Abnormalities in the cellular phase of blood fibrinolytic activity in systemic lupus erythematosus and in venous thromboembolism

Serum antibodies to distinct epitopes of the tissue-type plasminogen activator (t-PA) in patients with systemic lupus erythematosus

Defective fibrinolysis due to decreased tissue-type plasminogen activator (t-PA) activity is a well-established finding in patients with systemic lupus erythematosus (SLE). The possibility that this decrease in t-PA activity may be related to the presence of autoantibodies directed against t-PA, and the possible role of these autoantibodies in the pathophysiology of fibrinolysis in SLE, were investigated. Serum samples from 115 SLE patients and 63 normal volunteers were analyzed for the presence of such antibodies. The search for antibodies to t-PA was performed by means of several systems, allowing for the identification of epitopes presented in different conformational physical states of t-PA: free or associated to its inhibitor (PAI-1) in plasma, specifically bound to fibrin surface, or passively adsorbed to solid supports. Antibodies in variable amounts were detected by all systems used; however, t-PA activity was not inhibited by the IgG fraction of the positive sera in a fibrin-agar fibrinolysis system. Moreover, the demonstration of serum anti-t-PA antibodies was not associated with clinical or laboratory abnormalities related to vasoocclusive episodes. These results indicate that, as in the case of other autoantibodies, their detection in serum does not imply their direct participation in the pathophysiology of thrombosis in SLE.

Disturbances in the tissue plasminogen activator/plasminogen activator inhibitor (TPA/PAI) system in systemic lupus erythematosus

Increased thrombogenesis observed in systemic lupus erythematosus (SLE) is derived from multiple mechanisms, including: Enhanced coagulation factor VIII:VWf activity, lupus anticoagulants, anti-phospholipid antibodies, acquired deficiencies of natural anti-thrombotic mechanisms (protein C, protein S, anti-thrombin III), and impaired fibrinolytic mechanisms. We studied the fibrinolytic mechanisms of 18 patients with systemic lupus erythematosus, selected carefully to avoid other possible causes of abnormalities in the fibrinolytic activity. Despite the fact that the euglobulin lysis time in steady state was normal in all instances, disturbances in the tissue plasminogen activator/plasminogen activator inhibitor (TPA/PAI) system were found in all SLE patients: TPA activity was undetectable in all cases, whereas it was above 0.4 IU/ml in a control group. In 72 percent of patients, the undetectable TPA activity was correlated with abnormally high PAI activity; PAI levels were normal in all members of the control group, their mean value being 0.74 versus 8.63 IU/ml for SLE patients (P less than .01). Coagulation protein C deficiency was found in 3 patients (17%). Even though within normal range, fibrinogen levels were significantly higher in SLE than in normal controls (219 versus 192 mg/dl, P less than .01) and plasminogen levels were significantly higher in SLE than in controls (117 versus 78.2%, P less than .01). Cross-linked fibrin derivatives (D-D dimers) were negative in all patients with SLE. Sixty-eight percent of SLE patients had high levels of antiphospholipid antibodies, but no correlation with the disturbances of the TPA/PAI system was found. It is concluded that most patients with SLE display severe abnormalities in the TPA/PAI anti-thrombotic system and that these abnormalities may be related to the lupus thrombophilia, apparently multifactorial in its origin.

Cellular-phase fibrinolysis and coronary reperfusion during acute myocardial infarction: a study in patients receiving intravenous streptokinase-methylprednisolone therapy

Activation of plasma plasminogen to plasmin is the objective of current strategies for thrombolytic therapy. Although thrombolytic activity in blood involves a large cellular component as well as that in plasma, the contribution of this cellular phase to clinical thrombolysis has not been examined. Using a 125I-fibrin test tube assay, we determined blood, plasma and calculated cellular phase fibrinolytic activities in 39 patients with acute myocardial infarction before, immediately after, and at 2 hours after therapy with an intravenous streptokinase-methylprednisolone regimen. By coronary angiography and time to peak creatine phosphokinase levels, 32 patients had coronary reperfusion and 7 did not. Before streptokinase therapy, cellular phase activity of patients who reperfused was more than 2-fold greater than that of patients who did not reperfuse (p less than 0.001), while plasma activities were identical, suggesting that intrinsic cellular phase activity may be a determinant of the success of subsequent thrombolytic therapy. In both groups, in addition to the expected (and similar) increases in plasma activity, cellular phase activity increased when compared with pre-treatment values (+96% to +248%; p less than 0.001), with accompanying increase in blood granulocyte count (+23% to +65%), indicating that blood cells, as well as plasma, are major contributors to streptokinase-mediated fibrinolysis. Cellular phase stimulation was reproduced in a patient receiving streptokinase without methylprednisolone, and by addition of streptokinase to normal blood in vitro, indicating that streptokinase alone could account for these effects. Increased cellular phase activity in patients who reperfused after streptokinase was similar to that in those who did not reperfuse, when pre-treatment values were considered. These findings indicate that initial cellular phase activity in blood may determine subsequent fibrinolytic response, and that there is a significant cellular phase component to the fibrinolytic response to streptokinase, probably mediated by increased numbers of blood neutrophils, with a possible contribution from increased activity of individual neutrophils.

Fibrinolytic activity of normal human blood monocytes

Neutrophils (PMN) are important in the cellular phase of blood fibrino lytic activity (FA). The contribution of monocytes (MC), which have FA, is unclear. To determine the relative roles of these cells to activity in normal blood, we examined, by solid phase radiofibrin assay, FA of normal blood and plasma, and of purified PMN and MC, with and without plasminogen (PLG), mini-plasminogen (mPLG), the other major elastase fragment of PLG, or autologous plasma. PMN alone (0.5 x 10(6)/ml) had striking activity (292 +/- 25 SEM ng fibrin lysed/h; n = 10 normal subjects) while MC alone (0.5 x 10(6)/ml) had mean FA of 32 +/- 4 ng/h, which could be accounted for by contaminating PMN (36 +/- 8 ng/h). Thus, in a 1 h assay (when cellular FA accounts for 70-80% of FA in whole blood), normal numbers of MC (0.5 x 10(6)/ml) had no detectable FA when assayed with PLG or normal plasma. With longer assay times (2-6 h), PLG-dependent (plasminogen activator, PA) activity was demonstrated with mixtures of MC and PLG or plasma. This PA activity was released into the medium and required prior contact of MC and an intact, soluble PLG molecule for PA activity to be detected in medium (suggesting a PLG-MC triggering mechanism), since activity was reduced or absent when MC were exposed to mPLG, the other major elastase fragment of PLG, or solid phase PLG. Exposure of MC to solid phase fibrin did not result in PA release. MC PA activity was little affected by cycloheximide pretreatment, indicating preformed rather than newly synthesized PA. By SDS-PAGE and fibrin zymography, MC extracts revealed a single PA band with features of pro-urokinase (single chain urinary-type PA): Mr 55,000, inhibition by antiurokinase antibody (but not by anti-tPA), and resistance to inhibition by DFP. By ELISA assay, approximate normal monocyte content of this PA (as Mr 55,000 urokinase) was 0.03 fg (3.3 x 10(8) molecules) per cell.