Functional effects of haemoglobin can be rescued by haptoglobin in anin vitromodel of subarachnoid haemorrhage

Abstract

During subarachnoid haemorrhage, a blood clot forms in the subarachnoid space releasing extracellular haemoglobin (Hb), which causes oxidative damage and cell death in surrounding tissues. High rates of disability and cognitive decline in SAH survivors is attributed to loss of neurons and functional connections during secondary brain injury. Haptoglobin sequesters Hb for clearance, but this scavenging system is overwhelmed after a haemorrhage. Whilst exogenous haptoglobin application can attenuate cytotoxicity of Hb in vitro and in vivo, the functional effects of sub-lethal Hb concentrations on surviving neurons and whether cellular function can be protected with haptoglobin treatment remain unclear. Here we use cultured neurons to investigate neuronal health and function across a range of Hb concentrations to establish the thresholds for cellular damage and investigate synaptic function. Hb impairs ATP concentrations and cytoskeletal structure. At clinically relevant but sublethal Hb concentrations, synaptic AMPAR-driven currents are reduced, accompanied by a reduction in GluA1 subunit expression. Haptoglobin co-application can prevent these deficits by scavenging free Hb to reduce it to sub-threshold concentrations and does not need to be present at stoichiometric amounts to achieve efficacy. Haptoglobin itself does not impair measures of neuronal health and function at any concentration tested. Our data highlight a role for Hb in modifying synaptic function after SAH, which may link to impaired cognition or plasticity, and support the development of haptoglobin as a therapy for subarachnoid haemorrhage.

Haptoglobin attenuates cerebrospinal fluid hemoglobin-induced neurological deterioration in sheep

“…The CSF-Hb-induced neurological impairment in our study is most likely caused by neurovascular dysfunction and not by structural injury, which is consistent with the absence of radiographic or histological differences between the treatment groups. A recent study showed that Hb exposure in neuronal cell cultures reduces AMPA-receptor-mediated synaptic currents and a down-regulation of GluA1 at the postsynaptic membrane, leading to impaired neuronal electrical signaling capacity 7 . Even partial scavenging of Hb by haptoglobin below a certain threshold prevented neuronal dysfunction in these experiments.…”

Haptoglobin attenuates cerebrospinal fluid hemoglobin-induced neurological deterioration in sheep

“…In previous studies, we discovered that the delocalization of CSF-Hb into the brain's interstitial spaces and the muscular layers of cerebral arteries initiates toxicity, which can be blocked by haptoglobin through a size-dependent mechanism 5 . By design, these studies were constrained by only measuring surrogate markers of physiological impairment instead of directly demonstrating that CSF-Hb leads to preventable functional neurological adverse effects 2,[5][6][7] . Therefore, evidence for the protective effects of haptoglobin against CSF-Hb-induced neurological deterioration in vivo is currently limited to mice 8 .…”