Aryl Hydrocarbon Receptor Activation and Tissue Factor Induction by Fluid Shear Stress and Indoxyl Sulfate in Endothelial Cells.

Endogenous agonists of the transcription factor aryl hydrocarbon receptor (AHR) such as the indolic uremic toxin, indoxyl sulfate (IS), accumulate in patients with chronic kidney disease. AHR activation by indolic toxins has prothrombotic effects on the endothelium, especially via tissue factor (TF) induction. In contrast, physiological AHR activation by laminar shear stress (SS) is atheroprotective. We studied the activation of AHR and the regulation of TF by IS in cultured human umbilical vein endothelial cells subjected to laminar fluid SS (5 dynes/cm2). SS and IS markedly increased the expression of AHR target genes PTGS2 (encoding for COX2), AHRR, CYP1A1, and CYP1B1, as well as F3 (encoding for TF), in an AHR-dependent way. IS amplified SS-induced TF mRNA and protein expression and upregulation of AHR target genes. Interestingly, tyrosine kinase inhibition by genistein decreased SS- but not IS-induced TF expression. Finally, the increase in TF expression induced by laminar SS was not associated with increased TF activity. In contrast, IS increased TF activity, even under antithrombotic SS conditions. In conclusion, IS and SS induce AHR activation and AHR-dependent TF upregulation by different mechanisms. Impairment of the antithrombotic properties of shear stressed endothelium by toxic AHR agonists could favor cardiovascular diseases in CKD.

Determination of FVIIa-sTF Inhibitors in Toxic Microcystis Cyanobacteria by LC-MS Technique.

The blood coagulation cascade involves the human coagulation factors thrombin and an activated factor VII (fVIIa). Thrombin and fVIIa are vitamin-K-dependent clotting factors associated with bleeding, bleeding complications and disorders. Thrombin and fVIIa cause excessive bleeding when treated with vitamin-K antagonists. In this research, we explored different strains of toxic Microcystis aeruginosa and cyanobacteria blooms for the probable fVIIa-soluble Tissue Factor (fVIIa-sTF) inhibitors. The algal cells were subjected to acidification, and reverse phase (ODS) chromatography-solid phase extraction eluted by water to 100% MeOH with 20%-MeOH increments except for M. aeruginosa NIES-89, from the National Institute for Environmental Studies (NIES), which was eluted with 5%-MeOH increments as an isolation procedure to separate aeruginosins 89A and B from co-eluting microcystins. The 40%-80% MeOH fractions of the cyanobacterial extract are active against fVIIa-sTF. The fVIIa-sTF active fractions from cultured cyanobacteria and cyanobacteria blooms were subjected to liquid chromatography-mass spectrometry (LC-MS). The 60% MeOH fraction of M. aeruginosa K139 exhibited an m/z 603 [M + H]⁺ attributed to aeruginosin K139, and the 40% MeOH fraction of M. aeruginosa NIES-89 displayed ions with m/z 617 [M - SO3 + H]⁺ and m/z [M + H]⁺ 717, which attributed to aeruginosin 89. Aeruginosins 102A/B and 298A/B were also observed from other toxic strains of M. aeruginosa with positive fVIIa-sTF inhibitory activity. The active fractions contained cyanobacterial peptides of the aeruginosin class as fVIIa-sTF inhibitors detected by LC-MS.

Rivaroxaban delivery and reversal at a venous flow rate.

