A randomized clinical trial of high-intensity warfarin vs. conventional antithrombotic therapy for the prevention of recurrent thrombosis in patients with the antiphospholipid syndrome (WAPS).

BACKGROUND: The optimal intensity of oral anticoagulation for the prevention of recurrent thrombosis in patients with antiphospholipid antibody syndrome is uncertain. Retrospective studies show that only high-intensity oral anticoagulation [target international normalized ratio (INR) >3.0] is effective but a recent randomized clinical trial comparing high (INR range 3.0-4.0) vs. moderate (INR 2.0-3.0) intensities of anticoagulation failed to confirm this assumption. METHODS: We conducted a randomized trial in which 109 patients with antiphospholipid syndrome (APS) and previous thrombosis were given either high-intensity warfarin (INR range 3.0-4.5, 54 patients) or standard antithrombotic therapy (warfarin, INR range 2.0-3.0 in 52 patients or aspirin alone, 100 mg day(-1) in three patients) to determine whether intensive anticoagulation is superior to standard treatment in preventing symptomatic thromboembolism without increasing the bleeding risk. RESULTS: The 109 patients enrolled in the trial were followed up for a median time of 3.6 years. Mean INR during follow-up was 3.2 (SD 0.6) in the high-intensity warfarin group and 2.5 (SD 0.3) (P < 0.0001) in the conventional treatment patients given warfarin. Recurrent thrombosis was observed in six of 54 patients (11.1%) assigned to receive high-intensity warfarin and in three of 55 patients (5.5%) assigned to receive conventional treatment [hazard ratio for the high intensity group, 1.97; 95% confidence interval (CI) 0.49-7.89]. Major and minor bleeding occurred in 15 patients (two major) (27.8%) assigned to receive high-intensity warfarin and eight (three major) (14.6%) assigned to receive conventional treatment (hazard ratio 2.18; 95% CI 0.92-5.15). CONCLUSIONS: High-intensity warfarin was not superior to standard treatment in preventing recurrent thrombosis in patients with APS and was associated with an increased rate of minor hemorrhagic complications.

Pharmacokinetic evaluation of recombinant, activated factor VII in patients with inherited factor VII deficiency.

BACKGROUND AND OBJECTIVES: Recombinant factor VIIa (rFVIIa) has been widely used in the treatment of bleedings occurring in hemophiliacs with inhibitors. Very few reports exist on the use of rFVIIa in patients with inherited FVII deficiency. Pharmacokinetic studies on rFVIIa have been performed exclusively in hemophiliacs, patients with cirrhosis or volunteers pretreated with acenocoumarol. The aim of this study was to evaluate the kinetics of rFVIIa in patients naturally deficient of FVII. DESIGN AND METHODS: A single dose kinetic study with rFVIIa was performed in 5 patients affected by severe congenital deficiency of factor VII in order to evaluate the true kinetic parameters of rFVIIa without the interference of FVII. Two dosages, 15 and 30 microg/kg, were used in a crossover schedule. FVII:C and FVIIa concentration/time curves were analyzed by a model-independent method. Antithrombin (AT), prothombin fragment 1+2 (F1+2) and tissue factor pathway inhibitor (TFPI) were assayed. RESULTS: No differences emerged between the dosages with respect to dose-independent parameters [total body clearance (CL), volume of distribution area (VdArea), mean residence time (MRT)]. No significant changes of AT, TFPI, and F1+2 were observed. Comparing the results with those of other studies performed in adult hemophiliacs, in patients affected by cirrhosis or in volunteers on oral anticoagulant therapy (OAT), CL and VdArea of rFVIIa were definitely higher and in vivo recovery was lower. INTERPRETATION AND CONCLUSIONS: These findings suggest that the kinetics of rFVIIa are not dose-dependent. In the absence of FVII, the changes of VdArea and CL may be in agreement with a mechanism of competition between FVII and rFVIIa for tissue factor binding.

Tissue factor pathway inhibitor levels in patients with homocystinuria.

