Tissue factor initiated blood coagulation

Mutational analysis of pig tissue factor pathway inhibitor α to increase anti-coagulation activity in pig-to-human xenotransplantation

Blood coagulation mediated by pig tissue factor (TF), which is expressed in pig tissues, causes an instant blood-mediated inflammatory reaction during pig-to-human xenotransplantation. Previously, we generated a soluble pig tissue factor pathway inhibitor α fusion immunoglobulin (TFPI-Ig) which inhibits pig TF activity more efficiently than human TFPI-Ig in human plasma. In this study, we generated several pig TFPI-Ig mutants and tested the efficacy of these mutants in preventing pig-to-human xenogeneic blood coagulation. Structurally important amino acid residues of pig TFPI-Ig were changed into different residues by site-directed mutagenesis. Subsequently, a retroviral vector encoding each cDNA of several pig TFPI-Ig mutants was cloned and transduced into CHO-K1 cells. After establishing stable cell lines expressing each of the pig TFPI-Ig mutants, soluble proteins were produced and purified for evaluating their inhibitory effects on pig TF-mediated blood coagulation in human plasma. The replacement of K36 and K257 with R36 and H257, respectively, in pig TFPI-Ig more efficiently blocked pig TF activity in human plasma when compared with the wild-type pig TFPI-Ig. These results may provide additional information to understand the structure of pig TFPIα, and an improved pig TFPI-Ig variant that more efficiently blocks pig TF-mediated blood coagulation during pig-to-human xenotransplantation.

Clotting Factor Deficiencies as an Underlying Cause of Abnormal Uterine Bleeding in Women of Reproductive Age: A Literature Review

Clotting Factor deficiencies are rare disorders with variations in clinical presentation and severity of symptoms ranging from asymptomatic to mild to life-threatening bleeding. Thus, they pose a diagnostic and therapeutic challenge, mainly for the primary health care providers, general practitioners, and gynecologists who are more likely to first encounter these patients. An additional diagnostic challenge arises from the variable laboratory presentations, as PT, PTT, and BT are not always affected. The morbidity is higher among women of reproductive age since Abnormal Uterine Bleeding-specifically Heavy Menstrual Bleeding-is one of the most prevalent manifestations of these disorders, and in some cases of severe deficiencies has led to life-threatening episodes of bleeding requiring blood transfusions or even immediate surgical intervention. Physician awareness is important as, in the case of some of these disorders-i.e., Factor XIII deficiency-prophylactic treatment is available and recommended. Although uncommon, the potential for rare bleeding disorders and for hemophilia carrier states should be considered in women with HMB, after more prevalent causes have been excluded. Currently, there is no consensus on the management of women in these instances and it is reliant on the physicians' knowledge.

Reproductive health and hemostatic issues in women and girls with congenital factor VII deficiency: A systematic review

BACKGROUND

Congenital factor VII (FVII) deficiency is an inherited bleeding disorder, with heterogenous bleeding symptoms. Women with FVII deficiency face hemostatic challenges during menstruation, ovulation, and childbirth. This systematic review evaluated prevalence and management of bleeding symptoms associated with gynecological and obstetric issues in women with FVII deficiency.

METHODS

Databases (BIOSIS Previews, Current Contents Search, Embase, and MEDLINE) were searched for studies reporting FVII deficiency and gynecological or obstetric issues in women. Articles were screened using Joanna Briggs Institute checklists and relevant data extracted.

RESULTS

One hundred fourteen women were identified from 62 publications. Forty-six women had severe deficiency (FVII:C < 5% or <5 IU/dl). Heavy menstrual bleeding (HMB) was the most common bleeding symptom (n = 94; 82%); hospitalization and urgent medical/surgical interventions for acute HMB episodes were required in 16 women (14%). Seven women reported ovarian bleeding (6%); other bleeding symptoms varied. Patient management was inconsistent and included hemostatic and hormonal treatments. Only four women (7%) reporting vaginal bleeding during pregnancy. Postpartum hemorrhage (PPH) occurred following 12/45 deliveries (27%; 5 [42%] requiring blood transfusion) and was not necessarily prevented by prophylaxis (8 women).

CONCLUSION

Women with congenital FVII deficiency have an increased risk of HMB, ovarian bleeding, and PPH, impacting quality of life. Recognition of a bleeding disorder as the cause is often delayed. Management of bleeding complications is heterogeneous due to lack of treatment guidelines. Harmonizing severity classification of FVII deficiency may help standardize treatment strategies and development of specific guidelines for these women.

