Structure elucidation of duckweed polysaccharide from Spirodela oligorrhiza and its anti-inflammatory activity

Duckweed polysaccharides constitute an underexplored yet functionally important class of biomolecules within these rapidly proliferating aquatic plants. Although abundant in cell walls and implicated in diverse bioactivities, their structural elucidation beyond pectic fractions has remained scarce. In this study, the first comprehensive structural analysis of a purified polysaccharide (WHL-N1) derived from Spirodela oligorrhiza duckweed is reported. Monosaccharide composition analysis demonstrated galactose (46.15 mol%) and arabinose (39.44 mol%) as the predominant constituents. Structural investigation revealed a highly branched Type II arabinogalactan architecture with a weight-average molecular weight of 200.868 (± 4.392) kDa and a narrow polydispersity index (1.147 ± 0.076), comprising a backbone of →3,6)-β-ᴅ-Galp-(1→, →3)-β-ᴅ-Galp-(1→, and →6)-β-ᴅ-Galp-(1→ residues, decorated with side chains at the O-6 position of →3)-β-ᴅ-Galp-(1→ units. WHL-N1 displayed marked anti-inflammatory properties in a zebrafish model, significantly attenuating neutrophil migration and regulating pivotal inflammatory cytokines. Furthermore, in a dextran sulfate sodium (DSS)-induced colitis mice model, WHL-N1 reduced inflammatory cytokine levels, restored intestinal barrier integrity, and modulated gut microbiota composition, underscoring its promise potential for colonic inflammation. These findings position WHL-N1 as a promising candidate for nutraceutical and therapeutic development targeting colonic inflammation and microbiota dysbiosis, whilst offering a fundamental basis for future investigations into the structure-activity relationships of duckweed polysaccharides.