LDL increases inactive tissue factor on vascular smooth muscle cell surfaces: hydrogen peroxide activates latent cell surface tissue factor

Arterial myeloperoxidase in the detection and treatment of vulnerable atherosclerotic plaque: a new dawn for an old light

Intracellular myeloperoxidase (MPO) plays a specific role in the innate immune response; however, upon release into the extracellular space in the setting of inflammation, drives oxidative tissue injury. Extracellular MPO has recently been shown to be abundant in unstable atheroma and causally linked to plaque destabilization, erosion, and rupture, identifying it as a potential target for the surveillance and treatment of vulnerable atherosclerosis. Through the compartmentalization of MPO's protective and deleterious effects, extracellular MPO can be selectively detected using non-invasive molecular imaging and targeted by burgeoning pharmacotherapies. Given its causal relationship to plaque destabilization coupled with an ability to preserve its beneficial properties, MPO is potentially a superior translational inflammatory target compared with other immunomodulatory therapies and imaging biomarkers utilized to date. This review explores the role of MPO in plaque destabilization and provides insights into how it can be harnessed in the management of patients with vulnerable atherosclerotic plaque.

Sepsis: Evidence-based pathogenesis and treatment

Sepsis can develop during the body’s response to a critical illness leading to multiple organ failure, irreversible shock, and death. Sepsis has been vexing health care providers for centuries due to its insidious onset, generalized metabolic dysfunction, and lack of specific therapy. A common factor underlying sepsis is the characteristic hypermetabolic response as the body ramps up every physiological system in its fight against the underlying critical illness. A hypermetabolic response requires supraphysiological amounts of energy, which is mostly supplied via oxidative phosphorylation generated ATP. A by-product of oxidative phosphorylation is hydrogen peroxide (H₂O₂), a toxic, membrane-permeable oxidizing agent that is produced in far greater amounts during a hypermetabolic state. Continued production of mitochondrial H₂O₂ can overwhelm cellular reductive (antioxidant) capacity leading to a build-up within cells and eventual diffusion into the bloodstream. H₂O₂ is a metabolic poison that can inhibit enzyme systems leading to organ failure, microangiopathic dysfunction, and irreversible septic shock. The toxic effects of H₂O₂ mirror the clinical and laboratory abnormalities observed in sepsis, and toxic levels of blood H₂O₂ have been reported in patients with septic shock. This review provides evidence to support a causal role for H₂O₂ in the pathogenesis of sepsis, and an evidence-based therapeutic intervention to reduce H₂O₂ levels in the body and restore redox homeostasis, which is necessary for normal organ function and vascular responsiveness.

Oxidized low-density lipoprotein in inflammation-driven thrombosis

Thrombosis is the defining feature of the most prevalent causes of cardiovascular mortality, such as myocardial infarction, stroke, and pulmonary artery embolism. Although platelet activation and activation of the plasmatic coagulation system are the hallmarks of thrombus formation, inflammatory processes and the cellular responses involved are increasingly being recognized as critical modulators of thrombosis. In the context of many chronic inflammatory diseases that are associated with a high thrombotic risk, oxidized lipoproteins represent a prominent sterile trigger of inflammation. Oxidized low-density lipoprotein and its components play a central role in the initiation and progression of atherosclerotic plaques, but also in other processes that lead to thrombotic events. Moreover, dying cells and microvesicles can be decorated with some of the same oxidized lipid components that are found on oxidized lipoproteins, and thereby similar mechanisms of thromboinflammation may also be active in venous thrombosis. In this review, we summarize the current knowledge on how oxidized lipoproteins and components thereof affect the cells and pathways involved in thrombosis.

Protein disulphide-isomerase A2 regulated intracellular tissue factor mobilisation in migrating human vascular smooth muscle cells

Protein-disulphide isomerase family (PDI) are an ER-stress protein that controls TF-procoagulant activity but its role in HVSMC migration and coronary artery disease remains to be elucidated. We aimed to investigate whether in human coronary smooth muscle cells (HVSMC) the ER-stress protein-disulphide isomerase family A member 2 (PDIA2) regulates tissue factor (TF) polarisation during migration and atherosclerotic remodeling. PDIA2 and TF were analysed by confocal microscopy, silenced by small interfering RNAs (siRNA) and their function analysed by transwell and migration assays in vitro and in vivo. PDIA2and TF co-localise in the front edge of motile HVSMC. Silencing PDIA2, as well as silencing TF, reduces migration. PDIA2 silenced cells show increased TF-rich microparticle shedding. In vivo cell-loaded plug implants in nude mice of PDIA2 silenced HVSMC together with microvascular endothelial cells showed a significant impairment in mature microvessel formation. PDIA2 and TF are found in remodelled atherosclerotic plaques but not in healthy coronaries. In conclusion, we demonstrate that TF is chaperoned by PDIA2 to the HVSMC membrane and to the cell migratory front. Absence of PDIA2 impairs TF intracellular trafficking to its membrane docking favoring its uncontrolled release in microparticles. TF-regulated HVSMC migration and microvessel formation is under the control of the ER-protein PDIA2.

Reactive Oxygen Species and NOX Enzymes Are Emerging as Key Players in Cutaneous Wound Repair

Our understanding of the role of oxygen in cell physiology has evolved from its long-recognized importance as an essential factor in oxidative metabolism to its recognition as an important player in cell signaling. With regard to the latter, oxygen is needed for the generation of reactive oxygen species (ROS), which regulate a number of different cellular functions including differentiation, proliferation, apoptosis, migration, and contraction. Data specifically concerning the role of ROS-dependent signaling in cutaneous wound repair are very limited, especially regarding wound contraction. In this review we provide an overview of the current literature on the role of molecular and reactive oxygen in the physiology of wound repair as well as in the pathophysiology and therapy of chronic wounds, especially under ischemic and hyperglycemic conditions.

Hyperbaric oxygen, vasculogenic stem cells, and wound healing

SIGNIFICANCE

Oxidative stress is recognized as playing a role in stem cell mobilization from peripheral sites and also cell function.

RECENT ADVANCES

This review focuses on the impact of hyperoxia on vasculogenic stem cells and elements of wound healing.

