Glucose lowering effect in vitro of Astraeus odoratus extracts

Abstract

Astraeus odoratus C. Phosri, R. Watling, M.P. Martin & A.J.S. Whalley (Diplocystaceae) is a mushroom distributed in the Northeastern part of Thailand and has been widely used as food. Here we investigate the activity in vitro which is related to blood glucose lowering. The A. odoratus aqueous extract (yield 2.1% dry weight), and 95% EtOH extract (yield 2.4% dry weight) and its fractions, were assayed for alpha glucosidase inhibition in 96-well plates; the glucose uptake stimulation was determined by using 2-deoxy glucose assay in L6 myotube cells. Fractionation of the 95% EtOH extract was done by a Diaion HP20 column to obtain 5 fractions (H2O, 25% MeOH, 50% MeOH, 75% MeOH, and 100% MeOH respectively). The results indicated that A. odoratus extracts possessed alpha glucosidase inhibition with IC50 of 98.9 µg/mL for the aqueous extract and IC50 of 63.3 µg/mL for the 95% EtOH extract. The glucose uptake stimulation into L6 myotubes of the aqueous extract was found to be 22% at the concentration of 400 µg/mLwhile the 95% EtOH extract was inactive. Fractionation of the 95% EtOH extract led to increasing alpha glucosidase inhibition potency by the 75% MeOH fraction with IC50 23.4 µg/mL while the IC50 of acarbose was 3.6 mg/mL. For the glucose uptake stimulation, the 100% MeOH fraction (400 µg/mL) was the active fraction with increasing potency to 42% stimulation while the positive control 500 nM insulin provided 100% stimulation. It can be concluded that A. odoratus extracts mainly affected the postprandial blood glucose reduction rather than the glucose uptake stimulation into the muscle cells. In addition, the fractionation of 95%EtOH extract led to the increasing of glucose lowering effect.