1
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Rosenkilde MM, Lindquist P, Kizilkaya HS, Gasbjerg LS. GIP-derived GIP receptor antagonists - a review of their role in GIP receptor pharmacology. Peptides 2024; 177:171212. [PMID: 38608836 DOI: 10.1016/j.peptides.2024.171212] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/03/2024] [Revised: 04/01/2024] [Accepted: 04/08/2024] [Indexed: 04/14/2024]
Abstract
Surprisingly, agonists, as well as antagonists of the glucose-dependent insulinotropic polypeptide receptor (GIPR), are currently being used or investigated as treatment options for type 2 diabetes and obesity - and both, when combined with glucagon-like peptide 1 receptor (GLP-1R) agonism, enhance GLP-1-induced glycemia and weight loss further. This paradox raises several questions regarding not only the mechanisms of actions of GIP but also the processes engaged during the activation of both the GIP and GLP-1 receptors. Here, we provide an overview of studies of the properties and actions of peptide-derived GIPR antagonists, focusing on GIP(3-30)NH2, a naturally occurring N- and C-terminal truncation of GIP(1-42). GIP(3-30)NH2 was the first GIPR antagonist administered to humans. GIP(3-30)NH2 and a few additional antagonists, like Pro3-GIP, have been used in both in vitro and in vivo studies to elucidate the molecular and cellular consequences of GIPR inhibition, desensitization, and internalization and, at a larger scale, the role of the GIP system in health and disease. We provide an overview of these studies combined with recent knowledge regarding the effects of naturally occurring variants of the GIPR system and species differences within the GIP system to enhance our understanding of the GIPR as a drug target.
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Affiliation(s)
- Mette Marie Rosenkilde
- Molecular and Translational Pharmacology, Department of Biomedical Sciences, University of Copenhagen, Copenhagen, Denmark.
| | - Peter Lindquist
- Molecular and Translational Pharmacology, Department of Biomedical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Hüsün Sheyma Kizilkaya
- Molecular and Translational Pharmacology, Department of Biomedical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Lærke Smidt Gasbjerg
- Molecular and Translational Pharmacology, Department of Biomedical Sciences, University of Copenhagen, Copenhagen, Denmark.
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2
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Krogh LSL, Henriksen K, Stensen S, Skov-Jeppesen K, Bergmann NC, Størling J, Rosenkilde MM, Hartmann B, Holst JJ, Gasbjerg LS, Knop FK. The naturally occurring GIP(1-30)NH2 is a GIP receptor agonist in humans. Eur J Endocrinol 2023; 188:6979719. [PMID: 36651162 DOI: 10.1093/ejendo/lvac015] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/19/2022] [Revised: 11/30/2022] [Accepted: 12/14/2022] [Indexed: 01/11/2023]
Abstract
OBJECTIVE The gut hormone glucose-dependent insulinotropic polypeptide (GIP) is an important regulator of glucose and bone metabolism. In rodents, the naturally occurring GIP variant, GIP(1-30)NH2, has shown similar effects as full-length GIP (GIP(1-42)), but its effects in humans are unsettled. Here, we investigated the actions of GIP(1-30)NH2 compared to GIP(1-42) on glucose and bone metabolism in healthy men and in isolated human pancreatic islets. METHODS Nine healthy men completed three separate three-step glucose clamps (0-60 minutes at fasting plasma glucose (FPG) level, 60-120 minutes at 1.5× FPG, and 120-180 minutes at 2× FPG) with infusion of GIP(1-42) (4 pmol/kg/min), GIP(1-30)NH2 (4 pmol/kg/min), and saline (9 mg/mL) in randomised order. Blood was sampled for measurement of relevant hormones and bone turnover markers. Human islets were incubated with low (2 mmol/L) or high (20 mmol/L) d-glucose with or without GIP(1-42) or GIP(1-30)NH2 in three different concentrations for 30 minutes, and secreted insulin and glucagon were measured. RESULTS Plasma glucose (PG) levels at FPG, 1.5× FPG, and 2× FPG were obtained by infusion of 1.45 g/kg, 0.97 g/kg, and 0.6 g/kg of glucose during GIP(1-42), GIP(1-30)NH2, and saline, respectively (P = .18), and were similar on the three experimental days. Compared to placebo, GIP(1-30)NH2 resulted in similar glucagonotropic, insulinotropic, and carboxy-terminal type 1 collagen crosslinks-suppressing effects as GIP(1-42). In vitro experiments on human islets showed similar insulinotropic and glucagonotropic effects of the two GIP variants. CONCLUSIONS GIP(1-30)NH2 has similar effects on glucose and bone metabolism in healthy individuals and in human islets in vitro as GIP(1-42).