Structural model of tissue factor (TF) and TF-factor VIIa complex in a lipid membrane: A combined experimental and computational study

Tissue factor (TF) is a membrane protein involved in blood coagulation. TF initiates a cascade of proteolytic reactions, ultimately leading to the formation of a blood clot. The first reaction consists of the binding of the coagulation factor VII and its conversion to the activated form, FVIIa. Here, we combined experimental, i.e. quartz crystal microbalance with dissipation monitoring and neutron reflectometry, and computational, i.e. molecular dynamics (MD) simulation, methods to derive a complete structural model of TF and TF/FVIIa complex in a lipid bilayer. This model shows that the TF transmembrane domain (TMD), and the flexible linker connecting the TMD to the extracellular domain (ECD), define the location of the ECD on the membrane surface. The average orientation of the ECD relative to the bilayer surface is slightly tilted towards the lipid headgroups, a conformation that we suggest is promoted by phosphatidylserine lipids, and favours the binding of FVIIa. On the other hand, the formation of the TF/FVIIa complex induces minor changes in the TF structure, and reduces the conformational freedom of both TF and FVIIA. Altogether we describe the protein-protein and protein-lipid interactions favouring blood coagulation, but also instrumental to the development of new drugs.

The Multifaceted Function of Granzymes in Sepsis: Some Facts and a Lot to Discover

Sepsis is a serious global health problem. In addition to a high incidence, this syndrome has a high mortality and is responsible for huge health expenditure. The pathophysiology of sepsis is very complex and it is not well-understood yet. However, it is widely accepted that the initial phase of sepsis is characterized by a hyperinflammatory response while the late phase is characterized by immunosuppression and immune anergy, increasing the risk of secondary infections. Granzymes (Gzms) are a family of serine proteases classified according to their cleavage specificity. Traditionally, it was assumed that all Gzms acted as cytotoxic proteases. However, recent evidence suggests that GzmB is the one with the greatest cytotoxic capacity, while the cytotoxicity of others such as GzmA and GzmK is not clear. Recent studies have found that GzmA, GzmB, GzmK, and GzmM act as pro-inflammatory mediators. Specially, solid evidences show that GzmA and GzmK function as extracellular proteases that regulate the inflammatory response irrespectively of its ability to induce cell death. Indeed, studies in animal models indicate that GzmA is involved in the cytokine release syndrome characteristic of sepsis. Moreover, the GZM family also could regulate other biological processes involved in sepsis pathophysiology like the coagulation cascade, platelet function, endothelial barrier permeability, and, in addition, could be involved in the immunosuppressive stage of sepsis. In this review, we provide a comprehensive overview on the contribution of these novel functions of Gzms to sepsis and the new therapeutic opportunities emerging from targeting these proteases for the treatment of this serious health problem.

Di-(2-Ethylhexyl) Phthalate Promotes Release of Tissue Factor-Bearing Microparticles From Macrophages via the TGFβ1/Smad/PAI-1 Signaling Pathway

BACKGROUND

Plasminogen activator inhibitor type 1 promotes formation of endothelial microparticles with procoagulant activity. However, it remains unclear whether di-(2-ethylhexyl) phthalate, a peroxisome proliferator-activated receptor α agonist, influences microparticle formation.

MATERIALS AND METHODS

The effect of di-(2-ethylhexyl) phthalate on release of tissue factor-bearing microparticles was investigated using human M1 macrophages.

RESULTS

Exposure of M1 macrophages to di-(2-ethylhexyl) phthalate significantly upregulated expression of plasminogen activator inhibitor type 1, whereas incubation of macrophages with small interfering RNA for peroxisome proliferator-activated receptor α attenuated it. Di-(2-ethylhexyl) phthalate significantly increased the tissue factor protein level in culture supernatants of M1 macrophages, but not M2 macrophages. After purification of proteins by centrifugal filtration, western blotting detected 2 high molecular weight bands of tissue factor-bearing microparticles in culture supernatants of M1 macrophages. The upper band showed binding to factor VIIa and tissue factor pathway inhibitor, unlike the lower band. This suggested heterogeneity of the procoagulant activity of tissue factor-bearing microparticles, presumably dependent upon encryption/decryption of tissue factor. Phosphatidylserine contributes to tissue factor decryption, and western blotting revealed that the density of phosphatidylserine was reduced in the upper tissue factor band compared with the lower band. Di-(2-ethylhexyl) phthalate also upregulated transforming growth factor-β1 protein production by M1 macrophages. Moreover, silencing of Smad2, Smad3 or Smad4 attenuated plasminogen activator inhibitor type 1 expression and tissue factor-release from macrophages after di-(2-ethylhexyl) phthalate stimulation.

