Modified Jiaoqi powder ameliorates ulcerative colitis through gut microbiota-tryptophan metabolism-AhR signaling...

Ulcerative colitis (UC) occurs as a result of the interaction among intestinal microbiota, the intestinal barrier, and the immune system. The current treatment options have their limitations and come with side effects, thus there is an urgent need to develop new drug candidates for the treatment of UC. Modified Jiaoqi powder (MJQP) is a Traditional Chinese Medicine formulation improved from an empirical prescription prescribed by Tietao Deng, a celebrated master of Traditional Chinese Medicine. Although MJQP is a viable alternative medication for treating UC, the underlying mechanism is unclear yet.

Eight groups were designed: control, model, mesalazine group (400 mg/kg), MJQP low-, medium-, and high-dose (2.5, 5, 10 g/kg), AhR antagonist CH223191 (10 mg/kg) combined administration with MJQP (5 g/kg), and CH223191 group (10 mg/kg). The efficacy of MJQP was evaluated using the disease activity index (DAI), colonic length, and pathological alterations. RT-PCR, western blotting, alcian blue staining, immunofluorescence and transmission electron microscopy were used to detect tight junction proteins. The proportion and function of ILC2 and ILC3 were detected by flow cytometry and ELISA, and AhR signaling was examined by western blotting and RT-PCR. 16S rDNA sequencing and targeted tryptophan metabolite detection were used to detect the intestinal microflora and tryptophan metabolites.

MJQP substantially restored body weight and colonic length in UC, and reduced DAI and colonic pathological alterations, while MJQP restored tight junctions of the colon to repair the intestinal barrier. Moreover, MJQP increased the levels of IL-22 and the proportion of IL-22⁺ ILC3, while decreasing the proportion of IL-13⁺ ILC2 and the generation of IL-13. Furthermore, MJQP up-regulated AhR and CYP1A1 expression and down-regulated the expression of ST2. However, these effects were hardly observed when MJQP was administered in combination with an AhR antagonist. Most strikingly, MJQP restored the abundance of Lachnospiraceae, Lactobacillus and Clostridium, and increased the gut microbiota derived tryptophan metabolites Indole-3-acetic acid (IAA) and Indole-3-propionic acid (IPA), which serve as endogenous AhR ligands to enhance AhR signaling.

MJQP repaired the damaged intestinal barrier to facilitate the resolution of chronic colitis by modulating AhR-mediated ILC2/ILC3 balance through gut microbiota-related tryptophan metabolism.