. Serial blood samples were collected from 12 to 168 h following the thermal injury. The plasma t-PA level and the free PAI-1 level increased significantly in the immediate postburn period, and the percent increase in the latter over the values in the healthy controls was much greater than that of the former. The ratio of the concentrations of t-PA-PAI-1 complex to free PAI-1 decreased throughout the 7 postburn days. The fact that the decreases in this ratio clearly showed no dissociation of the euglobulin fraction suggests that the postburn hypofibrinolysis occurred as a result of increased synthesis of PAI-1. On the other hand, changes in several parameters of the coagulation or fibrinolysis system and in plasma thrombomodulin showed that postburn hypercoagulability is associated with secondary hyperfibrinolysis with no evidence of vascular endothelial injury. The paradoxical coexistence of postburn hyper- and hypofibrinolysis is a good reflection of the character of PAI-1, which is a biphasic protein that is both a functional protein and an acute phase reactant. Thus, increased synthesis of PAI-1 may not enhance postburn hypercoagulability to create a coagulation-dominant type of disseminated intravascular coagulation severe enough to trigger multiple organ dysfunction syndrome. In conclusion, increased synthesis of PAI-1 in the initial postburn period reflects an integrated endothelial response to burn stress, and because it is a functional protein, the concentration of free PAI-1 antigen may be an important index for predicting secondary consumption coagulopathy.

Endothelial function in patients with hyperthyroidism before and after treatment with propranolol and thiamazol

Hyperthyroidism is associated with a higher incidence of arterial thromboembolism; increasing age, atrial fibrillation, and mitral valve abnormalities are risk factors. However, the contribution of endogenous coagulation parameters is unclear. Because thyroid hormone influences receptor and transcription factors, it can be expected that it will influence proteins involved in coagulation processes synthetised in many cells. Fourteen hyperthyroid patients were studied untreated, after 1 week of treatment with propranolol, and after therapeutic treatment with thiamazol. Fourteen matched controls were used for comparison. On each occasion, endothelial marker proteins, coagulation/fibrinolysis factors, and inflammatory (liver) markers were measured. Excess thyroid hormone was associated with elevated levels of most endothelium-associated proteins. In addition, plasma fibronectin and fibrinogen were increased, while plasminogen was decreased. No evidence was found that hyperthyroidism was associated with coagulation/fibrinolysis activation, or with increased levels of the inflammation markers interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha) or C-reactive protein (CRP). Propranolol treatment only lowered the von Willebrand factor propeptide, and slightly increased plasminogen. Treatment with thiamazol returned all parameters to normal. Hyperthyroidism increased the plasma levels of most endothelial marker proteins, and of some liver-synthetized proteins. No evidence for coagulation/fibrinolysis activation was found. However, it appears that endothelial activation, which is indicative of a procoagulant state, is present in hyperthyroidism. This may explain the association between hyperthyroidism and thromboembolism especially if other risk factors are present. von Willebrand factor II (vWF:Ag-II) levels may be suitable markers to evaluate acute changes in endothelial function because this parameter responds more rapidly to changes in endothelial function than other factors.

Plasma Concentration of Endogenous Tissue Plasminogen Activator and the Occurrence of Future Cardiovascular Events

Data from recent prospective studies of hemostasis and thrombosis indicate that the plasma concentration of endogenous tissue-type plasminogen activator (tPA) is often elevated years in advance of a first arterial occlusion. Specifically, among healthy subjects with no prior cardiovasacular disease, the risk of future myocardial infarction and stroke appears to be three to four times higher among subjects with high baseline levels of tPA antigen as compared to subjects with lower levels. Whether this relationship represents activation of the endogenous fibrinolytic system in response to the presence of preclinical atherosclerosis or is a reflection of elevated concentrations of local plasminogen activator inhibitors is currently unresolved. However, cross-sectional data indicate that the plasma concentration of IPA antigen is related to several traditional atherosclerotic risk factors, including HDL cholesterol, findings that further support a direct relationship between endogenous IPA and vascular risk. In concert with data concerning the primary inhibitors of plasminogen activation, it has been hypothesizd that the endogenous fibrinolytic system varies within the general population such that certain individuals are prone to thrombosis, whereas others may be prone to hemorrhage. Thus, observations regarding fibrinolytic activation and inhibition raise the possibility that assessment of the intrinsic fibrinolytic system may prove useful in identifying individuals at increased risk for vascular thrombosis. In addition, available findings suggest that therapeutic agents capable of favorably shifting the net filerinolytic balance may provide a new strategy for cardiovascular disease prevention.

