Structural characterization and protective effects of a glucuronogalactomannan from Tetrastigma hemsleyanum against diabetic retinopathy via targeting ferroptosis pathway

A novel polysaccharide, THPE2-F, with an average molecular weight of 480.75 kDa, was isolated and characterized from the roots of Tetrastigma hemsleyanum Diels et Gilg. Extensive structural analyses revealed that THPE2-F is a GlcA-Gal-Man polymer. Its main chain is composed of →4)-β-D-GlcpA-(1→ and →2)-α-D-Manp-(1→ linkages. THPE2-F mainly consists of galactose, mannose, and glucuronic acid residues. The glycosidic linkages of THPE2-F were elucidated via methylation analysis and further corroborated by nuclear magnetic resonance (NMR) spectroscopy. In vitro, THPE2-F significantly decreased the levels of malondialdehyde (MDA) and reactive oxygen species (ROS), and enhanced cell viability at a concentration of 100 μg/mL. Additionally, treatment with THPE2-F downregulated the expression of NCOA4, thereby uncovering a molecular mechanism responsible for its protective effects. Biochemical analyses indicated that THPE2-F restored glutathione (GSH) levels under hyperglycemic conditions and regulated iron levels, subsequently affecting the expression of ferroptosis-related proteins, including COX2, NOX1, FACL4 and NCOA4. In vivo studies further validated these findings, as THPE2-F provided substantial protection against retinal damage in a diabetic retinopathy (DR) mouse model. Collectively, these results suggest that THPE2-F has potential as a therapeutic agent for diabetic retinopathy by targeting ferroptosis pathways.