Activation of coagulation factor XI, without detectable contact activation in dengue haemorrhagic fever

A prospective cohort study was performed in 50 patients with dengue haemorrhagic fever (DHF) to determine the potential role of the contact activation system and factor XI activation (intrinsic pathway) in the coagulation disorders in DHF. To establish whether TAFI (thrombin-activatable fibrinolysis inhibitor) was involved in the severity of the coagulation disorders, the TAFI antigen and activity levels were also determined. Markers of contact activation (kallikrein--C1-inhibitor complexes), the intrinsic pathway of coagulation (factor XIa--C1-inhibitor complexes) and TAFI were measured and correlated to thrombin generation markers (thrombin--anti-thrombin complexes (TAT), prothrombin fragment 1+2 (F1+2)) and a marker for fibrinolysis [plasmin--alpha 2--anti-plasmin complexes (PAP)]. Activation of the intrinsic pathway of coagulation was clearly demonstrated by elevated levels of factor XIa--C1-inhibitor complexes, without evidence of contact activation, reflected by undetectable kallikrein--C1-inhibitor complexes. Both TAFI antigen and activity levels were decreased in all patients, which may contribute to the severity of bleeding complications in DHF because of the impaired capacity of the coagulation system to protect the fibrin clot from fibrinolysis. These findings in a human viral infection model are in accordance with earlier findings in bacterial sepsis.     

Thrombin activatable fibrinolysis inhibitor (TAFI) and its importance in the regulation of fibrinolysis

Thrombin activatable fibrinolysis inhibitor (TAFI) also named procarboxypeptidase U (CPU), procarboxypeptidase R (CPR) and plasma procarboxypeptidase B (CPB) provides an important link between fibrinolysis and coagulation cascade. Activated TAFI (TAFIa) reduces a generation of plasmin because it cleaves off the carboxy-terminal lysine residues from partially degraded fibrin and thereby abrogates the fibrin cofactor function in the tPA-mediated catalysis of plasminogen to plasmin. TAFI is activated by thrombin-thrombomodulin complex. TAFI transformation to the activated TAFI (TAFIa) induced by thrombin supports the important role of coagulation cascade in regulation of fibrinolysis. This can be proved by a fact that the patients with a factor XI (FXI) deficiency are prone to bleeding from tissues with a high local fibrinolytic activity (urinary tract, nose, oral cavity, tonsils) that can be explained by a decreased thrombin-mediated TAFI activation. On the other hand the prothrombotic mutation of factor V (FV Leiden) associated with a resistance to activated protein C (APC-resistance) possess both mechanisms-an increased thrombin generation in coagulation cascade and a down regulation of fibrinolysis by a way of the thrombin-induced TAFI activation. For the future an inhibition of TAFI (e.g. by FXI inhibitors) offers the therapeutic possibilities to improve the decreased fibrinolysis and increase the efficiency of fibrinolytic therapy in thrombotic disorders. In bleeding disorders (hemophilia A, B) the drugs with a higher efficiency of TAFI for down regulation of an increased fibrinolysis could be used.     

Acquired alpha-2-antiplasmin deficiency in acute promyelocytic leukaemia

We report a prospective study in nine consecutive adult patients with acute promyelocytic leukaemia (APL). The study objective was to assess the prevalence of activation of blood coagulation and/or activation of fibrinolysis in APL. Coagulation and fibrinolytic parameters relevant to the objective included antithrombin III, plasminogen, fibrin/fibrinogen degradation products and alpha-2 antiplasmin activity and antigen levels. The results of this study revealed consistently normal antithrombin III levels, both before and in the course of antileukaemic treatment. Plasminogen levels were slightly decreased or normal. However, a distinct alpha-2 antiplasmin activity deficiency in all patients was observed with levels even reaching zero in three patients, during chemotherapy. Alpha-2 antiplasmin activity levels were consistently lower than the alpha-2 antiplasmin antigen levels. The in vitro binding of alpha-2 antiplasmin activity to fibrin clots was severely reduced which appeared to be due to the reduced alpha-2 antiplasmin plasma levels. Upon crossed-immunoelectrophoresis against alpha-2 antiplasmin antiserum two alpha-2 antiplasmin antigen peaks were observed in the plasma of all nine patients. All abnormalities were reversible 4 d after completion of chemotherapy. In a second series of 12 consecutive APL patients we confirmed the consistency of the alpha-2 antiplasmin activity deficiency and normal antithrombin III plasma levels. In addition Protein C activity and antigen levels were normal or near normal in 10 and reduced in two patients. Thrombin-antithrombin III complexes were increased in 10 and normal in two patients. We conclude that some activation of blood coagulation is present in APL (increased thrombin-antithrombin III complex levels) but its contribution to the coagulopathy seems to be minor (normal antithrombin III and only slightly reduced protein C levels). The observed reduced alpha-2 antiplasmin content of the fibrin clot in vitro may result in vivo in a fibrin clot that is highly susceptible to fibrin degradation, thus aggravating the coagulopathy in APL.     

