Natural heterogeneity of α2-antiplasmin: functional and clinical consequences

Targeting Fibrinolytic Inhibition for Venous Thromboembolism Treatment: Overview of an Emerging Therapeutic Approach

Venous thrombosis and pulmonary embolism (venous thromboembolism) are important causes of morbidity and mortality worldwide. In patients with venous thromboembolism, thrombi obstruct blood vessels and resist physiological dissolution (fibrinolysis), which can be life threatening and cause chronic complications. Plasminogen activator therapy, which was developed >50 years ago, is effective in dissolving thrombi but has unacceptable bleeding risks. Safe dissolution of thrombi in patients with venous thromboembolism has been elusive despite multiple innovations in plasminogen activator design and catheter-based therapy. Evidence now suggests that fibrinolysis is rigidly controlled by endogenous fibrinolysis inhibitors, including α2-antiplasmin, plasminogen activator inhibitor-1, and thrombin-activable fibrinolysis inhibitor. Elevated levels of these fibrinolysis inhibitors are associated with an increased risk of venous thromboembolism in humans. New therapeutic paradigms suggest that accelerated and effective fibrinolysis may be achieved safely by therapeutically targeting these fibrinolytic inhibitors in venous thromboembolism. In this article, we discuss the role of fibrinolytic components in venous thromboembolism and the current status of research and development targeting fibrinolysis inhibitors.

Expression of fibroblast activation protein-α in human deep vein thrombosis

BACKGROUND

Fibroblast activation protein-α (FAP), a type-II transmembrane serine protease, is associated with wound healing, cancer-associated fibroblasts, and chronic fibrosing diseases. However, its expression in deep vein thrombosis (DVT) remains unclear. Therefore, this study investigated FAP expression and localization in DVT.

METHODS

We performed pathological analyses of the aspirated thrombi of patients with DVT (n = 14), classifying thrombotic areas in terms of fresh, cellular lysis, and organizing reaction components. The organizing reaction included endothelialization and fibroblastic reaction. We immunohistochemically examined FAP-expressed areas and cells, and finally analyzed FAP expression in cultured dermal fibroblasts.

RESULTS

All the aspirated thrombi showed a heterogeneous mixture of at least two of the three thrombotic areas. Specifically, 83 % of aspirated thrombi showed fresh and organizing reaction components. Immunohistochemical expression of FAP was restricted to the organizing area. Double immunofluorescence staining showed that FAP in the thrombi was mainly expressed in vimentin-positive or α-smooth muscle actin-positive fibroblasts. Some CD163-positive macrophages expressed FAP. FAP mRNA and protein levels were higher in fibroblasts with low-proliferative activity cultured under 0.1 % fetal bovine serum (FBS) than that under 10 % FBS. Fibroblasts cultured in 10 % FBS showed a significant decrease in FAP mRNA levels following supplementation with hemin, but not with thrombin.

CONCLUSIONS

The heterogeneous composition of venous thrombi suggests a multistep thrombus formation process in human DVT. Further, fibroblasts or myofibroblasts may express FAP during the organizing process. FAP expression may be higher in fibroblasts with low proliferative activity.

Impaired endogenous fibrinolysis status: a potential prognostic predictor in ischemic stroke

Stroke confers a severe global healthcare burden, hence exploring risk factors for stroke occurrence and prognosis is important for stroke prevention and post-stroke management strategies. Endogenous fibrinolysis is a spontaneous physiological protective mechanism that dissolves thrombus to maintain vascular patency. Recently, impaired endogenous fibrinolysis has been considered as a potential novel cardiovascular risk factor, but its link with ischaemic stroke in the past has been underappreciated. In this review, we summarize the latest mechanisms of endogenous fibrinolysis, review the current evidence and data on endogenous fibrinolysis in ischemic stroke. It includes the structure of thrombus in ischemic stroke patients, the effect of fibrin structure on the endogenous fibrinolytic efficiency, and the association between intravenous thrombolytic therapy and endogenous fibrinolysis in ischemic stroke. It also includes the single factors (tissue plasminogen activator, urokinase plasminogen activator, plasminogen activator inhibitor-1, thrombin activatable fibrinolysis inhibitor, complement component 3, complement component 5, alpha-2-antiplasmin, plasmin-alpha-2-antiplasmin complex, and lipoprotein[a]), and the global assessments of endogenous fibrinolysis status (thromboelastography, rotational thromboelastometry, and global thrombosis test), and their potential as predictors to identify occurrence or unfavorable functional outcomes of ischemic stroke. All of these assessments present advantages and limitations, and we suggest that the global thrombosis test may be more appropriate for detecting impaired endogenous fibrinolysis status in ischemic stroke patients.

Genetics of ischemic stroke functional outcome

Ischemic stroke, which accounts for 87% of cerebrovascular accidents, is responsible for massive global burden both in terms of economic cost and personal hardship. Many stroke survivors face long-term disability-a phenotype associated with an increasing number of genetic variants. While clinical variables such as stroke severity greatly impact recovery, genetic polymorphisms linked to functional outcome may offer physicians a unique opportunity to deliver personalized care based on their patient's genetic makeup, leading to improved outcomes. A comprehensive catalogue of the variants at play is required for such an approach. In this review, we compile and describe the polymorphisms associated with outcome scores such as modified Rankin Scale and Barthel Index. Our search identified 74 known genetic polymorphisms spread across 48 features associated with various poststroke disability metrics. The known variants span diverse biological systems and are related to inflammation, vascular homeostasis, growth factors, metabolism, the p53 regulatory pathway, and mitochondrial variation. Understanding how these variants influence functional outcome may be helpful in maximizing poststroke recovery.

The Roles of Fibrinolytic Factors in Bone Destruction Caused by Inflammation

Chronic inflammatory diseases, such as rheumatoid arthritis, spondyloarthritis, systemic lupus erythematosus, Crohn's disease, periodontitis, and carcinoma metastasis frequently result in bone destruction. Pro-inflammatory cytokines such as tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), IL-6, and IL-17 are known to influence bone loss by promoting the differentiation and activation of osteoclasts. Fibrinolytic factors, such as plasminogen (Plg), plasmin, urokinase-type plasminogen activator (uPA), its receptor (uPAR), tissue-type plasminogen activator (tPA), α2-antiplasmin (α2AP), and plasminogen activator inhibitor-1 (PAI-1) are expressed in osteoclasts and osteoblasts and are considered essential in maintaining bone homeostasis by regulating the functions of both osteoclasts and osteoblasts. Additionally, fibrinolytic factors are associated with the regulation of inflammation and the immune system. This review explores the roles of fibrinolytic factors in bone destruction caused by inflammation.

Connecting impaired fibrinolysis and dyslipidemia

A State of the Art lecture entitled "Connecting Fibrinolysis and Dyslipidemia" was presented at the International Society on Thrombosis and Haemostasis Congress 2023. Hemostasis balances the consequences of blood clotting and bleeding. This balance relies on the proper formation of blood clots, as well as the breakdown of blood clots. The primary mechanism that breaks down blood clots is fibrinolysis, where the fibrin net becomes lysed and the blood clot dissolves. Dyslipidemia is a condition where blood lipid and lipoprotein levels are abnormal. Here, we review studies that observed connections between impaired fibrinolysis and dyslipidemia. We also summarize the different correlations between thrombosis and dyslipidemia in different racial and ethnic groups. Finally, we summarize relevant and new findings on this topic presented during the 2023 International Society on Thrombosis and Haemostasis Congress. More studies are needed to investigate the mechanistic connections between impaired fibrinolysis and dyslipidemia and whether these mechanisms differ in racially and ethnically diverse populations.

Fibroblast activation protein: Pivoting cancer/chemotherapeutic insight towards heart failure

An important mechanism for cancer progression is degradation of the extracellular matrix (ECM) which is accompanied by the emergence and proliferation of an activated fibroblast, termed the cancer associated fibroblast (CAF). More specifically, an enzyme pathway identified to be amplified with local cancer progression and proliferation of the CAF, is fibroblast activation protein (FAP). The development and progression of heart failure (HF) irrespective of the etiology is associated with left ventricular (LV) remodeling and changes in ECM structure and function. As with cancer, HF progression is associated with a change in LV myocardial fibroblast growth and function, and expresses a protein signature not dissimilar to the CAF. The overall goal of this review is to put forward the postulate that scientific discoveries regarding FAP in cancer as well as the development of specific chemotherapeutics could be pivoted to target the emergence of FAP in the activated fibroblast subtype and thus hold translationally relevant diagnostic and therapeutic targets in HF.

