Tissue factor pathway inhibitor dose-dependently inhibits coagulation activation without influencing the fibrinolytic and cytokine response during human endotoxemia

Validation of a novel tissue factor assay in experimental human endotoxemia

BACKGROUND

Nuclear factor kappa B (NF-kappa B) activation and tissue factor (TF) expression may contribute to lethality in sepsis. Inappropriate in vivo expression of TF is likely responsible for fibrin deposition in sepsis-associated disseminated intravascular coagulation (DIC). Clinical assessment of TF expression has remained a major challenge. No point-of-care assays are currently available to measure the level of TF activity in whole blood. The current study examined the suitability of the TiFaCT assay as a point-of-care assay to detect TF expression.

METHODS

30 healthy male volunteers received 2 ng/kg of LPS. Tissue factor-dependent coagulation was quantified with a novel assay called tissue factor clotting time (TiFaCT), and by measurement of activation markers of downstream coagulation.

RESULTS

Ex vivo addition of anti-TF antibodies to blood slightly increased clotting times at 0-24 h (p<0.01) indicating that some tissue factor activity was present in whole blood at any time. LPS bolus infusion decreased TiFaCT clotting time by -23% compared to baseline (p<0.01), when in vivo clotting increased, as demonstrated by a 10-fold increase in prothrombin fragment levels (F1+2). Ex vivo incubation with LPS considerably shortened TiFaCT (from 1000s to 400s as compared to control incubation; p<0.01). This effect was blunted at 2-4 h after LPS infusion (i.e. the time of monocytopenia), but twofold enhanced 24 h after LPS challenge (p<0.01).

CONCLUSIONS

In summary, the TiFaCT assay was validated in our in vivo model of LPS-induced coagulation. It detected minute quantities of circulating TF even at baseline. TiFaCT is shortened at times of in vivo thrombin generation.

Protease-activated receptor signaling in the regulation of inflammation

OBJECTIVE

To discuss recent studies addressing the relationship between protease-activated receptor signaling, coagulation, and inflammation.

DATA EXTRACTION AND SYNTHESIS

This review article covers relevant original articles published until October 2003 dealing with animal models, clinical trial data, and in vitro experiments.

CONCLUSIONS

Although activation of protease-activated receptors has been implicated in the proinflammatory effects of the coagulation cascade, current data provide evidence that protease-activated receptor signaling plays a more complex role in the regulation of inflammation and endothelial homeostasis. Sensitive assays for coagulation activation have provided clear evidence that targeting the coagulation pathway effectively reduces the coagulopathy in sepsis. However, the effect of these anticoagulant agents on sepsis-associated inflammation is less clear. Further insight into this question will require the development or use of additional biomarkers for assessing pharmacologic interference with coagulation-related cell-signaling pathways.

Protein C/activated protein C pathway: overview of clinical trial results in severe sepsis

OBJECTIVE

To review the results from clinical trials of treatments for severe sepsis involving the protein C/activated protein C pathway.

DATA SOURCE

Published research and review articles (PubMed, from 1985 to 2003) relating to clinical trials of compounds involving the protein C pathway.

DATA EXTRACTION AND SYNTHESIS

Protein C is converted to activated protein C when thrombin complexes with thrombomodulin. Sepsis is associated with rapid depletion of protein C and blunted endogenous protein C activation. Treatment with protein C concentrate is followed by increased activated protein C plasma levels and a dose-dependent decrease in d-dimer levels in children with purpura fulminans. This supplementation is safe. A phase III trial of recombinant human activated protein C (drotrecogin alfa [activated]) in severe sepsis demonstrated a 6.1% absolute reduction in 28-day mortality compared with placebo. The short- and long-term survival rates associated with drotrecogin alfa (activated) were better in patients at high risk of death associated with a better cost/effectiveness ratio. Treatment with drotrecogin alfa (activated) was associated with an increased risk of serious bleeding compared with placebo during the 28-day study period (3.5% vs. 2.0%).

CONCLUSIONS

Treatment with protein C concentrate is followed by an improvement of the coagulopathy and is safe in children with purpura fulminans; however, a large trial involving a high dose is required to determine its effect on mortality and morbidity. Treatment with drotrecogin alfa (activated) leads to substantial reduction in mortality and has an acceptable risk/benefit ratio in septic patients at high risk of death.

Tissue Factor Coagulation Pathway: A New Therapeutic Target in Atherothrombosis

Atherothrombosis, defined as atherosclerotic lesion disruption with superimposed thrombus formation, is the major cause of acute coronary syndromes and cardiovascular deaths. It is the leading cause of morbidity and mortality in the industrialized world. Plaque composition, rather than luminal stenosis, is recognized as the major determinant of this disease. Since tissue factor is found within atheroma and also in the bloodstream of atherosclerotic patients, it likely plays a key role in determining both plaque and blood thrombogenicity. Ongoing clinical and preclinical studies are evaluating the therapeutic possibilities of specific inhibition of the tissue factor pathway. Here, we will review the role of tissue factor in atherothrombosis and therapeutic applications.

Effect of interleukin-6 blockade on tissue factor-induced coagulation in human endotoxemia

OBJECTIVE

Clinical trials show that interleukin (IL)-6 represents a predictive marker in human sepsis. Furthermore, IL-6 has been proposed as a candidate mediator for endotoxin (lipopolysaccharide)-induced coagulation activation: In a primate model, an (alphaIL-6 antibody (alphaIL-6 Ab) almost abolished lipopolysaccharide-induced coagulation activation. Therefore, we wished to determine if an alphaIL-6 Ab (B-E8) may also attenuate lipopolysaccharide-induced activation of coagulation in humans.

DESIGN

The study was a randomized, double blind, placebo-controlled parallel group trial (n = 12 per group).

SETTING

University medical center.

PATIENTS

Healthy volunteers.

INTERVENTIONS

Healthy volunteers were randomized to receive either 80 mg of a monoclonal anti-IL-6 Ab (B-E8) or placebo intravenously before bolus infusion of 2 ng/kg lipopolysaccharide.

MEASUREMENTS AND MAIN RESULTS

B-E8 effectively decreased IL-6 bioactivity as measured by a Bg-bioassay in vitro and concentrations of C reactive protein. However, B-E8 did not decrease lipopolysaccharide-induced tissue factor-messenger RNA transcription or plasma concentrations of downstream coagulation variables (prothrombin fragment 1 + 2, thrombin-antithrombin III complexes, and D-dimer concentrations). Similarly, tumor necrosis factor-alpha concentrations, fibrinolytic activity (plasmin-antiplasmin complexes), endothelial activation (soluble E-selectin), and IL-10 were unaffected.

CONCLUSION

IL-6 does not appear to mediate early-phase lipopolysaccharide-induced coagulation activation in humans.

Why do animal models (sometimes) fail to mimic human sepsis?

OBJECTIVE

To describe potential mechanisms that may account for the observation that drugs that work in treating sepsis in animal models often fail in sepsis trials in patients.

DATA SOURCE

MEDLINE searches were used to provide the key information.

