Two different mechanisms in patients with venous thrombosis and defective fibrinolysis: low concentration of plasminogen activator or increased concentration of plasminogen activator inhibitor

Poor fibrinolytic response to venous occlusion by different criteria in patients with deep vein thrombosis

Five criteria for poor response to a 20 min venous occlusion test were applied to 58 patients 3 months or more after acute deep vein thrombosis (DVT). The criteria were arbitrarily defined as the last 5 percentiles of response distributions in an age- and sex-matched healthy control group of 51 subjects. The criteria were: 1. euglobulin clot lysis time after venous occlusion greater than or equal to 140 min; 2. t-PA activity after venous occlusion less than or equal to 0.04 IU/ml; 3. increase in t-PA antigen above resting value less than or equal to 2-fold; 4. ratio between t-PA antigen increase and resting PAI activity less than or equal to 0.5 ng/IU; 5. PAI activity after venous occlusion greater than or equal to 6 IU/ml. The last criterion of poor response was the only one that was significantly more frequently reached by patients than by controls: 28% (p less than 0.005) of all DVT patients and 35% (p less than 0.005) of the subgroup with idiopathic DVT (N = 34) were found to be poor responders. The percentage of poor responders according to the other four criteria was 7-11% in all patients and 9-15% in the subgroup with idiopathic DVT and thus was not significantly higher than in controls (5% by definition). It was concluded that residual PAI activity after venous occlusion might be a useful criterion for prospective studies on recurrence of DVT.

Effect of retinoic acid on the synthesis of tissue-type plasminogen activator and plasminogen activator inhibitor-1 in human endothelial cells

The synthesis of plasminogen activators and inhibitors in endothelial cells is highly regulated by hormones, drugs and growth factors. The present study evaluates the effect of retinoic acid on the synthesis of tissue-type plasminogen activator (t-PA) and of plasminogen activator inhibitor-1 (PAI-1) by cultured human umbilical vein endothelial cells (HUVEC). Retinoic acid produced a time- and concentration-dependent increase in the secretion of t-PA-related antigen but not of PAI-1 related antigen into the culture medium. A maximal sevenfold increase of t-PA antigen after 24 h was observed with 10 microM and a half-maximal increase with 0.1 microM retinoic acid. Retinoic acid induced a time-dependent increase of the t-PA mRNA, with a maximum at 8 h and returning to normal at 24 h. The protein kinase inhibitor H7 decreased the t-PA antigen induced by both retinoic acid and phorbol 12-myristate 13-acetate. These results suggest that treatment of HUVEC with retinoic acid increases t-PA production by a pathway which, at some level, involves protein kinases. Thus, retinoic acid induces t-PA synthesis in the absence of altered PAI-1 synthesis, which may enhance the fibrinolytic potential of the endothelium.

Hypercoagulability. Should every patient with venous thrombosis be tested?

Tests for anticoagulant protein deficiencies have a low predictive value for venous thrombosis in the general population. Such testing should be done only in patients with recurrent thrombosis, a family history of thrombosis, or atypical features such as young age at presentation or unusual site. Decreased fibrinolysis is another defect often seen in patients with venous thrombosis, but it lacks sufficient specificity to have a high predictive value. The presence of antiphospholipid antibodies has a fairly high predictive value, and testing beyond the partial thromboplastin time may be justified in patients who have (1) arterial thrombosis or (2) a history of fetal demise or recurrent spontaneous abortions.

Familial clustering of defective release of t-PA

91 unrelated patients with idiopathic or familial deep vein thrombosis (DVT) and 72 (34 with DVT) relatives from 26 families were screened for hypofibrinolysis by measuring tissue plasminogen activator antigen (t-PA:Ag) after venous occlusion (VO) for 10 and 20 min and by measuring t-PA inhibitor activity (PAI) at rest. 21 healthy subjects served as controls. Defective release of t-PA:Ag was found in eight out of the 91 patients (9%). A partial family study of six of these eight patients was performed. This study included 10 family members with and 21 without DVT. A defective release of t-PA:Ag was found in 50% (5/10) of the family members with DVT, which is significantly more frequent than the 9% (8/91) prevalence in the unrelated patients (P less than 0.001). Furthermore, 24% (5/21) of asymptomatic members of these families also had defective release of t-PA:Ag. In the 18 families where the propositus had a normal level of t-PA:Ag, none of the 24 studied family members with DVT had defective release of t-PA:Ag. In contrast to the defective release of t-PA:Ag, increased basal level of PAI did not show familial clustering. In conclusion, low release of t-PA during VO shows familial clustering in a proportion of the cases.

The formation of complexes between human plasminogen activator inhibitor-1 (PAI-1) and sodium dodecyl sulfate: possible implication in the functional properties of PAI-1

The effect of the anionic detergent sodium dodecyl sulfate (SDS) on human PAI-1 present in plasma, platelet extracts and endothelial cell cultures, was examined. Using the dye partitional extraction method of Mukerjee [1956) Anal. Chem. 28, 870-873) to quantitate ionic surfactants, and a discontinuous spectrophotometric assay for the titration of PAI-1 based on the measurement of residual active t-PA, we found (i) that SDS remains tightly bound to PAI-1 after equilibrium dialysis and (ii) that the activity of the latter was closely related to the amount of SDS carried over by the PAI-1 solution. The highest concentrations of SDS (ratio of SDS to protein greater than 0.1) were detected in the platelet-derived sources of PAI-1 which also showed the lowest residual t-PA activity. Moreover, it is demonstrated by SDS-PAGE and autoradiography that the tight binding of SDS to PAI-1 decreases its ability to form complexes with t-PA. Similar results were obtained with PAI-1 previously inactivated at 37 degrees C: the inability of PAI-1 to form complexes with t-PA was unchanged after SDS treatment. These observations suggest that the decrease in the residual activity of t-PA observed with the SDS-treated PAI-1 preparations is not related to an increase in the inhibitory activity of PAI-1. In fact, SDS was able to produce a decrease in both the binding of t-PA to fibrin and the activation of plasminogen by fibrin-bound t-PA. Bovine PAI-1 has been shown to exist in a latent SDS-activatable form. Our data indicate that such a form might not be present in the human sources of PAI-1 we have tested.

