Activation markers of coagulation

Lonomia obliqua Envenoming and Innovative Research

As a tribute to Butantan Institute in its 120th anniversary, this review describes some of the scientific research efforts carried out in the study of Lonomia envenoming in Brazil, a country where accidents with caterpillars reach over 42,000 individuals per year (especially in South and Southeast Brazil). Thus, the promising data regarding the studies with Lonomia’s toxins contributed to the creation of new research centers specialized in toxinology based at Butantan Institute, as well as to the production of the antilonomic serum (ALS), actions which are in line with the Butantan Institute mission “to research, develop, manufacture, and provide products and services for the health of the population”. In addition, the study of the components of the Lonomia obliqua bristle extract led to the discovery of new molecules with peculiar properties, opening a field of knowledge that could lead to the development and innovation of new drugs aimed at cell regeneration and inflammatory diseases.

Viscoelasticity and Ultrastructure in Coagulation and Inflammation: Two Diverse Techniques, One Conclusion

The process of blood clotting has been studied for centuries. A synopsis of current knowledge pertaining to haemostasis and the blood components, including platelets and fibrin networks which are closely involved in coagulation, are discussed. Special emphasis is placed on tissue factor (TF), calcium and thrombin since these components have been implicated in both the coagulation process and inflammation. Analysis of platelets and fibrin morphology indicate that calcium, tissue factor and thrombin at concentrations used during viscoelastic analysis (with thromboelastography or TEG) bring about alterations in platelet and fibrin network ultrastructure, which is similar to that seen in inflammation. Scanning electron microscopy indicated that, when investigating platelet structure in disease, addition of TF, calcium or thrombin will mask disease-induced alterations associated with platelet activation. Therefore, washed platelets without any additives is preferred for morphological analysis. Furthermore, morphological and viscoelastic analysis confirmed that thrombin activation is the preferred method of fibrin activation when investigating fibrin network ultrastructure.

[Thrombin generation assays and their clinical application]

Thrombin is a key enzyme of the coagulation system, having both pro- and anticoagulant functions. Thus, the generation of thrombin is one of the most important steps in coagulation. Global haemostasis assay, the so-called thrombin generation test is appropriate for its assessment. Since thrombin generation is sensible for both pro- and anticoagulant processes it can be applied for the general characterisation of the risk of thrombosis and bleeding, too. Clinical studies confirmed augmented thrombin generation in patients with high risk of venous or arterial thrombosis. Anticoagulant therapy (also novel oral anticoagulant treatment) can be monitored by thrombin generation. In case of haemophilia thrombin generation assays reflect bleeding severity. It is applicable for monitoring of both conventional haemophilia treatment and inhibitor-bypassing therapy, which is needed when inhibitors develop in patients. Standardization of thrombin generation methods and determination of cut off values are required before its application in clinical practice.

Venous thromboembolism does not share strong familial susceptibility with ischemic stroke: a nationwide family study in Sweden

BACKGROUND

Coagulation allelic variants associated with venous thromboembolism (VTE) have been suggested to be involved in the pathogenesis of ischemic stroke. This nationwide study aimed at determining whether VTE shares familial susceptibility with ischemic stroke.

METHOD AND RESULTS

The Swedish Multigeneration Register of 0- to 75-year-old subjects was linked to the Swedish Hospital Discharge Register and the Cause of Death Register for the period 1987 to 2007. Odds ratios (ORs) for VTE and ischemic stroke were determined in 2 ways: odds of ischemic stroke in offspring whose parents had been diagnosed with VTE, and odds of VTE in offspring whose parents had been diagnosed with ischemic stroke. The analyses were repeated for siblings and spouses. Offspring of parents with VTE (n=25,929) were at increased risk for ischemic stroke (n=5595): OR, 1.10 (95% confidence interval [CI], 1.06-1.14). Siblings of probands with VTE (n=45,132) had no increased risk of ischemic stroke (n=1716): OR, 1.05 (95% CI, 1.00-1.11). Spouses of probands with VTE (n=24,106) were at increased risk for ischemic stroke (n=940): OR, 1.18 (95% CI, 1.10-1.27). The risks for VTE in relatives of probands with ischemic stroke were OR, 1.15; 95% CI, 1.10-1.21 (offspring); OR, 1.07; 95% CI, 1.02-1.12 (siblings); and OR, 1.21; 95% CI, 1.11-1.32 (spouses).

