Factor XII: a novel target for safe prevention of thrombosis and inflammation

Plasma protein factor XII (FXII) activates the procoagulant and proinflammatory contact system that drives both the kallikrein–kinin system and the intrinsic pathway of coagulation. When zymogen FXII comes into contact with negatively charged surfaces, it auto‐activates to the serine proteaseactivated FXII (FXIIa). Recently, various in vivo activators of FXII have been identified including heparin, misfolded protein aggregates, polyphosphate and nucleic acids. Murine models have established a central role of FXII in arterial and venous thrombosis. Despite its central function in thrombosis, deficiency in FXII does not impair haemostasis in animals and humans. In a preclinical cardiopulmonary bypass system in large animals, the FXIIa‐blocking antibody 3F7 prevented thrombosis; however, in contrast to traditional anticoagulants, bleeding was not increased. In addition to its function in thrombosis, FXIIa initiates formation of the inflammatory mediator bradykinin. This mediator increases vascular leak, causes vasodilation, and induces chemotaxis with implications for septic, anaphylactic and allergic disease states. Therefore, targeting FXIIa appears to be a promising strategy for thromboprotection without associated bleeding risks but with anti‐inflammatory properties.     

Plasma and plasma components in the management of disseminated intravascular coagulation

A variety of clinical conditions can cause systemic activation of coagulation that ranges from insignificant laboratory changes to severe disseminated intravascular coagulation (DIC). DIC consists of a widespread systemic activation of coagulation, resulting in diffuse fibrin deposition in small and midsize vessels. There is compelling evidence from clinical and experimental studies that DIC is involved in the pathogenesis of microvascular dysfunction and contributes to organ failure. In addition, the massive and ongoing activation of coagulation can result in depletion of platelets and coagulation factors, which might cause bleeding. Recent insight into important pathogenetic mechanisms that might lead to DIC has resulted in novel preventive and therapeutic approaches to patients with sepsis and derangement of coagulation. Supportive strategies aimed at inhibition of coagulation activation might theoretically be justified and have been found beneficial in experimental and initial clinical studies. These strategies comprise inhibition of tissue factor-mediated activation of coagulation or restoration of physiological anticoagulant pathways.     

Infection and hemostasis

Localised and following systemic inflammatory reaction accompanying progression of infection causes generation of anti-inflammatory cytokines. They activate leucocytes, endothelium, coagulation and fibrinolysis. Sepsis is usually accompanied by already decompensated disseminated intravascular coagulation which significantly affects mortality of patients with this disease. The main cause of hypercoagulation state during sepsis seems to be inhibition of fibrinolysis as a result of overproduction of plasminogen activator inhibitor-1 in later stages of the disease. Some microorganisms have specific properties which affect individual components of hemostasis and thus increase their virulence. Because natural inhibitors of coagulation have not only anticoagulation but also strong anti-inflammatory effect, they seem to be an optimum remedy for fluorid coagulopathy during sepsis. Moreover, their use usually does not increase risk of bleeding.     

Disseminated intravascular coagulation,nonbacterial thrombotic endocarditis and adult pulmonary hyaline membranes-an interrelated triad?: Report of a case following small bowel resection for a strangulated inguinal hernia

After small bowel resection for a strangulated inguinal hernia, this seventy-five year old man had respiratory distress, oliguria and shock. At autopsy, disseminated intravascular coagulation, nonbacterial thrombotic endocarditis and pulmonary hyaline membranes were found. An attempt is made to relate the pulmonary hyaline membranes to the previously related disseminated intravascular coagulation and nonbacterial thrombotic endocarditis. The trigger for disseminated intravascular coagulation in this case could have been the release of a procoagulant such as thromboplastin or even a fibrinolytic inhibitor from the strangulated bowel. The pertinent literature is discussed.     

