Abstract-Text (inkl. Referenzen und Bildunterschriften)

Introduction

Aneurysmal subarachnoid hemorrhage (aSAH) comprises a small percentage of strokes. However, due to the young age of affected patients and the resulting morbidity, it significantly impacts productive live years in society. The delayed occurrence of secondary brain injury (SBI) contributes to unfavorable neurological outcomes. In the days following aSAH, progressive erythrolysis leads to a rise of cell-free hemoglobin in the cerebrospinal fluid (CSF-Hb). Previous research highlighted an association between elevated CSF-Hb concentrations and the occurrence of SBI. Although CSF-Hb has long been considered a contributor to brain injury and vasospasm after aSAH, there is no targeted therapeutic approach and only sparse evidence for direct effects of CSF-Hb on neurological function in vivo.

Methods

In this study, we replicated the subacute CSF-Hb exposure seen in aSAH patients by developing a translational animal model involving repeated intracerebroventricular Hb injections over three days in conscious sheep (n=6). Specific Hb toxicity effects were dissected upon comparison with a sheep group (n=6) injected with "detoxified" Hb bound to Haptoglobin 1-1 (Hp, CSL888). Treatment allocation was randomized 1:1 with blinding of investigators. The sheep model allowed repeated CSF sampling, confirming relevant brain exposure to CSF-Hb or Hp-Hb with concentrations comparable to those found in our observational studies in aSAH patients.

Results and Discussion

We found that prolonged CSF-Hb exposure resulted in decreased movement activity, reduced food intake, and overall neurological deterioration, while these effects were mitigated in the group injected with Hb-Hp complex. Preterminal magnetic resonance imaging (MRI) showed no CSF-Hb-specific structural brain alterations. Histological analysis displayed similar tissue changes in both groups, with slightly larger perivascular cell infiltrates in the Hp-Hb group. We did not find a significant difference in iron deposition in the brain between groups, suggesting similar clearance of Hb and Hp-Hb from the brain. At least for the exposure period of three days, the neurological manifestation of CSF-Hb toxicity seems more related to functional brain alterations than structural damage within this model. Remarkably, Hb complexed with haptoglobin did not provoke the same phenotype, indicating that haptoglobin is able to mitigate CSF-Hb induced neurological deterioration.