CONCLUSIONS

Di-(2-ethylhexyl) phthalate promotes formation of tissue factor-bearing microparticles in human M1 macrophages via the transforming growth factor-β1/Smad/ plasminogen activator inhibitor type 1 signaling pathway.

Early diagnosis of cerebral thrombosis by EGFP–EGF1 protein conjugated ferroferric oxide magnetic nanoparticles

Cerebral thrombosis disease is a worldwide problem, with high rates of morbidity, disability, and mortality. Magnetic resonance imaging diffusion-weighted imaging was used as an important early diagnostic method for cerebral thrombotic diseases; however, its diagnosis time is 2 h after onset. In this study, we designed EGFP–EGF1–NP–Fe3O4 for earlier diagnosis of cerebral thrombosis by taking advantage of EGFP–EGF1 fusion protein, in which EGF1 can bind with tissue factor and enhanced green fluorescent protein has previously been widely used as a fluorescent protein marker. EGFP–EGF1–NP–Fe3O4 or NP–Fe3O4 reaches the highest concentration in the infarction areas in 1 h. To evaluate the targeting ability of EGFP–EGF1–NP–Fe3O4, a fluorochrome dye, Dir, was loaded into the nanoparticle. As shown by the in vivo organ multispectral fluorescence imaging, Dir-loaded EGFP–EGF1–NP–Fe3O4 exhibited higher fluorescence than those of model rats treated with Dir-loaded NP–Fe3O4. Coronal frozen sections and transmission electron microscope further showed that EGFP–EGF1–NP–Fe3O4 was mainly accumulated in the tissue factor exposure region of brain. The data indicated that the EGFP–EGF1–NP–Fe3O4 targeted cerebral thrombosis and might be applied in the early diagnosis of intracranial thrombosis.

A tissue factor-cascade-targeted nanoparticle forsite-directed inducing thrombosis

Tissue factor is an upstream component of the cascade and a high-expressing factor under phathological conditions. In this study, a tissue factor cascade-targeted strategy for inducing local thrombosis was developed by combining ENP-HMME and photochemistry. In vitro study showed that protein EGFP-EGF1 conjugation to the nanoparticles could significantly contribute to the uptake of nanoparticles by tissue factor over-expressed brain capillary endothelial cells. Three-dimensional imaging and specklegram of brains in vivo showed that tissue factor cascade-targeted strategy successfully induced thrombosis of expected position. As shown by the in vivo multispectral fluorescent imaging, when ENP-HMME was combined with photochemistry, higher accumulation in the infarction hemisphere was observed, which might suggest that the photochemistry inducing tissue factor cascade recruited more ENP-HMME than HMME-loaded nanoparticles (NP-HMME). The data indicated the tissue factor cascade-targeted strategy has potential to induce local thrombosis, and might be applied in the treatment of a variety of hypervascular diseases.

The thrombotic potential of circulating tumor microemboli: computational modeling of circulating tumor cell-induced coagulation

Thrombotic events can herald the diagnosis of cancer, preceding any cancer-related clinical symptoms. Patients with cancer are at a 4- to 7-fold increased risk of suffering from venous thromboembolism (VTE), with ∼7,000 patients with lung cancer presenting from VTEs. However, the physical biology underlying cancer-associated VTE remains poorly understood. Several lines of evidence suggest that the shedding of tissue factor (TF)-positive circulating tumor cells (CTCs) and microparticles from primary tumors may serve as a trigger for cancer-associated thrombosis. To investigate the potential direct and indirect roles of CTCs in VTE, we characterized thrombin generation by CTCs in an interactive numerical model coupling blood flow with advection-diffusion kinetics. Geometric measurements of CTCs isolated from the peripheral blood of a lung cancer patient prior to undergoing lobectomy formed the basis of the simulations. Singlet, doublet, and aggregate circulating tumor microemboli (CTM) were investigated in the model. Our numerical model demonstrated that CTM could potentiate occlusive events that drastically reduce blood flow and serve as a platform for the promotion of thrombin generation in flowing blood. These results provide a characterization of CTM dynamics in the vasculature and demonstrate an integrative framework combining clinical, biophysical, and mathematical approaches to enhance our understanding of CTCs and their potential direct and indirect roles in VTE formation.

