Deviations in coagulation activation due to treatment with different haemodialysis membranes

Despite systemic heparinization, extracorporeal circulation will induce activation of blood coagulation. Thrombogenicity is associated with biocompatibility of dialysis membranes. Investigation of procoagulatory and fibrinolytic activity is performed prior to and during treatment with haemodialysis. In this study fluctuations of plasma coagulation factor XII, thrombin antithrombin complexes, prothrombin fragment 1 + 2 and thrombus precursor protein were monitored in 10 subjects during treatment with haemodialysis. Subjects were treated with both polysulphone high-flux dialyser membranes (F-60) and low-flux poly-methyl-methacrylate (PMMA) membranes. Immediately after start of treatment, blood in contact with artificial membrane surfaces resulted in a marked decrease in factor XII activity amounting to a mean reduction of 80% in the case of PMMA and a reduction of 40% in the case of F-60. In due course, a steady, on-going generation of thrombin antithrombin complexes was observed in several subjects, especially after treatment with F-60 membranes, amounting to increases exceeding 100% of initial values. Establishment of fibrinogen, prothrombin fragment 1 + 2 and thrombus precursor protein plasma concentrations yielded enhanced results for PMMA compared with the results for treatment with F-60 dialysis membranes. In order to prevent activation of clotting during several stages of haemodialysis, supplementation of anticoagulant can be established on the basis of analytical results of coagulation parameters.     

Tumor markers in an evidence-based medicine

Despite systemic heparinization, extracorporeal circulation will induce activation of blood coagulation. Thrombogenicity is associated with biocompatibility of dialysis membranes. Investigation of procoagulatory and fibrinolytic activity is performed prior to and during treatment with haemodialysis. In this study fluctuations of plasma coagulation factor XII, thrombin antithrombin complexes, prothrombin fragment 1+2 and thrombus precursor protein were monitored in 10 subjects during treatment with haemodialysis. Subjects were treated with both polysulphone high‐flux dialyser membranes (F‐60) and low‐flux poly‐methyl‐methacrylate (PMMA) membranes. Immediately after start of treatment, blood in contact with artificial membrane surfaces resulted in a marked decrease in factor XII activity amounting to a mean reduction of 80% in the case of PMMA and a reduction of 40% in the case of F‐60. In due course, a steady, on‐going generation of thrombin antithrombin complexes was observed in several subjects, especially after treatment with F‐60 membranes, amounting to increases exceeding 100% of initial values. Establishment of fibrinogen, prothrombin fragment 1+2 and thrombus precursor protein plasma concentrations yielded enhanced results for PMMA compared with the results for treatment with F‐60 dialysis membranes. In order to prevent activation of clotting during several stages of haemodialysis, supplementation of anticoagulant can be established on the basis of analytical results of coagulation parameters.     

Left atrial thrombus resolution in non-valvular atrial fibrillation or flutter: biomarker substudy results from a prospective study with rivaroxaban (X-TRA)

Abstract

Background: Non-vitamin K antagonist oral anticoagulants including rivaroxaban are widely used for stroke prevention in patients with atrial fibrillation (AF). We investigated the relationship between plasma biomarkers (indicative of thrombogenesis, fibrinolysis and inflammation) and left atrial thrombus resolution after rivaroxaban treatment.

Methods: This was an ancillary analysis of the X-TRA study, which was a prospective interventional study evaluating the use of rivaroxaban for left atrial/left atrial appendage (LA/LAA) thrombus resolution in AF patients. We assessed various biomarkers of thrombogenesis/fibrinolysis [D-dimer, plasminogen activator inhibitor-1 (PAI-1), prothrombin fragment 1?+?2 (F1,2), thrombin–antithrombin (TAT) complexes, von Willebrand factor (vWF)] and inflammation [high-sensitivity interleukin-6 (hsIL-6), and high-sensitivity C-reactive protein (hsCRP)], measured at baseline and after 6 weeks’ of rivaroxaban treatment.

