Saponins from the traditional medicinal plant Momordica charantia stimulate insulin secretion in vitro

The antidiabetic activity of Momordica charantia (L.), Cucurbitaceae, a widely-used treatment for diabetes in a number of traditional medicine systems, was investigated in vitro. Antidiabetic activity has been reported for certain saponins isolated from M. charantia. In this study insulin secretion was measured in MIN6 β-cells incubated with an ethanol extract, saponin-rich fraction, and five purified saponins and cucurbitane triterpenoids from M. charantia, 3β,7β,25-trihydroxycucurbita-5,23(E)-dien-19-al (1), momordicine I (2), momordicine II (3), 3-hydroxycucurbita-5,24-dien-19-al-7,23-di-O-β-glucopyranoside (4), and kuguaglycoside G (5). Treatments were compared to incubation with high glucose (27 mM) and the insulin secretagogue, glipizide (50 μM). At 125 μg/ml, an LC–ToF-MS characterized saponin-rich fraction stimulated insulin secretion significantly more than the DMSO vehicle, p = 0.02. At concentrations 10 and 25 μg/ml, compounds 3 and 5 also significantly stimulated insulin secretion as compared to the vehicle, p ≤ 0.007, and p = 0.002, respectively. This is the first report of a saponin-rich fraction, and isolated compounds from M. charantia, stimulating insulin secretion in an in vitro, static incubation assay.