Role of tissue factor in venous thrombosis

A computational model based on fibrin accumulation for the prediction of stasis thrombosis following flow-diverting treatment in cerebral aneurysms

Flow diverters, the specially designed low porosity stents, have been used to redirect blood flow from entering aneurysm, which induces flow stasis in aneurysm and promote thrombosis for repairing aneurysm. However, it is not clear how thrombus develops following flow-diversion treatment. Our objective was to develop a computation model for the prediction of stasis-induced thrombosis following flow-diversion treatment in cerebral aneurysms. We proposed a hypothesis to initiate coagulation following flow-diversion treatment. An experimental model was used by ligating rat's right common carotid artery (RCCA) to create flow-stasis environment. Thrombus formed in RCCA as a result of flow stasis. The fibrin distributions in different sections along the axial length of RCCA were measured. The fibrin distribution predicted by our computational model displayed a trend of increase from the proximal neck to the distal tip, consistent with the experimental results on rats. The model was applied on a saccular aneurysm treated with flow diverter to investigate thrombus development following flow diversion. Thrombus was predicted to form inside the sac, and the aneurysm was occluded with only a small remnant neck remained. Our model can serve as a tool to evaluate flow-diversion treatment outcome and optimize the design of flow diverters.

Simulated thrombin responses in venous valves

OBJECTIVE

Venous thromboembolism frequently results in thrombi formation near or within the pocket of a venous valve due to recirculating hemodynamics, which has been largely attributed to hypoxia-induced tissue factor (TF) expression. Numerical models are now capable of assessing the spatiotemporal behavior of the TF-initiated coagulation cascade under nonuniform hemodynamics. The aim of this study was to use such a numerical simulation to analyze the degree and location of thrombin formation with respect to TF position in the presence of disturbed flow induced by an open venous valve.

METHODS

Thrombin formation was simulated using a computational model that captures the hemodynamics, kinetics, and chemical transport of 22 biochemical species. Disturbed flow is described by the presence of a valve in the equilibrium phase of the valve cycle with leaflets in a fully open position. Three different positions of TF downstream of the valve opening were investigated.

RESULTS

The critical amount of TF required to initiate a thrombotic response is reduced by up to 80% when it is positioned underneath the recirculating regions near the valve opening. In addition, because of the increased surface area of the open valve cusp in conjunction with recirculating hemodynamics, it was observed that thrombin is generated inside the valve pocket even when the exposed region of TF is downstream of the valve.

CONCLUSIONS

The presence of prothrombotic surface reactions in conjunction with recirculating hemodynamics provides an additional mechanism for thrombus formation in venous valves that does not require direct damage or dysfunction to the valve itself.

At the Bench: Neutrophil extracellular traps (NETs) highlight novel aspects of innate immune system involvement in autoimmune diseases

The putative role of neutrophils in host defense against pathogens is a well-recognized aspect of neutrophil function. The discovery of neutrophil extracellular traps has expanded the known range of neutrophil defense mechanisms and catalyzed a discipline of research focused upon ways in which neutrophils can shape the immunologic landscape of certain autoimmune diseases, including systemic lupus erythematosus. Enhanced neutrophil extracellular trap formation and impaired neutrophil extracellular trap clearance may contribute to immunogenicity in systemic lupus erythematosus and other autoimmune diseases by promoting the externalization of modified autoantigens, inducing synthesis of type I IFNs, stimulating the inflammasome, and activating both the classic and alternative pathways of the complement system. Vasculopathy is a central feature of many autoimmune diseases, and neutrophil extracellular traps may contribute directly to endothelial cell dysfunction, atherosclerotic plaque burden, and thrombosis. The elucidation of the subcellular events of neutrophil extracellular trap formation may generate novel, therapeutic strategies that target the innate immune system in autoimmune and vascular diseases.

Simulated Thrombin Generation in the Presence of Surface-Bound Heparin and Circulating Tissue Factor

An expanded computational model of surface induced thrombin generation was developed that includes hemodynamic effects, 22 biochemical reactions and 44 distinct chemical species. Surface binding of factors V, VIII, IX, and X was included in order to more accurately simulate the formation of the surface complexes tenase and prothrombinase. In order to model these reactions, the non-activated, activated and inactivated forms were all considered. This model was used to investigate the impact of surface bound heparin on thrombin generation with and without the additive effects of thrombomodulin (TM). In total, 104 heparin/TM pairings were evaluated (52 under venous conditions, 52 under arterial conditions), the results demonstrating the synergistic ability of heparin and TM to reduce thrombin generation. Additionally, the role of circulating tissue factor (TF(p)) was investigated and compared to that of surface-bound tissue factor (TF(s)). The numerical results suggest that circulating TF has the power to amplify thrombin generation once the coagulation cascade is already initiated by surface-bound TF. TF(p) concentrations as low as 0.01 nM were found to have a significant impact on total thrombin generation.

Genetic polymorphisms and plasma levels of tissue factor and tissue factor pathway inhibitor in venous thromboembolism

Tissue factor (TF) and tissue factor pathway inhibitor (TFPI) play important roles in coagulation. The aim of this study was to investigate the distributions of TF and TFPI polymorphisms in Koreans and to analyze the association of these genetic polymorphisms with plasma levels and development of venous thromboembolism (VTE). The polymorphisms TF 5466 A > G, TF -603 A > G, TFPI -287 T > C and TFPI -33 T > C were investigated in 40 Korean VTE patients and 40 age-matched and sex-matched controls by real-time PCR followed by melting curve analysis and DNA sequence analysis. Plasma levels of TF and TFPI were measured by enzyme-linked immunosorbent assay. The G allele of TF 5466 was not detected, and allelic frequencies of TF -603 G, TFPI -287 C and TFPI -33 C were 27.5, 67.5 and 16.2%, respectively. The distributions of TF and TFPI polymorphisms were not different between patients and controls. The presence of TF -603 G allele was correlated with low plasma TF levels (P = 0.029). Mean plasma TFPI levels were similar between TFPI genotypic groups. Although not statistically significant, plasma TF and TFPI levels were higher in patients than controls. The distributions of TF and TFPI polymorphisms in Koreans were considerably different from whites, suggesting ethnic variations. The TF -603 A > G polymorphism was significantly correlated with decreased plasma TF levels. Neither genetic polymorphisms in TF and TFPI nor their plasma levels seem to act as direct risk factors for VTE.

