Expression, localization, and activity of tissue factor pathway inhibitor in normal and atherosclerotic human vessels

Non-severe COVID-19 is associated with endothelial damage and hypercoagulability despite pharmacological thromboprophylaxis

BACKGROUND

Hypercoagulability and endothelial dysfunction are hallmarks of coronavirus disease 2019 (COVID-19) and appear to predict disease severity. A high incidence of thrombosis despite thromboprophylaxis is reported in patients with moderate to severe COVID-19. Recent randomized clinical trials suggest that therapeutic-intensity heparin confers a survival benefit in moderate-severity COVID-19 compared to standard-intensity heparin, potentially by harnessing heparin-mediated endothelial-stabilizing and anti-inflammatory effects.

OBJECTIVE

We hypothesized that patients with moderate-severity COVID-19 exhibit enhanced hypercoagulability despite standard-intensity thromboprophylaxis with low molecular weight heparin (LMWH) compared to non-COVID-19 hospitalized patients.

METHODS

Patients with moderate COVID-19 and a control group (severe acute respiratory syndrome coronavirus 2 [SARS-CoV-2]-negative hospitalized patients) receiving LMWH thromboprophylaxis were recruited. Markers of endothelial damage and plasma thrombin generation parameters were assessed.

RESULTS

Tissue plasminogen activator levels were significantly increased in the COVID-19 group (8.3 ± 4.4 vs. 4.9 ± 2.4 ng/ml; P = .02) compared to non-COVID-19-hospitalized patients. Despite thromboprophylaxis, mean endogenous thrombin potential was significantly increased among COVID-19 patients (1929 ± 448 vs. 1528 ± 460.8 nM*min; P = .04) but lag time to thrombin generation was significantly prolonged (8.1 ± 1.8 vs. 6.2 ± 1.8 mins; P = .02). While tissue factor pathway inhibitor (TFPI) levels were similar in both groups, in the presence of an inhibitory anti-TFPI antibody, the difference in lag time between the groups was abrogated.

CONCLUSIONS

Collectively, these data demonstrate that COVID-19 of moderate severity is associated with increased plasma thrombin generation and endothelial damage, and that hypercoagulability persists despite standard LMWH thromboprophylaxis. These findings may be of clinical interest given recent clinical trial data which suggest escalated heparin dosing in non-severe COVID-19 may be associated with improved clinical outcomes.

Association of circulating proprotein convertase subtilisin/kexin type 9 concentration, prothrombin time and cardiovascular outcomes: a prospective cohort study

BACKGROUND

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is considered to have multiple roles in the development of atherosclerosis, which is recently reported to participate in the thrombotic process. We aimed to examine the relationship between PCSK9 concentration, coagulation indexes and cardiovascular events.

METHODS

A total of 2293 consecutive patients with angina-like chest pain and without lipid-lowering drugs treatment were enrolled and followed up for major adverse cardiovascular events (MACEs). Circulating PCSK9 concentration was determined by ELISA. The routine coagulation tests including activated partial thromboplastin time (APTT), prothrombin time (PT) and thrombin time were performed. The associations between PCSK9 concentration, routine coagulation indicators and MACEs were analyzed.

RESULTS

Patients with high PCSK9 levels had lower PT and APTT levels (all p <  0.05). However, PCSK9 concentration was only independently and negatively correlated with PT (β = - 0.115, p <  0.001). During a mean of 38.3 months, 186 (8.1%) MACEs were occurred. Multiple Cox regression analysis indicated high PCSK9 or low PT levels as risk factors related to MACEs. When the prognosis was analyzed by the combination of PCSK9 and PT levels, patients with high PCSK9 and low PT had higher incidence of MACEs compared to those with low PCSK9 and high PT.

CONCLUSIONS

Our study firstly suggested that PCSK9 concentration was negatively correlated with plasma levels of PT. Furthermore, high PCSK9 and low PT were associated with MACEs and the combination of PCSK9 with PT had an addictive effect on predicting cardiovascular outcomes in patients with chest pain, which was useful for further subdivision of cardiovascular risks.

Insights into the Functional Role of ADTRP (Androgen-Dependent TFPI-Regulating Protein) in Health and Disease

The novel protein ADTRP, identified and described by us in 2011, is androgen-inducible and regulates the expression and activity of Tissue Factor Pathway Inhibitor, the major inhibitor of the Tissue Factor-dependent pathway of coagulation on endothelial cells. Single-nucleotide polymorphisms in ADTRP associate with coronary artery disease and myocardial infarction, and deep vein thrombosis/venous thromboembolism. Some athero-protective effects of androgen could exert through up-regulation of ADTRP expression. We discovered a critical role of ADTRP in vascular development and vessel integrity and function, manifested through Wnt signaling-dependent regulation of matrix metalloproteinase-9. ADTRP also hydrolyses fatty acid esters of hydroxy-fatty acids, which have anti-diabetic and anti-inflammatory effects and can control metabolic disorders. Here we summarize and analyze the knowledge on ADTRP and try to decipher its functions in health and disease.

Confocal Blood Flow Videomicroscopy of Thrombus Formation over Human Arteries and Local Targeting of P2X7

Atherothrombosis exposes vascular components to blood. Currently, new antithrombotic therapies are emerging. Herein we investigated thrombogenesis of human arteries with/without atherosclerosis, and the interaction of coagulation and vascular components, we and explored the anti-thrombogenic efficacy of blockade of the P2X purinoceptor 7 (P2X7). A confocal blood flow videomicroscopy system was performed on cryosections of internal mammary artery (IMA) or carotid plaque (CPL) determining/localizing platelets and fibrin. Blood from healthy donors elicited thrombi over arterial layers. Confocal microscopy associated thrombus with tissue presence of collagen type I, laminin, fibrin(ogen) and tissue factor (TF). The addition of antibodies blocking TF (aTF) or factor XI (aFXI) to blood significantly reduced fibrin deposition, variable platelet aggregation and aTF + aFXI almost abolished thrombus formation, showing synergy between coagulation pathways. A scarce effect of aTF over sub-endothelial regions, more abundant in tissue TF and bundles of laminin and collagen type I than deep intima, may suggest tissue thrombogenicity as molecular structure-related. Consistently with TF-related vascular function and expression of P2X7, the sections from CPL but not IMA tissue cultures pre-treated with the P2X7 antagonist A740003 demonstrated poor thrombogenesis in flow experiments. These data hint to local targeting studies on P2X7 modulation for atherothrombosis prevention/therapy.

Rapid thrombelastography predicts perioperative massive blood transfusion in patients undergoing coronary artery bypass grafting: A retrospective study

Massive blood transfusion (MBT) is a relatively common complication of cardiac surgery, which is independently associated with severe postoperative adverse events. However, the value of using rapid thrombotomography (r-TEG) to predict MBT in perioperative period of cardiac surgery has not been explored. This study aimed to identify the effect of r-TEG in predicting MBT for patients undergoing coronary artery bypass grafting (CABG).This retrospective study included consecutive patients first time undergoing CABG at the Zhongnan Hospital of Wuhan University between March 2015 and November 2017. All the patients had done r-TEG tests before surgery. The MBT was defined as receiving at least 4 units of red blood cells intra-operatively and 5 units postoperatively (1 unit red blood cells from 200 mL whole blood).Lower preoperative hemoglobin level (P = .001) and longer cardiopulmonary bypass time (P = .001) were the independent risk factors for MBT during surgery, and no components of the r-TEG predicted MBT during surgery. Meanwhile, longer activated clotting time (P < .001), less autologous blood transfusion (P = .001), and older age (P = .008) were the independent risk factors for MBT within 24 hours of surgery.Preoperative r-TEG activated clotting time can predict the increase of postoperative MBT in patients undergoing CABG. We recommend the careful monitoring of coagulation system with r-TEG, which allows rapid diagnosis of coagulation abnormalities even before the start of surgery.

