Tissue factor pathway inhibitor is expressed by human monocyte-derived macrophages : relationship to tissue factor induction by cholesterol and oxidized LDL

Macrophage fate: to kill or not to kill?

Macrophages are dynamic innate immune cells that either reside in tissue, serving as sentinels, or recruited as monocytes from bone marrow into inflamed and infected tissue. In response to cues in the tissue microenvironment (TME), macrophages polarize on a continuum toward M1 or M2 with diverse roles in progression and resolution of disease. M1-like macrophages exhibit proinflammatory functions with antimicrobial and anti-tumorigenic activities, while M2-like macrophages have anti-inflammatory functions that generally resolve inflammatory responses and orchestrate a tissue healing process. Given these opposite phenotypes, proper spatiotemporal coordination of macrophage polarization in response to cues within the TME is critical to effectively resolve infectious disease and regulate wound healing. However, if this spatiotemporal coordination becomes disrupted due to persistent infection or dysregulated coagulation, macrophages' inappropriate response to these cues will result in the development of diseases with clinically unfavorable outcomes. Since plasticity and heterogeneity are hallmarks of macrophages, they are attractive targets for therapies to reprogram toward specific phenotypes that could resolve disease and favor clinical prognosis. In this review, we discuss how basic science studies have elucidated macrophage polarization mechanisms in TMEs during infections and inflammation, particularly coagulation. Therefore, understanding the dynamics of macrophage polarization within TMEs in diseases is important in further development of targeted therapies.

The Tissue Factor Pathway in Cancer: Overview and Role of Heparan Sulfate Proteoglycans

Historically, the only focus on tissue factor (TF) in clinical pathophysiology has been on its function as the initiation of the extrinsic coagulation cascade. This obsolete vessel-wall TF dogma is now being challenged by the findings that TF circulates throughout the body as a soluble form, a cell-associated protein, and a binding microparticle. Furthermore, it has been observed that TF is expressed by various cell types, including T-lymphocytes and platelets, and that certain pathological situations, such as chronic and acute inflammatory states, and cancer, may increase its expression and activity. Transmembrane G protein-coupled protease-activated receptors can be proteolytically cleaved by the TF:FVIIa complex that develops when TF binds to Factor VII (PARs). The TF:FVIIa complex can activate integrins, receptor tyrosine kinases (RTKs), and PARs in addition to PARs. Cancer cells use these signaling pathways to promote cell division, angiogenesis, metastasis, and the maintenance of cancer stem-like cells. Proteoglycans play a crucial role in the biochemical and mechanical properties of the cellular extracellular matrix, where they control cellular behavior via interacting with transmembrane receptors. For TFPI.fXa complexes, heparan sulfate proteoglycans (HSPGs) may serve as the primary receptor for uptake and degradation. The regulation of TF expression, TF signaling mechanisms, their pathogenic effects, and their therapeutic targeting in cancer are all covered in detail here.

Knockdown screening of chromatin binding and regulatory proteins in zebrafish identified Suz12b as a regulator of tfpia and an antithrombotic drug target

Tissue factor pathway inhibitor (TFPI) is an anticoagulant protein that inhibits factor VIIa and Xa in the coagulation cascade. It has been shown that forkhead box P3 protein is a TFPI transcriptional repressor. However, there are no studies on chromatin remodeling that control TFPI expression. We hypothesized that the genome-wide knockdowns of the chromatin binding and regulatory proteins (CBRPs) in zebrafish could identify novel tfpia gene regulators. As an initial step, we selected 69 CBRP genes from the list of zebrafish thrombocyte-expressed genes. We then performed a 3-gene piggyback knockdown screen of these 69 genes, followed by quantification of tfpia mRNA levels. The results revealed that knockdown of brd7, ing2, ing3, ing4, and suz12b increased tfpia mRNA levels. The simultaneous knockdown of these 5 genes also increased tfpia mRNA levels. We also performed individual gene and simultaneous 5-gene knockdowns on the 5 genes in zebrafish larvae. We found that after laser injury, it took a longer time for the formation of the thrombus to occlude the caudal vessel compared to the control larvae. We then treated the larvae and adults with a chemical UNC6852 known to proteolytically degrade polycomb repressor complex 2, where SUZ12 is a member, and observed prolongation of time to occlude (TTO) the caudal vein after laser injury and increased tfpia mRNA levels in larvae and adults, respectively. In summary, our results have identified novel epigenetic regulators for tfpia and exploited this information to discover a drug that enhances tfpia mRNA levels and prolongation of TTO. This discovery provides the basis for testing whether UNC6852 could be used as an antithrombotic drug. This approach could be used to study the regulation of other plasma proteins, including coagulant and anticoagulant factors.