Decreased plasma levels of activated factor VII in patients with deep vein thrombosis

BACKGROUND

The initiating trigger in the development of deep vein thrombosis (DVT) remains unidentified. It has been suggested that tissue factor (TF)-bearing microparticles play a key role, which indicates a role for the TF pathway in the initiation of DVT.

OBJECTIVE

To assess the role of the TF pathway in the initiation of venous thrombosis, we measured plasma levels of factor VII and VIIa in patients with acute DVT and in controls.

METHODS

We included 148 patients diagnosed with acute DVT and 179 controls in this study. Antigen levels of FVII and FVIIa were measured by using assays recently developed in our laboratory.

RESULTS

Median FVII levels in patients were 109.8% (interquartile range [IQR] 86.0-153.2) compared with 102.2% (IQR 76.1-141.7) in controls. Individuals with FVII levels in the upper quartile had a 1.6-fold increased risk for the presence of a DVT (odds ratio 1.6, 95% confidence interval 0.8-3.1). Median FVIIa levels in patients were 50.2 ng mL(-1) (IQR 25.2-86.1) compared with 96.6 ng mL(-1) (69.9-168.9) in controls. Individuals with FVIIa levels in the lowest quartile had a > 5-fold increased risk for the presence of a DVT (odds ratio 5.5, 95% confidence interval 2.8-10.6). Both risks did not change substantially after adjustment for potential confounders.

CONCLUSION

Decreased plasma levels of FVIIa in patients with deep vein thrombosis may indicate ongoing consumption of FVIIa and suggest a contributory role for TF in venous thrombus formation.

TLR4 is involved in the pathogenic effects observed in a murine model of antiphospholipid syndrome

Antiphospholipid (aPL)/anti-β2-glycoprotein I (β2GPI) antibodies are considered to play a pivotal pathogenic role in antiphospholipid syndrome (APS) by inducing an intracellular signaling and procoagulant/proinflammatory phenotype that leads to thrombosis. There is increasing evidence that Toll-like receptor 4 (TLR4) could serve as an important molecule for anti-β2GPI recognition on target cells. However, few studies have focused on the effects of TLR4 in in vivo models. Here, we investigated the role of TLR4 in the pathogenic effects of aPL/anti-β2GPI more precisely using TLR4-intact (C3H/HeN) and TLR4-defective (C3H/HeJ) mice. C3H/HeN and C3H/HeJ mice were injected with either IgG isolated from patient with APS (IgG-APS) or epitope-specific anti-β2GPI purified from β2GPI peptide-immunized rabbits. We found that, following anti-β2GPI injections and vascular injury, thrombus formation in both the carotid artery and femoral vein was markedly reduced in C3H/HeJ mice when compared with C3H/HeN mice. IgG-APS or anti-β2GPI-induced carotid artery and peritoneal macrophage tissue factor activity/expression was significantly lesser in C3H/HeJ than in C3H/HeN mice. Furthermore, the IgG-APS or anti-β2GPI induced expression of VCAM-1, ICAM-1, and E-selectin in the aorta and of IL-1β, IL-6, and TNF-α in peritoneal macrophages of C3H/HeJ mice was also significantly reduced compared to C3H/HeN mice. Together, these data suggest that TLR4 is involved in the pathogenic effects of aPL/anti-β2GPI antibodies in vivo.

New oral anticoagulants for the treatment of acute venous thromboembolism: are they safer than vitamin K antagonists? A meta-analysis of the interventional trials

New oral anticoagulants (NOACs) may represent an alternative to standard therapy with vitamin K antagonists (VKA). However, up to the present, it is unknown whether these drugs are safer than VKA. The aim of this study was to perform a meta-analysis of the interventional trials with NOACs vs VKA in patients with acute venous thromboembolism (VTE) to obtain the balance between clinical efficacy and complications. A meta-analysis of double blind randomized controlled trials (RCTs) was performed. We included RCTs that compared, in acute VTE, the beneficial and harmful effects of NOACs (ximelagatran, apixaban, dabigatran, edoxaban and rivaroxaban) vs VKA (warfarin). Seven studies including 29,482 patients were selected. Compared with warfarin, recurrent VTE and death from any cause were not significantly reduced by NOACs. Myocardial infarction was significantly increased with NOACs compared with warfarin (RR 2.55; 95% CI 1.1-5.6; p = 0.02). NOACs significantly reduced the major bleedings (RR 0.63; 95% CI 0.47-0.83; p = 0.001). This meta-analysis suggests that treatment with NOACs in patients with acute VTE is not inferior to conventional therapy with warfarin for recurrent VTE and death from any cause, but there might be an increased incidence of myocardial infarction.

