Expression of matrix metalloproteinase-9 in thrombin-induced brain edema formation in rats

Recent evidence has demonstrated that thrombin plays an important role in the development of brain edema by the blood-brain barrier disruption in intracerebral hemorrhage. Matrix metalloproteinases (MMPs), a family of proteolytic enzymes that degrade the extracellular matrix, are implicated in blood-brain barrier disruption. In this study, we examined whether thrombin injection into the brain parenchyma induces the MMP-9 expression in rats. Anesthetized adult rats received an injection of 10 U of thrombin into the basal ganglia. At 12, 24, and 72 hours after the thrombin injection, brain water content and the expression of MMP-9 messenger RNA (mRNA) and protein were determined. The effect of a specific thrombin inhibitor (hirudin) on MMP-9 expression and brain edema formation and general administration of synthetic MMPs inhibitor (GM6001) on brain edema formation were also examined for linking the injury and up-regulation of MMP-9. The brain water contents in the basal ganglia and overlying cortex were rapidly increased at 12 hours, maximized at 24 hours, and slightly decreased at 72 hours. The gelatinase activity of MMP-9 determined with gelatin zymography was detected in the basal ganglia and cortex at 12 hours, maximally expressed at 24 hours, and remained strong 72 hours after thrombin injection. The expression of MMP-9 mRNA in the cortex determined with reverse transcription-polymerase chain reaction was clearly seen at 12 and 24 hours, and became weak 72 hours after thrombin injection. Co-injection of thrombin and hirudin almost completely inhibited the brain edema formation and expressions of MMP-9 mRNA and protein. Administration of broad-spectrum metalloproteinase inhibitor GM6001 significantly reduced the brain edema formation in this model. These results indicate that intraparenchymal thrombin induces brain edema formation through MMP-9 expression in rats. Inhibition of MMPs activity may provide an approach to potentially reduce ongoing edema after intracerebral hemorrhage.