OBJECTIVE: Rivaroxaban is an oral anticoagulant that directly targets both free factor Xa and factor Xa in complex with its protein cofactor, factor Va, in the prothrombinase complex. It is approved in the United States for the prophylaxis of deep vein thrombosis and stroke in patients with atrial fibrillation; however, it also carries a black box warning regarding the risk of thrombosis after discontinuation of treatment. The purpose of this study was to determine the degree to which rivaroxaban, over a range of physiologically relevant free plasma concentrations, inhibits preassembled prothrombinase at a typical venous shear rate (100 s(-1)) and to determine the dynamics of rivaroxaban washout. METHODS AND RESULTS: Prothrombinase was assembled on phospholipid-coated glass capillaries. Its activity was characterized with respect to the activation of prothrombin (mean plasma concentration, 1.4 µmol/L) in the absence and presence of rivaroxaban (2, 5, and 10 nmol/L). The degree of inactivation of preassembled prothrombinase is sensitive to the solution-phase rivaroxaban concentration; however, prothrombinase unmasking upon removal of rivaroxaban is concentration independent. CONCLUSIONS: The model system presented suggests that when rivaroxaban plasma concentrations decrease after cessation of therapy, there will be an unmasking of thrombus-associated prothrombinase that may be related to the reported rebound phenomena.

The garlic-derived organosulfur compound diallyl trisulphide suppresses tissue factor function.

Tissue factor (TF) is a critical initiator of extrinsic coagulation that sometimes causes thromboembolism. Diallyl trisulphide (DATS) is a secondary metabolite of allicin generated in crushed garlic, with various pharmacological effects. This study aimed to clarify the effect of DATS on the extrinsic coagulation elicited by TF and arteriosclerosis. TF activity was measured using a clotting assay in TF-expressing HL60 cells. DATS inhibited TF activity in a dose-dependent manner. TF expression in TNF-α-stimulated human umbilical vein endothelial cells was examined using real-time PCR and western blotting. DATS inhibited TF mRNA and protein expression induced by TNF-α via inhibition of JNK signalling. The effect of DATS on arteriosclerosis was also examined in apolipoprotein E-deficient mice. DATS administration in these mice tended to decrease atherosclerotic lesion size. These results strongly suggest that DATS prevents thromboembolism triggered by atherosclerosis via the inhibition of plaque formation and TF function.

Effective treatment of chemoresistant breast cancer in vitro and in vivo by a factor VII-targeted photodynamic therapy.

BACKGROUND: The purpose of this study was to test a novel, dual tumour vascular endothelial cell (VEC)- and tumour cell-targeting factor VII-targeted Sn(IV) chlorin e6 photodynamic therapy (fVII-tPDT) by targeting a receptor tissue factor (TF) as an alternative treatment for chemoresistant breast cancer using a multidrug resistant (MDR) breast cancer line MCF-7/MDR. METHODS: The TF expression by the MCF-7/MDR breast cancer cells and tumour VECs in MCF-7/MDR tumours from mice was determined separately by flow cytometry and immunohistochemistry using anti-human or anti-murine TF antibodies. The efficacy of fVII-tPDT was tested in vitro and in vivo and was compared with non-targeted PDT for treatment of chemoresistant breast cancer. The in vitro efficacy was determined by a non-clonogenic assay using crystal violet staining for monolayers, and apoptosis and necrosis were assayed to elucidate the underlying mechanisms. The in vivo efficacy of fVII-tPDT was determined in a nude mouse model of subcutaneous MCF-7/MDR tumour xenograft by measuring tumour volume. RESULTS: To our knowledge, this is the first presentation showing that TF was expressed on tumour VECs in chemoresistant breast tumours from mice. The in vitro efficacy of fVII-tPDT was 12-fold stronger than that of ntPDT for MCF-7/MDR cancer cells, and the mechanism of action involved induction of apoptosis and necrosis. Moreover, fVII-tPDT was effective and safe for the treatment of chemoresistant breast tumours in the nude mouse model. CONCLUSIONS: We conclude that fVII-tPDT is effective and safe for the treatment of chemoresistant breast cancer, presumably by simultaneously targeting both the tumour neovasculature and chemoresistant cancer cells. Thus, this dual-targeting fVII-tPDT could also have therapeutic potential for the treatment of other chemoresistant cancers.

A key role for Toll-like receptor-3 in disrupting the hemostasis balance on endothelial cells.

