Researchers at Johns Hopkins have shown that brain damage was reduced by as much as 62.2 percent in mice who inhale low amounts of carbon monoxide after an induced stroke.
The scientists, in a report published online Dec. 15 in Neurotoxicity Research, say that although carbon monoxide (CO) gas has a long reputation as an odorless, colorless cause of organ damage and even death, there is now evidence that it can protect nerve cells from damage.
"CO is made naturally by the body and can serve a protective function under various circumstances," says lead author Sylvain Doré, Ph.D., an associate professor in the Department of Anesthesiology and Critical Care Medicine at Johns Hopkins University School of Medicine. "The idea for our experiment was to see if external CO could have a similar effect."
Some of the brain damage associated with stroke results directly from a cut-off in blood supply to nerve cells, but a good deal of the injury is also due to chemical reactions and the resulting release of tissue-damaging free radicals when blood flow is restored. Currently the only treatment for such strokes is to clear out the blood clot with clot busters, such as tissue plasminogen activator (tPA) or other means, but these offer no protection from so-called "reperfusion" damage.
Doré and his team induced stroke in the mice by briefly blocking an artery to one side of the brain. Afterwards, the mice were exposed to either 125 parts-per-million (ppm) or 250 ppm of CO. A control group was exposed only to air. Each was tested for physical brain damage and function, mainly by observing running patterns and reactions to certain stimuli.
Results showed that mice exposed only to air had brain damage to 49.9 percent of the side of the brain where the blood supply was cut off. In mice that inhaled 125 ppm of CO immediately after stroke, brain damage dropped to 33.9 percent, and in mice getting 250 ppm, CO damage fell to 18.8 percent. Neurological function test scores were also significantly improved for mice that received CO after stroke.