DATA SUMMARY

Most animal studies are performed acutely in young healthy animals, whereas a significant percentage of the clinical population is elderly with many secondary complications (e.g., diabetes, systemic vascular disease, high blood pressure, immune suppression, cancer). Furthermore, unlike the acute challenge presented in most animal studies, many of the septic patients' clinical histories indicate a relatively slow onset of the disease. In many animal studies, intervention occurs before or during the very early stages of sepsis, when inflammatory cytokine levels are still rising and both organ damage and vascular leakage are minimal. In contrast, current treatment strategies are started when many (probably most) patients are switching from a proinflammatory cytokine response to an anti-inflammatory response and organ damage is already apparent. Patients are also generally receiving some form of supportive therapy (e.g., fluids, vasopressors, ventilators). Because these are seldom used in the animal model, their effect on a particular drug response is difficult to assess. In the animal model, a well-defined bacterial strain, endotoxin challenge, or, in the most complex case, cecal ligation puncture at a defined site is employed to bring about the onset of sepsis. Generally, bacterial proliferation can be controlled in these situations by selecting the appropriate antibiotic (if desired). In human sepsis, the pathogenic bacteria are often not known, mixed infections involving both Gram-negative and Gram-positive bacteria are common, and antibiotic treatment is incomplete or ineffective. Anti-inflammatory strategies that impair bacterial killing may be helpful in cases in which antibiotics were effective and harmful when they were not. Thus, an intervention in human sepsis is attempted at a later stage and under very different conditions than it is during efficacy testing in animal models.

CONCLUSIONS

Differences in the nature of the initiating agent causing sepsis and the lack of co-morbidities in the animal models probably contribute to some of the differences in animal studies and clinical trials in sepsis.

Human models of endotoxemia and recombinant human activated protein C

OBJECTIVES

To review human models of endotoxemia with an emphasis on the inflammatory and coagulopathic effects of lipopolysaccharide to describe the possible mechanisms of clinical benefit of recombinant human activated protein C (drotrecogin alfa [activated]) in severe sepsis.

DATA SOURCE

A selected review of published literature in English on human endotoxemia models with special attention to studies using drotrecogin alfa (activated) in concert with endotoxemia.

DATA EXTRACTION AND SYNTHESIS

After intravenous administration of purified lipopolysaccharide, subjects report constitutional influenza-like symptoms associated with an increase in temperature. Within 1 hr of lipopolysaccharide infusion, total leukocyte counts decline. Sustained leukocytosis, due to an increase in neutrophils counts, follows. An increase in markers of neutrophil activation (e.g., serum elastase) accompanies this leukocytosis. Production of tumor necrosis factor-alpha, interleukin-6, and interleukin-8 is also increased. In association with an inflammatory response, lipopolysaccharide administration also activates the coagulation system. Lipopolysaccharide infusion generates thrombin and initially activates fibrinolysis but subsequently generates inhibitors of the fibrinolytic system. Serum levels of endogenous inhibitors of coagulation (e.g., antithrombin, protein C, tissue factor pathway inhibitor) are not affected. Data are available for 40 subjects who have participated in placebo-controlled studies of drotrecogin alfa (activated) infusion before an intravenous dose of lipopolysaccharide. In these subjects, drotrecogin alfa (activated) has minimal effects on measured variables, including physiologic variables, markers of inflammation, and measures of sepsis-induced coagulopathy.

CONCLUSION

Human endotoxemia is, at best, an incomplete model of human sepsis. In two studies using recombinant human activated protein C in the setting of human endotoxemia, there were minimal effects on hemodynamics, inflammation, thrombin generation, fibrinolysis, and markers of cellular activation. Other putative mechanisms of recombinant human activated protein C, such as inhibition of apoptosis and leukocyte recruitment, remain to be studied.

Coagulopathy in the equine critical care patient

Disseminated intravascular coagulation (DIC) is a clinicopathologic syndrome resulting from a multitude of underlying causes that manifests itself clinically as hemostatic/fibrinolytic failure. There is much debate on the definition, diagnosis, and treatment of DIC, a situation that is most likely the result of the multifaceted clinical presentation of the syndrome and the fact that patient outcome is often influenced by the underlying disease process. The fact that DIC increases morbidity and mortality in critical care patients is well established, but the exact mechanism of what specifically occurs on a microvascular level is still often argued.

Inhibition of Plasmin Activity by Tranexamic Acid Does Not Influence Inflammatory Pathways During Human Endotoxemia

OBJECTIVE

Plasmin activates several proinflammatory pathways at the cellular level in vitro. Lipopolysaccharide (LPS) administration to healthy humans results in a rapid generation of plasmin activity, accompanied by activation of a number of inflammatory systems.

METHODS AND RESULTS

To determine the role of early plasmin activity in LPS-induced inflammation in vivo, 16 healthy males received an intravenous bolus injection with LPS (from Escherichia coli, 4 ng/kg) directly preceded by a 30-minute intravenous infusion of tranexamic acid (2 g, n=8), a plasmin activation inhibitor, or placebo (n=8). LPS injection induced marked increases in the plasma levels of D-dimer and plasmin-alpha2-antiplasmin complexes, indicative of plasmin activation and generation, respectively, which were strongly attenuated by tranexamic acid (both P<0.01 versus placebo). However, tranexamic acid did not influence LPS-induced coagulation activation, granulocytosis, neutrophil activation (expression of CD11b, CD66b, and L-selectin) or degranulation (plasma concentrations of elastase-alpha1-antitrypsin and bactericidal permeability-increasing protein), endothelial cell activation (plasma levels of von Willebrand factor and soluble E-selectin), or cytokine release.

CONCLUSIONS

These data argue against a role of early plasmin generation in the subsequent activation of other inflammatory pathways during human endotoxemia.

Induction of microparticle- and cell-associated intravascular tissue factor in human endotoxemia

The precise role of intravascular tissue factor (TF) remains poorly defined, due to the limited availability of assays capable of measuring circulating TF procoagulant activity (PCA). As a model of inflammation-associated intravascular thrombin generation, we studied 18 volunteers receiving an infusion of endotoxin. A novel assay that measures microparticle (MP)-associated TF PCA from a number of cellular sources (but not platelets) demonstrated an 8-fold increase in activity at 3 to 4 hours after endotoxin administration (P <.001), with a return to baseline by 8 hours. TF antigen-positive MPs isolated from plasma were visualized by electron microscopy. Interindividual MP-associated TF response to lipopolysaccharide (LPS) was highly variable. In contrast, a previously described assay that measures total (cell and MP-borne) whole-blood TF PCA demonstrated a more modest increase, with a peak in activity (1.3-fold over baseline; P <.000 01) at 3 to 4 hours, and persistence for more than 24 hours. This surprisingly modest increase in whole-blood TF activity is likely explained by a profound although transient LPS-induced monocytopenia. MP-associated TF PCA was highly correlated with whole-blood TF PCA and total number of circulating MPs, and whole-blood TF PCA was highly correlated with TF mRNA levels.

