Autoantibodies against the fibrinolytic receptor, annexin 2, in antiphospholipid syndrome

The association of thrombosis and gestational morbidity with antiphospholipid antibodies is termed antiphospholipid syndrome (APS). Annexin 2 (A2) is a profibrinolytic endothelial cell surface receptor that binds plasminogen, its tissue activator (tPA), and beta(2)-glycoprotein I (beta2GPI), the main antigen for antiphospholipid antibodies. Here, we evaluate A2 as a target antigen in APS. Serum samples from 434 individuals (206 patients with systemic lupus erythematosus without thrombosis, 62 with APS, 21 with nonautoimmune thrombosis, and 145 healthy individuals) were analyzed by enzyme-linked immunosorbent assay (ELISA) and immunoblot for antiphospholipid and A2 antibodies. Anti-A2 antibodies (titer > 3 SDs) were significantly more prevalent in patients with APS (22.6%; venous, 17.5%; arterial, 34.3%; and mixed thrombosis, 40.4%) than in healthy individuals (2.1%, P < .001), patients with nonautoimmune thrombosis (0%, P = .017), or patients with lupus without thrombosis (6.3%, P < .001). Anti-A2 IgG enhanced the expression of tissue factor on endothelial cells (6.4-fold +/- 0.13-fold SE), blocked A2-supported plasmin generation in a tPA-dependent generation assay (19%-71%) independently of beta2GPI, and inhibited cell surface plasmin generation on human umbilical vein endothelial cells (HUVECs) by 34% to 83%. We propose that anti-A2 antibodies contribute to the prothrombotic diathesis in antiphospholipid syndrome.

Tissue Factor in Hemostasis and Thrombosis

Tissue factor (TF) plays an essential role in hemostasis. The tissue-specific pattern of TF expression is consistent with additional hemostatic protection in vital organs. An aberrant expression of TF within the vasculature occurs in a variety of diseases, including atherosclerosis, cancer, and sepsis. TF expression in these diseases is associated with thrombotic events. Future therapeutic strategies may prove beneficial in the treatment of thrombosis. However, these strategies should be designed to avoid compromising hemostasis.

Tissue Factor Expression in the Morphologic Spectrum of Vulnerable Atherosclerotic Plaques

Inflammation and thrombosis are key events in the long-lasting sequence of atherosclerotic plaque initiation, plaque growth, and eventual onset of complications leading to clinically manifest disease. Recent cellular and molecular studies have indicated that inside the plaque tissue complex, proinflammatory and prothrombotic mechanisms are intimately associated, and tissue factor (TF) is one of the main proteins that may link both processes. It is therefore not surprising that TF expression appeared to be a prominent feature in various types of vulnerable atherosclerotic plaques (i.e., lesions that specifically predispose to the onset of symptomatic atherosclerotic disease).

Tissue factor and thrombomodulin expression on endothelial cell-seeded collagen modules for tissue engineering

The creation of functional tissue engineering constructs to repair or replace diseased tissues requires a well-formed vasculature network within the construct and the endothelial cells lining that vascular bed must display a nonthrombogenic phenotype. A new approach to tissue engineering involves the assembly of smaller components (modules fabricated at the hundred micron scale) into larger constructs. The modules, collagen gel containing the particular tissue cell of interest, are covered with endothelial cells prior to assembly so that the interconnected channels that are formed are lined with endothelial cells, creating a mimic of a vascular network. Here, we confirmed (using confocal microscopy primarily) that the human umbilical vein endothelial cells, seeded on collagen gel modules without a second embedded cell and without flow, bore the molecular markers of low thrombogenicity. Two days, after seeding on the modules, endothelial cells displayed the typical cobblestone morphology, formed tight cell-cell junctions and covered the whole module surface. Immunofluorescence staining showed that at both 2 days and 7 days after seeding, only a few cells expressed tissue factor while this number was dramatically increased after TNFalpha stimulation. On the other hand, thrombomodulin was expressed by the majority of seeded cells and expression was reduced after TNFalpha stimulation.

