Thrombin generation in acute coronary syndrome and stable coronary artery disease: dependence on plasma factor composition

Inflammation in HIV and Its Impact on Atherosclerotic Cardiovascular Disease

People living with HIV have a 1.5- to 2-fold increased risk of developing cardiovascular disease. Despite treatment with highly effective antiretroviral therapy, people living with HIV have chronic inflammation that makes them susceptible to multiple comorbidities. Several factors, including the HIV reservoir, coinfections, clonal hematopoiesis of indeterminate potential (CHIP), microbial translocation, and antiretroviral therapy, may contribute to the chronic state of inflammation. Within the innate immune system, macrophages harbor latent HIV and are among the prominent immune cells present in atheroma during the progression of atherosclerosis. They secrete inflammatory cytokines such as IL (interleukin)-6 and tumor necrosis-α that stimulate the expression of adhesion molecules on the endothelium. This leads to the recruitment of other immune cells, including cluster of differentiation (CD)8+ and CD4+ T cells, also present in early and late atheroma. As such, cells of the innate and adaptive immune systems contribute to both systemic inflammation and vascular inflammation. On a molecular level, HIV-1 primes the NLRP3 (NLR family pyrin domain containing 3) inflammasome, leading to an increased expression of IL-1β, which is important for cardiovascular outcomes. Moreover, activation of TLRs (toll-like receptors) by HIV, gut microbes, and substance abuse further activates the NLRP3 inflammasome pathway. Finally, HIV proteins such as Nef (negative regulatory factor) can inhibit cholesterol efflux in monocytes and macrophages through direct action on the cholesterol transporter ABCA1 (ATP-binding cassette transporter A1), which promotes the formation of foam cells and the progression of atherosclerotic plaque. Here, we summarize the stages of atherosclerosis in the context of HIV, highlighting the effects of HIV, coinfections, and antiretroviral therapy on cells of the innate and adaptive immune system and describe current and future interventions to reduce residual inflammation and improve cardiovascular outcomes among people living with HIV.

Thrombin as target for prevention of recurrent events after acute coronary syndromes

The mechanism underlying thrombus formation in acute coronary syndrome (ACS) involves both platelets and thrombin. While both pathways are targeted in acute care, platelet inhibition has been predominantly administered in the chronic phase, yet thrombin plays a key role in platelet activation and fibrin formation. Among ACS patients, there is also a persistent chronic increase in thrombin generation, which is associated with a higher rate of adverse events. In the setting of post-ACS care with rivaroxaban or vorapaxar, targeting thrombin has been associated with decreased thrombin generation and reduced cardiovascular events, but has been associated with increased bleeding risk. We explored the evidence supporting thrombin generation in the pathophysiology of recurrent events post-ACS and the role of thrombin as a viable therapeutic target. One specific target is factor XI inhibition, which is involved in thrombin generation, but may also allow for the preservation of normal hemostasis.

Upstream anticoagulation in patients with ST-segment elevation myocardial infarction: a systematic review and meta-analysis

BACKGROUND AND AIM

Parenteral anticoagulation is recommended for all patients presenting with ST-segment elevation myocardial infarction (STEMI) during primary percutaneous coronary intervention (PPCI). Whether upstream anticoagulation improves clinical outcomes is not well established. We conducted a systematic review and meta-analysis of contemporary evidence on parenteral anticoagulation timing for STEMI patients.

METHODS

We performed a systematic search of electronic databases (PubMed, CENTRAL, and Scopus) until December 2022. Studies were eligible if they (a) compared upstream anticoagulation with administration at the catheterization laboratory and (b) enrolled patients with STEMI undergoing PPCI. Efficacy outcomes included in-hospital or 30-day mortality, in-hospital cardiogenic shock (CS), and TIMI flow grade pre- and post-PPCI. Safety outcome was defined as in-hospital or 30-day major bleeding.

RESULTS

Overall, seven studies were included (all observational), with a total of 69,403 patients. Upstream anticoagulation was associated with a significant reduction in the incidence of in-hospital or 30-day all-cause mortality (OR 0.61; 95% CI 0.45-0.81; p < 0.001) and in-hospital CS (OR 0.68; 95% CI 0.58-0.81; p < 0.001) and with an increase in spontaneous reperfusion (pre-PPCI TIMI > 0: OR 1.46; 95% CI 1.35-1.57; p < 0.001). Pretreatment was not associated with an increase in major bleeding (OR 1.02; 95% CI 0.70-1.48; p = 0.930).

CONCLUSIONS

Upstream anticoagulation was associated with a significantly lower risk of 30-day all-cause mortality, incidence of in-hospital CS, and improved reperfusion of the infarct-related artery (IRA). These findings were not accompanied by an increased risk of major bleeding, suggesting an overall clinical benefit of early anticoagulation in STEMI. These results require confirmation in a dedicated randomized clinical trial.

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.

Thrombin generation assays to personalize treatment in bleeding and thrombotic diseases

Treatment of bleeding and thrombotic disorders is highly standardized and based on evidence-based medicine guidelines. These evidence-based treatment schemes are well accepted but may lead to either insufficient treatment or over-dosing, because the individuals' hemostatic properties are not taken into account. This can potentially introduce bleeding or thrombotic complications in individual patients. With the incorporation of pharmacokinetic (PK) and pharmacodynamic (PK-PD) parameters, based on global assays such as thrombin generation assays (TGAs), a more personalized approach can be applied to treat either bleeding or thrombotic disorders. In this review, we will discuss the recent literature about the technical aspects of TGAs and the relation to diagnosis and management of bleeding and thrombotic disorders. In patients with bleeding disorders, such as hemophilia A or factor VII deficiency, TGAs can be used to identify patients with a more severe bleeding phenotype and also in the management with non-replacement therapy and/or bypassing therapy. These assays have also a role in patients with venous thrombo-embolism, but the usage of TGAs in patients with arterial thrombosis is less clear. However, there is a potential role for TGAs in the monitoring of (long-term) antithrombotic therapy, for example with the use of direct oral anticoagulants. Finally this review will discuss controversies, limitations and knowledge gaps in relation to the introduction of TGAs to personalize medicine in daily medical practice.

A System-Wide Investigation and Stratification of the Hemostatic Proteome in Premature Myocardial Infarction

Introduction

Advancing understanding of key factors that determine the magnitude of the hemostatic response may facilitate the identification of individuals at risk of generating an occlusive thrombus as a result of an atherothrombotic event such as an acute Myocardial Infarction (MI). While fibrinogen levels are a recognized risk factor for MI, the association of thrombotic risk with other coagulation proteins is inconsistent. This is likely due to the complex balance of pro- and anticoagulant factors in any individual.

Methods

We compared measured levels of pro- and anticoagulant proteins in plasma from 162 patients who suffered an MI at an early age (MI <50 y) and 186 age- and gender-matched healthy controls with no history of CAD. We then used the measurements from these individuals as inputs for an established mathematical model to investigate how small variations in hemostatic factors affect the overall amplitude of the hemostatic response and to identify differential key drivers of the hemostatic response in male and female patients and controls.

