Structural characterization and gut microbiota-mediated immunomodulatory effects of a novel fructose enriched polysaccharide from Platycodon grandiflorus.

This paper characterized PGP90, a novel low-molecular-weight (∼3.1 kDa) inulin-type fructan (α-D-Glcp-(1 → [1)-β-D-Fruf-(2]₁₈) isolated from Platycodon grandiflorus (P. grandiflorus), and demonstrated its potent immunomodulatory effects in CTX-induced immunosuppressed mice. Structural and cell cytotoxicity analysis confirmed the composition of PGP90 with less side effects. Oral administration of PGP90 (100 or 200 mg/kg) significantly restored CTX-suppressed immune parameters, including body weight, spleen weight, spleen index, splenic histoarchitecture, and the distribution of CD3+ T and CD19+ B cells in peripheral blood and spleen. These restorative effects were associated with the ability of PGP90 to remodel gut microbiota composition and to modulate microbial metabolism, particularly pathways related to vitamin B6 metabolism, which correlated with elevated levels of metabolites such as 4-pyridoxic acid. These findings suggest that PGP90 may serve as a promising prebiotic candidate that targets the gut microbiota to help alleviate immune dysfunction.