The delivery of thrombi-specific nanoparticles incorporating oligonucleotides into injured cerebrovascular endothelium

In acute vascular events, the endothelium derived tissue factor (TF) is the trigger of the coagulation cascade. In this study, EGFP-EGF1 protein-conjugated PEG-PLGA nanoparticle was employed as a TF targeting vehicle, the NF-κB decoy oligonucleotides (ODNs) was incorporated into it and the resulting EGF1-EGFP-NP-ODNs were evaluated as a vector for therapy of cortex infarction. At 2 h after transfection of TF expressed rat brain capillary endothelial cell, EGF1-EGFP-NP-ODNs was more efficiently internalized and located in the cytoplasm than NP-ODNs. At 4 h and 6 h after administration, ODNs were present in the nuclei and obviously inhibited the TF expression. At 6 h after i.v. administration in vivo, most EGF1-EGFP-NP were accumulated in the embolism vessels, distributed in the damaged endothelial cells and lowered the TF expression. At 24 h after i.v. administration, MR imaging of cortex infarcts were predominantly dwindled.

Holothurian glycosaminoglycan inhibits metastasis and thrombosis via targeting of nuclear factor-κB/tissue factor/Factor Xa pathway in melanoma B16F10 cells

Holothurian glycosaminoglycan (hGAG) is a high-molecular-weight form of fucosylated chondroitin sulfate and has an antithrombotic effect. Our previous studies demonstrated that hGAG efficiently inhibited tumor cell metastasis. The interplays between thrombosis and tumor progression may have a major impact on hematogenous metastasis. In this study, we demonstrated that the mouse melanoma B16F10 cells treated with hGAG displayed a significant reduction of metastasis and coagulation capacity in vitro and in vivo. Mechanistic studies revealed that hGAG treatment in B16F10 cells remarkably inhibited the formation of fibrin through attenuating the generation of activated Factor Xa (FXa), without affecting the expression of urokinase (uPA) and plasminogen activator inhibitor 1 (PAI-1) that involved in fibrinolysis. Moreover, hGAG treatment downregulated the transcription and protein expression of tissue factor (TF). Promoter deletions, site mutations and functional studies identified that the nuclear transcription factor NF-κB binding region is responsible for hGAG-induced inhibition of TF expression. While the hGAG treatment of B16F10 cells was unable to inhibit NF-κB expression and phosphorylation, hGAG significantly prevented nuclear translocation of NF-κB from the cytosol, a potential mechanism underlying the transcriptional suppression of TF. Moreover, hGAG markedly suppressed the activation of p38MAPK and ERK1/2 signaling pathways, the central regulators for the expression of metastasis-related matrix metalloproteinases (MMPs). Consequently, hGAG exerts a dual function in the inhibition of metastasis and coagulation activity in mouse melanoma B16F10 cells. Our studies suggest hGAG to be a promising therapeutic agent for metastatic cancer treatment.

Uremic serum and solutes increase post-vascular interventional thrombotic risk through altered stability of smooth muscle cell tissue factor

BACKGROUND

Stent thrombosis (ST), a postinterventional complication with a mortality rate of 50%, has an incidence that rises precipitously in patients at risk. Chronic renal failure and end-stage renal disease have emerged as particularly strong ST risk factors, yet the mechanism remains elusive. Tissue factor (TF) is a crucial mediator of injury-related thrombosis and has been implicated for ST. We posit that uremia modulates TF in the local vessel wall to induce postinterventional thrombosis in patients with end-stage renal disease.

METHODS AND RESULTS

As a model of the de-endothelialized, postinterventional state, we exposed primary human vascular smooth muscle cells (vSMCs) pretreated with uremic serum (obtained from ESRD patients on hemodialysis) to coronary-like blood flow. vSMC TF expression, activity, stability, and posttranslational modification were examined after vSMCs were treated with uremic serum or solutes. We found significantly greater clot formation after uremic serum exposure, which was substantially reduced with the prior treatment with anti-TF neutralizing antibody. Uremic sera induced 2- to 3-fold higher TF expression and activity in vSMCs independent of diabetes mellitus. Relevant concentrations of isolated uremic solutes such as indole-3-acetic acid (3.5 μg/mL), indoxyl sulfate (25 μg/mL), and uric acid (80 μg/mL) recapitulated these effects in cell culture and the flow loop model. We show further that TF undergoes ubiquitination at baseline and that uremic serum, indole-3-acetic acid, and indoxyl sulfate significantly prolong TF half-life by inhibiting its ubiquitination.

CONCLUSIONS

The uremic milieu is profoundly thrombogenic and upregulates vSMC TF levels by increasing TF stability and decreasing its ubiquitination. Together, these data demonstrate for the first time that the posttranslational regulation of TF in uremia may have a causative role in the increased ST risk observed in uremic patients. These data suggest that interventions that reduce vSMC TF may help to prevent ST and that uremic solutes should be considered as novel risk factors for ST in patients with chronic renal failure.