Total thrombin-activatable fibrinolysis inhibitor (TAFI) antigen and pro-TAFI in patients with haemophilia A

Pro-thrombin-activatable fibrinolysis inhibitor (pro-TAFI), also known as TAFI, procarboxypeptidase U, or procarboxypeptidase B, is a relatively recently described plasma glycoprotein synthesized in the liver. It can be catalysed into its active form, TAFI (TAFIa, carboxypeptidase U or B) by a complex of thrombin/thrombomodulin. TAFI can potentially inhibit fibrinolysis by removing carboxyterminal lysine residues from partially degraded fibrin, decreasing plasminogen binding on the surface of fibrin, which thereby results in a decrease of the fibrinolytic activity. As TAFI represents a connection between coagulation and fibrinolysis, it can be expected that TAFI levels are altered in different thrombotic and haemorrhagic diseases, such as haemophilia A. Total TAFI antigen (including pro-TAFI, TAFI and the inactive form of TAFI [TAFIi]) and pro-TAFI were determined in 17 patients with haemophilia A. Thirteen healthy age-matched volunteers served as controls. No significant difference in levels of total TAFI antigen was observed between controls and patients with haemophilia, although it was slightly decreased in patients with haemophilia. Pro-TAFI was significantly reduced in haemophilia patients compared to controls (P=0.0113). TAFI antigen levels similar to controls have already been described in different clinical conditions, including haemophilia A. Decrease of pro-TAFI in haemophilia A can be an additional factor, together with decrease in thrombin generation, which induces impaired activation of pro-TAFI to TAFI, and could cause accelerated fibrinolysis. This supports the validity of usage of antifibrinolytics in the treatment of haemophilia A. In this paper we use new nomenclature for TAFI, and we believe that this recommended terminology for different forms of TAFI can simplify further standardization in TAFI investigation.     

Role of blood coagulation factor XI in downregulation of fibrinolysis

Factor XI is a component of the intrinsic pathway of coagulation. A deficiency of factor XI is associated with a mild to moderate bleeding disorder especially from tissues with a high local fibrinolytic activity. In contrast, high levels of factor XI are a risk factor for venous thrombosis. The recent finding that factor XI can be activated by thrombin led to a revised model of coagulation. In this model the primary thrombin generation that results in fibrin formation takes place via the extrinsic pathway. Additional thrombin generation takes place inside the fibrin clot via the intrinsic pathway after the activation of factor XI by thrombin. High concentrations of thrombin are formed that are necessary for the activation of thrombin activatable fibrinolysis inhibitor (TAFI). Activated TAFI protects the fibrin clot against lysis. The role of factor XI in hemostasis can therefore be seen as a combination of procoagulant and antifibrinolytic actions. The new insights in the role of factor XI in coagulation and fibrinolysis may lead to new strategies for the treatment of thrombotic disorders.     

Thrombin-activatable fibrinolysis inhibitor deficiency in cirrhosis is not associated with increased plasma fibrinolysis.