Results

Plasma from the MI patients contained significantly higher levels of Tissue Factor (P = 0.007), the components of the tenase (FIX and FVIII; P < 0.0001 for both) and the prothrombinase complexes (FX; P = 0.003), and lower levels of Tissue Factor Pathway Inhibitor (TFPI; P = 0.033) than controls. The mathematical model, which generates time-dependent predictions describing the depletion, activation, and interaction of the main procoagulant factors and inhibitors, identified different patterns of hemostatic response between MI patients and controls, and additionally, between males and females. Whereas, in males, TF, FVIII, FIX, and the inhibitor TFPI contribute to the differences seen between case and controls, and in females, FII, FVIII, and FIX had the greatest influence on the generation of thrombin. We additionally show that further donor stratification may be possible according to the predicted donor response to anticoagulant therapy.

Conclusions

We suggest that modeling could be of value in enhancing our prediction of risk of premature MI, recurrent risk, and therapeutic efficacy.

Clinical use of thrombin generation assays

Determining patient's coagulation profile, i.e. detecting a bleeding tendency or the opposite, a thrombotic risk, is crucial for clinicians in many situations. Routine coagulation assays and even more specialized tests may not allow a relevant characterization of the hemostatic balance. In contrast, thrombin generation assay (TGA) is a global assay allowing the dynamic continuous and simultaneous recording of the combined effects of both thrombin generation and thrombin inactivation. TGA thus reflects the result of procoagulant and anticoagulant activities in blood and plasma. Because of this unique feature, TGA has been widely used in a wide array of settings from both research, clinical and pharmaceutical perspectives. This includes diagnosis, prognosis, prophylaxis, and treatment of inherited and acquired bleeding and thrombotic disorders. In addition, TGA has been shown to provide relevant information for the diagnosis of coagulopathies induced by infectious diseases, comprising also disturbance of the coagulation system in COVID-19, or for the assessment of early recurrence in breast cancer. This review article aims to document most clinical applications of TGA.

Plasmatic Coagulation Capacity Correlates With Inflammation and Abacavir Use During Chronic HIV Infection

BACKGROUND

D-dimer concentrations in people living with HIV (PLHIV) on combination antiretroviral therapy (cART) are increased and have been linked to mortality. D-dimer is a biomarker of in vivo coagulation. In contrast to reports on D-dimer, data on coagulation capacity in PLHIV are conflicting. In this study, we assessed the effect of cART and inflammation on coagulation capacity.

SETTING

We explored coagulation capacity using calibrated thrombin generation (TG) and linked this to persistent inflammation and cART in a cross-sectional study including PLHIV with viral suppression and uninfected controls.

METHODS

We used multivariate analyses to identify independent factors influencing in vivo coagulation (D-dimer) and ex vivo coagulation capacity (TG).

RESULTS

Among 208 PLHIV, 94 (45%) were on an abacavir-containing regimen. D-dimer levels (219.1 vs 170.5 ng/mL, P = 0.001) and inflammatory makers (sCD14, sCD163, and high-sensitive C-reactive protein) were increased in PLHIV compared with those in controls (n = 56). PLHIV experienced lower TG (reflected by endogenous thrombin potential [ETP]) when compared with controls, after correction for age, sex, and antiretroviral therapy. Abacavir use was independently associated with increased ETP. Prothrombin concentrations were strongly associated with ETP and lower in PLHIV on a non-abacavir-containing regimen compared with those in controls, suggesting consumption as a possible mechanism for HIV-associated reduction in TG. D-dimer concentrations were associated with inflammation, but not TG.

CONCLUSIONS

Abacavir use was associated with increased TG and could serve as an additional factor in the reported increase in thrombotic events during abacavir use. Increased exposure to triggers that propagate coagulation, such as inflammation, likely underlie increased D-dimer concentrations found in most PLHIV.

Patients with acute and chronic coronary syndromes have elevated long-term thrombin generation

Coronary artery disease is a leading cause of morbidity and mortality worldwide. Despite significant advances in revascularization strategies and antiplatelet therapy with aspirin and/or P2Y₁₂ receptor antagonist, patients with acute coronary syndrome (ACS) continue to be at long-term risk of further cardiovascular events. Besides platelet activation, the role of thrombin generation (TG) in atherothrombotic complications is widely recognized. In this study, we hypothesized that there is an elevation of coagulation activation persists beyond 12 months in patients with ACS and chronic coronary syndrome (CCS) when compared with healthy controls. We measured TG profiles of patients within 72 h after percutaneous coronary intervention, at 6-month, 12-month and 24-month. Our results demonstrated that TG of patients with ACS (n = 114) and CCS (n = 40) were persistently elevated when compared to healthy individuals (n = 50) in peak thrombin (ACS 273.1 nM vs CCS 287.3 nM vs healthy 234.3 nM) and velocity index (ACS 110.2 nM/min vs CCS 111.0 nM/min vs healthy 72.9 nM/min) at 24-month of follow-up. Our results suggest a rationale for addition of anticoagulation to antiplatelet therapy in preventing long-term ischemic events after ACS. Further research could clarify whether the use of TG parameters to enable risk stratification of patients at heightened long-term procoagulant risk who may benefit most from dual pathway inhibition.

Role of thrombin generation assays in the diagnosis of acute myocarditis and non-ST myocardial infarction

Myocarditis and myocardial infarction share a common clinical characteristics despite significant differences in etiology and pathogenesis. Current guidelines recommend using cardiac magnetic resonance imaging (MRI) or endocardial biopsy for a definite diagnosis; however, these guidelines are not fully implemented due to the high cost and low availability. We used a thrombin generation assay and simple blood test to characterize both diseases. We conducted a cross-sectional study from April to December 2018. Patients with initial clinical suspicions of non-ST elevation myocardial infarction (NSTEMI) or myocarditis were eligible. All patients were recruited prior to anticoagulant treatment. Patients in both groups underwent acceptable standard clinical evaluation. Twenty-eight patients were enrolled; 12 patients in the NSTEMI group and 16 in the myocarditis group. Patients in the NSTEMI group were significantly older than those in the myocarditis group (64.25 ± 9.67 vs. 37.94 ± 19.66 years, p < 0.01, respectively) with a higher prevalence of hyperlipidemia, diabetes mellitus, and ischemic heart disease (p < 0.01 for all). There was no difference between the groups regarding INR, PT, aPTT, and serum levels of creatinine, urea, CPK, troponin, and fibrinogen. Endogenous thrombin potential (ETP), which represents the total thrombin concentration in the plasma, was significantly higher in the myocarditis group than in the NSTEMI group (2091.88 ± 336.41 vs. 1860.75 ± 438.02 nM × min, p < 0.03). Myocarditis and myocardial infarction have a different pattern of thrombin generation Thrombogram. The myocarditis group had significantly higher plasma ETP than the NSTEMI group. This finding requires further evaluation to define a numerical threshold, thus avoiding invasive or expensive assessment of myocarditis.

