Intracerebral hemorrhage (ICH) is the primary event in 10-15% of strokes. A growing body of experimental evidence supports the hypothesis that release of hemin from the hematoma may contribute to oxidative cell injury in adjacent tissue. The heme oxygenase (HO) enzymes, which catalyze the rate-limiting step in hemin breakdown, regulate the response of CNS cells to hemin in a complex fashion. HO-1, the inducible isoform, has been associated with increased lesion volume and inflammation after experimental ICH, and worsened behavioral outcome. However, recent studies in the applicant's laboratory suggest that mice overexpressing HO-1 specifically in astrocytes are markedly less vulnerable to ICH than wild-type mice. Moreover, systemic administration of hemin, which is currently in clinical use to treat acute porphyrias, increased HO-1 expression in the mouse brain. When administered after ICH but before erythrocyte lysis, this treatment attenuated blood- brain barrier breakdown and cell injury surrounding a striatal hematoma. These results suggest that systemic hemin at clinically-tolerated doses provides a preconditioning stimulus that protects CNS cells from the hemin subsequently released in high concentrations from the hematoma. This safe, easily administered, and inexpensive compound may be a novel and highly effective treatment for ICH. The goal of this project is to define the therapeutic benefit of systemic hemin in two established ICH models.
The specific aims are as follows: 1) Administer hemin to mice via daily i.p. injections for 1-3 days; 24 hours after the last injection, harvest striata and quanify HO-1 protein expression and activity. Identify cell populations that express HO-1 via immunostaining. 2) Induce ICH by stereotactic injection of autologous blood or collagenase into the striata of mice. Treat with hemin or vehicle control 1, 3, 6, or 12 hours later, followed in 24 hours by an additional dose. Quantify blood-brain barrier disruption and striatal edema at 3 days. 3) Quantify the effect of hemin on striatal cell viability and perihematomal inflammatory infiltrates 3 and 8 days after ICH. Assess focal deficits at these time points using corner, adhesive removal and elevated body swing tests, and activity deficits by digital analysis of home cage video recordings. 4) Compare the effects of hemin treatment on blood-brain barrier disruption, edema, neuronal viability, inflammation, and behavioral deficits in wild-type mice with those in HO-1 knockout mice. Determine the effect of the heme binding protein hemopexin on hemin therapy by performing additional experiments using hemopexin knockout mice. It is hoped that the results of this project will define the benefits of systemic hemin after ICH, and rapidly lead to clinical trials for a disease process that currently has few therapeutic options.
The information gained in this project may lead to new treatments for victims of hemorrhagic brain injuries. These include hemorrhagic stroke and traumatic brain injuries associated with bleeding into the brain. The ultimate goal is to reduce the cell injury that occurs in tissue surrounding the blood clot, and thereby improve the likelihoo of survival and return to an independent, productive life.
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