Prevalence of antiphospholipid antibodies in deep vein thrombosis and their relationship to blood coagulation and fibrinolysis

Elevated levels of antiphospholipid antibodies are associated with an increased risk of thrombosis. To establish the prevalence of these antibodies in deep vein thrombosis (DVT), IgG and IgM antibodies to cardiolipin (aCL) and phosphatidylserine (aPS) were determined by enzyme-linked immunosorbent assay in 118 patients with DVT either during an acute episode (N = 53) or at least 2 months after acute DVT (N = 65). Most patients (76%) had proximal leg DVT and no one had evident autoimmune disorder. aCL and aPS values higher than 4 standard deviations above the mean value of the control group (147 blood donors) were considered increased. Increased IgG aCL were observed in 10% of DVT patients (controls: 5%, not significant), increased IgG aPS in 16% of DVT patients (controls: 5%, p less than 0.005) and both types in 4% of DVT patients (controls: 3%, not significant). In the subgroup of 41 patients with previous idiopathic DVT, prevalence of increased IgG aPS was the highest: 27% (p less than 0.001). Increased antibodies of IgM isotype were observed in 3% (aCL) and 2% (aPS) of all DVT patients (controls: 8% and 4%, respectively, not significant). Elevated IgG aCL or aPS were not associated with significant changes in platelet count, antithrombin III and protein C. However, in patients with increased IgG aPS deficient fibrinolysis due to high plasminogen activator inhibitor activity was observed before and after 20 min upper arm venous occlusion. DVT patients with increased IgG aPS might be exposed to a greater risk of rethrombosis due to deficient fibrinolysis than DVT patients without these antibodies.

A novel principle for assessment of stimulated fibrinolysis

After venous occlusion (VO), D-dimer levels were measured by means of an ELISA technique, in citrated plasma clotted by thrombin and in serum from whole blood. D-dimer levels increased with duration of incubation (30 min to 24 hours). D-dimer values, both in clotted plasma and in serum (n = 12), incubated 4 hours at room temperature, correlated well with euglobulin clot lysis time (ECLT) (r = -0.85 and -0.89, respectively, p less than 0.002) and tissue plasminogen activator (t-PA) activity, (r = 0.82 and 0.83, respectively, p less than 0.002). D-dimer concentrations from plasma and serum (n = 25) were compared (r = 0.90, p less than 0.001). Healthy volunteers (n = 65) were tested to establish reference values in serum from post-occlusive whole blood samples incubated 4 hours prior to centrifugation. Finally, a patient group (n = 62) was examined. For the whole material (n = 152) such D-dimer concentrations correlated well with both ECLT (r = -0.85, p less than 0.001) and t-PA activity (r = 0.81, p less than 0.001). D-dimer levels in serum were determined by a latex agglutination test as well. These semi-quantitative values also correlated significantly with both ECLT (r = -0.86, p less than 0.001) and t-PA activity (r = 0.87, p less than 0.001). We conclude that measurement of D-dimer as described above, represents a simple and accurate method for assessment of global fibrinolytic activity following VO. The latex agglutination test is particularly suitable as a screening procedure.

Plasma concentration of coagulation and fibrinolysis factors and platelet function in hypertension

Fifty-one patients with mild hypertension were evaluated in relation to the plasma concentrations of coagulation and fibrinolysis factors as well as for the aggregability of their platelets. In a considerable number of the patients (18/51), a significantly enhanced in vitro ADP (2 mumol/l)-induced aggregation was found. In the coagulation line significant increases could be demonstrated in fibrinogen, fibrin monomers and thrombin-antithrombin III. The fibrinolysis system showed significant increases for D-dimers, tissue plasminogen activator antigen and plasminogen activator inhibitor, whereas the tissue plasminogen activator activity was significantly diminished. Remarkably, there seems to be a discrepancy between the (low) tissue plasminogen activator activity and the (higher) plasminogen activator antigen concentration. Alterations in the plasma concentrations of the investigated coagulation and fibrinolysis factors and in the aggregability of the platelets are indicative of an involvement of coagulation, fibrinolysis and platelets in hypertension, which can be considered as partial risk factors for thrombophilia.

Metformin causes a reduction in basal and post-venous occlusion plasminogen activator inhibitor-1 in type 2 diabetic patients

The effects of metformin on the fibrinolytic system were studied pre- and post-venous occlusion in 38 Type 2 diabetic patients in a double-blind, placebo-controlled trial. After a 3-week run-in period, 21 patients received metformin and 17 placebo, for 6 weeks. In the metformin-treated patients basal plasminogen activator inhibitor-1 antigen (PAI-1Ag) fell from 57.4 micrograms l-1 before treatment to 36.1 (p less than 0.05) and 41.0 micrograms l-1 (p less than 0.01) after 3 and 6 weeks therapy. In this group post-venous occlusion PAI-1Ag also fell after 3 weeks (p less than 0.002) and 6 weeks (p less than 0.05) treatment. There were no changes in either basal or post-venous occlusion concentrations of PAI-1Ag in the placebo treated group. The fall in PAI-1Ag was not associated with an increase in basal plasminogen activator activity (PAA) which remained unchanged in both groups. Post-venous occlusion values for PAA in the metformin treated patients were increased at 3 weeks (p less than 0.05) although there was no difference at 6 weeks.

