Structural Characterization of an α-D-glucan from Bellamya purificata and Its Protective Effects on Non-Alcoholic Fatty Liver Disease in Zebrafish

Non-alcoholic fatty liver disease (NAFLD) is a primary metabolic disorder that threatens adolescent health globally, with no effective therapeutic agents currently available. Bellamya purificata is a traditional Chinese medicine categorized as "medicinal food", and polysaccharides are among its active components. However, its physicochemical structure remains poorly characterized, and no study has evaluated its effects on NAFLD. In this study, a homogeneous neutral polysaccharide, α-D-glucan (Mw = 6,412.704 kDa), was isolated from B. purificata. The structure of the polysaccharide was characterized using monosaccharide composition analysis, methylation analysis, NMR spectroscopy, and scanning electron microscopy. The backbone structure of the polysaccharide comprises →4)-α-D-Glcp-(1→ and →4,6)-α-D-Glcp-(1→, with side chains of α-D-Glcp-(1→ attached to the O-6 position of the 1→4,6)-α-D-Glcp-(1→ sugar residues. Additionally, QSPS-1D effectively reduced weight gain, hepatic lipid accumulation (TC and TG), and inflammatory responses (tnf-α and il-1β) in NAFLD zebrafish. Moreover, QSPS-1D alleviated dysbiosis by inhibiting harmful bacteria (e.g., Stenotrophomonas, Agrobacterium, and Chryseobacterium) and promoting beneficial microbiota (e.g., Rothia), which restored the Firmicutes-to-Bacteroidetes ratio. In parallel, it enhanced the expression of tight junction proteins (zo-1 and claudin-1), leading to the repair of the intestinal mucosal barrier. These findings suggest that B. purificata polysaccharides may be a potential functional food for early NAFLD intervention, with effects potentially associated with the modulation of the gut microbiota.