Tissue factor pathway inhibitor response does not correlate with tissue factor-induced disseminated intravascular coagulation and multiple organ dysfunction syndrome in trauma patients

Disseminated Intravascular Coagulation: An Update on Pathogenesis, Diagnosis, and Therapeutic Strategies

Disseminated intravascular coagulation (DIC) is an acquired clinicobiological syndrome characterized by widespread activation of coagulation leading to fibrin deposition in the vasculature, organ dysfunction, consumption of clotting factors and platelets, and life-threatening hemorrhage. Disseminated intravascular coagulation is provoked by several underlying disorders (sepsis, cancer, trauma, and pregnancy complicated with eclampsia or other calamities). Treatment of the underlying disease and elimination of the trigger mechanism are the cornerstone therapeutic approaches. Therapeutic strategies specific for DIC aim to control activation of blood coagulation and bleeding risk. The clinical trials using DIC as entry criterion are limited. Large randomized, phase III clinical trials have investigated the efficacy of antithrombin (AT), activated protein C (APC), tissue factor pathway inhibitor (TFPI), and thrombomodulin (TM) in patients with sepsis, but the diagnosis of DIC was not part of the inclusion criteria. Treatment with APC reduced 28-day mortality of patients with severe sepsis, including patients retrospectively assigned to a subgroup with sepsis-associated DIC. Treatment with APC did not have any positive effects in other patient groups. The APC treatment increased the bleeding risk in patients with sepsis, which led to the withdrawal of this drug from the market. Treatment with AT failed to reduce 28-day mortality in patients with severe sepsis, but a retrospective subgroup analysis suggested possible efficacy in patients with DIC. Clinical studies with recombinant TFPI or TM have been carried out showing promising results. The efficacy and safety of other anticoagulants (ie, unfractionated heparin, low-molecular-weight heparin) or transfusion of platelet concentrates or clotting factor concentrates have not been objectively assessed.

Tissue factor-bearing microparticles and inflammation: a potential mechanism for the development of venous thromboembolism in cancer

Cancer is associated with an increased risk of venous thromboembolism (VTE); the exact mechanisms for the induction of VTE remain to be fully elucidated, but it is widely acknowledged that tissue factor (TF)-bearing microparticles (TF-MPs) may play a significant role. However, TF-MPs have yet to be accepted as a genuine biomarker for cancer-associated VTE, as the presence of elevated TF-MP levels is not always accompanied by thrombosis; interestingly, in certain cases, particularly in pancreatic cancer, VTE seems to be more likely in the context of acute inflammation. Although several potential mechanisms for the development of VTE in cancer have been postulated, this review explores the homeostatic disruption of TF-MPs, as the main reservoir of bloodborne TF, in the context of cancer and inflammation, and considers the abrogated responses of the activated endothelium and mononuclear phagocyte system in mediating this disruption.

The association between the levels of CRP, IL-10, PLA2, Fbg and prognosis in traumatic fracture of lower limb

The aim of the present study was to examine changes of sera levels of C-reactive protein (CRP), interleukin-10 (IL-10), phospholipase A2 (PLA2) and fibrinogen β polypeptide chain gene (Fbg) in patients with traumatic fracture of lower limb, and to evaluate their association with prognosis. The changes in sera levels of CRP, IL-10, PLA2 and Fbg were observed at the time of injury, 24 h, and 5 and 7 days after surgery in 90 patients with traumatic fracture of lower limb. In addition, 50 cases, who presented for health examination, were included as the normal controls. The expression of sera levels of CRP, IL-10, PLA2 and Fbg in patients with traumatic fracture of lower limb, was markedly higher than that in the normal controls prior to surgery (P<0.05). The concentration of CRP significantly increased within 24 h after emergency, but decreased gradually as the wound healed, compared to the controls. Pre- and postoperative IL-10 levels increased within 24 h and then decreased gradually. The level of PLA2 in patients before and after surgery was increased, and then decreased gradually. The level of Fbg in patients with trauma was increased after 24 h and then decreased, and increased gradually. The correlation of serum CRP and IL-10 levels (r=0.634, P<0.05), and that of PLA2 and IL-10 levels (r=0.617, P<0.05) were positive. In conclusion, the expression of CRP, IL-10, PLA2 and Fbg levels in traumatic fracture of lower limb markedly increased and was closely associated with prognosis. CRP, IL-10, PLA2 and Fbg levels may therefore serve as useful indexes in determining the progression and prognosis of patients with traumatic fracture of lower limb.

Local hemostasis, immunothrombosis, and systemic disseminated intravascular coagulation in trauma and traumatic shock

Knowing the pathophysiology of trauma-induced coagulopathy is important for the management of severely injured trauma patients. The aims of this review are to provide a summary of the recent advances in our understanding of thrombosis and hemostasis following trauma and to discuss the pathogenesis of disseminated intravascular coagulation (DIC) at an early stage of trauma. Local hemostasis and thrombosis respectively act to induce physiological wound healing of injuries and innate immune responses to damaged-self following trauma. However, if overwhelmed by systemic inflammation caused by extensive tissue damage and tissue hypoperfusion, both of these processes foster systemic DIC associated with pathological fibrin(ogen)olysis. This is called DIC with the fibrinolytic phenotype, which is characterized by the activation of coagulation, consumption coagulopathy, insufficient control of coagulation, and increased fibrin(ogen)olysis. Irrespective of microvascular thrombosis, the condition shows systemic thrombin generation as well as its activation in the circulation and extensive damage to the microvasculature endothelium. DIC with the fibrinolytic phenotype gives rise to oozing-type non-surgical bleeding and greatly affects the prognosis of trauma patients. The coexistences of hypothermia, acidosis, and dilution aggravate DIC and lead to so-called trauma-induced coagulopathy.

He that would know what shall be must consider what has been.

The Analects of Confucius.

