A homologous series of -glucans from Hemicentrotus pulcherrimus and their immunomodulatory activity

Seven macromolecular polysaccharides (HPP-2S-HPP-8S) were purified from the gonads of sea urchin Hemicentrotus pulcherrimus. They were characterized as alpha-glucan homologues, sharing the same alpha-1,4-glucan backbone substituted at C-6 positions by glucose with HPP-1S that occurs as the major polysaccharide in H. pulcherrimus, while with higher degrees of branching, and additionally possessing minor amounts of mannose and ribose. The branching degree and amounts of non-glucose branches showed a generally increasing tendency across HPP-2S - HPP-8S. These polysaccharides exhibited significant macrophage-activating effects by augmenting the secretion of NO, TNF-alpha and IL-6, which probably involves the activation of NF-xB and MAPKs signaling pathways. Notably, the polysaccharides with a higher degree of branching exhibited markedly enhanced immunomodulatory capacity with a lowest effective concentration of 1.95 mu g/mL. This work provides new cases of bioactive alpha-glucans and reveals their potential application as immunomodulating agents.