Plasminogen activator-coated nanobubbles targeting cellbound ß2-glycoprotein I as a novel thrombus-specific thrombolytic strategy.

ß2-glycoprotein I (ß2-GPI) is a serum protein widely recognized as the main target of antibodies present in patients with antiphospholipid syndrome (APS). ß2-GPI binds to activated endothelial cells, platelets and leukocytes, key players in thrombus formation. We developed a new targeted thrombolytic agent consisting of nanobubbles (NB) coated with recombinant tissue plasminogen activator (rtPA) and a recombinant antibody specific for cell-bound ß2-GPI. The therapeutic efficacy of targeted NB was evaluated in vitro, using platelet-rich blood clots, and in vivo in three different animal models: i) thrombosis developed in a rat model of APS; ii) ferric chloride-induced mesenteric thrombosis in rats, and iii) thrombotic microangiopathy in a mouse model of atypical hemolytic uremic syndrome (C3-gain-of-function mice). Targeted NB bound preferentially to platelets and leukocytes within thrombi and to endothelial cells through ß2-GPI expressed on activated cells. In vitro, rtPA-targeted NB (rtPA-tNB) induced greater lysis of platelet-rich blood clots than untargeted NB. In a rat model of APS, administration of rtPA-tNB caused rapid dissolution of thrombi and, unlike soluble rtPA that induced transient thrombolysis, prevented new thrombus formation. In a rat model of ferric chloride triggered thrombosis, rtPA-tNB, but not untargeted NB and free rtPA, induced rapid and persistent recanalization of occluded vessels. Finally, treatment of C3-gain-of-function mice with rtPA-tNB, that target ß2-GPI deposited in kidney glomeruli, decreased fibrin deposition, and improved urinalysis data with a greater efficiency than untargeted NB. Our findings suggest that targeting cell-bound ß2-GPI may represent an efficient and thrombus-specific thrombolytic strategy in both APS-related and APS-unrelated thrombotic conditions.

FVIII/VWF complex displays a greater pro-haemostatic activity than FVIII preparations devoid of VWF: Study in plasma and cell-based models.

INTRODUCTION: Plasma-derived FVIII/VWF complex was reported to be less sensitive to inhibitors than FVIII preparations devoid of VWF. AIM: To compare the efficacy of FVIII/VWF complex (Fanhdi) and five different VWF-free FVIII preparations in restoring thrombin generation and activation of thrombin-activatable fibrinolysis inhibitor (TAFI) in haemophilic plasma, with and without inhibitor, and in cell-based models. METHODS: Experiments were performed in haemophilic plasma supplemented with inhibitory IgG or in plasma samples obtained from haemophilia A patients without (n = 11) and with inhibitor (n = 12). Thrombin generation was evaluated by calibrated automated thrombography (CAT) under standard conditions, in the presence of activated protein C (APC) or thrombomodulin (TM), and in cell-based models including endothelial cells, either alone or in combination with platelets or tissue factor-expressing blood mononuclear cells. The kinetics of TAFI activation was determined by a two-stage functional assay in the absence and in the presence of APC. RESULTS: In haemophilic plasma without inhibitor, Fanhdi enhanced thrombin generation and TAFI activation as well as recombinant (2nd-4th generation) and plasma-derived FVIII preparations devoid of VWF. On the contrary, in plasma with inhibitor, Fanhdi displayed a greater ability to restore thrombin generation and TAFI activation under all tested conditions. Notably, in cell-based models including endothelial cells, Fanhdi proved more efficient than all other preparations in improving thrombin generation even in the absence of inhibitor. CONCLUSION: The greater pro-haemostatic activity of FVIII/VWF complex, either in haemophilic plasma with inhibitor or in the presence of endothelial cells, may offer therapeutic advantages.

Randomised trial of chronic supplementation with a nutraceutical mixture in subjects with non-alcoholic fatty liver disease.