Cellular origin and procoagulant properties of microparticles in meningococcal sepsis

Patients with meningococcal sepsis generally suffer from disseminated intravascular coagulation (DIC). The aim of this study was to address whether these patients have elevated numbers of circulating microparticles that contribute to the development of DIC. Plasma samples from 5 survivors, 2 nonsurvivors, and 5 healthy volunteers were analyzed for the presence of microparticles by flow cytometry. Ongoing coagulation activation in vivo was quantified by enzyme-linked immunosorbent assay of plasma prothrombin fragment F(1 + 2), and procoagulant properties of microparticles in vitro were estimated by thrombin-generation assay. On admission, all patients had increased numbers of microparticles originating from platelets or granulocytes when compared with controls (P =.004 and P =.008, respectively). Patients had elevated levels of F(1 + 2) (P =.004), and their microparticles supported thrombin generation more strongly in vitro (P =.003) than those of controls. Plasma from the patient with the most fulminant disease course and severe DIC contained microparticles that expressed both CD14 and tissue factor, and these microparticles demonstrated extreme thrombin generation in vitro. We conclude that patients with meningococcal sepsis have elevated numbers of circulating microparticles that are procoagulant. These findings may suggest a novel therapeutic approach to combat clinical conditions with excessive coagulation activation.     

New Potential Therapeutic Modalities: Antithrombin III

The role of the disordered coagulation in the pathogenesis of the microcirculatory failure that frequently accompanies sepsis has been clearly established in a multitude of preclinical animal systems. There is consistent and reliable evidence of activation of the coagulation pathways resulting in a net procoagulant state in human septic shock. Despite this experimental and clinical information, there in no compelling evidence that the therapeutic administration of anticoagulants actually benefits patients with severe sepsis or septic shock.Antithrombin III has been used clinically for over twenty years for the prevention and treatment of disseminated intravascular coagulation and multi organ failure in patients with sepsis. A wealth of experimental evidence now supports the potential clinical utility of Antithrombin III in sepsis. This endogenous plasma protein has both anticoagulant and anti-inflammatory properties that may prove to be of therapeutic value. The practical clinical value of Antithrombin III in septic shock is currently being tested in a large phase III multinational study.     

Blood coagulation, inflammation, and malaria

Malaria remains a highly prevalent disease in more than 90 countries and accounts for at least 1 million deaths every year. Plasmodium falciparum infection is often associated with a procoagulant tonus characterized by thrombocytopenia and activation of the coagulation cascade and fibrinolytic system; however, bleeding and hemorrhage are uncommon events, suggesting that a compensated state of blood coagulation activation occurs in malaria. This article (i) reviews the literature related to blood coagulation and malaria in a historic perspective, (ii) describes basic mechanisms of coagulation, anticoagulation, and fibrinolysis, (iii) explains the laboratory changes in acute and compensated disseminated intravascular coagulation (DIC), (iv) discusses the implications of tissue factor (TF) expression in the endothelium of P. falciparum infected patients, and (v) emphasizes the procoagulant role of parasitized red blood cells (RBCs) and activated platelets in the pathogenesis of malaria. This article also presents the Tissue Factor Model (TFM) for malaria pathogenesis, which places TF as the interface between sequestration, endothelial cell (EC) activation, blood coagulation disorder, and inflammation often associated with the disease. The relevance of the coagulation-inflammation cycle for the multiorgan dysfunction and coma is discussed in the context of malaria pathogenesis.     

Potential role of recombinant activated factor VII for the treatment of severe bleeding associated with disseminated intravascular coagulation: a systematic review.

Recombinant activated factor VII (rFVIIa) is a novel hemostatic agent, originally developed for the treatment of hemorrhage in hemophiliacs with inhibitors, which has been successfully used recently in an increasing number of nonhemophilic bleeding conditions. In the present systematic review we report the existing literature data on the use of this hemostatic agent in severe bleeding, unresponsive to standard treatment, associated with disseminated intravascular coagulation. A total of 99 disseminated intravascular coagulation-associated bleeding episodes treated with rFVIIa were collected from 27 published articles: in the majority of the cases, the underlying disorder complicated by disseminated intravascular coagulation was a postpartum hemorrhage, while in the remaining cases it was a cancer, trauma, sepsis or liver failure. Although limited, the data available suggest that rFVIIa could have a potential role in this clinical setting. Large randomized trials are needed, however, to confirm the preliminary results and to assess the safety and dosing regimens of this agent in refractory bleeding associated with disseminated intravascular coagulation.     

