Abstract TP292: Thrombin-induced Cerebral Hemorrhage: Role Of Protease-activated Receptor-1

Abstract

Background and Purpose: Thrombin causes blood-brain barrier disruption and this study examined whether thrombin can cause brain hemorrhage through protease-activated receptor-1 (PAR-1). Methods: Male wild type and PAR-1 knockout mice had an intracerebral injection of thrombin or saline. Mice then underwent serial T2 magnetic resonance imaging and were euthanized for brain hemoglobin, iron and interleukin-1β measurements. Results: Mortality after intracerebral thrombin injection was not significantly different in WT (11%) and PAR-1 KO mice (9%). Thrombin but not saline resulted in massive T2 lesions in WT mice. MRI studies showed that the T2 lesions induced by thrombin were smaller in PAR-1 KO mice compared to those in WT mice (p<0.05). An examination of brain sections after thrombin injection showed areas of hemorrhage in the ipsilateral hemisphere. This hemorrhage was examined using Perls’ staining for iron and by measuring brain hemoglobin. Perls’ staining showed that thrombin caused significant brain hemorrhage in WT mice and that hemorrhage peaked at day-3. Perls’ positive cells were less in PAR-1 KO mice (p<0.05). Brain hemoglobin content was measured at day-3 after thrombin injection to assess hemorrhage volume. Thrombin-induced marked hemoglobin accumulation in the ipsilateral hemisphere in WT-type mice and this was markedly reduced in PAR-1 KO mice (hemoglobin: 327±134 vs. 913±221 μg in the WT mice, p<0.01). The role of PAR-1 in brain IL-1β levels after thrombin stimulation was also examined. The time course of brain IL-1β levels following thrombin injection in WT mice was examined. Brain IL-1β levels peaked at 12 hours and returned to low levels after 24 hours. We then measured brain IL-1β levels in WT and PAR-1 KO mice and found that thrombin-induced upregulation of brain IL-1β was basically absent in PAR-1 KO mice (p<0.01). Conclusions: Thrombin increases interleukin-1β levels and induces intracerebral hemorrhage through PAR-1 activation.