Reduced plasma fibrinolytic capacity as a potential risk factor for a first myocardial infarction in young men

Thrombosis and Aging: Fibrin Clot Properties and Oxidative Stress

Significance: Aging is a complex process associated with an increased risk of many diseases, including thrombosis. This review summarizes age-related prothrombotic mechanisms in clinical settings of thromboembolism, focusing on the role of fibrin structure and function modified by oxidative stress. Recent Advances: Aging affects blood coagulation and fibrinolysis via multiple mechanisms, including enhanced oxidative stress, with an imbalance in the oxidant/antioxidant mechanisms, leading to loss of function and accumulation of oxidized proteins, including fibrinogen. Age-related prothrombotic alterations are multifactorial involving enhanced platelet activation, endothelial dysfunction, and changes in coagulation factors and inhibitors. Formation of more compact fibrin clot networks displaying impaired susceptibility to fibrinolysis represents a novel mechanism, which might contribute to atherothrombosis and venous thrombosis. Alterations to fibrin clot structure/function are at least in part modulated by post-translational modifications of fibrinogen and other proteins involved in thrombus formation, with a major impact of carbonylation. Fibrin clot properties are also involved in the efficacy and safety of therapy with oral anticoagulants, statins, and/or aspirin. Critical Issues: Since a prothrombotic state is observed in very elderly individuals free of diseases associated with thromboembolism, the actual role of activated blood coagulation in health remains elusive. It is unclear to what extent oxidative modifications of coagulation and fibrinolytic proteins, in particular fibrinogen, contribute to a prothrombotic state in healthy aging. Future Directions: Ongoing studies will show whether novel therapies that may alter oxidative stress and fibrin characteristics are beneficial to prevent atherosclerosis and thromboembolic events associated with aging.

Fibrin clot properties in cardiovascular disease: from basic mechanisms to clinical practice

Fibrinogen conversion into insoluble fibrin and the formation of a stable clot is the final step of the coagulation cascade. Fibrin clot porosity and its susceptibility to plasmin-mediated lysis are the key fibrin measures, describing the properties of clots prepared ex vivo from citrated plasma. Cardiovascular disease (CVD), referring to coronary heart disease, heart failure, stroke, and hypertension, has been shown to be associated with the formation of dense fibrin networks that are relatively resistant to lysis. Denser fibrin mesh characterized acute patients at the onset of myocardial infarction or ischaemic stroke, while hypofibrinolysis has been identified as a persistent fibrin feature in patients following thrombotic events or in those with stable coronary artery disease. Traditional cardiovascular risk factors, such as smoking, diabetes mellitus, hyperlipidaemia, obesity, and hypertension, have also been linked with unfavourably altered fibrin clot properties, while some lifestyle modifications and pharmacological treatment, in particular statins and anticoagulants, may improve fibrin structure and function. Prospective studies have suggested that prothrombotic fibrin clot phenotype can predict cardiovascular events in short- and long-term follow-ups. Mutations and splice variants of the fibrinogen molecule that have been proved to be associated with thrombophilia or increased cardiovascular risk, along with fibrinogen post-translational modifications, prothrombotic state, inflammation, platelet activation, and neutrophil extracellular traps formation, contribute also to prothrombotic fibrin clot phenotype. Moreover, about 500 clot-bound proteins have been identified within plasma fibrin clots, including fibronectin, α2-antiplasmin, factor XIII, complement component C3, and histidine-rich glycoprotein. This review summarizes the current knowledge on the mechanisms underlying unfavourable fibrin clot properties and their implications in CVD and its thrombo-embolic manifestations.

Association of the metabolic syndrome with PAI 1act and clot lysis time over a 10-year follow up in an African population

BACKGROUND AND AIMS

The association between the metabolic syndrome (MetS) and plasminogen activator inhibitor-1 (PAI-1) has been well established in cross-sectional studies. It is less clear whether this translates into decreased clot lysis rates and very little information is available on non-European populations. Little is known regarding prospective associations and whether clot lysis progressively worsens in MetS individuals over time. We determined the prospective association of MetS with PAI-1 activity (PAI-1_act) and clot lysis time (CLT) over a 10-year period.

METHODS AND RESULTS

As many as 2010 African men and women aged ≥30 years were stratified according to MetS status and number of MetS criteria (0-5). We also determined the contribution of the PAI-1 4G/5G polymorphism to these associations and identified which MetS criteria had the strongest associations with PAI-1_act and CLT. Both PAI-1_act and CLT remained consistently elevated in individuals with MetS throughout the 10-year period. PAI-1_act and CLT did not increase more over time in MetS individuals than in controls. The 4G/5G genotype did not influence the association of PAI-1_act or clot lysis with MetS. Increased waist circumference, increased triglycerides and decreased HDL-C were the main predictors of PAI-1_act and CLT.

CONCLUSIONS

Black South Africans with MetS had increased PAI-1_act and longer CLTs than individuals without MetS. The inhibited clot lysis in MetS did, however, not deteriorate over time compared to controls. Of the MetS criteria, obesity and altered lipids were the main predictors of PAI-1_act and CLT and are thus potential targets for prevention strategies to decrease thrombotic risk.

Impaired fibrin clot lysis is associated with increased mortality in patients after coronary artery bypass grafting: A long-term follow-up study

BACKGROUND

Mortality after coronary artery bypass grafting (CABG) is primarily thromboembolic by nature. We investigated whether impaired fibrinolysis observed in cardiovascular diseases is associated with long-term mortality following CABG.

METHODS

The study population comprised 292 consecutive patients (aged 64.6 ± 8.1 years) who underwent scheduled CABG. We measured plasma clot lysis time (CLT) preoperatively as a measure of fibrinolysis capacity. Cardiovascular and all-cause deaths were recorded during a median follow-up of 13.8 years.

RESULT

CLT positively correlated with age (r = .56, p < .001), fibrinogen (r = .25, p = .002) and EuroSCORE I (r = .32, p < .001). The cardiovascular and overall mortality rates were 3.0 and 4.9 per 100 patient-years (32.4% vs 52.8%) respectively. In patients who died from cardiovascular and all causes, CLT was prolonged compared with survivors (both p < .050). Multivariable Cox regression analysis adjusted for potential confounders showed that long-term cardiovascular and all-cause deaths were associated with CLT (HR per 10 min 1.206; 95% CI 1.037-1.402, p = .015 and HR 1.164; 96% CI 1.032-1.309, p = .012), low-density lipoprotein cholesterol (HR per 1 mmol/L 1.556; 95% CI 1.205-2.010, p < .001 and HR 1.388; 96% CI 1.125-1.703, p = .002), C-reactive protein (HR per 10 mg/L 1.171; 95% CI 1.046-1.312, p = .006 and HR 1.127; 95% CI 1.005-1.237, p = .022) and EuroSCORE I (HR 1.173; 95% CI 1.016-1.355, p = .030 and HR 1.183; 95% CI 1.059-1.317, p = .003 respectively). Type 2 diabetes was solely associated with overall mortality (HR 1.594; 96% CI 1.088-2.334, p = .017).

CONCLUSIONS

In this study, we showed that reduced fibrin clot susceptibility to fibrinolysis is weekly associated with long-term mortality in advanced CAD.

