Insulin-secreting activity of the traditional antidiabetic plant Viscum album (mistletoe)

Viscum album (mistletoe) has been documented as a traditional treatment of diabetes. In acute 20-min tests, 1-10 mg/ml aqueous extract of mistletoe evoked a stepwise 1.1- to 12.2-fold stimulation of insulin secretion from clonal pancreatic B-cells. This effect was abolished by 0.5 mM diazoxide and prior exposure to extract did not alter subsequent stimulation of insulin secretion induced by 10 nnM L-alanine, thereby negating a detrimental effect on cell viability. The insulin-releasing effect of mistletoe extract was unaltered by 16.7 mM glucose, L-alanine (10 mM), 3-isobutyl-1-methylxanthine (IBMX) (1 mM), or a depolarising concentration of KCl (25 mM). The ability of extract to enhance insulin secretion did not depend upon the use of heat during extract preparation and was not mediated by lectins. These results demonstrate the presence of insulin-releasing natural product(s) in Viscum album which may contribute to the reported antidiabetic property of the plant.