Robust Vascular Protective Effect of Hydroxamic Acid Derivatives in a Sickle Mouse Model of Inflammation

OBJECTIVE

Clinically, the vascular pathobiology of human sickle cell disease includes an abnormal state of chronic inflammation and activation of the coagulation system. Since these biologies likely underlie development of vascular disease in sickle subjects, they offer attractive targets for novel therapeutics. Similar findings characterize the sickle transgenic mouse, which therefore provides a clinically relevant inflammation model.

METHOD

The authors tested two polyhydroxyphenyl hydroxamic acid derivatives, didox and trimidox, in sickle transgenic mice. Animals were examined by intravital microscopy (cremaster muscle and dorsal skin fold preparations) and by histochemistry before and after transient exposure to hypoxia, with versus without preadministration of study drug. Previous studies have validated the application of hypoxia/reoxygenation to sickle transgenic mice as a disease-relevant model.

RESULTS

Animals pretreated with these agents exhibited marked improvements in leukocyte/ endothelial interaction, hemodynamics and vascular stasis, and endothelial tissue factor expression. Thus, these drugs unexpectedly exert powerful inhibition on both the inflammation and coagulation systems.

CONCLUSIONS

Each of these changes is expected to be therapeutically beneficial in systemic inflammatory disease in general, and in sickle disease in particular. Thus, these novel compounds offer the advantage of having multiple therapeutic benefits in a single agent.

Preoperative serum tissue factor levels are an independent prognostic factor in patients with ovarian carcinoma

PURPOSE

Tissue factor (TF) is a procoagulant that plays an important part in tumor angiogenesis. We sought to determine the role of preoperative serum TF levels in predicting clinical outcome in patients with ovarian cancer.

MATERIALS AND METHODS

TF expression was determined by reverse transcriptase polymerase chain reaction in ovarian cell lines. Using enzyme-linked immunosorbent assay, we assessed preoperative serum TF levels in 98 women with invasive epithelial ovarian carcinoma, 30 with low malignant potential (LMP) tumors, 16 with benign tumors, and a separate validation group of 39 women with adnexal masses. Clinical information was gathered from chart review.

RESULTS

TF was expressed in four of the five ovarian cancer cell lines, but absent in the nontransformed cells. Ovarian cancer patients had a median preoperative serum TF level of 85.2 pg/mL, which was significantly higher than in those with LMP tumors (12.8 pg/mL; P < .01) and benign adnexal disease (30.7 pg/mL; P < .01). TF >or= 190 pg/mL was significantly associated with decreased patient survival (P < .01). After adjusting for other clinical variables in a multivariate Cox regression model, TF >or= 190 pg/mL was an independent prognostic factor (P < .01). Analysis of serum TF levels from the validation set confirmed that high TF (>or=190 pg/mL) was associated with a 3.4-fold increase in risk of death from disease (P = .02) and shorter survival (P = .01).

CONCLUSION

Preoperative serum TF levels are significantly elevated in patients with ovarian carcinoma. Elevated preoperative TF level is an independent prognostic factor for death from disease.

The role of tissue factor and P-selectin in the procoagulant response that occurs in the first month after on-pump and off-pump coronary artery bypass grafting

BACKGROUND

It has been previously shown that a persistent (up to 1 month) prothrombotic status occurs after coronary bypass surgery performed both on pump and off pump. To assess the pathways involved in the occurrence of postoperative prothrombotic state, in this study we evaluated plasma, monocyte-bound, and platelet-bound tissue factor expression, as well as platelet and soluble P-selectin expression, up to 1 month after off-pump and on-pump coronary artery bypass grafting.

METHODS

Thirty patient candidates for coronary surgery were randomized to undergo off-pump coronary artery bypass grafting (n = 15) or on-pump coronary artery bypass grafting (n = 15). Blood samples were collected before the intervention, after protamine administration, and 4, 8, and 30 days after surgical intervention.

