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Greco M, Munir A, Musarò D, Coppola C, Maffia M. Restoring autophagic function: a case for type 2 diabetes mellitus drug repurposing in Parkinson's disease. Front Neurosci 2023; 17:1244022. [PMID: 38027497 PMCID: PMC10654753 DOI: 10.3389/fnins.2023.1244022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2023] [Accepted: 10/16/2023] [Indexed: 12/01/2023] Open
Abstract
Parkinson's disease (PD) is a predominantly idiopathic pathological condition characterized by protein aggregation phenomena, whose main component is alpha-synuclein. Although the main risk factor is ageing, numerous evidence points to the role of type 2 diabetes mellitus (T2DM) as an etiological factor. Systemic alterations classically associated with T2DM like insulin resistance and hyperglycemia modify biological processes such as autophagy and mitochondrial homeostasis. High glucose levels also compromise protein stability through the formation of advanced glycation end products, promoting protein aggregation processes. The ability of antidiabetic drugs to act on pathways impaired in both T2DM and PD suggests that they may represent a useful tool to counteract the neurodegeneration process. Several clinical studies now in advanced stages are looking for confirmation in this regard.
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Affiliation(s)
- Marco Greco
- Department of Biological and Environmental Science and Technology, University of Salento, Lecce, Italy
| | - Anas Munir
- Department of Biological and Environmental Science and Technology, University of Salento, Lecce, Italy
- Department of Mathematics and Physics “E. De Giorgi”, University of Salento, Lecce, Italy
| | - Debora Musarò
- Department of Biological and Environmental Science and Technology, University of Salento, Lecce, Italy
| | - Chiara Coppola
- Department of Biological and Environmental Science and Technology, University of Salento, Lecce, Italy
- Department of Mathematics and Physics “E. De Giorgi”, University of Salento, Lecce, Italy
| | - Michele Maffia
- Department of Biological and Environmental Science and Technology, University of Salento, Lecce, Italy
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Ramu Y, Yamakaze J, Zhou Y, Hoshi T, Lu Z. Blocking Kir6.2 channels with SpTx1 potentiates glucose-stimulated insulin secretion from murine pancreatic β cells and lowers blood glucose in diabetic mice. eLife 2022; 11:77026. [PMID: 35212627 PMCID: PMC8880991 DOI: 10.7554/elife.77026] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2022] [Accepted: 01/26/2022] [Indexed: 11/16/2022] Open
Abstract
ATP-sensitive K+ (KATP) channels in pancreatic β cells are comprised of pore-forming subunits (Kir6.2) and modulatory sulfonylurea receptor subunits (SUR1). The ATP sensitivity of these channels enables them to couple metabolic state to insulin secretion in β cells. Antidiabetic sulfonylureas such as glibenclamide target SUR1 and indirectly suppress Kir6.2 activity. Glibenclamide acts as both a primary and a secondary secretagogue to trigger insulin secretion and potentiate glucose-stimulated insulin secretion, respectively. We tested whether blocking Kir6.2 itself causes the same effects as glibenclamide, and found that the Kir6.2 pore-blocking venom toxin SpTx1 acts as a strong secondary, but not a strong primary, secretagogue. SpTx1 triggered a transient rise of plasma insulin and lowered the elevated blood glucose of diabetic mice overexpressing Kir6.2 but did not affect those of nondiabetic mice. This proof-of-concept study suggests that blocking Kir6.2 may serve as an effective treatment for diabetes and other diseases stemming from KATP hyperactivity that cannot be adequately suppressed with sulfonylureas.
