Inhibitory effects of Synurus excelsus and Weigela subsessilis on aldose reductase and HPLC-UV analysis of scopolin, scopoletin, and quercetin

The inhibition of aldose reductase (AR) has been shown to prevent the progression of the many complications associated with diabetic hyperglycemia. Several compounds purified from various plant sources have exhibited potent inhibition against AR. In this study, the inhibitory effects of the methanol extracts of the flowers of Synurus excelsus and Weigela subsessilis on AR were determined in vitro. Scopolin and scopoletin are coumarins isolated from the flowers of S. excelsus and W. subsessilis; and quercetin is a known AR inhibitor present in many flowers. To determine and quantify their presence in both plants, HPLC-UV analysis of all three compounds was performed. S. excelsus and W. subsessilis showed potent inhibition against AR having $IC_{50}$ values of 0.17 and $0.14{\mu}g/mL$, respectively. The concentration of scopolin in S. excelsus and W. subsessilis were 34.71 and 174.14 mg/g extract, respectively. Scopoletin was detected in S. excelsus at 3.41 mg/g extract, whereas quercetin was not detected in both plants. This study shows that S. excelsus and W. subsessilis exhibited promising AR inhibitory effects and are both sources of coumarins.