Thrombotic events are a well-recognized complication of homocystinuria. However, the mechanisms involved in the atherogenic and thrombotic effects of homocyst(e)ine remain incompletely understood. The objective of this study was to determine the role of endothelial cell activation/damage as indicated by levels of thrombomodulin, tissue factor and tissue factor pathway inhibitor, and factor VII activity in patients with homocystinuria. Six patients with homocystinuria, nonresponsive to pyridoxine, treated only with trimethylglycine (betaine) were injected with a bolus of 20 IU/kg body weight of unfractionated commercial heparin to induce the release of tissue factor pathway inhibitor from the vascular endothelium. Tissue factor, thrombomodulin, and factor VII activity were measured by enzyme-linked immunosorbent assay and clotting assay before heparin administration. Tissue factor pathway inhibitor antigen and activity were measured before and 5 minutes after the bolus of heparin. Levels of homocyst(e)ine were elevated (patients: 144.2+/-19.2 micromol/L; controls: 10.2+/-0.9 micromol/L); however, levels of thrombomodulin, tissue factor, and tissue factor pathway inhibitor antigen were not statistically different from the control group. In contrast, tissue factor pathway inhibitor activity showed a significantly increased level (patients: 2.09+/-0.34 U/L; controls: 1.14+/-0.20 U/L; p<0.05) that was correlated with homocyst(e)ine. Factor VII activity was significantly decreased (patients: 64.7+/-5.1%; controls: 91.4+/-4.7%; p<0.05) and inversely correlated with homocyst(e)ine. After heparin the patients released higher amounts of tissue factor pathway inhibitor antigen and activity compared with the control group; however, the difference was not statistically significant. Although not treated with antithrombotic drugs, none of the patients had any thromboembolic complications after starting betaine. In addition to betaine treatment, the enhanced factor pathway inhibitor antigen activity observed in this small series of patients suggests that factor pathway inhibitor antigen may play an additional, as yet unexplained, role in this genetic disorder.

Management of oral anticoagulant therapy in Italy.

The clinical outcome of oral anticoagulant therapy (OAT) depends on how successful physicians and patients are in achieving and maintaining levels of anticoagulation capable of preventing thromboembolic events without increasing the risk of hemorrhagic complications. Concerning the patient, education and compliance are the major problems. Concerning the physicians, the management of patients receiving OAT is a complex task that requires frequent laboratory testing, dosage regulation, prompt diagnosis, and treatment of thromboembolic and hemorrhagic events. Anticoagulation clinics, which provide patient education, close monitoring of prothrombin times and continuous clinical surveillance, have been claimed to help in improving the overall quality of OAT. In 1989, following the experience of other countries, a national Federation of Centers for the Surveillance of Anticoagulant (FCSA) therapies was founded in Italy. In the last 10 years the main objectives of FCSA have been: (1) favoring the development of new centers in areas of the country lacking proper services; (2) standardazing the management of OAT by recommending organizational and technical procedures; (3) stimulating participation in laboratory quality-control programs; (4) implementing continuous education programs for medical and paramedical personnel and for the patients themselves; (5) making health administrators aware of the social impact of OAT and of the need for the formal recognition of the centers; and (6) planning and organizing multicenter studies. Some of these goals have been successfully achieved, but problems remain to be solved to guarantee an optimal control of OAT in the entire national territory.

Molecular mechanisms of FVII deficiency: expression of mutations clustered in the IVS7 donor splice site of factor VII gene.

In three Italian patients, two point mutations and a short deletion were found in the intron 7 of factor VII gene, clustered in the donor splice site and located in the first of several repeats. The mutation 9726+5G-->A, the most frequent cause of symptomatic factor VII deficiency in Italy, as well as the deletion (9729del4) gave rise in expression studies to abnormally spliced transcripts, which were exclusively produced from the cryptic site in the second repeat. The insertion in the mature mRNA of the first intronic repeat caused (9726+5G-->A) a reading frameshift, abolishing most of the factor VII catalytic domain, or produced (9729del4), an altered factor with 11 additional residues, the activity of which was not detectable in the cell medium after mutagenesis and expression studies. Studies of factor VII ectopic mRNA from leukocytes and expression studies indicated that the deleted gene produced 30% of normally spliced transcript. Differently, the 9726+5G-->A mutation permitted a very low level (0.2% to 1%) of correct splicing to occur, which could be of great importance to prevent the onset, in the homozygous patients, of most of the life-threatening bleeding symptoms. The 9726+7A-->G mutation was found to be a rare and functionally silent polymorphism. These findings, which provide further evidence of the interplay of sequence and position in the 5' splice site selection, throw light on the heterogeneous molecular bases and clinical phenotypes of FVII deficiency.