Damage control resuscitation: permissive hypotension and massive transfusion protocols

Evidence for changes in adult trauma management often precedes evidence for changes in pediatric trauma management. Many adult trauma centers have adopted damage-control resuscitation management strategies, which target the metabolic syndrome of acidosis, coagulopathy, and hypothermia often found in severe uncontrolled hemorrhage. Two key components of damage-control resuscitation are permissive hypotension, which is a fluid management strategy that targets a subnormal blood pressure, and hemostatic resuscitation, which is a transfusion strategy that targets coagulopathy with early blood product administration. Acceptance of damage-control resuscitation strategies is reflected in recent changes in the American College of Surgeons' Advanced Trauma Life Support curriculum; the most recent edition has decreased its initial fluid recommendation to 1 L from 2 L, and it now recommends early administration of blood products without specifying any specific ratio. These recommendations are not advocating permissive hypotension or hemostatic resuscitation directly but represent an initial step toward limiting fluid resuscitation and using blood products to treat coagulopathy earlier. Evidence for permissive hypotension exists in animal studies and few adult clinical trials. There is no evidence to support permissive hypotension strategies in pediatrics. Evidence for hemostatic resuscitation in adult trauma management is more comprehensive, and there are limited data to support its use in pediatric trauma patients with severe hemorrhage. Additional studies on the management of children with severe uncontrolled hemorrhage are needed.

Coagulopathy associated with traumatic brain injury

Coagulopathy is often observed after traumatic brain injury (TBI), but the pathogenic mechanisms of this phenomenon remain elusive. Brain injury is the leading cause of trauma deaths, and the development of coagulopathy after TBI is associated with increased morbidity and mortality in these patients. The coagulopathy after TBI comprises a hypocoagulable and a hypercoagulable state with hemorrhagic and thrombotic phenotypes that are both associated with worse outcome. Some theories of its pathogenesis include massive release of tissue factor, altered protein C homeostasis, microparticle upregulation, and platelet hyperactivity. This article aims to examine the coagulopathy associated with blunt head injury, to review its effect on progression of hemorrhagic injury, and to discuss the possible relevant pathophysiological mechanisms.

The contribution of group A streptococcal virulence determinants to the pathogenesis of sepsis

Streptococcus pyogenes (group A streptococcus, GAS) is responsible for a wide range of pathologies ranging from mild pharyngitis and impetigo to severe invasive soft tissue infections. Despite the continuing susceptibility of the bacterium to β-lactam antibiotics there has been an unexplained resurgence in the prevalence of invasive GAS infection over the past 30 years. Of particular importance was the emergence of a GAS-associated sepsis syndrome that is analogous to the systemic toxicosis associated with TSST-1 producing strains of Staphylococcus aureus. Despite being recognized for over 20 years, the etiology of GAS associated sepsis and the streptococcal toxic shock syndrome remains poorly understood. Here we review the virulence factors that contribute to the etiology of GAS associated sepsis with a particular focus on coagulation system interactions and the role of the superantigens in the development of streptococcal toxic shock syndrome.

Normal prothrombinase activity, increased systemic thrombin activity, and lower antithrombin levels in patients with disseminated intravascular coagulation at an early phase of trauma: comparison with acute coagulopathy of trauma-shock

BACKGROUND

We tested the hypotheses that an increase in systemic thrombin activity occurs in both disseminated intravascular coagulation (DIC) with the fibrinolytic phenotype and in acute coagulopathy of trauma shock (ACoTS), and that the patients diagnosed as having ACoTS overlap or are identical with those diagnosed as having DIC.

METHODS

We made a prospective study of 57 trauma patients, including 30 patients with DIC and 27 patients without DIC. Patients with ACoTS, defined as a prothrombin time ratio >1.2, were also investigated. We included 12 healthy volunteers as controls. The levels of soluble fibrin, antithrombin, prothrombinase activity, soluble thrombomodulin, and markers of fibrin(ogen)olysis were measured on days 1 and 3 after the trauma. The systemic inflammatory response syndrome and the Sequential Organ Failure Assessment were scored to evaluate the extent of inflammation and organ dysfunction.

RESULTS

Patients with DIC showed more systemic inflammation and greater Sequential Organ Failure Assessment scores and were transfused with more blood products than the patients without DIC. On day 1, normal prothrombinase activity, increased soluble fibrin, lesser levels of antithrombin, and increased soluble thrombomodulin were observed in patients with DIC in comparison with controls and non-DIC patients. These changes were more prominent in patients with DIC who met the overt criteria for DIC established by the International Society on Thrombosis and Haemostasis. Multiple regression analysis showed that antithrombin is an independent predictor of high soluble fibrin in DIC patients. Greater levels of fibrin and fibrinogen degradation products, D-dimer, and the fibrin and fibrinogen degradation products/D-dimer ratio indicated increased fibrin(ogen)olysis in DIC patients. Almost all ACoTS patients overlapped with the DIC patients. The changes in the measured variables in ACoTS patients coincided with those in DIC patients.

CONCLUSION

Normal prothrombinase activity and insufficient control of coagulation give rise to systemic increase in thrombin generation and its activity in patients with DIC with the fibrinolytic phenotype at an early phase of trauma. The same is true in patients with ACoTS, and shutoff of thrombin generation was not observed.

Resuscitation and transfusion management in trauma patients: emerging concepts

PURPOSE OF REVIEW

Severe trauma is associated with hemorrhage, coagulopathy and transfusion of blood and blood products, all associated with considerable mortality and morbidity. The aim of this review is to focus on resuscitation, transfusion strategies and the management of bleeding in trauma as well as to emphasize on why coagulation has to be monitored closely and to discuss the rationale of modern and future transfusion strategies.