Adult respiratory distress syndrome: do selective anticoagulants help?

The adult respiratory distress syndrome (ARDS) is a form of acute lung injury that is characterized by florid extravascular fibrin deposition. Thrombosis in the pulmonary vasculature and disseminated intravascular coagulation have also been observed in association with ARDS. Fibrin deposition does not occur in the normal lung but is virtually universal in acute lung injury induced by disparate insults. A large body of basic and preclinical evidence further implicates abnormalities of pathways of fibrin turnover in the pathogenesis of acute inflammation and fibrotic repair. Coagulation is locally upregulated in the injured lung, while fibrinolytic activity is depressed. These abnormalities occur concurrently and favor alveolar fibrin deposition. The systemic derangements of fibrin turnover in sepsis are similar to those that occur in the injured lung. Recent clinical trials demonstrate that interventions using selective anticoagulation can provide a mortality advantage and that selective anticoagulants differ in their ability to provide clinical benefit. Preclinical trials in primates with sepsis-induced ARDS now indicate that anticoagulant interventions that block the extrinsic coagulation pathway can protect against the development of pulmonary fibrin deposition as well as lung dysfunction and acute inflammation. These observations provide proof of principle that key steps in the coagulation cascade are appropriate therapeutic targets to prevent the development of acute lung injury in ARDS. Ongoing studies and prior publications also support the hypothesis that reversal of the fibrinolytic defect in ARDS could protect against the development of acute lung injury. In all, these studies suggest that fibrin deposition in the injured lung as well as abnormalities of coagulation and fibrinolysis are integral to the pathogenesis of ARDS. The ability of selective anticoagulants to effectively and safely alter clinical outcome in ARDS remains to be determined.

Tissue factor as an evolutionary conserved cytokine receptor: implications for inflammation and signal transduction

Tissue factor (TF) is a transmembrane protein that, in complex with factor VIIa (FVIIa), initiates coagulation. It also influences various other physiological and pathological events, such as inflammation, and negatively influences survival during sepsis. TF resembles a conserved class of pro-inflammatory cytokine receptors and activates a set of pro-inflammatory intracellular signal transduction routes. Interestingly, whereas the homology of TF to the class II cytokine receptors is reflected in a similar type of signal transduction, the mechanism by which the signal is transduced across the membrane differs greatly. This review discusses the role of TF and its ligand FVIIa in inflammation, sepsis, and signal transduction, and describes the way in which these processes interact.

New treatment strategies for disseminated intravascular coagulation based on current understanding of the pathophysiology

A variety of clinical conditions may cause systemic activation of coagulation, ranging from insignificant laboratory changes to severe disseminated intravascular coagulation (DIC). DIC consists of a widespread systemic activation of coagulation, resulting in diffuse fibrin deposition in small and midsize vessels. There is compelling evidence from clinical and experimental studies that DIC is involved in the pathogenesis of microvascular dysfunction and contributes to organ failure. In addition, the massive and ongoing activation of coagulation, may result in depletion of platelets and coagulation factors, which may cause bleeding. Recent understanding of important pathogenetic mechanisms that may lead to DIC has resulted in novel preventive and therapeutic approaches to patients with sepsis and a derangement of coagulation. Thrombin generation proceeds via the (extrinsic) tissue factor/factor VIIa route and simultaneously occurring depression of inhibitory mechanisms, such as antithrombin III and the protein C system. Also, impaired fibrin degradation, due to high circulating levels of the fibrinolytic inhibitor plasminogen activator inhibitor, type 1 (PAI-1), contributes to enhanced intravascular fibrin deposition. Interestingly, an extensive cross-talk between activation of inflammation and coagulation exists, where inflammatory mediators (such as cytokines) not only activate the coagulation system, but vice versa activated coagulation proteases and protease inhibitors may modulate inflammation through specific cell receptors. Supportive strategies aimed at the inhibition of coagulation activation may theoretically be justified and have been found beneficial in experimental and initial clinical studies. These strategies comprise inhibition of tissue factor-mediated activation of coagulation or restoration of physiological anticoagulant pathways, for example by means of the administration of recombinant human activated protein C.

Recombinant nematode anticoagulant protein c2, an inhibitor of tissue factor/factor VIIa, attenuates coagulation and the interleukin-10 response in human endotoxemia

The tissue factor-factor (F)VIIa complex (TF/FVIIa) is responsible for the initiation of blood coagulation under both physiological and pathological conditions. Recombinant nematode anticoagulant protein c2 (rNAPc2) is a potent inhibitor of TF/FVIIa, mechanistically distinct from tissue factor pathway inhibitor. The first aim of this study was to elucidate the pharmacokinetics and pharmacodynamics of a single intravenous (i.v.) dose of rNAPc2. The second aim was to study its effect on endotoxin-induced coagulation and inflammation. Initially, rNAPc2 was administered to healthy volunteers in three different doses. There were no safety concerns and the pharmacokinetics were consistent with previous studies, in which rNAPc2 was administered subcutaneously. rNAPc2 elicited a dose-dependent reduction of the endogenous thrombin potential and a selective prolongation of prothrombin time. Subsequently, the effect on endotoxin-induced coagulation and inflammation was studied. The administration of rNAPc2 completely blocked the endotoxin-induced thrombin generation, as measured by plasma prothrombin fragment F1+2. The endotoxin-induced effect on fibrinolytic parameters such as plasmin-antiplasmin complexes and plasminogen activator inhibitor type 1 was not affected by rNAPc2. The administration of rNAPc2 attenuated the endotoxin-induced rise in interleukin (IL)-10, without affecting the rise in other cytokines. In conclusion, rNAPc2 is a potent inhibitor of TF/FVIIa, which was well tolerated and could safely be used intravenously in this Phase I study in healthy male volunteers. A single i.v. dose rNAPc2 completely blocked endotoxin-induced thrombin generation without affecting the fibrinolytic response. In addition, rNAPc2 attenuated the endotoxin-induced rise in IL-10, without affecting the rises in other cytokines.

Recombinant nematode anticoagulant protein c2 and other inhibitors targeting blood coagulation factor VIIa/tissue factor

Originally isolated from a haematophagous hookworm, recombinant nematode anticoagulant protein c2 (rNAPc2) is an 85-amino acid protein with potent anticoagulant properties. Unlike conventional anticoagulants that attenuate blood coagulation via inhibition of thrombin or activated factor X (FXa) at the downstream portion of the cascade, rNAPc2 is a potent inhibitor of the activated factor VII/tissue factor complex (FVIIa/TF), the key physiological initiator of blood coagulation. Its mechanism of action requires prerequisite binding to circulating FXa or zymogen factor X (FX) to form a binary complex prior to its interaction and inhibition of membrane-bound FVIIa/TF. The binding of rNAPc2 to FX results in an elimination half-life of longer than 50 h following either subcutaneous or intravenous administration. Recombinant NAPc2, like other inhibitors of FVIIa/TF including tissue factor pathway inhibitor (TFPI) and active site-blocked FVIIa (ASIS, FFR-rFVIIa or FVIIai), may have a promising role in the prevention and treatment of venous and arterial thrombosis, as well as potential efficacy in the management of disseminated intravascular coagulopathies because of their potent and selective inhibition of FVIIa/TF.

