New insights into factors affecting clot stability: a role for thrombin activatable fibrinolysis inhibitor (TAFI; plasma procarboxypeptidase B, plasma procarboxypeptidase U, procarboxypeptidase R)

Separation of high-purity plasma extracellular vesicles for investigating proteomic signatures in diabetic retinopathy

Extracellular vesicles (EVs) play a multifaceted role in intercellular communication and hold significant promise as bio-functional indicators for clinical diagnosis. Although plasma samples represent one of the most critical sources of circulating EVs, the existing technical challenges associated with plasma-EV isolation have restricted their application in disease diagnosis and biomarker discovery. In this study, we introduce a two-step purification method utilizing ultracentrifugation (UC) to isolate crude extracellular vesicle (EV) samples, followed by a phospholipid affinity-based technique for the selective isolation of small EVs, ensuring a high level of purity for downstream proteomic analysis. Our research demonstrates that the UC & TiO2-coated magnetic bead (TiMB) purification system significantly improves the purity of EVs when compared to conventional UC or TiMB along. We further revealed that proteomic alterations in plasma EVs effectively reflect key gene ontology components associated with diabetic retinopathy (DR) pathogenesis, including the VEGF-activated neuropilin pathway, positive regulation of angiogenesis, angiogenesis, cellular response to vascular endothelial growth factor stimulus, and immune response. By employing a comprehensive analytical approach, which incorporates both time-series analysis (cluster analysis) and differential analysis, we have identified three potential protein signatures including LGALS3, MYH10, and CPB2 that closely associated with the retinopathy process. These proteins exhibit promising diagnostic and severity-classification capabilities for DR disease. This adaptable EV isolation system can be regarded as an effective analytical tool for enhancing plasma-based liquid biopsies toward clinical applications.

A review of hyperfibrinolysis in cats and dogs

The fibrinolytic system is activated concurrently with coagulation; it regulates haemostasis and prevents thrombosis by restricting clot formation to the area of vascular injury and dismantling the clot as healing occurs. Dysregulation of the fibrinolytic system, which results in hyperfibrinolysis, may manifest as clinically important haemorrhage. Hyperfibrinolysis occurs in cats and dogs secondary to a variety of congenital and acquired disorders. Acquired disorders associated with hyperfibrinolysis, such as trauma, cavitary effusions, liver disease and Angiostrongylus vasorum infection, are commonly encountered in primary care practice. In addition, delayed haemorrhage reported in greyhounds following trauma and routine surgical procedures has been attributed to a hyperfibrinolytic disorder, although this has yet to be characterised. The diagnosis of hyperfibrinolysis is challenging and, until recently, has relied on techniques that are not readily available outside referral hospitals. With the recent development of point-of-care viscoelastic techniques, assessment of fibrinolysis is now possible in referral practice. This will provide the opportunity to target haemorrhage due to hyperfibrinolysis with antifibrinolytic drugs and thereby reduce associated morbidity and mortality. The fibrinolytic system and the conditions associated with increased fibrinolytic activity in cats and dogs are the focus of this review article. In addition, laboratory and point-of-care techniques for assessing hyperfibrinolysis and antifibrinolytic treatment for patients with haemorrhage are reviewed.

Stable thrombus formation on irradiated microvascular endothelial cells under pulsatile flow: Pre-testing annexin V-thrombin conjugate for treatment of brain arteriovenous malformations

BACKGROUND

Our goal is to develop a vascular targeting treatment for brain arteriovenous malformations (AVMs). Externalized phosphatidylserine has been established as a potential biomarker on the endothelium of irradiated AVM blood vessels. We hypothesize that phosphatidylserine could be selectively targeted after AVM radiosurgery with a ligand-directed vascular targeting agent to achieve localized thrombosis and rapid occlusion of pathological AVM vessels.

OBJECTIVE

The study aim was to establish an in vitro parallel-plate flow chamber to test the efficacy of a pro-thrombotic conjugate targeting phosphatidylserine.

METHODS

Conjugate was prepared by Lys-Lys cross-linking of thrombin with the phosphatidylserine-targeting ligand, annexin V. Cerebral microvascular endothelial cells were irradiated (5, 15, and 25 Gy) and after 1 or 3 days assembled in a parallel-plate flow chamber containing whole human blood and conjugate (1.25 or 2.5 μg/mL). Confocal microscopy was used to assess thrombus formation after flow via binding and aggregation of fluorescently-labelled platelets and fibrinogen.

