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The present study describes a simple, quantitative assay for measuring the lysis of a plasma clot. The principle of the assay is based on the release of Coomassie brilliant blue R-250 dye from the clot. Thirty microliters of freshly prepared Coomassie brilliant blue R-250 (1 mg/ml) was added to 200 microliters of diluted human plasma (1:5). After mixing, 100 microliters of thrombin (2.5 NIH units/ml) were added to mediate a plasma clot. One milliliter of streptokinase (0.1 mg/ml) was used as a plasminogen activator to initiate clot lysis. During the course of lysis, 100 microliters of soluble material were transferred to microtiter wells and the absorbance at 540 nm was determined as a measure of clot lysis. This assay was used to measure clot lysis in 18 human plasma samples. The colorimetric method (X) developed in this report correlated well with that determined using a conventional 125I-fibrinogen method (Y): Y = 0.83X + 7.98 (r = 0.91). more...

Human plasma lipoprotein(a) (Lp(a)) is a macromolecular complex that contains a protein homologous to plasminogen, the precursor of plasmin. We confirmed recent reports that Lp(a) is not activated by streptokinase or tissue plasminogen activator (t-PA) to yield plasmin-like activity. In testing the hypothesis that Lp(a) can competitively inhibit plasma clot lysis mediated by plasmin, the present study shows that Lp(a) significantly enhanced plasma clot lysis mediated by streptokinase or t-PA. The enhancement, however, was not observed in a plasmin-mediated clot lysis using a purified fibrinogen system. The addition of alpha-2-antiplasmin (alpha 2-plasmin inhibitor) to this system inhibited fibrinolysis; however, no inhibition was observed in the presence of Lp(a). One potential explanation for the Lp(a)-enhanced plasma clot lysis is that Lp(a) neutralizes the activity of alpha 2-antiplasmin present in plasma, thereby restoring the activity of plasmin to lyse the clot. more...