Results: There was a significant decrease in the mean levels of hsCRP, D-dimer, vWF, and TAT from baseline to end of treatment with rivaroxaban. Although none of the thrombogenesis/fibrinolysis biomarkers showed a significant relationship with thrombus resolution, high inflammatory biomarkers at baseline were significantly associated with an increased chance of the thrombus being completely resolved (hsIL-6) or reduced/resolved (hsCRP).

Conclusions: Biomarkers of inflammation are significantly associated with LA/LAA thrombus outcomes in AF patients prospectively treated with rivaroxaban.     

Hemostatic abnormalities and the severity of illness in patients at the onset of clinically defined sepsis

Objective To find out whether changes within the hemostatic system are related to the severity of illness and organ failure in patients at the onset of clinically defined sepsis and to find some indications for the contribution of endothelial cell activation or perturbation to the patient's status. The following measurements were undertaken: Acute Physiology and Chronic Health Evaluation (APACHE) II score, multiple organ failure (MOF) score, plasma levels of thrombin—antithrombin III complexes (TAT), antithrombin III (AT III), protein C antigen, factor XII, and plasminogen activator inhibitor type 1 antigen (PAI-1), neopterin, and interleukin 6 (IL-6).Design A prospective case series study.Setting Intensive care unit (ICU) of the Department of Internal Medicine, Justus Liebig University, Giessen, Germany.Patients 28 consecutive patients (11 females, 17 males; mean age 58 years) with clinically defined sepsis. Eleven patients were admitted from the surgical ICU (9 after elective surgery, 2 after trauma surgery). The operations were done 1–26 days (mean 14 days) prior to the onset of sepsis.Main results At the onset of sepsis we found elevated plasma levels of TAT, PAI-1, neopterin, and IL-6, and lowered plasma levels of AT III, factor XII, and protein Cantigen. Neopterin, PAI-1, IL-6, and factor XII showed a statistically significant correlation with the APACHE II score. The MOF score is significantly correlated with IL-6 and neopterin. The extent of hemostatic abnormalities was related to increasing levels of IL-6.Conclusions Clinical evidence of a septic process is most likely to be preceded by activation of the hemostatic system, the vascular endothelium, and the monocyte/macrophage system. IL-6 may have a regulatory function for hemostasis in inflammation. Laboratory monitoring could be helpful in deciding whether to start early intensive therapy in patients at risk for sepsis.     

Production of thrombi on intact endothelium by use of antiheparin agents in vivo

It had been suggested that antithrombin activity on the surface of intact endothelial cells may play a role in inhibiting platelet adhesion and thrombus formation. The antithrombin activity may be due to thrombomodulin or to activation of antithrombin III by glycosaminoglycans or thrombomodulin, or possibly a combination of these. This inhibitory activity has been shown to be affected by such antiheparin agents as protamine, hexadimethrine bromide (Polybrene; Aldrich Chemical Co., Milwaukee, Wis.) and platelet factor 4, as well as by such enzymes as heparinase and heparitinase. We have used a hamster cheek pouch preparation to observe thrombus formation in vivo in a normal vascular flow, to determine whether the production of thrombi by thrombin can be enhanced by antiheparin agents. After intra-arterial injection or topical application of protamine or hexadimethrine bromide, platelet adhesion and thrombus formation on intact arteriolar endothelium was produced by a dose of thrombin, which when injected alone had no effect. No thrombi were found in venules or capillaries. Injection of heparin before or after the antiheparin agents necessitated a larger dose to enhance the action of thrombin. On electron microscopy the thrombi were found to consist primarily of platelets adherent to an intact endothelium. The possible clinical implications of these observations are discussed.     

