Purification and in vitro anti-proliferative effect of novel neutral polysaccharides from Lentinus edodes

A (1→6)-β-D-glucan (WPLE-N-1) and two mannogalactoglucans (WPLE-N-2 and WPLE-N-3) were isolated from the basidiocarps of Lentinus edodes by hot water extraction, ethanol precipitation, anion exchange chromatography, and further purified by gel-permeation chromatography (GPC). Their structural features were investigated by high performance liquid chromatography (HPLC), high performance gel-permeation chromatography (HPGPC), methylation analysis, periodate oxidation-Smith degradation, Fourier transform-infrared (FT-IR) and NMR spectroscopy, including two-dimensional (2D) NMR. HPLC analysis revealed that WPLE-N-1 was mainly composed of glucose (92%) with small amount of galactose (3.9%) and mannose (4.1%), WPLE-N-2 and WPLE-N-3 contained mannose-galactose-glucose in the molar ratio of 10:27:63 and 5:12:83, respectively. GPC and HPGPC showed that WPLE-N-1, WPLE-N-2 and WPLE-N-3 are homogeneous fractions and their molecular weights were estimated to be 757.5 kDa, 20.9 kDa and 4.7 kDa, respectively. Chemical and spectroscopic studies indicated that WPLE-N-1 consisted of (1→6)-β-D-glucopyranosyl residues; while WPLE-N-2 and WPLE-N-3 were found to contain (1→6)-, (1→4)- and (1→3)-α-D-glucopyranosyl residues, (1→6)-α-D-galactopyranosyl residues, (1→3,6)- and (1→2,4)-α-D-mannopyranosyl residues and terminal residues of D-glucopyranosyl residues. On a preliminary bioactivity test, these three polysaccharides exhibited antitumor activity against Sarcoma S-180, Carcinoma HCT-116 and HT-29 in vitro. This finding suggests that mannogalactoglucan should be explored as potential antitumor agents and utilized as tumor cell growth inhibitors for food and pharmaceutical industries.