201
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Godoy-Matos AF. The role of glucagon on type 2 diabetes at a glance. Diabetol Metab Syndr 2014; 6:91. [PMID: 25177371 PMCID: PMC4148933 DOI: 10.1186/1758-5996-6-91] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/27/2014] [Accepted: 08/20/2014] [Indexed: 12/25/2022] Open
Abstract
The opposite effects of insulin and glucagon in fuel homeostasis, the paracrine/endocrine inhibitory effects of insulin on glucagon secretion and the hyperglucagonemia in the pathogenesis of type 2 diabetes (T2D) have long been recognized. Inappropriately increased alpha-cell function importantly contributes to hyperglycemia and reflects the loss of tonic restraint normally exerted by high local concentrations of insulin on alpha-cells, possibly as a result of beta-cell failure and alpha-cell insulin resistance, but additional mechanisms, such as the participation of incretin hormones in this response, have also been suggested. Three classes of drugs already available for clinical use address the abnormalities of glucagon secretion in T2D, namely, the GLP-1 receptor agonists (GLP-1RA), the inhibitors of dipeptidyl peptidase-4 (DPP-4i) and the amylin agonist pramlintide; it has been proposed that the glucagonostatic and insulinotropic effects of GLP-1RA equally contribute to their hypoglycemic efficacy. In this review, the control of glucagon secretion and its participation in T2D pathogenesis are summarized.
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Affiliation(s)
- Amélio F Godoy-Matos
- Metabolism Unit, Instituto Estadual de Diabetes e Endocrinologia, Rio de Janeiro and Catholic University, Rio de Janeiro, Brazil
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202
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Guan HP, Chen G. Factors affecting insulin-regulated hepatic gene expression. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2014; 121:165-215. [PMID: 24373238 DOI: 10.1016/b978-0-12-800101-1.00006-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Obesity has become a major concern of public health. A common feature of obesity and related metabolic disorders such as noninsulin-dependent diabetes mellitus is insulin resistance, wherein a given amount of insulin produces less than normal physiological responses. Insulin controls hepatic glucose and fatty acid metabolism, at least in part, via the regulation of gene expression. When the liver is insulin-sensitive, insulin can stimulate the expression of genes for fatty acid synthesis and suppress those for gluconeogenesis. When the liver becomes insulin-resistant, the insulin-mediated suppression of gluconeogenic gene expression is lost, whereas the induction of fatty acid synthetic gene expression remains intact. In the past two decades, the mechanisms of insulin-regulated hepatic gene expression have been studied extensively and many components of insulin signal transduction pathways have been identified. Factors that alter these pathways, and the insulin-regulated hepatic gene expression, have been revealed and the underlying mechanisms have been proposed. This chapter summarizes the recent progresses in our understanding of the effects of dietary factors, drugs, bioactive compounds, hormones, and cytokines on insulin-regulated hepatic gene expression. Given the large amount of information and progresses regarding the roles of insulin, this chapter focuses on findings in the liver and hepatocytes and not those described for other tissues and cells. Typical insulin-regulated hepatic genes, such as insulin-induced glucokinase and sterol regulatory element-binding protein-1c and insulin-suppressed cytosolic phosphoenolpyruvate carboxyl kinase and insulin-like growth factor-binding protein 1, are used as examples to discuss the mechanisms such as insulin regulatory element-mediated transcriptional regulation. We also propose the potential mechanisms by which these factors affect insulin-regulated hepatic gene expression and discuss potential future directions of the area of research.
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Affiliation(s)
- Hong-Ping Guan
- Department of Diabetes, Merck Research Laboratories, Kenilworth, New Jersey, USA
| | - Guoxun Chen
- Department of Nutrition, University of Tennessee at Knoxville, Knoxville, Tennessee, USA
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203
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Ishihara H. [The cutting-edge of medicine; glucagon renaissance]. NIHON NAIKA GAKKAI ZASSHI. THE JOURNAL OF THE JAPANESE SOCIETY OF INTERNAL MEDICINE 2013; 102:3237-43. [PMID: 24605576 DOI: 10.2169/naika.102.3237] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Hisamitsu Ishihara
- Division of Diabetes and Metabolism, Nihon University School of Medicine, Japan
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204
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Yip L, Taylor C, Whiting CC, Fathman CG. Diminished adenosine A1 receptor expression in pancreatic α-cells may contribute to the pathology of type 1 diabetes. Diabetes 2013; 62:4208-19. [PMID: 24264405 PMCID: PMC3837064 DOI: 10.2337/db13-0614] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Prediabetic NOD mice exhibit hyperglucagonemia, possibly due to an intrinsic α-cell defect. Here, we show that the expression of a potential glucagon inhibitor, the adenosine A1 receptor (Adora1), is gradually diminished in α-cells of NOD mice, autoantibody-positive (AA(+)) and overtly type 1 diabetic (T1D) patients during the progression of disease. We demonstrated that islet inflammation was associated with loss of Adora1 expression through the alternative splicing of Adora1. Expression of the spliced variant (Adora1-Var) was upregulated in the pancreas of 12-week-old NOD versus age-matched NOD.B10 (non-diabetes-susceptible) control mice and was detected in the pancreas of AA(+) patients but not in control subjects or overtly diabetic patients, suggesting that inflammation drives the splicing of Adora1. We subsequently demonstrated that Adora1-Var expression was upregulated in the islets of NOD.B10 mice after exposure to inflammatory cytokines and in the pancreas of NOD.SCID mice after adoptive transfer of activated autologous splenocytes. Adora1-Var encodes a dominant-negative N-terminal truncated isoform of Adora1. The splicing of Adora1 and loss of Adora1 expression on α-cells may explain the hyperglucagonemia observed in prediabetic NOD mice and may contribute to the pathogenesis of human T1D and NOD disease.
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205
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Filippi BM, Abraham MA, Yue JTY, Lam TKT. Insulin and glucagon signaling in the central nervous system. Rev Endocr Metab Disord 2013; 14:365-75. [PMID: 23959343 DOI: 10.1007/s11154-013-9258-4] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The prevalence of the obesity and diabetes epidemic has triggered tremendous research investigating the role of the central nervous system (CNS) in the regulation of food intake, body weight gain and glucose homeostasis. This invited review focuses on the role of two pancreatic hormones--insulin and glucagon--that trigger signaling pathways in the brain to regulate energy and glucose homeostasis. Unlike in the periphery, insulin and glucagon signaling in the CNS does not seem to have opposing metabolic effects, as both hormones exert a suppressive effect on food intake and weight gain. They signal through different pathways and alter different neuronal populations suggesting a complementary action of the two hormones in regulating feeding behavior. Similar to its systemic effect, insulin signaling in the brain lowers glucose production. However, the ability of glucagon signaling in the brain to regulate glucose production remains unknown. Future studies that aim to dissect insulin and glucagon signaling in the CNS that regulate energy and glucose homeostasis could unveil novel signaling molecules to lower body weight and glucose levels in obesity and diabetes.
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206
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Abstract
ATP-sensitive potassium channels (K(ATP) channels) link cell metabolism to electrical activity by controlling the cell membrane potential. They participate in many physiological processes but have a particularly important role in systemic glucose homeostasis by regulating hormone secretion from pancreatic islet cells. Glucose-induced closure of K(ATP) channels is crucial for insulin secretion. Emerging data suggest that K(ATP) channels also play a key part in glucagon secretion, although precisely how they do so remains controversial. This Review highlights the role of K(ATP) channels in insulin and glucagon secretion. We discuss how K(ATP) channels might contribute not only to the initiation of insulin release but also to the graded stimulation of insulin secretion that occurs with increasing glucose concentrations. The various hypotheses concerning the role of K(ATP) channels in glucagon release are also reviewed. Furthermore, we illustrate how mutations in K(ATP) channel genes can cause hyposecretion or hypersecretion of insulin, as in neonatal diabetes mellitus and congenital hyperinsulinism, and how defective metabolic regulation of the channel may underlie the hypoinsulinaemia and the hyperglucagonaemia that characterize type 2 diabetes mellitus. Finally, we outline how sulphonylureas, which inhibit K(ATP) channels, stimulate insulin secretion in patients with neonatal diabetes mellitus or type 2 diabetes mellitus, and suggest their potential use to target the glucagon secretory defects found in diabetes mellitus.
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Affiliation(s)
- Frances M Ashcroft
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, Parks Road, Oxford OX1 3PT, UK
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207
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Li XC, Zhuo JL. Current insights and new perspectives on the roles of hyperglucagonemia in non-insulin-dependent type 2 diabetes. Curr Hypertens Rep 2013; 15:522-30. [PMID: 23996678 PMCID: PMC3810031 DOI: 10.1007/s11906-013-0383-y] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Type 2 diabetes is well recognized as a noninsulin-dependent diabetic disease. Clinical evidence indicates that the level of circulating insulin may be normal, subnormal, and even elevated in type 2 diabetic patients. Unlike type 1 diabetes, the key problem for type 2 diabetes is not due to the absolute deficiency of insulin secretion, but because the body is no longer sensitive to insulin. Thus, insulin resistance is increased and the sensitivity to insulin is reset, so increasing levels of insulin are required to maintain body glucose and metabolic homeostasis. How insulin resistance is increased and what factors contribute to its development in type 2 diabetes remain incompletely understood. Overemphasis of insulin deficiency alone may be too simplistic for us to understand how type 2 diabetes is developed and should be treated, since glucose metabolism and homeostasis are tightly controlled by both insulin and glucagon. Insulin acts as a YIN factor to lower blood glucose level by increasing cellular glucose uptake, whereas glucagon acts as a YANG factor to counter the action of insulin by increasing glucose production. Furthermore, other humoral factors other than insulin and glucagon may also directly or indirectly contribute to increased insulin resistance and the development of hyperglycemia. The purpose of this article is to briefly review recently published animal and human studies in this field, and provide new insights and perspectives on recent debates as to whether hyperglucagonemia and/or glucagon receptors should be targeted to treat insulin resistance and target organ injury in type 2 diabetes.