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Affiliation(s)
- Yajamana Ramu
- Department of Physiology, Perelman School of Medicine University of Pennsylvania, Philadelphia, United States
| | - Jayden Yamakaze
- Department of Physiology, Perelman School of Medicine University of Pennsylvania, Philadelphia, United States
| | - Yufeng Zhou
- Department of Physiology, Perelman School of Medicine University of Pennsylvania, Philadelphia, United States
| | - Toshinori Hoshi
- Department of Physiology, Perelman School of Medicine University of Pennsylvania, Philadelphia, United States
| | - Zhe Lu
- Department of Physiology, Perelman School of Medicine University of Pennsylvania, Philadelphia, United States
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3
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Rustenbeck I, Schulze T, Morsi M, Alshafei M, Panten U. What Is the Metabolic Amplification of Insulin Secretion and Is It (Still) Relevant? Metabolites 2021; 11:metabo11060355. [PMID: 34199454 PMCID: PMC8229681 DOI: 10.3390/metabo11060355] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2021] [Revised: 05/27/2021] [Accepted: 05/31/2021] [Indexed: 12/24/2022] Open
Abstract
The pancreatic beta-cell transduces the availability of nutrients into the secretion of insulin. While this process is extensively modified by hormones and neurotransmitters, it is the availability of nutrients, above all glucose, which sets the process of insulin synthesis and secretion in motion. The central role of the mitochondria in this process was identified decades ago, but how changes in mitochondrial activity are coupled to the exocytosis of insulin granules is still incompletely understood. The identification of ATP-sensitive K+-channels provided the link between the level of adenine nucleotides and the electrical activity of the beta cell, but the depolarization-induced Ca2+-influx into the beta cells, although necessary for stimulated secretion, is not sufficient to generate the secretion pattern as produced by glucose and other nutrient secretagogues. The metabolic amplification of insulin secretion is thus the sequence of events that enables the secretory response to a nutrient secretagogue to exceed the secretory response to a purely depolarizing stimulus and is thus of prime importance. Since the cataplerotic export of mitochondrial metabolites is involved in this signaling, an orienting overview on the topic of nutrient secretagogues beyond glucose is included. Their judicious use may help to define better the nature of the signals and their mechanism of action.
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Affiliation(s)
- Ingo Rustenbeck
- Institute of Pharmacology, Toxicology and Clinical Pharmacy, Technische Universität Braunschweig, D38106 Braunschweig, Germany; (T.S.); (M.M.); (M.A.); (U.P.)
- Correspondence: ; Tel.: +49-(0)53-139-156-70
| | - Torben Schulze
- Institute of Pharmacology, Toxicology and Clinical Pharmacy, Technische Universität Braunschweig, D38106 Braunschweig, Germany; (T.S.); (M.M.); (M.A.); (U.P.)
| | - Mai Morsi
- Institute of Pharmacology, Toxicology and Clinical Pharmacy, Technische Universität Braunschweig, D38106 Braunschweig, Germany; (T.S.); (M.M.); (M.A.); (U.P.)
- Department of Pharmacology, Faculty of Pharmacy, Assiut University, Assiut 71526, Egypt
| | - Mohammed Alshafei
- Institute of Pharmacology, Toxicology and Clinical Pharmacy, Technische Universität Braunschweig, D38106 Braunschweig, Germany; (T.S.); (M.M.); (M.A.); (U.P.)
| | - Uwe Panten
- Institute of Pharmacology, Toxicology and Clinical Pharmacy, Technische Universität Braunschweig, D38106 Braunschweig, Germany; (T.S.); (M.M.); (M.A.); (U.P.)