Advances of Blood Coagulation Factor XIII in Bone Healing

The biologic process of bone healing is complicated, involving a variety of cells, cytokines, and growth factors. As a result of bone damage, the activation of a clotting cascade leads to hematoma with a high osteogenic potential in the initial stages of healing. A major factor involved in this course of events is clotting factor XIII (FXIII), which can regulate bone defect repair in different ways during various stages of healing. Autografts and allografts often have defects in clinical practice, making the development of advanced materials that support bone regeneration a critical requirement. Few studies, however, have examined the promotion of bone healing by FXIII in combination with biomaterials, in particular, its effect on blood coagulation and osteogenesis. Therefore, we mainly summarized the role of FXIII in promoting bone regeneration by regulating the extracellular matrix and type I collagen, bone-related cells, angiogenesis, and platelets, and described the research progress of FXIII = related biomaterials on osteogenesis. This review provides a reference for investigators to explore the mechanism by which FXIII promotes bone healing and the combination of FXIII with biomaterials to achieve targeted bone tissue repair.

Maintaining the balance: the critical role of plasmin activity in orthopedic surgery injury response

The musculoskeletal system plays vital roles in the body, facilitating movement, protecting vital structures, and regulating hematopoiesis and mineral metabolism. Injuries to this system are common and can cause chronic pain, loss of range of motion, and disability. The acute phase response (APR) is a complex process necessary for surviving and repairing injured musculoskeletal tissue. To conceptualize the APR, it is useful to divide it into 2 distinct phases, survival and repair. During the survival-APR, a "damage matrix" primarily composed of fibrin, via thrombin activity, is produced to contain the zone of injury. Once containment is achieved, the APR transitions to the repair phase, where reparative inflammatory cells use plasmin to systematically remove the damage matrix and replace it with new permanent matrices produced by differentiated mesenchymal stem cells. The timing of thrombin and plasmin activation during their respective APR phases is crucial for appropriate regulation of the damage matrix. This review focuses on evidence indicating that inappropriate exuberant activation of plasmin during the survival-APR can result in an overactive APR, leading to an "immunocoagulopathy" that may cause "immunothrombosis" and death. Conversely, preclinical data suggest that too little plasmin activity during the repair-APR may contribute to failed tissue repair, such as a fracture nonunion, and chronic inflammatory degenerative diseases like osteoporosis. Future clinical studies are required to affirm these findings. Therefore, the temporal-spatial functions of plasmin in response to musculoskeletal injury and its pharmacologic manipulation are intriguing new targets for improving orthopedic care.

Diabetes- versus smoking-related thrombo-inflammation in peripheral artery disease

Peripheral artery disease (PAD) is a major health problem with increased cardiovascular mortality, morbidity and disabling critical limb threatening ischemia (CLTI) and amputation. Diabetes mellitus (DM) and cigarette smoke are the main risk factors for the development of PAD. Although diabetes related PAD shows an accelerated course with worse outcome regarding complications, mortality and amputations compared with non-diabetic patients, current medical treatment does not make this distinction and includes standard antiplatelet and lipid lowering drugs for all patients with PAD. In this review we discuss the pathophysiologic mechanisms of PAD, with focus on differences in thrombo-inflammatory processes between diabetes-related and smoking-related PAD, and hypothesize on possible mechanisms for the progressive course of PAD in DM. Furthermore, we comment on current medical treatment and speculate on alternative medical drug options for patients with PAD and DM.

Plasminogen System in the Pathophysiology of Sepsis: Upcoming Biomarkers

Severe hemostatic disturbances and impaired fibrinolysis occur in sepsis. In the most serious cases, the dysregulation of fibrinolysis contributes to septic shock, disseminated intravascular coagulation (DIC), and death. Therefore, an analysis of circulating concentrations of pro- and anti-fibrinolytic mediators could be a winning strategy in both the diagnosis and the treatment of sepsis. However, the optimal cutoff value, the timing of the measurements, and their combination with coagulation indicators should be further investigated. The purpose of this review is to summarize all relevant publications regarding the role of the main components of the plasminogen activation system (PAS) in the pathophysiology of sepsis. In addition, the clinical value of PAS-associated biomarkers in the diagnosis and the outcomes of patients with septic syndrome will be explored. In particular, experimental and clinical trials performed in emergency departments highlight the validity of soluble urokinase plasminogen activator receptor (suPAR) as a predictive and prognostic biomarker in patients with sepsis. The measurements of PAI-I may also be useful, as its increase is an early manifestation of sepsis and may precede the development of thrombocytopenia. The upcoming years will undoubtedly see progress in the use of PAS-associated laboratory parameters.

Identification by whole genome sequencing of genes associated with delayed postoperative hemorrhage in Scottish deerhounds

BACKGROUND

Delayed postoperative hemorrhage (DEPOH) is an important health concern for Scottish deerhounds.

HYPOTHESIS/OBJECTIVES

Identify genes associated with DEPOH in Scottish deerhounds.

ANIMALS

Two hundred sixty-nine privately owned Scottish deerhounds.

METHODS

Retrospective case-control study. DEPOH cases and controls were identified through an owner health survey. Genome-wide association analysis was performed using whole genome sequences from 8 cases and 17 controls. All cases and controls were genotyped for selected variants.

RESULTS

Of 269 dogs, 10 met inclusion and exclusion criteria for DEPOH, while 62 controls had undergone similar surgical procedures without DEPOH. Genome-wide association analysis identified a single locus on chromosome 9 spanning 40 genes. One of these genes (SERPINF2 encoding alpha-2 antiplasmin) was directly linked to the pathophysiology of DEPOH. The entire cohort was genotyped for a missense SERPINF2 variant (c.605 C>T; p.A202V). Compared to dogs with the reference C/C genotype, the likelihood of DEPOH was significantly higher for dogs with the T/T genotype (odds ratio [OR] = 1235; 95% confidence interval [CI] = 23-6752; P = 0.0005) and with the C/T genotype (OR = 28; 95% CI = 1.4-542; P = 0.03).

CONCLUSIONS AND CLINICAL IMPORTANCE

SERPINF2 is associated with DEPOH in Scottish deerhounds. Genetic testing might be able to identify dogs that are susceptible to DEPOH.

PLCL/PCL Dressings with Platelet Lysate and Growth Factors Embedded in Fibrin for Chronic Wound Regeneration

Introduction

The formation of diabetic ulcers (DU) is a common complication for diabetic patients resulting in serious chronic wounds. There is therefore, an urgent need for complex treatment of this problem. This study examines a bioactive wound dressing of a biodegradable electrospun nanofibrous blend of poly(L-lactide-co-ε-caprolactone) and poly(ε-caprolactone) (PLCL/PCL) covered by a thin fibrin layer for sustained delivery of bioactive molecules.

Methods

Electrospun PLCL/PCL nanofibers were coated with fibrin-based coating prepared by a controlled technique and enriched with human platelet lysate (hPL), fibroblast growth factor 2 (FGF), and vascular endothelial growth factor (VEGF). The coating was characterized by scanning electron microscopy and fluorescent microscopy. Protein content and its release rate and the effect on human saphenous vein endothelial cells (HSVEC) were evaluated.

Results

The highest protein amount is achieved by the coating of PLCL/PCL with a fibrin mesh containing 20% v/v hPL (NF20). The fibrin coating serves as an excellent scaffold to accumulate bioactive molecules from hPL such as PDGF-BB, fibronectin (Fn), and α-2 antiplasmin. The NF20 coating shows both fast and a sustained release of the attached bioactive molecules (Fn, VEGF, FGF). The dressing significantly increases the viability of human saphenous vein endothelial cells (HSVECs) cultivated on a collagen-based wound model. The exogenous addition of FGF and VEGF during the coating procedure further increases the HSVECs viability. In addition, the presence of α-2 antiplasmin significantly stabilizes the fibrin mesh and prevents its cleavage by plasmin.

