Microplasmin. A novel thrombolytic that improves behavioral outcome after embolic strokes in rabbits

Background and Purpose-It has been proposed that the novel thrombolytic microplasmin may be useful in the treatment of ischemic stroke In the present study the effects and safety profile of microplasmin were evaluated in 2 rabbit embolic stroke models that have been used successfully to develop tissue plasminogen activator (tPA) as the only Food and Drug Administration-approved treatment for stroke The rabbit small clot embolic stroke model (RSCEM) and rabbit large clot embolic stroke model (RLCEM) were used to determine the potential neuroprotective properties and safety profile of microplasmin respectively after an embolic stroke Methods-Rabbits were embolized by injecting small blood clots (RSCEM) or large blood clots (RLCEM) into the cerebral circulation For the RSCEM 126 rabbits were included with behavioral analysis conducted 24 hours later allowing for determination of the effective stroke dose (ES50) or clot amount (milligrams) that produces severe neurological deficits in 50% of rabbits For RLCEM safety study analysis 47 rabbits were included with postmortem analyses consisting of assessment of hemorrhage and infarct rate and size In test animals microplasmin was infused intravenously 60 minutes after embolization whereas control rabbits were given infusions of the saline/Plasma Lyte vehicle with all assessments performed in a blinded fashion Results-In the RSCEM a drug is considered neuroprotective if it significantly increases the ES50 compared with the vehicle treated control group The ES50 of the vehicle treated control group 24 hours after embolization was 1 36 0 42 mg (n=38) Microplasmin infused starting 60 minutes after embolization increased the ES50 to 2 32+/-0 57 (n=21) 189+/-0 48 (n=21) 2 81+/-0 55 (n=22) and 1 89+/-0 28 mg (n=24) for the 1 2 4 and 8 mg/kg doses respectively There was a statistically significant behavioral improvement in the 4 mg/kg dose arm (P=0 040) The microplasmin dose of microplasmin that was statistically significant (4 mg/kg) was subsequently determined to be safe in the RLCEM because it did not increase the incidence of hemorrhages (56%) compared with vehicle treated rabbits (63%) nor did it significantly alter hemorrhage volume infarct rate or infarct volume Conclusions-The present study shows that microplasmin improves behavioral rating scores in the RSCEM when administered 60 minutes after embolization at a dose that does not increase hemorrhages in the RLCEM This is in contrast to tPA which significantly enhances the hemorrhage rate in the RLCEM.