Relation between Tissue Factor Pathway Inhibitor Activity and Cardiovascular Risk Factors and Diseases in a Large Population Sample

OBJECTIVE

 Tissue factor pathway inhibitor (TFPI) is a potent anticoagulant protein in the extrinsic coagulation pathway. In the present study, we aim to identify the cardiovascular determinants for total TFPI activity and its association with cardiovascular disease (CVD) and total mortality.

METHODS

 Total TFPI activity was assessed in a selection of the population-based Gutenberg Health Study (n = 5,000). Statistical analysis was performed to identify the determinants for total TFPI activity as well as the associations with CVD and mortality.

RESULTS

 Multivariable linear regression analysis identified smoking (β 0.095 [0.054-0.136]) as a positive determinant for total TFPI activity, while diabetes (β -0.072 [-0.134 to -0.009]), obesity (β -0.063 [-0.101 to -0.024]), and history of coronary artery disease (CAD) were negatively associated with total TFPI activity, independent of age, sex, and the remaining cardiovascular risk factors. After adjustment for lipoprotein levels, the association between total TFPI activity levels and obesity and CAD was lost. The analysis additionally revealed a strong positive association between total TFPI activity levels and low-density lipoprotein (β 0.221 [0.204-0.237]). The Cox regression models revealed that a higher total TFPI activity, above 97.5th percentile of the reference group, was associated with an increased mortality risk (hazard ratio = 2.58 [95% confidence interval: 1.49-4.47]), independent of age, sex, and cardiovascular risk profile.

CONCLUSION

 In the Gutenberg Health Study population-based cohort, the highest percentage of total TFPI correlated with an increased mortality risk. While elevated TFPI may reflect endothelial cell activation, the associations between total TFPI activity and obesity and CAD, points to additional mechanistic interactions.

Tissue factor in atherosclerosis and atherothrombosis

Atherosclerosis is a chronic inflammatory disease that is characterized by the formation of lipid rich plaques in the wall of medium to large sized arteries. Atherothrombosis represents the terminal manifestation of this pathology in which atherosclerotic plaque rupture or erosion triggers the formation of occlusive thrombi. Occlusion of arteries and resultant tissue ischemia in the heart and brain causes myocardial infarction and stroke, respectively. Tissue factor (TF) is the receptor for the coagulation protease factor VIIa, and formation of the TF:factor VIIa complex triggers blood coagulation. TF is expressed at high levels in atherosclerotic plaques by both macrophage-derived foam cells and vascular smooth muscle cells, as well as extracellular vesicles derived from these cells. Importantly, TF mediated activation of coagulation is critically important for arterial thrombosis in the setting of atherosclerotic disease. The major endogenous inhibitor of the TF:factor VIIa complex is TF pathway inhibitor 1 (TFPI-1), which is also present in atherosclerotic plaques. In mouse models, increased or decreased expression of TFPI-1 has been found to alter atherosclerosis. This review highlights the contribution of TF-dependent activation of coagulation to atherthrombotic disease.

Tissue factor pathway inhibitor in atherosclerosis

Tissue factor pathway inhibitor (TFPI) reduces the development of atherosclerosis by regulating tissue factor (TF) mediated coagulation pathway. In this review, we focus on recent findings on the inhibitory effects of TFPI on endothelial cell activation, vascular smooth muscle cell (VSMC) proliferation and migration, inflammatory cell recruitment and extracellular matrix which are associated with the development of atherosclerosis. Meanwhile, we are also concerned about the impact of TFPI levels and genetic polymorphisms on clinical atherogenesis. This article aims to explain the mechanism in inhibiting the development of atherosclerosis and clinical effects of TFPI, and provide new ideas for the clinical researches and mechanism studies of atherothrombosis.

Association between carotid artery plaque inflammation and brain MRI

PURPOSE

To explore the association between presence of inflammatory cells in the carotid plaques surgically treated and brain MRI findings.

MATERIAL AND METHODS

Forty consecutive patients were prospectively analyzed. Brain MRI was performed with a 1.5 Tesla scanner and infacts (lacuna and non-lacunar) pertinence of the anterior circulation were recorded. All patients underwent carotid endarterectomy "en bloc"; carotid plaques histological sections were prepared and immuno-cytochemical analysis was performed to characterize and quantify the presence of inflammatory cells. ROC curve analysis, Pearson Rho correlation and Mann-Whitney test were applied.

RESULTS

The immuno-cytochemical analysis demonstrated that plaques of symptomatic patients (stroke\TIA; n = 25) had more inflammatory cells, mainly macrophages (CD68) compared with plaques of patients without symptoms (Mann-Whitney = P < 0.001, ROC curve area = 0.901). Correlation analysis showed a statistically significant association between the number of brain non-lacunar infarcts and the entity of macrophages (P < 0.001); whereas no association with lacunar infarcts (P = 0.1934) was found.

CONCLUSION

Results of this preliminary study suggest that the presence and amount of inflammatory cells within carotid artery plaque is associated with cerebrovascular events and with the number of MRI brain detectable infarct.

Tissue factor pathway inhibitor attenuates ER stress-induced inflammation in human M2-polarized macrophages

Endoplasmic reticulum (ER) stress has been shown to play a key role during the initiation and clinical progression of the cardiovascular diseases, such as atherosclerosis. We have recently shown that expression of tissue factor pathway inhibitor (TFPI) in human monocyte-derived macrophages (MDMs) was induced by cholesterol crystals (CC). In the present study we aimed to determine the role of TFPI under ER stress conditions using human MDMs. qRT-PCR and immunohistochemistry analysis were performed to determine the presence of the ER stress marker CCAAT/enhancer binding protein homologous protein (CHOP) and TFPI in human carotid plaque material and also in human MDMs polarized into pro-inflammatory M1 or anti-inflammatory M2 populations. CHOP mRNA levels were upregulated in the plaques compared to healthy vessels, and CHOP protein was localized in the same area as TFPI in the plaques. Both CHOP and TFPI mRNA levels were upregulated after CC treatment, especially in the M2 phenotype, and the ER stress inhibitor 4-phenylbutyric acid (PBA) reversed this effect. Furthermore, CC treatment increased the levels of the pro-inflammatory cytokines TNF-α, IL-6, and IL-8, which for TNF-α and IL-8 was inhibited by PBA, and reduced the levels of the anti-inflammatory cytokine IL-10 in M2-polarized macrophages. Knockdown of TFPI prior to CC treatment exacerbated TNF-α and IL-6 levels, but reduced IL-8 and IL-10 levels. Our results show that CC induce TFPI and cytokine expression in M2-polarized macrophages through activation of the ER stress pathway and that TFPI has a protective effect against TNF-α and IL-6 mediated inflammation. These mechanisms may have implications for the pathogenesis of atherosclerosis.

