Statins, fenofibrate, and quinapril increase clot permeability and enhance fibrinolysis in patients with coronary artery disease

C-reactive protein expression in acute ischemic stroke blood clots: Implications for etiology

INTRODUCTION

C-reactive protein (CRP) is a prototypic inflammation marker, with elevated levels associated with an increased risk of cerebrovascular events. To determine whether CRP could be a useful biomarker of stroke etiology, we investigated CRP expression in acute ischemic stroke (AIS) clots from large-artery atherosclerosis (LAA), cardio-embolism (CE) and cryptogenic (Crypt) subtypes.

PATIENTS AND METHODS

We analysed clot samples from AIS patients (LAA, CE, Crypt; n = 50 each), collected across five stroke centres in France, Serbia, Spain, and Japan between February 2021 and February 2024, as part of the prospective Clotbase International Registry of 460 patients who underwent mechanical thrombectomy. Clot components were assessed using Martius Scarlet Blue staining. CRP expression was examined using immunohistochemistry and its co-localisation with clot components was detected using immunofluorescence. Clinical parameters were compared across etiologies.

RESULTS

CRP expression varied significantly among clots. Most clots (65%) had minimal (⩽1%) CRP and 35% showed substantial (>1%) CRP. CE group had significantly more clots with substantial CRP than LAA and Crypt (48% vs 30% and 26%; p = 0.048). Clots with substantial CRP contained more fibrin (28.9%) than those with low CRP (20.6%; p = 0.005). Confocal microscopy showed CRP co-localised with fibrin and white blood cells (WBCs).

DISCUSSION AND CONCLUSION

Significantly more AIS clots of CE expressed substantial CRP compared to those of LAA and Crypt, suggesting CE strokes may be more strongly linked to inflammation. Clots with substantial CRP expression displayed significantly more fibrin compared to those with minimal CRP expression, suggesting a potential association between inflammation and fibrin-rich clots. Further study of the relationship between CRP, fibrin and WBCs in clots may improve our understanding of the processes of thrombo-inflammation.

Fibrin clot permeability (Ks) in patients on left ventricular assist device

Patients on left ventricular assist devices (LVAD) are prone to excessive hemostasis disturbances due to permanent contact of artificial pump surfaces with blood components. We aimed to investigate if fibrin clot permeability is altered in patients on long-term continuous-flow LVAD therapy and if the clot permeability is associated with clinical characteristics and adverse events. We investigated 85 end-stage heart failure patients (90.6% men, age 48.6-63.8 years) scheduled for continuous flow long-term LVAD support according to current clinical indications. The patients were assessed periodically: prior to LVAD implantation (T1), 3-6 months (T2) after LVAD implantation, 6-12 months after (T3) and then every 6 months. We tested the first three blood samples (T1-T3) and the last available blood sample (T4), but no longer than 5 years after LVAD implantation. We assessed hemostasis parameters (Activated Partial Thromboplastin Time (APTT) Prothrombin Time, Activated Partial Thromboplastin Time, Fibrinogen, D-dimer, Antithrombin, Thrombin Time, Factor VIII, and von Willebrand Factor, aspirin-induced platelet inhibition, adenosine-diphosphate test) changes during the study period. Fibrin Clot Permeability was evaluated using a pressure system and Permeability Coefficient (Ks) was calculated. We observed a decrease in fibrin clot permeability (Ks) between T1, T2, T3 and T4 time periods; P < 0.01 for each comparison. Fibrin clot permeability was negatively correlated with fibrinogen concentration: r = - 0.51, P < 0.001, factor VIII activity r = - 0.42, P < 0.001. There was no association of Ks with age, Left Ventricular Ejection Fraction (LVEF) and medications P > 0.001, however cumulative measurements in patients on aspirin showed shortening of Ks in this group P = 0.0123. Major adverse cardiac and cerebrovascular events (MACCE) occurred in 36.5% patients, bleeding events in 25.9%, Net Adverse Clinical Events (NACE) in 62.4%; 31.7% patients died, and 17.6% underwent transplantation. The transplantation was considered as the endpoint. Discrepancies in Ks were observed between patients with MACCE, bleeding, and NACE, and patients without adverse events. Ks showed a constant trend towards normalization (P < 0.01) only in patients without adverse events. Patients with advanced heart failure have disturbed clot structure. A trend towards normalization of the Ks values is associated with fewer thromboembolic and bleeding complications in this group of patients.

Neutrophil-activating Peptide 2 as a Novel Modulator of Fibrin Clot Properties in Patients with Atrial Fibrillation

Neutrophil-activating peptide 2 (NAP-2, CXCL7), a platelet-derived neutrophil chemoattractant, is involved in inflammation. We investigated associations between NAP-2 levels, neutrophil extracellular traps (NETs) formation, and fibrin clot properties in atrial fibrillation (AF). We recruited 237 consecutive patients with AF (mean age, 68 ± 11 years; median CHA2DS2VASc score of 3 [2-4]) and 30 apparently healthy controls. Plasma NAP-2 concentrations were measured, along with plasma fibrin clot permeability (Ks) and clot lysis time (CLT), thrombin generation, citrullinated histone H3 (citH3), as a marker of NETs formation, and 3-nitrotyrosine reflecting oxidative stress. NAP-2 levels were 89% higher in AF patients than in controls (626 [448-796] vs. 331 [226-430] ng/ml; p < 0.0001). NAP-2 levels were not associated with demographics, CHA2DS2-VASc score, or the AF manifestation. Patients with NAP-2 in the top quartile (> 796 ng/ml) were characterized by higher neutrophil count (+ 31.7%), fibrinogen (+ 20.8%), citH3 (+ 86%), and 3-nitrotyrosine (+ 111%) levels, along with 20.2% reduced Ks and 8.4% prolonged CLT as compared to the remaining subjects (all p < 0.05). NAP-2 levels were positively associated with fibrinogen in AF patients (r = 0.41, p = 0.0006) and controls (r = 0.65, p < 0.01), along with citH3 (r = 0.36, p < 0.0001) and 3-nitrotyrosine (r = 0.51, p < 0.0001) in the former group. After adjustment for fibrinogen, higher citH3 (per 1 ng/ml β = -0.046, 95% CI -0.029; -0.064) and NAP-2 (per 100 ng/ml β = -0.21, 95% CI -0.14; -0.28) levels were independently associated with reduced Ks. Elevated NAP-2, associated with increased oxidative stress, has been identified as a novel modulator of prothrombotic plasma fibrin clot properties in patients with AF.

Reviewing the Rich History of Fibrin Clot Research with a Focus on Clinical Relevance

Fibrin, described on a single-lens microscopy for the first time by Malpighi in 1666 and named by de Fourcroy, has been extensively studied by biochemists, biophysicists, and more recently by clinicians who recognized that fibrin is the major component of most thrombi. Elucidation of key reactions leading to fibrin clot formation in the 1950s and 1960s grew interest in the clinical relevance of altered fibrin characteristics. Implementation of scanning electron microscopy to image fibrin clots in 1947 and clot permeation studies in the 1970s to evaluate an average pore size enabled plasma clot characterization in cohorts of patients. Unfavorably altered fibrin clot structure was demonstrated by Blombäck's group in coronary artery disease in 1992 and in diabetes in 1996. Fifteen years ago, similar plasma fibrin clot alterations were reported in patients following venous thromboembolism. Multiple myeloma was the first malignant disease to be found to lead to abnormal fibrin clot phenotype in the 1970s. Apart from anticoagulant agents, in 1998, aspirin was first shown to increase fibrin clot permeability in cardiovascular patients. The current review presents key data on the rich history of fibrin research, in particular, those that first documented abnormal fibrin clot properties in a variety of human disease states, as well as factors affecting fibrin phenotype.

Atorvastatin-mediated inhibition of prenylation of Rab27b and Rap1a in platelets attenuates their prothrombotic capacity and modulates clot structure

Statins inhibit the mevalonate pathway by impairing protein prenylation via depletion of lipid geranylgeranyl diphosphate (GGPP). Rab27b and Rap1a are small GTPase proteins involved in dense granule secretion, platelet activation, and regulation. We analyzed the impact of statins on prenylation of Rab27b and Rap1a in platelets and the downstream effects on fibrin clot properties. Whole blood thromboelastography revealed that atorvastatin (ATV) delayed clot formation time (P < .005) and attenuated clot firmness (P < .005). ATV pre-treatment inhibited platelet aggregation and clot retraction. Binding of fibrinogen and P-selectin exposure on stimulated platelets was significantly lower following pre-treatment with ATV (P < .05). Confocal microscopy revealed that ATV significantly altered the structure of platelet-rich plasma clots, consistent with the reduced fibrinogen binding. ATV enhanced lysis of Chandler model thrombi 1.4-fold versus control (P < .05). Western blotting revealed that ATV induced a dose-dependent accumulation of unprenylated Rab27b and Rap1a in the platelet membrane. ATV dose-dependently inhibited ADP release from activated platelets. Exogenous GGPP rescued the prenylation of Rab27b and Rap1a, and partially restored the ADP release defect, suggesting these changes arise from reduced prenylation of Rab27b. These data demonstrate that statins attenuate platelet aggregation, degranulation, and binding of fibrinogen thereby having a significant impact on clot contraction and structure.