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Stermann T, Menzel F, Weidlich C, Jeruschke K, Weiss J, Altenhofen D, Benninghoff T, Pujol A, Bosch F, Rustenbeck I, Ouwens DM, Thoresen GH, de Wendt C, Lebek S, Schallschmidt T, Kragl M, Lammert E, Chadt A, Al-Hasani H. Deletion of the RabGAP TBC1D1 Leads to Enhanced Insulin Secretion and Fatty Acid Oxidation in Islets From Male Mice. Endocrinology 2018; 159:1748-1761. [PMID: 29481597 DOI: 10.1210/en.2018-00087] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/24/2018] [Accepted: 01/26/2018] [Indexed: 01/24/2023]
Abstract
The Rab guanosine triphosphatase-activating protein (RabGAP) TBC1D1 has been shown to be a key regulator of glucose and lipid metabolism in skeletal muscle. Its function in pancreatic islets, however, is not yet fully understood. Here, we aimed to clarify the specific impact of TBC1D1 on insulin secretion and substrate use in pancreatic islets. We analyzed the dynamics of glucose-stimulated insulin secretion (GSIS) and lipid metabolism in isolated islets from Tbc1d1-deficient (D1KO) mice. To further investigate the underlying cellular mechanisms, we conducted pharmacological studies in these islets. In addition, we determined morphology and number of both pancreatic islets and insulin vesicles in β-cells using light and transmission electron microscopy. Isolated pancreatic islets from D1KO mice exhibited substantially increased GSIS compared with wild-type (WT) controls. This was attributed to both enhanced first and second phase of insulin secretion, and this enhanced secretion persisted during repetitive glucose stimuli. Studies with sulfonylureas or KCl in isolated islets demonstrated that TBC1D1 exerts its function via a signaling pathway at the level of membrane depolarization. In line, ultrastructural analysis of isolated pancreatic islets revealed both higher insulin-granule density and number of docked granules in β-cells from D1KO mice compared with WT controls. Like in skeletal muscle, lipid use in isolated islets was enhanced upon D1KO, presumably as a result of a higher mitochondrial fission rate and/or higher mitochondrial activity. Our results clearly demonstrate a dual role of TBC1D1 in controlling substrate metabolism of the pancreatic islet.
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Affiliation(s)
- Torben Stermann
- German Diabetes Center, Leibniz Center for Diabetes Research, Heinrich Heine University, Medical Faculty, Duesseldorf, Germany
- German Center for Diabetes Research, Duesseldorf, Germany
| | - Franziska Menzel
- German Institute for Human Nutrition Potsdam-Rehbruecke, Nuthetal, Germany
| | - Carmen Weidlich
- German Diabetes Center, Leibniz Center for Diabetes Research, Heinrich Heine University, Medical Faculty, Duesseldorf, Germany
| | - Kay Jeruschke
- German Diabetes Center, Leibniz Center for Diabetes Research, Heinrich Heine University, Medical Faculty, Duesseldorf, Germany
| | - Jürgen Weiss
- German Diabetes Center, Leibniz Center for Diabetes Research, Heinrich Heine University, Medical Faculty, Duesseldorf, Germany
| | - Delsi Altenhofen
- German Diabetes Center, Leibniz Center for Diabetes Research, Heinrich Heine University, Medical Faculty, Duesseldorf, Germany
- German Center for Diabetes Research, Duesseldorf, Germany
| | - Tim Benninghoff
- German Diabetes Center, Leibniz Center for Diabetes Research, Heinrich Heine University, Medical Faculty, Duesseldorf, Germany
- German Center for Diabetes Research, Duesseldorf, Germany
| | - Anna Pujol
- Center of Animal Biotechnology and Gene Therapy, Universitat Autònoma de Barcelona, Barcelona, Spain
| | - Fatima Bosch
- Center of Animal Biotechnology and Gene Therapy, Universitat Autònoma de Barcelona, Barcelona, Spain
| | - Ingo Rustenbeck
- Institute of Pharmacology, Toxicology and Clinical Pharmacy, Technical University Braunschweig, Braunschweig, Germany
| | - D Margriet Ouwens
- German Diabetes Center, Leibniz Center for Diabetes Research, Heinrich Heine University, Medical Faculty, Duesseldorf, Germany
| | - G Hege Thoresen
- Department of Pharmaceutical Biosciences, School of Pharmacy, University of Oslo, Oslo, Norway
| | - Christian de Wendt
