Da-Jian-Zhong decoction alleviates diarrhea-predominant irritable bowel syndrome via modulation of gut microbiota and Th17/Treg balance

Da-Jian-Zhong decoction (DJZD) is a herbal formula clinically used for abdominal pain and diarrhea induced by spleen-Yang deficiency syndrome. Recently, treatment of diarrhea-predominant irritable bowel syndrome (IBS-D) with DJZD has received increasing attention, but the underlying mechanism of action remains elusive. We aimed to evaluate the therapeutic effect of DJZD on IBS-D rats and to elucidate the underlying mechanisms. An IBS-D rats model was constructed using a two-factor superposition method of neonatal maternal separation and Senna folium aqueous extract lavage. Moreover, the effect of DJZD was evaluated based on the body weight, rectal temperature, abdominal withdrawal reflex (AWR), and Bristol stool scale score (BSS). The factors that regulate the DJZD effects on IBS-D were estimated using whole microbial genome, transcriptome sequencing (RNA-Seq), flow cytometry, and quantitative reverse transcription polymerase chain reaction (RT-qPCR) analyses. We found that DJZD alleviated the symptoms of IBS-D rats, with the low-dose (2.4 g/kg) as the better ones, as shown by the higher body mass and lower AWR score and BSS. At the phylum level, the relative abundance of Bacteroidetes was obviously increased, and at the genus level, Bacteroides was increased, while that of Firmicutes_bacterium_424 and Ruminococcus gnavus was decreased in DJZD group. The significantly enriched GO terms after treatment with DJZD mainly included the immune response, positive regulation of activated T cell proliferation, and positive regulation of interleukin-17 (IL-17) production. Importantly, flow cytometry analysis further revealed that the T helper cell type 17/regulatory T cell (Th17/Treg) balance contributed to the DJZD-induced alleviation of IBS-D symptoms, as DJZD downregulated Th17/Treg ratio and Th17 cell-related cytokines IL-17 and IL-6 levels in the colon. These results demonstrate that DJZD has a good therapeutic effect on IBS-D rats, probably by maintaining the homeostasis of gut microbiota and regulating Th17/Treg balance and its related inflammatory factors.