Characterization of Wild-Type and Mutant 2-Antiplasmins: Fibrinolysis Enhancement by Reactive Site Mutant

During human blood clotting, 2-antiplasmin (2AP) becomes covalently linked to fibrin when activated blood clotting factor XIII (FXIIIa) catalyzes the formation of an isopeptide bond between glutamine at position two in 2AP and a specific ɛ-lysyl group in each of the -chains of fibrin. This causes fibrin to become resistant to plasmin-mediated lysis. We found that chemically Arg-modified 2AP, which lacked plasmin-inhibitory activity, competed effectively with native 2AP for becoming cross-linked to fibrin and as a consequence, enhanced fibrinolysis. Recombinant 2AP reported to date by other groups either lacked or possessed a low level of FXIIIa substrate activity. As a first step in the development of an engineered protein that might have potential as a localized fibrin-specific fibrinolytic enhancer, we expressed recombinant 2AP in Pichia pastoris yeast. Two forms of nonglycosylated recombinant 2AP were expressed, isolated and characterized: (1) wild-type, which was analogous to native 2AP, and (2) a mutant form, which had Ala substituted for the reactive-site Arg364. Both the wild-type and mutant forms of 2AP functioned as FXIIIa substrates with affinities and kinetic efficiencies comparable to those of native 2AP, despite each having an additional acetylated Met blocking group at their respective amino-termini. Wild-type recombinant 2AP displayed full plasmin inhibitory activity, while mutant 2AP had none. Neither the absence of glycosylation nor blockage of the amino-terminus affected plasmin-inhibitory or FXIIIa substrate activities of wild-type 2AP. When our mutant 2AP, which lacked plasmin-inhibitory function, was added to human plasma or whole blood clots, urokinase (UK)-induced clot lysis was enhanced in a dose-dependent manner, indicating that mutant 2AP augmented lysis by competing with native 2AP for FXIIIa-catalyzed incorporation into fibrin.

Fibrinolytic activity in laparoscopic cholecystectomy

The aim of this study was to examine the fibrinolytic activity in laparoscopic cholecystectomy (LC) to determine whether changes occur that might indicate a greater risk of thrombosis. The study was carried out in 20 patients who had undergone laparoscopic surgery for cholelithiasis without complications. The average age was 59.4 years (34-77 years). Seventy-five percent were women. The mean operating time was 70 minutes (35-120 minutes). Pneumoperitoneum at 14 mm Hg was maintained in all patients, and they were in 30 degrees reverse Trendelenburg position. Postoperative mobilization was obtained before 24 hours, and patients were discharged 48 hours after surgery. The control group was composed of 12 patients, evenly distributed by age, sex, and length of surgery, who had undergone Bassini herniorrhaphy without complications or relapses. The following hemostatic parameters were studied: plasma fibrinolytic activity (PFA), euglobulin fibrinolytic activity (EFA), tissue-type plasminogen activator (t-PA), fast-acting plasminogen activator inhibitor-1 (PAI-1), and D-dimer (D-D). Samples were obtained at the following times: (1) under basal conditions the day before surgery, (2) preoperatively, (3) at the end of surgery, (4) 24 hours after surgery, and (5) on the seventh day following surgery. No patient had clinical manifestations of thromboembolic disease immediately after surgery or during an average follow-up period of 16 months (range 15-18 months). Analysis of the results of global fibrinolysis showed that fibrinolytic activity was enhanced only in the postoperative period (third sample) of the LC patients. The fraction of euglobulins enhances fibrinolytic activity in both groups in the third sample with regard to the other determinations; the LC patients showed a higher degree of significance (p<0.005). A significant increase of postoperative t-PA in both groups was found, being more significant in the LC group (p<0.005). In the PAI-1 values, no significant differences existed between either determinations or groups. A significant increase in D-dimer (p<0.05) occurred in the immediate postoperative period (third sample) and 24 hours later (fourth sample), returning to normal basal values on the seventh day. No significant differences were found between the two groups. These results seem to indicate that LC produces an increase in the fibrinolytic activity in plasma as a result of the liberation of tissue plasminogen activator from the venous endothelium, which could indicate hypocoagulability during the immediate postoperative period and, therefore, signify less thrombotic risk for patients undergoing this procedure.