CRITICAL ISSUES

Components of the wound-healing process in which oxidative stress has a positive impact on the various cells involved in wound healing are highlighted. A slightly different view of wound-healing physiology is adopted by departing from the often used notion of sequential stages: hemostatic, inflammatory, proliferative, and remodeling and instead organizes the cascade of wound healing as overlapping events or waves pertaining to reactive oxygen species, lactate, and nitric oxide. This was done because hyperoxia has effects of a number of cell signaling events that converge to influence cell recruitment/chemotaxis and gene regulation/protein synthesis responses which mediate wound healing.

FUTURE DIRECTIONS

Our alternative perspective of the stages of wound healing eases recognition of the multiple sites where oxidative stress has an impact on wound healing. This aids the focus on mechanistic events and the interplay among various cell types and biochemical processes. It also highlights the areas where additional research is needed.

4-Hydroxy-2-nonenal enhances tissue factor activity in human monocytic cells via p38 mitogen-activated protein kinase activation-dependent phosphatidylserine exposure

OBJECTIVE

4-hydroxy-2-nonenal (HNE) is one of the major aldehydes formed during lipid peroxidation and is believed to play a role in the pathogenesis of atherosclerosis. The objective of the present study is to investigate the effect of HNE on tissue factor (TF) procoagulant activity expressed on cell surfaces.

APPROACH AND RESULTS

TF activity and antigen levels on intact cells were measured using factor Xa generation and TF monoclonal antibody binding assays, respectively. Exposure of phosphatidylserine on the cell surface was analyzed using thrombin generation assay or by binding of a fluorescent dye-conjugated annexin V. 2',7'-dichlorodihydrofluorescein diacetate was used to detect the generation of reactive oxygen species. Our data showed that HNE increased the procoagulant activity of unperturbed THP-1 cells that express traces of TF antigen, but had no effect on unperturbed endothelial cells that express no measurable TF antigen. HNE increased TF procoagulant activity but not TF antigen of both activated monocytic and endothelial cells. HNE treatment generated reactive oxygen species, activated p38 mitogen-activated protein kinase, and increased the exposure of phosphatidylserine at the outer leaflet in THP-1 cells. Treatment of THP-1 cells with an antioxidant, N-acetyl cysteine, suppressed the above HNE-induced responses and negated the HNE-mediated increase in TF activity. Blockade of p38 mitogen-activated protein kinase activation inhibited HNE-induced phosphatidylserine exposure and increased TF activity.

CONCLUSIONS

HNE increases TF coagulant activity in monocytic cells through a novel mechanism involving p38 mitogen-activated protein kinase activation that leads to enhanced phosphatidylserine exposure at the cell surface.

Myeloperoxidase may help to differentiate coronary plaque erosion from plaque rupture in patients with acute coronary syndromes

Coronary thrombosis is the most frequent final event leading to an acute coronary syndrome. In approximately two-thirds of cases, the thrombus overlies a ruptured plaque, whereas in one-third of cases it overlies an intact plaque with superficial endothelial erosion, a finding showed initially by histopathological postmortem studies and more recently confirmed by in vivo optical coherence tomography imaging. Interestingly, recent observations suggest that mechanisms leading to plaque rupture or erosion are different. In fact, in a recent study, we showed that myeloperoxidase levels in peripheral blood and expression within thrombi overlying the culprit plaque are much higher in patients with plaque erosion than in those with plaque rupture. These observations suggest that innate immunity activation is likely to play a key role, in particular, in plaque erosion and might become a therapeutic target in this subset of patients.

The chemotherapy metabolite acrolein upregulates thrombin generation and impairs the protein C anticoagulant pathway in animal-based and cell-based models

BACKGROUND

Thrombosis is a common complication in cancer patients receiving chemotherapy regimens that include cyclophosphamide. However, the mechanisms by which these agents increase this risk are largely uncharacterized.

OBJECTIVES

To examine the effects of cyclophosphamide and its metabolite acrolein on procoagulant and anticoagulant pathways in both cell-based and animal-based models.

METHODS

Thrombin and activated protein C (APC) generation were measured in defibrinated plasma exposed to acrolein-treated endothelial and smooth muscle cells. Tissue factor (TF) activity was measured on acrolein-treated cells. Cell surface levels of phosphatidylserine, TF, endothelial protein C receptor and thrombomodulin were measured. Healthy BALB/c mice received injections of saline (control), acrolein, or cyclophosphamide; blood was collected, and plasma thrombin-antithrombin (TAT) complex, protein C and APC levels were analyzed.

RESULTS

Exposure of acrolein-treated endothelial and smooth muscle cells to defibrinated plasma increased thrombin generation in the plasma. This was associated with enhanced phosphatidylserine exposure and/or increased TF activity on acrolein-treated cells. Despite elevated levels of thrombin generation, plasma APC levels were not elevated. In vivo, treatment of mice with cyclophosphamide and acrolein resulted in elevations of plasma TAT complex levels, whereas APC levels remained low.

CONCLUSIONS

This is the first study to examine thrombin generation and the APC pathway in chemotherapy-treated mice. Cyclophosphamide and acrolein appear to upregulate procoagulant pathways, while impairing endogenous anticoagulant pathways. This may explain, in part, the increased risk of thrombosis observed in cancer patients receiving cyclophosphamide-containing chemotherapy.

Evidence for enhanced tissue factor expression in age-related macular degeneration

Tissue factor (TF) is the primary initiator of blood coagulation. In addition to hemostasis, TF can initiate intracellular signaling and promote inflammation and angiogenesis, the key processes underlying the pathogenesis of age-related macular degeneration (AMD). AMD, the leading cause of irreversible blindness among the elderly, involves many genetic and environmental risk factors, including oxidative stress and inflammation. In this study, TF expression was examined in human AMD tissue and in the eyes of a model of AMD, the Ccl2(-/-)/Cx3cr1(-/-) (DKO) mouse, as well as in the ARPE-19 cell line after lipopolysaccharide (LPS) and H(2)O(2) stimulation. Total RNA was extracted from tissue samples and further analyzed by real-time RT-PCR. Immunohistochemistry was performed to evaluate TF protein expression. In the human retina, a 32-fold increase of TF mRNA expression was detected in AMD macular lesions compared with normal maculae. TF protein expression was also enhanced in human AMD maculae. Similarly, TF transcript and protein expression were moderately increased in retinal lesions, neuroretinal tissue, and cultured RPE cells of DKO mice compared with age-matched wild-type mice. TF expression level correlated with age in both wild-type and DKO mice. In order to better understand how AMD might lead to enhanced TF expression, 1, 5, and 10 μg/ml LPS as well as 100 and 200 μM H(2)O(2) were used to stimulate ARPE-19 cells for 24 and 2 h, respectively. LPS treatment consistently increased TF transcript and protein expression. H(2)O(2) alone or in combination with LPS also moderately enhanced TF expression. These results indicate that upregulated TF expression may be associated with AMD, and inflammatory and oxidative stress may contribute to TF expression in AMD eyes.

