Thrombolytic properties of Desmodus rotundus (vampire bat) salivary plasminogen activator in experimental pulmonary embolism in rats.

rDSPA alpha 1 (recombinant Desmodus salivary plasminogen activator alpha 1) is a recombinant protein corresponding to a natural plasminogen activator from the vampire bat Desmodus rotundus. The thrombolytic properties of rDSPA alpha 1 and tissue-type plasminogen activator (t-PA) were compared in a rat model of pulmonary embolism. Whole blood clots, produced in vitro and labeled with 125I-fibrinogen, were embolized into the lungs of anesthetized rats. Thrombolysis was calculated from the difference between initial clot radioactivity and that remaining in the lungs at 60 minutes. Blood was sampled for gamma counting, measurement of hemostatic factors, and plasminogen activator antigen levels. Thrombolysis at 3, 10, 30, and 100 nmol/kg intravenously (10% bolus, 90% over 60 minutes) amounted to 30% +/- 2%, 51% +/- 4%, 85% +/- 4%, 98% +/- 0% for rDSPA alpha 1 and 30% +/- 3%, 41% +/- 3%, 57% +/- 6%, 93% +/- 2% for t-PA (controls: 29% +/- 2%; mean +/- SEM, n greater than or equal to 6). t-PA at 100 nmol/kg significantly decreased fibrinogen, plasminogen, and alpha 2-antiplasmin levels by 33% +/- 7%, 38% +/- 8%, and 61% +/- 9%, whereas rDSPA alpha 1 at 100 nmol/kg only lowered alpha 2-antiplasmin significantly (by 29% +/- 6%). Compared with t-PA, rDSPA alpha 1 is the more potent and more clot selective (fibrin specific) thrombolytic agent. These results suggest that rDSPA alpha 1 may be safer and more efficacious than currently used thrombolytics.