The role of thrombin activatable fibrinolysis inhibitor in arterial thrombosis at a young age: the ATTAC study

Fibrinolysis in Acute and Chronic Cardiovascular Disease

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

Thrombin Activatable Fibrinolysis Inhibitor (TAFI): An Updated Narrative Review

Thrombin activatable fibrinolysis inhibitor (TAFI), a proenzyme, is converted to a potent attenuator of the fibrinolytic system upon activation by thrombin, plasmin, or the thrombin/thrombomodulin complex. Since TAFI forms a molecular link between coagulation and fibrinolysis and plays a potential role in venous and arterial thrombotic diseases, much interest has been tied to the development of molecules that antagonize its function. This review aims at providing a general overview on the biochemical properties of TAFI, its (patho)physiologic function, and various strategies to stimulate the fibrinolytic system by interfering with (activated) TAFI functionality.

Thrombin generation is associated with ischemic stroke at a young age

INTRODUCTION

Understanding the underlying mechanisms in ischemic stroke (IS) in young adults remains challenging. Thrombin activates processes that contribute to the development and progression of arterial diseases. We investigated the association between thrombin generation (TG) and a first IS or transient ischemic attack (TIA) in young adults.

METHODS

In this case-control study, we included consecutive patients (≤45 years in men, ≤55 years in women) with a first IS or TIA (n = 160) and healthy controls (n = 160). TG was determined with the calibrated automated thrombogram (CAT) assay. Logistic regression was used to analyze the association between TG and IS. Men and women were analyzed separately.

RESULTS

TG started earlier, reached its peak earlier and was also terminated earlier in patients than in healthy controls. Peak height (PH) was higher in patients than in controls, 227 nM (25th-75th percentile 145-326) versus 179 nM (110-294), p = 0.02. The endogenous thrombin potential (ETP) was not different in patients and controls, 1530 nM·min (1089-2045) versus 1454 nM·min (1011-2139), p = 0.52. Lag time (LT) (Odds Ratio (OR) 0.91 (95% confidence interval (CI) 0.83-0.99)), time to peak (TTP) (OR 0.91, 95% CI 0.84-0.97) and time to tail (TTT) (OR 0.92, 95% CI 0.88-0.97) were associated with a first IS and TIA. In men LT, TTP and TTT were associated with IS, but not in women.

CONCLUSIONS

We found that TG parameters are associated with a first IS in young patients. Further prospective studies are warranted to elucidate the role of TG in IS.

Carboxypeptidase U (CPU, TAFIa, CPB2) in Thromboembolic Disease: What Do We Know Three Decades after Its Discovery?

Procarboxypeptidase U (proCPU, TAFI, proCPB2) is a basic carboxypeptidase zymogen that is converted by thrombin(-thrombomodulin) or plasmin into the active carboxypeptidase U (CPU, TAFIa, CPB2), a potent attenuator of fibrinolysis. As CPU forms a molecular link between coagulation and fibrinolysis, the development of CPU inhibitors as profibrinolytic agents constitutes an attractive new concept to improve endogenous fibrinolysis or to increase the efficacy of thrombolytic therapy in thromboembolic diseases. Furthermore, extensive research has been conducted on the in vivo role of CPU in (the acute phase of) thromboembolic disease, as well as on the hypothesis that high proCPU levels and the Thr/Ile325 polymorphism may cause a thrombotic predisposition. In this paper, an overview is given of the methods available for measuring proCPU, CPU, and inactivated CPU (CPUi), together with a summary of the clinical data generated so far, ranging from the current knowledge on proCPU concentrations and polymorphisms as potential thromboembolic risk factors to the positioning of different CPU forms (proCPU, CPU, and CPUi) as diagnostic markers for thromboembolic disease, and the potential benefit of pharmacological inhibition of the CPU pathway.

Effects of Diabetes Mellitus on Fibrin Clot Structure and Mechanics in a Model of Acute Neutrophil Extracellular Traps (NETs) Formation

Subjects with diabetes mellitus (DM) have an increased risk of arterial thrombosis, to which changes in clot structure and mechanics may contribute. Another contributing factor might be an increased formation of neutrophil extracellular traps (NETs) in DM. NETs are mainly formed during the acute phase of disease and form a network within the fibrin matrix, thereby influencing clot properties. Previous research has shown separate effects of NETs and DM on clot properties, therefore our aim was to study how DM affects clot properties in a model resembling an acute phase of disease with NETs formation. Clots were prepared from citrated plasma from subjects with and without DM with the addition of NETs, induced in neutrophils by S. aureus bacteria or phorbol myristate acetate (PMA). Structural parameters were measured using scanning electron microscopy, mechanical properties using rheology, and sensitivity to lysis using a fluorescence-based fibrinolysis assay. Plasma clots from subjects with DM had significantly thicker fibers and fewer pores and branch points than clots from subjects without DM. In addition, fibrinolysis was significantly slower, while mechanical properties were similar between both groups. In conclusion, in a model of acute NETs formation, DM plasma shows prothrombotic effects on fibrin clots.

Hypofibrinolytic state and high thrombin generation may play a major role in SARS-COV2 associated thrombosis

BACKGROUND

Thirty percent of Covid-19 patients admitted to intensive care units present with thrombotic complications despite thromboprophylaxis. Bed rest, obesity, hypoxia, coagulopathy, and acute excessive inflammation are potential mechanisms reported by previous studies. Better understanding of the underlying mechanisms leading to thrombosis is crucial for developing more appropriate prophylaxis and treatment strategies.

OBJECTIVE

We aimed to assess fibrinolytic activity and thrombin generation in 78 Covid-19 patients.

PATIENTS AND METHODS

Forty-eight patients admitted to the intensive care unit and 30 patients admitted to the internal medicine department were included in the study. All patients received thromboprophylaxis. We measured fibrinolytic parameters (tissue plasminogen activator, PAI-1, thrombin activatable fibrinolysis inhibitor, alpha2 anti-plasmin, and tissue plasminogen activator-modified ROTEM device), thrombin generation, and other coagulation tests (D-dimer, fibrinogen, factor VIII, antithrombin).

RESULTS AND CONCLUSIONS

We observed two key findings: a high thrombin generation capacity that remained within normal values despite heparin therapy and a hypofibrinolysis mainly associated with increased PAI-1 levels. A modified ROTEM is able to detect both hypercoagulability and hypofibrinolysis simultaneously in Covid-19 patients with thrombosis.

Development and application of global assays of hyper- and hypofibrinolysis

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

Genetic Polymorphisms Associated with Thrombotic Disease Comparison of Two Territories: Myocardial Infarction and Ischemic Stroke

Background and Purpose

The thrombin-activatable fibrinolysis inhibitor (TAFI) is an important inhibitor of fibrinolysis and plays a critical role in the pathogenesis of arterial thrombosis; genetic polymorphisms of the TAFI gene affect its activity and increase the risk of thrombosis. Moreover, studies in young patients are still scarce. The aim was to examine the contribution of the Thr325Ile and Ala147Thr polymorphisms with ST acute myocardial infarction (STEMI) or idiopathic ischemic stroke (IIS) in the young Mexican population.

Methods

A total of 244 patients with STEMI ≤45 years of age and 244 controls. In a second study, 250 patients with IIS ≤45 years of age were recruited, including 250 controls. In both studies, cases and controls were matched by age and sex. The polymorphisms were determined in all participants by PCR-RFLP.