A mixture of natural ingredients, namely, DHA, phosphatidylcholine, silymarin, choline, curcumin and d-α-tocopherol, was studied in subjects with non-alcoholic fatty liver disease (NAFLD). Primary endpoints were serum levels of hepatic enzymes, and other parameters of liver function, the metabolic syndrome and inflammation were the secondary endpoints. The coagulation-fibrinolysis balance was also thoroughly investigated, as NAFLD is associated with haemostatic alterations, which might contribute to increased cardiovascular risk of this condition. The present study involved a double-blind, randomised, multicentre controlled trial of two parallel groups. Subjects with NAFLD (18-80 years, either sex) received the active or control treatment for 3 months. All assays were performed on a total of 113 subjects before and at the end of supplementation. The hepatic enzymes aspartate aminotransferase (AST), alanine aminotransferase and γ-glutamyl transpeptidase decreased from 23·2 to 3·7 % after treatment, only the AST levels reaching statistical significance. However, no differences were found between control and active groups. Metabolic and inflammatory variables were unchanged, except for a slight (less than 10 %) increase in cholesterol and glucose levels after the active treatment. Coagulation-fibrinolytic parameters were unaffected by either treatment. In conclusion, chronic supplementation with the mixture of dietary compounds was well tolerated and apparently safe in NAFLD subjects. The trial failed to demonstrate any efficacy on relevant physiopathological markers, but its protocol and results may be useful to design future studies with natural compounds.

Platelet Drop and Fibrinolytic Shutdown in Patients With Sepsis.

OBJECTIVE: Thrombocytopenia is the most common hemostatic disorder during sepsis and is associated with high mortality. We examined whether fibrinolytic changes precede incident thrombocytopenia and predict outcome in patients with severe sepsis. DESIGN: Nested study from the multicenter, randomized, controlled trial on the efficacy of albumin replacement in severe sepsis or septic shock (the Albumin Italian Outcome Sepsis trial). SETTING: Forty ICUs in Italy. PATIENTS: Three groups of patients were selected: 1) patients with platelet count less than or equal to 50 × 10/L at study entry (n = 85); 2) patients with baseline platelet count greater than or equal to 100 × 10/L who developed thrombocytopenia (≤ 50 × 10/L) within 28 days (n = 100); 3) patients with platelet count always more than or equal to 100 × 10/L (n = 95). INTERVENTIONS: Fibrinolytic variables, including fibrinolysis inhibitors and in vivo markers of plasmin generation, were measured on day 1. MEASUREMENTS AND MAIN RESULTS: Patients with early thrombocytopenia (group 1) and those who developed it later (group 2) had similar illness severity and 90-day mortality, whereas patients without thrombocytopenia (group 3) had milder disease and lower mortality. Fibrinolysis was markedly (and similarly) depressed in groups 1 and 2 as compared with group 3. Major fibrinolytic changes included increased levels of plasminogen activator inhibitor 1 and extensive activation/consumption of thrombin activatable fibrinolysis inhibitor. Most fibrinolytic variables were significantly associated with mortality in univariate models. However, only thrombin activatable fibrinolysis inhibitor level and in vivo markers of fibrinolysis activation, namely plasmin-antiplasmin complex, and D-dimer, were independently associated with mortality after adjustment for Simplified Acute Physiology Score-II score, sex, and platelet count. Furthermore, the coexistence of impaired fibrinolysis and low platelets was associated with an even greater mortality. CONCLUSIONS: Impaired fibrinolysis, mainly driven by plasminogen activator inhibitor-1 increase and thrombin activatable fibrinolysis inhibitor activation, is an early manifestation of sepsis and may precede the development of thrombocytopenia. Thrombin activatable fibrinolysis inhibitor level, in particular, proved to be an independent predictor of mortality, which may improve risk stratification of patients with severe sepsis.

Histones Differentially Modulate the Anticoagulant and Profibrinolytic Activities of Heparin, Heparin Derivatives, and Dabigatran.

