THE EFFECTS OF CALYSTEGINES ISOLATED FROM EDIBLE FRUITS AND VEGETABLES ON MAMMALIAN LIVER GLYCOSIDASES

The polyhydroxylated nortropane alkaloids called calystegines occur in many plants of the Convolvulaceae, Solanaceae, and Moraceae families. Certain of these alkaloids exhibit potent inhibitory activities again st glycosidases and the recently demonstrated occurrence of calystegin es in the leaves, skins, and sprouts of potatoes (Solanum tuberosum), and in the leaves of the eggplant (S.melongena), has raised concerns r egarding the safety of these vegetables in the human diet. We have sur veyed the occurrence of calystegines in edible fruits and vegetables o f the families Convolvulaceae, Solanaceae, and Moraceae by GC-MS. Caly stegines A3, B1, B2, and C1 were detected in all the edible fruits and vegetables tested; sweet and chili peppers, potatoes, eggplants, toma toes, Physalis fruits, sweet potatoes, and mulberries. Calystegines B1 and C1 were potent competitive inhibitors of the bovine, human, and r at beta-glucosidase activities, with K-i values of 150, 10, and 1.9 mu M, respectively for B1 and 15, 1.5, and 1 mu M, respectively, for C1. Calystegine B2 was a strong competitive inhibitor of the alpha-galact osidase activity in all the livers. Human beta-xylosidase was inhibite d by all four nortropanes, with calystegine C1 having a K-i of 0.13 mu M. Calystegines A3 and B2 selectively inhibited the rat liver beta-gl ucosidase activity. The potent inhibition of mammalian beta-glucosidas e and alpha-galactosidase activities in vitro raises the possibility o f toxicity in humans consuming large amounts of plants that contain th ese compounds.