Administration of recombinant activated factor VII (NovoSeven) in three cases of uncontrolled bleeding caused by disseminated intravascular coagulopathy.

Recombinant activated factor VII has been used successfully in many cases of traumatic and surgical bleeding complications that were unresponsive to standard treatment. However, because disseminated intravascular coagulation can develop from a thrombin burst as a side effect of recombinant activated factor VII, it is not yet established for bleeding complications induced by disseminated intravascular coagulation. This article presents 3 patients with severe sepsis and fulminant disseminated intravascular coagulation. Excessive microvascular bleeding persisted despite conventional therapy, and surgical intervention and radiologic embolization did not control bleeding. After administration of recombinant activated factor VII, bleeding ceased in all patients, and no overt thromboembolic events occurred. One patient survived to be discharged from the hospital. The other 2 patients died from refractory multiorgan failure and overall poor prognosis. Recombinant factor VIIa might be an option for the treatment of severe bleeding complications in the case of DIC refractory to the conventional therapy.     

Beta 2-Glycoprotein I binds factor XI and inhibits its activation by thrombin and factor XIIa: loss of inhibition by clipped beta 2-glycoprotein I

Activation of factor XI (FXI) by thrombin in vivo plays a role in coagulation by providing an important positive feedback mechanism for additional thrombin generation. FXI is activated in vitro by thrombin, or FXIIa in the presence of dextran sulfate. In this report, we investigated the effect of beta(2)-glycoprotein I (beta(2)GPI) on the activation of FXI. beta(2)GPI bound FXI in vitro and inhibited its activation to FXIa by thrombin and FXIIa. The affinity of the interaction between beta(2)GPI and FXI was equivalent to the interaction between FXI and high molecular weight kininogen. Inhibition of FXI activation occurred with lower concentrations of beta(2)GPI than found in human plasma. Proteolytic clipping of beta(2)GPI by plasmin abolished its inhibition of FXI activation. The results suggest a mechanism of regulation whereby physiological concentrations of beta(2)GPI may attenuate thrombin generation in vivo by inhibition of FXI activation. Plasmin cleavage of beta(2)GPI provides a negative feedback that counteracts its inhibition of FXI activation.     

Study of contact activation in endemic hepatosplenomegaly.

Factors of the contact activation complex--FXII, FXI, high-molecular-weight kininogen (HMWK) and prekallikrein (PK) as well as D-dimer were measured in 68 schistosomal patients with and without co-existing chronic hepatitis B virus infection (HBV). Fifty-four cases had mixed hepatosplenic schistosomiasis and HBV infection whereas 14 were suffering from hepatosplenic (HS) schistosomiasis alone. A group of twelve age-matched, healthy individuals served as controls. All coagulation parameters were significantly reduced in both disease groups compared to the healthy controls. The decreased activity of the contact proteins could be attributed to decreased hepatic synthesis, consumption due to disseminated intravascular coagulation (DIC) and to the effect of endotoxins. In mixed schistosomiasis and HBV infections, however, the levels of the contact activation factors were not significantly different from those obtained in patients with HS alone. This apparently paradoxical finding does not, however, exclude a role for co-existing HBV infection in speeding up complications in hepatosplenic schistosomiasis.     

Regulatory role of cytokines in disseminated intravascular coagulation.

Disseminated intravascular coagulation (DIC) can complicate a number of diseases. DIC in the setting of sepsis is considered to result from strong activation of the coagulation system and concurrent inhibition of fibrinolysis and other anticoagulant pathways. Cytokines have been implicated as important mediators in these hemostatic alterations. This article summarizes recent insights into which cytokines are likely to be involved in the procoagulant response to systemic infection.     

