Yanning Syrup ameliorates the lipopolysaccharide-induced inflammation: Adjusting the gut microbiota, short-chain fatty acids, and the CD4+ T cell balance

As a commercial Chinese patent medicine, Yanning Syrup (YN) is used to treat acute upper respiratory tract infections and acute enteritis effectively in clinical practice. However, the underlying mechanism remains unclear.To reveal the effect of YN on gut microbiota dysbiosis, and explore the potential role of the gut microecosystem and CD4⁺ T cell immune homeostasis in YN-treated respiratory and intestinal diseases in lipopolysaccharide (LPS)-induced inflammatory rats.Inflammation in rat models was induced by intraperitoneal injection of LPS (8 mg/kg). Histological changes were observed by H & E staining. Changes in gut microbiota and short-chain fatty acid (SCFA) production were analysed using 16S rRNA gene sequencing and targeted metabolomics. A Luminex cytokine microarray and enzyme-linked immunosorbent assay (ELISA) were conducted to evaluate the serum and colon cytokine profiles. The frequencies of immune cells, including Th1, Th2, Th17 and Treg cells in the mesenteric lymph nodes (MLNs), bronchoalveolar lavage fluid (BALF) and whole blood were phenotyped using flow cytometry.The YN-treated rats showed less colon inflammation, as evidenced by the reduction in mortality rate and histology score. Notably, YN was found to improve the immunosuppressed state induced by LPS in rats, which not only upregulated the levels of the proinflammatory cytokine IL-17A and the immunosuppressive cytokines IL-4 and IL-10 in colon tissue but also increased the levels of IL-1α, IL-5, IL-7, IL-12 (p70), GM-CSF and VEGF in serum. The numbers of Th17 cells and Treg cells in the MLNs, blood, and BALF of model rats were regulated by YN, with the restoration of the Th17/Treg balance. Additionally, the Th1/Th2 balance in MLNs and whole blood of model rats was restored after YN administration. Sequencing of 16S rRNA gene indicated that YN-treated rats exhibited greater gut microbial diversity and flora composition, specifically inhibiting some harmful bacteria such as Enterobacter and Blautia and increasing Firmicutes and Actinobacteria. Targeted metabolomics analysis demonstrated an increase of SCFA (acetic acid, butyric acid, valeric acid, and hexanoic acid) production in YN-treated rats. Most of the dominant bacterial genera regulated by YN administration were correlated with the concentrations of SCFA and inflammatory cytokines.These results demonstrated that YN could ameliorate LPS-induced inflammation in rats by modifying gut microbiota, increasing microbiota-derived SCFA production and regulating the balance of Th1/Th2 and Treg/Th17 cells.