Impaired fibrinolysis and postoperative thromboembolism in orthopedic patients

The incidence of deep vein thrombosis (DVT) and pulmonary embolism was studied prospectively in patients undergoing elective total hip replacement. 96 patients were randomly allocated to receive either low molecular weight heparin (LMWH) or unfractionated heparin (UFH). All patients had bilateral phlebography and pulmonary perfusion/ventilation scintigraphy 10-12 days after surgery. The following fibrinolytic variables were analysed in plasma and related to thromboembolism: tissue plasminogen activator (t-PA) activity, t-PA antigen (t-PA Ag), plasminogen activator inhibitor (PAI-1) activity and PAI-1 antigen (PAI-1 Ag). No significant difference was found, regarding the fibrinolytic response to surgery, between patients treated with LMWH and UFH. The level of PAI-1 activity was significantly increased before operation in patients developing DVT as compared to non-DVT patients (p less than 0.03). Immediately after surgery and in the morning the first postoperative day the levels of PAI-1 activity, PAI-1 Ag and t-PA Ag were positively correlated to thromboembolism. PAI-1 activity was the only preoperative fibrinolytic variable correlated to thromboembolism.

Plasminogen activator inhibitor in acute stroke

Plasminogen activator inhibitor activity was determined in patients (26 men, 6 women) with acute ischemic stroke (n = 28) and transient ischemic attack (TIA) (n = 4). Age-matched patients (22 men, 10 women) with various nonvascular neurologic diseases served as controls. Plasma levels of plasminogen activator inhibitor activity were significantly higher in the stroke group (p less than 0.003). Serum triglycerides and plasminogen activator inhibitor activity correlated positively in the stroke group (p less than 0.03) and in controls (p less than 0.0001). Our data suggest a possible involvement of plasminogen activator inhibitor activity in the pathophysiology of stroke.

The role of fibrinolytic factors in ischaemia

The fibrinolytic system is an enzymatic cascade system whose activation leads to formation of a trypsin-like serine protease, plasmin, which splits insoluble fibrin into soluble degradation products. It is believed that the main function of fibrinolysis is defence against thrombotic occlusion of vessels and dissolution of thrombi once they are formed (thrombolysis). The authors review the recent literature providing evidence that fibrinolysis plays a role in the pathogenesis of vascular occlusions. From earlier studies based on global assay methods it is known that fibrinolysis is depressed in patients with vascular occlusions. Selective assay methods show that almost invariably the fibrinolytic activity of these patients is depressed either following increased levels of fibrinolytic inhibitors (mainly plasminogen activator inhibitor 1 or PAI-1) and/or decreased levels of a plasminogen activator (tissue plasminogen activator or t-PA). In a few cases the molecule of plasminogen shows a conformational abnormality making it less susceptible to conversion to plasmin. In the last decade numerous studies have been published showing a connection between a depressed fibrinolysis and venous thrombosis. In patients with coronary artery occlusion fibrinolysis is depressed mainly because of increased levels of PAI-1. Hypertriglyceridaemia seems to aggravate the defective fibrinolysis. There is also evidence of a decreased fibrinolysis in patients with peripheral ischaemic diseases. A depressed fibrinolysis has also been documented in states predisposing to vascular occlusions. Thus two levels of t-PA/increased levels of PAI-1 have been found in obesity, diabetes mellitus, postoperative states, SLE, malignancies, and miscellaneous diseases often complicated with thrombosis such as Behçet's syndrome. In pregnancy fibrinolysis is depressed because of the presence in blood of PIA-2, an inhibitor of plasminogen activators secreted by the placenta.

The fibrinolytic response to venous occlusion and the natural anticoagulants in patients with antiphospholipid antibodies both with and without systemic lupus erythematosus

Patients with systemic lupus erythematosus (SLE) have an increased risk of thrombosis and this is increased in the presence of antiphospholipid antibodies (APA). These APA are also associated with thrombosis in patients who do not have SLE. We compared haemostatic parameters in SLE patients with and without APA, and also compared patients who had APA but not SLE with healthy normal controls. No relationships between the natural anticoagulants, antithrombin III, heparin cofactor II, protein C and protein S, and the presence of APA were found. In the patients with SLE both tissue plasminogen activator antigen and plasminogen activator inhibitor (PAI) were increased, but these changes were not due to APA which had no effect on fibrinolysis in these patients. In the patients with APA who did not have SLE the fibrinolytic response to venous occlusion was reduced due to raised levels of PAI; similar changes have, however, been reported in some patients with idiopathic thrombosis.

t-PA, PAI, and protein C before and after vascular occlusion of the upper limb in patients with Raynaud's phenomenon

Tissue plasminogen activator (t-PA) and its inhibitor (PAI) were assessed in venous blood drawn before and after venous occlusion (bvo, avo) for 33 patients with Raynaud's phenomenon (RP), 14 with primary RP (PRP), 9 with suspected secondary RP (SSRP), and 10 with definite collagen disease and secondary RP (SRP). There were significant differences in PAI values avo between PRP (and controls), SSRP, and SRP. PAI activity decreased significantly avo only in controls and in PRP, and there was significant t-PA antigen elevation avo in the same groups. In addition, since PAI is neutralized by activated protein C (PC), both PC antigen and PC activity were assessed avo and bvo. PC Ag remained unchanged in all groups, with PC activity significantly lower than controls in SRP and SSRP. Finally the authors looked for interference of anticardiolipin antibodies (ACA) and lupus-like anticoagulant (LAC) with the PC system in collagen disease-associated RP. Specific IgG ACA were found in only 1 patient with SRP. In conclusion, there is an endothelial derangement, involving t-PA release and PAI, in SSRP and SRP patients. The reduced PC activity in these latter groups appears to be due to increased PAI influence rather than to ACA/LAC.

