Quercetin Stimulates Insulin Secretion and Reduces the Viability of Rat INS-1 Beta-Cells

• Published in: Cellular physiology and biochemistry Vol. 39; no. 1; pp. 278 - 293
• Main Authors: Kittl, Michael, Beyreis, Marlena, Tumurkhuu, Munkhtuya, Fürst, Johannes, Helm, Katharina, Pitschmann, Anna, Gaisberger, Martin, Glasl, Sabine, Ritter, Markus, Jakab, Martin
• Format: Journal Article
• Language: English
• Published: Basel, Switzerland Cell Physiol Biochem Press GmbH & Co KG 01.01.2016
• Subjects: Animals; Antioxidants - pharmacology; Apoptosis; Apoptosis - drug effects; ATP-sensitive; Beta-cells; Blotting, Western; Calcium; Calcium - metabolism; Cell Line, Tumor; Cell Proliferation - drug effects; Cell Survival - drug effects; Current; Dose-Response Relationship, Drug; Extracellular Signal-Regulated MAP Kinases - metabolism; Flavonoid; Flow Cytometry; Glucose - pharmacology; INS-1; Insulin; Insulin - metabolism; Insulin Secretion; Insulin-Secreting Cells - drug effects; Insulin-Secreting Cells - metabolism; Insulin-Secreting Cells - physiology; KATP; Kir 6.2; Membrane Potentials - drug effects; Original Paper; Phosphatidylinositol 3-Kinases - metabolism; Phosphorylation - drug effects; Plant Extracts - pharmacology; Potassium; Proto-Oncogene Proteins c-akt - metabolism; Quercetin; Quercetin - pharmacology; Rats; Rutin; Rutin - pharmacology; Viability; Calcium; ATP-sensitive; Rutin; Flavonoid; Insulin; KATP; Beta-cells; Quercetin; Kir 6.2; INS-1; Viability; Current; Potassium; Apoptosis
• ISSN: 1015-8987; 1421-9778
• DOI: 10.1159/000445623

Background/Aims: Previously we described insulinotropic effects of Leonurus sibiricus L. plant extracts used for diabetes mellitus treatment in Traditional Mongolian Medicine. The flavonoid quercetin and its glycoside rutin, which exert anti-diabetic properties in vivo by interfering with insulin signaling in peripheral target tissues, are constituents of these extracts. This study was performed to better understand short- and long-term effects of quercetin and rutin on beta-cells. Methods: Cell viability, apoptosis, phospho-protein abundance and insulin release were determined using resazurin, annexin-V binding assays, Western blot and ELISA, respectively. Membrane potentials (V mem ), whole-cell Ca 2+ (ICa)- and ATP-sensitive K + (IK ATP ) currents were measured by patch clamp. Intracellular Ca 2+ (Ca i ) levels were measured by time-lapse imaging using the ratiometric Ca 2+ indicator Fura-2. Results: Rutin, quercetin and the phosphoinositide-3-kinase (PI3K) inhibitor LY294002 caused a dose-dependent reduction in cell viability with IC 50 values of ∼75 µM, ∼25 µM and ∼3.5 µM, respectively. Quercetin (50 µM) significantly increased the percentage of Annexin-V+ cells within 48 hrs. The mean cell volume (MCV) of quercetin-treated cells was significantly lower. Within 2 hrs, quercetin significantly decreased basal- and insulin-stimulated Akt(T308) phosphorylation and increased Erk1/2 phosphorylation, without affecting P-Akt(S473) abundance. Basal- and glucose-stimulated insulin release were significantly stimulated by quercetin. Quercetin significantly depolarized V mem by ∼25 mV which was prevented by the K ATP -channel opener diazoxide, but not by the L-type ICa inhibitor nifedipine. Quercetin significantly stimulated ICa and caused a 50% inhibition of IK ATP . The effects on V mem , ICa and IK ATP rapidly reached peak values and then gradually diminished to control values within ∼1 minute. With a similar time-response quercetin induced an elevation in Ca i which was completely abolished in the absence of Ca 2+ in the bath solution. Rutin (50 µM) did not significantly alter the percentage of Annexin-V+ cells, MCV, Akt or Erk1/2 phosphorylation, insulin secretion, or the electrophysiological behavior of INS-1 cells. Conclusion: We conclude that quercetin acutely stimulates insulin release, presumably by transient K ATP channel inhibition and ICa stimulation. Long term application of quercetin inhibits cell proliferation and induces apoptosis, most likely by inhibition of PI3K/Akt signaling.