Natural Compound α-PGG and Its Synthetic Derivative 6Cl-TGQ Alter Insulin Secretion: Evidence for Diminishing Glucose Uptake as a Mechanism

Abstract

Xiaozhuo Chen,1– 7 Nigel A Daniels,1,4,5,8 David Cottrill,2,3 Yanyang Cao,2,3 Xuan Wang,2,3 Yunsheng Li,2 Pratik Shriwas,2,3 Yanrong Qian,2 Michael W Archer,1,4 Nicholas B Whitticar,4,9 Ishrat Jahan,1,4 Craig S Nunemaker,1,3– 5 Aili Guo10 1The Diabetes Institute at Ohio University, Athens, OH, 45701, USA; 2The Edison Biotechnology Institute, Athens, OH, 45701, USA; 3Department of Biological Sciences, Athens, OH, 45701, USA; 4Department of Biomedical Sciences, Athens, OH, 45701, USA; 5Heritage College of Osteopathic Medicine, Athens, OH, 45701, USA; 6Interdisciplinary Graduate Program in Molecular and Cellular Biology, Athens, OH, 45701, USA; 7Department of Chemistry and Biochemistry, Athens, OH, 45701, USA; 8Department of Specialty Medicine, Athens, OH, 45701, USA; 9Translational Biomedical Sciences Program, Ohio University, Athens, OH, 45701, USA; 10Department of Internal Medicine, Division of Endocrinology, Diabetes and Metabolism, University of California at Davis (UC Davis) School of Medicine, UC Davis Health Science, Sacramento, CA, 95817, USACorrespondence: Aili GuoDepartment of Internal Medicine, Division of Endocrinology, Diabetes and Metabolism, University of California at Davis (UC Davis) School of Medicine, UC Davis Health Science, PSSB, G400, 4150 V St., Sacramento, CA, 95817, USATel [phone]Fax [phone]Email [email protected] S NunemakerDepartment of Biomedical Sciences, 1 Ohio University, Athens, OH, 45701, USATel [phone]Fax [phone]Email [email protected]: Previously we showed that natural compound α-penta-galloyl-glucose (α-PGG) and its synthetic derivative 6-chloro-6-deoxy-1,2,3,4-tetra-O-galloyl-α-D-glucopyranose (6Cl-TGQ) act to improve insulin signaling in adipocytes by increasing glucose transport. In this study, we investigated the mechanism of actions of α-PGG and 6Cl-TGQ on insulin secretion.Methods: Mouse islets and/or INS-1832/13 beta-cells were used to test the effects of our compounds on glucose-stimulated insulin secretion (GSIS), intracellular calcium [Ca2+]i using fura-2AM, glucose transport activity via a radioactive glucose uptake assay, intracellular ATP/ADP, and extracellular acidification (ECAR) and mitochondrial oxygen consumption rates (OCAR) using Seahorse metabolic analysis.Results: Both compounds reduced GSIS in beta-cells without negatively affecting cell viability. The compounds primarily diminished glucose uptake into islets and beta-cells. Despite insulin-like effects in the peripheral tissues, these compounds do not act through the insulin receptor in islets. Further interrogation of the stimulus-secretion pathway showed that all the key metabolic factors involved in GSIS including ECAR, OCAR, ATP/ADP ratios, and [Ca2+]i of INS-1832/13 cells were diminished after the compound treatment.Conclusion: The compounds suppress glucose uptake of the beta-cells, which consequently slows down the rates of glycolysis and ATP synthesis, leading to decrease in [Ca2+]i and GSIS. The difference between adipocytes and beta-cells in effects on glucose uptake is of great interest. Further structural and functional modifications could produce new compounds with optimized therapeutic potentials for different target cells. The higher potency of synthetic 6Cl-TGQ in enhancing insulin signaling in adipocytes but lower potency in reducing glucose uptake in beta-cells compared to α-PGG suggests the feasibility of such an approach.Keywords: glucose-stimulated insulin secretion, calcium influx, glucose transporter, α-PGG, 6Cl-TGQ

Keywords

• glucose-stimulated insulin secretion
• calcium influx
• glucose transporter
• α-pgg
• 6cl-tgq