Increased thrombin generation in persons with echogenic carotid plaques

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.

Thrombin generation assay: the present and the future

The need for a more precise test that replicates the in vivo hemostatic conditions is increasingly being recognized. Up to now, the thrombin generation assay (TGA) has become the most reliable approach to evaluate the status of coagulation activation. The clinical potential for the TGA is most promising in the prediction of venous thromboembolism recurrence. However, there is currently an urgent need for a standardized global test that can reliably detect, predict and monitor coagulation disorders in both clinical and experimental studies. We have recently modified the TGA to analyze not only tissue factor-driven coagulation, but the intrinsic coagulation pathway as well. In the present review, we discuss different TG tests, emphasizing the requirement for a better understanding of the evaluation of distinct coagulation pathways using this technique, as well as the standardization and clinical validation.

Factor XII deficiency evaluated by thrombin generation assay

INTRODUCTION

Coagulation factor XII (FXII) plays a role in thrombin generation, fibrinolysis, inflammation, angiogenesis, chemotaxis and diapedesis. FXII deficiency is not associated with bleeding risk unlike other coagulation factors.

MATERIALS/METHODS

We investigated thrombin generation assay (TGA) profile modification in FXII deficiency and the correlation with TGA and deficiency severity. TGA was performed in platelet poor plasma (PPP) with tissue factor (1 pmol/L) and phospholipid (4 µmol/L) standardized concentration. Thrombin generation profiles were compared in 54 patients with FXII deficiency, 25 healthy controls and 23 patients with hemophilia A (factor VIII (FVIII) deficiency. Patients with FXII deficiency were classified in three groups based on FXII activity (30-50%, 10-29%, <10%). FVIII deficiency was included as a bleeding control group.

RESULTS

As expected, we found a correlation between FXII deficiency and activated partial thromboplastin time (aPTT). A decrease of thrombin generation was observed in healthy controls and all FXII deficiency groups. A decrease of endogenous thrombin potential (ETP), peak and velocity was observed in patients with FVIII deficiency compared to FXII deficiency. A decrease of thrombin generation was noted in patients with FXII deficiency and bleeding history compared to patients with FXII deficiency and thrombosis history.

CONCLUSION

In this study, thrombin generation profiles were not sensitive to FXII deficiency. TGA could distinguish bleeding and thrombotic tendency in FXII deficiency. Our results should therefore be considered as exploratory and deserve confirmation.

Thrombin generation is associated with ischemic stroke at a young age

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Thrombin generation and intracranial atherosclerotic disease in patients with a transient ischaemic attack

BACKGROUND

Intracranial atherosclerotic disease (ICAD) is responsible for at least 10% of transient ischaemic attacks (TIA). Thrombin generation has been shown to be associated with several atherosclerotic conditions and may be relevant in the pathogenesis of TIA from ICAD.

OBJECTIVE

To evaluate the association between thrombin generation and ICAD in patients with TIA.

MATERIALS AND METHODS

Consecutive patients with confirmed diagnosis of TIA by vascular neurologist were enrolled. Within 24h from diagnosis, all the patients underwent: blood samples including thrombin generation search, electrocardiography, brain CT scan, blood pressure (BP) measurement, supra-aortic echo-Doppler, transcranial Doppler (TCD) and standard echocardiogram. Thrombin generation was measured as endogenous thrombin potential (ETP) in platelet-rich plasma (PRP) and in platelet-poor plasma (PPP), in the presence and in the absence of thrombomodulin (TM).

RESULTS

120 patients (male 52.5%), aged 69±16years were enrolled. Ten patients on warfarin treatment had significantly lower ETP than the others. Among the remaining, ETP in the presence or absence of TM did not differ according to TOAST classification aetiology (large vessel vs. cardioembolic vs. lacunar vs. others). In PRP, ETP was similar in patients with ICAD and in those without (1748±160 vs. 1851±36nM·min, p=0.393), whereas, ETP measured in presence of thrombomodulin was higher in patients with than in those without ICAD (2045±99 vs. 1715±41nM·min, p=0.011). In PPP, ETP was similar in patients with ICAD and in those without, whereas thrombin peak was higher in patients with ICAD than in those without both in the presence (165±17 vs. 130±5nM, p=0.036) and in the absence of TM (178±19 vs. 142±5nM, p=0.037).

CONCLUSION

ETP measured in presence of TM is enhanced in patients with ICAD, supporting that thrombomodulin-protein C pathways is relevant in TIA from ICAD. These hypothesis-generating data suggest that thrombin generation may be relevant in cerebral ischaemia from intracranial disease, and justify larger studies.

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.

