Can intestinal bacteria affect the aging of the brain?


Neurodegenerative diseases, such as Alzheimer’s and Parkinson’s, lead the patient to a constant cognitive and / or motor decline, greatly reducing his/her quality of life. Recent studies suggest a possible involvement of the microbiota-intestine-brain axis in the genesis and progression of these diseases.

Knowing and treating neurodegenerative diseases is a problem that is becoming more and more topical, as a result of the aging of the population and a longer life expectancy. Neurodegenerative diseases represent a group of chronic pathologies, which include Alzheimer’s disease and Parkinson’s disease, that lead to a constant cognitive and / or motor decline, greatly reducing the person’s and his/her family’s quality of life. The mechanisms underlying these diseases are not yet fully known. These are syndromes with a slow but progressive evolution, caused by multiple genetic and environmental factors.

Recent studies suggest a possible involvement of the microbiota-intestine-brain axis in the genesis and progression of these diseases. The gastrointestinal microbiota, the set of microbes (bacteria, fungi, yeasts) that colonize the tract that goes from the mouth to the intestine, is in constant communication with the central nervous system both indirectly, through the bloodstream, and directly, through the autonomic nervous system (in particular the vagus nerve), the trigeminal in the mouth and in the nasopharynx and the olfactory receptors in the roof of the nasal cavity.

It is thought that the alteration in the composition of the microbiota, a condition called “dysbiosis”, leads to alterations of the microbiota-intestine-brain axis, influencing the progression of neurodegenerative pathologies through:

  • The immunological mechanism, i.e. the activation of inflammatory cells of the immune system that induce inflammation of the central nervous system
  • The chemical mechanism, i.e. the induction of oxidative toxicity both due to the excessive release of free radicals and with the lower production of antioxidant factors of microbial origin
  • The inflammatory mechanism, i.e. the release of thousands of potentially harmful microbial molecules, which can directly and indirectly affect the central nervous system, such as the production of microbial amyloid proteins
  • The genetic mechanism, i.e. the presence of a genetic asset of the individual that leads to a greater presence of “unfavorable” microbial species at the expense of those “favorable”

A modulation of the microbiota-intestine-brain axis, using probiotics, prebiotics and dietary interventions, is increasingly taken into consideration in the scientific world as an adjuvant treatment line in neurodegenerative diseases. An example is the recent approval of a prebiotic drug in China that, by acting on the composition of the intestinal microbiota, will be used in the treatment of Alzheimer’s disease. However, scientists are not yet fully in agreement on the possible involvement of the microbiota-intestine-brain axis in the genesis and progression of these diseases.