BACKGROUND AND AIMS: The bleeding tendency of patients suffering from cirrhosis is in part ascribed to accelerated fibrinolysis. In this study, the role of the recently discovered inhibitor of fibrinolysis, thrombin-activatable fibrinolysis inhibitor (TAFI) in cirrhosis was examined. METHODS: In 64 patients with cirrhosis of varying severity, TAFI antigen levels were measured by enzyme-linked immunosorbent assay and compared with TAFI levels in control subjects. Furthermore, a plasma-based fibrinolysis assay was performed in the presence and absence of a specific inhibitor of activated TAFI. RESULTS: TAFI levels were decreased in cirrhosis. Mean TAFI levels were 66% in Child's A, 55% in Child's B, 47% in Child's C cirrhosis, and 26% in acute liver failure. Decreased TAFI antigen levels were highly correlated with antithrombin and alpha(2)-antiplasmin activity levels. Clot lysis times and clot lysis ratio (defined as ratio between clot lysis time in the absence and presence of a specific inhibitor of activated TAFI) of cirrhotics were not significantly different from healthy controls. CONCLUSIONS: Despite decreased levels of TAFI and other components of the fibrinolytic system, no evidence of increased plasma fibrinolytic potential in cirrhosis is observed using the plasma-based assay of this study. The reduction of antifibrinolytic factors in cirrhosis is compensated by the concomitant reduction in profibrinolytics.     

Evaluation of the profibrinolytic properties of an anti-TAFI monoclonal antibody in a mouse thromboembolism model

The enhancement of fibrinolysis constitutes a promising approach to treat thrombotic diseases. Activated thrombin activatable fibrinolysis inhibitor (TAFIa) attenuates fibrinolysis and is an attractive target to develop profibrinolytic drugs. TAFI can be activated by thrombin, thrombin/thrombomodulin, or plasmin, but the in vivo physiologic TAFI activator(s) are unknown. Here, we generated and characterized MA-TCK26D6, a monoclonal antibody raised against human TAFI, and examined its profibrinolytic properties in vitro and in vivo. In vitro, MA-TCK26D6 showed a strong profibrinolytic effect caused by inhibition of the plasmin-mediated TAFI activation. In vivo, MA-TCK26D6 significantly decreased fibrin deposition in the lungs of thromboembolism-induced mice. Moreover, in the presence of MA-TCK26D6, plasmin-α(2)-antiplasmin complexes in plasma of thromboembolism-induced mice were significantly increased compared with a control antibody, indicative of an acceleration of fibrinolysis through MA-TCK26D6. In this study, we show that plasmin is an important TAFI activator that hampers in vitro clot lysis. Furthermore, this is the first report on an anti-TAFI monoclonal antibody that demonstrates a strong profibrinolytic effect in a mouse thromboembolism model.     

The haemostatic balance -- Astrup revisited.

Prof. Tage Astrup first elaborated the notion that blood fluidity involved a balance between the tendency of blood to clot and for such clots to lyse. It would seem that, at that time, this haemostatic balance involved the notion that forming fibrin orchestrated its own destruction by stimulating fibrinolytic activity. In this review, we have clarified the detail of this balance and developed the thesis that Astrup's far-sighted balance notions involve a variety of control mechanisms. These involve the notion that thrombin, being at first sight a procoagulant, can also, in conjunction with thrombomodulin, act as a stimulus of anticoagulant activity by the generation of activated protein C. The thrombin-activatable fibrinolytic inhibitor (TAFI) is also involved in this balance since the generation of thrombin provokes the neutralisation of fibrinolysis by the TAFI pathway. The kallikrein/factor XII/urokinase pathway is discussed indicating yet another aspect of balance between the generation of coagulation and fibrinolysis. The overall theme of this review, apart from an insight into various aspects of the haemostatic balance, is that blood has a strong tendency to clot when tissue is damaged, and the intact vasculature requires major anticoagulant systems to prevent clots adhering to and stabilising in the vasculature.     

凝血酶激活的纤溶抑制物与缺血性脑血管病

凝血酶激活的纤溶抑制物(TAFI)是近年来发现的一种新型凝血和纤溶调控因子。活化的TAFI(TAFIa)能使纤溶酶失去与纤维蛋白的作用位点而发挥纤溶抑制作用和促进血栓形成。深入研究TAFI有可能为缺血性脑血管病的治疗提供一种新的选择。     

Effects of recombinant activated factor VII on thrombin-mediated feedback activation of coagulation