INCREASE OF ACTIVATED FACTOR VIIA AND HAEMOSTATIC MOLECULAR MARKERS IN JUVENILE CHRONIC ARTHRITIS

Activated factor VIIa (FVIIa), von Willebrand factor antigen(vWF:Ag), D-dimer and thombin-antithrombin III complex (TAT)were measured to monitor coagulation status in patients withjuvenile chronic arthritis (JCA). Subjects included 14 patientswith systemic JCA, 16 with pauciarticular JCA and 16 with polyarticularJCA without disseminated intravascular coagulopathy, thrombosisor liver dysfunction. All types of JCA showed an increase ofFVIIa, D-dimer and TAT, indicating enhanced activation of coagulation.In systemic JCA only there was also characteristically an elevationof vWF:Ag. We conclude that all types of JCA constitute a stateof subclinical hypercoagulopathy caused by tissue damage andthat additionally systemic JCA involves a prothrombotic stateassociated with or precipitated by vasculitis. KEY WORDS: Factor VIIa, Juvenile chronic arthritis     

Activation of the contact system of coagulation does not contribute to the hemostatic imbalance in hypertriglyceridemia.

In vitro, triglyceride-rich lipoproteins may act as a surface to initiate the contact system of coagulation. Therefore, we studied the activation of factor XII (FXII), prekallikrein, and FXI and the generation of thrombin in 52 hypertriglyceridemic patients before and after 12 weeks of triglyceride-lowering treatment with gemfibrozil or n-3 polyunsaturated fatty acids. Thrombin generation was assessed by measuring the levels of prothrombin fragment F1+2 and thrombin-antithrombin (TAT) complexes. Contact activation was assessed by measuring FXIIa, kallikrein, and FXIa in complex with their major inhibitor, C1 inhibitor, and FXIa was also determined as part of a complex with alpha(1)-antitrypsin. Triglyceride and cholesterol levels decreased equally in both treatment groups. In the gemfibrozil group, there was a significant decrease in F1+2, while TAT complexes did not change. FXIIa- and kallikrein-C1 inhibitor complexes were elevated in 13% and 9% of the patients before treatment, respectively, and no changes were observed on triglyceride-lowering therapy. Also, no significant changes in regard to FXIa-C1 inhibitor and FXIa-alpha(1)-antitrypsin complexes were seen. FXIa-alpha(1)-antitrypsin complexes were present in 70% of the patients before therapy and were positively correlated with the level of TAT complexes. In conclusion, we did not detect an effect on activation markers of the contact coagulation system in hypertriglyceridemic patients after triglyceride-lowering therapy. Therefore, contact activation is not likely to contribute to the hypercoagulability seen in these patients.     

Factor XIIa regulates the structure of the fibrin clot independently of thrombin generation through direct interaction with fibrin

Recent data indicate an important contribution of coagulation factor (F)XII to in vivo thrombus formation. Because fibrin structure plays a key role in clot stability and thrombosis, we hypothesized that FXII(a) interacts with fibrin(ogen) and thereby regulates clot structure and function. In plasma and purified system, we observed a dose-dependent increase in fibrin fiber density and decrease in turbidity, reflecting a denser structure, and a nonlinear increase in clot stiffness with FXIIa. In plasma, this increase was partly independent of thrombin generation, as shown in clots made in prothrombin-deficient plasma initiated with snake venom enzyme and in clots made from plasma deficient in FXII and prothrombin. Purified FXII and α-FXIIa, but not β-FXIIa, bound to purified fibrinogen and fibrin with nanomolar affinity. Immunostaining of human carotid artery thrombi showed that FXII colocalized with areas of dense fibrin deposition, providing evidence for the in vivo modulation of fibrin structure by FXIIa. These data demonstrate that FXIIa modulates fibrin clot structure independently of thrombin generation through direct binding of the N-terminus of FXIIa to fibrin(ogen). Modification of fibrin structure by FXIIa represents a novel physiologic role for the contact pathway that may contribute to the pathophysiology of thrombosis.     

The many faces of the contact pathway and their role in thrombosis

Understanding inherent differences between thrombosis and hemostasis in the vascular system are critical to developing safe and effective anticoagulants. To this end, constituents of the contact activated and intrinsic pathway of coagulation appear to be involved in pathological thrombus formation, but are not required for normal hemostasis. In addition to coagulation, activation of the contact system is involved in fibrinolytic, inflammatory, and angiogenic processes that can also contribute to the thrombotic environment. This review discusses the role of the contact system in these processes, and highlights the potential of FXII and FXI as safer targets for antithrombotic therapy.     

