Structural analysis and in vitro and in vivo antioxidant and immunomodulatory activities of R. tangutica polysaccharide TP1a

Abstract

Here, we elucidated the structural characteristics of a polysaccharide isolated from R. tangutica (labeled as TP1a) and its antioxidant and immunomodulatory activities.TP1a is an acidic polysaccharide with a molecular weight of 2.5 × 10⁶Da, which mainly contains arabinose and galacturonic acid. Methylation analysis showed that the main sugar residues in TP1a are t-Ara (24.94 %),5-Ara(18.83 %),and 4-Gal(p)-UA(13.86 %).Two structural fragments of the polysaccharide were identified using NMR analysis:→2)-α-l-Rhap-(1→,→4)-α-d-GalpA-(1→,→4)-α-d-Glcp-(1→and→4)-β-d-Galp and→5)-α-l-Araf-(1→and→2,3,5)-α-l-Araf-(1→),in which→5)-α-l-Araf-(1→)is connected at the end. Activity analysis showed that TP1a exhibits DPPH and ABTS free radical- scavenging activity. It showed no obvious toxicity to macrophages (RAW 264.7), reduced the production of H₂O₂-induced ROS in macrophages, and regulated the activity of antioxidant enzymes. In addition, TP1a enhanced cell viability and phagocytosis in a dose-and time-dependent manner.Compared with untreated cells, the production of nitric oxide and the secretion of cytokines (such as tumor necrosis factor-α, interleukin (IL)-1β,and IL-6) in TP1a-treated cells significantly increased after 24 h. Thus, TP1a is a pectin polysaccharide with antioxidant and immunomodulatory effects, and it has potential application value in the development of functional food and medicine.