Low-density lipoproteins cause atherosclerotic cardiovascular disease: pathophysiological, genetic, and therapeutic insights: a consensus statement from the European Atherosclerosis Society Consensus Panel

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Nonlinear optical responses of oxidized low-density lipoprotein: Cutoff point for z-scan peak-valley distance

The development of new methods to assess biomarkers of cardiovascular disease is currently a subject of scientific research. This article broadens our view of nonlinear optical responses of oxidized low density lipoprotein (LDL) evaluated using the Z-scan peak-valley distance and proposes a cutoff point. We investigated the association of peak-valley distance and some cardiovascular risk factors related with sociodemographic, clinical and anthropometric profiles and plasma biomarkers such as lipid and glucose profile, apolipoprotein, lipoprotein subfractions and omega 3 fatty acids. Z-scan analysis was performed using isolated LDL after ultracentrifugation in human blood samples collected after fasting. Peak-valley distance is a parameter that decreases directly depending on the oxidizability of LDL. As peak-valley distance was associated with relevant biomarkers of cardiovascular risk, we tested cutoff points for categorization and the best results were obtained using percentile < 75 (Low_z-scan) and percentile ≥ 75 (High_z-scan). The regression logistic models tested after establishing the cutoff point for peak-valley distance showed that increased levels of plasma high-density lipoprotein cholesterol, apolipoprotein A-I, large high-density lipoprotein subfractions and docosahexaenoic acid are directly associated with High_Z-scan. Conversely, high levels of small LDL were associated with decreased odds of presenting High_Z-scan. In conclusion, the cutoff point for peak-valley distance was able to identify atherogenic characteristics of LDL and its relationship with some parameters of high-density lipoprotein functionality.

Endogenous tissue factor pathway inhibitor in vascular smooth muscle cells inhibits arterial thrombosis

Tissue factor pathway inhibitor (TFPI) is the main inhibitor of tissue factor-mediated coagulation. TFPI is expressed by endothelial and smooth muscle cells in the vasculature. Endothelium-derived TFPI has been reported to play a regulatory role in arterial thrombosis. However, the role of endogenous TFPI in vascular smooth muscle cells (VSMCs) in thrombosis and vascular disease development has yet to be elucidated. In this TFPI^Flox mice crossbred with Sma-Cre mice were utilized to establish TFPI conditional knockout mice and to examine the effects of VSMC-directed TFPI deletion on development, hemostasis, and thrombosis. The mice with deleted TFPI in VSMCs (TFPI^Sma) reproduced viable offspring. Plasma TFPI concentration was reduced 7.2% in the TFPI^Sma mice compared with TFPI^Flox littermate controls. Plasma TFPI concentration was also detected in the TFPI^Tie2 (mice deleted TFPI in endothelial cells and cells of hematopoietic origin) mice. Plasma TFPI concentration of the TFPI^Tie2 mice was 80.4% lower (P < 0.001) than that of the TFPI^Flox mice. No difference in hemostatic measures (PT, APTT, and tail bleeding) was observed between TFPI^Sma and TFPI^Flox mice. However, TFPI^Sma mice had increased ferric chloride-induced arterial thrombosis compared with TFPI^Flox littermate controls. Taken together, these data indicated that endogenous TFPI from VSMCs inhibited ferric chloride-induced arterial thrombosis without causing hemostatic effects.

Peroxisome Proliferator-Activated Receptor γ Induces the Expression of Tissue Factor Pathway Inhibitor-1 (TFPI-1) in Human Macrophages

Tissue factor (TF) is the initiator of the blood coagulation cascade after interaction with the activated factor VII (FVIIa). Moreover, the TF/FVIIa complex also activates intracellular signalling pathways leading to the production of inflammatory cytokines. The TF/FVIIa complex is inhibited by the tissue factor pathway inhibitor-1 (TFPI-1). Peroxisome proliferator-activated receptor gamma (PPARγ) is a transcription factor that, together with PPARα and PPARβ/δ, controls macrophage functions. However, whether PPARγ activation modulates the expression of TFP1-1 in human macrophages is not known. Here we report that PPARγ activation increases the expression of TFPI-1 in human macrophages in vitro as well as in vivo in circulating peripheral blood mononuclear cells. The induction of TFPI-1 expression by PPARγ ligands, an effect shared by the activation of PPARα and PPARβ/δ, occurs also in proinflammatory M1 and in anti-inflammatory M2 polarized macrophages. As a functional consequence, treatment with PPARγ ligands significantly reduces the inflammatory response induced by FVIIa, as measured by variations in the IL-8, MMP-2, and MCP-1 expression. These data identify a novel role for PPARγ in the control of TF the pathway.

7-Ketocholesterol induces ATM/ATR, Chk1/Chk2, PI3K/Akt signalings, cytotoxicity and IL-8 production in endothelial cells

Cardiovascular diseases (atherosclerosis, stroke, myocardiac infarction etc.) are the major systemic diseases of elder peoples in the world. This is possibly due to increased levels of oxidized low-density lipoproteins (oxLDLs) such as 7-ketocholesterol (7-KC) and lysophosphatidylcholine (LPC) that damage vascular endothelial cells, induce inflammatory responses, to elevate the risk of cardiovascular diseases, Alzheimer's disease, and age-related macular degeneration. However the toxic effects of 7-KC on endothelial cells are not known. In this study, 7-KC showed cytotoxicity to endothelial cells at concentrations higher than 10 µg/ml. 7-KC stimulated ATM/Chk2, ATR-Chk1 and p53 signaling pathways in endothelial cells. 7-KC also induced G0/G1 cell cycle arrest and apoptosis with an inhibition of Cyclin dependent kinase 1 (Cdk1) and cyclin B1 expression. Secretion and expression of IL-8 in endothelial cells were stimulated by 7-KC. 7-KC further induced intracellular ROS production as shown by increase in DCF fluorescence and Akt phosphorylation. LY294002 attenuated the 7-KC-induced apoptosis and IL-8 mRNA expression of endothelial cells. These results indicate that oxLDLs such as 7-KC may contribute to the pathogenesis of atherosclerosis, thrombosis and cardiovascular diseases by induction of endothelial damage, apoptosis and inflammatory responses. These events are associated with ROS production, activation of ATM/Chk2, ATR/Chk1, p53 and PI3K/Akt signaling pathways.

