Investigating the mechanism of intestinal nerve sensitization in irritable bowel syndrome with diarrheal
Authors: Shen Andong , Wang Qi , Li Pingping , Feng Zheming , Luo Yu , Wang Yuzhen 
Published: May 2024

Background：The intestinal microbiome, mast cells and nerve fibers have been shown to regulate intestinal physiological functions. This study aimed to investigate peripheral nerve fiber remodeling in patients with irritable bowel syndrome with diarrhea (IBS-D), sensitivity of the enteric nervous system, and the impact of intestinal flora-mast cell-nerve fiber interactions in the mechanism of enteric nerve sensitization and its relationship with clinical symptoms and psychosomatic symptoms.
Methods： Absolute quantification of Enterobacteriaceae (E. coli) and Bifidobacterium (Blif) in feces was quantified by Q-PCR, and the intestinal colonization resistance (CR), i.e. B/E value, was calculated. The total number of mast cells (MCs) and the number of activated mast cells in the intestinal mucosa were deter by immunohistochemical staining, and the activation rate of mast cells was calculated. Moreover, the percentage of anti-transient receptor potential vanilloid receptor 1 (TRPV1) and nerve fibers in the intestinal mucosa, and the percentage of anti-TRPV1 immunoreactive nerve fibers were detected through double immunofluorescence staining. Finally, the distance from mast cells to nerve fibers in the intestinal mucosa and number of mast cells within the range of 5 μm was measured.
Key results：1. CR (B/E value) was significantly lower in the IBS-D group than in the control group (P=0.010). 2. Compared with the control group, the number of activated MCs (P=0.001) and MCs activation rate (P=0.004) were higher in the IBS-D group. 3. The mean distance from MCs to neurons in the intestinal mucosa of the IBS-D group was smaller relative to that of the control group (P=0.001), and the number of mast cells within 5 μm of the nerve fibers in the intestinal mucosa of the IBS-D group exceeded that of the control group (P=0.001). 4. The percentage of nerve fiber area in the intestinal mucosa (P=0.007) and the percentage of TRPV1-positive nerve fiber area (P=0.030) were significantly higher in the IBS-D group than in the control group. 5. SAS scores were significantly higher in the abdominal pain group compared with IBS-D patients without abdominal pain (P=0.02). 6. The number of intestinal luminal Blif was negatively correlated with IBS-SSS (r=-0.449, P=0.041) and defecation frequency (r=-0.519, P=0.016). CR showed a positive defecation frequency (r=-0.675, P=0.001). The number of MCs was positively correlated with the percentage of TRPV1 area (r=0.501, P=0.021), and the percentage of anti-TRPV1-IR positive nerve fiber area (r=0.599, P=0.004). 7. The number of MCs was positively correlated with the percentage of anti-TRPV1-IR positive nerve fiber area (r=0.605, P=0.022). The VAS score showed a positive correlation with the duration of the disease (r=0.617, P=0.019). 8. Specifically, in the anxious-depressed group of IBS-D patients, the number of MCs exhibited a positive correlation with both the percentage of anti-TRPV1-IR positive nerve fiber area (r=0.577, P=0.031) and the SDS score activation (r=0.652, P=0.012).
Conclusions：IBS-D patients present with intestinal flora imbalance, MC activation, and peripheral injury sensory nerve fiber remodeling in the gut. Moreover, a crosstalk exists among them and are closely associated with clinical symptoms and psychosomatic symptoms.
Datasets supporting the figures and tables in the published article:Data is provided within the supplementary information files.The complete datasets used and/or analysed during the current study available from the corresponding author on reasonable request.