Activated human protein C prevents thrombin-induced thromboembolism in mice. Evidence that activated protein c reduces intravascular fibrin accumulation through the inhibition of additional thrombin generation.

Activated protein C (APC) is a potent physiologic anticoagulant with profibrinolytic properties, and has been shown to prevent thrombosis in different experimental models. We investigated the effect of human APC on thrombin-induced thromboembolism in mice, a model of acute intravascular fibrin deposition leading to death within minutes. APC given intravenously (i.v.) as a bolus 2 min before thrombin challenge (1,250 U/kg) reduced mortality in a dose-dependent manner despite the lack of thrombin inhibitor activity. Significant inhibition of thrombin-induced death was observed at the dose of 0.05 mg/kg, and maximal protection was obtained with 2 mg/kg (> 85% reduction in mortality rate). Histology of lung tissue revealed that APC treatment (2 mg/kg) reduced significantly vascular occlusion rate (from 89.2 to 46.6%, P < 0.01). The protective effect of APC was due to the inhibition of endogenous thrombin formation as indicated by the fact that (a) the injection of human thrombin caused a marked decrease in the coagulation factors of the intrinsic and common pathways (but not of Factor VII), suggesting the activation of blood clotting via the contact system; (b) APC pretreatment reduced markedly prothrombin consumption; (c) the lethal effect of thrombin was almost abolished when the animals were made deficient in vitamin K-dependent factors by warfarin treatment, and could be restored only by doubling the dose of thrombin, indicating that the generation of endogenous thrombin contributes significantly to death; and (d) APC failed to protect warfarin-treated animals, in which mortality is entirely due to injected thrombin, even after protein S supplementation. Other results suggest that APC protects from thrombin-induced thromboembolism by rendering the formed fibrin more susceptible to plasmin degradation rather than by reducing fibrin formation: in thrombin-treated mice, fibrinogen consumption was not inhibited by APC; and inhibition of endogenous fibrinolysis by epsilon-aminocaproic or tranexamic acid resulted in a significant reduction of the protective effect of APC. Since APC did not enhance plasma fibrinolytic activity, as assessed by the measurement of plasminogen activator (PA) or PA inhibitor (PAI) activities, PAI-1 antigen, or 125I-fibrin degrading activity, we speculate that the inhibition of additional (endogenous) thrombin formation by APC interrupts thrombin-dependent mechanisms that make fibrin clots more resistant to lysis, so that the intravascular deposited fibrin can be removed more rapidly by the endogenous fibrinolytic system.

Anticoagulation clinics: the Italian experience.