Tissue factor in cardiovascular disease pathophysiology and pharmacological intervention

Tissue factor (TF) is the major trigger of the coagulation cascade and thereby crucially involved in the maintenance of vascular hemostasis. By binding factor VIIa, the resulting TF:VIIa complex activates the coagulation factors IX and X ultimately leading to fibrin and clot formation. In the vessel wall, TF expression and activity is detectable in vascular smooth muscle cells and fibroblasts and, at a much lower level, in endothelial cells and can be induced by various stimuli including cytokines. In addition, TF is found in the bloodstream in circulating cells such as monocytes, in TF containing microparticles, and as a soluble splicing isoform. Besides its well-known extracellular role as a trigger of coagulation, TF also functions as a transmembrane receptor, and TF-dependent intracellular signaling events regulate the expression of genes involved in cellular responses such as proliferation and migration. TF indeed appears to be involved in the pathogenesis of neointima formation and tumor growth, and increased levels of TF have been detected in patients with cardiovascular risk factors or coronary artery disease as well as in those with cancer. Therefore, pharmacological or genetic inhibition of TF may be an attractive target for the treatment of cardiovascular disease and cancer. Different strategies for inhibition of TF have been developed such as inhibition of TF synthesis and blockade of TF action. Clinical applications of such strategies need to be tested in appropriate trials, in particular for evaluating the advantages of targeted versus systemic delivery of the inhibitors.

Tissue factor: beyond coagulation in the cardiovascular system

TF (tissue factor) is the main trigger of the coagulation cascade; by binding Factor VIIa it activates Factor IX and Factor X, thereby resulting in fibrin formation. Various stimuli, such as cytokines, growth factors and biogenic amines, induce TF expression and activity in vascular cells. Downstream targets of these mediators include diverse signalling molecules such as MAPKs (mitogen-activated protein kinases), PI3K (phosphoinositide 3-kinase) and PKC (protein kinase C). In addition, TF can be detected in the bloodstream, known as circulating or blood-borne TF. Many cardiovascular risk factors, such as hypertension, diabetes, dyslipidaemia and smoking, are associated with increased expression of TF. Furthermore, in patients presenting with acute coronary syndromes, elevated levels of circulating TF are found. Apart from its role in thrombosis, TF has pro-atherogenic properties, as it is involved in neointima formation by inducing vascular smooth muscle cell migration. As inhibition of TF action appears to be an attractive target for the treatment of cardiovascular disease, therapeutic strategies are under investigation to specifically interfere with the action of TF or, alternatively, promote the effects of TFPI (TF pathway inhibitor).

Intracoronary β‐irradiation enhances balloon‐injury‐induced tissue factor expression in the porcine injury model

Intracoronary brachytherapy (ICBT) effectively reduces restenosis but is associated with late thrombosis. Since tissue factor (TF) is an important mediator of arterial thrombosis, we tested the hypothesis that ICBT results in persistently augmented TF expression. Coronary arteries from 12 pigs were randomized to: control (C; no injury), oversized balloon injury (BI), or BI followed by ICBT. Animals were sacrificed at 1, 7, 14, or 60 days postprocedure, and coronary arteries collected for expression analyses and immunostaining. ICBT-treated arteries had higher TF antigen and activity at all time-points compared to BI arteries (Western blot: 16 571 +/- 2090 vs 10 135 +/- 2939 densitometric units, p = 0.001; ELISA: 0.42 +/- 0.13 nM vs 0.25 +/- 0.14 nM, p = 0.001; TF activity assay: 0.303 +/- 0.11 nM vs 0.18 +/- 0.07 nM, p = 0.01; immunohistochemical staining: 30.6 +/- 6.6% vs 11.5% +/- 3.2%, p = 0.01). TF expression increased following BI, increased further following ICBT, and persisted for the duration of the study. We conclude that TF expression increases after BI, but is further increased and persists for a longer duration following ICBT, suggesting that a TF-mediated mechanism may play a role in late thrombosis following ICBT.

Chemotherapeutic agents doxorubicin and epirubicin induce a procoagulant phenotype on endothelial cells and blood monocytes

BACKGROUND

Although chemotherapy is associated with an increased risk of thrombosis, the pathogenic mechanisms by which chemotherapeutic agents exert prothrombotic effects are unclear.

OBJECTIVES

In this study we explored the possibility that chemotherapeutic agents doxorubicin, epirubicin, 5-fluorouracil and methotrexate induce a procoagulant phenotype on vascular endothelial cells and/or on blood monocytes.

METHODS

Thrombin generation was measured in defibrinated plasma exposed to chemotherapy-treated human umbilical vein endothelial cells (HUVECs). Tissue factor activity assays were performed on chemotherapy-treated HUVECs and blood monocytes. The effects of chemotherapy drugs on phosphatidylserine exposure and the protein C pathway were also measured.

RESULTS

Exposure of defibrinated plasma to either doxorubicin- or epirubicin-treated HUVECs resulted in an increase in plasma thrombin generation. The procoagulant activity of doxorubicin- and epirubicin-treated HUVECs reflects an increase in tissue factor activity and phosphatidylserine exposure. Doxorubicin-mediated increase in tissue factor activity is related to increased levels of phosphatidylserine rather than to protein disulfide isomerase activity, and is likely to involve reactive oxygen species generation. Unlike doxorubicin, epirubicin does not have an impact on the protein C anticoagulant pathway. Interestingly, neither methotrextate nor 5-fluorouracil altered endothelial or monocyte hemostatic properties.

CONCLUSIONS

These studies suggest that doxorubicin and epirubicin have the greatest 'prothrombotic potential' by virtue of their ability to alter endothelial and monocyte hemostatic properties.