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Affiliation(s)
- Xiao C Li
- Laboratory of Receptor and Signal Transduction, Department of Pharmacology & Toxicology, University of Mississippi Medical Center, Jackson, MS, 39216, USA
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208
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Vater A, Sell S, Kaczmarek P, Maasch C, Buchner K, Pruszynska-Oszmalek E, Kolodziejski P, Purschke WG, Nowak KW, Strowski MZ, Klussmann S. A mixed mirror-image DNA/RNA aptamer inhibits glucagon and acutely improves glucose tolerance in models of type 1 and type 2 diabetes. J Biol Chem 2013; 288:21136-21147. [PMID: 23744070 PMCID: PMC3774380 DOI: 10.1074/jbc.m112.444414] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2012] [Revised: 06/04/2013] [Indexed: 11/23/2022] Open
Abstract
Excessive secretion of glucagon, a functional insulin antagonist, significantly contributes to hyperglycemia in type 1 and type 2 diabetes. Accordingly, immunoneutralization of glucagon or genetic deletion of the glucagon receptor improved glucose homeostasis in animal models of diabetes. Despite this strong evidence, agents that selectively interfere with endogenous glucagon have not been implemented in clinical practice yet. We report the discovery of mirror-image DNA-aptamers (Spiegelmer®) that bind and inhibit glucagon. The affinity of the best binding DNA oligonucleotide was remarkably increased (>25-fold) by the introduction of oxygen atoms at selected 2'-positions through deoxyribo- to ribonucleotide exchanges resulting in a mixed DNA/RNA-Spiegelmer (NOX-G15) that binds glucagon with a Kd of 3 nm. NOX-G15 shows no cross-reactivity with related peptides such as glucagon-like peptide-1, glucagon-like peptide-2, gastric-inhibitory peptide, and prepro-vasoactive intestinal peptide. In vitro, NOX-G15 inhibits glucagon-stimulated cAMP production in CHO cells overexpressing the human glucagon receptor with an IC50 of 3.4 nm. A single injection of NOX-G15 ameliorated glucose excursions in intraperitoneal glucose tolerance tests in mice with streptozotocin-induced (type 1) diabetes and in a non-genetic mouse model of type 2 diabetes. In conclusion, the data suggest NOX-G15 as a therapeutic candidate with the potential to acutely attenuate hyperglycemia in type 1 and type 2 diabetes.
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MESH Headings
- Animals
- Aptamers, Nucleotide/blood
- Aptamers, Nucleotide/pharmacokinetics
- Aptamers, Nucleotide/pharmacology
- Aptamers, Nucleotide/therapeutic use
- Blood Glucose/metabolism
- Body Weight/drug effects
- CHO Cells
- Cricetinae
- Cricetulus
- Cyclic AMP/biosynthesis
- Diabetes Mellitus, Type 1/blood
- Diabetes Mellitus, Type 1/drug therapy
- Diabetes Mellitus, Type 2/blood
- Diabetes Mellitus, Type 2/drug therapy
- Disease Models, Animal
- Fasting/blood
- Glucagon/antagonists & inhibitors
- Glucagon/metabolism
- Glucose Tolerance Test
- Humans
- Kinetics
- Male
- Mice
- Mice, Inbred BALB C
- RNA/metabolism
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Affiliation(s)
- Axel Vater
- From the NOXXON Pharma AG, Max-Dohrn-Strasse 8-10, 10589 Berlin, Germany
| | - Simone Sell
- From the NOXXON Pharma AG, Max-Dohrn-Strasse 8-10, 10589 Berlin, Germany
| | - Przemyslaw Kaczmarek
- the Department of Animal Physiology and Biochemistry, Poznan University of Life Sciences, 35 Wolynska Street, 60637 Poznan, Poland, and
| | - Christian Maasch
- From the NOXXON Pharma AG, Max-Dohrn-Strasse 8-10, 10589 Berlin, Germany
| | - Klaus Buchner
- From the NOXXON Pharma AG, Max-Dohrn-Strasse 8-10, 10589 Berlin, Germany
| | - Ewa Pruszynska-Oszmalek
- the Department of Animal Physiology and Biochemistry, Poznan University of Life Sciences, 35 Wolynska Street, 60637 Poznan, Poland, and
| | - Pawel Kolodziejski
- the Department of Animal Physiology and Biochemistry, Poznan University of Life Sciences, 35 Wolynska Street, 60637 Poznan, Poland, and
| | - Werner G Purschke
- From the NOXXON Pharma AG, Max-Dohrn-Strasse 8-10, 10589 Berlin, Germany
| | - Krzysztof W Nowak
- the Department of Animal Physiology and Biochemistry, Poznan University of Life Sciences, 35 Wolynska Street, 60637 Poznan, Poland, and
| | - Mathias Z Strowski
- the Department of Hepatology and Gastroenterology and Interdisciplinary Centre of Metabolism: Endocrinology, Diabetes and Metabolism, Charité-Universitätsmedizin Berlin, Augustenburger Platz 1, 13353 Berlin, Germany
| | - Sven Klussmann
- From the NOXXON Pharma AG, Max-Dohrn-Strasse 8-10, 10589 Berlin, Germany,.
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209
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Cummings BP. Leptin therapy in type 2 diabetes. Diabetes Obes Metab 2013; 15:607-12. [PMID: 23216672 DOI: 10.1111/dom.12048] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/10/2012] [Revised: 12/03/2012] [Accepted: 12/03/2012] [Indexed: 02/06/2023]
Abstract
There is a pressing need for new effective therapeutic strategies for addressing the epidemic of type 2 diabetes. Leptin has been shown to reduce hyperglycaemia in rodent models of type 1 diabetes and has recently been shown to normalize fasting plasma glucose concentrations in a rodent model of polygenic obesity and type 2 diabetes. Overall, these findings suggest that leptin may be an effective therapeutic option for both type 1 and type 2 diabetes. However, short-term human clinical studies in overweight and obese patients with recently diagnosed type 2 diabetes have reported minimal efficacy of leptin administration to lower blood glucose levels. Herein, the role of leptin in the maintenance of glucose homeostasis and the potential use of leptin in the treatment of type 2 diabetes are discussed.
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Affiliation(s)
- B P Cummings
- Department of Molecular Biosciences, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616, USA.
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210
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McCall AL, Farhy LS. Treating type 1 diabetes: from strategies for insulin delivery to dual hormonal control. MINERVA ENDOCRINOL 2013; 38:145-63. [PMID: 23732369 PMCID: PMC4220674] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Type 1 diabetes is a disorder where slow destruction of pancreatic β-cells occurs through autoimmune mechanisms. The result is a progressive and ultimately complete lack of endogenous insulin. Due to β-cell lack, secondary abnormalities in glucagon and likely in incretins occur. These multiple hormonal abnormalities cause metabolic instability and extreme glycemic variability, which is the primary phenotype. As the disease progresses patients often develop hypoglycemia unawareness and defects in their counterregulatory defenses. Intensive insulin therapy may thus lead to 3-fold excess of severe hypoglycemia and severely hinder the effective and safe control of hyperglycemia. The main goal of the therapy for type 1 diabetes has long been physiological mimicry of normal insulin secretion based on monitoring which requires considerable effort and understanding of the underlying physiology. Attainment of this goal is challenged by the nature of the disease and our current lack of means to fully repair the abnormal endocrine pancreas interactive functions. As a result, various insulin preparations have been developed to partially compensate for the inability to deliver timely exogenous insulin directly to the portal/intrapancreatic circulation. It remains an ongoing task to identify the ideal routes and regimens of their delivery and potentially that of other hormones to restore the deficient and disordered hormonal environment of the pancreas to achieve a near normal metabolic state. Several recent technological advances help addressing these goals, including the rapid progress in insulin pumps, continuous glucose sensors, and ultimately the artificial pancreas closed-loop technology and the recent start of dual-hormone therapies.
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Affiliation(s)
- A L McCall
- Department of Medicine and Center for Diabetes Technology, University of Virginia, Charlottesville, VA 22908, USA.
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211
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Structural meta-analysis of regular human insulin in pharmaceutical formulations. Eur J Pharm Biopharm 2013; 85:1112-21. [PMID: 23692694 DOI: 10.1016/j.ejpb.2013.05.005] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2012] [Revised: 04/11/2013] [Accepted: 05/06/2013] [Indexed: 01/11/2023]
Abstract
We have studied regular acting, wild-type human insulin at potency of 100 U/mL from four different pharmaceutical products directly from their final finished formulation by the combined use of mass spectrometry (MS), dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), nuclear magnetic resonance (NMR), and single-crystal protein crystallography (PX). All products showed similar oligomeric assembly in solution as judged by DLS and SAXS measurements. The NMR spectra were compatible with well folded proteins, showing close conformational identity for the human insulin in the four products. Crystallographic assays conducted with the final formulated products resulted in all insulin crystals belonging to the R3 space group with two a dimer in the asymmetric unit, both with the B-chain in the T configuration. Meta-analysis of the 24 crystal structures solved from the four distinct insulin products revealed close similarity between them regardless of variables such as biological origin, product batch, country origin of the product, and analytical approach, revealing a low conformational variability for the converging insulin structural ensemble. We propose the use of MS, SAXS, NMR fingerprint, and PX as a precise chemical and structural proof of folding identity of regular insulin in the final, formulated product.
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212
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Harris RBS. Direct and indirect effects of leptin on adipocyte metabolism. Biochim Biophys Acta Mol Basis Dis 2013; 1842:414-23. [PMID: 23685313 DOI: 10.1016/j.bbadis.2013.05.009] [Citation(s) in RCA: 177] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2013] [Revised: 04/18/2013] [Accepted: 05/06/2013] [Indexed: 12/22/2022]
Abstract
Leptin is hypothesized to function as a negative feedback signal in the regulation of energy balance. It is produced primarily by adipose tissue and circulating concentrations correlate with the size of body fat stores. Administration of exogenous leptin to normal weight, leptin responsive animals inhibits food intake and reduces the size of body fat stores whereas mice that are deficient in either leptin or functional leptin receptors are hyperphagic and obese, consistent with a role for leptin in the control of body weight. This review discusses the effect of leptin on adipocyte metabolism. Because adipocytes express leptin receptors there is the potential for leptin to influence adipocyte metabolism directly. Adipocytes also are insulin responsive and receive sympathetic innervation, therefore leptin can also modify adipocyte metabolism indirectly. Studies published to date suggest that direct activation of adipocyte leptin receptors has little effect on cell metabolism in vivo, but that leptin modifies adipocyte sensitivity to insulin to inhibit lipid accumulation. In vivo administration of leptin leads to a suppression of lipogenesis, an increase in triglyceride hydrolysis and an increase in fatty acid and glucose oxidation. Activation of central leptin receptors also contributes to the development of a catabolic state in adipocytes, but this may vary between different fat depots. Leptin reduces the size of white fat depots by inhibiting cell proliferation both through induction of inhibitory circulating factors and by contributing to sympathetic tone which suppresses adipocyte proliferation. This article is part of a Special Issue entitled: Modulation of Adipose Tissue in Health and Disease.
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Affiliation(s)
- Ruth B S Harris
- Department of Physiology, Medical College of Georgia, Georgia Regents University, USA.