RESULTS

Plasma tissue factor levels were significantly higher than baseline both in the on-pump coronary artery bypass grafting group (from protamine administration up to 4 postoperative days) and in the off-pump coronary artery bypass grafting group (at 4 postoperative days), with no differences between groups. Basal and lipopolysaccharide-stimulated monocyte tissue factor expression, as well as basal and adenosine diphosphate-stimulated platelet tissue factor expression, did not show significant variations over time and were similar in the on-pump and off-pump coronary artery bypass grafting groups throughout the course of the study. Platelet expression of P-selectin, both basal and after adenosine diphosphate stimulation, did not significantly change over time and was not different in the on-pump and off-pump coronary artery bypass grafting groups. Soluble P-selectin levels in plasma were significantly higher in patients receiving on-pump coronary artery bypass grafting only at the time point after protamine administration, whereas this variable behaved similarly in the on-pump and off-pump coronary artery bypass grafting groups for the whole postoperative period.

CONCLUSIONS

The postoperative tissue factor and P-selectin expression did not differ between the on-pump and off-pump coronary artery bypass grafting groups. The distinct increase of plasma tissue factor occurring after both surgical procedures might represent a mechanism that might explain, in part, the early postoperative prothrombotic state occurring after on-pump and off-pump coronary artery bypass grafting.

Differential expression of tissue factor (TF) in calcineurin inhibitor-induced nephrotoxicity and rejection—implications for development of a possible diagnostic marker

Deposition of fibrin in the form of fibrinoid necrosis is a common feature of severe acute renal allograft rejection. The role of the coagulation system and its initiator tissue factor (TF) during this process is, however, still poorly understood. In this study, we analyzed the expression of TF in 88 renal transplants afflicted with different forms of rejection and calcineurin inhibitor-induced nephrotoxicity, to see whether there was differential expression of this protein. TF immunoreactivity was evaluated semiquantitatively in six different renal structures: the podocytes, Bowman epithelium, the endothelium of the glomeruli, the brush border of tubular cells, the thin ascending loop of Henle, and small arteries/arterioles. The TF expression of normal renal tissue (n=6) was restricted to the glomerular podocytes and Bowman epithelium, and to some extent the ascending loop of Henle. Renal allografts undergoing acute rejection (AR) of grades I-III, (n=13, n=17 and n=12, respectively) did not show any altered TF expression in the glomeruli or vascular endothelium. In the ascending loop of Henle, a reduced expression could be seen (ARI, p=0.015; and ARII, p=0.043). TF staining of the brush border of renal transplants undergoing acute cyclosporin A (CsA) nephrotoxicity (n=18) was significantly higher than in normal kidneys (p=0.0003), as well as in transplants undergoing various degrees of acute rejection (ARI, p=0.027; ARII, p=0.0012; and ARIII, p=0.0001). Tubular brush border-expressed TF was also evident in 10 of 15 allografts suffering from chronic CsA nephrotoxicity, compared to 4 out of 13 cases with chronic allograft vasculopathy (CAV), but the increase was not statistically significant relative to normal kidneys. The majority of the grafts afflicted with either of the two chronic conditions displayed a TF-positive arterial endothelium (CAV, p=0.0034; and chronic CsA nephrotoxicity, p=0.0026) relative to controls. In conclusion, these results indicate that vascular TF expression is not altered during acute rejection, but may be of importance in chronic allograft nephropathy. Furthermore, TF immunoreactivity in the tubular brush border may be specific to acute CsA nephrotoxicity and might be used as a biomarker for this condition. Further studies are required to evaluate the possible role of brush border-expressed TF in the pathogenesis of CsA nephrotoxicity.

The Recent Finding That Tissue Factor Is Produced by the Pancreatic Islets Constitutes a Possible Link Between Insulin Resistance and Cardiovascular Disease

Approximately 70% of the patients admitted to the hospital with an acute myocardial infarction have type 2 diabetes mellitus or impaired glucose tolerance (IGT). Insulin resistance with compensatory hyperinsulinemia is a feature that is common to both type 2 diabetes and IGT. Increased risk of coronary heart disease (CHD) in conditions characterized by insulin resistance has been associated with hyperinsulinemia and hyperproinsulinemia. As indicated in several studies, there exists a connection between postprandial hyperinsulinemia/hyperglycemia and activation of the coagulation cascade. The recent finding that tissue factor (TF) is produced and secreted by the alpha and beta cells of the islets of Langerhans maybe the link between these 2 conditions. The local production of TF in human islets and excretion of microparticle-bound or alternatively spliced soluble TF in response to prolonged periods of hyperglycemia provide a tentative explanation for the activation of the TF pathway during hyperinsulinemia. Here we review the field and set forth a hypothesis that links TF expression in the islets of Langerhans to the increased risk of CHD.