Redox signals in wound healing

Physical trauma represents one of the most primitive challenges that threatened survival. Healing a problem wound requires a multi-faceted comprehensive approach. First and foremost, the wound environment will have to be made receptive to therapies. Second, the appropriate therapeutic regimen needs to be identified and provided while managing systemic limitations that could secondarily limit the healing response. Unfortunately, most current solutions seem to aim at designing therapeutic regimen with little or no consideration of the specific details of the wound environment and systemic limitations. One factor that is centrally important in making the wound environment receptive is correction of wound hypoxia. Recent work have identified that oxygen is not only required to disinfect wounds and fuel healing but that oxygen-dependent redox-sensitive signaling processes represent an integral component of the healing cascade. Over a decade ago, it was proposed that in biological systems oxidants are not necessarily always the triggers for oxidative damage and that oxidants such as H2O2 could actually serve as signaling messengers and drive several aspects of cellular signaling. Today, that concept is much more developed and mature. Evidence supporting the role of oxidants such as H2O2 as signaling messenger is compelling. A complete understanding of the continuum between the classical and emergent roles of oxygen requires a thorough consideration of current concepts in redox biology. The objective of this review is to describe our current understanding of how redox-sensitive processes may drive dermal tissue repair.

Tissue factor activities of streptozotocin induced diabetic rat tissues and the effect of peanut consumption

BACKGROUND

Tissue factor (TF) is considered to be a major regulator of normal haemostasis and thrombosis. Circulating TF activity is suggested to be associated with diabetes mellitus. Various tissues and body fluids have TF activity. The aim of the present study was to investigate the TF activity of streptozotocin (STZ) induced diabetic rat tissues. Peanut consumption is reported to be associated with decreased risk of type 2 diabetes. Therefore, the effect of peanut consumption on the TF activity of STZ induced diabetic rat tissues, and haemostatic parameters such as protrombin time (PT), activated partial thromboplastin time (APTT) and fibrinogen levels were determined.

METHODS

Twenty-four Wistar rats were divided into 3 groups of 8 rats each as control, STZ-induced diabetic and diabetic + peanut group. Twelve weeks later, TF activity of liver, kidney, spleen, heart, kidney, lung, pancreas and aorta and haemostatic parameters were determined.

RESULTS

In the diabetic group, TF activities of liver, kidney and spleen increased (p < 0.01) whereas the TF activity of brain decreased (p < 0.01) compared to the control group. Peanut consumption in the diabetic group decreased the TF activity of spleen and aorta (p < 0.01; p < 0.05). Haemostatic parameters did not change significantly in the groups.

CONCLUSION

Elevated TF activity in diabetic rat tissues, may contribute to the increased risk of atherothrombotic disease that accompanies the diabetic complications whereas the decreased brain TF activity may be due to a different haemostatic mechanism to protect this vital organ from the diabetic status. The decreased TF activity of peanut given diabetic rat tissues might protect these tissues from the risk of thrombosis.

The principal eosinophil peroxidase product, HOSCN, is a uniquely potent phagocyte oxidant inducer of endothelial cell tissue factor activity: a potential mechanism for thrombosis in eosinophilic inflammatory states

In vivo, bromide (Br(-)), nitrite (NO(2)(-)), and thiocyanate (SCN(-)) compete for oxidation by eosinophil peroxidase (EPO) and H(2)O(2), yielding, respectively, HOBr, NO(2)., and HOSCN. We have recently shown that SCN(-) is the strongly preferred substrate for EPO in vivo and that HOSCN, in contrast with other EPO-generated oxidants and HOCl, is a relatively weak, cell-permeant, sulfhydryl (SH)-reactive oxidant. We here show that HOSCN is a uniquely potent (up to 100-fold) phagocyte oxidant inducer of tissue factor (TF) activity in human umbilical vein endothelial cells (HUVECs). This induction is attributable to transcriptional up-regulation of TF gene expression dependent upon both activation of the p65/c-Rel TF-kappaB transcription factor and activity of the ERK1/2 kinase pathway upstream of Egr-1 and was markedly further enhanced in the presence of wortmannin, an inhibitor of the PI3 kinase/Akt pathway. HOSCN also markedly activates the proinflammatory p65/p50 NF-kappaB pathway. Based on these findings we hypothesize that HOSCN generated by adherent and infiltrating eosinophils may provoke the development of a prothrombotic and proinflammatory endothelial/endocardial phenotype that promotes the pronounced thrombotic diathesis characteristic of the hypereosinophilic syndrome.

Cellular microparticles: a disseminated storage pool of bioactive vascular effectors

PURPOSE OF REVIEW

Microparticles (MP) or microvesicles are fragments shed from the plasma membrane of stimulated or apoptotic cells. Having long been considered inert debris reflecting cellular activation or damage, MP are now acknowledged as cellular effectors involved in cell-cell crosstalk. This review focuses on procoagulant MP circulating in the vascular compartment, their role in hemostasis and thrombosis, and possible impact in vascular functions.

RECENT FINDINGS

Microparticles can be viewed as a "storage pool" by themselves, disseminating blood-borne tissue factor activity and procoagulant phospholipids. Increasing evidences of integrated loops involving dynamic exchanges and transfer events through multiple MP-cell interactions are summarized.

SUMMARY

Microparticles can be considered true targets in the pharmacological control of thrombosis. Another challenging issue is to take advantage of their procoagulant potential for the management of hemophilia.

