Monocytes downregulate the early stage of collagen-induced platelet activation by a PECAM-1-dependent mechanism

BACKGROUND

Blood vessel damage results in exposure of the subendothelial matrix, to which platelets adhere. Monocytes are recruited and activated at the site of injury.

OBJECTIVES

Here we studied the effect of monocytes on platelet activation induced by exposure to fibrillar collagen.

METHODS

Washed platelets and isolated monocytes (100/1) were coincubated with type I collagen in static adhesion conditions or in suspension. Platelet activation was assessed by measuring RANTES production and alpha-granule secretion. Platelet adherence on immobilized collagen was analyzed by fluorescence confocal microscopy. Cell-cell contacts were prevented by incubating platelets and monocytes in transwell coculture dishes. Experiments were also performed in the presence of soluble recombinant platelet endothelial cell adhesion molecule-1 (PECAM-1) or of antibodies to PECAM-1.

RESULTS

Unexpectedly, unstimulated monocytes limited the initial phase of platelet activation by fibrillar collagen. In adhesion conditions, monocytes reduced the secretion by platelets of the inflammatory chemokine RANTES and of beta-thromboglobulin and the formation of platelet aggregates. The inhibitory effect of monocytes on platelet activation required direct cell-cell contacts between platelets and monocytes. Monocytes also inhibited collagen-induced platelet activation in suspension conditions as assessed by the reduction of P-selectin exposure and RANTES secretion. A recovery of platelet responses was observed in the presence of soluble PECAM-1 and of PECAM-1.3 Fab, indicating that PECAM-1 is involved in monocyte-triggered downregulation of platelet reactivity.

CONCLUSIONS

Our data provide the first evidence that unstimulated monocytes limit the initial phase of platelet activation by collagen via a mechanism that is, at least in part, PECAM-1-dependent.

Characterization of a novel dermatan sulfate with high antithrombin activity from ray skin (Raja radula)

INTRODUCTION

A novel dermatan sulfate (DS) from the skin of the ray Raja radula with high anticoagulant activity was identified and its monosaccharide composition and anticoagulant mode of action and potency were determined.

MATERIALS AND METHODS

The DS isolated from the ray skin was identified by chondroitinase treatment and characterized by FT-IR and (1)H NMR spectroscopy. Its anticoagulant activity was checked by activated partial thromboplastin time (aPTT), thrombin time (TT), thrombin generation (TG), heparin cofactor II (HCII) and antithrombin (AT)-mediated inhibition of thrombin. The effects on platelet activation and aggregation were investigated using flow cytometry and aggregometry, respectively.

RESULTS

Chemical backbone structures of DS from Raja radula were close to that of DS from porcine intestinal mucosa. However, (1)H NMR indicated that iduronic acid was the major hexuronic acid moiety in the ray skin DS and also suggested that the amount of 2-O-sulfonated iduronic acid was higher in comparison with mammalian DS along with the occurrence of 4-O-sulfonated N-acetylgalactosamine residues. The anticoagulant effect of the ray skin DS was mainly due to the potentiation of thrombin inhibition by HCII but also, although to a lesser extent, by AT and was higher than that of the DS standard. Moreover, it had no effect on platelet activation and aggregation induced by various agonists.

CONCLUSION

Altogether, these results indicated that DS from raja radula skin is an anticoagulant drug of interest potentially useful in anticoagulant therapy.

Dilation-dependent activation of platelets and prothrombin in human thoracic ascending aortic aneurysm

OBJECTIVE

The purpose of this study was to investigate whether thoracic ascending aortic aneurysm (TAAA) induces platelet activation as mural thrombus participates in aortic dilatation in abdominal aortic aneurysm and TAAA are associated with rheological factors favoring coagulation activation.

METHODS AND RESULTS

We studied the relation between coagulation activation and aortic diameter in Marfan patients (MFS) with various aortic diameters (n=52). We then studied patients presenting large aneurysms associated with bicuspid aortic valve (BAV) and degenerative form. Lastly, we used immunochemistry and biochemistry to investigate prothrombin/thrombin retention within the aortic wall. Microparticles, sGPV, tissue factor, and TAT complexes were increased in plasma from MFS with large aneurysms (>or=45 mm) compared to MFS with limited aortic dilatation (<45 mm). Similar elevations were observed in all patients with large aortic aneurysms, regardless of the etiology, the site of maximal aortic dilation, associated valvulopathy, risk factors, or treatments. P-selectin and platelet-bound fibrinogen were also increased, demonstrating platelet activation in large aneurysms. Significant increase in sCD146 plasma concentration suggested alteration of endothelium.