Fibrin moderates the catalytic action of heparin but not that of dermatan sulfate on thrombin inhibition in human plasma

Three recent studies have reported that fibrin in solution significantly inhibits the ability of heparin to catalyze the inhibition of thrombin by antithrombin III. In addition, heparin inhibits the release of fibrinopeptide A by clot-bound thrombin less effectively than it inhibits the release of fibrinopeptide A by thrombin in solution. We have also reported that dermatan sulfate, which catalyzes thrombin inhibition by heparin cofactor II, inhibits thrombus growth in rabbits more effectively than heparin. Because the results of these studies suggest that fibrin inhibits the reactivity of thrombin with antithrombin III-heparin but not with heparin cofactor II-dermatan sulfate, we compared the relative catalytic effects of heparin and dermatan sulfate on thrombin inhibition in plasma, both in the presence and absence of fibrin. We quantitated the rates of thrombin inhibition by antithrombin III and heparin cofactor II by specific enzyme-linked immunosorbent assays. When it was generated, fibrin was kept in solution by adding 2 mmol/L Gly-Pro-Arg-Pro to plasma. Fibrinogen-fibrin reduced the reactivity of thrombin with plasma antithrombin III, both in the presence of and in the absence of heparin. In contrast, the catalytic action of dermatan sulfate on thrombin inhibition by plasma heparin cofactor II was unimpaired by fibrinogen-fibrin. Based on the ability of dermatan sulfate to inhibit thrombus growth in rabbits, failure of fibrinogen-fibrin to moderate the catalytic action of dermatan sulfate may account for its greater antithrombotic effectiveness relative to that of heparin.     

Prorenin-renin conversion by the contact activation system in human plasma: role of plasma protease inhibitors

Acid-pretreated normal human plasma generates renin activity at 0 degree C and neutral pH by the activation of prorenin. The activation is caused by kallikrein generated from prekallikrein by activated factor XII. Nonacidified plasma also generates renin at 0 degree C, but at a lower rate (cold-promoted activation). In normal plasma, 14% +/- 1% of prorenin (mean +/- SEM, n = 30) was activated during incubation at 0 degree C for 7 days (range 6% to 26%). Cold-promoted activation of prorenin was within the normal range in plasma deficient in factor XI, X, IX, VIIIC, VII, V, prothrombin, or high mol wt kininogen. Cold-promoted activation of prorenin was less than or equal to 1% in plasma deficient in factor XII or prekallikrein. Reconstitution of these plasmas with highly purified factor XII or prekallikrein restored normal prorenin activation. Correction of high mol wt kininogen deficiency had no effect. Thus cold-promoted activation of prorenin depends on the presence of factor XII and prekallikrein, whereas the other clotting factors are not essential. The influence of the inhibitors C1 esterase-inhibitor, alpha 2-macroglobulin, antithrombin III, and alpha 1-antitrypsin on the activation of prorenin was studied in factor XII-deficient plasma from which one or more of these inhibitors had been selectively removed by immunoadsorption. Factor XII was subsequently added, and the generation of renin at 37 degrees C was observed after complete factor XII-high mol wt kininogen-mediated activation of prekallikrein induced by dextran sulfate. No activation of prorenin was observed at 37 degrees C after depletion of C1 esterase inhibitor, alpha 2-macroglobulin, antithrombin III, or alpha 1-antitrypsin. When prekallikrein was activated in plasma depleted of both C1 esterase-inhibitor and alpha 2-macroglobulin, 6% of prorenin was activated in 2 hours at 37 degrees C. After additional depletion of antithrombin III, the activation increased to 47%. These results indicate that the contact activation system is capable of activating prorenin in plasma at physiologic pH and temperature when the three most important kallikrein inhibitors, C1 esterase-inhibitor, alpha 2-macroglobulin, and antithrombin III, are absent.     

Continuous venovenous haemofiltration using polyacrylonitrile filters does not activate contact system and intrinsic coagulation pathways

