The Prothrombotic State Associated with SARS-CoV-2 Infection: Pathophysiological Aspects.

Severe coronavirus disease-2019 (COVID-19) is frequently associated with microvascular thrombosis, especially in the lung, or macrovascular thrombosis, mainly venous thromboembolism, which significantly contributes to the disease mortality burden. COVID-19 patients also exhibit distinctive laboratory abnormalities that are compatible with a prothrombotic state. The key event underlying COVID-19-associated thrombotic complications is an excessive host inflammatory response to severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) infection generating multiple inflammatory mediators, mainly cytokines and complement activation products. The latter, along with the virus itself, the increased levels of angiotensin II and hypoxia, drive the major cellular changes promoting thrombosis, which include: (1) aberrant expression of tissue factor by activated alveolar epithelial cells, monocytes-macrophages and neutrophils, and production of other prothrombotic factors by activated endothelial cells (ECs) and platelets; (2) reduced expression of physiological anticoagulants by dysfunctional ECs, and (3) suppression of fibrinolysis by the endothelial overproduction of plasminogen activator inhibitor-1 and, likely, by heightened thrombin-mediated activation of thrombin-activatable fibrinolysis inhibitor. Moreover, upon activation or death, neutrophils and other cells release nuclear materials that are endowed with potent prothrombotic properties. The ensuing thrombosis significantly contributes to lung injury and, in most severe COVID-19 patients, to multiple organ dysfunction. Insights into the pathogenesis of COVID-19-associated thrombosis may have implications for the development of new diagnostic and therapeutic tools.

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.

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.

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.

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.

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.

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.

The paradoxical antifibrinolytic effect of dabigatran and argatroban in the presence of soluble thrombomodulin is unrelated to protein C-dependent increase of thrombin generation.

BACKGROUND: Anticoagulants stimulate fibrinolysis in vitro, mainly by inhibiting thrombin-mediated TAFI activation. Surprisingly, however, direct thrombin inhibitors (DTIs) inhibit fibrinolysis and enhance thrombin generation in vitro when tested in the presence of high thrombomodulin (TM) concentrations. Because the paradoxical effect on thrombin generation was shown to be protein C (PC)-dependent, we investigated the role of PC in the antifibrinolytic effect of two DTIs, dabigatran and argatroban. METHODS AND RESULTS: In the presence of 10 nM TM, both dabigatran (0.5 µM) and argatroban (1 µM) prolonged clot lysis time and enhanced thrombin generation. This notwithstanding, the DTIs inhibited thrombin-mediated TAFI activation, peak TAFIa activity being reduced by >60%. A specific feature of TAFI activation curve in the presence of DTIs was a much slower disappearance of TAFIa activity, which was likely the cause of fibrinolysis inhibition. The addition of an anti-PC antibody (αPC) nullified the paradoxical effect of DTIs on thrombin generation but influenced neither TAFI activation nor the fibrinolysis time. CONCLUSIONS: Our results suggest that the inhibition of PC activation by DTIs in the presence of TM, while enhancing thrombin generation, has no effect on thrombin-mediated TAFI activation. The inhibition of fibrinolysis by DTIs can be explained by the prolonged activation of TAFI resulting from the sustained release of thrombin from thrombin-DTI complex. While the clinical relevance of these findings needs to be investigated by in vivo studies, our data might help understanding the role of the different players in the regulation of thrombin generation, TAFI activation and fibrinolysis resistance.

Co-administration of low molecular weight heparin enhances the profibrinolytic effect of warfarin through different mechanisms.

BACKGROUND AND OBJECTIVE: Treatment with vitamin K antagonists (VKA) reduces fibrinolytic resistance through the inhibition of thrombin-mediated activation of thrombin activatable fibrinolysis inhibitor (TAFI). Because low-molecular weight heparin (LMWH) is co-administered with VKA during initiation of anticoagulant treatment, we evaluated the effect of dual anticoagulation on fibrinolytic resistance. PATIENTS AND METHODS: Two groups of patients were studied: 1) patients on stable warfarin; 2) patients starting oral anticoagulant therapy, who were evaluated during dual anticoagulation and after enoxaparin withdrawal. Only samples with an INR between 2 and 3 were compared. The resistance of clots to t-PA-induced fibrinolysis was evaluated in blood and plasma by thromboelastography (TEG) and turbidimetry, respectively. RESULTS: In patients on dual anticoagulation, blood fibrinolysis time (TEG) was significantly shorter than in patients on warfarin alone and significantly correlated with LMWH level. The profibrinolytic effect was partly ascribable to a reduction of thrombin-dependent TAFI activation: 1) thrombin and TAFIa generation were significantly reduced by dual anticoagulation; 2) the addition of enoxaparin to warfarin-blood reduced TAFI-mediated fibrinolysis inhibition. Patients on dual anticoagulation also displayed a reduction in clot strength, a phenomenon known to reduce fibrinolytic resistance. The profibrinolytic effect of LMWH co-administration was not seen in plasma, likely because TAFIa generation was below the threshold required to inhibit fibrinolysis. CONCLUSIONS: Co-administration of LMWH in patients under VKA reduces the fibrinolytic resistance of blood clots via TAFI-dependent and TAFI-independent mechanisms. Further studies are warranted to assess the clinical implications of these findings.