BACKGROUND AND OBJECTIVE: The clinical quality of oral anticoagulant therapy (OAT) depends on how successful physicians and patients are in achieving and maintaining levels of anticoagulation capable of preventing thromboembolic events without increasing the risk of hemorrhagic complications. Concerning the patient, education and compliance are the major problems. As for the physician, on the other hand, the management of patients receiving OAT is a complex task that requires frequent laboratory testing, dosage regulation, prompt diagnosis and treatment of thromboembolic and hemorrhagic events. It requires educated and skilled personnel and a well-organized framework of services. Anticoagulation clinics, which provide patient education, close monitoring of prothrombin time and continuous clinical surveillance, may help in improving the overall quality of OAT. INFORMATION SOURCES: The authors have been working in this field contributing, original papers. In addition, the material examined in this article includes articles published in the journals covered by the Science Citation Index and Medline. STATE OF ART AND PERSPECTIVES: The concept of a coordinated network of medical services specifically devoted to the control of OAT was developed in the Netherlands following the model created by the late Professor Jordan, who in 1949 founded the first thrombosis center at the University of Utrecht. Many other anticoagulant clinics were organized on, a voluntary basis in the following decades in the Netherlands. The Dutch Federation of Thrombosis Centers was founded in 1971 and each affiliated Center is formally recognized and supported by the central Government. Today, there is a nation-wide system of regionally centralized anticoagulant control for outpatients and home patients that counts approximately 70 anticoagulant clinics (thrombosis centers), covering more than 90% of the country. Similar global approaches to the management of patients receiving OAT were proposed in other countries. In the 1950's, a group of internists and surgeons at the University of Michigan, USA, developed a unit specifically devoted to the diagnosis and treatment of thromboembolic disease, and proposed common strategies, teaching and research programs. In 1959, Sevitt and Gallagher were the first to propose a formal recognition of an anticoagulant unit in Great Britain. Finally, the Italian Federation of Centers for the Surveillance of Anticoagulant (FCSA) therapies was founded in 1989. Nowadays, Italian anticoagulation clinics operating in the framework of the FCSA are still voluntary organizations which provide a specific medical service by continuously reorganizing the personnel, structures and resources available to meet increasing demands. Since OAT has a profound social impact, its control should not be left to the good will of dedicated people, but should instead represent a specific task of the public health system. The achievement of a formal recognition of federated centers is essential for their growth, but the unavoidable increase of the expenses needed to support anticoagulation clinics is difficult to bear in a public care system which is currently facing a substantial reduction of financial resources. In a fixed health care budget, a redistribution of existing resources is the only possible solution, but to achieve this goal, public authorities have to be convinced that the management of OAT in specific anticoagulation clinics is cost-effective. A more accurate estimate of costs is needed and should be performed by the FCSA. Finally, the FCSA should strengthen its contacts with patient organizations and other scientific associations in order to develop common action strategies for improving the quality of OAT.

Thrombotic events during oral anticoagulant treatment: results of the inception-cohort, prospective, collaborative ISCOAT study: ISCOAT study group (Italian Study on Complications of Oral Anticoagulant Therapy).

The paper reports on rate and type of thrombotic events occurring during the observational, prospective, inception-cohort, multicenter ISCOAT study. 2,745 unselected, daily practice patients, consecutively referring to 34 Italian anticoagulation clinics to monitor the oral anticoagulant treatment, were included in the study from beginning of their first anticoagulant course. During a total follow-up of 2,011 patient-years of treatment 70 thrombotic events (3.5 per 100 patient years) were recorded in 67 patients: 20 fatal (1%), 39 major (1.9%) and 11 minor (0.6%). 34/70 events occurred within the first 90 days of treatment (relative risk - at multivariate analysis - of < or =90 days vs. >90 = 20.6, C.I. 12.7-33.5; p <0.0001). The risk was higher in patients aged > or =70 y (1.62, C.I. 1.0-2.61; p <0.05), and when indication for anticoagulant treatment was peripheral/cerebral arterial disease (1.84, C.I. 1.01-3.36; p <0.05). The frequency of thrombotic events was 17.5% when international normalised ratio (INR) levels were < 1.5, decreasing to 2.3% for INRs within the 2-2.99 category (relative risk of INRs <2.0 vs. > or =2 = 1.88, C.I. 1.16-3.07; p <0.05). The recorded rate of thrombotic events was lower than that reported in the few available studies. A greater risk should be expected during the first 90 days of treatment, when anticoagulation levels are <2.0 INR, in patients > 70 years and in those with cerebrovascular/peripheral arterial disease.

Bleeding complications of oral anticoagulant treatment: an inception-cohort, prospective collaborative study (ISCOAT). Italian Study on Complications of Oral Anticoagulant Therapy.