RECENT FINDINGS

Coagulopathy and uncontrolled bleeding remain leading causes of death in trauma, lead to blood transfusions and increased mortality as it has been recently shown that blood transfusion per se results in an adverse outcome. In the last years, damage control resuscitation, a combination of permissive hypotension, hemostatic resuscitation and damage control surgery, has been introduced to treat severely traumatized patients in hemorrhagic shock. Goals of treatment in trauma patients remain avoiding metabolic acidosis, hypothermia, treating coagulopathy and stabilizing the patient as soon as possible. The place of colloids and crystalloids in trauma resuscitation as well as the role of massive transfusion protocols with a certain FFP : RBC ratio and even platelets have to be reevaluated.

SUMMARY

Close monitoring of bleeding and coagulation in trauma patients allows goal-directed transfusions and thereby optimizes the patient's coagulation, reduces the exposure to blood products, reduces costs and may improve clinical outcome.

Differentiating disseminated intravascular coagulation (DIC) with the fibrinolytic phenotype from coagulopathy of trauma and acute coagulopathy of trauma-shock (COT/ACOTS)

Two concepts have been proposed for the hemostatic changes occurring early after trauma. Disseminated intravascular coagulation (DIC) with the fibrinolytic phenotype is characterized by activation of the coagulation pathways, insufficient anticoagulant mechanisms and increased fibrinolysis. Coagulopathy of trauma and acute coagulopathy of trauma-shock (COT/ACOTS) occurs as a result of increased activation of the thrombomodulin and protein C pathways, leading to the suppression of coagulation and activation of fibrinolysis. Despite the differences between these two conditions, independent consideration of COT/ACOTS from DIC with the fibrinolytic phenotype is probably incorrect. Robust diagnostic criteria based on its pathophysiology are required to establish COT/ACOTS as a new independent disease concept. In addition, the independency of its characteristics, laboratory data, time courses and prognosis from DIC should be confirmed. Confusion between two concepts may be based on studies of trauma lacking the following: (i) a clear distinction of the properties of blood between the inside and outside of vessels, (ii) a clear distinction between physiologic and pathologic hemostatic changes, (iii) attention to the time courses of the changes in hemostatic parameters, (iv) unification of the study population, and (v) recognition that massive bleeding is not synonymous with coagulation disorders. More information is needed to elucidate the pathogenesis of these two entities, DIC with the fibrinolytic phenotype and COT/ACOTS after trauma. However, available data suggest that COT/ACOTS is not a new concept but a disease entity similar to or the same as DIC with the fibrinolytic phenotype.

Tissue hemostasis and chronic inflammation in colon biopsies of patients with inflammatory bowel disease

Inflammatory bowel disease (IBD) is characterized by a chronic inflammation accompanied by procoagulation settings. However, tissue hemostasis in IBD patients was only incidentally reported. Accordingly, the current study characterizes changes in tissue hemostasis components in a colon inflammatory setting. Serial cryostat sections of endoscopic mucosal biopsy specimens taken from 26 consecutive IBD patients diagnosed de novo and normal colon resection specimens taken from 6 patients were immunohistochemically stained with monoclonal anti-human tissue factor (TF), tissue factor pathway inhibitor (TFPI), thrombomodulin (TM), as well as CD3 and CD68 positive cells. The hemostatic components studied differed significantly from the control subjects. Up-regulation predominated in the case of TF while down-regulation was mainly found in TM and TFPI in IBD. In the control sections, TF was observed in a few fibroblast-shaped cells in the lamina propria, while in the majority of IBD sections, TF positively stained small microvessels, infiltrating mononuclear cells and fibroblast-shaped cells tightly surrounding the colon crypts. Thrombomodulin intensively stained the endothelium of the small capillary vessels in the control, whereas such staining mainly accompanied infiltrating mononuclear cells of the IBD subjects. Tissue factor pathway inhibitor positively stained the endothelium of the small capillary vessels in the control group, whereas in the IBD group endothelial cells presented only weak TFPI staining. The mean number of CD3-positive lymphocytes in IBD was 23.3 ± 14.3, but the mean number of CD68-positive cells was 114.5 ± 55.8. In the control sections, it was 4.1 ± 2.4 and 39.6 ± 17.9, respectively. There was no relationship between CD3 and CD68 (+) cells and the hemostasis markers studied. The results of the current study indicate a shift of tissue hemostasis toward the procoagulant state irrespective of the severity of inflammatory infiltration. In addition, TF distribution in the colon sections of IBD patients may indicate a role in the restoration of the barrier function in injured intestinal mucosa.

What's new in resuscitation strategies for the patient with multiple trauma?

The last decade has seen a sea change in the management of major haemorrhage following traumatic injury. Damage control resuscitation (DCR), a strategy combining the techniques of permissive hypotension, haemostatic resuscitation and damage control surgery has been widely adopted as the preferred method of resuscitation in patients with haemorrhagic shock. The over-riding goals of DCR are to mitigate metabolic acidosis, hypothermia and coagulopathy and stabilise the patient as early as possible in a critical care setting. This narrative review examines the background to these changes in resuscitation practice, discusses the central importance of traumatic coagulopathy in driving these changes particularly in relation to the use of high FFP:RBC ratio and explores methods of predicting, diagnosing and treating the coagulopathy with massive transfusion protocols as well as newer coagulation factor concentrates. We discuss other areas of trauma haemorrhage management including the role of hypertonic saline and interventional radiology. Throughout this review we specifically examine whether the available evidence supports these newer practices.

Coagulopathy is prevalent and associated with adverse outcomes in transfused pediatric trauma patients

OBJECTIVE

To evaluate coagulopathy in pediatric trauma patients on presentation to the emergency department, and to quantify the relationship with mortality.

STUDY DESIGN

Pediatric trauma patients requiring a blood transfusion (red blood cells, fresh frozen plasma, platelets, or cryoprecipitate) within 24 hours of arrival were included. Coagulation values on emergency department arrival were analyzed, as were clinical details and outcome.