Discussion

The NF20 coating supplemented with FGF and VEGF provides a promising wound dressing for the complex treatment of DU. The incorporation of various bioactive molecules from hPL and growth factors has great potential to support the healing processes by providing appropriate stimuli in the chronic wound.

The uPA/uPAR System Orchestrates the Inflammatory Response, Vascular Homeostasis, and Immune System in Fibrosis Progression

Fibrotic diseases, such as systemic sclerosis (SSc), idiopathic pulmonary fibrosis, renal fibrosis and liver cirrhosis are characterized by tissue overgrowth due to excessive extracellular matrix (ECM) deposition. Fibrosis progression is caused by ECM overproduction and the inhibition of ECM degradation due to several events, including inflammation, vascular endothelial dysfunction, and immune abnormalities. Recently, it has been reported that urokinase plasminogen activator (uPA) and its receptor (uPAR), known to be fibrinolytic factors, orchestrate the inflammatory response, vascular homeostasis, and immune homeostasis system. The uPA/uPAR system may show promise as a potential therapeutic target for fibrotic diseases. This review considers the role of the uPA/uPAR system in the progression of fibrotic diseases.

"Super" SERPINs-A stabilizing force against fibrinolysis in thromboinflammatory conditions

The superfamily of serine protease inhibitors (SERPINs) are a class of inhibitors that utilise a dynamic conformational change to trap and inhibit their target enzymes. Their powerful nature lends itself well to regulation of complex physiological enzymatic cascades, such as the haemostatic, inflammatory and complement pathways. The SERPINs α2-antiplasmin, plasminogen-activator inhibitor-1, plasminogen-activator inhibitor-2, protease nexin-1, and C1-inhibitor play crucial inhibitory roles in regulation of the fibrinolytic system and inflammation. Elevated levels of these SERPINs are associated with increased risk of thrombotic complications, obesity, type 2 diabetes, and hypertension. Conversely, deficiencies of these SERPINs have been linked to hyperfibrinolysis with bleeding and angioedema. In recent years SERPINs have been implicated in the modulation of the immune response and various thromboinflammatory conditions, such as sepsis and COVID-19. Here, we highlight the current understanding of the physiological role of SERPINs in haemostasis and inflammatory disease progression, with emphasis on the fibrinolytic pathway, and how this becomes dysregulated during disease. Finally, we consider the role of these SERPINs as potential biomarkers of disease progression and therapeutic targets for thromboinflammatory diseases.

Establishment of a mouse model for ovarian cancer-associated venous thromboembolism

Patients with ovarian cancer are at increased risk of venous thromboembolism (VTE), and the cumulative incidence is high, particularly at advanced stages of this disease. Nevertheless, it is challenging to investigate the molecular mechanisms of ovarian cancer-associated VTE (OC-VTE), mainly due to the lack of a well-developed animal model for this disease. We generated a mouse model for developing OC-VTE using ovarian cancer cell injection in combination with the inferior vena cava stenosis method. The rate of thrombosis in the OC-VTE group was 50%, compared with 0 in the control group. Moreover, we conducted a proteomic analysis using platelets from these models and revealed differentially expressed proteins between the OC-VTE and control groups, including upregulated and downregulated proteins. Gene Ontology analysis revealed that these differentially expressed proteins were mostly enriched in the biological process of negative regulation of fibrinolysis and the cellular component of the fibrinogen complex, both of which play key roles in thrombosis. In conclusion, this study lays the foundation for further investigation of the underlying mechanisms of how ovarian cancer promotes VTE formation.

Plasmin Inhibitor in Health and Diabetes: Role of the Protein as a Therapeutic Target

The vascular obstructive thrombus is composed of a mesh of fibrin fibers with blood cells trapped in these networks. Enhanced fibrin clot formation and/or suppression of fibrinolysis are associated with an increased risk of vascular occlusive events. Inhibitors of coagulation factors and activators of plasminogen have been clinically used to limit fibrin network formation and enhance lysis. While these agents are effective at reducing vascular occlusion, they carry a significant risk of bleeding complications. Fibrin clot lysis, essential for normal hemostasis, is controlled by several factors including the incorporation of antifibrinolytic proteins into the clot. Plasmin inhibitor (PI), a key antifibrinolytic protein, is cross-linked into fibrin networks with higher concentrations of PI documented in fibrin clots and plasma from high vascular risk individuals. This review is focused on exploring PI as a target for the prevention and treatment of vascular occlusive disease. We first discuss the relationship between the PI structure and antifibrinolytic activity, followed by describing the function of the protein in normal physiology and its role in pathological vascular thrombosis. Subsequently, we describe in detail the potential use of PI as a therapeutic target, including the array of methods employed for the modulation of protein activity. Effective and safe inhibition of PI may prove to be an alternative and specific way to reduce vascular thrombotic events while keeping bleeding risk to a minimum. Key Points Plasmin inhibitor (PI) is a key protein that inhibits fibrinolysis and stabilizes the fibrin network.This review is focused on discussing mechanistic pathways for PI action, role of the molecule in disease states, and potential use as a therapeutic target.

Low α2-Plasmin Inhibitor Antigen Levels on Admission Are Associated With More Severe Stroke and Unfavorable Outcomes in Acute Ischemic Stroke Patients Treated With Intravenous Thrombolysis

Background

Intravenous administration of recombinant tissue plasminogen activator (rt-PA) fails to succeed in a subset of acute ischemic stroke (AIS) patients, while in approximately 6–8% of cases intracerebral hemorrhage (ICH) occurs as side effect.

Objective

Here, we aimed to investigate α2-plasmin inhibitor (α2-PI) levels during thrombolysis and to find out whether they predict therapy outcomes in AIS patients.

Patients/Methods

In this prospective, observational study, blood samples of 421 AIS patients, all undergoing i.v. thrombolysis by rt-PA within 4.5 h of their symptom onset, were taken before and 24 h after thrombolysis. In a subset of patients (n = 131), blood was also obtained immediately post-lysis. α2-PI activity and antigen levels were measured by chromogenic assay and an in-house ELISA detecting all forms of α2-PI. α2-PI Arg6Trp polymorphism was identified in all patients. Stroke severity was determined by NIHSS on admission and day 7. Therapy-associated ICH was classified according to ECASSII. Long-term outcomes were defined at 3 months post-event by the modified Rankin Scale (mRS).

Results

Median α2-PI activity and antigen levels showed a significant drop immediately post-lysis and increased to subnormal levels at 24 h post-event. Admission α2-PI levels showed a significant negative stepwise association with stroke severity. Patients with favorable long-term outcomes (mRS 0–1) had significantly higher admission α2-PI antigen levels (median:61.6 [IQR:55.9–70.5] mg/L) as compared to patients with poor outcomes (mRS 2–5: median:59.7 [IQR:54.5–69.1] and mRS 6: median:56.0 [IQR:48.5–61.0] mg/L, p < 0.001). In a Kaplan–Meier survival analysis, patients with an α2-PI antigen in the highest quartile on admission showed significantly better long-term survival as compared to those with α2-PI antigen in the lowest quartile (HR: 4.54; 95%CI:1.92–10.8, p < 0.001); however, in a multivariate analysis, a low admission α2-PI antigen did not prove to be an independent risk factor of poor long-term outcomes. In patients with therapy-related ICH (n = 34), admission α2-PI antigen levels were significantly, but only marginally, lower as compared to those without hemorrhage.

Conclusions

Low α2-PI antigen levels on admission were associated with more severe strokes and poor long-term outcomes in this cohort. Our results suggest that in case of more severe strokes, α2-PI may be involved in the limited efficacy of rt-PA thrombolysis.

Mass-spectrometric identification of oxidative modifications in plasma-purified plasminogen: Association with hypofibrinolysis in patients with acute pulmonary embolism

OBJECTIVES

Mechanisms behind disturbed fibrinolysis in pulmonary embolism (PE) are poorly understood. We hypothesized that oxidative stress-induced changes in plasminogen contribute to impaired fibrinolysis in patients with acute PE.

METHODS

Oxidative and other modifications were investigated using mass-spectrometry in plasminogen purified from pooled plasma of 5 acute PE patients on admission and after 3 months of anticoagulant treatment, along with plasma clot lysis time, a measure of global efficiency of fibrinolysis, and a stable oxidative stress marker, plasma 8-isoprostane.