Modeling and simulation of procoagulant circulating tumor cells in flow

We describe a mathematical/computational model for thrombin concentration gradients generated by procoagulant circulating tumor cells (CTCs) in flow. We examine how CTCs enhance blood coagulation as they diffuse tissue factor-dependent coagulation enzymes in a flow environment with vessel walls. Concentration fields of various enzymes, such as prothrombin and thrombin, diffuse, to, and from CTCs, respectively, as they propagate through the bloodstream. The diffusion-dependent generation of these enzymes sets up complex time-dependent concentration fields. The CTCs are modeled as diffusing point particles in an incompressible fluid, and we exploit exact analytical solutions based on three-dimensional Green’s functions for unbounded domains with one wall for high resolution numerical simulations. Time-dependent gradient trackers are used to highlight that concentration fields build-up (i) near boundaries (vessel walls), (ii) in regions surrounding the diffusing particles, and (iii) in complex time-dependent regions of the flow where fields associated with different particles overlap. Two flow conditions are modeled: no flow, and unidirectional constant flow. Our results indicate that the CTC-generated thrombin diffuses to and persists at the blood vessel wall, and that the spatial distribution of CTCs in flow determines local thrombin concentration. The magnitude of the diffusion gradient and local thrombin concentration is dependent upon bulk solution concentrations of coagulation factors within normal reported concentration ranges. Therefore, our model highlights the potential to determine patient-specific risks for CTC-induced hypercoagulability as a function of CTC number and individual patient concentration of coagulation factors.

The tick-derived inhibitor Ixolaris prevents tissue factor signaling on tumor cells

BACKGROUND

Tissue factor (TF) is frequently overexpressed in cancer cells and correlated with more aggressive tumor phenotypes and poor prognosis. In addition to promoting coagulation-dependent metastasis and cancer-associated thrombosis, tumor cell-expressed TF mediates direct cell signaling involving the protease-activated receptor (PAR) 2. Ixolaris is a tick-derived inhibitor of the TF-factor (F)VIIa-Xa coagulation initiation complex which blocks primary tumor growth and angiogenesis in glioblastoma and melanoma models.

METHODS

In this study we address the anti-tumor effects of Ixolaris in TF-VIIa-PAR2 signaling-dependent breast cancer models, a xenograft model of highly aggressive human MDA-MB-231 mfp cells and a syngeneic model of PAR2-deficient and replete PyMT mouse mammary carcinoma cells.

RESULTS

Ixolaris potently inhibited the procoagulant activity of human MDA-MB-231mfp or murine PyMT breast cancer cells. Ixolaris blocked signaling by the ternary TF-FVIIa-FXa complex, and, surprisingly, at higher concentrations also the binary TF-FVIIa complex on MDA-MB-231 cells. We show that Ixolaris interacts with certain residues in the human VIIa protease domain that are involved in PAR2 cleavage. In contrast to human VIIa, Ixolaris was a poor inhibitor of murine TF-FVIIa signaling and did not attenuate PAR2-dependent tumor growth in a syngeneic mouse model of breast cancer progression.

CONCLUSION

These data show that Ixolaris inhibits PAR2 cleavage specifically by human TF signaling complexes and suggest that Ixolaris may block tumor growth of human cell models with ectopic FVIIa expression through inhibition of direct TF-FVIIa-PAR2 signaling as well as its anticoagulant activity.

A tissue factor targeted nanomedical system for thrombi-specific drug delivery

Tissue factor (TF) is a 47 kDa membrane-bound glycoprotein, which is present at high concentrations on damaged endothelium, atherosclerotic plaques or tumor vasculature, and is an important trigger of coagulation cascade. In this study, we have expressed and purified the TF targeting protein-EGFP-EGF1, which was thiolated and conjugated to the malemide of the PEG-PLGA nanoparticle to form a TF targeting nanomedical system: EGF1-EGFP-NP. The system was carefully characterized and the targeting efficiency was systematically evaluated. The EGF1-EGFP-NP could significantly facilitate specific uptake by TF overexpressed BCEC via EGF1/TF mediated endocytosis pathway. In addition, the pharmacokinetic study demonstrated that EGF1-EGFP-NP has the same blood circulation time as NP. Enhanced accumulation of EGF1-EGFP-NP in the cortex infarction region was also observed by real-time fluorescence image. Confocal microscopy and TEM further showed that EGF1-EGFP-NP combined with TF and further transfected through the damaged endothelium. Moreover, in vitro cell viability experiment and in vivo coagulation ability confirmed that the EGF1-EGFP-NP was safe.