Predictive value of combining the level of fibrinogen and antithrombin III for contrast-induced nephropathy in coronary artery disease patients undergoing percutaneous coronary intervention

Contrast-induced nephropathy (CIN) is a common adverse event in the diagnosis and treatment of coronary intervention. The current study investigated the predictive effect of preoperative fibrinogen (FIB) combined with antithrombin III (AT-III) on CIN following percutaneous coronary intervention (PCI). A total of 394 patients who underwent PCI between October 2018 and May 2019 were selected for the present study. Pre-procedural FIB levels and AT-III activity were measured before PCI. CIN was defined as a 0.5 mg/dl or 25% increase in serum creatinine levels 48 to 72 h after exposure to a radiocontrast agent. Patients were classified into CIN and non-CIN groups. CIN occurred in 48 (12.2%) patients. The serum FIB levels were significantly higher in patients who developed CIN compared with those who did not develop CIN. In addition, AT-III levels ≤89.5% were associated with higher rates of CIN. Logistical regression analysis showed that high FIB, and low AT-III and albumin levels were high-risk factors associated with CIN. For FIB, the area under the receiver operating characteristic curve (AUC) for predicting CIN was 0.653. The optimal cut-off value was 3.48 g/l with a sensitivity of 45.8% and a specificity of 79.7% [95% confidence interval (CI): 0.603-0.701; P=0.0002)]. For AT-III, the AUC was 0.711, and the optimal cut-off value was 89.5%, with a sensitivity of 81.3% and specificity of 58.2% (95% CI: 0.659-0.758; P<0.0001). When combining FIB and AT-III, the AUC was 0.747. The optimal cut-off value was 0.090424, with a diagnostic sensitivity of 93.8% and specificity of 46.6% (95% CI: 0.697-0.792; P<0.0001). The results showed that FIB combined with AT-III resulted in improved predictive accuracy of CIN (FIB vs. AT-III, AUC=0.653 vs. 0.711, P=0.292; FIB vs. FIB + AT-III, AUC=0.653 vs. 0.747, P=0.012; AT-III vs. FIB + AT-III, AUC=0.711 vs. 0.747, P=0.138). Pre-procedural levels of FIB, AT-III and albumin were independently associated with an increased risk of CIN. Furthermore, the results suggested that the combination of FIB and AT-III was a better predictor of CIN after PCI.

Pharmacodynamic Effects of Vorapaxar in Prior Myocardial Infarction Patients Treated With Potent Oral P2Y12 Receptor Inhibitors With and Without Aspirin: Results of the VORA-PRATIC Study

Background Vorapaxar as an adjunct to dual antiplatelet therapy (DAPT) reduces thrombotic events in patients with prior myocardial infarction at the expense of increased bleeding. Withdrawal of aspirin has emerged as a bleeding reduction strategy. The pharmacodynamic effects of vorapaxar with potent P2Y12 inhibitors as well as the impact of dropping aspirin is unexplored and represented the aim of the VORA-PRATIC (Vorapaxar Therapy in Patients With Prior Myocardial Infarction Treated With Newer Generation P2Y12 Receptor Inhibitors Prasugrel and Ticagrelor) study. Methods and Results Post-myocardial infarction patients (n=130) on standard DAPT (aspirin+prasugrel or ticagrelor) were randomized to 1 of 3 arms: (1) triple therapy: aspirin+prasugrel/ticagrelor+vorapaxar; (2) dual therapy (drop aspirin): prasugrel/ticagrelor+vorapaxar; (3) DAPT: aspirin+prasugrel/ticagrelor. Pharmacodynamic assessments were performed at 3 time points (baseline and 7 and 30 days). Vorapaxar reduced CAT (collagen-ADP-TRAP)-induced platelet aggregation, a marker of platelet-mediated global thrombogenicity (triple therapy versus DAPT at 30 days: mean difference=-27; 95% CI,-35 to -19; P<0.001; primary end point). This effect was attenuated but still significant in the absence of aspirin (dual therapy versus DAPT at 30 days: mean difference=-15; 95% CI,-23 to -7; P<0.001; between-group comparisons, P<0.05). Vorapaxar abolished TRAP-induced aggregation (P<0.001), without affecting thrombin generation and clot strength. There were no differences in markers of P2Y12 reactivity. Markers sensitive to aspirin-induced effects increased (P<0.001) in the dual-therapy arm. Conclusions In post-myocardial infarction patients treated with potent P2Y12 inhibitors, vorapaxar reduces platelet-driven global thrombogenicity, an effect that persisted, albeit attenuated, in the absence of aspirin and without affecting markers of P2Y12 reactivity or clot kinetics. The clinical implications of these PD observations warrant future investigation. Registration URL: https://www.clini​caltr​ials.gov. Unique identifier: NCT02545933.

Dual-pathway inhibition for secondary and tertiary antithrombotic prevention in cardiovascular disease

Advances in antiplatelet therapies for patients with cardiovascular disease have improved patient outcomes over time, but the challenge of balancing the risks of ischaemia and bleeding remains substantial. Moreover, many patients with cardiovascular disease have a residual risk of ischaemic events despite receiving antiplatelet therapy. Therefore, novel strategies are needed to prevent clinical events through mechanisms beyond platelet inhibition and with an acceptable associated risk of bleeding. The advent of non-vitamin K antagonist oral anticoagulants, which attenuate fibrin formation by selective inhibition of factor Xa or thrombin, has renewed the interest in dual-pathway inhibition strategies that combine an antiplatelet agent with an anticoagulant drug. In this Review, we highlight the emerging pharmacological rationale and clinical development of dual-pathway inhibition strategies for the prevention of atherothrombotic events in patients with different manifestations of cardiovascular disease, such as coronary artery disease, cerebrovascular disease and peripheral artery disease.

Predictive value of combining the level of lipoprotein-associated phospholipase A2 and antithrombin III for acute coronary syndrome risk

The aim of the present study was to observe the role of lipoprotein-associated phospholipase A2 (Lp-PLA2) and antithrombin III (AT-III) in patients with acute coronary syndrome (ACS), and the combination of Global Registry of Acute Coronary Events (GRACE) score to determine the value of coronary heart disease risk stratification. A total of 309 patients admitted to the Affiliated Hospital of Xuzhou Medical University were enrolled. The patients were divided into two groups: The ACS (183 cases) and control (126 cases) groups. Blood levels of Lp-PLA2 and AT-III were measured. Based on GRACE score, the patients with ACS were divided into three subgroups: Low risk (GRACE score ≤108), middle risk (GRACE score 109-140) and high risk (GRACE score >140). The levels of Lp-PLA2 and AT-III were compared among different groups, and based on Gensini score, patients with ACS were divided into four groups by quartiles. Lp-PLA2 levels in the ACS group were significantly increased compared with the control group (P<0.05), but the AT-III levels were decreased compared with the control group (P<0.05). In the ACS group, Lp-PLA2 levels increased sequentially from the low risk to high risk subgroups (all P<0.05); compared with the low risk and middle risk subgroups, the AT-III activity levels were decreased in the high risk subgroup, and the Gensini scores were increased (all P<0.05). In the ACS group, with the increase of Gensini scores, the levels of Lp-PLA2 and AT-III exhibited increasing and decreasing trends, respectively (P<0.05). The logistic regression model demonstrated that Lp-PLA2 [odds ratio (OR) =1.077; P<0.001]; and GRACE score (OR=1.026; P=0.028) were risk factors, while AT-III was a protective factor (OR=0.958; P=0.012) for ACS. Correlation analysis indicated a positive association of Lp-PLA2 level with Gensini scores (r=0.52; P<0.01) and GRACE score (r=0.48; P<0.01), and a negative association between AT-III level and Gensini scores (r=-0.25; P<0.01) and GRACE scores (r=-0.34; P<0.01). The levels of Lp-PLA2 and AT-III exhibited predictive values in patients with ACS, and are associated with the severity of coronary artery stenosis.

Next-generation rapid serum tube technology using prothrombin activator coagulant: fast, high-quality serum from normal samples

Background

Incomplete blood clotting or latent clotting in serum is a common laboratory problem, especially for patients on anticoagulant therapy or when serum tubes are centrifuged before clotting is completed. We describe a novel approach to producing high-quality serum using snake venom prothrombin activator complex (OsPA) as an additive in blood collection tubes for non-anticoagulated (normal) individuals.

