Multicentre Evaluation of Commercial Kit Methods: Plasminogen Activator Inhibitor Activity

Measuring Fibrinolysis

Physiological fibrinolysis under normal conditions progresses slowly, in contrast to coagulation which is triggered rapidly to stop bleeding and defend against microbial invasion. Methods to detect fibrinolysis abnormalities are less simple and poorly standardized compared with common coagulation tests. Fibrinolysis can be accelerated by preparing euglobulin from plasma to reduce endogenous inhibitors, or by adding plasminogen activators to normal plasma. However, these manipulations complicate interpretation of results and diagnosis of a "fibrinolysis deficit." Many observational studies on antigen levels of fibrinolysis inhibitors, plasminogen activator inhibitor 1 or thrombin-activatable fibrinolysis inhibitor, zymogen or active enzyme have been published. However, conclusions are mixed and there are clear problems with harmonization of results. Viscoelastic methods have the advantage of being rapid and are used as point-of-care tests. They also work with whole blood, allowing the contribution of platelets to be explored. However, there are no agreed protocols for applying viscoelastic methods in acute care for the diagnosis of hyperfibrinolysis or to direct therapy. The emergence of SARS-CoV-2 and the dangers of associated coagulopathy provide new challenges. A common finding in hospitalized patients is high levels of D-dimer fibrin breakdown products, indicative of ongoing fibrinolysis. Well-established problems with D-dimer testing standardization signal that we should be cautious in using results from such tests as prognostic indicators or to target therapies.

Measuring fibrinolysis: from research to routine diagnostic assays

Development and standardization of fibrinolysis methods have progressed more slowly than coagulation testing and routine high-throughput screening tests for fibrinolysis are still lacking. In laboratory research, a variety of approaches are available and are applied to understand the regulation of fibrinolysis and its contribution to the hemostatic balance. Fibrinolysis in normal blood is slow to develop. For practical purposes plasminogen activators can be added to clotting plasma, or euglobulin prepared to reduce endogenous inhibitors, but results are complicated by these manipulations. Observational studies to identify a 'fibrinolysis deficit' have concluded that excess fibrinolysis inhibitors, plasminogen activator inhibitor 1 (PAI-1) or thrombin-activatable fibrinolysis inhibitor (TAFI), zymogen or active enzyme, may be associated with an increased risk of thrombosis. However, results are not always consistent and problems of adequate standardization are evident with these inhibitors and also for measurement of fibrin degradation products (D-dimer). Few methods are available to investigate fibrinolysis under flow, or in whole blood, but viscoelastic methods (VMs) such as ROTEM and TEG do permit the contribution of cells, and importantly platelets, to be explored. VMs are used to diagnose clinical hyperfibrinolysis, which is associated with high mortality. There is a debate on the usefulness of VMs as a point-of-care test method, particularly in trauma. Despite the difficulties of many fibrinolysis methods, research on the fibrinolysis system, taking in wider interactions with hemostasis proteins, is progressing so that in future we may have more complete models and better diagnostic methods and therapeutics.

The coagulation system in humans

Complex, interrelated systems exist to maintain the fluidity of the blood in the vascular system while allowing for the rapid formation of a solid blood clot to prevent hemorrhaging subsequent to blood vessel injury. These interrelated systems are collectively referred to as haemostasis. The components involved in the haemostatic mechanism consist of vessel walls, platelets, coagulation factors, inhibitors, and the fibrinolytic system. In the broadest sense, a series of cascades involving coagulation proteins and enzymes, as well as cell surfaces (platelets and endothelial cells), work together to generate thrombin, the key enzyme in coagulation, subsequently leading to the formation of a fibrin clot. However, there also exist direct and indirect inhibitors of thrombin to ensure that clot formation does not go uncontrolled. Once the fibrin clot is formed, the fibrinolytic system ensures that the clot is lysed so that it does not become a pathological complication. Taken together, the systems exist to balance each other and maintain order. The balance of coagulation and fibrinolysis keeps the haemostatic system functioning efficiently.

