Oat Beta-Glucans Modulate the Gut Microbiome, Barrier Function, and Immune Responses in an In Vivo Model of Early-Stage Colorectal Cancer

Oat beta-glucans (OBGs) are known for their beneficial effects on gut health, including anti-inflammatory and prebiotic effects. The aim of this study was to evaluate the impact of two doses (1% or 3% <i>w</i>/<i>w</i>) of dietary low-molar-mass OBG supplementation on colorectal cancer (CRC) development, immune cell profiles, intestinal barrier protein expression, and microbiota composition in a rat model of CRC induced by azoxymethane (AOM). Microbiome analysis revealed significant differences between the control and CRC groups. OBG supplementation influenced microbial diversity and abundance, particularly increasing the population of beneficial bacteria, such as <i>Lachnospiraceae</i> and <i>Ruminococcaceae</i>, associated with butyrate production. However, higher doses of OBG (3%) led to a decrease in butyrate-producing bacteria and a shift toward higher levels of <i>Akkermansia muciniphila</i> and <i>Enterococcus faecalis</i>. Immune cell profiling showed a higher percentage of T lymphocytes (CD3+) in rats fed a diet supplemented with 3% OBG, both in the intraepithelial (IEL) and lamina propria lymphocytes (LPLs). Immunohistochemical analysis of the large intestine revealed a significantly elevated expression of intestinal barrier proteins, i.e., claudin 3 and 4 in rats receiving 1% OBG, while claudin 7 expression was reduced in early-stage CRC. Gene expression analysis also revealed a significant downregulation of <i>Cldn1</i> in CRC rats. These findings suggest that dietary OBG supplementation modulates the gut microbiota, immune response, and intestinal barrier integrity, with potential implications for nutritional CRC development prevention and treatment strategies.