CONCLUSIONS

VTE does not share strong familial susceptibility with ischemic stroke in the Swedish population. Moreover, familial nongenetic factors contribute to the observed weak familial associations. The present study suggests that it is unlikely that strong shared disease-causing mutations exist to a large extent in the Swedish population.

Venous thromboembolism does not share strong familial susceptibility with coronary heart disease: a nationwide family study in Sweden

AIMS

This nationwide study aimed to determine whether venous thromboembolism (VTE) shares familial susceptibility with coronary heart disease (CHD).

METHODS AND RESULTS

Data from the Swedish Multigeneration Register for subjects aged 0-76 years old for the period 1964-2008 were linked to the Hospital Discharge Register and Cause of Death Register. Familial risks of VTE and CHD were examined in two ways: risk of CHD in offspring whose parents had been diagnosed with VTE, and risk of VTE in offspring whose parents had been diagnosed with CHD. The analyses were repeated separately for siblings and spouses. In total, 174 768 offspring had CHD and 56 302 VTE. No association between VTE and CHD was observed among siblings. Among offspring, a lower risk of CHD was observed in subjects whose parents had suffered from VTE [standardized incidence ratio (SIR) 0.94 (95% confidence interval (CI) 0.92-0.95)], while offspring of parents with CHD had an increased risk of VTE [SIR 1.03 (95% CI 1.01-1.04)]. In spouses of VTE patients, an increased risk of CHD was observed [SIR 1.02 (95% CI 1.01-1.03)]. Conversely, risk of VTE was increased among spouses of CHD patients [SIR 1.03 (95% CI 1.02-1.03)]. Subanalyses of cases of myocardial infarction and pulmonary embolism/deep venous thrombosis showed similar results.

CONCLUSION

The familial background of CHD is different from that of VTE. The present study suggests that it is unlikely that shared disease-causing mutations exist to a large extent in the population.

Bivalirudin is a dual inhibitor of thrombin and collagen-dependent platelet activation in patients undergoing percutaneous coronary intervention

BACKGROUND

Bivalirudin, a direct thrombin inhibitor, is a widely used adjunctive therapy in patients undergoing percutaneous intervention (PCI). Thrombin is a highly potent agonist of platelets and activates the protease-activated receptors, PAR1 and PAR4, but it is not known whether bivalirudin exerts antiplatelet effects in PCI patients. We tested the hypothesis that bivalirudin acts as an antiplatelet agent in PCI patients by preventing activation of PARs on the platelet surface.

METHODS AND RESULTS

The effect of bivalirudin on platelet function and systemic thrombin levels was assessed in patients undergoing elective PCI. Mean plasma levels of bivalirudin were 2.7±0.5 μmol/L during PCI, which correlated with marked inhibition of thrombin-induced platelet aggregation and significantly inhibited cleavage of PAR1. Unexpectedly, bivalirudin also significantly inhibited collagen-platelet aggregation during PCI. Collagen induced a conversion of the platelet surface to a procoagulant state in a thrombin-dependent manner that was blocked by bivalirudin. Consistent with this result, bivalirudin reduced systemic thrombin levels by >50% during PCI. Termination of the bivalirudin infusion resulted in rapid clearance of the drug with a half-life of 29.3 minutes.

CONCLUSIONS

Bivalirudin effectively suppresses thrombin-dependent platelet activation via inhibition of PAR1 cleavage and inhibits collagen-induced platelet procoagulant activity as well as systemic thrombin levels in patients undergoing PCI.