Antithrombotic activity of 12 table grape varieties. Relationship with polyphenolic profile.

The synthesis of tissue factor (TF) by monocytes/macrophages activated by inflammatory agents is of utmost importance in the pathogenesis of thrombotic diseases and substances inhibiting TF synthesis represent novel and promising antithrombotics. We investigated the effect of 12 table grape varieties (white, red and black) on TF synthesis and the possible relation with the phenolic profile. The ability of grape skin extracts (GSEs) to inhibit TF was evaluated in whole blood and isolated mononuclear cells challenged with endotoxin. TF expression was assayed by functional and immunological assays. All GSEs inhibited TF synthesis but with a different efficiency, red grapes being the most active. By correlation analysis, the compounds showing the strongest association with TF-inhibiting activity were quercetin and cyanidin. However, no single polyphenol was able to inhibit TF synthesis as efficiently as the crude grape extracts, unless it was combined with at least another compound, suggesting a synergism.

Skin extracts from 2 Italian table grapes (Italia and Palieri) inhibit tissue factor expression by human blood mononuclear cells.

UNLABELLED: Grape and its products such as red wine and grape juice have well-known antithrombotic properties, which have been attributed to their high content in polyphenolic compounds. Most studies on the mechanisms underlying these beneficial effects, among which the suppression of tissue factor (TF) synthesis in blood mononuclear cells (MNC) and vascular endothelium is a prominent one, have been performed with purified polyphenols, while little is known about the effect of fresh grapes which contain a multitude of phytochemicals whose interaction may lead to different cell responses. In this study, we investigated the effect of grape skin extracts (GSEs) on TF expression in isolated blood MNC and in whole blood. Alcoholic extracts from skins of 2 grape varieties (Palieri and Italia) inhibited TF expression in lipopolysaccharide (LPS)-stimulated MNC in a concentration-dependent manner with ≥90% inhibition of TF activity and antigen at 6 µg/mL of gallic acid equivalents. Noteworthy, GSEs were also able to inhibit the appearance of TF in whole blood challenged with LPS. The 2 grape varieties displayed a fairly similar TF-inhibiting capacity despite marked differences in phenolic profile. When selected purified polyphenols were tested, their ability to inhibit TF expression was markedly lower as compared to grape extracts, whereas a mixture of some representative polyphenols was much more efficient, supporting the occurrence of a synergistic effect. Given the key role of cell TF in thrombotic diseases, the inhibition of MNC-mediated clotting activation, if confirmed by in vivo studies, might represent an important antithrombotic mechanism. PRACTICAL APPLICATION: Our data indicate that the combination of different polyphenols, as in grape extracts, is much more efficient than the single constituents, a finding that might be useful as starting point for the development of new antithrombotic nutraceutics. In addition, our study validated a simple, inexpensive, and physiologically relevant in vitro method on whole blood that allows the evaluation of one of the most important antithrombotic activities of food and food-derived products. The simplicity of the method makes it suitable also for screening purposes in large-scale studies.

Evidence that fibrinolytic changes in paediatric obesity translate into a hypofibrinolytic state: relative contribution of TAFI and PAI-1.

Paediatric obesity, like adulthood obesity, is associated with an increase of fibrinolysis inhibitors. No study, however, has evaluated the impact of these changes on plasma fibrinolytic capacity. We investigated plasma fibrinolysis and the role therein of the fibrinolytic changes associated with obesity in 59 obese children (body mass index > 95th percentile) and 40 matched controls. Fibrinolysis was investigated by measuring 1) the plasma levels of relevant fibrinolytic factors; 2) the in vitro fibrinolytic capacity under different conditions, using a microplate plasma clot lysis assay; 3) the circulating levels of markers of clotting and fibrinolysis activation. Plasminogen activator inhibitor 1 (PAI-1), total thrombin activatable fibrinolysis inhibitor (TAFI) and fibrinogen levels were higher in obese children as compared to controls (p<0.01). Plasma clots from obese children lysed significantly slower than control clots when exposed to exogenous plasminogen activator, indicating a greater resistance to fibrinolysis. By the use of a selective inhibitor of activated TAFI and by regression analyses we found that fibrinolysis resistance in obese samples was attributable to PAI-1 increase and to enhanced TAFI activation. The ratio between the circulating levels of D-dimer and thrombin-antithrombin complex, a marker of in vivo fibrinolysis, was significantly lower in obese children, suggesting a reduced fibrinolytic efficiency. These data indicate that paediatric obesity is associated with a hypofibrinolytic state which might contribute to the increased thrombotic risk associated with this condition.