CONCLUSIONS

Platelet activation occurs in patients with large aneurysms of the ascending aorta, is dependent on aortic dilation, and is associated with thrombin generation, part of which appears to be retained in mucoid degeneration areas.

Involvement of intraplaque hemorrhage in atherothrombosis evolution via neutrophil protease enrichment

The pathological remodeling of the arterial wall in atherosclerosis involves protease activities, which play a major role in complications via plaque rupture. Circulating leukocytes and particularly neutrophils have been shown to be an independent predictor of recurrent ischemic events. However, neutrophils are poorly documented within atherosclerotic plaques. We hypothesized that intraplaque hemorrhage could convey neutrophils into the lesion, spreading into the necrotic core, thus participating in its protease enrichment. One hundred human carotid endarterectomy specimens were dissected into culprit-stenosing plaques (CPs) and adjacent noncomplicated plaques. Half of CPs exhibited hemorrhage, which was confirmed by the release of hemoglobin. Pro- and active forms of matrix metalloproteinase-9 (MMP-9) were increased in media conditioned by hemorrhagic plaques. Higher levels of lipocalin [neutrophil gelatinase-associated lipocalin (NGAL)]/MMP-9 complexes, specifically released by neutrophils, were also found in conditioned media from plaques with hemorrhage. Immunohistochemical analysis of the corresponding carotid samples showed that neutrophil markers such as elastase, NGAL/MMP-9, CD66b, and proteinase 3 colocalized with blood constituents (i.e., hemoglobin, plasminogen). All markers of neutrophil degranulation were positively correlated in CP-conditioned media (alpha1-antitrypsin/elastase complexes, myeloperoxidase, and alpha-defensins), and higher levels came from CPs containing intraplaque hemorrhages. Addition of an elastase inhibitor at the time of incubation led to a decrease in the proMMP-9 activation in CPs, suggesting cross-talk between proteases released by neutrophils. Finally, we found that neovessels observed at the interface between cap and core exhibit an activated endothelium, which may favor leukocyte diapedesis. Our study thus provides evidence for the involvement of neutrophils in plaque vulnerability.

Reduced Immunoregulatory CD31 + T Cells in Patients With Atherosclerotic Abdominal Aortic Aneurysm

Background— Cell-mediated immunity is considered to contribute to the pathogenesis of abdominal aortic aneurysms (AAA). In particular, infiltrating macrophages and CD8 + T lymphocytes participate in the destruction of the aortic wall extracellular matrix and smooth muscle cells. We surmise that these pathological events are controlled by circulating regulatory lymphocytes.

Methods and Results— Circulating CD4 + /CD31 + cells were reduced in AAA patients (n=80, 8.9±0.6%) as compared with controls (n=69, 13.7±0.8%; P <0.001) and inversely proportional to AAA size. Exclusion of the aneurysm by an endoprothesis did not affect CD31 + T cell values. Reduction of blood CD4 + /CD31 + cells was not attributable to their enrichment in AAA tissue. In contrast, CD8 + /CD31 + cells were slightly reduced in the blood while increased in the aneurysmal tissue (29.2±0.5 versus 20.2±4.7% in blood, n=6; P <0.05). Remarkably, high percentages of CD4 + /CD31 + cells were able to regulate proliferation and cytokine production of CD8 + lymphocytes, as well as CD8 + cell-mediated cytotoxicity of aortic smooth muscle cells ( P <0.01). Finally, CD4 + /CD31 + cells reduced the production and activity of metalloproteinase-9 by lipopolysaccharide-stimulated macrophages.

Conclusions— Circulating CD4 + /CD31 + T cells regulate macrophage and CD8 + T cell activation and effector function in the arterial wall. Their reduction might promote the development of AAA.

Interaction of rifalazil with oxidant-generating systems of human polymorphonuclear neutrophils

It is well acknowledged that ansamycins display immunosuppressive and anti-inflammatory properties in vitro and in vivo. Rifalazil, a new ansamycin derivative, has not been studied in the context of inflammation. In particular, there are no data on the possible interference of rifalazil with oxidant production by phagocytes. We have compared the antioxidant properties of rifalazil to those of rifampin, a drug well known in this context, by using cellular and acellular oxidant-generating systems. Oxidant production by polymorphonuclear neutrophils was measured in terms of cytochrome c reduction, lucigenin-amplified chemiluminescence (Lu-ACL), and the 2',7'-dichlorofluorescin diacetate H2 (DCFDA-H2) technique (intracellular oxidant production). Rifalazil impaired O2- production in a concentration-dependent manner, with 50% inhibitory concentrations (IC50) (concentrations which inhibit 50% of the response) of 5.4 (30 and 60 min of incubation) and 6.4 (30 min) mg/liter, respectively, for phorbol myristate acetate (PMA) and formyl-methionyl-leucyl-phenylalanine (fMLP) stimulation. In agreement with the published fMLP-like activity of rifampin, the inhibitory effect of rifampin was significantly greater for fMLP (IC50 of 5.6 mg/liter) than for PMA (IC50 of 58 mg/liter) stimulation. Alteration of intracellular oxidant production was also observed with IC50 values similar to those obtained by the cytochrome assay. In addition, rifalazil and rifampin (> or = 25 mg/liter) scavenged O2-, as demonstrated by the acellular (hypoxanthine-xanthine oxidase) system. Interference with light detection systems was evidenced for both drugs by Lu-ACL. The clinical relevance of the antioxidant effect of rifalazil demonstrated in vitro, in particular its potential anti-inflammatory activity, requires further investigation.