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Affiliation(s)
- Liva S L Krogh
- Center for Clinical Metabolic Research, Gentofte Hospital, University of Copenhagen, Hellerup, Denmark
| | - Kristine Henriksen
- Department of Clinical Research, Steno Diabetes Center Copenhagen, Herlev, Denmark
| | - Signe Stensen
- Center for Clinical Metabolic Research, Gentofte Hospital, University of Copenhagen, Hellerup, Denmark
| | - Kirsa Skov-Jeppesen
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
- Faculty of Health and Medical Sciences, Novo Nordisk Foundation Center for Basic Metabolic Research, University of Copenhagen, Copenhagen, Denmark
| | - Natasha C Bergmann
- Center for Clinical Metabolic Research, Gentofte Hospital, University of Copenhagen, Hellerup, Denmark
| | - Joachim Størling
- Department of Clinical Research, Steno Diabetes Center Copenhagen, Herlev, Denmark
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Mette M Rosenkilde
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Bolette Hartmann
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
- Faculty of Health and Medical Sciences, Novo Nordisk Foundation Center for Basic Metabolic Research, University of Copenhagen, Copenhagen, Denmark
| | - Jens J Holst
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
- Faculty of Health and Medical Sciences, Novo Nordisk Foundation Center for Basic Metabolic Research, University of Copenhagen, Copenhagen, Denmark
| | - Lærke S Gasbjerg
- Center for Clinical Metabolic Research, Gentofte Hospital, University of Copenhagen, Hellerup, Denmark
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Filip K Knop
- Center for Clinical Metabolic Research, Gentofte Hospital, University of Copenhagen, Hellerup, Denmark
- Department of Clinical Research, Steno Diabetes Center Copenhagen, Herlev, Denmark
- Faculty of Health and Medical Sciences, Novo Nordisk Foundation Center for Basic Metabolic Research, University of Copenhagen, Copenhagen, Denmark
- Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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3
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Smit FX, van der Velden WJC, Kizilkaya HS, Nørskov A, Lückmann M, Hansen TN, Sparre-Ulrich AH, Qvotrup K, Frimurer TM, Rosenkilde MM. Investigating GIPR (ant)agonism: A structural analysis of GIP and its receptor. Structure 2021; 29:679-693.e6. [PMID: 33891864 DOI: 10.1016/j.str.2021.04.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2020] [Revised: 02/01/2021] [Accepted: 04/02/2021] [Indexed: 12/21/2022]
Abstract
The glucose-dependent insulinotropic polypeptide (GIP) is a 42-residue metabolic hormone that is actively being targeted for its regulatory role of glycemia and energy balance. Limited structural data of its receptor has made ligand design tedious. This study investigates the structure and function of the GIP receptor (GIPR), using a homology model based on the GLP-1 receptor. Molecular dynamics combined with in vitro mutational data were used to pinpoint residues involved in ligand binding and/or receptor activation. Significant differences in binding mode were identified for the naturally occurring agonists GIP(1-30)NH2 and GIP(1-42) compared with high potency antagonists GIP(3-30)NH2 and GIP(5-30)NH2. Residues R1832.60, R1902.67, and R3005.40 are shown to be key for activation of the GIPR, and evidence suggests that a disruption of the K293ECL2-E362ECL3 salt bridge by GIPR antagonists strongly reduces GIPR activation. Combinatorial use of these findings can benefit rational design of ligands targeting the GIPR.