Statins Effects on Blood Clotting: A Review

Statins are powerful lipid-lowering drugs that inhibit cholesterol biosynthesis via downregulation of hydroxymethylglutaryl coenzyme-A reductase, which are largely used in patients with or at risk of cardiovascular disease. Available data on thromboembolic disease include primary and secondary prevention as well as bleeding and mortality rates in statin users during anticoagulation for VTE. Experimental studies indicate that statins alter blood clotting at various levels. Statins produce anticoagulant effects via downregulation of tissue factor expression and enhanced endothelial thrombomodulin expression resulting in reduced thrombin generation. Statins impair fibrinogen cleavage and reduce thrombin generation. A reduction of factor V and factor XIII activation has been observed in patients treated with statins. It is postulated that the mechanisms involved are downregulation of factor V and activated factor V, modulation of the protein C pathway and alteration of the tissue factor pathway inhibitor. Clinical and experimental studies have shown that statins exert antiplatelet effects through early and delayed inhibition of platelet activation, adhesion and aggregation. It has been postulated that statin-induced anticoagulant effects can explain, at least partially, a reduction in primary and secondary VTE and death. Evidence supporting the use of statins for prevention of arterial thrombosis-related cardiovascular events is robust, but their role in VTE remains to be further elucidated. In this review, we present biological evidence and experimental data supporting the ability of statins to directly interfere with the clotting system.

Tale of two systems: the intertwining duality of fibrinolysis and lipoprotein metabolism

Fibrinolysis is an enzymatic process that breaks down fibrin clots, while dyslipidemia refers to abnormal levels of lipids and lipoproteins in the blood. Both fibrinolysis and lipoprotein metabolism are critical mechanisms that regulate a myriad of functions in the body, and the imbalance of these mechanisms is linked to the development of pathologic conditions, such as thrombotic complications in atherosclerotic cardiovascular diseases. Accumulated evidence indicates the close relationship between the 2 seemingly distinct and complicated systems-fibrinolysis and lipoprotein metabolism. Observational studies in humans found that dyslipidemia, characterized by increased blood apoB-lipoprotein and decreased high-density lipoprotein, is associated with lower fibrinolytic potential. Genetic variants of some fibrinolytic regulators are associated with blood lipid levels, supporting a causal relationship between these regulators and lipoprotein metabolism. Mechanistic studies have elucidated many pathways that link the fibrinolytic system and lipoprotein metabolism. Moreover, profibrinolytic therapies improve lipid panels toward an overall cardiometabolic healthier phenotype, while some lipid-lowering treatments increase fibrinolytic potential. The complex relationship between lipoprotein and fibrinolysis warrants further research to improve our understanding of the bidirectional regulation between the mediators of fibrinolysis and lipoprotein metabolism.

Elevated factor XIa as a modulator of plasma fibrin clot properties in coronary artery disease

INTRODUCTION

Patients with coronary artery disease (CAD) display a prothrombotic fibrin clot phenotype, involving low permeability and resistance to lysis. The determinants of this phenotype remain elusive. Circulating tissue factor (TF) and activated factor XI (FXIa) are linked to arterial thromboembolism. We investigated whether detectable active TF and FXIa influence fibrin clot properties in CAD.

METHODS

In 118 CAD patients (median age 65 years, 78% men), we assessed Ks, an indicator of clot permeability, and clot lysis time (CLT) in plasma-based assays, along with the presence of active TF and FXIa. We also analysed proteins involved in clotting and thrombolysis, including fibrinogen, plasminogen activator inhibitor-1 (PAI-1) and thrombin activatable thrombolysis inhibitor (TAFI). During a median 106 month (interquartile range 95-119) follow-up, myocardial infarction (MI), stroke, systemic thromboembolism (SE) and cardiovascular (CV) death were recorded.

RESULTS

Circulating TF and FXIa, detected in 20.3% and 39.8% of patients, respectively, were associated with low Ks and prolonged CLT. Solely FXIa remained an independent predictor of low Ks and high CLT on multivariable analysis. Additionally, fibrinogen and PAI-1 were associated with low Ks, while PAI-1 and TAFI-with prolonged CLT. During follow-up low Ks and prolonged CLT increased the risk of MI and the latter also a composite endpoint of MI, stroke/SE or CV death.

CONCLUSIONS

To our knowledge, this study is the first to show that circulating FXIa is associated with prothrombotic fibrin clot properties in CAD, suggesting additional mechanisms through which FXIa inhibitors could act as novel antithrombotic agents in CAD.

Effect of high-dose statin therapy on coagulation factors: Lowering of factor XI as a modifier of fibrin clot properties in coronary artery disease

BACKGROUND

Multiple pleiotropic effects of statins include antithrombotic properties with formation of looser fibrin networks more susceptible to lysis. Recently, rosuvastatin 20 mg/d has been reported to decrease coagulation factors (F) VII, FVIII and FXI in venous thrombosis patients.

OBJECTIVES

We investigated how high-dose statin therapy recommended in coronary artery disease (CAD) alters plasma levels of coagulation factors and if such changes might affect fibrin clot properties.

METHODS

We studied 130 advanced CAD patients, who initially did not achieve the target low-density lipoprotein cholesterol (LDL-C). Before high-dose statin therapy (rosuvastatin 40 mg/d or atorvastatin 80 mg/d) and 6-12 months after its initiation, FII, FV, FVII, FVIII, FIX, FX, FXI and fibrinogen were assessed. We evaluated the impact of statin-induced alterations to the factors on plasma fibrin clot permeability (Ks) reflecting a fibrin pore size, and clot lysis time (CLT) reflecting fibrinolytic potential.

RESULTS

At baseline LDL-C (median 3.2, interquartile range 2.7-3.7 mmol/L) was independently associated solely with FXI (β = 0.58, P < 0.001). Median LDL-C reduction by 25% (P < 0.001) on high-dose statin treatment was accompanied by lowering of FVII, FVIII, and FXI (for all P < 0.001). On high-dose statin treatment, Ks (R = 0.65, P < 0.001) inversely associated with CRP (β = -0.41, P < 0.001), LDL-C (β = -0.26, P = 0.001), and FXI (β = -0.18, P = 0.016). In turn, CLT (R = 0.45, P < 0.001) was positively associated with LDL-C (β = 0.19, P = 0.043) and FXI (β = 0.17, P = 0.049).

CONCLUSIONS

High-dose statin therapy in CAD patients decreases FVII, FVIII, and FXI. The statin-induced reduction in FXI may contribute to less prothrombotic fibrin clot phenotype, indicating additional antithrombotic effect of high-dose statins.

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.

Congruent identification of imbalanced fibrinolysis by 2 distinct clot lysis time assays

Background

A plasma-based clot lysis time (CLT) assay is an established research test to assess plasma fibrinolytic potential, with application in hyperfibrinolytic or hypofibrinolytic conditions. Interprotocol variations make comparisons between laboratories challenging. The aim of this study was to compare the results of 2 different CLT assays performed by 2 distinct research laboratories by using their own protocol.

Methods

We evaluated fibrinolysis in the plasma of 60 patients undergoing hepatobiliary surgery and in plasma from a healthy donor that was spiked with commonly used anticoagulant drugs (enoxaparin, dabigatran, and rivaroxaban) in 2 distinct laboratories (Aarhus and Groningen) by using 2 different assays that differ, among others, in tissue plasminogen activator (tPA) concentration.

Results

Overall conclusions on fibrinolytic potential in patients undergoing hepatobiliary surgery were similar between the 2 CLT assays, with hyperfibrinolytic and hypofibrinolytic profiles identified at the same time points during and after surgery. Severe hypofibrinolysis was less commonly reported in the Aarhus assay (36/319 samples; 11%) than in the Groningen assay (55/319 samples; 17%). No clot formation was observed in 31 of 319 samples in the Aarhus assay vs 0 of 319 samples in the Groningen assay. Clotting times increased much more profoundly on the addition of all 3 anticoagulants in the Aarhus assay.

