Anti-hepatoma activity of the stiff branched beta-D-glucan and effects of molecular weight

The water soluble beta-(1 -> 3)-D-glucan with short branches (AF1) isolated from Auricularia auricula-judae was successfully fractionated by ultrasonication into three fractions with different weight-average molecular weights (M(w)s). The results of static and dynamic laser light scattering, viscometry and atomic force microscopy confirmed that the AF1 samples adopted a stiff chain conformation in water, and the coexistence of individuals and aggregates occurred gradually with increasing concentration. The AF1 sample with the highest M-w easily self-entangled, and exhibited a strong shear rate-dependence of viscosity in water. The glucans displayed anti-hepatoma activity and significantly inhibited H22 tumour growth without cytotoxicity towards normal tissues. They displayed both molecular weight-and dosage-dependencies of anti-tumour activity, and the sample with an M-w of 7.7 x 105 at the dosage of 5 mg kg(-1) exhibited the highest inhibition ratio of similar to 77% against H22 tumour, even significantly higher than the positive control of cytoxan. The immunohistochemical and western blot analyses revealed that the AF1 glucans triggered cell apoptosis, indicated by the activation of caspase 3/9 and down-regulated tumour angiogenesis factors of VEGF and CD31. The underlying antitumor mechanism was suggested to induce tumour cell apoptosis and to inhibit angiogenesis in tumour tissues via enhancement of the immune-response. Taken together, the AF1 beta-glucan was a potent natural drug candidate with high anti-cancer activities and less cytotoxicity, and the AF1 sample with a moderate molecular weight existed in aqueous solution as a more extended chain conformation, which plays an important role in activating immune responses.