Cerebral venous thrombosis with plasminogen deficiency

We describe a patient with inherited plasminogen deficiency who developed extensive cerebral venous thrombosis. Several other conditions that might have contributed to a hypercoagulable state, including mild thrombocytosis, thyrotoxicosis, and a chronic inflammatory lung disorder, were present. We also discuss the evidence linking plasminogen deficiency with a thrombophilic state. The diagnosis of cerebral venous thrombosis in this case was readily established by nuclear magnetic resonance imaging, a technique that is ideally suited for the evaluation and follow-up of patients with this condition.

Decreased fibrinolytic activity in juvenile chronic arthritis

The basal fibrinolytic activity in 17 children with active juvenile chronic arthritis (JCA) was investigated. It was found that patients with JCA, and particularly those with the systemic form, show decreased plasma fibrinolytic activity and a marked increase in plasminogen activator inhibitor. Additionally, it was found that patients with systemic JCA, but not those with the polyarticular or pauciarticular form, have increased circulating levels of tissue-type plasminogen activator, and endothelial cell protein, suggesting possible endothelial cell participation in systemic JCA.

Correlations between fibrinolytic function and acute myocardial infarction

The diurnal variation of tissue plasminogen activator and plasminogen activator inhibitor--2 important factors in regulation of fibrinolysis--is well established, but its clinical implications are not yet fully understood. Fibrinolytic function was measured in a group of 133 patients less than 45 years of age, 3 months after they presented with myocardial infarction, and they were compared with an equal group of carefully matched control subjects. A sub-sample of 71 patients and 50 control subjects was examined 3 years later. Tissue plasminogen activator inhibitor plasma levels were higher in patients versus control subjects at 3 months and at 3 years after myocardial infarction, with a high degree of correlation between the 2 determinations (r = 0.87). Of all hemostatic parameters studied, only low tissue plasminogen activator activity and increased tissue plasminogen activator inhibitor levels were significantly different between patients with and without recurrent infarction during the 3-year period. In those patients with a second infarction greater than 3 years later, however, tissue plasminogen activator inhibitor concentration was not significantly related to reinfarction.

Hemostatic variables in homozygous familial hypercholesterolemia. Effect of regular plasma cholesterol removal by low density lipoprotein apheresis

Plasma levels of tissue plasminogen activator (t-PA) and plasminogen activator inhibitor (PAI) and the in vitro ability of platelets to aggregate and of monocytes to express procoagulant (tissue factor) activity (PCA) were evaluated in five patients who are homozygous for familial hypercholesterolemia (FH) before and after a single and a regular 5-month cholesterol removal by low density lipoprotein (LDL) apheresis. The biweekly procedure resulted in a 25% to 30% reduction (approximately 150 mg/dl) in total and LDL cholesterol (both were greater than 550 mg/dl at the beginning of the study). The basal levels of t-PA antigen and fibrinolytic activity before and after 10 minutes of venous stasis, basal PAI activity, and PAI-1 antigen were comparable to controls and were not affected by LDL apheresis. Likewise, regardless of the cholesterol removal, the PCA of freshly isolated monocytes and that of monocytes incubated with lipopolysaccharide did not differ from control values. Finally, the pre-apheresis sensitivity of platelets to adenosine diphosphate, arachidonic acid, and collagen was 1.5 to 2 times the normal value. This ratio was unchanged throughout the 5-month procedure. We conclude that fibrinolysis and monocyte PCA are normal in FH patients, whereas platelet aggregation is abnormally high, and none of these parameters is significantly affected by a 25% to 30% reduction in total and LDL cholesterol by LDL apheresis. Furthermore, our data suggest that removal of cholesterol from plasma by LDL apheresis is important for gaining insight into the mechanisms involved in the ischemic complications of arteriosclerosis in FH patients.

Hematologic disorders and ischemic stroke. A selective review

More than a dozen primary hematologic disorders have been associated with ischemic stroke. Inherited deficiencies of antithrombin III, protein C, and protein S have been linked with stroke in case reports; optimal screening requires functional as well as antigenic assays. Antiphospholipid antibodies and lupus anticoagulants are the most frequently identified acquired states associated with ischemic stroke. Polycythemia vera, sickle cell anemia, sickle-C disease, and essential thrombocythemia are the major disorders of formed blood elements causing stroke. Special, step-wise screening for occult prothrombotic entities in stroke patients is recommended for young persons with stroke of uncertain cause, for those with prior venous thrombosis, for those with a family history of unusual thrombosis, and for those with no other explanation for recurrent stroke. Acquired, perhaps transient, abnormalities of platelets, coagulation inhibition, and fibrinolysis may contribute importantly to brain ischemia in synergy with other mechanisms, but at present these remain ill-defined. The contribution of prothrombotic diatheses to stroke is probably underrecognized and warrants further investigation.

