Structural characteristics, bioactivities, and structure-activity relationships of polysaccharides from three pharmacopeial Polygonatum species using ultrasound-assisted enzymatic extraction

Three Polygonatum species, namely Polygonatum sibiricum Red., Polygonatum kingianum Coll. et Hemsl., and Polygonatum cyrtonema Hua, are officially designated as Huangjing (Polygonati Rhizoma) in the Pharmacopoeia of the People's Republic of China (PPRC). This study aimed to compare the effects of different ultrasound-assisted enzymatic hydrolysis durations and these three species on the bioactivity of functional polysaccharides extracted therefrom. To achieve this goal, six homogeneous polysaccharides-PSP50N, PSP95N, PKP50N, PKP95N, PCP50N, and PCP95N-were successfully purified from the above-mentioned three Polygonatum species. Among these polysaccharides, those polysaccharides obtained via 50 min of ultrasound-assisted enzymatic hydrolysis exhibited significantly superior bioactivity compared with those obtained through 95 min of the same treatment. The primary structures of the six polysaccharides, including molecular weight, fructose content, and chain conformation, were characterized, and obvious differences were observed among them. Although all three Polygonatum species showed similar efficacy profiles in terms of antioxidant, glucose-lowering, antitumor, and immunomodulatory activities, their potencies differed significantly. Specifically, PSP95N exerted potent antitumor activity by inducing mitochondrial dysfunction, cell cycle arrest, and apoptosis, while PSP50N exerted stronger immunomodulatory effects by activating the TLR4/NF-κB pathway. Partial Least Squares (PLS) analysis identified molecular weight and fructose content (VIP > 1.2) as the key structural factors responsible for grouping the polysaccharides by ultrasound-assisted enzymatic hydrolysis duration. Entropy-weighted TOPSIS evaluation ranked their comprehensive bioactivity as follows: PSP50N > PCP50N > PKP50N > PCP95N > PSP95N > PKP95N, thus confirming 50 min as the optimal hydrolysis duration for extracting polysaccharides with high bioactivity. This study enhances the understanding of the structure-activity relationship of polysaccharides and provides a theoretical basis for the clinical Polygonatum species selection.