Objectives: To investigate whether continuous venovenous haemofiltration using polyacrylonitrile filters causes activation of the contact system and intrinsic coagulation pathways and if this, and/or low plasma levels of endogenous anticoagulants, influences filter lifespan. Design: Observational study. Setting: University Teaching Hospital Intensive Care Unit. Patients: Twelve critically ill patients with acute renal failure receiving continuous venovenous haemofiltration. Interventions: Blood samples were taken before starting haemofiltration, at 15 min, 1 h, 3–4 h, 8–12 h, 24 h and at 24-h intervals thereafter until filter blockage occurred. Measurement was made of the contact and intrinsic coagulation system proteins factor XII, activated factor XII and prekallikrein and the protease inhibitors antithrombin III, heparin co-factor II, alpha₂-macroglobulin and C1-esterase inhibitor. Thrombin-antithrombin complex levels were measured to provide evidence of thrombin generation. Results: (i) Factor XII, prekallikrein and contact system inhibitors were subnormal in 10/12 and activated factor XII raised in 11/12 patients at baseline, implying pre-existing contact pathway activation. (ii) No change occurred during haemofiltration in the intrinsic coagulation pathway factor or inhibitor levels. (iii) Clotting of the filter circuit within the first 24 h occurred in 5/12 and was associated with low baseline levels of antithrombin III and heparin co-factor II. Only in these patients did thrombin-antithrombin complex levels rise significantly. Conclusions: The contact system was not activated further by continuous venovenous haemofiltration using polyacrylonitrile filters in critically ill patients. Premature clotting of the haemofilter circuit was more common in patients with very low levels of antithrombin III and heparin co-factor II; although this was related to thrombin generation, the intrinsic coagulation pathway does not appear to be implicated. Received: 6 February 1995 Accepted: 4 October 1996     

Identification in vitro of an endothelial cell surface cofactor for antithrombin III. Parallel studies with isolated perfused rat hearts and microcarrier cultures of bovine endothelium.

Two in vitro systems were used to identify an antithrombin III cofactor activity on vascular endothelium. Langendorff rat heart preparations or columns packed with endothelium cultured on microcarrier beads were perfused with mixtures of purified thrombin and antithrombin III. With each preparation, accelerated inhibition of thrombin by antithrombin III occurred during passage over endothelium. Platelet factor 4, protamine sulfate and diisopropylphosphoryl thrombin, all antagonists of the antithrombin III cofactor activity of heparin, significantly reduced the capacity of the preparation to inhibit thrombin. It is concluded that a substance with the functional properties of a stationary phase cofactor for antithrombin III is present on the microvascular endothelium and there catalyzes the inactivation of circulating free thrombin.     

Role of Factor XII in hemostasis and thrombosis: clinical implications

The plasma coagulation system reacts quickly to limit blood loss from injury sites but also contributes to vascular thrombosis. In current models of hemostatic balance, normal coagulation and thrombosis represent two sides of the same coin, however, recent data from gene-deleted murine models have challenged this dogma. Deficiency of coagulation Factor XII (Hageman factor), a serine protease that initiates the intrinsic pathway of coagulation, severely impairs arterial thrombus formation but is not associated with excessive bleeding. These findings suggest that fibrin-generating mechanisms that operate during pathologic thrombus formation involve pathways distinct from those that are active during normal hemostasis. As Factor XII selectively contributes to thrombus formation in occlusive disease, but not to normal hemostasis, inhibition of this protease may offer a novel treatment strategy for prevention of arterial thrombosis with minimal or no risk of bleeding.     

Contact between a polymer and whole blood: sequence of events leading to thrombin generation

The mechanism by which thrombin is generated on a polymer surface in an extracorporeal circuit is not yet fully understood. To address this question we have developed an in vitro chamber model in which whole blood containing heparin (1 IU/mL) comes in contact with a commonly used biomaterial, polyvinyl chloride (PVC). Incubation of blood in the chamber for 60 minutes at 37 degrees C resulted in the binding of platelets to the material surface and the generation of thrombin-antithrombin complexes. Corn trypsin inhibitor, a specific inhibitor of factor XIIa, inhibited this thrombin-antithrombin complex generation in blood in contact with PVC, which is not considered an efficient activator of factor XII. The addition of the glycoprotein IIb/IIIa inhibitor Ro44-9883 abrogated platelet binding and aggregation and resulted in decreased generation of thrombin-antithrombin complexes. Thrombin-antithrombin generation was also negligible in platelet-rich plasma but could be partially restored in the presence of erythrocytes. Taken together, these data are compatible with a model in which thrombin generation is triggered by factor XII. The response to contact with PVC appears to begin with a low-grade generation of thrombin that involves both erythrocytes and leukocytes and that activates platelets, followed by the activation of a platelet-dependent amplification loop that produces most of the thrombin.     

