© Vogt et al./Scientific Reports
A team of researchers primarily based out of the University of Wisconsin-Madison examined the gut microbiota of twenty-five Alzheimer's patients at the Wisconsin Alzheimer's Disease Research Center and compared their samples with those of twenty-five control subjects matched for age, gender, and health.

Overall, Alzheimer's patients had reduced microbial diversity, as well as a few noteworthy differences in bacterial abundance.

"Alzheimer's disease participants had decreased abundance of Firmicutes and Actinobacteria, and increased abundance of Bacteroidetes compared to control participants," the researchers reported.

Firmicutes bacteria may aid in glucose metabolism. Diabetics and obese individuals have fewer of them. Many Actinobacteria, and particularly a subset called Bifidobacterium, are used as probiotics and possibly fight inflammation in the body. On the other hand, Bacteroides have been detected at higher levels in patients with Parkinson's disease, another neurodegenerative disorder.

The current study is only correlational, so the differences in gut bacteria may result from Alzheimer's disease rather than contribute to it. However, research published earlier this year showed that transferring the intestinal bacteria of mice afflicted with Alzheimer's into the guts of germ-free mice caused the germ-free mice to develop more beta-amyloid plaques in the brain compared to if they had received bacteria from healthy mice. Beta-amyloid plaques are a hallmark sign of Alzheimer's, accruing on the neurons of people afflicted with the disease.

The researchers admit that pharmaceuticals could be influencing their study's results. Nearly all of the Alzheimer's subjects were taking the medications donepezil or rivastigmine, and it is not known how these drugs affect the gut microbiome.

It's becoming very clear that the gut and brain are intimately linked. As many as 500 million neurons dwell in the gastrointestinal system and are connected to the brain via the vagus nerve. Thus, gut bacteria have access to the brain via a veritable a super-highway, and can influence it in both good and bad ways.

The present findings add Alzheimer's to a growing list of conditions linked to changes in gut bacteria, which includes obesity, diabetes, irritable bowel syndrome, and Parkinson's disease.

Alzheimer's disease affects more than 30 million people worldwide and there is presently no way to stop or even slow its progression. The researchers hope that gut bacteria could open doors to previously unforeseen treatments.

Source:
Vogt et al. "Gut microbiome alterations in Alzheimer's disease." Scientific Reports 7, Article number: 13537 (2017) doi:10.1038/s41598-017-13601-y