Recombinant human activated protein C (rhAPC; drotrecogin alfa [activated]) has minimal effect on markers of coagulation, fibrinolysis, and inflammation in acute human endotoxemia

Inflammatory and procoagulant host responses are closely related in sepsis. The protein C pathway serves as a regulatory pathway with anti-inflammatory and anticoagulant properties. Recently, recombinant human activated protein C (rhAPC) was shown to reduce mortality in severe sepsis. Nevertheless, the effects of rhAPC in humans are still ill defined. The infusion of low endotoxin doses into humans provides a standardized model to study inflammatory and hemostatic mechanisms. Thus, we investigated whether rhAPC acts as an anticoagulant or anti-inflammatory drug in human endotoxemia. There were 24 volunteers randomized to receive either 24 microg/kg per hour rhAPC or placebo intravenously for 8 hours. Lipopolysaccharide (LPS, 2 ng/kg) was administered 2 hours after starting the infusions. rhAPC decreased basal tissue factor (TF)-mRNA expression, and thrombin formation and action. In contrast, rhAPC did not significantly blunt LPS-induced thrombin generation. Consistently, rhAPC did not reduce LPS-induced levels of TF-mRNA or D-dimer and had no effect on fibrinolytic activity or inflammation. Finally, endogenous APC formation was enhanced during endotoxemia and appeared to be associated with inflammation rather than thrombin formation. In conclusion, even low-grade endotoxemia induces significant protein C activation. Infusion of rhAPC decreases "spontaneous" activation of coagulation but does not blunt LPS-induced, TF-mediated coagulation in healthy volunteers, which is in contrast to a number of anticoagulants.

Coagulation: consultative hemostasis

Clinical hematologists are frequently consulted for the care of hospitalized patients with complicated coagulopathies. This chapter provides an update on the scientific and clinical advances noted in disseminated intravascular coagulation (DIC) and discusses the challenges in hemostasis consultation. In Section I, Dr. Marcel Levi reviews advances in our understanding of the pathogenic mechanisms of DIC. Novel therapeutic strategies that have been developed and evaluated in patients with DIC are discussed, as are the clinical trials performed in patients with sepsis. In Section II, Dr. Lawrence Leung provides an overview of the challenging problems in thrombosis encountered in the inpatient setting. Patients with deep vein thrombosis that is refractory to conventional anticoagulation and those with extensive mesenteric thrombosis as well as the evaluation of a positive PF4/heparin ELISA in a post-operative setting are discussed. Novel treatments for recurrent catheter thrombosis in dialysis patients is addressed as well. In Section III, Dr. Julie Hambleton reviews the hemostatic complications of solid organ transplantation. Coagulopathy associated with liver transplantation, contribution of underlying thrombophilia to graft thrombosis, drug-induced microangiopathy, and the indication for postoperative prophylaxis are emphasized. Dr. Hambleton reviews the clinical trials evaluating hemostatic agents in patients undergoing liver transplantation.

Inhibition of coagulation, fibrinolysis, and endothelial cell activation by a p38 mitogen-activated protein kinase inhibitor during human endotoxemia

P38 mitogen-activated protein kinase (MAPK) is an important component of intracellular signaling cascades that initiate various inflammatory cellular responses. To determine the role of p38 MAPK in the procoagulant response to lipopolysaccharide (LPS), 24 healthy subjects were exposed to an intravenous dose of LPS (4 ng/kg), preceded 3 hours earlier by orally administered 600 or 50 mg BIRB 796 BS (a specific p38 MAPK inhibitor), or placebo. The 600-mg dose of BIRB 796 BS strongly inhibited LPS-induced coagulation activation, as measured by plasma concentrations of the prothrombin fragment F1 + 2. BIRB 796 BS also dose dependently attenuated the activation and subsequent inhibition of the fibrinolytic system (plasma tissue-type plasminogen activator, plasmin-alpha2-antiplasmin complexes, and plasminogen activator inhibitor type 1) and endothelial cell activation (plasma soluble E-selectin and von Willebrand factor). Activation of p38 MAPK plays an important role in the procoagulant and endothelial cell response after in vivo exposure to LPS.

Procoagulant protein levels are differentially increased during human endotoxemia

On the basis of plasma interleukin levels it was suggested that there is an inflammatory component to the risk of venous thrombotic disease. Other evidence shows that elevated levels of coagulation factor (F)VIII, FIX, FX and FXI are risk indicators for venous thrombosis, but the reasons for elevation remain unclear. We tested the hypothesis that the elevated levels could reflect an inflammatory reaction by measuring coagulation factor levels during experimental human endotoxemia. Male volunteers received endotoxin (4 ng kg-1), and blood samples were obtained before and at multiple time points after the challenge. Plasma was used for a panel of coagulation tests. Antigen levels of FVIII, von Willebrand factor (VWF), FIX, and FX were increased after endotoxin administration, reaching peak levels between 2 and 5 h. Within 24 h levels normalized, except for FVIII and VWF levels that remained at > 200%. Fibrinogen levels, and to a lesser extent FXI levels, also responded with an increase, but slower. These levels did not return to normal during the observation period. FVII levels were strongly depressed. FVIII, FIX and FX reacted immediately and strongly to endotoxin administration. The time pattern of this response is different from the slower so-called acute phase response, which appeared to be followed by FXI and fibrinogen. These increased levels of coagulation factors during an inflammatory state provide new ways of explaining why elevated levels of FVIII, FIX and FXI behave as risk indicators disease.

Activation of coagulation by administration of recombinant factor VIIa elicits interleukin 6 (IL-6) and IL-8 release in healthy human subjects

The activation of coagulation has been shown to contribute to proinflammatory responses in animal and in vitro experiments. Here we report that the activation of coagulation in healthy human subjects by the administration of recombinant factor VIIa also elicits a small but significant increase in the concentrations of interleukin 6 (IL-6) and IL-8 in plasma. This increase was absent when the subjects were pretreated with recombinant nematode anticoagulant protein c2, the inhibitor of tissue factor-factor VIIa.

Current clinical practice. DIC 2002: a review of disseminated intravascular coagulation

The turn of the millennium has seen clear advances in the understanding and management of Disseminated Intravascular Coagulation (DIC). The recognition that its pathogenesis stems from sustained thrombin generation in fuelling the cycle between inflammation and coagulation has seen the first successful treatment in severe sepsis through targeting this activity. An advance in treatment brings heightened relevance to laboratory testing, which now emphasises earlier detection and better monitoring to facilitate improved risk-identification and assessment of therapeutic efficacy. This review article also provides insights into future strategies that might build on the foundation of improving prognosis for the patient with DIC.

Plasminogen activator inhibitor activity is associated with raised lactate levels after cardiac surgery with cardiopulmonary bypass

OBJECTIVE

To investigate the pathophysiology underlying raised lactate levels after cardiac surgery with cardiopulmonary bypass (CPB).

