The effects of a new tissue plasminogen activator analogue, Fb‐Fb‐CF, on cerebral reperfusion in a rabbit embolic stroke model

Abstract

Early fibrinolytic therapy with full molecular tissue plasminogen activator (t-PA) has been observed to be both angiographically and clinically effective when employed in animal stroke models. Preliminary clinical trials with t-PA are in progress. It is possible to refine t-PA by developing fragments or analogues of the drug. Using recombinant DNA technology in the Escherichia coli system, a t-PA analogue consisting of the catalytic fragment of t-PA and a dimer of the B fragment of staphylococcal protein A (Fb-Fb-CF) has been produced. Because this analogue has a long serum half-life of 90 minutes, we employed Fb-Fb-CF in a rabbit cerebral embolic stroke model to assess its efficacy as a reperfusion agent. When given as a bolus to 10 animals 15 minutes after embolization, Fb-Fb-CF produced angiographic cerebral reperfusion in 48 +/- 21 minutes (+/- SD), while in 8 saline-treated controls, reperfusion was not observed at 180 minutes in any animal (p less than 0.01). In another experiment reperfusion was demonstrated at 66 +/- 32 minutes in 11 animals treated with Fb-Fb-CF 90 minutes after embolization as compared with 100 +/- 25 minutes in 12 saline-treated controls (p less than 0.01). A small macroscopic hemorrhage within an infarct was seen in 1 Fb-Fb-CF-treated animal in the 15-minute experiment and in none of the controls. In the 90-minute experiment, macroscopic hemorrhagic infarction was seen in 4 Fb-Fb-CF-treated animals and in 3 controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of tissue plasminogen activator and heparin on cerebral ischemia in a rabbit model.

“…Del Zoppo et al, 30 working with baboons, found no increased liability to intracerebral hemorrhage in treated animals over controls when t-PA treatment was given after 3 hours of MCA occlusion followed by 30 minutes of reperfusion. On the other hand, Lyden et al 8 found intracerebral hemorrhages in rabbits receiving 3-5 mg/kg t-PA over 30 minutes, whether this was commenced at 10 minutes, 8 hours, or 24 hours after embolization, while Phillips et al 14 saw hemorrhagic transformation of strokes in rabbits receiving a bolus of 0.8 mg/kg t-PA analogue either 15 or 90 minutes after embolization. These findings leave it uncertain to what extent the total dose of t-PA, its speed of administration, and the length of subsequent survival contribute to the finding of hemorrhagic change within the infarct of animals treated with thrombolytic agents.…”

“…14 However, streptokinase proved ineffective in causing clot lysis in the cerebral arteries of a rabbit model, whether given immediately 11 or 3 hours 15 after embolization. Moreover, the use of either streptokinase 16 or urokinase 17 ' 18 in the treatment of acute cerebral infarction in humans was sometimes followed by the development of hematomas intracranially or elsewhere, as well as being without demonstrable therapeutic benefit.…”

“…Other investigators have since employed either a rabbit or a rat model, administering t-PA or an analogue at varying intervals after embolization of the MCA with either single or multiple thrombi of various sizes. 7101415 - 22 It appears that thrombolysis can be achieved in rabbits when 3 hours 14 or even longer 8^22 elapses from embolization to the administration of t-PA. However, the thrombi used in these studies were in most instances <24 hours old and all were "red" thrombi prepared by preclotting autologous or heterologous venous blood.…”

Delayed treatment with a t-PA analogue and streptokinase in a rabbit embolic stroke model.

“…Just before the onset of treatment, angiography was performed a third time to document persistent arterial occlusion. Angiography was performed again 30 minutes after treatment was finished and repeated four more times at by guest on May 11, 2018 http://stroke.ahajournals.org/ 4 This analogue consists of the catalytic fragment of the t-PA molecule, including amino acid 262 from the amino terminal of the molecule to the carboxyl terminal, and fragment B of staphylococcal protein A. The protein was expressed in Escherichia coli.…”

“…3 ' 4 Other investigators have observed that t-PA can reduce neurologic damage when given as long as 45 minutes after stroke onset. 5 Hemorrhagic side effects are of major concern, but in these animal models of stroke such side effects have not been a substantial problem.…”