Neutrophils express tissue factor in a monkey model of sepsis

Challenge to the Intestinal Mucosa During Sepsis

Sepsis is a complex of life-threating organ dysfunction in critically ill patients, with a primary infectious cause or through secondary infection of damaged tissues. The systemic consequences of sepsis have been intensively examined and evidences of local alterations and repercussions in the intestinal mucosal compartment is gradually defining gut-associated changes during sepsis. In the present review, we focus on sepsis-induced dysfunction of the intestinal barrier, consisting of an increased permeability of the epithelial lining, which may facilitate bacterial translocation. We discuss disturbances in intestinal vascular tonus and perfusion and coagulopathies with respect to their proposed underlying molecular mechanisms. The consequences of enzymatic responses by pancreatic proteases, intestinal alkaline phosphatases, and several matrix metalloproteases are also described. We conclude our insight with a discussion on novel therapeutic interventions derived from crucial aspects of the gut mucosal dynamics during sepsis.

Tissue Factor Facilitates Wound Healing in Human Airway Epithelial Cells

BACKGROUND

Tissue factor (TF) canonically functions as the initiator of the coagulation cascade. TF levels are increased in inflamed airways and seem to be important for tumor growth and metastasis. We hypothesized that airway epithelia release TF as part of a wound repair program.

OBJECTIVES

The goal of this study was to evaluate whether airway epithelia release TF in response to pro-inflammatory stimuli and to investigate roles of TF in cell growth and repair.

METHODS

Airway epithelial cells were exposed to 10 μg/mL of lipopolysaccharide or 1 ng/mL of transforming growth factor β (TGF-β). TF and TGF-β messenger RNA and protein were measured in cell lysate and culture media, respectively. Signaling pathways were evaluated by using selective agonists and inhibitors. Airway epithelia were mechanically injured in the presence of TF and tissue factor pathway inhibitor to investigate their roles in wound repair.

RESULTS

TF protein levels increased in cell media after exposure to lipopolysaccharide (P < .01) but only in growing cells, and this action was blocked when exposed to an extracellular signal-regulated kinase inhibitor or a "small" worm phenotype and mothers against Decapentaplegic inhibitor. TF protein also increased in the presence of TGF-β (P < .05). Exposure to TF pathway inhibitor decreased the rate of cell growth by 60% (P < .05), and exposure to TF increased the rate of airway healing after injury by 19% (P < .05).

CONCLUSIONS

Growing airway epithelia release TF when exposed to lipopolysaccharide or TGF-β. TF reduces wound-healing time in airway epithelia and therefore may be important to airway recovery after injury.

Plasminogen Activator Inhibitor 1 for Predicting Sepsis Severity and Mortality Outcomes: A Systematic Review and Meta-Analysis

Objectives

Plasminogen activator inhibitor-1 (PAI-1), a crucial regulator of fibrinolysis, is increased in sepsis, but its values in predicting disease severity or mortality outcomes have been controversial. Therefore, we conducted a systematic review and meta-analysis of its predictive values in sepsis.

Methods

PubMed and Embase were searched until August 18, 2017 for studies that evaluated the relationships between PAI-1 levels and disease severity or mortality in sepsis.

Results

A total of 112 and 251 entries were retrieved from the databases, of which 18 studies were included in the final meta-analysis. A total of 4,467 patients (36% male, mean age: 62 years, mean follow-up duration: 36 days) were analyzed. PAI-1 levels were significantly higher in non-survivors than survivors [odds ratios (OR): 3.93, 95% confidence interval (CI): 2.31-6.67, P < 0.0001] and in patients with severe sepsis than in those less severe sepsis (OR: 3.26, 95% CI: 1.37-7.75, P = 0.008).

Conclusion

PAI-1 is a significant predictor of disease severity and all-cause mortality in sepsis. Although the predictive values of PAI-1 reached statistical significance, the clinical utility of PAI-1 in predicting outcomes will require carefully designed prospective trials.

Tissue Factor: An Essential Mediator of Hemostasis and Trigger of Thrombosis

Tissue factor (TF) is the high-affinity receptor and cofactor for factor (F)VII/VIIa. The TF-FVIIa complex is the primary initiator of blood coagulation and plays an essential role in hemostasis. TF is expressed on perivascular cells and epithelial cells at organ and body surfaces where it forms a hemostatic barrier. TF also provides additional hemostatic protection to vital organs, such as the brain, lung, and heart. Under pathological conditions, TF can trigger both arterial and venous thrombosis. For instance, atherosclerotic plaques contain high levels of TF on macrophage foam cells and microvesicles that drives thrombus formation after plaque rupture. In sepsis, inducible TF expression on monocytes leads to disseminated intravascular coagulation. In cancer patients, tumors release TF-positive microvesicles into the circulation that may contribute to venous thrombosis. TF also has nonhemostatic roles. For instance, TF-dependent activation of the coagulation cascade generates coagulation proteases, such as FVIIa, FXa, and thrombin, which induce signaling in a variety of cells by cleavage of protease-activated receptors. This review will focus on the roles of TF in protective hemostasis and pathological thrombosis.

Sepsis and disseminated intravascular coagulation

Sepsis is frequently complicated by coagulopathy and, in about 35 % of severe cases, by disseminated intravascular coagulation (DIC). In Japan, aggressive treatment of septic DIC is encouraged using antithrombin and recombinant thrombomodulin. The macrophages, monocytes, and neutrophils are a source of TF and participate in the direct activation of the coagulation cascade in the early phases of sepsis. And activated factor X (FXa), which is involved in hemostasis, thrombogenesis, inflammation, and cellular immune responses, induces TF expression in human peripheral monocytes and, conversely, that inhibition of FXa activity reduces TF expression. Both inflammation and coagulation play an important role in DIC due to sepsis. In addition to inflammatory cytokines (TNF-α, IL-1 and so on), HMGB1 has recently been shown to mediate the lethal late phase of sepsis and caused coagulopathy. TM not only binds HMGB1 but also aids the proteolytic cleavage of HMGB1 by thrombin. There have been many reports of the efficacy of recombinant TM and antithrombin for treatment of septic DIC from Japan. Further investigation of the efficacy of recombinant TM and AT in countries other than Japan, as well as the monitoring of medical costs incurred during hospitalization, will help validate the use of TM and AT for treatment of septic DIC.

