Evaluation for Antithrombotic Agents by a Thrombotic Model in Animals

Abstract

To investigate cerebral infarction and intracranial hemorrhage (ICH) in relation to antithrombotic agents, we established an animal stroke model induced by using a combination of a photosensitive dye and local green photoillumination. Microplasmin (μPli), a derivative of plasmin lacking the five "kringle" domains, was administered in this model, and its effect was studied using magnetic resonance imaging. μPli treatment reduced cerebral damage 24 h after middle cerebral artery occlusion; it also reduced the expansion of the positive area on perfusion-weighted images between 1 and 24 h and the degree of neurological deficits. Tissue-type plasminogen activator (t-PA), a serine proteinase that converts plasminogen to plasmin, has been approved for treating acute ischemic stroke, but delayed treatment is associated with increased risk of ICH. Plasmin participates in the degradation of fibrin, causing clot lysis, and of various extracellular matrix proteins, either directly or via the activation of matrix metalloproteinases (MMPs). In this study, we observed that MMP-3 is relatively important in the enhanced risk of ICH induced by delayed t-PA treatment for ischemic stroke. In particular, the binding of t-PA with low-density lipoprotein receptor-related protein (LRP) results in the release of MMP-3 by endothelial cells. LRP production is upregulated in endothelial cells exposed to ischemia, and elevated LRP levels have been implicated in the increased ICH risk associated with delayed t-PA treatment. This implies that the t-PA/LRP/MMP-3 pathway may be a suitable target for developing strategies to improve the therapeutic efficacy of t-PA in acute ischemic stroke.