Inhibitors of blood coagulation factors Xa and IIa synergize to reduce thrombus weight and thrombin generation in vivo and in vitro

BACKGROUND: Many compounds currently in development for treatment of thrombotic disorders demonstrate high specificity for single targets of blood coagulation such as factor Xa (FXa) or thrombin. AIM: The aim of this study is to determine if inhibition of both FXa and thrombin by simultaneous administration of PD0313052 and argatroban, respectively, synergistically increases the effect of either drug alone in vivo and in vitro. METHODS AND RESULTS: Analyses of thrombin generation from combined inhibition in human plasma using statistical methods of Bliss independence identified a synergistic reduction in thrombin production 30% lower than predicted by simple additivity. The greatest synergy occurred at concentrations of each compound below their individual IC50 values. In a rabbit arterio-venous shunt model (RAV) of thrombosis, co-administration of PD0313052 and argatroban reduced thrombus weight (TW) to a much greater degree than expected by additivity alone producing a synergistic decrease of 45% over the level predicted by additivity. Analyses of thrombin generation in plasma samples from the RAV also demonstrated 38% synergy ex vivo. Furthermore, at plasma concentrations with the greatest synergistic effect, no increase in bleeding or appreciable change in prothrombin time, activated partial thromboplastin time, or activated clotting time was observed, but thrombus weight reduction was greater than twofold higher than that expected from simple additivity. CONCLUSIONS: These results demonstrate a significant synergistic antithrombotic effect of combining low doses of PD0313052 and argatroban and support the hypothesis that simultaneous targeting of multiple coagulation enzymes may offer an improved therapeutic index in the prevention and treatment of thrombosis.     

Pharmacokinetics of desferrioxamine and of its iron and aluminium chelates in patients on haemodialysis

We have used a new analytical micromethod to study the pharmacokinetics of desferrioxamine and its aluminium chelates in patients with chronic renal failure on haemodialysis.

Desferrioxamine (Desferal®, CIBA, Basle) was given by 1-h infusion just after the haemodialysis at 20, 40, 80 mg/kg body wt. and during the first and the last hour of the haemodialysis at 40 mg/kg. The concentrations of desferrioxamine during infusions showed a linear increase with increasing doses. The maximum concentrations and the AUC obtained when desferrioxamine was infused during the haemodialysis were not statistically different but slightly lower than those obtained in post dialysis administration. This result indicates that the loss of desferrioxamine by transfer in the dialysate is quite moderate within 1 h. During the interdialysis period, there was a decrease of plasma desferrioxamine concentrations with a mean half-life of 18.7 ± 5.2 h and an increase in plasma concentrations of aluminium desferrioxamine chelate. In vitro studies show that a lengthy contact between desferrioxamine and plasma is necessary for complete chelation of Al already present in plasma. During the following dialysis session, there was an important decrease of desferrioxamine and of its iron and aluminium chelates in blood plasma representing their transfer to the dialysis fluid.     

Therapeutic modulation of coagulation in sepsis

Based on the increasing knowledge of defects in haemostasis in patients with sepsis as well as on the non-conclusive results of studies which tried to increase the prognosis by modulating cytokine response of the patients, in the last years the impact of therapeutic modulation of coagulation in sepsis has been investigated. In contrast to the results of phase III studies with the coagulation inhibitors antithrombin and tissue factor pathway inhibitor recombinant human activated protein C (rhAPC) resulted in a significant reduction in mortality for the whole study population. Data analyses showed, that treatment with rhAPC was clinically beneficial especially in patient groups who showed a high mortality in the placebo arm. Inhibition of thrombus formation due to the therapy with natural coagulation inhibitors resulted in an increase of sepsis-imminent haemorrhage, which became significant in some studies. Treatment with antithrombin and heparin resulted in a considerable increase in bleeding complications and on the other hand, may have antagonized the expected effect of antithrombin on the patient's prognosis. Some results suggesting beneficial effects of heparin on patient prognosis in the placebo arms and on the other hand negative effects of heparin in the verum arms -- especially with antithrombin or tissue factor pathway inhibitor -- let to a controversial discussion of the risk/benefit relation of heparin, given in prophylactic doses to patients with severe sepsis. Whereas the impact and optimal application of heparin to patients with severe sepsis needs to be clarified study results with rhAPC resulted in the approval of this therapy and the implementation in the guidelines of the treatment of patients with severe sepsis.     