Thrombin is a key hemostatic enzyme, which propagates its own generation by activating factors V, VIII, and XI. Sustained thrombin generation also activates thrombin-activatable fibrinolysis inhibitor (TAFI), which stabilizes fibrin clot against fibrinolysis. Recombinant activated factor VII (rFVIIa) is considered a novel hemostatic intervention for refractory bleeding, but rebleeding episodes related to fibrinolysis still occur. The present study aimed to investigate the antifibrinolytic effects of rFVIIa in relation to thrombin generation. Using thrombelastography, the effects of rFVIIa on thrombin-activated fibrin formation and on fibrinolysis induced by tissue plasminogen activator were evaluated in various factor-deficient plasma samples. A Thrombinoscope was used to quantitate thrombin generation. Thrombin increased antifibrinolytic activity in a concentration-dependent manner as demonstrated by a longer clot lysis time. In plasma deficient in factors V, VIII, IX, X, or XI, clot lysis occurred early (< 20 min), and rFVIIa addition had minimal effect, except for improved antifibrinolytic effect in factor-XI-deficient plasma. A normal clot lysis time was observed in factor-XIII-deficient or dual antithrombin/factor-VIII-deficient plasma. Inhibition of TAFI increased the rate of fibrinolysis. Thrombin generation was delayed or decreased in single factor-deficient plasma except for factor XIII deficiency. After rFVIIa addition, the peak thrombin generation reached over 100 nmol/l in factor-XI-deficient plasma, but not in plasma deficient in factors V, VIII, IX, or X. Thrombin generation and subsequent activation of TAFI were important for clot stability. We conclude that rFVIIa therapy does not compensate for increased susceptibility to fibrinolysis due to lack of factor(s) necessary for the formation of tenase and prothrombinase.     

Thrombin-thrombomodulin connects coagulation and fibrinolysis: more than an in vitro phenomenon

Thrombin activatable fibrinolysis inhibitor (TAFI), when activated, forms a basic carboxypeptidase that can inhibit fibrinolysis. Potential physiologic activators include both thrombin and plasmin. In vitro, thrombomodulin and glycosaminoglycans increase the catalytic efficiency of TAFI activation by thrombin and plasmin, respectively. The most relevant (patho-) physiologic activator of TAFI has not been disclosed. Our purpose was to identify the physiologic activator of TAFI in vivo. Activation of protein C (a thrombin-thrombomodulin-dependent reaction), prothrombin, and plasminogen occurs during sepsis. Thus, a baboon model of Escherichia coli-induced sepsis, where multiple potential activators of TAFI are elaborated, was used to study TAFI activation. A monoclonal antibody (mAbTAFI/TM#16) specifically inhibiting thrombin-thrombomodulin-dependent activation of TAFI was used to assess the contribution of thrombin-thrombomodulin in TAFI activation in vivo. Coinfusion of mAbTAFI/TM#16 with a lethal dose of E coli prevented the complete consumption of TAFI observed without mAbTAFI/TM#16. The rate of fibrin degradation products formation is enhanced in septic baboons treated with the mAbTAFI/TM#16; therefore, TAFI activation appears to play a key role in the extent of fibrin(ogen) consumption during E coli challenge, and thrombin-thrombomodulin, in a baboon model of E coli-induced sepsis, appears to be the predominant activator of TAFI.     

High dose factor VIIa improves clot structure and stability in a model of haemophilia B

Factor IX (FIX) deficiency results in haemophilia B and high dose recombinant activated factor VII (rFVIIa) can decrease bleeding. Previously, we showed that FIX deficiency results in a reduced rate and peak of thrombin generation. We have now used plasma and an in vitro coagulation model to examine the effect of these changes in thrombin generation on fibrin clot structure and stability. Low FIX delayed the clot formation onset and reduced the fibrin polymerisation rate. Clots formed without FIX were composed of thicker fibrin fibres than normal. rFVIIa shortened the clot formation onset time and improved the fibre structure of haemophilic clots. We also examined clot formation in the presence of a fibrinolytic challenge by including tissue plasminogen activator or plasmin in the reaction milieu. In these assays, normal FIX levels supported clot formation; however, clots did not form in the absence of FIX. rFVIIa partially restored haemophilic clot formation. These results were independent of the effects of the thrombin-activatable fibrinolysis inhibitor. Our data suggest that rFVIIa enhances haemostasis in haemophiliacs by increasing the thrombin generation rate to both promote formation of a structurally normal clot and improve clot formation and stability at sites with high endogenous fibrinolytic activities.     