Sirt1 protects against thrombomodulin down-regulation and lung coagulation after particulate matter exposure

Exposure to ambient particulate matter (PM) air pollution has been reported to trigger inflammation and thrombosis. However, molecular mechanisms underlying the modulation of coagulation pathways in PM-induced thrombosis remain largely unknown. We report here that Sirt1, a member of class III histone deacetylase, controls lung inflammation and coagulation after PM exposure. Sirt1 knock-out mice exhibited aggravated lung vascular leakage and inflammation after PM exposure, which was correlated with increased NF-κB acetylation and activation. Furthermore, Sirt1 knock-out mice were highly susceptible to PM-induced lung coagulation as demonstrated by increased fibrin formation. The increased fibrin formation was associated with reduced tissue factor pathway inhibitor (TFPI) expression and increased plasminogen activator inhibitor-1 (PAI-1) activity in the lungs, thus favoring elevated coagulation and disrupted fibrinolysis responses. Thrombomodulin (TM), a central player of the anticoagulant protein C system, is regulated by Kruppel-like factor 2 (KLF2) at the transcriptional level. Our data show that PM exposure led to decreased lung KLF2 and TM expression in wild-type mice, and lung KLF2 and TM protein levels were further decreased in Sirt1 knock-out mice. Importantly, Sirt1 gene delivery inhibited TM and KLF2 down-regulation and reduced lung coagulation after PM exposure. Collectively, our studies indicate that Sirt1 functions as a suppressor of coagulation after particulate matter exposure.

Microparticle formation after exposure of blood to activated endothelium under flow

Increased numbers of circulating microparticles (MPs) are indicative of poor clinical outcome in a number of inflammatory disorders, including atherosclerosis. Platelets and megakaryocytes are a major source of MP and are identified by presence of CD42b on the MP surface. MP shed from activated platelets can be identified by presence of P-selectin (CD62P). Tissue factor (TF) is the principal initiator of blood coagulation and its activity has been identified in MPs derived from patient plasma, which may contribute to thrombosis. Here, we have investigated by flow cytometry the expression of TF and CD62P on MP after exposure of diluted whole blood to TNF-activated endothelial cells (EC) both under static conditions and in our newly established model of flow. MPs were significantly increased in blood subjected to flow and this was further enhanced after exposure of blood to TNF-activated EC. MP surface expression of CD62P or TF was upregulated following exposure to TNF-activated EC under flow compared with flow with nonactivated EC or after static coculture with and without prior EC activation. These data strongly suggest that interactions of blood with inflamed EC can modulate production of CD62P and TF bearing MP under flow conditions, and thus may contribute to a prothrombotic environment.

Simultaneous tissue factor expression and phosphatidylserine exposure account for the highly procoagulant pattern of melanoma cell lines

A correlation between cancer and hypercoagulability has been described for more than a century. Patients with cancer are at increased risk for thrombotic complications, and the clotting initiator protein, tissue factor (TF), is possibly involved in this process. In addition to TF, the presence of negatively charged phospholipids, particularly phosphatidylserine (PS), is necessary to support some of the blood-clotting reactions. There are few reports describing PS exposure by tumor cells. In this study, we characterized the procoagulant properties of the murine B16F10 and the human WM-266-4 melanoma cell lines. Flow cytometry analyses showed constitutive TF expression by both cell lines, in contrast to negative staining observed for the nontumorigenic melanocyte lineage, melan-A. In addition, tumor cells accelerate plasma clotting in a number-dependent manner. For WM-266-4, this ability was partially reversed by an anti-TF antibody but not by aprotinin, a nonspecific serine-protease inhibitor. Furthermore, flow-cytometric analyses showed the presence of PS at the outer leaflet of both cell lines. This phenomenon was determinant for the assembly of the intrinsic tenase (FIXa/FVIIIa) and prothrombinase (FXa/FVa) complexes, resulting in the activation of FX to FXa and prothrombin to thrombin, respectively. As a result, incubation of WM-266-4 with human plasma produces robust thrombin generation. In conclusion, simultaneous TF expression and PS exposure are responsible for the highly procoagulant pattern of the aggressive melanoma cell lines B16F10 and WM-266-4. Therefore, these cell lines might be regarded as useful models for studying the role of blood coagulation proteins in tumor biology.

Ixolaris, a tissue factor inhibitor, blocks primary tumor growth and angiogenesis in a glioblastoma model

BACKGROUND

The expression levels of the clotting initiator protein Tissue Factor (TF) correlate with vessel density and the histological malignancy grade of glioma patients. Increased procoagulant tonus in high grade tumors (glioblastomas) also indicates a potential role for TF in progression of this disease, and suggests that anticoagulants could be used as adjuvants for its treatment.

OBJECTIVES

We hypothesized that blocking of TF activity with the tick anticoagulant Ixolaris might interfere with glioblastoma progression.

