Researchers piecing together the pieces of the giant Alzheimer’s disease puzzle have uncovered a new connection between the gut and the brain, bringing them closer to fitting the next piece into place.
Animal studies have demonstrated that Alzheimer’s disease can be transmitted to young mice through the transfer of gut bacteria, confirming a link between digestive and brain health.
A 2023 study further supports the theory that inflammation may be the mechanism behind this phenomenon.
“We find that people with Alzheimer’s are more likely to have intestinal inflammation,” says psychologist Barbara Bendlin of the University of Wisconsin. Said When the study was published, it was reported that “brain scans of Alzheimer’s disease patients showed that those with more severe intestinal inflammation had higher levels of amyloid plaque accumulation in the brain.”
The study was conducted by pathologist Margo Heston of the University of Wisconsin and an international team of researchers. Fecal calprotectinSigns of inflammation, or “Alzheimer’s signatures,” were found in stool samples from 125 people from two Alzheimer’s Prevention Cohort Studies.
Participants underwent several cognitive tests at enrollment, as well as interviews about their family history and testing for high-risk genes for Alzheimer’s disease. Some participants also underwent laboratory tests to look for signs of amyloid protein clumps, a common indicator of the progression of pathology that causes neurodegenerative diseases.
Calprotectin levels were generally higher in older patients, but were even higher in those with amyloid plaques characteristic of Alzheimer’s disease.
Levels of other biomarkers of Alzheimer’s disease also increased with levels of inflammation, and memory test scores decreased with increasing calprotectin levels. Even in participants without a diagnosis of Alzheimer’s disease, higher calprotectin levels were associated with poorer memory scores.
“We cannot infer causation from this study. For that we need to do animal studies.” Warned Heston.
Laboratory analyses have previously shown that chemicals from gut bacteria can stimulate inflammatory signals in the brain. Other studies Increased intestinal inflammation was found in Alzheimer’s patients compared to controls.
Heston and his colleagues suspect that changes in the microbiome trigger changes in the gut that lead to systemic inflammation that is mild but chronic, causing subtle, gradually progressing damage that ultimately reduces the sensitivity of the body’s barriers.
“Increased intestinal permeability can lead to increased blood levels of inflammatory molecules and toxins derived from the gut lumen, which can cause systemic inflammation. This can result in damage to the blood-brain barrier and promote neuroinflammation, leading to neuronal injury and neurodegeneration.” Said Federico Rey, a bacteriologist at the University of Wisconsin.
The researchers are now testing mice to see whether dietary changes linked to increased inflammation could trigger a rodent version of Alzheimer’s disease.
Despite decades of research, there is still no effective treatment for the millions of Alzheimer’s disease sufferers around the world, but a better understanding of the biological processes is bringing scientists closer to a solution.
This study Scientific Reports.
An earlier version of this article was published in January 2024.