Methods

Plasma clotting assays were performed using a Hyland-Clotek instrument. Blood clotting was visually observed, and thromboelastography was also performed to determine the important parameters of coagulation. Thrombin generation was assayed using the chromogenic substrate S-2238, and biochemical analytes in the serum were determined on chemistry and immunoassay analysers. Fibrinogen was determined by either ELISA or Clauss fibrinogen assay.

Results

We initially showed that OsPA had strong coagulation activity in clotting not only recalcified citrated plasma and recalcified citrated whole blood, but also fresh whole blood in a clinical setting. The use of TEG clearly showed improved speed of clotting and generation of a firmer clot. We also showed that the use of OsPA to produce serum did not interfere with the determination of commonly measured biochemical analytes. The underlying clotting mechanism involves a burst of thrombin production at the initial stages of the clotting process upon contact with prothrombin in blood.

Conclusions

These results demonstrate rapid generation of high-quality serum, contributing to faster turnaround times with standardised quality samples, for accurate analyte determinations in normal individuals.

In silico thrombin generation: Plasma composition imbalance and mortality in human immunodeficiency virus

Background

Effective HIV treatment with antiretroviral therapy has prolonged survival and shifted causes of death to non-AIDS illnesses such as cardiovascular disease. We have shown that inflammation and HIV viral load associate with pro- and anticoagulant factor imbalances resulting in increased thrombin generation when mathematically modeled. We explore the hypothesis that factor compositional imbalance, corresponding to increased in silico thrombin generation, predicts mortality among HIV+ persons.

Methods

In a nested case-control study of HIV+ individuals on continuous antiretroviral therapy in two large trials, we evaluated cases (any non-violent mortality, n = 114) and matched controls (n = 318). Thrombin generation in response to a tissue-factor initiator for each individual was calculated by a mathematical model incorporating levels of factors (F)II, V, VII, VIII, IX, X, antithrombin, tissue factor pathway inhibitor, and protein C (PC) measured at study entry to the trials. In silico thrombin generation metrics included clot time, maximum rate (MaxR), maximum level (MaxL), and area under the curve (AUC).

Results

Levels of antithrombin and PC decreased, while FV and FVIII were higher in cases vs controls. This resulted in a more procoagulant phenotype with increased MaxR, MaxL, and AUC in cases compared to controls (P < 0.05 for all).

Conclusions

Antithrombin, FV, FVIII, and PC were the major contributors to the increased thrombin generation associated with mortality risk. Our results suggest that mortality in HIV is associated with an increase in in silico thrombin generation via altered balance of pro- and anticoagulant factors, likely due to an inflammatory response signal, and resulting coagulopathy.

Association of FV G1691A Polymorphism but not A4070G With Coronary Artery Disease

Coronary artery disease (CAD) is one of the chief causes of death in the world. Several hypotheses have been promoted as for the origin of the disease, among which are genetic predispositions and/or environmental factors. The aim of this study was to determine the effect of factor V (FV) gene polymorphisms (Leiden, G1691A [FVL] and HR2 A4070G) and to analyze their association with traditional risk factors in assessing the risk of CAD. Our study population included 200 Tunisian patients with symptomatic CAD and a control group of 300 participants matched for age and sex. All participants were genotyped for the FVL and HR2 polymorphisms. Multivariate logistic regression was applied to analyze independent factors associated with the risk of CAD. Our analysis showed that the FVL A allele frequency (P < 10^–3, odds ratio [OR] = 2.81, 95% confidence interval [CI] = 1.6-4.9) and GA genotype (P < 10^–3, OR = 4.03, 95% CI = 2.1-7.6) are significantly more prevalent among patients with CAD compared to those controls and may be predisposing to CAD. We further found that the FVL mutation is an independent risk factor whose effect is not modified by other factors (smoking, diabetes, hypertension, dyslipidemia, and a family history of CAD) in increasing the risk of the disease. However, analysis of FV HR2 variation does not show any statistically significant association with CAD. The FVL polymorphism may be an independent risk factor for CAD. However, further investigations on these polymorphisms and their possible synergisms with traditional risk factors for CAD could help to ascertain better predictability for CAD susceptibility.

Antithrombotic efficacy of bivalirudin compared to unfractionated heparin during percutaneous coronary intervention for acute coronary syndrome

Bivalirudin is associated with an increased risk of acute stent thrombosis (AST) compared to unfractionated heparin (UFH) in acute coronary syndrome patients (ACS) during short-duration percutaneous coronary intervention (PCI). The mechanisms involved are unknown. We aimed to investigate the antithrombotic efficacy of bivalirudin compared to UFH during PCI. In a monocenter study, we prospectively enrolled 30 patients undergoing PCI for a non-ST elevation ACS. They were randomly assigned to a single intravenous (IV) bolus of UFH (70 IU/kg) or an IV bolus of bivalirudin 0.75 mg/kg followed by a 1.75 mg/kg/h infusion during PCI. All patients received a loading dose (LD) of 180 mg of ticagrelor at the time of PCI. The VASP index and activated partial thromboplastin time (aPTT) were used to assess the course of platelet reactivity (PR) and antithrombotic activity. The two groups were similar regarding baseline, angiographic, and interventional characteristics. There was no difference between the two groups in the course of PR following ticagrelor LD. An optimal PR inhibition was obtained 4 h after the LD of ticagrelor. The level of antithrombotic activity was significantly lower in the bivalirudin group compared to the UFH group (p < 0.001) during PCI but similar at 2 and 4 h post-PCI. We observed that, in ACS undergoing PCI, the antithrombotic efficacy of an IV bolus of bivalirudin is significantly lower than that of a 70-IU/kg UFH bolus. This could contribute to the excess in thrombotic acute events observed during short-duration PCI.

Thrombin generation assays for global evaluation of the hemostatic system: perspectives and limitations

The existing techniques to evaluate hemostasis in clinical laboratories are not sensitive enough to detect hypercoagulable and mild hypocoagulable states. Under different experimental conditions, the thrombin generation test may meet these requirements. This technique evaluates the overall balance between procoagulant and anticoagulant forces and has provided new insights in our understanding of the coagulation cascade, as well as of the diagnosis of hypocoagulability and hypercoagulability conditions. Thrombin generated in the thrombin generation test can be quantified as platelet-rich or platelet-poor plasma using the calibrated automated thrombogram method, which monitors the cleavage of a fluorogenic substrate that is simultaneously compared to the known thrombin activity in a non-clotting plasma sample. The calibrated automated thrombogram method is an open system, in which different antibodies, proteins, enzymes and peptides can be introduced to answer specific questions regarding hemostatic processes. The thrombin generation test has great clinical potential, such as in monitoring patients taking anticoagulants and antiplatelet drugs, screening for genetic or acquired thrombotic disorders, and evaluating bleeding risk control in patients with hemophilia using bypass agents or replacement therapy. Different to conventional coagulation tests, the thrombin generation test can be used for an overall evaluation of hemostasis, the results of which can then be used to evaluate specific characteristics of hemostasis, such as prothrombin time, activated partial thromboplastin time, and levels of fibrinogen and other coagulation factors. The introduction of this method will contribute to a better understanding and evaluation of overall hemostatic processes; however, this method still requires standardization and clinical validation.