DESIGN

Prospective observational study.

SETTING

Medical and surgical intensive care unit of a tertiary hospital.

PATIENTS

A total of 40 patients undergoing first-time coronary artery bypass grafting with CPB.

INTERVENTIONS

The prothrombotic response to cardiac surgery with CPB was assessed by measuring plasma levels of prothrombin fragment 1 + 2 and plasminogen activator inhibitor (PAI) activity. The hemodynamic responses to cardiac surgery with CPB were also measured using standard techniques.

MEASUREMENTS AND MAIN RESULTS

After cardiac surgery, prothrombin fragment 1 + 2 levels increased 6-fold and PAI activity increase 2- to 3-fold (p <.0001). Lactate levels were not associated with prothrombin fragment 1 + 2 and PAI activity levels after CPB. Lactate levels were associated with baseline PAI activity (p =.006), a history of hypertension (p =.02), raised baseline lactate levels (p =.02), an early increase in body temperature after CPB (p =.05), a late increase in oxygen consumption after CPB (p =.03), and a raised white cell count after CPB (p =.06). Lactate levels were inversely associated with the maximum activated clotting time level reached during CPB (p =.02). Multivariate linear regression demonstrated lactate levels were independently associated with baseline PAI activity.

CONCLUSION

We found cardiac surgery with CPB was associated with a marked prothrombotic response. Lactate levels were associated with elevated baseline PAI activity and evidence of an amplified inflammatory response to cardiac surgery with CPB. Our findings implicate aspects of the inflammatory response, including microvascular thrombosis, in the development of raised lactate levels after cardiac surgery with CPB.

Tissue factor-dependent coagulation protease signaling in acute lung injury

OBJECTIVES

To review the role of tissue factor-dependent coagulation in acute lung injury. To interpret preclinical and clinical data on therapeutic intervention of the coagulation cascade, focusing on the principles of proteolytic cell signaling of the coagulant and anticoagulant pathways.

DATA EXTRACTION AND SYNTHESIS

This review is based on published original research and relevant review articles on cell signaling by coagulation proteases and on experimental models that implicate the tissue factor-initiated coagulation cascade in acute lung injury and systemic inflammation.

CONCLUSIONS

The coagulation cascade signals via protease activated receptors in the tissue factor-initiation phase and downstream via the effector protease, thrombin. Bleomycin-induced acute lung injury is an example of thrombin signaling-dependent pathology. Frequently, thrombin signaling is a major contributor to inflammation in the extravascular space but intravascular thrombin signaling is a threshold-regulated event. At low concentrations, intravascular thrombin activates the protein C pathway by converting protein C (bound to endothelial cell protein C receptor) to activated protein C and this generates antiinflammatory signals along the activated protein C-endothelial cell protein C receptor-protease activated receptor 1 pathway on endothelial cells. Direct thrombin signaling only occurs when intravascular thrombin concentrations exceed a coagulant threshold. In systemic bacterial toxin-mediated inflammation, inhibition of thrombin is not sufficient to limit inflammation, whereas tissue factor inhibition interrupts a self-sustaining inflammatory escalation in acute lung injury. Therefore, in the vasculature, inflammatory signaling by the tissue factor initiation complex is favored over thrombin signaling.

Recent developments in the treatment of sepsis

Despite advances in supportive care, septic shock remains a major cause of morbidity and mortality. With the identification of the systemic inflammatory response as a major component in the pathogenesis of the septic shock syndrome, much of the recent work has focused on modulating this response. This includes antiendotoxin therapies in patients with Gram-negative sepsis, and therapies to modulate the pro-inflammatory mediators produced in response to infection, such as TNF-alpha, platelet-activating factor and complement. High-flow haemofiltration has the potential advantage of clearing both endotoxin and pro-inflammatory mediators. Antithrombotic strategies have been investigated and have yielded the first major success in the treatment of sepsis with activated protein C. Nitric oxide produces the cardiovascular features of sepsis and investigators have looked at both reducing its production and mopping up the excess. Attempts to reduce apoptosis have been a new focus in the treatment of sepsis. There have also been recent developments in supportive care suggesting a role for vasopressin and replacement corticosteroid therapy.

Bedside monitoring of coagulation activation after challenging healthy volunteers with intravenous endotoxin

INTRODUCTION

In the intensive care, many patients are at risk of developing procoagulant changes leading to severe coagulopathy and disseminated intravascular coagulation (DIC). Close monitoring of the coagulation is therefore crucial. In this study, we assess a novel bedside instrument based on free oscillating rheometry, measuring the degree of coagulation activity as clotting onset time, COT. COT measurements are conducted in whole blood, and thus reflect the overall hemostasis.

MATERIALS AND METHODS

Nine healthy volunteers were subjected to intravenous injection of 2 ng/kg endotoxin. To quantify the activation of the coagulation system, COT was assessed along with prothrombin fragment 1 + 2 (F1 + 2) and activated partial thromboplastin time (aPTT).

RESULTS

Baseline COT was 10.6 +/- 3.6 min. Three hours after endotoxin injection, maximal body temperature and heart rate were registered. At this time, an activation of the coagulation was observed as a significant decrease in COT to 8.0 +/- 1.0 min, a decrease in aPTT and increased levels of F1 + 2. COT levels, body temperature and heart rate subsequently normalized towards initial levels. F1 + 2 however continued to increase throughout the study.

CONCLUSIONS

COT is a rapid test, performed in less than 15 min. COT was superior to F1+ 2 in monitoring the endotoxin-induced activation of the coagulation, since COT covariated with clinical symptoms, whereas F1 + 2 did not. This is, to our knowledge, the first time an overall coagulation monitoring method has been assessed bedside to detect endotoxin-induced activation of the coagulation. The COT test shows promising results, but further studies are needed to reveal its potential in the intensive care monitoring arsenal.

The diagnosis of disseminated intravascular coagulation

Disseminated intravascular coagulation (DIC) is a syndrome characterized by systemic intravascular activation of coagulation, leading to widespread deposition of fibrin in the circulation. In recent years, the pathogenetic pathways leading to DIC have been largely identified, which could result in more precise diagnostic tests for this disorder. However, the clinical and laboratory diagnosis of DIC may remain difficult, since routinely available tests do not specifically assess ongoing thrombin generation. Molecular markers for activation of coagulation and fibrinogen to fibrin conversion are highly sensitive but also disappointedly aspecific for the diagnosis of DIC. Moreover, these tests are often not available in most settings for daily clinical care. A combination of widely available tests, however, may be helpful in making the diagnosis of DIC, according to a recently developed algorithm.

Ability of recombinant factor VIIa to reverse the anticoagulant effect of the pentasaccharide fondaparinux in healthy volunteers

BACKGROUND

The novel anticoagulant fondaparinux proved to be effective and safe in the postoperative prevention of venous thrombosis. Current phase III trials with this synthetic selective factor Xa inhibitor focus on its use in the treatment of patients with venous and arterial thrombosis. As with any anticoagulant therapy, there is a risk of bleeding complications; hence, a strategy to reverse the effects of fondaparinux is desirable. The aim of this study was to investigate whether recombinant factor VIIa (rFVIIa) could neutralize the anticoagulant effects of subcutaneously administered fondaparinux.