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213
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Affiliation(s)
- Eric D. Berglund
- Division of Hypothalamic Research, Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas
| | - Roger H. Unger
- Touchstone Center for Diabetes Research, University of Texas Southwestern Medical Center, Dallas, Texas
- Department of Medical Service, VA North Texas Health Care System, Dallas, Texas
- Corresponding author: Roger H. Unger,
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214
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Irwin N, Franklin ZJ, O'Harte FPM. desHis¹Glu⁹-glucagon-[mPEG] and desHis¹Glu⁹(Lys³⁰PAL)-glucagon: long-acting peptide-based PEGylated and acylated glucagon receptor antagonists with potential antidiabetic activity. Eur J Pharmacol 2013; 709:43-51. [PMID: 23562625 DOI: 10.1016/j.ejphar.2013.03.041] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2013] [Revised: 03/19/2013] [Accepted: 03/24/2013] [Indexed: 12/13/2022]
Abstract
Glucagon is hormone secreted from the pancreatic alpha-cells that is involved in blood glucose regulation. As such, antagonism of glucagon receptor signalling represents an exciting approach for treating diabetes. To harness these beneficial metabolic effects, two novel glucagon analogues, desHis¹Glu⁹-glucagon-[mPEG] and desHis¹Glu⁹(Lys³⁰PAL)-glucagon, has been evaluated for potential glucagon receptor antagonistic properties. Both novel peptides were completely resistant to enzymatic breakdown and significantly (P<0.05 to P<0.001) inhibited glucagon-mediated elevations of cAMP production in glucagon receptor transfected cells. Similarly, desHis¹Glu⁹-glucagon-[mPEG] and desHis¹Glu⁹(Lys³⁰PAL)-glucagon effectively antagonised glucagon-induced increases of insulin secretion from BRIN BD11 cells. When administered acutely to normal, high fat fed or ob/ob mice, both analogues had no significant effects on overall blood glucose or plasma insulin levels when compared to saline treated controls. However, desHis¹Glu⁹-glucagon-[mPEG] significantly (P<0.05) annulled glucagon-induced increases in blood glucose and plasma insulin levels in normal mice and had similar non-significant tendencies in high fat and ob/ob mice. In addition, desHis¹Glu⁹(Lys³⁰PAL)-glucagon effectively (P<0.05 to P<0.001) antagonised glucagon-mediated elevations of blood glucose levels in high fat fed and ob/ob mice, but was less efficacious in normal mice. Further studies confirmed the significant persistent glucagon receptor antagonistic properties of both novel enzyme-resistant analogues 4h post administration in normal mice. These studies emphasise the potential of longer-acting peptide-based glucagon receptor antagonists, and particularly acylated versions, for the treatment of diabetes.
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Affiliation(s)
- Nigel Irwin
- SAAD Centre for Pharmacy and Diabetes, School of Biomedical Sciences, University of Ulster, Coleraine, Northern Ireland BT52 1SA, UK.
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215
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He S, Wang D, Lu Y, Chen Y, Jin X, Wang C, Zhao J, Ren Y, Wang L, Li H, Cheng J. Increasing glucagon secretion could antagonize the action of exogenous insulin for glycemic control in streptozocin-induced diabetic rhesus monkeys. Exp Biol Med (Maywood) 2013; 238:385-91. [PMID: 23760004 DOI: 10.1177/1535370213477974] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Although intraislet insulin signaling is known to play a critical role in regulating glucagon secretion, it is unknown whether abnormal glucagon secretion influences the hypoglycemic effect of exogenous insulin with intraislet insulin deletion. We performed a longitudinal study using 16 streptozocin (STZ)-induced diabetic rhesus monkeys to explore α-cell function under the absence β-cells and to assess whether increasing glucagon secretion antagonizes the action of exogenous insulin for glycemic control. We found that although the α-cells were impaired and the basal secretion levels of glucagon decreased rapidly after STZ (80–90 mg/kg) administration, as based on long-term observation post-STZ injection, glucagon secretion and the number of α-cells were increased. Glycemic control was increasingly difficult, the insulin resistance (HOMA-IR) index was significantly higher, and the triglycerides (TG) levels were gradually decreased. Moreover, a significant correlation between the levels of glucagon and HOMA-IR was found. Under the long-term absence of β-cells, the inhibitory effect on α-cell activity is profoundly attenuated, leading to an increase in glucagon secretion and the amount of α-cells and even α-cell dysfunction. Increased glucagon levels have a serious impact on the insulin sensitivity in vivo and result in an antagonization of the hypoglycemic effect of exogenous insulin.
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Affiliation(s)
- Sirong He
- Laboratory of Transplant Engineering and Immunology, Regenerative Medicine Research Center, West China Hospital, Sichuan University
| | - Dan Wang
- Laboratory of Transplant Engineering and Immunology, Regenerative Medicine Research Center, West China Hospital, Sichuan University
| | - Yanrong Lu
- Laboratory of Transplant Engineering and Immunology, Regenerative Medicine Research Center, West China Hospital, Sichuan University
| | - Younan Chen
- Laboratory of Transplant Engineering and Immunology, Regenerative Medicine Research Center, West China Hospital, Sichuan University
| | - Xi Jin
- Laboratory of Transplant Engineering and Immunology, Regenerative Medicine Research Center, West China Hospital, Sichuan University
| | - Chengsi Wang
- Laboratory of Transplant Engineering and Immunology, Regenerative Medicine Research Center, West China Hospital, Sichuan University
| | - Jingming Zhao
- Laboratory of Transplant Engineering and Immunology, Regenerative Medicine Research Center, West China Hospital, Sichuan University
| | - Yan Ren
- Department of Endocrine, West China Hospital, Sichuan University, No.1 Keyuan 4th Road, Gao Peng Avenue
| | - Li Wang
- National Center for Safety Evaluation of Traditional Chinese Medicine,Chengdu, Sichuan 610041, PR China
| | - Hongxia Li
- National Center for Safety Evaluation of Traditional Chinese Medicine,Chengdu, Sichuan 610041, PR China
| | - Jingqiu Cheng
- Laboratory of Transplant Engineering and Immunology, Regenerative Medicine Research Center, West China Hospital, Sichuan University
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216
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Abstract
Islet hormones, especially insulin and glucagon, are important for glucose homeostasis. Insulin is a necessity for life, and disturbed insulin release results in disordered blood glucose regulation. Although isolated islets are fully capable of detecting changes in their local environment (particularly glucose fluctuations) and altering hormone release appropriately, experimentally manipulating pancreatic innervation alters islet hormone release in the whole animal. This article describes how brain may play a role in influencing and directing secretion of insulin and glucagon as a key part of the integrated physiology of blood glucose homeostasis.
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Affiliation(s)
- Mayowa A Osundiji
- Department of Medicine, Institute of Metabolic Science, University of Cambridge, Addenbrooke's Hospital, Cambridge, UK
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217
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Habener JF, Stanojevic V. Alpha cells come of age. Trends Endocrinol Metab 2013; 24:153-63. [PMID: 23260869 DOI: 10.1016/j.tem.2012.10.009] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/21/2012] [Revised: 10/27/2012] [Accepted: 10/30/2012] [Indexed: 02/07/2023]
Abstract
The alpha cells that coinhabit the islets with the insulin-producing beta cells have recently captured the attention of diabetes researchers because of new breakthrough findings highlighting the importance of these cells in the maintenance of beta cell health and functions. In normal physiological conditions alpha cells produce glucagon but in conditions of beta cell injury they also produce glucagon-like peptide-1 (GLP-1), a growth and survival factor for beta cells. In this review we consider these new findings on the functions of alpha cells. Alpha cells remain somewhat enigmatic inasmuch as they now appear to be important in the maintenance of the health of beta cells, but their production of glucagon promotes diabetes. This circumstance prompts an examination of approaches to coax alpha cells to produce GLP-1 instead of glucagon.
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Affiliation(s)
- Joel F Habener
- Laboratory of Molecular Endocrinology, Massachusetts General Hospital, Boston, MA 02114, USA.
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218
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Abstract
Despite improvements in the pharmacodynamics of injectable insulin and better insulin delivery systems, glucose control remains suboptimal in the majority of individuals with Type 1 diabetes. Profound defects in the physiological processes that normally maintain glucose homeostasis contribute to the difficulty in achieving glycaemic targets. Non-insulin-based adjunct treatments offer a potential means of complementing intensive insulin therapy in Type 1 diabetes through addressing some of the physiological disturbances that result from endogenous β-cell destruction, particularly through preservation of β-cell mass and prevention of apoptosis, and suppression of α-cell glucagon release in the postprandial state. The former approach applies most readily to newly diagnosed C-peptide-positive Type 1 diabetes, while the latter to established C-peptide-negative Type 1 diabetes. This review focuses primarily on the clinical trial data available on the use of non-insulin-based therapies in longer-duration Type 1 diabetes. We conclude that metformin may prove useful in macrovascular disease reduction, while pramlintide, glucagon-like peptide-1 agonists, dipeptidyl peptidase-4 inhibitors and leptin co-therapies may reduce HbA(1c) , glucose variability, postprandial glucose excursions and body weight. These early studies are encouraging and offer novel and potentially very effective approaches to the treatment of Type 1 diabetes, but the evidence is largely restricted to small, often uncontrolled trials. As such, these therapies cannot be currently recommended for routine clinical practice. There is a clear need to support large, multi-centre randomized controlled trials designed to establish whether adjunct insulin therapy has a place in the modern management of Type 1 diabetes.
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Affiliation(s)
- P George
- Medical Research Institute, University of Dundee, Ninewells Hospital and Medical School
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219
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Liu S, Kilic G, Meyers MS, Navarro G, Wang Y, Oberholzer J, Mauvais-Jarvis F. Oestrogens improve human pancreatic islet transplantation in a mouse model of insulin deficient diabetes. Diabetologia 2013; 56:370-81. [PMID: 23132340 PMCID: PMC3536964 DOI: 10.1007/s00125-012-2764-1] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/21/2012] [Accepted: 10/12/2012] [Indexed: 01/01/2023]
Abstract
AIMS/HYPOTHESIS Pancreatic islet transplantation (PIT) offers a physiological treatment for type 1 diabetes, but the failure of islet engraftment hinders its application. The female hormone 17β-oestradiol (E2) favours islet survival and stimulates angiogenesis, raising the possibility that E2 may enhance islet engraftment following PIT. METHODS To explore this hypothesis, we used an insulin-deficient model with xenotransplantation of a marginal dose of human islets in nude mice rendered diabetic with streptozotocin. This was followed by 4 weeks of treatment with vehicle, E2, the non-feminising oestrogen 17α-oestradiol (17α-E2), the oestrogen receptor (ER) α agonist propyl-pyrazole-triol (PPT), the ERβ agonist diarylpropionitrile (DPN) or the G protein-coupled oestrogen receptor (GPER) agonist G1. RESULTS Treatment with E2, 17α-E2, PPT, DPN or G1 acutely improved blood glucose and eventually promoted islet engraftment, thus reversing diabetes. The effects of E2 were retained in the presence of immunosuppression and persisted after discontinuation of E2 treatment. E2 produced an acute decrease in graft hypoxic damage and suppressed beta cell apoptosis. E2 also acutely suppressed hyperglucagonaemia without altering insulin secretion, leading to normalisation of blood glucose. CONCLUSIONS/INTERPRETATION During PIT, E2 synergistic actions contribute to enhancing human islet-graft survival, revascularisation and functional mass. This study identifies E2 as a short-term treatment to improve PIT.
