It has been demonstrated by numerous studies that apoptotic cell death pathways are implicated in ischemic cerebral injury in ischemia models in vivo. Experimental ischemia and reperfusion models, such as transient focal/global ischemia in rodents, have been thoroughly studied and the numerous reports suggest the involvement of cell survival/death signaling pathways in the pathogenesis of apoptotic cell death in ischemic lesions. In these models, reoxygenation during reperfusion provides oxygen as a substrate for numerous enzymatic oxidation reactions and for mitochondrial oxidative phosphorylation to produce adenosine triphosphate. Oxygen radicals, the products of these biochemical and physiological reactions, are known to damage cellular lipids, proteins, and nucleic acids and to initiate cell signaling pathways after cerebral ischemia. Genetic manipulation of intrinsic antioxidants and factors in the signaling pathways has provided substantial understanding of the mechanisms involved in cell death/survival signaling pathways and the role of oxygen radicals in ischemic cerebral injury. Future studies of these pathways could provide novel therapeutic strategies in clinical stroke.

This model is ideal for studying ischemia/reperfusion-induced vascular injury and secondary brain hemorrhage and offers a unique opportunity to evaluate antioxidant-based neurovascular protective strategies as potential adjunct treatments to currently approved stroke therapies such as thrombolysis and endovascular clot retrieval.

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Background and Purpose-Expression of matrix metalloproteinases (MMPs), proteolytic enzymes that degrade extracellular proteins, is altered after ischemia/reperfusion injury and may contribute to blood-brain barrier (BBB) breakdown. Neutrophils, a source of reactive oxygen species and MMP-9, infiltrate damaged tissue 6 to 24 hours after ischemia and have also been implicated in delayed secondary tissue damage. Here we examined the spatial-temporal relation between MMP-9 expression and neutrophil infiltration after stroke. Methods-Knockout mice containing 50% manganese superoxide dismutase activity (SOD2-KOs), which are more susceptible to ischemic damage than wild-type (WT) littermates, underwent quantitative antigen (MMP-9, myeloperoxidase) immunohistochemistry (24 and 72 hours) analysis and protein expression by Western blotting (6, 12, 24, 48, and 72 hours) after transient focal cerebral ischemia. BBB breakdown was determined by Evans blue extravasation. Results-There was a clear spatial relation between MMP-9 expression and Evans blue extravasation. MMP-9 -positive cell and vessel counts for SOD2-KOs (72 hours) were significantly different from SOD2-KO (24 hours, Pϭ0.004), WT (24 hours, Pϭ0.01), and WT (72 hours, Pϭ0.007) mice. In contrast, MMP-9 -positive neutrophil counts were comparatively low and did not differ by time or animal type. MMP-9 expression was biphasic in SOD2-KOs but not in WT littermates, with a significant increase observed 6 to 12 hours after ischemic insult and again at 48 to 72 hours. SOD2-KOs showed increased MMP-9 expression compared with WT littermates at all time points studied (PՅ0.05). Conclusions-In this model, neutrophils are not the primary source of MMP-9 protein and thus are unlikely the key contributor to BBB breakdown observed in SOD2-KOs.