- German Diabetes Center, Leibniz Center for Diabetes Research, Heinrich Heine University, Medical Faculty, Duesseldorf, Germany
- German Center for Diabetes Research, Duesseldorf, Germany
| | - Sandra Lebek
- German Diabetes Center, Leibniz Center for Diabetes Research, Heinrich Heine University, Medical Faculty, Duesseldorf, Germany
- German Center for Diabetes Research, Duesseldorf, Germany
| | - Tanja Schallschmidt
- German Diabetes Center, Leibniz Center for Diabetes Research, Heinrich Heine University, Medical Faculty, Duesseldorf, Germany
- German Center for Diabetes Research, Duesseldorf, Germany
| | - Martin Kragl
- German Diabetes Center, Leibniz Center for Diabetes Research, Heinrich Heine University, Medical Faculty, Duesseldorf, Germany
- German Center for Diabetes Research, Duesseldorf, Germany
| | - Eckhard Lammert
- German Diabetes Center, Leibniz Center for Diabetes Research, Heinrich Heine University, Medical Faculty, Duesseldorf, Germany
- German Center for Diabetes Research, Duesseldorf, Germany
| | - Alexandra Chadt
- German Diabetes Center, Leibniz Center for Diabetes Research, Heinrich Heine University, Medical Faculty, Duesseldorf, Germany
- German Center for Diabetes Research, Duesseldorf, Germany
| | - Hadi Al-Hasani
- German Diabetes Center, Leibniz Center for Diabetes Research, Heinrich Heine University, Medical Faculty, Duesseldorf, Germany
- German Center for Diabetes Research, Duesseldorf, Germany
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Lee KY, Kim JR, Choi HC. Gliclazide, a K ATP channel blocker, inhibits vascular smooth muscle cell proliferation through the CaMKKβ-AMPK pathway. Vascul Pharmacol 2018; 102:21-28. [PMID: 29337033 DOI: 10.1016/j.vph.2018.01.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2017] [Revised: 12/31/2017] [Accepted: 01/10/2018] [Indexed: 10/18/2022]
Abstract
Gliclazide, a sulfonylurea that is widely used to treat type II-diabetes, specifically blocks KATP channels and recombinant smooth muscle (SUR2B/Kir6.1) KATP channels with high potency. Furthermore, it exerts antioxidant properties and inhibits tumor cell proliferation. In this study, we investigated the inhibitory effect of gliclazide on vascular smooth muscle cell (VSMC) proliferation and tried to identify the underlying signaling pathway. We first investigated the effect of gliclazide-induced AMP-activated protein kinase (AMPK) activation on the proliferation of VSMCs. Gliclazide induced phosphorylation of AMPK in a dose- and time-dependent manner and inhibited VSMC proliferation following stimulation by platelet-derived growth factor (PDGF). However, KATP channel openers and Kir6.1 siRNA prevented gliclazide-mediated inhibition of VSMC proliferation. Gliclazide also increased the levels of Ca2+/calmodulin-dependent protein kinase kinase β (CaMKKβ), an upstream kinase of AMPK. These findings suggested that the effects of KATP channels on AMPK activity were mediated by the regulation of intracellular Ca2+ levels. Oral administration of 2mg/kg gliclazide resulted in the activation of CaMKKβ and AMPK in vivo, suggesting that gliclazide suppressed VSMC proliferation via the CaMKKβ-AMPK signaling pathway. Taken together, our observations indicated that gliclazide-induced AMPK activation may act to prevent diabetes-associated atherosclerosis.
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Affiliation(s)
- Kyung Young Lee
- Department of Pharmacology, Yeungnam University, 170 Hyunchung-Ro, Daegu 705-717, Republic of Korea; Smart-aging Convergence Research Center, College of Medicine, Yeungnam University, 170 Hyunchung-Ro, Daegu 705-717, Republic of Korea
| | - Jae-Ryong Kim
- Department of Biochemistry and Molecular Biology, Yeungnam University, 170 Hyunchung-Ro, Daegu 705-717, Republic of Korea; Smart-aging Convergence Research Center, College of Medicine, Yeungnam University, 170 Hyunchung-Ro, Daegu 705-717, Republic of Korea
| | - Hyoung Chul Choi
- Department of Pharmacology, Yeungnam University, 170 Hyunchung-Ro, Daegu 705-717, Republic of Korea; Smart-aging Convergence Research Center, College of Medicine, Yeungnam University, 170 Hyunchung-Ro, Daegu 705-717, Republic of Korea.
