Production of bioactive structural motifs from wheat arabinoxylan via colonic fermentation and enzymatic catalysis: evidence of interaction with toll-like receptors from in vitro, in silico and functional analysis

It is well known that dietary fibers (DF) from plant-source foods can induce beneficial health effects through their physicochemical properties and utilization by the gut microbiota during fermentation, which is mainly explored with a focus on changes in the gut microbiota profile and the production of microbial-derived metabolites. Here, we characterized structural motifs (i.e., oligomers) produced during DF breakdown upon colonic fermentation and explored their interaction with toll-like receptors (TLRs) present on the surface of human intestinal and immune system cells. Firstly, a source of wheat arabinoxylan (WAX) was subjected to in vitro simulation of human colonic fermentation, followed by characterization and quantification of WAX structural motifs to explore their dynamics throughout fermentation. The identified structural motifs were further produced through enzymatic catalysis of WAX using carbohydrate-active enzymes and fractionated into six well-defined fractions of arabinoxylans and linear xylans. These fractions of structural motifs were then tested for interaction with TLR2 and TLR4 using a reporter cell assay. Results revealed structure-dependent effects, primarily with inhibition of TLR2 and activation of TLR4 depending on the degree of polymerization and branching of WAX structural motifs. The role of the fine structure of WAX structural motifs was confirmed by molecular docking, which revealed that minor structural changes substantially influence the interaction between structural motifs and TLRs. The results from in vitro and in silico studies also support the hypothesis that the direct effects of oligomers and polysaccharides on cell receptors are likely the result of complex interactions involving multiple cell surface receptors. Finally, in addition to highlighting that direct effects of structural motifs might play an important role in the overall effects of DF, this work suggests that enzymatic-tailoring design of DF can be a potential tool for producing functional ingredients with specific effects on human health.