The human microbiome is closely related to many aspects of our health. The gut is thought to have a direct impact on the brain in a relationship known as the gut-brain axis. Researchers have been interested in deciphering the connections between the microbes in our guts and various diseases, in part because it may be possible to treat some diseases by modifying the microbiome. Probiotics have therapeutic potential, and may pose a much lower risk than some pharmaceuticals.
Researchers have now used a mouse model of Alzheimer's disease to investigate how a major changes in the gut microbiome impact the neurodegenerative disorder and primary cause of age-related dementia. Reporting in Frontiers in Behavioral Neuroscience, the study authors determined that in a mouse model of Alzheimer's disease, probiotics helped prevent the onset of dementia. Bacterial therapeutics may be useful in relieving the symptoms of Alzheimer's disease in humans too.
"We found that modulating the gut microbiome by fecal implants in germ-free mice induces behavioral and cognitive changes in an Alzheimer's disease model," said senior study author Jacob Raber, Ph.D., a professor at the Oregon Health & Science University School of Medicine. "To the best of my knowledge, no one has shown that before in an Alzheimer's disease model."
Previous work has shown that the gut microbiome of Alzheimer's patients is disrupted compared to normal mice, and there is an association between some bacterial genes and the cognition and behavior of mice that carry Alzheimer's disease risk genes.
This study used fecal transplants to study how changes the microbiome affected the mouse model. Fecal transplants are currently only used to treat the aftereffects of a severe type of gastrointestinal infection, but scientists are currently investigating how they might be used as therapeutics for other conditions.
This research revealed that groups of mice carrying three genotypes experienced behavioral and cognitive changes after the fecal microbiota transplants. Two of the three genotypes relate to an increase in there risk of Alzheimer's. The changes seen in the mice varied based on sex.
More research will be needed before researchers can determined exactly how the microbiome has this impact on disease progression, and how those impacts are mediated by genes, sex, or environmental influences.
"People can buy probiotics over the counter, but we want to make sure the right treatment is being used for each patient, and that it actually benefits them," Raber said. "The gut microbiome is a complex environment. If you change one element, you'll also change other elements, so you want to make sure to select a probiotic that promotes brain health and brain function for each patient, while limiting any negative side effects."