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6
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Misunderstandings and controversies about the insulin-secreting properties of antidiabetic sulfonylureas. Biochimie 2017; 143:3-9. [DOI: 10.1016/j.biochi.2017.07.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2017] [Accepted: 07/10/2017] [Indexed: 12/28/2022]
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Agrawalla BK, Lee HW, Phue WH, Raju A, Kim JJ, Kim HM, Kang NY, Chang YT. Two-Photon Dye Cocktail for Dual-Color 3D Imaging of Pancreatic Beta and Alpha Cells in Live Islets. J Am Chem Soc 2017; 139:3480-3487. [DOI: 10.1021/jacs.6b12122] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Affiliation(s)
- Bikram Keshari Agrawalla
- Department
of Chemistry and Medicinal Chemistry Program, National University of Singapore, 3 Science Drive 3, 117543 Singapore
| | - Hyo Won Lee
- Department
of Energy Systems Research, Ajou University, Suwon 443749, Korea
| | - Wut-Hmone Phue
- Department
of Chemistry and Medicinal Chemistry Program, National University of Singapore, 3 Science Drive 3, 117543 Singapore
| | - Anandhkumar Raju
- Laboratory
of Bioimaging Probe Development, Singapore Bioimaging Consortium, Agency for Science, Technology and Research, 11 Biopolis Way, # 02-02 Helios, 138667 Singapore
| | - Jong-Jin Kim
- Department
of Chemistry and Medicinal Chemistry Program, National University of Singapore, 3 Science Drive 3, 117543 Singapore
| | - Hwan Myung Kim
- Department
of Energy Systems Research, Ajou University, Suwon 443749, Korea
| | - Nam-Young Kang
- Laboratory
of Bioimaging Probe Development, Singapore Bioimaging Consortium, Agency for Science, Technology and Research, 11 Biopolis Way, # 02-02 Helios, 138667 Singapore
| | - Young-Tae Chang
- Department
of Chemistry and Medicinal Chemistry Program, National University of Singapore, 3 Science Drive 3, 117543 Singapore
- Laboratory
of Bioimaging Probe Development, Singapore Bioimaging Consortium, Agency for Science, Technology and Research, 11 Biopolis Way, # 02-02 Helios, 138667 Singapore
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Affiliation(s)
- Mark A Rizzo
- Department of Physiology, University of Maryland School of Medicine, Baltimore, MD
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Candasamy M, Murthy TEGK, Gubiyappa KS, Chellappan DK, Gupta G. Alteration of glucose lowering effect of glibenclamide on single and multiple treatments with fenofibrate in experimental rats and rabbit models. J Basic Clin Pharm 2014; 5:62-7. [PMID: 25278668 PMCID: PMC4160721 DOI: 10.4103/0976-0105.139728] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Objective: Diabetes mellitus is a syndrome of multiple etiologies. Both type 1 and type 2 diabetes lead to multiple abnormalities of lipid and lipoprotein metabolism. The aim of this investigation was to study the influence of fenofibrate on the blood glucose lowering effect of glibenclamide. Materials and Methods: Glibenclamide (0.45, 0.23 mg/kg) and fenofibrate (18.1, 9.38 mg/kg) was treated to normal, diabetic rats, and normal rabbits. Blood samples were collected at various time intervals and were analyzed for blood glucose levels using a glucometer. Results: Co-administration of fenofibrate with glibenclamide significantly elevated the blood glucose reduction exhibited by glibenclamide. Conclusion: The results obtained from single and multiple dose treatments clearly demonstrated the existence of drug-drug interaction at the dose tested in animal models. Hence, this investigation would serve as a preclinical evidence for the effect of fenofibrate on the therapeutic efficacy of glibenclamide.
