Inhibitory effects of amniotic fluid on the activated protein C anticoagulation system in maternal plasma

Pulmonary thromboembolism (PTE) is one of the leading causes of maternal mortality. We previously reported that possible contamination of amniotic fluid (AF) into maternal circulation accelerated thrombin production and activated platelet function in maternal blood through the extrinsic pathway, which may be associated with the high incidence of PTE in early puerperium. However, it remains unclear whether the maternal anticoagulation system, e.g., the activated protein C (APC) pathway, contributes to the hypercoagulable condition induced by AF. Our previous study using an endogenous thrombin potential (ETP)-based assay revealed that sensitivity to APC was reduced during the postpartum first day, i.e., immediately after delivery, when parturients were supposed to be exposed to AF. Our aim is to investigate the susceptibility of maternal plasma to APC when mixed with AF. We collected plasma from 51 pregnant females and mixed with AF as well as APC. APC-sensitivity ratio (APC-sr) was calculated using the ETP-based assay. Addition of AF to maternal plasma showed a significant increase of ETP in the presence of APC. APC-sr was significantly increased, indicating decreased sensitivity to APC, after AF mixture to maternal plasma. The present APC-sr difference with AF contamination was smaller than that we reported previously in venous thromboembolism cases. The inhibitory effects of AF on the APC anticoagulation pathway may contribute, at least partly, to further promotion of thrombin production induced by AF. Combined with other classical thrombophilic risk factors, the present findings support possible involvements of AF exposure in the high incidence of PTE in early puerperium.

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.

Body mass index reduction improves the baseline procoagulant imbalance of obese subjects

Obesity is a risk factor for cardiovascular diseases. The latter being dependent (at least in part) on plasma procoagulant imbalance (i.e., hypercoagulability). Information on hypercoagulability associated with obesity is scanty and mainly based on global traditional coagulation tests or on the measurement of individual components of coagulation (i.e., pro- and anticoagulants). Plasma from 33 obese subjects was investigated soon before endoscopic balloon placement and after removal (6 months later) by thrombin-generation procedures that are thought to represent much better than any other in vitro test the coagulation process occurring in vivo. We found that obese subjects possess a state of hypercoagulability as demonstrated by the modification of the main parameters of thrombin-generation. In particular, the median value (min-max) of the endogenous thrombin potential (ETP) of obese subjects at baseline was higher than that of controls [1968 (1335-2533) vs. 1710 (1010-2119), p < 0.001]. Endoscopic balloon placement achieved a BMI reduction from 38.9 (31.7-62.3) to 31.6 (21.9-53.3), p < 0.001 and a parallel reduction of thrombin-generation as demonstrated by the following findings. The ETP measured soon after balloon removal was significantly smaller than that measured at baseline [1783 (1224-2642) vs. 1968 (1335-2533), p < 0.01]. The other parameters of thrombin-generation, including lag-time, peak-thrombin, time-to-reach the peak and velocity index showed a pattern consistent with the ETP, both at baseline and soon after balloon removal. Endoscopic balloon placement achieves concomitant reduction of BMI and thrombin-generation in subjects with obesity.

The pattern and magnitude of "in vivo thrombin generation" differ in women with preeclampsia and in those with SGA fetuses without preeclampsia

OBJECTIVE

We aimed to determine the differences in the pattern and magnitude of thrombin generation between patients with preeclampsia (PE) and those with a small-for-gestational-age (SGA) fetus.

METHODS

This cross-sectional study included women in the following groups: (1) normal pregnancy (NP) (n = 49); (2) PE (n = 56); and (3) SGA (n = 28). Maternal plasma thrombin generation (TGA) was measured, calculating: (a) lag time (LT); (b) velocity index (VI); (c) peak thrombin concentration (PTC); (d) time-to-peak thrombin concentration (TPTC); and (e) endogenous thrombin potential (ETP).

RESULTS

(1) The median TPTC, VI, and ETP differed among the groups (p = .001, p = .006, p < .0001); 2) the median ETP was higher in the PE than in the NP (p < .0001) and SGA (p = .02) groups; 3) patients with SGA had a shorter median TPTC and a higher median VI than the NP (p = .002, p = .012) and PE (p < .0001, p = .006) groups.

