Aberrations of the tissue factor pathway in patients positive for lupus anticoagulant

Heparin-grafted dialysis membrane allows minimal systemic anticoagulation in regular hemodialysis patients: a prospective proof-of-concept study

This prospective, multicenter, proof-of-concept study aimed to evaluate the possibility to reduce the ordinary heparin dose and the systemic anti-Xa activity during hemodialysis (HD) sessions using a new heparin-grafted HD membrane. In 45 stable HD patients, the use of a heparin-grafted membrane with the ordinary heparin dose was followed by a stepwise weekly reduction of dose. Reduction was stopped when early signs of clotting (venous pressure, quality of rinse-back) occurred during two out of three weekly HD sessions. Heparin dose was decreased for 67% of patients resulting in the lowering of these patients' anti-Xa activity by 50%. Dose reductions were achieved with both types of heparin (low-molecular-weight heparin: 64 ± 14 to 35 ± 12 IU/kg, P < 0.0001; unfractionated heparin: 82 ± 18 to 46 ± 13 IU/kg, P < 0.0001) resulting in a decrease of anti-Xa activity at dialysis session end (low-molecular-weight heparin: 0.51 ± 0.25 to 0.25 ± 0.11 IU/mL, P < 0.0001; unfractionated heparin: 0.28 ± 0.23 to 0.13 ± 0.07 IU/mL, P < 0.0001). Failure to further decrease heparin dose was related to signs of clotting in blood lines (57% of sessions), in dialyzer (9%), or both (34%). Significant reduction of heparin dose and anti-Xa activity at the end of HD sessions was possible in stable HD patients using heparin-grafted membrane. HD patients who require low anti-Xa activity at the end of HD sessions might benefit from a heparin-grafted membrane to reduce bleeding risk and other heparin adverse events.

Adverse effects of heparin

All the adverse effects of heparins are related to their wide variety of biological activities, with bleeding being the most important safety issue, resulting directly from the potency of heparin as an anticoagulant. However, it is hard to define the bleeding risk, since it depends on numerous parameters including the indication, dosage, method, and duration of heparin application, the clinical study design and definition of bleeding as well as patient characteristics and determinants of bleeding such as type of surgery and co-medication. Nonbleeding complications of heparins are caused by binding of heparin molecules to proteins other than antithrombin and to cells, which is generally more pronounced with unfractionated heparin than with low-molecular-weight heparins. Accordingly, heparin-induced thrombocytopenia, the most severe nonbleeding adverse reaction, occurs about 10 times less with low-molecular-weight heparins than with unfractionated heparin. Frequent and therefore important adverse reactions of heparins are skin lesions resulting from delayed-type hypersensitivity reactions. All the other undesirable effects are discussed as well, but they are mostly clinically irrelevant.

Silencing of tissue factor by antisense deoxyoligonucleotide prevents monocrotaline/LPS renal injury in mice

Tissue factor (TF) is involved in monocrotaline (MCT)/lipopolysaccharide (LPS) hepatotoxicity. It is not known whether MCT/LPS can cause renal toxicity and whether TF is involved in this toxicity. Thus, the present study was undertaken to investigate the potential renal toxicity after MCT/LPS co-treatment and the involvement of TF in this toxicity. MCT was delivered to ND4 male mice (200 mg/kg) per os followed 4 h later by treatment with LPS ip (6 mg/kg) to investigate its effect on kidney. We injected TF antisense oligonucleotide (TF-AS) intravenously (i.v) in mice prior to LPS treatment, to block TF, and measured their blood urea nitrogen (BUN), creatinine (CRE), alkaline phosphatase (ALP), and potassium. In MCT/LPS co-treated group, fibrin was detected on the glomerular capillary lumina, distal tubules of renal cortex, and the necrotic tubules of renal medulla. An elevation of BUN, creatinine, and the BUN/creatinine ratio was seen in mice with MCT/LPS co-treatment, compared to animals receiving LPS or MCT alone. Simultaneously, an aggressive tubular necrosis was seen in the medullary tubules in the same group which may account for the oliguria observed in these animals. Fourfold inductions in the plasma TF level was detected at 10 h after MCT/LPS co-treatment which increased to 18-fold at 24 h. Increased blood level of leptin, interleukin-6 (IL-6) and downregulation of tubular chemokine (C-X-C motif) ligand 16 (CXCL16) are characteristic features in MCT/LPS co-treated animal. On the other hand, mice injected with TF-AS in the presence of MCT/LPS co-treatment showed no elevation of the blood BUN, creatinine, potassium, and normal levels of the proinflammatory molecules. TF-AS injection significantly prevented glomerular and tubular fibrin deposition, tubular necrosis, and improvement of the animal survivability. Renal toxicity involving TF can be prevented successfully by the use of TF-AS.