Effect of modified dairy fat on fasting and postprandial haemostatic variables in healthy young men

It has been suggested that milk fat, due to its content of saturated fatty acids, may have a thrombogenic effect. In the present study the fatty acid profile of milk fat was modified by changing the feeding regimens of cows and the effect on haemostatic variables of a diet containing the modified milk fat (M) was compared with that of a diet containing milk fat of typical Danish composition (D). In the modified fat 16% of the saturated fatty acid (C12–C16) content was replaced mainly by oleic acid. Eighteen subjects were fed on two strictly controlled isoenergetic diets containing 40% energy from total fat (30% energy from the test fats) for periods of 4 weeks in a study with a crossover design. Fasting samples were taken in the last week of each study period. Postprandial samples were taken on day 21, 3 h after lunch (n18), and on the last day of the study 2, 4, 6 and 8 h after a fat load containing 1·2 g of one of the milk fats/kg body weight (n8). After 4 weeks' dietary intervention fasting plasma factor VII coagulant (FVIIc) activity, tissue-type plasminogen activator (t-PA) activity, plasminogen activator inhibitor (PAI-1) antigen and β-thromboglobulin did not differ between diets M and D. Postprandially FVIIc and t-PA activities increased (P< 0·001) and PAI-1 antigen and PAI-1 activity decreased (P< 0·001) as compared with fasting values, regardless of diet. After the fat load, the postprandial increase in FVIIc was marginally lower after diet M than diet D (diet effect,P< 0·05). In conclusion, the modified milk fat obtained by the applied feeding strategy had virtually the same effects on haemostatic variables as conventional milk fat.

A 1-year study to compare the hemostatic effects of oral contraceptive containing 20 μg of ethinylestradiol and 100 μg of levonorgestrel with 30 μg of ethinylestradiol and 100 μg of levonorgestrel

OBJECTIVES

To comparatively evaluate the impact of a balanced one-third dose-reduced oral contraceptive on hemostatic variables.

METHODS

In an open-label, randomized study, a dose-reduced oral contraceptive containing 20 microg of ethinylestradiol (EE) and 100 microg of levonorgestrel (LNG) was compared with a reference preparation containing 30 microg of EE and 150 microg of LNG. One-year data were obtained from 48 volunteers.

RESULTS

The direction and magnitude of the changes (increase or decrease) in most of the hemostatic variables were similar in both treatment groups. The majority of changes of all investigated variables remained within the reference ranges of variation. The procoagulatory variables increased to some extent from baseline to treatment cycle 13, while the anticoagulatory variables slightly decreased. In particular, thrombin turnover measured by prothrombin fragments 1+2 increased during treatment by 35% in the 20 microg of EE group and by 38% in the 30 microg of EE group. Statistically significant differences between the two treatment groups were found only for TAT. For the profibrinolytic variables, plasminogen was increased by 42% (20 microg of EE) and 49% (30 microg of EE). While the plasma levels of tPA antigen were reduced during treatment, the levels of its activity were increased by 54% (20 microg of EE) and 20% (30 microg of EE). For PAI, both antigen and activity were decreased, somewhat more pronounced with 20 microg of EE. D-Dimer remained virtually unchanged. Finally, the median FbDP levels were elevated by 30% (20 microg of EE) and 38% (30 microg of EE).

Measuring plasminogen activator inhibitor activity in plasma by two enzymatic assays

We compared two methods that measure plasminogen activator inhibitor (PAI) activity in plasma based on the ability of PAI to inhibit tissue plasminogen activator (tPA) or urokinase (uPA) in order to determine which method most accurately measures plasma PAI activity after stressors, like hemorrhage. Plasma PAI activity was significantly elevated after hemorrhage in both assays. Using standard curves derived from rhPAI-1, we found that the tPA-PAI assay was more sensitive than the uPA-PAI assay. However, we measured a 10-fold difference in PAI activity as measured between assays, suggesting that some endogenous plasma constituents (tPA, uPA, plasminogen or plasmin) may interfere with the accurate determination of PAI activity. Increasing the amount of plasma in each assay led to a progressive increase in PAI activity. However, removing either tPA or plasminogen from the tPA-PAI assay unmasked the presence of some endogenous tPA and plasminogen. Furthermore, increasing plasma volume in either assay increases measured plasma tPA, but not uPA. Finally, plasma tPA is elevated after hemorrhage, whereas plasma uPA is not. These results suggest that endogenous tPA and plasminogen may interfere with the measurement of plasma PAI activity in the tPA-PAI assay after hemorrhage or other stresses. The uPA-PAI assay does not have this confounding problem because endogenous uPA does not interfere with the assay, nor does it rise during hemorrhage.

