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Gut microbiota: new tool allows precise analysis of gut-brain connections

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In recent years, the gut microbiota and how it interacts with the central nervous system has been a very active area of ​​research. However, the mechanisms involved in the gut-brain axis are still largely unknown, which often makes it difficult to test therapies that target the gut microbiota. A new study from the Baylor Institute of Medicine (Texas Children’s Hospital, USA) may have taken a key step by developing a protocol for accurately identifying and assessing synthesized metabolites by each microbiota. This new tool would be the best way to date to understand the complex processes that govern the brain-gut connection. This could pave the way for revolutionary therapeutic strategies.

Formed from birth and unique to all, the gut microbiota is the largest microbial reserve in our body. An extremely rich and diverse ecosystem, it has been known for several years to regulate a wide range of metabolic functions. Metabolites synthesized by this microbial population are found, in particular, in the bloodstream and modulate a large number of physiological processes in the host organism.

Previous research has shown that this modulation will be regulated by direct communication between the brain and the gut microbiota. The neurons of the hypothalamus will directly detect changes in the activity of the latter and will adapt according to appetite, thirst, body temperature, reproduction, etc. As a result, the change in the microbiota is an important factor in metabolic disorders such as diabetes and obesity, as well as mental disorders such as like anxiety, depression and schizophrenia, as well as neurological diseases such as Parkinson’s disease, Alzheimer’s disease, etc.

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Altered gut microbiota can be the result of overconsumption of certain foods (or chemicals such as industrial preservatives and antibiotics). Therefore, pharmacologists are now studying a way in which this process of change can be reversed. That is, we could develop treatments aimed at restoring a certain balance at the level of the microbiota in order to act on various pathologies.

However, before these therapeutic strategies can be developed, it is necessary to understand exactly how a microbial population or group of populations mediates a given physiological process. If today we know that bacteria produce metabolites via chemical signals (in the form of fatty acids and various proteins such as histamine) reaching the central nervous system, it is still difficult to understand the exact mechanisms.

“Currently, it is difficult to determine which microbial species cause certain brain changes in a living organism,” Thomas D. Horvath, a professor of pathology and immunology at Baylor Medical Institute and lead author, said in a statement about the new study. studying. In the latest, published in the journal Nature Protocols, the researchers propose a novel laboratory protocol to identify and fully evaluate the effects of metabolites produced by each microorganism in the gut microbiota at the cellular level in animal models.

“Animal models have been instrumental in linking microbes to these fundamental neural processes,” says Jennifer K. Spinler, assistant professor of pathology and immunology at Baylor and co-author of the new study. “The current study protocol allows researchers to take steps to elucidate the specific involvement of the gut-brain axis in these conditions, as well as its role in health,” she adds.

Three step protocol

To develop their new protocol, the researchers took samples of microorganisms commonly found in the gut microbiota and cultured them in the lab. They then collected the metabolites to be analyzed using mass spectrometry and targeted metabolomics methods (based on liquid chromatography). The first consists, in particular, in the identification and quantification of compounds according to their molecular weight, while the second consists of a method for large-scale examination of metabolites.

After that, the effect of the collected metabolites on human intestinal organelles, which have the same properties as the physiologically active small intestine, was analyzed. The metabolites can also be tested in vivo in mice. The latter included groups of mice with no gut microbes and another group populated with mono-associated Bifidobacterium dentium and Bacteroides ovatus (germ-free mice colonized with a single type of intestinal microorganism).

Namely, the earlier protocols usually examined only stool samples, while the new protocol includes bacterial cultures, organoid cultures, and in vivo models in addition to monitoring the content of metabolites in stool samples. In addition, the protocol would take 3 weeks for the experimental microorganisms to colonize the intestines of the mice. Then, one to two weeks were devoted to instrumental and quantitative analysis based on mass spectrometry in liquid and tandem chromatography, as well as post-processing and normalization of the sample. This three-step model will enhance the analysis of processes driven by microbial metabolites.

As a next step, the researchers plan to extend their protocol to a specific microbial community in order to study their synergy. “Our protocol offers a way to identify potential solutions when misunderstandings between the gut and the brain lead to disease,” concludes Horvath.

Protocols of Nature.

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