Thrombin preconditioning, heat shock proteins and thrombin-induced brain edema

Intracerebral injections of high concentrations of thrombin cause brain edema but, in vitro, low concentrations of thrombin may be neuroprotective. This study investigated whether a low dose of thrombin might induce tolerance to subsequent large doses of thrombin (thrombin preconditioning; TPC) in a manner analogous to ischemic preconditioning. The study involved five parts. The first tested the effect of intracerebral infusion of a small dose (1 U) of thrombin on brain water content. In the second part, the effect of such a small dose of thrombin on subsequent edema formation from a large dose of thrombin (5 U) was evaluated. The time course of TPC was examined in the third part. In the fourth part, heat shock protein (HSP) 27, HSP32 and HSP70 were quantitated by Western blotting analysis while the fifth identified the cell types expressing HSPs. Injection of a low dose of thrombin alone did not cause brain edema. However, TPC significantly attenuated the edema induced by a subsequent injection of a large dose of thrombin. This effect of TPC was abolished by co-injection of a thrombin inhibitor, hirudin. The maximal effect of TPC on edema formation was seven days after pretreatment. This time course was similar to that for a marked up-regulation in astrocytic HSP27. TPC also induced HSP32, but this effect occurred earlier than the effect on edema formation. TPC had no effect on HSP70. These results suggest that thrombin-induced brain tolerance may be related to HSP27 induction.