EXPERIMENTAL HEATSTROKE IN BABOON: ANALYSIS OF THE SYSTEMIC INFLAMMATORY RESPONSE

The objective of this study was to analyze the pattern of the inflammatory response to heatstroke in an experimental baboon model with a view to identifying potential target for therapeutic interventions. Blinded analysis of plasma collected from 12 juvenile baboons (Papio hamadryas) in heatstroke was used. Eight anesthetized animals were heat-stressed in an incubator at 44 degrees C to 47 degrees C until rectal temperature was 42.5 degrees C (moderate heatstroke; n = 4) or systolic arterial pressure fell to <90 mmHg (severe heatstroke; n = 4) and were allowed to recover at room temperature. Four sham-heated animals served as a control group. We performed sequential measurement of cytokines. The rectal temperature on completion of heat stress was 42.5 degrees C +/- 0.0 degrees C and 43.3 degrees C +/- 0.1 degrees C in moderate and severe heatstroke, respectively. Heat stress elicited early, simultaneous release of anti-inflammatory cytokines and chemokines (IL-10, IL-1ra, sTNFr I and II, and IL-8). Circulating levels of IL-12p40 were significantly decreased, whereas TNFalpha, IL-1beta, and IL-4 were below the detection limit in all animals. No baboon survived severe heatstroke; there was neurological morbidity without mortality in moderate heatstroke. Nonsurvivors displayed significantly greater activity/alterations in inflammation markers than survivors. Sham-heated animals had no evidence of inflammation activation. These results show that heatstroke activates complex systemic inflammatory and regulatory responses associated with outcome. Further definition of this ambivalent response is needed before identification of target of successful modulation may become possible.

NAD(P)H oxidase Nox-4 mediates 7-ketocholesterol-induced endoplasmic reticulum stress and apoptosis in human aortic smooth muscle cells

The mechanisms involved in the cytotoxic action of oxysterols in the pathogenesis of atherosclerosis still remain poorly understood. Among the major oxysterols present in oxidized low-density lipoprotein, we show here that 7-ketocholesterol (7-Kchol) induces oxidative stress and/or apoptotic events in human aortic smooth muscle cells (SMCs). This specific effect of 7-Kchol is mediated by a robust upregulation (threefold from the basal level) of Nox-4, a reactive oxygen species (ROS)-generating NAD(P)H oxidase homologue. This effect was highlighted by silencing Nox-4 expression with a specific small interfering RNA, which significantly reduced the 7-Kchol-induced production of ROS and abolished apoptotic events. Furthermore, the 7-Kchol activating pathway included an early triggering of endoplasmic reticulum stress, as assessed by transient intracellular Ca(2+) oscillations, and the induction of the expression of the cell death effector CHOP and of GRP78/Bip chaperone via the activation of IRE-1, all hallmarks of the unfolded protein response (UPR). We also showed that 7-Kchol activated the IRE-1/Jun-NH(2)-terminal kinase (JNK)/AP-1 signaling pathway to promote Nox-4 expression. Silencing of IRE-1 and JNK inhibition downregulated Nox-4 expression and subsequently prevented the UPR-dependent cell death induced by 7-Kchol. These findings demonstrate that Nox-4 plays a key role in 7-Kchol-induced SMC death, which is consistent with the hypothesis that Nox-4/oxysterols are involved in the pathogenesis of atherosclerosis.