Conclusions

Despite the differences in laboratory, protocol, reagents, operator, data processing, and analysis, overall conclusions on fibrinolytic capacity are similar between the 2 laboratories. With a higher concentration of tPA in the Aarhus assay, the test becomes less sensitive for the detection of hypofibrinolysis and is more sensitive to the addition of anticoagulants.

Statins and Hemostasis: Therapeutic Potential Based on Clinical Evidence

Hemostasis preserves blood fluidity and prevents its loss after vessel injury. The maintenance of blood fluidity requires a delicate balance between pro-coagulant and fibrinolytic status. Endothelial cells (ECs) in the inner face of blood vessels maintain hemostasis through balancing anti-thrombotic and pro-fibrinolytic activities. Dyslipidemias are linked to hemostatic alterations. Thus, it is necessary a better understanding of the underlying mechanisms linking hemostasis with dyslipidemia. Statins are drugs that decrease cholesterol levels in the blood and are the gold standard for treating hyperlipidemias. Statins can be classified into natural and synthetic molecules, approved for the treatment of hypercholesterolemia. The classical mechanism of action of statins is by competitive inhibition of a key enzyme in the synthesis pathway of cholesterol, the HMG-CoA reductase. Statins are frequently administrated by oral ingestion and its interaction with other drugs and food supplements is associated with altered bioavailability. In this review we deeply discuss the actions of statins beyond the control of dyslipidemias, focusing on the actions in thrombotic modulation, vascular and cardiovascular-related diseases, metabolic diseases including metabolic syndrome, diabetes, hyperlipidemia, and hypertension, and chronic diseases such as cancer, chronic obstructive pulmonary disease, and chronic kidney disease. Furthermore, we were prompted to delved deeper in the molecular mechanisms by means statins regulate coagulation acting on liver, platelets, and endothelium. Clinical evidence show that statins are effective regulators of dyslipidemia with a high impact in hemostasis regulation and its deleterious consequences. However, studies are required to elucidate its underlying molecular mechanism and improving their therapeutical actions.

Strategies for Therapeutic Amelioration of Aberrant Plasma Zn2+ Handling in Thrombotic Disease: Targeting Fatty Acid/Serum Albumin-Mediated Effects

The initiation, maintenance and regulation of blood coagulation is inexorably linked to the actions of Zn²⁺ in blood plasma. Zn²⁺ interacts with a variety of haemostatic proteins in the bloodstream including fibrinogen, histidine-rich glycoprotein (HRG) and high molecular weight kininogen (HMWK) to regulate haemostasis. The availability of Zn²⁺ to bind such proteins is controlled by human serum albumin (HSA), which binds 70–85% of plasma Zn²⁺ under basal conditions. HSA also binds and transports non-esterified fatty acids (NEFAs). Upon NEFA binding, there is a change in the structure of HSA which leads to a reduction in its affinity for Zn²⁺. This enables other plasma proteins to better compete for binding of Zn²⁺. In diseases where elevated plasma NEFA concentrations are a feature, such as obesity and diabetes, there is a concurrent increase in hypercoagulability. Evidence indicates that NEFA-induced perturbation of Zn²⁺-binding by HSA may contribute to the thrombotic complications frequently observed in these pathophysiological conditions. This review highlights potential interventions, both pharmaceutical and non-pharmaceutical that may be employed to combat this dysregulation. Lifestyle and dietary changes have been shown to reduce plasma NEFA concentrations. Furthermore, drugs that influence NEFA levels such as statins and fibrates may be useful in this context. In severely obese patients, more invasive therapies such as bariatric surgery may be useful. Finally, other potential treatments such as chelation therapies, use of cholesteryl transfer protein (CETP) inhibitors, lipase inhibitors, fatty acid inhibitors and other treatments are highlighted, which with additional research and appropriate clinical trials, could prove useful in the treatment and management of thrombotic disease through amelioration of plasma Zn²⁺ dysregulation in high-risk individuals.

Accelerated fibrin clot degradation is associated with arterial thromboembolism in patients following venous thrombosis: a cohort study

Several lines of evidence have suggested that patients following venous thromboembolism (VTE) are at higher risk of arterial thromboembolism (ATE). Prothrombotic fibrin clot characteristics were reported in individuals with cardiovascular risk factors. We investigated whether specific fibrin clot properties measured after 3-4 months of anticoagulation characterize VTE patients with subsequent ATE. We enrolled 320 patients following VTE aged below 70 years (median age, 46). Ten patients were lost to follow-up. ATE occurred in 21 individuals after a median 54 (31-68) months during a follow-up of 87.5 months (incidence 0.94%; 95% confidence interval [CI], 0.59-1.4 per patient-year). Patients with ATE had faster fibrin clot degradation, reflected by maximum rate of D-dimer increase during plasma clot lysis induced by tissue-type plasminogen activator (D-D_rate) at baseline. Clot permeability, turbidimetric variables, clot lysis time, and thrombin generation were unrelated to ATE. Univariable Cox proportional hazards analysis showed that age, diabetes, and D-D_rate were risk factors for subsequent ATE. Increased D-D_rate (by 0.001 mg/L/min; hazard ratio, 1.08; 95% CI 1.02-1.14) was an independent predictor of ATE after adjustment for potential confounders. Faster fibrin clot degradation at 3 months since VTE may increase the risk of ATE among VTE patients during follow-up.

The Hyperlipidaemic Drug Fenofibrate Significantly Reduces Infection by SARS-CoV-2 in Cell Culture Models

The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) pandemic has caused a significant number of fatalities and worldwide disruption. To identify drugs to repurpose to treat SARS-CoV-2 infections, we established a screen to measure the dimerization of angiotensin-converting enzyme 2 (ACE2), the primary receptor for the virus. This screen identified fenofibric acid, the active metabolite of fenofibrate. Fenofibric acid also destabilized the receptor-binding domain (RBD) of the viral spike protein and inhibited RBD binding to ACE2 in enzyme-linked immunosorbent assay (ELISA) and whole cell-binding assays. Fenofibrate and fenofibric acid were tested by two independent laboratories measuring infection of cultured Vero cells using two different SARS-CoV-2 isolates. In both settings at drug concentrations, which are clinically achievable, fenofibrate and fenofibric acid reduced viral infection by up to 70%. Together with its extensive history of clinical use and its relatively good safety profile, this study identifies fenofibrate as a potential therapeutic agent requiring an urgent clinical evaluation to treat SARS-CoV-2 infection.

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.

Fibrin Clot Formation under Oxidative Stress Conditions

During coagulation, the soluble fibrinogen is converted into insoluble fibrin. Fibrinogen is a multifunctional plasma protein, which is essential for hemostasis. Various oxidative posttranslational modifications influence fibrinogen structure as well as interactions between various partners in the coagulation process. The aim was to examine the effects of oxidative stress conditions on fibrin clot formation in arterial atherothrombotic disorders. We studied the changes in in vitro fibrin network formation in three groups of patients-with acute coronary syndrome (ACS), with significant carotid artery stenosis (SCAS), and with acute ischemic stroke (AIS), as well as a control group. The level of oxidative stress marker malondialdehyde measured by LC-MS/MS was higher in SCAS and AIS patients compared with controls. Turbidic methods revealed a higher final optical density and a prolonged lysis time in the clots of these patients. Electron microscopy was used to visualize changes in the in vitro-formed fibrin network. Fibers from patients with AIS were significantly thicker in comparison with control and ACS fibers. The number of fibrin fibers in patients with AIS was significantly lower in comparison with ACS and control groups. Thus, oxidative stress-mediated changes in fibrin clot formation, structure and dissolution may affect the effectiveness of thrombolytic therapy.

Plasma fibrin clot properties and cardiovascular mortality in patients with type 2 diabetes: a long-term follow-up study

Background

Patients with type 2 diabetes mellitus (T2DM) are at high risk of cardiovascular mortality, but the mechanisms behind this remain unclear. Prothrombotic fibrin clot properties have been shown in T2DM and cardiovascular disease. We hypothesized that formation of denser clots, which are resistant to fibrinolysis, has a negative impact on cardiovascular mortality in T2DM.

Methods

We studied 133 T2DM patients aged 43–83 years. Plasma fibrin clot turbidity, permeation, compaction, and efficiency of clot lysis using 3 assays including the determination of maximum concentration (D-D_max) and rate of increase in D-dimer concentration (D-D_rate) released during tissue plasminogen activator-induced degradation, were evaluated at the time of enrollment, along with thrombin generation and fibrinolytic proteins. During a median follow-up period of 72 months, cardiovascular mortality was recorded.