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Affiliation(s)
- S. Liu
- Department of Medicine, Division of Endocrinology, Metabolism and Molecular Medicine, Northwestern University Feinberg School of Medicine, 303 East Chicago Avenue, Tarry 15-761, Chicago, IL 60611 USA
- Present Address: Diabetes Institute, the First Affiliated Hospital of Xiamen University, Xiamen, China
| | - G. Kilic
- Department of Medicine, Division of Endocrinology, Metabolism and Molecular Medicine, Northwestern University Feinberg School of Medicine, 303 East Chicago Avenue, Tarry 15-761, Chicago, IL 60611 USA
| | - M. S. Meyers
- Department of Medicine, Division of Endocrinology, Metabolism and Molecular Medicine, Northwestern University Feinberg School of Medicine, 303 East Chicago Avenue, Tarry 15-761, Chicago, IL 60611 USA
| | - G. Navarro
- Department of Medicine, Division of Endocrinology, Metabolism and Molecular Medicine, Northwestern University Feinberg School of Medicine, 303 East Chicago Avenue, Tarry 15-761, Chicago, IL 60611 USA
| | - Y. Wang
- Department of Surgery, Division of Transplant Surgery, University of Illinois at Chicago, Chicago, IL USA
| | - J. Oberholzer
- Department of Surgery, Division of Transplant Surgery, University of Illinois at Chicago, Chicago, IL USA
| | - F. Mauvais-Jarvis
- Department of Medicine, Division of Endocrinology, Metabolism and Molecular Medicine, Northwestern University Feinberg School of Medicine, 303 East Chicago Avenue, Tarry 15-761, Chicago, IL 60611 USA
- Northwestern Comprehensive Center on Obesity, Northwestern University Feinberg School of Medicine, Chicago, IL USA
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220
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Abstract
Long in the shade, glucagon is now back on the front scene. We review here our 50 year personal journey in the glucagon field. Glucagon is not the miracle anti-inflammatory agent it had been suggested. Glucagon does not act in concert with insulin in promoting peripheral tissue glucose uptake. Glucagon was the first polypeptidic hormone to be determined in the plasma by radio-immunoassay. Some glucagon is produced outside the pancreas. The secretion of glucagon is pulsatile and this optimizes the effect of glucagon on the liver. Hyperglucagonaemia is present in all forms of diabetes. As proposed by Unger and Orci, diabetes should be seen as a paracrinopathy of the islets of Langerhans in which intra-islet insulin deficiency results in increased glucagon release from the islet α-cells. Being involved in glucagon research for over half-a-century has been a joy and a privilege.
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Affiliation(s)
- Pierre J. Lefèbvre
- Division of Diabetes, Nutrition and Metabolic Disorders, Department of Medicine, University of Liège, Belgium
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221
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Wang Q, Liang X, Wang S. Intra-islet glucagon secretion and action in the regulation of glucose homeostasis. Front Physiol 2013; 3:485. [PMID: 23316165 PMCID: PMC3539678 DOI: 10.3389/fphys.2012.00485] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2012] [Accepted: 12/12/2012] [Indexed: 11/13/2022] Open
Abstract
Glucagon, a key hormone in the regulation of glucose homeostasis, acts as a counter-regulatory hormone to insulin by promoting hepatic glucose output. Under normal conditions, insulin and glucagon operate in concert to maintain the glucose level within a narrow physiological range. In diabetes, however, while insulin secretion or action is insufficient, the production and secretion of glucagon are excessive, contributing to the development of diabetic hyperglycemia. Within an islet, intra-islet insulin, in cooperation with intra-islet GABA, suppresses glucagon secretion via direct modulation of α-cell intracellular signaling pathways involving Akt activation, GABA receptor phosphorylation and the receptor plasma membrane translocation, while intra-islet glucagon plays an important role in modulating β-cell function and insulin secretion. Defects in the insulin-glucagon fine-tuning machinery may result in β-cell glucose incompetence, leading to unsuppressed glucagon secretion and subsequent hyperglycemia, which often occur under extreme conditions of glucose influx or efflux. Therefore, deciphering the precise molecular mechanisms underlying glucagon secretion and action will facilitate our understanding of glucagon physiology, in particular, its role in regulating islet β-cell function, and hence the mechanisms behind glucose homeostasis.
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Affiliation(s)
- Qinghua Wang
- Division of Endocrinology and Metabolism, The Keenan Research Centre in the Li Ka Shing Knowledge Institute, St. Michael's Hospital Toronto, ON, Canada ; Department of Physiology, University of Toronto Toronto, ON, Canada ; Department of Medicine, University of Toronto Toronto, ON, Canada
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222
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Mu J, Qureshi SA, Brady EJ, Muise ES, Candelore MR, Jiang G, Li Z, Wu MS, Yang X, Dallas-Yang Q, Miller C, Xiong Y, Langdon RB, Parmee ER, Zhang BB. Anti-diabetic efficacy and impact on amino acid metabolism of GRA1, a novel small-molecule glucagon receptor antagonist. PLoS One 2012. [PMID: 23185367 PMCID: PMC3501516 DOI: 10.1371/journal.pone.0049572] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Hyperglucagonemia is implicated in the pathophysiology of hyperglycemia. Antagonism of the glucagon receptor (GCGR) thus represents a potential approach to diabetes treatment. Herein we report the characterization of GRA1, a novel small-molecule GCGR antagonist that blocks glucagon binding to the human GCGR (hGCGR) and antagonizes glucagon-induced intracellular accumulation of cAMP with nanomolar potency. GRA1 inhibited glycogenolysis dose-dependently in primary human hepatocytes and in perfused liver from hGCGR mice, a transgenic line of mouse that expresses the hGCGR instead of the murine GCGR. When administered orally to hGCGR mice and rhesus monkeys, GRA1 blocked hyperglycemic responses to exogenous glucagon. In several murine models of diabetes, acute and chronic dosing with GRA1 significantly reduced blood glucose concentrations and moderately increased plasma glucagon and glucagon-like peptide-1. Combination of GRA1 with a dipeptidyl peptidase-4 inhibitor had an additive antihyperglycemic effect in diabetic mice. Hepatic gene-expression profiling in monkeys treated with GRA1 revealed down-regulation of numerous genes involved in amino acid catabolism, an effect that was paralleled by increased amino acid levels in the circulation. In summary, GRA1 is a potent glucagon receptor antagonist with strong antihyperglycemic efficacy in preclinical models and prominent effects on hepatic gene-expression related to amino acid metabolism.
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Affiliation(s)
- James Mu
- Discovery and Preclinical Sciences, Merck Research Laboratories, Merck Sharp & Dohme Corp., Whitehouse Station, New Jersey, United States of America.
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223
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Cuny T, Guerci B, Cariou B. New avenues for the pharmacological management of type 2 diabetes: An update. ANNALES D'ENDOCRINOLOGIE 2012; 73:459-68. [DOI: 10.1016/j.ando.2012.09.002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
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224
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Zaman A. Docking studies and network analyses reveal capacity of compounds from Kandelia rheedii to strengthen cellular immunity by interacting with host proteins during tuberculosis infection. Bioinformation 2012; 8:1012-20. [PMID: 23275699 PMCID: PMC3524883 DOI: 10.6026/97320630081012] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2012] [Accepted: 10/15/2012] [Indexed: 01/09/2023] Open
Abstract
Kandelia rheedii (locally known as Guria or Rasunia), widely found and used in Indian subcontinent, is a well-known herbal cure to tuberculosis. However, neither the mechanism nor the active components of the plant extract responsible for mediating this action has yet been confirmed. Here in this study, molecular interactions of three compounds (emodin, fusaric acid and skyrin) from the plant extract with the host protein targets (casein kinase (CSNK), estrogen receptor (ERBB), dopamine β-hydroxylase (DBH) and glucagon receptor (Gcgr)) has been found. These protein targets are known to be responsible for strengthening cellular immunity against Mycobacteria tuberculosis. The specific interactions of these three compounds with the respective protein targets have been discussed here. The insights from study should further help us designing molecular medicines against tuberculosis.
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Affiliation(s)
- Aubhishek Zaman
- Molecular Biology Laboratory, Department of Biochemistry and Molecular Biology and Department of Genetic Engineering and Biotechnology, University of Dhaka, Dhaka-1000, Bangladesh
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225
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Soares AF, Carvalho RA, Veiga FJ, Alves MG, Martins FO, Viegas I, González JD, Metón I, Baanante IV, Jones JG. Restoration of direct pathway glycogen synthesis flux in the STZ-diabetes rat model by insulin administration. Am J Physiol Endocrinol Metab 2012; 303:E875-85. [PMID: 22850684 DOI: 10.1152/ajpendo.00161.2012] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Type 1 diabetes subjects are characterized by impaired direct pathway synthesis of hepatic glycogen that is unresponsive to insulin therapy. Since it is not known whether this is an irreversible defect of insulin-dependent diabetes, direct and indirect pathway glycogen fluxes were quantified in streptozotocin (STZ)-induced diabetic rats and compared with STZ rats that received subcutaneous or intraperitoneal insulin (I-SC or I-IP). Three groups of STZ rats were studied at 18 days post-STZ treatment. One group was administered I-SC and another I-IP as two daily injections of short-acting insulin at the start of each light and dark period for days 9-18. A third group did not receive any insulin, and a fourth group of nondiabetic rats was used as control. Glycogen synthesis via direct and indirect pathways, de novo lipogenesis, and gluconeogenesis were determined over the nocturnal feeding period using deuterated water. Direct pathway was residual in STZ rats, and glucokinase activity was also reduced significantly from control levels. Insulin administration restored both net glycogen synthesis via the direct pathway and glucokinase activity to nondiabetic control levels and improved the lipogenic pathway despite an inefficient normalization of the gluconeogenic pathway. We conclude that the reduced direct pathway flux is not an irreversible defect of insulin-dependent diabetes.