NMMHC IIA inhibition impedes tissue factor expression and venous thrombosis via Akt/GSK3β-NF-κB signalling pathways in the endothelium

Non-muscle myosin heavy chain IIA (NMMHC IIA) has been shown to be involved in thrombus formation and inflammatory microparticle release in endothelial cells. However, the role of NMMHC IIA in regulating the expression of tissue factor (TF) and deep venous thrombosis remains to be elucidated. In the present study, endothelial cells were stimulated with tumour necrosis factor-α (TNF-α) to induce TF expression. Pretreatment with the NMMHC II inhibitor blebbistatin suppressed the mRNA and protein expressions as well as the procoagulant activity of TF in a dose-dependent manner. Blebbistatin enhanced Akt and GSK3β phosphorylation and inhibited NF-κB p65 nuclear translocation and IκBα degradation. These observations were similar to the effect of CHIR99021, a GSK3β inhibitor. TF downregulation by blebbistatin was antagonised by the PI3K inhibitor, wortmannin. Furthermore, siRNA knockdown of NMMHC IIA, but not IIB or IIC, inhibited TF expression, activated Akt/GSK3β and suppressed NF-κB signalling pathways, whereas the overexpression of NMMHC IIA increased TF expression. The binding of NMMHC IIA and TNF receptor 2 mediated signal internalisation in TNF-α-stimulated endothelial cells. Importantly, blebbistatin decreased endothelium NMMHC IIA and TF expression, deactivated GSK3β by inducing its phosphorylation, suppressed p65 nuclear translocation, and inhibited thrombus formation in a mouse deep venous thrombosis model.Our findings provide solid evidence that inhibition of NMMHC II, most likely NMMHC IIA, impedes TF expression and venous thrombosis via Akt/GSK3β-NF-κB signalling pathways in the endothelium both in vitro and in vivo. NMMHC IIA might be a potential novel target for the treatment of thrombotic disorders.

Tissue factor-expressing tumor cells can bind to immobilized recombinant tissue factor pathway inhibitor under static and shear conditions in vitro

Mammary tumors and malignant breast cancer cell lines over-express the coagulation factor, tissue factor (TF). High expression of TF is associated with a poor prognosis in breast cancer. Tissue factor pathway inhibitor (TFPI), the endogenous inhibitor of TF, is constitutively expressed on the endothelium. We hypothesized that TF-expressing tumor cells can bind to immobilized recombinant TFPI, leading to arrest of the tumor cells under shear in vitro. We evaluated the adhesion of breast cancer cells to immobilized TFPI under static and shear conditions (0.35 – 1.3 dyn/cm²). We found that high-TF-expressing breast cancer cells, MDA-MB-231 (with a TF density of 460,000/cell), but not low TF-expressing MCF-7 (with a TF density of 1,400/cell), adhered to recombinant TFPI, under static and shear conditions. Adhesion of MDA-MB-231 cells to TFPI required activated factor VII (FVIIa), but not FX, and was inhibited by a factor VIIa-blocking anti-TF antibody. Under shear, adhesion to TFPI was dependent on the TFPI-coating concentration, FVIIa concentration and shear stress, with no observed adhesion at shear stresses greater than 1.0 dyn/cm². This is the first study showing that TF-expressing tumor cells can be captured by immobilized TFPI, a ligand constitutively expressed on the endothelium, under low shear in vitro. Based on our results, we hypothesize that TFPI could be a novel ligand mediating the arrest of TF-expressing tumor cells in high TFPI-expressing vessels under conditions of low shear during metastasis.

Two swine models of iliac vein occlusion: Which form most contributes to venous thrombosis?

OBJECTIVES

In the present study, we establish two swine models of iliac vein occlusion (IVO) with spontaneous thrombosis to understand the mechanisms linking IVO and thrombosis.

METHODS

Two IVO models were established in 12 swine either by ligating the common iliac vein (CIVO) or both the common and external iliac veins (CEIVO). Venography was performed to assess each model and the associated thrombosis. Invasive blood pressure was also measured, and the vessels were examined histologically to analyse the pathological changes after ligation.

RESULTS

On venography, the CIVO model showed common iliac vein (CIV) occlusion and reflux in the collateral veins whereas the CEIVO model showed occlusion in the CIV and external iliac vein (EIV), stasis in the EIV, and decreased collateral vasculature on venography. Thrombosis was only observed in the CEIVO model, which was with significantly higher venous blood pressure in the EIV and with significantly more thickened venous wall with lymphocytic infiltration histologically.

CONCLUSIONS

Two IVO models can be feasibly and reliably established in swine. The CEIVO model had a higher prevalence of thrombosis than the CIVO model. This CEIVO model produces comparatively less collateral drainage and greater inflammation that can contribute to the thrombosis prone to this type of model.

Complement inhibition in a xenogeneic model of interactions between human whole blood and porcine endothelium

Xenotransplantation (xeno-Tx) is considered as an alternative solution to overcome the shortage of human donor organs. However, the success of xeno-Tx is hindered by immune reactions against xenogeneic cells (e. g. of porcine origin). More specifically, activation of innate immune mechanisms such as complement and triggering of the coagulation cascade occur shortly after xeno-Tx, and adhesion of human leukocytes to porcine endothelium is another early critical step mediating the immune attack. To investigate the therapeutic potential of complement inhibition in the context of xenogeneic interactions, we have employed a whole-blood model in the present study. Incubation of human blood with porcine endothelial cells (PAECs) led to activation of complement and coagulation as well as to increased leukocyte adhesion. The observed responses can be attributed to the pig-to-human xenogeneicity, since the presence of human endothelium induced a minor cellular and plasmatic inflammatory response. Importantly, complement inhibition using a potent complement C3 inhibitor, compstatin analogue Cp40, abrogated the adhesion of leukocytes and, more specifically, the attachment of neutrophils to porcine endothelium. Moreover, Cp40 inhibited the activation of PAECs and leukocytes, since the levels of the adhesion molecules E-selectin, ICAM-1, ICAM-2, and VCAM-1 on PAECs and the surface expression of integrin CD11b on neutrophils were significantly decreased. Along the same line, inhibition of CD11b resulted in decreased leukocyte adhesion. Taken together, our findings provide a better understanding of the mechanisms regulating the acute innate immune complications in the context of xeno-Tx and could pave the way for complement-targeting therapeutic interventions.