Results

Cardiovascular deaths (n = 16, 12%) occurred more frequently in patients with increased D-D_max (> 4.26 mg/l, hazard ratio [HR] 5.43, 95% confidence interval [CI] 1.99–14.79), or decreased D-D_rate (< 0.07 mg/l/min, HR 2.97, 95% CI 1.07–8.23), or increased peak thrombin (> 283.5 nM, HR 5.65, 95% CI 2.07–15.51). These predictors had an even more potent impact on cardiovascular mortality in patients with prior cardiovascular disease (64.7%) and with corresponding risks as follows: HR 6.18, 95% CI 2.02–18.96; HR 8.98, 95% CI 2.99–26.96; and HR 5.35, 95% CI 1.62–17.72, respectively. Other investigated fibrin variables and fibrinolytic proteins did not associate with cardiovascular mortality. In multivariable analysis, cardiovascular mortality was predicted by D-D_max > 4.26 mg/l, age > 65 years, prior cardiovascular disease, and C-reactive protein > 3 mg/l.

Conclusions

This study is the first to show that formation of denser fibrin clots resistant to fibrinolysis could be a risk factor for long-term cardiovascular mortality in T2DM.

Relationship between lipoproteins, thrombosis and atrial fibrillation

The prothrombotic state in atrial fibrillation (AF) occurs as a result of multifaceted interactions, known as Virchow’s triad of hypercoagulability, structural abnormalities, and blood stasis. More recently, there is emerging evidence that lipoproteins are implicated in this process, beyond their traditional role in atherosclerosis. In this review, we provide an overview of the various lipoproteins and explore the association between lipoproteins and AF, the effects of lipoproteins on haemostasis, and the potential contribution of lipoproteins to thrombogenesis in AF. There are several types of lipoproteins based on size, lipid composition, and apolipoprotein category, namely: chylomicrons, very low-density lipoprotein, low-density lipoprotein (LDL), intermediate-density lipoprotein, and high-density lipoprotein. Each of these lipoproteins may contain numerous lipid species and proteins with a variety of different functions. Furthermore, the lipoprotein particles may be oxidized causing an alteration in their structure and content. Of note, there is a paradoxical inverse relationship between total cholesterol and LDL cholesterol (LDL-C) levels, and incident AF. The mechanism by which this occurs may be related to the stabilizing effect of cholesterol on myocardial membranes, along with its role in inflammation. Overall, specific lipoproteins may interact with haemostatic pathways to promote excess platelet activation and thrombin generation, as well as inhibiting fibrinolysis. In this regard, LDL-C has been shown to be an independent risk factor for thromboembolic events in AF. The complex relationship between lipoproteins, thrombosis and AF warrants further research with an aim to improve our knowledge base and contribute to our overall understanding of lipoprotein-mediated thrombosis.

Biomarkers of coagulation and fibrinolysis in acute myocardial infarction: a joint position paper of the Association for Acute CardioVascular Care and the European Society of Cardiology Working Group on Thrombosis

The formation of a thrombus in an epicardial artery may result in an acute myocardial infarction (AMI). Despite major advances in acute treatment using network approaches to allocate patients to timely reperfusion and optimal antithrombotic treatment, patients remain at high risk for thrombotic complications. Ongoing activation of the coagulation system as well as thrombin-mediated platelet activation may both play a crucial role in this context. Whether measurement of circulating biomarkers of coagulation and fibrinolysis could be useful for risk stratification in secondary prevention is currently not fully understood. In addition, measurement of such biomarkers could be helpful to identify thrombus formation as the leading mechanism for AMI. The introduction of biomarkers of myocardial injury such as high-sensitivity cardiac troponins made rule-out of AMI even more precise. However, elevated markers of myocardial injury cannot provide proof of a type 1 AMI, let alone thrombus formation. The combined measurement of markers of myocardial injury with biomarkers reflecting ongoing thrombus formation might be helpful for the fast and correct diagnosis of an atherothrombotic type 1 AMI. This position paper gives an overview of the current knowledge and possible role of biomarkers of coagulation and fibrinolysis for the diagnosis of AMI, risk stratification, and individualized treatment strategies in patients with AMI.

Fibrin Clot Formation and Lysis in Plasma

Disturbance in the balance between fibrin formation and fibrinolysis can lead to either bleeding or thrombosis; however, our current routine coagulation assays are not sensitive to altered fibrinolysis. The clot formation and lysis assay is a dynamic plasma-based analysis that assesses the patient’s capacity for fibrin formation and fibrinolysis by adding an activator of coagulation as well as fibrinolysis to plasma and measuring ex vivo fibrin clot formation and breakdown over time. This assay provides detailed information on the fibrinolytic activity but is currently used for research only, as the assay is prone to inter-laboratory variation and as it demands experienced laboratory technicians as well as specialized personnel to validate and interpret the results. Here, we describe a protocol for the clot formation and lysis assay used at our research laboratory.

Plasma Fibrin Clot Properties as Determinants of Bleeding Time in Human Subjects: Association with Histidine-Rich Glycoprotein

Aims

Fibrin formation and histidine-rich glycoprotein (HRG) are involved in primary hemostasis and wound healing. Little is known regarding the relationship of clot characteristics, bleeding time, and wound healing.

Methods and Results

We studied 154 patients with coronary artery disease (CAD) and 154 subjects free of CAD matched for age, obesity, and current smoking. We evaluated bleeding time (BT) using standardized skin incisions on a forearm, along with plasma clot permeability (K_s), clot lysis time (CLT), and histidine-rich glycoprotein (HRG). Compared with controls, BT was 45% shorter in CAD cases. CAD patients had 32% lower K_s), clot lysis time (CLT), and histidine-rich glycoprotein (HRG). Compared with controls, BT was 45% shorter in CAD cases. CAD patients had 32% lower p < 0.001). After adjusting for potential confounders, K_s), clot lysis time (CLT), and histidine-rich glycoprotein (HRG). Compared with controls, BT was 45% shorter in CAD cases. CAD patients had 32% lower n = 79, 25.6%) was independently predicted by both short and prolonged BT in CAD cases (OR 21.87, 95% CI 7.41-64.55 and OR 10.17, 95% CI 2.88-35.97) and controls (OR 5.94, 95% CI 2.29-15.41 and OR 14.76, 95% CI 4.29-50.77, respectively).

Conclusions

The study shows that plasma fibrin clot density and HRG may influence BT and that appropriate skin wound healing is associated with medium BT. Translational Perspective. Elucidation of the complex relationships between plasma fibrin clot phenotype and wound healing might have important practical implications.

Impaired Fibrinolysis Predicts Adverse Outcome in Acute Coronary Syndrome Patients with Diabetes: A PLATO Sub-Study

Hypofibrinolysis is a key abnormality in diabetes but the role of impaired clot lysis in predicting vascular events and mortality in this population is yet to be determined. We aimed to investigate the relationship between fibrin clot properties and clinical outcomes in patients with diabetes and recent acute coronary syndrome (ACS). Plasma samples were collected at hospital discharge from 974 ACS patients with diabetes randomised to clopidogrel or ticagrelor in the PLATO trial. A validated turbidimetric assay was employed to study fibrin clot lysis and maximum turbidity. One-year rates of cardiovascular (CV) death, spontaneous myocardial infarction (MI) and PLATO-defined major bleeding events were assessed after sample collection. Hazard ratios (HRs) were determined using Cox proportional analysis. After adjusting for CV risk factors, each 50% increase in lysis time was associated with increased risk of CV death/MI (HR 1.21; 95% confidence interval [CI] 1.02–1.44; p  = 0.026) and CV death alone (HR 1.38; 1.08–1.76; p  = 0.01). Similarly, each 50% increase in maximum turbidity was associated with increased risk of CV death/MI (HR 1.25; 1.02–1.53; p  = 0.031) and CV death alone (HR 1.49; 1.08–2.04; p  = 0.014). The relationship between lysis time and the combined outcome of CV death and MI remained significant after adjusting for multiple prognostic vascular biomarkers ( p  = 0.034). Neither lysis time nor maximum turbidity was associated with major bleeding events. Impaired fibrin clot lysis predicts 1-year CV death and MI in diabetes patients following ACS.

Clinical Trial Registration  URL: http://www.clinicaltrials.gov . Unique identifier NCT00391872.

