Antioxidant potential and carbohydrate digestive enzyme inhibitory effects of five Inula species and their major compounds

The present study was designed to examine in-vitro antidiabetic activities of different extracts of flowers, leaves and roots of Inula helenium ssp. turcoracemosa, I. montbretiana, I. peacockiana, I thapsoides ssp. thapsoides and I. viscosa extracts. I. viscosa and I. montbretiana flower, I. thapsoides and I. viscosa leaf and I. helenium root methanol extracts exhibited remarkable α-glucosidase inhibitory activity. Additionally, α-amylase inhibitory activities of the extracts were moderate at only 3000 μg/mL. Based on the results of in-vitro antidiabetic activity tests; antioxidant activities, total phenol and flavonoid contents of the most promising extracts were evaluated. To identify compounds responsible for the antidiabetic activity, major compounds of Inula species were analyzed for their in-vitro enzyme inhibitory activity. Quercetin, luteolin and rutin exhibited a significant inhibition on α-glucosidase at 10 mM concentrations. Consequently, Inula species could potentially be used by diabetic patients for their antidiabetic and antioxidant activities.