Bubble-induced platelet aggregation in a rat model of decompression sickness

Previous studies have highlighted that bubble-induced platelet aggregation is a predictor index of decompression sickness (DCS) severity in animals and bubble formation after a single air dive in humans. The present study attempted to investigate plasmatic indexes of the coagulation system and platelet activation in our rat model of DCS. Male Sprague-Dawley rats were assigned to one experimental group with a hyperbaric exposure and one control group maintained at atmospheric pressure. Rats were compressed to 1,000 kPa (90 m saltwater) for 45 min while breathing air. The onset of death time and DCS symptoms were recorded during a 30-min observed period after rats had surfaced. Plasmatic indexes were platelet factor 4 (PF4) for platelet activation, soluble glycoprotein V (sGPV) for thrombin generation, and thrombin-antithrombin complexes for the coagulation system. Blood samples for a platelet count and markers were taken 3 wk before the experimental protocol and within the 30 min after rats had surfaced. We confirmed a correlation between the percent fall in platelet count and DCS severity. Plasmatic levels of sGPV and PF4 were significantly increased after the hyperbaric exposure, with no change in the control group. The present study confirms platelet consumption as a potential index for evaluating decompression stress and DCS severity. The results point to the participation of thrombin generation in the coagulation cascade and platelet activation in bubble-induced platelet aggregation. In our animal model of DCS, the results cannot prejudge the mechanisms of platelet activation between bubble-induced vessel wall injury and bubble-blood component interactions.

Relationship of waist and hip circumference with coagulation and fibrinolysis in postmenopausal women

The contribution of obesity to the occurrence of cardiovascular events may not be wholly related to its influence on traditional risk factors. Coagulation and fibrinolysis may also influence cardiovascular risk, but the relationship of adiposity with these processes is unclear. The aim of the present study was to investigate the relationships of BMI (body mass index), waist circumference, hip circumference and WHR (waist-to-hip ratio) with VIIc (factor VII activity), plasma markers of thrombin generation [F1+2 (prothrombin fragment 1+2)], fibrin formation [SF (soluble fibrin)] and fibrin turnover (D-dimer), and PAI-1 (plasminogen activator inhibitor-1; a marker of fibrinolytic inhibitory capacity). The study cohort was 80 healthy postmenopausal women who were not diabetic, current smokers or taking hormone therapy and who had a fasting sample of blood collected. VIIc, F1+2, SF and PAI-1 were all positively correlated with BMI, waist circumference and WHR, whereas D-dimer was positively correlated with waist circumference and WHR, but not BMI. WHR was the strongest correlate of all the markers except for PAI-1, which was most closely related to BMI. Hip circumference became a negative correlate of F1+2 and D-dimer after adjusting for waist circumference. The relationships of WHR with F1+2 and SF, but not with VIIc and D-dimer, were independent of traditional risk factors. The positive association between waist circumference and markers of thrombin generation, fibrin production and fibrin turnover suggests that abdominal adiposity may contribute to atherothrombosis by activating intravascular coagulation. In contrast, a larger hip circumference appears to have a protective affect against coagulation activation.

Changes in haemostasis during normal pregnancy: does homocysteine play a role in maintaining homeostasis?

