Abstract 398: Inhibition of Tissue Factor Reduces Thrombosis and Inflammation Without Increased Bleeding in a Mouse Model of Ischemic Stroke

Abstract

Tissue factor (TF), the primary initiator of the extrinsic coagulation cascade, is highly expressed by astrocytes surrounding blood vessels in the central nervous system. Using mouse models of hemorrhagic and ischemic stroke, we previously demonstrated that astrocyte TF plays a critical role in brain hemostasis while also contributing to neuronal damage. Importantly, using mice with different levels of astrocyte TF expression, we determined that an astrocyte TF activity around 5% of the wild type level was sufficient to limit bleeding in hemorrhagic stroke and at the same time was low enough to reduce infarct size and behavioral deficits in ischemic stroke, without increased hemorrhagic transformation. Therefore, we hypothesized that pharmacologic inhibition of TF may improve outcomes after ischemic stroke and have a wide safety margin. To test this hypothesis, C56Bl/6J mice were subjected to middle cerebral artery occlusion (MCAO) for 1 hour followed by 24 hours of reperfusion. Inhibitory rat anti- mouse TF antibody (1H1) and control IgG were administered as a bolus intraperitoneal injection immediately after ischemia. Inhibition of TF dose-dependently reduced brain infarct size in female mice (36.6±1.4% of total brain volume in IgG group [n=19] vs 28.3 ± 1.7% in 25mg/kg 1H1 group [n=9, p<0.01] and 18.5 ±2.3% in 75mg/kg 1H1 group [n=8, p<0.001]; mean±SEM). Importantly, 1H1 did not exacerbate hemorrhagic transformation during the reperfusion phase. Furthermore, TF inhibition significantly reduced microvascular thrombosis (analyzed by fibrin staining), expression of inflammatory markers in the injured brain (IL-6, MCP-1 and KC levels- analyzed by ELISA) and attenuated behavioral deficit after ischemic stroke. Subjecting male mice to the same MCAO condition resulted in partial lethality in IgG treated group (4 out of 6 mice died with 24 hours) which was prevented by 1H1 (25mg/kg) treatment (0 out of 5, Log-rank test p=0.031). Altogether, our data suggest that the overabundance of astrocyte TF expression resulted from selective pressure to limit intracerebral hemorrhage after traumatic brain injury, but in the modern era poses the additional risk of increased injury during ischemic stroke.