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Affiliation(s)
- Ana F Soares
- Center for Neuroscience and Cell Biology, Dept. of Life Sciences, Univ. of Coimbra, Largo Marquês de Pombal, 3004 - 517, Coimbra, Portugal
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226
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Abstract
Pancreatic β cells secrete insulin, the body's only hormone capable of lowering plasma glucose levels. Impaired or insufficient insulin secretion results in diabetes mellitus. The β cell is electrically excitable; in response to an elevation of glucose, it depolarizes and starts generating action potentials. The electrophysiology of mouse β cells and the cell's role in insulin secretion have been extensively investigated. More recently, similar studies have been performed on human β cells. These studies have revealed numerous and important differences between human and rodent β cells. Here we discuss the properties of human pancreatic β cells: their glucose sensing, the ion channel complement underlying glucose-induced electrical activity that culminates in exocytotic release of insulin, the cellular control of exocytosis, and the modulation of insulin secretion by circulating hormones and locally released neurotransmitters. Finally, we consider the pathophysiology of insulin secretion and the interactions between genetics and environmental factors that may explain the current diabetes epidemic.
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Affiliation(s)
- Patrik Rorsman
- Oxford Center for Diabetes, Endocrinology and Metabolism, University of Oxford, Oxford OX3 7LJ, United Kingdom.
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227
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Gaisano HY, Macdonald PE, Vranic M. Glucagon secretion and signaling in the development of diabetes. Front Physiol 2012; 3:349. [PMID: 22969729 PMCID: PMC3432929 DOI: 10.3389/fphys.2012.00349] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2012] [Accepted: 08/10/2012] [Indexed: 12/19/2022] Open
Abstract
Normal release of glucagon from pancreatic islet α-cells promotes glucose mobilization, which counteracts the hypoglycemic actions of insulin, thereby ensuring glucose homeostasis. In treatment of diabetes aimed at rigorously reducing hyperglycemia to avoid chronic complications, the resulting hypoglycemia triggering glucagon release from α-cells is frequently impaired, with ensuing hypoglycemic complications. This review integrates the physiology of glucagon secretion regulating glucose homeostasis in vivo to single α-cell signaling, and how both become perturbed in diabetes. α-cells within the social milieu of the islet micro-organ are regulated not only by intrinsic signaling events but also by paracrine regulation, particularly by adjacent insulin-secreting β-cells and somatostatin-secreting δ-cells. We discuss the intrinsic α-cell signaling events, including glucose sensing and ion channel regulation leading to glucagon secretion. We then discuss the complex crosstalk between the islet cells and the breakdown of this crosstalk in diabetes contributing to the dysregulated glucagon secretion. Whereas, there are many secretory products released by β- and δ-cells that become deficient or excess in diabetes, we discuss the major ones, including the better known insulin and lesser known somatostatin, which act as putative paracrine on/off switches that very finely regulate α-cell secretory responses in health and diabetes. Of note in several type 1 diabetes (T1D) rodent models, blockade of excess somatostatin actions on α-cell could normalize glucagon secretion sufficient to attain normoglycemia in response to hypoglycemic assaults. There has been slow progress in fully elucidating the pathophysiology of the α-cell in diabetes because of the small number of α-cells within an islet and the islet mass becomes severely reduced and inflamed in diabetes. These limitations are just now being surmounted by new approaches.
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Affiliation(s)
- Herbert Y Gaisano
- Departments of Medicine and Physiology, University of Toronto Toronto, ON, Canada
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228
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Coppari R, Bjørbæk C. Leptin revisited: its mechanism of action and potential for treating diabetes. Nat Rev Drug Discov 2012; 11:692-708. [PMID: 22935803 PMCID: PMC4019022 DOI: 10.1038/nrd3757] [Citation(s) in RCA: 204] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Since the discovery of leptin in 1994, we now have a better understanding of the cellular and molecular mechanisms underlying its biological effects. In addition to its established anti-obesity effects, leptin exerts antidiabetic actions that are independent of its regulation of body weight and food intake. In particular, leptin can correct diabetes in animal models of type 1 and type 2 diabetes. In addition, long-term leptin replacement therapy improves glycaemic control, insulin sensitivity and plasma triglycerides in patients with severe insulin resistance due to lipodystrophy. These results have spurred enthusiasm for the use of leptin therapy to treat diabetes. Here, we review the current understanding of the glucoregulatory functions of leptin, emphasizing its central mechanisms of action and lessons learned from clinical studies, and discuss possible therapeutic applications of leptin in the treatment of type 1 and type 2 diabetes.
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Affiliation(s)
- Roberto Coppari
- Department of Internal Medicine, Division of Hypothalamic Research, The University of Texas Southwestern Medical Center, Dallas TX, 75390, USA
- Department of Cellular Physiology and Metabolism, Faculty of Medicine, University of Geneva, 1211 Geneva, Switzerland
- The Center for Epigenetics and Metabolism, University of California Irvine, Irvine, CA, 92697, USA
| | - Christian Bjørbæk
- Department of Medicine, Division of Endocrinology and Metabolism, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston MA, 02215, USA
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229
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Cho YM, Merchant CE, Kieffer TJ. Targeting the glucagon receptor family for diabetes and obesity therapy. Pharmacol Ther 2012; 135:247-78. [DOI: 10.1016/j.pharmthera.2012.05.009] [Citation(s) in RCA: 93] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2012] [Accepted: 05/15/2012] [Indexed: 12/11/2022]
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230
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Sugiyama C, Yamamoto M, Kotani T, Kikkawa F, Murata Y, Hayashi Y. Fertility and pregnancy-associated ß-cell proliferation in mice deficient in proglucagon-derived peptides. PLoS One 2012; 7:e43745. [PMID: 22928026 PMCID: PMC3426535 DOI: 10.1371/journal.pone.0043745] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2012] [Accepted: 07/23/2012] [Indexed: 12/15/2022] Open
Abstract
Proglucagon, which is encoded by the glucagon gene (Gcg), is the precursor of several peptide hormones, including glucagon and glucagon-like peptide 1 (GLP-1). Whereas glucagon stimulates hepatic glycogenolysis and gluconeogenesis, GLP-1 stimulates insulin secretion to lower blood glucose and also supports ß-cell proliferation and protection from apoptotic stimuli. Pregnancy is a strong inducer of change in islet function, however the roles of proglucagon-derived peptides in pregnancy are only partially understood. In the present study, we analyzed fertility and pregnancy-associated changes in homozygous glucagon-green fluorescent protein (gfp) knock-in mice (Gcggfp/gfp), which lack all the peptides derived from proglucagon. Female Gcggfp/gfp mice could deliver and raise Gcggfp/gfp pups to weaning and Gcggfp/gfp pups from Gcggfp/gfp dams were viable and fertile. Pregnancy induced ß-cell proliferation in Gcggfp/gfp mice as well as in control mice. However, serum insulin levels in pregnant Gcggfp/gfp females were lower than those in control pregnant females under ad libitum feeding, and blood glucose levels in pregnant Gcggfp/gfp females were higher after gestational day 12. Gcggfp/gfp females showed a decreased pregnancy rate and smaller litter size. The rate of successful breeding was significantly lower in Gcggfp/gfp females and was not improved by experience of breeding. Taken together, proglucagon-derived peptides are not required for pregnancy-associated ß-cell proliferation, however, are required for regulation of blood glucose levels and normal reproductive capacity. Gcggfp/gfp mice may serve as a novel model to analyze the effect of mild hyperglycemia during late gestational periods.
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Affiliation(s)
- Chisato Sugiyama
- Department of Genetics, Research Institute of Environmental Medicine, Nagoya University, Nagoya, Japan
- Department of Obstetrics and Gynecology, Nagoya University Graduate School of Medicine, Nagoya, Japan
| | - Michiyo Yamamoto
- Department of Genetics, Research Institute of Environmental Medicine, Nagoya University, Nagoya, Japan
| | - Tomomi Kotani
- Department of Obstetrics and Gynecology, Nagoya University Graduate School of Medicine, Nagoya, Japan
| | - Fumitaka Kikkawa
- Department of Obstetrics and Gynecology, Nagoya University Graduate School of Medicine, Nagoya, Japan
| | - Yoshiharu Murata
- Department of Genetics, Research Institute of Environmental Medicine, Nagoya University, Nagoya, Japan
| | - Yoshitaka Hayashi
- Department of Genetics, Research Institute of Environmental Medicine, Nagoya University, Nagoya, Japan
- * E-mail:
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231
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Metabolic manifestations of insulin deficiency do not occur without glucagon action. Proc Natl Acad Sci U S A 2012; 109:14972-6. [PMID: 22891336 DOI: 10.1073/pnas.1205983109] [Citation(s) in RCA: 118] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
To determine unambiguously if suppression of glucagon action will eliminate manifestations of diabetes, we expressed glucagon receptors in livers of glucagon receptor-null (GcgR(-/-)) mice before and after β-cell destruction by high-dose streptozotocin. Wild type (WT) mice developed fatal diabetic ketoacidosis after streptozotocin, whereas GcgR(-/-) mice with similar β-cell destruction remained clinically normal without hyperglycemia, impaired glucose tolerance, or hepatic glycogen depletion. Restoration of receptor expression using adenovirus containing the GcgR cDNA restored hepatic GcgR, phospho-cAMP response element binding protein (P-CREB), and phosphoenol pyruvate carboxykinase, markers of glucagon action, rose dramatically and severe hyperglycemia appeared. When GcgR mRNA spontaneously disappeared 7 d later, P-CREB declined and hyperglycemia disappeared. In conclusion, the metabolic manifestations of diabetes cannot occur without glucagon action and, once present, disappear promptly when glucagon action is abolished. Glucagon suppression should be a major therapeutic goal in diabetes.
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232
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Sloan JH, Siegel RW, Ivanova-Cox YT, Watson DE, Deeg MA, Konrad RJ. A novel high-sensitivity electrochemiluminescence (ECL) sandwich immunoassay for the specific quantitative measurement of plasma glucagon. Clin Biochem 2012; 45:1640-4. [PMID: 22890005 DOI: 10.1016/j.clinbiochem.2012.07.111] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2012] [Revised: 07/24/2012] [Accepted: 07/27/2012] [Indexed: 12/01/2022]
Abstract
OBJECTIVES To develop a novel, dual-monoclonal sandwich immunoassay with superior sensitivity that provides a rapid and convenient method for measuring glucagon. Glucagon is a 29-amino acid polypeptide hormone produced in the pancreas by the α-cells of the islets of Langerhans. Working in concert with insulin, glucagon is involved in regulating circulating glucose concentrations. DESIGN AND METHODS The immunoassay utilizes Meso Scale Discovery (MSD) electrochemiluminescence (ECL) technology and two affinity-optimized monoclonal antibodies. A series of experiments was performed to determine the linear range of the assay and to evaluate sensitivity, accuracy, recovery, precision, and linearity. RESULTS The sandwich assay was specific for glucagon and did not recognize the closely related peptide oxyntomodulin or other incretin peptides. The assay demonstrated excellent recovery, precision, and linearity, and a broad dynamic range of 0.14 pmol/L to 1950 pmol/L. In addition, assay results were highly correlated with those obtained using a previously described competitive RIA employing polyclonal antiserum. CONCLUSION The use of affinity-optimized monoclonal antibodies in a sandwich immunoassay format provides a robust, sensitive, and convenient method for measuring concentrations of glucagon that is highly sensitive and specific. This immunoassay should help to improve our understanding of the role of glucagon in the regulation of glucose metabolism.