RESULTS AND CONCLUSIONS

The annexin V-thrombin conjugate induced rapid thrombosis (fibrin deposition) on irradiated endothelial cells under shear stress in the parallel-plate flow device. Unconjugated, non-targeting thrombin did not induce fibrin deposition. A synergistic interaction between radiation and conjugate dose was observed. Thrombosis was greatest at the highest combined doses of radiation (25 Gy) and conjugate (2.5 μg/mL). The parallel-plate flow system provides a rapid method to pre-test pro-thrombotic vascular targeting agents. These findings validate the translation of the annexin V-thrombin conjugate to pre-clinical studies.

Decrements in the Thrombin Activatable Fibrinolysis Inhibitor (TAFI) Levels in Association with Orlistat Treatment in Obesity

Obesity and its associated metabolic complications can impair the physiologic regulation of fibrinolysis, leading to a hyper coagulable state. We aimed to assess circulating thrombin activatable fibrinolysis inhibitor (TAFI) levels in obese female patients and to test the effects of orlistat-induced weight loss on basal TAFI concentrations. Obese female outpatients age 18 and older, with a body mass index (BMI, calculated as weight in kilograms divided by the square of height in meters) of at least 30, were included into the study. Thirteen nonobese (median BMI, 22.60 kg/m2) age-matched females were taken as controls. Plasma TAFI levels were measured before orlistat administration and after 6 months of orlistat treatment in the obese group and only one measurement was done in the control group. Twenty-seven obese patients were recruited into the study. The median TAFI level of the control group was 124.00; this value was significantly lower than the basal TAFI level of the obese group (p < 0.001). TAFI levels after orlistat therapy were statistically significantly lower than basal TAFI levels (p < 0.001) in the obese group. Hemostatic abnormalities including TAFI alterations represent a link between obesity and vascular thrombosis. Effective interventions should be considered in improving the obesity-associated prothrombotic risk profile.

Lack of TAFI increases brain damage and microparticle generation after thrombolytic therapy in ischemic stroke

BACKGROUND

Thrombin-activatable fibrinolysis inhibitor (TAFI) plays an important role in coagulation and fibrinolysis. Whereas TAFI deficiency may lead to a haemorrhagic tendency, data from TAFI knockout mice (TAFI-/-) are controversial and no differences have been reported in these animals after ischemic stroke. There are also no data regarding the role of circulating microparticles (MPs) in TAFI-/-.

OBJECTIVES

to examine the effect of tPA on the rate of intracranial haemorrhage (ICH) and on MPs generated in a model of ischemic stroke in TAFI-/- mice.

METHODS

Thrombin was injected into the middle cerebral artery (MCA) to analyse the effect of tPA (10mg/Kg) on the infarct size and haemorrhage in the absence of TAFI. Immunofluorescence for Fluoro-Jade C was performed on frozen brain slides to analyse neuronal degeneration after ischemia. MPs were isolated from mouse blood and their concentrations calculated by flow cytometry.

RESULTS

Compared with saline, tPA significantly increased the infarct size in TAFI-/- mice (p<0.05). Although plasma fibrinolytic activity (fibrin plate assay) was higher in these animals, no macroscopic or microscopic ICH was detected. A positive signal for apoptosis and degenerating neurons was observed in the infarct area, being significantly higher in tPA treated TAFI-/- mice (p<0.05). Interestingly, higher numbers of MPs were found in TAFI-/- plasma as compared to wild type, after stroke (p<0.05).

CONCLUSIONS

TAFI deficiency results in increased brain damage in a model of thrombolysis after ischemic stroke, which was not associated with bleeding but with neuronal degeneration and MP production.

Carboxypeptidases in disease: insights from peptidomic studies

Carboxypeptidases (CPs) perform many diverse physiological functions by removing C-terminal amino acids from proteins and peptides. Some CPs function in the degradation of proteins in the digestive tract while other enzymes play biosynthetic roles in the formation of neuropeptides and peptide hormones. Another set of CPs modify tubulin by removing amino acids from the C-terminus and from polyglutamyl side chains, thereby altering the properties of microtubules. This review focuses on three CPs: carboxypeptidase E, carboxypeptidase A6, and cytosolic carboxypeptidase 1. Naturally occurring mutations in all three of these enzymes are associated with disease phenotypes, ranging from obesity to epilepsy to neurodegeneration. Peptidomics is a useful tool to investigate the relationship between these mutations and alterations in peptide levels. This technique has also been used to define the function and characteristics of CPs. Results from peptidomics studies have helped to elucidate the function of CPs and clarify the biological underpinnings of pathologies by identifying peptides altered in disease states. This review describes the use of peptidomic techniques to gain insights into the normal function of CPs and the molecular defects caused by mutations in the enzymes.