Various virus infections cause dysfunctional hemostasis and in some instances lead to the development of viral hemorrhagic fever syndrome. How do diverse viruses induce the expression of tissue factor on vascular cells? We hypothesize that a direct stimulation of pattern recognition receptors (PRR) by viral nucleic acids may be the key. Double-stranded RNA (dsRNA) is produced by many viruses and is recognized by various PRR, including Toll-like receptor-3 (TLR3). We have investigated whether poly I:C, a model for viral dsRNA, can influence cellular hemostasis. Poly I:C could up-regulate tissue factor and down-regulate thrombomodulin expression on endothelial cells but not on monocytes. The response to poly I:C was diminished upon small interfering RNA (siRNA)-mediated inhibition of TLR3, but not other PRR. In vivo, application of poly I:C induced similar changes in the aortic endothelium of mice as determined by enface microscopy. D-dimer, a circulating marker for enhanced coagulation and fibrinolysis, and tissue fibrin deposition was elevated. All the hemostasis-related responses to poly I:C, but not cytokine secretion, were blunted in TLR3(-/-) mice. Hence, the activation of TLR3 can induce the procoagulant state in the endothelium, and this could be relevant for understanding the mechanisms of viral stimulation of hemostasis.

Paclitaxel potentiates inflammatory cytokine-induced prothrombotic molecules in endothelial cells.

To overcome the limitations of balloon expandible metal stent-induced neointimal smooth muscle cell proliferation, drug-coated stent devices have been developed. Drug eluting stents release high concentrations of antiproliferative agents, such as paclitaxel, to reduce neointimal hyperplasia. The proinflammatory cytokine, tumor necrosis factor-alpha (TNF-alpha), is known to cause severe endothelial dysfunction and accelerate atherosclerotic lesion progression. The interaction of TNF-alpha and paclitaxel on the release of prothrombotic molecules was examined in endothelial cells. Treatment of endothelial cells with paclitaxel had no direct effect on tissue factor (TF) expression, but TNF-alpha increased TF. Cotreatment of paclitaxel with TNF-alpha markedly augmented the release of TF. TNF-alpha induced release of plasminogen activator inhibitor but no synergism occurred with paclitaxel. Treatment of endothelial cells with paclitaxel and TNF-alpha reduced expression of thrombomodulin and protein C receptor. Tissue factor pathway inhibitor expression was reduced by prolonged treatment with either paclitaxel or TNF-alpha. The adhesion molecule, CD62 E, was induced by TNF-alpha; however, CD31, CD62 P, and CD106 were not affected by paclitaxel and TNF-alpha. Apoptosis was not observed with cotreatment of endothelial cells with paclitaxel and TNF-alpha. CD59-positive microparticles were released in response to TNF-alpha, but the release was not augmented by paclitaxel. Paclitaxel and TNF-alpha increased the nitrotyrosination of proteins. These findings indicate that paclitaxel enhances TNF-alpha-induced release of TF, and downregulated thrombomodulin, increased protein nitration, which may subsequently favor prothrombotic intimal surface.

Guggulsterone, an anti-inflammatory phytosterol, inhibits tissue factor and arterial thrombosis.

BACKGROUND: The phytosterol guggulsterone is a potent anti-inflammatory mediator with less side effects than classic steroids. This study assesses the impact of guggulsterone on tissue factor (TF) expression and thrombus formation. METHODS AND RESULTS: Guggulsterone inhibited TNF-alpha-induced endothelial TF protein expression and surface activity in a concentration-dependent manner; in contrast, dexamethasone did not affect TNF-alpha-induced TF expression. Guggulsterone enhanced endothelial tissue factor pathway inhibitor and impaired plasminogen activator inhibitor-1 as well as vascular cell adhesion molecule-1 protein. Real-time polymerase chain reaction revealed that guggulsterone inhibited TNF-alpha-induced TF mRNA expression; moreover, it impaired activation of the MAP kinases JNK and p38, while that of ERK remained unaffected. In vivo, guggulsterone inhibited TF activity and photochemical injury induced thrombotic occlusion of mouse carotid artery. Guggulsterone also inhibited TF expression, proliferation, and migration of vascular smooth muscle cells in a concentration-dependent manner. CONCLUSIONS: Guggulsterone inhibits TF expression in vascular cells as well as thrombus formation in vivo; moreover, it impairs vascular smooth muscle cell activation. Hence, this phytosterol offers novel therapeutic options, in particular in inflammatory diseases associated with an increased risk of thrombosis.