CONCLUSIONS

(1) Patients with PE had higher in vivo thrombin generation than women with NP and those with an SGA fetus; (2) the difference in TGA patterns between PE and SGA suggests that the latter group had faster TGA, while patients with PE had a longer reaction, generating more thrombin. This observation is important for the identification of a subset of patients who might benefit from low molecular-weight heparin.

Endogenous thrombin potential changes during the first cycle of oral contraceptive use

OBJECTIVES

Venous thromboembolism (VTE) risk increases within months of combination oral contraceptive (COC) initiation. Because elevated endogenous thrombin potential (ETP) has been found in several studies to be a VTE risk factor, we evaluated the extent of ETP changes during the initial cycle of an ethinyl estradiol (EE) and levonorgestrel (LNG) COC. We also assessed the relationship between ETP changes and systemic EE and LNG concentrations.

STUDY DESIGN

Participants provided multiple blood samples during a first 21-day cycle of a 30-mcg EE/150-mcg LNG COC and after a further 7 days without an active COC. Thrombin generation measured with and without addition of activated protein C (APC) yielded ETP_+APC and ETP_-APC and the normalized APC sensitivity ratio (nAPCsr). EE and LNG pharmacokinetic analyses were conducted over 24 h after the first COC tablet and again at steady state.

RESULTS

Thrombin generation was determined in 16 of the 17 women who completed the study. Mean ETP_-APC increased steadily to 21% above baseline at 24 h after the 6th COC tablet (COC6₂₄; p<.001) and to 28% above baseline at steady state (COC21; p<.001). The percentage increase in mean ETP_+APC was considerably more - 54% at COC6₂₄ and 79% at steady state. Mean nAPCsr increased by 28% at COC6₂₄ and by 41% at steady state. Higher concentrations of EE or LNG were not correlated with greater increases in ETP.

CONCLUSIONS

ETP increases during the first COC cycle were substantial.

IMPLICATIONS

The early increases in ETP may provide biological support for the rapid increase in VTE risk during initial COC use. The lack of association between this clotting system perturbation and the systemic EE concentration is surprising and deserves further study.

Thrombin generation and international normalized ratio in inherited thrombophilia patients receiving thromboprophylactic therapy

BACKGROUND

Thrombin generation assay (TGA) is useful as a global functional test for assessing bleeding or thrombotic risk and its modification with therapy. We investigated TGA to assess anticoagulation status compared with the international normalized ratio (INR) system in patients with primary thrombophilia receiving and not undergoing thromboprophylaxis.

MATERIALS AND METHODS

We studied 50 patients with at least one thrombotic event and a confirmed diagnosis of inherited thrombophilia. Thrombin generation was measured in platelet-poor plasma by calibrated automated thrombography (CAT).

RESULTS

Patients in optimal anticoagulation (INR: 2.0-3.0) showed an endogenous thrombin potential (ETP) of 14-56% of normal and a peak of 18-55% of normal. A significant inverse relationship between INR and thrombin generation parameters (ETP, peak and velocity index) and a linear correlation for lag time was found in patients treated with vitamin-K antagonists (VKA). Receiver-operating characteristics (ROC) analysis showed that the optimal cutoff for ETP was 1600.2 nM · min (111.6% of normal, with a sensitivity of 96.6% and a specificity of 92.9%) and for the peak was 298.3 nM (112.1% of normal, with a sensitivity of 96.4% and a specificity of 100%). According to this analysis, ETP was able to identify patients with increased thrombotic and hemorrhagic risk, correlating with severe clinical complications.

CONCLUSION

TGA showed excellent sensitivity and specificity for assessing anticoagulation status in patients with primary thrombophilia receiving VKA, with significant advantages with regard to INR. Clinical data strongly support ETP as a valuable indicator of thrombotic or hemorrhagic risk in patients receiving or not receiving thromboprophylaxis.

Thrombin generation test in children and adolescents with chronic liver disease

INTRODUCTION

The aim of this study was to evaluate if real-time thrombin generation assay provides additional information to assess the hemostatic balance in children with liver disease as compared to routine coagulation tests.