The antithrombin activity of unfractionated heparin (UFH) is offset by extracellular histones, which, along with DNA, represent a novel mediator of thrombosis and a structural component of thrombi. Here, we systematically evaluated the effect of histones, DNA, and histone-DNA complexes on the anticoagulant and profibrinolytic activities of UFH, its derivatives enoxaparin and fondaparinux, and the direct thrombin inhibitor dabigatran. Thrombin generation was assessed by calibrated automated thrombinography, inhibition of factor Xa and thrombin by synthetic substrates, tissue plasminogen activator-mediated clot lysis by turbidimetry, and thrombin-activatable fibrinolysis inhibitor (TAFI) activation by a functional assay. Histones alone delayed coagulation and slightly stimulated fibrinolysis. The anticoagulant activity of UFH and enoxaparin was markedly inhibited by histones, whereas that of fondaparinux was enhanced. Histones neutralized both the anti-Xa and anti-IIa activities of UFH and preferentially blocked the anti-IIa activity of enoxaparin. The anti-Xa activity of fondaparinux was not influenced by histones when analyzed by chromogenic substrates, but was potentiated in a plasma prothrombinase assay. Histones inhibited the profibrinolytic activity of UFH and enoxaparin and enhanced that of fondaparinux by acting on the modulation of TAFI activation by anticoagulants. Histone H1 was mainly responsible for these effects. Histone-DNA complexes, as well as intact neutrophil extracellular traps, impaired the activities of UFH, enoxaparin, and fondaparinux. Dabigatran was not noticeably affected by histones and/or DNA, whatever the assay performed. In conclusion, histones and DNA present in the forming clot may variably influence the antithrombotic activities of anticoagulants, suggesting a potential therapeutic advantage of dabigatran and fondaparinux over heparins.

Coagulopathy of Acute Sepsis.

Coagulopathy is common in acute sepsis and may range from subclinical activation of blood coagulation (hypercoagulability), which may contribute to venous thromboembolism, to acute disseminated intravascular coagulation, characterized by widespread microvascular thrombosis and consumption of platelets and coagulation proteins, eventually causing bleeding. The key event underlying this life-threatening complication is the overwhelming inflammatory host response to the pathogen leading to the overexpression of inflammatory mediators. The latter, along with the microorganism and its derivatives drive the major changes responsible for massive thrombin formation and fibrin deposition: (1) aberrant expression of tissue factor mainly by monocytes-macrophages, (2) impairment of anticoagulant pathways, orchestrated by dysfunctional endothelial cells (ECs), and (3) suppression of fibrinolysis because of the overproduction of plasminogen activator inhibitor-1 by ECs and thrombin-mediated activation of thrombin-activatable fibrinolysis inhibitor. Neutrophils and other cells, upon activation or death, release nuclear materials (neutrophil extracellular traps and/or their components such as histones, DNA, lysosomal enzymes, and High Mobility Group Box-1), which have toxic, proinflammatory and prothrombotic properties thus contributing to clotting dysregulation. The ensuing microvascular thrombosis-ischemia significantly contributes to tissue injury and multiple organ dysfunction syndromes. These insights into the pathogenesis of sepsis-associated coagulopathy may have implications for the development of new diagnostic and therapeutic tools.

Platelet size for distinguishing between inherited thrombocytopenias and immune thrombocytopenia: a multicentric, real life study.

The most frequent forms of inherited thrombocytopenia (IT) are characterized by platelet size abnormalities and it has been suggested that this parameter is useful for their differentiation from immune thrombocytopenia (ITP). Recently, a monocentric study identified cut-off values for mean platelet volume (MPV) and mean platelet diameter (MPD) with good diagnostic accuracy in this respect. To validate these cut-off values in a different and larger case series of patients, we enrolled 130 subjects with ITP and 113 with IT in six different centres. The platelet count and MPV was each measured by the instrument routinely used in each institution. In some centres, platelet count was also measured by optical microscopy. MPD was evaluated centrally by image analysis of peripheral blood films. The previously identified cut-off value for MPV had 91% specificity in distinguishing ITP from inherited macrothrombocytopenias (mono and biallelic Bernard-Soulier, MYH9-related disease), while its sensitivity was greatly variable depending on the instrument used. With an appropriate instrument, specificity was 83%. The diagnostic accuracy of MPD was lower than that obtained with MPV. We concluded that MPV is a useful parameter for differentiating ITP from IT provided that it is measured by appropriate cell counters.

