A Novel Hypoglycemic Polysaccharide DOP 3-1 Purified from Danxia Dendrobium officinale

Polysaccharides are among the primary active constituents of Danxia Dendrobium officinale ; however, the structure–activity relationship underlying their hypoglycemic effects remains unclear. For this study, polysaccharides DOP 3-1 with hypoglycemic activity were purified from Danxia Dendrobium officinale using DEAE-Sepharose Fast Flow and Sephacryl S-200 HR column chromatography. Structural analysis revealed that DOP 3-1, with a molecular weight of 144.905 kDa, is primarily composed of D-glucose and D-mannose in a ratio of 3:17, with a predicted backbone consisting of alternating →4)-β-D-Glcp-(1→ and →4)-α-D-Manp-(1→ linkages. In vitro hypoglycemic assays showed that DOP 3-1 effectively inhibited α-amylase and α-glucosidase, with IC 50 values of 2.175 mg/mL and 2.727 mg/mL, respectively. Mechanistically, DOP 3-1 alleviated insulin resistance by activating the IRS-1/PI3K/AKT pathway and inhibiting PEPCK and GSK-3β. In HepG2 cells, it increased glucose consumption and glycogen content. In zebrafish, it reduced fasting glucose levels, improved BMI and dyslipidemia, and restored glycogen synthesis via the IRS-1/PI3K/AKT pathway. Additionally, it downregulated the pro-inflammatory cytokines IL-1β, IL-6 , and TNF-α , thereby reducing inflammation and contributing to its hypoglycemic effects. Collectively, this study systematically elucidates the structure–activity relationship of DOP 3-1 and demonstrates its multi-mechanistic hypoglycemic effects, providing a scientific basis for its potential application in functional foods or therapeutics.