Reperfusion After Venous Occlusion Caused Transient Increase in Plasminogen Activator Inhibitor-1 in Systemic Circulation

From the point of local regulation, we investigated fibrinolytic activity both in local and systemic circulations, using a venous occlusion test as a stimulus of tissue plasmin ogen activator (t-PA) release in human volunteers. Blood samples were taken before, during, and after venous occlusion from the occluded arm as trapped blood and the unoccluded arm as blood of systemic circulation. In these samples, fibri nolytic activity by euglobulin-clot lysis time and related factors in t-PA and plasminogen activator inhibitor-1 (PAI-1) were measured. Venous occlusion increased fibrinolytic activity ac companied by an increase in t-PA without an increase in PAI-1 on the occluded arm. The fibrinolytic activity on the unoc cluded arm did not change. Five minutes after reperfusion, however, a transient increase in PAI-1 and no change of fibri nolytic activity were observed in the unoccluded arm. Transient increase of PAI-1 after reperfusion was also observed in the occluded arm. These results suggested that increased t-PA by venous occlusion was neutralized by released PAI-1 after reperfusion. Key Words: Tissue-plasminogen activator— Euglobulin-clot lysis time—Fibrinolysis.

Effects of electric footshock and water immersion restraint stresses on fibrinolytic parameters in the plasma of rats

Wistar rats were exposed to electric footshock (ES) or water immersion restraint stress (WS). Blood was taken immediately after, 24, or 48 hours after the stress. The stomachs of rats taken 1 hour after stress application indicate that there were many bleeding spots in the stomachs of WS rats, but practically no visible bleeding spots in the stomachs of ES rats. Plasma levels of t-PA antigens increased in ES rats up to 24 hours after the stress, but the t-PA antigen levels decreased up to 48 hours in ES rats. There were no changes in t-PA activities in plasma of WS rats, but the levels in ES rats decreased immediately and 48 hours after the stress. PAI activity did not change immediately after WS but increased 24 hours after the stress. There was no change in PAI activity in ES rats up to 48 hours. ELT did not change in ES rats, but prolonged in WS rats at 24 hours after the stress. There were significant negative correlations between t-PA antigen levels or activities and ELT in control rats. No correlation was observed in ES or WS rats between t-PA antigen levels and ELT, and no correlation was shown in WS rats between t-PA activities and ELT. Plasma levels of catecholamines increased at the 20-minute period during ES, which may not explain the delayed effects of ES on hemostatic balance. Plasma levels of arginine vasopressin increased significantly immediately after the shock up to 2 hours, indicating that the stress was conveyed to the hypothalamus during the stress application. These results may indicate that some stressors induce an increase or decrease in the local balance of fibrinolytic activities, resulting in bleeding or thrombosis in the local vessels. Such changes may not be detected in the general circulation due to the neutralization of locally induced fibrinolytic changes or the involvement of other hepatically originated hemostatic factors induced by stressors.

Increased plasma tissue factor levels in acute myocardial infarction

BACKGROUND

Tissue factor (TF) is a low molecular weight glycoprotein that initiates the clotting cascade and is considered to be a major regulator of coagulation, hemostasis, and thrombosis.

METHODS AND RESULTS

We examined plasma TF levels in 31 consecutive patients with acute myocardial infarction (AMI) (within 6 hours after the onset of symptoms), 27 patients with stable exertional angina, and 27 control subjects. Ten patients with AMI had a history of unstable angina before infarction, and 21 had a sudden onset of infarction. The plasma TF level was higher in the AMI group than in the stable exertional angina and control groups (240 +/- 112 vs 184 +/- 46 pg/ml [p < 0.05] vs 177 +/- 37 pg/ml, p < 0.01, respectively). TF levels were decreased in the chronic phase (2 weeks after admission) compared with the acute phase of infarction (from 240 +/- 112 pg/ml to 222 +/- 97 pg/ml, p < 0.05). In addition, plasma TF levels were higher in patients with AMI with prodromal unstable angina than in patients with a sudden onset of infarction (300 +/- 169 pg/ml vs 212 +/- 57 pg/ml, p < 0.05). TF levels were similar in the acute and chronic phases in the patients with AMI with prodromal unstable angina (300 +/- 169 pg/ml vs 290 +/- 136 pg/ml, p = not significant) but were decreased in the chronic phase in the patients with AMI with sudden onset (from 212 +/- 57 pg/ml to 190 +/- 49 pg/ml, p < 0.05).

CONCLUSION

Increased plasma TF levels in patients with AMI may reflect enhanced intravascular procoagulant activity. The higher TF levels in patients with AMI with prodramol unstable angina may be associated with repeated episodes of myocardial ischemia and reperfusion.

