Cytoprotective role of haptoglobin in brain after experimental intracerebral hemorrhage.

After intracerebral hemorrhage (ICH), hemoglobin (Hb) that is released from erythrocytes within the brain hematoma is highly cytotoxic and leads to severe brain edema and direct neuronal damage. Therefore, neutralization of Hb could represent an important target for reducing the secondary injury after ICH. Haptoglobin (Hp), an endogenous Hb-binding protein in blood plasma, is found in this study to be upregulated in the hematoma-affected brain after ICH. Both in vivo and in vitro studies indicate that Hp upregulation is primarily mediated by oligodendrocytes. Hp acts as a secretory protein capable of neutralizing the cell-free Hb. We also found in an "ICH-like" injury that Hp-KO mice show the most severe brain injury and neurological deficits, whereas Hp-Tg mice are the most resistant to ICH injury, suggesting that a higher Hp level is associated with the increased resistance of animals to hemolytic product-mediated brain injury after ICH. We conclude that brain-derived Hp plays a cytoprotective role after ICH, and Hp may represent a new potential therapeutic target for management of ICH.