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Episode 26: The role of microbes in gut-brain communication

/in Podcast, Season Two /by Laura

 

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The Science, Microbes & Health Podcast 

This podcast covers emerging topics and challenges in the science of probiotics, prebiotics, synbiotics, postbiotics and fermented foods. This is the podcast of The International Scientific Association for Probiotics and Prebiotics (ISAPP), a nonprofit scientific organization dedicated to advancing the science of these fields.

The role of microbes in gut-brain communication, with Prof. Emeran Mayer MD

Episode summary:

In this episode, ISAPP podcast host Prof. Dan Tancredi PhD welcomes guest Prof. Emeran Mayer MD, a gastroenterologist and researcher at University of California Los Angeles. They talk about the microbiota-gut-brain axis, covering its evolutionary origins and how this complex system works in the human body to support overall health.

Key topics from this episode:

  • Microbiota-gut-brain communication has a long evolutionary history: microbes have been around for billions of years and they stored a lot of information in their genes. At some point in evolution microbes got inside the digestive tube of a primitive marine animal called hydra and it proved advantageous for this animal.
  • The hydra shows the origin of the human enteric nervous system (ENS): microbes live inside this tube and transfer genes to the nerve cells of this digestive tube, showing the origin of neurotransmitters.
  • Today in humans the neurotransmitters influence gene expression of microbes and change the microbial behaviors; the metabolites produced feed back to the brain.
  • Prof. Mayer’s initial interest as a gastroenterologist was the ENS and how it regulates motility. Subsequently the ENS was found to regulate many gut functions. The gut also houses a large part of the immune system and a complex hormonal system, and all these systems are connected with each other and communicate with the brain.
  • There is an increasing understanding that many chronic diseases relate to Inappropriate engagement of the immune system, starting in the gut.
  • When Prof. Mayer started in the field, the term “gut health” did not exist. Now it’s a ubiquitous term which has associations with wellbeing, acknowledging the gut has influence on many other body systems.
  • The associations between gut (microbiota) and brain health started with provocative animal experiments from Cork, Ireland, in which researchers manipulated the gut microbiome and found changes in emotion-like behaviors of animals. However, it has been difficult to translate to human interventions.
  • How do microbiome-targeted dietary interventions affect the brain? We do know the “Standard American Diet” (deficient in fiber) has changed the gut microbes in a way that compromises the production and maintenance of the gut barrier. 
  • There are many misconceptions about “leaky gut”, but basically contact between beneficial microbes and immune system sensors stimulate the immune system of the gut to low-grade inflammation. This can alter the tight junctions, making the gut more permeable, and ultimately this can affect the brain. Diet can affect the role of microbes in maintaining an effective gut barrier.
  • Prof. Mayer describes how he ended up studying the microbiota-gut-brain axis – he would not have predicted how important and popular this field would become.
  • In the future, there will be more sophisticated and personalized interventions. He sees a paradigm shift happening from reductionist approaches in medicine to systems biological approaches. This field is making us acknowledge that diet will play a major role.

Episode links:

About Prof. Emeran Mayer MD:

Emeran A Mayer is a Gastroenterologist, Neuroscientist and Distinguished Research Professor in the Department of Medicine at the David Geffen School of Medicine at UCLA, the Executive Director of the G. Oppenheimer Center for Neurobiology of Stress & Resilience and Founding Director of the Goodman Luskin Microbiome Center at UCLA. He is one of the pioneers and leading researchers in the bidirectional communication within the brain gut microbiome system with wide-ranging applications in intestinal and brain disorders. He has published 415 scientific papers, co edited 3 books and has an h-index of 125. He published the best selling books The Mind Gut Connection in 2016, the Gut Immune Connection in June 2021, and the recipe book Interconnected Plates in 2023. He is currently working on a MasterClass and a PBS documentary about the mind gut immune connection. He is the recipient of numerous awards, including the 2016 David McLean award from the American Psychosomatic Society and the 2017 Ismar Boas Medal from the German Society of Gastroenterology and Metabolic Disease.

The small intestinal ‘mysteriome’: A potentially important but uncharted microbiome

/in Consumer Blog, ISAPP Science Blog /by KC

By Eamonn MM Quigley MD FRCP FACP MACG FRCPI, Lynda K and David M Underwood, Center for Digestive Disorders, Division of Gastroenterology and Hepatology, Houston Methodist Hospital, Houston, Texas, USA

 

Over recent years, countless publications have documented the status of the microbiota of the gastrointestinal tract by examining fecal samples. While this approach does provide a “snapshot” or representation of what is going on in the gut, and especially in the colon, it is a crude measure of the complex interactions between micro-organisms in the gut, as well as between these same microorganisms and us (their hosts). Fecal samples comprise a terminal microbial ecosystem, characterized by depletion of readily fermentable substrates, with a concomitant change in microbial composition, even compared to those farther upstream in the colon. It is unlikely, for example, that studies using fecal samples provide a full picture of what happens when bacteria (or other microorganisms) “talk” to the lining of the gut (the mucosa) or interact with the immune system of the intestine. Even less likely is that they provide any insights into bacterial populations in the small intestine, where most of the digestion of food and absorption of nutrients takes place. The small intestine also possesses the most abundant immune tissue of the entire gastrointestinal tract.

Yet, details of which bacteria actually inhabit this long and important organ, the small intestine, are sketchy. This lack of knowledge has apparently not restricted much theorizing and speculation about the role of an overgrowth of colonic-type bacteria (referred to as small intestinal bacterial overgrowth – SIBO) in the small intestine in many symptoms, disorders, and diseases. According to one especially popular theory – the “leaky gut” hypothesis – the list of conditions is nearly endless. The “leaky gut” hypothesizes that dysbiosis in the small intestine (in other words SIBO) and a disruption of the gut barrier leads to “leakage” of bacteria and bacterial products into the circulation causing inflammation, allergy, and autoimmunity.

There are several leaps of faith involved in “leaky gut” including, of course, the definition and diagnosis of SIBO. Traditional methods of diagnosing SIBO (obtaining fluid samples directly from the upper small intestine or a variety of breath tests) are fraught with problems and, in essence, have precluded a universally accepted definition of SIBO.

Fundamental to this dilemma is the definition of the normal small intestinal microbiome – how can we diagnose abnormal when we do not know the limits of normality? I would contend that, while there are situations where it is undoubted (based on the clinical context and various laboratory and other findings) that SIBO is an issue, there are countless more instances where SIBO is over-diagnosed and incorrectly implicated as the cause of an individual’s symptoms. This is an important issue as it can lead to the inappropriate use of antibiotics – something we all wish to avoid.

There is some good news – clever techniques exist for obtaining uncontaminated fluid samples from the small intestine, a capsule technology that permits live sampling of intestinal gases (generated by bacteria) as it traverses the intestine and the application, at last, of high-throughput sequencing, metagenomics, metabolomics, and metatranscriptomics to small intestinal microbiota suggest that the accurate definition of the normal small intestinal microbiome is not far off. At that time, we can all agree on an accurate and clinically meaningful definition of SIBO.