METHODS AND RESULTS

TF was identified in U87-MG cells by flow-cytometric and functional assays (extrinsic tenase). In addition, flow-cytometric analysis demonstrated the exposure of phosphatidylserine in the surface of U87-MG cells, which supported the assembly of intrinsic tenase (FIXa/FVIIIa/FX) and prothrombinase (FVa/FXa/prothrombin) complexes, accounting for the production of FXa and thrombin, respectively. Ixolaris effectively blocked the in vitro TF-dependent procoagulant activity of the U87-MG human glioblastoma cell line and attenuated multimolecular coagulation complexes assembly. Notably, Ixolaris inhibited the in vivo tumorigenic potential of U87-MG cells in nude mice, without observable bleeding. This inhibitory effect of Ixolaris on tumor growth was associated with downregulation of VEGF and reduced tumor vascularization.

CONCLUSION

Our results suggest that Ixolaris might be a promising agent for anti-tumor therapy in humans.

Expression of blood coagulation factors on monocytes after exposure to TNF-treated endothelium in a novel whole blood model of arterial flow

Activated blood monocytes are a major source of tissue factor (TF), the principal initiator of blood coagulation. TF can be shed from the monocyte surface in association with microparticles (MPs) and increased numbers of circulating MPs are indicative of poor clinical outcome in a number of inflammatory disorders, including atherosclerosis. The mechanisms coupling inflammation with aberrant TF production/activity remain obscure but the protease-activated receptor (PAR) family has been implicated. We have previously shown (i) that freshly isolated human monocytes express low levels of cell surface PAR-2, (ii) that cell surface PAR-2 is rapidly upregulated from intracellular stores following mechanical stimulation, and (iii) that PAR-2 stimulation results in elevation of intracellular calcium and cytokine release. Here, we have investigated the expression of PAR-2 on monocytes exposed to TNF-activated endothelial cells both under static conditions and in our newly-established model of arterial flow, using diluted whole blood. Monocyte surface PAR-2 expression was upregulated following static exposure to activated EC and with laminar (atheroprotective) arterial flow there was a further increase in monocyte PAR-2 expression. We have also shown under arterial flow conditions that exposure to TNF-stimulated EC resulted in a significant increase in expression of TF on monocytes compared to that on cells exposed to quiescent EC. These data strongly suggest that direct or indirect interactions with inflamed EC can modulate expression of PAR-2 and TF on the monocyte cell surface.

The role of saliva in tick feeding

When attempting to feed on their hosts, ticks face the problem of host hemostasis (the vertebrate mechanisms that prevent blood loss), inflammation (that can produce itching or pain and thus initiate defensive behavior on their hosts) and adaptive immunity (by way of both cellular and humoral responses). Against these barriers, ticks evolved a complex and sophisticated pharmacological armamentarium, consisting of bioactive lipids and proteins, to assist blood feeding. Recent progress in transcriptome research has uncovered that hard ticks have hundreds of different proteins expressed in their salivary glands, the majority of which have no known function, and include many novel protein families (e.g., their primary structure is unique to ticks). This review will address the vertebrate mechanisms of these barriers as a guide to identify the possible targets of these large numbers of known salivary proteins with unknown function. We additionally provide a supplemental Table that catalogues over 3,500 putative salivary proteins from various tick species, which might assist the scientific community in the process of functional identification of these unique proteins. This supplemental file is accessble fromhttp://exon.niaid.nih.gov/transcriptome/tick_review/Sup-Table-1.xls.gz.

Protein disulfide isomerase acts as an injury response signal that enhances fibrin generation via tissue factor activation

The activation of initiator protein tissue factor (TF) is likely to be a crucial step in the blood coagulation process, which leads to fibrin formation. The stimuli responsible for inducing TF activation are largely undefined. Here we show that the oxidoreductase protein disulfide isomerase (PDI) directly promotes TF-dependent fibrin production during thrombus formation in vivo. After endothelial denudation of mouse carotid arteries, PDI was released at the injury site from adherent platelets and disrupted vessel wall cells. Inhibition of PDI decreased TF-triggered fibrin formation in different in vivo murine models of thrombus formation, as determined by intravital fluorescence microscopy. PDI infusion increased - and, under conditions of decreased platelet adhesion, PDI inhibition reduced - fibrin generation at the injury site, indicating that PDI can directly initiate blood coagulation. In vitro, human platelet-secreted PDI contributed to the activation of cryptic TF on microvesicles (microparticles). Mass spectrometry analyses indicated that part of the extracellular cysteine 209 of TF was constitutively glutathionylated. Mixed disulfide formation contributed to maintaining TF in a state of low functionality. We propose that reduced PDI activates TF by isomerization of a mixed disulfide and a free thiol to an intramolecular disulfide. Our findings suggest that disulfide isomerases can act as injury response signals that trigger the activation of fibrin formation following vessel injury.