Results

There was significant difference in the Thr325Ile genotype distribution (P = 0.001) and allele frequency (P = 0.001) between STEMI and control groups, but no difference in the Ala147Thr genotype distribution (P = 0.24) and allele frequency (P = 0.46), neither in the Thr325Ile genotype distribution (P = 0.25) nor in the Ala147Thr genotype distribution (P = 0.46) or their allele frequencies; there was significant difference between IIS and the control group. There were independent factors for STEMI: the Ile allele (P = 0.01), type 2 diabetes mellitus (P = 0.001), hypertension (P = 0.001), smoking (P = 0.001), dyslipidemia (P = 0.001), and family history of atherothrombotic disease (P = 0.001). The independent factors for IIS were hypertension (P = 0.001), smoking (P < 0.01), and family history of atherothrombotic disease (P < 0.01).

Conclusions

The Thr325Ile polymorphism, but no Ala147Thr polymorphism, represents an independent risk factor for STEMI in the young Mexican population.

Association of TAFI gene polymorphisms with severity of coronary stenosis in stable coronary artery disease

INTRODUCTION

Coronary stenosis is a consequence of atherosclerotic plaque progression that is associated with impaired fibrinolysis. Thrombin-activatable fibrinolysis inhibitor (TAFI) and plasminogen activator inhibitor 1 (PAI-1) are fibrinolysis inhibitors whose levels are influenced by acquired conditions and by polymorphisms. This study therefore aimed to investigate the association of TAFI and PAI-1 gene polymorphisms with severity of coronary stenosis in subjects with stable coronary artery disease (CAD).

MATERIALS AND METHODS

A total of 327 subjects suspected with CAD who underwent a coronary angiogram were recruited. Gensini score was applied to stratify the severity of coronary stenosis. Based on the Gensini score, the subjects were categorized into low-medium (<20) or high (≥20) groups. The study polymorphisms included TAFI Ala147Thr (505G/A), Thr325Ile (1040C/T), +1542C/G, +1583T/A and PAI-1 -675 4G/5G. Most polymorphisms were genotyped by allele-specific polymerase chain reaction, except for TAFI Thr325Ile that was genotyped by polymerase chain reaction-restriction fragment length polymorphism.

RESULTS

A significant increase in the Gensini score was found in TAFI 505A and +1583A allele carriers. Binary regression analysis revealed the independent association of the TAFI 505G/A and +1583T/A polymorphisms with a high Gensini score [adjusted OR = 1.67 (95% CI: 1.03, 2.73) and 1.69 (95% CI: 1.04, 2.76), respectively]. Neither the homozygous PAI-1 -675 4G/4G nor the heterozygous 4G/5G was associated with a high Gensini score.

CONCLUSIONS

The results indicated the contribution of TAFI polymorphisms to atherosclerosis progression and severity of coronary stenosis in stable CAD.

Generation and characterization of monoclonal antibodies against the N-terminus of alpha-2-antiplasmin

Around 70% of circulating alpha-2-antiplasmin (α2AP), the main natural plasmin inhibitor, is N-terminally cleaved between residues Pro12 and Asn13 by antiplasmin-cleaving enzyme. This converts native Met-α2AP into the more potent fibrinolysis inhibitor Asn-α2AP. The Arg6Trp (R6W) polymorphism affects the N-terminal cleavage rate of Met-α2AP in a purified system, with ~8-fold faster conversion of Met(R6)-α2AP than Met(W6)-α2AP. To date, assays to determine N-terminally intact Met-α2AP in plasma have been limited to an ELISA that only measures Met(R6)-α2AP. The aim of this study was to generate and characterize monoclonal antibodies (mAbs) against Met(R6)-α2AP, Met(W6)-α2AP and all α2AP forms (total-α2AP) in order to develop specific Met(R6)-α2AP and Met(W6)-α2AP ELISAs. Recombinant Met(R6)-α2AP, Met(W6)-α2AP and Asn-α2AP were expressed in Drosophila S2 cells. Using hybridoma technology, a panel of 25 mAbs was generated against a mixture of recombinant Met(R6)-α2AP and Met(W6)-α2AP. All mAbs were evaluated for their specific reactivity using the three recombinant α2APs in one-site non-competitive ELISAs. Three mAbs were selected to develop sandwich-type ELISAs. MA-AP37E2 and MA-AP34C4 were selected for their specific reactivity against Met(R6)-α2AP and Met(W6)-α2AP, respectively, and used for coating. MA-AP15D7 was selected for its reactivity against total-α2AP and used for detection. With the novel ELISAs we determined Met(R6)-α2AP and Met(W6)-α2AP levels in plasma samples and we showed that Met(R6)-α2AP was converted faster into Asn-α2AP than Met(W6)-α2AP in a plasma milieu. In conclusion, we developed two specific ELISAs for Met(R6)-α2AP and Met(W6)-α2AP, respectively, in plasma. This will enable us to determine N-terminal heterogeneity of α2AP in plasma samples.

Identification of genetic risk factors associated with ischaemic stroke in young Mexican patients

INTRODUCTION

Numerous polymorphisms in candidate genes coding for haemostatic system proteins have been proposed as risk factors for thrombosis.

METHODS

We performed a case-control study of consecutive ischaemic stroke survivors aged ≤ 45 years, treated at our neurology department from 2006 to 2014. Polymerase chain reaction-restriction fragment length polymorphism identified the following polymorphisms: Thr325Ile and Ala147Thr in TAFI, 4G/5G in PAI-1, PLA1/A2 in platelet glycoprotein IIb/IIIa, Glu298Asp in eNOS, and C677T in 5,10-MTHFR. A multivariate logistic regression analysis was performed to evaluate the independent risk of stroke.

RESULTS

204 cases and 204 age- and sex-matched controls were included in the study. Clinical and genetic variables associated with ischaemic stroke were hypertension (P=.03), tobacco use (P=.02), and the polymorphisms Glu298Asp (genotype: P=.001, allele frequency: P=.001) and C677T (genotype: P=.01); the Ala147Thr, Thr325IIe, 4G/5G, and PLA1/A2 mutations were not associated with ischaemic stroke. The 298Asp (P=.03) and T (P=.01) alleles, hypertension (P=.03), tobacco use (P=.01) and family history of stroke (P=.04) were identified as independent risk factors.

CONCLUSIONS

The polymorphisms Glu298Asp and C677T, affecting the eNOS and 5,10-MTHFR enzymes, respectively, and smoking, hypertension, and family history of stroke were associated with ischaemic stroke in young Mexican patients; this was not the case for the Thr325Ile, Ala147Thr, 4G/5G, and PLA1/A2 polymorphisms of the genes coding for fibrinolytic proteins and platelet receptors.

Procarboxypeptidase U (proCPU, TAFI, proCPB2) in cerebrospinal fluid during ischemic stroke is associated with stroke progression, outcome and blood-brain barrier dysfunction

Essentials Little is known of procarboxypeptidase U (proCPU) in cerebrospinal fluid (CSF) of stroke patients. ProCPU levels were studied in CSF of controls and non-thrombolyzed acute ischemic stroke patients. ProCPU is elevated in CSF of stroke patients compared with controls. ProCPU in CSF correlates with stroke progression, outcome, and blood-brain barrier dysfunction.