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Affiliation(s)
- Florent X Smit
- Laboratory for Molecular Pharmacology, Department of Biomedical Sciences, University of Copenhagen, Blegdamsvej 3B, Copenhagen 2200, Denmark; Section for Metabolic Receptology, Novo Nordisk Center for Basic Metabolic Research, University of Copenhagen, Copenhagen 2200, Denmark
| | - Wijnand J C van der Velden
- Laboratory for Molecular Pharmacology, Department of Biomedical Sciences, University of Copenhagen, Blegdamsvej 3B, Copenhagen 2200, Denmark
| | - Hüsün S Kizilkaya
- Laboratory for Molecular Pharmacology, Department of Biomedical Sciences, University of Copenhagen, Blegdamsvej 3B, Copenhagen 2200, Denmark
| | - Amalie Nørskov
- Department of Chemistry, Technical University of Denmark, Lyngby 2800, Denmark
| | - Michael Lückmann
- Section for Metabolic Receptology, Novo Nordisk Center for Basic Metabolic Research, University of Copenhagen, Copenhagen 2200, Denmark
| | - Tobias N Hansen
- Department of Chemistry, Technical University of Denmark, Lyngby 2800, Denmark
| | - Alexander H Sparre-Ulrich
- Laboratory for Molecular Pharmacology, Department of Biomedical Sciences, University of Copenhagen, Blegdamsvej 3B, Copenhagen 2200, Denmark
| | - Katrine Qvotrup
- Department of Chemistry, Technical University of Denmark, Lyngby 2800, Denmark
| | - Thomas M Frimurer
- Section for Metabolic Receptology, Novo Nordisk Center for Basic Metabolic Research, University of Copenhagen, Copenhagen 2200, Denmark
| | - Mette M Rosenkilde
- Laboratory for Molecular Pharmacology, Department of Biomedical Sciences, University of Copenhagen, Blegdamsvej 3B, Copenhagen 2200, Denmark.
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4
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Gabe MBN, van der Velden WJC, Smit FX, Gasbjerg LS, Rosenkilde MM. Molecular interactions of full-length and truncated GIP peptides with the GIP receptor - A comprehensive review. Peptides 2020; 125:170224. [PMID: 31809770 DOI: 10.1016/j.peptides.2019.170224] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/07/2019] [Revised: 11/25/2019] [Accepted: 11/27/2019] [Indexed: 12/17/2022]
Abstract
Enzymatic cleavage of endogenous peptides is a commonly used principle to initiate, modulate and terminate action for instance among cytokines and peptide hormones. The incretin hormones, glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1), and the related hormone glucagon-like peptide-2 (GLP-2) are all rapidly N-terminally truncated with severe loss of intrinsic activity. The most abundant circulating form of full length GIP(1-42) is GIP(3-42) (a dipeptidyl peptidase-4 (DPP-4) product). GIP(1-30)NH2 is another active form resulting from prohormone convertase 2 (PC2) cleavage of proGIP. Like GIP(1-42), GIP(1-30)NH2 is a substrate for DPP-4 generating GIP(3-30)NH2 which, compared to GIP(3-42), binds with higher affinity and very efficiently inhibits GIP receptor (GIPR) activity with no intrinsic activity. Here, we review the action of these four and multiple other N- and C-terminally truncated forms of GIP with an emphasis on molecular pharmacology, i.e. ligand binding, subsequent receptor activation and desensitization. Our overall conclusion is that the N-terminus is essential for receptor activation as GIP N-terminal truncation leads to decreased/lost intrinsic activity and antagonism (similar to GLP-1 and GLP-2), whereas the C-terminal extension of GIP(1-42), as compared to GLP-1, GLP-2 and glucagon (29-33 amino acids), has no apparent impact on the GIPR in vitro, but may play a role for other properties such as stability and tissue distribution. A deeper understanding of the molecular interaction of naturally occurring and designed GIP-based peptides, and their impact in vivo, may contribute to a future therapeutic targeting of the GIP system - either with agonists or with antagonists, or both.
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Affiliation(s)
- Maria Buur Nordskov Gabe
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
| | - Wijnand J C van der Velden
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
| | - Florent Xavier Smit
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
| | - Lærke Smidt Gasbjerg
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark; Center for Clinical Metabolic Research, Gentofte Hospital, University of Copenhagen, Hellerup, Denmark
| | - Mette Marie Rosenkilde
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark.