Hypofibrinolysis in type 2 diabetes and its clinical implications: from mechanisms to pharmacological modulation

A prothrombotic state is a typical feature of type 2 diabetes mellitus (T2DM). Apart from increased platelet reactivity, endothelial dysfunction, hyperfibrinogenemia, and hypofibrinolysis are observed in T2DM. A variety of poorly elucidated mechanisms behind impaired fibrinolysis in this disease have been reported, indicating complex associations between platelet activation, fibrin formation and clot structure, and fibrinolysis inhibitors, in particular, elevated plasminogen antigen inhibitor-1 levels which are closely associated with obesity. Abnormal fibrin clot structure is of paramount importance for relative resistance to plasmin-mediated lysis in T2DM. Enhanced thrombin generation, a proinflammatory state, increased release of neutrophil extracellular traps, elevated complement C3, along with posttranslational modifications of fibrinogen and plasminogen have been regarded to contribute to altered clot structure and impaired fibrinolysis in T2DM. Antidiabetic agents such as metformin and insulin, as well as antithrombotic agents, including anticoagulants, have been reported to improve fibrin properties and accelerate fibrinolysis in T2DM. Notably, recent evidence shows that hypofibrinolysis, assessed in plasma-based assays, has a predictive value in terms of cardiovascular events and cardiovascular mortality in T2DM patients. This review presents the current data on the mechanisms underlying arterial and venous thrombotic complications in T2DM patients, with an emphasis on hypofibrinolysis and its impact on clinical outcomes. We also discuss potential modulators of fibrinolysis in the search for optimal therapy in diabetic patients.

Fibrin Clot Properties in Atherosclerotic Vascular Disease: From Pathophysiology to Clinical Outcomes

Fibrin is a major component of thrombi formed on the surface of atherosclerotic plaques. Fibrin accumulation as a consequence of local blood coagulation activation takes place inside atherosclerotic lesions and contributes to their growth. The imbalance between thrombin-mediated fibrin formation and fibrin degradation might enhance atherosclerosis in relation to inflammatory states reflected by increased fibrinogen concentrations, the key determinant of fibrin characteristics. There are large interindividual differences in fibrin clot structure and function measured in plasma-based assays and in purified fibrinogen-based systems. Several observational studies have demonstrated that subjects who tend to generate denser fibrin networks displaying impaired clot lysis are at an increased risk of developing advanced atherosclerosis and arterial thromboembolic events. Moreover, the majority of cardiovascular risk factors are also associated with unfavorably altered fibrin clot properties, with their improvement following effective therapy, in particular with aspirin, statins, and anticoagulant agents. The prothrombotic fibrin clot phenotype has been reported to have a predictive value in terms of myocardial infarction, ischemic stroke, and acute limb ischemia. This review article summarizes available data on the association of fibrin clot characteristics with atherosclerotic vascular disease and its potential practical implications.

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.

Right ventricular echocardiographic parameters associated with prothrombotic abnormalities in normotensive patients with acute pulmonary embolism

BACKGROUND

In acute pulmonary embolism (PE) right ventricular (RV) pressure overload negatively affects prognosis. Recently we have shown that RV dilatation is associated with a prothrombotic state in PE. We investigated which RV echocardiographic parameters best indicate prothrombotic alterations in acute PE.

METHODS

In 121 normotensive, noncancer PE patients, markers of RV dilatation and dysfunction were evaluated on admission using transthoracic echocardiography, along with prothrombotic state markers, i.e. increased endogenous thrombin generation (ETP), low fibrin clot permeability (K_s, a measure of clot density), and prolonged clot lysis time (CLT).

RESULTS

RV parasternal long axis (RVOT PLAX) >30 mm was associated with ETP (OR 3.86; 95% CI 1.55-9.62; p = 0.004) and CLT (OR 4.08; 95% CI 1.58-10.54; p = 0.004) in the top quartiles, but not with K_s. RV short parasternal axis (RVOT PSAX) >27 mm showed similar associations with higher ETP (OR 3.54; 95% CI 1.50-8.37; p = 0.004) and prolonged CLT (OR 2.78; 95% CI 1.17-6.62; p = 0.021). RV basal diameter >41 mm solely predicted prolonged CLT (OR 2.93; 95% CI 1.23-6.99; p = 0.016). The right atrium area, pulmonary trunk diameter, and tricuspid regurgitation maximum velocity were not related to prothrombotic markers, except for tricuspid annular plane systolic excursion weakly associated with ETP. Multivariable analysis showed that RVOT PSAX is independently associated with prolonged CLT (OR 1.16; 95% CI 1.04-1.30; p = 0.007), low K_s (OR 1.21; 95% CI 1.02-1.44; p = 0.029), and higher ETP (OR 1.14; 95% CI 1.03-1.26; p = 0.009).

CONCLUSIONS

Among RV echocardiographic parameters, the RVOT dilatation measured in PSAX best predicts prothrombotic alterations in PE patients.

The association of alcohol with circulating total fibrinogen and plasma clot density is mediated by fibrinogen and FXIII genotypes

Background

Alcohol consumption is associated with haemostasis and so may influence cardiovascular conditions. It is unknown whether the association of alcohol with total and γ’ fibrinogen concentrations, as well as clot structure, are modulated by fibrinogen and factor (F) XIII single nucleotide polymorphisms (SNPs).

Methods

Total fibrinogen, γ’ fibrinogen and clot properties of 2010 healthy Africans residing in South Africa were measured in relation to alcohol intake as well as its markers – gamma-glutamyltransferase (GGT), percentage carbohydrate deficient transferrin (%CDT), aspartate aminotransferase (AST), and alanine aminotransferase (ALT). Fourteen fibrinogen and two SNPs in the FXIII gene were genotyped to determine their influence.

Results

Alcohol intake and its markers correlated negatively with fibrinogen and clot lysis time (CLT) as well as with most of the clot properties. Percentage γ’ fibrinogen correlated positively with AST and negatively with alcohol intake. We then stratified for alcohol intake and found inverse associations between γ’ fibrinogen and both %CDT and GGT–CDT in consumers, but the positive association with AST remained only in abstainers. Alcohol intake and its markers modulated the influence of fibrinogen SNPs on total fibrinogen concentrations and the fibrinogen SNPs as well as an FXIII SNP on clot density (all p < 0.004).

Conclusion/s

We show for the first time that some individuals harbour certain genotypes that, in combination with alcohol consumption, might predispose or protect them from haemostatic factors that might lead to the development of cardiovascular disease. Studies are needed to clarify the mechanisms related to the interplay between alcohol and the gene variants observed here.

Determinants of plasma fibrin clot lysis measured using three different assays in healthy subjects

INTRODUCTION

Several methods for measuring fibrinolytic capacity in plasma have been developed yielding frequently inconsistent results. We investigated which factors determine fibrinolytic capacity in three plasma-based assays.

MATERIAL AND METHODS

In 80 apparently healthy controls (aged 43 ± 10 years, 50 women [62.5%]) we evaluated fibrinolysis using three assays: (1) by Pieters et al. (CLT2018), (2) by Lisman et al. (CLT), and (3) by Carter et al. (Lys50). Coagulation factors and fibrinolytic proteins, including histidine-rich glycoprotein (HRG) and γ'-fibrinogen, were determined. Regression models were performed to identify determinants of lysis times.

RESULTS

Positive correlations were observed between CLT2018 and both CLT (r = 0.73) and Lys50 (r = 0.61), as well as between CLT and Lys50 (r = 0.46, all p < 0.001). The main determinants of both CLT2018 and CLT were plasminogen activator inhibitor-1 (PAI-1), followed by thrombin-activatable fibrinolysis inhibitor (TAFI) and α₂-antiplasmin. Histidine-rich glycoprotein was a predictor of the longest-normal CLT2018 alone (OR 1.04, 95% CI 1.02-1.06). α₂-Antiplasmin and fibrinogen levels, followed by PAI-1 and TAFI determined Lys50. After adjustment for age, sex, and body mass index, C-reactive protein (CRP) was an independent predictor of the top quartiles of the three lysis times.