SUMMARY

Background Procarboxypeptidase U (proCPU, TAFI, proCPB2), the zymogen of CPU, which is a potent antifibrinolytic enzyme and a modulator of inflammation, has previously been investigated in plasma of stroke patients, but so far, no information on the proCPU levels in cerebrospinal fluid (CSF) during acute ischemic stroke (AIS) is available. Objectives This case-control observational study investigates proCPU in CSF of AIS patients compared with controls with an intact blood-brain barrier (BBB) and evaluates the relationship of CSF/plasma proCPU ratios with stroke parameters. Methods A sensitive HPLC-based enzymatic assay was used to determine proCPU levels in CSF of non-thrombolyzed patients in the hyperacute phase (< 24 h after onset) of AIS (n = 72). Individuals (n = 32) without stroke, an intact BBB and no apparent abnormalities in biochemical and microbiological tests, served as controls. Relations between the CSF/plasma proCPU ratio and (i) stroke severity, (ii) stroke progression/recurrence, (iii) stroke outcome and (iv) BBB dysfunction (CSF/serum albumin ratio) were assessed. Results Mean (SEM) proCPU levels were elevated in the CSF of stroke patients compared with controls (4.36 (0.23) U L-1 vs. 3.50 (0.23) U L-1 ). Higher median [IQR] CSF/plasma proCPU ratios were found in patients with stroke progression ((6.0 [4.2-6.9]) × 10-3 ) and poor outcome ((6.4 [3.9-7.0]) × 10-3 ) after 3 months (modified Rankin Scale; mRS > 3) compared with patients without progression ((3.9 [2.7-5.4]) × 10-3 ) or better outcome ((4.0 [2.8-5.0]) × 10-3 ). In stroke patients with a disrupted BBB, proCPU ratios were higher compared with stroke patients with an intact BBB ((6.4 [5.8-9.0]) × 10-3 vs. (3.7 [2.8-5.0]) × 10-3 ). Conclusions ProCPU is increased in CSF during hyperacute ischemic stroke and is associated with stroke progression and outcome after 3 months, most likely due to BBB dysfunction in the hyperacute phase of ischemic stroke.

Dose-Response Relationship Between Thrombin-Activatable Fibrinolysis Inhibitor (TAFI) and Stroke: A Chinese Case-Control Study

BACKGROUND Because TAFI (thrombin-activatable fibrinolysis inhibitor) antigen varies widely among different populations, we performed this case-control study to explore the relationship between TAFI levels and stroke in a Chinese population. MATERIAL AND METHODS Our population-based case-control study included 217 stroke patients and 218 healthy controls. The plasma TAFI level was measured by immune turbidimetry. Univariate and multivariate logistic regression analyses were used to analyze the association between different TAFI levels and stroke and its subtypes. Restricted cubic spline (RCS) combined with logistic regression analysis were used to explore the dose-response relationship between TAFI levels and stroke. RESULTS The plasma TAFI levels of cases were much higher than in the control group (p=0.038) and this difference persisted even after adjustment (OR=2.2). In the elderly (aged over 60) and female subgroups, TAFI levels in stroke patients were higher than those in controls, and the results were also noted in ischemic stroke. The dose-response curve showed that, as a whole, with the increase of TAFI levels, the relative risk of stroke first increased and then decreased (p=0.0127). Similarly, in general, with the increase of TAFI levels, the curve showed that the relative risk of ischemic stroke first increased and then decreased (p=0.0110). CONCLUSIONS There was a definite correlation between TAFI levels and stroke in this Chinese population, and with the increase of TAFI levels, the relative risk of stroke or ischemic stroke first increased and then decreased.

Importance of Endogenous Fibrinolysis in Platelet Thrombus Formation

The processes of thrombosis and coagulation are finely regulated by endogenous fibrinolysis maintaining healthy equilibrium. When the balance is altered in favour of platelet activation and/or coagulation, or if endogenous fibrinolysis becomes less efficient, pathological thrombosis can occur. Arterial thrombosis remains a major cause of morbidity and mortality in the world despite advances in medical therapies. The role endogenous fibrinolysis in the pathogenesis of arterial thrombosis has gained increasing attention in recent years as it presents novel ways to prevent and treat existing diseases. In this review article, we discuss the role of endogenous fibrinolysis in platelet thrombus formation, methods of measurement of fibrinolytic activity, its role in predicting cardiovascular diseases and clinical outcomes and future directions.

Circulating fibroblast activation protein activity and antigen levels correlate strongly when measured in liver disease and coronary heart disease

BACKGROUND AND AIM

Circulating fibroblast activation protein (cFAP) is a constitutively active enzyme expressed by activated fibroblasts that has both dipeptidyl peptidase and endopeptidase activities. We aimed to assess the correlation between cFAP activity and antigen levels and to compare variations in levels.

METHODS

In plasma of 465 control individuals, 368 patients with coronary heart disease (CHD) and 102 hepatitis C virus (HCV) infected patients with severe liver disease before and after liver transplant, cFAP activity levels were measured with a newly developed cFAP activity assay. In the same samples, cFAP antigen levels were measured using a commercially available cFAP ELISA. Correlation analyses between activity and antigen levels were performed by calculating Pearson's correlation coefficient (ρ). Additionally, normal ranges, determinants and differences between cohorts and between anticoagulants were investigated.

RESULTS

cFAP activity and antigen levels significantly correlated in controls (ρ: 0.660, p<0.001) and in CHD patients (ρ: 0.709, p<0.001). cFAP activity and antigen levels in the HCV cohort were significantly lower in the samples taken after liver transplantation (p<0.001) and normalized toward levels of healthy individuals. Furthermore, cFAP activity and antigen levels were higher in men and significantly associated with body mass index. Also, cFAP activity and antigen levels were higher in EDTA plasma as compared to the levels in citrated plasma from the same healthy individuals.

CONCLUSIONS

For analyzing cFAP levels, either activity levels or antigen levels can be measured to investigate differences between individuals. However, it is of importance that blood samples are collected in the same anticoagulant.

Laboratory evaluation of patients with undiagnosed bleeding disorders

The evaluation of patients with a bleeding tendency represents a challenge as the routinely available tests for evaluating bleeding disorders are limited, complicating the laboratory determination of the clinically observed bleeding tendency. As a result, some bleeding disorders remain undiagnosed. The aim of the study was to evaluate whether global coagulation tests would contribute to the laboratory analysis of patients with undiagnosed bleeding disorders. Patients were evaluated for coagulation and fibrinolysis activities by thrombin generation test and euglobulin lysis time. In addition, plasma activity of factor XIII, plasminogen, α-2 antiplasmin, plasminogen activator inhibitor-1, and thrombin-activatable fibrinolysis inhibitor was also obtained. Forty-five patients were included. Eight per cent presented a mild bleeding disorder and 20% a moderate bleeding disorder. The thrombin generation test results were similar between patients and controls. Euglobulin lysis time results, however, were lower in patients than in controls, both before (median 175 vs. 250 min, respectively; P = 0.003) and after (median 145 vs. 115 min, respectively; P ≤ 0.001) arm constriction, suggesting that they were experiencing hyperfibrinolysis. Interestingly, patients' median thrombin-activatable fibrinolysis inhibitor activity was higher than in controls (21.2 vs. 19.46 μg/ml; P = 0.016). However, plasminogen, α-2 antiplasmin, plasminogen activator inhibitor-1, and factor XIII activities did not differ between the groups. Global coagulation and fibrinolysis tests proved to be limited in detecting the hemostatic disorders in some patients with a relevant bleeding tendency and may not be adequate to address their bleeding risk. Bleeding scores are currently the available medical approach for the evaluation of these patients.

Plasma levels of carboxypeptidase U (CPU, CPB2 or TAFIa) are elevated in patients with acute myocardial infarction

BACKGROUND

Two decades after its discovery, carboxypeptidase U (CPU, CPB2 or TAFIa) has become a compelling drug target in thrombosis research. However, given the difficulty of measuring CPU in the blood circulation and the demanding sample collecton requirements, previous clinical studies focused mainly on measuring its inactive precursor, proCPU (proCPB2 or TAFI).

OBJECTIVES

Using a sensitive and specific enzymatic assay, we investigated plasma CPU levels in patients presenting with acute myocardial infarction (AMI) and in controls.

METHODS

In this case-control study, peripheral arterial blood samples were collected from 45 patients with AMI (25 with ST segment elevation myocardial infarction [STEMI], 20 with non-ST segment elevation myocardial infarction [NSTEMI]) and 42 controls. Additionally, intracoronary blood samples were collected from 11 STEMI patients during thrombus aspiration. Subsequently, proCPU and CPU plasma concentrations in all samples were measured by means of an activity-based assay, using Bz-o-cyano-Phe-Arg as a selective substrate.