METHODS AND RESULTS

In a randomized, placebo-controlled design, 16 healthy male subjects received either a single subcutaneous dose of fondaparinux (10 mg) and a single intravenous bolus of rFVIIa (90 microg/kg; n=8), fondaparinux and placebo (n=4), or placebo and rFVIIa (n=4). Fondaparinux (or placebo) was administered 2 hours before rFVIIa (or placebo). Injection of rFVIIa after fondaparinux normalized the prolonged activated partial thromboplastin and prothrombin times and reversed the decrease in prothrombin activation fragments 1+2 (F(1+2)), as observed with fondaparinux alone. Thrombin-generation time and endogenous thrombin potential, which were inhibited by fondaparinux, normalized up to 6 hours after rFVIIa injection.

CONCLUSIONS

rFVIIa is capable of normalizing coagulation times and thrombin generation during fondaparinux treatment. The duration of this effect ranged from 2 to 6 hours after rFVIIa injection. These results suggest that rFVIIa may be useful to reverse the anticoagulant effect of fondaparinux in case of serious bleeding complications or need for acute surgery during treatment with fondaparinux.

Coagulation inhibition for sepsis

Following on the heels of multiple failed clinical trials of adjunctive therapeutic agents in sepsis, the positive outcome of a recent phase III study using activated protein C (APC) has led to a renewed optimism in targeted biotherapies for this syndrome. A growing body of data (both preclinical and clinical) suggests that the protection against death afforded by APC cannot be solely explained by its antithrombotic activity but rather is likely explained by its associated anti-inflammatory and profibrinolytic effects. Although a recent phase III study failed to demonstrate any protective effect of another important antithrombotic molecule, antithrombin, it is premature to conclude that the benefit observed with APC is unique among inhibitors of the coagulation system. The result of a third phase III study examining the effect of tissue factor pathway inhibitor (TFPI) in sepsis is currently awaited, and the possibility that other antithrombotic agents--and combinations thereof--have a place in the therapeutic armamentarium will undoubtedly be the topic of future studies.

Pathogenesis of venous thromboembolism

Three factors are related with the pathogenesis of venous thrombosis: (1) blood stasis, (2) hypercoagulability, and (3) vessel damage. Local and systemic factors are implicated in blood stasis. Remarkable advances have been recently achieved regarding the understanding of the concept of hypercoagulability, with special emphasis to thrombophilic molecular abnormalities. Increased thromboembolic risk has been described in patients with antithrombin III, protein C, or protein S deficiencies as well as factor V Leiden, prothrombin mutation G20210A, or hyperhomocystinemia. Vessel wall has a remarkable role in protecting against and in promoting thrombosis. The role of inflammation on venous thrombosis is under investigation.

A fish oil emulsion used for parenteral nutrition attenuates monocyte-endothelial interactions under flow

Monocyte adhesion contributes to perfusion abnormalities, tissue damage, and activation of the coagulation system seen during trauma, shock, or overwhelming inflammation. This study was performed to determine whether an intravenous fish oil emulsion used for parenteral nutrition attenuates monocyte-endothelial interactions under flow and reduces procoagulant activity, measured as tissue factor (TF) expression on adherent monocytes in vitro. Endothelial cell monolayers were incubated with either an intravenous fish oil emulsion or a conventional omega-6 lipid emulsion at 0.05 to 1 mg/ml for 24 h. Six hours following activation with TNFalpha (25 ng/ml), expression of endothelial cell adhesion molecules was measured by flow cytometry. Adhesion of isolated monocytes to pretreated endothelium was examined in a parallel plate flow chamber at a shear stress of 1.5 dynes/cm2. Following perfusion, the cells were cocultured for an additional 4 h and TF expression on monocytes was determined by flow cytometry. In contrast to omega-6 lipids, fish oil down-regulated E-selectin, intercellular adhesion molecule-1, and vascular cell adhesion molecule-1 in a dose-dependent manner. P-selectin, however, remained unchanged. In addition, firm adhesion was reduced to 54%, whereas rolling interactions remained unchanged. Fish oil exhibited no effect on the TF expression on cocultured monocytes. We conclude that intravenous fish oil emulsions reduce both endothelial cell adhesion molecule expression and monocyte adhesion. However, under postcapillary flow conditions, rolling interactions via P-selectin remain unaltered. The functional importance of this effect is illustrated by the corresponding upregulation of TF in response to residual monocyte-endothelial interactions.

Tissue factor production not balanced by tissue factor pathway inhibitor in sepsis promotes poor prognosis

OBJECTIVE

To determine the precise relationship among tissue factor, tissue factor pathway inhibitor (TFPI), and neutrophil elastase in sepsis, as well as to test the hypothesis that low TFPI concentrations are not sufficient to prevent tissue factor-dependent intravascular coagulation, leading to multiple organ dysfunction syndrome and death.

DESIGN

Prospective, cohort study.

SETTING

General intensive care unit of tertiary care emergency department.

PATIENTS

Thirty-one consecutive patients with sepsis, classified as 15 survivors and 16 nonsurvivors. Ten normal, healthy volunteers served as controls.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Tissue factor antigen concentration (tissue factor), TFPI, neutrophil elastase, and global variables of coagulation and fibrinolysis were measured on the day of diagnosis of sepsis, severe sepsis, and septic shock and days on 1-4 after diagnosis. The number of systemic inflammatory response syndrome criteria that patients met and the disseminated intravascular coagulation score were determined simultaneously. The results of these measurements were compared between the survivors and the nonsurvivors. In the nonsurvivors, significantly higher concentrations of tissue factor and neutrophil elastase were found compared with the survivors and control subjects. However, the TFPI values showed no difference between the two groups. No correlation was found between the peak concentrations of tissue factor and TFPI. Disseminated intravascular coagulation scores and numbers of the SIRS criteria met by the survivors significantly decreased from day 0 to day 4, but those of the nonsurvivors did not improve during the study period. The nonsurvivors showed thrombocytopenia and higher numbers of dysfunctioning organs than did the survivors.

CONCLUSIONS

We systematically elucidated the relationship between tissue factor and TFPI in patients with sepsis, severe sepsis, and septic shock. Activation of tissue factor-dependent coagulation pathway not adequately balanced by TFPI has important roles in sustaining DIC and systemic inflammatory response syndrome, and it contributes to multiple organ dysfunction syndrome and death. High concentrations of neutrophil elastase released from activated neutrophils may explain, in part, the imbalance of tissue factor and TFPI in sepsis.