Complex formation between plasminogen activator inhibitor 1 and vitronectin in purified systems and in plasma

Functionally active PAI-1 is bound to a discrete binding or carrier protein in plasma, which was recently identified as vitronectin. In the present study, the interaction between PAI-1 and vitronectin has been studied in purified systems and in plasma by agarose gel electrophoresis using non-denaturing conditions and by crossed immunoelectrophoresis using an antiserum produced towards purified PAI-1/vitronectin complex. Both methods revealed a clearly distinguishable complex with electrophoretic mobility in between the parent molecules. Virtually all of the purified vitronectin, which did not contain any appreciable amounts of polymerized material, and almost all of the vitronectin in plasma, had the capacity to form a complex with PAI-1. The results suggested a stoichiometry of 1:1 as the most likely ratio between the two molecules in the complex. In contrast to functionally active PAI-1, latent or chloramine T-inactivated PAI-1 did not form such a complex with vitronectin.

Development of venous occlusions in mice transgenic for the plasminogen activator inhibitor-1 gene

The fibrinolytic potential of the vasculature is modulated primarily by the availability and activity of plasminogen activators, which convert the zymogen plasminogen into the active fibrin-degrading enzyme plasmin. The activities of these key regulatory enzymes are directly neutralized by their primary endogenous inhibitor, plasminogen activator inhibitor-1 (PAI-1). Although some individuals with a tendency to develop thrombotic disorders exhibit elevated levels of PAI-1 in their plasma, the cause-and-effect relationship between increased PAI-1 and thrombosis is still unclear. Specifically, it is not known whether chronic depression of fibrinolytic activity results in the development of thrombosis. To address this question we developed transgenic mice in which the contribution of PAI-1 to thrombus formation could be evaluated. The results presented in this report indicate that elevated levels of PAI-1 contribute to the development of venous but not arterial occlusions.

Disorders of the hemostatic system and the risk of the development of thrombotic and cardiovascular diseases: limitations of laboratory diagnosis

The relationship between hemostatic abnormalities and thrombotic and cardiovascular diseases is summarized. All known congenital and acquired abnormalities in the biochemistry of hemostasis are related to thrombotic and cardiovascular diseases in the way that would be expected on the basis of theories about the role of balances between coagulation and fibrinolysis and between activating and inhibiting factors. Notwithstanding the consistency between theory and observed abnormalities, a causal relationship between biochemical abnormality and clinical symptoms has been proved only in a limited number of situations, and it is possible that certain abnormalities only (or also) mark pathologic events. The limitations of laboratory diagnosis of hemostatic disorders in relation to hemostasis as a local process are discussed. It is proposed that more attention be paid to methods of evaluating the local aspects, for example, methods that assess reaction products in the circulation and that can provide an averaged message of the local phenomena. In addition, such methods can provide information about the dynamic balances in the hemostatic system, whereas historically more attention has been paid to the static balances in the potential of hemostatic processes.

Tissue plasminogen activator levels in different types of polycythemia

The plasma level of tissue plasminogen activator antigen (t-PA-Ag) was examined in 86 patients with polycythemia (29 polycythemia vera, 11 secondary polycythemia and 46 with spurious polycythemia) and 24 healthy volunteers. Tissue plasminogen activator antigen was significantly decreased in patients with polycythemia vera in comparison with healthy controls. On the other hand, in patients with spurious polycythemia and secondary polycythemia t-PA-Ag concentration was significantly increased. There was no significant difference in t-PA-Ag levels in polycythemic patients with or without thromboembolic disease. A significant correlation was detected between t-PA-Ag level and hemoglobin or hematocrit concentration in patients with polycythemia vera (p = 0.02, r = 0.43). However, in patients with secondary polycythemia and spurious polycythemia, no significant correlation between t-PA-Ag and hemoglobin level was found. Plasminogen activator inhibitor (PAI) levels in patients with polycythemia vera and healthy volunteers did not differ significantly.

A modified quantitative whole blood clot lysis method for general laboratory analysis of fibrinolysis

Because fibrinolysis is now recognized as an important factor in hypercoagulable states, we have developed and characterized an easily performed, rapid, and quantitative screening test that assesses a patient's fibrinolytic activity. This modification of the dilute whole blood clotting time (DWBCT) counts the number of intact erythrocytes released from the clot formed in samples obtained before and after the application of a venous occlusion cuff. Samples were corrected for the plasma volume changes that occurred during venous occlusion. This test was performed on nine healthy volunteers. Specimens were diluted 1:1 with PBS, rapidly clotted with thrombin and incubated at 37 C. Starting thirty minutes after the thrombin was added and then at twenty minute intervals until 110 minutes, the number of RBCs released from the clot were counted using a Coulter S Plus counter. There were consistently more RBCs released at each time period after venous occlusion (p less than 0.001). Aliquots were also obtained for measuring PAI activity and TPA levels. PAI activity was lower post-cuff at every point (p less than 0.001). TPA level was higher at every point (p less than 0.001) post-cuff. The addition of exogenous TPA, activated protein C, or anti-PAI antibodies increased the amount of clot lysis; while the addition of anti-TPA antibodies and EACA each prevented the post-cuff increase. Unlike the euglobulin lysis time (ELT) this modified DWBCT (mDWBCT) measures the patients intact fibrinolytic system, including PAI and erythrocytes, in a quantitative fashion. Unlike either the ELT or the DWBCT the mDWBCT can be performed within two hours, so results are rapidly available for clinical decisions. These studies have demonstrated an easily performed, inexpensive, quantitative screening test of a patient's overall fibrinolytic system that reacts appropriately to pharmacologic manipulations.