BACKGROUND: Bleeding is the most serious complication of the use of oral anticoagulation in the prevention and treatment of thromoboembolic complications. We studied the frequency of bleeding complications in outpatients treated routinely in anticoagulation clinics. METHODS: In a prospective cohort from thirty-four Italian anticoagulation clinics, 2745 consecutive patients were studied from the start of their oral anticoagulation (warfarin in 64%, acenocourmarol in the rest). The target anticoagulation-intensity was low (international normalised ratio [INR] < or = 2.8) in 71% of the patients and high (> 2.8) in the remainder. We recorded demographic details and the main indication for treatment and, every 3-4 months, INR and outcome events. Such events included all complications (bleeding, thrombosis, other), although only bleeding events are reported here, and deaths. We divided bleeding into major and minor categories. FINDINGS: 43% of the patients were women. Nearly three-fifths of the patients were aged 60-79; 8% were over 80. The main indication for treatment was venous thrombolism (33%), followed by non-ischaemic heart disease (17%). Mean follow-up was 267 days. Over 2011 patient-years of follow-up, 153 bleeding complications occurred (7.6 per 100 patient-years). 5 were fatal (all cerebral haemorrhages, 0.25 per 100 patient-years), 23 were major (1.1), and 125 were minor (6.2). The rate of events was similar between sexes, coumarin type, size of enrolling centre, and target INR. The rate was higher in older patients: 10.5 per 100 patient-years in those aged 70 or over, 6.0 in those aged under 70 (relative risk 1.75, 95% Cl 1.29-2.39, p < 0.001). The rate was also higher when the indication was peripheral and/or cerebrovascular disease than venous thromboembolism plus other indications (12.5 vs 6.0 per 100 patient-years) (1.80, 1.2-2.7, p < 0.01), and during the first 90 days of treatment compared with later (11.0 vs 6.3, 1.75, 1.27-2.44, p < 0.001). A fifth of the bleeding events occurred at low anticoagulation intensity (INR < 2, rate 7.7 per 100 patient-years of follow-up). The rates were 4.8, 9.5, 40.5, and 200 at INRs 2.0-2.9, 3-4.4, 4.5-6.9, and over 7, respectively (relative risks for INR > 4.5, 7.91, 5.44-11.5, p < 0.0001). INTERPRETATION: We saw fewer bleeding events than those recorded in other observational and experimental studies. Oral anticoagulation has become safer in recent years, especially if monitored in anticoagulation clinics. Caution is required in elderly patients and anticoagulation intensity should be closely monitored to reduce periods of overdosing.

Natural history and risk factors for thrombosis in 360 patients with antiphospholipid antibodies: a four-year prospective study from the Italian Registry.

PURPOSE: To assess the natural history and risk factors for thrombosis in a large cohort of unselected patients with antiphospholipid antibodies. PATIENTS AND METHODS: Three hundred sixty consecutive patients (118 males, 242 females, median age 39 years [range 2 to 78]) fulfilling the currently accepted criteria for diagnosis of lupus anticoagulant (LAC) (n = 326) and/or raised immunoglobulin G anticardiolipin antibodies (IgG ACA) (n = 185) were collected from 16 Italian institutions and prospectively observed for a median of 3.9 years (range 0.5 to 5). Main endpoints were the occurrence of arterial or venous thrombosis, the outcome of pregnancies, and any severe complications leading to hospitalization or death. RESULTS: Thirty-four patients developed a thrombotic complication, with a total incidence of 2.5% patient-years. Multivariate logistic regression analysis identified two independent risk factors for thrombotic events: a previous thrombosis (RR 4.9; 95% CI, 1.76 to 13.7; P < 0.005) and IgG ACA titer above 40 units (RR 3.66; 95% CI, 1.24 to 10.8; P < 0.01). A total of 28 pregnancies were observed in 25 women and 11 (39%) were abortive. Adverse pregnancy outcomes were significantly more frequent in women with a history of miscarriage or vascular occlusion (9/16, 56%) than in asymptomatic women (2/12, 17%) (P = 0.035). Four patients developed non-Hodgkin's lymphoma during the follow-up. Eighteen patients died. Vascular events and hematological malignancies represented the most frequent causes of death (n = 5 for each). CONCLUSIONS: The present study shows that: (a) previous thrombosis and ACA titer > 40 U are independent predictors of thrombosis; (b) history of miscarriage or vascular disease is significantly associated with adverse pregnancy outcome; (c) hematological malignancies can develop during follow-up in patients with antiphospholipid antibodies.

