PAI-1-resistant t-PA: low doses prevent fibrin deposition in rabbits with increased PAI-1 activity

The present study compared the activities of recombinant tissue-type plasminogen activator (t-PA) and a plasminogen activator inhibitor-1 (PAI-1)-resistant variant t-PA (Kt-PA, KHRR 296-299 AAAA) in preventing renal fibrin deposition in rabbits with elevated PAI-1 activity. In this model, all rabbits were infused with endotoxin (10 micrograms/kg), followed by initiation of thrombin (130 U/kg) 4 hours later, when plasma PAI-1 activity was greater than 200 arbitrary units (AU)/mL (baseline, < 3 AU/mL). Thirty minutes after completion of the 1-hour thrombin infusion, rabbits were killed and the kidneys fixed and stained for identification of fibrin deposition. Rabbits received one of the following treatments initiated 30 minutes before thrombin and continued during the 1-hour thrombin infusion: (1) saline (n = 7); (2) low-dose t-PA (17 micrograms/kg, n = 4); (3) higher-dose t-PA (170 micrograms/kg, n = 4); or (4) low-dose Kt-PA (17 micrograms/kg, n = 6). Fibrin deposition occurred in 86% and 100% of the rabbits receiving saline or low-dose t-PA, respectively. Fibrin deposition did not occur in any of the rabbits receiving low-dose Kt-PA or higher-dose t-PA. Low-dose Kt-PA and higher dose t-PA also caused a reduction in fibrin deposition when infused after thrombin administration had been completed. The data provide in vivo evidence that Kt-PA is more effective than t-PA in preventing fibrin deposition in an animal model that combines thrombogenic stimulation with increased PAI-1 activity.