Effect of Grifola frondosa polysaccharide on immune function and gut microbiota in mice

Objective: Grifola frondosa , a medicinal mushroom, is widely used to enhance immunity and treat cancer. Polysaccharides are its primary active components. We aimed to investigate the effects of the alkaloid G. frondosa polysaccharide (GFP) extract on immunity and gut microbiota. Methods: Alkaloid GFP was extracted using an alkaline extraction method, followed by hollow-fiber microfiltration. The molecular weight of alkaloid GFP was determined by high-performance gel permeation chromatography (HPGPC). Monosaccharide composition was analyzed by pre-column derivatization combined with high-performance liquid chromatography (HPLC). Methylation analysis was performed to characterize glycosidic linkages in alkaloid GFP. The immune function of alkaloid GFP was assessed in a cyclophosphamide (CTX)-induced immunosuppressive mouse model. Splenic lymphocyte proliferation, macrophage phagocytic capacity, and natural killer (NK) cell cytotoxicity were evaluated. The effect of alkaloid GFP on gut microbiota was assessed by 16S rRNA sequencing. Results: The molecular weight distribution of alkaloid GFP ranged from 17 to 18 kDa. The alkaloid GFP contained a β-(1→6)-glucan backbone branched at O-3 by β-1,3-D-Glcp. Oral administration of alkaloid GFP mitigated the effects of CTX on spleen index, splenic lymphocyte proliferation, and peritoneal macrophage phagocytosis. Additionally, alkaloid GFP improved the gut microbiota composition of immunosuppressed mice, increasing the relative abundances of Ligilactobacillus and Lactobacillus . Conclusions: Alkaloid GFP demonstrated immune-enhancing effects and gut microbiota regulatory activity, providing a basis for developing related health food ingredients.