Increased plasma thrombin potential is associated with stable coronary artery disease: An angiographically-controlled study

INTRODUCTION

Coagulation plays a crucial role in coronary artery disease (CAD) contributing to both atherosclerotic plaque development and acute thrombotic complications, like myocardial infarction (MI). Coagulation biomarkers have been linked with ischemic heart disease, but results are still controversial.

MATERIALS AND METHODS

D-dimer and thrombin generation, two "overall" coagulation assays, were evaluated in 775 subjects with or without angiographically-proven CAD (170 CAD-free and 605 CAD, 355 of whom with history of previous MI). Subjects taking anticoagulant drugs or with any acute illness were excluded. D-dimer plasma concentration was determined by an immuno-turbidimetric assay. Thrombin generation was assessed as the ability of plasma to generate thrombin triggered by the addition of tissue factor ex-vivo by means of a chromogenic method.

RESULTS

Both D-dimer and thrombin generation parameters were associated with several traditional cardiovascular risk factors. Lag-time, time-to-peak, peak height, and Endogenous Thrombin Potential (ETP), as well as D-dimer levels, were higher in CAD patients than in CAD-free subjects. After adjustment for all the traditional risk factors, only ETP levels remained significantly associated with CAD (the highest versus the lowest tertile: OR 2.61 with 95%CI 1.14-5.99), but without improvement of C-statistic. The association of D-dimer vanished after adjustment for inflammatory markers. No difference of either D-dimer or thrombin generation parameters was found between CAD patients with or without previous MI history.

CONCLUSIONS

Our results suggest that an increased plasma thrombin potential is characteristic in patients with clinically stable CAD, irrespective of previous MI history and independent of traditional cardiovascular risk factors.

"One-Time" versus Staged Multivessel Intervention in Intermediate to Very High-Risk Patients with Non-ST-Segment Elevation Acute Coronary Syndromes

Background and Objectives

To compare clinical outcomes of staged versus "one-time" percutaneous coronary intervention (PCI) in intermediate to very high-risk patients with non–ST-segment elevation acute coronary syndromes (NSTE-ACS) and multivessel coronary disease (MVD).

Subjects and Methods

1531 NSTE-ACS patients with multivessel PCI and meeting the criteria of intermediate to very high risk were screened from a prospectively registered database obtained from General Hospital of Shenyang Military Region between 2008 and 2012. They were categorized into "one-time" PCI (n=859) and staged PCI (n=672) according to intervention strategy. The primary outcomes included a 3-year major adverse cardiac event (MACE), a composite of cardiac death, myocardial infarction (MI), and target vessel revascularization.

Results

At 3 years, no significant differences in MACE (20.8% vs. 19.7%, p=0.608) and cardiac death/MI (7.1% vs. 9.1%, p=0.129) were observed between the two groups. After propensity score matching, there was no statistical significance in MACE (18.9% vs. 21.8%, p=0.249); whereas cardiac death/MI was significantly lower in the staged PCI group (7.0% vs.11.1%, p=0.033). Ninety-day landmark analysis showed that the staged PCI group had a lower 90-day incidence of MACE (1.2% vs. 3.3%, p= 0.037) and cardiac death/MI (0.7% vs. 2.6%, p=0.031). For the 90-day to 3-year follow-up period, the incidences of MACE (17.9% vs. 19.1%, p=0.641) and cardiac death/MI (6.3% vs. 8.7%, p=0.191) were similar in both groups.

Conclusion

In intermediate- to very high-risk NSTE-ACS patients with MVD, staged PCI is superior to "one-time" PCI in terms of cardiac death/MI.

Potential mechanism of acute stent thrombosis with bivalirudin following percutaneous coronary intervention in acute coronary syndromes

BACKGROUND

Clinical trials have demonstrated an excess of acute stent thrombosis (AST) in acute coronary syndromes patients (ACS) undergoing percutaneous coronary intervention (PCI) with bivalirudin compared to heparin. We aimed to investigate the potential mechanisms responsible for thrombus formation under bivalirudin.

METHODS

We compared heparin and bivalirudin during PCI for ACS in a prospective monocentre randomized study. Twenty patients were included after coronary angiography and received a loading dose (LD) of 180mg of ticagrelor at the time of PCI. They were randomly assigned to heparin (70UI/kg) intra-venous (IV) bolus or bivalirudin IV bolus of 0.75mg/kg followed by an infusion of 1.75mg/kg/h until the end of the PCI. The VASP index and thrombin generation test were used to assess the course of platelet reactivity (PR) and thrombin generation.

RESULTS

Thrombin generation and PR were identical in both groups at baseline. There was no difference in the course of PR following the LD over time. An optimal PR inhibition was reached 4h after the LD of ticagrelor. Heparin and bivalirudin infusion effectively inhibited thrombin generation during PCI. However, 4h after the end of bivalirudin infusion, thrombin generation had returned to its baseline value whereas in the heparin group it remained significantly inhibited compared to baseline and to the bivalirudin group 4h after the end of the infusion (p<0.01 and p<0.02 respectively).

CONCLUSIONS

The present study suggests that the short half-life of bivalirudin and the quick restoration of thrombin activity at a time when optimal PR is not reached may be responsible for acute stent thrombosis. Clinicaltrial.gov: NCT02428725.

Random Forests Are Able to Identify Differences in Clotting Dynamics from Kinetic Models of Thrombin Generation

Current methods for distinguishing acute coronary syndromes such as heart attack from stable coronary artery disease, based on the kinetics of thrombin formation, have been limited to evaluating sensitivity of well-established chemical species (e.g., thrombin) using simple quantifiers of their concentration profiles (e.g., maximum level of thrombin concentration, area under the thrombin concentration versus time curve). In order to get an improved classifier, we use a 34-protein factor clotting cascade model and convert the simulation data into a high-dimensional representation (about 19000 features) using a piecewise cubic polynomial fit. Then, we systematically find plausible assays to effectively gauge changes in acute coronary syndrome/coronary artery disease populations by introducing a statistical learning technique called Random Forests. We find that differences associated with acute coronary syndromes emerge in combinations of a handful of features. For instance, concentrations of 3 chemical species, namely, active alpha-thrombin, tissue factor-factor VIIa-factor Xa ternary complex, and intrinsic tenase complex with factor X, at specific time windows, could be used to classify acute coronary syndromes to an accuracy of about 87.2%. Such a combination could be used to efficiently assay the coagulation system.

Platelet thrombin receptor antagonism with vorapaxar: pharmacology and clinical trial development

Oral antiplatelet therapies for secondary prevention of ischemic recurrences in patients with atherosclerotic disease manifestations include aspirin and P2Y12 receptor antagonists. Despite the use of these therapies, patients remain at risk for recurrent ischemic events, which may be attributed to other platelet signaling pathways which continue to be activated. More intense antithrombotic strategies have been investigated, including identifying additional targets to modulate platelet activation. Among these, thrombin-mediated platelet activation through PAR-1 has been subject to broad clinical investigation. Vorapaxar is the only PAR-1 receptor antagonists that completed large-scale clinical investigations and is approved for clinical use. This manuscript provides an overview of the pharmacology and clinical trial development of vorapaxar as well as its role in clinical practice.