Inflammatory, hemostatic, and clinical changes in a baboon experimental model for heatstroke

The mortality and neurological morbidity in heatstroke have been attributed to the host's inflammatory and hemostatic responses to heat stress, suggesting that immunomodulation may improve outcome. We postulated that an experimental baboon model of heatstroke will reproduce human responses and clinical outcome to allow testing of new therapeutic strategies. Eight anesthetized juvenile baboons (Papio hamadryas) were subjected to heat stress in an incubator maintained at 44-47 degrees C until rectal temperature attained 42.5 degrees C (moderate heatstroke; n = 4) or systolic arterial pressure fell to <90 mmHg (severe heatstroke; n = 4) and were allowed to recover at room temperature. Four sham-heated animals served as a control group. Rectal temperature at the end of heat stress was 42.5 +/- 0.0 and 43.3 +/- 0.1 degrees C, respectively. All heat-stressed animals had systemic inflammation and activated coagulation, indicated by increased plasma IL-6, prothrombin time, activated partial thromboplastin time, and D-dimer levels, and decreased platelet count. Biochemical markers and/or histology evidenced cellular injury/dysfunction: plasma levels of thrombomodulin, creatinine, creatine kinase, lactic dehydrogenase, and alanine aminotransferase were increased, and varying degrees of tissue damage were present in liver, brain, and gut. No baboon with severe heatstroke survived. Neurological morbidity but no mortality was observed in baboons with moderate heatstroke. Nonsurvivors displayed significantly greater coagulopathy, inflammatory activity, and tissue injury than survivors. Sham-heated animals had an uneventful course. Heat stress elicited distinct patterns of inflammatory and hemostatic responses associated with outcome. The baboon model of heatstroke appears suitable for testing whether immunomodulation of the host's responses can improve outcome.

Blockade of Vascular Endothelial Growth Factor Receptor I (VEGF-RI), but not VEGF-RII, Suppresses Joint Destruction in the K/BxN Model of Rheumatoid Arthritis

It was recently shown that vascular endothelial growth factor (VEGF), a growth factor for endothelial cells, plays a pivotal role in rheumatoid arthritis. VEGF binds to specific receptors, known as VEGF-RI and VEGF-RII. We assessed the physical and histological effects of selective blockade of VEGF and its receptors in transgenic K/BxN mice, a model of rheumatoid arthritis very close to the human disease. Mice were treated with anti-mouse VEGF Ab, anti-mouse VEGF-RI and -RII Abs, and an inhibitor of VEGF-RI tyrosine kinase. Disease activity was monitored using clinical indexes and by histological examination. We found that synovial cells from arthritic joints express VEGF, VEGF-RI, and VEGF-RII. Treatment with anti-VEGF-RI strongly attenuated the disease throughout the study period, while anti-VEGF only transiently delayed disease onset. Treatment with anti-VEGF-RII had no effect. Anti-VEGF-RI reduced the intensity of clinical manifestations and, based on qualitative and semiquantitative histological analyses, prevented joint damage. Treatment with a VEGF-RI tyrosine kinase inhibitor almost abolished the disease. These results show that VEGF is a key factor in pannus development, acting through the VEGF-RI pathway. The observation that in vivo administration of specific inhibitors targeting the VEGF-RI pathway suppressed arthritis and prevented bone destruction opens up new possibilities for the treatment of rheumatoid arthritis.

Association of the Toll-like receptor 4 gene Asp299Gly polymorphism with acute coronary events

OBJECTIVE

Atherosclerosis is a chronic inflammatory disease of the blood vessels. Toll-like receptor 4 (TLR4) is a transmembrane receptor that is involved in mediating inflammatory responses to bacterial endotoxin and other ligands. The aim of this study was to search for an association between a common functional polymorphism of TLR4--Asp299Gly--and acute coronary syndrome.

METHODS AND RESULTS

We conducted a case-control study of 183 patients with acute coronary syndromes and 216 controls. We screened the TLR4 gene for the Asp299Gly polymorphism using a 5' fluorogenic assay. The 299Gly allele was associated with a decreased risk of acute coronary events independently of standard coronary risk factors. The adjusted odds ratio associated with this allele was 0.41 (95% CI, 0.18 to 0.95; P=0.037). In controls, TLR4 heterozygosity was also associated with a significant decrease in plasma fibrinogen and soluble vascular cellular adhesion molecule-1 levels (P<0.01).

CONCLUSIONS

These results, which must be confirmed by a prospective longitudinal study, provide evidence of an association between the Asp299Gly polymorphism of the human TLR4 receptor and acute coronary syndromes. They confirm the previously reported involvement of TLR4 in carotid and femoral artery atherosclerosis.

