A comb-like branched β-D-glucan produced by a Cordyceps sinensis fungus and its protective effect against cyclophosphamide-induced immunosuppression in mice

An exopolysaccharide (EPS) was fractionated from fermentation media of a Cordyceps sinensis fungus (CsHK1) by ethanol precipitation at 2/5 volume ratio of ethanol/media. Its structural characteristics were elucidated by FT-IR, GC, GC-MS, 1D and 2D NMR combined with periodate oxidation, Smith degradation, partial acid hydrolysis, and methylation analysis. Furthermore, the immunomodulatory activity of EPS was evaluated by the model of cyclophosphamide-induced immunosuppression. The results from monosaccharide composition and partial acid hydrolysis indicated that EPS almost consisted of glucose excluding a trace amount of mannose. GC-MS and NMR analysis further confirmed EPS had a linear backbone of (1 -> 3) beta-D-glucopyranosyl residues with a single (1 -> 6) beta-D-glucopyranosyl side branching unit for every three p-u-glucopyranosyl residues, showing a comb-like beta-D-glucan with short and intensive branches, which was responsible for high viscosity. Moreover, EPS could significantly enhance immune organs and stimulate the release of major cytokines TNF-alpha. and INF-gamma, suggesting that EPS exhibited protective effect in immunocompromised mice. (C) 2016 Elsevier Ltd. All rights reserved.