Recombinant Human Tissue Factor Pathway Research Articles

Nebulized Recombinant Human Tissue Factor Pathway Inhibitor Attenuates Coagulation and Exerts Modest Anti-inflammatory Effects in Rat Models of Lung Injury.

Critically ill patients are at a constant risk of direct (e.g., by pneumonia) or indirect lung injury (e.g., by sepsis). Excessive alveolar fibrin deposition is a prominent feature of lung injury, undermining pulmonary integrity and function. We examined the effect of local administration of recombinant human tissue factor pathway inhibitor (rh-TFPI), a natural anticoagulant, in two well-established models of lung injury in rats. Rats received intratracheal instillation of Pseudomonas aeruginosa, causing direct lung injury, or they received an intravenous injection of Escherichia coli lipopolysaccharide (LPS), causing indirect lung injury. Rats were randomized to local treatment with rh-TFPI or placebo through repeated nebulization. Challenge with P. aeruginosa or LPS was associated with increased coagulation and decreased fibrinolysis in bronchoalveolar lavage fluid (BALF) and plasma. Rh-TFPI levels in BALF increased after nebulization, whereas plasma rh-TFPI levels remained low and systemic TFPI activity was not affected. Nebulization of rh-TFPI attenuated pulmonary and systemic coagulation in both models, without affecting fibrinolysis. Nebulization of rh-TFPI modestly reduced the inflammatory response and bacterial growth of P. aeruginosa in the alveolar compartment. Local treatment with rh-TFPI does not alter systemic TFPI activity; however, it attenuates both pulmonary and systemic coagulopathy. Furthermore, nebulized rh-TFPI modestly reduces the pulmonary inflammatory response and allows increased bacterial clearance in rats with direct lung injury caused by P. aeruginosa.

Feasibility and Safety of Local Treatment with Recombinant Human Tissue Factor Pathway Inhibitor in a Rat Model of Streptococcus pneumoniae Pneumonia.

Pulmonary coagulopathy is intrinsic to pulmonary injury including pneumonia. Anticoagulant strategies could benefit patients with pneumonia, but systemic administration of anticoagulant agents may lead to suboptimal local levels and may cause systemic hemorrhage. We hypothesized nebulization to provide a safer and more effective route for local administration of anticoagulants. Therefore, we aimed to examine feasibility and safety of nebulization of recombinant human tissue factor pathway inhibitor (rh-TFPI) in a well-established rat model of Streptococcus (S.) pneumoniae pneumonia. Thirty minutes before and every 6 hours after intratracheal instillation of S. pneumonia causing pneumonia, rats were subjected to local treatment with rh-TFPI or placebo, and sacrificed after 42 hours. Pneumonia was associated with local as well as systemic activation of coagulation. Nebulization of rh-TFPI resulted in high levels of rh-TFPI in bronchoalveolar lavage fluid, which was accompanied by an attenuation of pulmonary coagulation. Systemic rh-TFPI levels remained undetectable, and systemic TFPI activity and systemic coagulation were not affected. Histopathology revealed no bleeding in the lungs. We conclude that nebulization of rh-TFPI seems feasible and safe; local anticoagulant treatment with rh-TFPI attenuates pulmonary coagulation, while not affecting systemic coagulation in a rat model of S. pneumoniae pneumonia.

The effect of recombinant human tissue factor pathway inhibitor-1 on Myocardial infarction in rabbits

Objective To observe the function of recombinant human tissue factor pathway inhibitor1(rTFPI-1)in acute myocardial infarction in rabbit. Method Forty New Zealand White rabbits were subjected to coronary artery occlusion for 120 min and followed by reperfusion for 60 min,then they were ranlow dose rTFPI-1 group(n=10/group).The extent of ischemic area and the extent of myocardial infarction area were measured by Evan's blue stain and TTC stain,respectively.The degrees of infarction severity and ischemic severity were expressed as the ratios of the total left ventrieular wall area.The degrees of infarction severity and ischemic severity in different groups were compared by using one-way ANOVA and then followed by LSD procedure.Results The degree of infarction severity in the larger dose rTFPI-1 group was significantly lessened than that in low dose RTFPI-1 group and control group(P 0.05).Conclusions Human rTFPI-1 might decrease myocardial infarction severity and save the survival myocardial tissue. Key words: Acute myocardial infarction; Rabbits; Extrinsic pathway inhibitor I; Thromboplastin