RESULTS

A total of 102 children (mean age, 6 years; mean injury severity score 22, mean Glascow Coma Scale 7, 80% blunt trauma victims) were studied over a 4 year period. An abnormal prothrombin time was found in 72%, partial thromboplastin time in 38%, fibrinogen in 52%, hemoglobin in 58%, and platelet count in 23%. An abnormal prothrombin time, partial thromboplastin time, and platelet count were strongly associated with mortality (P=.005, .001, and <.0001, respectively) and remained significantly associated in multivariate analysis after adjusting for injury severity score.

CONCLUSIONS

Coagulopathy is prevalent in pediatric trauma patients ill enough to require a transfusion and is strongly associated with mortality. Studies are needed to determine whether early coagulation factor replacement and the institution of massive transfusion protocols may improve outcomes in these patients.

Early coagulopathy in trauma patients: an on-scene and hospital admission study

PURPOSE

Amongst trauma patients, early coagulopathy is common on hospital admission. No studies have evaluated the initial coagulation status in the pre-hospital setting. We hypothesise that the coagulopathic process begins at the time of trauma. We studied the on-scene and on hospital arrival coagulation profile of trauma patients.

METHODS

Prospective, observational study investigating the on-scene coagulation profile and its time course. We studied 45 patients at the scene of the accident, before fluid administration, and on hospital admission and classified their coagulopathy using the International Society on Thrombosis and Haemostasis score during a 2-month period. Prothrombin time, activated partial thromboplastin time, fibrinogen concentration, factors II, V and VII activity, fibrin degradation products, antithrombin and protein C activities, platelet counts and base deficit were measured.

RESULTS

The median injury severity score was 25 (13-35). On-scene, coagulation status was abnormal in 56% of patients. Protein C activities were decreased in the trauma-associated coagulopathy group (p=.02). Drops in protein C activities were associated with changes in activated partial thromboplastin time, prothrombin time, fibrinogen concentration, factor V and antithrombin activities. Only factor V levels decreased significantly with the severity of the trauma. On hospital admission, coagulation status was abnormal in 60% of patients. The on-scene coagulopathy was spontaneously normalised only in 2 patients whereas others had the same or a poorer coagulopathy status. All parameters of coagulation were significantly abnormal comparing to the on-scene phase. Decreases in protein C activities were related to the coagulation status (p<.0001) and changes in other coagulation parameters. Patients with base deficit ≤-6 mmol/L had changes in antithrombin, factor V and protein C activities but no significant coagulopathy.

CONCLUSION

Coagulopathy occurs very early after injury, before fluid administration, at the site of accident. Coagulation and fibrinolytic systems are activated early. The incidence of coagulopathy is high and its severity is related to the injury and not to hypoperfusion.

Implementation of a pediatric trauma massive transfusion protocol: one institution's experience

BACKGROUND

Massive transfusion protocols (MTPs) with fixed ratios of blood products may improve outcomes in coagulopathic adult trauma patients. However, there is a paucity of data on transfusion support protocols for pediatric trauma patients, whose mechanisms of injury may differ from those seen in adults. We hypothesized that an MTP would improve outcomes in children, through a balanced blood product resuscitation.

STUDY DESIGN AND METHODS

A pediatric trauma MTP, with a fixed ratio of red blood cells (RBCs):fresh-frozen plasma (FFP):platelets:cryoprecipitate in quantities based on the patient's weight, was initiated at a pediatric hospital. Data on clinical status, resuscitation volumes, and hospital course were collected and compared to data from pre-MTP trauma patients requiring transfusion.

RESULTS

Fifty-three patients were enrolled over a 15-month period and compared to 49 pre-MTP patients. Seventy-two percent of MTP patients had at least one coagulation value outside of the normal range upon emergency department (ED) arrival, and the median time to FFP transfusion decreased fourfold after MTP implementation (p<0.0001). A total of 49% of MTP patients received greater than 70 mL/kg blood products, and the 24-hour median FFP:RBC transfusion ratio was twofold higher in these patients than the pre-MTP cohort (median, 1:1.8 vs. 1:3.6; p=0.002). No improvement in mortality was observed after MTP implementation, taking into consideration injury severity, prothrombin time, and partial thromboplastin time.

CONCLUSIONS

A pediatric trauma MTP is feasible and allows for rapid provision of balanced blood products for transfusion to coagulopathic children. Larger studies are warranted to determine whether such protocols will improve outcomes for pediatric trauma patients.

The effect of cause of cadaveric kidney donors death on fibrinolysis and blood coagulation processes

BACKGROUND

Organ donors can be generally divided into two groups according to the cause of their death. The first group is composed of those who died because of physical injuries, especially road traffic injury, and the second group, those who died from central nervous system (CNS) stroke or bleeding. The aim of our work was to examine hemostatic processes among kidney donors.

MATERIALS AND METHODS

The 38 deceased kidney donors (KD) included 11 women and 27 men of overall average age of 37±12 years. The donor group of according to the cause of death, included 14 injured donors (ID) (41%) and 24 noninjured donors (ND) donors (59%). The control group consisted of 25 healthy volunteers matched for sex and age. We determined the following concentrations: antithrombin (AT), thrombin/antithrombin complexes (TAT), and prothrombin F1+2 fragments. The fibrinolytic parameter concentrations were: plasminogen (PL), plasmin/antiplasmin complexes (PAP), and D-dimers.

RESULTS

Deceased kidney donors showed an increased plasma concentrations of TAT complexes (P<.000001) and prothrombin fragments F1+2 (P<.0000001); however, the protein C concentration was decreased (P<.000001). The antithrombin activity was similar to the control group. The concentrations of PAP complexes and d-dimers were higher (both P<.000001), but the level of PL lower among KD compared with controls (P<.0000001). The higher of TAT, PAP complexes, d-dimers, and F1+2 concentrations as well and as lower plasminogen and PC concentrations were evidence for increased activation of blood coagulation and fibrinolysis in cadaveric KD. However, analysis compairing ID versus ND donors revealed increased concentrations of PAP complexes (P<.05) and decreased amounts of TAT complexes (P<.01) among ID subgroup. The positive predictive value (PPV) and negative (NPV) for PAP complexes were 75% and 68% and for TAT, 71% and 57%, respectively. On the basis of these observations, we concluded that an intensive activation of fibrinolytic process occurs among the ID. In contrast, ND show intensive activation of blood coagulation.