Extracellular histones promote thrombin generation through platelet-dependent mechanisms: involvement of platelet TLR2 and TLR4.

The release of histones from dying cells is associated with microvascular thrombosis and, because histones activate platelets, this could represent a possible pathogenic mechanism. In the present study, we assessed the influence of histones on the procoagulant potential of human platelets in platelet-rich plasma (PRP) and in purified systems. Histones dose-dependently enhanced thrombin generation in PRP in the absence of any trigger, as evaluated by calibrated automated thrombinography regardless of whether the contact phase was inhibited. Activation of coagulation required the presence of fully activatable platelets and was not ascribable to platelet tissue factor, whereas targeting polyphosphate with phosphatase reduced thrombin generation even when factor XII (FXII) was blocked or absent. In the presence of histones, purified polyphosphate was able to induce thrombin generation in plasma independently of FXII. In purified systems, histones induced platelet aggregation; P-selectin, phosphatidylserine, and FV/Va expression; and prothrombinase activity. Blocking platelet TLR2 and TLR4 with mAbs reduced the percentage of activated platelets and lowered the amount of thrombin generated in PRP. These data show that histone-activated platelets possess a procoagulant phenotype that drives plasma thrombin generation and suggest that TLR2 and TLR4 mediate the activation process.

Extracellular histones promote fibrinolysis by single-chain urokinase-type plasminogen activator in a factor seven activating protease-dependent way.

INTRODUCTION: Extracellular histones inhibit tissue plasminogen activator (t-PA)-mediated fibrinolysis by modifying fibrin structure and rheological properties. However, other plasminogen activators involved in intravascular and extravascular fibrinolysis have not been considered yet. OBJECTIVES: We investigated the effect of histones on fibrinolysis driven by different plasminogen activators. METHODS: Clot lysis induced by t-PA, urokinase (u-PA) and its single chain precursor (scu-PA) was evaluated by turbidimetry. Conversion of scu-PA to u-PA and activation of factor seven activating protease (FSAP) were assessed by fluorogenic and chromogenic assays, respectively. RESULTS: Histones delayed t-PA- and u-PA-mediated fibrinolysis but strongly accelerated scu-PA-driven clot lysis through the enhancement of scu-PA to u-PA conversion. This effect required a plasma factor identified as FSAP by the following findings: 1) histones enhanced neither scu-PA activation nor scu-PA-mediated clot lysis under purified conditions; 2) in plasma, the enhancement of fibrinolytic activity by histones was abolished by a neutralizing anti-FSAP antibody; and 3) histones promoted the activation of plasma FSAP. The effect of the natural mixture of histones on scu-PA-driven fibrinolysis was differentially recapitulated by the individual recombinant histones, H4 displaying the strongest activity. When complexed to DNA, histones still accelerated scu-PA-mediated fibrinolysis but with a lesser efficiency due to a reduced FSAP activation. Finally, preincubation of histones with heparin or activated protein C, two known inhibitors of histones, further amplified histone-mediated boost of scu-PA-driven fibrinolysis. CONCLUSIONS: Enhancement of FSAP-mediated scu-PA activity by histones may play yet unforeseen roles in intravascular fibrinolysis and contribute to extravascular proteolysis and tissue damage.

Thrombin activatable fibrinolysis inhibitor pathway alterations correlate with bleeding phenotype in patients with severe hemophilia A.

