Concomitant assessment of rivaroxaban concentration and its impact on thrombin generation.

BACKGROUND: Reliable assays to measure direct oral anticoagulant (DOAC) levels and their activity in critical situations are needed. Drug levels alone are not representative of the effect of DOACs on an individual's coagulation. We developed a technique that provides direct assessment of the global effect of rivaroxaban on the individual's coagulation in addition to plasma concentrations. METHODS: DOAC concentrations were determined in fifty patients using rivaroxaban, with the new assay, Xross-CAT. The effect of rivaroxaban on coagulation (activity) was measured with thrombin generation (TG) in platelet poor plasma using 5 pM tissue factor on the same device. The levels were validated with the Biophen DiXal assay. The prothrombin time (PT) and dilute Russell viper venom time (dRVVT) were performed to estimate the effect on coagulation. RESULTS: The variability of Xross-CAT was below 12%. Xross-CAT correlates well with Biophen DiXaI (rs = 0.885). The bias, determined by Bland-Altman analysis, was 4.9% and the Passing-Bablok equation was y = 1.1x - 2.1. The correlation of plasma levels with TG was moderate (ETP rs = -0.548; Peak rs = -0.559), as for the PT (rs = 0.739) and the dRVVT (rs = 0.692). CONCLUSIONS: Xross-CAT shows a good correlation with Biophen DiXaI that was previously confirmed to accurately assess rivaroxaban levels. Bleeding and thrombotic complications are not necessarily associated with drug levels and could be influenced by concomitant risk factors. The main benefit of Xross-CAT is that it can be performed simultaneously with thrombin generation, providing an overview of the global anticoagulation status of a patient in relation to circulating DOAC levels.

Alternative treatment options for pediatric hemophilia B patients with high-responding inhibitors: A thrombin generation-guided study.

Little is known about the challenging treatment of pediatric patients with hemophilia B and inhibitors due to disease rarity. We describe three patients diagnosed in childhood and followed up to 9 years. All three had allergic reactions to Factor IX, but two were later safely treated for bleeding episodes with activated prothrombin complex concentrates (APCC = FEIBA). The third was given only recombinant activated Factor VIIa. Based on ex vivo thrombin generation analysis, a new alternative treatment of combined bypassing agents was administered for bleeding episodes and several minor surgical procedures with no treatment-associated adverse events or thrombosis.

Phthalide Derivatives with Anticoagulation Activities from Angelica sinensis.

Two new phthalide derivatives, angesinenolides A and B (1 and 2), were isolated from the roots of Angelica sinensis. Their structures were elucidated using HRMS, NMR, and X-ray crystallographic data. Compound 1 is the first example of a phthalide trimer presumably formed through two [2+2] cycloaddition reactions. Compound 2 is a unique dimeric phthalide with a peroxy bridge between C-3a and C-6. Both phthalides were evaluated for in vitro anticoagulation activities. Compound 1 reduced the level of fibrinogen (FIB). Compound 2 significantly extended thrombin time and activated partial thromboplastin time, as well as markedly reduced the content of FIB.

Virtual screening for R-groups, including predicted pIC50 contributions, within large structural databases, using Topomer CoMFA.