Recombinant Tissue Factor Pathway Inhibitor in Severe Community-acquired Pneumonia

Severe community-acquired pneumonia (sCAP) is a leading cause of death worldwide. Adjunctive therapies for sCAP are needed to further improve outcome. A systemic inhibitor of coagulation, tifacogin (recombinant human tissue factor pathway inhibitor) seemed to provide mortality benefit in the sCAP subgroup of a previous sepsis trial. Evaluate the impact of adjunctive tifacogin on mortality in patients with sCAP. A multicenter, randomized, placebo-controlled, double-blind, three-arm study was conducted from July 2005 to June 2008 at 188 centers in North and South America, Europe, South Africa, Asia, Australia, and New Zealand. Adults with sCAP were randomized to receive a continuous intravenous infusion of tifacogin 0.025 mg/kg/h, tifacogin 0.075 mg/kg/h, or matching placebo over 96 hours. Severity-adjusted 28-day all-cause mortality. Of 2,138 randomized patients, 946, 238, and 918 received tifacogin 0.025 mg/kg/h, tifacogin 0.075 mg/kg/h, and placebo, respectively. Tifacogin 0.075 mg/kg/h was discontinued after the first interim analysis according to prespecified futility criterion. The 28-day all-cause mortality rates were similar between the 0.025 mg/kg/h (18%) and placebo groups (17.9%) (P = 0.56). Greater reduction in prothrombin fragment 1+2 and thrombin antithrombin complexes levels relative to baseline throughout the first 96 hours was found with tifacogin 0.025 mg/kg/h than with placebo. The incidence of adverse events and serious adverse events were comparable between the tifacogin 0.025 mg/kg/h and placebo groups. Tifacogin showed no mortality benefit in patients with sCAP despite evidence of biologic activity.

Recombinant human tissue factor pathway inhibitor exerts anticoagulant, anti‐inflammatory and antimicrobial effects in murine pneumococcal pneumonia

Streptococcus (S.) pneumoniae is the most common causative pathogen in community-acquired pneumonia and a major cause of sepsis. Recombinant human tissue factor pathway inhibitor (rh-TFPI) attenuates sepsis-induced coagulation and has been evaluated in clinical trials involving patients with sepsis and community-acquired pneumonia. To examine the effect of rh-TFPI on coagulation, inflammation and bacterial outgrowth in S. pneumoniae pneumonia in mice, with or without concurrent antibiotic treatment. Pneumonia was induced by intranasal inoculation with S. pneumoniae. Mice were treated with placebo, rh-TFPI, ceftriaxone or rh-TFPI combined with ceftriaxone. Early (8 h) and late (24 h) initiated treatments were evaluated. Samples were obtained 24 or 48 h after infection, for early and late initiated treatment, respectively. In vitro, placebo or rh-TFPI was added to a suspension of S. pneumoniae. Rh-TFPI reduced pneumonia-induced coagulation; rh-TFPI with ceftriaxone further attenuated coagulation relative to ceftriaxone alone. Rh-TFPI inhibited accumulation of neutrophils in lung tissue and reduced the levels of several cytokines and chemokines in lungs and plasma in mice not treated with antibiotics; in these animals, rh-TFPI initiated 24 h after infection decreased pulmonary bacterial loads. In vitro, rh-TFPI also inhibited growth of S. pneumoniae. Therapeutic rh-TFPI attenuates coagulation, inflammation and bacterial growth during pneumococcal pneumonia, whereby the latter two effects only become apparent in the absence of concurrent antibiotic treatment.

Tissue factor pathway inhibitor and bacterial infection

See also van den Boogaard FE, Brands X, Schultz MJ, Levi M, Roelofs JJTH, van 't Veer C, van der Poll T. Recombinant human tissue factor pathway inhibitor exerts anticoagulant, anti-inflammatory and antimicrobial effects in murine pneumococcal pneumonia. This issue, pp 122-32.

