Enhanced immunostimulatory and antitumor activity of different derivatives of κ-carrageenan oligosaccharides from Kappaphycus striatum

Chemical modification of carbohydrates can lead to differences in their biological activities. We previously showed that kappa-carrageenan oligosaccharides from Kappaphycus striatum have antitumor and immunomodulation effects on S180-bearing mice. In this study, we tested the hypothesis that different chemical modifications of carrageenan oligosaccharides enhance their activities. The mice inoculated with S180 cell suspension were treated p.o. with carrageenan oligosaccharides and their sulfated, acetylated, and phosphorylated derivatives (50, 100, and 200 mu g g(-1)) for 14 days. Transplantable tumor inhibition rate and macrophage phagocytosis, quantitative hemolysis of sheep red blood cells, lymphocyte proliferation, the activity of natural killer cells, production of interleukin-2, and tumor necrosis factor-alpha were also analyzed. As expected, treatment with different kappa-carrageenan oligosaccharides derivatives resulted in an increase in tumor inhibition rate and macrophage phagocytosis and cellular immunity, especially on spleen lymphocyte proliferation. The sulfated derivative at the dose 200 mu g g(-1) per day showed the highest antitumor activity with the 54.12% tumor weight inhibition and elicited an increase in nature killer cells activity up to 76.1% on S180-bearing mice, which were both significantly higher than the unmodified oligosaccharides. It suggested that chemical modification (especially sulfation) of carrageenan oligosaccharides can enhance their antitumor effect and boost their antitumor immunity.