Increased expression of TFPI in human carotid stenosis

INTRODUCTION

Tissue factor (TF) pathway inhibitor (TFPI) is the physiological inhibitor of TF induced blood coagulation and two isoforms exists, TFPIα and TFPIβ. In atherosclerotic plaques, TFPI may inhibit TF activity and thrombus formation, which is the main cause of ischemic stroke in carotid artery disease. We aimed to identify the isoforms of TFPI present in human carotid plaques and potential sources of TFPI.

MATERIALS AND METHODS

Human atherosclerotic plaques from carotid endarterectomies were used for mRNA and immunohistochemistry analyses. hPBMCs isolated from buffy coats and THP-1 cells were differentiated and polarized into M1 or M2 macrophages, and subsequently cultured with or without cholesterol crystals (CC). mRNA and protein expression were measured with qRT-PCR and ELISA, respectively, and procoagulant activity was assessed using a two-stage chromogenic assay.

RESULTS

TFPIα and TFPIβ mRNA levels were significantly increased in carotid plaques, whereas TF levels were unchanged as compared to healthy arteries. Antibodies against total TFPI showed elevated levels compared to antibodies against free TFPIα, both by immunohistochemical and ELISA detection in plaques. The antibody against total TFPI also co-localized with CD68 and the M1 and M2 markers CD80 and CD163, respectively. The TFPI mRNA expression was elevated and the procoagulant activity was decreased in M2 compared to M1 polarized human macrophages. TFPI was present in early foam cell formation and CC treatment increased the TFPI mRNA expression even further in M2 macrophages.

CONCLUSIONS

Our data indicate that both isoforms of TFPI are present in advanced plaques and that anti-inflammatory M2 macrophages may be a potential source of TFPI.

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.

Single nucleotide polymorphisms in an intergenic chromosome 2q region associated with tissue factor pathway inhibitor plasma levels and venous thromboembolism

Essentials Tissue factor pathway inhibitor (TFPI) regulates the blood coagulation cascade. We replicated previously reported linkage of TFPI plasma levels to the chromosome 2q region. The putative causal locus, rs62187992, was associated with TFPI plasma levels and thrombosis. rs62187992 was marginally associated with TFPI expression in human aortic endothelial cells. Click to hear Ann Gil's presentation on new insights into thrombin activatable fibrinolysis inhibitor SUMMARY: Background Tissue factor pathway inhibitor (TFPI) regulates fibrin clot formation, and low TFPI plasma levels increase the risk of arterial thromboembolism and venous thromboembolism (VTE). TFPI plasma levels are also heritable, and a previous linkage scan implicated the chromosome 2q region, but no specific genes. Objectives To replicate the finding of the linkage region in an independent sample, and to identify the causal locus. Methods We first performed a linkage analysis of microsatellite markers and TFPI plasma levels in 251 individuals from the F5L Family Study, and replicated the finding of the linkage peak on chromosome 2q (LOD = 3.06). We next defined a follow-up region that included 112 603 single nucleotide polymorphisms (SNPs) under the linkage peak, and meta-analyzed associations between these SNPs and TFPI plasma levels across the F5L Family Study and the Marseille Thrombosis Association (MARTHA) Study, a study of 1033 unrelated VTE patients. SNPs with false discovery rate q-values of < 0.10 were tested for association with TFPI plasma levels in 892 patients with coronary artery disease in the AtheroGene Study. Results and Conclusions One SNP, rs62187992, was associated with TFPI plasma levels in all three samples (β = + 0.14 and P = 4.23 × 10-6 combined; β = + 0.16 and P = 0.02 in the F5L Family Study; β = + 0.13 and P = 6.3 × 10-4 in the MARTHA Study; β = + 0.17 and P = 0.03 in the AtheroGene Study), and contributed to the linkage peak in the F5L Family Study. rs62187992 was also associated with clinical VTE (odds ratio 0.90, P = 0.03) in the INVENT Consortium of > 7000 cases and their controls, and was marginally associated with TFPI expression (β = + 0.19, P = 0.08) in human aortic endothelial cells, a primary site of TFPI synthesis. The biological mechanisms underlying these associations remain to be elucidated.

Emerging roles for vascular smooth muscle cell exosomes in calcification and coagulation

Vascular smooth muscle cell (VSMC) phenotypic conversion from a contractile to 'synthetic' state contributes to vascular pathologies including restenosis, atherosclerosis and vascular calcification. We have recently found that the secretion of exosomes is a feature of 'synthetic' VSMCs and that exosomes are novel players in vascular repair processes as well as pathological vascular thrombosis and calcification. Pro-inflammatory cytokines and growth factors as well as mineral imbalance stimulate exosome secretion by VSMCs, most likely by the activation of sphingomyelin phosphodiesterase 3 (SMPD3) and cytoskeletal remodelling. Calcium stress induces dramatic changes in VSMC exosome composition and accumulation of phosphatidylserine (PS), annexin A6 and matrix metalloproteinase-2, which converts exosomes into a nidus for calcification. In addition, by presenting PS, VSMC exosomes can also provide the catalytic surface for the activation of coagulation factors. Recent data showing that VSMC exosomes are loaded with proteins and miRNA regulating cell adhesion and migration highlight VSMC exosomes as potentially important communication messengers in vascular repair. Thus, the identification of signalling pathways regulating VSMC exosome secretion, including activation of SMPD3 and cytoskeletal rearrangements, opens up novel avenues for a deeper understanding of vascular remodelling processes.

EPAS1/HIF-2 alpha-mediated downregulation of tissue factor pathway inhibitor leads to a pro-thrombotic potential in endothelial cells

Neovascularization and hemorrhaging are evident in advanced atherosclerotic plaques due to hypoxic conditions, and mediate the accumulation of metabolic substrates, inflammatory cells, lipids, and other blood born factors inside the plaque. Tissue factor (TF) pathway inhibitor (TFPI) is mainly expressed by endothelial cells and is the endogenous inhibitor of the coagulation activator TF, which together with the downstream product thrombin can drive plaque progression and atherogenesis. We aimed to investigate the effect of hypoxic conditions on endothelial cell expression and activity of TFPI and TF that are important in coagulation initiation. Hypoxia was induced in primary human umbilical vein endothelial cells using chemicals or 1% oxygen tension, and mRNA and protein expressions were measured using qRT-PCR, ELISA, and Western blot analysis. Microscopy of fluorescence-labeled cells was used to visualize cell-associated TFPI. Cell-surface factor Xa (FXa) activity was measured using a two-stage chromogenic substrate method. We found that hypoxia reduced the TFPI mRNA and protein levels and increased the TF mRNA expression in a dose-dependent manner. The effect on TFPI was apparent on all the protein pools of TFPI, i.e., secreted TFPI, cell-surface associated TFPI, and intracellular TFPI, and seemed to be dependent upon hypoxia inducible factor-2α (HIF-2α). An increase in FXa activity was also observed on the endothelial cell surface, reflecting an increase in pro-thrombotic potential of the cells. Our findings indicate that hypoxic conditions may enhance the pro-coagulant activity of endothelial cells, which may promote atherogenesis in addition to clinical events and thus the severity of atherosclerotic disorders.

