Sagittaria sagittifolia polysaccharide regulates Nrf2-mediated antioxidant to improve apoptosis and ferroptosis in high glucose-induced lens epithelial cells.

Diabetic cataract (DC), a primary ocular complication of diabetes mellitus, remains a leading cause of global blindness. The bioactive polysaccharide Sagittaria sagittifolia polysaccharide (SSP) exhibits remarkable antioxidant and anti-apoptotic efficacy in age-related cataract models, yet its DC therapeutic potential is unexplored. This study investigated SSP's protective effects against high glucose (HG)-induced damage across three experimental models, focusing on nuclear factor erythroid 2-related factor 2 (Nrf2)-mediated antioxidant in apoptosis and ferroptosis regulation. In ex vivo rat lenses, SSP pretreatment (1 mg/mL, 24 h) significantly attenuated HG-induced (25 mM, 48 h) lens opacification. In human lens epithelial B3 (HLEB3) cells, SSP pretreatment (1 mg/mL, 24 h) markedly improved cell viability and proliferation under HG conditions (150 mM, 72 h). Mechanistically, SSP significantly decreased oxidative stress markers (malondialdehyde, protein carbonyls, reactive oxygen species) while restoring mitochondrial function and enhancing antioxidant capacity (glutathione levels, catalase activity). SSP activated the Nrf2 pathway, regulating key antioxidant proteins (NAD(P)H quinone dehydrogenase 1, heme oxygenase-1, thioredoxin (Trx), Trx2 and glutaredoxin 1 to mitigate HG-induced oxidative damage. SSP exerted anti-apoptotic effects by upregulating B-cell lymphoma-2 (Bcl-2) while suppressing Bcl-2-associated X and cleaved caspase-3 expression. SSP modulated ferroptosis by increasing Ferritin, system Xc, and glutathione peroxidase 4 (GPX4) while reducing Fe and acyl-CoA synthetase long-chain family member 4 (ACSL4) levels. In STZ-induced diabetic mice, SSP treatment ameliorated lens epithelial cells (LECs) morphological damage and reduced protein expression of caspase-3 and ACSL4, whereas increased protein expression of GPX4 and ferritin. Crucially, upon Nrf2 knockdown in HLEB3 cells via short interfering RNA, SSP confirmed its protective role by activating Nrf2 to inhibite apoptosis and ferroptosis. Collectively, these findings demonstrate that SSP protects LECs against HG-induced damage through Nrf2-mediated coordination of antioxidant defense, anti-apoptotic, and anti-ferroptotic mechanisms, highlighting its therapeutic potential for DC.