Effects of molecular structure on antitumor activities of (1→3)-β-d-glucans from different Lentinus Edodes

Four (1→3)-β-d-glucans coded as L-I1, L-I2, L-I3 and L-I4 with high molecular weight (1.47×106–1.67×106) were isolated from four kinds of fruiting bodies of Lentinus Edodes with different strains by extracting with NaOH/NaBH4, then precipitating with 1 M acetic acid. The results from element analysis indicated that the polysaccharides contained 4.6–15.2 wt% proteins. The polysaccharides were treated with acetone to remove the bound protein, coded as LNP, and by ultrasonic irradiation to degrade molecular weight, coded as LU. The weight-average molecular weight Mw, radii of gyration <s2>z1/2 and intrinsic viscosity [η] of the samples in aqueous 0.2 M NaCl/0.005 M NaOH and in dimethyl sulfoxide (DMSO) were measured by size exclusion chromatography combined with laser light scattering and viscometry at 25 oC, respectively. The Mw drop by a factor of 3 from in aqueous solution to in DMSO, and Mw dependence of <s2>z1/2 revealed that the β-glucan exists as triple-helical conformation in aqueous NaCl and as single flexible chains in DMSO. The single chain samples were prepared in DMSO, coded as LSC. The assay in vivo and in vitro antitumor activities against Sarcoma 180 (S-180) solid tumor for the polysaccharides showed that the native triple helical (1→3)-β-d-glucans containing protein exhibited obvious antitumor bioactivities (in vivo highest inhibition ratio ξ reached to 70.0% for L-I3), whereas that (ξ=2.2%) of LSC having only single flexible chains significantly decreased. Moreover, the antitumor activities of the LNP, LU and LSC samples are lower than those of the native ones, suggesting that the antitumor activities of polysaccharide were related with their conformation, molecular weight and content of the bound protein. The triple helical conformation plays an important role in enhancement of the antitumor activities.