Tissue Factor Reduction and Tissue Factor Pathway Inhibitor Release after Heparin Administration

Studies on Tissue Factor Pathway Inhibitor Antigen Release by Bovine, Ovine and Porcine Heparins Following Intravenous Administration to Non-Human Primates

Unfractionated heparin (UFH) is a sulfated glycosaminoglycan that consists of repeating disaccharides, containing iduronic acid (or glucuronic acid) and glucosamine, exhibiting variable degrees of sulfation. UFHs release tissue factor pathway inhibitor (TFPI) which inhibits the extrinsic pathway of coagulation by inactivating factor Xa and the factor VIIa/TF complex. Most heparins used clinically are derived from porcine intestinal mucosa however, heparins can also be derived from tissues of bovine and ovine origin. Currently there are some concerns about the shortage of the porcine heparins as they are widely used in the manufacturing of the low molecular weight heparins (LMWHs). Moreover, due to cultural and religious reasons in some countries, alternative sources of heparins are needed. Bovine mucosal heparins (BMH) are currently being developed for re-introduction to the US market for both medical and surgical indications. Compared to porcine mucosal heparin (PMH), BMH exhibits a somewhat weaker anti-coagulant activity. In this study, we determined the TFPI antigen level following administration of various dosages of UFHs from different origins. These studies demonstrated that IV administration of equigravemetric dosages of PMH and ovine mucosal heparin (OMH) to non-human primates resulted in comparable TFPI antigen release from endothelial cells. In addition, the levels of TFPI were significantly higher than TFPI antigen levels observed after BMH administration. Potency adjusted dosing resulted in comparable TFPI release profiles for all 3 heparins. Therefore, such dosing may provide uniform levels of anticoagulation for the parenteral indications for UFHs. These observations warrant further clinical validation in specific indications.

COVID-19, hemostasis disorders and risk of thrombotic complications

The spread of a new coronavirus infection worldwide since the end of 2019 has becomes a pandemic. Thrombotic complications are the leading cause of death in this disease. After entering the human body, the virus starts a cascade of reactions leading to the development of a cytokine storm, activation of all parts of the hemostasis and complement systems and other changes that result in disturbances in the circulation system with the development of multiple organ failures. Numerous studies have shown that a predictor of a severe course of COVID-19 is a sharp increase of D-dimer concentration in the blood and rise of some other markers of hemostasis activation. Based on the pathogenesis, the developed schemes for the prevention and treatment of COVID-19 severe complications include low molecular weight heparins (LMWH) which are also recommended for an outpatient COVID-19 patient. The prescription of low molecular weight heparin, the duration of their use and doses should be decided on the basis of a risk assessment of factors for each individual patient in combination with laboratory monitoring.

The Role of Tinzaparin in Oncology

Current guidelines recommend low-molecular-weight heparin treatment in patients with cancer with established venous thromboembolism (VTE). The aim of this article was to study the pharmacological properties and effectiveness of tinzaparin in patients with cancer as well as its potential anticancer properties. A search of PubMed and ScienceDirect databases up to March 2016 was carried out to identify published studies that detect the properties and use of tinzaparin in oncology. Protamine sulfate partially (60% to 65%) neutralized tinzaparin’s anti-Xa activity. No dose adjustment of tinzaparin is needed even in patients with severe renal impairment and Creatinine Clearance ≥20 mL/min. Tinzaparin demonstrated a statistically significant decline in VTE recurrence at 1 year post the index thromboembolic event. A statistically significant reduction in minor bleeding rates was also described, whereas major bleeding events did not decrease in patients with cancer treated with tinzaparin versus those who received vitamin K antagonists. Tinzaparin treatment in patients suffering from deep vein thrombosis reduced the incidence of postthrombotic syndrome and venous ulcers. Tinzaparin’s ability to prevent both metastatic dissemination of cancer cells and tumor angiogenesis has been delineated in preclinical research. Current data show that tinzaparin is safe and efficacious either for short-term or for long-term treatment of VTE in patients with cancer. Clinical trials are needed in order to examine the utility of tinzaparin in primary prevention of VTE and validate its potential anticancer advantages exhibited in preclinical research.

