Aldose Reductase Inhibitory Compounds from Glycyrrhiza uralensis

We evaluated the inhibitory effects of components from the root of Glycyrrhiza uralensis (G. uralensis) on aldose reductase (AR) and sorbitol formation in rat lenses with high levels of glucose as part of our ongoing search of natural sources for therapeutic and preventive agents for diabetic complications. In order to identify the bioactive components of G. uralensis, 5 prenylated flavonoids (semilicoisoflavone B, 7-O-methylluteone, dehydroglyasperin C, dehydroglyasperin D, and isoangustone A), three flavonoids (liquiritigenin, isoliquiritigenin, and licochalcone A), and two triterpenoids (glycyrrhizin and glycyrrhetinic acid) were isolated; their chemical structures were then elucidated on the basis of spectroscopic evidence and comparison with published data. The anti-diabetic complication activities of 10 G. uralensis-derived components were investigated via inhibitory assays using rat lens AR (rAR) and human recombinant AR (rhAR). From the 10 isolated compounds, semilicoisoflavone B showed the most potent inhibition, with the IC50 values of rAR and rhAR at 1.8 and 10.6 mu M, respectively. In the kinetic analyses using Lineweaver-Burk plots of 1/velocity and 1/concentration of substrate, semilicoisoflavone B showed noncompetitive inhibition against rhAR. The results clearly indicated that the presence of a gamma,gamma-dimethylchromene ring is partly responsible for the AR inhibitory activity of isoprenoid-type flavonoids. Further, semilicoisoflavone B inhibited sorbitol formation of rat lens incubated with a high concentration of glucose, indicating that this compound may be effective for preventing osmotic stress in hyperglycemia.