[Effect of tanshinone II A on NB4 cell induced procoagulant activity in human umbilical vein endothelial cells].

OBJECTIVE: To investigate the effect of tanshinone II A on the procoagulant activity (PCA) of human umbilical vein endothelial cells (HUVEC) induced by acute promyelocytic leukemia (APL) cell line NB4 cells. METHODS: The HUVEC were incubated for 6, 12, and 24 hours in different tanshinone II A conditioned medias (Tan II A-NB4-24h-CM, Tan II A-NB4-72h-CM, Tan II A-NB4-120h-CM). Then the HUVEC were incubated for 6, 12, 24, and 72 hours with Tan II A-NB4-120h-CM and different concentrations of Tan II A (0, 0.25, 0.5, 1.0 microg/mL). The HUVEC lysates were obtained by three repeated freezing and thrawing. Their PCA were tested using the one stage clotting assay. The activity of tissue factor (TF : act) was tested using the chromogenic substrate assay. The control groups included 0.3 microg/mL ATRA, 0.01% DMSO and RPMI 1640. RESULTS: Tan II A-(72 h,120 h)-NB4-CM elevated PCA of HUVEC and six hours of incubation in the 120 h-NB4-CM had the greatest PCA. The PCA of HUVEC in the 1.0 microg/mL Tan II A-NB4-CM was the same as in the 0.3 microg/mL ATRA-NB4-CM. (2) The NB4-CM induced PCA of HUVEC decreased with 5.0 microg/mL of Tan II A, at a level similar to the decrease with 0.3 microg/mL of ATRA. Less than 5.0 microg/mL of Tan II did not reduce the NB4-CM induced PCA of HUVEC. (3) Both Tan II A 120 h-NB4-CM and ATRA 120 h-NB4-CM elevated the TF : act of HUVEC. The TF : act reached the peak after 6 hours of incubation. The Tan II A 120 h-NB4-CM maintained the peak level of TF : act at the 12th hour and fell to the base line at the 24th hour. The ATRA 120 h-NB4-CM induced TF:act dropped down with time after reaching its peak at the 6th hour. (4) The 1.0 microg/mL of Tan II A did not reduce the TF : act of HUVEC induced by the Tan II A 120 h-NB4-CM. But the 0.3 microg/mL of ATRA reduced the TF : act of HUVEC at the 6th hour. CONCLUSION: TanIIA-NB4-CM increases PCA and TF : Act of HUVEC. TanIIA decreases PCA of HUVECs induces by TanIIA-NB4-CM.

Protective effect of Myrtle (Myrtus communis) on burn induced skin injury.

Thermal skin burns cause local injury as well as triggers acute systemic inflammation response where the imbalance between oxidative and antioxidative system occurs. As an alternative treatment, various medicinal herbs are used to treat burn injuries in many countries. In this study, the possible protective role of oral or topical Myrtle (Myrtus communis L.) treatment against burn-induced damage was investigated. The dorsum of the Wistar Albino rats was shaved and exposed to 90 °C water bath in burn group or 25 °C water bath in control group for 10 s under ether anesthesia. Myrtle extract was applied 100 mg/kg/day for 2 days either orally or topically. In skin samples; malondialdehyde and glutathione levels, catalase, superoxide dismutase, nitric oxide and tissue factor activities were determined. Skin tissues were also examined by light microscopy. Severe thermal skin burn injury caused a significant decrease in glutathione level, superoxide dismutase, catalase and tissue factor activities as well as nitric oxide level, which was accompanied with significant increases in skin malondialdehyde level. Myrtle treatment reversed all these biochemical indices except topical Myrtle treated group's nitric oxide level, as well as histopathological alterations, which were induced by thermal trauma. Both oral and topical Myrtle extract treatment was found to have protective role in the burn induced oxidative injury, which may be attributed to the potential antioxidant effect of Myrtle. As a conclusion, Myrtle significantly diminishes burn-induced damage in skin.

