Is there a link between stroke and changes in gut bacteria?

New research investigates whether a stroke can affect the diversity of bacterial populations in the gut and whether these changes could influence the brain’s recovery process.

The Centers for Disease Control and Prevention (CDC) notes that every 40 seconds, someone experiences a stroke, a cardiovascular event in which the brain’s supply of oxygenated blood is cut off. A stroke can cause damage to the brain, as its cells begin to die in the absence of oxygen and nutrients. However, recent studies suggest that a stroke could have an immediate and lasting impact on other parts of the body as well.

Now one such study indicates that after a stroke, the bacterial population in the gut undergoes major changes and that these effects can last for a long time.

Dr. Allison Brichacek and Associate Professor Candice Brown, Ph.D., from West Virginia University School of Medicine in Morgantown, led this study and presented their findings last month at the International Stroke Conference in Honolulu, HI.

“We are interested in the gut-brain axis: how the gut influences the brain and vice versa,” explains Brichacek.

Chronic alteration of the bacterial balance

To learn more about the effect of a stroke on the gut microbiota, the researchers worked with mouse models, which were divided into two groups. In the first group, the researchers induced an ischemic stroke, while the other group served as a control and included healthy rodents. After inducing stroke in the first group of mice, the researchers evaluated the rodents in both groups at 3, 14 and 28 days after the event.

The team found that mice in the stroke group showed lasting changes in their gut microbiota. Unlike the rodents in the control group, they had Bifidobacteriaceae bacteria at the 14-day and 28-day marks. This bacterial family contains beneficial probiotic bacteria, including Bifidobacterium, which manufacturers often add to probiotic dairy products. These types of bacteria not only help maintain a healthy digestive system, but according to Brichacek and Brown, they can also lead to better recovery in people who have been through a stroke.

The researchers also reported that the mice in the experimental group had higher levels of bacteria belonging to the Helicobacteraceae family at 28 days after the stroke. These bacteria, the researchers say, are linked to poorer health outcomes.

Another change was that in the mouse stroke models, the Firmicutes of Bacteroidetes whose bacterial ratio was considerably higher than in control mice.
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Specifically, it was almost six times higher at the 14-day mark and more than three times higher after 28 days.

Brichacek and Brown explain that this unbalanced relationship has links to an increased risk of obesity, diabetes, and abnormal inflammation.

Treating the gut to heal the brain?

The researchers also found not only a healthy imbalance in the bacterial populations in the gut after a stroke, but also changes in the structure of the gut tissue. Healthy gut tissue, Brichacek and Brown say, looks almost like a well-ordered coral colony, thanks to villi, which are tiny structures that help the intestines absorb nutrients. However, the intestinal tissue of the mice in the experimental group looked chaotic.

“There is disorganization here,” says Brichacek. “There is also less space between the villi to allow nutrients to move,” he adds.

If the intestines don’t properly absorb nutrients, the researchers explain, this could compromise recovery after health events, such as a stroke.

“Big picture: Seeing a persistent, chronic change 28 days after [a] stroke associated with this increase in some of the negative bacteria means that this could have negative effects on brain function and behavior,” says Brown.

Ultimately, “he warns,” this could slow or prevent post-stroke recovery. For this reason, the lead authors believe that further investigation should investigate whether we could treat the effects of a stroke by targeting, not brain changes, but changes in the gut.

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