RESULTS

CPU activity levels were higher in patients with AMI (median LOD-LOQ, range 0-1277 mU L(-1) ) than in controls (median < LOD, range 0-128 mU L(-1) ). No correlation was found between CPU levels and AMI type (NSTEMI [median between LOD-LOQ, range 0-465 mU L(-1) ] vs. STEMI [median between LOD-LOQ, range 0-1277 mU L(-1) ]). Intracoronary samples (median 109 mU L(-1) , range 0-759 mU L(-1) ) contained higher CPU levels than did peripheral samples (median between LOD-LOQ, range 0-107 mU L(-1) ), indicating increased local CPU generation. With regard to proCPU, we found lower levels in AMI patients (median 910 U L(-1) , range 706-1224 U L(-1) ) than in controls (median 1010 U L(-1) , range 753-1396 U L(-1) ).

CONCLUSIONS

AMI patients have higher plasma CPU levels and lower proCPU levels than controls. This finding indicates in vivo generation of functional active CPU in patients with AMI.

Thrombin-activatable fibrinolysis inhibitor influences disease severity in humans and mice with pneumococcal meningitis

BACKGROUND

Mortality and morbidity in patients with bacterial meningitis result from the proinflammatory response and dysregulation of coagulation and fibrinolysis. Thrombin-activatable fibrinolysis inhibitor (TAFI) is activated by free thrombin or thrombin in complex with thrombomodulin, and plays an antifibrinolytic role during fibrin clot degradation, but also has an anti-inflammatory role by inactivating proinflammatory mediators, such as complement activation products.

OBJECTIVE

To assess the role of TAFI in pneumococcal meningitis.

METHODS

We performed a prospective nationwide genetic association study in patients with bacterial meningitis, determined TAFI and complement levels in cerebrospinal fluid (CSF), and assessed the function of TAFI in a pneumococcal meningitis mouse model by using Cpb2 (TAFI) knockout mice.

RESULTS

Polymorphisms (reference sequences: rs1926447 and rs3742264) in the CPB2 gene, coding for TAFI, were related to the development of systemic complications in patients with pneumococcal meningitis. Higher protein levels of TAFI in CSF were significantly associated with CSF complement levels (C3a, iC3b, and C5b-9) and with more systemic complications in patients with bacterial meningitis. The risk allele of rs1926447 (TT) was associated with higher levels of TAFI in CSF. In the murine model, consistent with the human data, Cpb2-deficient mice had decreased disease severity, as reflected by lower mortality, and attenuated cytokine levels and bacterial outgrowth in the systemic compartment during disease, without differences in the brain compartment, as compared with wild-type mice.

CONCLUSIONS

These findings suggest that TAFI plays an important role during pneumococcal meningitis, which is likely to be mediated through inhibition of the complement system, and influences the occurrence of systemic complications and inflammation.

Impact of genetic polymorphisms in thrombin activatable fibrinolysis inhibitor (TAFI) on venous thrombosis disease: A meta-analysis

BACKGROUND

Reported studies have showed that Thrombin Activatable Fibrinolysis Inhibitor (TAFI) may be associated with an increased risk of venous thromboembolism. But the relation of VT with TAFI gene SNPs could not be clearly demonstrated. Thus, we conducted a meta-analysis to analyze the associations between three TAFI variants -438G/A, 505G/A and 1040C/T and the risk of venous thrombosis.

METHODS

We carried out a systematic search to obtain all the eligible studies published before 30th October 2014. Pooled odds ratios (ORs) and 95% confidence intervals (95% CIs) were computed to assess the association.

RESULTS

13 eligible studies were enrolled including 2321 patients and 2464 controls. There was a significant association between 505G/A and the risk of VTD under all models except recessive model (G vs. A: OR=1.13, 95% CI: 1.02, 1.26; GG vs. AA:OR=1.47, 95% CI: 1.14, 1.88; GA vs. AA: OR=1.36, 95% CI: 1.06, 1.73; GG+GA vs. AA: OR=1.41, 95% CI: 1.12, 1.77). Similarly, obvious relationship was observed in subgroup analyses in light of type of disease and ethnicity. Likewise, for 1040C/T variant, significant associations were identified under homozygote, heterozygote and dominant models (CC vs. TT: OR=1.65, 95% CI: 1.06, 2.59; CT vs. TT: OR=1.55, 95% CI: 1.19, 2.03; CC+CT vs. TT: OR=1.55, 95% CI: 1.20, 2.00). Sub-analysis presented significant associations in non-CVT and non-Asian group under homozygote, heterozygote, and dominant models and CVT group in recessive model.

CONCLUSION

This meta-analysis showed that -438G/A variant was not associated with the incidence of venous thrombosis. But in non-Asian populations, G allele and GG genotype of 505G/A may increase the risk of venous thrombosis diseases. GG genotype of 505G/A and one C carrier (CC and CT) of 1040C/T gave rise to the development of venous thrombosis diseases except CVT. Additionally, the heterozygote CT may be a potential contributing factor of gene effect in venous thrombosis.

Innovative thrombolytic strategy using a heterodimer diabody against TAFI and PAI-1 in mouse models of thrombosis and stroke

Circulating thrombin-activatable fibrinolysis inhibitor (TAFI) and plasminogen activator inhibitor-1 (PAI-1) are causal factors for thrombolytic failure. Therefore, we evaluated an antibody-engineered bispecific inhibitor against TAFI and PAI-1 (heterodimer diabody, Db-TCK26D6x33H1F7) in several mouse models of thrombosis and stroke. Prophylactic administration of the diabody (0.8 mg/kg) in a thromboplastin-induced model of thromboembolism led to decreased lung fibrin deposition. In a model of cerebral ischemia and reperfusion, diabody administration (0.8 mg/kg, 1 hour postocclusion) led to a mitigated cerebral injury with a 2.3-fold reduced lesion and improved functional outcomes. In a mouse model of thrombin-induced middle cerebral artery occlusion, the efficacy of the diabody was compared to the standard thrombolytic treatment with recombinant tissue-type plasminogen activator (tPA). Early administration of diabody (0.8 mg/kg) caused a twofold decrease in brain lesion size, whereas that of tPA (10 mg/kg) had a much smaller effect. Delayed administration of diabody or tPA had no effect on lesion size, whereas the combined administration of diabody with tPA caused a 1.7-fold decrease in lesion size. In contrast to tPA, the diabody did not increase accumulative bleeding. In conclusion, administration of a bispecific inhibitor against TAFI and PAI-1 results in a prominent profibrinolytic effect in mice without increased bleeding.

Plasma levels of soluble fibroblast activation protein in arterial thrombosis: determinants and cleavage of its substrate alpha-2-antiplasmin

BACKGROUND

Fibroblast activation protein (FAP) is a transmembrane glycoprotein with dipeptidyl-peptidase and endopeptidase activities and circulates in blood in a truncated, soluble form (sFAP). Fibrinolysis inhibitor α2-antiplasmin (α2AP) has been described as a potential in vivo substrate of sFAP. We aimed to investigate sFAP levels and α2AP cleavage in young arterial thrombosis patients and in control individuals, study the correlation between sFAP levels and α2AP cleavage and investigate determinants of these variables.

METHODS

sFAP levels and α2AP cleavage were determined by ELISA in the plasma samples of 391 coronary heart disease (CHD) patients, 221 ischemic stroke patients, 51 peripheral arterial disease patients and 501 control individuals.

RESULTS

Median sFAP levels were similar in arterial thrombotic patients and in control individuals, but in CHD patients sFAP levels significantly increased with time (number of months) between the event and study inclusion (Spearman's rho: 0.209, p<0.001), indicating reduced sFAP levels at time of event. sFAP levels and percentage α2AP cleavage significantly correlated in controls and in patients. Furthermore, sex, use of oral contraceptives and hyperlipidemia were significant determinants of sFAP levels.