Increased plasma levels of tissue factor pathway inhibitor (TFPI) after n-3 polyunsaturated fatty acids supplementation in patients with chronic atherosclerotic disease.

This double-blind, randomised, controlled study examined the effect of a daily dosage of 3 g n-3 polyunsaturated fatty acids (n-3 PUFA) on plasma lipids and some haemostatic factors in 40 patients with chronic atherosclerotic diseases. Serum lipids, factor VII, tissue factor pathway inhibitor (TFPI) and prothrombin activation fragment 1 + 2 (F1 + 2) were measured at baseline and after 2, 8, and 16-week supplementation of either n-3 PUFA or corn oil. Administration of n-3 PUFA promptly lowered serum triglycerides and increased LDL-cholesterol (-32% and +33%, respectively, after 2 weeks of treatment) while a significant increase (+31%) in HDL-cholesterol was documented at the end of the observation period. Treatment with n-3 PUFA induced a progressive significant increase of TFPI plasma levels (+21% after 16 weeks; p = 0.029). TFPI activity was significantly correlated with LDL-cholesterol, and multiple stepwise regression analysis showed that LDL-cholesterol was the most important predictor of TFPI activity. Plasma levels of the inhibitor showed also a very high parallelism in their trend over time (ANOVA model for homogeneity of slopes) with both HDL-cholesterol (p = 0.82) and LDL-cholesterol (p = 0.67). Patients treated with n-PUFA also showed a significant reduction of F1 + 2 plasma levels (p = 0.016) while no significant changes were detected in plasma factor VII clotting activity. Lipid and haemostatic parameters were not modified at any study time in patients receiving corn oil as placebo. The results of this study confirm the effects of n-3 PUFA administration on plasma lipids and show that in patients with chronic atherosclerotic disease a 16-week supplementation with these compounds induces a small but statistically significant increase of TFPI plasma levels with a parallel down-regulation of the extrinsic pathway of blood coagulation which may be relevant to the antithrombotic activity of fish diet and fish oil derivatives.

A simple chromogenic substrate assay of tissue factor pathway inhibitor activity in plasma and serum.

A simple chromogenic substrate assay for the quantitation of tissue factor pathway inhibitor (TFPI) activity in plasma or serum samples was developed. After immobilization on microtiter plates for 20 hours at 4 degrees C, a commercial thromboplastin was incubated for 1 hour at room temperature with 1 U/mL of a prothrombin complex concentrate (Protromplex). After washing, solid-phase Factor Xa activity was measured by a chromogenic substrate (S-2222). Factor Xa generation was progressively inhibited when increasing amounts (1-12 microL) of heated serum or plasma, and recombinant TFPI (1-5 ng/mL), were coincubated with Protromplex. Inhibition by serum or plasma was abolished by anti-TFPI polyclonal antibodies. Plasma levels of TFPI in 25 healthy volunteers were found to be 0.98 +/- 0.19 U/mL (range 0.71-1.52), with an intra- and inter-assay coefficient of variation of 10.7 and 11.1%, respectively. The use of a recombinant human thromboplastin improved the sensitivity and reproducibility of the assay. Plasma levels of TFPI were found to be normal in 10 women at the end of their pregnancies, in 10 patients receiving oral anticoagulant therapy, and in 10 diabetic patients. Significantly higher levels were detected in 10 patients with chronic liver disease and in 10 patients with unexplained juvenile thrombosis. In patients with cardiovascular disease, a 7-day treatment with subcutaneous standard heparin increased TFPI activity. The availability of a simple and rapid assay to measure TFPI that does not require purified coagulation proteins may facilitate studies of the pathophysiologic relevance of this inhibitor.

Assembly and expression of an intrinsic factor IX activator complex on the surface of cultured human endothelial cells.

