How can gut microbes (bacteria) affect the the severity of a stroke?

Since the gut and brain have two different functions in the body, one may ask, “How can microbes, or bacteria contained in the gut affect the brain and the severity of a stroke?” A new study performed on mice by researchers at Cornell University and published in Nature Medicine show that by tweaking the correct microbial balance creates changes in the immune system, which leads to a significant reduction in brain damage for stroke sufferers. Scientific American notes that strokes are the second leading cause of disability as well as death in people worldwide. 

Approximately 800,000 people in the U.S. suffer a stroke each year and though the results of this study don’t guarantee a cure from stroke brain damage, it does shed a new light on the partnership between the workings of the brain and gut. The study’s results offer new hope to stroke sufferers and the severity of their resulting brain damage. 

Strokes are defined as medical emergencies where blood flow to the brain becomes disrupted due to either some type of blockage or a hemorrhage. If the stroke doesn’t cause a fatality, the resulting effects usually include impaired physical function and often, permanent disability. Stroke patients may suffer physical problems such as partial paralysis, losses in hearing and vision, which may result in emotional and psychological issues. For some, partial function can be regained, but for others, the disability is permanent. Emergency medical services to help prevent severe effects of a stroke may include removing the clot creating the blockage, whether by drug intervention or surgery. 

Scientific experts have known for a while that the severity of a stroke is affected by the existence of two cell types, both of which calibrate the immune system and are abundant in the intestines. Regulatory T-cells are known to have a favorable inflammatory effect, when it comes to protecting stroke victims, whereas, gamma delta T-cells trigger the effects of harmful inflammation after a stroke due to their production of cytokine. 

Once a stroke occurs and the first wave of damage happens when the neurons are starved of blood, the second surge of injury happens when the damaging gamma delta T-cells rush to the meninges, which is the interface between the spinal cord and the brain. 

During the study, researchers bred two groups of mice and tinkered with their body’s bacteria to see if they could tilt the amount of these two cell types to favor the beneficial regulatory T-cells. The researchers used fecal transplants from mice treated with antibiotics and used antibiotics to tailor the gut bacteria in the mice used in the study. They found by doing so, the production of harmful gamma delta T-cells were reduced, while the beneficial regulatory T-cells were boosted. These T-cells made their way to the brain and resulting in less inflammation, which in turn led to less damage from the stroke. 

In regards to the study’s results, neurologist Constantino Iadecola, director of the Brain and Mind Research Institute at Weill Cornell stated, “These cells determine what kind of inflammatory immune response the brain is going to experience after stroke. By changing the bacterial landscape of the gut, immune cells end up helping out instead of contributing to the damage that occurs.”

“Now the microbiome is another element in this equation—it’s not just diabetes, high blood pressure and obesity,” Iadecola notes. “There are also other factors which we need to know in order to tailor treatment.” As the study suggests, tailoring treatment to promote production of beneficial regulatory T-cells and the reduction of the damaging delta gamma T-cells may encompass changes to the diet, the use of probiotics and antibiotics. Iadecola continues, “For example, patients undergoing heart surgery, many of whom end up suffering a stroke, might go on a special preemptive diet.”

Though this study is a start to further research on how to lessen stroke damage with gut microbes, there is still quite a bit of work to be done. A mouse’s microbiome isn’t exactly like a human’s, so these positive effects will require more extensive testing and refinement.  “This emphasis on the microbiome, and sequencing it, is a young field,” says Josef Anrather, Weill Cornell neuroscientist and study researcher and author. “Obviously it takes time. But the implications are there.”


Scientific American: A Hidden Factor in Stroke Severity: The Microbe in Your Gut

Motherboard: Neuroscientists Fight Brain Damage with Gut Microbes

Nature Medicine: Commensal Microbiota Affects Ischemic Stroke Outcome by Regulating Intestinal yo T Cells