Myeloid tissue factor does not modulate lung inflammation or permeability during experimental acute lung injury

Tissue factor (TF) is a critical mediator of direct acute lung injury (ALI) with global TF deficiency resulting in increased airspace inflammation, alveolar-capillary permeability, and alveolar hemorrhage after intra-tracheal lipopolysaccharide (LPS). In the lung, TF is expressed diffusely on the lung epithelium and intensely on cells of the myeloid lineage. We recently reported that TF on the lung epithelium, but not on myeloid cells, was the major source of TF during intra-tracheal LPS-induced ALI. Because of a growing body of literature demonstrating important pathophysiologic differences between ALI caused by different etiologies, we hypothesized that TF on myeloid cells may have distinct contributions to airspace inflammation and permeability between direct and indirect causes of ALI. To test this, we compared mice lacking TF on myeloid cells (TF^∆mye, LysM.Cre^+/−TF^flox/flox) to littermate controls during direct (bacterial pneumonia, ventilator-induced ALI, bleomycin-induced ALI) and indirect ALI (systemic LPS, cecal ligation and puncture). ALI was quantified by weight loss, bronchoalveolar lavage (BAL) inflammatory cell number, cytokine concentration, protein concentration, and BAL procoagulant activity. There was no significant contribution of TF on myeloid cells in multiple models of experimental ALI, leading to the conclusion that TF in myeloid cells is not a major contributor to experimental ALI.

Is the neutrophil a 'prima donna' in the procoagulant process during sepsis?

Activation of the coagulation system is a fundamental host defense mechanism. Microorganisms that have invaded the body are trapped and disposed of in clots. Monocytes/macrophages are widely accepted as the main players in the procoagulant process; however, recent evidence suggests that neutrophils also play important roles. Tissue factor, which initiates the extrinsic coagulation cascade, is reportedly expressed on the surface of neutrophils, as well as on microparticles derived from neutrophils. Neutrophil extracellular traps (NETs) are another source of tissue factor. The components of NETs, such as DNA, histones, and granule proteins, also provide procoagulant activities. For instance, DNA initiates the intrinsic pathway, histones are a strong generator of thrombin, and granule proteins such as neutrophil elastase, cathepsin G and myeloperoxidase contribute to the suppression of the anticoagulation systems. Although understanding of the mechanisms that are involved in coagulation/fibrinolysis in sepsis has gradually progressed, the impact of neutrophils on thrombogenicity during sepsis remains to be addressed. Since the importance of the connection between coagulation and inflammation is advocated nowadays, further research on neutrophils is required.

Prohibitin-1 deficiency promotes inflammation and increases sensitivity to liver injury

Liver diseases are the fifth cause of mortality in Western countries, and as opposed to other major causes of mortality, their incidence is increasing. Understanding the molecular background contributing to the progression of liver ailments will surely open new perspectives for the better management of patients. The aim of this study is to elucidate mechanisms underlying the progression of liver injury associated with deficient prohibitin 1, an essential protein to maintain mitochondrial homeostasis and gene expression. PHB1+/- mice developed a more severe steatohepatitis than WT littermates when exposed to a choline and methionine deficient diet. The increased sensitivity was mediated by mitochondrial dysfunction and metabolic impairment in PHB1+/- livers, including inactivation of AMP kinase, measured under a non-restricted diet. Moreover, pro-inflammatory challenges induced higher mortality and liver injury in PHB+/- mice. The increased proliferative capacity of PHB+/- splenocytes, resulting from constitutive defects in central molecular pathways as stated by deregulation of GSK3β, Erk, Akt or SHP-1, and the concomitant overproduction of pro-inflammatory mediators in Phb1 deficient mice, might account for these effects. In light of these results it might be concluded that Phb1 deficiency is a potential driver of chronic liver diseases by inducing hepatocyte damage and inflammation.

Activated factor XI inhibits chemotaxis of polymorphonuclear leukocytes

PMN leukocytes are the most abundant leukocytes in the circulation and play an important role in host defense. PMN leukocyte recruitment and inflammatory responses at sites of infection are critical components in innate immunity. Although inflammation and coagulation are known to have bidirectional relationships, little is known about the interaction between PMN leukocytes and coagulation factors. Coagulation FXI participates in the intrinsic coagulation pathway upon its activation, contributing to hemostasis and thrombosis. We have shown previously that FXI-deficient mice have an increased survival and less leukocyte accumulation into the peritoneum in severe polymicrobial peritonitis. This result suggests a role for FXI in leukocyte trafficking and/or function. In this study, we characterized the functional consequences of FXIa binding to PMN leukocytes. FXIa reduced PMN leukocyte chemotaxis triggered by the chemokine, IL-8, or the bacterial-derived peptide, fMLP, perhaps as a result of the loss of directed migration. In summary, our data suggest that FXIa modulates the inflammatory response of PMN leukocytes by altering migration. These studies highlight the interplay between inflammation and coagulation and suggest that FXIa may play a role in innate immunity.

