Extraction, purification, structure, and antioxidant activity of polysaccharide from Rhodiola rosea

Rhodiola rosea polysaccharides are generally extracted using hot water, however, the structure and antioxidant activity of polysaccharides extracted by cold water are rarely reported. In this paper, a pectic polysaccharide (RRP-4) was successively prepared from Rhodiola rosea using a cold-water extraction method to explore its structural characteristics and antioxidant activity. Our findings revealed that RRP-4 (1.38×106 Da) was composed of Rha, Ara, Gal, and GalA with the molar ratio of 0.23:1.00:0.24:0.42. The backbone was composed of →4)-α-GalpA-(1→, →4)-α-GalpA-6-OMe-(1→ and →2,4)-α-Rhap-(1→, while Araf-based branches (α-Araf-(1→, 3)-α-Araf-(1→, →3,5)-α-Araf-(1→) and Galp-based branches (→3)-β-Galp-(1→) were attached to Rhap, suggesting that RRP-4 was a pectic polysaccharide including homogalacturonan (HG) and rhamnogalacturonan I (RG-I) domains. RRP-4 showed obvious scavenging activities on DPPH, ABTS, hydroxyl radicals and superoxide anion radicals in a concentration-dependent manner (0.25–3.00 mg/mL of RRP-4), indicating that RRP-4 exhibited a good antioxidant activity in vitro. Animal experiments revealed that RRP-4 markedly increased the release of cytokines (IL-2, TNF-α and IFN-γ) and proliferation and secretion of T lymphocyte cells (CD4+ and CD8+ T cells) dosage-dependently (50, 100, 200 mg/kg) via significantly reducing the oxygenation levels in cyclophosphamide (CTX)-induced mice. After administration of RRP-4, the activities of antioxidant enzymes (SOD, GSH-PX and CAT) were markedly increased and the level of MDA was reduced in a dose-dependent manner (50, 100, 200 mg/kg). These results indicated that the polysaccharide had the potential as a natural antioxidant and an immunoregulation adjuvant for the treatment of oxidative damage and immunosuppression-related diseases.