A trial of nebulised heparin to limit lung injury following cardiac surgery

Cardiac surgery with cardiopulmonary bypass triggers an acute inflammatory response in the lungs. This response gives rise to fibrin deposition in the microvasculature and alveoli of the lungs. Fibrin deposition in the microvasculature increases alveolar dead space, while fibrin deposition in alveoli causes shunting. We investigated whether prophylactic nebulised heparin could limit this form of lung injury. We undertook a single-centre double-blind randomised trial. Forty patients undergoing elective cardiac surgery with cardiopulmonary bypass were randomised to prophylactic nebulised heparin (50,000 U) or placebo. The primary endpoint was the change in arterial oxygen levels over the operative period. Secondary endpoints included end-tidal CO₂, the alveolar dead space fraction and bleeding complications. We found nebulised heparin did not improve arterial oxygen levels. Nebulised heparin was, however, associated with a lower alveolar dead space fraction (P <0.05) and lower tidal volumes at the end of surgery (P <0.01). Nebulised heparin was not associated with bleeding complications. In conclusion, prophylactic nebulised heparin did not improve oxygenation, but was associated with evidence of better alveolar perfusion and CO₂elimination at the end of surgery.

Low anticoagulant heparin blocks thrombin-induced endothelial permeability in a PAR-dependent manner

Acute lung injury and acute respiratory distress syndrome are accompanied by thrombin activation and fibrin deposition that enhance lung inflammation, activate endothelial cells and disrupt lung paracellular permeability. Heparin possesses anti-inflammatory properties but its clinical use is limited by hemorrhage and heparin induced thrombocytopenia. We studied the effects of heparin and low anticoagulant 2-O, 3-O desulfated heparin (ODSH) on thrombin-induced increases in paracellular permeability of cultured human pulmonary endothelial cells (ECs). Pretreatment with heparin or ODSH blocked thrombin-induced decrease in the EC transendothelial electrical resistance (TER), attenuated thrombin-stimulated paracellular gap formation and actin cytoskeletal rearrangement. Our data demonstrated that heparin and ODSH had inhibitory effects on thrombin-induced RhoA activation and intracellular calcium elevation. Thrombin-stimulated phosphorylation of the cytoskeletal regulatory proteins, myosin light chain and ezrin/radixin/moesin was also reduced. In these effects, low anticoagulant ODSH was more potent than heparin. Heparin or ODSH alone produced decreases in the EC TER that were abolished by siRNA-mediated depletion of the thrombin receptor, PAR-1. We also demonstrated that, in contrast to heparin, ODSH did not possess thrombin-binding activity. Results suggest that heparin and low anticoagulant ODSH can interfere with thrombin-activated signaling.

Evaluation of the blood compatibility of materials, cells, and tissues: basic concepts, test models, and practical guidelines

Medicine today uses a wide range of biomaterials, most of which make contact with blood permanently or transiently upon implantation. Contact between blood and nonbiological materials or cells or tissue of nonhematologic origin initiates activation of the cascade systems (complement, contact activation/coagulation) of the blood, which induces platelet and leukocyte activation. Although substantial progress regarding biocompatibility has been made, many materials and medical treatment procedures are still associated with severe side effects. Therefore, there is a great need for adequate models and guidelines for evaluating the blood compatibility of biomaterials. Due to the substantial amount of cross talk between the different cascade systems and cell populations in the blood, it is advisable to use an intact system for evaluation. Here, we describe three such in vitro models for the evaluation of the biocompatibility of materials and therapeutic cells and tissues. The use of different anticoagulants and specific inhibitors in order to be able to dissect interactions between the different cascade systems and cells of the blood is discussed. In addition, we describe two clinically relevant medical treatment modalities, the integration of titanium implants and transplantation of islets of Langerhans to patients with type 1 diabetes, whose mechanisms of action we have addressed using these in vitro models.

Tissue factor, blood coagulation, and beyond: an overview

Emerging evidence shows a broad spectrum of biological functions of tissue factor (TF). TF classical role in initiating the extrinsic blood coagulation and its direct thrombotic action in close relation to cardiovascular risks have long been established. TF overexpression/hypercoagulability often observed in many clinical conditions certainly expands its role in proinflammation, diabetes, obesity, cardiovascular diseases, angiogenesis, tumor metastasis, wound repairs, embryonic development, cell adhesion/migration, innate immunity, infection, pregnancy loss, and many others. This paper broadly covers seminal observations to discuss TF pathogenic roles in relation to diverse disease development or manifestation. Biochemically, extracellular TF signaling interfaced through protease-activated receptors (PARs) elicits cellular activation and inflammatory responses. TF diverse biological roles are associated with either coagulation-dependent or noncoagulation-mediated actions. Apparently, TF hypercoagulability refuels a coagulation-inflammation-thrombosis circuit in “autocrine” or “paracrine” fashions, which triggers a wide spectrum of pathophysiology. Accordingly, TF suppression, anticoagulation, PAR blockade, or general anti-inflammation offers an array of therapeutical benefits for easing diverse pathological conditions.