Sepsis-associated disseminated intravascular coagulation and thromboembolic disease

Sepsis is almost invariably associated with haemostatic abnormalities ranging from subclinical activation of blood coagulation (hypercoagulability), which may contribute to localized venous thromboembolism, to acute disseminated intravascular coagulation (DIC), characterized by massive thrombin formation and widespread microvascular thrombosis, partly responsible of the multiple organ dysfunction syndrome (MODS), and subsequent consumption of platelets and coagulation proteins causing, in most severe cases, bleeding manifestations. There is general agreement that the key event underlying this life-threatening sepsis complication is the overwhelming inflammatory host response to the infectious agent leading to the overexpression of inflammatory mediators. Mechanistically, the latter, together with the micro-organism and its derivatives, causes DIC by 1) up-regulation of procoagulant molecules, primarily tissue factor (TF), which is produced mainly by stimulated monocytes-macrophages and by specific cells in target tissues; 2) impairment of physiological anticoagulant pathways (antithrombin, protein C pathway, tissue factor pathway inhibitor), which is orchestrated mainly by dysfunctional endothelial cells (ECs); and 3) suppression of fibrinolysis due to increased plasminogen activator inhibitor-1 (PAI-1) by ECs and likely also to thrombin-mediated activation of thrombin-activatable fibrinolysis inhibitor (TAFI). Notably, clotting enzymes non only lead to microvascular thrombosis but can also elicit cellular responses that amplify the inflammatory reactions. Inflammatory mediators can also cause, directly or indirectly, cell apoptosis or necrosis and recent evidence indicates that products released from dead cells, such as nuclear proteins (particularly extracellular histones), are able to propagate further inflammation, coagulation, cell death and MODS. These insights into the pathogenetic mechanisms of DIC and MODS may have important implications for the development of new therapeutic agents that could be potentially useful particularly for the management of severe sepsis.

Tissue factor expression in blood cells

The popular concept of TF serving predominantly as a hemostatic envelope encapsulating the vascular bed, has recently been challenged by the observation that blood of healthy individuals may form TF-induced thrombus under conditions entailing shear stress and activated platelets, corroborating the notion of blood borne TF. Accordingly, small amounts of TF activity is detected in calcium ionophore-stimulated monocytes, whereas it is questionable whether neutrophils and eosinophils express TF. Still there are contradicting reports on TF synthesis and expression in activated platelets, but when using a very sensitive and specific assay for TF activity measurements, we fail to detect TF activity associated with platelets activated with various agonists. However, activated platelets may play a role in decrypting monocyte TF activity in a process entailing transfer of TF to activated platelets in a P-selectin-PSGL-1 reaction whereby inactive TF (encrypted) becomes active through the availability of clusters of phosphatidylserine. Microparticles from plasma of healthy subjects possess weak TF-like activity which is not inactivated by anti-TF antibody. Endothelial cells are well documented to synthesize TF by several agonists in vitro. In contrast, there is little evidence that these cells are capable of synthesizing TF in vivo, and a recent report fails to show that TF on the endothelium may play any role in thrombin generation in a murine endotoxemia model. It may be concluded that monocytes are the only blood cells that synthesize and express TF and which may be the only source for TF-induced thrombosis when the endothelium is intact.

The protein C pathway and pathologic processes

Alterations in expression of protein C (PC) pathway components have been identified in patients with active inflammatory disease states. While the PC pathway plays a pivotal role in regulating coagulation and fibrinolysis, activated PC (aPC) also exhibits cytoprotective properties. For example, PC-deficient mice challenged in septic/endotoxemic models exhibit phenotypes that include hypotension, disseminated intravascular coagulation, elevated inflammatory mediators, neutrophil adhesion to the microvascular endothelium, and loss of protective endothelial and epithelial cell barriers. Further, inflammatory bowel disease has been correlated with diminished endothelial PC receptor and thrombomodulin levels in the intestinal mucosa. Downregulated expression of the cofactor, protein S, as well as PC, is also associated with ischemic stroke. Studies to elucidate further the structural elements that differentiate the various functions of PC will serve to identify novel therapeutic approaches toward regulating these and other diseases.

The innate immune response and activation of coagulation in alpha1,3-galactosyltransferase gene-knockout xenograft recipients

BACKGROUND

The role of the innate immune system in the development of thrombotic microangiopathy (TM) after alpha1,3-galactosyltransferase gene-knockout (GTKO) pig organ transplantation in primates is uncertain.

METHODS

Twelve organs (nine hearts, three kidneys) from GTKO pigs were transplanted into baboons that received no immunosuppressive therapy, partial regimens, or a full regimen based on costimulation blockade. After graft failure, histologic and immunohistologic examinations were carried out.

RESULTS

Graft survival of less than 1 day was prolonged to 2 to 12 days with partial regimens (acute humoral xenograft rejection) and to 5 and 8 weeks with the full regimen (TM). Clinical or laboratory features of consumptive coagulopathy occurred in 7 of 12 baboons. Immunohistochemistry demonstrated IgM, IgG, and complement deposition in most cases. Histopathology demonstrated neutrophil and macrophage infiltrates, intravascular fibrin deposition, and platelet aggregation (TM). Grafts showed expression of primate tissue factor (TF), with increased mRNA levels, and TF was also expressed on baboon macrophages/monocytes infiltrating the graft.

CONCLUSIONS

Our data suggest that (1) irrespective of the presence or absence of the adaptive immune response, early or late xenograft rejection is associated with activation of the innate immune system; and (2) porcine endothelial cell activation and primate TF expression by recipient innate immune cells may both contribute to the development of TM.

Influence of obesity on sepsis

Sepsis is the leading cause of death in non-coronary intensive care units worldwide, with a very high cost of care. There is a growing body of evidence suggesting that the increase in morbidity associated with severe obesity in critically ill patients results in increased resource utilization adding further to the cost of care. There is a relative paucity of information regarding the pathophysiology and treatment of obese critically ill patients, especially with sepsis. Obesity as an exclusion criterion in landmark trials is partly responsible for this paucity. While the preventive strategies for obesity will be the most definitive long-term solution, it will take a long time to affect outcomes in our intensive care units. In the meantime, our hospitals, including the intensive care units must continue to treat obese/morbidly obese critically ill patients with sepsis, making it essential to study and understand the pathophysiology and develop treatment strategies for obese with sepsis. Available laboratory data suggests an increased inflammatory response in obese septic individuals. However, the association between obesity and sepsis in the clinical setting is unclear due to controversial results. This article reviews the available clinical and laboratory data that addresses the effects of obesity on sepsis.

