Brasenia schreberi Polysaccharides: Extraction, Structural Characterization, and Immunomodulatory Activity

Brasenia schreberi, a valuable aquatic vegetable in East Asia prized for its unique and delicious taste, is rich in bioactive compounds, including polysaccharides, proteins, vitamins, and trace elements. This study compared enzymatic and alkaline extraction techniques to isolate polysaccharides from B. schreberi. Extraction yield, total sugar, protein, uronic acid contents, and monosaccharide composition were determined, and structural characteristics were analyzed using Fourier-transform infrared (FT-IR) spectroscopy. Following alkaline extraction, the crude polysaccharide (BSP-A) was then purified by DEAE-52 cellulose and Sepharose CL-6B chromatography to obtain a homogeneous fraction, BSP-2, with a molecular weight of 544.2 kDa. The physicochemical properties and structure of BSP-2 were analyzed using comprehensive techniques including FT-IR, Congo red assay, scanning electron microscope (SEM), high performance liquid chromatography (HPLC), gas chromatography mass spectrometry (GC-MS), methylation analysis, and thermogravimetric analysis. Results showed that BSP-2 is a flat, sheet-like polysaccharide devoid of a triple-helix structure. It comprises nine monosaccharides, including mannose, rhamnose, glucuronic acid, galacturonic acid, glucose, galactose, xylose, arabinose, and fucose, via 18 distinct glycosidic bond types of linkage. Rheological tests of BSP-2 indicated the gel-like behavior at low angular frequencies and the fluid-like behavior at high frequencies. Additionally, the immunomodulatory activities of BSP-2 on the RAW264.7 macrophage cells were investigated, with key assessments of cytotoxicity, nitric oxide (NO) production, the mRNA expression levels of various cytokines, and the expression of key proteins in the mitogen-activated protein kinase (MAPK) pathway. These results establish a foundational framework for the extraction and identification of polysaccharides from B. schreberi and demonstrate their value in immunoregulatory applications.