Impaired control of the tissue factor pathway of blood coagulation in systemic lupus erythematosus

Thrombosis is a frequent manifestation in patients with systemic lupus erythematosus (SLE), although precise mechanisms remain unclear. This study investigated whether the major physiological trigger of blood coagulation, the tissue factor (TF) pathway, was altered in SLE patients. Furthermore, we investigated potential associations between the TF pathway, the presence of antiphospholipid (APL) antibodies and other abnormalities present in SLE. A total of 101 participants (40 SLE patients and 61 age- and sex-matched controls) were recruited from Tasmania, Australia. Markers of the TF pathway, hypercoagulability, inflammation and endothelial cell damage were measured in plasma. Serum levels of APL antibodies (anti-cardiolipin antibodies [ACL], lupus anticoagulants [LAC], anti-beta2-glycoprotein-1 [anti-β2GP1] and anti-prothrombin antibodies) were also determined. Despite similar TF and TF pathway inhibitor (TFPI) total antigen levels, SLE patients had significantly increased levels of TFPI free antigen (patients vs controls; mean ± SD) (11.6 ± 0.9 ng/mL vs 6.4 ± 0.4 ng/mL; p < 0.001) but significantly reduced TFPI activity (0.66 ± 0.07 U/mL vs 1.22 ± 0.03 U/mL; p < 0.001), compared with healthy controls. Anti-TFPI activity, designated as the ability of isolated IgG fractions to inhibit TFPI activity in normal plasma, was detected in 19/40 (47.5%) of SLE patients and 3/40 (7.5%) of healthy controls. The significant reduction in TFPI activity in SLE patients reflects impaired functional control of the TF pathway. Moreover, SLE patients with a history of thrombosis demonstrated higher levels of TFPI activity compared with patients without a previous thrombotic event (0.97 ± 0.07 U/mL vs 0.53 ± 0.14 U/mL; p = 0.0026). Changes to the TF pathway were not associated with manifestations of SLE such as inflammation or endothelial cell damage. The results from this study suggest hypercoagulability in SLE may (in part) be due to reduced TFPI activity, a mechanism that appears to be independent of other abnormalities in SLE.

Pathophysiology of early trauma-induced coagulopathy: emerging evidence for hemodilution and coagulation factor depletion

BACKGROUND

Trauma patients present with a coagulopathy, termed early trauma-induced coagulopathy (ETIC), that is associated with increased mortality. This study investigated hemostatic changes responsible for ETIC.

METHODS

Case-control study of trauma patients with and without ETIC, defined as prolonged prothrombin time (PT), was performed from prospective cohort of consecutive trauma patients who presented to Level I trauma center. Univariate and multivariate analyses were performed.

RESULTS

The case-control study group (n = 91) was 80% male, with mean age of 37 years, 17% penetrating trauma and 7% mortality rate. Patients with ETIC demonstrated decreased common and extrinsic pathway factor activities (factors V and VII) and decreased inhibition of the coagulation cascade (antithrombin and protein C activities) when compared with the matched control patients without ETIC. Both cohorts had evidence of increased thrombin and fibrin generation (prothrombin fragment 1.2 levels, thrombin-antithrombin complexes, and soluble fibrin monomer), increased fibrinolysis (d-dimer levels), and increased inhibition of fibrinolysis (plasminogen activator inhibitor-1 activity) above normal reference values. Patients with versus without ETIC had increased mortality and received increased amount of blood products.

CONCLUSION

ETIC following injury is associated with decreased factor activities without significant differences in thrombin and fibrin generation, suggesting that despite these perturbations in the coagulation cascade, patients displayed a balanced hemostatic response to injury. The lower factor activities are likely secondary to increased hemodilution and coagulation factor depletion. Thus, decreasing the amount of crystalloid infused in the early phases following trauma and administration of coagulation factors may prevent the development.

The role of tissue factor and tissue factor pathway inhibitor in health and disease states

OBJECTIVE

To review the veterinary and human literature on the role of tissue factor (TF) and tissue factor pathway inhibitor (TFPI) in health and disease states.

DATA SOURCES

Original research articles and scientific reviews from both human and veterinary literature were searched for relevance to TF and TFPI.

HUMAN DATA SYNTHESIS

Interest in both TF and TFPI has grown widely over the last several years. The impact TF plays in coagulation, inflammation, angiogenesis, tumor metastasis, and cellular signaling has become apparent. Treatment with TFPI for severe sepsis has been examined and is still currently under investigation. Inhibition of the TF pathway is being studied as an aid in the treatment of neoplasia. The important physiologic and pathophysiologic role these molecules play has only begun to be understood.

VETERINARY DATA SYNTHESIS

There is a paucity of publications that discuss the importance of TF and TFPI in veterinary medicine. An enhanced understanding of the TF pathway in human medicine, in experimental animal models treating sepsis with TFPI, and in animal models demonstrating the proangiogenic properties of TF provides relevance to veterinary medicine.

CONCLUSION

It is apparent that TF and TFPI are important in health and disease. An enhanced understanding of the physiologic and pathophysiologic roles of these factors provides better insight into coagulation, inflammation, angiogenesis, disseminated intravascular coagulation, and tumor metastasis. This greater understanding may provide for the development of therapeutics for sepsis, disseminated intravascular coagulation, and neoplasia.

