Gut microbes affect brain injury after stroke: study

Altering the gut microbes of mice can reduce brain damage after a stroke, which highlights a previously unrecognized link between the intestine and the brain, according to a study published online Monday in the journal Nature Medicine.

The microbiome, communities of microbes, colonize the gut and other barrier surfaces in the body early in life, and they have a pronounced influence on the development of the immune system and on metabolic processes. Alterations in the microbiome have been identified in several diseases, including inflammatory bowel disease, obesity and asthma, and they influence disease outcome.

A team of U.S. researchers used a mouse model of stroke to show that microbes in the gut regulate the development of pro-inflammatory immune cells, which migrate from the intestine to the brain after a stroke is induced.

The researchers treated mice with antibiotics. Two weeks later, the researchers induced the most common type of stroke, called ischemic stroke. Mice treated with antibiotics experienced a stroke that was about 60 percent smaller than rodents that did not receive the medication.

They found that the medication shifted the balance of pro- and anti-inflammatory immune cell types in the gut, increasing the number of anti-inflammatory T cells present. These microbial shifts ultimately reduce the number of pro-inflammatory cells that travel to the brain after stroke, which results in reduced brain damage.

The transferal of microbes from mice treated with antibiotics to untreated mice provided similar protection from brain damage after stroke, according to the study.

The researchers conclude that the subset of immune cells identified in the study and the cells' migration to the brain could potentially be targeted therapeutically to affect stroke outcomes, if this specific link between the intestine and the brain is also found in humans.

"One of the most surprising findings was that the immune system made strokes smaller by orchestrating the response from outside the brain, like a conductor who doesn't play an instrument himself but instructs the others, which ultimately creates music," said Costantino Iadecola from Weill Cornell Medical College, who is one of the authors of the study.

Further investigation is needed to understand exactly which microbial components elicited their protective message, according to the study. Endit