Tibolone and its metabolites enhance tissue factor and PAI-1 expression in human endometrial stromal cells: Evidence of progestogenic effects

Tibolone is a highly effective postmenopausal hormone treatment that has its biological activity dependent on metabolism to 3alpha- and 3beta-OH tibolone, which bind solely to the estrogen receptor. Despite the high levels of estrogen receptor-binding metabolites in the circulation, the endometrium becomes atrophic, suggesting inactivation of the estrogen response in this tissue which may be due to the progestogenic activity of tibolone and the Delta-4 tibolone metabolite. We evaluated the effects of tibolone and its metabolites on tissue factor (TF) and plasminogen activator inhibitor type 1 (PAI-1) expression in human endometrial stromal cells (HESCs). Since TF and PAI-1 exhibit long-term in vivo and in vitro up-regulation by progestin they serve as endpoints for assessing chronic effects of progestin exposure. Confluent HESCs were primed in serum-containing medium with vehicle control, 10(-8)mol/L estradiol, 10(-7)mol/L medroxyprogesterone acetate, or 10(-8) to 10(-6)mol/L tibolone or its metabolites, then switched to a defined medium with corresponding vehicle or steroids. After 24h, ELISAs indicated that the progestin elevated TF (6.2-fold +/-3.0; p<0.05) and PAI-1 (eight-fold +/-2.1; p<0.05) levels, whereas the cells were refractory to estradiol exposure. Tibolone and Delta-4 tibolone (10(-8) to 10(-6)mol/L) were as effective as 10(-7)mol/L medroxyprogesterone acetate in enhancing TF and PAI-1 output (p<0.05). Unexpectedly, at the higher concentrations 3alpha- and 3beta-OH tibolone also elevated TF and PAI-1 expression (p<0.05). Western blotting confirmed the ELISA results. Our findings suggest that HESCs metabolize 3alpha- and 3beta-OH tibolone to tibolone and subsequently to Delta-4 tibolone, which can both stimulate the progesterone receptor. Since TF and PAI-1 promote hemostasis by complementary mechanisms, our findings account for the reduced occurrence of abnormal uterine bleeding associated with tibolone therapy.

Peptidoglycan and bacterial DNA induce inflammation and coagulation markers in synergy

Bacterial compounds signal the presence of foreign pathogens in the innate immune system. These microbial components are key players in infectious diseases and implicate toll-like receptors in the activation of inflammation and coagulation. Nevertheless, the existence of a synergistic relationship between peptidoglycan and bacterial DNA on these two physiological responses has not been investigated. The present study reports new findings on the regulation of tumor necrosis factor alpha and tissue factor in peripheral blood mononuclear cells by peptidoglycan and bacterial DNA. These were found to induce tumor necrosis factor alpha and tissue factor simultaneously and in a synergistic manner. These findings provide a new proinflammatory and procoagulant mechanism likely to play a role in sepsis pathogenesis.

[The role of tissue factor in the invasion and metastasis of colorectal carcinoma cells]

OBJECTIVE

To investigate the role of tissue factor (TF) in the invasion and hematogenous metastasis of human colorectal carcinoma cells.

METHODS

The eukaryotic expression vectors pcDNA3.1/Zeo bearing either sense or antisense TFcDNA were transfected into HT-29 and LoVo cells by the way of lipofactamine 2000. TF proteins in transfected cells were detected by Western Blot. Then the transfected and un-transfected tumor cells were implanted into nude mice (Balb/c Nu/Nu) to produce primary tumor, lung metastasis and liver metastasis respectively.

RESULTS

HT-29 and LoVo cells with sense-TFcDNA transfection showed increased TF expression compared with the cells without transfection, but the cells with antisense-TFcDNA transfection got the contrary change. The primary tumor growth and invasive range, lung metastasis and live metastasis all increased in sense transfectants but reduced in antisense transfectants.

