Hoping for Gut Microbiome Rejuvenation to Reduce the Incidence of Alzheimer's Disease

It has only comparatively recently become widely understood that the microbial populations making up the gut microbiome change in abundance in characteristic ways with age. Similarly, that the gut microbiome tends to be different in characteristic ways in older people who go on to develop Alzheimer's disease. It remains to be seen as to whether an altered gut microbiome is a meaningful contributing cause to Alzheimer's disease, such as via increased chronic inflammation, or a side effect of some other meaningful contribution, such as the aging of the immune system. At the least, it presents a novel way to assess risk in older people. We might hope that it will be more than that, and that means of rejuvenating the gut microbiome, such as fecal microbiota transplantation using young donors, will significantly reduce the incidence of Alzheimer's disease.

Studies have shown that the gut microbiomes of people with symptomatic Alzheimer's differ from those of healthy people with normal cognition. Now, new work shows that these differences arise early on in people who will develop Alzheimer's, even before any obvious symptoms appear. The science still has a way to go before we'll know if specific dietary changes can alter the gut microbiome and modify its influence on the brain in the right ways. But what's exciting about this finding is it raises the possibility that doctors one day could test a patient's stool sample to determine if what's present from their gut microbiome correlates with greater early risk for Alzheimer's dementia. Such a test would help doctors detect Alzheimer's earlier and intervene sooner to slow or ideally even halt its advance.

Researchers enrolled 164 healthy volunteers, age 68 to 94, who performed normally on standard tests of cognition. They also collected stool samples from each volunteer and thoroughly analyzed all the microbes from their gut microbiome. Study participants also kept food diaries and underwent extensive testing, including two types of brain scans, to look for signs of beta-amyloid plaques and tau protein accumulation that precede the onset of Alzheimer's symptoms.

Among the volunteers, about a third (49 individuals) unfortunately had signs of early Alzheimer's. And, as it turned out, their microbiomes showed differences, too. The researchers found that those with preclinical Alzheimer's had markedly different assemblages of gut bacteria. Their microbiomes differed in many of the bacterial species present. Those species-level differences also point to differences in the way their microbiomes would be expected to function at a metabolic level. These microbiome changes were observed even though the individuals didn't seem to have any apparent differences in their diets.

The team is now conducting a five-year study that will follow volunteers to get a better handle on whether the differences observed in the gut microbiome are a cause or a consequence of the brain changes seen in Alzheimer's. If it's a cause, this discovery would raise the tantalizing possibility that specially formulated probiotics or fecal transplants that promote the growth of "good" bacteria over "bad" bacteria in the gut might slow the development of Alzheimer's and its most devastating symptoms.

Link: https://www.nia.nih.gov/news/changes-human-microbiome-precede-alzheimers-cognitive-declines