Low molecular weight heparin downregulates tissue factor expression and activity by modulating growth factor receptor-mediated induction of nuclear factor-κB

Treatment of cancer patients with low molecular weight heparin (LMWH) appears to have beneficial effects. In this study, the influence of low molecular weight heparin (LMWH) on tissue factor (TF) expression and activity in five cell lines from various tissues was analysed and explored. Incubation of cells with LMWH (0-2000μg/ml) resulted in the downregulation of TF mRNA expression which was both LMWH concentration-dependent and time-dependent. Downregulation of TF was also measured as decreased cellular TF antigen and activity. Consistently, incubation of cells with LMWH suppressed the nuclear localisation and the transcriptional activity of NFκB. Decreased TF mRNA was largely achievable by incubating the cells with an NFκB inhibitor alone whilst incubation with betulinic acid to activate NFκB reversed the inhibitory influence of LMWH. Cells were also incubated with a range of concentrations of EGF (0-10ng/ml), bFGF (0-20ng/ml) or VEGF (0-4ng/ml) in the presence or absence of LMWH (200μg/ml) for 24h and TF antigen measured. Inclusion of LMWH reduced TF expression in response to EGF, bFGF or VEGF but TF expression was partially restored by increasing concentrations of the growth factors. We conclude that LMWH downregulates TF expression in vitro through a mechanism that involves interference with the function of growth factors which in turn is mediated through the downregulation of the transcriptional activity of NFκB. This mechanism may also explain some of the beneficial influences attributed to LMWH therapy in the treatment of cancer patients.

Low molecular weight heparin suppresses tissue factor-mediated cancer cell invasion and migration in vitro

Elevated expression of tissue factor (TF) has been associated with an increased risk of thrombosis in the majority of cancers. Moreover, treatment of cancer patients with low molecular weight heparin (LMWH) appears to have beneficial effects that reach beyond controlling the immediate hypercoagulable state. In this study, we investigated the influence of the treatment of cancer cells with LMWH (0-2,000 μg/ml) on cell invasiveness and migration in cancer cell lines from five separate tissues; pancreatic, breast, colocarcinoma, ovarian and melanoma. The rate of cell invasion across collagen IV-coated membranes was suppressed in all cell lines tested on incubation with 2,000 μg/ml LMWH, but BxPC-3 and MDA-MB-231 cells also responded to the lowest concentration of 20 μg/ml LMWH. Furthermore, the rate of cell migration was reduced to varying extents in all of the cell lines tested on incubation with 20 μg/ml or higher concentrations of LMWH. The decrease in the rates of invasion and migration also strongly correlated with the reduction in TF protein expression and TF activity in these cells following incubation with LMWH. Moreover, the LMWH-mediated decreases in cellular invasion in the most affected cell lines (BxPC-3 and MDA-MB-231) were restored by transfection of the cells with the mammalian pCMV-XL5-TF expression vector allowing independent overexpression of TF. In conclusion, LMWH appears to suppress the rate of cancer cell invasion and migration in vitro, through a mechanism that is at least in part dependent on the TF protein expression and activity in cancer cells.

Effects of enoxaparin preparations on thrombin generation and their correlation with their anti-FXa activity

OBJECTIVE

Anticoagulant effect of LMWHs is monitored by anti-factor Xa (anti-FXa) activity assay. Since this test has several limitations, the aim of this study was to explore the activity of two LMWHs by thrombin generation assay (TG, which presents an overall picture of hemostatic balance) and its correlation with their anti-FXa activity.

METHODS

In an open-label, randomized cross-over study, 40  mg of two enoxaparins, the original branded formulation (R) and another one, also marketed in Argentina (T), were daily injected subcutaneously, for 7 days, to 20 healthy volunteers, with a 7-day washout interval. Blood samples were collected before treatment and 180  minutes after the injection on days 3 and 7. TG in platelet-poor plasma activated with tissue factor was assessed by lag time (LT), time to peak (TTP), peak (PTG), and endogenous thrombin potential (ETP). Anti-FXa and anti-FIIa activities, free tissue factor pathway inhibitor (free TFPI), tissue plasminogen activator (t-PA), plasminogen activator inhibitor type 1 (PAI-1), and euglobulin lysis time (ELT) were also assayed.