Course and blood coagulation findings following systemic short-term fibrinolysis in acute myocardial infarct

A series of 16 consecutive patients with acute myocardial infarction was investigated with respect to changes in coagulatory parameters after intravenous short-term treatment with 1,500 000 IU streptokinase (SK) over a period of 90 minutes. Samples for coagulation assays (fibrinogen, thrombin, time activated partial thromboplastin time (aPTT), normotest, thrombin-coagulase time, platelets, antithrombin III, plasminogen and antiplasmin activity, alpha 2-macroglobulin, alpha 1-antitrypsin, factor X a were collected before and immediately after iv SK, and after 4, 8, 12, 24, 36, 48 and 72 hours. Platelets, antithrombin III, factor X a, alpha 1-antitrypsin and alpha 2-macroglobulin showed no changes over the observed period. The concentrations of fibrinogen and the activities of plasminogen and antiplasmin decreased clearly during the first 24 hours, reaching a minimum immediately after SK administration. Thrombin time and aPTT were prolonged for 36 hours, with a maximum in the first hours after lysis. Conclusions: Invasive diagnostic and/or therapeutic procedures during the first 24 hours after SK lysis should be carried out only for a definite, strict indication and under repeated control of the coagulatory status. After 24-36 hours there is a trend to normalisation of haemostasis. After 36 hours, surgery may be performed without fear of complications due to abnormal coagulability.     

Characterization of proteases in AHF concentrates: effect on factor VIII:von Willebrand protein as assessed by high-pressure gel permeation chromatography

Antihemophilic factor concentrates were surveyed for amidolytic activity on the chromogenic substrates S2238, S2302, S2222, and S2251, which are sensitive to thrombin, kallikrein, factor Xa, and plasmin, respectively. For antihemophilic factor concentrates from two manufacturers, the rates of amidolysis of S2238 and S2302 were approximately an order of magnitude greater than the rates of amidolysis of S2222 and S2251. The S2238 and S2302 activities were characterized by quantitating their interactions with specific substrates or inhibitors. The Km for amidolysis of S2238 was 558 mumol/L, which is 80 times higher than for thrombin but in close agreement to the reported value for activated protein C. The S2238 activity was not inhibited by the thrombin-specific inhibitor dansylarginine N-(3-ethyl-1,5-pentanediyl)amide, nor by soybean trypsin inhibitor or micromolar concentrations of antithrombin III in the presence of heparin. The S2238 activity was inhibited by D-Phe-Pro-Arg-CH2Cl, but with an estimated second-order rate constant of 3 X 10(5) mol/L-1 minute-1, approximately 1000 times less than for thrombin. These data are consistent with the identity of the S2238 activity as activated protein C. On the other hand, the S2302 activity in antihemophilic factor concentrates was most likely attributable to kallikrein. This was based on the agreement with authentic kallikrein of the Km for S2302 of 154 mumol/L as well as by the rapid inactivation by nanomolar concentrations of the kallikrein-specific inhibitor D-Phe-Phe-Arg-CH2Cl. However, the relative resistance of the S2302 activity to inhibition by soybean trypsin inhibitor or antithrombin III and the partial inhibition by aprotinin suggested that a large proportion of the kallikrein was bound to alpha 2-macroglobulin. This was confirmed by immunoprecipitation using specific anti alpha 2-macroglobulin IgG. The potential for proteolysis of factor VIII:von Willebrand protein during its purification from antihemophilic factor concentrates was demonstrated, and the proteolyzed factor VIII coagulant species was characterized. High-pressure gel permeation chromatography of purified factor VIII:von Willebrand protein at high ionic strength resulted in two sharp peaks of factor VIII procoagulant activity. The earlier eluting peak corresponded with the void volume, and the later peak eluted with an apparent molecular weight of 53,000 daltons. Immediately after separation, the 53,000-dalton factor VIII coagulant had at least a 100-fold higher specific activity than the factor VIII coagulant present in the void volume. However, the 53,000-dalton factor VIII coagulant was labile, with a half-life of 80 minutes.(ABSTRACT TRUNCATED AT 400 WORDS)     

