Anti-Inflammatory and Immunomodulatory Effects of Glycyrrhiza uralensis Fisch. on Ulcerative Colitis in Rats: Role of Nucleotide-binding oligomerization domain 2/Receptor-interacting protein 2/Nuclear factor-kappa B Signaling Pathway.

Abstract

Ethnopharmacological relevance: As a traditional Chinese herb, Glycyrrhiza uralensis Fisch. exhibits a range of pharmacological activities, including anti-inflammatory, immunomodulatory and antifibrotic, which suggests its therapeutic potential for inflammatory bowel disease, and related mechanisms need to be further clarified.

Aim of the study: To evaluate in vivo anti-inflammatory effects of Glycyrrhiza uralensis Fisch. aqueous extract (GE) on 2, 4, 6-trinitrobenzene sulfonic acid (TNBS)-induced acute experimental colitis rat model and its potential mechanisms.

Materials and methods: The protective effects of GE on IBD were evaluated in vivo using a TNBS and 75% ethanol-induced ulcerative colitis (UC) model. The evaluated clinical and anatomical indexes included body weight, colon length, disease activity index (DAI) score, Colonic Mucosal Damage Index (CMDI) score. The percentages of T, B lymphocytes, NK cells, and macrophages in the colon, spleen and peripheral blood were investigated by flow cytometry. Colon tissues were stained with Hematoxylin and Eosin (H&E) for histopathological examination. After using transcriptome sequencing to screen targeted genes, the expression of related genes was detected by Real-Time Quantitative Polymerase Chain Reaction (RT-qPCR) and Western blot (WB).

Results: The decrease of food intake, soft feces, and colon histopathological injury were observed in colitis rats, which were alleviated by GE, with the best therapeutic effect in the 100 mg/kg GE group. The average CMDI scores of colon in UC rats were decreased from 4.0 to 1.5. The percentages of CD161a⁺ NK cells, CD68⁺ total macrophages, CD68⁺/CD161a⁺ M1 type macrophages, CD3⁺ T lymphocytes, and CD45RA⁺ B lymphocytes were decreased in the spleen and colon. The transcriptomics analysis of colon showed that the results were mainly related to the TNF signaling pathway and NF-κB signaling pathway. The RT-qPCR and WB results determined that the upregulated expression of nucleotide-binding oligomerization domain 2 (NOD2), receptor-interacting protein 2 (RIP2), nuclear factor-kappa B (NF-κB), tumor necrosis factor-α (TNF-α) in the colon of the colitis rats were downregulated by GE treatment.

Conclusion: The research results indicate that GE can exert therapeutic effects on TNBS-induced UC in rats by alleviating cell injury and inflammatory responses, and its mechanisms may be related to the regulation of NOD2/RIP2/NF-κB signaling pathway.