Tissue factor (TF) is the essential cofactor for FVIIa. Binding to transmembrane tissue factor increases the catalytic efficiency of FVIIa allowing activation of FX and FIX which initiates coagulation and propagates stable clot. Transmembrane TF resides in a cryptic configuration on the cell surface and in the circulation with low procoagulant activity. However TF can be rapidly switched to an active configuration in order to contribute to thrombus propagation. The precise nature of this switch is unknown, however it is known to be an extracellular event. The extracellular part of TF consists of 2 fibronectin type III domains. The disulfidebond in the membrane proximal domain (Cys186-Cys209) is a cross-strand bond which links adjacent strands in the same ?? sheet. It has the configuration, characteristic dihedral strain energy and bond length of an allosteric disulfide bond. This indicates that it has the potential to undergo thiol/disulfide exchange to change the function of the TF protein. We confirm that the integrity of the Cys186-Cys209 disulfide is required for coagulant function and that tissue factor contains free thiols in the cryptic state which are lost when TF becomes de-encrypted. Membrane based tissue factor procoagulant activity is blocked by the mono-thiol alkylators N-ethylmaleimide and methyl methanethiosulfonate; but increased by ECl/formation of the disulfide via the thiol oxidiser, HgCb or thiol cross-linkers, eimidohexane and bismalemidoethane. The increase in activity correlates with a conformation change in the TF protein adjacent to the disulfide. We show that redox active protein disulfide isomerase is associated with cryptic tissue factor and propose that the cryptic conformation of tissue factor is maintained through formation of an Snitrosylated complex with protein disulfide isomerase. Our results indicate that the activation of TF involves a change of conformation of the domain 2 of TF caused by formation of the cross-strand Cys186-Cys209 disulfide bond. We suggest that this is likely to be the physiological change that facilitates productive binding of FIX and FX in coagulation.

A descriptive study was conducted to test the null hypothesis: There will be no statistically significant difference between serum activated partial thromboplastin time (aPTT) obtained by two methods; venipuncture and large bore femoral arterial catheter. The convenience sample consisted of seventeen adults who had undergone percutaneous transluminal coronary angioplasty (PTCA) for the treatment of coronary artery disease. After the PTCA procedure, patients returned to an intensive care unit with a femoral intra-arterial catheter in place. Seventeen pairs of serum samples were obtained; one by venipuncture and one through the femoral intra-arterial catheter. Prior to obtaining the sample from the femoral intra-arterial catheter, 6.0 milliliters (3 times the deadspace of the catheter) of blood was withdrawn and discarded. aPTT samples were analyzed. T-tests were used to compare the results. Findings revealed that there was no statistically significant difference in the aPTT value when drawn from venipuncture versus the femoral intra-arterial catheter.

Thesis (doctoral)--Universiteit van Amsterdam.

Tissue factor (TF) is a cell-associated receptor for coagulation factor VIIa (FVIIa) that initiates the coagulation cascade and transmits intracellular signals through protease activated receptors (PARs). This thesis documents for the first time that in human glioma cells (U373) oncogenic epidermal growth factor receptor (EGFRvIII) simultaneously upregulates the expression of several elements of the TF pathway (TF, FVIIa, PAR-1 and PAR-2). In the absence of EGFRvIII, TF triggers tumor formation, albeit with a long latency, while treatment of glioma cells with FVIIa activates MAPK phosphorylation and stimulates the expression of angiogenic factors (VEGF and IL-8). Moreover, selective targeting of the host (mouse) TF reveals its independent role in glioma tumorigenesis. We propose that TF may represent an attractive potential target to treat human brain tumors.

Sepsis is a life threatening condition caused by infectious agents, including the Gram-positive bacterium Staphylococcus aureus. Symptoms of sepsis often include intravascular coagulation and organ failure. Tissue factor (TF), the initiator of coagulation, may contribute to fibrin deposition in the lungs of patients with sepsis. We have found that lung epithelial cells constitutively express TF on the cell surface and in intracellular pools. Levels of TF diminished in response to S. aureus invasion possibly indicating a release in the form of shedding vesicles. TF levels diminish in response to viable bacteria, but not in response to heat killed (HK) bacteria. Our studies indicate that bacterial attachment at the host cell surface is insufficient to diminish levels of constitutive TF. Finally, we established that levels of constitutive intracellular TF diminish in response to the bacterial toxin, α-hemolysin, alone. This approach may provide a basis for understanding the role of TF in coagulation seen in sepsis. / Department of Biology

Diss. (sammanfattning) Uppsala : Uppsala universitet, 2006. / Härtill 4 uppsatser.

Thesis (Ph. D.)--University of Washington, 1998. / Vita. Includes bibliographical references (leaves [137]-148).

No description available.

Thesis (Ph. D.)--University of Oklahoma. / Bibliography: leaves 173-211.

<p>For prevention and treatment of thrombotic diseases with an anticoagulant drug it is important that an adequate dose is given to avoid occurrence or recurrence of thrombosis, without increasing the risk of bleeding and other adverse events to unacceptable levels. The aim of this thesis was to develop mathematical models that describe the dose-concentration (pharmacokinetic) and concentration-response (pharmacodynamic) relationships of direct thrombin inhibitors, in order to estimate optimal dosages for treatment and long-term secondary prevention of venous thromboembolism (VTE).</p><p>Population pharmacokinetic-pharmacodynamic models were developed, based on data from clinical investigations in healthy volunteers and patients receiving intravenous inogatran, subcutaneous melagatran and/or its oral prodrug ximelagatran. The benefit-risk profiles of different ximelagatran dosages were estimated using clinical utility functions. These functions were based on the probabilities and fatal consequences of thrombosis, bleeding and elevation of the hepatic enzyme alanine aminotransferase (ALAT).</p><p>The studies demonstrate that the pharmacokinetics of melagatran and ximelagatran were predictable and well correlated to renal function. The coagulation marker, activated partial thromboplastin time (APTT), increased non-linearly with increasing thrombin inhibitor plasma concentration. Overall, the systemic melagatran exposure (AUC) and APTT were similarly predictive of thrombosis and bleedings. The identified relationship between the risk of ALAT-elevation and melagatran AUC suggests that the incidence approaches a maximum at high exposures. The estimated clinical utility was favourable compared to placebo in the overall study population and in special subgroups of patients following fixed dosing of ximelagatran for long-term secondary prevention of VTE. Individualized dosing was predicted to add limited clinical benefit in this indication.</p><p>The models developed can be used to support the studied dosage and for selection of alternative dosing strategies that may improve the clinical outcome of ximelagatran treatment. In addition, the models may be extrapolated to aid the dose selection in clinical trials with other direct thrombin inhibitors.</p>