CONCLUSIONS

We showed that apart from PAI-1, TAFI, and α₂-antiplasmin, several other factors, in particular CRP, can affect the results of global fibrinolysis tests used in research. Our findings may help understand why the choice of a specific fibrinolysis assay can affect the presence and/or magnitude of intergroup differences in fibrinolytic capacity in a given disease state.

Smoking and Endothelial Dysfunction

Cigarette smoking is one of the most important health concerns worldwide. Even though the rate of smoking is declining in developed countries, it is still experiencing growth in developing regions. Many studies have examined the relationship between smoking, as an established risk factor, and cardiovascular diseases. We provide an updated review of the underlying mechanisms of smokinginduced cardiovascular diseases, with a focus on the relationship between smoking and oxidative stress, particularly from the perspective of endothelial cell dysfunction. We review smoking-induced oxidative stress as a trigger for a generalized vascular inflammation associated with cytokine release, adhesion of inflammatory cells and, ultimately, disruption of endothelial integrity as a protective barrier layer. We also briefly discuss the harms related to the vaping of electronic cigarettes, which many erroneously consider as a safe alternative to smoking. We conclude that even though e-cigarette could be a helpful device during the transition period of cigarette quitting, it is by no means a safe substitute.

Impaired Spontaneous/Endogenous Fibrinolytic Status as New Cardiovascular Risk Factor?: JACC Review Topic of the Week

Endogenous fibrinolysis is a powerful natural defense mechanism against lasting arterial thrombotic occlusion. Recent prospective studies have shown that impaired endogenous fibrinolysis (or hypofibrinolysis) can be detected in a significant number of patients with acute coronary syndrome (ACS) using global assays and is a strong marker of future cardiovascular risk. This novel risk biomarker is independent of traditional cardiovascular risk factors and unaffected by antiplatelet therapy. Most prospective prognostic data have been obtained using a global assay using native whole blood at high shear or plasma turbidimetric assays, which are described herein. Tests of endogenous fibrinolysis could be used to identify patients with ACS who, despite antiplatelet therapy, remain at high cardiovascular risk. This review discusses the impact of currently available medications and those in development that favorably modulate fibrinolytic status and may offer a potential new avenue to improve outcomes in ACS.

Patho- physiological role of BDNF in fibrin clotting

Circulating levels of Brain Derived Neurotrophic Factor (BDNF) are lower in coronary heart disease (CHD) than in healthy subjects and are associated with coronary events and mortality. However, the mechanism(s) underling this association is not fully understood. We hypothesize that BDNF may influence fibrin fiber structure and clot stability, favoring clot lysis and thrombus resolution. We showed that recombinant BDNF (rh-BDNF) influenced with clot formation in a concentration-dependent manner in both purified fibrinogen and plasma from healthy subjects. In particular, rh-BDNF reduced the density of fibrin fibers, the maximum clot firmness (MCF) and the maximum clot turbidity, and affected the lysis of clot. In addition, both thrombin and reptilase clotting time were prolonged by rh-BDNF, despite the amount of thrombin formed was greater. Intriguingly, CHD patients had lower levels of BDNF, greater fibrin fibers density, higher MCF than control subjects, and a negative correlation between BDNF and MCF was found. Of note, rh-BDNF markedly modified fibrin clot profile restoring physiological clot morphology in CHD plasma. In conclusion, we provide evidence that low levels of BDNF correlate with the formation of bigger thrombi (in vitro) and that this effect is mediated, at least partially, by the alteration of fibrin fibers formation.

Fibrin clot properties and their modulation in thrombotic disorders

Accumulating evidence indicates that accelerated formation of fibrin clots composed of compact, highly-branched networks with thin fibres which are relatively resistant to plasmin-mediated lysis can be commonly observed in patients with venous or arterial thrombosis. This review discusses characteristics of fibrin clot structure and function in patients with various thromboembolic manifestations, in particular myocardial infarction, ischaemic stroke and venous thromboembolism, based on the publications till December 2013. Moreover, factors will be presented that in vivo unfavourably determine altered fibrin clot properties in thrombotic disorders and modalities that can improve clot phenotype.

A history of early stent thrombosis is associated with prolonged clot lysis time

It has been demonstrated that formation of compact plasma fibrin clots resistant to plasmin-mediated lysis characterises patients following instent thrombosis (IST). The relationship between defective fibrinolysis, reflected as prolonged clot lysis time (CLT) and IST is unclear. We sought to investigate whether patients with acute and subacute IST have impaired fibrinolytic capacity. We studied 41 definite IST patients, including 15 with acute and 26 with subacute IST experienced 2–73 months prior to enrollment, versus 41 controls matched for demographics, cardiovascular risk factors, concomitant treatment and angiographic/stent parameters. CLT, reflecting lysis of a tissue factor-induced plasma clot by exogenous tissue plasminogen activator, together with plasminogen activator inhibitor-1 (PAI-1) antigen and activity, thrombin-activatable fibrinolysis inhibitor (TAFI) antigen and activity, thrombomodulin (TM), plasminogen and α2-antiplasmin (α2AP) were measured. There were no inter-group differences in angiographic parameters, indication to the first PCI, culprit vessel or a type of stent. Patients with IST had 11% longer CLT (p=0.005) and 13% higher PAI-1 antigen (p=0.04) compared to controls. There were positive correlations in both groups between CLT and PAI-1 antigen and TAFI activity (all p<0.001). Multiple regression analysis showed that CLT (odds ratio [OR]=1.04 per 1 minute, 95% CI 1.01–1.08, p=0.02) and platelet count (OR=1.01 per 1,000/μl, 95% CI 1.00–1.02, p=0.034) were independent predictors of IST (R2=0.28, p<0.05). Concluding, impaired fibrinolytic potential, that is in part determined by plasma PAI-1 antigen and TAFI activity, characterises patients with a history of acute and subacute IST, which might help identify patients at higher risk of IST.

Impaired plasma clot lysis and its determinants in patients with obstructive sleep apnea syndrome

Evidence indicates that hypercoagulability and impaired fibrinolysis have been observed in patients with obstructive sleep apnea syndrome (OSAS). It is unclear which factors determine prolonged fibrin clot lysis in OSAS. One hundred and sixty-five consecutive patients suspected of OSAS underwent overnight polysomnography. Prior to polysomnography, we determined plasma clot lysis time (CLT), plasminogen activator inhibitor (PAI)-1 antigen, activated thrombin-activatable fibrinolysis inhibitor (TAFIa), plasmin, and antiplasmin. OSAS was diagnosed in 110 (66.7%) patients, including 35 (31.8%) with severe OSAS, 26 (23.6%) with moderate OSAS, and 49 (44.6%) mild OSAS. Compared with 55 (33.3%) individuals in whom OSAS was not confirmed, OSAS patients had prolonged CLT (+12.8%), associated with higher PAI-1 antigen (+18.1%) (after adjustment for age, diabetes, and body mass index; both P < 0.01) and similar levels of TAFIa, plasmin, or antiplasmin. PAI-1, TAFIa, and CLT correlated positively with apnea/hypopnea index, which reflects the severity of OSAS (R = 0.66, P < 0.001; R = 0.29, P = 0.002; R = 0.55, P = 0.001, respectively), and with other polysomnography parameters, with the most potent correlations observed for desaturation index. Regression analysis adjusted for potential confounders showed that in OSAS, CLT was independently predicted by apnea/hypopnea index (B = 0.29, P = 0.002), PAI-1 (B = 0.42, P < 0.001), and TAFIa (B = 0.81, P = 0.044), whereas both PAI-1 and TAFIa were predicted only by desaturation index (B = 0.24, P = 0.002; and B = 0.14, P = 0.001, respectively). The severity of OSAS is closely associated with hypofibrinolysis measured in a global plasma-based assay, driven largely by PAI-1. Attenuated fibrinolysis might contribute to high risk of thromboembolic events in this disease.