Deficiency of thrombin activatable fibrinolysis inhibitor in cirrhosis is associated with increased plasma fibrinolysis

Hyperfibrinolysis is thought to contribute to bleeding associated with advanced cirrhosis. Thrombin activatable fibrinolysis inhibitor (TAFI) is a plasma precursor of a carboxypeptidase (TAFIa) with antifibrinolytic activity and was recently shown to be reduced in cirrhosis. In this study, we evaluated the influence of TAFI deficiency on in vitro fibrinolysis in cirrhotic patients. Fifty-three patients with cirrhosis and 43 healthy controls were studied. TAFI antigen was measured by enzyme-linked immunosorbent assay and TAFI activity by chromogenic assay. Fibrinolysis was evaluated as tissue plasminogen activator-induced plasma clot lysis time in the absence and in the presence of a specific inhibitor of TAFIa. TAFI antigen and activity levels were markedly reduced in cirrhotic patients (P <.0001). In these patients, the lysis time of plasma clots was shorter than in controls (median, interquartile range: 25 minutes, 21-36 minutes vs. 48 minutes, 40-60 minutes, respectively; P <.0001) and was poorly influenced by the TAFIa inhibitor. Accordingly, TAFIa and thrombin activity, generated in cirrhotic samples during clot lysis, were significantly lower than in control samples. Addition of purified TAFI to cirrhotic plasma prolonged the lysis time and enhanced the response to TAFIa inhibitor in a dose-dependent manner. In conclusion, our results indicate that in vitro plasma hyperfibrinolysis in cirrhosis is largely due to a defective TAFIa generation resulting from low TAFI levels and probably from impaired thrombin generation. Impairment of the antifibrinolytic TAFI pathway might contribute to bleeding associated with this disease.     

Thrombin-activatable fibrinolysis inhibitor antigen levels and cardiovascular risk factors

Thrombin-activatable fibrinolysis inhibitor (TAFI) is a recently described fibrinolysis inhibitor that circulates in plasma as a procarboxypeptidase and is converted into an active form during coagulation. The physiological relevance of TAFI is not known, but it might be involved in pathways regulating fibrin deposition. Our aim was to determine the interindividual variability of plasma TAFI antigen values and their associations with conventional cardiovascular risk factors. Six hundred twenty-six consecutive patients (277 men) attending a metabolic ward for primary prevention were studied. TAFI antigen presented a large range of values, with a 2- to 3-fold increase between the 10th and 90th percentiles. No difference was observed between the 2 sexes. A significant correlation was observed between age and TAFI levels in women only. After adjustment for age, TAFI antigen was positively correlated in men for the waist-to-hip circumference ratio and blood pressure, whereas no significant correlation was observed in women. Stepwise multiple linear regression analysis indicated a low contribution of the parameters studied to the variability of TAFI antigen levels; the waist-to-hip circumference ratio accounted for only 2% in men, and age accounted for only 3% in women. Results were compared with those of fibrinogen and plasminogen activator inhibitor-1; cardiovascular risk factors in men and women accounted for 16% and 9. 5%, respectively, of the fibrinogen variance and 36% and 32%, respectively, of the plasminogen activator inhibitor-1 variance. These observations did not attribute an important role to lifestyle characteristics in the control of TAFI antigen concentration in plasma. Because of the large interindividual variability of TAFI levels in plasma, genetic control may be involved.     

Thrombin activatable fibrinolysis inhibitor and an antifibrinolytic pathway

Coagulation and fibrinolysis are processes that form and dissolve fibrin, respectively. These processes are exquisitely regulated and protect the organism from excessive blood loss or excessive fibrin deposition. Regulation of these cascades is accomplished by a variety of mechanisms involving cellular responses, flow, and protein-protein interactions. With respect to regulation mediated by protein-protein interaction, the coagulation cascade appears to be more complex than the fibrinolytic cascade because it has more components. Yet each cascade is regulated by initiators, cofactors, feedback reactions, and inhibitors. Coagulation is also controlled by an anticoagulant pathway composed of (minimally) thrombin, thrombomodulin, and protein C.(1) Protein C is converted by the thrombin/thrombomodulin complex to activated protein C (APC), which catalyzes the proteolytic inactivation of the essential cofactors required for thrombin formation, factors Va and VIIIa. An analogous antifibrinolytic pathway has been identified recently. This pathway provides an apparent symmetry between coagulation and fibrinolysis and is also composed of thrombin, thrombomodulin, and a zymogen that is activated to an enzyme. The enzyme proteolytically inactivates a cofactor to attenuate fibrinolysis. However, unlike APC, which is a serine protease, the antifibrinolytic enzyme is a metalloprotease that exhibits carboxypeptidase B-like activity. Within a few years of each other, 5 groups independently described a molecule that accounts for this antifibrinolytic activity. We refer to this molecule as thrombin activatable fibrinolysis inhibitor (TAFI), a name that is based on functional properties by which it was identified, assayed, and purified. (Because of the preferences of some journals "activatable" is occasionally referred to as "activable.") This review will encompass a historical account of efforts to isolate TAFI and characterize it with respect to its activation, activity, regulation, and potential function in vivo.     

