Purification, structural elucidation and antitumor activity of a novel mannogalactoglucan from the fruiting bodies of Lentinus edodes.

A mannogalactoglucan, named LE-MGG, was isolated from the basidiocarps of Lentinus edodes by hot water-extraction, ethanol precipitation anion exchange chromatography, and further purified by gel-permeation chromatography (GPC). Its structural features were investigated by high performance liquid chromatography (HPLC), high performance gel-permeation chromatography (HPGPC), methylation analysis, periodate oxidation-Smith degradation, and by IR and NMR spectroscopy, including two-dimensional (2D) NMR. HPLC analysis revealed that LE-MGG contained mannose-galactose-glucose in the molar ratio of 10:18:72. GPC and HPGPC showed that LE-MGG was a homogeneous fraction (d=1.34) and its molecular weight was estimated to be 18kDa. Chemical and spectroscopic studies indicated that LE-MGG consists of (1→6)-, (1→4)- and (1→3)-linked β-d-glucopyranosyl residues, (1→6)-linked α-d-galactopyranosyl residues, (1→3,6)- and (1→2,4)-linked α-d-mannopyranosyl residues and terminal residues of β-d-glucopyranosyl. Cytotoxicity assay showed that LE-MGG presented higher antitumor activities against S-180 cell with a dose-dependent manner, and exhibited lower cytotoxicity to carcinoma HCT-116 and HT-29 cells. Our studies showed also that LE-MGG presented antitumor bioactivities on Sarcoma 180 solid tumor cell implanted in Kunming mice. This finding suggests that mannogalactoglucan should be explored as potential antitumor agents and could be potentially applied as a natural antitumor drug.