A polysaccharide from mycelia of Metarhizium taii: Structural characterization, inhibition on α-glucosidase and improvement of insulin resistance in HepG2 cells

Polysaccharide is one of the important bioactive components of Metarhizium taii. A homogeneous polysaccharide named as HLP-S was first purified from the mycelium of M. taii. HLP-S had a molecular weight of 2.81 x 103 kDa and consisted mainly of mannose, glucose, and galactose in a ratio of 2.31:2.89:3.59. The structure of HLP-S was determined by various chemical structure analysis methods, which showed that the sugar linkage units of HLP-S consist of T-Manp, T-Glcp, -> 4,6)-Glcp-(1 ->, -> 2)-Manp-(1 ->, -> 4)-Glcp-(1 ->, -> 4)-Galp-(1 ->, -> 4,6)-Manp-(1 ->, -> 3,4)-Glcp-(1 ->). The Hypoglycemic activity of HLP-S was investigated by enzyme inhibition assay in vitro and a model of insulin resistance in HepG2 cells. The results of alpha-glucosidase activity inhibition assay in vitro showed that different concentrations of HLP-S inhibited alpha-glucosidase activity with a mixture of competitive and non-competitive inhibition types. Various concentrations of HLP-S were applied to HepG2-IR cells. The results of the experiments suggested that HLP-S might effectively improve the glucose consumption of HepG2-IR cells and promote the synthesis of glycogen, hence reducing insulin resistance.