RESULTS

Twenty sites of oxidation, 3 sites of carbonylation and 4 sites of S-nitrosylation were identified in plasminogen. The intensity of peptides oxidized at cysteine residues with respect to unmodified peptides decreased after 3 months of anticoagulation (p = 0.018). This was not observed for oxidized methionine residues (p = 0.9). Oxidized tryptophan (n = 4) and proline (n = 2), as well as carbonylation at 3 threonine residues were selectively identified in acute PE episode, not after 3 months. This was accompanied by 12.8% decrease in clot lysis time (p = 0.043). Deamidation occurred at the arginine, previously identified to undergo the cleavage by plasminogen activator. Methylated were two lysine-binding sites important for an interaction of plasminogen with fibrin. Other identified modifications involved: glycation, acetylation, phosphorylation, homocysteinylation, carbamylation and dichlorination (88 modifications at 162 sites).

CONCLUSIONS

Data suggest that oxidative stress-induced changes in plasminogen molecules may contribute to less effective global fibrinolysis in patients with acute PE. The comprehensive library of posttranslational modifications in plasminogen molecules was provided, including modifications of sites reported to be involved in important biological functions.

α2-Antiplasmin as a Potential Therapeutic Target for Systemic Sclerosis

Systemic sclerosis is a connective tissue disease of unknown origin that is characterized by immune system abnormalities, vascular damage, and extensive fibrosis of the skin and visceral organs. α2-antiplasmin is known to be the main plasmin inhibitor and has various functions such as cell differentiation and cytokine production, as well as the regulation of the maintenance of the immune system, endothelial homeostasis, and extracellular matrix metabolism. The expression of α2-antiplasmin is elevated in dermal fibroblasts from systemic sclerosis patients, and the blockade of α2-antiplasmin suppresses fibrosis progression and vascular dysfunction in systemic sclerosis model mice. α2-antiplasmin may have promise as a potential therapeutic target for systemic sclerosis. This review considers the role of α2-antiplasmin in the progression of systemic sclerosis.

New Insights on Plasmin Long Term Stability and the Mechanism of Its Activity Inhibition Analyzed by Quartz Crystal Microbalance

We used the research quartz crystal microbalance (RQCM) to monitor regulatory effects of plasmin and trypsin in the presence of their inhibitor α₂-antiplasmin. The gold surface of quartz crystals was modified with a β-casein layer that served as a substrate for protease digestion. The addition of plasmin or trypsin as well as their mixtures with α₂-antiplasmin resulted in an increase of resonant frequency, f, and in a decrease of motional resistance, R_m, depending on the molar ratio of protease: antiplasmin. At equimolar concentrations of protease and α₂-antiplasmin (5 nM:5 nM) full inhibition of protease activity took place. Monitoring of plasmin activity on an hourly and daily basis revealed a prominent effect of autolysis and decrease of plasmin activity in freshly activated samples. The degree of inhibition as well as plasmin half-life (t_1/2 = 2.48 ± 0.28 days) connected with its degradation was determined.

Alpha2-antiplasmin deficiency affects depression and anxiety-like behavior and apoptosis induced by stress in mice

OBJECTIVES

Depression is a psychiatric disorder that affects about 10% of the world's population and is accompanied by anxiety. Depression and anxiety are often caused by various stresses. However, the etiology of depression and anxiety remains unknown. It has been reported that alpha2-antiplasmin (α2AP) not only inhibits plasmin but also has various functions such as cytokine production and cell growth. This study aimed to determine the roles of α2AP on the stress-induced depression and anxiety.

METHODS

We investigated the mild repeated restraint stress-induced depressive and anxiety-like behavior in the α2AP^+/+ and α2AP^-/- mice using the social interaction test (SIT), sucrose preference test (SPT), and elevated plus maze (EPM).

RESULTS

The stresses such as the mild repeated restraint stress suppressed α2AP expression in the hippocampus of mice, and the treatment of fluoxetine (selective serotonin reuptake inhibitor [SSRI]) recovered the stress-caused α2AP suppression. We also showed that α2AP deficiency promoted the mild restraint stress-stimulated depression-like behavior such as social withdrawal and apathy and apoptosis in mice. In contrast, α2AP deficiency attenuated the mild restraint stress induced the anxiety-like behavior in mice.

CONCLUSIONS

α2AP affects the pathogenesis of depression and anxiety induced by stress.

Fibrinogen and Antifibrinolytic Proteins: Interactions and Future Therapeutics

Thrombus formation remains a major cause of morbidity and mortality worldwide. Current antiplatelet and anticoagulant therapies have been effective at reducing vascular events, but at the expense of increased bleeding risk. Targeting proteins that interact with fibrinogen and which are involved in hypofibrinolysis represents a more specific approach for the development of effective and safe therapeutic agents. The antifibrinolytic proteins alpha-2 antiplasmin (α2AP), thrombin activatable fibrinolysis inhibitor (TAFI), complement C3 and plasminogen activator inhibitor-2 (PAI-2), can be incorporated into the fibrin clot by FXIIIa and affect fibrinolysis by different mechanisms. Therefore, these antifibrinolytic proteins are attractive targets for the development of novel therapeutics, both for the modulation of thrombosis risk, but also for potentially improving clot instability in bleeding disorders. This review summarises the main properties of fibrinogen-bound antifibrinolytic proteins, their effect on clot lysis and association with thrombotic or bleeding conditions. The role of these proteins in therapeutic strategies targeting the fibrinolytic system for thrombotic diseases or bleeding disorders is also discussed.

Burn-Induced Coagulopathies: a Comprehensive Review

Burn-induced coagulopathy is not well understood, and consensus on diagnosis, prevention, and treatments are lacking. In this review, literature on burn-induced (and associated) coagulopathy is presented along with the current understanding of the effects of burn injury on the interactions among coagulation, fibrinolysis, and inflammation in the acute resuscitative phase and reconstructive phase of care. The role of conventional tests of coagulopathy and functional assays like thromboelastography or thromboelastometry will also be discussed. Finally, reported methods for the prevention and treatment of complications related to burn-induced coagulopathy will be reviewed.

Altered fibrin clot properties and fibrinolysis in patients with atrial fibrillation: practical implications

Compelling evidence indicates that a hypercoagulable state occurs in patients with atrial fibrillation (AF) including those in sinus rhythm following paroxysmal and persistent AF. Activation of blood coagulation in AF reflects heightened thrombin generation with the subsequent increased formation of fibrin as evidenced by elevated soluble fibrin monomers and D-dimer. Formation of denser fibrin meshworks, relatively resistant to plasmin-mediated lysis has been demonstrated in patients with AF. The presence of stroke risk factors in AF, such as diabetes, heart failure, hypertension, previous myocardial infarction, or stroke, advanced age have been shown to be linked to the prothrombotic clot characteristics, including reduced clot permeability and lysability. Importantly, biomarkers, including cardiac troponins and N-terminal pro-brain natriuretic peptide, are associated with thrombin generation and fibrin-related markers in AF patients. Recently, increased fibrin clot density (low clot permeability measured in plasma-based assays) and impaired fibrinolysis measured off anticoagulation have been demonstrated to predict ischaemic cerebrovascular events in patients with AF receiving vitamin K antagonists and those on rivaroxaban. The current review summarizes evidence for a role of altered fibrin clot properties and hypofibrinolysis in AF and their prognostic value in terms of adverse events.

Effect of α2-plasmin inhibitor heterogeneity on the risk of venous thromboembolism

INTRODUCTION

Alpha2-plasmin inhibitor (α2-PI) has a heterogeneous composition in the plasma. Both N- and C-terminal cleavages occur that modify the function of the molecule. C-terminal cleavage converts the plasminogen-binding form (PB-α2-PI) to a non-plasminogen-binding form (NPB-α2-PI). N-terminal cleavage by soluble fibroblast activation protein (sFAP) results in a form shortened by 12 amino acids, which is more quickly cross-linked to fibrin. The p.Arg6Trp polymorphism of α2-PI affects N-terminal cleavage. In this work, we aimed to investigate the association between α2-PI heterogeneity and the risk of venous thromboembolism.

