Abstract T P253: Clinical Application of Haptoglobin in Models of Supraphysiologic Extracellular Brain Hemoglobin Levels

Abstract

Hemorrhagic stroke can occur from traumatic or spontaneous causes, is associated with high morbidity and mortality, and represents a worldwide major public health problem. With breakdown of the blood-brain barrier, and entry of toxic blood components and metabolites within the brain, a highly oxidative environment ensues and leads to a toxic neuroinflammatory cascade. A major cause of the debilitation following brain hemorrhage is due to the direct toxicity of blood components, namely hemoglobin (Hb), the most upstream precipitating factor. The acute phase plasma protein haptoglobin (Hp) binds Hb and inhibits its cytotoxic, pro-oxidative, and pro-inflammatory properties. Therefore, we hypothesized that local and specific overexpression of Hp within the brain would aid in the safe detoxification and clearance of free Hb, thereby protecting the neuropil from Hb-mediated oxidative stress, ultimately leading to improved anatomical and functional recovery. Here, we overexpressed Hp within the brain using specifically designed adeno-associated viral vectors, and induced hemorrhagic brain injury using two models – intrastriatal autologous whole blood injection and collagenase-induced spontaneous bleeding, which is accompanied by intraventricular hemorrhage in most cases. At 72h post-hemorrhage, mice were sacrificed and brains collected for Cresyl Violet staining and lesion volume quantification. Functional outcomes were assessed by a 24-point neurological deficit score. In both models, Hp-overexpressing mice demonstrated reduced lesion volume (p<0.05) and improved neurologic status at 24h, 48h, and 72h post-hemorrhage (p<0.05), when compared to an identically treated control group (n=7-9/group). In conclusion, locally modulating Hp expression within the brain could represent an important clinically relevant strategy for the treatment of acute hemorrhagic brain injury by attenuating the toxicity of free Hb and improving its clearance from the brain.