Inhibition of human intestinal α-glucosidases by calystegines.

Calystegines are polyhydroxylated nortropane alkaloids found in Convolvulaceae, Solanaceae, and other plant families. These plants produce common fruits and vegetables. The calystegine structures resemble sugars and suggest interaction with enzymes of carbohydrate metabolism. Maltase and sucrase are alpha-glucosidases contributing to human carbohydrate degradation in the small intestine. Inhibition of these enzymes by orally administered drugs is one option for treatment of diabetes mellitus type 2. In this study, inhibition of maltase and sucrase by calystegines A(3) and B-2 purified from potatoes was investigated. In silico docking studies confirmed binding of both calystegines to the active sites of the enzymes. Calystegine A(3) showed low in vitro enzyme inhibition; calystegine B-2 inhibited mainly sucrose activity. Both compounds were not transported by Caco-2 cells indicating low systemic availability. Vegetables rich M calystegine B-2 should be further investigated as possible components of a diet preventing a steep increase in blood glucose after a carbohydrate rich meal.