Celecoxib, a Selective Cyclooxygenase-2 Inhibitor, Decreases Monocyte Chemoattractant Protein-1 Expression and Neointimal Hyperplasia in the Rabbit Atherosclerotic Balloon Injury Model

The inflammation in response to vascular injury is becoming increasingly recognized as a potential contributor to restenosis. Cyclooxygenase-2 (COX-2) is the inducible form of cyclooxygenase and has been shown to be involved in the proinflammatory response of vascular tissue. Bilateral femoral artery lesions were induced by air desiccation in New Zealand White rabbits followed by high cholesterol diet feeding for 28 days. Balloon injury and stent implantation were performed at the preinjured vessel segments. Immunostaining showed that uninjured vessel segments stained positive only for COX-1 but not for COX-2. Injured vessel segments showed, in addition to COX-1, significant positive staining for COX-2. In the efficacy study, celecoxib (75 mg/kg/d) was administered orally beginning 3 hours before balloon injury or stent implantation on day 28 and daily for 21 days. Monocyte chemoattractant protein-1 (MCP-1) and matrix metalloproteinase-2 and -9 (MMPs) expression were quantified in arterial extracts 4 days after balloon injury by Western blot and gelatin zymography. Morphometric analysis and immunostaining for macrophages were performed 21 days after balloon injury. Celecoxib treatment significantly decreased MCP-1 expression (P < 0.01). Neointimal hyperplasia was significantly inhibited by celecoxib in both balloon injury and stent models (0.49 +/- 0.20 versus 0.70 +/- 0.35 mm2 from balloon injury model, P < 0.05, and 0.81 +/- 0.25 versus 1.69 +/- 0.43 mm2 from stent model, P < 0.05), accompanied by reduced macrophage infiltration. We conclude that celecoxib decreases the inflammatory response and intimal hyperplasia following vascular injury, possibly through inhibition of MCP-1 expression, implying a pivotal role of inflammation in the pathogenesis of restenosis.

Acute cholesterol depletion impairs functional expression of tissue factor in fibroblasts: modulation of tissue factor activity by membrane cholesterol

Cholesterol, in addition to providing rigidity to the fluid membrane, plays a critical role in receptor function, endocytosis, recycling, and signal transduction. In the present study, we examined the effect of membrane cholesterol on functional expression of tissue factor (TF), a cellular receptor for clotting factor VIIa. Depletion of cholesterol in human fibroblasts (WI-38) with methyl-beta-cyclodextrin-reduced TF activity at the cell surface. Binding studies with radiolabeled VIIa and TF monoclonal antibody (mAB) revealed that reduced TF activity in cholesterol-depleted cells stems from the impairment of VIIa interaction with TF rather than the loss of TF receptors at the cell surface. Repletion of cholesterol-depleted cells with cholesterol restored TF function. Loss of caveolar structure on cholesterol removal is not responsible for reduced TF activity. Solubilization of cellular TF in different detergents indicated that a substantial portion of TF in fibroblasts is associated with noncaveolar lipid rafts. Cholesterol depletion studies showed that the TF association with these rafts is cholesterol dependent. Overall, the data presented herein suggest that membrane cholesterol functions as a positive regulator of TF function by maintaining TF receptors, probably in noncaveolar lipid rafts, in a high-affinity state for VIIa binding.

Insights into the redox control of blood coagulation: role of vascular NADPH oxidase-derived reactive oxygen species in the thrombogenic cycle

Various cardiovascular diseases including thrombosis, atherosclerosis, (pulmonary) hypertension and diabetes, are associated with disturbed coagulation. Alterations in the vessel wall common to many cardiovascular disorders have been shown to initiate the activity of the coagulation system, but also to be the result of an abnormal coagulation system. The primary link between the coagulation and the vascular system appears to be tissue factor (TF), which is induced on the surface of vascular cells and initiates the extrinsic pathway of the blood coagulation cascade, leading to the formation of thrombin. Thrombin can also interact with the vascular wall via specific receptors and can increase vascular TF expression. Such a "thrombogenic cycle" may be essentially involved in the pathogenesis of cardiovascular disorders associated with an abnormal coagulation. Therefore, the identification of the signaling pathways regulating this cycle and each of its relevant connecting links is of fundamental importance for the understanding of these disorders and their putative therapeutic potential. Reactive oxygen species (ROS) and the ROS-generating NADPH oxidases have been shown to play important roles as signaling molecules in the vasculature. In this review, we summarize the data supporting a substantial role of ROS in promoting a thrombogenic cycle in the vascular system.

Tissue factor expression is decreased in monocytes obtained from blood during Mediterranean or high carbohydrate diets

BACKGROUND

Mediterranean and high carbohydrate diets play a dominant role in the prevention of atherosclerosis as a result of their lipid lowering effect. However, diets can also have a protective effect in other ways, such as modulating tissue factor expression in circulating monocytes.

METHODS AND RESULTS

Forty-one subjects participated in this randomised crossover study consisting of three dietary periods: a saturated fat enriched diet (SFA), a low fat and high carbohydrate diet (CHO), and a Mediterranean diet. Plasma levels of total cholesterol, triglycerides, low density lipoprotein (LDL-C) and high density lipoprotein (HDL-C) were determined at the end of each dietary period, as was the expression of tissue factor (TF) in circulating monocytes isolated from blood samples. Total cholesterol, LDL-C, HDL-C and TF expression were lower after the Mediterranean and high carbohydrate diets than after the SFA diet, and there was a positive correlation between LDL-C levels and monocyte TF expression.

CONCLUSIONS

High carbohydrate and Mediterranean diets reduce the expression of TF in circulating monocytes.

Mechanisms of autoantibody-induced monocyte tissue factor expression

The expression of tissue factor (TF) activity to flowing blood is the trigger for physiological coagulation as well as many types of thrombosis. A growing body of evidence suggests that increased tissue factor activity is a significant contributor towards the hypercoagulability associated with the antiphospholipid syndrome (APS). The increase in tissue factor activity appears to be due to increased transcription and translation of nascent tissue factor molecules but is not due to de-encryption of existing tissue factor molecules on cells. Autoantibodies and/or immune complexes circulating in APS patients appear to enhance the expression of tissue factor activity on monocytes and endothelial cells. Anti-beta2-glycoprotein I (beta2GPI) autoantibodies have been specifically implicated in the antibody-mediated enhancement of tissue factor activity. The presence of antibodies against tissue factor pathway inhibitor (TFPI) in certain APS patients suggests that negative regulation of tissue factor activity might also be impaired in these patients. Given a mechanism involving increased tissue factor activity in APS-associated thrombosis, agents specifically targeting tissue factor activity may be a novel and efficacious therapy that is safer than current approaches to the management of APS.