CONCLUSIONS

TF can increase the invasion and hematogenous metastatic ability of human colorectal carcinoma cells.

Expression of protease-activated receptors and tissue factor in human liver

Thrombin, acting via protease-activated receptors (PARs), and tissue factor (TF) are involved in inflammation, tissue repair and tumorigenesis. Hepatocellular carcinomas (HCCs) usually complicate chronic liver diseases characterised by inflammation and fibrosis. The aim of this study was to describe the expression of PARs and TF in normal liver, cirrhosis and HCCs. We performed an immunohistochemical detection of PAR-1, PAR-3, PAR-4 and human TF in human tissue samples from 19 subnormal livers, 33 cirrhosis and 30 HCCs. PAR-1 was found on endothelial cells of sinusoids and larger vessels. In cirrhosis, spindle-shaped cells within septa and T lymphocytes were PAR-1 positive. A few PAR-1-positive tumour cells were found in 10% of HCCs. PAR-4 expression was restricted to macrophages, B lymphocytes and nerves. PAR-3 expression was rare. Unexpectedly, TF was expressed in 95% of normal livers and in 94% of cirrhosis but only in 50% of HCCs (p<0.001). Staining was mostly hepatocellular. No association existed between TF labelling and clinicopathological characteristics of HCCs. In conclusion, the pattern of expression of PARs is compatible with its role in chronic liver disease by promoting inflammation via immune cells and neurogenic stimulation. However, our data do not support a role for PARs or TF in HCC progression.

Activation of coagulation and inhibition of fibrinolysis in the lung after inhalation of lipopolysaccharide by healthy volunteers

Pneumonia is frequently associated with changes in coagulation and fibrinolysis in the bronchoalveolar space. To determine the effect of lipopolysaccharide (LPS) on the hemostatic balance in the human lung, six healthy subjects inhaled nebulized LPS or saline in a randomized cross-over study and bronchoalveolar lavage fluid was obtained six hours thereafter. LPS induced soluble tissue factor and thrombin-antithrombin complexes and inhibited plasminogen activator activity in BALF. Additionally plasminogen activator inhibitor type 1 production was upregulated after LPS inhalation. LPS also elicited local activation of neutrophils (release of elastase, myeloperoxidase and bactericidal/permeability increasing protein) and secretion of interleukin (IL)-6 and IL-8. Inhalation of LPS by healthy humans reproduces major features of the procoagulant response to inflammatory and infectious lung diseases and may be used as a novel model to evaluate pathogenetic mechanisms and new interventions.

Hypercoagulant states in malignant lymphoma

The incidence of severe complications, such as disseminated intravascular coagulation (DIC) in malignant lymphoma, differs between clinical stages and histological types of the disease, but they occur frequently in stage IV or natural killer (NK) cell lymphoma. Patients with stage IV or NK cell lymphoma exhibit abnormal thrombotic and hemostatic states. One of the mechanisms in DIC might involve elevated cytokine expression by lymphoma cells stimulating the expression of tissue factor (TF) in blood cells or surrounding tissue. During chemotherapy for lymphoma, the white blood cell count was significantly reduced at days 1 and 3, but significantly increased at days 7 and 9. At day 7 of chemotherapy, leukocyte TF mRNA levels were significantly increased. Plasma concentrations of granulocyte elastase derived-XDP (GEXDP) levels correlated with D-dimer levels, suggesting that almost all elevated D-dimer is GE-XDP. C-reactive protein (CRP), GE-XDP and D-dimer were significantly elevated in patients with infection, DIC or acute respiratory distress syndrome (ARDS). Analysis of patients with DIC or ARDS revealed that TF mRNA correlated with D-dimer, and GE-XDP correlated with leukocyte count, CRP and D-dimer, suggesting that inflammatory changes due to thrombosis may cause the activation of leukocytes during chemotherapy.

Up-regulation of tissue factor activity on human proximal tubular epithelial cells in response to Shiga toxin

BACKGROUND

The pathophysiology of hemolytic uremic syndrome (HUS) is incompletely established. Based on clinical studies demonstrating the presence of prothrombotic plasma markers in patients with HUS, we hypothesized that Shiga toxin might cause activation of the coagulation pathway by augmenting tissue factor, the major initiator of coagulation.

