Chang'an II Recipe alleviates visceral hypersensitivity in IBS-D rats by inhibiting mast cell activation through the AhR-Notch1 pathway

Irritable bowel syndrome with diarrhea (IBS-D) is a common functional gastrointestinal disorder. It is often accompanied by anxiety and depression, and severely impacts patients' quality of life. Visceral hypersensitivity is closely associated with the pathogenesis of IBS-D, potentially involving activation of the AhR-Notch1 signaling pathway in mast cells. Chang'an II recipe is a formulation developed by Prof. Tang Xudong based on the classical formula of Tong-Xie-Yao-Fang, which has documented clinical efficacy in the treatment of IBS-D. However, the mechanism underlying the action of the Chang'an II recipe in treating IBS-D is not fully understood. To investigate the ameliorative efficacy of the Chang'an II recipe on rat models of IBS-D, as well as its underlying mechanism in IBS-D rats and the RBL-2H3 rat basophilic leukemia cell line. The IBS-D model rats received high, medium, and low doses of the Chang'an Ⅱ recipe and the AhR inhibitor Kyn by oral gavage for 14 days. The body weight, food intake, fecal water content (FWC), abdominal withdrawal reflex (AWR), and severity of diarrhea symptoms were assessed. Sera and colonic tissues were collected for histopathological analyses, and relevant indices were measured in tissues and RBL-2H3 cells. The Chang'an II recipe effectively alleviated weight loss and increased food intake and intestinal absorption in IBS-D rats. It also alleviated diarrhea, decreased visceral hypersensitivity, and reduced intestinal inflammation. The mechanism underlying the reduction in visceral hypersensitivity was associated with AhR upregulation and Notch1 downregulation, reducing activation of p-p38, p-JNK, and p-ERK1/2. This process suppressed mast cell activation and inhibited the production of biologically active substances such as mast cell tryptase, histamine, IL-4, and TNF-α. The Chang’an II recipe alleviates IBS-D symptoms by modulating the AhR/Notch1 signaling pathway, suppressing mast cell activation, and downregulating the PAR2/TRPV1 axis in intestinal afferent nerves. These findings provide novel mechanistic insights into its therapeutic effects, highlighting its potential as a targeted treatment for IBS-D.