Tissue factor and biotechnology

Tissue factor (TF) and tissue factor pathway inhibitor (TFPI) in the placenta and myometrium

BACKGROUND

Placental abruption is mainly due to the rupture of the uterine spiral arteries, but adjacent tissues are also damaged and substances derived from disintegrated placenta and myometrium probably cause coagulation disturbances, such as hypofibrinogenemia and disseminated intravascular coagulation (DIC).

AIM

To measure whether placenta and myometrium are significant sources of tissue factor (TF) and tissue factor pathway inhibitor (TFPI), the components of key role in the initiation of coagulation.

MATERIALS AND METHODS

Strips of placenta and myometrium were obtained from 48 women delivered by cesarean section at term. TF and TFPI concentrations were measured by immunoenzymatic method (ELISA) in tissue homogenates.

MAIN RESULTS

Concentration of TF in placenta and myometrium was 31 (25-37) and 7.4 (4.9-11.4) ng/mg of total protein, respectively. In the plasma of the same women, it was 0.004ng/mg of total protein. TFPI concentration was 13 (10-17) ng/mg of total protein in placenta, 4.5 (3.1-7.3) ng/mg in myometrium, and 0.70 (0.50-0.80) ng/mg in blood plasma protein.

CONCLUSION

The levels of TF in placenta and myometrium, over TF in blood plasma may be clinically significant in obstetrics, for instance, in the etiology of DIC in placental abruption. The concentration of TFPI-natural inhibitor of TF-seems to be too low to prevent initiation of coagulation.

Factor VIIa induces tissue factor-dependent up-regulation of interleukin-8 in a human keratinocyte line

Tissue factor (TF), a transmembrane receptor for the serine protease coagulation factor VII(a) (FVIIa), is the main initiator of the coagulation cascade. Through incompletely elucidated mechanisms, TF serves additional functions in tumor-associated angiogenesis and metastasis. We have studied interleukin-8 (IL-8) as a possible link between TF-FVIIa complex formation and subsequent processes. Recombinant human FVIIa induced the up-regulation of both IL-8 mRNA and protein in a FVIIa dose- and time-dependent fashion. A neutralizing antibody to TF reduced this induction by 93 +/- 5%. Active site-inhibited FVIIa had no stimulatory effect and completely blocked that of FVIIa. This confirms that the increased IL-8 production was dependent on the formation of TF-FVIIa complexes and the proteolytic activity of FVIIa. The IL-8 promoter contains DNA binding sites for nuclear factor-kappaB (NF-kappaB) and activator protein-1 (AP-1). In response to FVIIa, the DNA binding activity of both NF-kappaB and AP-1 was enhanced in an electrophoretic mobility shift assay. In addition, the IL-8 promoter was transcriptionally activated both in a luciferase reporter system and a nuclear run-off assay. Moreover, IL-8 mRNA stability was significantly enhanced by FVIIa-induced activation of the mitogen-activated protein kinases ERK1/2 and p38. Taken together, TF-FVIIa signaling induced increased transcription as well as mRNA stabilization leading to the significant up-regulation of IL-8 protein synthesis.

Human mesothelial cells express tissue factor when switched to proliferating state. Pharmacological modulation in vitro

Covering the inner surface of small-diameter arterial prostheses with endothelial cells (ECs) has been proposed as a means of improving biocompatibility and thrombosis resistance. Because the availability of autologous ECs is limited, autologous human mesothelial cells (HMCs) have been suggested as a substitute for ECs. However, HMCs express tissue factor (TF) in vitro, a deleterious characteristic in vivo. We investigated the distribution of TF antigen and of its inhibitor, tissue factor pathway inhibitor, on HMCs and the effect of pharmacological agents on TF expression. TF antigen was measured by enzyme-linked immunosorbent assay and localized by confocal microscopy. Three distinct pools of TF antigen were demonstrated: within the cells, at the cell surface, and in the extracellular matrix. The effects of ilomedin (10 microg/ml) and heparin (500 U/ml), known to affect procoagulant activity, were evaluated by incubating HMCs for 24 h with or without these agents. Ilomedin, but not heparin, decreased TF antigen expression by 30% (P < 0.05). Despite the theoretical potential of HMCs as a vascular prosthesis lining, TF expression by HMCs remains a major drawback. A technique capable of blocking TF expression until the HMCs return to their resting state is needed. Genetic manipulation of HMCs may hold promise for such a technique.