Phospholipid composition of in vitro endothelial microparticles and their in vivo thrombogenic properties.

INTRODUCTION: Microparticles from activated endothelial cells (EMP) are well known to expose tissue factor (TF) and initiate coagulation in vitro. TF coagulant activity is critically dependent on the presence of aminophospholipids, such as phosphatidylserine (PS) and phosphatidylethanolamine (PE), but it is unknown whether or not TF-exposing EMP are enriched in such aminophospholipids. Furthermore, despite the fact that EMP have been reported in several pathological conditions, direct evidence for their (putative) coagulant properties in vivo is still lacking. We investigated the phospholipid composition of endothelial MP (EMP) and their thrombogenic properties in vivo. MATERIALS AND METHODS: Human umbilical vein endothelial cells (HUVEC; n=3) were incubated with or without interleukin (IL)-1alpha (5 ng/mL; 0-72 h). Phospholipid composition of EMP was determined by high-performance thin layer chromatography. The association between EMP, TF antigen and activity was confirmed in vitro (ELISA, Western blot and thrombin generation). Thrombogenic activity of EMP in vivo was determined in a rat venous stasis model. RESULTS: Levels of TF antigen increased 3-fold in culture medium of IL-1alpha-treated cells (P<0.0001). This TF antigen was associated with EMP and appeared as a 45-47 kDa protein on Western blot. In addition, EMP from activated cells were enriched in both PS (P<0.0001) and PE (P<0.0001), and triggered TF-dependent thrombin formation in vitro and thrombus formation in vivo. In contrast, EMP from control cells neither initiated coagulation in vitro nor thrombus formation in vivo. CONCLUSIONS: EMP from activated endothelial cells expose coagulant tissue factor and are enriched in its cofactors PS and PE.

Inhibition of 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase blunts factor VIIa/tissue factor and prothrombinase activities via effects on membrane phosphatidylserine.

OBJECTIVE: 3-Hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase inhibitors (statins) exhibit antithrombotic properties that are independent of reductions in circulating LDL cholesterol. We hypothesized that these antithrombotic properties are mediated by membrane alterations secondary to disrupted lipid metabolism. METHODS AND RESULTS: EA.hy926 cells were incubated in the presence of 1 micromol/L atorvastatin supplemented with fetal bovine serum or lipid-depleted serum mixtures. Lipid restriction alone had no effect on cell lipid composition but when atorvastatin was included, phosphatidylserine, sphingomyelin, and cholesterol were reduced by 50% while ceramide content decreased by 70%. These changes in lipid composition did not alter the association of decay accelerating factor or tissue factor with lipid rafts. Atorvastatin in combination with lipid restriction reduced factor VIIa/tissue factor activity by as much as 75% but did not alter tissue factor expression. Prothrombinase activity was reduced to an extent similar to factor VIIa/tissue factor. Mevalonic acid but not LDL reversed the observed changes in lipid content and prothrombinase activity induced by atorvastatin. These findings were confirmed in primary cells. CONCLUSIONS: Inhibition of HMG-CoA reductase limits exposure of phosphatidylserine at the cell surface by restricting the cellular pool of mevalonate-derived isoprenoids. This membrane alteration restricts the activity of proteolytic enzyme complexes that propagate the coagulation cascade.