Role of tissue factor in feto-maternal development: a xiphos

In this review, the dual role of tissue factor (TF) in pregnancy is described. On the one hand, TF is required for embryonic and placental development in a successful pregnancy, and on the other hand, pathologic expression of TF can lead to serious pregnancy complications in humans and mice. Human studies show increased TF levels in plasma, amniotic fluid and and/or placentas of abnormal pregnancies affected by miscarriages, preterm birth, or pre-eclampsia. Interestingly, using two mouse models, we found that blood-borne TF plays a crucial role in the pathogenesis of pregnancy complications. TF on neutrophils and monocytes is a critical mediator in trophoblast injury and embryo damage in pregnancy loss induced by antiphospholipid antibodies and in the antibody-independent CBA/J × DBA/2 model of miscarriages. Blockade of TF or genetic diminution prevented pregnancy complications, suggesting that TF may be a good target for therapy in patients with recurrent miscarriages, pregnancy loss, and pre-eclampsia. In addition, statins, which downregulate TF, may constitute a good therapeutic option for women with pregnancy complications. Clinical trials should be conducted to confirm these observations in women.

Thrombin receptor (PAR-1) antagonists as novel antithrombotic agents

In addition to its central role in haemostasis and wound healing, thrombin activates platelets and smooth muscle cells by proteolytic activation of cell surface protease-activated receptor-1 (PAR-1), which is also known as the thrombin receptor. Thrombin is the most potent activator of human platelets and, as such, a thrombin receptor antagonist is likely to exert potent antithrombotic effect in platelet-rich arterial thrombosis. As thrombin receptor antagonism does not inhibit the ability of thrombin to generate fibrin, such an agent is likely to have less bleeding liability than conventional anticoagulants. The proof-of-concept of the antithrombotic effect of PAR-1 antagonists has been established in several non-human primate models. The current success of PAR-1 research is underscored by the advancement of two candidates into clinical trails for acute coronary syndrome by Schering-Plough and Eisai Company.

Shiga toxin and lipopolysaccharide induce platelet-leukocyte aggregates and tissue factor release, a thrombotic mechanism in hemolytic uremic syndrome

Background

Aggregates formed between leukocytes and platelets in the circulation lead to release of tissue factor (TF)–bearing microparticles contributing to a prothrombotic state. As enterohemorrhagic Escherichia coli (EHEC) may cause hemolytic uremic syndrome (HUS), in which microthrombi cause tissue damage, this study investigated whether the interaction between blood cells and EHEC virulence factors Shiga toxin (Stx) and lipopolysaccharide (LPS) led to release of TF.

Methodology/Principal Findings

The interaction between Stx or LPS and blood cells induced platelet-leukocyte aggregate formation and tissue factor (TF) release, as detected by flow cytometry in whole blood. O157LPS was more potent than other LPS serotypes. Aggregates formed mainly between monocytes and platelets and less so between neutrophils and platelets. Stimulated blood cells in complex expressed activation markers, and microparticles were released. Microparticles originated mainly from platelets and monocytes and expressed TF. TF–expressing microparticles, and functional TF in plasma, increased when blood cells were simultaneously exposed to the EHEC virulence factors and high shear stress. Stx and LPS in combination had a more pronounced effect on platelet-monocyte aggregate formation, and TF expression on these aggregates, than each virulence factor alone. Whole blood and plasma from HUS patients (n = 4) were analyzed. All patients had an increase in leukocyte-platelet aggregates, mainly between monocytes and platelets, on which TF was expressed during the acute phase of disease. Patients also exhibited an increase in microparticles, mainly originating from platelets and monocytes, bearing surface-bound TF, and functional TF was detected in their plasma. Blood cell aggregates, microparticles, and TF decreased upon recovery.

