Revisiting the structure of arabinogalactan from Lycium barbarum and the impact of its side chain on anti-ageing activity

In this study, we obtained all the homogeneous LBGP70 (arabinogalactan-protein complex), LBGP70-OL (sugar chain of LBGP70), and LBGP70-OL-I (backbone part of LBGP70-OL) fraction from crude Lycium barbarum polysaccharides (LBP) by stepwise precipitation. The structural features of LBGP70-OL were investigated by a series of analytical techniques and chemical methods, which was identified as a highly branched polysaccharide with an average of 9 branches per 10 sugar backbone units. The backbone was only →6)-β-Galp-(1→ residues, substituted at the C3 position. The side chains contained β-Galp-(1→, α-Araf-(1→, α-Araf-(1 → 3)-β-Araf-(1 → 3)-β-Araf-(1→, α-Araf-(1 → 3)-β-Gap-(1 → 3)-β-Galp-(1→, α-Araf-(1 → [5)-β-Araf-(1]4 → 3)-β-Galp-(1→. LBGP70-OL had the highest anti-ageing activity, with its side chain and backbone exhibiting a synergistic effect. LBGP70-OL exerted the anti-ageing activity by attenuating SA-β-Gal activity, preventing cell cycle arrest, increasing antioxidant enzyme activity, protecting the cell membranes from oxidative damage, and regulating the senescence-related genes Sirt1, NAMPT, and Prx1. These results lay the fundamental for further studies on the structure-function relationships of LBP.