The inhibition of human factor Xa by plasminogen activator inhibitor type 1 in the presence of calcium ion, and its enhancement by heparin and vitronectin

Plasminogen activator inhibitor type 1 (PAI-1), a member of serine proteinase inhibitor superfamily, is known to inhibit thrombin in the presence of either heparin or vitronectin. We analyzed possible inhibitory activity of PAI-1 on human factor Xa. PAI-1 inhibited factor Xa in the presence of calcium ion (Ca2+), whereas no inhibition was observed in the absence of Ca2+. Half maximal enhancement by Ca2+ was obtained at 0.8 mM. An equimolar complex formation between factor Xa and PAI-1 in the presence of Ca2+ was observed by SDS polyacrylamide gel electrophoresis. Both unfractionated heparin and vitronectin enhanced the inhibition only in the presence of Ca2+. Apparent second-order rate constant (ki) for the inhibition of factor Xa by PAI-1 at 5 mM Ca2+ was 1.6 x 10(4) M-1 s-1, and was enhanced 3-fold by 2 u/ml of heparin (4.6 x 10(4) M-1 s-1) and 10-fold by 100 nM vitronectin (1.6 x 10(5) M-1 s-1), respectively. The interaction between Ca(2+)-bound factor Xa and PAI-1 could be important from the view of PAI-1 neutralization and enhancement of fibrinolysis.

Fibrinolytic factors and the risk of myocardial infarction or sudden death in patients with angina pectoris. ECAT Study Group. European Concerted Action on Thrombosis and Disabilities

BACKGROUND

Disturbances of the fibrinolytic system that lead to decreased removal of fibrin deposits may be important risk factors for coronary thrombosis. There is as yet no consensus on the prognostic value of fibrinolytic parameters, which may be attributed in part to the choice of confounding variables controlled for.

METHODS AND RESULTS

The ECAT study is a prospective multicenter study of 3043 patients with angina pectoris followed for 2 years. Baseline measurements included 10 fibrinolytic variables. The results were analyzed in relation to the subsequent incidence of myocardial infarction or sudden coronary death. They are presented before and after adjustment for clusters of confounding variables that are markers of different mechanisms: insulin resistance (body mass index, triglyceride, and HDL cholesterol), inflammation (fibrinogen and C-reactive protein), and endothelial cell damage (von Willebrand factor). An increased incidence of events was associated with higher baseline concentrations of tissue plasminogen activator (TPA) antigen (P = .0002), plasminogen activator inhibitor-1 (PAI-1) activity (P = .02), and PAI-1 antigen (P = .001). The associations of PAI-1 activity and PAI-1 antigen with risk of events disappeared after adjustment for parameters reflecting insulin resistance but were not affected by other adjustments. TPA antigen was affected to a similar extent by adjustment for parameters reflecting insulin resistance. Inflammation, or endothelial cell damage, but the risk association disappeared only after combined adjustments.

CONCLUSIONS

The prognostic role of PAI-1 in predicting coronary events is related principally to insulin resistance, whereas that of TPA antigen could be explained only by its relationship with different mechanisms, including insulin resistance, inflammation and endothelial cell damage.

Hemostasis, platelet function and serotonin in acute and chronic renal failure

A pathogenetic role for fibrin deposition and platelet activation in the kidney is thought to play a role in the pathogenesis of acute renal failure (ARF). Thus, some fibrinolytic parameters and platelet function have been studied in 17 patients with ARF and compared to healthy volunteers and subjects with chronic renal failure (CRF). Since serotonin may participate in pathological processes resulting from platelet/vessel wall interactions, its level in the whole blood and plasma was also assayed. In ARF and CRF platelet aggregatory responses in both whole blood and in platelet rich plasma upon stimulation with various agonists (collagen, arachidonic acid, ADP, ristocetin) were lower than those obtained in healthy volunteers. Increased levels of lipoprotein (a), von Willebrand factor (vWF) and fibronectin were found in ARF relative to controls. Protein C activity was significantly lower in patients with ARF. Euglobulin clot lysis time was prolonged in ARF and CRF, reflecting a decreased overall fibrinolytic activity. Activity of tissue plasminogen activator (tPA) inhibitor (PAI) and PAI:Ag were higher in ARF, whereas tPA:Ag, urokinase, tPA/PAI complexes, thrombin-antithrombin complexes (TAT), plasmin-antiplasmin (PAP) complexes, fibrinogen, and F1+2 did not differ between ARF and controls. In CRF elevated levels of TAT, PAP, fibrinogen and prothrombin fragments F1+2 were found, whereas concentration of fibronectin was lowered when compared to controls. In both groups of renal failure patients increased levels of fibrin monomers and d-dimer were found relative to healthy volunteers. Whole blood serotonin was significantly lower, whereas plasma serotonin was significantly higher in patients with ARF and CRF relative to controls. Serotonin uptake and its release from platelets were markedly diminished in patients with ARF and CRF. Chronic renal failure exhibit a slightly different pattern of coagulopathies that acute renal failure.