Inhibition rather than Enhancement of Hemostatic System Activation during Initiation of Oral Anticoagulant Treatment

Ex Vivo Thrombin Generation in Patients With Venous Thromboembolic Disease or Atrial Fibrillation on Long-Term Oral Anticoagulation

International normalized ratio (INR) is used to monitor chronic oral anticoagulant (OA) treatment; however, it is poorly understood how this simple test reflects in vivo hemostatic reactions, culminating in thrombin generation and clot formation. We studied the process of thrombin generation using an ex vivo model, where thrombin—antithrombin (TAT) complexes are measured in blood emerging from standardized skin incisions in 55 patients (35 with venous thromboembolism [VTE] and 20 with sustained atrial fibrillation [AF]) treated with acenocoumarol (INR 2.0-3.0). In addition, in venous blood, we measured the activity of factor VIII (FVIII) and vitamin K-dependent coagulation proteins. Chronic anticoagulation led to significant reductions in maximum TAT concentrations as compared to 35 healthy controls, in maximum TAT generation rates, and in mean amount of thrombin generated. Parameters of thrombin generation did not correlate with INR or any coagulation factor measured. International normalized ratio was significantly and independently affected by the decrease in the activity of all vitamin K-dependent coagulation proteins. The strongest influence was shown for FVII. Factor VIII activity was increased in all patients studied independently of the duration of anticoagulation and did not change over time. In conclusion, in patients with VTE and AF on OA, there is no correlation between INR values and parameters of ex vivo thrombin generation. This may indicate an important role of protein C (PC) system and possibly other endothelium-dependent mechanisms in controlling hemostasis. Increased FVIII activity in patients with VTE and AF does not change significantly during anticoagulation and is probably related to the pretreatment prothrombotic state.

Thrombin generation determined by calibrated automated thrombography (CAT) in pediatric patients with congenital heart disease

INTRODUCTION

Thrombin generation was studied in pediatric patients with congenital heart disease (CHD) undergoing cardiac surgery using the calibrated automated thrombography (CAT) in terms of the lag time until the onset of thrombin formation, time to thrombin peak maximum (TTP), endogenous thrombin potential (ETP), and thrombin peak height. The possible suitability to determine the coagulation status of these patients was investigated.

MATERIALS AND METHODS

CAT data of 40 patients with CHD (age range from newborn to 18 years) were compared to data using standard coagulation parameters such as prothrombin (FII), antithrombin (AT), tissue factor pathway inhibitor (TFPI), prothrombin fragment 1.2 (F 1.2), thrombin-antithrombin (TAT), activated partial thromboplastin time (aPTT), and prothrombin time (PT).

RESULTS

A significant positive correlation was seen between ETP and FII (p<0.01; r=0.369), as well as between peak height and F II (p<0.01; r=0.483). A significant negative correlation was seen between ETP and TFPI values (p<0.05; r=-0.225) while no significant correlation was seen between peak height and TFPI. A significant negative correlation was seen between F 1.2 generation and ETP (p<0.05; r=-0.254) and between F 1.2 generation and peak height (p<0.05; r=-0.236). No correlation was seen between AT and ETP or peak.

CONCLUSIONS

Our data indicate that CAT is a good global test reflecting procoagulatory and inhibitory factors of the hemostatic system in pediatric patients with CHD.

Factor XIII Val34Leu polymorphism and gamma-chain cross-linking at the site of microvascular injury in healthy and coumadin-treated subjects