CONCLUSIONS

sFAP levels were reduced in the CHD patient population, but only in the first months after the event, indicating that over time sFAP levels may normalize. The significant correlation between sFAP level and α2AP cleavage indicates that in vivo sFAP (at least partly) regulates cleavage of α2AP, irrespective of disease status. Differences in sFAP level due to sex, use of oral contraceptives and hyperlipidemia might suggest hormonal control of sFAP levels.

Active PAI-1 as marker for venous thromboembolism: case-control study using a comprehensive panel of PAI-1 and TAFI assays

BACKGROUND

Both activated Thrombin Activatable Fibrinolysis Inhibitor (TAFI) and active Plasminogen Activator Inhibitor-1 (PAI-1) attenuate fibrinolysis and may therefore contribute to the pathophysiology of Venous ThromboEmbolism (VTE). Whether increased TAFI and/or PAI-1 concentrations are associated with VTE is unclear.

OBJECTIVE

To study an association of impaired fibrinolysis and VTE using a comprehensive panel of in-house developed assays measuring intact TAFI, activation peptide of TAFI (AP-TAFI), PAI-1 antigen, endogenous PAI-1:t-PA complex (PAI-1:t-PA) and active PAI-1 levels in 102 VTE patients and in 113 healthy controls (HC).

RESULTS

Active PAI-1 was significantly higher in VTE patients compared to HC (20.9 [9.6-37.8] ng/ml vs. 6.2 [3.5-9.7] ng/ml, respectively). Active PAI-1 was the best discriminator with an area under the ROC curve and 95% confidence interval (AUROC [95%CI]) of 0.84 [0.79-0.90] compared to 0.75 [0.68-0.72] for PAI-1:t-PA, 0.65 [0.58-0.73] for PAI-1 antigen, 0.62 [0.54-0.69] for AP-TAFI and 0.51 [0.44-0.59] for intact TAFI. Using ROC analysis, we defined an optimal cut-off of 12.8 ng/ml for active PAI-1, with corresponding sensitivity of 71 [61-79] % and specificity of 89 [82-94] %. A lack of association with the time between VTE event and sample collection or with the intake of anticoagulant treatment suggests that active PAI-1 levels are sustainable high in VTE patients.

CONCLUSIONS

This case-control study emphasizes the clinical importance of measuring active PAI-1 instead of PAI-1 antigen and identifies active PAI-1 as a potential marker of VTE. Prognostic studies will need to address the clinical significance of active PAI-1 as biomarker.

Genetic variations in the thrombin-activatable fibrinolysis inhibitor gene and risk of cardiovascular disease: a systematic review and meta-analysis

BACKGROUND

An imbalance between coagulation and fibrinolytic system plays an important role in the pathogenesis of arterial thrombosis. It has been identified that elevated plasma thrombin-activatable fibrinolysis inhibitor (TAFI) concentration, an anti-fibrinolytic factor, is associated with an increased risk of cardiovascular disease (CVD). But the effect of genetic variations in TAFI gene on the risk of CVD is inconclusive.

OBJECTIVES

To investigate the associations between two variants Ala147Thr(rs3742264) and Thr325Ile(rs1926447) in TAFI and the risk of CVD.

METHODS

Systematic review and meta-analysis of eligible studies published before January 2014. Coronary heart disease(CHD) and stroke are regarded as end-points of CVD.

RESULTS

A total of 18 articles including 23 studies were enrolled. Among these articles were 19 studies of Ala147Thr and 15 of Thr325Ile variants, comprising 4,977 CVD patients and 8,082 controls together with 4,890 cases and 8,311 controls, respectively. There were no significant associations between Ala147Thr variant and CVD under allele, dominant, recessive genetic models. Similar results were observed when end-point, ethnicity, sample size, genotyping method were taken into account. Likewise, meta-analysis of Thr325Ile variant did not show significant associations with CVD under three genetic models. Nevertheless, in sub-analysis based on end-point, the TT(Ile/Ile) genotype was associated with a 25% higher risk of coronary heart disease(CHD) (OR=1.25, 95%CI, 1.02-1.54; P=0.03) compared with TC+CC(Thr/Ile+Thr/Thr) genotype(recessive model).

CONCLUSIONS

The present meta-analysis failed to confirm the influence of Ala147Thr and Thr325Ile variants on the susceptibility to CVD. However, potentially increased risk of CHD was detected in Ile325 allele carriers under recessive model.

Thrombin-activatable fibrinolysis inhibitor (TAFI) levels and its polymorphism rs3742264 are associated with dyslipidemia in a cohort of Brazilian subjects

BACKGROUND

Dyslipidemia, a metabolic alteration that affects lipoprotein levels, is considered a major risk factor for atherosclerosis and its complications. Dyslipidemia also affects the hemostatic system, especially impairing fibrinolysis, and increased levels of thrombin-activatable fibrinolysis inhibitor (TAFI) have been associated with cardiovascular events.

OBJECTIVES AND METHODS

This study evaluated the association of acquired risk factors (hypertension, body mass index - BMI, smoking, sedentary lifestyle, use or not of oral contraceptives and hormone replacement therapy, and post-menopause status), the polymorphisms Thr325Ile (rs1926447), Ala147Thr (rs3742264) and +1542C/G (rs940) in the TAFI gene, and TAFI plasma levels in 109 dyslipidemic and 105 normolipemic individuals. Biochemical analyses and TAFI levels were evaluated by colorimetric/turbidimetric assays and ELISA, respectively. Genotypic and allelic frequencies were determined by polymerase chain reaction (PCR).

RESULTS

Hypertension, increased BMI, and menopause were more common in dyslipidemic individuals, who had higher TAFI levels. The alleles 325Ile, Ala147, and C showed association with lower TAFI levels. The rs3742264 polymorphism was associated with dyslipidemia in males.

CONCLUSIONS

The results suggest that TAFI levels are independently associated to dyslipidemia and that the polymorphism rs3742264 may be related to cardiovascular risk in male subjects.

Haplotypes of TAFI gene and the risk of cerebral venous thrombosis--a case-control study

INTRODUCTION

Cerebral venous thrombosis (CVT) is an uncommon disease with some differences compared to other-site thrombosis, including a higher frequency in young people, female sex and oral contraceptive users. Thrombin-activatable fibrinolysis inhibitor (TAFI) is a regulator of fibrinolysis, whose levels are genetically controlled and its increase is associated to thrombosis. Our objective was to investigate in a case-control study the association between CVT and TAFI single nucleotide polymorphisms (SNPs) and its haplotypes in comparison to other-site venous thrombosis and controls.

MATERIALS AND METHODS

Seventy two patients with CVT were compared to 143 individuals with no history of thromboembolic events (control group) and to 128 patients with deep vein thrombosis in the limbs and/or pulmonary embolism (venous thromboembolism-VTE group). SNPs were genotyped by restriction fragment length polymorphism or allele-specific PCR for F2 20210G>A, F5 1691G>A, TAFI (-1053C>T, -438G>A, 505G>A, 1040C>T and +1542C>G).

RESULTS

The GTC haplotype for TAFI 505G>A/1040C>T/+1542C>G SNPs was associated with an increased risk of CVT compared to controls [odds ratio (OR) 2.67, 95% confidence interval (CI): 1.13 - 6.34) and VTE group (OR 2.51, 95%CI: 1.07 - 8.06). The CVT risk became even more pronounced when evaluating unprovoked or hormone-related thrombosis cases: CVT compared to controls (OR 3.24, 95%CI: 1.19 - 8.82) and VTE group (OR 4.32, 95%CI: 1.27 - 14.63).

