Antihyperglycemic activity of polyphenolic components of black/bitter cumin Centratherum anthelminticum (L.) Kuntze seeds

The effect of black/bitter cumin seeds Centratherum anthelminticum (L.) Kuntze extract (CA) containing mixture of polyphenolic compounds was tested on rat intestinal alpha-glucosidases, human salivary alpha-amylase activity and postprandial hyperglycemia in rats. Polyphenolic components of C. anthelminticum seeds (CA) dose dependently inhibited rat intestinal disaccharidases. IC50 values were found to be 34.1 +/- 3.8, 62.2 +/- 4.5 and 500.5 +/- 11.9 mu g of CA for rat intestinal sucrase, maltase and p-nitrophenyl alpha-D-glucopyranoside (PNP-glycoside), respectively. CA also inhibited human salivary alpha-amylase activity with IC50 value of 185.5 +/- 4.9 mu g. The inhibitory effect of CA was found to be 8-32 fold more potent than DL-catechin but less effective than acarbose on rat intestinal disaccharidases and salivary alpha-amylase. The enzyme kinetic studies showed a non-competitive type of inhibition with a low K-i value of 30.24 mu g, 76.67 mu g and 341.60 mu g of CA for maltase, sucrase and PNP-glycoside hydrolysis activities, respectively. The in vitro inhibition of glucosidases was further confirmed by in vivo maltose tolerance test in rats. Feeding of CA at 50-200 mg/kg body weight (b.wt) to maltose (2.0 g/kg b.wt), loaded rats significantly reduced the postprandial plasma glucose levels compared with acarbose. The inhibitory components of CA were identified as a mixture of polyphenolic compounds viz., gallic acid, protocatechuic acid, caffeic acid, ellagic acid, ferulic acid, quercetin and kaempferol. This study demonstrated that CA exerts antihyperglycemic effect by decreasing postprandial glucose in rats by modulating alpha- amylase and glucosidases (sucrase and maltase) activity and thus may be useful for the management of diabetes mellitus.