Depletion of circulating α2-antiplasmin by intravenous plasmin or immunoneutralization reduces focal cerebral ischemic injury in the absence of arterial recanalization

In the absence of arterial recanalization, thrombolytic agents induce a dose-related extension of focal cerebral ischemic injury (FII) in experimental animals. However, Fil is smaller in mice lacking alpha (2)-antiplasmin (alpha (2)-AP), the physiologic inhibitor of plasmin, suggesting its depletion might reduce FII in the absence of reperfusion. Therefore, the effect of human plasmin (Pli), human miniplasmin (mPli), and an Fab fragment neutralizing murine alpha (2)-AP (Fab-4H9) on FII after middle cerebral artery (MCA) ligation was studied in mice and in hamsters. In BALB/c mice, the median FII after 24 hours was 28 muL (range, 20-34) (n = 10) with saline and 23 muL (range, 17-26) (n = 9) with a single bolus of 0.07 mg Pli, given after MCA ligation (P =.010), which reduced alpha (2)-AP to 44% and fibrinogen from 0.75 to 0.44 g/L. FII was 20 muL (range, 13-26) (n = 6, P =.025) with 0.2 mg mPli and was 24 rhoL (range, 20-27) (n = 6, P =.020) with 1.7 mg Fab-4H9. Neuronal atrophy and reduction of laminin immunoreactivity were comparably observed in the infarct area after saline and Pli. In hamsters, a single bolus injection of 1 mg Pli, after MCA ligation, depleted alpha (2)-AP and fibrinogen and reduced Fil at 24 hours from 20 muL (range, 9.9-38) (n = 6) to 7.0 muL (range, 0.44-31) (n = 7, P =.032). Thus, reduction of circulating alpha (2)-AP, with a single bolus of plasmin or of a neutralizing antibody fragment, significantly reduced FII after MCA ligation in mouse and hamster models, suggesting that, provided these observations can be extrapolated to human beings, transient depletion of circulating alpha (2)-AP might reduce ischemic stroke in the absence of reperfusion. (Blood. 2001;97:3086-3092) (C) 2001 by The American Society of Hematology.