The relationships between insulin and plasminogen activator inhibitor 1 levels: assessment in groups of subjects with dyslipidaemia and hypertension

Elevated plasminogen activator inhibitor-1 (PAI-1) levels have been described in some populations to associate with hyperinsulinaemia in the metabolic syndrome which predisposes to coronary heart disease (CHD). This association, if consistently present, could provide more evidence for a synergistic role for insulin resistance and altered fibrinolysis in the pathogenesis of CHD. To test the hypothesis further therefore, we explored the relationships between the fasting levels of insulin and PAI-1 and lipids in groups of non-diabetic Arab subjects classified as: A: normolipidaemic (n = 148); B: hyperlipidaemic: (n = 99), subdivided into - C: normotensive (n = 71) and D: hypertensive (n = 28); and E: patients with CHD (n = 12). In Group A, fasting insulin (FI) was 7.2+/-(SD) 3.4 mU/l, PAI-1 30.6+/-9.7 ng/ml, both levels significantly lower (P < 0.05) than in Group B as a whole (FI 9.7+/-5.2, PAI-1 36.9+/-10.6), or as normotensive Group C (FI 9.4+/-5.4, PAI-1 36.7+/-10.3) or hypertensive Group D (FI 10.9+/-4.8, PAI-1 37.2+/-11.5). These values were highest in the hyperlipidaemic hypertensive Group D. There were no significant differences relative to the hyperlipidaemic phenotype of predominant hypercholesterolaemia, hypertriglyceridaemia or mixed hyperlipidaemia. PAI-1 (34.7+/-13.8) and FI (7.0+/-2.4) levels in Group E with CHD were similar to those of Group A but lower than values seen in Groups B, C and D. Consistent positive correlations (r = 0.32-0.41, P <0.01) were demonstrable in all the groups between PAI-1 and triglycerides levels. There were also significant correlations between insulin and PAI-1 (r = 0.20, P<0.1) in all the subjects (grouped as a whole, n = 259) and in normolipidaemic Group A (r = 0.29, P < 0.01) but not in any of the hyperlipidaemic groups or in patients with CHD. This study therefore suggests that levels of insulin and PAI-1 are increased in hyperlipidaemic subjects, particularly when also hypertensive. The further observation of significant correlations between insulin and PAI-1 levels only in normolipidaemic subjects and not those who were hyperlipidaemic or with CHD is at variance with observations in Caucasians in whom strong positive correlations between insulin and PAI-1 had suggested that elevated PAI-1 levels should constitute one more component of the metabolic syndrome which strongly predisposes to CHD. Whether this is a racial variation or an artifact of the insulin/PAI-1 assay methodology is unclear and deserves further study.

Range of antinuclear antibodies in "healthy" individuals

OBJECTIVE

To determine the range of antinuclear antibodies (ANA) in "healthy" individuals compared with that in patients with systemic lupus erythematosus (SLE), systemic sclerosis (SSc; scleroderma), Sjögren's syndrome (SS), rheumatoid arthritis (RA), or soft tissue rheumatism (STR).

METHODS

Fifteen international laboratories experienced in performing tests for ANA by indirect immunofluorescence participated in analyzing coded sera from healthy individuals and from patients in the 5 different disease groups described above. Except for the stipulation that HEp-2 cells should be used as substrate, each laboratory used its own in-house methodology so that the data might be expected to reflect the output of a cross-section of worldwide ANA reference laboratories. The sera were analyzed at 4 dilutions: 1:40, 1:80, 1:160, and 1:320.

RESULTS

In healthy individuals, the frequency of ANA did not differ significantly across the 4 age subgroups spanning 20-60 years of age. This putatively normal population was ANA positive in 31.7% of individuals at 1:40 serum dilution, 13.3% at 1:80, 5.0% at 1:160, and 3.3% at 1:320. In comparison with the findings among the disease groups, a low cutoff point at 1:40 serum dilution (high sensitivity, low specificity) could have diagnostic value, since it would classify virtually all patients with SLE, SSc, or SS as ANA positive. Conversely, a high positive cutoff at 1:160 serum dilution (high specificity, low sensitivity) would be useful to confirm the presence of disease in only a portion of cases, but would be likely to exclude 95% of normal individuals.

CONCLUSION

It is recommended that laboratories performing immunofluorescent ANA tests should report results at both the 1:40 and 1:160 dilutions, and should supply information on the percentage of normal individuals who are positive at these dilutions. A low-titer ANA is not necessarily insignificant and might depend on at least 4 specific factors. ANA assays can be a useful discriminant in recognizing certain disease conditions, but can create misunderstanding when the limitations are not fully appreciated.

