Abstract: The antioxidant, analgesic and anti-inflammatory activities of the extracellular polysaccharide from Nostoc flagelliforme cultured in a liquid medium with 0.3 mol/L NaCl were studied. The in vitro antioxidant activity was investigated by determining the scavenging capacity against hydroxyl radical (·OH), superoxide anion radical (O2-·) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical. The mouse warm-water tail-flick test was used to study the analgesic effect of subcutaneous versus intraperitoneal administration of the extracellular polysaccharide. The anti-inflammatory effect was assessed by observing the inhibition of dimethylbenzene-induced ear edema in mice. The results showed that the scavenging capacities against ·OH, O2-· and DPPH radical of the extracellular polysaccharide produced under salt stress were higher than those in the absence of salt stress. In addition, the former had a stronger analgesic activity than did the latter with a significant higher pain threshold (P < 0.05). The extracellular polysaccharide was absorbed faster when administered subcutaneously?than when administered?intraperitoneally, and the efficacy of subcutaneous injection reached its peak at 30 min, whereas the efficacy of intraperitoneal injection reached its peak at 20 min. Moreover, the anti-inflammatory activity of the extracellular polysaccharide produced under salt stress was stronger and in a dose-dependent manner, and it at a high dose (30 mg/kg mb) showed the best anti-inflammatory effect.

Key words: Nostoc flagelliforme; extracellular polysaccharide; salt stress; antioxidant activity; analgesic activity; anti-inflammatory activity