Overview of the coagulation system

Coagulation is a dynamic process and the understanding of the blood coagulation system has evolved over the recent years in anaesthetic practice. Although the traditional classification of the coagulation system into extrinsic and intrinsic pathway is still valid, the newer insights into coagulation provide more authentic description of the same. Normal coagulation pathway represents a balance between the pro coagulant pathway that is responsible for clot formation and the mechanisms that inhibit the same beyond the injury site. Imbalance of the coagulation system may occur in the perioperative period or during critical illness, which may be secondary to numerous factors leading to a tendency of either thrombosis or bleeding. A systematic search of literature on PubMed with MeSH terms ‘coagulation system, haemostasis and anaesthesia revealed twenty eight related clinical trials and review articles in last 10 years. Since the balance of the coagulation system may tilt towards bleeding and thrombosis in many situations, it is mandatory for the clinicians to understand physiologic basis of haemostasis in order to diagnose and manage the abnormalities of the coagulation process and to interpret the diagnostic tests done for the same.

Role of tissue factor in Mycobacterium tuberculosis-induced inflammation and disease pathogenesis

Tuberculosis (TB) is a chronic lung infectious disease characterized by severe inflammation and lung granulomatous lesion formation. Clinical manifestations of TB include hypercoagulable states and thrombotic complications. We previously showed that Mycobacterium tuberculosis (M.tb) infection induces tissue factor (TF) expression in macrophages in vitro. TF plays a key role in coagulation and inflammation. In the present study, we investigated the role of TF in M.tb-induced inflammatory responses, mycobacterial growth in the lung and dissemination to other organs. Wild-type C57BL/6 and transgenic mice expressing human TF, either very low levels (low TF) or near to the level of wild-type (HTF), in place of murine TF were infected with M.tb via aerosol exposure. Levels of TF expression, proinflammatory cytokines and thrombin-antithrombin complexes were measured post M.tb infection and mycobacterial burden in the tissue homogenates were evaluated. Our results showed that M.tb infection did not increase the overall TF expression in lungs. However, macrophages in the granulomatous lung lesions in all M.tb-infected mice, including low TF mice, showed increased levels of TF expression. Conspicuous fibrin deposition in the granuloma was detected in wild-type and HTF mice but not in low TF mice. M.tb infection significantly increased expression levels of cytokines IFN-γ, TNF-α, IL-6 and IL-1ß in lung tissues. However, no significant differences were found in proinflammatory cytokines among the three experimental groups. Mycobacterial burden in lungs and dissemination into spleen and liver were essentially similar in all three genotypes. Our data indicate, in contrast to that observed in acute bacterial infections, that TF-mediated coagulation and/or signaling does not appear to contribute to the host-defense in experimental tuberculosis.

The Effect of Vitamin D Supplementation on Thrombin Generation Assessed by the Calibrated Automated Thrombogram

Observational and in vitro studies suggest that vitamin D may have antithrombotic activity. This study aimed to examine the relationship between vitamin D supplementation and thrombin generation. Serum 25-hydroxyvitamin D (25(OH)D) and thrombin generation parameters were measured in 73 healthy volunteers. Participants with serum 25(OH)D <50 nmol/L (n = 53) were treated with vitamin D3and tested for 25(OH)D and thrombin generation at the end of treatment. Lag time and time to peak decreased after treatment by a mean of -0.49 ± 0.51 minute (P< .001) and -0.76 ± 0.70 minute (P< .001), respectively, whereas endogenous thrombin potential and peak height increased after treatment by a mean of 170.1 ± 339.8 nmol/L minute (P= .001) and 34.2 ± 47.8 nmol/L (P< .001), respectively. Treatment with vitamin D supplementation seems to have prothrombotic effect in patients with vitamin D insufficiency. These findings should be interpreted with caution and need to be replicated in future studies.

PARP-14 combines with tristetraprolin in the selective posttranscriptional control of macrophage tissue factor expression

Tissue factor (TF) (CD142) is a 47 kDa transmembrane cell surface glycoprotein that triggers the extrinsic coagulation cascade and links thrombosis with inflammation. Although macrophage TF expression is known to be regulated at the RNA level, very little is known about the mechanisms involved. Poly(adenosine 5'-diphosphate [ADP]-ribose)-polymerase (PARP)-14 belongs to a family of intracellular proteins that generate ADP-ribose posttranslational adducts. Functional screening of PARP-14-deficient macrophages mice revealed that PARP-14 deficiency leads to increased TF expression and functional activity in macrophages after challenge with bacterial lipopolysaccharide. This was related to an increase in TF messenger RNA (mRNA) stability. Ribonucleoprotein complex immunoprecipitation and biotinylated RNA pull-down assays demonstrated that PARP-14 forms a complex with the mRNA-destabilizing protein tristetraprolin (TTP) and a conserved adenylate-uridylate-rich element in the TF mRNA 3' untranslated region. TF mRNA regulation by PARP-14 was selective, as tumor necrosis factor (TNF)α mRNA, which is also regulated by TTP, was not altered in PARP-14 deficient macrophages. Consistent with the in vitro data, TF expression and TF activity, but not TNFα expression, were increased in Parp14(-/-) mice in vivo. Our study provides a novel mechanism for the posttranscriptional regulation of TF expression, indicating that this is selectively regulated by PARP-14.

The 'procoagulopathy' of trauma: too much, too late?

PURPOSE OF REVIEW

Although early acute traumatic coagulopathy has received much recent attention, the procoagulopathy that often follows appears less appreciated. Thromboembolic disease following trauma is common and lethal, but very effective prophylactic strategies are available. These strategies are variably implemented because of the difficulty in quantifying the magnitude of procoagulopathy in individual patients.