Lipid rafts are necessary for tonic inhibition of cellular tissue factor procoagulant activity

A fraction of total cellular tissue factor procoagulant activity remains masked or "encrypted" in intact cells. Decryption of this activity partly involves the extracellular exposure of anionic phospholipids such as phosphatidylserine. Because of the potential association of tissue factor and phospholipid scramblase activity with lipid rafts, we have explored the role of lipid rafts in regulating factor VIIa/tissue factor activity. In HEK293 cells, tissue factor antigen was not stably associated with lipid rafts, yet disruption of rafts with methyl-beta-cyclodextrin resulted in a 3-fold stimulation of tissue factor procoagulant activity. Treatment with methyl-beta-cyclodextrin was not associated with cytotoxicity and did not result in the exposure of additional tissue factor antigen. Factor VIIa/tissue factor activity decrypted with methyl-beta-cyclodextrin was quantitatively similar to that obtained by using lytic concentrations of octyl glucoside but more sensitive to inhibition by cell surface tissue factor pathway inhibitor and the phospholipid binding protein, annexin V. Partial decryption of tissue factor was achieved with methyl-beta-cyclodextrin prior to complete disruption of lipid rafts, suggesting the role of an enzyme localized to lipid rafts in the transbilayer transport of phosphatidylserine. We conclude that lipid rafts are required for the maintenance of cellular tissue factor in an encrypted state.

Overexpression of the 78-kDa glucose-regulated protein/immunoglobulin-binding protein (GRP78/BiP) inhibits tissue factor procoagulant activity

Previous studies have demonstrated that overexpression of GRP78/BiP, an endoplasmic reticulum (ER)-resident molecular chaperone, in mammalian cells inhibits the secretion of specific coagulation factors. However, the effects of GRP78/BiP on activation of the coagulation cascade leading to thrombin generation are not known. In this study, we examined whether GRP78/BiP overexpression mediates cell surface thrombin generation in a human bladder cancer cell line T24/83 having prothrombotic characteristics. We report here that cells overexpressing GRP78/BiP exhibited significant decreases in cell surface-mediated thrombin generation, prothrombin consumption and the formation of thrombin-inhibitor complexes, compared with wild-type or vector-transfected cells. This effect was attributed to the ability of GRP78/BiP to inhibit cell surface tissue factor (TF) procoagulant activity (PCA) because conversion of factor X to Xa and factor VII to VIIa were significantly lower on the surface of GRP78/BiP-overexpressing cells. The additional findings that (i) cell surface factor Xa generation was inhibited in the absence of factor VIIa and (ii) TF PCA was inhibited by a neutralizing antibody to human TF suggests that thrombin generation is mediated exclusively by TF. GRP78/BiP overexpression did not decrease cell surface levels of TF, suggesting that the inhibition in TF PCA does not result from retention of TF in the ER by GRP78/BiP. The additional observations that both adenovirus-mediated and stable GRP78/BiP overexpression attenuated TF PCA stimulated by ionomycin or hydrogen peroxide suggest that GRP78/BiP indirectly alters TF PCA through a mechanism involving cellular Ca(2+) and/or oxidative stress. Similar results were also observed in human aortic smooth muscle cells transfected with the GRP78/BiP adenovirus. Taken together, these findings demonstrate that overexpression of GRP78/BiP decreases thrombin generation by inhibiting cell surface TF PCA, thereby suppressing the prothrombotic potential of cells.

Intravascular tissue factor initiates coagulation via circulating microvesicles and platelets

Although tissue factor (TF), the principial initiator of physiological coagulation and pathological thrombosis, has recently been proposed to be present in human blood, the functional significance and location of the intravascular TF is unknown. In the plasma portion of blood, we found TF to be mainly associated with circulating microvesicles. By cell sorting with the specific marker CD42b, platelet-derived microvesicles were identified as a major location of the plasma TF. This was confirmed by the presence of full-length TF in microvesicles acutely shedded from the activated platelets. TF was observed to be stored in the alpha-granules and the open canalicular system of resting platelets and to be exposed on the cell surface after platelet activation. Functional competence of the blood-based TF was enabled when the microvesicles and platelets adhered to neutrophils, as mediated by P-selectin and neutrophil counterreceptor (PSGL-1, CD18 integrins) interactions. Moreover, neutrophil-secreted oxygen radical species supported the intravascular TF activity. The pools of platelet and microvesicle TF contributed additively and to a comparable extent to the overall blood TF activity, indicating a substantial participation of the microvesicle TF. Our results introduce a new concept of TF-mediated coagulation crucially dependent on TF associated with microvesicles and activated platelets, which principally enables the entire coagulation system to proceed on a restricted cell surface.

Evolving role of tissue factor and its pathway inhibitor

OBJECTIVE

To review the experimental and clinical evidence of the emerging role of tissue factor in intravascular thrombosis and to examine evidence supporting the potential use of tissue factor pathway inhibitor as an antithrombotic therapeutic agent.

DATA SOURCES AND STUDY SELECTION

A PubMed search was conducted encompassing articles in the English language relating to tissue factor and tissue factor pathway inhibitor in intravascular coagulation.

CONCLUSIONS

Tissue factor, a membrane-bound procoagulant glycoprotein, is the initiator of the extrinsic clotting cascade, which is the predominant coagulation pathway in vivo. The traditional view localizes tissue factor to extravascular sites, where it remains sequestered from circulating factor VII until vascular integrity is disrupted or until tissue factor expression is induced in endothelial cells or monocytes. This perspective has been challenged since the discovery of tissue factor antigen in plasma, on circulating microparticles, and on leukocytes in whole blood. Recently, the apparent role of tissue factor has expanded with the demonstration that this molecule also functions as a signaling receptor. Recombinant tissue factor pathway inhibitor, an analogue of the physiologic inhibitor of tissue factor, is a potent inhibitor of thrombus formation in experimental models. In summary, the tissue factor pathway initiates thrombosis in vivo. In addition to its classic tissue-bound distribution, recently discovered blood-borne tissue factor may have an important procoagulant function. Despite showing promise in early human studies, a recently completed phase 3 trial of recombinant tissue factor pathway inhibitor in severe sepsis failed to show a reduction in the primary end point of 28-day all-cause mortality. Tissue factor pathway inhibitor, however, remains a plausible therapeutic agent in other conditions of increased thrombogenicity, such as acute coronary syndromes, and further studies to examine this potential are warranted.

