Degraded Polysaccharides from Noni (Morinda citrifolia L.) juice Mitigate Glucose Metabolism Disorders by Regulating PI3K/AKT-Nrf2-GSK3β Signaling Pathways in HepG2 Cells

Noni juice polysaccharides demonstrate promising hypoglycemic activity, but their high molecular weight restricts bioavailability. This study established a controlled degradation approach to optimize the functional properties of Noni juice polysaccharides. Molecular characterization demonstrated that the degraded Noni juice polysaccharides (DNJPs, Mw 191.8 kDa) retained the core monosaccharide composition, while exhibiting enhanced solubility. In vitro experiments with insulin-resistant HepG2 cells showed that DNJPs (0.5–2 mg/mL) significantly enhanced glucose consumption (p < 0.01) and mitigated oxidative stress by upregulating antioxidant enzymes (SOD, CAT, and GSH-Px) and decreasing malondialdehyde (MDA) levels. DNJPs activated the PI3K/AKT-Nrf2-GSK3β signaling axis through a multifaceted mechanism involving the following: upregulating the phosphorylation levels of PI3K and AKT; enhancing Nrf2 nuclear translocation, which in turn promotes the expression of downstream targets such as HO-1 and NQO1; inhibiting GSK3β activity; and suppressing FOXO1-mediated gluconeogenesis. These findings underscore DNJPs as promising functional food ingredients that modulate two key pathways to improve glucose metabolism.