Objective: Our study was aimed to determine the aldose reductase (AR) inhibitory activity of Enicostemma hyssopifolium (EH) and isolation and characterization of the bioactive principle responsible for the activity.Methods: An enzyme, aldose reductase, was isolated from the lenses of Wistar rats. An enzyme inhibitory assay was performed on the extract and bitter fraction of aerial parts. Two major components from methanol extract were isolated and characterized and subjected for AR inhibitory assay. Their anticataract potential was assessed in vitro by studying their effect on polyol accumulation in rat lenses.Results: Methanol extract, bitter fraction and two isolated compounds of EH were found to inhibit lens AR to various extents. An isolated C- glycosidic flavonoid was found to be a potent AR inhibitor, having an IC50 value of 0.71 ?g/ml, and is comparable with that of the positive standard quercetin (0.62 ?g/ml). Similarly, it showed significant anticataract potential in vitro, decreasing polyol accumulation by 41.67 % compared to control lenses.Conclusion: Swertisin, a C-glycosidic flavonoid from Enicostemma hyssopifolium has significant activity against sugar-induced cataract in vitro. This effect of swertisin is due to its aldose reductase inhibitory potential.
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