Tissue factor pathway inhibitor and P-selectin as markers of sepsis-induced non-overt disseminated intravascular coagulopathy

Inflammation and coagulation occur concomitantly in sepsis. Thrombin activates platelet that leads to P-selectin translocation, which upregulate tissue factor (TF) generation. Tissue factor pathway inhibitor (TFPI) is an anticoagulant that modulates coagulation induced by TF. The term non-overt disseminated intravascular coagulation (DIC) refers to a state of affairs prevalent before the occurrence of overt DIC. It was suggested that an initiation of treatment in non-overt DIC has better outcome than overt DIC. This study investigated the role of TFPI level, P-selectin, and thrombin activation markers in non-overt and overt DIC induced by sepsis and its relationship to outcome and organ dysfunction as measured by the Sequential Organ Failure Assessment (SOFA) score. It included 176 patients with sepsis. They were admitted to the pediatric intensive care unit (ICU).They included 144 cases of non-overt DIC and 32 cases of overt DIC. There was a significant difference in hemostatic markers, platelet count, partial thromboplastin time (PTT), P-selectin, thrombin activation markers, TFPI, and DIC score between overt and non-overt DIC in both groups. It was noticed that P-selectin was positively correlated with DIC score, fibrinogen consumption, fibrinolysis (D-dimer), thrombin activation markers, and TFPI. Tissue factor pathway inhibitor was significantly correlated with fibrinolysis, DIC score, and prothrombin fragment 1+2. Sequential Organ Failure Assessment score was correlated with DIC score and other hemostatic markers in patients with overt DIC. To improve the outcome of patients with DIC, there is a need to establish more diagnostic criteria for non-overt-DIC. Plasma levels of TFPI and P-selectin may be helpful in this respect.

Transfusion management of trauma patients

The management of massively transfused trauma patients has improved with a better understanding of trauma-induced coagulopathy, the limitations of crystalloid infusion, and the implementation of massive transfusion protocols (MTPs), which encompass transfusion management and other patient care needs to mitigate the "lethal triad" of acidosis, hypothermia, and coagulopathy. MTPs are currently changing in the United States and worldwide because of recent data showing that earlier and more aggressive transfusion intervention and resuscitation with blood components that approximate whole blood significantly decrease mortality. In this context, MTPs are a key element of "damage control resuscitation," which is defined as the systematic approach to major trauma that addresses the lethal triad mentioned above. MTPs using adequate volumes of plasma, and thus coagulation factors, improve patient outcome. The ideal amounts of plasma, platelet, cryoprecipitate and other coagulation factors given in MTPs in relationship to the red blood cell transfusion volume are not known precisely, but until prospective, randomized, clinical trials are performed and more clinical data are obtained, current data support a target ratio of plasma:red blood cell:platelet transfusions of 1:1:1. Future prospective clinical trials will allow continued improvement in MTPs and thus in the overall management of patients with trauma.

The role of tissue factor in patients undergoing open repair of ruptured and nonruptured abdominal aortic aneurysms

BACKGROUND

Ruptured abdominal aortic aneurysm (AAA) is associated with the development of a procoagulant and hypofibrinolytic state. Tissue factor (TF) and its naturally occurring inhibitor, tissue factor pathway inhibitor (TFPI), play a central role in the initiation and progression of such a hypercoagulable state, but their role in patients undergoing open AAA repair has not previously been examined.

METHODS

A prospective study was conducted of 17 patients undergoing elective AAA repair and 10 patients undergoing emergency AAA repair. Blood was taken before induction, and 5 minutes, 24 hours, and 48 hours after aortic cross-clamp release and assayed for plasma TF, TFPI, tissue plasminogen activator (t-PA), plasminogen activator inhibitor (PAI), and thrombin-activatable fibrinolysis inhibitor (TAFI) activities.

RESULTS

TF activity was significantly higher at all time points in patients with ruptured AAA compared with nonruptured AAA. The median (interquartile range, IRQ) TF activity (AU/mL) was 9.9 vs 3.2 (IRQ, 5.9 to 12.6 vs 2.0 to 7.6; P = .005) at preinduction; 10.7 vs 1.5 (IRQ, 9.2 to 18.3 vs 0.1 to 6.6; P = .003) at 5 minutes after clamp release; 9.5 vs 3.3 (IRQ, 7.0 to 13.5 vs 1.0 to 7.9; P = .013) at 24 hours, and 9.6 vs 3.9 (IRQ, 7.6 to 12.6 vs 2.4 to 8.7; P = .006) at 48 hours. TFPI levels were not significantly different between ruptured AAA and nonruptured AAA before or during operation but became significantly elevated at 24 and 48 hours in patients who had undergone repair of ruptured AAA. Ruptured AAA repair was associated with a hypofibrinolytic state compared with nonruptured AAA.

CONCLUSIONS

The present study has demonstrated for the first time, to our knowledge, that ruptured AAA is associated with significantly higher perioperative levels of circulating TF compared with nonruptured AAA. Furthermore, in the immediate perioperative period, the high levels of TF are not associated with a corresponding rise in TFPI levels, indicating an unopposed prothrombotic state. Direct inhibition of TF by administration of anti-TF antibodies or recombinant TFPI remains to be evaluated in subjects presenting with hemorrhage due to ruptured AAA, but if given early enough, it may attenuate the early deleterious effects of unopposed TF expression and ultimately contribute to improved outcomes.

Acute traumatic coagulopathy: initiated by hypoperfusion: modulated through the protein C pathway?

OBJECTIVES

Coagulopathy following major trauma is conventionally attributed to activation and consumption of coagulation factors. Recent studies have identified an acute coagulopathy present on admission that is independent of injury severity. We hypothesized that early coagulopathy is due to tissue hypoperfusion, and investigated derangements in coagulation associated with this.

METHODS

This was a prospective cohort study of major trauma patients admitted to a single trauma center. Blood was drawn within 10 minutes of arrival for analysis of partial thromboplastin and prothrombin times, prothrombin fragments 1+2, fibrinogen, thrombomodulin, protein C, plasminogen activator inhibitor-1, and D-dimers. Base deficit (BD) was used as a measure of tissue hypoperfusion.