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

INTRODUCTION

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Interpretation and Validation of Maximum Absorbance Data Obtained from Turbidimetry Analysis of Plasma Clots

Turbidimetry is used to characterize fibrin clot properties. In purified systems, maximum absorbance (MA) directly relates to fibrin fiber cross-sectional area. However, in plasma samples there are discrepancies in the relationships between MA and fibrinogen concentration, fiber diameter, other clot properties, and cardiovascular disease outcomes, which complicate data interpretation. This study aims to advance understanding of MA of plasma clots through testing how well it relates to fundamental dependence on fibrinogen concentration and fiber diameter as predicted by light scattering theory, other clot properties and lifestyle, and biochemical variables. Plasma samples from 30 apparently healthy individuals with a fibrinogen concentration from 2.4 to 6.4 g/L were included. We performed turbidimetry, permeability, scanning electron microscopy, and rheometry on in vitro formed plasma clots. MA correlated more strongly with fibrinogen concentration (r = 0.65; p < 0.001) than with fiber diameter (r = 0.47; p = 0.01), which combined explained only 46% of the MA variance. Of additional variables measured, only low-density lipoprotein cholesterol correlated with MA (r = 0.46; p = 0.01) and clot lysis (r = 0.62; p < 0.0001) but not with fiber diameter or fibrinogen concentration. MA correlated with clot lysis time (r = 0.59; p = 0.001), storage modulus (r = 0.61; p = 0.001), and loss modulus (r = 0.59; p = 0.001), and negatively with clot permeability (r = -0.60; p = 0.001) also after adjustment for fibrinogen concentration and fiber diameter. Increased MA is indicative of a prothrombotic clot phenotype irrespective of fibrinogen concentration. MA is more indicative of overall clot density than of fiber diameter. Other plasma components can alter internal fiber density without altering fiber diameter and should be considered when interpreting MA of plasma samples.

Plasma Fibrin Clot Properties Are Unfavorably Altered in Women following Venous Thromboembolism Associated with Combined Hormonal Contraception

The use of hormonal contraception is associated with an increased risk of venous thromboembolism (VTE). Unfavorably altered fibrin clot phenotype has been reported in patients following unprovoked VTE who are at risk of recurrences. It remains unknown whether fibrin clot characteristics in women with contraception-related VTE differ from those in unprovoked VTE. We studied three age-matched groups of women: (1) after contraception-related VTE, (n = 48) (2) after unprovoked VTE (n = 48), and (3) controls (n = 48). Plasma fibrin clot permeability (K _s), turbidity of clot formation, efficiency of fibrinolysis using clot lysis time (CLT), and rate of increase in D-dimer during lytic clot degradation (D-D_rate), along with thrombin generation and fibrinolysis proteins were determined. Compared with the controls, patients following contraception-related and unprovoked VTE formed faster (lag phase, -8.8% and -20.4%, respectively) fibrin clots of increased density (K _{s ,} -8.6% and -13.4%, respectively) displaying impaired fibrinolysis as evidenced by prolonged CLT (+11.5% and +14.5%, respectively) and lower D-D_rate (-7.1% and -5.6%, respectively), accompanied with higher plasminogen activator inhibitor-1 (PAI-1, +14.9% and +17.8%, respectively) and elevated peak thrombin generation (+63.8% and +36.7%, respectively). The only differences between women with unprovoked and contraception-related VTE were lower fibrin mass in plasma clots (D-D_max, -8.6%), along with higher peak thrombin generation (+19.8%) and shorter lag phase (-6.8%) in the latter group. This study suggests that women after contraception-related VTE, similar to those following unprovoked VTE, have denser fibrin clot formation and impaired clot lysis. These findings might imply higher risk of VTE recurrence in women with the prothrombotic clot phenotype.

Plasma fibrin clot proteomics in healthy subjects: Relation to clot permeability and lysis time

BACKGROUND

Little is known about fibrin clot composition in relation to its structure and lysability. We investigated plasma clots protein composition and its associations with clot properties.

METHODS

We studied 20 healthy subjects aged 31-49 years in whom plasma fibrin clot permeability (K_s) and clot lysis time (CLT) were determined. A proteomic analysis of plasma fibrin clots was based on quantitative liquid chromatography-mass spectrometry.

RESULTS

Among 494 clot-bound proteins identified in all clots, the highest concentrations were for fibrinogen chains (about 64% of the clot mass) and fibronectin (13%). α₂-antiplasmin (2.7%), factor XIIIA (1.2%), complement component C3 (1.2%), and histidine-rich glycoprotein (HRG, 0.61%) were present at relatively high concentrations. Proteins present in concentrations <0.5% included (pro)thrombin, plasminogen, apolipoproteins, or platelet factor 4 (PF4). Fibrinogen-α and -γ chains were associated with age, while body-mass index with clot-bound apolipoproteins (all p < .05). K_s correlated with fibrinogen-γ and PF4 amounts within plasma clots. CLT was associated with fibrinogen-α and -γ, PF4, and HRG (all p < .05).

CONCLUSIONS

This study is the first to show associations of two key measures of clot properties with protein content within plasma clots, suggesting that looser fibrin clots with enhanced lysability contain less fibrinogen-γ chain, platelet-derived PF4, and HRG.

SIGNIFICANCE

Our study for the first time suggests that more permeable fibrin clots with enhanced lysability contain less fibrinogen-γ chain, platelet-derived factor 4, and histidine-rich glycoprotein, which is related to accelerated clot lysis. The current findings might have functional consequences regarding clot structure, stability, and propagation of thrombin generation, and detailed proteomic analysis of clots in various disorders opens new perspective for coagulation and fibrin research.

The effect of atorvastatin on haemostatic parameters in apparently healthy dogs

OBJECTIVE

To determine the effect of atorvastatin on haemostatic parameters as measured by prothrombin time, activated partial thromboplastin time and thromboelastography in apparently healthy dogs administered 2 mg/kg orally once daily for 1 week.

MATERIALS AND METHODS

Prospective study of 20 apparently healthy client-owned dogs at a small animal specialty hospital. Dogs had a baseline complete blood count, serum chemistry profile, fibrinogen, platelet count, prothrombin time, activated partial thromboplastin time and thromboelastography performed. Each dog was then administered approximately 2 mg/kg of atorvastatin orally once daily for 1 week, and the laboratory tests were repeated. Adverse effects attributed to atorvastatin were recorded.

RESULTS

All 20 enrolled dogs completed the study. Dogs received a median dose of 2.06 mg/kg (range 1.94 to 2.44 mg/kg) atorvastatin once daily, which was associated with a significant increase in pulse rate, mean corpuscular haemoglobin concentration, albumin and a significant decrease in mean corpuscular volume, cholesterol and lipase values compared with baseline. On thromboelastography, there was a significant increase in maximum amplitude, G, coagulation index, amplitude at 30 minutes, amplitude at 60 minutes and significant decrease in percentage of clot lysed at 30 minutes and percentage of clot lysed at 60 minutes values compared with baseline. Six dogs had a noticeable increase in appetite.

CLINICAL SIGNIFICANCE

The results of this study suggest that atorvastatin may produce a procoagulant effect in dogs, although the clinical significance is unclear. Polyphagia was the most commonly reported adverse effect.

Restenosis is associated with prothrombotic plasma fibrin clot characteristics in endovascularly treated patients with critical limb ischemia

INTRODUCTION

Hypolysible fibrin clots composed of tightly packed fibers characterize patients with peripheral artery disease (PAD) especially those with critical limb ischemia (CLI). Little is known about the impact of a prothrombotic clot phenotype on restenosis following endovascular revascularization in CLI. The goal of this study was to compare fibrin clot properties and their determinants in CLI patients with restenosis after endovascular treatment (ET) and those free of this complication.

METHODS

85 patients with CLI and restenosis within 1 year after ET on optimal pharmacotherapy and 47 PAD control patients without restenosis were included into the study. Plasma fibrin clot permeability (Ks, a measure of the average pore size in the fibrin network) and clot lysis time (CLT) with its potential determinants were determined. During follow-up, the composite endpoint including re-intervention, amputation and death was assessed.

RESULTS

Compared with the control group, patients with restenosis had reduced Ks (- 9.5%, p < 0.001), prolonged CLT (+ 12.4%, p = 0.003), higher thrombin generation (+ 7.9%, p < 0.001) and elevated von Willebrand factor (vWF) antigen (+ 14.2%, p < 0.001). During a 24 months follow-up the composite endpoint occurred in 54 CLI patients with restenosis (63.5%) and nine control patients (19.1%, p < 0.001) with no association with baseline Ks and CLT.

CONCLUSION

The increased thrombin formation and unfavorable fibrin clot properties occur in patients with CLI who experienced restenosis despite optimal endovascular and pharmacological therapy.