Interaction of daptomycin with two recombinant thromboplastin reagents leads to falsely prolonged patient prothrombin time/International Normalized Ratio results.

A cluster of patients experiencing elevations of International Normalized Ratio without clinical bleeding in temporal association with daptomycin therapy was identified during postmarketing safety surveillance. A common element was the thromboplastin reagent used for the laboratory assay. The present study evaluated the effect of daptomycin on measured prothrombin time using commercially available thromboplastin reagent kits commonly used in the United States. Thirty reagent kits were obtained. Daptomycin was added to pooled normal human plasma samples to achieve final concentrations of 0-200 microg/ml. Quality control ranges were established for each reagent kit using normal and abnormal control plasmas. Triplicate assays of the prothrombin time were performed on the daptomycin-spiked plasma samples using each of the 30 kits. The activated partial thromboplastin time and thrombin time were also assessed. Statistical comparisons of interest were performed using analysis of variance with the Bonferroni t-test for multiple comparisons; alpha = 0.05 was used. Addition of daptomycin to human plasma samples dose-dependently prolonged measured prothrombin times when two recombinant thromboplastin reagents were utilized. The findings were statistically and clinically significant. No clinically meaningful effect was observed with the other reagents. The activated partial thromboplastin time and thrombin time were not affected. Prolonged International Normalized Ratio patient values were an artifact caused by the interaction of daptomycin with the in-vitro prothrombin time test reagent; an in-vivo anticoagulant effect was not observed. Healthcare providers should consider a possible drug-laboratory test interaction if prolonged prothrombin time or elevated International Normalized Ratio values are observed in patients receiving daptomycin.

Effects of peroxisome proliferator-activated receptor ligands in modulating tissue factor and tissue factor pathway inhibitor in acutely symptomatic carotid atheromas.

BACKGROUND AND PURPOSE: Severely stenotic, symptomatic carotid atheromas are associated with a high risk of stroke in the short term. Although carotid endarterectomy is effective in reducing this stroke risk, it is frequently not applied within the time window for significant benefit. We investigated the effect of peroxisome proliferator-activated receptor (PPAR) -alpha and -gamma ligands in acutely modifying tissue factor (TF) and tissue factor pathway inhibitor (TFPI) in unstable carotid atheromas. METHODS: During a 3-year period, 64 patients who had experienced a transient ischemic attack or stroke with good recovery within 6 weeks before surgery and 12 asymptomatic patients with a >70% carotid stenosis were recruited. The expression of PPAR-alpha and -gamma was investigated in endarterectomy samples. The effects of the PPAR-alpha and -gamma ligands fenofibrate and rosiglitazone were investigated in cell culture experiments. Targeted biopsy specimens from endarterectomy samples (n=48) were incubated with medication for 4 days. TF and TFPI were assessed by immunohistochemistry, Western blot analysis, flow cytometry, and activity assays. RESULTS: PPAR-gamma1 but not -alpha was downregulated in atheromas removed from patients with recent symptoms and no evidence of diabetes. Fenofibrate but not rosiglitazone impaired the induction of TF in human endothelial cells and reduced resting levels of TF activity in vascular smooth muscle cells. Rosiglitazone but not fenofibrate increased TFPI secretion from human endothelial cells. Both fenofibrate (100+/-18.7% to 56.6+/-8.8%, P=0.005; 0.2664+/-0.0696 to 0.1771+/-0.0310, P=0.02) and rosiglitazone (100+/-22% to 88.3+/-20%, P=0.02; 0.3113+/-0.0729 to 0.2287+/-0.0415, P=0.04) reduced TF expression and activity, respectively, in atheroma biopsy specimens. A low expression of TFPI was found in atheroma biopsy specimens with little evidence of TFPI activity. CONCLUSIONS: This study suggests that both PPAR-alpha and -gamma ligands have beneficial effects in acutely reducing TF in unstable carotid atheromas.