Conclusions/Significance

By triggering TF release in the circulation, Stx and LPS can induce a prothrombotic state contributing to the pathogenesis of HUS.

Tissue factor in antiphospholipid antibody-induced pregnancy loss: a pro-inflammatory molecule

Fetal loss in patients with antiphospholipid antibodies (aPL) has been ascribed to thrombosis of placental vessels. However, we have shown that inflammation, specifically complement activation with generation of the anaphylotoxin C5a, is an essential mediator of fetal injury. We have analysed the role of tissue factor (TF) in a mouse model of aPL-induced pregnancy loss. TF is the major cellular activator of the coagulation cascade but also has cell signaling activity. Mice that received aPL-IgG showed strong TF staining throughout the decidua and on embryonic debris. This TF staining was not associated with either fibrin staining or thrombi in deciduas. The absence of fibrin deposition and thrombi suggests that TF-dependent activation of coagulation does not mediate aPL-induced pregnancy loss.We found that either blockade of TF with a monoclonal antibody in wild type mice or a genetic reduction of TF prevented aPL-induced inflammation and pregnancy loss indicated a pathogenic role for TF in aPL-induced pregnancy complications. In response to aPL-generated C5a, neutrophils express TF potentiating inflammation in the deciduas and leading to miscarriages. Importantly, we showed that TF in myeloid cells, but not fetal-derived cells (trophoblasts), was associated with fetal injury, suggesting that the site for pathologic TF expression is neutrophils. We found that TF expression in neutrophils contributes to respiratory burst and subsequent trophoblast injury and pregnancy loss induced by aPL. The identification of TF, acting as an important pro-inflammatory mediator in aPL-induced fetal injury, provides a new target for therapy to prevent pregnancy loss in the aPL syndrome.

Tissue factor: a link between C5a and neutrophil activation in antiphospholipid antibody induced fetal injury

Fetal loss in patients with antiphospholipid (aPL) antibodies has been ascribed to thrombosis of placental vessels. However, we have shown that inflammation, specifically activation of complement with generation of the anaphylotoxin C5a, is an essential trigger of fetal injury. In this study, we analyzed the role of the procoagulant molecule tissue factor (TF) in a mouse model of aPL antibody-induced pregnancy loss. We found that either blockade of TF with a monoclonal antibody in wild-type mice or a genetic reduction of TF prevented aPL antibody-induced inflammation and pregnancy loss. In response to aPL antibody-generated C5a, neutrophils express TF potentiating inflammation in the deciduas and leading to miscarriages. Importantly, we showed that TF in myeloid cells but not fetal-derived cells (trophoblasts) was associated with fetal injury, suggesting that the site for pathologic TF expression is neutrophils. We found that TF expression in neutrophils contributes to respiratory burst and subsequent trophoblast injury and pregnancy loss induced by aPL antibodies. The identification of TF as an important mediator of C5a-induced oxidative burst in neutrophils in aPL-induced fetal injury provides a new target for therapy to prevent pregnancy loss in the antiphospholipid syndrome.

Polymorphisms of the tissue factor pathway inhibitor gene are associated with venous thromboembolism in the antiphospholipid syndrome and carriers of factor V Leiden

Polymorphisms within the tissue factor pathway inhibitor (TFPI) gene may determine TFPI expression and increase the risk of venous thromboembolism (VTE) in predisposed individuals. We tested this hypothesis by comparing TFPI activity and the frequency of common TFPI polymorphisms, -33T->C, -399C->T and -287T->C, in patients with antiphospholipid syndrome (APS) (n = 24) or factor V Leiden (n = 44) who had a history of VTE (n = 26), compared with those without VTE (n = 42) and also with normal control individuals (n = 56). TFPI activity was measured using a modified amidolytic assay and genotypes were determined by polymerase chain reaction and restriction fragment length polymorphism. We found that only APS patients with a history of venous thrombosis had TFPI activity levels significantly different from control individuals (1.77 +/- 0.60 vs 0.77 +/- 0.19 U/ml; P = 0.0001), and this was associated with inheritance of the TFPI -33C allele (1.70 +/- 0.72 U/ml for TC/CC genotypes vs 0.97 +/- 0.56 U/ml for TT; P = 0.01). Multivariate analysis of APS and factor V Leiden patients revealed that the greatest independent contributor to VTE was TFPI activity (adjusted odds ratio = 16.84; 95% confidence interval = 2.47-114.36, P = 0.004), while inheritance of either the TFPI -33C or -399T alleles each increased the odds of VTE by nearly 13 times (95% confidence interval = 2.39-69.91, P = 0.003; and 95% confidence interval = 2.25-71.23, P = 0.004, respectively). These results indicate that the TFPI -33T->C and -399C->T polymorphisms are significantly associated with venous thrombosis in the presence of other risk factors, especially APS, and may be clinically relevant in patients who are prone to hypercoagulability.