RESULTS

The mean (SD) anti-FXa (UI/ml) for T and R increased on days 3 and 7. LT and TTP were significantly prolonged by both LMWHs, with no differences between them. The mean ETP (nmol/L) for T and R at 3 and 7 days after treatment were significantly reduced when compared with basal values (p = 0.001 for all). On day 3, a significant correlation was shown between the variables describing TG and anti-FXa for T and R, without differences between them, for LT (r: 0.516 and 0486), ETP (r: 0.532 and 0.574), PEAK (r: 0.482 and 0.501), and TTP (r: 0.577 and 0.503), respectively. This correlation was also significant on day 7. Anti-FIIa activity and free TFPI increased significantly at 3 and 7 days for both LMWHs, without differences between them. R and T decreased ELT and PAI-1, but had no effect on t-PA. There were no differences between both LMWHs in routine hemostatic tests. No adverse events were reported.

CONCLUSIONS

Correlation between TG and anti-FXa activity was good. Both enoxaparins induced similar change of coagulation parameters, with a significant increase in fibrinolytic activity.

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.

Biomarkers and coagulation tests for assessing the biosimilarity of a generic low-molecular-weight heparin: results of a study in healthy subjects with enoxaparin

Low-molecular-weight heparins (LMWHs) differ considerably in their influence on clotting tests and release of tissue factor pathway inhibitor (TFPI). Biosimilarity therefore becomes an issue when generic forms of LMWHs are developed. So far, no bioequivalence study with a generic LMWH has been reported. A generic enoxaparin (test) was compared with the originator (reference) in 20 volunteers after single-dose subcutaneous administration (40 mg enoxaparin sodium, 4000 IU/mL anti-factor Xa (anti-FXa; activity). Target variables were anti-FXa and anti-FIIa activity, activated partial thromboplastin time (aPTT), prothrombinase-induced clotting time (PiCT), and TFPI over 24 hours. The statistical evaluation of the anti-FXa activity profile demonstrated bioequivalence of test and reference with confidence intervals of area under the plasma concentration-time curve (AUC0-tlast) (93%-99%) and Amax (88%-95%). Confidence intervals of AUC(0-tlast) (89%-102%) and Amax (90%-103%) of anti-FIIa activity also fulfill bioequivalence criteria. The 90% confidence interval for the maximum concentration of TFPI ranged from 90% to 113%. The claim of similarity was also supported by aPTT and PiCT profiles. Bioequivalence with the originator enoxaparin could be demonstrated by ex vivo inhibition of FXa and FIIa activity, by coagulation tests (aPTT and PiCT), and by in vivo release of TFPI. Whether such data also prove biosimilarity of the generic enoxaparin needs to be determined.

Elevated pulmonary dead space and coagulation abnormalities suggest lung microvascular thrombosis in patients undergoing cardiac surgery

OBJECTIVE

Inflammation has been shown to trigger microvascular thrombosis. Patients undergoing cardiac surgery sustain significant inflammatory insults to the lungs and in addition are routinely given anti-fibrinolytic agents to promote thrombosis. In view of these risk factors we investigated if evidence of pulmonary microvascular thrombosis occurs following cardiac surgery and, if so, whether a pre-operative heparin infusion may limit this.

DESIGN

Double-blind randomised controlled trial.

SETTING

Tertiary university affiliated hospital.

PATIENTS

Twenty patients undergoing elective cardiac surgery.

INTERVENTIONS

Patients were randomised to receive a pre-operative heparin infusion or placebo. All patients were administered aprotinin.

MEASUREMENTS AND RESULTS

Pulmonary microvascular obstruction was estimated by measuring the alveolar dead-space fraction. Pulmonary coagulation activation was estimated by measuring the ratio of prothrombin fragment levels in radial and pulmonary arterial blood. Systemic tissue plasminogen activator (t-PA) levels were also assessed. In the placebo group cardiac surgery triggered increased alveolar dead-space fraction levels and the onset of prothrombin fragment production in the pulmonary circulation. Administration of pre-operative heparin was associated with a lower alveolar dead-space fraction (p < 0.05) and reduced prothrombin fragment production in the pulmonary circulation (p < 0.05). Pre-operative heparin also increased baseline t-PA levels (p < 0.05).

CONCLUSION

The changes in the alveolar dead-space fraction and pulmonary coagulation activation suggest that pulmonary microvascular thrombosis develops during cardiac surgery and this may be limited by a pre-operative heparin infusion.

The haemostatic role of tissue factor pathway inhibitor

Under normal conditions the blood circulates freely within the confines of the vascular system, carrying oxygen, nutrients, and hormonal information around the body and removing metabolic waste. If blood gains access to extravascular sites, or the vasculature becomes pathologically challenged, hemostasis may be activated. This process is finely regulated by positive and negative feedback loops that modulate fibrin clot formation. Blood coagulation revolves around the activation and assembly of the components of the prothrombinase complex, which converts the inactive zymogen, prothrombin, into its active form, thrombin. This serine protease catalyzes the conversion of fibrinogen to fibrin, the structural scaffold that stabilizes platelet aggregates at sites of vascular injury. The extent of the hemostatic response is controlled by the action of inhibitory pathways, which ensure that thrombin activity and the spread of the hemostatic plug is limited to the site of vessel damage. This review article focuses on the major physiological regulator of tissue factor-induced coagulation, tissue factor pathway inhibitor, its expression, anticoagulant function, and its role in normal hemostasis.

