Role of tissue factor in hemostasis and thrombosis

Tissue factor (TF) is a transmembrane glycoprotein that functions as the primary cellular initiator of blood coagulation. Perivascular cells express TF and provide a hemostatic barrier to limit hemorrhage after vessel injury. In addition, TF is expressed in a tissue-specific manner with high levels in vital organs, such as the heart and lung. TF expression in these tissues may provide additional hemostatic protection from mechanical injury to blood vessels. Recent studies have also detected TF in the blood. This circulating TF is present in the form of microparticles (MPs), which are membrane vesicles shed from cells, and possibly platelets. At present, the cell types that contribute to this pool of TF-positive MPs have not been fully defined. Monocytes, endothelial cells and platelets are the most likely sources of this circulating TF. However, TF-positive MPs represent only a minor subset of circulating MPs. Importantly, TF-negative MPs also possess procoagulant activity. In various diseases, such as sepsis and cancer, TF is expressed by vascular cells and this leads to thrombosis. Levels of circulating TF are also elevated in these diseases and may contribute to thrombosis. Recent studies have analyzed the role of TF-positive MPs in thrombus propagation using different in vivo models. Circulating TF was found to contribute to thrombosis in some models but not others. Inhibition of TF activity in patients with TF expression in vascular cells and with elevated levels of circulating TF may decrease thrombosis associated with a variety of diseases.     

Activated factor X and thrombin formation triggered by tissue factor on endothelial cell matrix in a flow model: effect of the tissue factor pathway inhibitor

The procoagulant subcellular matrix of stimulated endothelial cells that contains tissue factor (TF) was used to investigate the mechanism by which TF pathway inhibitor (TFPI) inhibits thrombin formation initiated by TF/factor VIIa (FVIIa) under flow conditions. Purified coagulation factors VII, X, and V and prothrombin were perfused at a wall shear rate of 100 s-1 through a flow chamber containing a coverslip covered with matrix of cultured human umbilical vein endothelial cells. This resulted in a TF- and FVII-dependent FXa and thrombin generation as measured in the effluent at the outlet of the system. Inhibition of this TF/FVIIa-triggered thrombin formation by TFPI purified from plasma was dependent on the amount of TF present on the endothelial cell matrix. The rate of prothrombinase assembly and steady-state levels of thrombin formation were decreased by TFPI. Because persistent albeit decreased steady-state levels of thrombin formation occurred in the presence of TFPI, we conclude that plasma- TFPI does not inhibit FXa present in the prothrombinase complex. The addition of FIX and FVIII to perfusates containing FVII and FX increased the FXa generation on endothelial matrices, and counteracted the inhibition of thrombin formation on endothelial cell matrices by TFPI. Our data provide further evidence for the hypothesis that the rapid inactivation of TF/FVIIa by TFPI in combination with the absence of either FVIII or FIX causes the bleeding tendency of patients with hemophilia A or B.     

Activated protein C up-regulates procoagulant tissue factor activity on endothelial cells by shedding the TFPI Kunitz 1 domain

Thrombin and activated protein C (APC) signaling can mediate opposite biologic responses in endothelial cells. Given that thrombin induces procoagulant tissue factor (TF), we examined how TF activity is affected by APC. Exogenous or endogenously generated APC led to increased TF-dependent factor Xa activity. Induction required APC's proteolytic activity and binding to endothelial cell protein C receptor but not protease activated receptors. APC did not affect total TF antigen expression or the availability of anionic phospholipids on the apical cell membrane. Western blotting and cell surface immunoassays demonstrated that APC sheds the Kunitz 1 domain from tissue factor pathway inhibitor (TFPI). A TFPI Lys86Ala mutation between the Kunitz 1 and 2 domains eliminated both cleavage and the enhanced TF activity in response to APC in overexpression studies, indicating that APC up-regulates TF activity by endothelial cell protein C receptor-dependent shedding of the Kunitz 1 domain from membrane-associated TFPI. Our results demonstrate an unexpected procoagulant role of the protein C pathway that may have important implications for the regulation of TF- and TFPI-dependent biologic responses and for fine tuning of the hemostatic balance in the vascular system.     

