Extraction, Purification, Structural Characterization, and Antitumor Effects of Water-Soluble Intracellular Polysaccharide (IPSW-1) from <i>Phellinus igniarius</i> Mycelia

<i>Phellinus igniarius</i> is a commonly used Chinese medicine fungus, and its polysaccharide is a valuable bioactive with antioxidant, antiaging, antitumor activities, etc. However, their bioactivities are influenced by their structural and physicochemical properties. Hence, this research isolated and purified homogeneous water-soluble intracellular polysaccharide (IPSW-1) from <i>P. igniarius</i> mycelia. A coherent study of its structural characteristics, conformation, and antitumor mechanisms was evaluated. The results showed IPSW-1 has no triple helical conformation according to the Congo red test. Based on FT-IR, periodate oxidation, Smith degradation, methylation analysis, ¹H and ¹³C NMR spectroscopy data, and IPSW-1 consisted of α-d-glucopyranose (Glc<i>p</i>). The backbone of IPSW-1 consisted primarily of repeating three (1 → 6)-linked α-d-Glc<i>p</i> and one (1 → 3,4)-linked α-d-Glc<i>p</i>, with one terminal α-d-Glc<i>p</i> as side chains of 3-O-connected to the main chain for every four residues. The IPSW-1 had an inhibitory influence on HepG2 cell proliferation and inhibited the migration and invasion ability by down-regulating the expression levels of MMP-7 and RhoA. Moreover, IPSW-1 could inhibit the lysis of autophagosomes to inhibit autophagy and regulate mitochondrial membrane potential and pro-apoptotic protein Bax, which causes the caspase cascade to promote apoptosis, thereby inhibiting the role of tumor cells. These findings show IPSW-1 holds potential as an innovative functional food.