Biochemical and biological aspects of the plasminogen activation system

Plasminogen activators (PAs) are specific proteolytic enzymes which convert the inactive proenzyme plasminogen to plasmin. The plasmin formed is a potent and nonspecific protease which cleaves blood fibrin clots and several other extracellular proteins. In addition to their primary role in the initiation of fibrinolysis, PAs are implicated in a variety of basic biological processes, such as, degradation of the extracellular matrix, tumor invasiveness, tissue remodelling, and cellular differentiation. This review describes recent observations on the biochemical and biophysical characteristics of the different components of the plasminogen activation system. This complex system includes: the proenzymes of tissue type PA (tPA) and urokinase type PA (uPA); the active enzymes tPA, uPA and plasmin; the substrate plasminogen; several natural inhibitors of PA and plasmin activity; and the cellular receptors that bind the proenzymes, enzymes, and inhibitor-enzyme complexes. Through the coordinated interactions of these components, the location, timing, and extent of potent proteolytic activity is controlled. Recent findings on the structure, properties, biological functions, and regulation of the different components of the plasminogen activation cascade are reviewed. Current methods for assay of the amount and activity of the enzymes, inhibitors, and receptors are described. Observations implying specific functions of the system in health and disease, and its potential utilization for diagnosis are examined. Specifically, the potential application of PAs as laboratory markers of neoplasia, as diagnostic tools in diseases of the blood clotting system, their use for monitoring of thrombolytic therapy, and their possible relevance in certain disease states are described.

Relationship between plasma levels of components of the fibrinolytic system and acute-phase reactants in patients with uterine malignancies

Plasma samples from 17 patients with endometrial cancer and from 52 patients with cervical carcinoma were determined with respect to their levels of components of the fibrinolytic system (tissue-type plasminogen activator antigen, urokinase-type plasminogen activator antigen, plasminogen activator inhibitor activity) and related to the observed alterations of three acute-phase reactants (C-reactive protein, coeruloplasmin, alpha-1-antitrypsin). As shown previously, uterine malignancies, especially at later stages, exhibited significant increases in plasma levels of urokinase-type plasminogen activator antigen as compared to an age-matched control group. In contrast, tissue-type plasminogen activator antigen and plasminogen activator inhibitor activity remained unchanged. Determination of the acute-phase reactants revealed significant changes in the case of C-reactive protein and coeruloplasmin in later tumour stages. However, the increase in urokinase-type plasminogen activator antigen did not correlate with the increase of either C-reactive protein or coeruloplasmin plasma level. These data indicate that the increase in plasma urokinase-type plasminogen activator antigen in patients with uterine malignancies does not follow the pattern of common acute-phase reactants, like C-reactive protein or coeruloplasmin.

Plasmin-a2-plasmin inhibitor complex in plasma of patients with thromboembolic diseases

Plasmin generation in vivo was assessed by measuring plasma levels of plasmin-a2-plasmin inhibitor complex (PAP) with an ELISA in 42 patients with arterial or venous thromboembolic diseases. Plasma concentration of PAP was markedly elevated in patients with venous thromboembolic diseases during acute illness (3.32 +/- 3.71 ug/ml, mean +/- SD) as compared to healthy subjects (0.24 +/- 0.13 ug/ml, n = 14), while it was nearly normal (0.30 +/- 0.13 ug/ml) in patients with venous thromboembolic diseases in chronic stage. Patients with arterial thromboembolism had modestly elevated PAP; 1.05 +/- 0.77 ug/ml during acute episode, and 0.84 +/- 0.40 ug/ml in chronic stage. These results indicate that excessive activation of fibrinolytic system (plasmin generation in vivo) occurs actually in many patients with thrombotic diseases, especially in venous thromboembolic diseases during acute illness.

Primary hypercoagulable states in general and vascular surgery

Primary hypercoagulable states are increasingly recognized as causes of venous and arterial thromboembolism in surgical patients. Herein, we describe 10 patients with this syndrome who were diagnosed during a recent 1-year period. A family history and past medical history of thromboembolism and an unusual site of thrombosis are emphasized for accurate diagnosis. Although antithrombin III deficiencies were the most common abnormality found, we describe three patients with hypofibrinolytic syndromes and increased levels of tissue plasminogen activator inhibitor. The effectiveness of anticoagulation therapy in preventing recurrent thromboembolism is stressed.

Fibrinolytic response in normal subjects to venous occlusion and DDAVP infusion

A set of fibrinolytic parameters was measured in 40 healthy subjects before and after a venous occlusion (VO) test lasting 10 min. After VO, plasma levels of tissue-type plasminogen activator (t-PA) antigen increased in all subjects, t-PA activity increased only in 25 subjects who were considered responders and remained unchanged in 15 (non-responders). High levels of plasminogen activator inhibitor (PAI) in the non-responder group explain this discrepancy. The non-responders had basal levels of PAI activity and t-PA antigen higher than responders (p less than 0.0001) and their basal levels of t-PA activity were lower (p less than 0.001). DDAVP infusion elicited good responses in 7 of 9 non-responders to VO with a fall of PAI activity to 0. Our data indicate that a high proportion of healthy subjects do not have a fibrinolytic response after VO, that a lack of fibrinolytic response to VO is due to high plasma levels of PAI and that DDAVP infusion appear to be more selective than VO for detecting non-responders.

