Researchers at Washington University School of Medicine in St. Louis have found that mice fed tryptophan developed immune cells that enable a more balanced gut. Tryptophan is an α-amino acid that is used in the making of proteins and an essential building block for a very important brain chemical, serotonin. Low levels of tryptophan are associated with insomnia and a host of other mental health issues like depression, anxiety, ADHD, and binge eating. If you have ever experienced feeling very tired after having a turkey dinner or warm milk before bed you can probably thank tryptophan. But this important amino acid is the least common in our bodies.
The paper’s senior author Marco Colonna, MD, the Robert Rock Belliveau MD Professor of Pathology states (via ScienceDaily) the study found a link between bacterial species and popular probiotic Lactobacillus reuteri and the development of a population of cells that promote a neutralizing effect on inflammation. The study got its eureka moment when a researcher noticed that two genetically identical groups differed greatly in these immune cells that promote balance. Since these 2 groups grew up separately it seemed to indicate there was an environmental factor at work. The paper published in the journal Science described how the research team sequenced DNA from the intestines of the two groups of mice, to find six bacterial species present in the mice with the immune cells but missing from the mice without them. The researchers turned next to a group of mice raised in a completely sterile environment so that they lacked a gut microbiome and therefore did not develop this kind of immune cell. When L. reuteri was introduced to the sterile environment mice, the vital immune cells were repopulated.
Next the the researchers grew L. reuteri in liquid and purified the active component from the liquid, which turned out to be a byproduct of tryptophan metabolism known as indole-3-lactic acid. The researchers doubled the amount of tryptophan, which was already in the mice diet. The result was the number of the vital immune cells rose by about 50 percent, but when tryptophan levels were cut in half, the number of cells sank by half.
So while we always need to be cautious in getting our hopes up on encouraging studies using mice, we humans have the same tolerance-promoting cells, and most of us host L. reuteri in our gastrointestinal tracts. Until this study is applied to people we will not know whether tryptophan byproducts from L. reuteri induce the cells to develop in people. But it is perhaps not a coincidence that defects in genes related to tryptophan have been associated with people with inflammatory bowel disease.
- Cervantes-Barragan L, Chai JN, Tianero MD, DiLuccia B, Ahern PP, Merriman J, Cortez VS, Caparon MG, Donia MS, Gilfillan S, Cella M, Gordon JI, Hsieh C-S, Colonna M. Lactobacillus reuteri induces gut intraepithelial CD4 CD8 alpha alpha T cells. Science, Aug. 3, 2017