Recombinant human tissue factor pathway inhibitor prevents thrombosis in a venous tuck model

Microvascular free tissue transfer has become a mainstay of reconstruction after resections for head and neck cancer. With current techniques, free flap failure is typically low; however, failure rates have been reported as high as 10%. Most thrombotic failures occur within the first few days postoperatively and tend to involve the venous anastomoses. We evaluated the efficacy of recombinant human tissue factor pathway inhibitor (rhTFPI), an anticoagulant that directly inhibits the extrinsic coagulation pathway, using a rat model of microvenous thrombosis. Prospective, randomized. Sprague-Dawley rats were randomly assigned to either rhTFPI or saline groups. We performed a venous tuck procedure in the common femoral vein. Prior to closure, the anastamosis was irrigated with either rhTPFI (20 μg/mL) or normal saline. Survival of the anastomosis was measured via clinical assessment at regular postoperative intervals. After a postoperative period of 48 hours, sites were intraoperatively assessed and the vessels harvested. There was a significant increase in vessel patency in rats treated topically with rhTFPI compared to controls receiving saline. There was no increase in bleeding complications in the treated group versus controls. Our data suggests that the use of topical rhTPFI increases venous anastomotic patency rates in vivo. The topical means of administration is attractive, as there seems to be a low percentage of systemic complications as is often seen with anticoagulation therapies. Future studies will investigate the potential efficacy in patients undergoing microvascular free tissue transfer.

Thrombin generation by intimal tissue factor contributes to thrombus formation on macrophage-rich neointima but not normal intima of hyperlipidemic rabbits

Arterial thrombosis occurs in atherosclerotic, but rarely in non-atherosclerotic arteries. The present study investigates how hyperlipidemic condition affects thrombus formation on macrophage-rich neointima or normal intima in rabbits. Rabbits were fed with a 0.5% cholesterol diet, and then the femoral artery on one side of each rabbit was injured with a balloon catheter. Three weeks later, bilateral femoral arteries were similarly injured with a balloon catheter to produce thrombi on neointima and normal intima. We compared the expression and activity of intimal tissue factor (TF) as well as thrombus size and composition between these femoral arteries. 0.5% cholesterol diet combined with a balloon injury induced macrophage-rich neointima in injured arteries. The whole blood coagulation activity or plasma thrombin generation activity did not differ after consuming the 0.5% cholesterol diet for 4 weeks, and an anti-TF antibody did not affect the measured parameters. TF activities were increased in the neointima/media compared with normal intima/media. Balloon injury induced large platelet–fibrin thrombi on macrophage-rich neointima, whereas small platelet thrombi were produced in normal arteries even under hyperlipidemic conditions. Recombinant human tissue factor pathway inhibitor (25 μg/(kg min)) and argatroban (100 μg/(kg min)), a specific thrombin inhibitor, significantly reduced thrombus formation on induced neointima, but not on normal intima. Thrombin generation mediated by TF in intima contributes to thrombus formation on macrophage-rich neointima, but not on normal intima. The TF content in disrupted atherosclerotic plaques might play a more important role than hyperlipidemia in the development of atherothrombosis.

Recombinant human tissue factor pathway inhibitor exerts anticoagulant, anti-inflammatory and antibacterial effects in murine pneumococcal pneumonia

Streptococcus pneumoniae is the most common causative pathogen in community-acquired pneumonia and a major cause of sepsis. Pneumonia elicits a procoagulant state in the lung resulting from activation of coagulation, downregulation of anticoagulant pathways and concurrent inhibition of fibrinolysis. Tissue factor is the main initiator of coagulation. Recombinant human tissue factor pathway inhibitor (rh-TFPI) attenuates sepsis-induced coagulation and has been evaluated in clinical trials involving patients with sepsis and community-acquired pneumonia.