Ixolaris, a novel recombinant tissue factor pathway inhibitor (TFPI) from the salivary gland of the tick, Ixodes scapularis: identification of factor X and factor Xa as scaffolds for the inhibition of factor VIIa/tissue factor complex

Saliva of the hard tick and Lyme disease vector, Ixodes scapularis, has a repertoire of compounds that counteract host defenses. Following sequencing of an I scapularis salivary gland complementary DNA (cDNA) library, a clone with sequence homology to tissue factor pathway inhibitor (TFPI) was identified. This cDNA codes for a mature protein, herein called Ixolaris, with 140 amino acids containing 10 cysteines and 2 Kunitz-like domains. Recombinant Ixolaris was expressed in insect cells and shown to inhibit factor VIIa (FVIIa)/tissue factor (TF)-induced factor X (FX) activation with an inhibitory concentration of 50% (IC(50)) in the picomolar range. In nondenaturing gel, Ixolaris interacted stoichiometrically with FX and FXa but not FVIIa. Ixolaris behaves as a fast-and-tight ligand of the exosites of FXa and gamma-carboxyglutamic acid domainless FXa (des-Gla-FXa), increasing its amidolytic activity. At high concentration, Ixolaris attenuates the amidolytic activity of FVIIa/TF; however, in the presence of DEGR-FX or DEGR-FXa (but not des-Gla-DEGR-FXa), Ixolaris becomes a tight inhibitor of FVIIa/TF as assessed by recombinant factor IX (BeneFIX) activation assays. This indicates that FX and FXa are scaffolds for Ixolaris in the inhibition of FVIIa/TF and implies that the Gla domain is necessary for FVIIa/TF/Ixolaris/FX(a) complex formation. Additionally, we show that Ixolaris blocks FXa generation by endothelial cells expressing TF. Ixolaris may be a useful tool to study the structural features of FVIIa, FX, and FXa, and an alternative anticoagulant in cardiovascular diseases.

Endothelium: interface between coagulation and inflammation

OBJECTIVE

To review the involvement of endothelial cells in the pathogenesis of coagulation abnormalities during severe infection, the differential role of proinflammatory cytokines in these mechanisms, and the cross talk between coagulation and inflammation.

DATA SOURCES

Published articles on experimental studies of coagulation activation during inflammation and clinical studies of patients with sepsis and associated hemostatic abnormalities.

DATA SYNTHESIS AND CONCLUSION

The endothelium plays a central role in all major pathways involved in the pathogenesis of the hemostatic derangement observed during severe inflammation (i.e., initiation and regulation of thrombin generation and inhibition of fibrinolysis). Rather than being a unidirectional relationship, the interaction between inflammation and coagulation involves significant cross talk in which the endothelium seems to play a pivotal role.

Evolving role of tissue factor and its pathway inhibitor

OBJECTIVE

To review the experimental and clinical evidence of the emerging role of tissue factor in intravascular thrombosis and to examine evidence supporting the potential use of tissue factor pathway inhibitor as an antithrombotic therapeutic agent.

DATA SOURCES AND STUDY SELECTION

A PubMed search was conducted encompassing articles in the English language relating to tissue factor and tissue factor pathway inhibitor in intravascular coagulation.

CONCLUSIONS

Tissue factor, a membrane-bound procoagulant glycoprotein, is the initiator of the extrinsic clotting cascade, which is the predominant coagulation pathway in vivo. The traditional view localizes tissue factor to extravascular sites, where it remains sequestered from circulating factor VII until vascular integrity is disrupted or until tissue factor expression is induced in endothelial cells or monocytes. This perspective has been challenged since the discovery of tissue factor antigen in plasma, on circulating microparticles, and on leukocytes in whole blood. Recently, the apparent role of tissue factor has expanded with the demonstration that this molecule also functions as a signaling receptor. Recombinant tissue factor pathway inhibitor, an analogue of the physiologic inhibitor of tissue factor, is a potent inhibitor of thrombus formation in experimental models. In summary, the tissue factor pathway initiates thrombosis in vivo. In addition to its classic tissue-bound distribution, recently discovered blood-borne tissue factor may have an important procoagulant function. Despite showing promise in early human studies, a recently completed phase 3 trial of recombinant tissue factor pathway inhibitor in severe sepsis failed to show a reduction in the primary end point of 28-day all-cause mortality. Tissue factor pathway inhibitor, however, remains a plausible therapeutic agent in other conditions of increased thrombogenicity, such as acute coronary syndromes, and further studies to examine this potential are warranted.

Factor VIIa/tissue factor-induced signaling: a link between clotting and disease

Tissue factor is a cellular receptor for plasma clotting factor VII. In health, tissue factor is constitutively expressed in many cells, such as fibroblasts and keratinocytes, but is absent in vascular cells that come in contact with blood. However, tissue factor is induced in vascular cells in certain pathophysiological conditions. Thus, vessel wall injury or a disease condition allows blood to come in contact with tissue factor, resulting in factor VII binding to tissue factor. Once native factor VII complexed with tissue factor is converted to the enzyme factor VIIa, the complex triggers the clotting cascade that ultimately leads to fibrin formation. In addition to its established role in coagulation, molecular links between factor VIIa/tissue factor and various biological processes, such as development, inflammation, and tumor metastasis, are also evident. Recent studies suggest that factor VIIa/tissue factor affects various cellular processes by inducing intracellular signaling. Emerging evidence suggest that factor VIIa/tissue factor participates in cell signaling by two distinct mechanisms: proteolysis-independent signaling via the cytoplasmic domain of tissue factor, and proteolysis-dependent signaling, which is independent of tissue factor's cytoplasmic tail. In proteolysis-independent signaling, filamin 1 is recruited to tissue factor upon its ligation, and this probably provides an essential intracellular link in transmitting signals from tissue factor. In proteolysis-dependent signaling, factor VIIa/tissue factor activates one or more protease-activated receptors, which couple to G proteins, to impact multiple signaling pathways. In this chapter, we review various nonhemostatic functions attributed to factor VIIa and tissue factor, describe signaling mechanisms initiated upon factor VIIa binding to tissue factor, and discuss how factor VIIa/tissue factor-induced signaling could contribute to various pathophysiological processes. The relationship between increased clotting and manifestation of various diseases is well recognized. Although aberrant activation of the coagulation pathway is primarily the consequence of a disease, activation of the coagulation pathway during the disease process, in turn, could contribute to pathogenesis of the disease. Further, recent transgenic studies in mouse suggest that the coagulation system also plays a role in embryogenesis and development. Then the question arises, how do proteins involved in the clotting regulate cellular functions? The coagulant proteases can regulate cell behavior in a number of ways. They can function like hormones, activating multiple signaling pathways, as well as release bioactive fragments and growth factors by proteolysis of cell-surface and extracellular matrix (ECM) components. This chapter reviews our current understanding of the role of factor VIIa/tissue factor (VIIa/TF), an enzyme/cofactor complex that triggers the clotting cascade, in affecting various cellular functions not related to the clotting, and discusses potential mechanisms by which it regulates cellular functions.

