For instance some studies have found compelling links between one species of gut bacteria Morganella morganii and major depressive disorder. But until now no one could tell whether this bacterium somehow helps drive the disorder the disorder alters the microbiome or something else is at play.

The findings published Jan. 16 in the Journal of the American Chemical Society implicate an inflammation-stimulating molecule and offer a new target that could be useful for diagnosing or treating certain cases of the disorder. They also provide a roadmap for probing how other members of the gut microbiome influence human health and behavior.

There is a story out there linking the gut microbiome with depression and this study takes it one step further toward a real understanding of the molecular mechanisms behind the link said senior author Jon Clardy the Christopher T. Walsh PhD Professor of Biological Chemistry and Molecular Pharmacology in the Blavatnik Institute at HMS.

An inflammatory discovery
The study reveals that an environmental contaminant known as diethanolamine or DEA sometimes takes the place of a sugar alcohol in a molecule that M. morganii makes in the gut.

This abnormal molecule then activates an immune response that the normal molecule does not, stimulating the release of inflammatory proteins called cytokines particularly interleukin-6 (IL-6) the team found.

We knew that micropollutants can be incorporated into fatty molecules in the body but we didn’t know how this occurs or what happens next Clardy said. DEA’s metabolism into an immune signal was completely unexpected.

The team proposes that DEA could be added to the growing list of biomarkers used to detect some cases of major depressive disorder.

The study also strengthens arguments that major depressive disorder or a subset of cases could be considered an autoinflammatory or autoimmune disease and be successfully treated with immune modulator drugs Clardy said.

More broadly revealing how a bacterial product can alter human immune function by incorporating a contaminant opens the door to probing the effects of other gut bacteria in immunity and other human biological systems the authors said.

Now that we know what we’re looking for I think we can start surveying other bacteria to see whether they do similar chemistry and begin to find other examples of how metabolites can affect us said Clardy.

The advance was enabled by combining the Clardy Lab’s focus on the chemistry of small medically relevant bacteria-made molecules with the lab of Ramnik Xavier the HMS Kurt J. Isselbacher Professor of Medicine at Massachusetts General Hospital which has expertise in uncovering how the microbiome affects health and disease at the molecular level.

Source: https://hms.harvard.edu/news/drawing-line-gut-microbiome-inflammation-depression