Various harmful metabolites and toxins are produced when the different strains of microbes that make their home in our intestines are out of balance. While such changes are known to occur in patients with Alzheimer’s, this could be no more than coincidence and not related to the disease at all.
Well, that notion has been blown out of the water thanks to a new study which proves a causal connection.
For the study, scientists in England, Ireland and Italy recruited 69 patients with Alzheimer’s disease and 64 cognitively healthy control subjects. They took blood samples from each participant and stool samples from a subset of them.
Next, the researchers relied on a group of laboratory rats. After a course of antibiotics to wipe out their gut bacteria, 32 rats were divided into two groups. One group received a fecal microbiota transplant (FMT) from the Alzheimer’s patients while the other half received an FMT from the controls.
Memory Impairments Grew
After ten days the researchers gave the rats a range of tests to evaluate cognition and behavior. The rats with an FMT from Alzheimer’s patients displayed memory impairments. This showed, for the first time, that Alzheimer’s could be transferred to young animals through transplant of gut microbiota.
In the fecal samples, Alzheimer’s patients had more inflammation-promoting bacteria, and these changes were directly associated with their cognitive status.
One of the research team, Professor Sandrine Thuret, explained, saying, “This study represents an important step forward in our understanding of the disease, confirming that the make-up of our gut microbiota has a causal role in the development of the disease.”
The Importance of Hippocampal
Neurogenesis
The researchers were particularly interested in studying the hippocampus, a key memory and mood area of the brain, and one of the first to be impacted by Alzheimer’s.
The hippocampus is also host to a population of neural stem cells, which generate new neurons throughout life in a process called adult hippocampal neurogenesis (AHN).
Neuroscientist and senior researcher Yvonne Nolan explained its importance, saying: “The memory tests we investigated rely on the growth of new nerve cells in the hippocampus region of the brain. Animals with gut bacteria from people with Alzheimer’s produced fewer new nerve cells and had impaired memory.”
And rats receiving FMT from patients with poorer cognitive status displayed greater impairment in hippocampal neurogenesis. In addition, impairment was seen in various metabolites in the hippocampus involved with maintenance and growth.
In further lab tests, serum from Alzheimer’s patients lowered neurogenesis in human neural stem cells. What’s more, the levels of gene expression corresponded to cognitive status and species of bacteria in their stools.
The team wrote in the journal Brain in October that their findings “support the hypothesis that impaired neurogenesis may be the converging link between the observed altered gut microbiota composition and cognitive impairment in Alzheimer’s disease.”
Keeping Your Microbiome in Good Shape
The authors point out that diet, physical activity, stress, and other environmental factors, such as medication use, influence the composition of the gut microbiota.
It’s important, therefore, to eat gut friendly prebiotic foods like vegetables, fruit, and whole grains, and probiotic foods such as yogurt, kefir, sauerkraut, and green olives. Regular exercise and managing stress also promote good gut health.
There’s another nutrient to take note of, specifically for its actions in the brain. I’m talking about taurine. Taurine appears to help protect the brain against damage from bad intestinal microbes, as the scientists wrote in their paper:
“Critically, taurine has been found to regulate adult and developmental AHN. Taurine was decreased in the hippocampus of Alzheimer’s-FMT rats. Taurine administration has repeatedly been shown to increase hippocampal neural stem and progenitor cell proliferation, survival, and neurogenesis both in vivo [animals] and in vitro [cellular studies].
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