Increased circulating plasminogen activator inhibitor-1 in patients with patent femoro-distal venous bypass

Veins used for arterial bypass grafting undergo wall remodeling when exposed to altered flow, which may affect fibrinolytic mechanisms and subsequently the fate of the graft. Our aim was to study the extent of blood coagulation and fibrinolysis activation in 27 patients with patent grafts two years after femoro-distal bypass surgery. The two matched control groups included 10 and 19 conservatively treated patients having similar degree of arterial insufficiency (mean ankle/brachial blood pressure index) as the bypass group pre- and post-operatively, respectively. Plasma samples for coagulation and fibrinolysis activation were determined using ELISA and chromogenic assays. When compared with the control groups circulating tissue-type plasminogen activator antigen, and especially plasminogen activator inhibitor type-1, PAI-1 antigen and activity were significantly increased, the mean increase ranging between 54% and 140% in the bypass group. Thrombin-antithrombin III complex, fibrinogen, and C-reactive protein, did not differ, while triglycerides were elevated in the bypass group. Ten patients in the bypass group were insulin resistant, but this did not explain the differences in the fibrinolytic parameters between the bypassed and control patients. Patients with peripheral vein grafts had upregulation of PAI-1 in their circulation implying reduced fibrinolytic capacity. Increased PAI-1, a risk factor for venous thrombosis, might reflect developing intimal hyperplasia, and it remains to be studied whether upregulation of PAI-1 in venous grafts associates with graft failure.

Blood and tissue fibrinolytic profiles in patients with colorectal carcinoma

In patients with colorectal cancer, profound alterations of the plasminogen activator system have been described at the tumor level, but conflicting results have been obtained for fibrinolytic parameters in plasma. Components of the fibrinolytic system, including tissue-type and urokinase-type plasminogen activators and their inhibitors type 1 and 2, were measured in tissue and/or plasma from 41 patients with colorectal cancer and in 40 controls. Procoagulant activity of freshly isolated mononuclear cells (basal activity) and the procoagulant activity and fibrinolytic proteins produced by the cells after incubation for 18 h without exogenous stimulation were also evaluated. Malignant tissue extracts had significantly higher levels of urokinase-type plasminogen activator and plasminogen activator inhibitor-1, but lower levels of tissue-type plasminogen activator than normal mucosa. Plasminogen activator inhibitor-1 alone was higher in advanced (Dukes' stages C + D) than limited (B) tumors. Plasminogen activator inhibitor-2 was not different in malignant tissue and normal mucosa. Plasma levels of plasminogen activator inhibitor-1 antigen were significantly increased in cancer patients compared with controls, but there were no differences in tissue-type and urokinase-type plasminogen activator, in plasminogen activator inhibitor-2, and D-dimer levels. Intra-patient analysis revealed no significant correlation between tumor and plasma levels of plasminogen activators or type 1 inhibitor. Tissue-type plasminogen activator, but not the urokinase type or inhibitor type 1, was higher in venous than in arterial blood collected at the tumor site during surgery. Basal procoagulant activity of mononuclear cells and the procoagulant activity and inhibitor type-2 produced by the cells after short-term culture were comparable in patients and controls. These findings indicate that, at least in our patients with colorectal cancer, the profound changes occurring at tumor level are barely detectable in the blood. Thus, the clinical relevance of plasma fibrinolytic parameters, especially urokinase-type plasminogen activator antigen, as tumor markers in colorectal cancer remains to be established.

Molecular characterization of plasminogen activators in human gingival crevicular fluid

Plasminogen activators (PAs), a family of serine proteases, and their inhibitors (PAIs) are important in fibrinolysis, wound healing and tissue remodelling. Previous studies revealed differences in the localization of PA activity between healthy and diseased gingival tissues, suggesting that PAs and PAIs could play a part in periodontal homeostasis and disease. PAs and PAIs are synthesized by most of the cells types making up the periodontium and can be identified in gingival crevicular fluid (GCF). These studies sought to characterize the molecular species of PAs and their inhibitors in GCF collected from clinically healthy sites. PA enzymatic activity in GCF samples demonstrated by fibrin zymography revealed the presence of only tissue-type PA (tPA) activity. No urokinase-type PA (uPA) enzymatic activity was detected. tPA enzymatic activity appeared predominantly as an uncomplexed 70-kDa species, although some samples contained enzyme-inhibitor complexes. Quantitation of total tPA by enzyme immunoassay showed a mean concentration of 1.6 ng/microl. Analysis of GCF samples for uPA by immunoblotting and enzyme immunoassay disclosed the presence of small amounts of uPA (0.2 ng/microl), which were present predominantly in activator-inhibitor complexes. Immunoblotting showed specific PAI-2 immunoreactivity bands in high molecular-weight complexes and low molecular-weight degradation products, but less than nanogram amounts of free PAI-2 molecules. Enzyme immunoassay revealed that PAI-2 was present in an at least a seven times greater amount than PAI-1. These observations support the hypothesis that PA-generated proteolysis and its regulation by endogenous inhibitors has a role in the diverse biochemical mechanisms underlying periodontal physiology and pathology including host-microbial interaction, polymorphonuclear leucocyte infiltration, turnover and migration of epithelial cells, connective tissue degradation and remodelling, fibrinolysis and wound healing.