A clinical evaluation committee assessment of recombinant human tissue factor pathway inhibitor (tifacogin) in patients with severe community-acquired pneumonia

IntroductionThe purpose of this analysis was to determine the potential efficacy of recombinant human tissue factor pathway inhibitor (tifacogin) in a subpopulation of patients with community-acquired pneumonia (CAP) from a phase III study of severe sepsis.MethodsA retrospective review of patients with suspected pneumonia was conducted by an independent clinical evaluation committee (CEC) blinded to treatment assignment. The CEC reanalyzed data from patients enrolled in an international multicenter clinical trial of sepsis who had a diagnosis of pneumonia as the probable source of sepsis. The primary efficacy measure was all-cause 28-day mortality.ResultsOf 847 patients identified on case report forms with a clinical diagnosis of pneumonia, 780 (92%) were confirmed by the CEC to have pneumonia. Of confirmed pneumonia cases, 496 (63.6%) met the definition for CAP. In the CEC CAP population, the mortality rates of the tifacogin and placebo groups were 70/251 (27.9%) and 80/245 (32.7%), respectively. The strongest signals were seen in patients with CAP not receiving concomitant heparin, having microbiologically confirmed infection, or having the combination of documented infection and no heparin. The reduction in mortality in this narrowly defined subgroup when treated with tifacogin compared with placebo was statistically significant (17/58 [29.3%] with tifacogin and 28/54 [51.9%] with placebo; unadjusted P value of less than 0.02).ConclusionsTifacogin administration did not significantly reduce mortality in any severe CAP patient. Exploratory analyses showed an improved survival in patients who did not receive concomitant heparin with microbiologically confirmed infections. These data support the rationale of an ongoing phase III study exploring the potential benefit of tifacogin in severe CAP.Trial RegistrationClinicalTrials.gov identifier NCT00084071.

Natural anticoagulants limit lipopolysaccharide-induced pulmonary coagulation but not inflammation

Pulmonary coagulopathy and hyperinflammation may contribute to an adverse outcome in sepsis. The present study determines the effects of natural inhibitors of coagulation on bronchoalveolar haemostasis and inflammation in a rat model of endotoxaemia. Male Sprague-Dawley rats were randomised to treatment with normal saline, recombinant human activated protein C (APC), plasma-derived antithrombin (AT), recombinant human tissue factor pathway inhibitor (TFPI), heparin or recombinant tissue plasminogen activator (tPA). Rats were intravenously injected with lipopolysaccharide (LPS), which induced a systemic inflammatory response and pulmonary inflammation. Blood and bronchoalveolar lavage were obtained at 4 and 16 h after LPS injection, and markers of coagulation and inflammation were measured. LPS injection caused an increase in the levels of thrombin-AT complexes, whereas plasminogen activator activity was attenuated, both systemically and within the bronchoalveolar compartment. Administration of APC, AT and TFPI significantly limited LPS-induced generation of thrombin-AT complexes in the lungs, and tPA stimulated pulmonary fibrinolytic activity. However, none of the agents had significant effects on the production of pulmonary cytokines, chemokines, neutrophil influx and myeloperoxidase activity. Natural inhibitors of coagulation prevent bronchoalveolar activation of coagulation, but do not induce major alterations of the pulmonary inflammatory response in rat endotoxaemia.

Tissue factor pathway inhibitor activity in severe sepsis

To review the preclinical and clinical evidence that provides the therapeutic rationale for recombinant human tissue factor pathway inhibitor (rTFPI) as a novel treatment for human sepsis. A summary of published English-language literature regarding preclinical studies and limited information published about three phase II clinical studies for the evaluation of rTFPI safety in sepsis patients. Tissue factor pathway inhibitor, the physiologic inhibitor of the tissue factor pathway, interrupts activation of coagulation at multiple steps, including tissue factor VIIa activity, Xa activity, prothrombinase complex, and thrombin generation. Recombinant human TFPI exhibits anticoagulant and anti-inflammatory activities in animal models and humans with sepsis. These activities appear to have an important therapeutic role in protecting the microvasculature from injury and preventing multiple organ failure in sepsis. Tissue factor pathway inhibitor is a potent inhibitor of clotting in the microvasculature, which is thought to protect organs from injury. Recombinant TFPI improved survival of septic animals in multiple models. Recent phase II results suggest that rTFPI is well tolerated, and they show a trend toward reduction in 28-day all-cause mortality in rTFPI-treated patients; in addition, rTFPI demonstrated significant reduction in thrombin generation. These results suggest that a powered study is indicated to further evaluate rTFPI utility for the adjunctive management of severe sepsis.

Extremely low doses of tissue factor pathway inhibitor decrease mortality in a rabbit model of septic shock.

