Antioxidative Effects of Defatted Rice Bran in Rats on AOM/DSS-Induced Colon Oxidative Stress and Correlations Between Gut Microbiota and Antioxidant Biomarkers

Abstract

Defatted rice bran (DRB), a by-product of Thai Oryza sativa, is rich in dietary fiber and antioxidant phytochemicals. This study investigated the bioaccessibility, antioxidative efficacy, and prebiotic potential of DRB in colorectal cancer (CRC) models. Simulated gastrointestinal digestion demonstrated high bioaccessibility of flavonoids (79%) and phenolics (62%), along with substantial antioxidant activity: DPPH (57%), FRAP (83%), and ORAC (74%). In vitro, digested DRB significantly reduced intracellular reactive oxygen species (ROS; −33%, p < 0.05) and suppressed IL-6, IL-8, and TNF-α production in Caco-2 cells. In vivo, male Wistar rats (n = 5/group) were exposed to azoxymethane/dextran sulfate sodium (AOM/DSS) and supplemented with DRB (3 or 6 g/kg body weight/day) for 90 days. High-dose DRB markedly reduced protein carbonyls (−71%) and 8-OHdG (−29%), while restoring glutathione (+26%), superoxide dismutase (+125%), and catalase (+50%) relative to AOM/DSS controls (p < 0.05). 16S rRNA sequencing revealed a reduction in Proteobacteria (−58%) and an increased abundance of Akkermansia, Lactobacillus, and a genus belonging to Ruminococcaceae, which positively correlated with short-chain fatty acids and antioxidant biomarkers (r > 0.6, FDR < 0.05). These findings indicate that DRB possesses potent antioxidative and prebiotic properties, supporting its use as a safe, multifunctional dietary ingredient for CRC risk reduction.