Scientists know that the microbes in our gastrointestinal tract, collectively known as the gut microbiome, have a powerful impact on our health and well-being. Investigations of the close connections between the gut and the brain have indicated that there may be a link between the gut microbiome and Alzheimer’s disease. Now researchers have used a mouse model of the disease to show that by altering the microbiome with antibiotics, the development of Alzheimer’s disease can be halted. Long-term exposure to antibiotics reduced inflammation and amyloid plaque growth in male mouse brains. One important caveat, however, is that the same effect was not observed in female mice. The findings have been reported in the Journal of Experimental Medicine.
"Recent evidence suggests that intestinal bacteria could play a major role in various neurological conditions including autism spectrum disorders, multiple sclerosis, Parkinson's disease, and Alzheimer's disease," noted Professor Sangram S. Sisodia, director of the Center for Molecular Neurobiology at The University of Chicago.
Amyloid plaques in the brain, as well as the activation of a type of brain immune cell called microglia, are a hallmark of Alzheimer’s disease. While microglia can help get rid of plaques, they may also make the disease worse by inducing neuroinflammation. Scientists have previously determined that changes in the gut microbiome are observed in Alzheimer’s patients; preliminary work by Sisodia’s team suggested that gut flora can affect the disease. "While compelling, our published studies on the role of the gut microbiome on amyloid plaque formation were limited to a single strain of mice," Sisodia acknowledged.
In this work, Sisodia and colleagues used a different mouse model of Alzheimer's. In these male mice, the antibiotic treatment reduced amyloid plaques formation in males but didn’t impact female mice. In the males, microglia were changed to a state that didn’t promote neuroinflammation. The findings were confirmed by transplanting gut microbiota from treated to untreated mice, which had the same impact on the disease symptoms.
Learn more about the links between Alzheimer's disease and the gut microbiome from the video above.
The antibiotics appear to have different effects on the gut microbiota of male and female mice. In females, the drugs raised the levels of proinflammatory factors that may play a role in microglia activation.
"Our study shows that antibiotic-mediated perturbations of the gut microbiome have selective, sex-specific influences on amyloid plaque formation and microglial activity in the brain," Sisodia said. "We now want to investigate whether these outcomes can be attributed to changes in any particular type of bacteria."
The video above discusses the connection between the gastrointestinal tract and our central nervous system - the gut-brain axis.