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Nagy L, Márton J, Vida A, Kis G, Bokor É, Kun S, Gönczi M, Docsa T, Tóth A, Antal M, Gergely P, Csóka B, Pacher P, Somsák L, Bai P. Glycogen phosphorylase inhibition improves beta cell function. Br J Pharmacol 2017; 175:301-319. [PMID: 28409826 DOI: 10.1111/bph.13819] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2016] [Revised: 04/03/2017] [Accepted: 04/05/2017] [Indexed: 12/17/2022] Open
Abstract
BACKGROUND AND PURPOSE Glycogen phosphorylase (GP) is the key enzyme for glycogen degradation. GP inhibitors (GPi-s) are glucose lowering agents that cause the accumulation of glucose in the liver as glycogen. Glycogen metabolism has implications in beta cell function. Glycogen degradation can maintain cellular glucose levels, which feeds into catabolism to maintain insulin secretion, and elevated glycogen degradation levels contribute to glucotoxicity. The purpose of this study was to assess whether influencing glycogen metabolism in beta cells by GPi-s affects the function of these cells. EXPERIMENTAL APPROACH The effects of structurally different GPi-s were investigated on MIN6 insulinoma cells and in a mouse model of diabetes. KEY RESULTS GPi treatment increased glycogen content and, consequently, the surface area of glycogen in MIN6 cells. Furthermore, GPi treatment induced insulin receptor β (InsRβ), Akt and p70S6K phosphorylation, as well as pancreatic and duodenal homeobox 1(PDX1) and insulin expression. In line with these findings, GPi-s enhanced non-stimulated and glucose-stimulated insulin secretion in MIN6 cells. The InsRβ was shown to co-localize with glycogen particles as confirmed by in silico screening, where components of InsR signalling were identified as glycogen-bound proteins. GPi-s also activated the pathway of insulin secretion, indicated by enhanced glycolysis, mitochondrial oxidation and calcium signalling. Finally, GPi-s increased the size of islets of Langerhans and improved glucose-induced insulin release in mice. CONCLUSION AND IMPLICATIONS These data suggest that GPi-s also target beta cells and can be repurposed as agents to preserve beta cell function or even ameliorate beta cell dysfunction in different forms of diabetes. LINKED ARTICLES This article is part of a themed section on Inventing New Therapies Without Reinventing the Wheel: The Power of Drug Repurposing. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.2/issuetoc.
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Affiliation(s)
- Lilla Nagy
- Department of Medical Chemistry, Faculty of Medicine, University of Debrecen, Debrecen, Hungary.,MTA-DE Cell Biology and Signaling Research Group, Debrecen, Hungary
| | - Judit Márton
- Department of Medical Chemistry, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - András Vida
- Department of Medical Chemistry, Faculty of Medicine, University of Debrecen, Debrecen, Hungary.,MTA-DE Lendület Laboratory of Cellular Metabolism, Debrecen, Hungary
| | - Gréta Kis
- Department of Anatomy, Histology and Embryology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Éva Bokor
- Department of Organic Chemistry, Faculty of Science and Technology, University of Debrecen, Debrecen, Hungary
| | - Sándor Kun
- Department of Organic Chemistry, Faculty of Science and Technology, University of Debrecen, Debrecen, Hungary
| | - Mónika Gönczi
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Tibor Docsa
- Department of Medical Chemistry, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Attila Tóth
- Department of Cardiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Miklós Antal
- Department of Anatomy, Histology and Embryology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary.,MTA-DE Neuroscience Research Group, Debrecen, Hungary
| | - Pál Gergely
- Department of Medical Chemistry, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Balázs Csóka
- Department of Surgery, Rutgers - New Jersey Medical School, Newark, NJ, USA.,Center for Immunity and Inflammation, Rutgers - New Jersey Medical School, Newark, NJ, USA
| | - Pal Pacher