Fractalkine/CX3CL1 production by human aortic smooth muscle cells impairs monocyte procoagulant and inflammatory responses

Expression of membrane-bound CX3CL1, a CX(3)C chemokine, can be strongly induced by inflammatory cytokines in primary endothelial cells, mediating capture and tight adhesion of cells, such as monocytes, that carry the CX(3)CR1 receptor. Here, we measured CX3CL1 mRNA and protein induction by human aortic smooth muscle cells (SMCs), another major component of vessel walls, in response to inflammatory stimuli, and analyzed the effect of membrane-bound CX3CL1 on monocyte adhesion, tissue factor (TF) expression, and tumor necrosis factor-alpha (TNF-alpha) released. In human vascular SMCs, CX3CL1 transcripts were induced after 4h of stimulation with a combination of TNF-alpha and interferon-gamma. Cell-associated and shedded CX3CL1 were measured with a specific ELISA, showing that only 30% of the protein was cleaved from the membrane. Expression of CX3CL1 by SMC increased adhesion of monocytic cells, an effect, which was blocked by soluble CX3CL1. Interestingly, monocyte adhesion to CX3CL1-coated plates partially inhibited lipopolysaccharide-induced TF expression and TNF-alpha release. Thus, CX3CL1, in addition to its adhesive/chemotactic functions, directly promotes monocyte antiinflammatory and antiprocoagulant responses. This could have important implications in clinical settings such as atherosclerosis, in which SMCs and monocytic cells are in close proximity.

Interleukin-10 deficiency increases atherosclerosis, thrombosis, and low-density lipoproteins in apolipoprotein E knockout mice

Interleukin (IL)-10 is an anti-inflammatory cytokine that may play a protective role in atherosclerosis. The aim of this study was to assess the effect of IL-10 deficiency in the apolipoprotein E knockout mouse. Apolipoprotein E deficient (E-/-) and IL-10 deficient (-/-) mice were crossed to generate E-/- x IL-10-/- double knockout mice. By 16 wk, cholesterol and triglycerides were similar in double and single knockouts but the lack of IL-10 led to increased low-density lipoprotein cholesterol whereas very-low-density lipoprotein was reduced. In parallel, T-helper 1 responses and lesion size were dramatically increased in double knockout compared with E-/- controls. At 48 wk, matrix metalloproteinases and tissue factor activities were increased in lesions of double-knockout mice. Furthermore, markers of systemic coagulation were increased, and vascular thrombosis in response to i.v. thrombin occurred more frequently in E-/- x IL-10-/- than in E-/- mice. Our findings suggest that IL-10 deficiency plays a deleterious role in atherosclerosis. The early phase of lesion development was increased, and the proteolytic and procoagulant activity was elevated in advanced lesions. These data show that IL-10 may reduce atherogenesis and improve the stability of plaques.

Hemostasis imbalance in experimental hypertension

BACKGROUND

The rat model of chronic intoxication by N(G) -nitro-L-arginine methyl ester (L-NAME) induces severe systemic arterial hypertension and progressive ischemic lesions in the central nervous system and kidneys. We investigated the possible molecular basis of these thrombotic events.

METHODS AND RESULTS

Administration of L-NAME increased plasma markers of thrombin generation, thrombin-antithrombin complexes, and soluble glycoprotein V, measured by specific ELISA. Thrombin generation in vivo was associated with ex vivo platelet desensitization to adenosine 5'-diphosphate and collagen-induced aggregation. In the aortic layers and renal arterioles, tissue factor mRNA (semi-quantitative RT-PCR) and activity (coagulation assay) were increased. In contrast, tissue factor activity was not modified in glomeruli. In parallel, an impairment of the fibrinolytic system was demonstrated by an increase in plasma levels and arterial secretion of plasminogen activator inhibitor-1. In the arterial wall, plasminogen activator inhibtor-1 mRNA was significantly increased. Moreover, antifibrinolytic activity, studied by fibrin reverse zymography, was increased whereas all tissue-plasminogen activator activity secreted by the hypertensive arterial wall was detected as complexes with its specific inhibitor. In animals treated with the angiotensin-converting enzyme (ACE) inhibitor Zofenil, all of these parameters remained at control levels.

CONCLUSIONS

These results indicate that chronic blockade of nitric oxide production in rats results in enhancement of blood markers of thrombin generation associated with tissue factor induction and impairment of fibrinolysis in the vascular wall, which may contribute to the thrombotic complications associated with hypertension.

Polymorphisms of the tissue factor pathway inhibitor gene and the risk of restenosis after coronary angioplasty