Inhibition of tissue factor-activated platelets by low-molecular-weight heparins and glycoprotein IIb/IIIa receptor antagonist

Thrombotic disorders can lead to vascular distress and platelet activation eventually resulting in the rupture of the lesions where a sizable amount of tissue factor (TF) is generated during the pathogenesis of arterial diseases. Since low-molecular-weight heparins (LMWHs) and platelet glycoprotein (GP) IIb/IIIa inhibitors are clinically used for the management of acute coronary syndrome (ACS), studies were taken to determine the effects of these agents on TF-mediated activation of platelets. Freshly drawn native whole blood (WB) from normal healthy volunteers (n = 6) supplemented with a predetermined amount of TF was incubated with equivalent anti-Xa adjusted amounts of various LMWHs at 0.01-1.0 U/ml and tirofiban from 10 to 100 ng/ml. Platelet activation was assessed by measuring the expression of P-selectin (CD62) and the generation of platelet aggregates. At 0.01 U/ml, enoxaparin exhibited a stronger inhibition of TF-induced platelet activation compared to ardeparin and dalteparin. At 0.1 U/ml, these LMWHs produced a comparable inhibition of total P-selectin expression, and at 1.0 U/ml, a marked inhibition was noted. Since enoxaparin produced the best concentration-dependent inhibition of P-selectin expression (saline: 76 +/- 10% vs. 1.0 U/ml enoxaparin: 18 +/- 7%; P < .02) and platelet aggregate formation (saline: 63 +/- 7% vs. 1.0 U/ml enoxaparin: 35 +/- 6%, P < .035), this agent was used for additional studies. Unlike enoxaparin, tirofiban produced a weak concentration-dependent inhibition of platelet activation. At 100 ng/ml, tirofiban produced a 40% inhibition of P-selectin expression and about 60% inhibition of platelet aggregate formation. To elucidate the potential interaction between tirofiban and enoxaparin, the effect of 10 and 100 ng/ml tirofiban was studied with enoxaparin-supplemented WB in a 0.01-1.0 U/ml range. Additive effects between these two agents were noted only at lower concentrations. Thus, at therapeutic concentrations (0.8-1.2 U/ml), enoxaparin itself was capable of inhibiting TF-mediated activation of platelets to > 70%; whereas tirofiban failed to produce such concentration-dependent inhibition. This suggests that the simultaneous administration of GPIIb/IIIa receptor antagonist with LMWH may not have any added benefit in the clinical management of patients with ACS.

Role of zymogen and activated factor X as scaffolds for the inhibition of the blood coagulation factor VIIa-tissue factor complex by recombinant nematode anticoagulant protein c2

Recombinant nematode anticoagulant protein c2 (rNAPc2) is a potent, factor Xa (fXa)-dependent small protein inhibitor of factor VIIa-tissue factor (fVIIa.TF), which binds to a site on fXa that is distinct from the catalytic center (exo-site). In the present study, the role of other fX derivatives in presenting rNAPc2 to fVIIa.TF is investigated. Catalytically active and active site blocked fXa, as well as a plasma-derived and an activation-resistant mutant of zymogen fX bound to rNAPc2 with comparable affinities (K(D) = 1-10 nm), and similarly supported the inhibition of fVIIa.TF (K(i)* = approximately 10 pm). The roles of phospholipid membrane composition in the inhibition of fVIIa.TF by rNAPc2 were investigated using TF that was either detergent-solubilized (TF(S)), or reconstituted into membranes, containing phosphatidylcholine (TF(PC)) or a mixture of phosphatidylcholine and phosphatidylserine (TF(PCPS)). In the absence of the fX derivative, inhibition of fVIIa.TF was similar for all three conditions (K(i) approximately 1 microm), whereas the addition of the fX derivative increased the respective inhibition by 35-, 150-, or 100,000-fold for TF(S), TF(PC), and TF(PCPS). The removal of the gamma-carboxyglutamic acid-containing domain from the fX derivative did not affect the binding to rNAPc2, but abolished the effect of factor Xa as a scaffold for the inhibition of fVIIa.TF by rNAPc2. The overall anticoagulant potency of rNAPc2, therefore, results from a coordinated recognition of an exo-site on fX/fXa and of the active site of fVIIa, both of which are properly positioned in the ternary fVIIa.TF.fX(a) complex assembled on an appropriate phospholipid surface.