RESULTS

A total of 208 patients were enrolled. Patients without tissue hypoperfusion were not coagulopathic, irrespective of the amount of thrombin generated. Prolongation of the partial thromboplastin and prothrombin times was only observed with an increased BD. An increasing BD was associated with high soluble thrombomodulin and low protein C levels. Low protein C levels were associated with prolongation of the partial thromboplastin and prothrombin times and hyperfibrinolysis with low levels of plasminogen activator inhibitor-1 and high D-dimer levels. High thrombomodulin and low protein C levels were significantly associated with increased mortality, blood transfusion requirements, acute renal injury, and reduced ventilator-free days.

CONCLUSIONS

Early traumatic coagulopathy occurs only in the presence of tissue hypoperfusion and appears to occur without significant consumption of coagulation factors. Alterations in the thrombomodulin-protein C pathway are consistent with activated protein C activation and systemic anticoagulation. Admission plasma thrombomodulin and protein C levels are predictive of clinical outcomes following major trauma.

Diagnosis of early coagulation abnormalities in trauma patients by rotation thrombelastography

BACKGROUND

Reagent-supported thromboelastometry with the rotation thrombelastography (e.g. ROTEM) is a whole blood assay that evaluates the visco-elastic properties during blood clot formation and clot lysis. A hemostatic monitor capable of rapid and accurate detection of clinical coagulopathy within the resuscitation room could improve management of bleeding after trauma.

OBJECTIVES

The goals of this study were to establish whether ROTEM correlated with standard coagulation parameters to rapidly detect bleeding disorders and whether it can help to guide transfusion.

METHODS

Ninety trauma patients were included in the study. At admission, standard coagulation assays were performed and ROTEM parameters such as clot formation time (CFT) and clot amplitude (CA) were obtained at 15 min (CA(15)) with two activated tests (INTEM, EXTEM) and at 10 min (CA(10)) with a test analyzing specifically the fibrin component of coagulation (FIBTEM).

RESULTS

Trauma induced significant modifications of coagulation as assessed by standard assays and ROTEM. A significant correlation was found between prothrombin time (PT) and CA(15)-EXTEM (r = 0.66, P < 0.0001), between activated partial thromboplastin time and CFT-INTEM (r = 0.91, P < 0.0001), between fibrinogen level and CA(10)-FIBTEM (r = 0.85, P < 0.0001), and between platelet count and CA(15)-INTEM (r = 0.57, P < 0.0001). A cutoff value of CA(15)-EXTEM at 32 mm and CA(10)-FIBTEM at 5 mm presented a good sensitivity (87% and 91%) and specificity (100% and 85%) to detect a PT > 1.5 of control value and a fibrinogen less than 1 g L(-1), respectively.

CONCLUSIONS

ROTEM is a point-of-care device that rapidly detects systemic changes of in vivo coagulation in trauma patients, and it might be a helpful device in guiding transfusion.

Immunologic quantitation of tissue factors

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

Role of coagulation FVIII in septic peritonitis assessed in hemophilic mice

BACKGROUND

Inhibition of blood coagulation appears to be an important therapeutic strategy to improve the outcome in sepsis. However, the beneficial effect of anticoagulant treatment in sepsis is solely based on experimental data using inhibitors of the extrinsic coagulant pathway. The role of the intrinsic pathway of coagulation in the pathogenesis of sepsis has not been explored yet.

OBJECTIVE

In the current study, we contribute to determine the role of factor (F)VIII, the key player of the intrinsic coagulant pathway, on host defense against peritonitis.

METHOD

Hemizygous FVIII-deficient mice and their wild-type littermates were challenged with 1 x 10(4) bacteria in a septic peritonitis model.

RESULTS

The intraperitoneal injection of Escherichia coli led to growth and dissemination of bacteria and provoked an inflammatory response as evident from elevated cytokine levels, increased cell influx into tissues, liver necrosis, and endothelialitis resulting in mortality. The FVIII-deficient genotype slightly reduced bacterial outgrowth but had no effect on markers of inflammation and/or survival. In addition, FVIII-deficient mice showed profound activation of coagulation, thereby improving the hemophilic phenotype of FVIII-deficient mice.

CONCLUSION

FVIII deficiency slightly modifies host defense in septic peritonitis in mice, but does not influence the final outcome of peritonitis. Therefore, we question the importance of the intrinsic coagulant pathway during sepsis.

Disseminated Intravascular Coagulation in Sepsis

Disseminated intravascular coagulation is a frequent complication of sepsis. Coagulation activation, inhibition of fibrinolysis, and consumption of coagulation inhibitors lead to a procoagulant state resulting in inadequate fibrin removal and fibrin deposition in the microvasculature. As a consequence, microvascular thrombosis contributes to promotion of organ dysfunction. Recently, three randomized, double-blind, placebo-controlled trials investigated the efficacy of antithrombin, activated protein C (APC), and tissue factor pathway inhibitor, respectively, in sepsis patients. A significant reduction in mortality was demonstrated in the APC trial. In this article, we first discuss the physiology of coagulation and fibrinolysis activation. Then, the pathophysiology of coagulation activation, consumption of coagulation inhibitors, and the inhibition of fibrinolysis leading to a procoagulant state are described in more detail. Moreover, therapeutic concepts as well as the three randomized, double-blind, placebo-controlled studies are discussed.

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Recombinant Factor VIIa as Adjunctive Therapy for Bleeding Control in Severely Injured Trauma Patients: Two Parallel Randomized, Placebo-Controlled, Double-Blind Clinical Trials

BACKGROUND

Uncontrolled bleeding is a leading cause of death in trauma. Two randomized, placebo-controlled, double-blind trials (one in blunt trauma and one in penetrating trauma) were conducted simultaneously to evaluate the efficacy and safety of recombinant factor VIIa (rFVIIa) as adjunctive therapy for control of bleeding in patients with severe blunt or penetrating trauma.