Plasma tissue factor and tissue factor pathway inhibitor levels in patients with disseminated intravascular coagulation

We measured the plasma levels of tissue factor (TF) and tissue factor pathway inhibitor (TFPI) in patients with disseminated intravascular coagulation (DIC) to examine the relationship between TFPI and vascular endothelial cell injury. Plasma TF (273 ± 90 pg/ml) and TFPI (252 ± 125 ng/ml) levels were significantly increased in patients with DIC compared with non-DIC patients. Plasma TF antigen level was significantly increased in pre-DIC patients (285 ± 85 pg/ml), while the plasma TFPI level (152 ± 54 ng/ml) was not markedly increased in such a state. The plasma TF/TFPI ratio was high in the pre-DIC patients (2.10 ± 0.90), and low in the DIC patients (1.40 ± 0.87) and healthy volunteers (0.84 ± 0.26). There was no significant difference between the DIC patients with a good outcome and those with a poor outcome in terms of plasma TF levels, although the plasma TFPI level in the DIC patients with a good outcome (289 ± 133 ng/ml) was significantly higher than that in those with a poor outcome (187 ± 75 ng/ml). During the clinical course of DIC, plasma TF antigen was increased first, and an increase of the plasma TFPI level followed the increase in plasma TF level. These findings suggest that plasma TFPI is released from vascular endothelial cells and it may reflect vascular endothelial cell injury. It is conceivable that TF and TFPI may play an important role in the onset of DIC. © 1996 Wiley-Liss, Inc.     

A balance between tissue factor and tissue factor pathway inhibitor is required for embryonic development and hemostasis in adult mice

Inactivation of the murine tissue factor (TF) gene or tissue factor pathway inhibitor 1 (TFPI) gene results in embryonic lethality, indicating that both are required for embryonic development. We have shown that expression of low levels of TF from a transgene (hTF) rescues TF-null embryos. However, low-TF mice (mTF(-/-)/hTF+) have hemostatic defects in the uterus, placenta, heart, and lung. In this study, we hypothesized that the death of TFPI-/- embryos was due to unregulated TF/FVIIa activity and that the hemostatic defects in low-TF mice were due to insufficient TF expression. Therefore, we attempted to rescue TFPI-/- embryos by reducing TF expression, and to restore hemostasis in low-TF mice by abolishing TFPI expression. Intercrossing TFPI(+/-)/mTF(+/-)/hTF+/- mice generated close to the expected number of TFPI(-/-)/low-TF mice at weaning age from 128 offspring, indicating rescue of TFPI-/- embryos from embryonic lethality. Conversely, a decrease in TFPI levels dose-dependently prolonged the survival of low-TF mice and rescued the hemorrhagic defects in the lung and placenta but not in the heart or uterus. These results indicate that the correct balance between TF and TFPI in different organs is required to maintain hemostasis during embryonic development and in adult mice.     

Plasma tissue factor and tissue factor pathway inhibitor levels in patients with disseminated intravascular coagulation

We measured the plasma levels of tissue factor (TF) and tissue factor pathway inhibitor (TFPI) in patients with disseminated intravascular coagulation (DIC) to examine the relationship between TFPI and vascular endothelial cell injury. Plasma TF (273 ± 90 pg/ml) and TFPI (252 ± 125 ng/ml) levels were significantly increased in patients with DIC compared with non-DIC patients. Plasma TF antigen level was significantly increased in pre-DIC patients (285 ± 85 pg/ml), while the plasma TFPI level (152 ± 54 ng/ml) was not markedly increased in such a state. The plasma TF/TFPI ratio was high in the pre-DIC patients (2.10 ± 0.90), and low in the DIC patients (1.40 ± 0.87) and healthy volunteers (0.84 ± 0.26). There was no significant difference between the DIC patients with a good outcome and those with a poor outcome in terms of plasma TF levels, although the plasma TFPI level in the DIC patients with a good outcome (289 ± 133 ng/ml) was significantly higher than those with a poor outcome (187 ± 75 ng/ml). During the clinical course of DIC, plasma TF antigen was increased first, and an increase of the plasma TFPI level followed the increase in plasma TF level. These findings suggest that plasma TFPI is released from vascular endothelial cells and it may reflect vascular endothelial cell injury. It is conceivable that TF and TFPI may play an important role in the onset of DIC. Am. J. Hematol. 55:169–174, 1997. © 1997 Wiley-Liss, Inc.     