Intracoronary stent implantation is associated with a significantly lower risk of restenosis compared with balloon angioplasty. However, restenosis still occurs in some cases. Experimental studies suggest that the tissue factor pathway is involved in this phenomenon. We investigated a possible relationship between three previously identified polymorphisms of the tissue factor pathway inhibitor (TFPI) gene and restenosis in 443 patients who underwent angioplasty, with or without stent implantation. The effect of the intron 7-33T<--C polymorphism and that of the combined intron 7 and promoter genotype on plasma TFPI levels was also investigated in 58 healthy subjects. DNA analysis was performed by polymerase chain reaction amplification of genomic DNA extracted from white blood cells, followed by digestion with the restriction enzymes Hind III, Nde I and Mae III for the detection of promoter, intron 7 and exon IX polymorphisms, respectively. The minimal luminal diameter, percent stenosis, acute gain, late loss and loss index did not differ according to the genotype before, immediately after or 6 months after angioplasty, regardless of stent implantation. Interestingly, subjects with the intron 7 CC genotype had significantly higher total TFPI levels than those with the TT genotype before and after an enoxaparin injection. Moreover, subjects with the -287TT/Int7TT combined genotype had the lowest plasma TFPI levels. Despite significant variations in plasma TFPI levels, we found no evidence that three polymorphisms of the TFPI gene influence the risk of restenosis. These results do not exclude the possibility that other polymorphisms in the TFPI gene may influence this risk.

Tissue factor is not involved in the mitogenic activity of factor VIIa

The present study was undertaken to evaluate in vitro the importance of tissue factor in the mitogenic effect of factor VIIa for embryonic fibroblasts. For that purpose, embryonic fibroblasts were isolated from either wild-type or transgenic mice showing a single inactivation of the tissue factor gene or expressing a truncated form (lacking the cytosolic domain) of this protein. Factor VIIa stimulated in a dose-dependent manner the growth of the 3 types of fibroblasts, thus showing that TF is not involved in the mitogenic activity of factor VIIa. The mitogenic activity of factor VIIa disappeared in serum immunopurified in factor X and was almost totally inhibited by DX9065, a selective factor Xa inhibitor, showing that this effect of factor VIIa occurred via factor Xa generated during the incubation period. Hirudin did not show any significant effect on factor VIIa-induced fibroblast proliferation, thus showing that the effect observed for factor VIIa was selectively mediated by factor Xa and was not due to thrombin formation. Our results therefore represent the first evidence for the possible importance of factor Xa in the mitogenic effect of factor VIIa and show the negligible role of tissue factor in this process.

Vascular endothelial growth factor production by fibroblasts in response to factor VIIa binding to tissue factor involves thrombin and factor Xa

Tissue factor (TF) assembled with activated factor VII (FVIIa) initiates the coagulation cascade. We recently showed that TF was essential for FVIIa-induced vascular endothelial growth factor (VEGF) production by human fibroblasts. We investigated whether this production resulted from TF activation by its binding to FVIIa or from the production of clotting factors activated downstream. Incubation of fibroblasts with a plasma-derived FVIIa concentrate induced the generation of activated factor X (FXa) and thrombin and the secretion of VEGF, which was inhibited by hirudin and FXa inhibitors. By contrast, the addition of recombinant FVIIa to fibroblasts did not induce VEGF secretion unless factor X was present. Moreover, thrombin and FXa induced VEGF secretion and VEGF mRNA accumulation, which were blocked by hirudin and FXa inhibitors, respectively. The effect of thrombin was mediated by its specific receptor, protease-activated receptor-1; in contrast, the effect of FXa did not appear to involve effector cell protease receptor-1, because it was not affected by an anti-effector cell protease receptor-1 antibody. An increase in intracellular calcium with the calcium ionophore A23187 or intracellular calcium chelation by BAPTA-AM had no effect on either basal or FXa-induced VEGF secretion, suggesting that the calcium signaling pathway was not sufficient to induce VEGF secretion. Finally, FVIIa, by itself, had no effect on mitogen-activated protein (MAP) kinase activation, contrary to thrombin and FXa, which activate the p44/p42 MAP kinase pathway, as shown by the blocking effect of PD 98059 and by Western blotting of activated MAP kinases. These findings indicate that FVIIa protease induction of VEGF expression is mediated by thrombin and FXa generated in response to FVIIa binding to TF-expressing fibroblasts; they also exclude a direct signaling involving MAP kinase activation via the intracellular domain of TF when expressed by these cells.

Polymorphisms of the tissue factor pathway inhibitor (TFPI) gene in patients with acute coronary syndromes and in healthy subjects : impact of the V264M substitution on plasma levels of TFPI