Granulocytes do not express but acquire monocyte-derived tissue factor in whole blood: evidence for a direct transfer

Unlike unanimous opinion on tissue factor (TF) expression in monocytes, the quest for TF presence in granulocytes has been going on for decades. To study the cell origin and track the blood-borne TF, we assessed TF activity and protein levels, knocked-down endogenous TF expression with small interfering RNA (siRNA), and overexpressed TF–yellow fluorescent protein (TF-YFP) fusion in immunologically isolated human monocytes and granulocytes. Monocytes and, to a much lesser extent, granulocytes isolated from lipopolysaccharide (LPS)/phorbol 12-myristate-13-acetate (PMA)–stimulated whole blood contained active TF antigen. However, only monocytes possessed significant TF activity and protein levels when stimulated with LPS/PMA in suspension. Reintroduction of TF-silenced monocytes to whole blood led to a profound reduction of LPS/PMA-stimulated TF activity in both mononuclear cell (MNC) and granulocyte fractions. No reduction in TF activity in MNC and granulocyte fractions was observed when TF-silenced granulocytes were reintroduced to whole blood. As shown by immunoblotting, flow cytometry, and confocal microscopy, granulocytes became positive for TF-YFP when isolated from whole blood reconstituted with TF-YFP–expressing monocytes. Together, we pinpoint monocytes as a major source of TF and provide solid experimental evidence for a direct transfer of TF protein from the monocytes to granulocytes in the blood.

Sepsis and cholestasis

Cholestasis is a common complication of bacterial infections and sepsis. This article gives a comprehensive overview of the underlying molecular mechanisms of sepsis-associated cholestasis and jaundice, their clinical presentation, and diagnostic and therapeutic management.

Vascular biology in sepsis: pathophysiological and therapeutic significance of vascular dysfunction

Sepsis is the leading cause of mortality in critically ill patients. In this pathological syndrome, septic shock and sequential multiple organ failure correlate with poor outcome. The pathophysiology of sepsis with acute organ dysfunction involves a highly complex, integrated response that includes activation of number of cell types, inflammatory mediators, and the hemostatic system. Central to this process may be alterations in vascular functions. This review article provides a growing body of evidence for the potential impact of vascular dysfunction on sepsis pathophysiology with a major emphasis on the endothelium. Furthermore, the role of apoptotic signaling molecules in the mechanisms underlying endothelial cell injury and death during sepsis and its potential value as a target for sepsis therapy will be discussed, which may help in the assessment of ongoing therapeutic strategies.

Sepsis-induced coagulation in the baboon lung is associated with decreased tissue factor pathway inhibitor

Increased tissue factor (TF)-dependent procoagulant activity in sepsis may be partly due to decreased expression or function of tissue factor pathway inhibitor (TFPI). To test this hypothesis, baboons were infused with live Escherichia coli and sacrificed after 2, 8, or 24 hours. Confocal and electron microscopy revealed increased leukocyte infiltration and fibrin deposition in the intravascular and interstitial compartments. Large amounts of TF were detected by immunostaining in leukocytes and platelet-rich microthrombi. TF induction was documented by quantitative reverse transcriptase-polymerase chain reaction, enzyme-linked immunosorbent assay, and coagulation assays. Lung-associated TFPI antigen and mRNA decreased during sepsis, and TFPI activity diminished abruptly at 2 hours. Blocking antibodies against TFPI increased fibrin deposition in septic baboon lungs, suggesting that TF-dependent coagulation might be aggravated by reduced endothelial TFPI. Decreased TFPI activity coincided with the release of tissue plasminogen activator and the peak of plasmin generation, suggesting that TFPI could undergo proteolytic inactivation by plasmin. Enhanced plasmin produced in septic baboons by infusion of blocking antibodies against plasminogen activator inhibitor-1 led to decreased lung-associated TFPI and unforeseen massive fibrin deposition. We conclude that activation of TF-driven coagulation not adequately countered by TFPI may underlie the widespread thrombotic complications of sepsis.

Role of the extrinsic pathway of blood coagulation in hemostasis and thrombosis

Hemostasis requires both platelets and the coagulation system. At sites of vessel injury, bleeding is minimized by the formation of a hemostatic plug consisting of platelets and fibrin. The traditional view of the regulation of blood coagulation is that the initiation phase is triggered by the extrinsic pathway, whereas amplification requires the intrinsic pathway. The extrinsic pathway consists of the transmembrane receptor tissue factor (TF) and plasma factor VII/VIIa (FVII/FVIIa), and the intrinsic pathway consists of plasma FXI, FIX, and FVIII. Under physiological conditions, TF is constitutively expressed by adventitial cells surrounding blood vessels and initiates clotting. In addition so-called blood-borne TF in the form of cell-derived microparticles (MPs) and TF expression within platelets suggests that TF may play a role in the amplification phase of the coagulation cascade. Under pathologic conditions, TF is expressed by monocytes, neutrophils, endothelial cells, and platelets, which results in an elevation of the levels of circulating TF-positive MPs. TF expression within the vasculature likely contributes to thrombosis in a variety of diseases. Understanding how the extrinsic pathway of blood coagulation contributes to hemostasis and thrombosis may lead to the development of safe and effective hemostatic agents and antithrombotic drugs.

A novel C5a receptor-tissue factor cross-talk in neutrophils links innate immunity to coagulation pathways

Neutrophils and complement are key sentinels of innate immunity and mediators of acute inflammation. Recent studies have suggested that inflammatory processes modulate thrombogenic pathways. To date, the potential cross-talk between innate immunity and thrombosis and the precise molecular pathway by which complement and neutrophils trigger the coagulation process have remained elusive. In this study, we demonstrate that antiphospholipid Ab-induced complement activation and downstream signaling via C5a receptors in neutrophils leads to the induction of tissue factor (TF), a key initiating component of the blood coagulation cascade. TF expression by neutrophils was associated with an enhanced procoagulant activity, as verified by a modified prothrombin time assay inhibited by anti-TF mAb. Inhibition studies using the complement inhibitor compstatin revealed that complement activation is triggered by antiphospholipid syndrome (APS) IgG and leads to the induction of a TF-dependent coagulant activity. Blockade studies using a selective C5a receptor antagonist and stimulation of neutrophils with recombinant human C5a demonstrated that C5a, and its receptor C5aR, mediate the expression of TF in neutrophils and thereby significantly enhance the procoagulant activity of neutrophils exposed to APS serum. These results identify a novel cross-talk between the complement and coagulation cascades that can potentially be exploited therapeutically in the treatment of APS and other complement-associated thrombotic diseases.