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Affiliation(s)
- John H Sloan
- Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, IN 46285, USA.
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233
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Sheng L, Zhou Y, Chen Z, Ren D, Cho KW, Jiang L, Shen H, Sasaki Y, Rui L. NF-κB–inducing kinase (NIK) promotes hyperglycemia and glucose intolerance in obesity by augmenting glucagon action. Nat Med 2012; 18:943-9. [PMID: 22581287 PMCID: PMC3766969 DOI: 10.1038/nm.2756] [Citation(s) in RCA: 77] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2012] [Accepted: 03/29/2011] [Indexed: 02/06/2023]
Abstract
The canonical inhibitor of nuclear factor κB kinase subunit β (IKK-β)–nuclear factor of κ light polypeptide gene enhancer in B cells 1 (NF-κB1) pathway has been well documented to promote insulin resistance; however, the noncanonical NF-κB–inducing kinase (NIK)–NF-κB2 pathway is not well understood in obesity. Additionally, the contribution of counter-regulatory hormones, particularly glucagon, to hyperglycemia in obesity is unclear. Here we show that NIK promotes glucagon responses in obesity. Hepatic NIK was abnormally activated in mice with dietary or genetic obesity. Systemic deletion of Map3k14, encoding NIK, resulted in reduced glucagon responses and hepatic glucose production (HGP). Obesity is associated with high glucagon responses, and liver-specific inhibition of NIK led to lower glucagon responses and HGP and protected against hyperglycemia and glucose intolerance in obese mice. Conversely, hepatocyte-specific overexpression of NIK resulted in higher glucagon responses and HGP. In isolated mouse livers and primary hepatocytes, NIK also promoted glucagon action and glucose production, at least in part by increasing cAMP response element-binding (CREB) stability. Therefore, overactivation of liver NIK in obesity promotes hyperglycemia and glucose intolerance by increasing the hyperglycemic response to glucagon and other factors that activate CREB.
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Affiliation(s)
- Liang Sheng
- Department of Molecular & Integrative Physiology, University of Michigan Medical School, Ann Arbor, MI 48109, USA
| | - Yingjiang Zhou
- Department of Molecular & Integrative Physiology, University of Michigan Medical School, Ann Arbor, MI 48109, USA
| | - Zheng Chen
- Department of Molecular & Integrative Physiology, University of Michigan Medical School, Ann Arbor, MI 48109, USA
| | - Decheng Ren
- Department of Molecular & Integrative Physiology, University of Michigan Medical School, Ann Arbor, MI 48109, USA
| | - Kae Won Cho
- Department of Molecular & Integrative Physiology, University of Michigan Medical School, Ann Arbor, MI 48109, USA
| | - Lin Jiang
- Department of Molecular & Integrative Physiology, University of Michigan Medical School, Ann Arbor, MI 48109, USA
| | - Hong Shen
- Department of Molecular & Integrative Physiology, University of Michigan Medical School, Ann Arbor, MI 48109, USA
| | - Yoshiteru Sasaki
- Laboratory for Stem Cell Biology, Riken Center for Developmental Biology, Kobe 650-0047, Japan
| | - Liangyou Rui
- Department of Molecular & Integrative Physiology, University of Michigan Medical School, Ann Arbor, MI 48109, USA
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234
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Bagyánszki M, Bódi N. Diabetes-related alterations in the enteric nervous system and its microenvironment. World J Diabetes 2012; 3:80-93. [PMID: 22645637 PMCID: PMC3360223 DOI: 10.4239/wjd.v3.i5.80] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/05/2011] [Revised: 04/06/2012] [Accepted: 05/11/2012] [Indexed: 02/05/2023] Open
Abstract
Gastric intestinal symptoms common among diabetic patients are often caused by intestinal motility abnormalities related to enteric neuropathy. It has recently been demonstrated that the nitrergic subpopulation of myenteric neurons are especially susceptible to the development of diabetic neuropathy. Additionally, different susceptibility of nitrergic neurons located in different intestinal segments to diabetic damage and their different levels of responsiveness to insulin treatment have been revealed. These findings indicate the importance of the neuronal microenvironment in the pathogenesis of diabetic nitrergic neuropathy. The main focus of this review therefore was to summarize recent advances related to the diabetes-related selective nitrergic neuropathy and associated motility disturbances. Special attention was given to the findings on capillary endothelium and enteric glial cells. Growing evidence indicates that capillary endothelium adjacent to the myenteric ganglia and enteric glial cells surrounding them are determinative in establishing the ganglionic microenvironment. Additionally, recent advances in the development of new strategies to improve glycemic control in type 1 and type 2 diabetes mellitus are also considered in this review. Finally, looking to the future, the recent and promising results of metagenomics for the characterization of the gut microbiome in health and disease such as diabetes are highlighted.
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Affiliation(s)
- Mária Bagyánszki
- Mária Bagyánszki, Nikolett Bódi, Department of Physiology, Anatomy and Neuroscience, Faculty of Science, University of Szeged, H-6726 Szeged, Hungary
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235
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Chen L, Philippe J, Unger RH. Glucagon responses of isolated α cells to glucose, insulin, somatostatin, and leptin. Endocr Pract 2012; 17:819-25. [PMID: 21940282 DOI: 10.4158/ep11101.or] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
OBJECTIVE To determine whether glucagon suppression by leptin represents a direct effect on α cells rather than an indirect effect mediated via the hypothalamus. METHODS We devised an in vitro α-cell suppression assay in cultured hamster InR1G9 cells. InR1G9 hamster cells were infected with adenovirus containing mouse leptin receptors, and they were then incubated with leptin, insulin, or somatostatin in concentrations known to suppress glucagon in vivo. RESULTS Whereas somatostatin and insulin both suppressed the increase in glucagon secretion stimulated by high levels of glucose, leptin had no such effect. This inability of leptin to suppress glucagon in vitro could signify that it acts indirectly by causing the release of glucagon-suppressing peptides from the hypothalamus or stomach. To search for such a peptide, we studied the effects on glucagon secretion of 6 neuropeptides: orexin, melanocyte-stimulating hormone, neuropeptide Y, cocaine and amphetamine regulated transcript, neurotensin, and Agouti-related peptide that might be involved in the hypothalamic action of leptin. None of these peptides suppressed glucagon at low, normal, or elevated glucose concentrations. CONCLUSIONS If the cultured α cells used faithfully mimic the leptin response of in situ α cells of the diabetic animal, the glucagon-suppressing action of leptin is indirect, but is not mediated by any 1 of the 6 neuropeptides tested.
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Affiliation(s)
- Lijun Chen
- Touchstone Center for Diabetes Research, Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, USA
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236
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Implication of mitochondrial cytoprotection in human islet isolation and transplantation. Biochem Res Int 2012; 2012:395974. [PMID: 22611495 PMCID: PMC3352213 DOI: 10.1155/2012/395974] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2011] [Accepted: 01/30/2012] [Indexed: 12/23/2022] Open
Abstract
Islet transplantation is a promising therapy for type 1 diabetes mellitus; however, success rates in achieving both short- and long-term insulin independence are not consistent, due in part to inconsistent islet quality and quantity caused by the complex nature and multistep process of islet isolation and transplantation. Since the introduction of the Edmonton Protocol in 2000, more attention has been placed on preserving mitochondrial function as increasing evidences suggest that impaired mitochondrial integrity can adversely affect clinical outcomes. Some recent studies have demonstrated that it is possible to achieve islet cytoprotection by maintaining mitochondrial function and subsequently to improve islet transplantation outcomes. However, the benefits of mitoprotection in many cases are controversial and the underlying mechanisms are unclear. This article summarizes the recent progress associated with mitochondrial cytoprotection in each step of the islet isolation and transplantation process, as well as islet potency and viability assays based on the measurement of mitochondrial integrity. In addition, we briefly discuss immunosuppression side effects on islet graft function and how transplant site selection affects islet engraftment and clinical outcomes.
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237
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Abstract
This review considers the role of α-cells in β-cell generation and regeneration. We present recent evidence obtained from lineage-tracing studies showing that α-cells can serve as progenitors of β-cells and present a hypothetical model how injured β-cells might activate α-cells in adult islets to promote β-cell regeneration. β-cells appear to arise by way of their trans-differentiation from undifferentiated α progenitor cells, pro-α-cells, both during embryonic development of the islets and in the adult pancreas in response to β-cell injuries. Plasticity of α-cells is endowed by the expression of the gene encoding proglucagon, a prohormone that can give rise to glucagon and glucagon-like peptides (GLPs). The production of glucagon from proglucagon is characteristic of fully-differentiated α-cells whereas GLP-1 is a product of undifferentiated α-cells. GLP-1, a cell growth and survival factor, is proposed to promote the expansion of neurogenin3-expressing, undifferentiated pro-α-cells during development. β-cells arise from pro-α-cells by a change in the relative amounts of the transcription factors Arx and Pax4, master regulators of the α- and β-cell lineages, respectively. A paracrine/autocrine model is proposed whereby injuries of β-cells in adult islets induce the production and release of factors, such as stromal cell-derived factor-1, that cause the de-differentiation of adjacent α-cells into pro-α-cells. Pro-α-cells produce GLP-1 and its receptor that renders them competent to trans-differentiate into β-cells. The trans-differentiation of pro-α-cells into β-cells provides a potentially exploitable mechanism for the regeneration of β-cells in individuals with type 1 diabetes.
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Affiliation(s)
- Joel F Habener
- Laboratory of Molecular Endocrinology, Massachusetts General Hospital, Boston, MA, USA.
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238
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Xiao C, Lewis GF. Regulation of chylomicron production in humans. Biochim Biophys Acta Mol Cell Biol Lipids 2012; 1821:736-46. [DOI: 10.1016/j.bbalip.2011.09.019] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2011] [Revised: 09/20/2011] [Accepted: 09/21/2011] [Indexed: 12/18/2022]
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239
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Iori E, Vinci B, Murphy E, Marescotti MC, Avogaro A, Ahluwalia A. Glucose and fatty acid metabolism in a 3 tissue in-vitro model challenged with normo- and hyperglycaemia. PLoS One 2012; 7:e34704. [PMID: 22509346 PMCID: PMC3324505 DOI: 10.1371/journal.pone.0034704] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2012] [Accepted: 03/08/2012] [Indexed: 11/18/2022] Open
Abstract
Nutrient balance in the human body is maintained through systemic signaling between different cells and tissues. Breaking down this circuitry to its most basic elements and reconstructing the metabolic network in-vitro provides a systematic method to gain a better understanding of how cross-talk between the organs contributes to the whole body metabolic profile and of the specific role of each different cell type. To this end, a 3-way connected culture of hepatocytes, adipose tissue and endothelial cells representing a simplified model of energetic substrate metabolism in the visceral region was developed. The 3-way culture was shown to maintain glucose and fatty acid homeostasis in-vitro. Subsequently it was challenged with insulin and high glucose concentrations to simulate hyperglycaemia. The aim was to study the capacity of the 3-way culture to maintain or restore normal circulating glucose concentrations in response to insulin and to investigate the effects these conditions on other metabolites involved in glucose and lipid metabolism. The results show that the system’s metabolic profile changes dramatically in the presence of high concentrations of glucose, and that these changes are modulated by the presence of insulin. Furthermore, we observed an increase in E-selectin levels in hyperglycaemic conditions and increased IL-6 concentrations in insulin-free-hyperglycaemic conditions, indicating, respectively, endothelial injury and proinflammatory stress in the challenged 3-way system.
