Characterization of a major polysaccharide from Sagittaria trifolia L. and its protective effects on cataract

The objective of this study was to isolate and characterize polysaccharides from Sagittaria trifolia L. tubers and to investigate their potential protective effects against cataract. A homogeneous polysaccharide, designated Sagittaria trifolia tuber polysaccharide 1 (STTP1), was obtained through hot-water extraction followed by column chromatography. Structural characterization revealed that STTP1 is an α-D-glucan with a molecular weight of 432.95 kDa, consisting of a →4)-α-D-Glcp-(1→ backbone with branching at O-6 positions. In vitro assays demonstrated that STTP1 exhibited concentration-dependent antioxidant activity. In a selenite-induced rat cataract model, STTP1 significantly reduced lens opacity and alleviated histopathological damage. Further mechanistic analysis showed STTP1 enhanced lenticular antioxidant capacity, upregulated the thioredoxin and glutaredoxin systems, activated the nuclear factor erythroid 2–related factor 2/heme oxygenase-1 (Nrf2/HO-1) signaling pathway, and exerted anti-apoptotic effects by increasing B-cell lymphoma 2 (Bcl-2) expression. These results indicate that STTP1 protects against selenite-induced cataract through coordinated regulation of antioxidant defense and apoptosis, suggesting its potential application as a functional food component or a natural agent for cataract prevention. • A homogeneous polysaccharide (STTP1) was isolated and purified from Sagittaria trifolia L. tubers. • STTP1 was identified as a high-molecular-weight α-D-glucan with a →4)-α-D-Glcp-(1→ backbone and O-6 branching. • STTP1 exhibited concentration-dependent antioxidant activity in vitro. • STTP1 significantly reduced lens opacity and histopathological damage in a selenite-induced rat cataract model. • STTP1 protected against cataract formation by enhancing antioxidant defenses, activating the Nrf2/HO-1 pathway, and inhibiting apoptosis.