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Affiliation(s)
- Mayuren Candasamy
- Department of Life Sciences, School of Pharmacy, International Medical University, Bukit Jalil, Kuala Lumpur, Malaysia
| | | | - Kumar Shiva Gubiyappa
- Department of Life Sciences, School of Pharmacy, International Medical University, Bukit Jalil, Kuala Lumpur, Malaysia
| | - Dinesh Kumar Chellappan
- Department of Life Sciences, School of Pharmacy, International Medical University, Bukit Jalil, Kuala Lumpur, Malaysia
| | - Gaurav Gupta
- Department of Life Sciences, School of Pharmacy, International Medical University, Bukit Jalil, Kuala Lumpur, Malaysia
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Abstract
In addition to the common blood glucose lowering effect, sulfonylurea compounds are different in many aspects from each other. Based on earlier findings the second generation gliclazide has special advantages within this group. Although the number of experimental and clinical observations on gliclazide is continuously increasing, these novel findings are not in the focus anymore due to the appearance of new antidiabetics. This article reviews recent experimental (effect on receptors, the absence of Epac2 activation, antioxidant properties, possible incentive of factors participating in beta-cell differentiation) and pharmacogenomic data, and compares them with clinical observations obtained from gliclazide treatment (hypoglycemias, parameters of cardiovascular outcome). The data underline the advantages of gliclazide, the highly pancreas-selective nature, preservation of the ischemic precondition, favourable hemodynamic properties and potential reduction of the beta-cell loss as compared to other compounds of the group. However, gliclazide is not free from disadvantages characteristic to sulfonylureas in general (blood glucose independent insulin stimulation, beta-cell depletion). Comparing gliclazide with other derivatives of the group, the above data indicate individual benefits for the application when sulfonylurea compound is the drug of choice.
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Affiliation(s)
- Gábor Winkler
- Szent János Kórház II. Belgyógyászat-Diabetológia Budapest Diós árok 1-3. 1125 Miskolci Egyetem, Egészségügyi Kar Elméleti Egészségtudományi Intézet Miskolc
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12
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Nasry M, Abo-Youssef A, Abd El-Latif H. Anti-diabetic activity of the petroleum ether extract of Guar gum in streptozotocin-induced diabetic rats: A comparative study. BENI-SUEF UNIVERSITY JOURNAL OF BASIC AND APPLIED SCIENCES 2013. [DOI: 10.1016/j.bjbas.2013.09.008] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
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Willenborg M, Belz M, Schumacher K, Paufler A, Hatlapatka K, Rustenbeck I. Ca(2+)-dependent desensitization of insulin secretion by strong potassium depolarization. Am J Physiol Endocrinol Metab 2012; 303:E223-33. [PMID: 22550068 DOI: 10.1152/ajpendo.00010.2012] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Depolarization by a high K(+) concentration is a widely used experimental tool to stimulate insulin secretion. The effects occurring after the initial rise in secretion were investigated here. After the initial peak a fast decline occurred, which was followed by a slowly progressive decrease in secretion when a strong K(+) depolarization was used. At 40 mM KCl, but not at lower concentrations, the decrease continued when the glucose concentration was raised from 5 to 10 mM, suggesting an inhibitory effect of the K(+) depolarization. When tolbutamide was added instead of the glucose concentration being raised, a complete inhibition down to prestimulatory values was observed. Equimolar reduction of the NaCl concentration to preserve isoosmolarity enabled an increase in secretion in response to glucose. Unexpectedly, the same was true when the Na(+)-reduced media were made hyperosmolar by choline chloride or mannitol. The insulinotropic effect of tolbutamide was not rescued by the compensatory reduction of NaCl, suggesting a requirement for activated energy metabolism. These inhibitory effects could not be explained by a lack of depolarizing strength or by a diminished free cytosolic Ca(2+) concentration ([Ca(2+)](i)). Rather, the complexation of extracellular Ca(2+) concomitant with the K(+) depolarization markedly diminished [Ca(2+)](i) and attenuated the inhibitory action of 40 mM KCl. This suggests that a strong but not a moderate depolarization by K(+) induces a [Ca(2+)](i)-dependent, slowly progressive desensitization of the secretory machinery. In contrast, the decline immediately following the initial peak of secretion may result from the inactivation of voltage-dependent Ca(2+) channels.
