Haemoglobin causes neuronal damage in vivo which is preventable by haptoglobin
Patrick Garland, Matthew J Morton, William Haskins, Ardalan Zolnourian, Andrew Durnford, Ben Gaastra, Jamie Toombs, Amanda Heslegrave, John More, Azubuike I. Okemefuna, Jessica L. Teeling, Jonas Heilskov Graversen, Henrik Zetterberg, Søren K. Moestrup, Diederik Bulters, Ian Galea
Abstract
and its prevention. In humans after subarachnoid haemorrhage, haemoglobin in cerebrospinal fluid was associated with neurofilament light chain, a marker of neuronal damage. Most haemoglobin was not complexed with haptoglobin, an endogenous haemoglobin scavenger present at very low concentration in the brain. Exogenously added haptoglobin bound most uncomplexed haemoglobin, in the first 2 weeks after human subarachnoid haemorrhage, indicating a wide therapeutic window. In mice, the behavioural, vascular, cellular and molecular changes seen after human subarachnoid haemorrhage were recapitulated by modelling a single aspect of subarachnoid haemorrhage: prolonged intrathecal exposure to haemoglobin. Haemoglobin-induced behavioural deficits and astrocytic, microglial and synaptic changes were attenuated by haptoglobin. Haptoglobin treatment did not attenuate large-vessel vasospasm, yet improved clinical outcome by restricting diffusion of haemoglobin into the parenchyma and reducing small-vessel vasospasm. In summary, haemoglobin toxicity is of clinical importance and preventable by haptoglobin, independent of large-vessel vasospasm.