Providing accurate information to patients who develop deep vein thrombosis

Venous thromboembolism is an increasingly recognised complication in the community and in hospital in-patients. Nowadays, most physicians are familiar with the algorithmic approach to the management of suspected deep vein thrombosis. However, a lack of understanding remains with regard to certain aspects of the diagnostic and treatment pathways, which has resulted in the wrong information being imparted to patients. Some of these issues are discussed in this paper, with considerations for changes in management.

Tissue factor, blood coagulation, and beyond: an overview

Emerging evidence shows a broad spectrum of biological functions of tissue factor (TF). TF classical role in initiating the extrinsic blood coagulation and its direct thrombotic action in close relation to cardiovascular risks have long been established. TF overexpression/hypercoagulability often observed in many clinical conditions certainly expands its role in proinflammation, diabetes, obesity, cardiovascular diseases, angiogenesis, tumor metastasis, wound repairs, embryonic development, cell adhesion/migration, innate immunity, infection, pregnancy loss, and many others. This paper broadly covers seminal observations to discuss TF pathogenic roles in relation to diverse disease development or manifestation. Biochemically, extracellular TF signaling interfaced through protease-activated receptors (PARs) elicits cellular activation and inflammatory responses. TF diverse biological roles are associated with either coagulation-dependent or noncoagulation-mediated actions. Apparently, TF hypercoagulability refuels a coagulation-inflammation-thrombosis circuit in “autocrine” or “paracrine” fashions, which triggers a wide spectrum of pathophysiology. Accordingly, TF suppression, anticoagulation, PAR blockade, or general anti-inflammation offers an array of therapeutical benefits for easing diverse pathological conditions.

Structure and function of factor XI

Factor XI (FXI) is the zymogen of an enzyme (FXIa) that contributes to hemostasis by activating factor IX. Although bleeding associated with FXI deficiency is relatively mild, there has been resurgence of interest in FXI because of studies indicating it makes contributions to thrombosis and other processes associated with dysregulated coagulation. FXI is an unusual dimeric protease, with structural features that distinguish it from vitamin K-dependent coagulation proteases. The recent availability of crystal structures for zymogen FXI and the FXIa catalytic domain have enhanced our understanding of structure-function relationships for this molecule. FXI contains 4 "apple domains" that form a disk structure with extensive interfaces at the base of the catalytic domain. The characterization of the apple disk structure, and its relationship to the catalytic domain, have provided new insight into the mechanism of FXI activation, the interaction of FXIa with the substrate factor IX, and the binding of FXI to platelets. Analyses of missense mutations associated with FXI deficiency have provided additional clues to localization of ligand-binding sites on the protein surface. Together, these data will facilitate efforts to understand the physiology and pathology of this unusual protease, and development of therapeutics to treat thrombotic disorders.

Pregnancy-associated changes in the hemostatic system

Pregnancy, from implantation to parturition, presents unique and profound challenges to a women's hemostatic system. During pregnancy, potentially catastrophic bleeding can occur during implantation and endovascular trophoblast invasion of the maternal spiral arteries. The risk of hemorrhage reaches a peak during the third stage of labor when the placenta is shorn from the decidua basalis exposing 120 spiral arteries largely denuded of their smooth muscle, and thus, their ability to constrict in response to injury. These challenges are met by dramatic changes in the local uterine, and systemic hemostatic systems. The net effect of these changes is to increase the efficiency of clotting and to impair fibrinolysis. Unfortunately, they also lead to an increase in the prevalence of venous thromboembolism, which is otherwise uncommon in reproductive age women.