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Affiliation(s)
- Elisabetta Iori
- Division of Metabolic Diseases, Department of Clinical and Experimental Medicine, University of Padua, Padua, Italy
| | - Bruna Vinci
- Centro Interdipartimentale di Ricerca ″E.Piaggio″, University of Pisa, Pisa, Italy
- CNR Institute of Clinical Physiology, Pisa, Italy
| | - Ellen Murphy
- Division of Metabolic Diseases, Department of Clinical and Experimental Medicine, University of Padua, Padua, Italy
| | - Maria Cristina Marescotti
- Division of Metabolic Diseases, Department of Clinical and Experimental Medicine, University of Padua, Padua, Italy
| | - Angelo Avogaro
- Division of Metabolic Diseases, Department of Clinical and Experimental Medicine, University of Padua, Padua, Italy
| | - Arti Ahluwalia
- Centro Interdipartimentale di Ricerca ″E.Piaggio″, University of Pisa, Pisa, Italy
- CNR Institute of Clinical Physiology, Pisa, Italy
- * E-mail:
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240
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Cryer PE. Minireview: Glucagon in the pathogenesis of hypoglycemia and hyperglycemia in diabetes. Endocrinology 2012; 153:1039-48. [PMID: 22166985 PMCID: PMC3281526 DOI: 10.1210/en.2011-1499] [Citation(s) in RCA: 160] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/13/2011] [Accepted: 11/22/2011] [Indexed: 01/22/2023]
Abstract
Pancreatic islet α-cell glucagon secretion is critically dependent on pancreatic islet β-cell insulin secretion. Normally, a decrease in the plasma glucose concentration causes a decrease in β-cell insulin secretion that signals an increase in α-cell glucagon secretion during hypoglycemia. In contrast, an increase in the plasma glucose concentration, among other stimuli, causes an increase in β-cell insulin secretion that signals a decrease, or at least no change, in α-cell glucagon secretion after a meal. In absolute endogenous insulin deficiency (i.e. in type 1 diabetes and in advanced type 2 diabetes), however, β-cell failure results in no decrease in β-cell insulin secretion and thus no increase in α-cell glucagon secretion during hypoglycemia and no increase in β-cell insulin secretion and thus an increase in α-cell glucagon secretion after a meal. In type 1 diabetes and advanced type 2 diabetes, the absence of an increment in glucagon secretion, in the setting of an absent decrement in insulin secretion and an attenuated increment in sympathoadrenal activity, in response to falling plasma glucose concentrations plays a key role in the pathogenesis of iatrogenic hypoglycemia. In addition, there is increasing evidence that, in the aggregate, suggests that relative hyperglucagonemia, in the setting of deficient insulin secretion, plays a role in the pathogenesis of hyperglycemia in diabetes. If so, abnormal glucagon secretion is involved in the pathogenesis of both hypoglycemia and hyperglycemia in diabetes.
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Affiliation(s)
- Philip E Cryer
- Division of Endocrinology, Metabolism, and Lipid Research, Washington University, St. Louis, Missouri 63110, USA.
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241
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Abstract
Current therapies for type 1 diabetes (T1D) involve insulin replacement or transplantation of insulin-secreting tissue, both of which suffer from numerous limitations and complications. Here, we show that subcutaneous transplants of embryonic brown adipose tissue (BAT) can correct T1D in streptozotocin-treated mice (both immune competent and immune deficient) with severely impaired glucose tolerance and significant loss of adipose tissue. BAT transplants result in euglycemia, normalized glucose tolerance, reduced tissue inflammation, and reversal of clinical diabetes markers such as polyuria, polydipsia, and polyphagia. These effects are independent of insulin but correlate with recovery of the animals' white adipose tissue. BAT transplants lead to significant increases in adiponectin and leptin, but with levels that are static and not responsive to glucose. Pharmacological blockade of the insulin receptor in BAT transplant mice leads to impaired glucose tolerance, similar to what is seen in nondiabetic animals, indicating that insulin receptor activity plays a role in the reversal of diabetes. One possible candidate for activating the insulin receptor is IGF-1, whose levels are also significantly elevated in BAT transplant mice. Thus, we propose that the combined action of multiple adipokines establishes a new equilibrium in the animal that allows for chronic glycemic control without insulin.
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Affiliation(s)
- Subhadra C Gunawardana
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee, USA.
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242
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Abstract
The discovery of the adipocyte hormone leptin completely changed our view of energy metabolism. In addition, the discovery of leptin rapidly progressed to clinical development. After a decade of clinical studies, leptin appears not to be the magic bullet therapy for obesity; however, it has a robust role in rare human conditions characterized by its deficiency. Recent exciting work from the Unger laboratory suggests that leptin therapy may also have a potential role for the treatment of Type 1 diabetes. In this review we discuss the positive evidence why such an approach is worthwhile. In order to achieve this broad goal, we reviewed available literature and provided our interpretation of the evidence presented in the original research papers. The potential cautionary aspects of this novel approach will be discussed in an accompanying article.
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Affiliation(s)
- Elif A Oral
- Metabolism, Endocrine and Diabetes Division (MEND), University of Michigan, Ann Arbor, MI, USA.
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243
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Unger RH, Cherrington AD. Glucagonocentric restructuring of diabetes: a pathophysiologic and therapeutic makeover. J Clin Invest 2012; 122:4-12. [PMID: 22214853 DOI: 10.1172/jci60016] [Citation(s) in RCA: 497] [Impact Index Per Article: 41.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The hormone glucagon has long been dismissed as a minor contributor to metabolic disease. Here we propose that glucagon excess, rather than insulin deficiency, is the sine qua non of diabetes. We base this on the following evidence: (a) glucagon increases hepatic glucose and ketone production, catabolic features present in insulin deficiency; (b) hyperglucagonemia is present in every form of poorly controlled diabetes; (c) the glucagon suppressors leptin and somatostatin suppress all catabolic manifestations of diabetes during total insulin deficiency; (d) total β cell destruction in glucagon receptor-null mice does not cause diabetes; and (e) perfusion of normal pancreas with anti-insulin serum causes marked hyperglucagonemia. From this and other evidence, we conclude that glucose-responsive β cells normally regulate juxtaposed α cells and that without intraislet insulin, unregulated α cells hypersecrete glucagon, which directly causes the symptoms of diabetes. This indicates that glucagon suppression or inactivation may provide therapeutic advantages over insulin monotherapy.
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Affiliation(s)
- Roger H Unger
- Touchstone Center for Diabetes Research, Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas 75390-8854, USA.
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244
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Watanabe C, Seino Y, Miyahira H, Yamamoto M, Fukami A, Ozaki N, Takagishi Y, Sato J, Fukuwatari T, Shibata K, Oiso Y, Murata Y, Hayashi Y. Remodeling of hepatic metabolism and hyperaminoacidemia in mice deficient in proglucagon-derived peptides. Diabetes 2012; 61:74-84. [PMID: 22187375 PMCID: PMC3237648 DOI: 10.2337/db11-0739] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Glucagon is believed to be one of the most important peptides for upregulating blood glucose levels. However, homozygous glucagon-green fluorescent protein (gfp) knock-in mice (Gcg(gfp/gfp): GCGKO) are normoglycemic despite the absence of proglucagon-derived peptides, including glucagon. To characterize metabolism in the GCGKO mice, we analyzed gene expression and metabolome in the liver. The expression of genes encoding rate-limiting enzymes for gluconeogenesis was only marginally altered. On the other hand, genes encoding enzymes involved in conversion of amino acids to metabolites available for the tricarboxylic acid cycle and/or gluconeogenesis showed lower expression in the GCGKO liver. The expression of genes involved in the metabolism of fatty acids and nicotinamide was also altered. Concentrations of the metabolites in the GCGKO liver were altered in manners concordant with alteration in the gene expression patterns, and the plasma concentrations of amino acids were elevated in the GCGKO mice. The insulin concentration in serum and phosphorylation of Akt protein kinase in liver were reduced in GCGKO mice. These results indicated that proglucagon-derived peptides should play important roles in regulating various metabolic pathways, especially that of amino acids. Serum insulin concentration is lowered to compensate the impacts of absent proglucagon-derived peptide on glucose metabolism. On the other hand, impacts on other metabolic pathways are only partially compensated by reduced insulin action.
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Affiliation(s)
- Chika Watanabe
- Department of Genetics, Research Institute of Environmental Medicine, Nagoya University, Nagoya, Japan
- Department of Endocrinology and Diabetes, Nagoya University Graduate School of Medicine, Nagoya, Japan
| | - Yusuke Seino
- Department of Endocrinology and Diabetes, Nagoya University Graduate School of Medicine, Nagoya, Japan
| | - Hiroki Miyahira
- Department of Genetics, Research Institute of Environmental Medicine, Nagoya University, Nagoya, Japan
| | - Michiyo Yamamoto
- Department of Genetics, Research Institute of Environmental Medicine, Nagoya University, Nagoya, Japan
| | - Ayako Fukami
- Department of Endocrinology and Diabetes, Nagoya University Graduate School of Medicine, Nagoya, Japan
| | - Nobuaki Ozaki
- Department of Endocrinology and Diabetes, Nagoya University Graduate School of Medicine, Nagoya, Japan
| | - Yoshiko Takagishi
- Department of Genetics, Research Institute of Environmental Medicine, Nagoya University, Nagoya, Japan
| | - Jun Sato
- Futuristic Environmental Stimulation Center, Research Institute of Environmental Medicine, Nagoya University, Nagoya, Japan
| | - Tsutomu Fukuwatari
- Department of Food Science and Nutrition, School of Human Cultures, University of Shiga Prefecture, Hikone, Shiga, Japan
| | - Katsumi Shibata
- Department of Food Science and Nutrition, School of Human Cultures, University of Shiga Prefecture, Hikone, Shiga, Japan
| | - Yutaka Oiso
- Department of Endocrinology and Diabetes, Nagoya University Graduate School of Medicine, Nagoya, Japan
| | - Yoshiharu Murata
- Department of Genetics, Research Institute of Environmental Medicine, Nagoya University, Nagoya, Japan
| | - Yoshitaka Hayashi
- Department of Genetics, Research Institute of Environmental Medicine, Nagoya University, Nagoya, Japan
- Corresponding author: Yoshitaka Hayashi,
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245
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Gustavsson N, Wu B, Han W. Calcium sensing in exocytosis. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 740:731-57. [PMID: 22453967 DOI: 10.1007/978-94-007-2888-2_32] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Neurotransmitters, neuropeptides and hormones are released through regulated exocytosis of synaptic vesicles and large dense core vesicles. This complex and highly regulated process is orchestrated by SNAREs and their associated proteins. The triggering signal for regulated exocytosis is usually an increase in intracellular calcium levels. Besides the triggering role, calcium signaling modulates the precise amount and kinetics of vesicle release. Thus, it is a central question to understand the molecular machineries responsible for calcium sensing in exocytosis. Here we provide an overview of our current understanding of calcium sensing in neurotransmitter release and hormone secretion.
