Introduction
Thrombolysis by recombinant tissue plasminogen activator(rt-PA) is effective for acute cerebral ischemia. Because of short therapeutic time window and risk for hemorrhagic transformation(HT) which is most harmful side effect of thrombolysis, rt-PA has been used only limited number of patients. There are clinical demands for neuroprotective agents that can extend the therapeutic time window or reduce hemorrhage. On the other hand, FK-506 is reported to damage vascular endothelial cell and increase BBB permeability in animal experiment, and brings about cerebral vasculitis or cerebral hemorrhage in clinical cases. These results evoke us the concern with the adverse interaction of rt-PA and FK506 to increase the risk of hemorrhagic transformation. From these points of view, we evaluated therapeutic efficacy and influence against HT of combined therapy with rt-PA and FK506 for embolic model in rats.
Material and Methods
18pieces of 1 mm length from the fibrin rich portion in clots were gently infused via ICA of Sprague-Dawley rats(n=66). Intravenously, 0.3 mg/kg of FK506 was administered after 60 minutes from embolization. 10% of total 10 mg/kg of Alteplase was injected as a bolus and remainder was infused continuously for 30 minutes at 60, 90 and 120 minutes after embolization. Eight groups(n=6 respectively); control(saline only), namely FK506, Alteplase-60 min, Alteplase90 min, Alteplase120 min, FK506+Alteplase60 min, FK506+Alteplase90 min and FK506+Alteplase120 min, were compared by relative regional(rr) CBF using laser-doppler flowmetry, final infarct volume from TTC stain and HT using spectrophotometric assay of extraction. and lesion measurement of ADC and CBV map using MRI was undergone on other set of Alteplase90 min, FK506+Alteplase90 min, and control(n=6 respectively).
Results
After embolization, rrCBF decreased to about 20% in all groups. Control and FK506 group shows persistent rrCBF decline for at least six hours. Administration of rt-PA partially restored rrCBF to about 70% of pre-ischemic level. Combined treatment of FK506 did not alter the restoration of rrCBF. In the groups rt-PA alone at 60 minutes after embolization, infarct volume were significantly smaller than control group, however group of 90 and 120 minutes after embolization did not ameliorate the infarction. In the group of combined FK506+rt-PA at 60 and 90 minutes, infarct volume were significantly smaller than control group, however group of 120 minutes did not ameliorate the infarction. FK506 alone did not diminish the infarct volume compared with control. FK-506 did not affect the hemorrhagic volume on each pair of the group with identical rt-PA administration schedules. In MRI study, both ADC and rCBV lesion volumes before rt-PA administration did not differ among three groups. In rt-PA alone group, final infarct volume, which revealed by TTC stain, was significantly smaller than rCBV lesion volume, but not ADC lesion volume. Final infarct volume of combined therapy group was significantly smaller than both ADC and rCBV lesion volume. Final infarct volume of combined therapy was significantly smaller than that of control.
Conclusions
FK506 extend therapeutic time windows of thrombolysis without increasing risk of hemorrhagic transformation. FK506 did not ameliorated ADC revealed ischemic lesion during ischemia, however salvaged part of ADC revealed lesion which was destined to infarct in rt-PA alone treated rat.