The antithrombotic effects of statins

Hypercholesterolemia is considered the primary risk factor for cardiovascular disease. An estimated 200 million prescriptions are issued per year for statins to treat hypercholesterolemia. Importantly, statins have additional beneficial effects independent of their effects on lipids. Recent studies have shown that statins reduce thrombosis via multiple pathways, including inhibiting platelet activation and reducing the pathologic expression of the procoagulant protein tissue factor. Many of the antithrombotic effects of statins are attributed to inhibiting prenylation of RhoA and effects on other intracellular signaling molecules such as NF-κB and KLF2. These antithrombotic activities of statins likely contribute to the ability of statins to reduce the incidence of cardiovascular death.

Biology of tissue factor pathway inhibitor

Recent studies of the anticoagulant activities of the tissue factor (TF) pathway inhibitor (TFPI) isoforms, TFPIα and TFPIβ, have provided new insight into the biochemical and physiological mechanisms that underlie bleeding and clotting disorders. TFPIα and TFPIβ have tissue-specific expression patterns and anticoagulant activities. An alternative splicing event in the 5' untranslated region allows for translational regulation of TFPIβ expression. TFPIα has 3 Kunitz-type inhibitor domains (K1, K2, K3) and a basic C terminus, whereas TFPIβ has the K1 and K2 domains attached to a glycosylphosphatidyl inositol-anchored C terminus. TFPIα is the only isoform present in platelets, whereas endothelial cells produce both isoforms, secreting TFPIα and expressing TFPIβ on the cell surface. TFPIα and TFPIβ inhibit both TF-factor VIIa-dependent factor Xa (FXa) generation and free FXa. Protein S enhances FXa inhibition by TFPIα. TFPIα produces isoform-specific inhibition of prothrombinase during the initiation of coagulation, an anticoagulant activity that requires an exosite interaction between its basic C terminus and an acidic region in the factor Va B domain. Platelet TFPIα may be optimally localized to dampen initial thrombin generation. Similarly, endothelial TFPIβ may be optimally localized to inhibit processes that occur when endothelial TF is present, such as during the inflammatory response.

Quantitation of nanoparticle accumulation in flow using optimized microfluidic chambers

BACKGROUND

The vascular cell adhesion molecule-1 (VCAM-1) targeting peptide sequence, VHPKQHR, is a promising moiety for targeting atherosclerosis through incorporation into nanoparticles such as dendrimers and liposomes.

PURPOSE

We aim to develop VCAM-1-targeted nanoparticles that effectively accumulate on the endothelium under shear conditions and to develop robust microfluidic chambers able to house sufficient cells for flow cytometric measurements.

METHODS

Carboxyfluorescein-labeled monomeric VHP-peptide, tetrameric VHP-dendrimers (bisbidentate or radial architecture, with or without N-terminal acetylation) and VHP-peptide liposomes were prepared. Human umbilical vein endothelial cells were treated with nanoparticles under 0 or 2.9 dyne/cm(2) shear, and particle binding was quantified. Flow chambers cured at various temperatures, with or without glass backings were fabricated, characterized for deformation and applied in experiments.

RESULTS

Although liposomes accumulated with highest efficiency, dendrimers also demonstrated specific binding. N-terminal acetylation significantly reduced dendrimer binding, and despite shorter movement range, bisbidentate dendrimers outperformed radial dendrimers, suggesting multiple epitope presence within its estimated arm-span of 57 Å. Under shear, while liposome binding increased 300%, dendrimer binding to cells decreased 65%. Through higher temperature curing and glass backing insertion, polydimethylsiloxane flow chambers maintaining rectangular cross-section with aspect-ratio as low as 1:111 were achieved.

CONCLUSION

Optimized dendrimers and liposomal nanocarriers specifically accumulated onto cells within microfluidic chambers.

Plasma tissue factor pathway inhibitor levels in angiographically defined coronary artery disease among saudis

OBJECTIVES

This study was aimed to determine plasma levels of total (TFPI-T) and free (TFPI-F) tissue factor pathway inhibitor, plasminogen activator inhibitor-1 (PAI-1), and tissue plasminogen activator (t-PA) in a cohort of Saudi patients with chronic stable angiographically defined coronary artery disease (CAD) and to determine its correlation with its severity.

METHODS

This cross sectional study was conducted in the department of physiology and department of cardiology, College of Medicine, and King Khalid University Hospital and King Saud University, Riyadh. Sixty known cases of CAD who had undergone angiography (35 males and 25 females) were selected. A control group included 39 (20 males and 19 females) healthy subjects. Fasting venous blood samples were analyzed for total (TFPI-T) and free (TFPI-F) tissue factor pathway inhibitor, plasminogen activator inhibitor-1 (PAI-1), and tissue plasminogen activator (t-PA). Gensini scores and vessel scores were determined for assessing CAD severity.

