Protective Effect of Saccharomyces boulardii on Intestinal Mucosal Barrier of Dextran Sodium Sulfate-Induced Colitis in Mice
Inflammatory bowel disease (IBD) is a chronic and recurrent intestinal inflammatory condition that includes ulcerative colitis (UC) and Crohn’s disease (CD). UC is characterized by mucosal inflammation limited to the colon, while CD can cause transmural inflammation and affect any part of the gastrointestinal tract, often leading to complications such as abscesses, fistulas, and strictures. Although the pathogenesis of IBD remains unclear, intestinal microbial flora is thought to play a pivotal role. The intestinal mucosal barrier, composed of a single layer of epithelial cells, prevents the uncontrolled access of bacteria to the bowel wall. When this barrier is disrupted, bacteria can penetrate the bowel wall, evoking a deregulated immune response, which is involved in the pathophysiology of IBD. Probiotics are widely used in the treatment of IBD, but the role of yeast probiotics, such as Saccharomyces boulardii (Sb), remains unclear. This study aimed to evaluate the effects of Sb on colitis and intestinal flora in a dextran sodium sulfate (DSS)-induced colitis mouse model.
Methods
The study was conducted using forty six-week-old male C57BL/6J mice, which were randomly assigned to five groups: normal control group (A), pathologic control group (B), Sb treatment group (C), mesalazine treatment group (D), and Sb combined with mesalazine treatment group (E). Colitis was induced in groups B, C, D, and E by adding 2.5% (wt/vol) DSS to their drinking water for 7 days. Group A received purified water. Groups C, D, and E were treated with Sb (0.46 mg/g per day), mesalazine (0.605 mg/g per day), or a combination of both, respectively, twice a day. The disease activity index (DAI) was evaluated daily based on body weight loss, stool consistency, and the presence of occult or gross blood. At the end of the experiment, blood and colon tissues were collected for analysis.
Results
Disease Activity Index and Histological Score
The DAI score was significantly higher in group B (2.708 ± 0.628) compared to group A (0.458 ± 0.173, P < 0.001). Treatment with Sb (group C: 1.542 ± 0.616, P = 0.005) and mesalazine (group D: 1.833 ± 0.713, P = 0.031) significantly reduced the DAI score. However, the combination treatment (group E: 2.292 ± 0.825) did not show a significant improvement compared to group B (P = 0.392). Histological analysis revealed severe colitis in group B, characterized by inflammatory cell accumulation and crypt distortion. Groups C, D, and E showed ameliorated inflammatory reactions, with significantly lower histological scores compared to group B (group C: 4.750 ± 1.832, P = 0.005; group D: 4.125 ± 0.991, P = 0.001; group E: 6.250 ± 2.550, P = 0.033).
Expression of Tight Junction Proteins
Immunohistochemical staining showed decreased expression of zona occludens-1 (ZO-1) and occludin in group B compared to group A. Treatment with Sb significantly increased the expression of ZO-1 (group C: 4.225 ± 1.316, P = 0.019) and occludin (group C: 3.525 ± 1.047, P = 0.023) compared to group B. Similar results were observed in groups D and E, but there were no significant differences among the treatment groups.
Levels of Inflammatory Cytokines
The levels of tumor necrosis factor-alpha (TNF-α) and interleukin-8 (IL-8) were significantly higher in group B (TNF-α: 716.323 ± 44.691 ng/L; IL-8: 128.992 ± 11.475 pg/mL) compared to group A (TNF-α: 509.776 ± 99.409 ng/L, P = 0.001; IL-8: 103.734 ± 18.646 pg/mL, P = 0.016). Treatment with Sb significantly reduced the levels of TNF-α (group C: 521.740 ± 90.121 ng/L, P = 0.001) and IL-8 (group C: 106.283 ± 15.906 pg/mL, P = 0.012). Similar reductions were observed in groups D and E.
Ultrastructural Changes
Transmission electron microscopy (TEM) revealed intact tight junctions in group A, while group B showed severely disrupted tight junctions, irregular microvilli, and an enlarged inter-cellular space. Treatment with Sb preserved the tight junctions and ameliorated the microvilli and inter-cellular space. Mesalazine also preserved tight junctions and microvilli, but the inter-cellular space remained enlarged. The combination treatment preserved tight junctions and microvilli but did not reduce the inter-cellular space.
Intestinal Flora Analysis
Analysis of intestinal flora at the phylum level showed that Bacteroidetes and Firmicutes were the major phyla in group A. DSS treatment increased the levels of Proteobacteria and decreased Firmicutes in group B. Treatment with Sb resulted in a higher percentage of Bacteroidetes and a lower percentage of Firmicutes, with a significant increase in the proportion of the S24-7 family. Linear discriminant analysis effect size (LEfSe) revealed that Sb specifically up-regulated the percentage of S24-7.
Discussion
This study demonstrated that Sb has a protective effect on the intestinal mucosal barrier in DSS-induced colitis in mice. Sb reduced the DAI and histological scores, preserved the expression of tight junction proteins (ZO-1 and occludin), and decreased the levels of inflammatory cytokines (TNF-α and IL-8). Additionally, Sb ameliorated ultrastructural changes in the intestinal epithelium and modulated the intestinal flora by increasing the proportion of the S24-7 family.
The anti-inflammatory effects of Sb are likely mediated through the inhibition of NF-κB and MAPK signaling pathways, which are involved in the production of pro-inflammatory cytokines. The preservation of tight junctions by Sb may be attributed to its ability to reduce the levels of inflammatory cytokines, which are known to disrupt the intestinal barrier. The specific increase in the S24-7 family by Sb suggests a potential mechanism for its protective effects, as S24-7 is involved in the degradation of polysaccharides and may play a role in maintaining intestinal homeostasis.
Interestingly, the combination of Sb and mesalazine did not show a significant advantage over monotherapy. This could be due to the short duration of the treatment in the acute colitis model, potential interactions between Sb and mesalazine, or the pH-dependent breakdown of mesalazine in the presence of Sb.
Conclusion
In conclusion, Sb is as effective as mesalazine in reducing inflammation and protecting the intestinal mucosal barrier in DSS-induced colitis in mice. The specific up-regulation of the S24-7 family by Sb suggests a potential mechanism for its protective effects. Further studies are needed to explore the long-term effects of Sb and its potential interactions with other medications in the treatment of IBD.
doi.org/10.1097/CM9.0000000000000364
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