METHODS

Human proximal tubular epithelial cells (PTECs) [human kidney-2 (HK-2 cells)] were exposed to Shiga toxin-1, and expression of tissue factor, cell detachment, protein synthesis, caspase-3 activity, and Shiga toxin-1 binding were examined. Results. HK-2 cells expressed constitutive surface tissue factor activity and increased their tissue factor expression upon exposure to Shiga toxin-1. Shiga toxin-1 bound to HK-2 cells and inhibited protein synthesis. The up-regulation of tissue factor was dose- and time-dependent and strongly correlated with cell detachment and increase in caspase-3 activity caused by Shiga toxin-1 exposure. A general caspase inhibitor simultaneously inhibited HK-2 cell detachment and tissue factor up-regulation while mutant Shiga toxin-1 neither caused cell detachment, protein synthesis inhibition, nor increase in tissue factor activity. Tissue factor activity elicited by Shiga toxin-1 was abrogated by a monoclonal antitissue factor antibody. Calphostin C, a protein kinase C (PKC) inhibitor, partially blocked tissue factor up-regulation, indicating possible involvement of PKC-dependent mechanism.

CONCLUSION

These data, taken together, suggest a strong link between Shiga toxin-induced up-regulation of tissue factor activity, cytotoxicity, and apoptosis in HK-2 cells. The proximal tubule is a target of Shiga toxin in HUS, and it seems plausible that injured proximal tubular cells trigger the activation of the coagulation system, the formation of intrarenal platelet-fibrin thrombi, and the development of acute renal failure in HUS.

Einfluss verminderter Scherkräfte auf Entzündungsreaktionen in vitro

BACKGROUND

During malperfusion and inflammation leukocyte adhesion is common. The purpose of this study was to examine the effects of reduced shear stress on leukocyte-endothelial interactions and subsequent inflammatory reactions such as up-regulation of tissue factor.

METHODS

Isolated neutrophils and monocytes were co-incubated with human umbilical venous endothelium at 0-3 dynes/cm(2) in a flow chamber. Adhesion and tissue factor expression on adherent leukocytes were examined at various flow conditions.

RESULTS

At 2-3 dynes/cm(2) adhesion occurred only on TNFalpha-activated endothelium. Below 1 dyne/cm(2) similarly increased adhesion was also observed on non-activated endothelium. As was observed for leukocyte adhesion, these shear stress-dependent cell interactions also resulted in an up-regulation of tissue factor on adherent monocytes from non-activated co-cultures.

CONCLUSION

Apart from additional activators of inflammation, reduced shear forces may directly contribute to inflammation.

Histamine Induces Tissue Factor Expression

Background— Histamine can induce coronary vasospasm, leading to variant angina and acute myocardial infarction. However, the role of histamine in thrombus formation is ill defined. Hence, this study investigates whether histamine induces tissue factor (TF) expression in vascular cells.

Methods and Results— Histamine (10 −8 to 10 −5 mol/L) induced TF expression in a concentration-dependent manner in human aortic endothelial and vascular smooth muscle cells, whereas TF pathway inhibitor expression remained unaffected. RT-PCR and Northern blotting revealed that histamine stimulated TF mRNA transcription, peaking at 1 hour. Protein expression increased 18-fold ( P <0.02) with a maximum at 5 hours, which was paralleled by a 4-fold augmentation in surface activity ( P <0.01). These effects were completely prevented by pretreatment with the H 1 receptor antagonists mepyramine ( P <0.0001), chlorpheniramine, and diphenhydramine but not the H 2 receptor antagonist cimetidine ( P =NS). Histamine induced a time-dependent, H 1 receptor–mediated activation of p38 MAP kinase (p38), p44/42 MAP kinase (ERK), and c-jun terminal NH 2 kinase (JNK). Blocking of p38, ERK, or JNK with SB203580 ( P <0.0001), PD98059 ( P <0.0001), or SP600125 ( P <0.0001), respectively, impaired histamine-induced TF expression in a concentration-dependent manner. In contrast, histamine-stimulated TF expression was increased by phosphatidylinositol 3-kinase inhibition with LY294002 or wortmannin, whereas it was not affected by Rho-kinase inhibition with Y-27632 or hydroxyfasudil.