Plasma markers of activated hemostasis in the early diagnosis of acute coronary syndromes

BACKGROUND

Because acute coronary syndromes (ACS) are caused by intracoronary thrombosis, plasma markers of coagulation have relevance for early diagnosis.

AIMS AND OBJECTIVES

To provide a critical review of these studies and specific attempts to close the diagnostic time gap left by traditional plasma markers of heart injury.

METHODS

Studies of ACS patients, with at least one control group, were included when blood samples were taken within 24 h after first symptoms prior to medication or intervention. Special attention was paid to studies reporting diagnostic performance, or combination of several markers into a single diagnostic index.

RESULTS

Markers with short plasma half-life (FPA, TAT, etc.) reflect ongoing thrombosis and may identify patients at increased risk. Markers with longer half-life (F1+2, D-Dimer, etc.) may be more useful to indicate a single acute thrombotic event. However, results are highly variable and depend on sampling time, clot property, degree of coronary obstruction and physiological condition. Early diagnostic performance of hemostatic markers was poor even when combined with heart injury markers.

CONCLUSIONS

Early measurement of hemostatic plasma markers in ACS patients provides pathophysiological information and may be helpful in risk stratification or to monitor anticoagulant therapy, but does not seem useful in routine clinical diagnosis of ACS.

Immunologic quantitation of tissue factors

The large number of conflicting reports on the presence and concentration of circulating tissue factor (TF) in blood generates uncertainties regarding its relevance to hemostasis and association with specific diseases. We believe that the source of these controversies lies in part in the assays used for TF quantitation. We have developed a highly sensitive and specific double monoclonal antibody fluorescence-based immunoassay and integrated it into the Luminex Multi-Analyte Platform. This assay, which uses physiologically relevant standard and appropriate specificity controls, measures TF antigen in recombinant products and natural sources including placenta, plasma, cell lysates and cell membranes. Comparisons of reactivity patterns of various full-length and truncated TFs on an equimolar basis revealed quantitative differences in the immune recognition of TFs by our antibodies in the order of TF 1-263 > 1-242 > 1-218 > placental TF. Despite this differential recognition, all TF species are quantifiable at concentrations < or = 2 pM. Using a calibration curve constructed with recombinant TF 1-263 and plasma from healthy individuals (n = 91), we observed the concentration of TF antigen in plasma to be substantially lower than that generally reported in the literature: TF antigen in plasma of 72 individuals (79%) was below 2 pM (quantitative limit of our assay); TF antigen levels between 2.0 and 5.0 pM could be detected in six individuals (7%); and in 14% (13 plasmas), the non-specific signal was higher than the specific signal, and thus TF levels could not be determined. These differential recognition patterns affect TF quantitation in plasma and should be considered when evaluating plasma TF-like antigen concentrations.

Combinations of Low Doses of Unfractionated Heparin and of Low-Molecular-Weight Heparin Prevent Experimental Venous Thrombosis

Synergism between low-molecular-weight heparin and low doses of unfractionated heparin (UH) enhancing anti-factor Xa activity and the release of tissue factor pathway inhibitor was observed. The aim of this study was to verify whether this association is effective in preventing experimental venous thrombosis. Seventy rats were allocated into 7 groups: the control group treated with distilled water, the H(350) group treated with UH 350 IU/kg, the E(2) group treated with enoxaparin 2 mg/kg, the H(175) group treated with UH 175 IU/kg, the E(1) group treated with enoxaparin 1 mg/kg, the H(175) + E(1) group treated with UH 175 IU/kg plus enoxaparin 1 mg/kg, and the H(100) + E(0.5) group treated with UH 100 IU/kg plus enoxaparin 0.5 mg/kg. Forty minutes after subcutaneous injection, thrombosis was induced in vena cava. Three hours later, if present, thrombi were withdrawn and weighed. Bleeding time, activated partial thromboplastin time, thrombin time (TT), and anti-factor Xa were measured at the beginning and end of the experiment. Forty-eight other animals were treated, but without inducing thrombus, and tests were performed 40 min after injection. Thrombus developed in 90.9% of control animals, 20% of the H(350) group, 22.2% of the E(2) group, 10% of the H(175) + E(1) group, and 30% of the H(100) + E(0.5) group; there was a difference between group C and the other groups. Only in the H(350) and H(175) + E(1) groups were TT and activated partial thromboplastin time prolonged in relation to control at the end of the experiment. Forty minutes after injection, TT was prolonged in the H(350) and H(175) + E(1) groups. In conclusion, combinations of low doses of low-molecular-weight heparin and low doses of UH were as effective as high doses of each one used alone in preventing thrombus development in rat vena cava.