Ultrasound and Biochemical Diagnostic Tools for the Characterization of Vulnerable Carotid Atherosclerotic Plaque

Stroke is a leading cause of morbidity and mortality worldwide, and characterization of vulnerable carotid plaque remains the spearhead of scientific research. Plaque destabilization, the key factor that induces the series of events leading to the clinical symptoms of carotid artery disease, is a consequence of complex mechanical, structural and biochemical processes. Novel imaging and molecular markers have been studied as predictors of disease outcome with promising results. The aim of this review is to present the current state of research on the association between ultrasound-derived echogenicity indices and blood parameters indicative of carotid plaque stability and activity. Bibliographic research revealed that there are limited available data. Among the biomarkers studied, those related to oxidative stress, lipoproteins and diabetes/insulin resistance are associated with echolucent plaques, whereas adipokines are associated with echogenic plaques. Biomarkers of inflammation and coagulation have not exhibited any conclusive relationship with plaque echogenicity, and it is not possible to come to any conclusion regarding calcification-, apoptosis- and neo-angiogenesis-related parameters because of the extremely limited bibliographic data.

Increased thrombin generation potential in symptomatic versus asymptomatic moderate or severe carotid stenosis and relationship with cerebral microemboli

INTRODUCTION

The importance of thrombin generation in the pathogenesis of TIA or stroke and its relationship with cerebral microembolic signals (MES) in asymptomatic and symptomatic carotid stenosis has not been comprehensively assessed.

METHODS

Plasma thrombin generation parameters from patients with moderate or severe (≥ 50%) asymptomatic carotid stenosis were compared with those from patients with symptomatic carotid stenosis in the early (≤ 4 weeks) and late phases (≥ 3 months) after TIA or stroke in this prospective, pilot observational study. Thrombin generation profile was longitudinally assessed in symptomatic patients with data at each time point. Bilateral transcranial Doppler ultrasound monitoring of the middle cerebral arteries was performed whenever possible to classify patients as MES-positive or MES-negative.

RESULTS

Data from 31 asymptomatic, 46 'early symptomatic' and 35 'late symptomatic' patients were analysed. Peak thrombin (344.2 nM vs 305.3 nM; p = 0.01) and endogenous thrombin potential (1772.4 vs 1589.7; p = 0.047) were higher in early symptomatic than asymptomatic patients. Peak thrombin production decreased in symptomatic patients followed up from the early to late phase after TIA or stroke (339.7 nM vs 308.6 nM; p = 0.02). Transcranial Doppler ultrasound data were available in 25 asymptomatic, 31 early symptomatic and 27 late symptomatic patients. Early symptomatic MES-positive patients had a shorter 'time-to-peak thrombin' than asymptomatic MES-positive patients (p=0.04), suggesting a more procoagulant state in this early symptomatic subgroup.

DISCUSSION

Thrombin generation potential is greater in patients with recently symptomatic than asymptomatic carotid stenosis, and decreases over time following TIA or stroke associated with carotid stenosis. These data improve our understanding of the haemostatic/thrombotic biomarker profile in moderate-severe carotid stenosis.

Measurement of dabigatran in standardly used clinical assays, whole blood viscoelastic coagulation, and thrombin generation assays

Dabigatran, a direct thrombin inhibitor, is increasingly used clinically as one of the new oral anticoagulants. This review summarizes the assays available to measure its activity and includes the relative sensitivity of the different assays for this agent. In addition to plasma-based clotting tests, assays commonly used in surgical/emergency settings, such as activated clotting time and thromboelastometry/thromboelastography, are reviewed. In addition, the thrombin generation assay is discussed as an important method to determine the potential risk of thrombosis or bleeding and its relevance to the measurement of direct thrombin inhibitors.

Platelet activation, function, and reactivity in atherosclerotic carotid artery stenosis: a systematic review of the literature

An important proportion of transient ischemic attack or ischemic stroke is attributable to moderate or severe (50-99%) atherosclerotic carotid stenosis or occlusion. Platelet biomarkers have the potential to improve our understanding of the pathogenesis of vascular events in this patient population. A detailed systematic review was performed to collate all available data on ex vivo platelet activation and platelet function/reactivity in patients with carotid stenosis. Two hundred thirteen potentially relevant articles were initially identified; 26 manuscripts met criteria for inclusion in this systematic review. There was no consistent evidence of clinically informative data from urinary or soluble blood markers of platelet activation in patients with symptomatic moderate or severe carotid stenosis who might be considered suitable for carotid intervention. Data from flow cytometry studies revealed evidence of excessive platelet activation in patients in the early, sub-acute, or late phases after transient ischemic attack or stroke in association with moderate or severe carotid stenosis and in asymptomatic moderate or severe carotid stenosis compared with controls. Furthermore, pilot data suggest that platelet activation may be increased in recently symptomatic than in asymptomatic severe carotid stenosis. Excessive platelet activation and platelet hyperreactivity may play a role in the pathogenesis of first or subsequent transient ischemic attack or stroke in patients with moderate or severe carotid stenosis. Larger longitudinal studies assessing platelet activation status with flow cytometry and platelet function/reactivity in symptomatic vs. asymptomatic carotid stenosis are warranted to improve our understanding of the mechanisms responsible for transient ischemic attack or stroke.

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.