24 November 2017

Microflora and brain: chicken or egg?

The connection between the composition of the gut microbiome and the development of neurodegenerative diseases was confirmed in experiments

Marina Astvatsaturyan, Echo of Moscow

At the recent in At the Washington conference of the Neurobiological Society (Society for Neuroscience), several groups of scientists presented data indicating a close relationship between gastrointestinal pathologies and neurodegenerative diseases of Parkinson's and Alzheimer's.

According to The Scientist (Research Links Gut Health to Neurodegeneration), comparing the microbial composition of the intestines of mice with Alzheimer's disease modeled with healthy control mice, Harpreet Kaur from The University of North Dakota and his colleagues found noticeable differences in the composition of the microbiome of two groups of rodents. Having eliminated with the help of probiotics the increased permeability and inflammation of the intestine in animals with alzheimer's-like symptoms, the scientists observed an improvement in their cognitive abilities: mice began to cope better with memory tests.

In another study, Ishita Parikh's group of The University of Kentucky applied a similar approach, but compared the microbiomes not of sick and healthy animals, but of mice with different variants of the APOE gene, which is uniquely associated with the risk of developing Alzheimer's disease in humans. And again, scientists found clear differences in the microbial profiles of mouse lines, which indicated "the connection of the gut microbiome with the APOE genotype, at least in this mouse model," Parikh said at a press conference following a meeting of neuroscientists. 

Another neurodegenerative disease associated with the state of the intestinal flora is Parkinson's disease: recently, Levi's corpuscles, pathological protein formations usually present in the neurons of the brain of sick people, were found in the cells of the gastrointestinal tract of animals with a model of Parkinsonism. Doris Doudet from the Vancouver Coastal Health Research Institute and colleagues exposed rats to a neurotoxin (BSSG, beta-sitosterol glycoside), which causes symptoms of parkinsonism in laboratory animals, and saw that the result was an increase in intestinal levels of CD68 protein, a marker of the inflammatory process. According to Dude, "inflammation of the lining layer in the intestine may be as indicative of Parkinson's disease as inflammation in the brain."

The main question today is what comes first, intestinal or brain symptoms, says Erwan Bezard from the Institute of Neurodegenerative Diseases at the University of Bordeaux (University of Bordeaux's Institute of Neurodegenerative Diseases). He reported finding the same symptoms of Parkinsonism in monkeys two years after he injected human Levi bodies either into the brain or into the intestines.

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