Endothelium and its alterations in cardiovascular diseases: life style intervention

The endothelium, which forms the inner cellular lining of blood vessels and lymphatics, is a highly metabolically active organ that is involved in many physiopathological processes, including the control of vasomotor tone, barrier function, leukocyte adhesion, and trafficking and inflammation. In this review, we summarized and described the following: (i) endothelial cell function in physiological conditions and (ii) endothelial cell activation and dysfunction in the main cardiovascular diseases (such as atherosclerosis, and hypertension) and to diabetes, cigarette smoking, and aging physiological process. Finally, we presented the currently available evidence that supports the beneficial effects of physical activity and various dietary compounds on endothelial functions.

The extrinsic coagulation cascade and tissue factor pathway inhibitor in macrophages: a potential therapeutic opportunity for atherosclerotic thrombosis

OBJECTIVES

The coagulation protease cascade plays the central requisite role in initiation of arterial atherothrombosis. However, the relative participation of the extrinsic as compared to the intrinsic pathway is incompletely resolved. We have investigated in vivo the relative importance of the extrinsic and intrinsic pathways to define which is more essential to atherothrombosis and therefore the preferable prophylactic therapeutic target. We further addressed which type of plaque associated macrophage population is associated with the thrombotic propensity of atherosclerotic plaques.

METHODS

Both photochemical injury and ferric chloride vascular injury models demonstrated arterial thrombosis formation in ApoE deficient mice. We found that direct interference with the extrinsic pathway, but not the intrinsic pathway, markedly diminished the rate of thrombus formation and occlusion of atherosclerotic carotid arteries following experimental challenge. To explore which plaque macrophage subtype may participate in plaque thrombosis in regard to expression tissue factor pathway inhibitor (TFPI), bone marrow derived macrophages of both M and GM phenotypes expressed tissue factor (TF), but the level of TFPI was much greater in M- type macrophages, which exhibited diminished thrombogenic activity, compared to type GM-macrophages.

RESULTS AND CONCLUSIONS

Our works support the hypothesis that the TF-initiated and direct extrinsic pathway provides the more significant contribution to arterial plaque thrombogenesis. Activation of the TF driven extrinsic pathway can be influenced by differing colony-stimulating factor influenced macrophage TFPI-1 expression. These results advance our understanding of atherothrombosis and identify potential therapeutic targets associated with the extrinsic pathway and with macrophages populating arterial atherosclerotic plaques.

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.

Plasmin-dependent proteolysis of tissue factor pathway inhibitor in a mouse model of endotoxemia

BACKGROUND

The development of a procoagulant state in sepsis, owing to aberrant expression of tissue factor (TF) and a sharp decrease in the level of its major inhibitor, TF pathway inhibitor (TFPI), could lead to microthrombotic organ failure. The mechanism for the decline in TFPI activity in the lung could involve plasmin-mediated cleavage of the inhibitor.

OBJECTIVE

To investigate the effect of plasmin generation on lung-associated TFPI activity, in normal conditions and during infusion of endotoxin (lipopolysaccharide [LPS]) in mice.

METHODS

Plasmin generation and TFPI activity were assayed in the lungs of mice deficient in tissue-type plasminogen (Plg) activator (t-PA) or Plg, at 2 h after LPS or saline injection.

RESULTS

The sharp loss of lung-associated TFPI activity at 2 h after LPS challenge paralleled the abrupt increase in plasmin generation. TFPI activity was significantly retained in both t-PA(-/-) and Plg(-/-) mice, which are unable to generate plasmin.

CONCLUSION

The increased plasmin generation during the early stages of sepsis could cleave/inactivate TFPI and thus lead to thrombotic complications.

Laboratory methods for the assay of tissue factor pathway inhibitor in human plasma

Tissue factor pathway inhibitor (TFPI) is being assayed with increasing frequency by researchers attempting to further understand the complexities of the coagulation system. There are a number of methods available for measurement of TFPI; however immunological measurement by ELIZA is the most common assay used. There are a number of commercial kits available for this assay and close attention to detail is critical for accurate results.

Cyclic strain delays the expression of tissue factor induced by thrombin in human umbilical vein endothelial cells

Most studies of tissue factor (TF) expression in endothelial cells (EC) are performed under stationary culture conditions. The purpose of this study was to determine the influence of mechanical stimuli such as cyclic strain (CS) on the expression of TF in EC exposed to thrombin (Thr). Human umbilical vein endothelial cells (HUVEC) were exposed to 4 U·mL(-1) Thr in the presence or absence of 10% average CS at 60 cycles·min(-1) and then TF expression was measured. TF messenger RNA (mRNA) expression peaked at 2 hours in HUVEC exposed to Thr, but at 4 hours in HUVEC exposed to both Thr + CS. TF expression was inhibited by p38 and extracellular signal-regulated protein kinase (ERK) inhibitors. For both Thr or Thr + CS stimuli, p38 and ERK activity peaked at 5 minutes (p < 0.05). Nuclear factor-kappa B levels remained high in the Thr group but not in the Thr + CS group, while Egr-1 levels were elevated in the Thr + CS group. We demonstrated CS-delayed, Thr-induced TF mRNA expression in HUVEC, which may be modulated by p38 and ERK inhibitors.

Tissue factor pathway inhibitor: structure-function

TFPI is a multivalent, Kunitz-type proteinase inhibitor, which, due to alternative mRNA splicing, is transcribed in three isoforms: TFPIalpha, TFPIdelta, and glycosyl phosphatidyl inositol (GPI)-anchored TFPIbeta. The microvascular endothelium is thought to be the principal source of TFPI and TFPIalpha is the predominant isoform expressed in humans. TFPIalpha, apparently attached to the surface of the endothelium in an indirect GPI-anchor-dependent fashion, represents the greatest in vivo reservoir of TFPI. The Kunitz-2 domain of TFPI is responsible for factor Xa inhibition and the Kunitz-1 domain is responsible for factor Xa-dependent inhibition of the factor VIIa/tissue factor catalytic complex. The anticoagulant activity of TFPI in one-stage coagulation assays is due mainly to its inhibition of factor Xa through a process that is enhanced by protein S and dependent upon the Kunitz-3 and carboxyterminal domains of full-length TFPIalpha. Carboxyterminal truncated forms of TFPI as well as TFPIalpha in plasma, however, inhibit factor VIIa/tissue factor in two-stage assay systems. Studies in gene-disrupted mice demonstrate the physiological importance of TFPI.

Circulating monocytes mirror the imbalance in TF and TFPI expression in carotid atherosclerotic plaques with lipid-rich and calcified morphology

BACKGROUND

Thrombogenicity of atherosclerotic plaque largely depends on plaque morphology and their content of tissue factor (TF) and tissue factor pathway inhibitor (TFPI). The relationship between morphological composition of plaque (lipid-rich or calcified) and expression of TF and TFPI in circulating blood monocytes and within the plaques is not characterized.

OBJECTIVE

To investigate whether lipid-rich (echolucent) or calcified (echogenic) morphology of carotid atherosclerotic plaques is associated with differences in TF and TFPI expression in circulating blood monocytes and within carotid atherosclerotic plaques.

