Aims: Steviol glycosides are the sweet components extracted from medicinal plant Stevia rebaudiana Bertoni, which have antihyperglycaemic effects. Steviol glucuronide (SVG) is the metabolite excreted in human urine after oral administration of steviol glycosides. We aimed to clarify whether SVG exerts direct insulin stimulation from pancreatic islets and to explore its mode of action.
Materials and methods: Insulin secretion was measured after 60 minutes static incubation of isolated mouse islets with (a) 10-9-10-5 mol/L SVG at 16.7 mmol/L glucose and (b) 10-7 mol/L SVG at 3.3-16.7 mmol/L glucose. Islets were perifused with 3.3 or 16.7 mmol/L glucose in the presence or absence of 10-7 mol/L SVG. Gene transcription was measured after 72 hours incubation in the presence or absence of 10-7 mol/L SVG.
Results: SVG dose-dependently increased insulin secretion from mouse islets with 10-7 mol/L exerting the maximum effect in the presence of 16.7 mmol/L glucose (P < .001). The insulinotropic effect of SVG was critically dependent on the prevailing glucose concentration, and SVG (10-7 mol/L) enhanced insulin secretion at or above 11.1 mmol/L glucose (P < .001) and showed no effect at lower glucose concentrations. During perifusion of islets, SVG (10-7 mol/L) had a long-acting and apparently reversible insulinotropic effect in the presence of 16.7 mmol/L glucose (P < .05). Gene-transcript levels of B2m and Gcgr were markedly altered.
Conclusion: This is the first report to demonstrate that SVG stimulates insulin secretion in a dose- and glucose-dependent manner from isolated mouse islets of Langerhans. SVG may be the main active metabolite after oral intake of steviol glycosides.
Keywords: insulin secretion; mouse pancreatic islets; steviol glucuronide; steviol glycosides.
© 2019 The Authors. Endocrinology, Diabetes & Metabolism published by John Wiley & Sons Ltd.