Fibrinolytic response to venous occlusion for 10 and 20 minutes in healthy subjects and in patients with deep vein thrombosis

Tissue plasminogen activator (t-PA) activity, t-PA antigen (t-PA:Ag) and t-PA inhibitor activity (PAI) were measured at rest and during venous occlusion (VO) for 10 and 20 min in 21 healthy subjects and 80 patients with venous thromboembolic disease. The expected t-PA release was seen in the controls. However, the release was found to be nonlinear and 63% of the t-PA:Ag was released during the last 10 min of VO. Defective release of t-PA:Ag and/or t-PA activity was found in 25 patients (31%). Three subgroups could be identified: 10 patients (13%) with low t-PA:Ag release (PRI), 6 patients (8%) with a high basal level of PAI (PR II) and 9 patients (11%) who had only low t-PA activity after VO. Using VO for 10 min only, 60%, 83% and 44% of the patients in PR I, PR II and PR III, respectively, were recognized. Using VO for 20 min only, the figures were 80%, 83% and 89%, respectively. The use of t-PA values corrected for the haemoconcentration during VO influenced the patients' classification as poor responders to only a minor degree. It is concluded that in screening for hypofibrinolysis VO is needed for at least 20 min, but that the sensitivity of the test increased by using VO for both 10 and 20 min.

Impaired fibrinolysis in patients with thrombotic or haemostatic defects

In a retrospective study of the 47 patients examined for thrombotic defects, 34 had prolonged euglobulin lysis times (ELT) with 27 of these also having elevated tissue-plasminogen activator inhibitor (t-PAI) activity. Twenty three of the 57 patients examined for possible bleeding problems had prolonged ELT with 15 of this group also having raised levels of t-PAI. There was a statistically greater (P less than 0.005) incidence of elevated t-PAI in the thrombotic group. The incidence of 40% patients with prolonged ELT in the haemostasis group was surprising and perhaps represents some compensatory mechanism to combat bleeding. Thus in vitro tests showed that a reduced capacity for fibrinolysis was present in diametrically opposed groups.

Tissue-type plasminogen activator. A review of its pharmacology and therapeutic use as a thrombolytic agent

Coronary arterial thrombolysis is becoming an established treatment of acute myocardial infarction. If given early enough, it recanalises occluded coronary arteries, salvages myocardial function and reduces mortality. A reduction of mortality in patients with acute myocardial infarction has now been demonstrated for streptokinase, anisoylated plasminogen streptokinase activator complex (APSAC; anistreplase) and recombinant tissue-type plasminogen activator (rt-PA). From the biochemical point of view, rt-PA has several attractive properties. It is similar to or identical with the physiological plasminogen activator in blood, it does not induce an antibody response, and it is more fibrin-specific than most or all other currently known thrombolytic agents. The rate of recanalisation of occluded coronary arteries with rt-PA is about 60 to 80% in non-comparative and placebo-controlled trials. rt-PA was similar in efficacy to urokinase in the only trial to compare the 2 agents. In 2 comparative trials evaluated by meta-analysis, rt-PA appeared more effective than streptokinase for the early recanalisation of occluded arteries. Both agents were comparable in their effects on left ventricular function in 2 comparative trials, but further study is needed to conclusively evaluate this parameter. Moreover, both agents reduce inhospital mortality, but much larger direct comparative trials are required before scientifically valid statements can be made on the relative clinical efficacy of available thrombolytic agents in terms of their effects on both morbidity and mortality. Thus, rt-PA constitutes a notable contribution of recombinant DNA technology to the treatment of thromboembolic disease, the main cause of death and disability in Western societies.

Prothrombotic abnormalities in inflammatory bowel disease

Inflammatory bowel disease (IBD) is known to be associated with a thrombotic tendency, which is often attributed to thrombocytosis, elevated fibrinogen, or decreased antithrombin III. We prospectively studied eight patients with IBD, seven of whom had little or no disease activity, to determine if they had any laboratory abnormality known to be associated with an increased risk of thrombosis. Abnormalities in fibrinolysis were noted in five patients: four with high plasminogen activator inhibitor levels and one with poor release of tissue plasminogen activator following venous occlusion. Circulating immune complexes were present in the sera of five patients. Fibrinogen was mildly elevated in one patient, and two patients had mild thrombocytosis. Decreased levels of antithrombin III, protein C, or protein S were not observed. There appears to be a high incidence of abnormalities in fibrinolysis in inactive IBD, which may contribute to the high frequency of thrombosis seen in IBD. The presence of circulating immune complexes may contribute to vascular injury and thrombosis.

Clotting activation and impairment of fibrinolysis in malignancy

Different coagulation and fibrinolysis parameters were investigated in 149 patients with metastatic and non-metastatic tumours and results were compared with those obtained in a healthy population. Results showed a significant increase of thrombin-antithrombin complexes, fibrinopeptide A (FPA) and fibrin monomers in the group of patients (p less than 0.001). There was also a significant prolongation of euglobulin lysis time (p less than 0.005) and an increase of plasminogen activator inhibitor activity (p less than 0.0001), fibrinogen degradation products (p less than 0.001), and D-dimer (p less than 0.05) in the group of patients as compared to controls; FPA levels were also increased in patients with metastases (p less than 0.005). This study demonstrates clotting activation, at the level of fibrinogen to fibrin conversion, and impairment of fibrinolysis in patients with malignancy.

