Inhibition of alpha-glucosidase and amylase by luteolin, a flavonoid.

Twenty-one naturally occurring flavonoids were tested for inhibitory activities against alpha-glucosidase (EC 3.2.1.20) and alpha-amylase (EC 3.2.1.1). Luteolin, amentoflavone, luteolin 7-O-glucoside, and daidzein were the strongest inhibitors among the compounds tested. Luteolin inhibited alpha-glucosidase by 36% at the concentration of 0.5 mg/ml and was stronger than acarbose, the most widely prescribed drug, in inhibitory potency, suggesting that it has the possibility to effectively suppress postprandial hyperglycemia in patients with non-insulin dependent diabetes mellitus. Luteolin also inhibited alpha-amylase effectively although it was less potent than acarbose. The clinical value of luteolin needs to be further evaluated.