Hypofibrinolysis in diabetes: a therapeutic target for the reduction of cardiovascular risk

An enhanced thrombotic environment and premature atherosclerosis are key factors for the increased cardiovascular risk in diabetes. The occlusive vascular thrombus, formed secondary to interactions between platelets and coagulation proteins, is composed of a skeleton of fibrin fibres with cellular elements embedded in this network. Diabetes is characterised by quantitative and qualitative changes in coagulation proteins, which collectively increase resistance to fibrinolysis, consequently augmenting thrombosis risk. Current long-term therapies to prevent arterial occlusion in diabetes are focussed on anti-platelet agents, a strategy that fails to address the contribution of coagulation proteins to the enhanced thrombotic milieu. Moreover, antiplatelet treatment is associated with bleeding complications, particularly with newer agents and more aggressive combination therapies, questioning the safety of this approach. Therefore, to safely control thrombosis risk in diabetes, an alternative approach is required with the fibrin network representing a credible therapeutic target. In the current review, we address diabetes-specific mechanistic pathways responsible for hypofibrinolysis including the role of clot structure, defects in the fibrinolytic system and increased incorporation of anti-fibrinolytic proteins into the clot. Future anti-thrombotic therapeutic options are discussed with special emphasis on the potential advantages of modulating incorporation of the anti-fibrinolytic proteins into fibrin networks. This latter approach carries theoretical advantages, including specificity for diabetes, ability to target a particular protein with a possible favourable risk of bleeding. The development of alternative treatment strategies to better control residual thrombosis risk in diabetes will help to reduce vascular events, which remain the main cause of mortality in this condition.

Preserved hemostatic status in patients with non-alcoholic fatty liver disease

BACKGROUND & AIMS

Non-alcoholic fatty liver disease (NAFLD) is associated with an increased risk of thrombosis. However, it remains unclear if hypercoagulability contributes to this risk. We, therefore, determined an in-depth hemostatic profile in a cohort of well-defined patients with NAFLD.

METHODS

We drew blood samples from 68 patients with biopsy-proven NAFLD (simple steatosis n=24, NASH n=22, and NASH cirrhosis n=22), 30 lean controls, 30 overweight controls (body mass index (BMI) >25kg/m²), and 15 patients with alcoholic (ASH) cirrhosis, and performed in-depth hemostatic profiling.

RESULTS

Basal and agonist-induced platelet activation, plasma levels of markers of platelet activation, and plasma levels of the platelet adhesion regulators von Willebrand factor and ADAMTS13 were comparable between patients with non-cirrhotic NAFLD and controls. Agonist-induced platelet activation was decreased in patients with cirrhosis. Thrombomodulin-modified thrombin generation was comparable between all patients and controls, although patients with cirrhosis had a reduced anticoagulant response to thrombomodulin. Thromboelastography test results were comparable between controls and non-cirrhotic NAFLD patients, but revealed moderate hypocoagulability in cirrhosis. Plasma fibrinolytic potential was decreased in overweight controls and non-cirrhotic NAFLD, but accelerated fibrinolysis was observed in ASH cirrhosis. Clot permeability was decreased in overweight controls and patients with NAFLD.

CONCLUSIONS

The overall hemostatic profile is comparable between patients with non-cirrhotic NAFLD and controls. Additionally, pro-thrombotic features (hypofibrinolysis and a pro-thrombotic structure of fibrin clot) in patients with NAFLD are likely driven by obesity. Our study suggests a limited role for hyperactive hemostasis in the increased thrombotic risk in NAFLD.

LAY SUMMARY

The combined results of this study show that the overall hemostatic status is comparable between healthy individuals and patients with a fatty liver disease.

Increased plasminogen activator inhibitor results in a hypofibrinolytic state in adolescents with obesity: in vivo and ex vivo evidence

Obesity in adolescents increases their risk for deep vein thrombosis. The objectives of this study were to determine potential mechanisms for thrombotic risk by investigating the fibrinolytic pathway in a sample of adolescents with and without obesity. Thirty-seven adolescents with obesity and 16 normal weight age-matched controls were recruited. Plasma levels of components of the fibrinolytic system were measured in addition to a Global Haemostasis Potential assay (GHP), which assesses plasma capacity to generate and lyse a fibrin clot. Levels of plasminogen activator inhibitor (PAI) and tissue plasminogen activator (tPA)/PAI complexes were increased in adolescents with obesity when compared to normal weight controls. There was a significant inverse association of increasing PAI with a decrease in plasmin-antiplasmin complexes. The GHP in obese adolescents displayed a hypofibrinolytic response with a markedly increased t_½ clot lysis time, as well as an increase in fibrin clot density as indicated by increased absorbance at maximum peak height. In the obese group, immunodepletion of PAI decreased both t_½ lysis time and absorbance at maximum peak height. We have shown in vivo and ex vivo there is a hypofibrinolytic state in obese adolescents and have established the hypofibrinolytic state is due to increased PAI levels.

Natural heterogeneity of α2-antiplasmin: functional and clinical consequences

Human α2-antiplasmin (α2AP, also called α2-plasmin inhibitor) is the main physiological inhibitor of the fibrinolytic enzyme plasmin. α2AP inhibits plasmin on the fibrin clot or in the circulation by forming plasmin-antiplasmin complexes. Severely reduced α2AP levels in hereditary α2AP deficiency may lead to bleeding symptoms, whereas increased α2AP levels have been associated with increased thrombotic risk. α2AP is a very heterogeneous protein. In the circulation, α2AP undergoes both amino terminal (N-terminal) and carboxyl terminal (C-terminal) proteolytic modifications that significantly modify its activities. About 70% of α2AP is cleaved at the N terminus by antiplasmin-cleaving enzyme (or soluble fibroblast activation protein), resulting in a 12-amino-acid residue shorter form. The glutamine residue that serves as a substrate for activated factor XIII becomes more efficient after removal of the N terminus, leading to faster crosslinking of α2AP to fibrin and consequently prolonged clot lysis. In approximately 35% of circulating α2AP, the C terminus is absent. This C terminus contains the binding site for plasmin(ogen), the key component necessary for the rapid and efficient inhibitory mechanism of α2AP. Without its C terminus, α2AP can no longer bind to the lysine binding sites of plasmin(ogen) and is only a kinetically slow plasmin inhibitor. Thus, proteolytic modifications of the N and C termini of α2AP constitute major regulatory mechanisms for the inhibitory function of the protein and may therefore have clinical consequences. This review presents recent findings regarding the main aspects of the natural heterogeneity of α2AP with particular focus on the functional and possible clinical implications.

The association of clot lysis time with total obesity is partly independent from the association of PAI-1 with central obesity in African adults

INTRODUCTION

Preliminary evidence indicates that the association of fibrinolytic potential, measured as clot lysis time (CLT), with body composition may differ from that of plasminogen activator inhibitor type-1 (PAI-1). We therefore investigated the association between fibrinolytic markers (plasminogen activator inhibitor type-1 activity (PAI-1act) and CLT) and body composition using detailed body composition analyses.

MATERIALS AND METHODS

Data from 1288 Africans were cross-sectionally analyzed. Body composition analysis included BMI, waist circumference (WC); waist to height ratio (WHtR), skinfolds and body fat percentage measured with air-displacement plethysmography and bioelectrical impedance analysis.

