Gut Bacteria Linked to Stroke Severity, Risk

Two new studies identifying strains of gut microbiota associated with more severe strokes and worse post-stroke recovery point to a possible role for the gut microbiome in preventing stroke and improving outcomes.

Researchers identified gut microbiota that were different in stroke patients compared to control persons, including more than two dozen bacteria associated with a range of stroke subtypes and strains specifically associated with worse stroke severity 6 hours and 24 hours after the event.

The findings add to a growing body of evidence that researchers say could eventually lead to therapies to improve stroke outcomes.

"There are no specific neuroprotective treatments to prevent neurological worsening after stroke," Miquel Lledós, MSc, a doctoral student at Stroke Pharmacogenomics and Genetics Laboratory at the Sant Pau Research Institute, Barcelona, Spain, who led one of the studies, told Medscape Medical News. "The use of new therapies such as changes in the microbiome through nutritional changes or fecal transplantation could be useful to improve post-stroke evolution or to decrease stroke risk."

The findings were presented at the European Stroke Organisation Conference (ESOC) 2022 on May 4.

A Role for Gut Bacteria?

Gut microbiota have been implicated in dementia risk, cardiovascular disease, and multiple sclerosis relapse. Prior research has also pointed to a possible link between gut bacteria and stroke. Emerging evidence suggests a possible link between gut bacteria and stroke risk, although most work so far has been conducted in animal models.

"In humans, the role of the intestinal microbiota and its relationship with neurological evolution and post-stroke disability are beginning to be analyzed," Lledós said. He said their main goal was "to identify if the gut microbiota was associated with the neurological outcome in the acute phase and functional recovery at 3 months after stroke."

For their study, Lledós and colleagues analyzed microbiota in the first fecal samples from 89 patients following an ischemic stroke. They compared the results to those from 12 control persons.

After adjusting for age, sex, stroke subtype, and other confounders, they identified multiple taxa associated with ischemic stroke risk (Fusobacterium, P = 1.40x10^-6, ß = 2.62) and confirmed others that had previously been identified (Lactobacillus, P = 4.27x10^-11, ß = 3.40).

Researchers further identified new taxa associated with higher risk of stroke severity in the acute phase at 6 hours (Prevotella copri, Negativibacillus) and at 24 hours (Lentisphaeria). They also identified one class (Kiritimatiellae), one genus (Acidaminococcus), and one species (Paraprevotella xylaniphila) that are related to poor functional outcome 3 months after ischemic stroke.

A Modifiable Risk Factor

Researchers from Yale University offered similar findings in another study presented at ESOC.

Using data from the Flemish Gut Flora Project and the MEGASTROKE consortium, researchers identified 26 bacteria species associated with acute ischemic stroke or one of its subtypes. Of these, genus Ruminococcus was associated with all four outcomes.

"The most surprising finding was that so many bacteria were associated with the risk of ischemic stroke," lead researcher Cyprien Rivier, a postdoctoral fellow in neurology at the Yale School of Medicine, told Medscape Medical News. "This suggests a delicate balance in the gut microbiota which can change the risk of stroke when altered."

That would mean that gut microbiota could be a potentially modifiable factor that could decrease stroke risk entirely or possibly reduce stroke severity, Rivier said.

"A potential future development of our study would be to investigate the effects of altering the gut microbiota of patients at high risk of stroke by giving them probiotics, prebiotics, or performing fecal matter transplants and measuring whether their risk of stroke is reduced," Rivier said. "This could potentially pave the way for noninvasive and low-risk stroke prevention therapies."

The exact mechanisms by which gut bacteria might influence neurologic conditions such as stroke are uncertain, but one possibility is that they could cause changes to the immune system.

"The gut microbiome has already been identified as a potential risk factor for susceptibility to various chronic metabolic diseases," Lledós said. "Studies in this field indicate that microbial dysbiosis in the digestive tract can influence systemic inflammation by altering intestinal permeability."

Lledós' study was funded by Instituto de Salud Carlos III. Rivier's study was funded by Bugher Centers of Excellence in Hemorrhagic Stroke Research. Lledós and Rivier reported no financial conflicts.

European Stroke Organisation Conference (ESOC) 2022: ePoster P0452 and Abstract 0115. Presented May 4, 2022.

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