MATERIALS AND METHODS

Two hundred and eighteen patients with venous thromboembolism (VTE) and the same number of age and sex-matched healthy controls were enrolled. Total-α2-PI, PB-α2-PI and NPB-α2-PI antigen levels, α2-PI activity, sFAP antigen levels and p.Arg6Trp polymorphism were investigated.

RESULTS

Total-α2-PI and NPB-α2-PI levels were significantly elevated in VTE patients, while PB-α2-PI levels did not change. Elevated NPB-α2-PI levels independently associated with VTE risk (adjusted OR: 9.868; CI: 4.095-23.783). Soluble FAP levels were significantly elevated in the VTE group, however, elevated sFAP levels did not show a significant association with VTE risk. The α2-PI p.Arg6Trp polymorphism did not influence VTE risk, however, in the case of elevated sFAP levels the carriage of Trp6 allele associated with lower VTE risk.

CONCLUSION

Our results showed that the elevation of total-α2-PI levels in VTE is caused by the elevation of NPB-α2-PI levels. Elevated sFAP level or p.Arg6Trp polymorphism alone did not influence VTE risk. However, an interaction can be detected between the polymorphism and high sFAP levels.

Alpha 2-antiplasmin deficiency in a Sudanese child: a case report

Background

The plasma serine protease inhibitor alpha 2-antiplasmin (α₂-AP, otherwise known as α₂-plasmin inhibitor) is a rapid-acting plasmin inhibitor recently found in human plasma, which seems to have a significant role in the regulation of in vivo fibrinolysis. Congenital deficiency of α₂-AP is extremely uncommon.

Case presentation

We report here a case of absolute deficiency of α₂-AP in an 11-year-old Sudanese boy, who had a lifelong intermittent hemorrhagic tendency (gum bleeding, epistaxis, and exaggerated bleeding after trauma). Coagulation tests including prothrombin time, partial thromboplastin time, thrombin time, bleeding time, platelet count, clot retraction test, antithrombin, and factor VIII levels were within normal limits. Hepatic function tests and complete blood count were also normal. The main interesting finding in this patient was that the whole blood clot lysis was extremely fast, completed within 5–8 hours. The second abnormal finding is that the euglobulin clot lysis time was short. Nevertheless, the concentration of α₂-AP in the patient's plasma was 0.2 IU/ml (reference range is 0.80–1.20 IU/ml). The addition of pooled plasma (with normal α₂-AP) to the patient's whole blood corrected the accelerated fibrinolysis.

Conclusion

The study showed that α₂-AP deficiency resulted in uninhibited fibrinolysis that caused the hemorrhagic tendency in this patient. Thus, this report demonstrates the significant role of α₂-AP in coagulation.

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.

MicroRNA-30c attenuates fibrosis progression and vascular dysfunction in systemic sclerosis model mice

Systemic sclerosis (SSc) is characterized by peripheral circulatory disturbance and fibrosis in skin and visceral organs. We recently demonstrated that α2-antiplasmin (α2AP) is elevated in SSc dermal fibroblasts and SSc model mice, and is associated with fibrosis progression and vascular dysfunction. In the present study, we predicted that α2AP could be a target of microRNA-30c (miR-30c) using TargetScan online database, and investigated the effect of miR-30c on the pathogenesis of SSc using a bleomycin-induced SSc model mice. miR-30c attenuated α2AP expression, and prevented the pro-fibrotic changes (increased dermal thickness, collagen deposition, myofibroblast accmulation) and the vascular dysfunction (the reduction of vascular endothelial cells (ECs) and blood flow) in the skin of SSc model mice. Furthermore, miR-30c suppressed pulmonary fibrosis progression in the SSc model mice. miR-30c exerts the anti-fibrotic and anti-angiopathy effects on SSc model mice, and might provide a basis for clinical strategies for SSc.

Fibrinolytic Serine Proteases, Therapeutic Serpins and Inflammation: Fire Dancers and Firestorms

The making and breaking of clots orchestrated by the thrombotic and thrombolytic serine protease cascades are critical determinants of morbidity and mortality during infection and with vascular or tissue injury. Both the clot forming (thrombotic) and the clot dissolving (thrombolytic or fibrinolytic) cascades are composed of a highly sensitive and complex relationship of sequentially activated serine proteases and their regulatory inhibitors in the circulating blood. The proteases and inhibitors interact continuously throughout all branches of the cardiovascular system in the human body, representing one of the most abundant groups of proteins in the blood. There is an intricate interaction of the coagulation cascades with endothelial cell surface receptors lining the vascular tree, circulating immune cells, platelets and connective tissue encasing the arterial layers. Beyond their role in control of bleeding and clotting, the thrombotic and thrombolytic cascades initiate immune cell responses, representing a front line, "off-the-shelf" system for inducing inflammatory responses. These hemostatic pathways are one of the first response systems after injury with the fibrinolytic cascade being one of the earliest to evolve in primordial immune responses. An equally important contributor and parallel ancient component of these thrombotic and thrombolytic serine protease cascades are the serine protease inhibitors, termed serpins. Serpins are metastable suicide inhibitors with ubiquitous roles in coagulation and fibrinolysis as well as multiple central regulatory pathways throughout the body. Serpins are now known to also modulate the immune response, either via control of thrombotic and thrombolytic cascades or via direct effects on cellular phenotypes, among many other functions. Here we review the co-evolution of the thrombolytic cascade and the immune response in disease and in treatment. We will focus on the relevance of these recent advances in the context of the ongoing COVID-19 pandemic. SARS-CoV-2 is a "respiratory" coronavirus that causes extensive cardiovascular pathogenesis, with microthrombi throughout the vascular tree, resulting in severe and potentially fatal coagulopathies.

Association of fibrinogen and plasmin inhibitor, but not coagulation factor XIII gene polymorphisms with coronary artery disease

BACKGROUND

In the final phase of clot formation, fibrinogen constitutes frame, whereas factor XIII (FXIII) active form is responsible for the covalent cross-linking of fibrin fibres and plasmin inhibitor (PI), thus contributing to clot stability. It could be expected that any change of coagulation factors' structure affects the clot formation and modulates the atherothrombotic risk. The aim was to determine the frequency of four single nucleotide polymorphisms: (i) A > G in codon 312 of the fibrinogen α-chain gene (rs6050, Thr312AlaFGA), (ii) C > T at position 10034 of the 3 - untranslated region in the fibrinogen γ-chain gene (rs2066865, 10034C > T FGG), (iii) C > T in codon 564 of the FXIII-A subunit gene (rs5982, Pro564LeuFXIII-A), and (iv) C > T in codon 6 of the plasmin inhibitor gene (rs2070863, Arg6TrpPI) in Croatian patients and their association with coronary artery disease (CAD).

METHODS

We performed the unrelated case-control association study on the consecutive sample of patients 18 years old, who had undergone coronary angiography for investigation of chest pain and suspected CAD. The cases were patients with confirmed CAD (N=201), and the controls were the subjects with no CAD (N=119). Samples were genotyped using PCR-RFLP analysis.

RESULTS

Observed frequencies of the rare alleles of Thr312Ala FGA, 10034C > T FGG, Leu564Pro FXIII-A and Arg6Trp PI polymorphisms were 21%, 17%, 14%, 20%, respectively. Patients with 10034C > T FGG CC genotype had 3.5 times (95% CI 1.02-12.03) higher adjusted odds for CAD than patients with 10034C > T FGG TT genotype. Patients with Arg6Trp PI CC genotype had 3.86 times (95% CI 1.23-12.12) higher odds for CAD than patients with Arg6Trp PI TT genotype. It seems that those genotype-related higher odds are also male-gender related. No difference was observed regarding any other investigated polymorphism.

CONCLUSIONS

Our finding suggests that 10034C > T FGG and Arg6Trp PI are associated with CAD.