RESULTS

PAI-1act and CLT were significantly higher in women than in men, despite adjustment for differences in body composition. PAI-1act and CLT showed similar linear positive relationships with body composition (BMI, WC, WHtR, skinfolds) in men. In women CLT also showed a linear relationship with body composition, while PAI-1act levels plateaued at higher BMI and did not differ across skinfold categories. PAI-1act showed stronger correlations with body composition markers in men than it did in women, while no sex differences existed for CLT. PAI-1act associated more strongly with central obesity, while CLT associated with total body fat.

CONCLUSIONS

Observed differences may be related to differences in adipose tissue type, distribution and sequence of accumulation between sexes. PAI-1act is strongly influenced by accumulation of visceral adipose tissue, whereas CLT is associated with obesity independent of type and sequence of body fat accumulation in this African adult study population.

Low fasting glucose is associated with enhanced thrombin generation and unfavorable fibrin clot properties in type 2 diabetic patients with high cardiovascular risk

Objective

To investigate the effect of low blood glucose on thrombin generation and fibrin clot properties in type 2 diabetes (T2DM).

Methods

In 165 patients with T2DM and high cardiovascular risk, we measured ex vivo plasma fibrin clot permeation [K_s], turbidity and efficiency of fibrinolysis including clot lysis time [t_50%], together with thrombin generation and platelet activation markers in relation to fasting blood glucose.

Results

As compared to patients in medium (4.5-6.0 mmol/l, n = 52) and higher (>6.0 mmol/l, n = 75) glucose group, subjects with low glycemia (<4.5 mmol/l, n = 38) had lower K_s by 11% (p < 0.001) and 8% (p = 0.01), respectively, prolonged t_50% by 10% (p < 0.001) and 7% (p = 0.016), respectively, and higher peak thrombin generation by 21% and 16%, respectively (p < 0.001 for both). There were no significant differences in K_s and t_50% between patients in medium and higher glucose group. In the whole group, a J-shape relationship was observed between glycemia and the following factors: peak thrombin generation, K_s and t_50%. Only in patients with HbA1c < 6.0% (42 mmol/mol) (n = 26) fasting glucose positively correlated with K_s (r = 0.53, P = 0.006) and inversely with t_50% (r = −0.46, P = 0.02).

By multiple regression analysis, after adjustment for age, fibrinogen, HbA1c, insulin treatment and T2DM duration, fasting glycemia was the independent predictor of K_s (F = 6.6, df = 2, P = 0.002), t_50% (F = 8.0, df = 2, P < 0.001) and peak thrombin generation (F = 13.5, df = 2, P < 0.0001).

Conclusions

In T2DM patients fasting glycemia <4.5 mmol/l is associated with enhanced thrombin formation and formation of denser fibrin clots displaying lower lysability, especially when strict glycemia control was achieved (HbA1c<6.0%).

Global hypercoagulability in patients with schizophrenia receiving long-term antipsychotic therapy

BACKGROUND

Patients with schizophrenia are at increased risk of venous thromboembolism. The mechanisms underlying this association are poorly understood.

AIMS

We investigated whether there is a global hypercoagulable state in patients with schizophrenia utilising the overall haemostatic potential (OHP) assay which assesses overall coagulation potential (OCP), haemostatic potential (OHP) and fibrinolytic potential (OFP).

METHOD

Citrated plasma was collected for OHP assays from patients with schizophrenia on long-term antipsychotic treatment and compared with healthy age- and sex-matched controls. Time courses of fibrin formation and degradation were measured by spectrophotometry (absorption of 405nm) after the addition of tissue factor and tissue plasminogen activator to plasma.

RESULTS

Ninety patients with schizophrenia (antipsychotic treatment-15.9±9.7years) and 30 controls were recruited. Patients with schizophrenia had higher rates of smoking and levels of inflammatory markers (high-sensitivity C-reactive protein and neutrophil-to-lymphocyte ratio) than controls. Whilst D-dimer, fibrinogen and platelet count did not differ between patients with schizophrenia and controls, the OCP (54.0±12.6 vs 45.9±9.1, p=0.002) and OHP (12.6±5.8 vs 7.2±3.7, p<0.001) were higher, and OFP was lower (76.6±9.8% vs 84.9±6.4%, p<0.001) in patients with schizophrenia, implying both a hypercoagulable and hypofibrinolytic state in these patients. Importantly, abnormalities in overall coagulation were independently predicted by levels of plasminogen-activator-inhibitor-1, fibrinogen, platelet count, inflammatory markers and plasma triglycerides, suggesting a multifactorial aetiology.

CONCLUSION

Patients with schizophrenia have evidence of a global hypercoagulable and hypofibrinolytic state which may contribute to their increased risk of venous thromboembolism.

Fibrinolysis and the control of blood coagulation

Fibrin plays an essential role in hemostasis as both the primary product of the coagulation cascade and the ultimate substrate for fibrinolysis. Fibrinolysis efficiency is greatly influenced by clot structure, fibrinogen isoforms and polymorphisms, the rate of thrombin generation, the reactivity of thrombus-associated cells such as platelets, and the overall biochemical environment. Regulation of the fibrinolytic system, like that of the coagulation cascade, is accomplished by a wide array of cofactors, receptors, and inhibitors. Fibrinolytic activity can be generated either on the surface of a fibrin-containing thrombus, or on cells that express profibrinolytic receptors. In a widening spectrum of clinical disorders, acquired and congenital defects in fibrinolysis contribute to disease morbidity, and new assays of global fibrinolysis now have potential predictive value in multiple clinical settings. Here, we summarize the basic elements of the fibrinolytic system, points of interaction with the coagulation pathway, and some recent clinical advances.

Increased incorporation of antiplasmin into the fibrin network in patients with type 1 diabetes

OBJECTIVE

Diabetes is associated with various vascular complications and is suggested to induce a prothrombotic state. In the current study, we characterized antiplasmin incorporation into fibrin in relation to other fibrinolytic compounds in patients with type 1 diabetes.

RESEARCH DESIGN AND METHODS

A total of 236 patients with type 1 diabetes and 78 control subjects were investigated. The incorporation of antiplasmin into the fibrin network and the plasma levels of plasminogen activator inhibitor type 1 (PAI-1) activity, tissue plasminogen activator (tPA) activity, tPA/PAI-1 complex, plasmin-antiplasmin complex, antiplasmin, factor XIII, and d-dimer were measured. In addition, we used global assays to study fibrinolysis.

RESULTS

The incorporation of antiplasmin into the fibrin network was significantly higher in patients with type 1 diabetes than in control subjects without diabetes (1.65 ± 0.25 vs. 1.35 ± 0.18 mg/L, respectively; P < 0.0001). The patients also had lower PAI-1 activity (2.19 units/mL [interquartile range 0.96-5.42] vs. 4.25 units/mL [1.95-9.0]; P = 0.0012) and antiplasmin level in plasma (78.5 ± 13.3 vs. 83.2 ± 15.4 mg/L; P < 0.05), resulting in a higher fibrinolytic capacity (shorter clot lysis time; P = 0.0090). We did not find any important sex differences regarding fibrinolysis in the patients or in the control subjects.

CONCLUSIONS

Patients with type 1 diabetes incorporate more antiplasmin into the fibrin network than control subjects without diabetes do and have a reduced PAI-1 activity and a shorter clot lysis time. These results suggest that patients with type 1 diabetes produce a fibrin clot that is more resistant to fibrinolysis, which, however, may be counteracted by an increased fibrinolytic potential in plasma.

