Structural Analysis of a Non-Starch Polysaccharide Derived from Red Rice Bran and Its Immunomodulatory Properties
Juan Liu1, Dagang Chen1, Xinqiao Zhou1
1Rice Research Institute, Guangdong Academy of Agricultural Sciences, Key Laboratory of Genetics and Breeding of High Quality Rice in Southern China (Co-Construction by Ministry and Province), Ministry of Agriculture and Rural Affairs/Guangdong Key Laboratory of Rice Science and Technology, Guangzhou 510640, China.
Abstract:
A polysaccharide with water solubility named RRBP was extracted from red rice bran (Oryza sativa L.), and its structural characterization was analyzed. The polysaccharide exhibited a monodisperse molecular weight distribution with an average of 51.4 kDa, and also comprised glucose (98.1%, w/w) and small amounts of arabinose, galactose, xylose, and mannose. Structural investigations using methylation analysis combined with UV and FT-IR spectroscopy demonstrated that RRBP is a structurally complex hyperbranched glucan characterized by an extensive branch with "→4)-α-d-Glcp-(1"→linkages constituting 30.6% of the backbone. RRBP demonstrated concentration-dependent stimulation of nitric oxide (NO) generation along with elevated secretion levels of IL-6 and TNF-α but showed minimal effect on IL-12 production in assays with RAW264.7 macrophage cells. Gene expression profiling verified the enhanced transcription of genes encoding iNOS and pro-inflammatory cytokines including IL-6, TNF-α, and IL-12 following RRBP treatment. Moreover, it is important to note that RRBP was able to promote M1 macrophage activation and exhibited no cytotoxicity, and this implied that RRBP could serve as a biocompatible pro-inflammatory immunostimulant. In summary, these findings suggested that RRBP is a distinctive glucan that possesses selective immunomodulatory properties and could be applied in the development of functional food products designed for targeted immune system modulation.