Multiple R-groups (monovalent fragments) are implicitly accessible within most of the molecular structures that populate large structural databases. R-group searching would desirably consider pIC50 contribution forecasts as well as ligand similarities or docking scores. However, R-group searching, with or without pIC50 forecasts, is currently not practical. The most prevalent and reliable source of pIC50 predictions, existing 3D-QSAR approaches, is also difficult and somewhat subjective. Yet in 25 of 25 trials on data sets on which a field-based 3D-QSAR treatment had already succeeded, substitution of objective (canonically generated) topomer poses for the original structure-guided manual alignments produced acceptable 3D-QSAR models, on average having almost equivalent statistical quality to the published models, and with negligible effort. Their overall pIC50 prediction error is 0.805, calculated as the average over these 25 topomer CoMFA models in the standard deviations of pIC50 predictions, derived from the 1109 possible "leave-out-one-R-group" (LOORG) pIC50 contributions. (This novel LOORG protocol provides a more realistic and stringent test of prediction accuracy than the customary "leave-out-one-compound" LOO approach.) The associated average predictive r(2) of 0.495 indicates a pIC50 prediction accuracy roughly halfway between perfect and useless. To assess the ability of topomer-CoMFA based virtual screening to identify "highly active" R-groups, a Receiver Operating Curve (ROC) approach was adopted. Using, as the binary criterion for a "highly active" R-group, a predicted pIC50 greater than the top 25% of the observed pIC50 range, the ROC area averaged across the 25 topomer CoMFA models is 0.729. Conventionally interpreted, the odds that a "highly active" R-group will indeed confer such a high pIC50 are 0.729/(1-0.729) or almost 3 to 1. To confirm that virtual screening within large collections of realized structures would provide a useful quantity and variety of R-group suggestions, combining shape similarity with the "highly active" pIC50, the 50 searches provided by these 25 models were applied to 2.2 million structurally distinct R-group candidates among 2.0 million structures within a ZINC database, identifying an average of 5705 R-groups per search, with the highest predicted pIC50 combination averaging 1.6 log units greater than the highest reported pIC50s.

alpha-Chymotrypsin inhibition studies on the lignans from Vitex negundo Linn.

The lignans (1-8) isolated from the roots of Vitex negundo Linn. were screened against the serine proteases alpha-chymotrypsin, thrombin and prolyl endopeptidase. Compounds 3 and 4 were found to be active only against alpha-chymotrypsin and were noncompetitive and competitive inhibitors of the enzyme, respectively. Ki values were found to be in the range 31.75-47.11 microM.

Anticoagulant effects of a Cannabis extract in an obese rat model.

Blood coagulation studies were conducted to determine the possible anti-/prothrombotic effect of an organic cannabis extract and the three major cannabinoids, THC, CBD and CBN. The in vitro effect of the cannabis extract on thrombin activity produced an IC50 value of 9.89 mg/ml, compared to THC at 1.79 mg/ml. It was also found that the extract, THC and CBN showed considerable inhibition of thrombin-induced clot formation in vitro with IC50 values of 600, 87 and 83 microg/ml for the extract, THC and CBN respectively. In an in vivo model used to determine clotting times of lean and obese rats treated with a cannabis extract, 50% clotting times were found to be 1.5 and 2 fold greater than their respective control groups, supporting the results obtained in the in vitro model. The study thus shows that Cannabis sativa and the cannabinoids, THC and CBN, display anticoagulant activity and may be useful in the treatment of diseases such as type 2 diabetes in which a hypercoagulable state exists.

Atorvastatin reduces thrombin generation after percutaneous coronary intervention independent of soluble tissue factor.

INTRODUCTION: Statins were previously shown to suppress cellular tissue factor (TF) in vitro. Here, we investigated the effect of atorvastatin on the TF-pathway and thrombin generation after coronary angioplasty and stenting in vivo. MATERIALS AND METHODS: A cohort of 30 patients with coronary artery disease (CAD) was randomised to treatment with either none (n=10), 10 mg (n=10) or 80 mg (n=10) atorvastatin per day for the postinterventional period of 6 months starting the day before percutaneous coronary intervention (PCI). Fasting blood samples were collected on admission and after 6 weeks and 6 months of statin therapy to determine sTF, free tissue factor pathway inhibitor (TFPI) and prothrombin fragment F1.2 by immunoassay. RESULTS: Soluble TF (sTF) significantly correlated with thrombin generation as measured by prothrombin fragment F1.2 at baseline. This correlation was lost 6 weeks and 6 months after initiation of statin therapy. In vivo, F1.2 was significantly lowered after 6 months of statin therapy by both, low dose (0 vs. 10 mg: 1.3+/-0.3 vs. 0.7+/-0.2 ng/ml; P<0.05) and high dose (0 vs. 80 mg: 1.2+/-0.3 vs. 0.6+/-0.2 ng/ml; P=0.01) atorvastatin compared to control. However, sTF and free TFPI did not change significantly with atorvastatin therapy when compared to baseline or control. CONCLUSIONS: Our results demonstrate reduced in vivo generation of thrombin six months after percutaneous coronary intervention and statin therapy independent of sTF and free TFPI.

Anticoagulant effect and action mechanism of sulphated flavonoids from Flaveria bidentis.