Endothelial cells expose specific receptors for blood clotting factors and, upon perturbation, can initiate and propagate the reactions of the extrinsic pathway of blood coagulation leading to fibrin formation on the cell surface. The existence of an intrinsic mechanism of Factor IX activation on cultured human umbilical vein cells (HUVECs) was investigated by studies of the interaction between HUVECs and two proteins of the contact activation system, the cofactor high molecular weight kininogen (H-kininogen) and the zymogen Factor XI. In the presence of zinc ions (10-300 microM), 125I-labeled H-kininogen bound to HUVECs in a time-dependent, reversible, and saturable manner, with calcium ions exerting an inhibitory effect on the zinc-dependent binding. Analysis of the binding data by the LIGAND computer program indicated that HUVECs, in the presence of 2 mM CaCl2 and 100 microM ZnCl2 at 37 degrees C, bound 1.14 x 10(7) H-kininogen molecules per cell with an apparent dissociation constant of 55 nM. HUVEC-bound H-kininogen functions as the cell surface receptor for both 125I-labeled Factor XI and 125I-labeled Factor XIa, since HUVECs cultured in contact factor-depleted serum do not detectably bind either the zymogen or the enzyme in the absence of H-kininogen and zinc ions. In the presence of saturating concentrations of H-kininogen, 2 mM CaCl2 and 100 microM ZnCl2, the binding of 125I-labeled Factor XI and Factor XIa to HUVECs was time-dependent, reversible, and saturable, with apparent dissociation constants of 4.5 and 1.5 nM, respectively. HUVEC-bound complexes of H-kininogen and Factor XI generated Factor XIa activity only after the addition of purified Factor XIIa, and cell-bound Factor XIa in turn activated Factor IX, as documented by a 3H-labeled activation peptide release assay for 3H-Factor IX activation. The results indicate that cultured HUVECs provide a surface for the assembly and expression of an intrinsic Factor IX activator complex that may participate in the initiation of blood coagulation at sites of vascular injury.

Failure to demonstrate beneficial effect of prostacyclin (PGI2) infusion on red blood cell deformability in patients with peripheral vascular disease: a possible role of the leukocytes.

The effect of prostacyclin (PGI2) on red blood cell deformability is still controversial. The authors have evaluated some hemorrheologic parameters during PGI2 infusion to patients with severe obstructive peripheral arterial disease not suitable for surgery and not responsive to other medical treatments. PGI2 infusion resulted in a positive clinical effect in 12 of 16 patients, who experienced a significant improvement of their rest pain lasting from two days to more than seven months. Hematocrit, platelet count, and fibrinogen were not modified during PGI2 infusion whereas leukocyte count rose significantly. The evaluation of red blood cell filterability (VRBC) (volume of RBC filtered in one minute) by a whole blood filtration technique showed no significant changes during PGI2 treatment. However, since whole blood filterability is negatively correlated to leukocyte count, a specific regression line was elaborated to remove the potential negative influence of the increased leukocyte counts. VRBC values adjusted to a standard leukocyte number significantly increased during PGI2 treatment.

"In vitro" and "ex vivo" effects of picotamide, a combined thromboxane A2-synthase inhibitor and -receptor antagonist, on human platelets.

Picotamide (G 137), a new non prostanoid inhibitor of in vitro arachidonic acid induced platelet aggregation, has been further characterized in in vitro and ex vivo studies. When whole blood was activated with collagen in the presence of picotamide 5 x 10(-4) M, thromboxane B2 production was decreased, and 6-keto-PGF1 alpha generation was significantly increased, suggesting a reorientation of platelet endoperoxide metabolism following blockade of thromboxane synthetase. Picotamide also inhibited platelet aggregation and clot retraction induced by the endoperoxide analogue U46619 in human platelets, indicating thromboxane A2-receptor antagonism, possibly of competitive nature. A single oral dose of picotamide 1 g in 24 healthy volunteers produced a significant inhibition of collagen, arachidonic acid and U46619-induced platelet aggregation. Serum levels of thromboxane B2 were also reduced. Chronic administration of picotamide 1.2 g/d to patients with vascular disease resulted in a prompt and persistent fall in their increased plasma levels of beta-thromboglobulin. The results indicate that picotamide is a combined thromboxane B2-synthetase inhibitor and thromboxane A2-receptor antagonist in human platelets, and that it may prove useful as an antithrombotic agent.