-Mutations of the gene encoding tissue factor pathway inhibitor (TFPI), an inhibitor of TF-induced activation of the coagulation cascade, were screened for in 130 patients and 142 healthy controls to determine whether these variants contribute to acute coronary syndromes or modify plasma TFPI levels. The following 3 new polymorphisms were identified: 384T-->C in exon IV, which does not change the corresponding amino acid (tyrosine 57); -33C-->T in intron 7 (the T/T, C/T, and C/C genotypes were found in approximately 50%, 40%, and 10% of subjects in both groups); and 874G-->A in exon IX (GTG-->ATG), which predicts a valine to methionine change (V264M) in the carboxy-terminus tail of TFPI. The V264M polymorphism was found in 9.2% of the cases and 4.9% of the controls; the associated odds ratio (OR) for acute coronary syndromes was 2.0 (95% confidence interval [CI], 0.7 to 5.1). The OR increased to 3.6 (95% CI, 0.8 to 15.7) and 3.2 (95% CI, 0.9 to 11.8) in nonsmokers and patients without other risk factors, respectively. The possible link between the V264M polymorphism and coronary heart disease was checked in a large case-control study of myocardial infarction (Etude Cas-Témoins de l'Infarctus du Myocarde [the ECTIM Study]). The results showed no link between the V264M polymorphism and coronary syndromes. Interestingly, however, 5 patients heterozygous for the V264M polymorphism had significantly lower plasma TFPI levels than did 13 patients with the most common genotype. Although our present results do not support an association between TFPI polymorphisms and acute coronary syndromes, the possibility that 1 of them, especially the exon IX polymorphism, is associated with subtypes of myocardial infarction or to evolutive particularities that were not assessed in this study, cannot be excluded and is currently being evaluated.

Tissue factor-dependent vascular endothelial growth factor production by human fibroblasts in response to activated factor VII

The transmembrane protein tissue factor (TF) is the cell surface receptor for coagulation factor VII (FVII) and activated factor VII (FVIIa). Recently, TF has been identified as a regulator of angiogenesis, tumor growth, and metastasis. This study was designed to link the binding of FVII(a) to its receptor, TF, with the subsequent triggering of angiogenesis through vascular endothelial growth factor (VEGF) production by human lung fibroblasts. We report that incubation of fibroblasts, which express constitutive surface TF, with FVII(a) induces VEGF synthesis. FVII(a)-induced VEGF secretion, assessed by a specific enzyme-linked immunosorbent assay, was time- and concentration-dependent. VEGF secretion was maximal after 24 hours of incubation of the cells with 100 nmol/L FVII(a) and represented a threefold induction of the basal VEGF level. Reverse transcriptase-polymerase chain reaction analysis of VEGF detected three mRNA species of 180, 312, and 384 bp corresponding, respectively, to VEGF121, VEGF165, and VEGF189. A 2.5- to 3.5-fold increase was observed for the 180- and 312-bp transcripts at 12 and 24 hours, respectively. FVII(a)-dependent VEGF production was inhibited by a pool of antibodies against TF, pointing to the involvement of this receptor. On specific active-site inhibition with dansyl-glutamyl-glycinyl-arginyl chloromethyl ketone, FVIIa lost 70% of its capacity to elicit VEGF production. Consistent with this, the native form (zymogen) of FVII only had a 1.8-fold stimulating effect. Protein tyrosine kinase and protein kinase C are involved in signal transduction leading to VEGF production, as shown by the inhibitory effects of genistein and GF 109203X. The results of this study indicate that TF is essential for VIIa-induced VEGF production by human fibroblasts and that its role is mainly linked to the proteolytic activity of the TF-VIIa complex.

Effect of advanced glycation end product-modified albumin on tissue factor expression by monocytes. Role of oxidant stress and protein tyrosine kinase activation

Diabetes is associated with a hypercoagulable state that contributes to macrovascular complications, including cardiovascular events. The glycation reaction, a consequence of chronic hyperglycemia, has also been implicated in the pathogenesis of diabetic complications. Glycated proteins have receptors on monocytes and generate reactive oxygen species that can regulate the expression of a number of genes. As abnormal monocyte expression of tissue factor (TF), the main initiator of the coagulation cascade, is responsible for thrombosis in a number of clinical settings, we studied the effect of glycated albumin on monocyte TF expression. Mononuclear cells were incubated with glycated albumin for 24 hours, and monocyte TF activity was measured with a plasma recalcification time assay; TF antigen was measured by ELISA and TF mRNA by RT-PCR. Glycated albumin induced blood monocyte expression of the procoagulant protein TF at the mRNA level. Oxidative stress appeared to be involved in this effect, as the antioxidant N-acetylcysteine diminished TF mRNA accumulation in stimulated monocytes. Hydroxyl radicals, which may be generated inside cells from H2O2 via the Fenton reaction, also appeared to be involved in this effect, as hydroxyl radical scavengers downregulated TF activity and antigen levels (but not TF mRNA). Finally, the involvement of activated protein tyrosine kinase in the transmission of the signal from the membrane to the nucleus was suggested by the inhibitory effect of herbimycin A. These results point to a new mechanism for the hypercoagulability often described in diabetic patients and suggest that antioxidants or protein tyrosine kinase inhibitors might be of therapeutic value in this setting.