PATIENTS AND METHODS

Sixty-three children with chronic liver disease were enrolled at our tertiary referral center for pediatric hepatology, eight whose routine coagulation tests gave abnormal results (Group A) and 55 whose test results were normal (Group B). Abnormal routine coagulation test was defined as at least one of the following: international normalized ratio≥1.4, activated partial thromboplastin time>44 sec., fibrinogen<1.5 g/L. Platelet-poor plasma was analyzed with the fluorogenic Calibrated Automated Thrombogram to test for thrombin generation, including endogenous thrombin potential. Further, routine coagulation tests and plasma levels of pro- and anticoagulant factors were measured. Twenty age-matched children without liver disease served as controls.

RESULTS

The endogenous thrombin potential in the 55 patients with normal routine coagulation tests was not significantly different from that in controls. Group A had significantly lower levels not only of procoagulant factors (II, V, VII, X) but simultaneously also of the anticoagulant factors antithrombin, protein S free, and protein C. These patients had a reduced endogenous thrombin potential compared to Group B, in agreement with their routine coagulation test results.

CONCLUSION

Thrombin generation analysis seems to give information on the hemostatic balance consistent with routine coagulation test results in children with liver disease. Further development and clinical evaluation of the method are warranted.

Statins decrease thrombin generation in patients with hypercholesterolemia

OBJECTIVE

Statins are cholesterol-lowering agents with antithrombotic effect possibly unrelated to their lipid-lowering properties. Traditional global coagulation tests failed, however, to reveal clinically relevant change after treatment. We therefore sought to investigate whether statins were able to modify thrombin generation in hypercholesterolemia.

METHODS

Fifty-one patients who needed treatment with statins were enrolled in this study. Thrombin generation, assessed as endogenous thrombin potential (the amount of thrombin generated after triggering coagulation with small amount of tissue factor) was measured at pre- and two months post-treatment with statins.

RESULTS

The median (inter-quartile range) level of total cholesterol that was 325 mg/dL (278-405) decreased significantly [211 mg/dL (197-247)] at post-treatment (p<0.001); the median level of HDL cholesterol that was 49 mg/dL (43-56) increased significantly [55 mg/dL (47-66)] at post-treatment (p<0.001). The median endogenous thrombin potential (inter-quartile range) before treatment was 2372 nM·min (2008-2617) and decreased to 2,048 nM·min (1764-2375) (p<0.001) after treatment.

CONCLUSION

The results support the hypothesis of a direct link between statins and coagulation through their capacity to lower thrombin generation in patients with hypercholesterolemia.

PRACTICE IMPLICATIONS

The antithrombotic properties of statins could be mediated (at least in part) by their endogenous thrombin potential lowering effect. This interesting hypothesis warrants evaluation by clinical trials.

Comparison of markers of coagulation activation and thrombin generation test in uncomplicated pregnancies

INTRODUCTION

Pregnancy is a well-established risk factor for venous thromboembolism, and is associated with a state of hypercoagulability or parameters of thrombin generation. Currently, there is a lack of consensual data on thrombin generation during pregnancy. This study aimed to find a sensitive and specific biological marker of coagulation activation and to identify parameters of thrombin generation.

PATIENTS AND METHODS

The population included 101 women with uncomplicated pregnancies. The objective of this study was to correlate thrombin generation test (measured at 5pM tissue factor, 4μM lipids and without thrombomodulin), with fibrinogen and markers of blood coagulation activation: D-dimer, prothrombin fragments 1+2 (F1+2), thrombin-antithrombin complexes (TAT) and fibrin monomer complexes (FMC) in these women. Internal quality control was performed in each set of experiments.

RESULTS

Fibrinogen, D-dimer, F1+2, and TAT concentrations increased significantly throughout pregnancy, and were correlated with term of pregnancy. In our study, thrombin generation seemed to increase early on, and then remained stable throughout normal pregnancy, in contrast with other markers of blood coagulation activation, excepting FMC. The latter are subject to large inter-individual variations, especially during second trimester. No correlation was demonstrated between thrombin generation parameters and other activation markers.

CONCLUSION

While markers of coagulation activation significantly increased during pregnancy, thrombin generation increased only early on and remains stable during pregnancy. Finding a sensitive and specific biological marker for vascular pregnancy complications, such as FMC and thrombin generation levels, requires further investigation.