Carbon monoxide works against stroke damage

Low doses of carbon monoxide as a help after a stroke?
Carbon monoxide could help patients after a stroke. The research team around Dr. Nils Schallner of the Department of Anaesthesiology and Intensive Care at the University Hospital of Freiburg and colleagues at Beth Israel Deaconess Medical Center (BIDMC) and Harvard Medical School Boston, USA, found that low levels of carbon monoxide protect the brain, reduce brain damage and brain function to improve a stroke.

In fact, carbon monoxide is known as a poisonous gas that can lead to brain damage, confusion, memory loss and, in the worst case, death. However, the international research team with the participation of scientists from the Freiburg University Hospital has now been able to prove that low doses in the case of a stroke have a positive effect. Low doses of carbon monoxide could protect the brain from damage caused by a bleeding stroke, the researchers report. Their results have been published in the journal "Journal of Clinical Investigation".

Microglia cells (red) degrade the blood component heme after SAB, forming carbon monoxide. If they can not make the gas themselves, the external dose improves the recovery of the brain cells. The blue dots are the nerve cell nuclei. (Image: Nils Schallner / University Hospital Freiburg)

Heme molecule causes damage after cerebral hemorrhage
According to the researchers, around 10,000 people suffer from subarachnoid hemorrhage (abbreviated to SAB) every year. This particular stroke form goes back to a burst artery in the brain with subsequent blood leakage. In this case, sudden onset of very strong headache is the central symptom. Especially women between the ages of 45 and 55 are affected, according to the University of Freiburg. Only one in two sufferers survived for more than a year after the SAB, and many would suffer from brain function limitations in the long term. For a large part of the damage after a cerebral hemorrhage is responsible for the molecule heme, which is important in the red blood cells for oxygen transport, but outside of the cells highly toxic.

Tests on mice show the positive effect of carbon monoxide
The SAB is doubly dangerous for patients, because on the one hand uses an oxygen deficiency and on the other hand, the leaked blood for the brain is toxic, the scientists report. In the current study, the team led by Professor Khalid Hanafy, Neurological Director of the BIDMC Neurointensive Unit; Leo E. Otterbein, a researcher at the BIDMC Transplant Institute, is now studying how two groups of mice recovered after cerebral hemorrhage, with one group kept in normal breathing air for one week and the other group for a week in addition to one low daily for one week Amount of carbon monoxide received. In the subsequent spatial memory tests, "the animals who inhaled carbon monoxide performed significantly better," says Dr. Schallner from the University Hospital Freiburg.

Basis for clinical studies
According to the researchers, the damage to the brain tissue and the cognitive impairment in the stroke mice were significantly reduced by the administration of carbon monoxide. "We concluded that low-dose, normally toxic gas carbon monoxide could improve recovery after a stroke," Dr. Nils Schallner. The scientists had already demonstrated "that special brain cells, called microglia, detoxify the heme by the enzyme heme oxygenase 1 (HO-1)" and that "in this degradation carbon monoxide is released," according to the University of Freiburg. The gas is not only a by-product of the degradation, but has a positive effect on the heme degradation itself. Thus, animals that did not form HO-1 and, correspondingly, carbon monoxide also benefited from the carbon monoxide administration. A carbon monoxide gift "from the outside" could compensate for a lack of endogenous carbon monoxide production, Dr. Schallner. According to the researchers, the current results may serve as a basis for clinical trials with patients who have had a bleeding stroke. (Fp)