Isolation, structural characterization, immunomodulatory and indirect tumoricidal activities of an inulin-type fructan from Platycodon grandiflorus via macrophage M1 polarization through the TLR4/NF-κB pathway

In this study, a homogeneous polysaccharide, designated PGP-1, was successfully isolated and purified from the roots of Platycodon grandiflorus. Comprehensive structural characterization via methylation analysis, GC-MS, and NMR spectroscopy identified PGP-1 as an inulin-type fructan predominantly composed of →1)-β-D-Fruf-(2→ as the main chain with terminal β-D-Fruf-(2→ and α-D-Glcp-(1→ residues, consistent with the structural features of previously reported Platycodon grandiflorus fructans. Unlike conventional chemotherapeutic agents that rely on broad-spectrum and non-specific cytotoxicity, biological evaluations revealed that PGP-1 acts as a safe and targeted immunomodulator. Specifically, PGP-1 effectively induced M1 macrophage polarization in RAW264.7 cells through the TLR4/NF-κB signaling pathway, significantly enhancing their phagocytic capacity and promoting the robust release of tumoricidal factors, including nitric oxide (NO), TNF-α, and IL-6. Crucially, utilizing a macrophage-tumor transwell co-culture model to simulate the tumor microenvironment, it was demonstrated that PGP-1 exhibited negligible direct cytotoxicity to cancer cells but exerted potent indirect tumoricidal activity against hepatocellular (H22) and lung (LLC) carcinoma cells by augmenting macrophage-mediated immune responses. These findings provide preliminary evidence linking the polysaccharide's safety profile with its tumor-suppressive efficacy, suggesting the potential of PGP-1 as a low-toxicity natural immune enhancer for cancer immunotherapy.