We sought to determine the lowest dose of recombinant human tissue factor pathway inhibitor (TFPI) that can provide protection from lethality in a rabbit model of septic shock. Sepsis was induced in New Zealand white rabbits by intraperitoneal implantation of 7.0 ml of a solution containing hemoglobin (4.8 g/dl), porcine mucin (6 g/dl), and 0.8-1.4 x 10(4) viable Escherichia coli (strain O:18 K+). Gentamicin (5 mg/kg) was administered 4 h following surgery, and this dose was repeated every 12 h for 3 days. Beginning 4 h following the induction of sepsis, animals were treated with a bolus (1 ml) plus a continuous infusion (100 ml over 24) of either TFPI (various doses) or its vehicle. Four different doses of TFPI were studied, and each experiment included a contemporaneous control group. The primary outcome parameter was survival time. Results were analyzed using the Wilcoxen log rank test. The average survival time for rabbits treated with the highest dose of TFPI tested (50 microg/kg bolus and 0.5 microg/kg per minute infusion) was 118 h, as compared to 81 h in vehicle-treated controls). The average survival time for septic rabbits treated with a much lower dose of TFPI (100 ng/kg bolus and 1.0 ng/kg per minute infusion) was 119 h as compared to 57 h in surviving vehicle-treated controls. Treatment with an even lower dose of TFPI (10 ng/kg bolus and 0.1 ng/kg per minute infusion) still produced a marginally significant prolongation of average survival time (80 h) relative to contemporaneously studied controls (47 h). When the dose of TFPI was decreased still further (1.0 ng/kg bolus and 0.01 ng/kg per minute infusion), average survival times were not significantly different between TFPI-treated and vehicle-treated rabbits (77 and 51 h, respectively). Delayed infusion with remarkably low doses of recombinant human TFPI prolongs survival in a rabbit model of antibiotic-treated Gram-negative bacterial sepsis. In planning human trials of TFPI as an adjuvant treatment for sepsis it may be reasonable to use much lower doses of the agent than were heretofore contemplated.

Local treatment with recombinant tissue factor pathway inhibitor reduces the development of intimal hyperplasia in experimental vein grafts

Background: Tissue factor (TF)–initiated thrombin generation has been implicated in the development of intimal hyperplasia after arterial injury. An increase in intimal TF expression has been shown to precede the development of intimal hyperplasia in vein grafts. This study examines the effects of local treatment with recombinant human tissue factor pathway inhibitor (rTFPI) in experimental vein grafts. Methods: Thirty-six male New Zealand white rabbits underwent bypass grafting of the carotid artery by use of the reversed ipsilateral jugular vein and were divided into four groups. Twenty animals had ex vivo incubation with rTFPI treatment (50 μg · mL–1; n = 10) or placebo vehicle (control; n = 10). Sixteen animals received both ex vivo incubation and in vivo gel treatment with rTFPI (50 μg · mL–1; n = 8) or without rTFPI (gel-control; n = 8). After operation, vein grafts were harvested at 3 days for immunohistochemical and Western analyses and at 28 days for histomorphologic study. Results: Western analysis demonstrated a 6.2-fold reduction in the expression of TF protein with rTFPI treatment in comparison to without rTFPI treatment. CD-18 leukocyte staining was diminished, whereas Tie-2 endothelial staining was increased in all rTFPI-treated vein grafts, compared with control and gel-control vein grafts. Intimal thickness was reduced by 21% with ex vivo rTFPI treatment compared with placebo (69 ± 4 versus 87 ± 5 μm; P <.05) and by 30% with the addition of rTFPI in vivo compared with gel-control (60 ± 4 versus 86 ± 5 μm; P <.01). Conclusion: Local administration of rTFPI exerts early beneficial effects and limits the development of intimal hyperplasia in vein grafts. Therefore blocking TF-mediated pathway may offer new therapeutic options to reduce vein graft failure. (J Vasc Surg 2001;33:400-7.)

