Attenuation of thrombin-induced brain edema by cerebral thrombin preconditioning.
OBJECTIVE
Edema formation after intracerebral hemorrhage has been linked to thrombin toxicity induced by the clot. However, thrombin at low concentrations actually protects neurons and astrocytes in culture from hypoglycemic and ischemic cell death. It is also known that a brief episode of brain ischemia increases neuronal tolerance to a subsequent severe ischemic episode. The objective of this study was to investigate whether pretreatment of the brain with low-dose thrombin induces tolerance to a subsequent large dose of thrombin injected into brain parenchyma.


METHODS
The rat brain was preconditioned with 1 U thrombin by direct infusion into the right caudate nucleus. After thrombin pretreatment, the effects of a large dose (5 U) of thrombin on brain edema formation were studied at different intervals. We examined whether heat-shock protein (HSP) 27, HSP32, and HSP70 were induced by Western blot analysis, immunocytochemistry, and immunofluorescent double staining.


RESULTS
Thrombin pretreatment significantly attenuated the brain edema that normally follows the infusion of a large dose of thrombin (79.2+/-0.4 versus 84.0+/-0.3; P<0.01). This effect was abolished by the thrombin inhibitor hirudin. Time course studies showed that the maximal effect of thrombin preconditioning (TPC) on brain edema formation was 7 days after pretreatment. This time course corresponded to marked upregulation of HSP27 in the ipsilateral brain. TPC also induced HSP32, but this effect occurred earlier than the effect on edema formation. TPC had no effect on HSP70. Immunocytochemistry and immunofluorescent double labeling showed that HSP27 and HSP32 were expressed in astrocytes after TPC.


CONCLUSIONS
OFF phenomenon of thrombin-induced tolerance of the brain to edema formation may be related to HSP27 induction.
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Department of Surgery (Neurosurgery), University of Michigan, Ann Arbor, MI, USA. guohuaxi@umich.edu
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D000818:Animals; D001921:Brain / Q000187:drug effects*; D001929:Brain Edema / Q000139:chemically induced* / Q000517:prevention & control*; D003213:Conditioning, Psychological / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004361:Drug Tolerance; D055551:HSP27 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000378:metabolism; D006419:Heme Oxygenase (Decyclizing); D007267:Injections; D008297:Male; D009363:Neoplasm Proteins / Q000378:metabolism; D010105:Oxygenases; D051381:Rats; D017207:Rats, Sprague-Dawley; D013917:Thrombin / Q000008:administration & dosage / Q000494:pharmacology*
D055551:HSP27 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; C486114:Hspb1 protein, rat; D009363:Neoplasm Proteins; D010105:Oxygenases; D006419:Heme Oxygenase (Decyclizing); C491523:Hmox1 protein, rat; D013917:Thrombin