An illustration of the human microbiome. Research shows that bacteria in the gut can affect our mental health.
MEHAU KULYK/Getty Images/RF Science Photo Library
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MEHAU KULYK/Getty Images/RF Science Photo Library
The gut microbiome – the ecosystem of tiny organisms inside all of us – has emerged as a fertile new territory to study a variety of psychiatric and neurological conditions.
Research has demonstrated that the brain and gut communicate continuously and that changes in the microbiome are linked to mood and mental health. Now one The study was published this month IN Natural mental health found distinct biomarkers in the microbiota of people who are highly resilient in the face of stressful events.
“The precision with which these samples appear is truly astonishing,” said Arpana Churcha neuroscientist at UCLA’s Goodman-Luskin Center for Microbiology who led the new study.
The study is a starting point for future human studies that some researchers believe could eventually lead to treatments. It may also reveal biomarkers in the microbiome that help guide decisions related to treatment and mental health.
Resilience linked to anti-inflammatory bacteria
For their analysis, Church and her team separated 116 adults without a mental health diagnosis into two groups based on how they scored on a scale of psychological resilience.
Next, they sifted through large amounts of data collected from brain images, stool samples, and psychological questionnaires and fed it into a machine learning model to find patterns.
Analysis of gene activity, metabolites and other data revealed several key associations within the highly resilient group. In the brain, there are increased characteristics associated with improved emotional regulation and cognition.
“Think of this front part of the brain like brakes,” Church says. Highly resilient people have really effective braking systems and are less likely to overreact.”
They then delved deeper into the microbiome, looking not only at the abundance of different microorganisms but also at their genetic activity to see what they were doing.
Two main patterns emerged in people with greater stress resilience: Activity in their microbiome was associated with reduced inflammation and improved intestinal barrier integrity.
Study showed that patients with a variety of psychiatric conditions have a gut microbial balance that includes more of certain pro-inflammatory bacteria and less of anti-inflammatory bacteria.
Church notes that the intestinal barrier absorbs nutrients and keeps toxins and pathogens from entering the bloodstream. When that substance becomes more permeable or “leaks,” the inflammation that occurs acts as a stress signal to the brain that everything is not right.
Bacteria ‘talk’ to our nervous system
The new study fits into the rapidly expanding body of research into the brain-gut connection.
“I’m really excited to see this being done in a fairly large group of people,” said Thomas Bastiaanssena bioinformatician studying the gut microbiome and mood at the Amsterdam University Medical Center.
In recent years, he said scientists have demonstrated that there is a strong “two-way relationship” between the gut and the brain. The majority of them are based on preclinical laboratory studies using animal models, as well as some human observational studies and in vitro studies.
“All of this points to about four ways in which the microbiome communicates with the host,” Bastiaanssen said.
Along with the immune system, there is also the vagus nerve which functions like a highway, running from the brain to the gut and communicating directly with the microbiome.
These gut microbiota also “communicate” with the central nervous system by secreting neurotransmitters, such as serotonin and dopamine (about 90% of serotonin is produced in the gut and about 50% of dopamine). .
Additionally, the microbiome can produce short-chain fatty acids that help maintain the integrity of the intestinal barrier and have anti-inflammatory effects for the brain, among other things.
Just last year, Foster and her team establish that the bacterial community involved in the production of these short-chain fatty acids was reduced in depressed people with high levels of anxiety.
In recent years, other observational studies have strengthened the evidence linking the gut microbiome and mental health in humans.
For example, major studies from researchers in the Netherlands found microbiomes with less bacterial diversity predicted depression and that there is more or less of certain bacteria involved in the synthesis of neurotransmitters and short-chain fatty acids may be the key.
Foster praised the UCLA study as “novel” because it offers a comprehensive look at the brain-gut microbiome and its potential role in resilience.
She noted that the analysis showed a link between anxiety and the microbiome, which is already well established. research area. More than a decade ago, Foster and others showed this link in laboratory experiments with “germ-free” mice and anxiety.
In the context of stress, scientists have found that even short-term exposure to stress can lead to changes in the microbiome and that changes in the composition of the microbiome can lead to changes in the microbiome. may make some mice more resistant to stress.
Probiotic treatments for stress? Not yet
There are increasing efforts to translate this research into actionable treatments, using diet, prebiotic supplements and probiotics. But Bastiaanssen said the complexity of the microbiome requires a different approach than that typically used in pharmaceutical development, which tends to focus on finding a single molecule or drug.
He said it was like trying to grow a forest in the desert by planting a few seeds.
“Obviously it wouldn’t work,” he said, “because there’s no ecosystem to support it.”
He said the field of microorganisms is still in its infancy.
“We have established a link in the microbiome, gut-brain axis. We have really compelling evidence,” he said. “The next question we need to understand is how exactly does it work?”
He notes that there is some promising evidence from small human studies showing targeting the microbiome with certain diets (in one case, rich in fermented foods) may reduce inflammation.
Another trial, this one by Bastiaanssen and a team at University College Cork, found that a diet focused on vegetables and foods known to influence the microbiome, can reduce perceived stress.
While these efforts are absolutely “valuable,” Foster says the power of these studies is that they could lead to the discovery of biomarkers that can help make decisions about how to use What treatments are currently available and who would be the best candidates?
“Can I measure something in your microbiome, maybe in your blood and maybe in your brain to determine if you have depression? she speaks. “Should I give you an antidepressant… or a stimulant? Should I do cognitive behavioral therapy or tell you to exercise?”
She says that could be the value of a measurable global marker in your microbiome. And she thinks it could become an effective tool for clinical care over the next decade.
For his part, Church figured, Hypothetically, this area of research will one day be leveraged to “engineer a probiotic cocktail that could help reduce stress” and prevent the onset of certain diseases.
“The biggest problem is that we need more research to actually test these things in human trials,” she said. She admits there are a lot of unsubstantiated claims when it comes to improving the microbiome. For now, she tells people the data isn’t strong enough to know which treatments to try.
“There really isn’t anything out there that has been truly tested,” she said, “I say come back to me in a year or so and I’ll let you know.”
