Quinoa bran alleviates the pathological manifestations of ulcerative colitis through the Bacteroides thetaiotaomicron-indole-3-carboxaldehyde-AHR axis

Imbalances in gut microbiota are associated with the development of ulcerative colitis (UC), and tryptophan metabolism has been shown to play a crucial role in maintaining intestinal homeostasis. Gut microbe-directed diets have great potential for maintaining intestinal homeostasis by modulating tryptophan metabolism. This study aims to ascertain the key gut microbiota and tryptophan metabolites that quinoa bran exerts in ameliorating UC. The pivotal role of gut microbiota in alleviating UC was evaluated by antibiotic pretreatment and metagenomics sequencing, and the key flora and effector substances that played a role in this process were verified by metabolomic analysis and targeted bacteria/metabolite gavage. The results showed that quinoa bran (QB) intervention group restored the balance of intestinal microorganisms and significantly relieved the symptoms of UC in the way of intestinal microbial dependence. QB significantly increased the microbial tryptophan metabolites indole-3-carboxaldehyde (ICA) and indoleacetic acid (IAA). Simultaneously, the expression of the aryl hydrocarbon receptor (AHR) and its target, cytochrome P450 1A1 (CYP1A1), was elevated. Specifically, QB treatment increased the relative abundance of Lactobacillus, Akkermansia, Mucispirillum, Lachnospiraceae, and Bacteroides. Among these, only Bacteroides thetaiotaomicron and Bacteroides vulgatus are closely associated with tryptophan metabolism. In vitro and animal studies indicate that these 2 strains operate through distinct mechanisms: B. thetaiotaomicron acts through ICA-AHR axis, while B. vulgatus plays a role in alleviating intestinal inflammation. In this process, the intervention of B. thetaiotaomicron shows greater potential. Thus, this experiment demonstrated the ability of quinoa bran to prevent UC by modulating the gut microbiota and tryptophan metabolism.