BACKGROUND: Patients with severe hemophilia A display varied bleeding phenotypes despite similar factor VIII (FVIII) activity levels. OBJECTIVE: We investigated different thrombin activatable fibrinolysis inhibitor (TAFI)-related variables in patients with severe hemophilia A and their possible correlation with bleeding tendency. PATIENTS/METHODS: Sixty-one patients with severe hemophilia A (FVIII:C <1%], treated on demand, were included. Patients were categorized as mild, moderate, and severe bleeders according to number of bleeds per year (≤2, 3-24, ≥25, respectively). Thirty healthy males served as controls. Clot lysis time was assessed by turbidimetric assay, TAFI activation by two-stage functional assay, and response to TAFIa as the prolongation of fibrinolysis time upon addition of purified TAFIa. Circulating levels of activated TAFI (TAFIa/ai) were measured by specific enzyme-linked immunosorbent assay. RESULTS: As compared to controls, hemophilic patients displayed shorter lysis time, less TAFIa generation, and reduced response to TAFIa, but similar TAFIa/ai levels. Clot lysis time was similar in mild, moderate, and severe bleeders, whereas TAFIa generation and response to TAFIa decreased with the increase in bleeding tendency; moreover, circulating TAFIa/ai levels were highest in severe bleeders. Patients with markedly impaired TAFIa generation or TAFIa response (below median) displayed 3-fold to 4-fold higher bleeding rate and factor consumption than patients whose TAFI-related values approached the control ones. CONCLUSION: The TAFI pathway impairment correlates with bleeding phenotype in severe hemophilia and may represent a promising tool to stratify the bleeding risk.

D-dimer corrected for thrombin and plasmin generation is a strong predictor of mortality in patients with sepsis.

BACKGROUND: D-dimer (DD) is the most used fibrin-related marker and has been proposed, either alone or in combination with other variables, as prognostic factor in patients with sepsis. However, DD generation depends on both coagulation and fibrinolysis, meaning that it may give false negative results in conditions associated with marked fibrinolytic inhibition such as sepsis. In this study, we tested whether correction of DD for thrombin and plasmin generation could improve its prognostic significance in septic patients. MATERIAL AND METHODS: We performed a nested study in 269 septic patients from the ALBIOS trial. DD, prothrombin fragment 1+2 (F1+2) and plasmin-antiplasmin complex (PAP) were assayed at day 1. Corrected DD (DDcorr) was calculated by the formula DD×PAP/F1+2, such that the lower the DDcorr the greater the imbalance in favour of fibrin formation over fibrin lysis, and vice-versa. Primary outcome was 90-day mortality. RESULTS: DDcorr showed a J-shaped relationship with mortality, which was highest in the first DDcorr tertile (low fibrinolysis), intermediate in the 3rd (high fibrinolysis), and lowest in the 2nd (balanced fibrinolysis), suggesting an increased risk whenever the coagulation-fibrinolysis balance is tilted (p<0.0001). Neither DD, nor PAP or F1+2 showed a comparable association with mortality. DDcorr was an independent prognostic factor in multivariable Cox models and significantly improved risk stratification (cNRI≥0.28). Finally, by combining DDcorr and SOFA tertiles, we developed a score with high discriminatory power. DISCUSSION: DDcorr is a good marker of the in vivo coagulation-fibrinolysis balance and displays a prognostic value in sepsis much higher than DD.

Microarray data and pathway analyses of peripheral blood mononuclear cells from healthy subjects after a three weeks grape-rich diet.

Using Human Gene Expression Microarrays (Agilent) technologies, we investigated changes of the level of gene expression in peripheral blood mononuclear cells of healthy subjects after 21 days of fresh table grape-rich diet and after an additional 28-day washout. Several hundreds of genes were differentially expressed after grape intake or after washout. The functional analysis of these genes detected significant changes in key processes such as inflammation and immunity, thrombosis, DNA and protein repair, autophagy and mitochondrial biogenesis. Moreover, fresh grape intake was found to influence the expression of many long non-coding RNA genes. The data can be valuable for researchers interested in nutrigenetics and nutrigenomics studies and are related to the research article "Gene expression signature induced by grape intake in healthy subjects reveals wide-spread beneficial effects on PBMCs" [1].