- NIAAA, National Institutes of Health, Laboratory of Physiologic Studies, Rockville, MD, USA
| | - László Somsák
- Department of Organic Chemistry, Faculty of Science and Technology, University of Debrecen, Debrecen, Hungary
| | - Péter Bai
- Department of Medical Chemistry, Faculty of Medicine, University of Debrecen, Debrecen, Hungary.,MTA-DE Lendület Laboratory of Cellular Metabolism, Debrecen, Hungary.,Research Center for Molecular Medicine, University of Debrecen, Debrecen, Hungary
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Nagy L, Docsa T, Szántó M, Brunyánszki A, Hegedűs C, Márton J, Kónya B, Virág L, Somsák L, Gergely P, Bai P. Glycogen phosphorylase inhibitor N-(3,5-dimethyl-Benzoyl)-N'-(β-D-glucopyranosyl)urea improves glucose tolerance under normoglycemic and diabetic conditions and rearranges hepatic metabolism. PLoS One 2013; 8:e69420. [PMID: 23936011 PMCID: PMC3723905 DOI: 10.1371/journal.pone.0069420] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2013] [Accepted: 06/10/2013] [Indexed: 12/22/2022] Open
Abstract
Glycogen phosphorylase (GP) catalyzes the breakdown of glycogen and largely contributes to hepatic glucose production making GP inhibition an attractive target to modulate glucose levels in diabetes. Hereby we present the metabolic effects of a novel, potent, glucose-based GP inhibitor (KB228) tested in vitro and in vivo under normoglycemic and diabetic conditions. KB228 administration enhanced glucose sensitivity in chow-fed and obese, diabetic mice that was a result of higher hepatic glucose uptake. Besides improved glucose sensitivity, we have observed further unexpected metabolic rearrangements. KB228 administration increased oxygen consumption that was probably due to the overexpression of uncoupling protein-2 (UCP2) that was observed in animal and cellular models. Furthermore, KB228 treatment induced mammalian target of rapamycin complex 2 (mTORC2) in mice. Our data demonstrate that glucose based GP inhibitors are capable of reducing glucose levels in mice under normo and hyperglycemic conditions. Moreover, these GP inhibitors induce accommodation in addition to GP inhibition - such as enhanced mitochondrial oxidation and mTORC2 signaling – to cope with the glucose influx and increased glycogen deposition in the cells, however the molecular mechanism of accommodation is unexplored.
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Affiliation(s)
- Lilla Nagy
- Department of Medical Chemistry, University of Debrecen Medical and Health Science Center, Debrecen, Hungary
| | - Tibor Docsa
- Department of Medical Chemistry, University of Debrecen Medical and Health Science Center, Debrecen, Hungary
| | - Magdolna Szántó
- Department of Medical Chemistry, University of Debrecen Medical and Health Science Center, Debrecen, Hungary
- Cell Biology and Signaling Research Group of the Hungarian Academy of Sciences, Debrecen, Hungary
| | - Attila Brunyánszki
- Department of Medical Chemistry, University of Debrecen Medical and Health Science Center, Debrecen, Hungary
| | - Csaba Hegedűs
- Department of Medical Chemistry, University of Debrecen Medical and Health Science Center, Debrecen, Hungary
| | - Judit Márton
- Department of Medical Chemistry, University of Debrecen Medical and Health Science Center, Debrecen, Hungary
| | - Bálint Kónya
- Department of Organic Chemistry, University of Debrecen, Debrecen, Hungary
| | - László Virág
- Department of Medical Chemistry, University of Debrecen Medical and Health Science Center, Debrecen, Hungary
- Cell Biology and Signaling Research Group of the Hungarian Academy of Sciences, Debrecen, Hungary
| | - László Somsák
- Department of Organic Chemistry, University of Debrecen, Debrecen, Hungary
| | - Pál Gergely
- Department of Medical Chemistry, University of Debrecen Medical and Health Science Center, Debrecen, Hungary
- Cell Biology and Signaling Research Group of the Hungarian Academy of Sciences, Debrecen, Hungary
| | - Péter Bai
- Department of Medical Chemistry, University of Debrecen Medical and Health Science Center, Debrecen, Hungary