Factor XI deficiency

Although factor XI (FXI) deficiency has a particularly high incidence in Ashkenazi Jews, it is now frequently diagnosed in other ethnic groups. This review gives an overview of the basic pathophysiology, clinical manifestations, and management of FXI deficiency. The correlation between FXI levels and the bleeding phenotype is much less clear than in the haemophilias, and consequently the bleeding risk can be difficult to predict. Two well-characterized mutations in the F11 gene are responsible for the majority of Jewish cases, but new mutations are becoming increasingly recognized. The publication of the crystal structure has greatly enhanced our understanding of the structure-function relationship in FXI. The impact of recent studies on our understanding of the role of FXI in coagulation is discussed.

The Influence of Blood on In Vivo Adenovirus Bio-distribution and Transduction

Intravascular delivery of adenovirus (Ad) vectors is being developed for liver-directed gene therapy for targeting disseminated disease in cancer therapeutics and for targeting non-hepatic tissues and organs through vector engineering strategies. The utility of Ad vectors is not limited to serotype 5 (Ad5), and many alternate human serotypes and non-human serotypes of Ad are currently being investigated. Critical to intravascular delivery of Ad is the interaction of the virus with host blood cells and plasma proteins, because immediate contact is observed following injection. Although incompletely understood, recent studies suggest that these interactions are critical in dictating the particle bio-distribution and resulting transduction properties of Ad in vivo. For example, plasma proteins-in particular, vitamin K-dependent coagulation zymogens-are able to directly bind to Ad, and "bridge" the virus to receptors in the liver. Unraveling and characterizing these mechanisms will be of fundamental importance both for understanding basic Ad biology in vivo and for refinement and optimization of Ad vectors for human gene therapy.

The quest for Factor VIIa exosite inhibitors

Coagulation proteases are involved in a highly orchestrated proteolytic cascade which is essential for haemostasis and blood clotting. In particular, the initiator of the coagulation cascade, Factor VIIa, binds to its cofactor, tissue factor, and its substrate, Factor X, via exosite interactions to form a ternary catalytic complex named extrinsic Xase. These exosite interactions have also been shown to allosterically induce the active conformation of the catalytic site of Factor VIIa. We have developed a direct continuous fluorescence polarization-based extrinsic Xase assay, which has been used to screen in excess of 1 million structurally diverse low-molecular-mass compounds as a potential starting point for the development of anticoagulants. The primary screen hits were categorized with deconvolution assays into either active-site or exosite inhibitors. The latter category of hits displayed both competitive and uncompetitive modalities of inhibition with respect to Factor X activation. An uncompetitive mechanism of action is of particular interest as it offers a hypothetical inhibitory advantage in the context of inhibiting a proteolytic cascade such as the blood coagulation pathway.

Expression patterns and action analysis of genes associated with blood coagulation responses during rat liver regeneration

AIM: To study the blood coagulation response after partial hepatectomy (PH) at transcriptional level.

METHODS: After PH of rats, the associated genes with blood coagulation were obtained through reference to the databases, and the gene expression changes in rat regenerating liver were analyzed by the Rat Genome 230 2.0 array.

RESULTS: It was found that 107 genes were associated with liver regeneration. The initially and totally expressing gene numbers occurring in initiation phase of liver regeneration (0.5-4 h after PH), G₀/G₁ transition (4-6 h after PH), cell proliferation (6-66 h after PH), cell differentiation and structure-function reconstruction (66-168 h after PH) were 44, 11, 58, 7 and 44, 33, 100, 71 respectively, showing that the associated genes were mainly triggered in the forepart and prophase, and worked at different phases. According to their expression similarity, these genes were classified into 5 groups: only up-, predominantly up-, only down-, predominantly down-, up- and down-regulation, involving 44, 8, 36, 13 and 6 genes, respectively, and the total times of their up- and down-regulation expression were 342 and 253, respectively, demonstrating that the number of the up-regulated genes was more than that of the down- regulated genes. Their time relevance was classified into 15 groups, showing that the cellular physiological and biochemical activities were staggered during liver regeneration. According to gene expression patterns, they were classified into 29 types, suggesting that their protein activities were diverse and complex during liver regeneration.

CONCLUSION: The blood coagulation response is enhanced mainly in the forepart, prophase and anaphase of liver regeneration, in which the response in the forepart, prophase of liver regeneration can prevent the bleeding caused by partial hepatectomy, whereas that in the anaphase contributes to the structure-function reorganization of regenerating liver. In the process, 107 genes associated with liver regeneration play an important role.