METHODS

We studied levels of monocyte TF and TFPI mRNA and protein expression and association with traditional risk factors for atherosclerosis in asymptomatic subjects with echolucent (n=20) or echogenic (n=20) carotid plaques, or controls without carotid atherosclerosis (n=20) determined by ultrasonography. Sections of calcified or lipid-rich carotid plaques obtained from symptomatic patients were assessed for TF and TFPI antigen expression.

RESULTS

TF and TFPI surface presentation, surface TF/TFPI ratio, and TF activity were higher in monocytes obtained from subjects with echolucent than with echogenic plaques or controls without carotid atherosclerosis. Multiple regression analyses revealed inverse association between serum apoA1 and monocyte surface TF antigen expression (p=0.007), and positive association between serum apoB and monocyte surface TFPI expression (p=0.028). Sections from lipid-rich carotid plaques contained 2.5-fold more TF and 1.5-fold more TFPI antigens relative to calcified lesions, also yielding a higher TF/TFPI ratio.

CONCLUSIONS

Our findings indicate that circulating monocytes of asymptomatic individuals with echolucent lipid-rich carotid atherosclerosis express an imbalance between TF and TFPI expression cohering with changes found within advanced carotid atherosclerotic plaques obtained from symptomatic patients.

Increased tissue factor pathway inhibitor activity is associated with myocardial infarction in young women: results from the RATIO study

BACKGROUND

The tissue factor pathway inhibitor (TFPI)/protein S anticoagulant system is a potent inhibitor of blood coagulation. TFPI and protein S are major determinants of thrombin generation (TG) tests determined at low tissue factor (TF) and at high TF concentrations in the presence of activated protein C (APC). Both TFPI and protein S protect against venous thrombosis, but the importance of the TFPI/protein S system in arterial thrombosis remains unclear.

OBJECTIVES

To investigate the influence of the TFPI/protein S anticoagulant system on the risk of myocardial infarction (MI) in young women.

METHODS

The RATIO study is a case-control study in women under 50 years of age, including 205 patients and 638 controls. TFPI and protein S were quantified using ELISA. The TFPI/protein S activity (nTFPIr) and the APC sensitivity ratio (nAPCsr) were determined using TG tests. Odds ratios (ORs) adjusted for putative confounders and corresponding 95% confidence intervals (95% CI) were determined.

RESULTS

Women with MI had higher TFPI levels than controls (135.9 ± 40% vs. 124.2 ± 41%), resulting in increased TFPI/protein S activities and increased APC sensitivity. Furthermore, an increased TFPI activity was associated with MI [nTFPIr: adjusted OR Q1 vs. Q4 = 2.1 (95%CI 1.1-4.1)]. Additionally, an increased APC sensitivity was associated with MI [nAPCsr: adjusted OR Q1 vs. Q4 = 1.7 (95% CI 0.9-3.2)]

CONCLUSION

Women with MI had increased TFPI levels compared with controls. Consequently, the TFPI/protein S activity and APC sensitivity are increased in women with MI. Whether this increase in TFPI activity acts as a compensating mechanism for an increased procoagulant state or is a marker of endothelial damage remains to be investigated.

Laminar shear, but not orbital shear, has a synergistic effect with thrombin stimulation on tissue factor expression in human umbilical vein endothelial cells

INTRODUCTION

High levels of tissue factor (TF) have been associated with atherosclerotic plaques. The specific pathways linked to TF expression in endothelial cells (ECs) have not been well defined. This study compared TF expression in human umbilical vein ECs (HUVECs) exposed to laminar shear stress (LSS) using a parallel flow chamber and to orbital shear stress (OSS) using an orbital shaker. We also compared the effects of thrombin (TH) stimulation of ECs exposed to different shear forces on the expression of TF and investigated the role that second messengers, p38 and extracellular signal-regulated kinase 1 and 2 (ERK1/2), had in the EC response.

METHODS

HUVECs were subjected to 2, 4, or 6 hours of LSS or OSS in the presence or absence of 4 U/mL of TH. Western blot analysis of ERK1/2 and p38 activation and polymerase chain reaction analysis of TF in the presence of inhibitors to these second messengers was performed in HUVECs subjected to OSS or LSS in the presence or absence of TH.

RESULTS

TF expression was increased and peaked at 2 hours in all HUVECs exposed to LSS or TH. Stimulation of static HUVECs with TH resulted in an increase in TF expression of 5.68 ± 1.58-, 3.80 ± 1.21-, and 2.54 ± 0.38-fold at 2, 4, and 6 hours, respectively (n = 6 experiments). In the absence of TH, HUVECs exposed to LSS demonstrated a 9.51 ± 0.62-, 7.31 ± 1.43-, and 4.39 ± 1.32-fold increase in TF expression at 2, 4, and 6 hours, respectively (n = 6 experiments). TF was increased significantly more when exposed to LSS in the presence of TH (18.85 ± 1.43-, 15.05 ± 0.95-, and 8.91 ± 1.06-fold increases at 2, 4, and 6 hours, respectively [n = 6 experiments], P < .01). Between-group analysis showed a significant difference between groups (P < .001). OSS did not significantly increase TF expression in the presence or absence of TH. ERK1/2 and p38 activation was increased in LSS and LSS + TH but not in OSS or OSS + TH (n = 3 experiments).

CONCLUSION

LSS and TH independently increased TF expression, but OSS did not. LSS + TH stimulation showed a synergistic effect, which suggests that these mechanical and chemical stimuli work through different pathways or that an intracellular interaction between TH and LSS may be present that does not occur in OSS.

Resistin level is positively correlated with thrombotic complications in Southern Chinese metabolic syndrome patients

BACKGROUND

The metabolic syndrome (MetS) has been found to be closely related with thrombotic diseases. The mechanism, however, is far from elucidated.

AIM

This study was designed to investigate the relationship between endogenous resistin and thrombosis mediating factors, as well as its potential effects on the gene expression of cardiovascular disease biomarkers.

METHODS

Ninety patients satisfied the MetS criteria, and 55 healthy subjects were recruited as part of a single-center clinical study. Plasma levels of resistin, tissue factor (TF), tissue factor pathway inhibitor (TFPI), tissue plasminogen activator (tPA), plasminogen activator inhibitor-1 (PAI-1) were measured by enzymelinked immunosorbent assays. The effect of resistin on the expression of cardiovascular disease biomarkers in human umbilical vein endothelial cells (HUVEC) was assayed by gene microarray.

RESULTS

1) The average levels of resistin in MetS patients with or without acute myocardial or cerebral infarction were significantly higher than those of the controls. 2) The TF and TFPI increase was higher in MetS with infarction patients than in MetS patients. 3) In MetS with infarction patients, resistin was positively correlated with TF and PAI-1 (r=0.313, p=0.008; r=0.401, p=0.002, respectively). 4) In HUVEC, the microarray showed that apolipoprotein C-I, ACE, tumor necrosis factor receptor superfamily member 1A (TNFRSF1A) and member 5 (CD40) genes expression were dramatically increased by resistin.

CONCLUSION

In patients with MetS, resistin is strongly associated with hypercoagulative and hypofibrinolitic activities. Moreover, resistin may induce thrombotic complications via mediating the lipoprotein metabolism and stimulating inflammation.