CONCLUSIONS

Our data indicate that the GTC haplotype for TAFI 505G>A/1040C>T/+1542C>G SNPs increased the risk of CVT in comparison to controls and VTE cases. Further studies are required to confirm our findings.

TAFI gene polymorphisms in patients with cerebral venous thrombosis

Gene polymorphisms of thrombin activatable fibrinolysis inhibition (TAFI) factor have been investigated in various studies in terms of etiology (recurrence) and treatment (fibrinolytic effect) of thrombus formation. Cerebral venous thrombosis (CVT) is a life-threatening disease observed in young persons. Fifty-nine patients with CVT and 100 healthy control subjects were enrolled in the case/control study. The association between TAFI gene polymorphisms -438G>A, +505A>G and +1040C>T and cerebral venous thrombosis was investigated. It was found that frequencies of polymorphic genotype and allele were not different in patients than in control group and that they were not significant for cerebral venous thrombosis.

Insights into thrombin activatable fibrinolysis inhibitor function and regulation

Fibrinolysis is initiated when the zymogen plasminogen is converted to plasmin via the action of plasminogen activators. Proteolytic cleavage of fibrin by plasmin generates C-terminal lysine residues capable of binding both plasminogen and the plasminogen activator, thereby stimulating plasminogen activator-mediated plasminogen activation and propagating fibrinolysis. This positive feedback mechanism is regulated by activated thrombin activatable fibrinolysis inhibitor (TAFIa), which cleaves C-terminal lysine residues from the fibrin surface, thereby decreasing its cofactor activity. TAFI can be activated by thrombin alone, but the rate of activation is accelerated when in complex with thrombomodulin. Plasmin is also known to activate TAFI. TAFIa has no known physiologic inhibitors and consequently, its primary regulatory mechanism involves its intrinsic thermal instability. The rate of TAFI activation and stability of the active form, TAFIa, function in maintaining its concentration above the threshold value required to down-regulate fibrinolysis. Although all methods to quantify TAFI or TAFIa have their limitations, epidemiologic studies have indicated that elevated TAFI levels are correlated with an increased risk of venous thrombosis. Major efforts have been made to develop TAFI inhibitors that can either directly interfere with TAFIa activity or impair its activation. However, the anti-inflammatory properties of TAFIa might complicate the development and application of a TAFIa inhibitor that aims to increase the efficiency of thrombolytic therapy.

Prognostic markers in young patients with premature coronary heart disease

OBJECTIVES

To evaluate the survival and prognostic implications of cardiovascular, inflammatory and prothrombotic risk factors in young patients with premature coronary heart disease (CHD).

METHODS

Follow-up data were obtained from 353 young patients with a first cardiac event (men ≤45 years and women ≤55 years). Baseline characteristics on traditional risk factors were collected at the time of the first event, and plasma levels of C-reactive protein (CRP), von Willebrand Factor (VWF), and fibrinogen were measured one to three months after the first event to exclude an acute phase response. We performed age and sex adjusted Cox regression analyses to assess the relationship between these factors and recurrent events with three different endpoints: all cause mortality, recurrent cardiac event (myocardial infarction or revascularisation procedure), and any recurrent event (cardiac event, cerebrovascular event or all cause mortality).

RESULTS

During a total follow-up time of 1483 person years (mean 4.2 years), 11 patients died (3%), 42 patients had a recurrent cardiac event (12%), and 53 patients had any recurrent event (15%). CRP was associated with an increased risk of any recurrent event (HR 1.28[95% CI = 1.02-1.59] per unit increase in lnCRP). Also, both CRP (5.00[1.04-24.04]) and fibrinogen (5.04[1.05-24.23]) were associated with all cause mortality when levels were above the 50th percentile.

CONCLUSIONS

Fifteen percent of young patients with a first cardiac event have a recurrent event or die within a median follow-up of 4.2 years. In these young patients we have shown that, independently of cardiovascular risk factors, high CRP levels contribute to the risk of recurrent events, including all cause mortality, and high fibrinogen levels are associated with all cause mortality.

von Willebrand factor plasma levels, genetic variations and coronary heart disease in an older population

BACKGROUND

High von Willebrand factor (VWF) levels are associated with an increased risk of coronary heart disease (CHD). However, it remains unclear whether VWF is causally related to the occurrence of CHD or primarily mirrors endothelial dysfunction, which predisposes to atherosclerosis and subsequent CHD.

OBJECTIVES

Because VWF is largely determined by genetic factors, we investigated whether VWF antigen levels (VWF:Ag) and the risk of CHD are affected by common variations in the VWF gene.

METHODS

We included 7002 participants (≥ 55 years) from the large prospective population-based Rotterdam Study in the discovery cohort. The extension cohort of the Rotterdam Study, consisting of 3011 participants, was used as a replication cohort. We determined VWF:Ag levels and genotype data of 38 single-nucleotide polymorphisms (SNPs) in VWF. Subsequently, hazard ratios for CHD were calculated and genetic analyses were performed to assess the relationship between SNPs, VWF:Ag levels and CHD risk.

RESULTS

We identified and replicated three SNPs that were associated with VWF:Ag: rs216321 (β = 0.10 [95% confidence interval, CI, 0.06;0.13]) (Ala852Gln), rs1063856 (β = 0.05 [95% CI 0.03;0.07]) (Thr789Ala) and rs2283333 (β = 0.09 [95% CI 0.05;0.21]) (intron 15). However, genetic polymorphisms in the VWF gene were not associated with the risk of CHD.

CONCLUSIONS

In this study we have shown that genetic variations in VWF strongly affect VWF plasma levels, but are not associated with the risk of CHD. Our findings therefore do not support a strong causal relationship between VWF and CHD in elderly individuals of ≥ 55 years, but suggest that VWF is primarily a marker of CHD.

Identification of tristetraprolin as a factor that modulates the stability of the TAFI transcript through binding to the 3'-untranslated region

BACKGROUND

Thrombin-activatable fibrinolysis inhibitor (TAFI) is a basic carboxypeptidase zymogen encoded by the human gene CPB2. TAFI constitutes a molecular link between coagulation and fibrinolysis, and between coagulation and inflammation. The 3'-untranslated region (UTR) of the human CPB2 mRNA plays a key role in regulating CPB2 mRNA abundance, but the exact mechanisms that mediate this regulation are largely unexplored.

OBJECTIVES

To pinpoint cis-acting elements in the CPB2 3'-UTR that act as stability determinants and to identify protein factors binding to these sites.

METHODS

We constructed a series of plasmids encoding mRNAs containing rabbit β-globin sequences (as a reporter) fused to sequences of the CPB2 3'-UTR (encompassing 5' and internal deletions). These plasmids were transfected into HepG2 (human hepatoma) cells and the stability of the fusion transcripts measured. We performed a series of gel mobility shift analyses using RNA probes encompassing putative (in)stability elements.

RESULTS

We identified one element conferring stability and three elements conferring instability. Supershift assays identified the protein bound to the site between the second and third polyadenylation sites as tristetraprolin (TTP). Mutation of the TTP site abolished TTP binding in gel mobility shift assays and also stabilized β-globin/CPB2 fusion transcripts. TTP knockdown stabilized the fusion transcript containing the TTP site, but not a fusion transcript in which this site was mutated.

CONCLUSIONS

Our findings are indicative of a role for TTP in constitutive, and perhaps regulated, control of CPB2 mRNA stability and hence abundance.