Incorporation of α2-Plasmin Inhibitor into Fibrin Clots and Its Association with the Clinical Outcome of Acute Ischemic Stroke Patients

Cross-linking of α2-plasmin inhibitor (α2-PI) to fibrin by activated factor XIII (FXIIIa) is essential for the inhibition of fibrinolysis. Little is known about the factors modifying α2-PI incorporation into the fibrin clot and whether the extent of incorporation has clinical consequences. Herein we calculated the extent of α2-PI incorporation by measuring α2-PI antigen levels from plasma and serum obtained after clotting the plasma by thrombin and Ca²⁺. The modifying effect of FXIII was studied by spiking of FXIII-A-deficient plasma with purified plasma FXIII. Fibrinogen, FXIII, α2-PI incorporation, in vitro clot-lysis, soluble fibroblast activation protein and α2-PI p.Arg6Trp polymorphism were measured from samples of 57 acute ischemic stroke patients obtained before thrombolysis and of 26 healthy controls. Increasing FXIII levels even at levels above the upper limit of normal increased α2-PI incorporation into the fibrin clot. α2-PI incorporation of controls and patients with good outcomes did not differ significantly (49.4 ± 4.6% vs. 47.4 ± 6.7%, p = 1.000), however it was significantly lower in patients suffering post-lysis intracranial hemorrhage (37.3 ± 14.0%, p = 0.004). In conclusion, increased FXIII levels resulted in elevated incorporation of α2-PI into fibrin clots. In stroke patients undergoing intravenous thrombolysis treatment, α2-PI incorporation shows an association with the outcome of therapy, particularly with thrombolysis-associated intracranial hemorrhage.

Role, Laboratory Assessment and Clinical Relevance of Fibrin, Factor XIII and Endogenous Fibrinolysis in Arterial and Venous Thrombosis

Diseases such as myocardial infarction, ischaemic stroke, peripheral vascular disease and venous thromboembolism are major contributors to morbidity and mortality. Procoagulant, anticoagulant and fibrinolytic pathways are finely regulated in healthy individuals and dysregulated procoagulant, anticoagulant and fibrinolytic pathways lead to arterial and venous thrombosis. In this review article, we discuss the (patho)physiological role and laboratory assessment of fibrin, factor XIII and endogenous fibrinolysis, which are key players in the terminal phase of the coagulation cascade and fibrinolysis. Finally, we present the most up-to-date evidence for their involvement in various disease states and assessment of cardiovascular risk.

The Central Role of Fibrinolytic Response in COVID-19-A Hematologist's Perspective

The novel coronavirus disease (COVID-19) has many characteristics common to those in two other coronavirus acute respiratory diseases, severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS). They are all highly contagious and have severe pulmonary complications. Clinically, patients with COVID-19 run a rapidly progressive course of an acute respiratory tract infection with fever, sore throat, cough, headache and fatigue, complicated by severe pneumonia often leading to acute respiratory distress syndrome (ARDS). The infection also involves other organs throughout the body. In all three viral illnesses, the fibrinolytic system plays an active role in each phase of the pathogenesis. During transmission, the renin-aldosterone-angiotensin-system (RAAS) is involved with the spike protein of SARS-CoV-2, attaching to its natural receptor angiotensin-converting enzyme 2 (ACE 2) in host cells. Both tissue plasminogen activator (tPA) and plasminogen activator inhibitor 1 (PAI-1) are closely linked to the RAAS. In lesions in the lung, kidney and other organs, the two plasminogen activators urokinase-type plasminogen activator (uPA) and tissue plasminogen activator (tPA), along with their inhibitor, plasminogen activator 1 (PAI-1), are involved. The altered fibrinolytic balance enables the development of a hypercoagulable state. In this article, evidence for the central role of fibrinolysis is reviewed, and the possible drug targets at multiple sites in the fibrinolytic pathways are discussed.

The fibrinolytic system in the cornea: A key regulator of corneal wound healing and biological defense

The cornea is a relatively unique tissue in the body in that it possesses specific features such as a lack of blood vessels that contribute to its transparency. The cornea is supplied with soluble blood components such as albumin, globulin, and fibrinogen as well as with nutrients, oxygen, and bioactive substances by diffusion from aqueous humor and limbal vessels as well as a result of its exposure to tear fluid. The healthy cornea is largely devoid of cellular components of blood such as polymorphonuclear leukocytes, monocytes-macrophages, and platelets. The location of the cornea at the ocular surface renders it susceptible to external insults, and its avascular nature necessitates the operation of healing and defense mechanisms in a manner independent of a direct blood supply. The fibrinolytic system, which was first recognized for its role in the degradation of fibrin clots in the vasculature, has also been found to contribute to various biological processes outside of blood vessels. Fibrinolytic factors thus play an important role in biological defense of the cornea. In this review, we address the function of the fibrinolytic system in corneal defense including wound healing and the inflammatory response.

Alpha2-Antiplasmin: The Devil You Don't Know in Cerebrovascular and Cardiovascular Disease

Alpha2-antiplasmin (α2AP), the fast-reacting, serine protease inhibitor (serpin) of plasmin, was originally thought to play a key role in protection against uncontrolled, plasmin-mediated proteolysis of coagulation factors and other molecules. However, studies of humans and mice with genetic deficiency of α2AP have expanded our understanding of this serpin, particularly in disease states. Epidemiology studies have shown an association between high α2AP levels and increased risk or poor outcome in cardiovascular diseases. Mechanistic studies in disease models indicate that α2AP stops the body's own fibrinolytic system from dissolving pathologic thrombi that cause venous thrombosis, pulmonary embolism, arterial thrombosis, and ischemic stroke. In addition, α2AP fosters the development of microvascular thrombosis and enhances matrix metalloproteinase-9 expression. Through these mechanisms and others, α2AP contributes to brain injury, hemorrhage and swelling in experimental ischemic stroke. Recent studies also show that α2AP is required for the development of stasis thrombosis by inhibiting the early activation of effective fibrinolysis. In this review, we will discuss the key role played by α2AP in controlling thrombosis and fibrinolysis and, we will consider its potential value as a therapeutic target in cardiovascular diseases and ischemic stroke.

Plasmin Generation Potential and Recanalization in Acute Ischaemic Stroke; an Observational Cohort Study of Stroke Biobank Samples

Rationale: More than half of patients who receive thrombolysis for acute ischaemic stroke fail to recanalize. Elucidating biological factors which predict recanalization could identify therapeutic targets for increasing thrombolysis success.

Hypothesis: We hypothesize that individual patient plasmin potential, as measured by in vitro response to recombinant tissue-type plasminogen activator (rt-PA), is a biomarker of rt-PA response, and that patients with greater plasmin response are more likely to recanalize early.

Methods: This study will use historical samples from the Barcelona Stroke Thrombolysis Biobank, comprised of 350 pre-thrombolysis plasma samples from ischaemic stroke patients who received serial transcranial-Doppler (TCD) measurements before and after thrombolysis. The plasmin potential of each patient will be measured using the level of plasmin-antiplasmin complex (PAP) generated after in-vitro addition of rt-PA. Levels of antiplasmin, plasminogen, t-PA activity, and PAI-1 activity will also be determined. Association between plasmin potential variables and time to recanalization [assessed on serial TCD using the thrombolysis in brain ischemia (TIBI) score] will be assessed using Cox proportional hazards models, adjusted for potential confounders.

Outcomes: The primary outcome will be time to recanalization detected by TCD (defined as TIBI ≥4). Secondary outcomes will be recanalization within 6-h and recanalization and/or haemorrhagic transformation at 24-h. This analysis will utilize an expanded cohort including ~120 patients from the Targeting Optimal Thrombolysis Outcomes (TOTO) study.

Discussion: If association between proteolytic response to rt-PA and recanalization is confirmed, future clinical treatment may customize thrombolytic therapy to maximize outcomes and minimize adverse effects for individual patients.

Advances in Analysis of Milk Proteases Activity at Surfaces and in a Volume by Acoustic Methods

This review is focused on the application of surface and volume-sensitive acoustic methods for the detection of milk proteases such as trypsin and plasmin. While trypsin is an important protein of human milk, plasmin is a protease that plays an important role in the quality of bovine, sheep and goat milks. The increased activity of plasmin can cause an extensive cleavage of β-casein and, thus, affect the milk gelation and taste. The basic principles of surface-sensitive acoustic methods, as well as high-resolution ultrasonic spectroscopy (HR-US), are presented. The current state-of-the-art examples of the application of acoustic sensors for protease detection in real time are discussed. The application of the HR-US method for studying the kinetics of the enzyme reaction is demonstrated. The sensitivity of the acoustics biosensors and HR-US methods for protease detection are compared.