Bleeding diathesis due to decreased functional activity of type 1 plasminogen activator inhibitor

We evaluated an elderly patient with a lifelong history of severe bleeding after surgery or trauma and with evidence of persistent hyperfibrinolysis. Routine coagulation studies were normal. Serum plasminogen (40%, normal 72-128%) and alpha 2-antiplasmin (55%, normal 70-145%) activities were decreased. Euglobulin clot lysis was abnormally shortened (50 min) and normalized in vitro with epsilon-aminocaproic acid (EACA). The patient was treated with EACA with prompt cessation of bleeding. Patient tissue-plasminogen activator (t-PA) levels in serum were normal (4.7 ng/ml, control 3.5-7.2) as detected by a two-site immunoradiometric assay (IRMA). Patient fibrinolytic inhibitor activities were assessed by incubating 125I-labeled t-PA with either whole blood or serum followed by SDS-PAGE and autoradiography to identify the resultant protease/protease inhibitor complexes. In comparison to blood samples obtained from normal donors, patient plasma and serum demonstrated reduced binding of a fast-acting plasminogen activator inhibitor to 125I-labeled t-PA. Immunoprecipitation experiments indicated diminished complex formation between type 1 plasminogen activator inhibitor (PAI-1) in patient serum and 125I-labeled t-PA. Low patient PAI-1 activity was confirmed in serum (0.36 U/ml, control 0.87-1.81; n = 3) and in platelet lysates using a functional IRMA to quantitate PAI-1 binding to immobilized t-PA. However, patient serum PAI-1 antigen was within the normal range when analyzed by IRMA (31.8 ng/ml, control 19.6-42.2); this result was confirmed in both serum and platelets by Western blot (n = 3). Mixing experiments using purified PAI-1 as well as patient and control sera did not show evidence for an inhibitor against PAI-1. We conclude that this patient's bleeding diathesis was due to hyperfibrinolysis and defective PAI-1. This patient provides the first demonstration of a link between decreased in vivo PAI-1 activity and disordered hemostasis, and supports a role for PAI-1 in control of vivo fibrinolysis.

Abnormal fibrinolysis in healthy male cigarette smokers: role of plasminogen activator inhibitors

The extrinsic fibrinolytic system and its response to cigarette smoking was studied in five healthy male smokers 35-45 years old. Tissue plasminogen activator (t-PA) release in response to venous occlusion was intact both at 8:00 A.M. and 3:00 P.M. Acutely smoking two cigarettes neither stimulated fibrinolysis nor changed levels of t-PA or plasminogen activator inhibitors. Functional plasminogen activator inhibitor (PA-I) levels and euglobulin lysis times were higher in the smoking group than in a control group matched for age, sex, and body mass. Antigenic levels of PA-I 1, the PA-I derived from vascular endothelial cells and platelets, were similar in both groups. While smoking did not acutely alter fibrinolysis in chronic smokers, these individuals had a high frequency of abnormal fibrinolysis characterized by high levels of PA-I activity. This abnormality is due to either high specific activity of PA-I 1 or to the presence of other antigenically distinct plasminogen activator inhibitors. Abnormal fibrinolysis may be one mechanism contributing to the thrombotic diathesis of cigarette smokers.

Thrombosis after hip replacement. Relationship to the fibrinolytic system

Twenty-nine patients were operated on with the Charnley hip prosthesis. All the patients were given dextran 70 as thrombosis prophylaxis. Deep vein thrombosis (DVT) was diagnosed in 10 patients with the radioactive fibrinogen uptake test and phlebography. Variables of coagulation and fibrinolysis were studied before and after surgery. Tissue plasminogen activator (t-PA) activity in the plasma without venous occlusion decreased postoperatively, but there was no correlation with DVT. The t-PA activity in venous occlusion plasma was not reduced after surgery. Plasminogen activator inhibitor (PAI-1) levels were raised immediately postoperatively. There was a significant correlation between preoperative PAI-1 activity and development of postoperative DVT (P less than 0.05). Patients developing DVT had higher levels of PAI-1 postoperatively than patients not developing DVT. A defective fibrinolytic system, as defined by high PAI-1 activity, thus predisposed to postoperative DVT.

Plasma plasminogen concentrations in clinically normal horses: the effect of age, sex and pregnancy

Plasma concentrations of plasminogen were determined in 28 clinically normal horses, including 13 adult geldings, five non-pregnant mares, five pregnant mares and five yearlings (two fillies, three geldings). Plasminogen was quantitated by a chromogenic assay based on activation of plasmin by excess urokinase. The overall mean plasma plasminogen for these horses was 2.94 +/- 0.54 CTA units (casein units, as defined by the Committee on Thrombolytic Agents) per ml. There were no significant differences in mean plasma plasminogen values among adult geldings, non-pregnant mares, pregnant mares or yearling horses (P greater than 0.05).

Familial hypofibrinolysis and venous thrombosis

Nine patients with, and 11 without, venous thromboses (DVT) from two families were studied. In family 1, four members with, and one without, DVT had t-PA activity below the lower limit of the controls (21.3 IU/ml, n = 19) after 20 min venous occlusion (VO). After VO t-PA antigen (t-PA:Ag) was below the lowest value of the controls (22.8 ng/ml) in all five cases with low t-PA activity. All the family members, both with and without thrombosis, had normal t-PA inhibitor activities (PAI). In family 2 t-PA activity after VO was low in three symptomatic and four asymptomatic family members. t-PA:Ag was also low in four of these. PAI level was normal in all but one family member. Mild type I von Willebrand's disease was discovered in four members of family 2. Deficient t-PA:Ag response was found in two of these. Antithrombin III, protein C and protein S were normal in both families. It is concluded that low fibrinolytic capacity, independent of PAI, is associated with familial DVT. Our data suggests autosomal dominant inheritance.