Human polymorphonuclear leukocytes produce and express functional tissue factor upon stimulation

BACKGROUND

Blood-borne tissue factor (TF) plays a crucial role in thrombogenesis.

AIM

To study whether polymorphonuclear leukocytes (PMN) are a source of TF.

METHODS AND RESULTS

Human PMN were carefully separated from other blood cells and stimulated for 3 min with purified P-selectin or the chemotactic peptide formyl-MetLeuPhe (fMLP): they expressed both TF procoagulant activity, as identified by specific TF MoAb and inactivated factor VIIa blockade; and TF:Ag (four to six times), as shown by flow-cytometry and immunocytochemistry. About 40% of permeabilized PMN, both resting and stimulated, contained TF:Ag, indicating that stimulation only modifies the location of TF:Ag within PMN. By real time-polymerase chain reaction (RT-PCR), a very low amount of TF mRNA was detectable in resting PMN, but a 3- to 5-fold increase was observed after 1-h stimulation with P-selectin or fMLP, respectively.

CONCLUSIONS

These findings suggest that TF is not constitutively expressed in peripheral PMN, but can be up-regulated and produced upon stimulation and specific gene transcription, as for instance during contact with activated platelets or endothelium. The stored TF is rapidly expressed in vitro as a functional molecule on the surface of activated PMN. The availability of PMN TF supports the relevance of inflammatory cells and their interaction with platelets for fibrin deposition and thrombus formation.

Tissue factor-dependent coagulation is preferentially up-regulated within arterial branching areas in a baboon model of Escherichia coli sepsis

Endothelium plays a critical role in the pathobiology of sepsis by integrating systemic host responses and local rheological stimuli. We studied the differential expression and activation of tissue factor (TF)-dependent coagulation on linear versus branched arterial segments in a baboon sepsis model. Animals were injected intravenously with lethal doses of Escherichia coli or saline and sacrificed after 2 to 8 hours. Whole-mount arterial segments were stained for TF, TF-pathway inhibitor (TFPI), factor VII (FVII), and markers for endothelial cells (ECs), leukocytes, and platelets, followed by confocal microscopy and image analysis. In septic animals, TF localized preferentially at branches, EC surface, leukocytes, and platelet aggregates and accumulated in large amounts in the subendothelial space. FVII strongly co-localized with TF on ECs and leukocytes but less so with subendothelial TF. TFPI co-localized with TF and FVII on endothelium and leukocytes but not in the subendothelial space. Focal TF increases correlated with fibrin deposition and increased endothelial permeability to plasma proteins. Biochemical analysis confirmed that aortas of septic baboons expressed more TF mRNA and protein than controls. Branched segments contained higher TF protein levels and coagulant activity than equivalent linear areas. These data suggest that site-dependent endothelial heterogeneity and rheological factors contribute to focal procoagulant responses to E. coli.

Tissue factor: (patho)physiology and cellular biology

The transmembrane glycoprotein tissue factor (TF) is the initiator of the coagulation cascade in vivo. When TF is exposed to blood, it forms a high-affinity complex with the coagulation factors factor VII/activated factor VIIa (FVII/VIIa), activating factor IX and factor X, and ultimately leading to the formation of an insoluble fibrin clot. TF plays an essential role in hemostasis by restraining hemorrhage after vessel wall injury. An overview of biological and physiological aspects of TF, covering aspects consequential for thrombosis and hemostasis such as TF cell biology and biochemistry, blood-borne (circulating) TF, TF associated with microparticles, TF encryption-decryption, and regulation of TF activity and expression is presented. However, the emerging role of TF in the pathogenesis of diseases such as sepsis, atherosclerosis, certain cancers and diseases characterized by pathological fibrin deposition such as disseminated intravascular coagulation and thrombosis, has directed attention to the development of novel inhibitors of tissue factor for use as antithrombotic drugs. The main advantage of inhibitors of the TF*FVIIa pathway is that such inhibitors have the potential of inhibiting the coagulation cascade at its earliest stage. Thus, such therapeutics exert minimal disturbance of systemic hemostasis since they act locally at the site of vascular injury.

Comparative thrombotic event incidence after infusion of recombinant factor VIIa versus factor VIII inhibitor bypass activity

Thrombosis is a rare but well-recognized potential complication of Factor VIII Inhibitor Bypass Activity (FEIBA) infusion. Recombinant factor VIIa (rFVIIa) is increasingly used as an alternative to FEIBA; however, the thrombotic safety profile of rFVIIa remains incompletely characterized. To determine the incidence rates of thrombotic adverse events (AEs) after infusion of rFVIIa and FEIBA. Data from the MedWatch pharmacovigilance program of the US Food and Drug Administration, as supplemented by published case reports, were used in conjunction with estimated numbers of infusions available from manufacturers to assess comparative incidence of thrombotic AEs in patients receiving rFVIIa or FEIBA in the period from April 1999 through June 2002. Reported thrombotic AEs were rare, with incidence rates of 24.6 per 10(5) infusions (CI, 19.1-31.2 per 10(5) infusions) for rFVIIa and 8.24 per 10(5) infusions (CI, 4.71-13.4 per 10(5) infusions) for FEIBA. Thrombotic AEs were significantly more frequent in rFVIIa than FEIBA recipients (incidence rate ratio, 2.98; CI, 1.71-5.52). The most commonly documented single type of thrombotic AE after rFVIIa infusion was cerebrovascular thrombosis, while myocardial infarction was the most frequent type in patients receiving FEIBA. Contrasting AE reporting patterns between rFVIIa and FEIBA may have contributed to the observed difference in thrombotic event incidence. Nevertheless, this comprehensive pharmacovigilance assessment does not support superior thrombotic safety of rFVIIa and suggests that thrombotic AE risk may be higher in rFVIIa than FEIBA recipients.