RESULTS

There were non-significant differences between age, body mass index (BMI) and Blood pressure between the controls and CAD subjects. A comparison of hemostatic markers between control and CAD patients showed significantly higher levels of Fibrinogen, PAI-1, TFPI-T and TFPI-F in CAD patients compared to control subjects. But there was no difference in plasma t-PA levels. TFPI-T had a significant positive correlation with severity of disease determined by Gensini Scores (r=0.344; p=0.006) and vessel scores (r=0.338; p=0.015).

CONCLUSION

Plasma levels of total tissue factor pathway inhibitor are significantly related with the presence and severity of CAD. Elevated levels of TFPI-T may be considered as useful diagnostic and prognostic markers in patients with CAD.

The role of tissue factor pathway inhibitor in atherosclerosis and arterial thrombosis

Tissue factor pathway inhibitor (TFPI) is the main inhibitor of tissue factor (TF)-mediated coagulation. In atherosclerotic plaques TFPI co-localizes with TF, where it is believed to play an important role in attenuating TF activity. Findings in animal models such as TFPI knockout models and gene transfer models are consistent on the role of TFPI in arterial thrombosis as they reveal an active role for TFPI in attenuating arterial thrombus formation. In addition, ample experimental evidence exists indicating that TFPI has inhibitory effects on both smooth muscle cell migration and proliferation, both which are recognized as important pathological features in atherosclerosis development. Nonetheless, the clinical relevance of these antithrombotic and atheroprotective effects remains unclear. Paradoxically, the majority of clinical studies find increased instead of decreased TFPI antigen and activity levels in atherothrombotic disease, particularly in atherosclerosis and coronary artery disease (CAD). Increased TFPI levels in cardiovascular disease might result from complex interactions with established cardiovascular risk factors, such as hypercholesterolemia, diabetes and smoking. Moreover, it is postulated that increased TFPI levels reflect either the amount of endothelial perturbation and platelet activation, or a compensatory mechanism for the increased procoagulant state observed in cardiovascular disease. In all, the prognostic value of plasma TFPI in cardiovascular disease remains to be established. The current review focuses on TFPI in clinical studies of asymptomatic and symptomatic atherosclerosis, coronary artery disease and ischemic stroke, and discusses potential atheroprotective actions of TFPI.

Hemostatic effect of a monoclonal antibody mAb 2021 blocking the interaction between FXa and TFPI in a rabbit hemophilia model

Hemophilia is treated by IV replacement therapy with Factor VIII (FVIII) or Factor IX (FIX), either on demand to resolve bleeding, or as prophylaxis. Improved treatment may be provided by drugs designed for subcutaneous and less frequent administration with a reduced risk of inhibitor formation. Tissue factor pathway inhibitor (TFPI) down-regulates the initiation of coagulation by inhibition of Factor VIIa (FVIIa)/tissue factor/Factor Xa (FVIIa/TF/FXa). Blockage of TFPI inhibition may facilitate thrombin generation in a hemophilic setting. A high-affinity (KD = 25pM) mAb, mAb 2021, against TFPI was investigated. Binding of mAb 2021 to TFPI effectively prevented inhibition of FVIIa/TF/FXa and improved clot formation in hemophilia blood and plasma. The binding epitope on the Kunitz-type protease inhibitor domain 2 of TFPI was mapped by crystallography, and showed an extensive overlap with the FXa contact region highlighting a structural basis for its mechanism of action. In a rabbit hemophilia model, an intravenous or subcutaneous dose significantly reduced cuticle bleeding. mAb 2021 showed an effect comparable with that of rFVIIa. Cuticle bleeding in the model was reduced for at least 7 days by a single intravenous dose of mAb 2021. This study suggests that neutralization of TFPI by mAb 2021 may constitute a novel treatment option in hemophilia.

Interleukin-6 protects human macrophages from cellular cholesterol accumulation and attenuates the proinflammatory response

Cholesterol-laden monocyte-derived macrophages are phagocytic cells characteristic of early and advanced atherosclerotic lesions. Interleukin-6 (IL-6) is a macrophage secretory product that is abundantly expressed in atherosclerotic plaques but whose precise role in atherogenesis is unclear. The capacity of macrophages to clear apoptotic cells, through the efferocytosis mechanism, as well as to reduce cellular cholesterol accumulation contributes to prevent plaque progression and instability. By virtue of its capacity to promote cellular cholesterol efflux from phagocyte-macrophages, ABCA1 was reported to reduce atherosclerosis. We demonstrated that lipid loading in human macrophages was accompanied by a strong increase of IL-6 secretion. Interestingly, IL-6 markedly induced ABCA1 expression and enhanced ABCA1-mediated cholesterol efflux from human macrophages to apoAI. Stimulation of ABCA1-mediated cholesterol efflux by IL-6 was, however, abolished by selective inhibition of the Jak-2/Stat3 signaling pathway. In addition, we observed that the expression of molecules described to promote efferocytosis, i.e. c-mer proto-oncogene-tyrosine kinase, thrombospondin-1, and transglutaminase 2, was significantly induced in human macrophages upon treatment with IL-6. Consistent with these findings, IL-6 enhanced the capacity of human macrophages to phagocytose apoptotic cells; moreover, we observed that IL-6 stimulates the ABCA1-mediated efflux of cholesterol derived from the ingestion of free cholesterol-loaded apoptotic macrophages. Finally, the treatment of human macrophages with IL-6 led to the establishment of an anti-inflammatory cytokine profile, characterized by an increased secretion of IL-4 and IL-10 together with a decrease of that of IL-1β. Taken together, our results indicate that IL-6 favors the elimination of excess cholesterol in human macrophages and phagocytes by stimulation of ABCA1-mediated cellular free cholesterol efflux and attenuates the macrophage proinflammatory phenotype. Thus, high amounts of IL-6 secreted by lipid laden human macrophages may constitute a protective response from macrophages to prevent accumulation of cytotoxic-free cholesterol. Such a cellular recycling of free cholesterol may contribute to reduce both foam cell formation and the accumulation of apoptotic bodies as well as intraplaque inflammation in atherosclerotic lesions.