C-reactive protein contributes to the hypercoagulable state in coronary artery disease

OBJECTIVES

Elevated plasma C-reactive protein (CRP) levels predict coronary events, but it is unclear whether CRP plays a role in thrombosis associated with these events. We investigated tissue factor (TF) induction by CRP on peripheral blood mononuclear cells (PBMC) from patients with coronary disease.

PATIENTS AND METHODS

PBMC from 35 patients with stable angina (SA) in study 1, 10 male patients with SA, 10 with unstable angina (UA) and 10 matched controls in study 2, and 25 patients with inflammatory disorders (ID) and 24 normal controls in study 3 were stimulated with CRP, interferon-gamma (IFN) or lipopolysaccharide (LPS), or their combination. PBMC from additional normal donors were also stimulated with CRP in adherent and non-adherent conditions, and TF activity, antigen and mRNA expression detected.

RESULTS

CRP (5-25 microg mL(-1)) dose dependently induced more TF on PBMC from SA patients than 42 contemporary controls (P = 0.001, study 1). Compared with controls, patients with SA or UA had higher basal, and much higher CRP- or CRP/LPS-induced monocyte TF activity although serum CRP levels were similar (study 2). IFN induced monocyte TF activity in patients with angina, but not in controls. Basal or CRP-induced TF levels did not differ between controls and ID, even though ID patients had much higher serum CRP levels (study 3). CRP-induced monocyte TF activity correlated with serum CRP levels in controls (P = 0.005) and ID (P = 0.007) in study 3, but not in patients with angina (P =0.84) in study 2. CRP induced more TF activity, protein and mRNA under adherent than non-adherent conditions implying that it may mainly target macrophages in lymphocyte-rich lesions.

CONCLUSIONS

Our results indicate that monocytes from patients with angina are preactivated and express TF but CRP is unlikely to be a major priming factor in vivo. IFN and CRP further increase TF levels that may contribute to the hypercoagulable state in coronary disease.

Quantification of heparin-induced TFPI release: a maximum release at low heparin dose

AIMS

Heparin releases tissue factor pathway inhibitor (TFPI) from the endothelium and this release may decrease after repeated high dose heparin administration. The primary aim was to investigate and quantify this phenomenon during a short low dose heparin infusion. Also, the effects of heparin on tissue plasminogen activator (t-PA) were studied.

METHODS

Nine healthy, nonsmoking, male volunteers (range 19-23 years) received a continuous heparin infusion (2000 IU) over 40 min. The endothelial TFPI release rate was estimated from the total TFPI concentration profile using a pharmacokinetic model.

RESULTS

Mean +/- s.d. total and free TFPI increased from 62.9 +/- 9.4/8.3 +/- 2.1 ng ml-1 at baseline to 237.2 +/- 40.9/111.0 +/- 19.9 ng ml-1 after 40 min infusion. The relationship between heparin concentration (anti-IIa activity) and TFPI concentration followed a maximum effect model and a clockwise loop (proteresis) was observed. The TFPI release rate rapidly increased to maximum of 200 +/- 45 micro g min-1 after 17.5 min heparin infusion but did not increase further although heparin concentrations further doubled. In contrast to TFPI, t-PA antigen decreased from 5.6 +/- 1.0 at baseline to 4.5 +/- 1.0 ng ml-1 at the end of infusion (t = 40 min) (difference of 1.1 ng ml-1 (95% confidence interval; 0.9, 1.3).

CONCLUSIONS

Our application of concentration-effect models and pharmacokinetic principles to these haemostatic variables showed that endothelial TFPI release has a maximum that is already reached at low heparin dose, corresponding with an anti-IIa activity of 0.08 IU ml-1. The relationship between anti-IIa activity and TFPI release rate showed signs of acute tolerance (clockwise loop) indicating exhaustion of endothelial TFPI pools. These findings may be of importance for the heparin dose used in conditions such as unstable angina, in which the favourable effects of heparin have been ascribed to its ability to release TFPI.

