Oligomannan Prebiotic Attenuates Immunological, Clinical and Behavioral Symptoms in Mouse Model of Inflammatory Bowel Disease

Abstract

Inflammatory bowel disease shows increasing prevalence, however its pathomechanism and treatment is not fully resolved. Prebiotics are non-digestible carbohydrates which might provide an alternative to treat inflammatory conditions in the gut due to their positive effects either on the microbiome or through their direct effect on macrophages and mucosa. To test the protective effects of an oligomannan prebiotic, yeast cell wall mannooligosaccharide (MOS) was administered in dextran-sulphate-sodium (DSS)-induced mouse model of acute colitis. MOS reduced DSS-induced clinical- (weight loss, diarrhea) and histological scores (mucosal damage) as well as sickness-related anxiety. DSS treatment resulted in changes in colon microbiome with selective increase of Coliform bacteria. MOS administration attenuated colitis-related increase of Coliforms, normalized colonic muc2 expression and attenuated local expression of proinflammatory cytokines IL-1a, IL1b, IL6, KC, G-CSF and MCP1 as well as toll-like receptor TLR4 and NLRP3 inflammasome. Some of the protective effects of MOS were likely be mediated directly through local macrophages because MOS dose-dependently inhibited IL-1b and G-CSF induction following in vitro DSS challenge and IL1a, IL1b, G-SCF-, and IL6 increases after LPS treatment in mouse macrophage cell line RAW264.7. These results highlight oligomannan prebiotics as therapeutic functional food for testing in clinical trials.

Figure 1. MOS attenuates disease activity in mice during dextran sulphate sodium (DSS)- induced colitis.

Mean ± SEM values for body weight gain during 8 days’ treatment (A) and daily food intake (B). At autopsy the colon weight/length ratio was calculated (C), mucosa thickness (D) was measured on histological sections. **p < 0.01 and *p < 0.05 compared to control mice; ⁺⁺p < 0.01 and p < 0.05 compared to DSS-treated animals.

Figure 2. Representative photomicrographs taken from hematoxylin-eosin stained colon sections of control, MOS treated, DSS-treated and DSS + MOS-treated mice.

Note the epithelial erosion, disintegrated crypts and piling of leukocytes in DSS-treated animals.

Figure 3. Changes in Coliform bacteria in the colon.

Data are expressed as log₁₀ copy number/ng genomic DNA isolated from colon content of control, MOS-treated, DSS-treated and DSS + MOS-treated animals. ***p < 0.001 compared to control.

Figure 4. MOS affects mouse anxiety behavior.

Effects of MOS and DSS on the locomotor activity, exploratory behavior and time spent in the centrum of open field test. Mean ± SEM values. Mice with DSS-induced colitis display decreased locomotion and exploration, corresponding to sickness behavior. MOS-treated mice are less anxious than control as they spend more time in the open field centrum. *p < 0.05 vs control.

Figure 5. MOS prevents DSS-induced upregulation of select proinflammatory cytokines and chemokines in the colon.

Mean ± SEM values of relative mRNA quantities in the colon of mice that were treated with MOS, DSS or DSS + MOS. Cytokine mRNA levels were normalized to GAPDH levels and expressed as relative quantity (RQ) compared to the value of untreated control set to 1. *p < 0.05, **p < 0.01, ***p < 0.001 compared to control mice; ⁺p < 0.05, ⁺⁺⁺p < 0.001 compared to DSS treated animals.

Figure 6. Dextran sulphate sodium and MOS exposure affects Toll-like and NOD-like receptors in the mouse colon.

Mean ± SEM values of relative mRNA quantities in the colon samples of mice that were treated with MOS, DSS or DSS + MOS. Receptor mRNA levels were normalized to GAPDH levels and expressed as relative quantity compared to the value of untreated control set to 1. *p < 0.05, **p < 0.01, ***p < 0.001 compared to control mice; ⁺p < 0.05 compared to DSS treated animals.

Figure 7. DSS treatment elevates plasma levels of KC, G-CSF and IL-6.

Mean ± SEM values of KC, G-CSF and IL-6 in plasma samples of mice that were control or exposed to DSS and treated with vehicle or MOS. *p < 0.05, **p < 0.01 compared to control mice; ⁺p < 0.05 compared to DSS treated animals.

Figure 8. MOS prevents LPS or DSS-induced cytokines in RAW 264.7 mouse macrophage cell line.

Mean ± SEM values of relative mRNA quantities measured in RAW 264.7 macrophages following DSS (5 μg/ml) or LPS (100 ng/ml) and 0, 10, 100, 500 μg/ml MOS administration. **p < 0.01, ***p < 0.001, ****p < 0.0001.