Blood coagulation and fibrinolysis in aortic valve stenosis: links with inflammation and calcification

Aortic valve stenosis (AS) increasingly afflicts our aging population. However, the pathobiology of the disease is still poorly understood and there is no effective pharmacotherapy for treating those at risk for clinical progression. The progression of AS involves complex inflammatory and fibroproliferative processes that resemble to some extent atherosclerosis. Accumulating evidence indicates that several coagulation proteins and its inhibitors, including tissue factor, tissue factor pathway inhibitor, prothrombin, factor XIII, von Willebrand factor, display increased expression within aortic stenotic valves, predominantly on macrophages and myofibroblasts around calcified areas. Systemic impaired fibrinolysis, along with increased plasma and valvular expression of plasminogen activator inhibitor-1, has also been observed in patients with AS in association with the severity of the disease. There is an extensive cross-talk between inflammation and coagulation in stenotic valve tissue which contributes to the calcification and mineralisation of the aortic valve leaflets. This review summarises the available data on blood coagulation and fibrinolysis in AS with the emphasis on their interactions with inflammation and calcification.

Modeling thrombin generation: plasma composition based approach

Thrombin has multiple functions in blood coagulation and its regulation is central to maintaining the balance between hemorrhage and thrombosis. Empirical and computational methods that capture thrombin generation can provide advancements to current clinical screening of the hemostatic balance at the level of the individual. In any individual, procoagulant and anticoagulant factor levels together act to generate a unique coagulation phenotype (net balance) that is reflective of the sum of its developmental, environmental, genetic, nutritional and pharmacological influences. Defining such thrombin phenotypes may provide a means to track disease progression pre-crisis. In this review we briefly describe thrombin function, methods for assessing thrombin dynamics as a phenotypic marker, computationally derived thrombin phenotypes versus determined clinical phenotypes, the boundaries of normal range thrombin generation using plasma composition based approaches and the feasibility of these approaches for predicting risk.

Inflammatory role and prognostic value of platelet chemokines in acute coronary syndrome

Activated platelets and neutrophils exacerbate atherosclerosis. Platelets release the chemokines CXCL4, CXCL4L1 and CCL5, whereas myeloperoxidase (MPO) and azurocidin are neutrophil-derived. We investigated whether plasma levels of these platelet and neutrophil mediators are affected by the acute coronary syndrome (ACS), its medical treatment, concomitant clinical or laboratory parameters, and predictive for the progression of coronary artery disease (CAD). In an observational study, the association of various factors with plasma concentrations of platelet chemokines and neutrophil mediators in 204 patients, either upon admission with ACS and 6 hours later or without ACS or CAD, was determined by multiple linear regression. Mediator release was further analysed after activation of blood with ACS-associated triggers such as plaque material. CXCL4, CXCL4L1, CCL5, MPO and azurocidin levels were elevated in ACS. CXCL4 and CCL5 but not CXCL4L1 or MPO were associated with platelet counts and CRP. CXCL4 (in association with heparin treatment) and MPO declined over 6 hours during ACS. Elevated CCL5 was associated with a progression of CAD. Incubating blood with plaque material, PAR1 and PAR4 activation induced a marked release of CXCL4 and CCL5, whereas CXCL4L1 and MPO were hardly or not altered. Platelet chemokines and neutrophil products are concomitantly elevated in ACS and differentially modulated by heparin treatment. CCL5 levels during ACS predict a progression of preexisting CAD. Platelet-derived products appear to dominate the inflammatory response during ACS, adding to the emerging evidence that ACS per se may promote vascular inflammation.

Massive exploration of perturbed conditions of the blood coagulation cascade through GPU parallelization

The introduction of general-purpose Graphics Processing Units (GPUs) is boosting scientific applications in Bioinformatics, Systems Biology, and Computational Biology. In these fields, the use of high-performance computing solutions is motivated by the need of performing large numbers of in silico analysis to study the behavior of biological systems in different conditions, which necessitate a computing power that usually overtakes the capability of standard desktop computers. In this work we present coagSODA, a CUDA-powered computational tool that was purposely developed for the analysis of a large mechanistic model of the blood coagulation cascade (BCC), defined according to both mass-action kinetics and Hill functions. coagSODA allows the execution of parallel simulations of the dynamics of the BCC by automatically deriving the system of ordinary differential equations and then exploiting the numerical integration algorithm LSODA. We present the biological results achieved with a massive exploration of perturbed conditions of the BCC, carried out with one-dimensional and bi-dimensional parameter sweep analysis, and show that GPU-accelerated parallel simulations of this model can increase the computational performances up to a 181× speedup compared to the corresponding sequential simulations.

Thrombin generation and platelet reactivity at hospital discharge and 6-month outcome after the acute coronary syndrome in diabetic and nondiabetic patients

OBJECTIVES

Increased plasma thrombogenesis and blood platelet reactivity are associated with a worse outcome in patients with the acute coronary syndrome (ACS). The aim of this study was to test the clinical utility of combining a thrombin generation test and platelet aggregation in predicting future ischemic events after ACS.

METHODS

The study included patients hospitalized due to ST-elevation myocardial infarction (STEMI) treated with primary percutaneous coronary intervention with stent implantation. Blood for platelet aggregation and thrombin generation was collected at hospital discharge. We performed whole-blood platelet aggregation with arachidonic acid (AA), collagen, adenosine diphosphate and thrombin receptor-activating peptide (TRAP) as agonists and the thrombin generation test using a fluorescence method. Patients were followed for up to 6 months. The combined end point of the study consisted of death, stroke, myocardial infarction or repeated target vessel revascularization.

RESULTS

The study enrolled 161 patients. The end point occurred in 30 patients (18.6%). Thrombin generation showed a significantly prolonged lag time, time to thrombogram peak and start of the tail of the thrombogram in diabetic patients who reached the study end point but not in nondiabetics. End point occurrence was not connected with platelet reactivity at hospital discharge in the whole group. In the diabetic subgroup, increased platelet aggregation induced with AA and TRAP at hospital discharge was connected with a more frequent occurrence of the study end point.

CONCLUSIONS

In diabetic patients after STEMI, thrombin generation measures as well as TRAP- and AA-induced platelet aggregation at hospital discharge are associated with an ensuing ischemic event during the 6-month follow-up.

Potential role of oral anticoagulants in the treatment of patients with coronary artery disease: focus on dabigatran

The pharmacologic management of patients with high-risk coronary artery disease consists of aspirin and a P2Y12 receptor inhibitor. Chronic oral anticoagulation with warfarin is the major treatment strategy to attenuate thromboembolism or stroke in patients with deep vein thrombosis, pulmonary embolism, heart failure and atrial fibrillation. A substantial percentage of the latter group of patients have coronary artery disease and may require stenting with long-term dual antiplatelet therapy in addition to therapy with warfarin to reduce arterial ischemic events in addition to stroke. These new oral anticoagulants have been developed for long-term therapy to overcome the limitations of warfarin. Dabigatran is a direct thrombin inhibitor and its role in patients with acute coronary syndrome is being explored.

HIV replication alters the composition of extrinsic pathway coagulation factors and increases thrombin generation

Background

HIV infection leads to activation of coagulation, which may increase the risk for atherosclerosis and venous thromboembolic disease. We hypothesized that HIV replication increases coagulation potentially through alterations in extrinsic pathway factors.

