Background

Delayed cerebral ischaemia is a delayed neurological deterioration seen in patientsfollowing subarachnoid haemorrhage. There is currently no efficacious therapy available and approximately 30% of initial haemorrhage survivors develop this complication. Delayed cerebral ischaemia can be fatal and survivors often have lasting neurological impairments. Haemoglobin is believed to be central to the development of delayed cerebral ischaemia due to its high oxidative and inflammatory reactivity, and therefore may provide an effective target for novel therapeutics. A candidate for this is haptoglobin, an endogenous blood protein that in the periphery efficiently binds, stabalises and

prompts clearance of haemoglobin via CD163. However, there is a 50,000-fold deficiency of haptoglobin in the central nervous system making the brain vulnerable to haemoglobin toxicity following subarachnoid haemorrhage. In a two part study we first test a novel experimental model to isolate haemoglobin toxicity in the brain then utilize this model to evaluate the ability of infused haptoglobin to ameliorate haemoglobin induced brain

injury from.

Methods

35 C57BL male mice were challenged intracerebroventricularly with saline,

haemolysate, haemolysate + haptoglobin or haptoglobin for 14 days. Open-field behavioral assessment and histological analyses for iba-1 (microglia), GFAP (astrocytes), Synaptophysin (Synapses), Perl's (iron) and caspase-3 (apoptosis) were performed.

Results

Haemolysate caused significantly reduced ambulation and increased anxiety behavior compared to saline animals. Further, a significant increase in microglia/macrophages and astrocytes were observed alongside increased iron deposition and synapse loss also in haemolysate animals when compared to saline. Infusion of haptoglobin alongside haemolysate reduced all aforementioned markers of brain injury to a level not significantly different to saline animals. Importantly, haptoglobin independently did not cause any deleterious effects.

Conclusions

In this study using a novel experimental model we exemplify haemolysate to

cause widespread brain injury in the absence of ischaemia and large vessel vasospasm, and infusion of haptoglobin reduces these pathological changes. These encouraging results give grounds for further investigation into the therapeutic use of haptoglobin in subarachnoid haemorrhage to reduce haemoglobin mediated toxicity and improve patient outcomes.