Involvement of matrix metalloproteinase in thrombolysis-associated hemorrhagic transformation after embolic focal ischemia in rats.

BACKGROUND AND PURPOSE Thrombolytic therapy with tissue plasminogen activator (tPA) for acute ischemic stroke remains complicated by risks of hemorrhagic transformation. In this study we used a previously established quantitative rat model of tPA-associated hemorrhage to test the hypothesis that matrix metalloproteinases (MMPs) are involved. METHODS Spontaneously hypertensive rats were subjected to embolic focal ischemia by placing homologous blood clots into the middle cerebral artery. Three groups of rats were studied: (1) untreated controls that received saline at 6 hours after ischemia; (2) rats that received tPA alone (10 mg/kg at 6 hours after ischemia); and (3) rats that received tPA plus the broad-spectrum MMP inhibitor BB-94 (50 mg/kg of BB-94 before ischemia and at 3 and 6 hours after ischemia plus tPA at 6 hours). Gelatin zymography was used to quantify MMP levels. A hemoglobin spectrophotometry method was used to quantify cerebral hemorrhage. Ischemic lesions were measured at 24 hours with tetrazolium staining. RESULTS At 6, 12, and 24 hours, pro-MMP-9 and cleaved MMP-9 were upregulated in ischemic brain. At 12 hours, tPA-treated rats showed significantly higher levels of pro-MMP-9 and cleaved MMP-9 than untreated controls. By 24 hours, all rats showed evidence of hemorrhagic transformation in the ischemic territory. Rats treated with BB-94 and tPA showed significantly reduced hemorrhage volumes compared with those that received tPA alone. There was no effect on infarct size. CONCLUSIONS These results indicate that (1) tPA treatment increases levels of MMP-9 after embolic focal cerebral ischemia, (2) MMPs are involved in the mechanism of tPA-associated hemorrhage, and (3) combination therapies with MMP inhibitors may be useful for decreasing the risk and severity of this dreaded complication of thrombolytic therapy.