Polysaccharides from Dioscorea opposita Thunb.: isolation, structural characterization, and anti-inflammatory and anti-tumor effects against hepatocellular carcinoma

Abstract

Background: Dioscorea opposita Thunb, as a dual-purpose edible plant with excellent nutritional and medical value, accumulates abundant bioactive compounds, including polysaccharides. Polysaccharides from D. opposita have been widely recognized and studied due to various biological activities, such as anti-inflammatory and anti-cancer, which are influenced by their complex structures. In recent years, numerous studies have investigated the structures and activities of D. opposita polysaccharides, and the relationships between them. However, the detailed structures remain different because the structures are susceptible to various species, producing areas, growth conditions (weather, soil, temperature, moisture, etc.), and extraction and separation methods. In this study, the structures of purified polysaccharides from D. opposita were determined and the biological activities were preliminarily investigated including anti-inflammatory and anti-tumor activities. Results: The crude polysaccharides DOP1 and DOP2 were isolated and purified via DEAE-52 and Sephadex G-100 to obtain two purified polysaccharides fractions (DOP1-1 and DOP2-1), with the molecular weights of 15.63 kDa and 32.32 kDa, respectively. The structures of DOP1-1 and DOP2-1 were analyzed by HPLC, FT-IR, methylation, and 1D (1H, 13C) and 2D (HSQC, COSY, TOCSY, and ROESY) NMR spectra. The results indicated the presence of → 2)-β-Manp-(1 → 4)-α-Glcp-(1 → 2)-β-Manp-(1 → , → 1)-β-Manp-(2 → 1)-α-GalpA-(4 →, and → 2)-β-Manp-(1 → 2)-β-Manp-(1 → in DOP1-1, and the ratio was 2:11:5. The bone structure of DOP2-1 was predicted as → 1)-β-d-Galp-(4 → , along with two main branching structures composed of arabinose of different degrees of polymerization. Preliminary anti-inflammatory and anti-tumor activities were investigated. DOP1-1 and DOP2-1 demonstrated inhibitory effects on macrophages cells (RAW264.7). DOP2-1 exhibited anti-tumor effects against hepatocellular carcinoma (SNU-739 and HepG2). Conclusions: The structures and bioactivities of DOP1-1 and DOP2-1 were analyzed to provide a basis for the establishment of structure/function relationships. The polysaccharides derived from Dioscorea opposita could be potentially employed in functional food, health care, and pharmaceutical industries. Graphical Abstract: [Figure not available: see fulltext.].