Methods and Results

Extrinsic pathway factors were measured among a subset of HIV participants from the Strategies for Management of Anti‐Retroviral Therapy (SMART) trial. Thrombin generation was estimated using validated computational modeling based on factor composition. We characterized the effect of antiretroviral therapy (ART) treatment versus the untreated state (HIV replication) via 3 separate analyses: (1) a cross‐sectional comparison of those on and off ART (n=717); (2) a randomized comparison of deferring versus starting ART (n=217); and (3) a randomized comparison of stopping versus continuing ART (n=500). Compared with viral suppression, HIV replication consistently showed short‐term increases in some procoagulants (eg, 15% to 23% higher FVIII; P<0.001) and decreases in key anticoagulants (eg, 5% to 9% lower antithrombin [AT] and 6% to 10% lower protein C; P<0.01). The net effect of HIV replication was to increase coagulation potential (eg, 24% to 48% greater thrombin generation from computational models; P<0.01 for all). The pattern of changes from HIV replication was reversed with ART treatment and consistent across all 3 independent comparisons.

Conclusions

HIV replication leads to complex changes in extrinsic pathway factors, with the net effect of increasing coagulation potential to a degree that may be clinically relevant. The key influence of changes in FVIII and AT suggests that HIV‐related coagulation abnormalities may involve changes in hepatocyte function in the context of systemic inflammation.

Clinical Trial Registration

URL: ClinicalTrials.gov. Unique identifier: NCT00027352.

Computational analysis of the effects of reduced temperature on thrombin generation: the contributions of hypothermia to coagulopathy

BACKGROUND

Hypothermia, which can result from tissue hypoperfusion, body exposure, and transfusion of cold resuscitation fluids, is a major factor contributing to coagulopathy of trauma and surgery. Despite considerable efforts, the mechanisms of hypothermia-induced blood coagulation impairment have not been fully understood. We introduce a kinetic modeling approach to investigate the effects of hypothermia on thrombin generation.

METHODS

We extended a validated computational model to predict and analyze the impact of low temperatures (with or without concomitant blood dilution) on thrombin generation and its quantitative parameters. The computational model reflects the existing knowledge about the mechanistic details of thrombin generation biochemistry. We performed the analysis for an "average" subject, as well as for 472 subjects in the control group of the Leiden Thrombophilia Study.

RESULTS

We computed and analyzed thousands of kinetic curves characterizing the generation of thrombin and the formation of the thrombin-antithrombin complex (TAT). In all simulations, hypothermia in the temperature interval 31°C to 36°C progressively slowed down thrombin generation, as reflected by clotting time, thrombin peak time, and prothrombin time, which increased in all subjects (P < 10(-5)). Maximum slope of the thrombin curve was progressively decreased, and the area under the thrombin curve was increased in hypothermia (P < 10(-5)); thrombin peak height remained practically unaffected. TAT formation was noticeably delayed (P < 10(-5)), but the final TAT levels were not significantly affected. Hypothermia-induced fold changes in the affected thrombin generation parameters were larger for lower temperatures, but were practically independent of the parameter itself and of the subjects' clotting factor composition, despite substantial variability in the subject group. Hypothermia and blood dilution acted additively on the thrombin generation parameters.

CONCLUSIONS

We developed a general computational strategy that can be used to simulate the effects of changing temperature on the kinetics of biochemical systems and applied this strategy to analyze the effects of hypothermia on thrombin generation. We found that thrombin generation can be noticeably impaired in subjects with different blood plasma composition even in moderate hypothermia. Our work provides mechanistic support to the notion that thrombin generation impairment may be a key factor in coagulopathy induced by hypothermia and complicated by blood plasma dilution.

Models for thrombin generation and risk of disease

Computational models can offer an integrated view of blood clotting dynamics and may ultimately be instructive regarding an individual's risk of bleeding or clotting. Appropriately, developed and validated models could allow clinicians to simulate the outcomes of therapeutics and estimate risk of disease. Computational models that describe the dynamics of thrombin generation have been developed and have been used in combination with empirical studies to understand thrombin dynamics on a mechanistic basis. The translation of an individual's specific coagulation factor composition data using these models into an integrated assessment of hemostatic status may provide a route for advancing the long-term goal of individualized medicine. This review details the integrated approaches to understanding: (i) What is normal thrombin generation in individuals? (ii) What is the effect of normal range plasma composition variation on thrombin generation in pathologic states? (iii) Can disease progression or anticoagulation be followed by understanding the boundaries of normal thrombin generation defined by plasma composition? (iv) What are the controversies and limitations of current computational approaches? Progress in these areas can bring us closer to developing models that can be used to aid in identifying hemostatic risk.

Thrombin generation assay: a new tool to predict and optimize clinical outcome in cardiovascular patients?

Antithrombotic therapy (including antiplatelet and anticoagulant drugs) is the cornerstone of the current medical treatment of patients with acute coronary syndromes (ACS). This therapy and particularly the new antiplatelet and anticoagulant drugs have significantly reduced the ischemic risk, but have increased bleeding complications. Recently, several studies have emphasized the negative prognostic impact on long-term mortality of these bleeding adverse events. Thus, new assays to estimate the bleeding risk and the efficacy of these antithrombotic drugs are clearly in demand. Regarding the anticoagulant drugs, new promising data have emerged about the thrombin generation assay (TGA). TGA measures the ability of plasma to generate thrombin. TGA may be used to check coagulation function, to value risk of thrombosis and to compare the efficacy of different anticoagulants employed in clinical management of patients with ACS. The TGA result is a curve which describes the variation of thrombin's amount during the activation of the coagulation cascade. All available anticoagulant drugs influence the principal parameters generated by TGA and so it is possible to evaluate the effects of the medical treatment. In this review we provide a brief description of the assay and we summarize the principals of previous studies by analyzing the relationship between anticoagulant drugs and TGA. Moreover, a brief summary of its ability to predict ischemic and bleeding risks has been provided.

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.

From principle to practice: bridging the gap in patient profiling

The standard clinical coagulation assays, activated partial thromboplastin time (aPTT) and prothrombin time (PT) cannot predict thrombotic or bleeding risk. Since thrombin generation is central to haemorrhage control and when unregulated, is the likely cause of thrombosis, thrombin generation assays (TGA) have gained acceptance as "global assays" of haemostasis. These assays generate an enormous amount of data including four key thrombin parameters (lag time, maximum rate, peak and total thrombin) that may change to varying degrees over time in longitudinal studies. Currently, each thrombin parameter is averaged and presented individually in a table, bar graph or box plot; no method exists to visualize comprehensive thrombin generation data over time. To address this need, we have created a method that visualizes all four thrombin parameters simultaneously and can be animated to evaluate how thrombin generation changes over time. This method uses all thrombin parameters to intrinsically rank individuals based on their haemostatic status. The thrombin generation parameters can be derived empirically using TGA or simulated using computational models (CM). To establish the utility and diverse applicability of our method we demonstrate how warfarin therapy (CM), factor VIII prophylaxis for haemophilia A (CM), and pregnancy (TGA) affects thrombin generation over time. The method is especially suited to evaluate an individual's thrombotic and bleeding risk during "normal" processes (e.g pregnancy or aging) or during therapeutic challenges to the haemostatic system. Ultimately, our method is designed to visualize individualized patient profiles which are becoming evermore important as personalized medicine strategies become routine clinical practice.

