Anti-diabetic properties of chrysophanol and its glucoside from rhubarb rhizome.

An ethanol extract of rhubarb rhizome exhibited marked glucose transport activity in differentiated L6 rat myotubes. Activity-guided fractionation resulted in the isolation of two anthraquinones, chrysophanol-8-O-beta-D-glucopyranoside (1) and chrysophanol (2). The anti-diabetic effect was examined by glucose transport activity, glucose transporter 4 (Glut4) expression in myotubes, and the level of insulin receptor (IR) tyrosine phosphorylation as influenced by tyrosine phosphatase 1B, each of which is a major target of diabetes treatment. Chrysophanol-8-O-beta-D-glucopyranoside up to 25 microM dose-dependently activated glucose transport in insulin-stimulated myotubes. Increased tyrosine phosphorylation of IR due to tyrosine phosphatase 1B inhibitory activity with an IC50 value of 18.34+/-0.29 microM and unchanged Glut4 mRNA levels was observed following chrysophanol-8-O-beta-D-glucopyranoside treatment. Chrysophanol up to 100 microM exerted mild glucose transport activity and elevated the tyrosine phosphorylation of IR via tyrosine phosphatase 1B inhibition (IC50=79.86+/-0.12 microM); Glut4 mRNA expression was also significantly increased by 100 microM. The ED50 values of the two compounds were 59.38+/-0.66 and 79.69+/-0.03 microM, respectively. Therefore, these two anthraquinones from rhubarb rhizome, chrysophanol-8-O-beta-D-glucopyranoside and chrysophanol, have mild cytotoxicity and anti-diabetic properties and could play metabolic roles in the insulin-stimulated glucose transport pathway.