Structural elucidation of a novel heteropolysaccharide from Arca inflata Reeve and its immunomodulatory and antioxidant activities

A novel acidic homogeneous polysaccharide (AIPW50-1) with a molecular weight of 214.5 kDa was isolated by hot water extraction and several column chromatographic purification methods from Arca inflata Reeve. The repeating structural units of AIPW50-1 were elucidated by the combined chemical and instrumental analyses. AIPW50-1 is composed of glucose, glucuronic acid and galactose with molar ratio of 18.06: 1.00: 1.56. The backbone of AIPW50-1 consisted of →4)-α-D-GlcpA-(1→, →4)-α-D-Glcp-(1→ and →4,6)-α-D-Glcp-(1→ with two branches of α-D-Glcp-(1→ and →6)-β-D-Galp-(1→ terminated with α-D-Glcp-(1→, respectively. The antioxidant assay demonstrated that AIPW50-1 possessed strong ABTS free radical scavenging activity and prominently stimulated the secretion of a cytotoxic molecule (NO), cytokines (TNF-α and IL-6) by murine RAW 264.7 macrophages. The in vivo antioxidative effect of AIPW50-1 was further evaluated using Caenorhabdiyis elegans oxidative stress model. AIPW50-1 could prolong the lifespan, improve locomotory behavior and reproductive ability, and significantly enhance intracellular activities of catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) of C. elegans by 19.80 %, 17.05 % and 17.22 % at 4 mg/mL. These results suggested that AIPW50-1 has the potential to be used as a functional additive with antioxidant and immunomodulatory effects.