The intestinal flora can also have an impact on our cognitive functions and the brain via the gut-brain axis. Certain compositions of the intestinal flora appear to be associated with neurodegenerative diseases such as Alzheimer’s, Parkinson’s and multiple sclerosis.
An Indian research team has summarized the current state of knowledge about the connection between the intestinal flora and neurodegenerative diseases in a current study and also identified possible underlying mechanisms.
Far-reaching effects of the intestinal flora
Billions or perhaps even trillions of microscopic organisms (microbes) live in our gastrointestinal tract, which together form the so-called intestinal microbiome (intestinal flora), the researchers explain.
These microbes have, among other things, a significant influence on the immune system, digestion and the formation of vitamins and enzymes. In addition, according to recent study results, the intestinal flora can also influence the brain and behavior via the gut-brain axis.
Connection with neurodegenerative diseases
In addition, initial studies have already shown a connection between the intestinal microbiota and neurodegenerative diseases, which are characterized by the slow degeneration of neurons in the central nervous system, the researchers report.
Neurodegenerative diseases often lead to debilitating cognitive, physical and psychological problems and ultimately to the loss of certain brain functions, experts continue. The most well-known include Alzheimer’s, Parkinson’s, multiple sclerosis and amyotrophic lateral sclerosis (ALS).
In order to determine the connection between neurodegenerative diseases and the intestinal flora more precisely and to determine the possible mechanisms, the team looked at almost 2,000 research papers in the new study, of which 415 were ultimately taken into account.
Changes in intestinal flora can be detected
It was shown that people with Alzheimer’s have a special microbiota profile with an overpopulation of certain microbes compared to healthy people. According to the researchers, similar changes in the composition of the intestinal microbiota were also found in people with multiple sclerosis and Parkinson’s disease.
In addition, the most recent study taken into account indicated that dysbiosis (imbalance of intestinal flora) has a significant influence on the risk of neurodegenerative diseases.
Connection via the gut-brain axis
The central nervous system and the gastrointestinal system interact in a complicated network known as the gut-brain axis, the researchers explain. There is a dynamic connection between the intestinal flora and the brain via complex microbial, neurological, hormonal and immunological pathways.
This interaction affects a variety of physiological processes, such as mood regulation, cognitive abilities, regulation of the immune response and even behavior.
How does the connection arise?
The dysbiosis of the intestinal microbiota could play a role in neurodegenerative diseases in various ways. Here, the researchers particularly emphasize the promotion of inflammation, the altered production of metabolites and the misfolding and aggregation of proteins.
Chronic inflammation in the brain is often associated with neurodegenerative diseases such as Alzheimer’s, Parkinson’s and ALS, and dysbiosis in the gut microbiota can promote an inflammatory environment in various ways, the experts explain.
For example, it is possible to promote inflammation through the metabolic products of dysbiotic microorganisms, and in the event of a dysbiosis-related disruption of the intestinal barrier function, microbial compounds can enter the bloodstream and set an inflammatory cascade in motion, the researchers continue.
A healthy intestinal flora also produces metabolites (metabolic products of the microbiota) that have neuroprotective properties. However, in dysbiosis, the body may lack these metabolites, which can be a factor in the development of neurodegenerative diseases, explains the research team.
Misfolded proteins are also a possible factor, as they are associated with neurodegenerative diseases and, according to recent studies, may be able to reach the brain from the intestine via prion-like pathways. Dysbiosis supports this process by promoting the accumulation of misfolded proteins and their subsequent transport to the brain.
- Gut-brain axis: Dialogue between gut and brain decoded
- Gut-brain connection: How the brain fights inflammation with gut signals
- Gut-brain axis: Gut bacteria influence depression
New therapeutic approaches
Overall, it is becoming increasingly clear that the gut-brain axis can be the key to new therapeutic approaches against neurodegenerative diseases. On the one hand, determining the intestinal microbiota could be helpful in early diagnosis and, on the other hand, targeted stimulation of the intestinal flora could contribute to prevention and therapy.
However, since much of the research to date has been carried out on animals and the results may not be directly transferable to humans, further studies must first be carried out to verify the results on humans, the researchers add. (fp)