Selenium-dependent antitumor immunomodulating activity of polysaccharides from roots of A. membranaceus

Roots of Astragalus membranaceus (Fish.) Bge. var. mongholicus (Bge.) Hsiao (A. membranaceus) have been long used as an auxiliary reagent supporting cancer treatment. Here, we compared the chemical composition and antitumor immunomodulating activity of polysaccharides from roots of A. membranaceus (PAMs) from five major habitats in Inner Mongolia, PR China. We revealed that compositions of monosaccharides and amino acids were comparable among PAMs from different habitats. However, amounts of selenium varied widely in roots of A. membranaceus and PAMs. PAMs selenium-dependently repressed the in vivo proliferation of transplanted H22 ascitic hepatoma and S180 sarcoma cells with low toxic impacts on tumor-bearing mice. Selenium-containing PAMs ameliorated host CD4+ T cell apoptosis and serum cytokine dysregulation induced by tumor transplantation, leading to the enhancement of cytotoxic activities of natural killer and CD8+ T cells. Moreover, PAMs also selenium-dependently improved the phagocytotic function of intra-abdominal macrophages and suppressed M2-like polarization of tumor-associated macrophages. These data suggested that the selenium content varies in the roots of A. membranaceus and PAMs from different geographical origins dramatically and selenium is an important contributor to the antitumor immunomodulation activities of PAMs.