Fibrin (Fn) cross-linking by activated factor (F) XIII is essential for clot stability. In vitro, a common Leu34 polymorphism of the FXIIIA-subunit increases the rate of thrombin-mediated FXIII activation, but not cross-linking activity upon complete FXIII activation. The effect of FXIII Val34Leu polymorphism on fibrin(ogen) cross-linking in vivo when vascular injury triggers the blood coagulation has not been studied yet. Using quantitative immunoblotting with antibodies raised against FXIIIA-subunits, fibrinogen, and gamma-gamma-dimers, the rates of FXIIIA cleavage and fibrin(ogen) cross-link formation in the fluid phase of 30-s blood samples collected at the site of microvascular injury were compared in the Leu34-positive and -negative healthy individuals and patients on long-term oral anticoagulation. In addition to accelerated FXIII activation, in healthy subjects the presence of FXIII Leu34 allele was associated with increased soluble gamma-gamma-dimer formation by 40% (1355 +/- 17 microg L(-1) for Leu34 carriers vs. 804.3 +/- 17 microg L(-1) for Leu34 non-carriers; P = 0.028) at the site of microvascular injury. This solution phase effect was abolished in coumadin-treated patients (369.4 +/- 75.9 microg L(-1) for Leu34 carriers vs. 290.5 +/- 35.9 microg L(-1) for Leu34 non-carriers; P > 0.05). The present study indicates that the Leu34 allele affects soluble gamma-gamma-dimer formation in untreated individuals, but not in those receiving acenocoumarol. Our data may help elucidate the impact of the FXIII Val34Leu polymorphism on Fn cross-linking in vivo and its modulation by oral anticoagulants.

Early overanticoagulation with acenocoumarol due to a genetic polymorphism of cytochrome P450 CYP2C9

We report the case of a young healthy woman who presented an early overanticoagulation when receiving acenocoumarol for a first thromboembolic episode. The patient had none of the risk factors known to influence the response to the coumarinic derivative except that she carried the rare *3 allelic variant of the cytochrome P450 CYP2C9 in a homozygous status. This case illustrates the role of the *3 polymorphism of the cytochrome P450 CYP2C9 as an independent risk factor modulating the sensitivity of patients to the anticoagulant effect of acenocoumarol. The usefulness of CYP2C9 genotyping before starting coumarinic treatments is discussed.

Effects of Melilotus officinalis on acute inflammation

Our study investigated the effects of Melilotus officinalis L. extract, containing 0.25% coumarin, on acute inflammation induced with oil of turpentine in male rabbits. The results were compared with those from a group treated with hydrocortisone sodium hemisuccinate and one injected with coumarin before inflammation was induced. The effects were evaluated by measuring serum citrulline, a test of in vitro phagocytosis, total leukocyte count and differential leukocyte count expressed as a percentage. M. officinalis had antiinflammatory effects because it reduced the activation of circulating phagocytes and lowered citrulline production. These properties were similar to those of hydrocortisone sodium hemisuccinate and coumarin. In the bone marrow acute phase response, M. officinalis had an inhibitory action that was lower than that of hydrocortisone sodium hemisuccinate and similar to coumarin.

Natural anticoagulants (antithrombin III, protein C, and protein S) in patients with mild to moderate ischemic stroke

BACKGROUND AND PURPOSE

The role of the natural anticoagulants, antithrombin III (AT III), protein C (PC), and protein S (PS), in patients with mild to moderate ischemic stroke remains uncertain. We aimed to find out whether their levels in peripheral blood correlated with the severity of neurological deficit or can predict clinical outcome and recurrence.

METHODS

We studied AT III, PC, and free PS levels in 55 consecutive patients likely to survive the study period on admission, 1 week, 1 month and 3 months after a first-ever ischemic stroke. Sex- and age-matched controls were studied once. All patients underwent a full neurological examination and blood sampling at each study time point; comprehensive stroke risk factors were recorded, and the etiology of the ischemic stroke was determined. All patients were contacted 3 years later for possible recurrent ischemic events.

RESULTS

AT III level was found to be significantly lower at all time points after stroke; PC level was significantly increased on admission and normal at subsequent measurements, and PS level was normal on admission but significantly decreased later. The levels of the natural anticoagulants did not correlate with the etiology of stroke, any stroke risk factor, or neurological scores, except that the AT III level on admission showed significant correlation with stroke severity and disability at 3 months. Natural anticoagulant levels did not predict recurrence of ischemic stroke.

CONCLUSIONS

The measurements of the level of AT III, PC, or PS did not deliver useful information for management of patients with mild or moderate ischemic stroke, expect that AT III level on admission might predict outcome.