Optimization of conditions for in vitro production of radical oxygen species and expression of tissue factor by canine mononuclear cells and granulocytes for use in high-throughput assays

The purpose of this study was to optimize conditions for high throughput measurement of radical oxygen species (ROS) production and expression of tissue factor, also termed procoagulant activity, by canine leukocytes. Granulocytes and mononuclear cells were separated by density gradient centrifugation from peripheral blood collected on several occasions from three healthy large breed dogs. To determine optimal conditions for ROS production, granulocytes were incubated for 1 or 3h in PBG (PBS containing 0.5% BSA and 5mM glucose) or RPMI containing 10% fetal bovine serum (FBS); lipopolysaccharide (LPS), zymosan, peptidoglycan (PGN) and phorbol myristate acetate (PMA) were used as stimuli. ROS was assessed by conversion of the nonfluorescent dye dihydrorhodamine 123 to fluorescent rhodamine 123 by radical species released into the media. To identify optimal conditions for expression of tissue factor, mononuclear cells were incubated for 5h in RPMI containing different concentrations of heat-inactivated FBS (HI-FBS), and LPS, zymosan, PGN or PMA as stimuli. Expression of tissue factor was determined using a one-stage recalcification assay performed in an automated nephelometric coagulation analyzer. Neither LPS nor zymosan increased ROS production by granulocytes incubated in PBG media. In contrast, granulocytes incubated in RPMI had dose-dependent increases in ROS production in response to zymosan and PGN. ROS production was significantly increased by incubation with concentrations of LPS of 0.01microg/ml or greater, and by zymosan concentrations of 0.1microg/ml or greater. ROS production in response to incubation with PMA was significantly increased starting at 10(-7)M, and was significantly greater for cells incubated in RPMI than cells incubated in PBG. LPS-, zymosan- and PGN-stimulated procoagulant activity increased in a dose-dependent manner, whereas PMA-stimulated procoagulant activity peaked at 10(-7)M. Increasing concentrations of HI-FBS significantly increased LPS-, zymosan- and PGN-induced procoagulant activity of mononuclear cells. Results obtained in this study indicate production of ROS by canine granulocytes is optimal when these cells are incubated for 3h in RPMI with LPS (0.1microg/ml), zymosan (10 microg/ml), PGN (10 microg/ml), and PMA (10(-7)M). Furthermore, canine mononuclear cells express procoagulant activity in response to LPS, zymosan, PGN, and PMA, and responses to LPS, zymosan and PGN are enhanced by the addition of HI-FBS. These findings suggest that HI-FBS retains important serum proteins that facilitate interactions between each of these bacterial or yeast derived products and the mononuclear cells. Consequently, future studies regarding the regulation of procoagulant activity by canine mononuclear cells should be performed in the presence of HI-FBS. Both assays utilized in this study allow high throughput of samples, and therefore are appropriate choices for rapid screening of conditions and/or therapeutic interventions affecting the canine inflammatory system.

The Direct Thrombin Inhibitors: Their Role and Use for Rational Anticoagulation

Major clinical advantages are achieved when direct thrombin inhibitors are used in venous thromboembolism. These agents provide more reliable anticoagulant response patterns because they are not significantly bound to plasma proteins and few, if any, drug-drug interactions are seen. The studies to date confirm that not all direct thrombin inhibitors are the same. The new reversible, short-acting catalytic site-specific drugs provide an excellent safety profile and high degree of efficacy for the prophylaxis and treatment of venous thromboembolism and pulmonary embolic states. The availability of the oral prodrug ximelagatran allows reproducible, effective, and safe direct thrombin inhibition without the requirement for coagulation laboratory monitoring; it appears destined to be the oral anticoagulant of the future.

