New Approaches to Improve tPA Mediated Therapeutic Effect in Stroke

 

Prof. Abd Al-Roof Higazi

 

Summary of the application.

 

Tissue plasminogen activator (tPA) is the only FDA-approved treatment for ischemic stroke, but its clinical use is compromised by its short therapeutic window, intracerebral hemorrhage (ICH) and neurotoxicity. Our published and preliminary data indicate that: 1) tPA induces dilation of the cerebral vasculature in-vivo in rats and pigs, 2) Vasodilation induced by tPA is abolished by inhibitors of the low density lipoprotein-related protein (LRP), antagonists of the integrin αvβ3 and by a PAI-1 derived hexapeptide that corresponds to amino acids 350-355 in PAI-1 (EEIIMD) and that's bind to the corresponding docking site is in the tPA, composed of amino acids 296 through 299, 3) LRP and αvβ3 form complexes in vascular cells as will in middle cerebral artery (MCA) extracts, 4) The concentration of LRP/ αvβ3 complex is regulated by tPA, 5) The vasoactivity of tPA is regulated by oxygen tension. Using a mechanical and thrombotic stroke model in rats in which MCA was obstructed, EEIIMD decreased the size of the infarcted area after tPA treatment and the frequency and intensity of intracranial hemorrhage. Neuroprotective effect was obtained when EEIIMD was given after stroke or before head trauma.   Our hypothesis is that tPA released from ischemic CNS, or given as part of the thrombolytic therapy, regulates cerebral vascular contractility; tPA induced cerebrovascular dilation, diverts blood from the ischemic area to healthy tissue leading to exacerbation of the hypoxic/anoxic conditions in the infarcted zone. In addition, tPA opens the blood-brain barrier (BBB), which exacerbates intracerebral edema and ICH. We hypothesize that inhibiting tPA signaling will prevent its deleterious effects and improve the clinical outcome of stroke and head trauma. In Specific Aim 1, we propose to study the effect of tPA on blood brain barrier (BBB) permeability and the capacity of its antagonists (EEIIMD), LRP and αvβ3.to neutralize its deleterious effect exerted on the BBB In Specific Aim 2, we propose to examine the capacity of tPA and LRP antagonists to inhibit its neurotoxic effect using mechanical and thrombotic models of stroke. Taken together, these studies will provide new insights into tPA-mediated neurotoxicity, identify a novel signal-transuding pathway and reveal potential classes of antagonists that should translate into novel tools to ameliorate the severity of stroke and improve its treatment and will be added to improve further the outcome obtained with EEIIMD alone(1).