Tissue factor-expressing monocytes inhibit fibrinolysis through a TAFI-mediated mechanism, and make clots resistant to heparins.

BACKGROUND: Thrombin is the main activator of the fibrinolysis inhibitor TAFI (thrombin activatable fibrinolysis inhibitor) and heightened clotting activation is believed to impair fibrinolysis through the increase of thrombin activatable fibrinolysis inhibitor activation. However, the enhancement of thrombin generation by soluble tissue factor was reported to have no effect on plasma fibrinolysis and it is not known whether the same is true for cell-associated tissue factor. The aim of this study was to evaluate the effect of tissue factor-expressing monocytes on plasma fibrinolysis in vitro. DESIGN AND METHODS: Tissue factor expression by human blood mononuclear cells (MNC) and monocytes was induced by LPS stimulation. Fibrinolysis was spectrophotometrically evaluated by measuring the lysis time of plasma clots containing LPS-stimulated or control cells and a low concentration of exogenous tissue plasminogen activator. RESULTS: LPS-stimulated MNC (LPS-MNC) prolonged fibrinolysis time as compared to unstimulated MNC (C-MNC) in contact-inhibited but not in normal citrated plasma. A significantly prolonged lysis time was observed using as few as 30 activated cells/microL. Fibrinolysis was also impaired when clots were generated on adherent LPS-stimulated monocytes. The antifibrinolytic effect of LPS-MNC or LPS-monocytes was abolished by an anti-tissue factor antibody, by an antibody preventing thrombin-mediated thrombin activatable fibrinolysis inhibitor activation, and by a TAFIa inhibitor (PTCI). Assays of thrombin and TAFIa in contact-inhibited plasma confirmed the greater generation of these enzymes in the presence of LPS-MNC. Finally, the profibrinolytic effect of unfractionated heparin and enoxaparin was markedly lower (approximately 50%) in the presence of LPS-MNC than in the presence of a thromboplastin preparation displaying an identical tissue factor activity. CONCLUSIONS: Our data indicate that LPS-stimulated monocytes inhibit fibrinolysis through a tissue factor-mediated enhancement of thrombin activatable fibrinolysis inhibitor activation and make clots resistant to the profibrinolytic activity of heparins, thus providing an additional mechanism whereby tissue factor-expressing monocytes/macrophages may favor fibrin accumulation and diminish the antithrombotic efficacy of heparins.

Profibrinolytic activity of the direct thrombin inhibitor melagatran and unfractionated heparin in platelet-poor and platelet-rich clots.

Anticoagulants have been shown to stimulate fibrinolysis principally via inhibition of thrombin-mediated activation of TAFI (thrombin activatable fibrinolysis inhibitor). Their profibrinolytic effect, however, may vary according to their mechanism of action and to the clot composition. We compared the fibrinolytic activity of the direct thrombin inhibitor melagatran with that of unfractionated heparin in platelet-poor (PPP) and platelet-rich (PRP) models consisting of tissue-factor-induced clots exposed to exogenous t-PA (25 ng/ml). In the PPP clot model, both heparin (0.1-0.6 U/ml) and melagatran (20-320 ng/ml) caused a concentration-dependent shortening of lysis time. However, when drug profibrinolytic activity (lysis ratio) was expressed in function of the aPTT prolongation (aPTT ratio), melagatran was more efficient than heparin. In the PRP clot model, melagatran displayed a fibrinolytic activity fairly comparable to that observed in PPP whilst heparin caused a modest reduction of lysis time only at the highest concentrations. Assay of thrombin and TAFIa generation in defibrinated plasma showed that the presence of platelets markedly reduced the ability of heparin, but not that of melagatran, to inhibit the formation of these enzymes. Altogether these data indicate that melagatran is more efficient than heparin in promoting fibrinolysis, particularly in plateletrich clots, and may thus grant a greater antithrombotic activity by enhancing thrombus dissolution.

Grape intake reduces thrombin generation and enhances plasma fibrinolysis. Potential role of circulating procoagulant microparticles.