RECENT FINDINGS

The principal mechanisms of the procoagulopathy of trauma include inflammation and disseminated intravascular coagulation, tissue factor and thrombin dysregulation, and circulating microparticles and phospholipids. Quantification of these factors may allow better risk assessment in individual patients, but as yet none of these tests is in routine practice. Viscoelastic measurement of developing clot strength identifies a procoagulant state in many trauma patients, and may be a guide to the best choice of the many options for thromboembolic prophylaxis.

SUMMARY

The logical next step following from the improved pathophysiological understanding of the procoagulopathy of trauma should be a simultaneous clinical trial of procoagulopathy diagnosis and thromboembolic prophylaxis.

Padua prediction score and thrombin generation in hospitalized medical patients

INTRODUCTION

The Padua prediction score is a risk assessment model used to identify medical patients at high risk for venous thromboembolim (VTE).We aimed to assess the relationship between the severity of Padua score and thrombin generation as a measure of overall thrombotic activity.

MATERIALS AND METHODS

A total of 253 patients hospitalized in the medical wards, at the Haemek Medical Center, Israel, were enrolled in the study. Patients treated with anticoagulation, and those admitted for VTE were excluded. Padua score was classified into two categories; low-risk for VTE (<4 points), and high-risk for VTE (≥4 points). Thrombin generation was assessed by the Calibrated Automated Thrombogram (CAT) method.

RESULTS

Overall 187 (73.9%) patients had Padua score<4, and 66 (26.1%) patients had Padua score ≥4. Comparison of the thrombogram parameters between the two Padua score categories showed no significant difference; lag time (P=0.066), ETP (P=0.266), peak height (P=0.418), and time to peak (P=0.415). Among the individual Padua score risk factors, only active cancer was significantly associated with peak height, myocardial infarction or stroke with lag time, and none of the risk factors was significantly associated with ETP. Because of their low frequency, the association with previous VTE, known thrombophilia, hormonal treatment, and recent trauma or/and surgery was not assessed.

CONCLUSIONS

Single thrombin generation measurement obtained at the same time in acutely hospitalized patients didn't bear any correlation with the Padua prediction score. This finding should be interpreted with caution considering the underrepresentation of risk factors that may influence thrombin generation.

Outer membrane vesicles alter inflammation and coagulation mediators

INTRODUCTION

Outer membrane vesicles (OMVs) were previously shown to be capable of initiating the inflammatory response seen in the transition of an infection to sepsis. However, another tenet of sepsis is the development of a hypercoagulable state and the role of OMVs in the development of this hypercoagulability has not been evaluated. The objective of this study was to evaluate the ability of OMVs to elicit endothelial mediators of coagulation and inflammation and induce platelet activation.

METHODS

Human umbilical vein endothelial cells (HUVECs) were incubated with OMVs and were analyzed for the expression of tissue factor (TF), thrombomodulin, and the adhesion molecules P-selectin and E-selectin. Supernatants of OMV-treated HUVECs were mixed with whole blood and assessed for prothrombotic monocyte-platelet aggregates (MPA).

RESULTS

OMVs induce significantly increased expression of TF, E-selectin, and P-selectin, whereas, the expression of thrombomodulin by HUVECs is significantly decreased (P < 0.05). The lipopolysaccharide inhibitor clearly inhibited the expression of E-selectin following incubation with OMVs, although its impact on TF and thrombomodulin expression was nominal. Incubation of whole blood with supernatant from HUVECs exposed to OVMs resulted in increased MPAs.

CONCLUSIONS

This study demonstrates that, at the cellular level, OMVs from pathogenic bacteria play a complex role in endothelial activation. Although OMV-bound lipopolysaccharide modulates inflammatory proteins, including E-selectin, it has a negligible effect on the tested coagulation mediators. Additionally, endothelial activation by OMVs facilitates platelet activation as indicated by increased MPAs. By influencing the inflammatory and coagulation cascades, OMVs may contribute to the hypercoagulable response seen in sepsis.

Prognostic value of tissue factor in patients with abdominal aortic and iliac arterial aneurysms - preliminary study

INTRODUCTION

The decision on the time and choice of strategy of treatment of abdominal aortic aneurysm must be especially carefully balanced. The aim of the study was to evaluate the tissue factor (TF) plasma level as a potential factor useful in anticipation of abdominal aortic aneurysm and/or iliac arterial aneurysm via comparison of plasma TF level in patients with ruptured and non-ruptured aneurysms.

MATERIAL AND METHODS

The study included 33 patients with aneurysm (17 operated on electively because of non-ruptured aneurysm and 16 operated on emergently due to ruptured aneurysm), 33 claudicant patients with atherosclerosis of the abdominal aorta and iliac arteries with normal diameter of arteries, and 30 healthy controls. Plasma TF level was assessed by ELISA method using the IMUBIND Tissue Factor ELISA Kit (American Diagnostica Inc.).

RESULTS

The study showed an increased TF level in patients with aneurysm (134 ±54 pg/ml) and in patients with atherosclerosis without concomitant aneurysm (91 ±30 pg/ml) in comparison with the control group (62 ±20 pg/ml), respectively p < 0.001 and p = 0.008. A significantly higher TF plasma level was observed in patients with ruptured abdominal aortic aneurysms (160 ±57 pg/ml) as compared to patients with non-ruptured aortic aneurysms (109 ±39 pg/ml) or peripheral arterial occlusive disease (91 ±30 pg/ml), respectively p < 0.001 and p < 0.001. The difference in TF level between the group with non-ruptured aortic aneurysms (109 ±39 pg/ml) and the patients with atherosclerosis without aneurysm (91 ±30 pg/ml) was not statistically significant.