Oxidized low-density lipoprotein and tissue factor are involved in monocrotaline/lipopolysaccharide-induced hepatotoxicity

These studies were aimed at characterizing an animal model of inflammation-induced hepatotoxicity that would mimic features of idiosyncratic liver toxicity observed in humans. An attempt was made to identify oxidative damage and the involvement of coagulation system in liver after monocrotaline (MCT) administration under the modest inflammatory condition induced by lipopolysaccharide (LPS) exposure. Mice were given MCT (200 mg/kg) or an equivalent volume of sterile saline (Veh.) po followed 4 h later by ip injection of LPS (6 mg/kg) or vehicle. Mice co-treated with MCT and LPS showed increased plasma alanine aminotransferase (ALT), decrease in platelet number, and a reduction in hematocrit. Accumulation of oxidized low-density lipoprotein (ox-LDL) was remarkably higher in the liver sections of mice co-treated with MCT and LPS compared to those given MCT or LPS alone. A similar trend was observed in the expression of CXCL16 receptor in the same liver sections. Elevated expression of tissue factor (TF) and fibrinogen was also observed in the liver sections of MCT/LPS co-treated mice. The in vitro results showed that incubation of HepG2 cells with CXCL16 antibody strongly diminished uptake of ox-LDL. Expression of ox-LDL, CXCL16, and TF represents an early event in the onset of hepatotoxicity induced by MCT/LPS; thus, it may contribute to our understanding of idiosyncratic liver injury and points to potential targets for protection or intervention.

Metformin, an antidiabetic agent, suppresses the production of tumor necrosis factor and tissue factor by inhibiting early growth response factor-1 expression in human monocytes in vitro

Metformin, an antidiabetic agent, has been shown to reduce atherothrombotic disease in diabetic patients independent of antihyperglycemic effect. Recent studies have demonstrated that metformin attenuates the proinflammatory responses in human vascular wall cells and macrophages. However, the detailed molecular mechanisms underlying these therapeutic effects remain unclear. In the present study, we investigated the effects of metformin on tumor necrosis factor (TNF) production and tissue factor (TF) expression in isolated human monocytes stimulated with lipopolysaccharide (LPS) or oxidized low-density lipoprotein (oxLDL). Metformin significantly inhibited both TNF production and TF expression in isolated human monocytes stimulated with LPS or oxLDL. Metformin also significantly inhibited TNF and TF mRNA in human monocytes stimulated with LPS. Although metformin did not inhibit the activation of either nuclear factor-kappaB or activator protein-1, it inhibited the expression of early growth response factor-1 (Egr-1) and phosphorylation of extracellular signal-regulated protein kinase (ERK) 1/2 in monocytes stimulated with LPS or oxLDL. These results suggest that metformin may attenuate the inflammatory responses, at least in part, by suppressing the production of both TNF and TF through the inhibition of the ERK1/2-Egr-1 pathway in human monocytes.

Recombinant tissue factor pathway inhibitor induces apoptosis in cultured rat mesangial cells via its Kunitz-3 domain and C-terminal through inhibiting PI3-kinase/Akt pathway

Tissue factor pathway inhibitor (TFPI) is an endogenous inhibitor of tissue factor (TF) induced coagulation. In addition to its anticoagulation activity, TFPI has other functions such as antiproliferation and inducing apoptosis. In the present study, we investigated whether or not TFPI induced apoptosis in cultured rat mesangial cells (MsCs) and the possible signal pathway that involved in the apoptotic process. We demonstrated that recombinant TFPI (rTFPI) induced apoptosis in cultured MsCs via its Kunitz-3 domain and C-terminal in a dose- and time-dependent manner by Hoechst 33258 assay, flow cytometry, nucleosomal laddering of DNA, caspase 3 assay. Because the serine/threonine protein kinase Akt has attracted attention as a mediator of survival (anti-apoptotic) signal in MsCs, we investigated the expression of phosphospecific-Akt and its downstream signal phospho-IkappaB-alpha and some other signal molecules like Fas and bcl-2. The results indicated that the process of apoptosis triggered by rTFPI is, at least in part, actively conducted by rat MsCs possibly through PI3-Kinase-Akt signal pathway not by binding to tissue factor. Our findings suggest that rTFPI has the potential usefulness in inducing apoptosis of MsCs under inflammatory conditions.