Sepsis, thrombosis and organ dysfunction.

Sepsis is often associated with haemostatic changes ranging from subclinical activation of blood coagulation (hypercoagulability), which may contribute to localized venous thromboembolism, to acute disseminated intravascular coagulation (DIC), characterized by widespread microvascular thrombosis and subsequent consumption of platelets and coagulation proteins, eventually causing bleeding manifestations. The key event underlying this life-threatening complication is the overwhelming inflammatory host response to the infectious agent leading to the overexpression of inflammatory mediators. The latter, along with the micro-organism and its derivatives are now believed to drive the major changes responsible for massive thrombin formation and fibrin deposition, namely 1) the aberrant expression of the TF by different cells (especially monocytes-macrophages), 2) the impairment of physiological anticoagulant pathways, orchestrated mainly by dysfunctional endothelial cells (ECs) and 3) the suppression of fibrinolysis due to overproduction of plasminogen activator inhibitor-1 (PAI-1) by ECs and likely also to thrombin-mediated activation of thrombin-activatable fibrinolysis inhibitor (TAFI). The ensuing microvascular thrombosis and ischemia are thought to contribute to tissue injury and multiple organ dysfunction syndrome (MODS). Recent evidence indicates that extracellular nuclear materials released from activated and especially apoptotic or necrotic cells, e.g. High Mobility Group Box-1 (HMGB-1) and histones, are endowed with cell toxicity, proinflammatory and clot-promoting properties and thus, during sepsis, they may represent late mediators that propagate further inflammation, coagulation, cell death and MODS. These insights into the pathogenesis of DIC and MODS may have implications for the development of new therapeutic agents potentially useful for the management of severe sepsis.

Thrombin activatable fibrinolysis inhibitor: at the nexus of fibrinolysis and inflammation.

TAFI (thrombin activatable fibrinolysis inhibitor) is the precursor of a basic carboxypeptidase (TAFIa) with strong antifibrinolytic and anti-inflammatory activity. Compelling evidence indicates that thrombin, either alone or in complex with thrombomodulin, is the main physiological activator of TAFI. For this reason derangements of thrombin formation, whatever the cause, may influence the fibrinolytic process too. Experimental models of thrombosis suggest that TAFI may participate in thrombus development and persistence under certain circumstances. In several models of pharmacological thrombolysis, the administration of TAFI inhibitors along with the fibrinolytic agent leads to a marked improvement of thrombus lysis, underscoring the potential of TAFI inhibitors as adjuvants for thrombolytic therapy. The role of TAFI in inflammatory diseases is more complex as it may serve as a defense mechanism, exacerbate the disease, or have no influence, depending on the nature of the model and the role played by the mediators controlled by TAFIa. Finally, the numerous clinical studies in patients with thrombotic disease support the idea that increased levels of TAFI and/or the enhancement of TAFI activation may represent a new risk factor for venous and arterial thrombosis.

Coagulation-fibrinolysis changes during off-pump bypass: effect of two heparin doses.

BACKGROUND: To date, no study has tested the effect of different heparin dosages on the hemostatic changes during off-pump coronary artery bypass graft (OPCABG) surgery, and a wide variety of empirical anticoagulation protocols are being applied. We tested the effect of two different heparin dosages on the activation of the hemostatic system in patients undergoing OPCABG procedures. METHODS: Forty-two patients eligible for OPCABG procedures were assigned in a randomized fashion to low-dose heparin (150 IU/kg) or high-dose heparin (300 IU/kg). Prothrombin fragment 1+2, plasmin/alpha(2)-plasmin inhibitor complex, D-dimer, soluble tissue factor, tissue factor pathway inhibitor, total thrombin activatable fibrinolysis inhibitor (TAFI), and activated TAFIa were assayed by specific enzyme-linked immunosorbent assays at six different timepoints, before, during, and after surgery. Platelet function was evaluated by means of an in vitro bleeding time test, platelet function analyzer-100. RESULTS: The OPCABG surgery was accompanied by significant changes of all plasma biomarkers, indicative of systemic activation of coagulation and fibrinolysis. A significant increase in circulating TAFIa was detected perioperatively and postoperatively, and multiple regression analysis indicated that prothrombin F1+2 but not plasmin/alpha(2)-antiplasmin complex was independently associated with TAFIa level. Platelet function analyzer-100 values did not change significantly after OPCABG. All hemostatic changes were similar in the two heparin groups, even perioperatively, when the difference in anticoagulation was maximal. CONCLUSIONS: Both early and late hemostatic changes, including TAFI activation, are similarly affected in the low-dose and high-dose heparin groups, suggesting that the increase in heparin dosage is not accompanied by a better control of clotting activation during OPCABG surgery.