gut bacteria alzheimer's

Study: Clear Link Between Gut Bacteria and Alzheimer’s

By Hanna Nelson | December 15th, 2020

As scientists search for ways to prevent Alzheimer’s, a team of researchers in Switzerland and Italy confirm the link between an imbalance in gut microbiota and the hallmark proteins of the disease.

Scientists have long speculated whether intestinal bacteria accelerates the development of Alzheimer’s, and now, some helpful new data has emerged: Previously, researchers discovered that people with Alzheimer’s have a different gut microbiome than people without the disease. Now we not only know that the body’s microbial composition may play a role in Alzheimer’s, but that proteins in gut bacteria may trigger the disease

New research by a team of Swiss and Italian researchers found a clear correlation between the gut microbiota and amyloid plaques in the brain. Amyloid plaques are linked to the neurodegeneration that accompanies diseases like Alzheimer’s. According to the study, published in the Journal of Alzheimer’s Disease, proteins produced by gut bacteria may alter the responses of the nervous and immune systems. These altered responses may, in turn, trigger Alzheimer’s. 

“Our results are indisputable,” Moira Marizzoni, a researcher at the Fatebenefratelli Center in Brescia and a co-author on the study, said in a news release. “Certain bacterial products of the intestinal microbiota are correlated with the quantity of amyloid plaques in the brain.” 

The study featured 89 participants between ages 65 and 85. Many participants had been diagnosed with Alzheimer’s or similar neurological diseases, and some did not report any memory problems. The researchers used PET brain imaging to measure the participants’ levels of beta-amyloid. The team then examined participants’ blood to identify certain proteins and markers of inflammation produced by intestinal bacteria. The proteins in question were lipopolysaccharides and certain short-chain fatty acids like acetate, valerate, which correlated to larger amyloid deposits in the brain.

According to Barbara Bendlin, an associate professor of medicine at the University of Wisconsin-Madison who is not involved in the study, what remains unclear is the reason that the link between bacteria in the gut and beta-amyloid in the brain exists. One theory suggests that beta-amyloid is an antimicrobial peptide, defending the brain from microbes that enter the brain. 

“Some people have studied this, and there seems to be a little bit of evidence for it,” Bendlin told Being Patient. “For example, if you take an animal and you put microbes in its brain, amyloid could come in to almost protect the brain by surrounding that microbe … but we don’t have good evidence yet that microbes get into the brain.

Research in gut microbiome and neurodegenerative diseases is a nascent field, she noted, and more studies are needed to better understand how the composition of the gut is related to brain health. 

“Some people are still fairly skeptical,” Bendlin said. “And it’s good: We need to be skeptical because the studies just aren’t there yet. But there are more and more investigators who are getting interested in this idea.” 

“Overall, in the field of Alzheimer’s disease and other related dementias, the doors have really been opened,” she continued. “People are coming at this from all possible angles, and that’s what we really need to beat this disease.”

According to Giovanni Frisoni, a co-author of the study and director of the University Hospitals of Geneva Memory Centre, the findings of the recent study may bring rise to protective strategies against Alzheimer’s, such as administering a bacterial cocktail to feed ‘good’ bacteria to people’s intestines. 

“However, we shouldn’t be too quick to rejoice,” Frisoni said in a news release. “Indeed, we must first identify the strains of the cocktail. Then, a neuroprotective effect could only be effective at a very early stage of the disease, with a view to prevention rather than therapy.” 

Additional reporting by Nicholas Chan 

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