The fibrinogen γA/γ' isoform does not promote acute arterial thrombosis in mice

BACKGROUND

Elevated plasma fibrinogen is associated with arterial thrombosis in humans and promotes thrombosis in mice by increasing fibrin formation and thrombus fibrin content. Fibrinogen is composed of six polypeptide chains: (Aα, Bβ, and γ)2. Alternative splicing of the γ chain leads to a dominant form (γA/γA) and a minor species (γA/γ'). Epidemiological studies have detected elevated γA/γ' fibrinogen in patients with arterial thrombosis, suggesting that this isoform promotes thrombosis. However, in vitro data show that γA/γ' is anticoagulant due to its ability to sequester thrombin and suggest its expression is upregulated in response to inflammatory processes.

OBJECTIVE

To determine whether γA/γ' fibrinogen is prothrombotic in vivo.

METHODS

We separated γA/γA and γA/γ' fibrinogen from human plasma-purified fibrinogen and determined the effects on in vitro plasma clot formation and on in vivo thrombus formation and circulating thrombin-antithrombin complexes in mice.

RESULTS AND CONCLUSIONS

Both γA/γA and γA/γ' fibrinogen were cleaved by murine and human thrombin and were incorporated into murine and human clots. When γA/γA or γA/γ' was spiked into plasma, γA/γA increased the fibrin formation rate to a greater extent than γA/γ'. In mice, compared to controls, γA/γA infusion shortened the time to carotid artery occlusion, whereas γA/γ' infusion did not. Additionally, γA/γ' infusion led to lower levels of plasma thrombin-antithrombin complexes following arterial injury, whereas γA/γA infusion did not. These data suggest that γA/γ' binds thrombin in vivo and decreases prothrombotic activity. Together, these findings indicate that elevated levels of γA/γA fibrinogen promote arterial thrombosis in vivo, whereas γA/γ' does not.

D-dimer relates positively with increased blood pressure in black South Africans: the SABPA study

INTRODUCTION

Hypertension is highly prevalent in black South Africans in which morbidity and mortality from stroke are on the increase. Elevated blood pressure and haemostatic markers can induce changes in blood rheology and endothelial function which could result in a procoagulant state that increases the risk for cerebrovascular disease. Information about the coagulation and fibrinolytic systems of people from African descent are limited. We therefore, investigated the haemostatic profile and its relationships with blood pressure in black South Africans.

MATERIALS AND METHODS

We measured ambulatory blood pressure and haemostatic markers of 201 black and 208 white school teachers. The haemostatic markers included measurements representing coagulation and fibrinolysis (von Willebrand factor, fibrinogen, plasminogen activator inhibitor-1, fibrin D-dimer and clot lysis time).

RESULTS

Black participants displayed significantly higher blood pressure, von Willebrand factor, fibrinogen, plasminogen activator inhibitor-1 and D-dimer levels and longer clot lysis times (p≤0.001). Single, partial and multiple regression analyses showed that systolic (p≤0.011) and diastolic blood pressure (p=0.010) correlated positively with D-dimer in black participants, while systolic (p≤0.001) and daytime diastolic blood pressure (p=0.011) correlated negatively with clot lysis time in white participants.

CONCLUSION

The black population had a more prothrombotic profile, with higher levels of coagulation markers and inhibited fibrinolysis, than the white study participants. The positive association between blood pressure and elevated D-dimer in the blacks may contribute to the high prevalence of hypertension and related increased cardiovascular and cerebrovascular risk in this group.

High-density cholesterol and apolipoprotein AI as modifiers of plasma fibrin clot properties in apparently healthy individuals

Low high-density lipoprotein cholesterol (HDL-C) increases cardiovascular risk, whereas its high levels protect against atherosclerosis via multiple beneficial effects. Dense and poorly lysable fibrin clot formation is observed in cardiovascular disease. We sought to investigate whether HDL-C and its major component apolipoprotein A (Apo A)-I affect fibrin clot properties. In 136 apparently healthy individuals (99 men, 37 women, aged 49-69 years) we determined plasma fibrin clot permeability (Ks coefficient) and lysis time (t50%) together with Apo A-I and lipoprotein (a) [Lp(a)] levels. The median HDL-C level was 1.33  mmol/l (range from 0.77 to 2.19  mmol/l). HDL-C was positively associated with Apo A-I (r = 0.62, P < 0.00001). HDL-C and Apo A-I were positively correlated with Ks (r = 0.52, P < 0.00001 and r = 0.44, P < 0.00001, respectively) and inversely with t50% (r = -0.44, P < 0.00001 and r = -0.35, P = 0.00003, respectively). No such associations were seen for other lipid variables. Ks and t50% were associated with Lp(a) (r = -0.42, P < 0.00001 and r = 0.42, P < 0.00001, respectively) and fibrinogen (r = -0.31, P = 0.00024 and r = 0.39, P < 0.00001, respectively). Individuals with HDL-C at least 1.4 mmol/l (n = 54) had 19% higher Ks (P = 0.00016) and 17% shorter t50% (P = 0.0012) than the remainder. After adjustment for age, fibrinogen, and Lp(a), HDL-C was the independent predictor of Ks (β = 0.7, P < 0.00001) and t50% (β = -0.62, P < 0.00001). This study shows that elevated HDL-C levels are associated with improved fibrin clot permeability and lysis, indicating a novel antithrombotic mechanism underlying the postulated beneficial effects of therapy targeted at HDL-C.

Detection of hypofibrinolysis in stable coronary artery disease using the overall haemostatic potential assay

INTRODUCTION

Patients with stable coronary artery disease (CAD) are at risk of arterial thrombosis causing myocardial infarction. Detection of global haemostatic markers of hypercoagulability and hypofibrinolysis may be important for risk stratification and individualised treatment. We examined overall haemostatic potential (OHP) and thrombin generation in a group of stable CAD patients. We also sought to investigate associations between fibrinolytic inhibitors and abnormal global fibrinolysis in these patients.

MATERIALS AND METHODS

Blood samples were collected from 56 patients defined by coronary anatomy as symptomatically stable CAD. Medications were recorded. Samples were analysed using the global coagulation assays OHP and thrombin generation (calibrated automated thrombogram, CAT), platelet aggregometry measured by Multiplate®, and levels of plasminogen activator inhibitor-1 (PAI-1) antigen measured by ELISA. Results were compared with a reference group of healthy controls.

RESULTS

Stable CAD patients displayed increased fibrin and thrombin generation and impaired fibrinolysis (decreased overall fibrinolytic potential, OFP, and increased clot lysis time) compared with healthy controls. No effect of antiplatelet agents or other medications on these parameters was observed using platelet-poor plasma. After multivariate adjustment, OFP of healthy individuals was significantly associated with fibrinogen, but in CAD patients PAI-1 became an important determinant.

CONCLUSIONS

Hypercoagulability of plasma is observed in stable CAD, with both increased thrombin generation and reduced fibrinolytic potential making a significant contribution. The OHP assay may provide a simple method of identifying hypercoagulability in individual patients.

Impaired fibrinolysis is associated with the severity of aortic stenosis in humans

BACKGROUND

A role of fibrinolysis in the pathogenesis of aortic valve stenosis (AS) is unknown, although fibrinolytic proteins have been detected in aortic stenotic valves.

OBJECTIVE

To investigate whether impaired fibrinolysis could be associated with AS.