Molecular imaging and therapy of atherosclerosis with targeted nanoparticles

Advances in bionanotechnology are poised to impact the field of cardiovascular diagnosis and therapy for decades to come. This review seeks to illustrate selected examples of newly developed diagnostic and therapeutic nanosystems that have been evaluated in experimental atherosclerosis, thrombosis, and vascular biology. We review a variety of nanotechnologies that are capable of detecting early cardiovascular pathology, as well as associated imaging approaches and conjunctive strategies for site-targeted treatment with nanoparticle delivery systems.

Dyslipidemia shifts the tissue factor/tissue factor pathway inhibitor balance toward increased thrombogenicity in atherosclerotic plaques: evidence for a corrective effect of statins

BACKGROUND

Tissue factor (TF) is a key mediator of atherosclerotic plaque thrombogenicity and may be regulated by plaque TF pathway inhibitor (TFPI). High atherogenic lipoproteins are a well-known arterial risk factor, but their effects on the TF/TFPI balance in atherosclerotic plaques, as well as those of widely used lipid-lowering agents such as statins, are incompletely understood.

OBJECTIVES

We analyzed the TF/TFPI balance in carotid plaques from 86 patients, according to the presence of dyslipidemia and statin therapy.

RESULTS

In patients with untreated dyslipidemia (ApoB/ApoA1 ratio >0.7) (D+) (n=44), TF antigen (TF) tended to be higher than in those without dyslipidemia (D-) (n=16). In patients with statins (S+) (n=26), TF was lower than in D+ (p=0.02) and similar to that of D- patients. TFPI antigen was higher in D- than in D+ and S+ patients (p<or=0.02). As a result, the TF/TFPI (mol/mol) ratio was higher in D+ than in D- or S+ patients (p<or=0.005). TF activity correlated to TF/TFPI ratio (p<0.0001), and was higher in the D+ than in the D- and in the S+ patients (p=0.02). Among analyzed clinical risk factors and biological parameters, including CRP, dyslipidemia was the only independent predictor for low plaque TFPI and high TF/TFPI ratio. Histochemistry showed that TF and TFPI were mainly expressed in macrophage-rich regions surrounding the lipid-rich core in the three groups.

CONCLUSIONS

These results indicate that dyslipidemia is associated with a shift of the TF/TFPI balance and of TF activity toward higher plaque thrombotic potential. Statins correct this equilibrium mainly by decreasing plaque TF together with blood atherogenic lipoproteins.

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.

Quantitative ?magnetic resonance immunohistochemistry? with ligand-targeted19F nanoparticles

Unstable atherosclerotic plaques exhibit microdeposits of fibrin that may indicate the potential for a future rupture. However, current methods for evaluating the stage of an atherosclerotic lesion only involve characterizing the level of vessel stenosis, without delineating which lesions are beginning to rupture. Previous work has shown that fibrin-targeted, liquid perfluorocarbon nanoparticles, which carry a high payload of gadolinium, have a high sensitivity and specificity for detecting fibrin with clinical (1)H MRI. In this work, the perfluorocarbon content of the targeted nanoparticles is exploited for the purposes of (19)F imaging and spectroscopy to demonstrate a method for quantifiable molecular imaging of fibrin in vitro at 4.7 T. Additionally, the quantity of bound nanoparticles formulated with different perfluorocarbon species was calculated using spectroscopy. Results indicate that the high degree of nanoparticle binding to fibrin clots and the lack of background (19)F signal allow accurate quantification using spectroscopy at 4.7 T, as corroborated with proton relaxation rate measurements at 1.5 T and trace element (gadolinium) analysis. Finally, the extension of these techniques to a clinically relevant application, the evaluation of the fibrin burden within an ex vivo human carotid endarterectomy sample, demonstrates the potential use of these particles for uniquely identifying unstable atherosclerotic lesions in vivo.

Role of monocytes in atherogenesis

This review focuses on the role of monocytes in the early phase of atherogenesis, before foam cell formation. An emerging consensus underscores the importance of the cellular inflammatory system in atherogenesis. Initiation of the process apparently hinges on accumulating low-density lipoproteins (LDL) undergoing oxidation and glycation, providing stimuli for the release of monocyte attracting chemokines and for the upregulation of endothelial adhesive molecules. These conditions favor monocyte transmigration to the intima, where chemically modified, aggregated, or proteoglycan- or antibody-complexed LDL may be endocytotically internalized via scavenger receptors present on the emergent macrophage surface. The differentiating monocytes in concert with T lymphocytes exert a modulating effect on lipoproteins. These events propagate a series of reactions entailing generation of lipid peroxides and expression of chemokines, adhesion molecules, cytokines, and growth factors, thereby sustaining an ongoing inflammatory process leading ultimately to lesion formation. New data emerging from studies using transgenic animals, notably mice, have provided novel insights into many of the cellular interactions and signaling mechanisms involving monocytes/macrophages in the atherogenic processes. A number of these studies, focusing on mechanisms for monocyte activation and the roles of adhesive molecules, chemokines, cytokines and growth factors, are addressed in this review.