Interference with tissue factor prolongs intrahepatic islet allograft survival in a nonhuman primate marginal mass model.

BACKGROUND: Tissue factor (TF) expression on islets can result in an instant blood-mediated inflammatory reaction (IBMIR) that contributes to early islet loss. We tested whether peritransplant protection of islets from IBMIR with a monoclonal anti-TF antibody (CNTO859) would enhance engraftment in our nonhuman primate marginal mass model. METHODS: Each of six pairs of cynomolgus monkeys (CM) with streptozotocin-induced diabetes was closely matched for metabolic control and was transplanted with 5,000 IEQ/kg allogeneic, ABO-compatible islets from the same donor under the cover of steroid-free immunosuppression. For each pair, experimental animals received islets cultured with 20 microg/mL anti-TF and were dosed with 6 mg/kg anti-TF intravenously, 10-25 min before islet infusion; control monkeys received an equal number of islets from the same preparation cultured without anti-TF and no in vivo treatment. RESULTS: Early fasting C-peptide (CP) values were different between (P<0.01), but not within, pairs and correlated with in vitro functional capacity of islets as assessed by perifusion (r=0.60; P=0.022). Compared to their matched controls, experimental animals had decreased posttransplant markers of coagulation, higher fasting CP levels (1 month posttransplant and end of study) and prolonged graft function. CONCLUSIONS: These data suggest that pretreatment of islets and the recipient with anti-TF may limit the effects of IBMIR, thereby enhancing islet engraftment and survival.

In vivo effects of an inhibitor of nuclear factor-kappa B on thrombogenic properties of antiphospholipid antibodies.

It has been shown that endothelial cell (EC) activation and tissue factor (TF) upregulation in EC and monocytes by antiphospholipid antibodies (aPL Abs) leads to a prothrombotic state and involves translocation of nuclear factor-kappa B (NF-kappaB). Here we examined the effects of an NF-kappaB inhibitor on aPL-induced thrombosis, TF activity, and EC in vivo. We treated CD1 mice with IgG from a patient with antiphospholipid syndrome (IgG-APS) or with control IgG (IgG-NHS). The adhesion of leukocytes (number of white blood cells) to EC in cremaster muscle (as an indication of EC activation) as well as the size of an induced thrombus in the femoral vein of the mice were examined. Some mice in each group were infused with 10 microM MG132 (an inhibitor of NF-kappaB). TF activity was determined using a chromogenic assay in homogenates of carotid arteries and in peritoneal cells of mice. In vivo, IgG-APS increased significantly the number of white blood cells adhering to ECs (4.7 +/- 2.2) when compared to control mice (1.5 +/- 0.8), and these effects were significantly reduced when mice were pretreated with MG132 (0.8 +/- 0.2). IgG-APS increased significantly the thrombus size and MG132 inhibited that effect (93%). Treatment of the mice with IgG-APS also induced significantly increased TF function in peritoneal cells and in homogenates of carotid arteries. Pretreatment of the mice with MG132 abrogated those effects significantly. Mice injected with IgG-APS or with IgM-APS with or without the inhibitor had medium-high titers of anticardiolipin antibodies in serum at the time of the surgical procedures. The data show that prothrombotic and proinflammatory properties of IgG-APS and IgM-APS are downregulated in vivo by an NF-kappaB inhibitor. These findings may be important in designing new modalities of targeted therapies to treat thrombosis in patients with APS.

Tissue factor and PAR signaling in tumor progression.

Tumor development depends on multiple reciprocal interactions of tumor cells with the host cell compartment. Tumor cells initiate TF-dependent crosstalks with the tumor microenvironment by releasing procoagulant microparticles, soluble cytokines and angiogenic growth factors. Conversely, the hemostatic system in the host compartment provides multiple circuits that regulate tumor growth and sustain angiogenesis. A combination of experimental models of spontaneous and transplanted tumor development and metastasis start to delineate the role of TF in tumor progression and identified potential therapeutic approaches to target the TF pathway.