Administration of granulocyte-colony-stimulating factor for allogeneic hematopoietic cell collection may induce the tissue factor-dependent pathway in healthy donors

The hypercoagulable state caused by the use of recombinant human granulocyte colony-stimulating factor (rhG-CSF) has been cited in anecdotal reports. Since tissue factor (TF) is the main initiator of the coagulation cascade, we examined if rhG-CSF had an inductive effect on the TF-dependent pathway in 18 healthy donors receiving rhG-CSF (10 microg/kg/day x 5 days) for peripheral blood progenitor cell mobilization. After rhG-CSF, there were increases both in TF antigen (TF:Ag) (P=0.01) and TF procoagulant activity (TF:PCA) (P=0.06) plasma levels and in TF:Ag cytofluorimetric expression on CD33 (+) cells (P=0.04). Mean activities of FVIII and vWF also increased significantly. Thrombin time was slightly prolonged (P=0.06) due to significant increases in plasma D-dimer levels. In addition, while FIX activity remained stable, there were marked reductions in mean plasma FX and FII activities and a slight decrease in FVII activity that resulted in a significant prolongation of prothrombin time within normal ranges. In conclusion, the administration of rhG-CSF led to a "prothrombotic state" via stimulation of TF and increased endothelial markers, such as F VIII and vWF. In the light of these findings, the use of rhG-CSF for stem cell mobilization should be undertaken cautiously in healthy donors with underlying thrombotic risk factors.

Tissue factor

As early as the nineteenth century, it was recognized that tissues exhibit clot-promoting activity. The realization that a single protein was responsible for this procoagulant effect led to the discovery of tissue factor (TF), but for many years it was thought that TF activity was restricted to the activation of an auxiliary pathway that had little biological relevance. Research over recent decades has greatly improved our understanding of TF function, and today the protein is recognized to be the primary biological initiator of the coagulation cascade. Furthermore, it is now clear that TF is a major player in several other physiological processes. We present recent data suggesting that TF is vital not only for effective haemostasis, but also for angiogenesis and tumour metastasis, for embryonic development, and for induction of a pro-inflammatory response. These advances in our knowledge of TF function will improve our understanding of several pathophysiological conditions, and may expand the therapeutic options available for their treatment.

The coagulation system contributes to synergistic liver injury from exposure to monocrotaline and bacterial lipopolysaccharide

Coexposure to a noninjurious dose of bacterial lipopolysaccharide (LPS; 7.4 x 106 EU/kg) and a nontoxic dose of the food-borne toxin monocrotaline (MCT; 100 mg/kg) leads to synergistic hepatotoxicity in Sprague-Dawley rats. Inflammatory factors, such as Kupffer cells (KCs), tumor necrosis factor-alpha (TNF)-alpha, and neutrophils (polymorphonuclear leukocytes; PMNs), are critical to the pathogenesis. Inasmuch as activation of the coagulation system and sinusoidal endothelial cell (SEC) injury precede hepatic parenchymal cell (HPC) injury, and since fibrin deposition occurs within liver lesions, the coagulation system might be a critical component of injury. In this study, this hypothesis is tested, and the interdependence of the coagulation system and inflammatory factors is explored. Administration of the anticoagulants heparin or warfarin to MCT/LPS-cotreated animals attenuated HPC and SEC injury. Morphometric analysis revealed that anticoagulant treatment significantly reduced the area of centrilobular and midzonal lesions. Heparin treatment also reduced fibrin deposition in these regions. Furthermore, anticoagulant treatment decreased hepatic PMN accumulation but did not affect plasma TNF-alpha concentration. Neither KC inactivation nor TNF-alpha depletion prevented activation of the coagulation system. PMN depletion, however, prevented coagulation system activation, suggesting that PMNs are needed for this response. These results provide evidence that the coagulation system and its interplay with PMNs are important in the pathogenesis of MCT/LPS-induced liver injury.

The role of tissue factor in colorectal cancer

The possible role of tissue factor (TF) in colorectal cancer (CRC) is reviewed. A correlation between TF expression and advanced stages of malignancy, and a correlation between TF expression and overall survival have been suggested in CRC. This is supported by experimental studies indicating that TF plays a key role in growth, invasion and dissemination of tumour cells, and in tumour related angiogenesis as well. In addition, the activation of TF in CRC patients in relation to the surgical trauma, perioperative blood transfusion and development of postoperative bacterial infectious complications are discussed. Finally, future directions for the development of anticancer modalities directed against regulation of TF are considered.

The role of the endothelium in severe sepsis and multiple organ dysfunction syndrome

Severe sepsis, defined as sepsis with acute organ dysfunction, is associated with high morbidity and mortality rates. The development of novel therapies for sepsis is critically dependent on an understanding of the basic mechanisms of the disease. The pathophysiology of severe sepsis involves a highly complex, integrated response that includes the activation of a number of cell types, inflammatory mediators, and the hemostatic system. Central to this process is an alteration of endothelial cell function. The goals of this article are to (1) provide an overview of sepsis and its complications, (2) discuss the role of the endothelium in orchestrating the host response in sepsis, and (3) emphasize the potential value of the endothelium as a target for sepsis therapy.