Simvastatin inhibits expression of tissue factor in advanced atherosclerotic lesions of apolipoprotein E deficient mice independently of lipid lowering: potential role of simvastatin-mediated inhibition of Egr-1 expression and activation

Recent studies suggest that the beneficial effects of 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase inhibitors (statins) in reducing cardiovascular events may in part, be independent of their capacity to lower plasma lipids. To test this hypothesis, simvastatin (50 mg/kg/d) was administered to 30-week-old apolipoprotein E deficient mice (apo E-/-) for 12, 18 and 24 weeks. In contrast to other experimental models and humans, simvastatin treatment increases plasma cholesterol levels in apo E-/- mice. Quantitative real-time polymerase chain reaction was used to quantify expression of tissue factor (TF) and monocyte chemoattractant protein-1 (MCP-1) in the aorta of each mouse. Expression of TF was reduced to 34, 24, and 13% of control levels at 12, 18 and 24 weeks, respectively, of simvastatin administration. Advanced lesions in the innominate arteries of the simvastatin treated mice had reduced levels of TF, fewer macrophages and reduced expression of early growth response-1 (Egr-1). In vitro studies in mouse macrophages demonstrated decreased lipopolysaccharide induced binding of nuclear proteins to the Egr-1 consensus DNA sequence following pretreatment with simvastatin. RNA levels for MCP-1 were reduced to 30% of control values following 24 weeks of simvastatin treatment. In conclusion, these data suggest that chronic administration of simvastatin to older apo E-/- mice can inhibit the expression of pro-thrombotic/pro-inflammatory genes within established atherosclerotic lesions via mechanisms that are independent of reductions in plasma lipids.

Demonstration of inducible TFPI-2 mRNA synthesis in BeWo and JEG-3 trophoblast cells using a competitive RT-PCR

Tissue factor pathway inhibitor-2 (TFPI-2) displays structural similarities with TFPI-1, the major inhibitor of tissue factor (TF)/, factor VIIa. It is synthesized mostly by syncytiotrophoblast in the placenta, but its physiological functions are not fully understood. We studied the synthesis of TFPI-2 mRNA and that of TFPI-1 and TF in three human trophoblast cell lines, JAR, BeWo, and JEG-3. We first developed specific competitive reverse transcription-polymerase chain reaction (RT-PCR) assays for each gene studied using human umbilical vein endothelial cells (HUVEC). The three trophoblast cell lines strongly synthesized TF mRNA whereas the synthesis of TFPI-1 mRNA was very low. TFPI-2 mRNA was not detected in unstimulated or stimulated JAR cells. In contrast, JEG-3 and, to a lesser extent, BeWo produced significant amounts of TFPI-2 mRNA, which were significantly increased after stimulation with phorbol 12-myristate 13-acetate (PMA). However, tumor necrosis factor-alpha (TNF-alpha) had no effect on this synthesis. JEG-3 and BeWo are thus two cell lines that could be used to study TFPI-2 gene regulation and to investigate the role of TF, TFPI-1, and TFPI-2 during trophoblast differentiation.

Oxidized LDL and HDL: antagonists in atherothrombosis

Increased LDL oxidation is associated with coronary artery disease. The predictive value of circulating oxidized LDL is additive to the Global Risk Assessment Score for cardiovascular risk prediction based on age, gender, total and HDL cholesterol, diabetes, hypertension, and smoking. Circulating oxidized LDL does not originate from extensive metal ion-induced oxidation in the blood but from mild oxidation in the arterial wall by cell-associated lipoxygenase and/or myeloperoxidase. Oxidized LDL induces atherosclerosis by stimulating monocyte infiltration and smooth muscle cell migration and proliferation. It contributes to atherothrombosis by inducing endothelial cell apoptosis, and thus plaque erosion, by impairing the anticoagulant balance in endothelium, stimulating tissue factor production by smooth muscle cells, and inducing apoptosis in macrophages. HDL cholesterol levels are inversely related to risk of coronary artery disease. HDL prevents atherosclerosis by reverting the stimulatory effect of oxidized LDL on monocyte infiltration. The HDL-associated enzyme paraoxonase inhibits the oxidation of LDL. PAF-acetyl hydrolase, which circulates in association with HDL and is produced in the arterial wall by macrophages, degrades bioactive oxidized phospholipids. Both enzymes actively protect hypercholesterolemic mice against atherosclerosis. Oxidized LDL inhibits these enzymes. Thus, oxidized LDL and HDL are indeed antagonists in the development of cardiovascular disease.

Did the antioxidant trials fail to validate the oxidation hypothesis?

Most clinical trials on antioxidants using vitamin E or beta-carotene have failed to note any significant change in cardiovascular endpoints. The results of these studies have been interpreted as a setback for the oxidation hypothesis. An analysis of the hypothesis and the trials, however, points out major misconceptions about the hypothesis and unjustified outcome expectations. Wrong selection of patient population, endpoints that are incompatible with the hypothesis, poor choice of antioxidants, and lack of inclusion of biochemical markers of oxidative stress and markers of vascular response are some of the contributors to the "failure" of these trials.

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.