Heparin blunts endotoxin-induced coagulation activation

BACKGROUND

Lipopolysaccharide (LPS) is a major trigger of sepsis-induced disseminated intravascular coagulation (DIC) via the tissue factor (TF)/factor VIIa-dependent pathway of coagulation. Experimental endotoxemia has been used repeatedly to explore this complex pathophysiology, but little is known about the effects of clinically used anticoagulants in this setting. Therefore, we compared with placebo the effects of unfractionated heparin (UFH) and low-molecular-weight heparin (LMWH) on LPS-induced coagulation.

METHODS AND RESULTS

In a randomized, double-blind, placebo-controlled trial, 30 healthy male volunteers received LPS 2 ng/kg IV followed by a bolus-primed continuous infusion of UFH, LMWH, or placebo. In the placebo group, activation of coagulation caused marked increases in plasma levels of prothrombin fragment F(1+2) (P<0.01) and polymerized soluble fibrin, termed thrombus precursor protein (TpP; P<0.01); TF-positive monocytes doubled in response to LPS, whereas levels of activated factor VII slightly decreased and levels of TF pathway inhibitor remained unchanged. UFH and LMWH markedly decreased activation of coagulation caused by LPS, as F(1+2) and TpP levels only slightly increased; TF expression on monocytes was also markedly reduced by UFH. TF pathway inhibitor values increased after either heparin infusion (P<0.01). Concomitantly, factor VIIa levels dropped by >50% at 50 minutes after initiation of either heparin infusion (P<0.01).

CONCLUSIONS

This experimental model proved the anticoagulatory potency of UFH and LMWH in the initial phase of experimental LPS-induced coagulation. Successful inhibition of thrombin generation also translates into blunted activation of coagulation factors upstream and downstream of thrombin.

Large amounts of vascular endothelial growth factor at the site of hemostatic plug formation in vivo

Vascular endothelial growth factor (VEGF) is important for the proliferation, differentiation, and survival of microvascular endothelial cells. It is a potent angiogenic factor and a specific endothelial cell mitogen that increases fenestration and extravasation of plasma macromolecules. Recently, large quantities of VEGF were detected in human megakaryocytes. Incubation of human platelets with thrombin in vitro resulted in the release of large amounts of VEGF. To investigate whether VEGF is released from platelets during coagulation activation in vivo, we measured in human subjects VEGF at the site of plug formation, ie, in blood emerging from a standardized injury made to determine bleeding time (shed blood). VEGF was also determined in the same volunteers after treatment with the specific thrombin inhibitor recombinant hirudin (r-hirudin). In a double-blind, randomized, crossover study, 17 healthy male volunteers (aged 20 to 35 years) were investigated. VEGF concentrations were measured in venous blood and in shed blood by the use of an immunoassay 10 minutes after intravenous administration of r-hirudin (0.35 mg/kg of body weight) or physiological saline. Prothrombin fragment f1.2 (f1.2) and beta-thromboglobulin (beta-TG) were determined as indicators of coagulation and platelet activation, respectively. Concentrations of VEGF, f1.2, and beta-TG in shed blood 4 minutes after injury were significantly higher than in venous blood (VEGF, 55.8+/-9.2 versus <20 pg/mL, P<0.001; f1.2, 71.3+/-10.4 versus 0.78+/-0.03 nmol/L, P<0. 001; beta-TG, 2290+/-170 versus 53.2+/-14.0 ng/mL, P<0.001). Administration of r-hirudin caused a >50% inhibition of the beta-TG and f1.2 levels in shed blood. In a similar manner, much lower amounts of VEGF were detectable at the site of plug formation after r-hirudin treatment (69.0+/-9.5 versus 37.8+/-2.6 pg/mL per minute; P=0.0015). Our data indicate that substantial quantities of VEGF are released from platelets during the interaction with the injured vessel wall in vivo. This finding may be relevant with respect to wound healing and tissue repair, tumor vascularization, or arterial thrombus formation.