Inhibition of tissue factor limits the growth of venous thrombus in the rabbit

Antibody mediated inhibition of tissue factor (TF) function reduces thrombus size in ex vivo perfusion of human blood over a TF-free surface at venous shear rates suggesting that TF might be involved in the mechanism of deep vein thrombosis. Moreover, TF-bearing monocytes and polymorphonuclear (PMN) leukocytes were identified in human ex vivo formed thrombi and in circulating blood. To understand the role of TF in thrombus growth, we applied a rabbit venous thrombosis model in which a collagen-coated thread was installed within the jugular vein or within a silicon vein shunt. The effect of an inhibitory monoclonal antirabbit TF antibody (AP-1) or Napsagatran, a specific inhibitor of thrombin, was quantified by continuously monitoring 125I-fibrinogen incorporation into the growing thrombi. The antithrombotic effect obtained with the anti-TF antibody was comparable to the effect observed with the thrombin inhibitor napsagatran suggesting that in this animal model the thrombus propagation is highly TF dependent. Immunostaining revealed that TF was mostly associated with leukocytes within the thrombi formed in the jugular vein or in the silicon vein shunt. Ex vivo perfusion experiments over collagen-coated coverslips demonstrated the presence of TF-bearing PMN leukocytes in circulating blood. The results suggest that in rabbits venous thrombus growth is mediated by clot-bound TF and that blocking the TF activity can inhibit thrombus propagation.

Liver in sepsis and systemic inflammatory response syndrome

In patients with sepsis and SIRS, the liver has two opposing roles: a source of inflammatory mediators and a target organ for the effects of the inflammatory mediators. The liver is pivotal in modulating the systemic response to severe infection, because it contains the largest mass of macrophages (Kupffer cells) in the body; these macrophages can clear the endotoxin and bacteria that initiate the systemic inflammatory response. This article summarizes the functional changes that take place in the liver during sepsis and systemic inflammatory response syndrome and discusses the cellular and molecular mechanisms that underlie clinical outcomes.

Cell-derived microparticles in synovial fluid from inflamed arthritic joints support coagulation exclusively via a factor VII-dependent mechanism

OBJECTIVE

To determine the cellular origin of synovial microparticles, their procoagulant properties, and their relationship to local hypercoagulation.

METHODS

Microparticles in synovial fluid and plasma from patients with rheumatoid arthritis (RA; n = 10) and patients with other forms of arthritis (non-RA; n = 10) and in plasma from healthy subjects (n = 20) were isolated by centrifugation. Microparticles were identified by flow cytometry. The ability of microparticles to support coagulation was determined in normal plasma. Concentrations of prothrombin fragment F(1+2) (by enzyme-linked immunosorbent assay [ELISA]) and thrombin-antithrombin (TAT) complexes (by ELISA) were determined as estimates of the coagulation activation status in vivo.

RESULTS

Plasma from patients and healthy controls contained comparable numbers of microparticles, which originated from platelets and erythrocytes. Synovial microparticles from RA patients and non-RA patients originated mainly from monocytes and granulocytes; few originated from platelets and erythrocytes. Synovial microparticles bound less annexin V (which binds to negatively charged phospholipids) than did plasma microparticles, exposed tissue factor, and supported thrombin generation via factor VII. F(1+2) (median 66 nM) and TAT complex (median 710 microg/liter) concentrations were elevated in synovial fluid compared with plasma from the patients (1.6 nM and 7.0 microg/liter, respectively) as well as the controls (1.0 nM and 2.9 microg/liter, respectively).

CONCLUSION

Synovial fluid contains high numbers of microparticles derived from leukocytes that are strongly coagulant via the factor VII-dependent pathway. We propose that these microparticles contribute to the local hypercoagulation and fibrin deposition in inflamed joints of patients with RA and other arthritic disorders.

New functions of neutrophils in the arthus reaction: expression of tissue factor, the clotting initiator, and fibrinolysis by elastase

The products of the blood clotting reaction, eg, thrombin and fibrinopeptides, have various proinflammatory activities and are suggested to modulate inflammation. The macrophage expression of tissue factor (TF), the clotting initiator, has been shown to cause clotting in the site of the delayed-type hypersensitivity reaction, a cellular immune response. However, the mechanism of the clotting induction in humoral immune response has been insufficiently studied. Therefore, the Arthus reaction, a model of immune-complex diseases, was produced in monkey skin that was examined for TF expression and fibrin deposition. TF antigen was positive on most of polymorphonuclear leukocytes, which were the main leukocytes in the lesions and were identified as neutrophils with an anti-neutrophil-elastase mAb. TF mRNA was detected in neutrophils by in situ hybridization using TF RNA probes, indicating de novo TF synthesis by the leukocytes. Specific binding of activated factor VII onto TF-positive neutrophils suggested the activity of neutrophil TF to trigger the cascade reaction of clotting. The number of TF-positive neutrophils were correlated in time with the intensity and extent of fibrin deposition that was visualized with an mAb specific for fibrin and peaked in 24 hours. Interestingly, the fibrin deposit was partially positive for an mAb specific for neutrophil elastase-digested fibrin. These results show in vivo evidence of a close relationship between neutrophils and both clotting and fibrinolysis in the Arthus reaction and may suggest that these neutrophil functions contribute to the pathogenesis of this hypersensitivity inflammation.

Relationship between cytokine mRNA expression and organ damage following cecal ligation and puncture

AIM: To investigate the role of cytokine gene expression in organ damage at different tissue sites during sepsis.

METHODS: Male NIH mice were subjected to cecal ligation and puncture (CLP) or sham operation (Sham). Pro-inflammatory cytokine (TNFα, IL-1β and IL-6) and anti-inflammatory cytokine (IL-4) gene expression in the liver and lung tissue were assessed by RT-PCR. The permeability of microvascular and water content in the lungs and liver were also examined.

RESULTS: Significant increase in TNFα, IL-1β and IL-6 gene expression was observed at 3 and 12 h after CLP both in the liver and lungs (P < 0.01).The level of IL-4 gene expression was not changed after CLP in the lungs, but increased at 12 h after CLP (P < 0.01) in the liver tissue. Both the liver and lungs showed a significant increase in microcirculatory permeability at 12 h after CLP(P < 0.01), and the increase in the lungs was higher than that in the liver. The water mass fractions in the liver (P < 0.05) and lungs (P < 0.01) were increased after CLP, and the increase in the lungs happened earlier and more severely than that in the liver.