Alternatively spliced isoforms of tissue factor pathway inhibitor

Tissue factor pathway inhibitor (TFPI) is the major regulator of tissue factor (TF)-induced coagulation. It down regulates coagulation by binding to the TF/fVIIa complex in a fXa dependent manner. It is predominantly produced by microvascular endothelial cells, though it is also found in platelets, monocytes, smooth muscle cells, and plasma. Its physiological importance is demonstrated by the embryonic lethality observed in TFPI knockout mice and by the increase in thrombotic burden that occurs when heterozygous TFPI mice are bred with mice carrying genetic risk factors for thrombotic disease, such as factor V Leiden. Multiple TFPI isoforms, termed TFPIalpha, TFPIbeta, and TFPIdelta in humans and TFPIalpha, TFPIbeta, and TFPIgamma in mice, have been described, which differ in their domain structure and method for cell surface attachment. A significant functional difference between these isoforms has yet to be described in vivo. Both human and mouse tissues produce, on average, approximately 10 times more TFPIalpha message when compared to that of TFPIbeta. Consistent with this finding, several lines of evidence suggest that TFPIalpha is the predominant protein isoform in humans. In contrast, recent work from our laboratory demonstrates that TFPIbeta is the major protein isoform produced in adult mice, suggesting that TFPI isoform production is translationally regulated.

Circulating thrombotic and haemostatic components in patients with coronary artery disease

The study aimed to analyze the circulating levels of thrombotic and haemostatic components; tissue factor, tissue factor pathway inhibitor, tissue plasminogen activator and plasminogen activator inhibitor-1 in patients with acute myocardial infarction at presentation (Group 1, n=49), unstable angina and Non-ST elevated MI after treatment (Group 2, n=22), stable angina (Group 3, n=18) and healthy individuals (Group 4, n=31). Significant finding was increase in tissue factor not only in Group 1 (2.0 fold, P=0.001), Group 2 (2.2 fold, P=0.015) but also in Group 3 (1.8 fold, P=0.018) as compared to controls. In Group 1 Plasminogen activator inhibitor-1 increased significantly (35.8%, P=0.02). Tissue factor pathway inhibitor and tissue plasminogen activator demonstrated increase in Group 1 of age<40 years while insignificant changes in elder patients. Increased thrombotic and decreased fibrinolytic conditions in acute myocardial infarction patients were observed. Increase TF in stable angina demonstrates procoagulant status in these patients as well.

Emerging hematological targets and therapy for cardiovascular disease: From bench to bedside

Atherosclerotic cardiovascular disease is the leading cause of death and a major part of its pathophysiology remains obscure. Some hematological targets have been related to the development and clinical outcome of this disease, especially soluble cytokines, leukocytes, red blood cells, hemostatic factors and platelets, and bone-marrow vascular progenitors. These emerging factors may be modulated by current antiatherosclerotic pharmacotherapy, target-designed novel drugs or progenitor cell therapy. The aim of current review article is to comprehensively review the role of these antiatherosclerotic targets and therapy.

Expression and location of intracellular tissue factor in atherosclerosis stable plaque of ApoE(-/-) mice

In the ApoE(-/-) mouse model of atherosclerosis (AS) stable plaque, the expression and location of intracellular tissue factor (TF) in the cellular components of AS stable plaque were investigated in order to explore the cellular mechanism of AS thrombosis. Pathological changes of the stable plaque were observed under a microscope. The expression of TF protein was examined in aortic stable plaque of mice by using immunohistochemistry. Color image planimetric system was used to analyze the histological components of the stable plaque and the TF distribution. Under the confocal microscope, the intracellular TF location in the stable plaque of mice was observed. The results showed the cellular area was the major part of stable plaque (67.36%+/-6.52%, P<0.01). The percentage of total area occupied by cellular area was significantly larger than atheromatous gruel and acellular area (P<0.01). Macrophages and smooth muscle cells (SMC) were major cells in the cellular area. The percentage of total area occupied by SMC was significantly larger than by macrophages (P<0.01). Multiple linear regression analysis showed there was a positive correlation between TF area and SMC area (r=0.616, P=0.008), and no correlation was found between TF area and macrophage area (r=0.437, P=0.08). Pictures of color image planimetric analysis of TF and SMC were merged to highlight areas with co-localization (yellow), it was concluded that the process could be a cell-mediated TF expression in the stable plaque. SMC may be the major source of TF in AS without plaque rupture.

Murine strain differences in hemostasis and thrombosis and tissue factor pathway inhibitor

INTRODUCTION

Differences among murine strains often lead to differential responses in models of human disease. The aim of the current study was to investigate whether differences exist among strains in models of hemostasis and thrombosis and whether these differences are reflected in differences in the tissue factor (TF) pathway.

METHODS

We examined baseline hemostatic parameters and the response to FeCl3-induced arterial thrombosis and a tail vein bleeding model in C57BL/6J (C57), 129S1/SvImJ (129S), and Balb/cJ (BalbC) mice. Finally, we examined TF and tissue factor pathway inhibitor (TFPI) activities in blood and expression in vascular tissue to determine whether these factors covary with a thrombotic phenotype.

RESULTS

No differences were observed in PT or aPTT among strains. 129S mice had lower platelet counts (p<0.001). BalbC had an increased rate of occlusion (mean occlusion time of 330+/-45 sec) in a FeCl(3)-induced model of thrombosis when compared to C57 (1182+/-349 sec) or 129 S (1442+/-281 sec) (p<0.05). Similarly, BalbC demonstrated reduced blood loss in tail bleeding experiments when compared to C57 and 129S. Vascular expression of TF and TFPI content did not correlate with the thrombotic phenotype of BalbC. However, circulating TFPI activities were lower in BalbC compared to both C57 and 129S mice. When normalized to circulating TF activities, BalbC had lower circulating TFPI activity than C57 and 129S, and there was a significant correlation between tail bleeding and normalized TFPI activity (r=0.67).

CONCLUSIONS

These data suggest that there are significant differences among strains in thrombosis and hemostasis and that circulating TFPI activity correlates with these differences.

Tissue factor pathway inhibitor, vascular risk factors and subclinical atherosclerosis: the Multi-Ethnic Study of Atherosclerosis

BACKGROUND

Tissue factor pathway inhibitor (TFPI) is an endothelial membrane-associated anticoagulant protein. Higher circulating levels might reflect endothelial damage.

OBJECTIVE

We hypothesized an association of higher total TFPI with subclinical atherosclerosis.

PATIENTS/METHODS

Total TFPI was measured in 1000 participants of the Multi-Ethnic Study of Atherosclerosis, a cohort of 6814 men and women without clinical vascular disease, aged 45-84, from four ethnic groups. Subclinical atherosclerosis measures were coronary artery calcium (CAC), carotid intima-media thickness (IMT) and ankle-brachial index (ABI).

RESULTS

TFPI was higher with age, male gender, higher LDL-cholesterol, smoking and diabetes, but not ethnicity. Adjusting for risk factors, TFPI in the 4th quartile versus 1st quartile was associated with a 1.2-fold increased risk of detectable CAC (95% CI 1.0-1.4), a 2.1-fold increased risk of CAC >400 Agatston units (95% CI 1.1-4.0) and a 1.6-fold (95% CI 1.1-2.5) increased risk of internal carotid IMT above the 80th percentile, but not with external carotid IMT or low ABI. Findings were consistent across ethnic groups.