Circulating tissue factor, tissue factor pathway inhibitor and D-dimer in umbilical cord blood of normal term neonates and adult plasma

The investigation of many hemostatic defects in newborns is restricted by the lack of normal reference values. The coagulation system of the neonate differs in many ways from that of the adult. The present study was designed to compare the concentrations of tissue factor (TF), tissue factor pathway inhibitor (TFPI) and D-dimer (DD) in the umbilical cord blood of healthy newborns and in adult plasma. TF antigen was quantified using an in-house enzyme-linked immunosorbent assay, whereas TFPI and DD levels were measured with commercial kits. The mean TF level in cord blood (mean standard deviation, 183.94 103.63 pg/ml) was significantly higher ( = 0.008) than that in adults (136.64 65.09 pg/ml). Cord blood exhibited enhanced fibrinolysis, as was reflected by a significantly higher level of DD (924.57 733.87 ng/ml, 0.001) than that in adults (45.57 17.21 ng/ml). Conversely, cord blood (30.88 10.16 ng/ml) demonstrated significantly lower ( 0.001) TFPI levels than that in adults (55.77 21.16 ng/ml). However, no significant differences of these three hemostatic markers were noted between both gender groups in newborns and adults. Our findings indicate that an active and dynamic state of hemostasis exists in cord blood, as the fluidity of cord blood remains preserved in the presence of birth injury.

Tissue factor as a proinflammatory agent

Tissue factor (TF) is a transmembrane glycoprotein and the main triggering element of blood coagulation. TF expression on monocytes and endothelial cells is induced by exposure to endotoxin, tumor necrosis factor, and IL-1 and is considered to appear in consequence of inflammation. In order to assess the proinflammatory capacity of TF itself, the recombinant extracellular domain of TF was injected intra-articularly into healthy mice. To characterize the role of immune cells in the TF-induced arthritis, mice deprived of lymphocytes, neutrophils and monocytes were used. Histomorphological analysis of the joints with respect to inflammatory cell infiltration, pannus formation and erosion formation revealed development of arthritis in 80% of animals injected with TF. In most of the cases synovial proliferation was accompanied by pannus formation and cartilage destruction. Inflammatory cell infiltrate consisted of CD4-Mac1+ macrophages. Depletion of monocytes was, however, not enough to abolish inflammation. Indeed, combined deficiency of monocytes and lymphocytes was required to prevent inflammation following the injection of TF. We observed that TF induced chemokine production (MIP-1alpha and RANTES), but did not induce a proliferative response nor cytokine release by mouse spleen cells. TF has strong inflammatogenic properties mediated predominantly by monocytes and their release of chemokines. Our study shows that TF can simultaneously trigger the immune and coagulation systems.

Anti-tissue factor pathway inhibitor activity in patients with primary antiphospholipid syndrome

The association between antiphospholipid antibodies and an increased risk of thrombosis in antiphospholipid syndrome (aPS) patients is probably caused by numerous mechanisms, including the effects of antibodies to phospholipid-binding proteins such as beta(2)-glycoprotein I and prothrombin. In this study, we investigated the inhibition of tissue factor pathway inhibitor (TFPI) in 33 patients with primary antiphospholipid syndrome (PAPS). TFPI was measured in PAPS patients using an amidolytic assay, dependent on the generation of activated factor X (Fxa), and this was compared with 55 healthy subjects. Functional levels of TFPI (mean +/- SD) were significantly lower in PAPS patients (0.89 +/- 0.37 U/ml) than the control group (1.05 +/- 0.15 U/ml) (P = 0.02). The difference was caused by a subset of five patients who had TFPI levels below the lower 99% confidence interval of the normal reference range, representing increased FXa generation in the assay system. IgG fractions were isolated from these five patients and five control subjects, then incorporated into normal plasma to measure FXa generation in the TFPI assay system. FXa generation was increased when polyclonal rabbit anti-human TFPI IgG (P < 0.0001) or PAPS IgG (P = 0.0001) were added to normal plasma, demonstrating inhibition of TFPI. The apparent anti-TFPI activity demonstrated in the five subjects with PAPS in this study may represent a significant new mechanism for thrombosis in patients with aPS, as it implies that increased tissue factor FVIIa-mediated thrombin generation might occur.