Coagulation and fibrinolysis in amniotic fluid: physiology and observations on amniotic fluid embolism, preterm fetal membrane rupture, and pre-eclampsia

Two dangerous obstetric complications, amniotic fluid embolism and preterm prelabor rupture of membranes (PROM), can be caused by amniotic fluid (AF) constituents. Disseminated intravascular coagulation (DIC) is related to the former complication, whereas local thrombin/plasmin-dependent collagenolysis in the decidua and fetal membranes is associated with the latter. In AF, most proteins of the coagulation and fibrinolysis system, known as plasma constituents, have been identified based on the activity and/or presence of antigen. The AF levels of most of these proteins are low (< 2 to 5% of the respective maternal plasma levels). However, there are some exceptions: tissue factor (TF), urokinase plasminogen activator (uPA) and its receptor (uPAR), as well as plasminogen activator inhibitors. The AF level of fetal fibrinogen is trace, which is a particular exception. The key enzymes of coagulation and fibrinolysis, thrombin and plasmin, are generated in AF. Thrombin generation is four- to fivefold higher than in maternal plasma as measured by the concentration of the prothrombin fragments 1 + 2 (F 1 + 2) and thrombin-antithrombin complexes, whereas plasmin generation is relatively low as measured by the plasmin-α-2-antiplasmin complexes. Phosphatidylserine, a phospholipid, and thrombin-activatable fibrinolysis inhibitor (TAFI) are novel components of AF. Phosphatidylserine contributes to DIC in AF embolism; TAFI is considered a link between coagulation and fibrinolysis. uPA and uPAR are the factors contributing to PROM via plasmin-dependent proteolysis. Intriguing is the assumption that TF and its inhibitor can be risk factors for PROM through thrombin-dependent activation of matrix prometalloproteinases in the decidua and fetal membranes. It is unknown whether the amniotic pool of hemostatic components is involved in pre-eclampsia pathogenesis.     

Regulation of fibrinolysis by thrombin activatable fibrinolysis inhibitor, an unstable carboxypeptidase B that unites the pathways of coagulation and fibrinolysis

The coagulation and fibrinolytic systems safeguard the patency of the vasculature and surrounding tissue. Cross regulation of coagulation and fibrinolysis plays an important role in preserving a balanced hemostatic process. Identification of Thrombin Activatable Fibrinolysis Inhibitor (TAFI) as an inhibitor of fibrinolysis and one of the main intermediates between coagulation and fibrinolysis, greatly improved our understanding of cross regulation of coagulation and fibrinolysis. As TAFI is an enzyme that is activated by thrombin generated by the coagulation system, its activation is sensitive to the dynamics of the coagulation system. Defects in coagulation, such as in thrombosis or hemophilia, resonate in TAFI-mediated regulation of fibrinolysis and imply that clinical symptoms of coagulation defects are amplified by unbalanced fibrinolysis. Thrombomodulin promotes the generation of both antithrombotic activated protein C (APC) and prothrombotic (antifibrinolytic) activated TAFI, illustrating the paradoxical effects of thrombomodulin on the regulation of coagulation and fibrinolysis. This review will discuss the role of TAFI in the regulation of fibrinolysis and detail its regulation of activation and its potential therapeutic applications in thrombotic disease and bleeding disorders.     

