Targeting heme oxygenase after intracerebral hemorrhage.

Intracerebral hemorrhage (ICH) is the primary event in approximately 10% of strokes, and has higher rates of morbidity and mortality than ischemic stroke.  Experimental evidence suggests that the toxicity of hemoglobin and its degradation products contributes to secondary injury that may be amenable to therapeutic intervention. Hemin, the oxidized form of heme, accumulates in intracranial hematomas to cytotoxic levels. The rate limiting step of its breakdown is catalyzed by the heme oxygenase (HO) enzymes, which consist of inducible HO-1 and constitutively-expressed HO-2. The effect of these enzymes on perihematomal injury and neurological outcome has been investigated in ICH models using both genetic and pharmacological approaches to alter their expression, with variable results reported.  These findings are summarized and reconciled in this review; therapeutic strategies that may optimize HO expression and activity after ICH are described.