Published online: September 23, 2016
Currently available pharmaceuticals for allergic asthma improve symptoms but cannot cure the disease. Probiotic bacteria have been proposed as food additives for prevention of allergic diseases. However, clinical intervention trials yielded inconsistent results. One important reason for the conflicting outcomes is most likely the complexity of the reciprocal crosstalk between probiotic bacteria and the host’s microbiota and immune cells.
In an article recently published in The Journal of Allergy & Clinical Immunology, (JACI) Kepert and colleagues hypothesized that using specified substances derived from probiotic microbes could provide an attractive alternative. Other than living bacteria with complex fates and response patterns in the host, they should have definable properties with a provable mode of action.
The researchers therefore screened supernatants from 37 probiotic bacterial strains for their ability to reduce the secretion of the allergy-promoting chemokine CCL17 by a human T-cell line. They detected bioactivity in 13 strains, which was further confirmed in a second bioassay which was based on the downregulation of co-stimulatory molecules on human dendritic cells. The fractionation of two selected supernatants from Lactobacillus rhamnosus GG and L. casei W56 was followed by detailed chemical characterization and thus lead to the identification of the amino acid D-tryptophan (D-Trp) as bioactive substance. Of note, L-tryptophan and 11 other D-amino acids were inactive.
D-Trp was feed to mice via drinking water. Mice subsequently challenged with an allergen displayed reduced allergic airway inflammation (AAI) and improved lung function as compared to mice without D-Trp supplementation. In addition, oral D-Trp supplementation increased the diversity of the gut microbiome which was diminished in non-supplemented AAI-mice.
The researchers propose that bacteria-derived D-tryptophan could play a wider role in human health than previously thought. Overall, their findings support the concept that defined bacterial products can be exploited for future development of preventive strategies for chronic inflammatory disorders.
The Journal of Allergy and Clinical Immunology (JACI) is an official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.