Tissue factor - a therapeutic target for thrombotic disorders

Exposure of blood to tissue factor (TF) sets off the coagulation cascade. TF is a transmembrane protein that serves as an essential cofactor for activated coagulation factor VII (FVIIa). TF may be exposed locally by vascular injury (such as balloon angioplasty) or by spontaneous rupture of an atherosclerotic plaque. Expression of TF may also be induced on monocytes and endothelial cells in conditions like sepsis and cancer, causing a more generalised activation of clotting. TF may thus play a central role in thrombosis in a number of settings, and attention has turned to blocking TF as a means to prevent thrombosis. Inhibiting the inducible expression of TF by monocytes can be achieved by 'deactivating' cytokines, such as interleukin (IL)-4, -10 and -13, or by certain prostanoids; by drugs that modify signal transduction, such as pentoxifylline, retinoic acid or vitamin D(3), or by antisense oligonucleotides. Such approaches are for the most part at a preclinical stage. The function of TF can be blocked by antibodies that prevent the binding of FVIIa to TF; by active site-inhibited FVIIa, which competes with native FVIIa for binding; by antibodies or small molecules that block the function of the TF/FVIIa complex; and by molecules, such as TF pathway inhibitor or nematode anticoagulant peptide C2, which inhibit the active site of FVIIa in the TF/FVIIa complex after first binding to activated factor X. The latter two agents have entered Phase II clinical trials. Perhaps most intriguing is the use of anti-TF agents locally, which holds the promise of stopping thrombosis at a specific site of injury without the bleeding risk associated with systemic anticoagulation.

Regulation of functions of vascular wall cells by tissue factor pathway inhibitor: basic and clinical aspects

Tissue factor pathway inhibitor (TFPI) is a Kunitz-type protease inhibitor that inhibits the initial reactions of blood coagulation. A major pool of TFPI is the form associated with the surface of endothelial cells, which is speculated to play an important role in regulating the functions of vascular wall cells. TFPI consists of 3 tandem Kunitz inhibitor domains, the first and second of which inhibit the tissue factor-factor VIIa complex and factor Xa, respectively. Recent findings indicate that TFPI has another function, ie, the modulation of cell proliferation. This function is based on the interaction of the C-terminal region of TFPI with these cells. In addition to endothelial cells, it has been shown that many other vascular wall cells can synthesize TFPI, eg, mesangial cells, smooth muscle cells, monocytes, fibroblasts, and cardiomyocytes. TFPI is associated with these cells mainly through heparan sulfate proteoglycans on their surface. However, recent findings suggest that there are several other candidates for TFPI-binding proteins on these cells. On the other hand, studies on plasma levels of TFPI in patients with various diseases suggest that TFPI may be a marker of endothelial cell dysfunction. An increasing number of reports suggest that recombinant TFPI may attenuate thrombosis and prevent restenosis. Clinical trials are needed to explore these possibilities. Recent reports also indicate that the application of recombinant TFPI or TFPI gene transfer prevents restenosis in addition to thrombosis after arterial injury in the animal model; corroboration of these reports awaits clinical investigation.

Management of the patient with coagulation disorders

Understanding normal haemostasis and the pathophysiology of its disorders is essential for providing optimal care and ensuring judicious usage of blood products, as is keeping abreast of novel therapeutic modalities in a rapidly evolving field. The growing availability of synthetic coagulation factors has (at least in the western hemisphere) helped to reduce morbidity and therapeutic complications, while expanding the indications and usage of these agents. Promising advances in gene therapy may indeed introduce a sea change in the next decade or two.

Pathogenesis and treatment of disseminated intravascular coagulation in the septic patient

The incidence of sepsis and complications stemming from septicemia has remained constant in recent years despite improved levels of monitoring and care. Disseminated intravascular coagulation (DIC), a syndrome that occurs frequently in septic patients, is associated with increased mortality. Organ dysfunction is also a common sequela that is strongly correlated with DIC. Cytokines released early in the course of sepsis stimulate a procoagulant state that causes development of intravascular fibrin deposition. In a later stage of DIC, bleeding may occur in parallel because of consumption of clotting factors and inhibitors. Therapeutic strategies to attenuate or reverse these conditions have focused on multiple stages of the molecular cascade of events, including preventing cytokine induction, inhibiting coagulation processes, and promoting fibrinolysis. Recent clinical trials have supported the use of antithrombin and activated protein C supplementation in DIC associated with severe sepsis. Studies of other novel therapeutic avenues are still ongoing. Future efforts may be directed at combining 2 or more agents to achieve prompt and successful reversal of DIC.

Coagulation blockade prevents sepsis-induced respiratory and renal failure in baboons

Sepsis-induced tissue factor (TF) expression activates coagulation in the lung and leads to a procoagulant environment, which results in fibrin deposition and potentiates inflammation. We hypothesized that preventing initiation of coagulation at TF-Factor VIIa (FVIIa) complex would block fibrin deposition and control inflammation in sepsis, thereby limiting acute lung injury (ALI) and other organ damage in baboons. A model of ALI was used in which adult baboons were primed with killed Escherichia coli (1 x 10(9) CFU/kg), and bacteremic sepsis was induced 12 h later by infusion of live E. coli at 1 x 10(10) CFU/kg. Animals in the treatment group were given a competitive inhibitor of TF, site-inactivated FVIIa (FVIIai), intravenously at the time of the infusion of live bacteria and monitored physiologically for another 36 h. FVIIai dramatically protected gas exchange and lung compliance, prevented lung edema and pulmonary hypertension, and preserved renal function relative to vehicle (all p < 0.05). Treatment attenuated sepsis-induced fibrinogen depletion (p < 0.01) and decreased systemic proinflammatory cytokine responses, for example, interleukin 6 (p < 0.01). The protective effects of TF blockade in sepsis-induced ALI were confirmed by using tissue factor pathway inhibitor. The results show that TF-FVIIa complex contributes to organ injury in septic primates in part through selective stimulation of proinflammatory cytokine release and fibrin deposition.

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.

Experimental and emerging therapies for sepsis and septic shock

The underlying principles of sepsis therapy have remained unchanged for decades. These include: prompt institution of antimicrobial agents aimed at the inciting pathogen, source control directed at removal of the infection nidus whenever possible, and support of organ dysfunction. Despite advances in antibiotics, surgical techniques and organ support technology, the morbidity and mortality from sepsis-related diseases have remained substantially unchanged (30 - 50%). Immunomodulation of the inflammatory cascade has been suggested as a crucial but inadequately addressed element in the treatment of sepsis. The list of potential therapeutic targets has been growing as more and more mediators are identified in the pathogenesis of sepsis. To date, numerous anti-inflammatory agents, found to have favourable effects in animal models of septic shock, have been tested in a number of clinical trials on thousands of patients. In this first of a three part series, we go through some of the background and current strategies in sepsis therapy. In this review, we include the two novel therapies that have shown clear survival benefit in large, randomised, placebo-controlled, multi-centre trials, low-dose steroids and recombinant activated protein C. Also included in this review are studies on antithrombin III, platelet-activating factor antagonists, complement modulators, nitric oxide synthase inhibitors and caspase inhibitors (apoptosis inhibitors).