The prothrombotic phenotypes in familial protein C deficiency are differentiated by computational modeling of thrombin generation

The underlying cause of thrombosis in a large protein C (PC) deficient Vermont kindred appears to be multicausal and not explained by PC deficiency alone. We evaluated the contribution of coagulation factors to thrombin generation in this population utilizing a mathematical model that incorporates a mechanistic description of the PC pathway. Thrombin generation profiles for each individual were generated with and without the contribution of the PC pathway. Parameters that describe thrombin generation: maximum level (MaxL) and rate (MaxR), their respective times (TMaxL, TMaxR), area under the curve (AUC) and clotting time (CT) were examined in individuals ± PC mutation, ± prothrombin G20210A polymorphism and ± thrombosis history (DVT or PE). This family (n = 364) is shifted towards greater thrombin generation relative to the mean physiologic control. When this family was analyzed with the PC pathway, our results showed that: carriers of the PC mutation (n = 81) had higher MaxL and MaxR and greater AUC (all p<0.001) than non-carriers (n = 283); and individuals with a DVT and/or PE history (n = 13) had higher MaxL (p = 0.005) and greater AUC (p<0.001) than individuals without a thrombosis history (n = 351). These differences were further stratified by gender, with women in all categories generating more thrombin than males. These results show that all individuals within this family with or without PC deficiency have an increased baseline procoagulant potential reflective of increased thrombin generation. In addition, variations within the plasma composition of each individual can further segregate out increased procoagulant phenotypes, with gender-associated plasma compositional differences playing a large role.

Thrombin generation in type 2 diabetes with albuminuria and macrovascular disease

BACKGROUND

Albuminuria is an indicator of cardiovascular morbidity and mortality in patients with type 2 diabetic mellitus (T2DM).

MATERIALS AND METHODS

In our cross-sectional study, we measured thrombin generation (TG), a key process in haemostasis and a tool to detect an individual's coagulation potential, in normo-, micro- and macroalbuminuria in T2DM with and without macrovascular disease (MVD). The TG-assay was performed, and the TG-curve [including the lag phase, peak thrombin and area under the curve (AUC)] was analysed.

RESULTS

A total of 160 patients (62 women; mean age ± SD: 67 ± 11 years) with T2DM and normo-, micro- or macroalbuminuria were investigated. Of those, 90 (56%) patients had normoalbuminuria, 40 (25%) microalbuminuria and 30 (19%) macroalbuminuria. The AUC between the groups of patients with normo-, micro- and macroalbuminuria was statistically significantly different [3297 (2785; 3764) vs. 3222 (2381; 3678) vs. 3726 (3153; 4235) nM Thrombin; P = 0AE019]. T2DM patients with MVD (n = 121) had a significantly shorter lag phase [12 (9; 16) vs. 20 (15; 25) min; P < 0AE001], a significantly higher peak thrombin [233 (130; 339) vs. 133 (82; 187) nM; P < 0AE001] and a significantly higher AUC [3464 (2969; 3868) vs. 3091 (2384; 3619) nM Thrombin; P = 0AE01] than T2DM patients without MVD (n = 39), indicating an earlier and higher thrombin generation.

CONCLUSION

Our results support the hypothesis that TG may be involved in the pathogenesis of MVD in diabetic nephropathy as for the first time, we could show that patients with T2DM in different stages of diabetic nephropathy had disturbances in thrombin generation.

Factor Xa generation by computational modeling: an additional discriminator to thrombin generation evaluation

Factor (f)Xa is a critical enzyme in blood coagulation that is responsible for the initiation and propagation of thrombin generation. Previously we have shown that analysis of computationally generated thrombin profiles is a tool to investigate hemostasis in various populations. In this study, we evaluate the potential of computationally derived time courses of fXa generation as another approach for investigating thrombotic risk. Utilizing the case (n = 473) and control (n = 426) population from the Leiden Thrombophilia Study and each individual's plasma protein factor composition for fII, fV, fVII, fVIII, fIX, fX, antithrombin and tissue factor pathway inhibitor, tissue factor-initiated total active fXa generation was assessed using a mathematical model. FXa generation was evaluated by the area under the curve (AUC), the maximum rate (MaxR) and level (MaxL) and the time to reach these, TMaxR and TMaxL, respectively. FXa generation was analyzed in the entire populations and in defined subgroups (by sex, age, body mass index, oral contraceptive use). The maximum rates and levels of fXa generation occur over a 10- to 12- fold range in both cases and controls. This variation is larger than that observed with thrombin (3–6 fold) in the same population. The greatest risk association was obtained using either MaxR or MaxL of fXa generation; with an ∼2.2 fold increased risk for individuals exceeding the 90^th percentile. This risk was similar to that of thrombin generation(MaxR OR 2.6). Grouping defined by oral contraceptive (OC) use in the control population showed the biggest differences in fXa generation; a >60% increase in the MaxR upon OC use. FXa generation can distinguish between a subset of individuals characterized by overlapping thrombin generation profiles. Analysis of fXa generation is a phenotypic characteristic which may prove to be a more sensitive discriminator than thrombin generation among all individuals.

Anticoagulants and the propagation phase of thrombin generation

The view that clot time-based assays do not provide a sufficient assessment of an individual's hemostatic competence, especially in the context of anticoagulant therapy, has provoked a search for new metrics, with significant focus directed at techniques that define the propagation phase of thrombin generation. Here we use our deterministic mathematical model of tissue-factor initiated thrombin generation in combination with reconstructions using purified protein components to characterize how the interplay between anticoagulant mechanisms and variable composition of the coagulation proteome result in differential regulation of the propagation phase of thrombin generation. Thrombin parameters were extracted from computationally derived thrombin generation profiles generated using coagulation proteome factor data from warfarin-treated individuals (N = 54) and matching groups of control individuals (N = 37). A computational clot time prolongation value (cINR) was devised that correlated with their actual International Normalized Ratio (INR) values, with differences between individual INR and cINR values shown to derive from the insensitivity of the INR to tissue factor pathway inhibitor (TFPI). The analysis suggests that normal range variation in TFPI levels could be an important contributor to the failure of the INR to adequately reflect the anticoagulated state in some individuals. Warfarin-induced changes in thrombin propagation phase parameters were then compared to those induced by unfractionated heparin, fondaparinux, rivaroxaban, and a reversible thrombin inhibitor. Anticoagulants were assessed at concentrations yielding equivalent cINR values, with each anticoagulant evaluated using 32 unique coagulation proteome compositions. The analyses showed that no anticoagulant recapitulated all features of warfarin propagation phase dynamics; differences in propagation phase effects suggest that anticoagulants that selectively target fXa or thrombin may provoke fewer bleeding episodes. More generally, the study shows that computational modeling of the response of core elements of the coagulation proteome to a physiologically relevant tissue factor stimulus may improve the monitoring of a broad range of anticoagulants.

Thrombin generation in clinical conditions

Commercial assays for determining thrombin generation in plasma are being tested in clinical conditions associated with thrombosis or bleeding. While pre-analytical conditions remain a source of inter laboratory variation, demanding for further standardization, clinical research proceeds. In patients at risk of venous thrombosis thrombin generation (TG) analysis may be utilized to detect underlying thrombophilia and this has been achieved both with addition of thrombomodulin or activated protein C, to test the contribution of the protein C system. In patients with documented venous thromboembolism, increased TG values are seen in those patients at greatest risk for recurrence, although the data are not consistent yet. In patients with arterial vascular disease, effects on TG patterns are seen that both reflect atherosclerosis (and its risk factors) and link to risk of recurrent atherothrombosis (coronary or stroke), but the data are limited. In patients with a bleeding diathesis, like hemophilia, the main importance of TG assays lies in the application for monitoring replacement therapy, either with factor concentrate or rFVIIa. An interesting application is in conjunction with thromboelastography, for monitoring peri-operative transfusion policy. Finally, TG analysis may contribute to monitoring anticoagulant drug treatment, but these and other applications would greatly benefit from whole blood, point of care applications of TG testing.