CONCLUSIONS

No difference in TF level between patients with non-ruptured AAA/IAA and patients with aortic and iliac atherosclerosis without aneurysm indicates that an increased TF plasma level is not specific for any of the above-mentioned vascular pathologies.

Time-dependent hardening of blood clots quantitatively measured in vivo with shear-wave ultrasound imaging in a rabbit model of venous thrombosis

OBJECTIVE

Provide in vivo blood clot hardening evolution with ultrasound using supersonic imaging of shear waves.

METHODS

We conducted a prospective study in flow stasis-induced venous thrombosis within jugular veins of white female New Zealand rabbits. Blood clot elasticity was noninvasively measured in vivo using the Young's modulus (in kilopascals), on a 2-hour and a 2-week periods after thrombus induction. Monitoring was followed by a necropsy and ex vivo mechanical characterization to validate the existence and elasticity of explanted thrombi.

RESULTS

Stagnant blood in the region of interest underwent clotting and progressive hardening with thrombus aging. The mean Young's moduli varied from 1.0 ± 0.6 kPa (at 10 min) to 5.3 ± 1.6 kPa (at 2 hours), then to 25.0 ± 6.8 kPa (at 14 days) post-surgery. Mean ex vivo moduli of 6.2 ± 0.7 kPa at 2 hours and 29.0 ± 2.4 kPa at 2 weeks agreed with in vivo measures.

CONCLUSIONS

Supersonic imaging of shear waves provides consistent quantitative non-invasive elasticity measurements not available with standard compression ultrasound imaging for diagnosing and following venous thromboembolism. This information translatable to humans could aid in determining whether continued anticoagulant treatment is necessary, especially in the setting of unprovoked venous thromboembolism.

Tumor-derived tissue factor-positive microparticles and venous thrombosis in cancer patients

Patients with cancer have an increased risk for venous thrombosis. Interestingly, different cancer types have different rates of thrombosis, with pancreatic cancer having one of the highest rates. However, the mechanisms responsible for the increase in venous thrombosis in patients with cancer are not understood. Tissue factor (TF) is a transmembrane receptor and primary initiator of blood coagulation. Tumor cells express TF and spontaneously release TF-positive microparticles (MPs) into the blood. MPs are small membrane vesicles that are highly procoagulant. It has been proposed that these circulating tumor-derived, TF-positive MPs may explain the increased rates of venous thrombosis seen in patients with cancer. In animal models, increased levels of tumor-derived, TF-positive MPs are associated with activation of coagulation. Moreover, these MPs bind to sites of vascular injury and enhance thrombosis. We and others have found that patients with cancer have elevated levels of circulating TF-positive MPs. These MPs are derived from tumors because they express tumor markers and are decreased by tumor resection. Importantly, several studies have shown that increased levels of TF-positive MPs correlate with venous thrombosis in patients with cancer. Taken together, these results suggest that TF-positive MPs may be a useful biomarker to identify patients with cancer who are at high risk for thrombosis.

Bench to bedside: new developments in our understanding of the pathophysiology of thrombosis

There has been a resurgent interest in the molecular and cellular mechanisms of thrombogenesis in venous thromboembolism (VTE). Improved animal models of VTE, combined with high-resolution microscopy techniques, have helped to uncover novel roles for blood cells including platelets and innate immune cells, particularly neutrophils. These insights are likely to result in novel disease biomarkers and perhaps even adjunctive anti-thrombotic therapies.

Microparticles in vascular disorders: how tissue factor-exposing vesicles contribute to pathology and physiology

Coagulation is initiated by tissue factor (TF). Coagulant TF is constitutively expressed by extravascular cells, but there is increasing evidence that TF can also be present within the blood, in particular during pathological conditions. Such TF is exposed on circulating cell-derived vesicles, and its presence has been associated with development of disseminated intravascular coagulation and venous thrombosis. For example, the presence of TF-exposing vesicles in the blood of cancer patients may be associated with their high risk of developing venous thromboembolism. Remarkably, high levels of coagulant TF-exposing vesicles are present in other body fluids such as saliva and urine of healthy persons, suggesting that these vesicles play a physiological role. We postulate that the presence of TF-exposing vesicles in body fluids as saliva and urine provides an additional source of coagulant TF that promotes coagulation, thereby reducing blood loss and contributing to host defence by reducing the risk of microorganisms entering the "milieu intérieur".

The emerging role of neutrophils in thrombosis-the journey of TF through NETs

The production of TF by neutrophils and their contribution in thrombosis was until recently a matter of scientific debate. Experimental data suggested the de novo TF production by neutrophils under inflammatory stimuli, while others proposed that these cells acquired microparticle-derived TF. Recent experimental evidence revealed the critical role of neutrophils in thrombotic events. Neutrophil derived TF has been implicated in this process in several human and animal models. Additionally, neutrophil extracellular trap (NET) release has emerged as a major contributor in neutrophil-driven thrombogenicity in disease models including sepsis, deep venous thrombosis, and malignancy. It is suggested that NETs provide the scaffold for fibrin deposition and platelet entrapment and subsequent activation. The recently reported autophagy-dependent extracellular delivery of TF in NETs further supports the involvement of neutrophils in thrombosis. Herein, we seek to review novel data regarding the role of neutrophils in thrombosis, emphasizing the implication of TF and NETs.