Hemostasis factors and aging

With advancing age, an increasing number of healthy individuals have laboratory signs of heightened coagulation enzyme activity. Such biochemical hypercoagulability might be the basis of either the increased thrombotic tendency occurring with age or a harmless manifestation of this process. Centenarians had striking signs of heightened coagulation enzyme activity, accompanied by signs of enhanced formation of fibrin and secondary hyperfibrinolysis. Plasma concentrations of fibrinogen and factor VIII were higher than in controls, whereas other coagulation factors were not elevated. It is of interest that centenarians have a significantly higher frequency than young individuals of the high risk 4G allele of the PAI-1-675 (4G/5G) polymorphism, mutant factor V (Arg506Gln) and prothrombin gene G20210A mutation. Von Willebrand factor (VWF), a well-known independent predictor of atherothrombotic disease, was increased in centenarians, independently of the blood group, confirming the previous results of a state of hypercoagulability. The finding that the VWF cleaving proteases levels are low when VWF levels are high in centenarians could be a corollary of the previous described paradox of successful aging, adding another marker of increased risk of atherothrombosis to the scenario. Alike, high prevalence of anti-phospholipids antibodies, not associated with an anti-phospholipid syndrome has been described in centenarians. In conclusion, the data show the oldest old do not escape the state of hypercoagulability associated with aging, but that this phenomenon is compatible with health and longevity. Hence, high plasma levels of the coagulation activation markers in older populations do not necessarily mirror a high risk of arterial or venous thrombosis.

Plasma activity of thrombin activatable fibrinolysis inhibitor in Crimean-Congo hemorrhagic fever

OBJECTIVES

Crimean-Congo hemorrhagic fever (CCHF) is a potentially fatal viral infection. The exact mechanism for hemorrhage remains unknown. Thrombin activatable fibrinolysis inhibitor (TAFI) is a plasma procarboxypeptidase B-like proenzyme and synthesized in the liver, down-regulating fibrinolysis. In this study, we measured the TAFI activity in plasma of patients with CCHF to examine the relationship between hemorrhage and the pathogenesis of CCHF.

METHODS

Twenty-one patients and similar number of controls were included in the study. The diagnosis of CCHF was confirmed through detection of IgM by ELISA and/or PCR. TAFI activity was measured in plasma samples.

RESULTS

TAFI activity in CCHF patient group was mean 7.2+/-2.3 microg/ml (range: 0.95-10.31 microg/ml) and in the control group was mean 11.7+/-4.1 microg/ml (range: 3.07-23.9 microg/ml). There was a significant decrease of TAFI activity in CCHF patients when compared to controls. A positive correlation between CRP, PT, INR, serum albumin and TAFI activity levels were found. We suggest that the decrease of TAFI activity may be due to liver dysfunction during viral active disease state.

CONCLUSIONS

Low TAFI activity may be an attributable factor, leading to imbalance in fibrinolysis, resulting in bleeding complications in CCHF.

The influence of inflation rate on the hematologic and hemodynamic effects of intermittent pneumatic calf compression for deep vein thrombosis prophylaxis

OBJECTIVE

The study was conducted to determine whether the different inflation rates of intermittent pneumatic compression systems used in deep vein thrombosis prophylaxis influence their hematologic and hemodynamic effects.

METHODS

A rapidly inflating intermittent calf compression system and a more gently inflating equivalent were applied to 20 healthy male volunteers for 2 hours each. Venous blood samples were taken for analysis of blood coagulation and fibrinolytic potential. Blood flow velocity was measured in the femoral vein with Doppler ultrasound.

RESULTS

Tissue factor pathway inhibitor significantly increased after the 2 hours of compression for both pumps (78.0 to 85.0 ng/mL rapid, P = .004; 76.5 to 78.0 ng/mL gentle, P = .5), as did plasminogen activator activity (0.85 to 1.05 IU/mL rapid, P = .006; 0.85 to 1.5 IU/mL gentle, P = 0.5). Plasminogen activator inhibitor 1 activity was reduced, although only approaching significance for the gentle system (16.5 to 14.3 AU/mL, P = .06). A D-dimer test for global fibrinolysis showed significant increases for the gently inflating system (97 to 411 ng/mL P < .001) but not for the rapidly inflating system (276 to 350 ng/mL P = .9). The rapidly inflating system produced significantly higher venous peak velocities and augmentations as expected.

CONCLUSIONS

Although the data confirm that both types of intermittent compression suppress procoagulant activation, rapid inflation clearly produced no extra benefit in increasing global fibrinolysis, and may be less hematologically effective.