Homocysteine, derived from the demethylation of the ammo acid methionine, is either further catabolised by trans-sulfuration to cysteine or remethylated to methionine. Remethylation to methionine requires the cofactors, folate and vitamin B12. Folate is an effective homocysteine-lowering agent and, thus, homocysteine and folate status are inversely related. Hyperhomocysteinaemia is a strong independent risk factor for venous thromboembolism (VTE) and is associated with adverse pregnancy outcomes such as pre-eclampsia, placental abruption, early pregnancy loss and neural-tube defects. Pregnancy is a risk factor for VTE as a result of prothrombotic changes in levels of haemostatic factors. However, despite this hypercoagulable state, the incidence of pregnancy-associated VTE is relatively low. Hyperhomocysteinaemia is associated with abnormalities in markers of coagulation activation, and recent research suggests that folic acid supplementation, as well as lowering homocysteine, lowers markers of coagulation activation and increases levels of coagulation inhibitors. Tissue factor (TF) is the initiator of blood coagulationin vivo, and homocysteine induces TF expressionin vitro. During pregnancy, monocyte TF expression is lower than that in the non-pregnant state, and this lowering of TF may act to counterbalance increases in coagulation activation. Furthermore, despite a high folate requirement, several studies have reported that homocysteine is lower in normal pregnancy than in the non-pregnant state. Although the exact mechanism of homocysteine lowering during pregnancy is unclear, one possible outcome of lower homocysteine may be the protection of women from pregnancy complications and VTE, and thus lower homocysteine may contribute to maintaining homeostasis in haemostasis.

The APC–PCI complex concentration predicts outcome of aortic surgery

INTRODUCTION

Coagulation activation may be related to complications during surgery for abdominal aortic aneurysm. The complex formed between activated protein C (APC) and the serpin, protein C inhibitor (PCI), is a sensitive indicator of the activation of blood coagulation. The purpose of the study was to establish whether the APC-PCI complex can provide information useful for the assessment of outcome after aortic surgery.

MATERIALS AND METHODS

In 38 patients, the APC-PCI complex was initially determined every 6 h and daily from day three. Protein C, antithrombin, global haemostatic tests, and clinical scores were investigated. Length of stay at the intensive care unit (ICU) and hospital, and vital status up to two years were recorded.

RESULTS

The median APC-PCI complex concentration in samples drawn 0-6 h after surgery was more than 20-fold higher than the upper limit of the reference interval. The level then declined rapidly, but remained elevated during the first two days. In patients with higher initial APC-PCI complex concentrations, Sequential Organ Failure Assessment (SOFA) scores were higher, the ICU stay was longer, and survival up to two years was lower. Patients who did not survive the ICU care had higher APC-PCI complex levels at 6-12 h and 12-18 h.

CONCLUSIONS

High concentrations of the APC-PCI complex within 6-18 h after the aortic surgery predict a sinister outcome. The results suggest that the APC-PCI complex is indicative of the severity of the disease.

Plasma markers of activated hemostasis in the early diagnosis of acute coronary syndromes

BACKGROUND

Because acute coronary syndromes (ACS) are caused by intracoronary thrombosis, plasma markers of coagulation have relevance for early diagnosis.

AIMS AND OBJECTIVES

To provide a critical review of these studies and specific attempts to close the diagnostic time gap left by traditional plasma markers of heart injury.

METHODS

Studies of ACS patients, with at least one control group, were included when blood samples were taken within 24 h after first symptoms prior to medication or intervention. Special attention was paid to studies reporting diagnostic performance, or combination of several markers into a single diagnostic index.

RESULTS

Markers with short plasma half-life (FPA, TAT, etc.) reflect ongoing thrombosis and may identify patients at increased risk. Markers with longer half-life (F1+2, D-Dimer, etc.) may be more useful to indicate a single acute thrombotic event. However, results are highly variable and depend on sampling time, clot property, degree of coronary obstruction and physiological condition. Early diagnostic performance of hemostatic markers was poor even when combined with heart injury markers.

CONCLUSIONS

Early measurement of hemostatic plasma markers in ACS patients provides pathophysiological information and may be helpful in risk stratification or to monitor anticoagulant therapy, but does not seem useful in routine clinical diagnosis of ACS.

Early identification of acute myocardial infarction by activated protein C–protein C inhibitor complex

INTRODUCTION

Increased coagulation activity due to coronary thrombosis in a ruptured plaque should result in activation of the protein C anticoagulant system with formation of complexes between activated protein C (APC) and the protein C inhibitor (PCI), which reflects coagulation activity. We hypothesized that elevated APC-PCI concentration might allow earlier detection of ongoing myocardial infarction than traditional biochemical markers. We have evaluated a newly devised immunofluorimetric assay for measuring plasma concentration of APC-PCI complexes among patients with suspected acute coronary syndrome.

