Lactobacillus plantarum and Galacto-Oligosaccharides Synbiotic Relieve Irritable Bowel Syndrome by Reshaping Gut Microbiota and Attenuating Mast Cell Hyperactivation

Abstract

Background: Irritable bowel syndrome (IBS) significantly impairs the lifestyle and quality of life of the global population. However, the underlying pathophysiological mechanisms remain largely elusive. While conventional pharmacological approaches show limited therapeutic efficacy, emerging microbiota-targeted dietary interventions present promising alternatives.

Objectives: The present study aimed to elucidate the molecular mechanisms by which a synbiotic mitigates IBS and associated colonic dysfunctions in C57BL/6 mice.

Methods: The mouse model was induced by a Citrobacter rodentium (C. rodentium) infection combined with water avoidance stress (WAS). Galacto-oligosaccharides (GOS) were identified as the optimal carbon source for the growth of Lactobacillus plantarum ZYC501 (L. plantarum ZYC501), leading to the establishment of the synbiotic formulation.

Results: The 32-day synbiotic intervention, consisting of L. plantarum ZYC501 (1 × 10⁹ CFU/day) and GOS (10 g/L, w/w), significantly alleviated colonic transit dysfunction, visceral hypersensitivity, and anxiety-like behaviors in IBS mice. The synbiotic treatment significantly inhibited the expression levels of histamine, mast cell tryptase, and prostaglandin E2 (PGE2) (p < 0.05). The synbiotic also suppressed colonic inflammation by reducing the levels of lipopolysaccharide (LPS), TNF-α, and IL-6 (p < 0.05). Moreover, the synbiotic increased the expression of MUC2 and the production of short-chain fatty acids (SCFAs), including acetate, propionate, and butyrate (p < 0.05). In terms of gut microbiota modulation, the synbiotic reshaped the gut microbiota composition, increasing the abundance of Lactobacillus and Akkermansia while decreasing the levels of Helicobacter and Saccharibacteria. Correlation analysis further revealed a strong association among SCFAs, colonic inflammation, and the gut microbiota.

Conclusions: In conclusion, the synbiotic composed of L. plantarum ZYC501 and GOS effectively alleviates IBS and associated colonic dysfunctions by modulating the gut microbiota, reducing mast cell hyperactivity, and enhancing colonic barrier integrity. These findings provide a theoretical basis for developing gut microbiota-targeted dietary interventions for the management of IBS and improvement in gut health.

Keywords: IBS; gut microbiota; inflammation; mast cells; synbiotic.

Figure 1

The effects of the synbiotic on the behavioral assessments. (A) Growth curves of L. plantarum ZYC501 at 10 g/L sucrose, FOS, inulin, GOS, XOS, glucose, and GAM. (B) Schematic of the treatment with GOS and/or L. plantarum ZYC501. (C) Colonic transit function (n = 10). (D–F) Comparison of the AWR scores of different groups. Air pressures of 100 μL, 200 μL, and 300 μL (n = 10). (G) Central area time/ peripheral area time ratio in the open field test (n = 10). (H) Number of buried marbles (n = 10). Means with different letters (a, b, c) are significantly different from each other (p < 0.05).

Figure 2

Effect of the synbiotic on mast cell hyperactivation. (A) Representative immunohistochemical-stained images of COX-2 expression in the colon. (n = 3). The expression sites of the COX-2 were marked by the white arrows. Scale bars: 100 µm. (B) Quantification of COX-2 area based on immunohistochemical staining by ImageJ 1.52a software (n = 3). (C) Levels of histamine in the colon (ng/mg protein) (n = 6). (D) Levels of mast cell tryptase in the colon (ng/mg protein) (n = 6). (E) Levels of PGE2 in the colon (ng/mg protein) (n = 6). Means with different letters (a, b) are significantly different from each other (p < 0.05).

Figure 3

Synbiotic treatment alleviated colonic barrier integrity and inflammation in IBS mice. (A) Representative H&E-stained images of the colon tissue. Scale bars: 100 µm. (B) Representative Alcian blue-stained images of the colon. Scale bars: 100 µm. (C) Representative immunohistochemical-stained images of MUC2 expression in the colon. The expression sites of the MUC2 were marked by the white arrows. Scale bars: 100 µm. (D) Histopathological scores (n = 3). (E) Quantification of goblet cells’ area based on Alcian blue staining by ImageJ software (n = 3). (F) Quantification of MUC2 area based on immunohistochemical staining by ImageJ software (n = 3). (G) The mRNA levels of MUC2 in the colon (n = 6). (H) Levels of LPS in the colon (ng/mg protein) (n = 6). (I–K) The mRNA levels of TNF-α, IL-6, and TRPV1 in the colon (n = 6). Means with different letters (a, b, c) are significantly different from each other (p < 0.05).

Figure 4

Effects of synbiotic on SCFAs in the feces of IBS mice. The level of SCFAs in the feces (μg/g): (A–F) acetate; propionate; butyrate; isobutyrate; valerate; isovalerate (n = 6). Means with different letters (a, b, c) are significantly different from each other (p < 0.05).

Figure 5

Synbiotic modulated gut microbiota diversity in the IBS mice. (A) Venn diagram of the CON, IBS, and SYN groups. (B) PCoA of groups. (C) Representative differentially abundant gut microbiota at the genus level among the CON, IBS, and SYN groups. (D) A display diagram of significantly different species with an LDA score greater than 4.0 (n = 6). (E) Genus-level microbial diversity analysis of the CON, IBS, and SYN groups. Data presented as mean ± SEM * p < 0.05, ** p < 0.01 versus the CON group. (F–I) Relative abundance of Lactobacillus, Akkermansia, Helicobacteraceae, and Saccharibacteria at the genus level (n = 6). Means with different letters (a, b, c) are significantly different from each other (p < 0.05).

Figure 6

Correlation analysis among behavior, the level of SCFAs, and gut microbiota. In the upper right quadrant of the figure, the diameter of the circles signified the magnitude of the correlation index. The size and color of the circles indicate the degree of correlation: red denoted a positive correlation, while blue indicated a negative correlation (n = 6).