Reduction of contact activation related fibrinolytic activity in factor XII deficient patients. Further evidence for the role of the contact system in fibrinolysis in vivo.

In this study the contribution of activation of the contact system to activation of the fibrinolytic system in vivo was investigated in healthy volunteers and in factor XII deficient patients. The plasminogen activating activity in plasma from healthy volunteers after infusion of desamino D-arginine vasopressin (DDAVP) was only partially blocked (for 77%) with specific antibodies to tissue-type plasminogen activator and urokinase type plasminogen activator. The residual activity could be quenched by a monoclonal antibody that inhibits factor XII activity and was not present in patients with a factor XII deficiency. The formation of plasmin upon the DDAVP stimulus as reflected by circulating plasmin-alpha 2-antiplasmin complexes was lower in factor XII deficient patients than in healthy volunteers. Activation of the contact system occurred after DDAVP infusion in healthy volunteers and was absent in factor XII deficient patients. These results indicate that DDAVP induces a plasminogen activating activity that is partially dependent on activation of the contact system and that contributes to the overall fibrinolytic activity as indicated by the formation of plasmin-alpha 2-antiplasmin complexes. This fibrinolytic activity is impaired in factor XII deficient patients which may explain the occurrence of thromboembolic complications in these patients.     

Human alpha2-macroglobulin and its antitrypsic and antithrombin activities in serum and plasma.

alpha2-Macroglobulin level, trypsin protein esterase and progressive antithrombin activities were measured in normal and nephrotic sera and plasma. Trypsin protein esterase activity was proportional to the alpha2-macroglobulin concentration in serum and plasma from both normal and nephrotic patients. The results were different, however, with progressive antithrombin activity: in normal plasma, antithrombin III is the main thrombin inhibitor, then alpha2-macroglobulin and alpha1-antitrypsin, whereas in nephrotic syndrome patients, alpha2-macroglobulin is the main thrombin inhibitor.     

Defective thrombus formation in mice lacking coagulation factor XII

Blood coagulation is thought to be initiated by plasma protease factor VIIa in complex with the membrane protein tissue factor. In contrast, coagulation factor XII (FXII)-mediated fibrin formation is not believed to play an important role for coagulation in vivo. We used FXII-deficient mice to study the contributions of FXII to thrombus formation in vivo. Intravital fluorescence microscopy and blood flow measurements in three distinct arterial beds revealed a severe defect in the formation and stabilization of platelet-rich occlusive thrombi. Although FXII-deficient mice do not experience spontaneous or excessive injury-related bleeding, they are protected against collagen- and epinephrine-induced thromboembolism. Infusion of human FXII into FXII-null mice restored injury-induced thrombus formation. These unexpected findings change the long-standing concept that the FXII-induced intrinsic coagulation pathway is not important for clotting in vivo. The results establish FXII as essential for thrombus formation, and identify FXII as a novel target for antithrombotic therapy.     

Some clotting factors in plasma during danazol therapy: free and total protein S, but not C4b-binding protein, are elevated by danazol therapy.

Anabolic steroids are known to increase the plasma concentrations of certain plasma proteins. In four patients given treatment with danazol, an attenuated androgen, the concentrations of heparin cofactor II, Hageman factor (factor XII), protein C, and both free and total protein S increased significantly when tested 39 to 103 days after the start of therapy. The titers of these proteins in samples obtained 21 days to 5 years after therapy was discontinued were similar to those before treatment, except for total protein S, the titer of which remained elevated. No significant changes in the titers of C4b binding protein or plasma plasmin inhibitory activity were found.