Measurements of plasmin-alpha 2 plasmin inhibitor complex and FDP.D dimer levels in the fibrinolytic therapy of acute pulmonary thromboembolism]

The key enzyme for fibrinolysis is plasmin, which is converted from plasminogen by plasminogen activator. Activated plasmin lyses fibrinogen and fibrin to make fibrin degradation products(FDPs) and plasmin is inactivated immediately by alpha 2 plasmin inhibitor. As FDP.D dimer is derived solely from insoluble fibrin, FDP.D dimer is thought of as an index for clot lysis. We measured plasmin-alpha 2 plasmin inhibitor complex(PIC) and FDP.D dimer plasma levels in 3 patients with acute pulmonary thromboembolism treated with recombinant tissue plasminogen activator(tPA). Fifteen million units of tPA(TD-2061) were infused in one hour on the first, second and third hospital days. PIC and FDP.D dimer before tPA infusion showed slightly elevated values as compared to normal ranges. They increased markedly after tPA infusion. These findings suggest that the fibrinolytic system is slightly activated in the acute phase of pulmonary thromboembolism and also strongly activated by tPA infusion. Increased FDP D dimer suggests that fibrin clots are dissolved by activated plasmin. Improvement of arterial oxygen tension was observed after tPA infusion. As sustained higher FDP.D dimer means the existence of fibrin clots, heparin treatment should be continued for prevention of clot formation as long as FDP.D dimer shows higher value. In conclusion, PIC and FDP.D dimer are useful indices not only to detect the activated state of the fibrinolytic system but also to know clot lysis in tPA treatment.     

A novel simultaneous clot-fibrinolysis waveform analysis for assessing fibrin formation and clot lysis in haemorrhagic disorders

Simultaneous evaluation of coagulation and fibrinolysis facilitates an overall understanding of normal and pathological haemostasis. We established an assay for assessing clot formation and fibrinolysis simultaneously using clot waveform analysis by the trigger of a mixture of activated partial thromboplastin time reagent and an optimized concentration of tissue-type plasminogen activator (0·63 μg/ml) to examine the temporal reactions in a short monitoring time (<500 s). The interplay between clot formation and fibrinolysis was confirmed by analysing the effects of argatroban, tranexamic acid and thrombomodulin. Fibrinogen levels positively correlated with coagulation and fibrinolytic potential and initial fibrin clot formation was independent of plasminogen concentration. Plasminogen activator inhibitor-1-deficient (-def) and α2-antiplasmin-def plasmas demonstrated different characteristic hyper-fibrinolytic patterns. For the specificity of individual clotting factor-def plasmas, factor (F)VIII-def and FIX-def plasmas in particular demonstrated shortened fibrinolysis lag-times (FLT) and enhanced endogenous fibrinolysis potential in addition to decreased maximum coagulation velocity, possibly reflecting the fragile formation of fibrin clots. Tranexamic acid depressed fibrinolysis to a similar extent in FVIII-def and FIX-def plasmas. We concluded that the clot-fibrinolysis waveform analysis technique could sensitively monitor both sides of fibrin clot formation and fibrinolysis, and could provide an easy-to-use assay to help clarify the underlying pathogenesis of bleeding disorders in routine clinical practice.     

Demonstration of enhanced endogenous fibrinolysis in thrombin activatable fibrinolysis inhibitor-deficient mice.

To investigate the importance of thrombin activatable fibrinolysis inhibitor (TAFI) in the stabilization of plasma clots, we have compared fibrinolysis in TAFI-deficient (KO) and wild-type (WT) littermate mice. TAFI-deficient mice were previously generated by targeted gene disruption. The level of TAFI activity generated in plasma from WT mice in the presence of added thrombin and thrombomodulin (activatable TAFI) is twice that of plasma from TAFI heterozygous mice (HET); no activatable TAFI is detected in TAFI KO plasma. In vitro, TAFI KO plasma clots lysed faster than WT plasma clots, and HET plasma clots lysed at an intermediate rate. The rate of clot lysis for KO mice is not changed in the presence of potato carboxypeptidase inhibitor, a specific inhibitor of TAFIa, whereas the WT and HET clot lysis rates are increased in the presence of potato carboxypeptidase inhibitor. C-terminal lysine residues are preserved on partially degraded clots from KO mice, but are absent from partially degraded WT clots. In vivo, in a batroxobin-induced pulmonary embolism model, KO mice displayed a lower retention of fibrin in the lungs than did WT mice. These results are the first demonstration of enhanced endogenous fibrinolysis in an in vivo model without the addition of exogenous thrombolytic.