Down-regulation of murine tissue factor pathway inhibitor mRNA by endotoxin and tumor necrosis factor-alpha in vitro and in vivo

Tissue factor pathway inhibitor (TFPI) is the protease inhibitor that regulates the extrinsic coagulation pathway initiated by the factor VIIa/TF complex. In this study, we first investigated tissue distribution of TFPI mRNA in the mouse and found that TFPI mRNA expression level was by far the highest in the lung, followed by the heart, adrenal, and adipose tissue. Since little has been known concerning the regulation of TFPI gene expression in vivo, we further analyzed the changes in the TFPI mRNA level in murine tissues after intraperitoneal injection of lipopolysaccharide (LPS), tumor necrosis factor-alpha (TNF-alpha), and interleukin-1 (IL-1). LPS and TNF-alpha dramatically decreased TFPI mRNA expression in four tissues examined (e.g., lung, heart, kidney, and adipose tissue), whereas the suppressive effect of IL-1 on TFPI mRNA was limited. The down-regulation of TFPI mRNA expression by LPS and TNF-alpha was also observed in cultured mouse endothelial cells and in cardiomyocyte cell lines. The decreased TFPI mRNA expression by LPS and TNF-alpha in tissues and in the specific cell types may contribute to an increase in the local procoagulant potential, resulting in the thrombotic tendency under septic and/or inflammatory conditions.

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.

Metabolism of oxidized LDL by macrophages

Oxidation products of lipids and proteins are found in atherosclerotic plaque and in macrophage foam cells. Macrophages avidly endocytose in-vitro oxidized LDL and accumulate sterols. What is the evidence that such a process is involved in in-vivo foam cell formation? The present review surveys current knowledge on the metabolism of oxidized LDL by macrophages, and the types, amounts and location of oxidation products that accumulate in these cells. Comparable studies of lesion lipoproteins and foam cells indicate that limited extracellular lipoprotein oxidation, perhaps followed by more extensive intracellular oxidation subsequent to uptake by macrophages, is a more likely scenario in vivo.

Effects of HMG-CoA reductase inhibitor on hemostasis

Clinical trials of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor (statin) therapy have demonstrated improvement in coronary atherosclerosis progression and reduction in risk of cardiovascular events. However, improvement in cardiovascular end-points is incompletely explained by the baseline or treated LDL cholesterol level. The beneficial effects of statins on clinical events may involve nonlipid mechanisms that modify hemostasis. Local activation of platelets and thrombus formation adjacent to atheromatous plaques, especially where ruptured or eroded, are now recognized to be of pathophysiological importance in the acute and chronic clinical expression of coronary heart disease. Thus, favorable effects of statins on hemostasis may be relevant to decreasing or delaying the progression and clinical manifestations of atherosclerosis.

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.

Monocyte tissue factor response is decreased in patients with hyperlipidemia

Monocytes are potent regulators of blood coagulation through the expression of tissue factor (TF) on stimulation and of tissue factor pathway inhibitor (TFPI), a selective inhibitor of TF pathway. As hyperlipidemia can modify some monocyte functions, we compared the TF and TFPI expression by circulating monocytes and the plasma TFPI levels between 65 healthy normolipemic controls and 38 nontreated hyperlipemic patients. TF and TFPI relationships with plasma lipoproteins are also examined. TF and TFPI expression were evaluated in peripheral mononuclear cells after isolation from blood by density gradient centrifugation and after short culture with or without lipopolysaccharide (LPS). TF and TFPI activity and antigen were measured in mononuclear cell lysates using amidolytic assay and enzyme-linked immunosorbent assay, respectively. TFPI activity and antigen were measured in plasma using the same methods. Plasma factor VII (FVII) activity and antigen were also determined. LPS-stimulated monocyte TF activity and antigen were lower in hyperlipidemic patients than in controls (0.0001<p<0.03). This decrease of monocyte TF expression in hyperlipidemic patients was not related to an increase of monocyte TFPI. Monocyte TF activity was negatively correlated to atherogenic fractions and positively correlated to protective fractions, specially after ex vivo LPS stimulation. Increased TFPI and FVII plasma levels were found in hyperlipidemic patients compared to controls. These results indicate an impairment of TF production by circulating monocytes from hyperlipidemic subjects, which is linked to the increase of atherogenic lipoprotein fractions. Further studies are required to elucidate the mechanism of this inhibition.

The promoter of human tissue factor pathway inhibitor gene: identification of potential regulatory elements

Tissue factor pathway inhibitor is the major potent physiologic inhibitor of tissue factor-induced coagulation. Several potential binding sites for transcription factors have been described in the 750 bp of the 5' flanking region of the human tissue factor pathway inhibitor gene reported earlier. To identify elements that regulate the expression of tissue factor pathway inhibitor in endothelial, hepatocyte, and monocyte cells, the sequence of an additional 770 bp of tissue factor pathway inhibitor was determined. Comparison of this new sequence as well as that reported earlier with consensus sequences for transcription factor binding sites provided matches for GATA-2, SP1, and c-Myc sequences. Moreover, plasmids containing deletion mutants of the 5' tissue factor pathway inhibitor promoter region and the luciferase reporter gene were transfected into HepG2, ECV304, and THP1 cells. Three negative regulatory elements were localized between -548 to -390, - 390 to -75, and -1158 to -796 relative to the transcriptional start, respectively, in HepG2, ECV304 and THP-1 cells.