Conclusions— Histamine induces expression of TF, but not TF pathway inhibitor, in vascular cells via activation of the H 1 , but not H 2 , receptor. This effect is mediated by the MAP kinases p38, ERK, and JNK. This observation may open novel perspectives in the treatment of variant angina and acute coronary syndromes.

Sirolimus increases tissue factor expression but not activity in cultured human vascular smooth muscle cells

Background

Sirolimus-eluting stents (CYPHER stents) demonstrated remarkable efficacy in reducing restenosis rates in patients with coronary artery disease. There is a concern of sub-acute and late stent thrombosis. Tissue factor (TF) is critical in thrombosis. This study investigated the effect of sirolimus on TF expression and activity in cultured human vascular smooth muscle cells (SMCs).

Methods

SMCs were cultured from human saphenous veins and aortas. Quiescent cells were stimulated with sirolimus (0.1 – 20 ng/ml) over 24 hours. Cellular TF expression and activity released into culture medium were measured. The effect of sirolimus on activation of mammalian target of rapamycin (mTOR) was measured by phosphorylation of the substrate p70s6k at T389, and activation of RhoA was measured by pull-down assay.

Results

Sirolimus increased TF protein level in cultured human SMCs in a concentration and time-dependent manner (about 2-fold, p < 0.01) reaching maximal effect at 5 ng/ml. The stimulation of TF expression by sirolimus was associated with inhibition of basal activity of mTOR. No effects of sirolimus on RhoA or p38mapk activation that are positive regulators of TF in vascular wall cells were observed. The stimulation of TF expression by sirolimus (20 ng/ml) was prevented by the HMG-CoA reductase inhibitor fluvastatin (1 μmol/L). However, no increase in TF activity released from SMC into culture medium was observed after sirolimus treatment.

Conclusion

Although sirolimus stimulates TF protein expression in human SMC associated with inhibition of mTOR, it does not enhance TF activity released from the cells, suggesting a relatively safe profile of CYPHER stents. The inhibition of TF expression by fluvastatin favors clinical use of statins in patients undergoing coronary stenting.

Incorporation of Factor Va into Prothrombinase Is Required for Coordinated Cleavage of Prothrombin by Factor Xa

Prothrombin is activated to thrombin by two sequential factor Xa-catalyzed cleavages, at Arg271 followed by cleavage at Arg320. Factor Va, along with phospholipid and Ca2+, enhances the rate of the process by 300,000-fold, reverses the order of cleavages, and directs the process through the meizothrombin pathway, characterized by initial cleavage at Arg320. Previous work indicated reduced rates of prothrombin activation with recombinant mutant factor Va defective in factor Xa binding (E323F/Y324F and E330M/V331I, designated factor VaFF/MI). The present studies were undertaken to determine whether loss of activity can be attributed to selective loss of efficiency at one or both of the two prothrombin-activating cleavage sites. Kinetic constants for the overall activation of prothrombin by prothrombinase assembled with saturating concentrations of recombinant mutant factor Va were calculated, prothrombin activation was assessed by SDS-PAGE, and rate constants for both cleavages were analyzed from the time course of the concentration of meizothrombin. Prothrombinase assembled with factor VaFF/MI had decreased k(cat) for prothrombin activation with Km remaining unaffected. Prothrombinase assembled with saturating concentrations of factor VaFF/MI showed significantly lower rate for cleavage of plasma-derived prothrombin at Arg320 than prothrombinase assembled with saturating concentrations of wild type factor Va. These results were corroborated by analysis of cleavage of recombinant prothrombin mutants rMz-II (R155A/R284A/R271A) and rP2-II (R155A/R284A/R320A), which can be cleaved only at Arg320 or Arg271, respectively. Time courses of these mutants indicated that mutations in the factor Xa binding site of factor Va reduce rates for both bonds. These data indicate that the interaction of factor Xa with the heavy chain of factor Va strongly influences the catalytic activity of the enzyme resulting in increased rates for both prothrombin-activating cleavages.