A Phase II Trial of Intraluminal Irrigation with Recombinant Human Tissue Factor Pathway Inhibitor to Prevent Thrombosis in Free Flap Surgery

A Phase II Trial of Intraluminal Irrigation with Recombinant Human Tissue Factor Pathway Inhibitor to Prevent Thrombosis in Free Flap Surgery

The activity of tissue factor pathway inhibitor in experimental models of superantigen-induced shock and polymicrobial intra-abdominal sepsis.

To study recombinant human tissue factor pathway inhibitor (rhTFPI) in a superantigen-induced shock model and in a cecal ligation and puncture (CLP) model of peritonitis in mice. Prospective, randomized, experimental study. An experimental animal research laboratory. Eighty BALB/c mice for the superantigen model, and 56 BALB/c mice for the CLP model. In the superantigen-induced shock model, animals received rhTFPI (350 mg/kg) subcutaneously every 12 hrs (n = 30) or saline control (n = 30) for 60 hrs after staphylococcal enterotoxin B (SEB; 10 microg iv) and a sublethal dose of E. coli 0111:B4 lipopolysaccharide (LPS; 75 microg ip). Control groups received SEB alone (n = 10) and LPS alone (n = 10). In the CLP model, rhTFPI or saline was given every 8 hrs for 48 hrs by using a 21-gauge needle (n = 9) or 23-gauge needle (n = 14) for CLP. A sham surgery control group (n = 10) was also included. There was 0% mortality in the SEB and LPS control groups. The mortality rate was 64% in the saline control group that received both SEB and LPS (19 of 30), whereas the rhTFPI- treated animals had a mortality rate of 20% (6 of 30; p < .01). The rhTFPI-treated group had significantly lower interleukin-6 levels (61.8 +/- 41 pg/mL vs. 285 +/- 63 pg/mL; p < .05) than the control group but no differences in tumor necrosis factor-alpha or interferon-gamma levels. In the CLP experiment, rhTFPI-treated animals did not have any survival advantage over the control group after the large-bore (21-gauge) needle puncture. The rhTFPI group had significantly improved 7-day mortality rate after CLP with the small-bore needle (23-gauge; 21.4% [rhTFPI] vs. 71.4% [control], p < .01). Plasma LPS, interleukin-6, interferon-gamma, and tumor necrosis factor-alpha levels were unchanged by rhTFPI treatment, but significantly reduced LPS (p = .006) and IFNgamma (p = .001) levels were found in the peritoneal fluid. Tissue factor pathway inhibitor significantly improves the mortality rate in models of superantigen-induced shock and polymicrobial intra-abdominal infection, supporting its potential use in clinical trials for septic shock.

Solubility of recombinant human tissue factor pathway inhibitor

Study of recombinant human tissue factor pathway inhibitor (rhTFPI) solubility shows (1) an inverted bell‐shaped pH–solubility profile with a broad solubility minimum between pH 5 and 10 such that the solubility minimum midpoint is 2–3 pH units away from its isoelectric point; (2) a negative temperature–solubility coefficient; (3) a strong dependence of solubility on the valence of electrolytes, with both multivalent cations and anions enhancing this effect; and (4) a significant increase of solubility in the presence of charged polymers. At pH 6–7, rhTFPI solubility–salt profiles display typical salting‐in and salting‐out biphasic effects. At a slightly lower pH (pH 5), a third phase in addition to the salting‐in and salting‐out phases was observed at low ionic strength conditions (5 to 50 mM) where rhTFPI solubility increased as salt concentration decreased. The salting‐out constant for rhTFPI in NaCl is 1.04 M−1 and is independent of the pH of the solution. Resolubilization of rhTFPI precipitates revealed that “insolubility precipitates” (seen during buffer exchanges) resulted from protein solute saturation and could be redissolved by “native” solvent conditions. On the other hand, “instability precipitates” (typically seen after exposure to elevated temperatures or extended storage periods) were caused by insoluble protein aggregate formation and required strongly denaturing conditions to redissolve.

Delayed treatment with recombinant human tissue factor pathway inhibitor improves survival in rabbits with gram-negative peritonitis.