The low molecular weight heparin, tinzaparin, in thrombosis and beyond

Standard unfractionated heparin (UFH) has been in clinical use for over 50 years. The commercial use of low molecular weight heparins (LMWHs) began in the mid 1980s for hemodialysis and the prophylaxis of deep vein thrombosis (DVT). Initially, the clinical development of LMWHs was concentrated on the European continent. Subsequently, LMWHs were introduced in North America as well. In the initial stages of development of these drugs only nadroparin, dalteparin and enoxaparin were used. Subsequently, several other LMWHs such as ardeparin, tinzaparin, reviparin and parnaparin were introduced. LMWHs constitute a group of important medications with total sales reaching nearly 2.5 billion dollars with expanded indications reaching far beyond the initial indications for the prophylaxis of post-surgical DVT. This review highlights the pharmacology of tinzaparin. Unlike other LMWHs, tinzaparin is prepared by enzymatic hydrolysis with heparinase, while various chemical depolymerization methods are used for the synthesis of other LMWHs. As compared with the standard heparin, LMWHs have different pharmacodynamic, and pharmacokinetic properties; they also differ in clinical benefits.

Unfractionated heparin is associated with a lower rise of serum vascular cell adhesion molecule-1 in acute ischemic stroke patients

We sought to assess the anti-inflammatory properties of unfractionated heparin (UFH) in patients with ischemic stroke treated within 24 h from the onset of symptoms. We studied prospectively 167 patients that received 1000 IU/h intravenous UFH (n=70) or 300 mg oral aspirin (n=97) at a mean treatment delay of 6.7 h. Repeated plasma levels of interleukin (IL)-6, IL-10, IL-4, tumor necrosis factor (TNF)-alpha, soluble intercellular adhesion molecule-1 (sICAM-1), and soluble vascular cell adhesion molecule-1 (sVCAM-1) were compared in both groups using multivariate analyses. Whereas TNF-alpha and sICAM-1 decreased at 48 h, IL-6, IL-4, and sVCAM-1 increased compared with baseline values (P<0.01). The rise of sVCAM-1 levels at 48 h was significantly lower in patients treated with UFH (P=0.017) and a two-fold increase of baseline sVCAM-1 was an independent predictor of poor outcome (odds ratio, 2.19, 1.1-4.39). These results suggest that adjusted high-dose UFH has anti-inflammatory effects which might improve recovery if administered early after stroke onset.

Tissue factor and tissue factor pathway inhibitor levels in unstable angina patients during short-term low-molecular-weight heparin administration

High tissue factor (TF), tissue factor pathway inhibitor (TFPI) levels and a hypercoagulability state have been documented in unstable angina patients. We evaluated whether short-term enoxaparin administration (100 IU/kg b.i.d. for 3 d) reduces the high TF levels and the hypercoagulability state, and whether it influences the fibrinolytic system in 20 unstable angina patients. On d 3, we observed a significant reduction in TF levels both 1 h and 4 h after the morning injection (-25.6% and -21.7%; P < 0.001 respectively) in comparison with the base-line levels. Both 1 and 4 h after the morning injection on the d 3, TFPI levels significantly (P < 0.001) increased (+96.4%, +96.9% respectively) with respect to the base-line values. After enoxaparin administration, at all observation times, thrombin-antithrombin complexes and prothrombin fragment F1 + 2 levels were significantly (P < 0.001) lower with respect to base-line levels. We observed a slight but significant increase in tissue plasminogen activator antigen levels in preinjection samples, as well as 1 h and 4 h after enoxaparin administration, in comparison with the base-line values. This study provides evidence that low-molecular-weight heparin (LMWH) administration, in addition to a reduction of hypercoagulability and a mild fibrinolytic activation, is associated with decreased TF levels, so indicating a novel mechanism of interference of LMWH with the haemostatic system.

Effects of a low molecular weight heparin, bemiparin, and unfractionated heparin on hemostatic properties of endothelium

Human endothelial cells synthesize and secrete a variety of molecules involved in fibrinolysis and coagulation. The effects of a low molecular weight heparin, Bemiparin, and unfractionated heparin (UFH) were compared on plasminogen activator inhibitor-1 (PAI-1), tissue-plasminogen activator (t-PA), tissue factor (TF), tissue factor pathway inhibitor (TFPI) release, and PAI-1 gene expression by human umbilical vein endothelial cells (HUVEC). Cell cultures were supplemented with Bemiparin or UFH at 1 or 10 U/mL. Culture media samples were obtained before the addition of the drugs and 2, 6, and 24 hours afterward to measure the antigen levels of TF, TFPI, t-PA, and PAI-1. RNA was obtained to study the endothelial expression of PAI-1 by reverse transcriptase-polymerase chain reaction (RT-PCR). Bemiparin at 1 U/mL resulted in a decreased messenger RNA (mRNA) PAI-1 expression, which remained unaltered when UFH had been added. PAI-1 levels increased after the cultures had been supplemented with either Bemiparin or UFH at both doses. UFH induced an increase in t-PA either at 1 or 10 U/mL. Both doses of UFH, but not Bemiparin, induced an important increase in TF secretion. An increase in the TFPI levels was seen with UFH at 1 U/mL. The decrease in PAI-1 gene expression observed with a therapeutic dose of Bemiparin might confer this drug interesting profibrinolytic properties. The fact that Bemiparin, in contrast with UFH, does not induce an increase in TF could give this drug another positive feature.