Phytochemicals contained in grapes down-regulate several prothrombotic pathways in vitro. We evaluated the effect of grape consumption on coagulation and fibrinolysis in healthy volunteers. Thirty subjects were enrolled: 20 were given grape (5 g/kg body weight/day for 3 weeks), while 10 served as controls. Blood samples were taken at baseline (T0), at the end of the grape diet (T1) and after 4-week wash-out (T2). Grape intake caused a significant decrease of the procoagulant and inflammatory responses of whole blood and/or mononuclear cells to bacterial lipopolysaccharide at both T1 and T2. At plasma level, grape diet decreased thrombin generation at T1 and T2, largely through a reduction in the number and/or activity of procoagulant microparticles. This anticoagulant effect resulted in the formation of clots that were more susceptible to fibrinolysis, mainly because of a lesser activation of thrombin activatable fibrinolysis inhibitor. No difference in any variables was detected in controls at the time points considered. In conclusion, chronic grape consumption induces sustained anticoagulant and profibrinolytic effects with potential benefits for human health.

Hypercoagulability in patients with Cushing disease detected by thrombin generation assay is associated with increased levels of neutrophil extracellular trap-related factors.

Patients with Cushing disease (CD) are at increased risk of venous thromboembolism (VTE). It was surmised, but not conclusively shown that the risk is related to plasma hypercoagulability secondary to the glucocorticoids effect. This study is aimed at detecting hypercoagulability in patients with CD. Case-control study of 48 CD patients and controls enrolled at two Italian clinics for whom we assessed the thrombin-forming-potential in the presence of optimal activation of protein C obtained by adding into the assay system its main endothelial activator, thrombomodulin. These experimental conditions mimic more closely than any other test the in vivo situation. We observed enhanced thrombin-generation in CD patients, as shown by the modification of thrombin-generation parameters [i.e., shortened lag-time and time-to-peak, increased thrombin peak and endogenous thrombin potential (ETP)]. Moreover, the ETP ratio (with/without thrombomodulin), recognized as an index of hypercoagulability, was increased in patients as compared to controls. We attempted to explain such hypercoagulability by measuring both procoagulant and anticoagulant factors, and some other non-coagulation parameters (i.e., neutrophil extracellular traps (NET), recently associated with the VTE risk and/or increased hypercoagulability. We showed that the hypercoagulability in patients with CD is associated with increased levels of factor VIII and NET-related variables. We detected plasma hypercoagulability in patients with CD and found experimental explanation for its occurrence. Whether this hypercoagulability can entirely explain the occurrence of VTE in patients with CD should be investigated by ad-hoc clinical trials. However, until these studies will be available the evidence supports the concept that patients with CD are candidates for antithrombotic prophylaxis.

Impairment of adipose tissue development by hypoxia is not mediated by plasminogen activator inhibitor-1.

Hypoxia in rodents and humans is associated with a reduction of body fat on the one hand, and with enhanced expression of plasminogen activator inhibitor-1 (PAI-1), the main inhibitor of the fibrinolytic system, on the other hand. It was the objective of this study to investigate whether impairment of adipose tissue development by hypoxia may be mediated by PAI-1. Five week old male wild-type (WT) C57Bl/6 mice were fed a standard (SFD) or high fat (HFD) diet and kept under normoxic or hypoxic (10% O(2)) conditions. In addition, PAI-1 deficient mice and WT littermates were kept on HFD under normoxia or hypoxia. In vitro, the effect of hypoxia (2% O(2)) was investigated on differentiation of 3T3-L1 cells into adipocytes. Hypoxia induced a significant reduction of weight gain in WT mice on either SFD or HFD, accompanied by lower weights of subcutaneous (SC) and gonadal (GON) fat. Under hypoxic conditions, adipocytes in the adipose tissues were significantly smaller, whereas blood vessel size and density were larger. Serum PAI-1 levels were enhanced in hypoxic mice on SFD but not on HFD, and overall did not correlate with the observed changes in adipose tissue composition. Furthermore, the effects of hypoxia on adipose tissue in mice on HFD were not affected by deficiency of PAI-1. The inhibiting effect of hypoxia on in vitro preadipocyte differentiation was not mediated by PAI-1 activity. In conclusion, impairment of in vivo adipose tissue development and in vitro differentiation of preadipocytes by hypoxia is not mediated by PAI-1.