Quercetin 3-acetyl-7,3',4'-trisulphate (ATS) and quercetin 3,7,3',4'-tetrasulphate (QTS) obtained from Flaveria bidentis (Asteraceae) were investigated in vitro for anticoagulant activity. Three different concentrations of each flavonoid were assayed at different incubation times, showing at 1 mM significant prolongation on the activated partial thromboplastin time (APTT), less on the prothrombin time (PT), and no effect on the thrombin time (TT). In order to define the action mechanism of the anticoagulant activity, all coagulation factors were evaluated and no important activity decrease was observed, indicating that another mechanism is involved. Thus, thrombin inhibition mediated by antithrombin III (ATIII) and heparin cofactor II (HCII) activation was investigated in comparison to the physiological activators, heparin and dermatan sulphate (DS), respectively. As a conclusion, no activation on ATIII for neither flavonoids was observed. On the contrary, QTS much more than ATS produced an activation on HCII comparable to the one of DS, indicating that these flavonoids act as agonists of this inhibitor. A plausible explanation of the effects of both flavonoids could be due to the different degree of sulphation of these molecules. According to the results obtained, and taking in account the high solubility of these natural products in aqueous media and the nontoxic nature of this family of compounds, further investigation on the antithrombotic effects of these flavonoids are merited.

Neutral inhibitors of the serine protease factor Xa.

A neutral inhibitor of the serine protease factor Xa was identified via a high-throughput screen of a commercial library. The initial lead 1 demonstrated reversible and competitive inhibition kinetics for factor Xa and possessed a high degree of selectivity versus other related serine proteases. Initial modeling efforts and the generation of a series of analogues of 1 are described.

Activated human protein C prevents thrombin-induced thromboembolism in mice. Evidence that activated protein c reduces intravascular fibrin accumulation through the inhibition of additional thrombin generation.

Activated protein C (APC) is a potent physiologic anticoagulant with profibrinolytic properties, and has been shown to prevent thrombosis in different experimental models. We investigated the effect of human APC on thrombin-induced thromboembolism in mice, a model of acute intravascular fibrin deposition leading to death within minutes. APC given intravenously (i.v.) as a bolus 2 min before thrombin challenge (1,250 U/kg) reduced mortality in a dose-dependent manner despite the lack of thrombin inhibitor activity. Significant inhibition of thrombin-induced death was observed at the dose of 0.05 mg/kg, and maximal protection was obtained with 2 mg/kg (> 85% reduction in mortality rate). Histology of lung tissue revealed that APC treatment (2 mg/kg) reduced significantly vascular occlusion rate (from 89.2 to 46.6%, P < 0.01). The protective effect of APC was due to the inhibition of endogenous thrombin formation as indicated by the fact that (a) the injection of human thrombin caused a marked decrease in the coagulation factors of the intrinsic and common pathways (but not of Factor VII), suggesting the activation of blood clotting via the contact system; (b) APC pretreatment reduced markedly prothrombin consumption; (c) the lethal effect of thrombin was almost abolished when the animals were made deficient in vitamin K-dependent factors by warfarin treatment, and could be restored only by doubling the dose of thrombin, indicating that the generation of endogenous thrombin contributes significantly to death; and (d) APC failed to protect warfarin-treated animals, in which mortality is entirely due to injected thrombin, even after protein S supplementation. Other results suggest that APC protects from thrombin-induced thromboembolism by rendering the formed fibrin more susceptible to plasmin degradation rather than by reducing fibrin formation: in thrombin-treated mice, fibrinogen consumption was not inhibited by APC; and inhibition of endogenous fibrinolysis by epsilon-aminocaproic or tranexamic acid resulted in a significant reduction of the protective effect of APC. Since APC did not enhance plasma fibrinolytic activity, as assessed by the measurement of plasminogen activator (PA) or PA inhibitor (PAI) activities, PAI-1 antigen, or 125I-fibrin degrading activity, we speculate that the inhibition of additional (endogenous) thrombin formation by APC interrupts thrombin-dependent mechanisms that make fibrin clots more resistant to lysis, so that the intravascular deposited fibrin can be removed more rapidly by the endogenous fibrinolytic system.