METHODS AND RESULTS

We studied 74 patients with AS (43 male, 31 female, aged 62.7 ± 10.7 years) without documented atherosclerotic valvular disease scheduled for isolated valve replacement and 68 controls. The plasma fibrin clot lysis time (CLT) in the presence of tissue factor (TF) and tissue plasminogen activator (tPA), along with plasma plasminogen activator inhibitor-1 (PAI-1) were determined. Valvular expression of fibrin and PAI-1 together with macrophages and mast cells (MC) was evaluated by immunostaining. Patients with AS compared with controls were characterized by a prolonged CLT (median, 110 [54-153] vs. 92.5 [58-115] min, P = 0.0007) and increased plasma PAI-1 (78.6 [35.5-149] vs. 38.5 [18-61] ng mL(-1) , P < 0.0001). CLT was correlated with maximal (r = 0.43, P = 0.0002) and mean (r = 0.38, P = 0.001) transvalvular pressure gradients, and aortic valve area (r = -0.59, P < 0.0001). In AS patients, the CLT was positively correlated with the valve leaflet thickness (r = 0.67, P = 0.003), the degree of valve calcification (r = 0.65, P < 0.00001), valvular fibrin (r = 0.54, P = 0.007) and PAI-1 expression (r = 0.48, P = 0.007). Double-immunostaining revealed colocalization of valvular PAI-1 with MC (87 ± 17% cells) and macrophages (48 ± 11% cells) within stenotic valves.

CONCLUSIONS

Hypofibrinolysis might be a marker of severe AS and be implicated in AS progression.

TAFI deficiency promotes liver damage in murine models of liver failure through defective down-regulation of hepatic inflammation

Emerging evidence indicates that various haemostatic components can regulate the progression of liver disease. Thrombin-activatable fibrinolysis inhibitor (TAFI) possesses anti-inflammatory properties besides its anti-fibrinolytic function. Here, we investigated the contribution of TAFI to the progression of disease in murine models of chronic and acute liver failure. Chronic carbon tetrachloride (CCL4) administration induced liver damage and fibrosis both in TAFI knockout (TAFI-/-) mice and wild-type controls. Smooth muscle actin-α (α-SMA) content of liver tissue was significantly increased after 1 and 3 weeks, and pro-collagen α1 expression was significantly increased after 3 and 6 weeks in TAFI-/- mice. TAFI-/- mice showed significantly elevated levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) after 3 weeks of CCL4. Neutrophil influx was significantly increased in TAFI-/- mice after 6 weeks of CCL4. No difference in hepatic fibrin deposition between TAFI-/- and wild-types was observed. After acetaminophen intoxication, necrosis was significantly increased in TAFI-/- mice at 24 hours (h) after injection. AST and ALT levels were decreased at 2 and 6 h after acetaminophen injection in TAFI-/- mice, but were significantly higher in the TAFI-/- mice at 24 h. Similarly, hepatic fibrin deposition was decreased at 6 h in TAFI-/- mice, but was comparable to wild-types at 24 h after injection. In conclusion, TAFI deficiency results in accelerated fibrogenesis and increased liver damage in murine models of chronic and acute liver disease, which may be related to increased inflammation.

Plasma clot lysis time and its association with cardiovascular risk factors in black Africans

Studies in populations of European descent show longer plasma clot lysis times (CLT) in patients with cardiovascular disease (CVD) than in controls. No data are available on the association between CVD risk factors and fibrinolytic potential in black Africans, a group undergoing rapid urbanisation with increased CVD prevalence. We investigated associations between known CVD risk factors and CLT in black Africans and whether CLTs differ between rural and urban participants in light of differences in CVD risk.

Data from 1000 rural and 1000 urban apparently healthy black South Africans (35–60 years) were cross-sectionally analysed.

Increased PAI-1_act, BMI, HbA1c, triglycerides, the metabolic syndrome, fibrinogen concentration, CRP, female sex and positive HIV status were associated with increased CLTs, while habitual alcohol consumption associated with decreased CLT. No differences in CLT were found between age and smoking categories, contraceptive use or hyper- and normotensive participants. Urban women had longer CLT than rural women while no differences were observed for men.

CLT was associated with many known CVD risk factors in black Africans. Differences were however observed, compared to data from populations of European descent available in the literature, suggesting possible ethnic differences. The effect of urbanisation on CLT is influenced by traditional CVD risk factors and their prevalence in urban and rural communities.

Impaired fibrinolytic capacity and increased fibrin formation associate with myocardial infarction

We assessed whether abnormality of haemostasis measured by a newly developed global method is associated with risk of a first myocardial infarction (MI). The global markers coagulation activation profile (Cp), fibrinolysis activation profile (Fp) and sum of fibrin optical density over time (Fibrin OD-sum) were determined in plasma from 800 MI cases and 1,123 controls included in the Stockholm Heart Epidemiology Program. Clot lysis time (CLT) was also determined based on raw data of fibrin OD from the global assay. Odds ratios (OR) of MI with 95% confidence intervals (CI) were calculated using logistic regression. A Fp value <10th percentile value in controls was significantly associated with increased MI risk; OR after multivariate adjustments for conventional cardiovascular risk factors 1.66 (95% CI 1.22-2.27). For an abnormally long CLT (>90th percentile value in controls) the adjusted OR of MI was 2.62 (95% CI 1.87-3.66) and for a high Fibrin OD-sum value (>90th percentile in controls) it was 1.86 (95% CI 1.37-2.53). A high Cp value was not significantly associated with MI. In conclusion, we found that abnormal haemostasis in platelet-poor plasma, reflected either as an attenuated fibrinolytic capacity or the resulting increase of fibrin formation, was associated with increased MI risk.

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.

Activation of hemostasis in brain dead organ donors: an observational study

BACKGROUND

Brain death is associated with a systemic inflammatory response resulting in diminished organ function in individuals transplanted with organs from brain dead donors. As inflammation is accompanied by activation of coagulation, we hypothesized that activation of hemostasis occurs in brain dead organ donors.

OBJECTIVES

To assess the hemostatic status in brain dead organ donors.

PATIENTS AND METHODS

In this study, we systematically assessed the hemostatic system in samples taken from 30 brain dead donors. As controls, blood samples from 30 living kidney donors were included.

RESULTS AND CONCLUSIONS

Compared with the living donors, brain dead donors showed significant platelet activation (assessed by glycocalicin plasma levels), and a profound dysbalance in the von Willebrand factor/ADAMTS13 axis, which is key in platelet attachment to damaged vasculature. Furthermore, compared with the living donors, brain dead donors showed a significantly increased activation of secondary hemostasis with formation of fibrin (assessed by plasma levels of prothrombin fragment 1 + 2, fibrinopeptide A and D-dimer). Finally, brain dead donors showed profound hypofibrinolysis as assessed by a global clot lysis assay, which was attributed to substantially elevated plasma levels of plasminogen activator inhibitor type 1. Collectively, our results show activation of hemostasis and dysregulated fibrinolysis in brain dead organ donors. This prothrombotic state may contribute to formation of microthrombi in transplantable organs, which potentially contributes to deterioration of organ function.