CONCLUSIONS

In this diverse population, higher total TFPI was associated with prevalent CAC (limited to levels >400 units), and elevated internal carotid IMT, independent of other factors. Higher TFPI may indicate endothelial dysfunction. Further study is needed of TFPI and progression of atherosclerosis.

A case of acute myocardial infarction with repetitive stent thrombosis during emergent percutaneous coronary intervention. Transient decrease in antithrombin III activity and heparin resistance

A 59-year-old woman was admitted to our hospital for the treatment of an acute anterior myocardial infarction. She had a history of uncontrolled diabetes mellitus, hypertension, hyperlipidemia, obesity, and smoking. Coronary angiography revealed 90% stenosis with spontaneous dissection in the proximal portion of the left anterior descending artery. At this time, heparin was initiated for the first time. Although direct stenting (Be-stent, 3.0-18 mm) was performed for the culprit lesion, coronary dissection occurred at the left main trunk and additional stenting (Multi Link ZETA stent 3.5-15mm) was performed for the left main trunk. Soon after stenting, repetitive stent thrombosis occurred. Aspiration of the thrombus using an aspiration catheter was ineffective and repetitive angioplasty and intraaortic balloon pumping were required. Although we used 17,000 units of unfractionated heparin during the intervention, the activated coagulation time (ACT) was not prolonged (157 seconds). In the coronary care unit, the ACT and activated partial prothrombin time (aPTT) were not prolonged despite the use of large amounts of heparin (69,000 units in 2 days). Protein-S, protein-C, and hepaplastin testing were within normal limits and heparin-platelet factor IV complex antibody was not detected. In the acute phase, a decrease in the antithrombin III activity (65%) was noted and with administration of argatroban, prolongation of the aPTT was achieved. In the chronic phase, the decrease in antithrombin III activity and heparin resistance had improved spontaneously. It is important to recognize the existence of transient decreases in antithrombin III activity in the acute phase of myocardial infarction.

Elevated tissue expression of thrombomodulatory factors correlates with acute symptomatic carotid plaque phenotype

OBJECTIVES

Thrombomodulatory factors have been implicated in plaque instability. The aim was to examine the relationship between thrombomodulatory gene expression, timing of clinical events and plaque histology.

DESIGN OF STUDY

Plaques were obtained from 40 consecutive patients undergoing carotid endarterectomy and divided into three groups (group 1, early symptomatic, within 1 month; group 2, late symptomatic, 1-6 months and group 3, asymptomatic). Total RNA was isolated to determine the expression of tissue plasminogen activator (t-PA), urokinase plasminogen activator (u-PA), plasminogen activator inhibitor-1 (PAI-1), tissue factor (TF), tissue factor pathway inhibitor (TFPI), thrombomodulin (TM), CD68 and vascular endothelial-cadherin (VE-Cadherin).

RESULTS

Expression of t-PA, PAI-1, TF, TFPI, TM, CD68 and VE-cadherin were significantly increased in the early symptomatic group (p=0.019, 0.028, 0.018, 0.025, 0.038, 0.016 and 0.027 respectively), but the level of gene expression in the late symptomatic group was indistinguishable from the asymptomatic group. The incidence of plaque rupture and intraplaque haemorrhage was significantly increased in the early symptomatic groups (58% versus 18%/18% group 2/3, and 55% versus 6%/9% respectively, p<0.05 for both).

CONCLUSIONS

Expression of thrombomodulatory genes is increased in unstable plaques, though levels after 1 month are comparable to asymptomatic plaques. This transient rise may influence plaque instability, and rapid resolution mirrors the clinical reduction in risk of further thrombo-embolic events.

Porphyromonas gingivalis infection and prothrombotic effects in human aortic smooth muscle cells

INTRODUCTION

Accumulating evidence has demonstrated an association between periodontal infectious agents, such as Porphyromonas gingivalis, and vascular disease. Tissue factor (TF) and its specific tissue factor pathway inhibitor (TFPI) are produced by vascular cells and are important regulators of the coagulation cascade.

MATERIALS AND METHODS

To assess the role of P. gingivalis in atherothrombosis, we infected primary human aortic smooth muscle cells (HASMC) with either P. gingivalis 381, its non-invasive mutant DPG3, or heat-killed P. gingivalis 381. Levels and activity of TF and TFPI were measured 8 and 24 hours after infection in cell extracts and cell culture supernatants.

RESULTS

P. gingivalis 381 did not affect total TF antigen or TF activity in HASMC, but it significantly suppressed TFPI levels and activity compared to uninfected control cells, and those infected with the non-invasive mutant strain or the heat-killed bacteria. Further, P. gingivalis' LPS (up to a concentration of 5 microg/ml) failed to induce prothrombotic effects in HASMC, suggesting a significant role for the ability of whole viable bacteria to invade this cell type.

CONCLUSION

These data demonstrate for the first time that infection with a periodontal pathogen induces a prothrombotic response in HASMC.

E-selectin and TFPI are associated with carotid intima-media thickness in stable IHD patients: the baseline findings of the MIAMI study

OBJECTIVE

MIAMI was a prospective multicenter clinical study designed to investigate the relationship between changes in carotid intima-media thickness (C-IMT) and those in the levels of circulating markers of inflammation, thrombosis and endothelial dysfunction. The study was performed in a group of stable coronary patients treated for two years with a moderate dosage of atorvastatin (20mg/day). In this paper the cross-sectional relationship between C-IMT and the same circulating markers of inflammation, thrombosis and endothelial dysfunction measured at baseline was investigated.

METHODS

Eighty-five subjects that had not used statins for at least two months were enrolled in the study. At time of enrollment, the levels of vascular cell adhesion molecule-1 (VCAM-1), intracellular adhesion molecule-1 (ICAM-1), E-selectin, interleukin (IL)-6, IL-8, tumor necrosis factor (TNF)-alpha, high-sensitivity C-reactive protein (hs-CRP), tissue factor (TF), tissue factor pathway inhibitor (TFPI), von Willebrand factor (vWF), fibrinogen, total cholesterol (TC), high-density lipoprotein (HDL) and low-density lipoprotein (LDL), and triglycerides were measured, in parallel with C-IMT assessment.

RESULTS

In cross-sectional analyses, markers of endothelial perturbation (i.e. E-selectin) and TFPI were more strongly correlated with arherosclerotic burden than markers of inflammation. The baseline picture in this study indicates that E-selectin and TFPI are linked with atherosclerotic burden.