CONCLUSION: The inflammatory response in the liver and lungs was different during sepsis. At the early stage of sepsis, pro-inflammatory reaction dominates both in the liver and lungs. But at the later stage of sepsis, induction of compensatory anti-inflammatory response was seen in the liver but not in the lungs. This difference in situ activity may contribute to the different vulnerability of organ damage during sepsis. The strategy of systemic administration of anti-inflammatory drugs to sepsis should be reconsidered.

Enhanced monocyte tissue factor expression in hepatosplenic schistosomiasis

Monocyte tissue factor expression was evaluated in 67 patients with hepatosplenic Schistosomiasis. They were classified as Child A (n = 15), Child B (n = 15), Child C (n = 12) and Bleeders (n = 10), in addition to 15 healthy controls. Mononuclear cells were cultured in vitro with and without lipopolysaccharide (LPS) to assess monocyte tissue factor (TF) antigen (Ag) and activity (Act) in cell lysate, in addition to measurement of prothrombin fragment 1 + 2 (F1 + 2) as a marker of in vivo thrombin generation. A significant increase in monocyte TF Ag and TF Act was noted in all stages of the disease compared with the control group, with marked accentuation during an acute attack of variceal bleeding. This enhanced monocyte expression was noted before the addition of LPS and became more obvious with addition of LPS. An increasing level of F1 + 2 was similarly noted. These findings constitute further evidence for an existing prothrombotic state in hepatosplenic Schistosomiasis, and also that monocytes are closely implicated in the haemostatic diathesis characterizing the disease.

Inhibition of factor Xa suppresses the expression of tissue factor in human monocytes and lipopolysaccharide-induced endotoxemia in rats

BACKGROUND

Activated factor X (FXa) is involved in hemostasis, thrombogenesis, inflammation, and cellular immune response. Tissue factor (TF) is an initiator of blood coagulation. We investigated whether FXa induces TF expression in human peripheral monocytes and whether treatment with FXa inhibitor reduces TF expression in an experimental model of rat endotoxemia.

METHODS

Human peripheral mononuclear cells were used to determine TF expression induced by FXa. Experimental rat endotoxemia was induced by intravenous bolus injection of lipopolysaccharide (LPS). A specific FXa inhibitor, DX-9065a, was administered subcutaneously immediately after LPS injection.

RESULTS

FXa induced TF expression in monocytes without intervention of thrombin and the expression was suppressed by FXa inhibitor. In the experimental model of rat endotoxemia, TF and TF mRNA expression levels in the liver were reduced by DX-9065a. Moreover, administration of DX-9065a suppressed the rise in plasma concentrations of thrombin-antithrombin III complex (TAT) and monocyte chemoattractant protein-1 (MCP-1).

CONCLUSIONS

Our results indicated that FXa can induce TF expression in human peripheral monocytes and that inhibition of FXa reduces TF expression in the liver of rat endotoxemia. These results suggest that FXa is an important factor for TF expression in sepsis.

Vascular bed-specific hemostasis: role of endothelium in sepsis pathogenesis

OBJECTIVES

To examine the role of vascular bed-specific pathways in determining the hemostatic phenotype in sepsis.

DATA SOURCES/STUDY SELECTION

Published research and review articles related to hemostasis and endothelial cell biology.

DATA EXTRACTION AND SYNTHESIS

The results of published studies have been used to generate a hypothesis of vascular bed-specific hemostasis in sepsis.

CONCLUSIONS

In sepsis, coagulation is initiated by the extrinsic pathway and is amplified through the intrinsic pathway. In addition, the body's natural anticoagulant mechanisms are significantly dampened. Together, these changes result in a net imbalance of hemostasis. The nature of this imbalance varies from one vascular bed to the next according to the local set point of the endothelium. These concepts lay an important foundation for understanding the pathophysiology of sepsis.

Hepatic response to sepsis: interaction between coagulation and inflammatory processes

OBJECTIVES

a) To review the hepatic response to sepsis and to establish how this response contributes to coagulation and inflammatory processes; b) to review the physiologic and biochemical mechanisms that suggest hepatic dysfunction may occur during sepsis, enhance procoagulant and proinflammatory activities, and participate in the potential evolution to multiple organ dysfunction syndrome.

DATA SOURCES

A summary of published medical literature from MEDLINE search files and published reviews on liver function in experimental and human sepsis.

DATA SUMMARY

In sepsis, the liver plays a major role in host defense mechanisms. Kupffer cells are responsible for bacterial scavenging, bacterial products inactivation, and inflammatory mediators clearance and production. Hepatocytes, via receptors for many proinflammatory cytokines, modify their metabolic pathway toward gluconeogenesis, amino-acid uptake, and increased synthesis of coagulant and complement factors and protease inhibitors. The acute-phase protein (APP) response also contributes to the procoagulant state, especially by enhancing the inhibition of protein C (alpha1-antitrypsin and alpha2-macroglobulin) and by decreasing liver synthesis of protein C and antithrombin (negative APPs). Elevated C-reactive protein levels (positive APPs) promote the expression of tissue factor by mononuclear cells. Increased liver production of thrombin-activatable fibrinolytic inhibitor (positive APPs) enhances fibrinolysis inhibition. Conversely, such hepatic inflammatory and coagulation processes in sepsis may alter the function of this organ. Indeed, the liver can be injured by activated Kupffer cells that release chemokines, attract blood neutrophils into the liver, and activate them. Neutrophils up-regulate their surface adhesion molecules, tissue factor, and Kupffer cells, whereas tissue factor pathway inhibitor and thrombomodulin are almost undetectable in endothelial cells. This may lead to microcirculatory disturbances, fibrin deposition, hepatocyte injury, endotoxin and bacteria spillover, and multiple organ failure.

CONCLUSIONS

In sepsis, the liver participates in host defense and tissue repair through hepatic cell cross-talk that controls most of the coagulation and inflammatory processes. When this control is not adequate, a secondary hepatic dysfunction may occur and may sometimes lead to bacterial products spillover, enhanced procoagulant and inflammatory processes, and in turn, multiple organ failure and death.