UC is an autoimmune disease of the bowel with colonic inflammation and high frequencies of remission and relapse [23]. FMT as a novel treatment of bowel disease is developing rapidly, and its indications are increasing, for example, as a therapy for recurrent clostridium difficile infection, UC, obesity, and Alzheimer Disease [3, 24–27]. However, the effect of FMT in the treatment of UC has been unsatisfactory, with significant therapeutic effects ranging from as low as 30.4% to as high as 67.7% [28, 29]. The results of the present study indicated that combining FMT with a blend of prebiotics substantially ameliorated UC in a mouse model. The blend of prebiotics with GOS:FOS at a ratio of 9:1 was better than the other ratios tested for ameliorating clinical indications of UC, and the use of this prebiotic blend with FMT provided significantly better therapeutic effects than FMT alone, including as assessed using the DAI score and pathological analyses.
The factors contributing to UC are complex and multiple, including internal factors, such as genes and the autoimmune system, and external environmental factors, such as intestinal bacteria, living habits, and work stress [30]. Clinical research has shown that the richness and diversity of the fecal microbiota among patients with UC are significantly lower than those in healthy individuals [31]. Oral administration of 5% DSS is the most commonly used method to establish an animal model of UC in mice [32]. Previous studies have found that the fecal microbiota undergoes a significant change in this mouse model of UC [33]. Consistent with those previous clinical and animal studies, our analyses indicated that both the Chao1 index and the Shannon index were lower in the UC group compared with health control group, suggesting decreased richness and diversity of fecal microbiota in the UC mice (Fig. 3B, C).
For the preparation of the fecal microbiota in FMT group, we referred to the study by Bárcena et al., [21] and FMT was introduced after the animal model of UC was established. It has been shown that FMT regulates the intestinal microbiota community and improves clinical indicators in a UC model [34]. In the present study, FMT improved some clinical indicators, such as weight loss and the DAI score, but co-treatment with FMT and the prebiotic blend GOS:FOS 9:1 showed a better overall therapeutic effect than FMT alone, especially in the histopathologic (Fig. 1E) and anti-inflammatory responses (Fig. 2B). TNF-α and IL-6 as proinflammatory cytokines, and TGF-β and IL-10 as anti-inflammatory cytokines, contribute to the initiation of UC [35]. Our study showed that co-treatment with FMT and the prebiotic blend GOS:FOS 9:1 promoted an increase in these anti-inflammatory factors and a decrease in these pro-inflammatory factors in colonic tissue, with no significant change in either factor in peripheral blood (Fig. 2A, B). In our study, the UC model was established during 7 days and the various treatments were administered starting immediately afterward for the next 7 days. Given this time frame, it is not unexpected that the inflammatory reactions occurred in local tissues but were not detected in peripheral blood.
FOS and GOS are two beneficial prebiotics in the human intestinal intact [36, 37]. Previous studies have shown that GOS and FOS play important roles in calming the intestinal microecology, alleviating mental diseases, and regulating the immune system [38, 39]. The composition of gut microbiota can be easily modified by consuming a diet containing prebiotics [40]. In a study by Shoemaker et al. [41], Bifidobacterium in the intestine are probiotics and show an obvious dose response to GOS. Human milk contains a small amount of oligosaccharides and requires substantial work for an infant to obtain at useful doses [42]. The addition of a 9:1 mixture of GOS:FOS to infant formula has shown a variety of health promoting effects and a reduction in infection rates [43, 44]. Moreover, prebiotics can prevent and ameliorate UC, [8, 45] and a previous study showed that a blend of prebiotics moderated the microbiota community [46]. In the present study, a blend of two prebiotics (GOS and FOS) in three proportions (9:1, 1:1, 1:9) was administrated to groups of mice. We found non-statistically significant differences in the microbiota community among the prebiotic-treated groups compared with the UC group. The relative abundance of the fecal microbiota in the UC group was significantly decreased compared with the control group (Fig. 3A). By contrast, the group treated with FMT plus GOS:FOS 9:1 showed an increase in the diversity of intestinal microbiota, which was restored to nearly control levels. In other studies with animal models of obesity and Parkinson disease, FMT ameliorated the flora imbalance [47, 48].
Our study showed increases in the Chao1 index and Shannon index for gut microbiota after treatment with FMT alone compared with the UC group [34]. The balance between pro- and anti-inflammatory factors is typically shifted in UC [35]. In the present study, the levels of the pro-inflammatory cytokines IL-6 and TNF-α, which are associated with human inflammatory bowel disease, were significantly increased in the UC group but were decreased after FMT treatment alone or in combination with GOS:FOS 9:1. This result is consistent with previous reports [34, 49]. In our study, the levels of the anti-inflammatory cytokines IL-10 and TGF-β showed the opposite tendency. Those inflammatory-related factors are mainly produced by monocytes/macrophages and lymphocytes in colonic tissue, which may be a reason for the small changes in the levels of these factors in peripheral blood [28, 35]. Several reports have indicated that the occurrence of inflammatory factors is related to intestinal bacteria. Saccharomyces boulardii significantly decreased TNF-α and IL-6 to levels in azoxymethane/DSS-induced UC carcinogenesis [49]. The administration of a probiotic mixture containing Lactobacillus acidophilus LA-14, Lactobacillus casei LC-11, Lactococcus lactis LL-23, Bifidobacterium bifidum BB-06, and Bifidobacterium lactis BL-4 significantly increased TNF-α levels in a double-blind randomized trial [50]. The mechanisms whereby intestinal microbiota affect the inflammatory response remain unclear. Thus, we did not analyze the relationship between the gut microbiota and the four cytokines. SCFAs are metabolites of the intestinal flora that regulate the pH of the intestinal environment and provide energy to intestinal epithelial cells [51]. Fecal samples from humans with UC show reduced acetic acid and propionic acid levels but not butyric acid levels [52, 53]. A previous study using the same mouse model of UC as our study showed a reduction in SCFAs levels consistent with our study results [54]. The effect of SCFAs on colonic inflammation has been inconsistent. One study showed that butyrate relieved mucosal damage and inflammation, [55] but another study showed that butyrate had no effect on anti-inflammatory responses [56]. We found that the combination of FMT and blended prebiotics significantly increased the levels of acetic acid and butyric acid in feces (Fig. 3D, E) although other SCFAs did not change. Our correlation analysis indicated that Lactobaciius, Bifidobacterium, Prevotella, and Pediococcus had a positive relationship with the levels of SCFAs, whereas Odoribacter, unidentified S24-7, and Turicibacter had a negative relationship. Lactobaciius, Biffidobacterium, and Prevotella have been shown in previous studies to produce acid [57–59].