Changes of plasma tissue factor and tissue factor pathway inhibitor antigen levels and induction of tissue factor expression on the monocytes in coronary artery disease

BACKGROUND: Several studies have shown that thrombosis and inflammation play an important role in the pathogenesis of coronary artery disease (CAD). Tissue factor (TF) is responsible for the thrombogenicity of the atherosclerotic plaque and plays a key in triggering thrombin generation. The aim of this study was to assess the levels of TF and tissue factor pathway inhibitor (TFPI) in patients with angiographically documented CAD and also to evaluate TF induction on monocytes in vitro in the presence of these plasmas from patients with CAD. METHODS: Plasma antigen levels of soluble TF and TFPI were measured in 65 CAD patients and 22 healthy controls. Surface TF expression on monocytes from a healthy donor treated with plasma samples was evaluated by flow cytometry with a direct double-color immunofluorescence technique. RESULTS: Significantly elevated levels of both TF and TFPI were found in CAD patients compared with healthy controls (303.6 +/- 134.1 vs. 187.3 +/- 108.7 pg/ml, p < 0.05; 85.2 +/- 48.6 vs. 65.0 +/- 29.0 ng/ml, p < 0.05). By flow cytometry, monocytes from a healthy donor displayed higher TF antigen expression when incubated in the presence of CAD plasmas than in control plasmas (34.6 +/- 10.7 vs. 23.2 +/- 10.2%, p < 0.05). CONCLUSIONS: The high levels of circulating TF are present in CAD, which were not sufficiently inhibited by the elevated TFPI plasma levels. Although the source of circulating TF is unclear, TF induction of monocytes by plasma from CAD patients may contribute to the hypercoagulable state.     

Platelet microparticles and vascular cells interactions: a checkpoint between the haemostatic and thrombotic responses

Described 40 years ago as cell dust, microparticles (MPs) are now considered a key component in the haemostatic response. Owing to their plasma membrane reactivity, platelets are believed to constitute the main source of circulating procoagulant microparticles and behave as true sensors for the haemostatic response. Erythrocytes, leukocytes and endothelial cells are also able to shed MPs in the blood flow, their respective contribution varying with the pathophysiologic circumstances and extent of the cellular damage. The catalytic properties of MPs rely on a procoagulant anionic phospholipid, phosphatidylserine, made accessible at the outer leaflet following plasma membrane remodelling and on the eventual presence of tissue factor (TF). Under resting conditions, most membrane-bound TF is encrypted. Although able to bind to FVIIa, it does not trigger blood coagulation. Under prothrombotic conditions, TF decryption would occur through intricate pathways involving platelets, monocytes, endothelial cells and derived MPs. P-selectin/P-selectin glycoprotein Ligand-1 (PSGL-1) interactions and reactive oxygen species would promote TF decryption in cell-MP aggregates. At sites of endothelium injury, the swift recruitment of TF+-MPs through P-selectin/PSGL-1 interactions enables the concentration of TF activity above a threshold allowing coagulation to be triggered. Another crucial feature in the initiation of blood coagulation, possibly tuned by MPs, is the balance between TF and TFPI. In specific pathophysiologic contents with elevated levels of circulating TF+-MPs, accessible TFPI at the MP surface would be overwhelmed. Beyond their procoagulant properties demonstrated in vitro, a number of pieces of evidence points to procoagulant MPs as efficient effectors in the haemostatic response, and as pathogenic markers of thrombotic disorders and vascular damage. This review will focus on the pathophysiological significance of platelet-derived MPs and their interaction with vascular cells.     

Long-term incubation with IL-4 and IL-10 oppositely modifies procoagulant activity of monocytes and modulates the surface expression of tissue factor and tissue factor pathway inhibitor

