Iron Accumulation and Metabolic Alterations in Aneurysmal Subarachnoid Hemorrhage

Aneurysmal subarachnoid hemorrhage (aSAH) is a severe type of stroke that is associated with poor outcome. A subset of patients with aSAH will develop secondary complications, most notably delayed cerebral ischemia (DCI), which potentiates neurological injury. In this study, we investigate the relationship between cerebrospinal fluid (CSF) iron accumulation, brain metabolism, and neuronal injury in patients with aSAH with or without DCI.

We collected longitudinal CSF samples of patients immediately after hospitalization and 5 to 8 days after onset of ictus. CSF was analyzed with electron paramagnetic resonance spectroscopy and metabolomics to determine the presence of redox-active iron species and metabolic alterations associated with aSAH and DCI. Neuronal pathology induced by iron overload was characterized in neuronal and meningeal cell models.

Electron paramagnetic resonance spectroscopy identified higher levels of an Fe(III) protoporphyrin IX (hemin)-like molecule in the CSF of patients who developed DCI compared with patients who did not show secondary ischemic injury after aSAH or controls without neurological disease. Treatment of a human neuronal cell line with Fe(III)-containing hemin resulted in the disruption of the axonal mitochondrial network and loss of viability. This was cell-type dependent as a meningeal cell line was resistant to hemin treatment, despite both cell types upregulating the iron ferroxidase ceruloplasmin. Metabolomic profiling of the same CSF samples uncovered significant dysregulation of metabolic pathways associated with energy generation and amino acid utilization, consistent with mitochondrial dysfunction. Using machine learning, we identified a set of metabolites that predicted intensive care unit length of stay.

aSAH leads to the accumulation of an Fe(III)-containing heme species in the CSF of a subset of patients who subsequently develop DCI. The accumulation of an Fe(III) protoporphyrin induces axonal mitochondrial dysfunction, leading to cell death. aSAH alters the CSF metabolome involved in mitochondrial function and a subset of these metabolites are predictive of intensive care unit stay. These results identify potential biomarkers for mitochondrial pathology and provide insight into alterations in brain iron metabolism triggered by aSAH.