Thrombin activatable fibrinolysis inhibitor: at the nexus of fibrinolysis and inflammation

TAFI (thrombin activatable fibrinolysis inhibitor) is the precursor of a basic carboxypeptidase (TAFIa) with strong antifibrinolytic and anti-inflammatory activity. Compelling evidence indicates that thrombin, either alone or in complex with thrombomodulin, is the main physiological activator of TAFI. For this reason derangements of thrombin formation, whatever the cause, may influence the fibrinolytic process too. Experimental models of thrombosis suggest that TAFI may participate in thrombus development and persistence under certain circumstances. In several models of pharmacological thrombolysis, the administration of TAFI inhibitors along with the fibrinolytic agent leads to a marked improvement of thrombus lysis, underscoring the potential of TAFI inhibitors as adjuvants for thrombolytic therapy. The role of TAFI in inflammatory diseases is more complex as it may serve as a defense mechanism, exacerbate the disease, or have no influence, depending on the nature of the model and the role played by the mediators controlled by TAFIa. Finally, the numerous clinical studies in patients with thrombotic disease support the idea that increased levels of TAFI and/or the enhancement of TAFI activation may represent a new risk factor for venous and arterial thrombosis.

Plasma carboxypeptidase B downregulates inflammatory responses in autoimmune arthritis

The immune and coagulation systems are both implicated in the pathogenesis of rheumatoid arthritis (RA). Plasma carboxypeptidase B (CPB), which is activated by the thrombin/thrombomodulin complex, plays a procoagulant role during fibrin clot formation. However, an antiinflammatory role for CPB is suggested by the recent observation that CPB can cleave proinflammatory mediators, such as C5a, bradykinin, and osteopontin. Here, we show that CPB plays a central role in downregulating C5a-mediated inflammatory responses in autoimmune arthritis. CPB deficiency exacerbated inflammatory arthritis in a mouse model of RA, and cleavage of C5a by CPB suppressed the ability of C5a to recruit immune cells in vivo. In human patients with RA, genotyping of nonsynonymous SNPs in the CPB-encoding gene revealed that the allele encoding a CPB variant with longer half-life was associated with a lower risk of developing radiographically severe RA. Functionally, this CPB variant was more effective at abrogating the proinflammatory properties of C5a. Additionally, expression of both CPB and C5a in synovial fluid was higher in patients with RA than in those with osteoarthritis. These findings suggest that CPB plays a critical role in dampening local, C5a-mediated inflammation and represents a molecular link between inflammation and coagulation in autoimmune arthritis.

Effect of genetic variations in syntaxin-binding protein-5 and syntaxin-2 on von Willebrand factor concentration and cardiovascular risk

BACKGROUND

Elevated von Willebrand factor (VWF) plasma levels are associated with an increased risk of cardiovascular disease. A meta-analysis of genomewide association studies on VWF identified novel candidate genes, that is, syntaxin-binding protein 5 (STXBP5) and syntaxin 2 (STX2), which are possibly involved in the secretion of VWF. We investigated whether VWF antigen levels (VWF:Ag), VWF collagen-binding activity (VWF:CB) and the risk of arterial thrombosis are affected by common genetic variations in these genes.

METHODS AND RESULTS

In 463 young white subjects (men ≤45 years of age and women ≤55 years of age), who were included 1 to 3 months after a first event of arterial thrombosis, and 406 control subjects, we measured VWF:Ag and VWF:CB. Nine haplotype tagging single-nucleotide polymorphisms of STXBP5 and STX2 were selected and subsequently analyzed using linear regression with additive genetic models adjusted for age, sex, and ABO blood group. The minor alleles of rs9399599 and rs1039084 in STXBP5 were associated with lower VWF plasma levels and activity, whereas the minor allele of rs7978987 in STX2 was associated with higher VWF plasma levels and activity. The minor alleles of the single-nucleotide polymorphisms in STX2 were associated with a reduced risk of arterial thrombosis (rs1236: odds ratio, 0.73 [95% confidence interval, 0.59, 0.89]; rs7978987: odds ratio, 0.81 [95% confidence interval, 0.65, 1.00]; rs11061158: odds ratio, 0.69 [95% confidence interval, 0.55, 0.88]).

CONCLUSIONS

Genetic variability in STXBP5 and STX2 affects both VWF concentration and activity in young individuals with premature arterial thrombosis. Furthermore, in our study, genetic variability in STX2 is associated with the risk of arterial thrombosis. However, at this point, the underlying mechanism remains unclear.

Identification of human thrombin-activatable fibrinolysis inhibitor in vascular and inflammatory cells

TAFI (thrombin-activatable fibrinolysis inhibitor) is a carboxypeptidase zymogen originally identified in plasma. The TAFI pathway helps to regulate the balance between the coagulation and fibrinolytic cascades. Activated TAFI (TAFIa) can also inactivate certain pro-inflammatory mediators, suggesting that the TAFI pathway may also regulate communication between coagulation and inflammation. Expression in the liver is considered to be the source of plasma TAFI. TAFI has also been identified in platelets and CPB2 (the gene encoding TAFI) mRNA has been detected in megakaryocytic cell lines as well as in endothelial cells. We have undertaken a quantitative analysis of CPB2 mRNA and TAFI protein in extrahepatic cell types relevant to vascular disease. Using RT-PCR and quantitative RT-PCR, we detected CPB2 mRNA in the human megakaryoblastic cell lines MEG-01 and Dami, the human monocytoid cell line THP-1 as well as THP-1 cells differentiated into a macrophage-like phenotype, and in primary human umbilical vein and coronary artery endothelial cells. CPB2 mRNA abundance in MEG-01, Dami, and THP-1 cells was modulated by the state of differentiation of these cells. Using a recently developed TAFIa assay, we detected TAFI protein in the lysates of the human hepatocellular carcinoma cell line HepG2 as well as in MEG-01 and Dami cells and in the conditioned medium of HepG2 cells, differentiated Dami cells, and THP-1 macrophages. We have obtained clear evidence for extrahepatic expression of TAFI, which has clear implications for the physiological and pathophysiological functions of the TAFI pathway.

[Prognosis value of thrombin activatable fibrinolysis inhibitor concentration and C1040T polymorphism in acute myocardial infarction treated with fibrinolysis]

OBJECTIVE

To analyze the prognostic value of thrombin activatable fibrinolysis inhibitor (TAFI) and C1040T polymorphism in acute myocardial infarction treated with fibrinolysis. To analyze C1040T polymorphism influence on its plasma level.

DESIGN

An observational, prospective study performed from November 2003 to November 2005 and with a 3 month follow-up.

SETTING

Intensive Medicine Service from a university-affiliated teaching hospital.

PATIENTS

A total of 53 patients with acute myocardial infarction with persistent ST segment elevation treated with the same fibrinolytic therapy. A control group of 53 biologically similar subjects was included.

INTERVENTIONS

None.

MAIN MEASUREMENTS

Baseline characteristics; frequency of wild-type genotype (Thr325Thr) and of those corresponding to the mutation (Thr325LLe and LLe325lle), TAFI levels at 6 h, 34 h and 3 months post-fibrinolysis; ejection fraction; Killip-Kimball; reperfusion; ischemic recurrence; death.

RESULTS

No relationship was found between biological features and TAFI concentration. The latter was significantly higher in infarct patients (p<0.01) and in the mutation group (p<0.01). The homozygotic mutation (Ile325Ile) was significantly higher in infarct patients (p<0.01). Reperfusion was significantly associated with lower body mass index (p=0.02. OR 0.22. 95% CI), ejection fraction (p=0.004. OR 0.91. 95% CI), triglyceride level (p=0.01. OR 1.02. 95% CI) and cholesterol levels (p=0.001. OR=0.84. 95% CI). Mutation was associated to a significant fall in post-fibrinolysis concentration TAFI antigen and functional TAFI (p=0.01) and (p=0.02), and lower frequency of reperfusion. Reperfusion was associated with a significant post-fibrinolysis reduction in the level of TAFI antigen (p=0.02). Recurrence was associated to a significantly higher post-fibrinolysis level (p=0.05. OR=0.84. 95% CI). This was more frequent in mutation. Post-fibrinolysis TAFI antigen concentration was significantly lower in non-recurrence patients (p=0.028. OR=1.03. 95% CI).

