Mechanisms of neuroprotection by hemopexin: modeling the control of heme and iron homeostasis in brain neurons in inflammatory states

Abstract Hemopexin provides neuroprotection in mouse models of stroke and intracerebral hemorrhage and protects neurons in vitro against heme or reactive oxygen species (ROS) toxicity via heme oxygenase‐1 (HO1) activity. To model human brain neurons experiencing hemorrhages and inflammation, we used human neuroblastoma cells, heme‐hemopexin complexes and physiologically‐relevant ROS, e.g. H2O2 and HOCl, to provide novel insights into the underlying mechanism whereby hemopexin safely maintains heme and iron homeostasis. Human amyloid precursor protein (hAPP), needed for iron export from neurons, is induced ~2‐fold after heme‐hemopexin endocytosis by iron from heme catabolism via the iron regulatory element of hAPP mRNA. Heme‐hemopexin is relatively resistant to damage by ROS and retains its ability to induce the cytoprotective HO1 after exposure to tert‐butylhydroperoxide, although induction is impaired, but not eliminated, by exposure to high concentrations of H2O2 in vitro. Apo‐hemopexin, which predominates in non‐hemolytic states, resists damage by H2O2 and HOCl except for the highest concentrations likely in vivo. Heme‐albumin and albumin are preferential targets for ROS; thus, albumin protects hemopexin in biological fluids like CSF and plasma where it is abundant. These observations provide strong evidence that hemopexin will be neuroprotective after traumatic brain injury, with heme release in the CNS, and during the ensuing inflammation. Hemopexin s...
Source: Journal of Neurochemistry - Category: Neurology Authors: Tags: Original Article Source Type: research