Clot lysis time in platelet-rich plasma: method assessment, comparison with assays in platelet-free and platelet-poor plasmas, and response to tranexamic acid

Fibrinolysis dysfunctions cause bleeding or predisposition to thrombosis. Platelets contain several factors of the fibrinolytic system, which could up or down regulate this process. However, the temporal relationship and relative contributions of plasma and platelet components in clot lysis are mostly unknown. We developed a clot lysis time (CLT) assay in platelet-rich plasma (PRP-CLT, with and without stimulation) and compared it to a similar one in platelet-free plasma (PFP) and to another previously reported test in platelet-poor plasma (PPP). We also studied the differential effects of a single dose of tranexamic acid (TXA) on these tests in healthy subjects. PFP- and PPP-CLT were significantly shorter than PRP-CLT, and the three assays were highly correlated (p < 0.0001). PFP- and PPP-, but more significantly PRP-CLT, were positively correlated with age and plasma PAI-1, von Willebrand factor, fibrinogen, LDL-cholesterol, and triglycerides (p < 0.001). All these CLT assays had no significant correlations with platelet aggregation/secretion, platelet counts, and pro-coagulant tests to explore factor X activation by platelets, PRP clotting time, and thrombin generation in PRP. Among all the studied variables, PFP-CLT was independently associated with plasma PAI-1, LDL-cholesterol, and triglycerides and, additionally, stimulated PRP-CLT was also independently associated with plasma fibrinogen. A single 1 g dose of TXA strikingly prolonged all three CLTs, but in contrast to the results without the drug, the lysis times were substantially shorter in non-stimulated or stimulated PRP than in PFP and PPP. This standardized PRP-CLT may become a useful tool to study the role of platelets in clot resistance and lysis. Our results suggest that initially, the platelets enmeshed in the clot slow down the fibrinolysis process. However, the increased clot resistance to lysis induced by TXA is overcome earlier in platelet-rich clots than in PFP or PPP clots. This is likely explained by the display of platelet pro-fibrinolytic effects. Focused research is needed to disclose the mechanisms for the relationship between CLT and plasma cholesterol and its potential pathophysiologic and clinical relevance.

Genome scan of clot lysis time and its association with thrombosis in a protein C-deficient kindred

BACKGROUND

 Previously, we found increased clot-lysis time (CLT), as measured with a plasma-based assay, to increase the risk of venous thrombosis in two population-based case-control studies. The genes influencing CLT are as yet unknown.

PATIENTS/METHODS

 We tested CLT as risk factor for venous thrombosis in Kindred Vermont II (n = 346), a pedigree suffering from a high thrombosis risk, partially attributable to a type I protein C deficiency. Furthermore, we tested for quantitative trait loci (QTLs) for CLT, using variance component linkage analysis.

RESULTS

 Protein C-deficient family members had shorter CLTs than non-deficient members (median CLT 67 min vs. 75 min). One standard deviation increase in CLT increased the risk of venous thrombosis 2.4-fold in non-deficient family members. Protein C deficiency without elevated CLT increased the risk 6.9-fold. Combining both risk factors yielded a 27.8-fold increased risk. The heritability of CLT was 42-52%. We found suggestive evidence of linkage on chromosome 11 (62 cM), partly explained by the prothrombin 20210A mutation, and on chromosome 13 (52 cM). Thrombin-activatable fibrinolysis inhibitor genotypes did not explain the variation in CLT.

CONCLUSION

Hypofibrinolysis appears to increase thrombosis risk in this family, especially in combination with protein C deficiency. Protein C deficiency is associated with short CLT. CLT is partly genetically regulated. Suggestive QTLs were found on chromosomes 11 and 13.

Reduced plasma fibrinolytic potential in patients with recurrent implantation failure after IVF and embryo transfer

BACKGROUND

Recurrent implantation failure (RIF) following embryo transfer (ET) is a major continuing problem in IVF. Women with haemostatic defects may be at increased risk of miscarriage and preclinical pregnancy loss. The fibrinolytic system is considered, at present, the key to new thrombotic pathogenic mechanisms. Patients with unexplained recurrent miscarriage have an impairment of fibrinolysis, as demonstrated by prolonged clot lysis time (CLT) in association with increased plasma levels of thrombin-activatable fibrinolysis inhibitor (TAFI). In this study, we investigated fibrinolytic potential in patients with RIF.

METHODS

Three groups of patients were studied: 30 women with RIF (RIF group), 60 patients undergoing a first successful IVF-ET cycle (IVF group) and 60 healthy fertile women (FER group). Plasma CLT was measured using a global fibrinolysis assay. TAFI antigen plasma levels and polymorphisms in the TAFI gene (+505A/G and +1542C/G) were analysed using enzyme-linked immunosorbent assay and allele-specific PCR, respectively.

RESULTS

CLT was significantly longer (P < 0.0001 and P < 0.0009, respectively) and TAFI antigen levels were significantly higher (both P < 0.0001) in the RIF versus the IVF and FER groups. A direct relationship between CLT and TAFI antigen levels (r = 0.40; P = 0.001) was detected in the whole study population. There were no differences in distribution of TAFI polymorphisms between groups.

CONCLUSIONS

Patients with RIF have reduced plasma fibrinolytic potential, as shown by a prolonged CLT, and this may be explained, at least in part, by increased TAFI antigen levels.

Hyperglycemia: a prothrombotic factor?

Diabetes mellitus is characterized by a high risk of atherothrombotic events. What is more, venous thrombosis has also been found to occur more frequently in this patient group. This prothrombotic condition in diabetes is underpinned by laboratory findings of elevated coagulation factors and impaired fibrinolysis. Hyperglycemia plays an important role in the development of these hemostatic abnormalities, as is illustrated by the association with glycemic control and the improvement upon treatment of hyperglycemia. Interestingly, stress induced hyperglycemia, which is often transient, has also been associated with poor outcome in thrombotic disease. Similar laboratory findings suggest a common effect of acute vs. chronic hyperglycemia on the coagulation system. Many mechanisms have been proposed to explain this prothrombotic shift in hyperglycemia, such as a direct effect on gene transcription of coagulation factors caused by hyperglycemia-induced oxidative stress, loss of the endothelial glycocalyx layer, which harbours coagulation factors, and direct glycation of coagulation factors, altering their activity. In addition, both chronic and acute hyperglycemia are often accompanied by hyperinsulinemia, which has been shown to have prothrombotic effects as well. In conclusion, the laboratory evidence of the effects of both chronic and acute hyperglycemia suggests a prothrombotic shift. Additionally, hyperglycemia is associated with poor clinical outcome of thrombotic events. Whether intensive treatment of hyperglycemia can prevent hypercoagulability and improve clinical outcome remains to be investigated.

Plasma levels of fibrinolytic proteins and the risk of myocardial infarction in men

Hypofibrinolysis as measured with overall clot lysis assays is associated with risk of arterial thrombosis. Individual components of the fibrinolytic system, however, have not been studied extensively in relation to arterial disease, or results of studies were inconsistent. The relation between plasminogen and α2-antiplasmin levels and cardiovascular risk factors and the association between plasminogen, α2-antiplasmin, tissue-plasminogen activator (t-PA), and plasminogen activator inhibitor-1 (PAI-1) and risk of myocardial infarction was investigated in the Study of Myocardial Infarctions Leiden (555 men with a first myocardial infarction and 635 controls). α2-antiplasmin was associated with age and lipid levels, whereas plasminogen correlated with lipids, C-reactive protein, and smoking. Increased levels of all fibrinolytic factors were associated with myocardial infarction. Age-adjusted odds ratios (ORs; 95% confidence interval) for quartile 4 compared with 1 were 1.7 (1.2-2.3) for plasminogen, 1.9 (1.3-2.6) for α2-antiplasmin, 1.7 (1.2-2.3) for t-PA, and 1.7 (1.2-2.4) for PAI-1. After adjusting for cardiovascular risk factors, only α2-antiplasmin levels remained associated with risk (OR, 1.4; [1.0-2.0]). t-PA and PAI-1 levels predominantly reflected lipid levels, whereas plasminogen reflected the inflammatory state. Concluding, elevated α2-antiplasmin levels are independently associated with risk of myocardial infarction. t-PA, PAI-1, and plasminogen levels appear to reflect other cardiovascular risk factors.