Results from a new study suggest that small controlled doses of carbon monoxide may protect the brain from damage after a subarachnoid hemorrhage by speeding up the clearance of heme that accumulates. Findings from the study are published in The Journal of Clinical Investigation.

Prior research has shown several therapeutic applications for the gas thought by many to be poisonous: treatment of pulmonary hypertension, organ rejection prophylaxis, reduction of vascular restonsis, shrinkage of cancerous tumors, and infectious diseases. A team of researchers from Harvard Medical School observed that a group of brain cells called microglia were functioning as a ‘trash collector’ for the brain. Following a subarachnoid hemorrhage, heme pigment was released from the protein and caused inflammation and death to surrounding brain tissue . Microglia then acted by removing the heme via an enzyme called heme oxygenase-1 (HO-1) where it then quickly transforms it into iron, bile pigments, and carbon monoxide.

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Once carbon monoxide was established as the protective element with HO-1, the team tested whether safe levels of inhaled carbon monoxide could help lessen brain damage following a subarachnoid hemorrhage. One group of mice was exposed to normal air, and a second group was exposed to one hour of inhaled carbon monoxide daily for seven days following a subarachnoid hemorrhage.

Researchers were able to conclude that neuronal injury and cognitive function were normalized when mice were exposed to safe amounts of carbon monoxide. This was also the case even when HO-1 was absent. Carbon monoxide-based therapies may be a future area of research in patients with ruptured cerebral aneurysms.

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