Agents that restore vascular patency in
stroke also increase the risk of
intracerebral hemorrhage (ICH). As
Factor IXa is a key intermediary in the intrinsic pathway of coagulation, targeted inhibition of
Factor IXa-dependent coagulation might inhibit microvascular
thrombosis in
stroke without impairing extrinsic
hemostatic mechanisms that limit ICH. A competitive inhibitor of native
Factor IXa for assembly into the
intrinsic Factor X activation complex, Factor IXai, was prepared by covalent modification of the
Factor IXa active site. In a modified
cephalin clotting time assay, in vivo administration of Factor IXai caused a dose-dependent increase in time to clot formation (3.6-fold increase at the 300 micrograms/kg dose compared with vehicle-treated control animals, P < 0.05). Mice given Factor IXai and subjected to
middle cerebral artery occlusion and reperfusion demonstrated reduced microvascular
fibrin accumulation by immunoblotting and immunostaining, reduced 111In-labeled platelet deposition (42% decrease, P < 0.05), increased cerebral perfusion (2.6-fold increase in ipsilateral blood flow by
laser doppler, P < 0.05), and smaller
cerebral infarcts than vehicle-treated controls (70% reduction, P < 0.05) based on triphenyl tetrazolium
chloride staining of serial cerebral sections. At therapeutically effective doses, Factor IXai was not associated with increased ICH, as opposed to
tissue plasminogen activator (tPA) or
heparin, both of which significantly increased ICH. Factor IXai was cerebroprotective even when given after the onset of
stroke, indicating that microvascular
thrombosis continues to evolve (and may be inhibited) even after primary occlusion of a major cerebrovascular tributary.