Plasma level of stromal derived factor-1 (SDF-1) is increased in disseminated intravascular coagulation patients who have poor outcomes: in vitro effect of SDF-1 on coagulopathy.

Stromal cell-derived factor-1 (SDF-1) is a CXC chemokine that activates and directs the migration of leukocytes that have CXCR4, which is the unique receptor for SDF-1. Although SDF-1/CXCR4 interaction has been implicated in various inflammatory conditions, its role in modulating coagulation has not been determined. We studied the plasma SDF-1 levels in 90 patients with suspected disseminated intravascular coagulation (DIC) and we found that circulating SDF-1 was significantly increased in the overt DIC patients and was also increased in overt DIC patients who have a poor outcome. We then tested in vitro whether SDF-1 can affect the expression of monocyte tissue factor (TF) and endothelial thrombomodulin (TM), and both of these play important roles in coagulopathy. SDF-1 did not affect the expression of surface TF protein and its function and the TF mRNA level in both monocytes and the monocytic leukemia cell line THP-1. SDF-1 also did not change the surface TM expression of endothelial cells. SDF-1 could enhance low-dose ADP induced platelet aggregation, although it failed by itself to induce aggregation. These findings suggest that plasma SDF-1 might be closely associated with hypercoagulability though its action as a platelet activator.

Calcium ionophore-induced de-encryption of tissue factor in monocytes is associated with extensive cell death.

INTRODUCTION: Cell surface tissue factor (TF) is normally encrypted, but can be activated by various cellular perturbations. Exposure of TF bearing cells to calcium ionophore has been reported to increase TF activity, de-encrypt TF, by phosphatidylserine (PS)-dependent and -independent mechanisms. Our aim has been to examine at the single cell level, if increased cell surface PS coincided with increased cell surface TF antigen, and cell death (necrosis, 7-AAD-intercalation), and relate this to monocyte- and microparticle (MP)-associated procoagulant activity. MATERIALS AND METHODS: We exposed lipopolysaccharide-stimulated, human, elutriation-purified, cryopreserved TF bearing monocytes to increasing concentrations of calcium ionophore (A23187) and measured procoagulant activity in cells and supernatants. These measurements were compared with quantification of cell surface TF and PS (Annexin V) and of cell necrosis (7-AAD) by flow cytometry, and complemented by confocal microscopy. RESULTS: We observed that calcium ionophore increased cellular and MP-associated TF activity, but not cell surface TF antigen. The discrepancy between TF activity and TF antigen coincided with a dose-dependent increase in the number of cells expressing PS. These cells were to a large extent necrotic and many of them also expressed TF. CONCLUSIONS: We suggest such TF positive dying cells to contribute to the discordance between TF activity and TF expression. Calcium ionophore also increased MP-associated TF activity and release of MPs may be a way to disseminate procoagulant activity. Our findings emphasize the importance of adequately assessing cell death and taking into consideration its possible role in experiments with calcium ionophore.

A functional clotting assay to monitor the hirudin dosage.

Hirudin, a direct thrombin inhibitor, has potential advantages over indirect thrombin inhibitors and is increasingly used in clinical settings. There are, however, large variations in individual responses to this drug and no recognized clinical laboratory tests used to monitor its anticoagulant effects. We evaluated the use of the thromboelastograph, a common clinical coagulation instrument, to monitor the effects of hirudin in vitro. We developed a novel, whole blood clotting assay that utilizes the tissue factor stimulating properties of mercuric ion to measure the anticoagulant potential of therapeutic doses of hirudin. At doses equivalent to those found in the therapeutic range, the thromboelastograph was capable of showing significant changes when compared with control and different concentrations of hirudin (P < 0.05). A linear relationship was observed between increasing concentrations of recombinant hirudin and clotting times. In conclusion, the use of this test system warrants further investigation for monitoring hirudin.