Spatiotemporal evolution of blood brain barrier damage and tissue infarction within the first 3h after ischemia onset

Blood brain barrier (BBB) damage that occurs within the thrombolytic time window is increasingly appreciated to negatively impact the safety and efficacy profiles of thrombolytic therapy for ischemic stroke. However, the spatiotemporal evolution of BBB damage in this early stroke stage and the underlying mechanisms remain unclear. Here, we investigated the topographical distribution of BBB damage and its association with tissue injury within the first 3 h after ischemia onset and the roles of matrix metalloproteinase (MMP)-2/9 in this process. Rats were subjected to 1, 2, or 3 h of middle cerebral artery occlusion (MCAO) followed by 10 min reperfusion with fluorescence-labeled dextran as BBB permeability marker. Acute tissue infarction was evidenced by staining defect with triphenyltetrazolium chloride (TTC). Cerebral blood flow (CBF) was measured by magnetic resonance imaging. MMP-2/9 were assessed by gel and in situ zymography. After 2-h MCAO, dextran leakage was seen in the ischemic ventromedial striatum and the preoptic area which showed ~70% CBF reduction, and expanded to other MCA regions including the cortex after 3-h MCAO. Interestingly, high (2000 kDa) and low (70 kDa) molecular weight dextrans displayed almost identical leakage patterns. Different from BBB damage, tissue infarction was first seen in the ischemic dorsal striatum and the parietal/insular cortex which experienced ~90% CBF reduction. Increased gelatinolytic activity colocalized with dextran leakage, and MMP-2 was found to be the major enzymatic source on gelatin zymograms. Pretreatment with MMP inhibitor GM6001 significantly reduced dextran leakage induced by 2-h and 3-h MCAO. Taken together, our findings reveal substantial differences in the topographic distribution of BBB damage and tissue infarction within the first 3 h after MCAO onset. Unlike ischemic neuronal damage, BBB damage appears to develop faster in brain regions with moderately severe ischemia, and MMP-2 contributes to this early ischemic BBB damage.