Abstract TP102: Modulation of Neuroinflammation by Haptoglobin Reduces Oxidative Stress and Improves ICH Outcomes

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Intracerebral hemorrhage (ICH) is a stroke subtype associated with high morbidity and mortality. 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, notably hemoglobin (Hb), the most upstream precipitating factor in the cascade. The acute phase plasma protein haptoglobin (Hp) binds Hb and inhibits its cytotoxic, pro-oxidative, and pro-inflammatory properties. In this study, we investigated whether the local and specific overexpression of Hp would aid in the safe detoxification and clearance of free Hb, thereby protecting the neuropil from Hb-mediated oxidative stress and improving ICH outcomes. Hp was overexpressed locally within the brain using uniquely designed adeno-associated viral vectors and ICH was induced using the intrastriatal autologous whole blood injection model. Functional outcomes were assessed by a 24-point neurological deficit score. At 72h post-hemorrhage, mice were sacrificed and brains collected for histological staining. Hp-overexpressing mice demonstrated smaller lesion volumes (p<0.05) with less blood accumulation (p<0.05) and improve neurologic status after ICH (p<0.05) when compared to an identically treated control group (n=11-13/group). Histological staining for Iba-1, GFAP, heme oxygenase-1, 4-hydroxynonenal, ferric iron, and myeloperoxidase was performed and revealed: 1) significantly less heme oxygenase-1 expression and lipid peroxidation, 2) a trend towards reduced peripheral neutrophil infiltration, 3) significantly increased cortical microgliosis and cortical and striatal astrogliosis, and 4) no changes in ferric iron content or striatal microgliosis. In conclusion, Hp overexpression in the brain reduces ICH-induced brain injury and improves functional outcomes. Locally modulating brain Hp levels could represent an important clinically relevant strategy for the treatment of ICH.

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