Faster fibrin clot degradation characterizes patients with central pulmonary embolism at a low risk of recurrent peripheral embolism

It is unclear whether thrombus location in pulmonary arteries is associated with particular clot characteristics. We assessed 156 patients following either central or peripheral pulmonary embolism (PE). Plasma clot lysis time, the rate of D-dimer release from plasma clots (D-D_rate) with the maximum D-dimer concentration achieved (D-D_max), as well as fibrin formation on turbidimetry, plasma clot permeation, thrombin generation, and fibrinolytic parameters were measured 3–6 months after PE. Patients following central PE (n = 108, 69.3%) were more likely smokers (38.9% vs 18.8%; p = 0.01), less likely carriers of factor XIII Val34Leu allele (40.7% vs 62.5%, p = 0.01), exhibited 16.7% higher D-D_rate and 12.7% higher tissue plasminogen activator antigen (tPA:Ag) compared with peripheral PE (p = 0.02 and p < 0.0001, respectively). Saddle PE patients (n = 31, 19.9%) had 11.1% higher D-D_rate and 7.3% higher D-D_max compared with central PE (both p < 0.05). Twenty-three recurrent PE episodes, including 15 central episodes, during a median follow-up of 52.5 months were recorded. Plasma D-dimer and tPA:Ag were independent predictors for central recurrent PE, whereas D-D_rate and peak thrombin predicted peripheral recurrent PE. Plasma clots degradation is faster in patients following central PE compared with peripheral PE and fibrinolysis markers might help to predict a type of recurrent PE.

Statin Therapy and Diabetes Do Not Affect Aneurysm Occlusion or Clinical Outcomes After Pipeline Embolization Device Treatment: A Preliminary Study

BACKGROUND

The effect of statins and diabetes on angiographic and clinical outcomes in aneurysms treated with pipelines has not been adequately reported. Our aim is to assess the effect of concurrent statin medications and diabetes mellitus (DM) on aneurysm occlusion status and outcomes in patients treated with the pipeline embolization device.

METHODS

A retrospective review of our institution's database of aneurysms treated with the pipeline embolization device between 2013 and 2017 was conducted. We collected data about statin therapy status and intensity, and identified patients with a documented history of DM. Our primary outcome was aneurysm obliteration seen on digital subtracted angiography or magnetic resonance angiography at last follow-up.

RESULTS

We identified 151 patients with 182 aneurysms for this cohort, with a median radiographic follow-up time of 7.2 months (6.1-14.5). Thirty-nine patients were taking statins, and 112 patients did not receive statins. Log-rank tests revealed no statistically significant difference in occlusion rates between patients with and without statin therapy (P = 0.30). A history of DM was documented in 11 patients, with 14 aneurysms in total; 140 patients with 168 aneurysms had no history of DM. Similarly, there were no differences in occlusion rates between the diabetic and nondiabetic groups in multivariate analysis (P = 0.24). Only 2 patients showed significant in-stent stenosis on angiographic follow up, and both were diabetic.

CONCLUSIONS

Our analysis did not identify a statistically significant association between statin therapy or DM and higher occlusion rates or better outcomes after pipeline embolization. Diabetic patients may have a theoretic risk of significant in-stent stenosis.

Altered plasma clot properties increase the risk of recurrent deep vein thrombosis: a cohort study

It has been demonstrated that fibrin clots generated from plasma samples obtained from patients with prior thromboembolic events are denser and less susceptible to lysis. Such a prothrombotic fibrin clot phenotype has been suggested as a new risk factor for venous thromboembolism, but its prognostic value is unclear. To assess whether abnormal clot properties can predict recurrent deep vein thrombosis (DVT), we studied 320 consecutive patients aged 18 to 70 years following the first-ever DVT. Plasma clot properties were evaluated after 3 months of anticoagulant treatment since the index event. A mean duration of anticoagulation was 10 months (range, 4-20). Recurrent DVT was observed in 77 patients (25%; 6.6%/year) during a median follow-up of 44 months. Recurrences of DVT were associated with faster formation (-9% lag phase) of denser fibrin networks (-12% fibrin clot permeability [K_s]) and 4% higher maximum absorbance of plasma clots that displayed impaired fibrinolytic degradation (+25% prolonged clot lysis time [CLT]) and a 5% slower rate of increase in D-dimer levels during clot degradation (D-D_rate; all P < .05). Proximal DVT alone, higher C-reactive protein, D-dimer, peak thrombin, lower K_s, shorter lag phase, decreased D-D_rate, and prolonged CLT were independent predictors of recurrences (all P < .05). Individuals characterized by low K_s (≤7.3 × 10^-9 cm²) and prolonged CLT (>96 min) were at the highest risk of recurrent DVT (odds ratio, 15.8; 95% confidence interval, 7.5-33.5). Kaplan-Meier curves showed that reduced K_s and prolonged CLT predicted recurrent DVT. We demonstrate that unfavorably altered clot properties may predict recurrent DVT after anticoagulation withdrawal.

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.

Short-term effects of the smoke-free legislation on haemostasis and systemic inflammation due to second hand smoke exposure

It was the objective of this study to assess the effect of the implementation of the smoke-free legislation on haemostasis and systemic inflammation in second-hand smoking (SHS)-exposed healthy volunteers. Fibrin-rich clot properties, platelet reactivity and inflammatory biomarkers were measured before and four months following the implementation of the smoke-free legislation in gender and age-matched healthy volunteers exposed (n=23, exposed) and unexposed (n=23, controls) to occupational SHS. The primary objective was to compare fibrin-rich clot stiffness before and after implementation of the smoke-free legislation. There was 40% reduction in fibrin-rich clot stiffness following the implementation of the smoke-free legislation in SHS-exposed volunteers (17 ± 7 vs. 10.6 ± 7 dynes/cm², before and after, respectively, p=0.001). These dramatic changes were associated with a 20% reduction in fibrin fiber density (p<0.01) and a 20% reduction inclot lysis time (p=0.05). No change in fibrin properties was observed in the control group of SHS-unexposed volunteers related to the implementation of the smoke-free legislation. Of interest, neither platelet reactivity nor systemic inflammatory biomarkers were changed in either group. The smoke-free legislation is associated with significant changes in fibrin-rich clot properties toward a less thrombogenic conformation with a better fibrinolysis response while neither platelet reactivity nor systemic inflammatory biomarkers are modified. These improvements may explain the observed reduction in acute coronary syndrome following the implementation of the smoke-free legislation.

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.

Fibrin Clot Permeability as a Predictor of Stroke and Bleeding in Anticoagulated Patients With Atrial Fibrillation

BACKGROUND AND PURPOSE

Formation of denser fiber networks has been reported in atrial fibrillation and ischemic stroke. In this longitudinal cohort study, we evaluated whether fibrin clot density may predict thromboembolic and bleeding risk in patients with atrial fibrillation on vitamin K antagonists.

METHODS

In 236 patients with atrial fibrillation receiving vitamin K antagonists treatment, we measured ex vivo plasma clot permeability (K_s), a measure of the pore size in fibrin networks.

RESULTS

During a median follow-up of 4.3 (interquartile range, 3.7-4.8) years, annual rates of ischemic stroke or transient ischemic attack and major bleeds were 2.96% and 3.45%, respectively. In multivariate Cox regression analysis, patients with lower K_s (<6.8 cm²×10^-9, median) had increased risk of ischemic stroke or transient ischemic attack (hazard ratio [HR], 6.55; 95% confidence interval [CI], 2.17-19.82) and major bleeds (HR, 10.65; 95% CI, 3.52-32.22). Patients with elevated K_s (≥6.8 cm²×10^-9) had an increased rate of minor bleeding compared with the remainder (11.63% per year versus 3.55% per year; P<0.0001). The independent predictors of stroke or transient ischemic attack were low K_s (<6.8 cm²×10^-9; HR, 7.24; 95% CI, 2.53-20.76), age (HR, 1.05; 95% CI, 1.01-1.10), and treatment with angiotensin-converting enzyme inhibitors (HR, 2.27; 95% CI, 1.08-4.77). Major bleeds were predicted by low K_s (<6.8 cm²×10^-9; HR, 8.48; 95% CI, 2.99-24.1) and HAS-BLED score ≥3 (HR, 2.22; 95% CI, 1.12-4.38).

CONCLUSIONS

This study is the first to show that unfavorable fibrin properties reflected by formation of denser fibrin networks determine, in part, the efficacy and safety of anticoagulation with vitamin K antagonists in patients with atrial fibrillation.