Involvement of p38 MAPK in the up-regulation of tissue factor on endothelial cells by antiphospholipid antibodies

OBJECTIVE

To study the intracellular mechanism involved in the up-regulation of tissue factor (TF) on endothelial cells (ECs) by antiphospholipid antibodies (aPL), we examined the effects of aPL on the transcription, expression, and function of TF, the expression of interleukin-6 (IL-6) and IL-8, the induction of inducible nitric oxide synthase (iNOS), and the phosphorylation of p38 MAPK on human umbilical vein ECs (HUVECs).

METHODS

Cultured HUVECs were treated with IgG aPL (from patients with antiphospholipid syndrome [APS]) or with control IgG (from normal human serum). Phorbol myristate acetate (PMA) and bacterial lipopolysaccharide (LPS) were used as positive controls. TF expression was determined on the surface of HUVECs using an enzyme-linked immunosorbent assay (ELISA). TF activity was determined with the use of a chromogenic assay in cell lysates, and TF messenger RNA (mRNA) was determined by real-time quantitative polymerase chain reaction. Phosphorylation of p38 MAPK and induction of iNOS were determined by Western blotting, and levels of IL-6 and IL-8 were determined by ELISA.

RESULTS

PMA, LPS, and aPL significantly increased the expression of TF compared with controls. This up-regulation was significantly inhibited by SB203580 (a specific inhibitor of p38 MAPK) and by MG132 (a specific inhibitor of NF-kappaB). TF activity was significantly increased by treatment with IgG aPL and this effect was also inhibited by SB203580. Incubation of HUVECs with aPL increased TF mRNA 2-15-fold; these effects were abrogated by SB203580. IgG aPL induced significant phosphorylation of p38 MAPK and produced iNOS on HUVECs in a time-dependent manner. Treatment with IgG aPL also induced increased expression of IL-6 and IL-8 on HUVECs.

CONCLUSION

Our data show that aPL induces significant increases in TF transcription, function, and expression, in IL-6 and IL-8 up-regulation, and in iNOS expression on HUVECs and that these processes involve phosphorylation of p38 MAPK and activation of NF-kappaB. Understanding intracellular events in aPL-mediated EC activation may help in designing new targeted therapies for thrombosis in APS.

Procoagulant Soluble Tissue Factor Is Released From Endothelial Cells in Response to Inflammatory Cytokines

Inflammatory cytokines alter the hemostatic balance of endothelial cells (ECs). Alternatively spliced human tissue factor (asHTF), a soluble isoform of tissue factor (TF), has recently been detected in ECs, possibly contributing to procoagulability. Agonists regulating asHTF expression and release are yet unknown. This study examines the effect of TNF-alpha and IL-6 on the endothelial expression of both TF variants and delineates the impact of asHTF on the procoagulability of extracellular fluids. asHTF and TF mRNA were assessed by real-time PCR, and asHTF, TF, and tissue factor pathway inhibitor (TFPI) proteins by Western blot and fluorescence microscopy before and after stimulation with TNF-alpha (10 ng/mL) or IL-6 (10 ng/L). The procoagulability of cell supernatant was analyzed by a chromogenic assay with or without phospholipid vesicles. We found asHTF mRNA to be maximally increased 10 minutes after TNF-alpha and 40 minutes after IL-6 treatment (asHTF/GAPDH ratio 0.0223+/-0.0069 versus 0.0012+/-0.0006 for control, P<0.001 and 0.0022+/-0.0004 versus 0.0012+/-0.0007, P<0.05, respectively). Not only was asHTF increased, but also TFPI decreased after cytokine treatment. asHTF was found in the supernatant as early as 5 hours after TNF-alpha stimulation, supporting factor Xa generation after relipidation (6.55+/-1.13 U versus 2.99+/-0.59 U in control supernatant, P<0.00001). Removal of asHTF from supernatants by immunoprecipitation diminished its procoagulability to baseline. The soluble TF isoform expressed and released from ECs in response to inflammatory cytokines becomes procoagulant in the presence of phospholipids. Thus, asHTF released from ECs is a marker for and a contributor to imbalanced hemostasis.