Analysis of inflammatory gene induction by oxidized phospholipids in vivo by quantitative real-time RT-PCR in comparison with effects of LPS

Oxidized phospholipids are thought to play a role in the development of atherosclerosis and other chronic inflammatory processes. In this study, we analyzed the expression of inflammatory genes induced by oxidized L-alpha-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholin (OxPAPC) in vitro and in vivo using quantitative real-time reverse transcriptase-polymerase chain reaction (RT-PCR). Cultured human umbilical vein endothelial cells (HUVEC) and monocyte-like U937 cells were treated with OxPAPC or lipopolysaccharide (LPS) for 3 h. For in vivo studies, OxPAPC or LPS was injected intravenously into female C57Bl/6J mice and different tissues were isolated after 3 h. We found that both OxPAPC and LPS induced expression of early growth response factor 1 (EGR-1) and monocyte chemoattractant protein 1 (MCP-1) in HUVEC and of JE, the mouse homologue of MCP-1, in liver and heart. Interestingly, OxPAPC but not LPS increased expression of heme oxygenase 1 (HO-1) in U937 cells, HUVEC, aorta, heart, liver, and isolated blood cells. In contrast, E-selectin was selectively induced by LPS, but not by OxPAPC. Finally, OxPAPC-induced expression of HO-1 was blocked by a platelet-activating factor (PAF) receptor antagonist. We conclude that oxidized phospholipids are biologically active in vivo and exert a specific response inducing a pattern of genes that is different from that induced by LPS. In addition, we demonstrate that the quantitative real-time RT-PCR technology is a proper tool to investigate differential inflammatory gene induction in vivo.

Smooth muscle cell surface tissue factor pathway activation by oxidized low-density lipoprotein requires cellular lipid peroxidation

Tissue factor, which is expressed in vascular lesions, increases thrombin production, blood coagulation, and smooth muscle cell proliferation. We demonstrate that oxidized low-density lipoprotein (LDL) induces surface tissue factor pathway activity (ie, activity of the tissue factor:factor VIIa complex) on human and rat smooth muscle cells. Tissue factor messenger RNA (mRNA) was induced by oxidized LDL or native LDL; however, native LDL did not markedly increase tissue factor activity. We hypothesized that oxidized LDL mediated the activation of the tissue factor pathway via an oxidant-dependent mechanism, because antioxidants blocked the enhanced tissue factor pathway activity by oxidized LDL, but not the increased mRNA or protein induction. We separated total lipid extracts of oxidized LDL using high-performance liquid chromatography (HPLC). This yielded 2 major peaks that induced tissue factor activity. Of the known oxysterols contained in the first peak, 7α- or 7β-hydroxy or 7-ketocholesterol had no effect on tissue factor pathway activity; however, 7β-hydroperoxycholesterol increased tissue factor pathway activity without induction of tissue factor mRNA. Tertiary butyl hydroperoxide also increased tissue factor pathway activity, suggesting that lipid hydroperoxides, some of which exist in atherosclerotic lesions, activate the tissue factor pathway. We speculate that thrombin production could be elevated via a mechanism involving peroxidation of cellular lipids, contributing to arterial thrombosis after plaque rupture. Our data suggest a mechanism by which antioxidants may offer a clinical benefit in acute coronary syndrome and restenosis.

Smooth muscle cell surface tissue factor pathway activation by oxidized low-density lipoprotein requires cellular lipid peroxidation

Tissue factor, which is expressed in vascular lesions, increases thrombin production, blood coagulation, and smooth muscle cell proliferation. We demonstrate that oxidized low-density lipoprotein (LDL) induces surface tissue factor pathway activity (ie, activity of the tissue factor:factor VIIa complex) on human and rat smooth muscle cells. Tissue factor messenger RNA (mRNA) was induced by oxidized LDL or native LDL; however, native LDL did not markedly increase tissue factor activity. We hypothesized that oxidized LDL mediated the activation of the tissue factor pathway via an oxidant-dependent mechanism, because antioxidants blocked the enhanced tissue factor pathway activity by oxidized LDL, but not the increased mRNA or protein induction. We separated total lipid extracts of oxidized LDL using high-performance liquid chromatography (HPLC). This yielded 2 major peaks that induced tissue factor activity. Of the known oxysterols contained in the first peak, 7α- or 7β-hydroxy or 7-ketocholesterol had no effect on tissue factor pathway activity; however, 7β-hydroperoxycholesterol increased tissue factor pathway activity without induction of tissue factor mRNA. Tertiary butyl hydroperoxide also increased tissue factor pathway activity, suggesting that lipid hydroperoxides, some of which exist in atherosclerotic lesions, activate the tissue factor pathway. We speculate that thrombin production could be elevated via a mechanism involving peroxidation of cellular lipids, contributing to arterial thrombosis after plaque rupture. Our data suggest a mechanism by which antioxidants may offer a clinical benefit in acute coronary syndrome and restenosis.

Differences in free and total tissue factor pathway inhibitor, and tissue factor in peripheral artery disease compared to healthy controls

Tissue factor (TF) is one of the major initiators of coagulation and raised plasma levels have been found in various cardiovascular diseases. TF activity is, however, regulated by tissue factor pathway inhibitor (TFPI), and alteration in levels of TF and/or TFPI may thus relate to thrombogenesis and atherogenesis. To investigate possible abnormalities in TF and free TFPI (i.e. unbound to TF) and total TFPI among patients with peripheral artery disease (PAD), we studied 42 patients (mean age 57, 35 men) with objectively proven (by ABPI/Doppler) disease and 42 age- and sex- matched healthy controls. TF, free TFPI and total TFPI were measured in citrated plasma by ELISA. TF was higher in the patients with PAD compared to controls (275+/-122 pg/ml versus 158+/-60, P<0.0001) but levels of total TFPI were lower in the patients (43+/-10 ng/ml versus 50+/-15, P=0.021). There was no significant difference in levels of free TFPI between patients and controls (7.2+/-1.5 ng/ml in controls, 7.5+/-1. 6 among patients, P=0.39). Within the control patients, levels of free and total TFPI were significantly correlated (Spearman r=0.51, P=0.001) but in the patients with PAD this correlation was poor (r=0. 21, P=0.178). We suggest that reduced levels of total TFPI and raised levels of TF may contribute to the process of atherogenesis and the increased risk of thrombosis among patients with cardiovascular disease.