Interaction of glycated and acetylated human α2-antiplasmin with fibrin clots

: In type 2 diabetes mellitus (T2DM), increased α2-antiplasmin incorporation in fibrin and impaired fibrinolysis have been reported. Acetylsalicylic acid (ASA), used in cardiovascular prevention, modulates fibrinolysis and exerts weaker therapeutic effect in this disease. We investigated how glycation and acetylation of α2-antiplasmin affects its interaction with fibrin. Using surface plasmon resonance, we analyzed fibrin binding by α2-antiplasmin incubated with no β-D-glucose or ASA (control); incubated with β-D-glucose (5, 10, 50 mmol/l); (3) incubated with 1.6 mmol/l acetylsalicylic acid (ASA) and (4) incubated with 1.6 mmol/l ASA and 50 mmol/l β-D-glucose. Incubation with glucose decreased affinity of α2-antiplasmin for fibrin compared with control α2-antiplasmin in a glucose concentration-depending manner. α2-Antiplasmin incubation with ASA did not affect its affinity to fibrin. α2-Antiplasmin incubation with ASA and glucose resulted in 4.2-fold increased affinity to fibrin compared with α2-antiplasmin incubated with 50 mmol/l glucose (P < 0.001). In conclusion, α2-antiplasmin incubation with glucose at concentrations encountered in T2DM is associated with decreased binding affinity of α2-antiplasmin to fibrin. ASA alone does not affect the binding affinity of α2-antiplasmin to fibrin, but partly reverses the effect introduced by the incubation with 50 mmol/l glucose. This study suggests new mechanisms involved in regulating fibrinolysis efficiency in hyperglycemia.

Extracellular vesicle Cystatin C and CD14 are associated with both renal dysfunction and heart failure

AIMS

Extracellular vesicles (EVs) are small double-membrane plasma vesicles that play key roles in cellular crosstalk and mechanisms such as inflammation. The role of EVs in combined organ failure such as cardiorenal syndrome has not been investigated. The aim of this study is to identify EV proteins that are associated with renal dysfunction, heart failure, and their combination in dyspnoeic patients.

METHODS AND RESULTS

Blood samples were prospectively collected in 404 patients presenting with breathlessness at the emergency department at National University Hospital, Singapore. Renal dysfunction was defined as estimated glomerular filtration rate < 60 mL/min/1.73 m² . The presence of heart failure was independently adjudicated by two clinicians on the basis of the criteria of the European Society of Cardiology guidelines. Protein levels of SerpinG1, SerpinF2, Cystatin C, and CD14 were measured with a quantitative immune assay within three EV sub-fractions and in plasma and were tested for their associations with renal dysfunction, heart failure, and the concurrence of both conditions using multinomial regression analysis, thereby correcting for confounders such as age, gender, ethnicity, and co-morbidities. Renal dysfunction was found in 92 patients (23%), while heart failure was present in 141 (35%). In total, 58 patients (14%) were diagnosed with both renal dysfunction and heart failure. Regression analysis showed that Cystatin C was associated with renal dysfunction, heart failure, and their combination in all three EV sub-fractions and in plasma. CD14 was associated with both renal dysfunction and the combined renal dysfunction and heart failure in all EV sub-fractions, and with presence of heart failure in the high density lipoprotein sub-fraction. SerpinG1 and SerpinF2 were associated with heart failure in, respectively, two and one out of three EV sub-fractions and in plasma, but not with renal dysfunction.

CONCLUSIONS

We provide the first data showing that Cystatin C and CD14 in circulating EVs are associated with both renal dysfunction and heart failure in patients presenting with acute dyspnoea. This suggests that EV proteins may be involved in the combined organ failure of the cardiorenal syndrome and may represent possible targets for prevention or treatment.

Impaired Fibrinolysis in Patients with Isolated Aortic Stenosis is Associated with Enhanced Oxidative Stress

Aortic stenosis (AS) has been associated with impaired fibrinolysis and increased oxidative stress. This study aimed to investigate whether oxidative stress could alter fibrin clot properties in AS. We studied 173 non-diabetic patients, aged 51–79 years, with isolated AS. We measured plasma protein carbonylation (PC) and thiobarbituric acid reactive substances (TBARS), along with plasma clot permeability (K_s), thrombin generation, and fibrinolytic efficiency, which were evaluated by two assays: clot lysis time (CLT) and lysis time (Lys50). Coagulation factors and fibrinolytic proteins were also determined. Plasma PC showed an association with AS severity, reflected by the aortic valve area and the mean and maximum aortic gradients. Plasma PC was positively correlated with CLT, Lys50, plasminogen activator inhibitor-1 (PAI-1), and tissue factor (TF) antigens. TBARS were positively correlated with maximum aortic gradient, Lys50, and TF antigen. Regression analysis showed that PC predicted prolonged CLT (>104 min; odds ratio (OR) 6.41, 95% confidence interval (CI) 2.58–17.83, p < 0.001) and Lys50 (>565 s; OR 5.83, 95% CI 2.23–15.21, p < 0.001). Multivariate regression analysis showed that mean aortic gradient, PC, α2-antiplasmin, PAI-1, and triglycerides were predictors of prolonged CLT, while PC, α2-antiplasmin, and fibrinogen were predictors of Lys50. Our findings suggest that elevated oxidative stress contributes to impaired fibrinolysis in AS and is associated with AS severity.

On the localization of the cleavage site in human alpha-2-antiplasmin, involved in the generation of the non-plasminogen binding form

BACKGROUND

Alpha-2-antiplasmin (α2AP) is the main natural inhibitor of plasmin. The C-terminus of α2AP is crucial for the initial interaction with plasmin(ogen) and the rapid inhibitory mechanism. Approximately 35% of circulating α2AP has lost its C-terminus (non-plasminogen binding α2AP/NPB-α2AP) and thereby its rapid inhibitory capacity. The C-terminal cleavage site of α2AP is still unknown. A commercially available monoclonal antibody against α2AP (TC 3AP) detects intact but not NPB-α2AP, suggesting that the cleavage site is located N-terminally from the epitope of TC 3AP.

OBJECTIVES

To determine the epitope of TC 3AP and then to localize the C-terminal cleavage site of α2AP.

METHODS

For epitope mapping of TC 3AP, commercially available plasma purified α2AP was enzymatically digested with Asp-N, Glu-C, or Lys-N. The resulting peptides were immunoprecipitated using TC 3AP-loaded Dynabeads® Protein G. Bound peptides were eluted and analyzed by liquid chromatography-tandem mass spectometry (LC-MS/MS). To localize the C-terminal cleavage site precisely, α2AP (intact and NPB) was purified from plasma and analyzed by LC-MS/MS after enzymatic digestion with Arg-C.

RESULTS

We localized the epitope of TC 3AP between amino acid residues Asp428 and Gly439. LC-MS/MS data from plasma purified α2AP showed that NPB-α2AP results from cleavage at Gln421-Asp422 as preferred site, but also after Leu417, Glu419, Gln420, or Asp422.

CONCLUSIONS

The C-terminal cleavage site of human α2AP is located N-terminally from the TC 3AP epitope. Because C-terminal cleavage of α2AP can occur after multiple residues, different proteases may be responsible for the generation of NPB-α2AP.

Plasmin inhibitor deficiency: A case report

Plasmin inhibitor deficiency is an overlooked cause of hemorrhage. It is a rare disease. Delayed post-traumatic occurrence of bleeding is an essential feature. The specific dosage must be performed to diagnose cases of severe, persistent bleeding, contrasting with normal usual tests of hemostasis.

Association of imbalanced sex hormone production with excessive procoagulation factor SerpinF2 in preeclampsia

BACKGROUND

Preeclampsia, a serious pregnancy-associated syndrome, is the leading cause of maternal and perinatal morbidity and mortality. Significant exacerbation of the hypercoagulation status as well as imbalanced steroid hormones have been reported in developed preeclampsia. However, it remains unclear whether the two pathological changes are directly associated.

