Isolation, characterization and palliative effect of D-gal-induced liver injury of Stropharia rugosoannulata exopolysaccharide.

In this study, a homogeneous polysaccharide component, namely SREP-1, was purified from Stropharia rugosoannulata fermentation broth. SREP-1 was identified as a novel water-soluble neutral polysaccharide, with a molecular weight of 9.6 kDa. Monosaccharide composition analysis showed that SREP-1 was composed of glucose, galactose and mannose in a molar ratio of 78.6: 13.6: 7.8. The primary structure was elucidated through FT-IR, methylation analysis and NMR spectroscopy, revealing a backbone of →4)-α-D-Glcp-(1 → and →4,6)-α-D-Glcp-(1 → residues, and →6)-α-D-Galp-(1→, β-D-Manp-(1 → and α-D-Glcp-(→1 residues for the branched chains. Results indicated that SREP-1 possessed an amorphous globular-like structure, good thermally stability and triple-helix conformation in water. In vivo results showed that SREP-1 reversed D-galactose (D-gal)-induced body weight and organ indexes decrease, and alleviated liver damage according to improved histopathology and declined indicators in serum. Amelioration of oxidative stress and abnormal inflammation of aging liver might be due to the elevated nuclear factor-erythroid 2-related factor 2 (Nrf2) expression and decreased that of nuclear factor-κB p65 (NF-κB p65). Interestingly, the beneficial effects of SREP-1 were abolished after pretreatment with antibiotics. Our findings demonstrated that the role of SREP-1 in attenuating aging-related liver injury might involve the regulation of Nrf2-NF-κB signaling pathway and its prebiotic effect.