CONCLUSIONS

A higher concentration of TAFI is associated to a worse prognosis in reperfusion and recurrence in acute myocardial infarction treated with fibrinolysis. Homozygotic mutation was more frequent in myocardial infarction patients. Wild genotype is associated to a better prognosis. Mutation is associated to a higher expression of TAFI.

Variation in the von Willebrand factor gene is associated with von Willebrand factor levels and with the risk for cardiovascular disease

High levels of von Willebrand factor (VWF) are associated with an increased risk for cardiovascular disease (CVD). Although VWF levels are strongly heritable and genetic susceptibility is an important risk factor for CVD, information on the contribution of common VWF gene variants to VWF levels and CVD risk is limited. In a case-control study of 421 young patients with a first event of acute coronary heart disease (CHD) or ischemic stroke (IS), and 409 healthy control participants (men aged ≤ 45 years, women aged ≤ 55 years), 27 haplotype-tagging single-nucleotide polymorphisms (ht-SNPs), covering the total common VWF gene variation, were selected and genotyped. The associations between these SNPs, VWF antigen (VWF:Ag) levels, VWF collagen-binding (VWF:CB) activity, and CVD risk was investigated. Two new associations were identified. For ht-SNP rs4764478 (intron 45), the increase in VWF:Ag levels and VWF:CB activity per minor allele was 0.082 (± 0.026) IU/mL (P = .001) and 0.096 (± 0.030) IU/mL (P = .002), respectively. ht-SNP rs216293 (intron 17) was associated with CVD risk (odds ratio, 1.44; 95% confidence interval [CI], 1.12-1.86 per minor allele). We confirmed the association between rs1063857 and CVD risk. Our data show that common variants in the VWF gene are associated with VWF levels and with the risk for CVD.

High thrombin activatable fibrinolysis inhibitor levels are associated with an increased risk of premature peripheral arterial disease

BACKGROUND

Previous studies suggested that hypofibrinolysis is associated with increased risk of peripheral arterial disease. Thrombin activatable fibrinolysis inhibitor (TAFI) has been identified as an important inhibitor of fibrinolysis. The aim of our study was to assess the role of TAFI in young patients with peripheral arterial disease.

METHODS

In a single-center case-control study we measured plasma TAFI antigen levels and functional TAFI in consecutive young patients (men 18-45 years and women 18-55 years) with a first manifestation of peripheral arterial disease and compared these with a population-based control group.

RESULTS

A total of 47 peripheral arterial disease patients and 141 controls (mean age 43) were included. Intact TAFI antigen levels were significantly higher in patients with peripheral arterial disease (112.4±21.1%) than in controls (104.9±19.9%, p=0.03). The risk of peripheral arterial disease increased with 18% (OR 1.18; CI 1.01-1.34) per 10% increase of TAFI antigen. Functional TAFI levels were slightly higher in patients compared to controls, however this difference was not significant. For individuals with the highest functional TAFI levels, above the 90th percentile, the increased risk for peripheral arterial disease was most pronounced (OR 3.1; CI 1.02-9.41).

CONCLUSION

High TAFI levels are associated with increased risk of premature peripheral arterial disease.

Disease-associated mutations that alter the RNA structural ensemble

Genome-wide association studies (GWAS) often identify disease-associated mutations in intergenic and non-coding regions of the genome. Given the high percentage of the human genome that is transcribed, we postulate that for some observed associations the disease phenotype is caused by a structural rearrangement in a regulatory region of the RNA transcript. To identify such mutations, we have performed a genome-wide analysis of all known disease-associated Single Nucleotide Polymorphisms (SNPs) from the Human Gene Mutation Database (HGMD) that map to the untranslated regions (UTRs) of a gene. Rather than using minimum free energy approaches (e.g. mFold), we use a partition function calculation that takes into consideration the ensemble of possible RNA conformations for a given sequence. We identified in the human genome disease-associated SNPs that significantly alter the global conformation of the UTR to which they map. For six disease-states (Hyperferritinemia Cataract Syndrome, β-Thalassemia, Cartilage-Hair Hypoplasia, Retinoblastoma, Chronic Obstructive Pulmonary Disease (COPD), and Hypertension), we identified multiple SNPs in UTRs that alter the mRNA structural ensemble of the associated genes. Using a Boltzmann sampling procedure for sub-optimal RNA structures, we are able to characterize and visualize the nature of the conformational changes induced by the disease-associated mutations in the structural ensemble. We observe in several cases (specifically the 5′ UTRs of FTL and RB1) SNP–induced conformational changes analogous to those observed in bacterial regulatory Riboswitches when specific ligands bind. We propose that the UTR and SNP combinations we identify constitute a “RiboSNitch,” that is a regulatory RNA in which a specific SNP has a structural consequence that results in a disease phenotype. Our SNPfold algorithm can help identify RiboSNitches by leveraging GWAS data and an analysis of the mRNA structural ensemble.

Genome-wide association studies identify mutations in the human genome that correlate with a particular disease. It is common to find mutations associated with disease in the non-coding region of the genome. These non-coding mutations are more difficult to interpret at a molecular level, because they do not affect the protein sequence. In this study, we analyze disease-associated mutations in non-coding regions of our genome in the context of their structural effect on the message of genetic information in our cells, Ribonucleic Acid (RNA). We focus in particular on the regulatory parts of our genes known as untranslated regions. We find that certain disease-associated mutations in these regulatory untranslated regions have a significant effect on the structure of the RNA message. We call these elements “RiboSNitches,” because they act like switches turning on and off genes, but are caused by Single Nucleotide Polymorphisms (SNPs), which are single point mutations in our genome. The RiboSNitches we identify are potentially a new class of pharmaceutical targets, as it is possible to change the structure of RNA with small drug-like molecules.

Thrombin-activatable fibrinolysis inhibitor (TAFI) deficient mice are susceptible to intracerebral thrombosis and ischemic stroke

BACKGROUND

Thrombus formation is a key step in the pathophysiology of acute ischemic stroke and results from the activation of the coagulation cascade. Thrombin plays a central role in this coagulation system and contributes to thrombus stability via activation of thrombin-activatable fibrinolysis inhibitor (TAFIa). TAFIa counteracts endogenous fibrinolysis at different stages and elevated TAFI levels are a risk factor for thrombotic events including ischemic stroke. Although substantial in vitro data on the influence of TAFI on the coagulation-fibrinolysis-system exist, investigations on the consequences of TAFI inhibition in animal models of cerebral ischemia are still lacking. In the present study we analyzed stroke development and post stroke functional outcome in TAFI-/- mice.

METHODOLOGY/PRINCIPAL FINDINGS

TAFI-/- mice and wild-type controls were subjected to 60 min transient middle cerebral artery occlusion (tMCAO) using the intraluminal filament method. After 24 hours, functional outcome scores were assessed and infarct volumes were measured from 2,3,5-Triphenyltetrazoliumchloride (TTC)-stained brain slices. Hematoxylin and eosin (H&E) staining was used to estimate the extent of neuronal cell damage. Thrombus formation within the infarcted brain areas was analyzed by immunoblot. Infarct volumes and functional outcomes did not significantly differ between TAFI-/- mice and controls (p>0.05). Histology revealed extensive ischemic neuronal damage regularly including the cortex and the basal ganglia in both groups. TAFI deficiency also had no influence on intracerebral fibrin(ogen) formation after tMCAO.

CONCLUSION

Our study shows that TAFI does not play a major role for thrombus formation and neuronal degeneration after ischemic brain challenge.

Prognostic value of plasma fibrinolysis activation markers in cardiovascular disease

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