Ischemic brain tissue dies in the core of the infarct within a few hours after vessel occlusion, while inflammation leads to progressive damage to the cells in the penumbra. Pharmacological strategies limiting the delayed phase of the damage are important in stroke therapy. Inhibition of the production of COX-2-derived pro-inflammatory mediators is a potential neuroprotective strategy for limiting secondary damage in stroke. We showed that the COX-2 inhibitor, nimesulide, reduces blood-brain barrier (BBB) damage, leukocyte infiltration, and edema in a rat model of focal cerebral ischemia. Our preliminary data indicate that COX-2 inhibition or COX-2 gene deletion reduces MMP-9 expression in models of ischemic stroke, which is important since MMPs breakdown the BBB. Disruption of the BBB integrity causes brain edema and accelerates cell death. We propose to test the hypothesis that COX-2 inhibition protects the BBB and reduces neuronal death by inhibition of MMP expression and activity. The goal of these studies is to establish the role of the COX-2/PGE2 pathway in the regulation of ischemia- induced MMP expression and BBB opening. The significance of these studies is that the COX-2/MMP- mediated injury events occur late in the ischemic damage at a time when treatment may still be possible. Understanding the relationship of COX-2/PGE2 to the MMPs may provide novel treatment options. COX-2 is an important delayed mechanism of neuronal injury after ischemia. We have shown that post-treatment with COX-2 inhibitors hours after ischemia can reduce infarction and improve neurological function, which has great human translational potential. This relatively long therapeutic time window of protection after the ischemia onset during which COX-2 inhibitors are still effective suggests that COX-2 inhibition could be a practical treatment in human stroke.
Specific Aim #1 : To investigate the role of COX-2 in BBB damage and MMP expression/activity in ischemic stroke. We will use pharmacological (COX-2 inhibitors) and genetic approaches (COX-2 knockouts) to determine the link between COX-2, MMPs, and BBB damage following focal cerebral ischemia. Since MMPs open the BBB by attacking tight junction proteins (TJPs), we will study the effect of COX-2 inhibition or COX-2 gene ablation on ischemia-induced TJP degradation.
Specific Aim #2 : To elucidate the downstream effectors of COX-2-mediated increase in MMP expression/activity and damage to the BBB after ischemia. Since PGE2 production is an important mechanism associated with the detrimental effects of COX-2 in brain ischemia, we will clarify the role of PGE2 and its EP receptor(s) in BBB damage and MMP-3/-9 production utilizing in vivo pharmacological approaches.
Specific Aim #3 : To study the therapeutic time window of protection and long-term effects of drugs modulating the COX-2/PGE2 pathway. We will investigate if the delayed administration of these drugs reduces BBB damage, infarction, and improves neurological outcome in a rat stroke model. We will utilize selective inhibitors of COX-2, PGE2 synthase, and an EP antagonist. Long-term effects of these pharmacological agents will be studied using MRI, neurological tests and histological approaches.
The relevance of this proposal is that the COX-2/MMP-mediated injury events occur late in the ischemic cascade, at a time when treatment may still be possible. Experiments are designed to better understand the involvement of COX-2-derived products in the expression of MMPs and disruption of the BBB in ischemia. This may provide new treatment options for stroke and other brain diseases associated with BBB damage.