Limited mutagenesis increases the stability of human carboxypeptidase U (TAFIa) and demonstrates the importance of CPU stability over proCPU concentration in down-regulating fibrinolysis

Procarboxypeptidase U [proCPU, thrombin-activatable fibrinolysis inhibitor (TAFI), EC 3.4.17.20] belongs to the metallocarboxypeptidase family and is a zymogen found in human plasma. ProCPU has been proposed to be a molecular link between coagulation and fibrinolysis. Upon activation of proCPU, the active enzyme (CPU) rapidly becomes inactive due to its intrinsic instability. The inherent instability of CPU is likely to be of major importance for the in vivo down-regulation of its activity, but the underlying structural mechanisms of this fast and spontaneous loss of activity of CPU have not yet been explained, and they severely inhibit the structural characterization of CPU. In this study, we screened for more thermostable versions of CPU to increase our understanding of the mechanism underlying the instability of CPU's activity. We have shown that single as well as a few 2-4 mutations in human CPU can prolong the half-life of CPU's activity at 37 degrees C from 0.2 h of wild-type CPU to 0.5-5.5 h for the mutants. We provide evidence that the gain in stable activity is accompanied by a gain in thermostability of the enzyme and increased resistance to proteolytic digest by trypsin. Using one of the stable mutants, we demonstrate the importance of CPU stability over proCPU concentration in down-regulating fibrinolysis.

Thrombin activatable fibrinolysis inhibitor (TAFI)--how does thrombin regulate fibrinolysis?

The thrombin-catalysed conversion of plasma fibrinogen into fibrin and the development of an insoluble fibrin clot are the final steps of the coagulation cascade during haemostasis. A delicate balance between coagulation and fibrinolysis determines the stability of the fibrin clot. Thrombin plays a central role in this process, it not only forms the clot but it is also involved in stabilizing the clot by activating thrombin activatable fibrinolysis inhibitor (TAFI). Activated TAFI protects the fibrin clot against lysis. Here we will discuss the mechanisms for regulation of fibrinolysis by thrombin. The role of the coagulation system for the generation of thrombin and for the activation of TAFI implies that defects in thrombin generation will directly affect the protection of clots against lysis. Thus, defects in activation of TAFI might contribute to the severity of bleeding disorders. Vice versa an increased activation of TAFI due to an increased rate of thrombin generation might lead to thrombotic disorders. Specific inhibitors of activated TAFI or inhibitors that interfere with the generation of thrombin might provide novel therapeutic strategies for thrombolytic therapy. Besides having a role in the regulation of fibrinolysis, TAFI may also have an important function in the regulation of inflammation, wound healing and blood pressure.

Thrombin activatable fibrinolysis inhibitor in Behçet's disease

INTRODUCTION

Thrombin activatable fibrinolysis inhibitor (TAFI) is a procarboxypeptidase downregulating plasmin formation, thereby causing a tendency for thrombosis development. Since, Behçet's disease (BD) is a systemic vasculitis, which is commonly complicated by arterial and venous thrombosis, we aimed to find out plasma TAFI levels in BD, compared with healthy controls. We also searched whether plasma TAFI levels were significantly different between Behçet's subgroups with and without thrombosis.

MATERIALS AND METHODS

In this study, 105 BD patients (M/F: 64/41; mean age 36+/-1 years), followed up by Ege University Rheumatology Department were enrolled. The exclusion criteria were hemophilia, hyperlipidemia, diabetes mellitus, hepatic diseases renal failure, antiphospholipid positivity, oral contraceptive use and pregnancy. Age-and sex-matched healthy controls (n=53) were also included. Plasma TAFI levels were measured by ELISA. Since TAFI is also an acute-phase reactant, we also measured other inflammatory markers such as C-reactive protein (CRP).

RESULTS

Plasma TAFI levels were significantly higher in Behçet's patients (91.1+/-7.4 ng/ml) compared with healthy controls (14.3+/-4.5 ng/ml) (P<0.001), but there were no significant difference between the subgroups with and without thrombosis. In BD, there was no correlation between plasma TAFI levels and CRP.

CONCLUSIONS

Regardless of manifest thrombosis, plasma TAFI levels in BD were significantly higher than in healthy controls. High TAFI levels might possibly contribute to the thrombotic tendency in BD. Future studies investigating TAFI gene polymorphism and functional activity are clearly needed, to clarify the exact role of TAFI in Behçet's thrombosis.