Characterization, antioxidant and immunomodulatory activities of polysaccharides from Prunella vulgaris Linn

•Three polysaccharide fractions were extracted from Prunella vulgaris using hot water.•Their primary chemical composition and structures were determined.•Their antioxidant activities were evaluated by the methods of scavenging radicals.•Their immunomodulatory activities were evaluated using RAW264.7 macrophages model. Water-soluble polysaccharides from Prunella vulgaris Linn (P. vulgaris) were fractionated using DEAE-Sepharose fast-flow column to obtain several eluents of water (PV-P1), 0.1M NaCl (PV-P2) and 0.2M NaCl (PV-P3). Structural analyses showed that PV-P1 had a higher molecular weight and degree of branching as compared to PV-P2 and PV-P3. Tertiary structure analyses indicated that PV-P1, PV-P2 and PV-P3 did not have triple-helical conformation. PV-P2 and PV-P3 showed stronger antioxidant activities than PV-P1, as measured radical scavenging capacities. PV-P1 showed stronger immunomodulatory activities than PV-P2 and PV-P3 in term of stimulation of the production of pro-inflammatory cytokines, including nitric oxide (NO), tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6) in murine macrophage RAW 264.7 cells. PV-P1, PV-P2 and PV-P3 did not exhibit cytotoxicities against RAW 264.7 at the concentrations tested. These results suggest that P. vulgaris polysaccharides could be explored as potential antioxidant and immunomodulatory agents for the complementary medicine or functional foods.