Monocytes can be induced to express both tissue factor (TF) and its inhibitor, TF pathway inhibitor-1 (TFPI-1). A short incubation (<6 h) with interleukin (IL)-4 and IL-10, two potent deactivators of monocyte functions, has been shown to modulate the synthesis and expression of TF by monocytes activated by lipopolysaccharide, but the consequences of longer incubations (up to 96 h) on both TF and TFPI-1 are unknown. The results of this study showed that adherent monocytes in culture spontaneously expressed TF and TFPI and that prolonged incubation with IL-10 induced a time- and dose-dependent decrease of monocyte TF synthesis, and an accumulation of TF/TFPI-1 complexes at the moncyte surface, suggesting a decreased clearance of these complexes. In contrast, IL-4 induced a time- and dose-dependent increase in TF synthesis, which remained intracytoplasmic, as shown by confocal microscopy. Surprisingly, TF:antigen (Ag) was decreased at the monocyte surface, but the procoagulant activity (PCA) of IL-4-treated monocytes was increased, as a result of more pronounced decrease of TFPI-1:Ag expression than that of TF. In conclusion, prolonged incubation with IL-4 and IL-10 oppositely modified PCA of cultured monocytes, and altered TF and TFPI trafficking and clearance. These data explain the respective deleterious or benefit effects of IL-4 or IL-10 in atherothrombosis.     

Expression, localization, and activity of tissue factor pathway inhibitor in normal and atherosclerotic human vessels

Tissue factor (TF) pathway inhibitor (TFPI) is the major downregulator of the procoagulant activity of the TF-factor VIIa (FVIIa) complex (TF. FVII). The active TF present in the atherosclerotic vessel wall is proposed to be responsible for the major complication of primary atherosclerosis, namely, acute thrombosis after plaque rupture, but our knowledge of the sites of TFPI expression in relation to TF remains fragmentary. The aim of this study was to investigate the expression, localization, and activity of TFPI and its relation to the activity and distribution of TF in the normal and atherosclerotic vessel wall. We applied a novel approach in which serial cross sections of human vascular segments were used to perform a complete set of assays: immunolabeling for TFPI and/or TF, in situ hybridization for the expression of TFPI mRNA, ELISA for the determination of TFPI antigen, and functional assay for the activity of TFPI and TF. In healthy vessels, TFPI protein and mRNA are present in luminal and microvascular endothelial cells (ECs) and in the medial smooth muscle cells (SMCs). In atherosclerotic vessels, TFPI protein and mRNA frequently colocalized with TF in ECs overlying the plaque and in microvessels, as well as in the medial and neointimal SMCs, and in macrophages and T cells in areas surrounding the necrotic core. At the ultrastructural level, immunogold electron microscopy confirmed the localization of TFPI in ECs, macrophages/foam cells, and SMCs. In ECs and SMCs, the gold particles decorated the plasmalemma proper and the caveolae. ELISA on cross sections revealed that atherosclerotic tissues contain more TFPI than do the healthy vessels. TFPI was functionally active against TF. FVIIa-induced coagulation, and its activity was higher in those tissues that display less TF. The largest amount of TFPI and TF were detected in complicated arterial plaques. By immunofluorescence, TFPI colocalized with platelet- and fibrin-rich areas within the organized thrombi. Atherosclerotic vessel sections promote activation of factor X, which is dependent on the presence of TF and enhanced by preincubation of the sections with anti-TFPI IgG. Taken altogether, our results suggest that TFPI is largely expressed in the normal vessel wall and enhanced in the atherosclerotic vessel, in a manner suggesting a significant role of TFPI in the regulation of TF activity.     

Oncostatin M induces procoagulant activity in human vascular smooth muscle cells by modulating the balance between tissue factor and tissue factor pathway inhibitor.

Oncostatin M (OSM) is a cytokine of the interleukin-6 (IL-6) family secreted by activated monocytes, and is expressed in atherosclerotic plaque. Smooth muscle cells (SMC), by expressing tissue factor (TF) and tissue factor pathway inhibitor (TFPI) can contribute to the thrombogenicity of atherosclerotic plaque. Consequently, the aim of this study was to evaluate the effects of OSM on the procoagulant activity of SMC. We observed that OSM induced in a concentration-dependent manner a potent procoagulant activity (PCA) that was related in part to an increased synthesis of TF, both at the cell membrane and in SMC lysates. The increased expression of TF on SMC membrane induced by OSM was sustained and was still observed 24 h after stimulation by OSM. IL-6 and leukaemia inhibitory factor (LIF), two OSM-related cytokines, did not significantly modify TF expression at the surface of SMC. In addition to its effects on TF, OSM decreased the secretion of TFPI in the supernatants of SMC, as well as in the lysates, but was devoid of effect on TFPI bound at the membrane of SMC. IL-6 and LIF reduced also TFPI secretion, which could explain why the PCA of SMC lysates treated by IL-6 or LIF was increased, despite an absence of effect on TF expression. In conclusion, these data support the hypothesis that by increasing the PCA of SMC, OSM might be involved in the thrombotic complications associated with plaque rupture.     