Heterogeneity of human macrophages in culture and in atherosclerotic plaques

Research suggests that monocytes differentiate into unique lineage-determined macrophage subpopulations in response to the local cytokine environment. The present study evaluated the atherogenic potential of two divergent lineage-determined human monocyte-derived macrophage subpopulations. Monocytes were differentiated for 7 days in the presence of alternative macrophage development cytokines: granulocyte-macrophage colony-stimulating factor to produce granulocyte-macrophage-CSF macrophages (GM-Mac), or macrophage colony-stimulating factor (M-CSF) to produce M-Mac. Gene chip analyses of three monocyte donors demonstrated differential expression of inflammatory and cholesterol homeostasis genes in the macrophage subpopulations. Quantitative PCR confirmed a fivefold elevation in the expression of genes that promote reverse cholesterol transport (PPAR-gamma, LXR-alpha, and ABCG1) and macrophage emigration from lesions (CCR7) in GM-Mac compared to that in M-Mac. Immunocytochemistry confirmed enhanced expression of the proinflammatory marker CD14 in M-Mac relative to GM-Mac. M-Mac spontaneously accumulated cholesterol when incubated with unmodified low-density lipoprotein whereas GM-Mac only accumulated similar levels of cholesterol after protein kinase C activation. Immunostained human coronary arteries showed that macrophages with similar antigen expression to that of M-Mac (CD68(+)/CD14(+)) were predominant within atherosclerotic lesions whereas macrophages with antigen expression similar to GM-Mac (CD68(+)/CD14(-)) were predominant in areas devoid of disease. The identification of macrophage subpopulations with different gene expression patterns and, thus, different potentials for promoting atherosclerosis has important experimental and clinical implications and could prove to be a valuable finding in developing therapeutic interventions in diseases dependent on macrophage function.

Determination of surface tissue factor thresholds that trigger coagulation at venous and arterial shear rates: amplification of 100 fM circulating tissue factor requires flow

Protein microarrays presenting spots of collagen and lipidated tissue factor (TF) allowed a determination of the critical surface concentration of TF required to trigger coagulation under flow. Whole blood supplemented with corn trypsin inhibitor (to inhibit factor XIIa) was perfused over microarrays for 5 minutes. Immunofluorescence staining of platelet glycoprotein GPIbalpha and fibrin(ogen) revealed a critical TF concentration (EC50) of 3.6, 8.4, and 10.2 molecules-TF/microm2 at wall shear rates of 100, 500, and 1000 s(-1), respectively. For collagen arrays where only the center lane of spots (in the direction of flow) contained TF, a downstream distance of 14 mm was required for the thrombus to widen enough to reach across a 300-micrometer gap to the adjacent TF-free lanes of collagen spots, in agreement with numerical simulation. To investigate the effect of low levels of circulating TF, whole blood (+/-100 fM added TF) was tested under static and flow conditions. After 5 minutes, the addition of 100 fM TF to whole blood had negligible effect under static conditions, but caused a 2.5-fold increase in fibrin formation under flow. This report defines the threshold concentrations of surface TF required to trigger coagulation under flow.

Sepsis-induced coagulation in the baboon lung is associated with decreased tissue factor pathway inhibitor

Increased tissue factor (TF)-dependent procoagulant activity in sepsis may be partly due to decreased expression or function of tissue factor pathway inhibitor (TFPI). To test this hypothesis, baboons were infused with live Escherichia coli and sacrificed after 2, 8, or 24 hours. Confocal and electron microscopy revealed increased leukocyte infiltration and fibrin deposition in the intravascular and interstitial compartments. Large amounts of TF were detected by immunostaining in leukocytes and platelet-rich microthrombi. TF induction was documented by quantitative reverse transcriptase-polymerase chain reaction, enzyme-linked immunosorbent assay, and coagulation assays. Lung-associated TFPI antigen and mRNA decreased during sepsis, and TFPI activity diminished abruptly at 2 hours. Blocking antibodies against TFPI increased fibrin deposition in septic baboon lungs, suggesting that TF-dependent coagulation might be aggravated by reduced endothelial TFPI. Decreased TFPI activity coincided with the release of tissue plasminogen activator and the peak of plasmin generation, suggesting that TFPI could undergo proteolytic inactivation by plasmin. Enhanced plasmin produced in septic baboons by infusion of blocking antibodies against plasminogen activator inhibitor-1 led to decreased lung-associated TFPI and unforeseen massive fibrin deposition. We conclude that activation of TF-driven coagulation not adequately countered by TFPI may underlie the widespread thrombotic complications of sepsis.

Vascular bed-specific thrombosis

Hemostasis represents a finely tuned balance between procoagulant and anticoagulant forces. An imbalance of these forces may lead to clinically significant disease, including arterial, venous and/or microvascular thrombosis. The vast majority of hypercoagulable states are associated with local thrombus formation. The goal of this review is to discuss the mechanisms underlying site-specific thrombosis.

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.

Tissue factor pathway inhibitor: structure, biology and involvement in disease

Tissue factor (TF)-initiated coagulation plays a significant role in the pathophysiology of many diseases, including cancer and inflammation. Tissue factor pathway inhibitor (TFPI) is a plasma Kunitz-type serine protease inhibitor, which modulates initiations of coagulation induced by TF. In a factor (F) Xa-dependent feedback system, TFPI binds directly and inhibits the TF-FVII/FVIIa complex. Normally, TFPI exists in plasma both as a full-length molecule and as variably carboxy-terminal truncated forms. TFPI also circulates in complex with plasma lipoproteins. The levels and the dual inhibitor effect of TFPI on FXa and TF-FVII/FVIIa complex offers insight into the mechanisms of various pathological conditions triggered by TF. The use of selective pharmacological inhibitors has become an indispensable tool in experimental haemostasis and thrombosis research. In vivo administration of recombinant TFPI (rTFPI) in an experimental animal model prevents thrombosis (and re-thrombosis after thrombolysis), reduces mortality from E. coli-induced-septic shock, prevents fibrin deposition on subendothelial human matrix and protects against disseminated intravascular coagulation (DIC). Thus, TFPI may play an important role in modulating TF-induced thrombogenesis and it may also provide a unique therapeutic approach for prophylaxis and/or treatment of various diseases. In this review, we consider structural and biochemical aspects of the TFPI molecule and detail its inhibitory mechanisms and therapeutic implications in various disease conditions.

Thrombin generation in vascular tissue

BACKGROUND

Classically, it is thought that the vast majority of thrombin is generated on the surface of platelets, however, thrombotic events occur in patients despite treatment with potent antiplatelet agents.

METHODS AND RESULTS

In freshly harvested left internal mammary artery (IMA) sections, addition of CaCl2 and platelet-poor plasma (PPP) were sufficient to stimulate a profound burst of thrombin and this effect was inhibited by antitissue factor antibodies. Ultracentrifugation of PPP to remove platelet microparticles had no effect on thrombin generation. Both the extrinsic and factor VIII-dependent pathways were necessary for IMA-supported thrombin generation as PPP derived from individuals deficient in factors V, VII, VIII or X did not support thrombin production. Small amounts of thrombin were generated utilizing factor IX (FIX)-deficient plasma, however, thrombin was not generated by aorta from FIX-deficient mice when FIX-deficient plasma was used. The addition of non-lipidated tissue factor (0.6 pM) and CaCl2 to actively proliferating cultured human aortic smooth muscle cells (SMC) resulted in a pronounced burst of thrombin generation occurring between 3 and 15 min after treatment. In the absence of tissue factor, thrombin was generated but at a slower rate and with a peak value 26% of that observed in the presence of tissue factor.

CONCLUSION

Significant thrombin generation can occur on vascular tissue in the absence of platelets or platelet microparticles and on the surface of non-apoptotic SMC.