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Affiliation(s)
- M Willenborg
- Institute of Pharmacology and Toxicology, University of Braunschweig, Braunschweig, Germany
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15
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Geng X, Lou H, Wang J, Li L, Swanson AL, Sun M, Beers-Stolz D, Watkins S, Perez RG, Drain P. α-Synuclein binds the K(ATP) channel at insulin-secretory granules and inhibits insulin secretion. Am J Physiol Endocrinol Metab 2011; 300:E276-86. [PMID: 20858756 PMCID: PMC4459921 DOI: 10.1152/ajpendo.00262.2010] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
α-Synuclein has been studied in numerous cell types often associated with secretory processes. In pancreatic β-cells, α-synuclein might therefore play a similar role by interacting with organelles involved in insulin secretion. We tested for α-synuclein localizing to insulin-secretory granules and characterized its role in glucose-stimulated insulin secretion. Immunohistochemistry and fluorescent sulfonylureas were used to test for α-synuclein localization to insulin granules in β-cells, immunoprecipitation with Western blot analysis for interaction between α-synuclein and K(ATP) channels, and ELISA assays for the effect of altering α-synuclein expression up or down on insulin secretion in INS1 cells or mouse islets, respectively. Differences in cellular phenotype between α-synuclein knockout and wild-type β-cells were found by using confocal microscopy to image the fluorescent insulin biosensor Ins-C-emGFP and by using transmission electron microscopy. The results show that anti-α-synuclein antibodies labeled secretory organelles within β-cells. Anti-α-synuclein antibodies colocalized with K(ATP) channel, anti-insulin, and anti-C-peptide antibodies. α-Synuclein coimmunoprecipitated in complexes with K(ATP) channels. Expression of α-synuclein downregulated insulin secretion at 2.8 mM glucose with little effect following 16.7 mM glucose stimulation. α-Synuclein knockout islets upregulated insulin secretion at 2.8 and 8.4 mM but not 16.7 mM glucose, consistent with the depleted insulin granule density at the β-cell surface membranes observed in these islets. These findings demonstrate that α-synuclein interacts with K(ATP) channels and insulin-secretory granules and functionally acts as a brake on secretion that glucose stimulation can override. α-Synuclein might play similar roles in diabetes as it does in other degenerative diseases, including Alzheimer's and Parkinson's diseases.
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Affiliation(s)
- Xuehui Geng
- Department of Cell Biology and Physiology, University of Pittsburgh School of Medicine, Pennsylvania, USA
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16
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Szollosi A, Nenquin M, Henquin JC. Pharmacological stimulation and inhibition of insulin secretion in mouse islets lacking ATP-sensitive K+ channels. Br J Pharmacol 2010; 159:669-77. [PMID: 20128805 DOI: 10.1111/j.1476-5381.2009.00588.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
BACKGROUND AND PURPOSE ATP-sensitive potassium channels (K(ATP) channels) in beta cells are a major target for insulinotropic drugs. Here, we studied the effects of selected stimulatory and inhibitory pharmacological agents in islets lacking K(ATP) channels. EXPERIMENTAL APPROACH We compared insulin secretion (IS) and cytosolic calcium ([Ca(2+)](c)) changes in islets isolated from control mice and mice lacking sulphonylurea receptor1 (SUR1), and thus K(ATP) channels in their beta cells (Sur1KO). KEY RESULTS While similarly increasing [Ca(2+)](c) and IS in controls, agents binding to site A (tolbutamide) or site B (meglitinide) of SUR1 were ineffective in Sur1KO islets. Of two non-selective blockers of potassium channels, quinine was inactive, whereas tetraethylammonium was more active in Sur1KO compared with control islets. Phentolamine, efaroxan and alinidine, three imidazolines binding to K(IR)6.2 (pore of K(ATP) channels), stimulated control islets, but only phentolamine retained weaker stimulatory effects on [Ca(2+)](c) and IS in Sur1KO islets. Neither K(ATP) channel opener (diazoxide, pinacidil) inhibited Sur1KO islets. Calcium channel blockers (nimodipine, verapamil) or diphenylhydantoin decreased [Ca(2+)](c) and IS in both types of islets, verapamil and diphenylhydantoin being more efficient in Sur1KO islets. Activation of alpha(2)-adrenoceptors or dopamine receptors strongly inhibited IS while partially (clonidine > dopamine) lowering [Ca(2+)](c) (control > Sur1KO islets). CONCLUSIONS AND IMPLICATIONS Those drugs retaining effects on IS in islets lacking K(ATP) channels, also affected [Ca(2+)](c), indicating actions on other ionic channels. The greater effects of some inhibitors in Sur1KO than in control islets might be relevant to medical treatment of congenital hyperinsulinism caused by inactivating mutations of K(ATP) channels.