The in vivo kinetics of tissue factor messenger RNA expression during human endotoxemia: relationship with activation of coagulation

Triggering of the tissue factor (TF)-dependent coagulation pathway is considered to underlie the generation of a procoagulant state during endotoxemia. To determine the in vivo pattern of monocytic TF messenger RNA (mRNA) expression during endotoxemia, 10 healthy volunteers were injected with lipopolysaccharide (LPS, 4 ng/kg) and blood was collected before and 0.5, 1, 2, 3, 4, 6, 8, and 24 hours after LPS administration. Total blood RNA was isolated and amplified by NASBA (nucleic acid sequence-based amplification), followed by quantitation of TF mRNA by an electrochemiluminescence (ECL) assay. To compare the pattern of coagulation activation with the kinetics of monocytic TF mRNA expression, we measured plasma levels of markers of thrombin generation, thrombin-antithrombin (TAT) complexes, and prothrombin fragment 1 + 2 (F1 + 2). Baseline value (mean ± SEM) of the number of TF mRNA molecules per monocytic cell was 0.08 ± 0.02. A progressive and significant (P < .0001) increase in TF expression was observed after LPS injection (+0.5 hour: 0.3 ± 0.1, +1 hour: 1.3 ± 0.9, +2 hours: 4.1 ± 0.9), peaking at +3 hours (10 ± 1.9 TF mRNA molecules per monocyte). As TF mRNA levels increased, thrombin generation was augmented. Peak levels of TAT and F1 + 2 were reached later (at t +4 hours) than those of TF mRNA. TF mRNA, TAT, and F1 + 2 levels returned to baseline after 24 hours. In conclusion, we used a NASBA/ECL-based technique to quantify TF mRNA in whole blood during human endotoxemia and observed a 125-fold increase in TF mRNA levels. Our data demonstrate a pivotal role for enhanced TF gene activity in the activation of coagulation after LPS challenge.

The in vivo kinetics of tissue factor messenger RNA expression during human endotoxemia: relationship with activation of coagulation

Triggering of the tissue factor (TF)-dependent coagulation pathway is considered to underlie the generation of a procoagulant state during endotoxemia. To determine the in vivo pattern of monocytic TF messenger RNA (mRNA) expression during endotoxemia, 10 healthy volunteers were injected with lipopolysaccharide (LPS, 4 ng/kg) and blood was collected before and 0.5, 1, 2, 3, 4, 6, 8, and 24 hours after LPS administration. Total blood RNA was isolated and amplified by NASBA (nucleic acid sequence-based amplification), followed by quantitation of TF mRNA by an electrochemiluminescence (ECL) assay. To compare the pattern of coagulation activation with the kinetics of monocytic TF mRNA expression, we measured plasma levels of markers of thrombin generation, thrombin-antithrombin (TAT) complexes, and prothrombin fragment 1 + 2 (F1 + 2). Baseline value (mean ± SEM) of the number of TF mRNA molecules per monocytic cell was 0.08 ± 0.02. A progressive and significant (P &lt; .0001) increase in TF expression was observed after LPS injection (+0.5 hour: 0.3 ± 0.1, +1 hour: 1.3 ± 0.9, +2 hours: 4.1 ± 0.9), peaking at +3 hours (10 ± 1.9 TF mRNA molecules per monocyte). As TF mRNA levels increased, thrombin generation was augmented. Peak levels of TAT and F1 + 2 were reached later (at t +4 hours) than those of TF mRNA. TF mRNA, TAT, and F1 + 2 levels returned to baseline after 24 hours. In conclusion, we used a NASBA/ECL-based technique to quantify TF mRNA in whole blood during human endotoxemia and observed a 125-fold increase in TF mRNA levels. Our data demonstrate a pivotal role for enhanced TF gene activity in the activation of coagulation after LPS challenge.

Native and oxidized low density lipoprotein induction of tissue factor gene expression in smooth muscle cells is mediated by both Egr-1 and Sp1

Tissue factor, in association with factor VIIa, initiates the coagulation cascade. We studied the influences of two pathophysiological stimuli, native (unmodified) and oxidized low density lipoprotein, on tissue factor gene expression in a cell important in vascular remodeling and vascular diseases, the smooth muscle cell. Our results demonstrated that both lipoproteins significantly induced tissue factor gene expression in rat aortic smooth muscle cells; oxidized low density lipoprotein was slightly more potent. Both lipoproteins increased tissue factor mRNA in a concentration- and time-dependent manner. Results from nuclear run-on assays and mRNA stability experiments indicated that increased tissue factor mRNA accumulation in response to the lipoproteins was principally controlled at the transcriptional level. By using lipid extracts of low density lipoprotein or methylation of the intact lipoprotein to block receptor recognition, we showed that this lipoprotein induced tissue factor mRNA via both receptor-independent and receptor-augmented pathways. Transfection studies using a series of deleted tissue factor promoters revealed that a -143- to +106-base pair region of the rat tissue factor promoter contained regulatory elements required for lipoprotein-mediated induction. Electrophoretic mobility shift assays showed that the binding activities of the transcription factor Egr-1, but not Sp1, were markedly elevated in response to these lipoproteins. Transfection of site-directed mutants of the tissue factor (TF) promoter demonstrated that not only Egr-1 but also Sp1 cis-acting elements in the TF (-143) promoter construct were necessary for optimal TF gene induction. Our data show for the first time that both low density lipoprotein and oxidized low density lipoprotein induce tissue factor gene expression in smooth muscle cells and that this tissue factor gene expression is mediated by both Egr-1 and Sp1 transcription factors.

Lipoproteins and the haemostatic system in atherothrombotic disorders

The remarkable extent to which interactions between the plasma lipoproteins, inflammatory factors and the haemostatic system contribute to the response to injury and growth of the plaque in atherosclerosis is being increasingly documented. High plasma concentrations of very-low density (VLDL) and low-density lipoproteins (LDL), together with oxidatively modified LDL and lipoprotein (a), can induce responses in vascular endothelial cells, smooth muscle cells, monocytes/macrophages, platelets, neutrophils and humoral factors that are in a variety of ways both procoagulant and antifibrinolytic. Plasma high-density lipoproteins appear to promote anticoagulant mechanisms. Post-prandial lipaemia is associated with transient changes in factor VII which may be indicative of temporary hypercoagulability. The cellular and humoral effects of LDL and VLDL on the haemostatic system appear to be largely reversible, which may help to explain the prompt improvement in the atherothrombotic state gained by correction of hyperlipidaemia.