METHOD AND RESULTS

Our proteomic analysis revealed a significantly elevated SerpinF2/α2-antiplasmin level in preeclampsia plasma. Measurement of the longitudinally gestational change of plasmin-α2-antiplasmin (PAP) complex, testosterone, estradiol in preeclampsia patients and normal pregnant women demonstrated that the circulating PAP and testosterone levels in the early-onset preeclampsia (E-PE) patients were substantially higher, whereas estradiol concentration was significantly lower than that in normal pregnant controls from early pregnancy throughout gestation. Correlation analysis revealed that circulating PAP is in positive correlation with the concentration of testosterone, and in negative correlation with estradiol in E-PE patients. In E-PE placenta, the productions and activities of 17β-hydroxysteroid dehydrogenases 3 and aromatase, the essential enzymes for testosterone and estradiol synthesis, were compromised. In human renal and trophoblastic cells, testosterone and estradiol could regulate SerpinF2 expression in opposite ways. In addition, obvious fibrin deposition was colocalized with SerpinF2 in intervillous spaces and the area surrounding syncytiotrophoblasts in E-PE placenta.

CONCLUSION

The findings reveal a tight correlation between the imbalanced steroid hormone production and the procoagulation factor in E-PE patients, which provide potential biomarkers to predict preeclampsia, and bring new insight into the pathogenesis of preeclampsia.

A prothrombotic state and denser clot formation in patients following acute limb ischemia of unknown cause

INTRODUCTION

Fibrin clot structure differs between healthy individuals and those following thromboembolic events. Dense and poorly lysable fibrin clots have also been reported in peripheral artery disease. We studied fibrin clot properties and its determinants in individuals with a history of acute lower limb ischemia (ALI) of unknown cause.

MATERIALS AND METHODS

In this case-control study, we enrolled 43 patients who experienced ALI of unknown cause, and two age-and sex-matched reference groups: (1) patients with cryptogenic non-lacunar stroke (n = 43) and (2) individuals without any history of thromboembolism (n = 43, control group). Plasma fibrin clot properties, along with thrombin generation and fibrinolysis markers were assessed following ≥3 months of anticoagulation.

RESULTS

Compared with the control group, the ALI group exhibited more compact plasma fibrin clots (13.4% lower permeability [K_s], p = .001), decreased formed clot lysis (12.5% lower D-D_rate, p = .001) and unaltered clot lysis potential, along with enhanced thrombin generation potential (49% higher peak thrombin concentration, p < .0001). There were no differences in these variables between ALI and stroke patients. Patients with ALI had slightly higher α₂-antiplasmin and lower plasminogen activator inhibitor 1 levels compared with the stroke and control groups (all p < .01).

CONCLUSIONS

Patients who experienced ALI of unknown cause display a prothrombotic fibrin clot phenotype, including increased clot density and hypofibrinolysis associated with higher thrombin generation, which might suggest potential benefits from prolonged anticoagulation in this disease.

Prothrombotic clot properties can predict venous ulcers in patients following deep vein thrombosis: a cohort study

Venous ulcers are the most severe manifestation of post-thrombotic syndrome (PTS). We have previously demonstrated that formation of compact fibrin clots resistant to lysis is observed in patients following deep-vein thrombosis (DVT) who developed PTS. The current study investigated whether unfavourable fibrin clot properties can predict post-thrombotic venous ulcers. In a cohort study on 186 consecutive patients following DVT, we determined plasma fibrin clot characteristics, including clot permeability and lysability, inflammatory markers, thrombin generation, fibrinolysis proteins at 3 months since the index event. Occurrence of PTS and venous ulcers was recorded during follow-up (median, 53; range 24 to 76 months). Fifty-seven DVT patients (30.6%) developed PTS, including 12 subjects (6.45%) with a venous ulcer (4 individuals with recurrent ulcers). Patients who developed ulcers compared with the remainder had at enrolment 13.0% lower clot permeability (Ks), 17.4% longer clot lysis time (CLT), 13.1% longer lag phase of clot formation, and 5.0% higher maximum absorbance, with no difference in fibrinogen, C-reactive protein, and thrombin generation. The baseline prothrombotic fibrin clot phenotype (Ks ≤ 6.5 × 10-9 cm2 and CLT > 100 min) was associated with a higher risk of ulcers [hazard ratio (HR), 5.37; 95% confidence interval (CI), 1.3-21.5]. A multivariate model adjusted for age, sex, and fibrinogen showed that independent predictors of the ulcer occurrence were body mass index (HR 1.53; 95% CI 1.30-1.86), CLT (HR 1.43; 95% CI 1.04-2.05), and α2-antiplasmin (HR 0.95; 95% CI 0.90-0.99). This study suggests that formation of denser fibrin clots with impaired fibrinolysis predisposes to post-thrombotic venous ulcers.

Effect of quinolinic acid - A uremic toxin from tryptophan metabolism - On hemostatic profile in rat and mouse thrombosis models

PURPOSE

We aimed to determine the effect of quinolinic acid (QA) on hemostasis in rat and mouse models of thrombosis.

MATERIAL AND METHODS

Wistar rats (male, n = 72) received QA dissolved in drinking water in doses of 3, 10, 30 mg/kg or pure drinking water (vehicle control group -VEH) for 14 days. On the 14^th day of the experiment the effect of QA on hemostasis was evaluated using electrically induced arterial thrombosis model. The following parameters were measured: thrombus weight, hematology, thromboelastometric (ROTEM) parameters, TXA₂ and 6-keto-PGF_1α concentration, coagulation and fibrinolytic markers activity and concentration. GFP mice (male, n = 30) were assigned to the group receiving QA (30 mg/kg) or VEH for 14 days and to the group receiving: single intravenous dose of QA (30 mg/kg) or VEH or the same dose of QA and anti-CD31 (platelet endothelial cell adhesion molecule-1, PECAM-1) antibody conjugated with Alexa Fluor 647. The effect of QA on hemostasis was evaluated in the model of laser-induced injury of mesentery vein using intravital confocal microscopy.

RESULTS

Administering QA for 14 days resulted in a divergent, depending on dose, increase in concentration of active form of tPA and PAI-1 and concentration of total PAI-1 and PAP complexes in rats' plasma. In turn, administering QA for 14 days in mice revealed its prothrombotic activity, while single-dose IV administration revealed its antithrombotic activity, through the up-regulation of PECAM-1 expression.

CONCLUSIONS

We demonstrated the first evidence for the opposite biological effects of QA on hemostasis in rat and mouse thrombosis models.

Prothrombotic fibrin clot properties are associated with post-discharge venous thromboembolism in acutely ill medical patients

INTRODUCTION

Reduced clot permeability and lysability have been reported in patients who experienced venous thromboembolism (VTE) following lower limb injury despite pharmacological thromboprophylaxis. We hypothesized that similarly altered fibrin clot properties characterize patients with post-discharge VTE despite thromboprophylaxis during prior hospitalization due to acute medical illnesses.

METHODS

In a case-control study, we assessed 48 patients who developed VTE within 4 weeks post-discharge despite pharmacological thromboprophylaxis during hospitalization (the thromboprophylaxis group) and three age- and sex-matched control groups (n = 48 each): (1) patients who developed VTE following hospitalization without pharmacological thromboprophylaxis (the no-thromboprophylaxis group), (2) patients with unprovoked VTE and (3) individuals without history of VTE (the no-VTE group). Blood samples were obtained following ≥3 months of anticoagulation in VTE patients. Fibrin clot properties, thrombin generation and fibrinolysis activators and inhibitors were assessed.

RESULTS

Compared with the no-VTE group, the thromboprophylaxis group formed denser fibrin networks reflected by lower clot permeability (K_s, -13%) and impaired fibrinolysis, as evidenced by prolonged clot lysis time (CLT, +14%) and lower rate of D-dimer release from clots (D-D_rate, -9%) accompanied by elevated high-sensitivity C-reactive protein (hsCRP, +79%), peak thrombin generation (+55%) and α₂-antiplasmin (+10%, all p < 0.05). Similar fibrin clot features were observed following unprovoked VTE. The thromboprophylaxis group had also lower K_s (-13%), elevated α₂-antiplasmin (+18%) and higher peak thrombin generation (+25%, all p < 0.05) as compared with the no-thromboprophylaxis group.

CONCLUSIONS

Unfavorably altered plasma clot properties and increased thrombin generation characterize medical patients with post-discharge VTE despite receiving pharmacological thromboprophylaxis during hospitalization for acute conditions.