Comparison of Antioxidant Potential and Rat intestinal a-Glucosidases inhibitory Activities of Quercetin, Rutin, and Isoquercetin

Abstract

Summary: Inhibition of α-amylase and α-glucosidases involved in the digestion and absorption of carbohydrates can decrease the postprandial increase  of blood glucose level after a mixed carbohydrate diet. Therefore, the inhibitory activity of quercetin and its glycoside derivatives such as rutin and isoquercetin against rat intestinal α- glucosidases (sucrase, maltase, glucoamylase, and isomaltase) and porcine pancreatic α-amylase were compared in vitro. Among the tested three flavonols, quercetin had the highest maltase, glucoamylase, and isomaltase inhibitory activities. The isomaltase and α-amylase inhibitory activities of the above three flavonols were also compared to a known type 2 diabetes drug (Acarbose), strong  α-amylase inhibitor. Compared  to acarbose, quercetin and its derivatives showed a significant inhibition of isomaltase but did not show high inhibitory activity against porcine pancreatic  α-amylase. Furthermore, the oxygen radical absorbance capacity (ORAC) of these flavonols was evaluated. Quercetin had the highest peroxyl radical absorbing activity, followed by rutin and isoquercetin. These results suggest that the selected flavonols which have high ORAC value with α-glucosidase inhibitory activity and low α-amylase activity could be physiologically useful for treatment of diabetes, although in vivo experiments are needed. Industrial relevance: The α-glucosidase inhibitory activity and antioxidant activity in quercetin would be helpful to manage glucose uptake and the glucose-induced increased levels of mitochondrial reactive oxygen species (ROS) linked to hyperglycemia. This in vitro study therefore provides the biochemical rationale for the benefit of quercetin- based dietary supplement and enzymatic conversion from rutin or isoquercetin to quercetin for enhancing bioactive food components using high rutin-contained grain such as buckwheat.