Relevance of tissue factor in cardiovascular disease

Overexpression and exposition of tissue factor (TF) in atherosclerotic plaques and/or arterial thrombi are critical events in atherothrombosis. TF, the receptor for factor VII (FVII) and activated factor VII (FVIIa), is the principal initiator of blood coagulation and induces thrombin generation leading to fibrin formation and platelet activation. TF also plays a major role in cell migration and angiogenesis. TF activity is downregulated by Tissue Factor Pathway Inhibitor (TFPI), a Kunitz-type inhibitor, which forms a neutralizing complex with TF, FVIIa and activated factor X. In physiological conditions, TF is absent from vascular cells which come into contact with flowing blood and is present as an inactive pool in fibroblasts and smooth muscle cells (SMC). In contrast, TF is widely expressed in atherosclerotic plaques and is found in macrophages, SMCs, and foam-cells and also in extracellular matrix and acellular lipid-rich core. TF expression is up-regulated by inflammatory cytokines and oxidized lipids. Plaque thrombogenicity is directly correlated to their TF content. After fibrous cap disruption, TF is exposed on plaque surface and triggers thrombus formation leading to arterial lumen occlusion and/or downstream embolization. In coronary and carotid plaques, TF content was found to be higher in plaques from symptomatic than asymptomatic patients. Soluble forms of TF and microparticles of monocyte and platelet origin, and bearing TF, constitute "blood-born TF". The contribution of this TF pool to arterial thrombosis is still under discussion. TF pathway is a target for new therapeutic agents that can decrease TF activity, such as active site-inactivated factor VIIa, recombinant TFPI and antibodies against TF or peptides interfering with TF-FVIIa complex activity.     

Inhibition of tissue factor pathway during intermittent pneumatic compression: A possible mechanism for antithrombotic effect

Intermittent pneumatic compression (IPC) devices are an effective prophylaxis against lower extremity deep vein thrombosis. Their antithrombotic effect has been attributed to a reduction in venous stasis and enhanced fibrinolysis. The initiating mechanism for blood coagulation is the tissue factor (TF) dependent pathway, which is inhibited by tissue factor pathway inhibitor (TFPI). We have investigated the effect of IPC on the TF pathway in 6 normal subjects and 6 patients with postthrombotic venous disease undergoing IPC for 120 minutes; all subjects were studied with each of 5 IPC devices. In normal subjects and patients, plasma factor VIIa (FVIIa) activity (the activated form of factor VII [FVII]) declined from mean values ranging 51 to 65 and 50 to 53 mU/mL before IPC with different devices to 10 to 13 and 20 to 22 mU/mL at 180 minutes, respectively (P<0.001 for all groups). FVII antigen levels were unchanged. Plasma TFPI (P<0.001) rose from mean baseline values ranging 69 to 79 and 57 to 61 ng/mL to 76 to 123 and 71 to 79 ng/mL at 180 minutes in normal subjects and patients, respectively (P<0. 001 for all groups). Plasma prothrombin fragment F1.2 levels showed minimal changes. There was an inverse relationship between TFPI and FVIIa in normal subjects (r=-0.31, P=0.001) and patients (r=-0.37, P<0.001). IPC results in an increase in plasma TFPI and decline in FVIIa. Inhibition of TF pathway, the initiating mechanism of blood coagulation, is a possible mechanism for the antithrombotic effect of IPC.     

Role of platelet P-selectin and CD40 ligand in the induction of monocytic tissue factor expression

