Chemical Structure and Immunomodulating Activities of an α-Glucan Purified from Lobelia chinensis Lour

A neutral alpha-glucan, named BP1, with a molecular mass of approximately 9.45 kDa, was isolated from Lobelia chinensis by hot-water extraction, a Q-Sepharose Fast Flow column and Superdex-75 column chromatography. Its chemical structure was characterized by monosaccharide analysis, methylation analysis and analysis of its FT-IR, high performance gel permeation chromatography (HPGPC) and 1D/2D-NMR spectra data. The backbone of BP1 consists of ->(6)alpha-D-Glcp(1)->(6,3)alpha-D-Glcp(1)->((6)alpha-D-Glcp(1))x-(6,3)alpha-D-Glcp(1)-((6)alpha-D-Glcp(1))y ->. The side chains were terminal alpha-D-Glcp(1)-> and alpha-D-Glcp(1)-> ((6)alpha-D-Glcp(1))z ->(4)alpha-D-Glcp(1)-> 3 alpha-D-Glcp(1)->(4)alpha-D-Glcp(1) -> (x + y + z = 5), which are attached to the backbone at O-3 of (3,6)alpha-D-Glcp(1). The results of the effect of BP1 on mouse macrophage cell line RAW 264.7 indicate that BP1 enhances the cell proliferation, phagocytosis, nitric oxide production and cytokine secretion in a dose-dependent manner. Because the inhibitor of Toll-like receptor 4 blocks the BP1-induced secretion of TNF-alpha and IL-6, we hypothesize that alpha-glucan BP1 activates TLR4, which mediates the above-mentioned immunomodulating effects.