Glycyrrhiza uralensis Polysaccharide Modulates Characteristic Bacteria and Metabolites, Improving the Immune Function of Healthy Mice

Polysaccharides from Glycyrrhiza are known to have several bioactive effects. Previous studies have found that low-molecular-weight Glycyrrhiza polysaccharide (GP1) is degraded by Muribaculum_sp_H5 and promotes the production of beneficial bacteria and metabolites, which improves immune disorder and intestinal injury, and then enhances the body's immune regulation ability. However, the immune regulation effect of GP1 on a healthy body has not been studied. In this study, we aimed to reveal the immune enhancement effect and mechanism of GP1 on healthy mice. The cytotoxicity and immunomodulatory activity of GP1 were analyzed by cell experiment; the effects of GP1 on antioxidation, immune regulation and gut microbiota structure of healthy body were studied in vivo. In addition, the mechanism of GP1 enhancing immune response of healthy body was analyzed by multi-omics. The results show that GP1 enhanced the immune function of healthy mice by increasing the index of immune organs, improving the organizational structure of immune organs, and increasing the secretion of immune cytokines and immunoglobulin. GP1 also increased the contents of antioxidant factors such as total antioxidant capacity (T-AOC), glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD) in various organs and reduced the content of oxide malondialdehyde (MDA), thus enhancing the body's antioxidant capacity, promoting cell proliferation and prolonging life. Moreover, GP1 promoted the proliferation of beneficial bacteria, including Muribaculaceae_unclassified, Muribaculum, Prevotellaceae_UCG-001, and Paramuribaculum, and the production of characteristic metabolites (collectively referred to as postbiotics), including α-tocopherol, arachidonic acid, melibiose, taurine, and nicotinic acid. These beneficial bacteria and postbiotics have been proven to have health maintaining functions. GP1 promoted the proliferation of beneficial bacteria and increased the production of postbiotics, which should be the mechanism of its beneficial effect. It is expected to be a promising immune dietary supplement.