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Affiliation(s)
- A Szollosi
- Unité d'Endocrinologie et Métabolisme, Faculty of Medicine, University of Louvain, Brussels, Belgium
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Krisanapun C, Peungvicha P, Temsiririrkkul R, Wongkrajang Y. Aqueous extract of Abutilon indicum Sweet inhibits glucose absorption and stimulates insulin secretion in rodents. Nutr Res 2009; 29:579-87. [PMID: 19761892 DOI: 10.1016/j.nutres.2009.07.006] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2009] [Revised: 07/15/2009] [Accepted: 07/16/2009] [Indexed: 12/20/2022]
Abstract
The objective of this study was to evaluate the antidiabetic effects of the aqueous extract derived from the Thai Abutilon indicum Sweet plant and to explore its effects on intestinal glucose absorption and insulin secretion. The authors hypothesized that the plasma glucose level could be reduced through the inhibition of glucose absorption and/or the enhancement of insulin secretion. Administration of the extract (0.5 and 1 g/kg body weight) in an oral glucose tolerance test led to a significant reduction in plasma glucose levels in 30 minutes after the administration in moderately diabetic rats, as compared with untreated rats (P < .05), and this was at a faster rate than the use of an antidiabetic drug, glibenclamide. The inhibition of glucose absorption through the small intestine was investigated using an everted intestinal sac. The results showed that the extract at concentrations of 0.156 to 5 mg/mL caused a reduction of glucose absorption in a dose response manner. The maximum response was noted at a dose of 2.5 mg/mL. The promotion of the extract on insulin secretion was confirmed by incubating beta cell of pancreatic islets and INS-1E insulinoma cells with the extract at 1 to 1000 microg/mL. These observations suggest that the aqueous extract from the A indicum plant has antidiabetic properties, which inhibited glucose absorption and stimulated insulin secretion. Phytochemical screening also revealed that the extract contained alkaloids, flavonoids, tannins, glycosides, and saponins that could account for the observed pharmacologic effects of the plant extract.
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Affiliation(s)
- Chutwadee Krisanapun
- Department of Physiology, Faculty of Pharmacy, Mahidol University, Bangkok 10400, Thailand
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Zhang CL, Katoh M, Shibasaki T, Minami K, Sunaga Y, Takahashi H, Yokoi N, Iwasaki M, Miki T, Seino S. The cAMP sensor Epac2 is a direct target of antidiabetic sulfonylurea drugs. Science 2009; 325:607-10. [PMID: 19644119 DOI: 10.1126/science.1172256] [Citation(s) in RCA: 170] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Epac2, a guanine nucleotide exchange factor for the small guanosine triphosphatase Rap1, is activated by adenosine 3',5'-monophosphate. Fluorescence resonance energy transfer and binding experiments revealed that sulfonylureas, widely used antidiabetic drugs, interact directly with Epac2. Sulfonylureas activated Rap1 specifically through Epac2. Sulfonylurea-stimulated insulin secretion was reduced both in vitro and in vivo in mice lacking Epac2, and the glucose-lowering effect of the sulfonylurea tolbutamide was decreased in these mice. Epac2 thus contributes to the effect of sulfonylureas to promote insulin secretion. Because Epac2 is also required for the action of incretins, gut hormones crucial for potentiating insulin secretion, it may be a promising target for antidiabetic drug development.
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Affiliation(s)
- Chang-Liang Zhang
- Division of Cellular and Molecular Medicine, Department of Physiology and Cell Biology, Kobe University Graduate School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe 650-0017, Japan
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