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Affiliation(s)
- Natalia Gustavsson
- Laboratory of Metabolic Medicine, Singapore Bioimaging Consortium, Agency for Science, Technology and Research, Singapore.
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246
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Regulation of calcium in pancreatic α- and β-cells in health and disease. Cell Calcium 2011; 51:300-8. [PMID: 22177710 PMCID: PMC3334273 DOI: 10.1016/j.ceca.2011.11.006] [Citation(s) in RCA: 169] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2011] [Revised: 11/10/2011] [Accepted: 11/17/2011] [Indexed: 12/15/2022]
Abstract
The glucoregulatory hormones insulin and glucagon are released from the β- and α-cells of the pancreatic islets. In both cell types, secretion is secondary to firing of action potentials, Ca2+-influx via voltage-gated Ca2+-channels, elevation of [Ca2+]i and initiation of Ca2+-dependent exocytosis. Here we discuss the mechanisms that underlie the reciprocal regulation of insulin and glucagon secretion by changes in plasma glucose, the roles played by different types of voltage-gated Ca2+-channel present in α- and β-cells and the modulation of hormone secretion by Ca2+-dependent and -independent processes. We also consider how subtle changes in Ca2+-signalling may have profound impact on β-cell performance and increase risk of developing type-2 diabetes.
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247
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Lang V, Youssef N, Light PE. The molecular genetics of sulfonylurea receptors in the pathogenesis and treatment of insulin secretory disorders and type 2 diabetes. Curr Diab Rep 2011; 11:543-51. [PMID: 21968738 DOI: 10.1007/s11892-011-0233-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Sulfonylurea receptors (SURs) form an integral part of the ATP-sensitive potassium (K(ATP)) channel complex that is present in most excitable cell types. K(ATP) channels couple cellular metabolism to electrical activity and provide a wide range of cellular functions including stimulus secretion coupling in pancreatic β cells. K(ATP) channels are composed of SURs and inward rectifier potassium channel (Kir6.x) subunits encoded by the ABCC8/9 and KCNJ8/11 genes, respectively. Recent advances in the genetics, molecular biology, and pharmacology of SURs have led to an increased understanding of these channels in the etiology and treatment of rare genetic insulin secretory disorders. Furthermore, common genetic variants in these genes are associated with an increased risk for type 2 diabetes. In this review we summarize the molecular biology, pharmacology, and physiology of SURs and K(ATP) channels, highlighting recent advances in their genetics and understanding of rare insulin secretory disorders and susceptibility to type 2 diabetes.
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Affiliation(s)
- Veronica Lang
- Department of Pharmacology, Alberta Diabetes Institute and Cardiovascular Research Centre, University of Alberta, Edmonton, Alberta T6G 2E1, Canada
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248
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Christensen M, Bagger JI, Vilsbøll T, Knop FK. The alpha-cell as target for type 2 diabetes therapy. Rev Diabet Stud 2011; 8:369-81. [PMID: 22262074 DOI: 10.1900/rds.2011.8.369] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Glucagon is the main secretory product of the pancreatic alpha-cells. The main function of this peptide hormone is to provide sustained glucose supply to the brain and other vital organs during fasting conditions. This is exerted by stimulation of hepatic glucose production via specific G protein-coupled receptors in the hepatocytes. Type 2 diabetic patients are characterized by elevated glucagon levels contributing decisively to hyperglycemia in these patients. Accumulating evidence demonstrates that targeting the pancreatic alpha-cell and its main secretory product glucagon is a possible treatment for type 2 diabetes. Several lines of preclinical evidence have paved the way for the development of drugs, which suppress glucagon secretion or antagonize the glucagon receptor. In this review, the physiological actions of glucagon and the role of glucagon in type 2 diabetic pathophysiology are outlined. Furthermore, potential advantages and limitations of antagonizing the glucagon receptor or suppressing glucagon secretion in the treatment of type 2 diabetes are discussed with a focus on already marketed drugs and drugs in clinical development. It is concluded that the development of novel glucagon receptor antagonists are confronted with several safety issues. At present, available pharmacological agents based on the glucose-dependent glucagonostatic effects of GLP-1 represent the most favorable way to apply constraints to the alpha-cell in type 2 diabetes.
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Affiliation(s)
- Mikkel Christensen
- Diabetes Research Division, Department of Internal Medicine F, Gentofte Hospital, University of Copenhagen, Denmark
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249
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Thorel F, Damond N, Chera S, Wiederkehr A, Thorens B, Meda P, Wollheim CB, Herrera PL. Normal glucagon signaling and β-cell function after near-total α-cell ablation in adult mice. Diabetes 2011; 60:2872-82. [PMID: 21926270 PMCID: PMC3198058 DOI: 10.2337/db11-0876] [Citation(s) in RCA: 89] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
OBJECTIVE To evaluate whether healthy or diabetic adult mice can tolerate an extreme loss of pancreatic α-cells and how this sudden massive depletion affects β-cell function and blood glucose homeostasis. RESEARCH DESIGN AND METHODS We generated a new transgenic model allowing near-total α-cell removal specifically in adult mice. Massive α-cell ablation was triggered in normally grown and healthy adult animals upon diphtheria toxin (DT) administration. The metabolic status of these mice was assessed in 1) physiologic conditions, 2) a situation requiring glucagon action, and 3) after β-cell loss. RESULTS Adult transgenic mice enduring extreme (98%) α-cell removal remained healthy and did not display major defects in insulin counter-regulatory response. We observed that 2% of the normal α-cell mass produced enough glucagon to ensure near-normal glucagonemia. β-Cell function and blood glucose homeostasis remained unaltered after α-cell loss, indicating that direct local intraislet signaling between α- and β-cells is dispensable. Escaping α-cells increased their glucagon content during subsequent months, but there was no significant α-cell regeneration. Near-total α-cell ablation did not prevent hyperglycemia in mice having also undergone massive β-cell loss, indicating that a minimal amount of α-cells can still guarantee normal glucagon signaling in diabetic conditions. CONCLUSIONS An extremely low amount of α-cells is sufficient to prevent a major counter-regulatory deregulation, both under physiologic and diabetic conditions. We previously reported that α-cells reprogram to insulin production after extreme β-cell loss and now conjecture that the low α-cell requirement could be exploited in future diabetic therapies aimed at regenerating β-cells by reprogramming adult α-cells.
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Affiliation(s)
- Fabrizio Thorel
- Department of Cell Physiology and Metabolism, Faculty of Medicine, University of Geneva, Geneva, Switzerland
| | - Nicolas Damond
- Department of Cell Physiology and Metabolism, Faculty of Medicine, University of Geneva, Geneva, Switzerland
| | - Simona Chera
- Department of Cell Physiology and Metabolism, Faculty of Medicine, University of Geneva, Geneva, Switzerland
| | - Andreas Wiederkehr
- Department of Cell Physiology and Metabolism, Faculty of Medicine, University of Geneva, Geneva, Switzerland
| | - Bernard Thorens
- Department of Physiology and Center for Integrative Genomics, University of Lausanne, Lausanne, Switzerland
| | - Paolo Meda
- Department of Cell Physiology and Metabolism, Faculty of Medicine, University of Geneva, Geneva, Switzerland
| | - Claes B. Wollheim
- Department of Cell Physiology and Metabolism, Faculty of Medicine, University of Geneva, Geneva, Switzerland
| | - Pedro L. Herrera
- Department of Cell Physiology and Metabolism, Faculty of Medicine, University of Geneva, Geneva, Switzerland
- Corresponding author: Pedro L. Herrera,
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250
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Lou PH, Gustavsson N, Wang Y, Radda GK, Han W. Increased lipolysis and energy expenditure in a mouse model with severely impaired glucagon secretion. PLoS One 2011; 6:e26671. [PMID: 22046328 PMCID: PMC3203149 DOI: 10.1371/journal.pone.0026671] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2011] [Accepted: 09/30/2011] [Indexed: 12/23/2022] Open
Abstract
Background Secretion of insulin and glucagon is triggered by elevated intracellular calcium levels. Although the precise mechanism by which the calcium signal is coupled to insulin and glucagon granule exocytosis is unclear, synaptotagmin-7 has been shown to be a positive regulator of calcium-dependent insulin and glucagon secretion, and may function as a calcium sensor for insulin and glucagon granule exocytosis. Deletion of synaptotagmin-7 leads to impaired glucose-stimulated insulin secretion and nearly abolished Ca2+-dependent glucagon secretion in mice. Under non-stressed resting state, however, synaptotagmin-7 KO mice exhibit normal insulin level but severely reduced glucagon level. Methodology/Principal Findings We studied energy expenditure and metabolism in synaptotagmin-7 KO and control mice using indirect calorimetry and biochemical techniques. Synaptotagmin-7 KO mice had lower body weight and body fat content, and exhibited higher oxygen consumption and basal metabolic rate. Respiratory exchange ratio (RER) was lower in synaptotagmin-7 KO mice, suggesting an increased use of lipid in their energy production. Consistent with lower RER, gene expression profiles suggest enhanced lipolysis and increased capacity for fatty acid transport and oxidation in synaptotagmin-7 KO mice. Furthermore, expression of uncoupling protein 3 (UCP3) in skeletal muscle was approximately doubled in the KO mice compared with control mice. Conclusions These results show that the lean phenotype in synaptotagmin-7 KO mice was mostly attributed to increased lipolysis and energy expenditure, and suggest that reduced glucagon level may have broad influence on the overall metabolism in the mouse model.
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Affiliation(s)
- Phing-How Lou
- Laboratory of Metabolic Medicine, Singapore Bioimaging Consortium, Agency for Science, Technology and Research, Singapore, Singapore
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