Structure Elucidation and Immunostimulatory Activity Evaluation of a Galactoglucan from Alpinia officinarum Hance

<i>Alpinia officinarum</i> Hance has a medicinal history of thousands of years in treating cough, diabetes, and gastrointestinal system diseases, and it is also a medicine food homology (MFH) plant in China. To evaluate the pharmacological activities of polysaccharides from the rhizomes of <i>A. officinarum</i>, polysaccharides were initially obtained by hot-water extraction and the ethanol precipitation method. A homogenous polysaccharide designated as AOP-w was isolated by a DE-52 column. The proposed structure was elucidated and the immunoregulatory effects on RAW 264.7 macrophage cells were evaluated. The results showed that AOP-w had a molecular weight of 5.26 kDa, and mainly consisted of galactose and glucose (molar ratio of 0.12:0.88). Its backbone comprised α-(1→4)-Glc<i>p</i>, α-(1→4,6)-Glc<i>p</i> and β-(1→3,4)-Gal<i>p</i> residues, terminated by α-(1→6)-Glc<i>p</i> and T-Glc<i>p</i> residues. AOP-w was nontoxic to RAW 264.7 cells, but demonstrated promotion in cell proliferation within a 100 μg/mL concentration. The immunostimulatory effects of AOP-w were confirmed by the elevated NO production of AOP-w-treated cells. Moreover, the RNAseq was conducted and the results showed that AOP-w may activate the TNF and NF-κB signaling pathways by binding to Toll-like receptors, thereby affecting the immune modulatory activity of RAW264.7 cells. These results suggest a high potential of AOP-w from <i>A. officinarum</i> for immunotherapeutic applications.