Triterpenoid Saponin from Momordica tuberosa (Cucurbitaceae) Stimulates Insulin Secretion from Isolated Mouse Pancreatic Islets and Provides Protection from Streptozotocin and High-Glucose Induced Injury

Abstract:

Background: Momordica tuberosa, belonging to the family Cucurbitaceae, is a tropical plant that is widely cultivated in the southern states of India. Objectives: Momordica tuberosa possesses a saponin, triterpenoid in nature that has been reported to exhibit anti-hyperglycaemic activity in vivo and in vitro. In this study we intend to isolate the saponin in pure purified state, assess its anti-hyperglycaemic activity on isolated mice pancreatic islets and evaluate its protective role against streptozotocin and highglucose induced islet injury, a central event in the pathogenesis of uncontrolled diabetes. Methods: Saponin purification and identification was carried out using chromatography followed by its structure elucidation IR, ¹H-NMR, ¹³C-NMR and mass spectrometry. Islets were obtained from mice employing the pancreas perfusion method with collagenase type XI. Islet viability and specificity were determined by trypan blue-DTZ double staining followed by insulin secretion and intra-islet content measurement by ELISA. STZ-induced oxidative damage was assessed by lipid peroxidation and nitric oxide assay. High glucose-induced islet cell death/viability was assessed by MTT assay. Key findings: Approximately 650 islets per pancreas were recovered after isolation. The islets retained normal membrane integrity, viability and glucose-stimulated insulin secretion (GSIS). The saponin stimulated secretion of insulin from the isolated islets, protected from STZand high glucose-induced cytotoxicity and also from oxidative stress. Conclusion: The saponin acted as an insulin secretagogue and protected the islets from cytotoxic and oxidative stress induced by STZ and high glucose. We thus conclude that the saponin may be considered for effective use in IDDM.

Key words: Saponin, Momordica tuberosa, Insulin secretagogue, Islet viability, High glucose-induced cytotoxicity.