Purification and characterization of plasma protein C inhibitor.

Plasma protein C inhibitor (PCI) was purified to homogeneity (greater than 95%) with good recovery (greater than 25%) and reproducibility, and the inhibition of a number of blood clotting and fibrinolytic enzymes by purified PCI was studied. PCI inhibited activated protein C (APC), two-chain urokinase (2c-uPA), two-chain tissue plasminogen activator (2c-tPA), thrombin, factor Xa, plasma kallikrein and factor XIa, and this inhibition was accelerated by heparin. The inhibition of each enzyme was accompanied by formation of enzyme inhibitor complexes and by degradation of the inhibitor to lower molecular weight derivatives. Plasma kallikrein and factor XIa cleaved PCI of native Mr = 57,000 into two products with Mr = 54,000 and 52,000 whereas the other enzymes converted the PCI to a product with Mr = 54,000. PCI did not detectably inhibit alpha-factor XIIa or plasmin. Kinetic studies using PCI yielded the following second-order rate constants for inhibition of human APC, 2c-uPA, 2c-tPA, thrombin, factor Xa, kallikrein and factor XIa respectively: 0.65 x 10(4), 0.22 x 10(4), 0.08 x 10(4), 0.61 x 10(4), 2.01 x 10(4), 6.50 x 10(4), and 9.03 x 10(4) M-1s-1 in the absence of heparin and 1.58 x 10(6), 0.43 x 10(6), 0.03 x 10(6), 0.52 x 10(6), 0.09 x 10(6), 0.18 x 10(6) and 0.74 x 10(6) M-1s-1 in the presence of optimal concentrations of heparin. The rate constants for the inhibition of factor XIa and 2c-uPA by PCI suggest a possible role of PCI in the physiologic regulation of these enzymes. The second order rate constants for inhibition of bovine APC and Gla-domainless bovine APC by human PCI were 0.61 x 10(4) and 0.26 x 10(4) M-1s-1 in the absence of heparin and 0.54 x 10(6) and 0.71 x 10(6) M-1s-1 in the presence of heparin, respectively. Calcium ions (0.05 to 4 mM) did not affect these rate constants. The results obtained with normal and Gla-domainless APC indicate that the Gla domain of APC is not required for inactivation by PGI and is not essential for the heparin stimulation of this reaction.

Interaction of type 1 plasminogen activator inhibitor with the enzymes of the contact activation system.

The interaction between type 1 plasminogen activator inhibitor (PAI-1), a serine protease inhibitor, and the three serine proteases generated during contact activation of plasma was studied using functional and immunologic approaches. Incubation of Factor XIIa, Factor XIa, and plasma kallikrein with either purified PAI-1 or platelet-derived PAI-1 resulted in the formation of sodium dodecyl sulfate-stable complexes as revealed by immunoblotting techniques. Functional assays indicated that Factor XIa and, to a lesser extent, Factor XIIa and plasma kallikrein neutralized the ability of purified PAI-1 to bind to immobilized tissue-type plasminogen activator (t-PA). Immunoblotting demonstrated that these enzymes also neutralized the ability of PAI-1 to form complexes with fluid-phase t-PA. Clot lysis assays employing purified proteins and 125I-fibrinogen were used to investigate the profibrinolytic effect of these contact activation enzymes. At enzyme concentrations that did not result in direct activation of plasminogen, only Factor XIa was capable of stimulating the lysis of clots supplemented with both t-PA and PAI-1. As a consequence of their interactions with PAI-1, the amidolytic activity of Factor XIIa, Factor XIa, and plasma kallikrein was neutralized by this inhibitor in a time-dependent and concentration-dependent manner. Minimum values estimated for the apparent second-order rate constant of inhibition were 1.6 x 10(4), 2.1 x 10(5), and 6.0 x 10(4) M-1 s-1 for Factor XIIa, Factor XIa, and plasma kallikrein, respectively. These data define new reactions between coagulation and fibrinolysis proteins and suggest that a major mechanism for stimulation of the intrinsic fibrinolytic pathway may involve neutralization of PAI-1 by Factor XIa.