Hyperprothrombinaemia-induced APC resistance: differential influence on fibrin formation and fibrinolysis.

The prothrombin gene mutation G20210A is a common risk factor for thrombosis and has been reported to cause APC resistance. However, the inhibition of thrombin formation by APC not only limits fibrin formation but also stimulates fibrinolysis by reducing TAFI activation. We evaluated the influence of prothrombin G20210A mutation on the anticoagulant and fibrinolytic activities of APC (1 microg/ml). Thirty-two heterozygous carriers and 32 non carriers were studied. APC anticoagulant activity was assessed by aPTT prolongation whereas APC fibrinolytic activity was determined by a microplate clot lysis assay. APC-induced aPTT prolongation was markedly less pronounced in carriers than in non carriers. On the contrary, fibrinolysis time was shortened by APC to a comparable extent in both groups. Accordingly, prothrombin levels were strongly correlated with APC-induced aPTT prolongation but not with APC-induced shortening of lysis time. The addition of purified prothrombin to normal plasma (final concentration 150%) caused APC resistance in the clotting assay over the whole range of tested APC concentrations (0.125-1.5 microg/ml). In the fibrinolytic assay, instead, prothrombin supplementation made the sample resistant to low but not to high concentrations of APC (>0.5 microg/ml). Thrombin and TAFIa determination in the presence of 1 microg/ml APC revealed that hyperprothrombinemia, although capable of enhancing thrombin generation, was unable to induce detectable TAFIa formation. It is suggested that APC resistance caused by hyperprothrombinaemia does not translate in impaired fibrinolysis, at least in the presence of high APC levels, because the increase in thrombin formation is insufficient to activate the amount of TAFI required to inhibit plasminogen conversion. These data might help to better understand the relationship between thrombin formation and fibrinolysis down-regulation.

Dabigatran but not rivaroxaban or apixaban treatment decreases fibrinolytic resistance in patients with atrial fibrillation.

INTRODUCTION: Most anticoagulants stimulate fibrinolysis in vitro through mechanisms dependent on and independent of thrombin activatable fibrinolysis inhibitor (TAFI). We evaluated the effect of dabigatran, rivaroxaban and apixaban treatment on plasma fibrinolysis in patients with non-valvular atrial fibrillation. METHODS AND RESULTS: Patients treated with dabigatran etexilate (n=22), rivaroxaban (n=24) or apixaban (n=22) were studied. Plasma was obtained before (trough) and 2h after drug intake (peak). Fibrinolytic resistance of clots exposed to exogenous tissue plasminogen activator was significantly lower in peak than in trough samples and correlated with drug concentration only in dabigatran group. Moreover, fibrinolytic resistance at peak was lower in dabigatran than in rivaroxaban and apixaban groups. This difference disappeared if the TAFI pathway was inhibited. Thrombin generation and TAFI activation were markedly lower in peak than in trough samples in all three groups. However, TAFIa levels in trough and peak samples were significantly lower in dabigatran group than in rivaroxaban and apixaban groups. Circulating levels of prothrombin fragment F1+2 (reflecting in vivo thrombin generation) and plasmin-antiplasmin complex (reflecting plasmin generation) were not or barely influenced by drug levels in all groups. CONCLUSIONS: Our data suggest that dabigatran, contrary to rivaroxaban and apixaban, reduces fibrinolytic resistance by virtue of its greater impact on TAFI activation. The profibrinolytic effect of dabigatran may play a role locally, at sites of fibrin formation, by making the nascent thrombus more susceptible to plasminogen-dependent degradation.