Activated platelets can express CD40 ligand (CD40L) and trigger inflammatory response and tissue factor (TF) expression in endothelial cells through interaction with CD40. This pathway is also important for T cell-induced monocyte and endothelial cell procoagulant activity. We have studied the potential role of the CD40-CD40L pathway in platelet-induced TF expression in a monocytic cell line and in whole-blood monocytes. In vitamin D(3)-differentiated U-937 cells, thrombin-stimulated platelets increased TF expression as measured by mRNA quantification, flow cytometry, and procoagulant activity. Maximum antigen expression occurred after 2 hours. Neutralizing anti-P-selectin antibody yielded a 50% suppression of procoagulant activity, whereas antibody to CD40L had no effect. In thrombin receptor activator-stimulated citrated blood, monocytes were up to 77% TF-positive, with peak expression after only 15 minutes. However, no TF mRNA was detectable at that time. Anti-P-selectin antibody reduced TF by 50%, whereas antibody to CD40L gave a 17% reduction. Thus, we conclude that P-selectin exposed on activated platelets induces the expression of TF in both U-937 cells and whole-blood monocytes but by different mechanisms. Platelet CD40L does not display any significant effect on U-937 cells but may be of some importance on whole-blood monocytes. This suggests a possible functional difference between U-937 and monocyte CD40. Another important finding in this study is the rapid appearance of surface TF on monocytes without detectable mRNA formation. This indicates that TF may be stored intracellularly in these cells and can be exposed on the surface independent of de novo protein synthesis.     

Importance of C-reactive protein in regulating monocyte tissue factor expression in patients with inflammatory rheumatic diseases

OBJECTIVE: To determine the relationship between plasma C-reactive protein (CRP) concentrations and monocyte tissue factor (TF) expression induced in vitro by combinations of CRP, ss2-glycoprotein I (ss2-GPI), and lipopolysaccharide (LPS). METHODS: Peripheral blood mononuclear cells (PBMC) from 26 healthy individuals and 31 patients with inflammatory rheumatic diseases (IRD) were cultured with combinations of CRP, purified or recombinant ss2-GPI, and LPS and monocyte TF procoagulant activity, TF antigen, and TF mRNA were measured. Results were examined against plasma CRP levels. RESULTS: Monocytes from patients with IRD expressed significantly more TF when stimulated with CRP compared to normal monocytes (p = 0.002). An incremental positive correlation was observed between plasma CRP levels and TF induced by CRP or ss2-GPI. Significantly more TF was induced with CRP combined with ss2-GPI, compared to ss2-GPI alone, either with costimulation or CRP priming. Conversely, when combined with LPS, ss2-GPI suppressed TF induction in a dose-dependent manner on normal PBMC but not on PBMC from patients with IRD. The loss of suppression correlated strongly with plasma CRP levels. CONCLUSION: This study shows a remarkably consistent effect of CRP on monocyte TF expression. Systemic inflammation associated with elevated plasma CRP conferred a phenotype on PBMC, whereby incremental priming with respect to TF expression (induced by CRP itself or ss2-GPI) was apparent, and ss2-GPI-mediated inhibition of TF expression induced by LPS was incrementally lost. CRP regulation of monocyte TF could contribute to the higher than expected atherosclerotic vascular disease seen in patients with IRD.     

Angiotensin-converting enzyme inhibition reduces monocyte chemoattractant protein-1 and tissue factor levels in patients with myocardial infarction.

OBJECTIVES: We investigated the effects of enalapril therapy on plasma tissue factor (TF), tissue factor pathway inhibitor (TFPI) and monocyte chemoattractant protein-1 (MCP-1) levels in patients with acute myocardial infarction. BACKGROUND: Macrophages express TF in human coronary atherosclerotic plaques. Both TF and TFPI are major regulators of coagulation and thrombosis. Monocyte chemoattractant protein-1 is a monocyte and macrophage chemotactic and activating factor. METHODS: In a randomized, double-blind, placebo-controlled study beginning about two weeks after myocardial infarction, 16 patients received four weeks of placebo (placebo group) and another 16 patients received four weeks of enalapril 5 mg daily therapy (enalapril group). We performed blood sampling after administration of the doses. RESULTS: There were no significant differences in the serum angiotensin-converting enzyme (ACE) activity, plasma TF, free TFPI or MCP-1 levels before administration between the enalapril and placebo groups. In the enalapril group, ACE activity (IU/liter) (14.0 before, 5.2 on day 3, 5.8 on day 7, 6.3 on day 28), TF levels (pg/ml) (223, 203, 182, 178) and MCP-1 levels (pg/ml) (919, 789, 790, 803) significantly decreased by day 28. However, the free TFPI levels (ng/ml) (28.2, 26.5, 26.8, 28.4) did not change. These four variables were unchanged during the study period in the placebo group. CONCLUSIONS: This study demonstrated that administration of enalapril reduces the increased procoagulant activity in patients with myocardial infarction associated with inhibition of the activation and accumulation of macrophages and monocytes.     