To determine whether treatment with recombinant human tissue factor pathway inhibitor (TFPI), an inhibitor of the extrinsic coagulation pathway, can improve survival in a clinically relevant model of gram-negative sepsis, rabbits were given an intraperitoneal inoculation of a suspension containing hemoglobin (40 microg/mL), porcine mucin (150 microg/mL), and viable Escherichia coli O18:K1 (1.0 +/- 0.5 x 10(5) cfu/kg). Treatment with gentamicin (5 mg/kg every 12 h for five doses) was instituted 4 h after induction of peritonitis. At the same time point, rabbits were randomized to receive a 24-h infusion of vehicle or one of three different doses of TFPI. Treatment groups, 7-day survival rates, and significance versus control were as follows: control, 1 of 20; TFPI(LOW DOSE) (0.1 mg/kg, then 1 microg/kg/min), 3 of 12 (P = .14); TFPI(MID DOSE), (0.5 mg/kg, then 5 microg/kg/min), 7 of 12 (P = .002); TFPI(HIGH DOSE) (10 mg/kg, then 10 microg/kg/min), 4 of 13 (P = .04). Thus, delayed treatment with TFPI improves survival in septic rabbits.

RECOMBINANT HUMAN TISSUE FACTOR PATHWAY INHIBITOR AS A POSSIBLE ANTICOAGULANT TARGETING HEPATIC SINUSOIDAL WALLS

The expression of tissue factor pathway inhibitor (TFPI) was investigated in sinusoidal endothelial cells in the liver and endothelial cells in the lung. Northern blot analysis revealed that TFPI mRNA was expressed in the lung, but minimal in the liver. Also, immunohistochemical examination showed that TFPI was not expressed on the sinusoidal endothelial cells in contrast to marked expression on endothelial cells in the lung, suggesting that anticoagulant activity to inhibit blood coagulation induced by tissue factor is reduced in the hepatic sinusoids compared to the microvessels of other organs. When recombinant human TFPI was intravenously injected in rats, it disappeared rapidly from the circulation, but was detected by electron microscopy on the surface of sinusoidal endothelial cells and microvilli of hepatocytes in the space of Disse. In these rats, the TFPI reappeared in the circulation following an intravenous injection of heparin sodium with reduced immunohistochemical staining of the TFPI on hepatic sinusoidal walls. It is concluded that exogenous TFPI can increase anticoagulant activity on the hepatic sinusoidal walls by binding to heparinoids on the cell surface. It may act effectively even in the hepatic sinusoids with damaged endothelial cells. © 1997 Elsevier Science Ltd

Effects of recombinant human tissue factor pathway inhibitor on thrombus formation and its in vivo distribution in a rat DIC model.

Tissue factor pathway inhibitor (TFPI) plays a key role in modulating tissue factor-dependent blood coagulation. This study was done to determine not only the inhibitory effects of recombinant human TFPI (rTFPI) on thrombus formation in rat models with disseminated intravascular coagulation (DIC), but also to identify the distribution of exogenous TFPI in vivo. Disseminated intravascular coagulation was induced by administering a priming dose of carrageenan 10 mg/kg body weight and was followed 24 hours later by a provocative dose of lipopolysaccharide (LPS) 500 mg/kg body weight. The rTFPI was administered intravenously at a dose of either 1 or 4 mg/kg body weight immediately after LPS treatment. Exogenous rTFPI at a dose of 4 mg/kg significantly inhibited the consumption of fibrinogen, platelets and factor VIIa (P < .05) and also reduced the number of fibrin thrombi formed in the liver, lungs, kidneys, and spleen (P < .05), whereas rTFPI at a dose of 1 mg/kg had no significant inhibitory effect on these DIC parameters. Recombinant human rTFPI activity was rapidly cleared from the plasma; however, a significant amount of the inhibitor was still present in tissues even 3 to 6 hours after intravenous administration. Exogenous TFPI was mainly identified in Kupffer cells, macrophages, and on the microvascular endothelial lining of different organs. In the kidney, rTFPI was identified on both the abluminal surface of the renal tubules and the luminal surface of the proximal convoluted tubules. No rTFPI, however, was detected in the hepatocytes. Tissue factor was mainly expressed by monocytes/macrophages. These findings suggest that TFPI plays an important role in modulating TF-dependent thrombogenesis. The elucidation of the rTFPI distribution and interactions in vivo might thus provide valuable insight into its inhibitory mechanisms as well as its therapeutic implications in DIC.