Acoustic determination of performance and equivalence of plasminogen activators

A reliable method for the measurement of different plasminogen activators is of great interest for both manufacturing and clinical medicine. A one-step assay based on a thickness shear mode acoustic sensor has been developed for this purpose. Two separate mixtures of substrates (fibrinogen and plasminogen) and enzymes (thrombin and the plasminogen activator) were mixed, and placed on the acoustic sensor surface. During the assay, the resonant frequency of a quartz crystal oscillating in the thickness shear mode was measured and used to find a characteristic clot dissolution time, from the sample addition to the time at the maximum dissolution rate. Calibrations of the acoustic assay were done for tissue-type plasminogen activator (t-PA) as well as for the other plasminogen activators: urokinase (u-PA); streptokinase (SK) and staphylokinase (SAK). All gave relative standard deviations of about 12%. Since the same method was used for all of the activators, their activities were compared, resolving the differences between their unit definitions. Linear relationships were found between urokinase and streptokinase which activate plasminogen directly and between t-PA and staphylokinase which require fibrin as a cofactor. The relationship between the groups was found to curve, indicating the difference between the two mechanisms. The acoustic method, therefore, may be used as a rapid and cost-effective reference method for the standardization and comparison of different plasminogen activators.