Effects of water-insoluble wheat bran-fraction powder on disease activity and caecal microbiota in dextran sodium sulphate-induced inflammatory bowel disease mouse model.

Background: Water-soluble arabinoxylan exerts anti-colitic effect and exhibits ameliorative activity in an inflammatory bowel disease (IBD) mouse model. Water soluble fibre from wheat bran (WB) also exhibits anti-colitic effect. However, arabinoxylan is a primary compound of insoluble polysaccharide (hemicellulose) in WB. This study aimed to clarify the anti-IBD effects of the WB water-soluble (WBS) and water-insoluble (WBI) fractions.

Methods and results: WB suspension was autoclaved and fractionated to WBS and WBI. C57BL/6 mice were divided into control (CT), dextran sodium sulphate (DSS), WBI, and WBS groups. They were fed as follows from day 1: CT, standard diet and distilled water; DSS and WBI, 3% (w/v) DSS in drinking water; WBI, 8% (w/w) WBI diet; and WBS, 50% (v/v) WBS and 3% (w/v) DSS in water. DSS group mice showed diarrhoea, body weight reduction, and blood in faeces by day 5 and colon tissue damage by day 6. These inflammatory indices were significantly inhibited by treatment with WBI. Amplicon sequencing of the 16S rDNA (V4) gene of the caecal contents of the CT, DSS, and WBI groups showed that the abundances of Escherichia, Allobaculum, and Bacteroidaceae increased and that of Faecalibaculum decreased in the DSS group. KEGG pathway prediction showed that amino acid metabolism and lipopolysaccharide biosynthesis decreased and increased, respectively, in the DSS group. However, WBI treatment tended to suppress these effects.

Conclusion: WBI, rather than WBS, reduces inflammation and maintains the gut microbiota. However, further studies are warranted to elucidate the properties of the WBI active components and efficacy of WBI metabolites on gut microbiota, particularly on Faecalibaculum.