METHODS

Severely bleeding trauma patients were randomized to rFVIIa (200, 100, and 100 microg/kg) or placebo in addition to standard treatment. The first dose followed transfusion of the eighth red blood cell (RBC) unit, with additional doses 1 and 3 hours later. The primary endpoint for bleeding control in patients alive at 48 hours was units of RBCs transfused within 48 hours of the first dose.

RESULTS

Among 301 patients randomized, 143 blunt trauma patients and 134 penetrating trauma patients were eligible for analysis. In blunt trauma, RBC transfusion was significantly reduced with rFVIIa relative to placebo (estimated reduction of 2.6 RBC units, p = 0.02), and the need for massive transfusion (>20 units of RBCs) was reduced (14% vs. 33% of patients; p = 0.03). In penetrating trauma, similar analyses showed trends toward rFVIIa reducing RBC transfusion (estimated reduction of 1.0 RBC units, p = 0.10) and massive transfusion (7% vs. 19%; p = 0.08). Trends toward a reduction in mortality and critical complications were observed. Adverse events including thromboembolic events were evenly distributed between treatment groups.

CONCLUSION

Recombinant FVIIa resulted in a significant reduction in RBC transfusion in severe blunt trauma. Similar trends were observed in penetrating trauma. The safety of rFVIIa was established in these trauma populations within the investigated dose range.

Coagulation dysfunction in sepsis and multiple organ system failure

In patients diagnosed with sepsis, severe sepsis or septic shock, cytokine-mediated endothelial injury, and TF activation initiate a cascade of events that culminate in the development of coagulation dysfunction characterized as procoagulant and antifibrinolytic. This abnormal state predisposes the patient to develop microvascular thrombosis, tissue ischemia, and organ hypoperfusion. Multiple organ dysfunction syndrome may be a product of this pertubation in coagulation regulation. Treatments aimed at correcting this coagulation dysfunction have met with mixed success. Current data suggest that AT III replacement therapy has limited efficacy in adults with severe sepsis. In contrast, adult patients diagnosed with severe sepsis and organ failure and treated with aPC (drotrecogin alfa activate) have a significantly reduced risk of death when compared with placebo-treated patients. A phase III trial examining the efficacy of protein C replacement therapy in pediatric patients with severe sepsis and organ failure is underway.

Imbalances between the levels of tissue factor and tissue factor pathway inhibitor in ARDS patients

INTRODUCTION

To evaluate the pathogenetic role of tissue factor (TF), tissue factor pathway inhibitor (TFPI), and neutrophil elastase in acute respiratory distress syndrome (ARDS), as well as to test the hypothesis that TFPI levels modified by neutrophil activation are not sufficient to prevent TF-dependent intravascular coagulation, leading to sustained systemic inflammatory response syndrome (SIRS) and multiple organ dysfunction syndrome (MODS), which determine the prognosis of these patients.

MATERIALS AND METHODS

The study subjects consisted of 55 patients with trauma and sepsis who were divided into three groups according to the Lung Injury Score. Ten normal healthy volunteers served as control. Plasma levels of TF, TFPI, and neutrophil elastase were measured on the day of injury or the day of diagnosis of sepsis (day 0) and days 1 through 4. The number of SIRS criteria that the patient met and the disseminated intravascular coagulation (DIC) score is determined daily.

RESULTS

Patients (15) developed ARDS, 23 were at risk for but did not develop the syndrome, and 17 patients were without risk for ARDS. TF and neutrophil elastase levels in ARDS patients were persistently higher than those in other two groups and control subjects. However, the TFPI levels showed no difference among the three groups, which retained normal or slightly elevated levels compared to the control subjects. DIC scores did not improve and SIRS continued during the study period in patients with ARDS. The ARDS patients showed higher numbers of dysfunctioning organs and associated with poorer outcome than the other two groups.

CONCLUSION

Systemic activation of the TF-dependent pathway not adequately balanced by TFPI is one of the aggravating factors of ARDS. High levels of neutrophil elastase released from activated neutrophils may explain the imbalance of TF and TFPI. Persistent DIC and sustained SIRS contribute to MODS, determining the prognosis of ARDS patients.

Effect of stress hormones on the expression of fibrinogen-binding receptors in platelets

Acute coagulopathy is a common clinical complication after trauma, and contributes to posttraumatic multiple organ failure. The phenomenon may be due to the effect of stress hormones on platelet adhesion molecule expression after trauma. Catecholamine levels correlate with injury severity scores and changes of L-selectin expression on leucocytes, whilst adrenaline (ADR) (epinephrine) alone also activates platelets. This study thus investigates the effects of ADR and noradrenaline (NOR) (norepinephrine) on platelets, at doses similar to those found in the plasma of normal and trauma subjects. Blood was taken from 19 healthy subjects and placed in tubes containing sodium citrate. Anti-platelet-bound fibrinogen monoclonal antibody was used to identify the activated platelets while anti-CD41 was used to identify platelets with and without activation. Five increasing concentrations of ADR and NOR (1, 3, 5, 10, 30 nmol/l) as well as one negative control (0.9% normal saline) and one positive control (10 micromol/l adenosine diphosphate/ADP) were prepared for the stimulation. A whole blood protocol was used in order to minimize any activation artefacts, which might be created by centrifugation. The percentage of platelets expressing fibrinogen receptors increased significantly with ADR and NOR even at the lowest dose (1 nmol/l) and continued to increase in a dose-dependent manner. Although the effect of ADR was greater than NOR in stimulating platelets to express fibrinogen receptors, the average number of fibrinogen receptors on each platelet was constant. ADR and NOR activated platelets to express fibrinogen receptors at doses that are similar to those found in the plasma of trauma patients.

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.

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.

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.