Two low molecular weight-polysaccharides isolated from the edible fungus Sarcodon imbricatus: Isolation,...

This study investigates the distinct biological activities of two structurally different polysaccharides, SIP-1 and SIP-2, isolated from the mushroom Sarcodon imbricatus. SIP-1 is a 2.4 kDa heteropolysaccharide composed of a β-(1 → 6)-glucan backbone with glucuronic acid-containing side chains. In contrast, SIP-2 is a 4.1 kDa branched β-(1 → 4)-glucan notable for its terminal mannose residues. Biologically, SIP-1 significantly enhanced intestinal barrier function, demonstrated by increased transepithelial electrical resistance and reduced fluorescently labeled dextran permeability. It also exhibited anti-inflammatory effects in vitro and in vivo, modulating pro-inflammatory cytokines and enriched beneficial gut microbes like Muribaculaceae. Conversely, SIP-2 showed limited barrier-protective properties but acted as a pronounced immunomodulator. It enhanced immune responses in normal macrophages while reducing inflammation in lipopolysaccharide-stimulated cells, and its administration was associated with increased abundance of immune-regulating bacteria such as Blautia and Akkermansia. This work shows that two purified S. imbricatus polysaccharide fractions with different glycosidic linkages and terminal sugar residues exhibit distinct biological profiles under the experimental conditions examined. Overall, these findings provide new insight into how variations in composition and linkage patterns in fungal polysaccharides may relate to different effects on gut barrier function, immune responses, and microbiota and they highlight their potential relevance for gut health and immune modulation.