Intracerebral hemorrhage constitutes up to 15 percent of all strokes. Yet, compared to ischemic strokes, the mechanisms of brain cell damage after hemorrhage remain relatively unexplored. Prognosis after hemorrhage is less favorable compared to ischemia. Furthermore, with the risks of hemorrhage associated with thromblytic therapy, it becomes increasingly important to understand the mechanisms of brain damage after hemorrhage. In this proposal, we will use rat and mouse models of intrastriatal hemorrhage to test the overall hypothesis that cell death after hemorrhage is mediated, in large part, by apoptosis. Our preliminary data show that (i) parancymal ischemia accompanying hemorrhage is mild therefore this may favor apoptotic pathways of cell death; (ii) extensive internucleosomal DNA fragmentation occurs in cells surrounding the hemorrhage; (iii) DNA fragmentation post-hemorrhage is reduced by caspase inhibitors; and (iv) pro-apoptotic factors are released into extracellular space after hemorrhage and can be recovered by in vivo microdialysis.
Our specific aims are: 1) establish the spatial and temporeal profile of apoptosis after hemorrhage, 2) quantify the levels of parenchymal ischemia adjacent to the hemorrhage and assess the accompanying release of pro-apoptotic factors (Fe2+, thrombin, FasL, TNF) into extracellular space, 3) test the efficacy of caspase inhibitors for reducing brain cell death after hemorrhage, and 4) investigate possible interactions between tissue plasminogen activator (tPA) and hemorrhagic apoptosis. For the 1st aim, we will map morphological, biochemical, and molecular markers of apoptosis after intracerebral hemorrhage. For the 2nd, parenchymal ischemia will be assessed with in vivo MRI methods that measure hemorrhagic progression, blood-brain barrier breakdown, and perfusion deficit. Additionally, we will use in vivo microdialysis to sample extracellular space after hemorrhage and assess the pro-apoptotic activity of Fe2+, thrombin, FasL and TNF with in vitro cultured cells. Experiments will also be performed in TNFR knockout and MnSOD overexpressing transgenic mice. For the third aim, we will characterize the therapeutic window for the caspase inhibitor zVADfmk, compare it with the free radical spin trap alphaPBN, and explore the benefits of combination therapy. Finally, since hemorrhage can be a serious complication of tPA therapy, we will examine as our 4th aim, the effects of tPA on apoptosis in our models. These proposed 3expeiments are expected to synergize with ongoing work in our labs that examine mechanisms that mediate tPA-induced hemorrhage in ischemic stroke (Lo, R01NS37074) and the efficacy of caspase inhibition for cerebral ischemia (Moskowitz, R01NS37141). Results may be used to improve the clinical management and treatment of intracerebral hemorrhage.
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