A case of acute hepatitis E associated with multidrug hypersensitivity and cytomegalovirus reactivation

A 65-year-old Japanese man was hospitalized because of acute hepatitis and severe cholestasis due to hepatitis E virus (HEV) infection combined with a drug reaction to a cold preparation. He died of disseminated intravascular coagulation and severe intestinal bleeding due to systemic cytomegalovirus reactivation following the development of severe eruptions with marked eosinophilia due to drug hypersensitivity to taurine and ursodeoxycholate preparations. The close interaction between viral infection or reactivation and drug hypersensitivity was considered as a pathophysiology in this case, which emphasizes the need for further study of the immunological mechanism of the interaction.     

What role does the measurement of fibrinogen and its derivatives have in the diagnosis of disseminated intravascular coagulation?

Diagnosis of disseminated intravascular coagulation (DIC) is based on the detection of indicators of in vivo coagulation activation in patients without evidence of localized thrombus formation. DIC is a frequent finding in patients with sepsis and malignancy, as well as other conditions associated with the exposition of procoagulant cellular or non-cellular surfaces to the flowing blood. DIC may lead to microvascular occlusion, as well as to consumption of procoagulant activity. Early diagnosis of DIC is achieved by measurement of fibrin-related parameters such as D-dimer antigen, fibrin monomer antigen, soluble fibrin complexes, or fibrin degradation products. Quantitative assays allow diagnosis and monitoring of DIC. New assays using monoclonal antibodies directed against epitopes specific for elastase-mediated fibrin degradation may add valuable diagnostic information in patients with septic conditions.     

Protein C inhibitor as an anti-disseminated intravascular coagulation agent--mechanism and modification

Gram-negative sepsis is associated with disseminated intravascular coagulation (DIC) due to endothelial damage, which is induced by inflammatory mediators released from phagocytes activated by lipopolysaccharide (LPS). DIC is a systemic hemorrhagic syndrome, which results from the consumption of coagulation factors for the formation of multiple thrombi in the systemic microvessels; it is associated with multiple organ failure. Therefore, not only the systemic activation of coagulation but also the inflammatory response has been perceived as the therapeutic target for DIC in sepsis. We gave attention that protein C inhibitor (PCI) acts as an inhibitor of both plasma kallikrein and thrombin, which are known to act not only as procoagulant proteases but also as chemotactic factors toward phagocytes. Then, we hypothesized that PCI possibly acts as an anti-DIC agent rather than an inhibitor of the protein C anticoagulant pathway under the pathophysiology of DIC, accompanied by the decrease in the thrombomodulin expression on endothelial cells. Our studies have suggested that PCI purified from human urine (uPCI) improves the pathophysiology of DIC through the inhibition of activities of plasma kallikrein and thrombin, and the activities of PCI are regulated by N-glycans. This review introduces the anti-DIC action of PCI and about the modification of N-glycosylation site(s) of PCI to heighten the value of PCI as an anti-DIC agent.     

Activated protein C action in inflammation

Activated protein C (APC) is a natural anticoagulant that plays an important role in coagulation homeostasis by inactivating the procoagulation factor Va and VIIIa. In addition to its anticoagulation functions, APC also has cytoprotective effects such as anti‐inflammatory, anti‐apoptotic, and endothelial barrier protection. Recently, a recombinant form of human APC (rhAPC or drotrecogin alfa activated; known commercially as ‘Xigris’) was approved by the US Federal Drug Administration for treatment of severe sepsis associated with a high risk of mortality. Sepsis, also known as systemic inflammatory response syndrome (SIRS) resulting from infection, is a serious medical condition in critical care patients. In sepsis, hyperactive and dysregulated inflammatory responses lead to secretion of pro‐ and anti‐inflammatory cytokines, activation and migration of leucocytes, activation of coagulation, inhibition of fibrinolysis, and increased apoptosis. Although initial hypotheses focused on antithrombotic and profibrinolytic functions of APC in sepsis, other agents with more potent anticoagulation functions were not effective in treating severe sepsis. Furthermore, APC therapy is also associated with the risk of severe bleeding in treated patients. Therefore, the cytoprotective effects, rather than the anticoagulant effect of APC are postulated to be responsible for the therapeutic benefit of APC in the treatment of severe sepsis.