Skin extracts from 2 Italian table grapes (Italia and Palieri) inhibit tissue factor expression by human blood mononuclear cells

Grape and its products such as red wine and grape juice have well-known antithrombotic properties, which have been attributed to their high content in polyphenolic compounds. Most studies on the mechanisms underlying these beneficial effects, among which the suppression of tissue factor (TF) synthesis in blood mononuclear cells (MNC) and vascular endothelium is a prominent one, have been performed with purified polyphenols, while little is known about the effect of fresh grapes which contain a multitude of phytochemicals whose interaction may lead to different cell responses. In this study, we investigated the effect of grape skin extracts (GSEs) on TF expression in isolated blood MNC and in whole blood. Alcoholic extracts from skins of 2 grape varieties (Palieri and Italia) inhibited TF expression in lipopolysaccharide (LPS)-stimulated MNC in a concentration-dependent manner with ≥90% inhibition of TF activity and antigen at 6 μg/mL of gallic acid equivalents. Noteworthy, GSEs were also able to inhibit the appearance of TF in whole blood challenged with LPS. The 2 grape varieties displayed a fairly similar TF-inhibiting capacity despite marked differences in phenolic profile. When selected purified polyphenols were tested, their ability to inhibit TF expression was markedly lower as compared to grape extracts, whereas a mixture of some representative polyphenols was much more efficient, supporting the occurrence of a synergistic effect. Given the key role of cell TF in thrombotic diseases, the inhibition of MNC-mediated clotting activation, if confirmed by in vivo studies, might represent an important antithrombotic mechanism.

PRACTICAL APPLICATION

Our data indicate that the combination of different polyphenols, as in grape extracts, is much more efficient than the single constituents, a finding that might be useful as starting point for the development of new antithrombotic nutraceutics. In addition, our study validated a simple, inexpensive, and physiologically relevant in vitro method on whole blood that allows the evaluation of one of the most important antithrombotic activities of food and food-derived products. The simplicity of the method makes it suitable also for screening purposes in large-scale studies.

Antithrombotic activity of 12 table grape varieties. Relationship with polyphenolic profile

The synthesis of tissue factor (TF) by monocytes/macrophages activated by inflammatory agents is of utmost importance in the pathogenesis of thrombotic diseases and substances inhibiting TF synthesis represent novel and promising antithrombotics. We investigated the effect of 12 table grape varieties (white, red and black) on TF synthesis and the possible relation with the phenolic profile. The ability of grape skin extracts (GSEs) to inhibit TF was evaluated in whole blood and isolated mononuclear cells challenged with endotoxin. TF expression was assayed by functional and immunological assays. All GSEs inhibited TF synthesis but with a different efficiency, red grapes being the most active. By correlation analysis, the compounds showing the strongest association with TF-inhibiting activity were quercetin and cyanidin. However, no single polyphenol was able to inhibit TF synthesis as efficiently as the crude grape extracts, unless it was combined with at least another compound, suggesting a synergism.

Quercetin 3,7,3',4'-tetrasulphated isolated from Flaveria bidentis inhibits tissue factor expression in human monocyte

Sulphated esters of the flavonoids sulphated quercetin 3,7,3',4'-tetrasulphated (QTS) and quercetin 3-acetyl-7,3,4'-trisulphate (ATS), isolated from Flaveria bidentis, have demonstrated anticoagulant and antiplatelet properties. In this study, we examined if both compounds affected the expression of the procoagulant tissue factor (TF) induced by lipopolysaccharide (LPS) on human monocyte. Monocytes were pretreated with different concentrations of each flavonoid (0.1-500 μM), followed by a 4h incubation with LPS in order to induce TF expression. Results of the TF expression showed different behaviors for the two flavonoids studied. A slight inhibitory effect on the TF expression was detected at a QTS concentration of 0.1 μM, but from 1 μM onwards a significant inhibitory effect that remained up to 500 μM could be observed. In contrast, ATS induced a poor inhibitory effect on TF expression at all concentrations tested. These results suggest that QTS has another antithrombotic property, to be added to its already renowned ability as an anticoagulant and antiplatelet compound.

How I manage venous thromboembolism risk in hospitalized medical patients

Venous thromboembolism is a significant cause of illness and death worldwide. Large bodies of evidence support the heightened risk status of hospitalized medical patients, and that prophylactic measures significantly reduce the risk of thrombosis, yet these patients often fail to receive adequate prophylactic therapy. This failure may be accounted for by a lack of awareness of the relevant indications, poorly designed implementation systems, and clinical concerns over the side effects of anticoagulant medications. This article briefly summarizes our understanding of the clinical factors relevant to the evaluation of venous thromboembolism risk in hospitalized medical patients. We describe our approach to the use of thromboprophylaxis, through which we aim to minimize the disease burden of this under-recognized and preventable pathology.

Neutrophil extracellular trap (NET) impact on deep vein thrombosis

Deep vein thrombosis (DVT) is a major health problem that requires improved prophylaxis and treatment. Inflammatory conditions such as infection, cancer, and autoimmune diseases are risk factors for DVT. We and others have recently shown that extracellular DNA fibers produced in inflammation and known as neutrophil extracellular traps (NETs) contribute to experimental DVT. NETs stimulate thrombus formation and coagulation and are abundant in thrombi in animal models of DVT. It appears that, in addition to fibrin and von Willebrand factor, NETs represent a third thrombus scaffold. Here, we review how NETs stimulate thrombosis and discuss known and potential interactions of NETs with endothelium, platelets, red blood cells, and coagulation factors and how NETs could influence thrombolysis. We propose that drugs that inhibit NET formation or facilitate NET degradation may prevent or treat DVT.