- Cell Biology and Signaling Research Group of the Hungarian Academy of Sciences, Debrecen, Hungary
- * E-mail:
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Gilham D, Perreault KR, Holmes CFB, Brindley DN, Vance DE, Lehner R. Insulin, glucagon and fatty acid treatment of hepatocytes does not result in phosphorylation or changes in activity of triacylglycerol hydrolase. Biochim Biophys Acta Mol Cell Biol Lipids 2005; 1736:189-99. [PMID: 16168708 DOI: 10.1016/j.bbalip.2005.08.013] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2005] [Revised: 07/19/2005] [Accepted: 08/09/2005] [Indexed: 10/25/2022]
Abstract
It is recognized that the majority of very low density lipoprotein (VLDL) associated triacylglycerol (TG) is synthesized from fatty acids and partial acylglycerols generated by lipolysis of intra-hepatic storage rather than made de novo. Triacylglycerol hydrolase (TGH) is involved in mobilizing stored TG. Modulating the ability of TGH to hydrolyze stored lipids represents a potentially regulated and rate limiting step in VLDL assembly. Phosphorylation of lipases and carboxylesterases trigger diverse but functionally significant events. We explored the potential for regulating the mobilization of hepatic TG through phosphorylation of TGH. Insulin is known to suppress VLDL secretion from liver, and glucagon can be considered an opposing hormone. However, neither insulin nor glucagon treatment of hepatocytes led to phosphorylation of TGH or changes in its activity. Augmenting intracellular TG stores by incubations with oleic acid also did not lead to changes in TGH activity. Therefore, changes in phosphorylation state are not a mechanism for regulating TGH activity, access to TG substrate pools or for TGH-mediated contributions to VLDL assembly and secretion.
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Affiliation(s)
- Dean Gilham
- Department of Cell Biology, University of Alberta, Edmonton, Alberta, Canada T6G 2S2
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Kalamidas SA, Kotoulas OB, Hann AC. Studies on glycogen autophagy: effects of phorbol myristate acetate, ionophore A23187, or phentolamine. Microsc Res Tech 2002; 57:507-11. [PMID: 12112433 DOI: 10.1002/jemt.10104] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The effects of agents that could manipulate the lysosomal calcium such as phorbol myristate acetate, ionophore A23187, and phentolamine on the lysosomal glycogen degradation were studied by electron microscopy, morphometric analysis, and biochemical assays in newborn rat hepatocytes. Phorbol myristate acetate, which promotes the input of calcium to lysosomes, increased the total volume of autophagic vacuoles and the activity of lysosomal glycogen-hydrolyzing acid alpha 1,4 glucosidase and decreased the fractional volume of undigested glycogen inside the autophagic vacuoles and also decreased the activity of acid mannose 6-phosphatase. Ionophore A23187, which releases lysosomal calcium, produced opposite results in these enzyme activities. Phentolamine, an alpha-adrenergic blocking agent which interferes with the generation of phosphoinositides and may activate the lysosomal calcium uptake pump, increased the total volume of autophagic vacuoles and the activity of lysosomal glycogen-hydrolyzing acid glucosidase and decreased the fractional volume of undigested glycogen inside the autophagic vacuoles. The results of this study constitute evidence that changes in lysosomal calcium may influence certain aspects of autophagy, including the degradation of glycogen inside the autophagic vacuoles. They also support our previous postulate [Kalamidas and Kotoulas (2000a,b) Histol Histopathol 15:29-35, 1011-1018] that stimulation of autophagic mechanisms in newborn rat hepatocytes may be associated with acid mannose 6-phosphatase activity-deficient lysosomes.
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Affiliation(s)
- S A Kalamidas
- Department of Anatomy, Histology and Embryology, Medical School, University of Ioannina, Ioannina, Greece
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