Lipopolysaccharide-binding protein (LBP) reverses the amyloid state of fibrin seen in plasma of type 2 diabetics with cardiovascular co-morbidities

Type 2 diabetes (T2D) has many cardiovascular complications, including a thrombotic propensity. Many such chronic, inflammatory diseases are accompanied (and may be exacerbated, and possibly even largely caused) by amyloid fibril formation. Recognising that there are few strong genetic associations underpinning T2D, but that amyloidogenesis of amylin is closely involved, we have been seeking to understand what might trigger the disease. Serum levels of bacterial lipopolysaccharide are raised in T2D, and we recently showed that fibrin(ogen) polymerisation during blood clotting can be affected strongly by LPS. The selectivity was indicated by the regularisation of clotting by lipopolysaccharide-binding protein (LBP). Since coagulopathies are a hallmark of T2D, we wondered whether they might too be caused by LPS (and reversed by LBP). We show here, using SEM and confocal microscopy, that platelet-poor-plasma from subjects with T2D had a much greater propensity for hypercoagulability and for amyloidogenesis, and that these could both be reversed by LBP. These data imply that coagulopathies are an important feature of T2D, and may be driven by ‘hidden’ LPS. Given the prevalence of amyloid formation in the sequelae of diabetes, this opens up novel strategies for both the prevention and treatment of T2D.

Prothrombotic Fibrin Clot Phenotype in Patients with Deep Vein Thrombosis and Pulmonary Embolism: A New Risk Factor for Recurrence

Prothrombotic fibrin clot phenotype, involving faster formation of dense meshwork composed of thinner and highly branched fibers that are relatively resistant to plasmin-induced lysis, has been reported in patients with not only myocardial infarction or stroke, but also venous thromboembolism (VTE), encompassing deep vein thrombosis (DVT), and/or pulmonary embolism (PE). Prothrombotic fibrin clot phenotype, in particular prolonged clot lysis time, is considered a novel risk factor for VTE as well as venous thrombosis at unusual location, for example, cerebral sinus venous thrombosis, retinal vein obstruction, and Budd-Chiari syndrome. Growing evidence from observational studies indicates that abnormal fibrin clot properties can predict recurrent DVT and PE and they are involved in serious complications of VTE, for example, thromboembolic pulmonary hypertension and postthrombotic syndrome. The purpose of this article is to review our current understanding of the role of fibrin clot structure and function in venous thrombosis with emphasis on clinical issues ranging from prognosis to therapy.

Characterisation of clot microstructure properties in stable coronary artery disease

Background

Coronary artery disease (CAD) is associated with an increased prothrombotic tendency and is also linked to unfavourably altered clot microstructure. We have previously described a biomarker of clot microstructure (d_f) that is unfavourably altered in acute myocardial infarction. The d_f biomarker assesses whether the blood will form denser or looser microstructures when it clots. In this study we assessed in patients with stable chest pain whether d_f can differentiate between obstructed and unobstructed CAD.

Methods

A blood sample prior to angiography was obtained from 251 consecutive patients undergoing diagnostic coronary angiography. Patients were categorised based on angiographic findings as presence or absence of obstructive CAD (stenosis ≥50%). The blood sample was assessed using the d_f biomarker, standard laboratory markers and platelet aggregometry (Multiplate).

Results

A significant difference (p=0.028) in d_f was observed between obstructive CAD (1.748±0.057, n=83) and unobstructive CAD (1.732±0.052, n=168), where patients with significant CAD produce denser, more tightly packed clots. d_f was also raised in men with obstructive CAD compared with women (1.745±0.055 vs 1.723±0.052, p=0.007). Additionally d_f significantly correlated with the platelets response to arachidonic acid as measured by the ASPItest area under the curve readings from platelet aggregometry (correlation coefficient=0.166, p=0.008), a low value of the ASPItest indicating effective aspirin use was associated with looser, less dense clots.

Conclusions

For the first time, we characterise clot microstructure, as measured by d_f, in patients with stable CAD. d_f can potentially be used to risk-stratify patients with stable CAD and assess the efficacy of therapeutic interventions by measuring changes in clot microstructure.

Fibrin clot characteristics in acute ischaemic stroke patients treated with thrombolysis: the impact on clinical outcome

Fibrin clot properties in acute ischaemic stroke (AIS) are unfavourably altered, including faster formation of denser and poorly lysable fibre networks. We investigated clot properties in AIS patients treated with recombinant tissue plasminogen activator (rtPA) and their impact on clinical outcome. In 74 consecutive AIS patients eligible for rtPA treatment, we assessed ex vivo plasma fibrin clot formation, permeability (K_s), and rtPA-induced lysis, along with peak thrombin generation, fibrinolysis proteins and inhibitors at three time points - on admission, after 24 hours and 3 months since stroke. Clinical outcome was assessed using the NIHSS and mRS scores. Compared with the pretreatment values, fibrin networks assessed 24 hours since thrombolysis were formed more slowly (+20.5 % lag phase on turbidimetry), were less compact (+36.9 % K_s), composed of thinner fibres (-10.6 % lower maximum absorbancy [ΔAb]), which were lysed more rapidly (-20.8 % clot lysis time [CLT] and +7.1 % the rate of rtPA-induced D-dimer release from clots [D-D_rate]). Thrombin generation and fibrinolysis proteins remained elevated. Lower ΔAb (<0.86 at 405 nm), shorter CLT (<105 min), and higher D-D_rate (>0.072 mg/l/min) assessed at baseline predicted good outcome (mRS 0-2) at 3 months after adjustment for age and fibrinogen. Logistic regression adjusted for potential confounders showed that good outcome at 3 months was predicted by pretreatment D-D_rate, while pretreatment CLT predicted excellent outcome (mRS of 0-1). In conclusion, formation of denser fibrin clots displaying impaired lysability and pattern of their changes induced by thrombolysis may affect clinical outcome in AIS patients.

Statin use after intracerebral hemorrhage: a 10-year nationwide cohort study

INTRODUCTION

Although statin therapy is beneficial to patients with ischemic stroke, statin use, and intracerebral hemorrhage (ICH) remain a concern. ICH survivors commonly have comorbid cardiovascular risk factors that would otherwise warrant cholesterol-lowering medication, thus emphasizing the importance of assessing the characteristics of statin therapy in this population.

METHODS

We performed a cohort study by using 10 years of data collected from the National Health Insurance Research Database in Taiwan. We enrolled 726 patients admitted for newly diagnosed ICH from January 1, 2001 to December 31, 2010. The patients were categorized into high- (92), moderate- (545), and low-intensity (89) statin groups, and into hydrophilic (295) and lipophilic (431) statin groups. The composite outcomes included all-cause mortality, recurrent ICH, ischemic stroke, transient ischemic attack, and acute coronary events.

RESULTS

The patients in the low-intensity group did not differ significantly from the patients in the high-intensity group in risk of all-cause mortality (adjusted hazard ratio [aHR] = 0.65, 95% confidence interval [CI] = 0.28-1.55) and recurrent ICH (aHR = 0.66, 95% CI = 0.30-1.44). In contrast, the patients in the hydrophilic group had a significantly lower risk of recurrent ICH than did those in the lipophilic group (aHR = 0.69, 95% CI = 0.48-0.99). We determined no significant differences in other composite endpoints between hydrophilic and lipophilic statin use.

CONCLUSION

Hydrophilic statin therapy is associated with a reduced risk of recurrent ICH in post-ICH patients. The intensity of statin use had no significant effect on recurrent ICH or other components of the composite outcome. Additional studies are required to clarify the biological mechanisms underlying these observations.

Structural properties of fracture haematoma: current status and future clinical implications

Blood clots (haematomas) that form immediately following a bone fracture have been shown to be vital for the subsequent healing process. During the clotting process, a number of factors can influence the fibrin clot structure, such as fibrin polymerization, growth factor binding, cellular infiltration (including platelet retraction), protein concentrations and cytokines. The modulation of the fibrin clot structure within the fracture site has important clinical implications and could result in the development of multifunctional scaffolds that mimic the natural structure of a haematoma. Artificial haematoma structures such as these can be created from the patient's own blood and can therefore act as an ideal bone defect filling material for potential clinical application to accelerate bone regeneration. Copyright © 2016 John Wiley & Sons, Ltd.