Role of Tissue Factor in Atherothrombosis

Atherothrombosis describes the acute thrombotic event that occurs after rupture of an atherosclerotic plaque. It often leads to arterial occlusion and subsequent clinical manifestations of myocardial infarction, stroke, and sudden death. Tissue factor (TF) is the receptor for plasma factor VIIa (FVIIa) and, once formed, the TF:FVIIa complex activates the coagulation cascade. TF is present at high levels within atherosclerotic lesions and is also present on circulating monocytes and microparticles in patients with advanced cardiovascular disease (CVD). Formation of the TF:FVIIa complex plays a central role in atherothrombosis. This review will describe the cellular sources of TF, the potential of TF-positive microparticles as a biomarker of thrombotic risk, and current pharmacologic approaches to inhibit TF as a therapeutic intervention in patients with CVD.     

Sickle blood contains tissue factor-positive microparticles derived from endothelial cells and monocytes

Blood microparticles (MPs) in sickle cell disease (SCD) are reportedly derived only from erythrocytes and platelets. Yet in SCD, endothelial cells and monocytes are activated and abnormally express tissue factor (TF). Thus, sickle blood might contain TF-positive MPs derived from these cells. With the use of flow cytometry to enumerate and characterize MPs, we found total MPs to be elevated in crisis (P =.0001) and steady state (P =.02) in subjects with sickle cell disease versus control subjects. These MPs were derived from erythrocytes, platelets, monocytes, and endothelial cells. Erythrocyte-derived MPs were elevated in sickle crisis (P =.0001) and steady state (P =.02) versus control subjects, as were monocyte-derived MPs (P =.0004 and P =.009, respectively). Endothelial and platelet-derived MPs were elevated in sickle crisis versus control subjects. Total TF-positive MPs were elevated in sickle crisis versus steady state (P =.004) and control subjects (P <.0001) and were derived from both monocytes and endothelial cells. Sickle MPs shortened plasma-clotting time compared with control MPs, and a TF antibody partially inhibited this procoagulant activity. Markers of coagulation were elevated in patients with sickle cell disease versus control subjects and correlated with total MPs and TF-positive MPs (P <.01 for both). These data support the concept that SCD is an inflammatory state with monocyte and endothelial activation and abnormal TF activity.     

Tissue factor, tissue pathway factor inhibitor and risk factors of atherosclerosis in patients with chronic limbs ischemia: preliminary study

AIM: Thrombus formation plays a critical role in pathogenesis of cardiovascular complications in atherosclerotic peripheral arterial occlusive disease (PAOD). Tissue factor (TF) initiates the clotting cascade and is considered an important regulator of hemostasis and thrombosis. TF activity is regulated by TF pathway inhibitor (TFPI). The aim of our study was to evaluate plasma levels of the TF, TFPI and their relation to coagulation system and various other risk factors of atherosclerosis in patients with chronic limbs ischemia. METHODS: Plasma TF, total TFPI, truncated TFPI, full-length TFPI were assessed by ELISA using commercially available kits (IMUBIND Tissue Factor; Total TFPI; Truncated TFPI ELISA Kit; American Diagnostica Inc. Stamford) in 62 claudicant patients with PAOD and 20 healthy controls. RESULTS: We observed statistically higher levels of TF (94+/-52 pg/mL), total TFPI (43+/-8 ng/mL), and truncated TFPI (22+/-7 ng/mL) in patients with PAOD compared to healthy individuals (TF: 66+/-15 pg/mL; total TFPI: 36+/-4 ng/mL; truncated TFPI: 14+/-5 ng/mL). Full-length TFPI (20+/-4 ng/mL) is lower in patients with PAOD than in controls (23+/-5 ng/mL). The study indicated a positive correlation between TF and truncated TFPI (r=0.34), total TFPI and full TFPI (r=0.5), total TFPI and truncated TFPI (r=0.83) in patients with PAOD, and negative correlation between full TFPI and truncated TFPI (r=-0.65) in the control. CONCLUSION: Elevated levels of TF, disorders of balance between full-length TFPI and truncated TFPI as well as significantly increased truncated TFPI level in patients with PAOD can be independent risk factors of atherosclerotic complications.