Monocytes, neutrophils, and platelets cooperate to initiate and propagate venous thrombosis in mice in vivo

Deep vein thrombosis (DVT) is a major cause of cardiovascular death. The sequence of events that promote DVT remains obscure, largely as a result of the lack of an appropriate rodent model. We describe a novel mouse model of DVT which reproduces a frequent trigger and resembles the time course, histological features, and clinical presentation of DVT in humans. We demonstrate by intravital two-photon and epifluorescence microscopy that blood monocytes and neutrophils crawling along and adhering to the venous endothelium provide the initiating stimulus for DVT development. Using conditional mutants and bone marrow chimeras, we show that intravascular activation of the extrinsic pathway of coagulation via tissue factor (TF) derived from myeloid leukocytes causes the extensive intraluminal fibrin formation characteristic of DVT. We demonstrate that thrombus-resident neutrophils are indispensable for subsequent DVT propagation by binding factor XII (FXII) and by supporting its activation through the release of neutrophil extracellular traps (NETs). Correspondingly, neutropenia, genetic ablation of FXII, or disintegration of NETs each confers protection against DVT amplification. Platelets associate with innate immune cells via glycoprotein Ibα and contribute to DVT progression by promoting leukocyte recruitment and stimulating neutrophil-dependent coagulation. Hence, we identified a cross talk between monocytes, neutrophils, and platelets responsible for the initiation and amplification of DVT and for inducing its unique clinical features.

Tissue factor/TFPI and blood cells

Vascular injury-induced access of blood to tissue factor (TF) leads to the formation of a TF-FVII/FVIIa complex and the triggering of blood coagulation. The activated TF-dependent pathway is regulated by Tissue Factor Pathway Inhibitor (TFPI), which binds and inhibits FXa, but more importantly forms an inactive quaternary complex with TF-FVIIa-FXa, effectively shutting off the TF activity. The old view of TF residing in extravascular sites exclusively has recently been challenged by several reports on TF expression in various blood cells. The latter arena has unfortunately been marred by many contradictions, apparently related to inferior tools and/or study design, notably the widespread use of antibodies with inferior and misleading specificity and TF activity assays of low sensitivity/specificity. Our own studies along with many other reports, compels the conclusion that in blood of healthy individuals TF is exclusively associated with and expressed in circulating monocytes. In this short review the distribution of TF and TFPI in blood is discussed.

Microparticles in hemostasis and thrombosis

Blood contains microparticles (MPs) derived from a variety of cell types, including platelets, monocytes, and endothelial cells. In addition, tumors release MPs into the circulation. MPs are formed from membrane blebs that are released from the cell surface by proteolytic cleavage of the cytoskeleton. All MPs are procoagulant because they provide a membrane surface for the assembly of components of the coagulation protease cascade. Importantly, procoagulant activity is increased by the presence of anionic phospholipids, particularly phosphatidylserine (PS), and the procoagulant protein tissue factor (TF), which is the major cellular activator of the clotting cascade. High levels of platelet-derived PS(+) MPs are present in healthy individuals, whereas the number of TF(+), PS(+) MPs is undetectable or very low. However, levels of PS(+), TF(+) MPs are readily detected in a variety of diseases, and monocytes appear to be the primary cellular source. In cancer, PS(+), TF(+) MPs are derived from tumors and may serve as a useful biomarker to identify patients at risk for venous thrombosis. This review will summarize our current knowledge of the role of procoagulant MPs in hemostasis and thrombosis.

Anthracycline treatment of the human monocytic leukemia cell line THP-1 increases phosphatidylserine exposure and tissue factor activity

INTRODUCTION

Cancer associated thrombosis is a well-recognized phenomenon that results in considerable patient morbidity and mortality. Malignancy conveys an increased risk for thrombosis and chemotherapy further elevates this risk. The pathophysiological mechanisms underlying this process remain poorly defined.

MATERIALS AND METHODS

A human acute monocytic leukemia cell line (THP-1) was treated with commonly used anthracycline chemotherapeutics at concentrations similar to those found in the plasma of cancer patients. Cells were analyzed for tissue factor (TF) mRNA, protein, and activity. Microparticle (MP) TF activity was also measured. Phosphatidylserine (PS) exposure on cells and MPs was analyzed by flow cytometry. PS levels on MPs was also evaluated in an annexin V capture assay.

RESULTS

Anthracycline treatment of THP-1 cells resulted in a concentration-dependent increase in cellular TF activity without a change in TF protein, which was associated with increased PS exposure on the cell surface and apoptosis. The increase in TF activity was abolished by annexin V or lactadherin indicating that PS exposure was required. Anthracycline treatment of THP-1 cells also increased the number of TF-positive MPs.

CONCLUSION

Treatment of THP-1 cells with anthracyclines induces apoptosis and increases cellular TF activity. The increased activity required an increase in exposure of PS. Additionally, anthracyclines increase the release of TF-positive MPs from THP-1 cells. We propose that the increase in cellular TF activity in circulating leukemic cells, combined with increased numbers of TF-positive MPs, may contribute to thrombosis in cancer patients receiving chemotherapy.

The link between vascular features and thrombosis

The mechanisms of vascular control of thrombotic events remain unclear. The vasculature possesses essential anticoagulant factors that regulate coagulation. Because the endothelium-to-blood ratios are much higher in the microcirculation, it is likely that stasis contributes to thrombotic risk, due in large part to failure to rapidly access the microcirculation and to gain access to this highly anticoagulant environment. Inflammation can potentiate thrombosis in part through downregulation of the vascular anticoagulants, a process that appears to be exacerbated in aging, a well-known risk factor for thrombosis. Surgery and trauma, two major risk factors for thrombosis, result in the release of a variety of cellular components that trigger coagulation through separate mechanisms.

Leukocytes and the natural history of deep vein thrombosis: current concepts and future directions

Observational studies have shown that inflammatory cells accumulate within the thrombus and surrounding vein wall during the natural history of venous thrombosis. More recent studies have begun to unravel the mechanisms that regulate this interaction and have confirmed that thrombosis and inflammation are intimately linked. This review outlines our current knowledge of the complex relationship between inflammatory cell activity and venous thrombosis and highlights new areas of research in this field. A better understanding of this relationship could lead to the development of novel therapeutic targets that inhibit thrombus formation or promote its resolution.