Tissue factor pathway inhibitor: an update of potential implications in the treatment of cardiovascular disorders

Tissue factor (TF) plays a crucial role in the pathogenesis of thrombotic, vascular and inflammatory disorders. Thus, the inhibition of this membrane protein provides a unique therapeutic approach for prophylaxis and/or treatment of various diseases. Tissue factor pathway inhibitor (TFPI), the only endogenous inhibitor of the TF/Factor VIIa (FVIIa) complex, has recently been characterised biochemically and pharmacologically. Studies in patients demonstrated that both TF and TFPI may be indicators for the course and the outcome of cardiovascular and other diseases. Based on experimental and clinical data, TFPI might become an important drug for several clinical indications. TFPI is expected to inhibit the development of post-injury intimal hyperplasia and thrombotic occlusion in atherosclerotic vessels as well as to be effective in acute coronary syndromes, such as unstable angina and myocardial infarction. Of special interest is the inhibition of TF-mediated processes in sepsis and disseminated intravascular coagulation (DIC), which are associated with the activation of various inflammatory pathways as well as of the coagulation system. A Phase II trial of the efficacy of TFPI in patients with severe sepsis showed a mortality reduction in TFPI- compared to placebo-treated patients and an improvement of organ dysfunctions. TFPI can be administered exogenously in high doses to suppress TF-mediated effects, alternatively high amounts of TFPI can be released from intravascular stores by other drugs, such as heparin and low molecular weight heparins (LMWH). Using this method high concentrations of the inhibitor are provided at sites of tissue damage and ongoing thrombosis. At present, clinical studies with TFPI are rather limited so that the clinical potential of the drug cannot be assessed properly. However, TFPI and its variants are expected to undergo further development and to find indications in various clinical states.

Inhibition of tissue factor reduces thrombus formation and intimal hyperplasia after porcine coronary angioplasty

OBJECTIVES

We investigated the in vivo effects of tissue factor (TF) inhibition with recombinant tissue factor pathway inhibitor (rTFPI) on acute thrombus formation and intimal hyperplasia and the in vitro effects on smooth muscle cell migration and proliferation.

BACKGROUND

Inhibition of TF with TFPI has been shown to reduce intimal hyperplasia in experimental models. However, its effects after coronary angioplasty and the cellular mechanisms involved have not been investigated.

METHODS

Twenty-three swine underwent multivessel coronary angioplasty. Fifteen (n = 25 arteries) were euthanized at 72 h to assess thrombus formation and eight (n = 24 arteries) at 28 days to assess intimal hyperplasia. Animals in the 72-h time point received: 1) human rTFPI (0.5 mg bolus plus 25 microg/kg/min continuous infusion for 3 days) plus heparin (150 IU/kg intravenous bolus) plus acetyl salicylic acid (ASA) (325 mg/day); 2) rTFPI regimen plus ASA and 3) heparin (150 IU/kg intravenous bolus) plus ASA.

RESULTS

On histology the control group had evidence of mural thrombus (area 0.8+/-0.4 mm2). Treatment with TFPI plus heparin abolished thrombus formation (mean area: 0.0+/-0.0 mm2, p < 0.05) but was associated with prolonged activated partial thromboplastin time and extravascular hemorrhage. Recombinant TFPI alone inhibited thrombosis without bleeding complications (mean area: 0.03+/-0.02 mm2, p < 0.05 vs. control). Animals in the 28-day time point received continuous intravenous infusion of rTFPI or control solution for 14 days. Tissue factor pathway inhibitor reduced neointimal formation with mean intimal area of 1.2+/-0.3 mm2 versus 3.2+/-0.4 mm2 in the control group; p < 0.01. Recombinant TFPI had no effect on human aortic smooth muscle cell growth but inhibited platelet-derived growth factor BB-induced migration.

CONCLUSIONS

Inhibition of TF with rTFPI can prevent acute thrombosis and intimal hyperplasia after injury. Tissue factor plasma inhibitor may prove useful as an adjunct to intracoronary interventions.