The association of statin therapy with the risk of recurrent venous thrombosis

Essentials A lowered risk of recurrent venous thrombosis (VT) with statin treatment is controversial. Among observational inception cohort of 2,798 adults with incident VT, 457 had recurrent VT. Time-to-event models with time-varying statin use and adjustment for potential confounders was used for analysis. Compared to nonuse, current statin use was associated with 26% lower risk of recurrent VT. Click to hear Prof. Büller's perspective on Anticoagulant Therapy in the Treatment of Venous Thromboembolism

SUMMARY

Background Meta-analyses of randomized controlled trials suggest that treatment with hydroxymethylglutaryl-coenzyme A reductase inhibitors (statins) lowers the risk of incident venous thrombosis (VT), particularly among those without prevalent clinical cardiovascular disease (CVD). Whether this is true for the prevention of recurrent VT is debated. We used an observational inception cohort to estimate the association of current statin use with the risk of recurrent VT. Methods and Results The study setting was a large healthcare organization with detailed medical record and pharmacy information at cohort entry and throughout follow-up. We followed 2798 subjects 18-89 years of age who experienced a validated incident VT between January 1, 2002, and December 31, 2010, for a first recurrent VT, validated by medical record review. During follow-up, 457 (16%) developed a first recurrent VT. In time-to-event models incorporating time-varying statin use and adjusting for potential confounders, current statin use was associated with a 26% lower risk of recurrent VT: hazard ratio 0.74, 95% confidence interval 0.59-0.94. Among cohort members free of CVD (n = 2134), current statin use was also associated with a lower risk (38%) of recurrent VT: hazard ratio 0.62, 95% confidence interval 0.45-0.85. We found similar results when restricting to new users of statins and in subgroups of different statin types and doses. Conclusions In a population-based cohort of subjects who had experienced an incident VT, statin use, compared with nonuse, was associated with a clinically relevant lower risk of recurrent VT. These findings suggest a potential secondary benefit of statins among patients who have experienced an incident VT.

High-dose statin therapy and risk of intracerebral hemorrhage: a meta-analysis

Statin plays a major role in the primary and secondary prevention of cardiovascular disease (CVD). Inconsistent findings in the studies have been observed toward the risk of intracerebral hemorrhage (ICH) using higher dose of statin. To examine this issue, we performed a meta-analysis of randomized controlled trials (RCTs) to assess the association between higher dose of various statins and risk of ICH among patients with CVD. Literature was searched for studies published before June 10, 2015, using electronic database 'PubMed', 'EMBASE', and 'Google Scholar' as well as from many trial databases. The following search terms were used: 'Statin therapy' AND 'Cardiovascular Disease', AND 'Dose' AND 'Intracerebral hemorrhage', AND 'Randomized Controlled Trials' AND 'High Dose Statin'. High dose of statins was defined as atorvastatin 80 mg, simvastatin 80 mg, pravastatin 40 mg, rosuvastatin 20 mg per day. Fixed-effect model was used to estimate the risk ratio (RR) and 95% confidence interval (CI) if heterogeneity was <50%; otherwise, random-effect model was used. Begg's funnel plot was used to assess the publication bias. Seven RCTs involving 31,099 subjects receiving high-dose statin and 31,105 subjects receiving placebo were analyzed in our meta-analysis. A significant risk of ICH was observed in subjects with higher dose of statin (RR = 1.53; 95% CI: 1.16-2.01; P = 0.002). There was no difference in all-cause mortality between the two groups (RR = 0.95; 95% CI: 0.86-1.06; P = 0.36). No publication bias was observed through Begg's funnel plot. Higher dose of statins was found to be associated with the risk of ICH. Future studies are needed to confirm these findings.

Prothrombotic State in Patients With a Left Atrial Appendage Thrombus of Unknown Origin and Cerebrovascular Events

BACKGROUND AND PURPOSE

We hypothesized that formation of left atrial appendage (LAA) thrombi of unknown origin is associated with altered fibrin clot properties and blood hypercoagulability.

METHODS

In a case-control study, we investigated 32 patients with a history of LAA thrombus after successful anticoagulant treatment versus 32 control subjects matched for age, sex, and diabetes mellitus. All subjects had previous ischemic stroke, transient ischemic attack, or migraine associated with patent foramen ovale. Patients with documented atrial fibrillation were excluded. We determined plasma fibrin clot permeability, fibrinolytic efficiency, thrombin generation, platelet and endothelial markers. Stroke or transient ischemic attack were assessed during a median follow-up of 74 (range 19-98) months.

RESULTS

Compared with controls, patients with LAA thrombus more frequently were smokers (43.8% versus 18.8%) and had 20% prolonged clot lysis time, lower plasminogen (-14%), and higher plasminogen activator inhibitor-1 (+17%), thrombin-antithrombin complexes (+17%), CD40 ligand (+30%), P-selectin (+29%), and von Willebrand factor (+30%, all P<0.05). Occurrence of LAA thrombus was predicted by von Willebrand factor (β=0.038, P=0.004), plasminogen (β=-0.048, P=0.01), plasminogen activator inhibitor-1 (β=-0.161, P=0.03), and clot permeability (β=-1.076, P=0.03). During follow-up, cerebrovascular events occurred in 10 (33.33%) of the 30 available patients in the LAA thrombus group, including 7 (23.3%) with recurrent LAA thrombus and 4 (13.33%) with documented atrial fibrillation. Recurrent LAA thrombus was associated with lower baseline Ks and higher thrombin generation, fibrinogen, plasminogen activator inhibitor-1, and soluble CD40 ligand (all P<0.05).

CONCLUSIONS

Prothrombotic blood alterations could be involved in the LAA thrombus formation in patients without documented atrial fibrillation and are associated with increased risk of stroke or transient ischemic attack during follow-up.

Reduced plasma fibrin clot permeability and susceptibility to lysis are associated with increased risk of postthrombotic syndrome

BACKGROUND

The postthrombotic syndrome (PTS) is a severe complication of deep vein thrombosis (DVT). Reduced plasma clot permeability and lysability have been linked to DVT and residual vein obstruction. OBJECTIVES We investigated whether altered fibrin clot properties are associated with the occurrence of PTS.

PATIENTS AND METHODS

Plasma fibrin clot permeability (Ks ) and lysability were investigated in a cohort of 197 consecutive patients aged 18 to 65 years recruited 3 months following the first-ever DVT. Patients with severe thrombophilia or comorbidities known to adversely affect clot phenotype were ineligible.

RESULTS

During a 1-year follow-up PTS developed in 48 (24%) patients, who were characterized by lower Ks , prolonged fibrin clot lysis time (CLT) and slower release of D-dimer from clots (D-Drate ), together with higher plasma D-dimer, C-reactive protein and thrombin-activatable fibrinolysis inhibitor (TAFI). No PTS-associated differences in fibrinogen, thrombin generation, factor VIII, other fibrinolysis proteins and the quality of anticoagulation were observed. Ks (r = -0.71), CLT (r = 0.45), D-Drate (r = -0.30) and TAFI activity (r = 0.38) were associated with the Villalta scale (all P < 0.05). Recurrent VTE occurred also more commonly in PTS patients during follow-up and the 26 (13.2%) patients had lower Ks , longer CLT and lower D-Drate (all P < 0.05). A multivariate model adjusted for age, body mass index, fibrinogen and glucose showed that independent predictors of PTS were idiopathic DVT, plasma D-dimer, Ks , D-Drate , tissue plasminogen activator and TAFI activity.

CONCLUSIONS

This study demonstrates that formation of more compact fibrin clots displaying impaired susceptibility to lysis predisposes to PTS.

Variable Resistance to Plasminogen Activator Initiated Fibrinolysis for Intermediate-Risk Pulmonary Embolism

Background

We examine the clinical significance and biomarkers of tissue plasminogen activator (tPA)-catalyzed clot lysis time (CLT) in patients with intermediate-risk pulmonary embolism (PE).

Methods

Platelet-poor, citrated plasma was obtained from patients with PE. Healthy age- and sex-matched patients served as disease-negative controls. Fibrinogen, α₂-antiplasmin, plasminogen, thrombin activatable fibrinolysis inhibitor (TAFI), plasminogen activator Inhibitor 1 (PAI-1), thrombin time and D-dimer were quantified. Clotting was induced using CaCl₂, tissue factor, and phospholipid. Lysis was induced using 60 ng/mL tPA. Time to 50% clot lysis (CLT) was assessed by both thromboelastography (TEG) and turbidimetry (A405).

Results

Compared with disease-negative controls, patients with PE exhibited significantly longer mean CLT on TEG (+2,580 seconds, 95% CI 1,380 to 3,720 sec). Patients with PE and a short CLT who were treated with tenecteplase had increased risk of bleeding, whereas those with long CLT had significantly worse exercise tolerance and psychometric testing for quality of life at 3 months. A multivariate stepwise removal regression model selected PAI-1 and TAFI as predictive biomarkers of CLT.

Conclusion

The CLT from TEG predicted increased risk of bleeding and clinical failure with tenecteplase treatment for intermediate-risk PE. Plasmatic PAI-1 and TAFI were independent predictors of CLT.