Induction of interleukin-1 and subsequent tissue factor expression by anti-proteinase 3 antibodies in human umbilical vein endothelial cells

OBJECTIVE

To assess the ability of anti-proteinase 3 (anti-PR3) classic antineutrophil cytoplasmic antibodies (cANCA) to stimulate endothelial expression of tissue factor (TF), which is the main initiator of the coagulation cascade that can lead to endothelial injury and thrombosis in patients with Wegener's granulomatosis.

METHODS

Human umbilical vein endothelial cells (HUVEC) were grown to confluence and stimulated with affinity-purified anti-PR3 antibodies, Igs from healthy subjects, and endotoxin (lipopolysaccharide) as positive control.

RESULTS

TF activity was generated in anti-PR3-stimulated cells, as shown by a chromogenic test. This activity was inhibited by specific anti-TF antibodies. TF messenger RNA (mRNA) was found in anti-PR3-stimulated cells, as detected by reverse transcriptase-polymerase chain reaction, but not in cells stimulated with irrelevant human Igs or Igs from normal control sera. TF expression reached maximum levels 12 hours after exposure to the anti-PR3 cANCA, and did not require complement. TF mRNA expression was inhibited by cycloheximide, suggesting a requirement for protein synthesis. When added to the incubation medium, interleukin-1 (IL-1) receptor antagonist inhibited the induced TF mRNA expression, suggesting that cANCA-stimulated cells initiate IL-1 synthesis. Moreover, cANCA induced IL-1alpha mRNA before TF mRNA.

CONCLUSION

This study showed that anti-PR3 treatment of HUVEC induces sequential expression of IL-1alpha mRNA and TF mRNA, as well as their corresponding proteins. Both proteins could have pathogenic roles in the vasculitic process, since TF is the main initiator of the coagulation cascade.

Elevated cyclic AMP inhibits NF-kappaB-mediated transcription in human monocytic cells and endothelial cells

The NF-kappaB/Rel family of transcription factors regulates the inducible expression of many genes in activated human monocytes and endothelial cells. In this study, we examined the molecular mechanism by which agents that elevate intracellular cAMP inhibit the expression of the tumor necrosis factor alpha (TNFalpha), tissue factor, endothelial leukocyte adhesion molecule-1, and vascular cell adhesion molecule-1 genes. Both forskolin and dibutyryl cAMP, which elevate intracellular cAMP by independent mechanisms, inhibited TNFalpha and tissue factor expression at the level of transcription. Induction of NF-kappaB-dependent gene expression in transiently transfected human monocytic THP-1 cells and human umbilical vein endothelial cells was inhibited by elevated cAMP and by overexpression of the catalytic subunit of protein kinase A (PKA). Elevated cAMP did not prevent nuclear translocation of p50/p65 and c-Rel/p65 heterodimers, decrease nuclear translocation of p65, or significantly modify TNFalpha-induced phosphorylation of p65. Functional studies demonstrated that transcriptional activation of a plasmid containing multimerized kappaB sites by p65 was inhibited by agents that elevate cAMP and by overexpression of the catalytic subunit of PKA. This study indicates that activation of PKA reduces the induction of a distinct set of genes in monocytes and endothelial cells by inhibiting NF-kappaB-mediated transcription.

[Mass screening for colorectal cancer in France. Experience in 165,000 people in the department of Calvados]

OBJECTIVES

Screening for colorectal cancer is a major public health problem in France as in most developed countries. Several controlled trials are on-going in Europe. The aim of the study was to determine requirements for success of mass-screening for colorectal cancer in France.

METHODS

A mass-screening program has been conducted between April 1991 and June 1994 in the department of Calvados for 164,364 people aged 45-74 years. The screening test was first proposed by general practitioners and occupational doctors during appointments. Secondly, a postal invitation to obtain the test, free of charge, by doctor or chemist, was sent.

RESULTS

Global participation rate was 43.4%; 40.2% of tests were distributed during the first phase, 47.1% during the second phase and 12.7% were distributed by a private health institute. Participation was higher for females (47.1%) than males (39.2%) and for urban districts (46.5%) than rural districts (24.4%). In case of positive test, colonoscopy has been more frequently achieved in urban districts and when test has been distributed by a physician. Positivity rate was 2.8%. Positive predictive value was 8.0% for a cancer and 13.5% for an adenoma larger than 1 cm. Because both positivity rate and positive predictive value were higher for males than females and increased with age, rate of cancer or large adenoma screened was almost three times higher for males than females and markedly increased with age.

CONCLUSIONS

In France, different recruitment methods have to be used to reach a satisfactory participation to a mass-screening campaign. Such a program requires involvement of general practitioners and close coordination between practitioners and health care insurance agencies.