Structural Characterizations and In Vitro Bioactivities of a d-Fructose-Rich Polysaccharide from Gymnopetalum cochinchinense as a Potential Candidate for Alleviating Alzheimer’s Disease

The presented investigation attempts to unveil the structural characteristics, bioactivities, and potential application of Gymnopetalum cochinchinense-derived d-fructose-rich heteropolysaccharide (denoted as PS-HB5) for the treatment of Alzheimer's disease (AD). Structural analyses of the PS-HB5 evaluated by FT-IR, GC–MS, and NMR techniques reveal a novel repeating unit composed of d-glucose and d-fructose linked through (1 → 6)-glucosyl, (2 → 6)-fructosyl, and (2 → 4)-fructosyl bonds, and possesses a molecular weight of 1.217 × 105 Da. The PS-HB5 exhibits strong antioxidant activity, as evidenced by its DPPH and ABTS radical scavenging rates of 84.12% and 74.14%, associated with the IC50 values of 0.80 and 3.06 mg.mL–1, respectively. In addition, the PS-HB5 shows an inhibition rate of 78.37% (IC50 = 221.96 μg.mL–1) toward nitric oxide (NO) production in LPS-stimulated macrophages. Cytotoxicity assays indicate selective inhibition of the PS-HB5 against HepG2 and KB cancer cell lines (IC50 = 449.95 and 408.34 μg/mL), with minimal impact on MCF-7 and SK-LU-1. Interestingly, PS-HB5 demonstrates an outstanding AChE inhibitory effect, achieving 41.01% inhibition at 500 μg.mL–1, placing it among the most active AChE-inhibitory polysaccharides. These findings unveil the PS-HB5 potential as a candidate for the treatment of Alzheimer's Disease.