MATERIALS AND METHODS

Blood samples were taken from 340 patients (median 71 years, range 31-97) with suspected acute coronary syndrome at first presentation in the emergency department. Electrocardiogram was recorded and APC-PCI, Troponin I and Creatine kinase-MB concentrations were repeatedly measured 3 times at 6 h interval.

RESULTS

The 74 patients who were eventually diagnosed with myocardial infarction had a higher median level of APC-PCI complex than those without myocardial damage; 0.27 vs. 0.20 microg/L (p = 0.001). In a multivariate regression model, APC-PCI level in the fourth quartile (>0.32 microg/L) independently predicted myocardial infarction with an odds ratio of 3.7 (95% CI 1.4-9.6, p < 0.01).

CONCLUSION

Early APC-PCI elevation can be detected among patients with a normal first Troponin I and non-ST-elevation myocardial infarction and provides additional risk assessment in acute coronary syndrome.

The Significance of Circulating Factor IXa in Blood

The presence of activation peptides (AP) of the vitamin K-dependent proteins in the phlebotomy blood of human subjects suggests that active serine proteases may circulate in blood as well. The goal of the current study was to evaluate the influence of trace amounts of key coagulation proteases on tissue factor-independent thrombin generation using three models of coagulation. With procoagulants and select coagulation inhibitors at mean physiological concentrations, concentrations of factor IXa, factor Xa, and thrombin were set either equal to those of their AP or to values that would result based upon the rates of AP/enzyme generation and steady state enzyme inhibition. In the latter case, numerical simulation predicts that sufficient thrombin to produce a solid clot would be generated in approximately 2 min. Empirical data from the synthetic plasma suggest clotting times of 3-5 min, which are similar to that observed in contact pathway-inhibited whole blood (4.3 min) initiated with the same concentrations of factors IXa and Xa and thrombin. Numerical simulations performed with the concentrations of two of the enzymes held constant and one varied suggest that the presence of any pair of enzymes is sufficient to yield rapid clot formation. Modeling of states (numerical simulation and whole blood) where only one circulating protease is present at steady state concentration shows significant thrombin generation only for factor IXa. The addition of factor Xa and thrombin has little effect (if any) on thrombin generation induced by factor IXa alone. These data indicate that 1) concentrations of active coagulation enzymes circulating in vivo are significantly lower than can be predicted from the concentrations of their AP, and 2) expected trace amounts of factor IXa can trigger thrombin generation in the absence of tissue factor.

Is clinical outcome of dengue-virus infections influenced by coagulation and fibrinolysis? A critical review of the evidence

Despite efforts to elucidate the pathogenesis of dengue fever, the progression into severe disease remains poorly understood. In-vitro findings suggest that coagulopathy and disturbances in fibrinolysis have a pivotal role in the pathophysiology. If disturbances in these processes are predictive of clinical outcome in this disease, there could be important consequences for both diagnosis and treatment. We have critically reviewed publications on this topic to assess whether there is an association between activation of coagulation and fibrinolysis and clinical outcome of dengue-virus infections. In general, the selected studies showed activation of both the coagulation and fibrinolytic systems in this infection. The activation was more pronounced in severe infections and in cases with a poor clinical outcome. However, the findings were not consistent, and owing to a lack of detailed information on characteristics of patients, disease, and study design, we could not ascertain whether inconsistencies were caused by differences in these characteristics, selection bias, or confounding factors. We conclude that an association between activation of coagulation and fibrinolysis and clinical outcome of dengue-virus infections is conceivable but has been inadequately assessed and that methodologically sound studies, complemented with complete and reliable reporting, are needed to show whether there is a true association.