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5
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Perry RA, Craig SL, Ng MT, Gault VA, Flatt PR, Irwin N. Characterisation of Glucose-Dependent Insulinotropic Polypeptide Receptor Antagonists in Rodent Pancreatic Beta Cells and Mice. CLINICAL MEDICINE INSIGHTS-ENDOCRINOLOGY AND DIABETES 2019; 12:1179551419875453. [PMID: 31548798 PMCID: PMC6743192 DOI: 10.1177/1179551419875453] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/14/2019] [Accepted: 08/21/2019] [Indexed: 12/18/2022]
Abstract
Hypersecretion and alterations in the biological activity of the incretin
hormone, glucose-dependent insulinotropic polypeptide (GIP), have been
postulated as contributing factors in the development of obesity-related
diabetes. However, recent studies also point to weight-reducing effects of GIP
receptor activation. Therefore, generating precise experimental tools, such as
specific and effective GIP receptor (GIPR) antagonists, is of key significance
to better understand GIP physiology. Thus, the primary aim of the current study
was to uncover improved GIPR antagonists for use in rodent studies, using human
and mouse GIP sequences with N- and C-terminal deletions. Initial in
vitro studies revealed that the GIPR agonists, human (h) GIP(1-42),
hGIP(1-30) and mouse (m) GIP(1-30), stimulated (P < 0.01 to
P < 0.001) insulin secretion from rat BRIN-BD11 cells.
Analysis of insulin secretory effects of the N- and C-terminally cleaved GIP
peptides, including hGIP(3-30), mGIP(3-30), h(Pro3)GIP(3-30),
hGIP(5-30), hGIP(3-42) and hGIP(5-42), revealed that these peptides did not
modulate insulin secretion. More pertinently, only hGIP(3-30), mGIP(3-30) and
h(Pro3)GIP(3-30) were able to significantly (P
< 0.01 to P < 0.001) inhibit hGIP(1-42)-stimulated
insulin secretion. The human-derived GIPR agonist sequences, hGIP(1-42) and
hGIP(1-30), reduced (P < 0.05) glucose levels in mice
following conjoint injection with glucose, but mGIP(1-30) was ineffective. None
of the N- and C-terminally cleaved GIP peptides affected glucose homeostasis
when injected alone with glucose. However, hGIP(5-30) and mGIP(3-30)
significantly (P < 0.05 to P < 0.01)
impaired the glucose-lowering action of hGIP(1-42). Further evaluation of these
most effective sequences demonstrated that mGIP(3-30), but not hGIP(5-30),
effectively prevented GIP-induced elevations of plasma insulin concentrations.
These data highlight, for the first time, that mGIP(3-30) represents an
effective molecule to inhibit GIPR activity in mice.
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Affiliation(s)
- R A Perry
- SAAD Centre for Pharmacy and Diabetes, Ulster University, Coleraine, UK
| | - S L Craig
- SAAD Centre for Pharmacy and Diabetes, Ulster University, Coleraine, UK
| | - M T Ng
- SAAD Centre for Pharmacy and Diabetes, Ulster University, Coleraine, UK
| | - V A Gault
- SAAD Centre for Pharmacy and Diabetes, Ulster University, Coleraine, UK
| | - P R Flatt
- SAAD Centre for Pharmacy and Diabetes, Ulster University, Coleraine, UK
| | - N Irwin
- SAAD Centre for Pharmacy and Diabetes, Ulster University, Coleraine, UK
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6
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Gasbjerg LS, Gabe MBN, Hartmann B, Christensen MB, Knop FK, Holst JJ, Rosenkilde MM. Glucose-dependent insulinotropic polypeptide (GIP) receptor antagonists as anti-diabetic agents. Peptides 2018; 100:173-181. [PMID: 29412817 DOI: 10.1016/j.peptides.2017.11.021] [Citation(s) in RCA: 47] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/01/2017] [Revised: 11/27/2017] [Accepted: 11/28/2017] [Indexed: 01/07/2023]
Abstract
Glucose-dependent insulinotropic polypeptide (GIP) is an intestinal hormone with a broad range of physiological actions. In the postprandial state, the hormone stimulates insulin secretion and during eu- and hypoglycemia, it stimulates glucagon secretion. In addition, GIP increases triacylglycerol (TAG) uptake in adipose tissue and decreases bone resorption. However, the importance of these actions in humans are not clearly understood as a specific GIP receptor (GIPR) antagonist - an essential tool to study GIP physiology - has been missing. Several different GIPR antagonists have been identified comprising both peptides, vaccines against GIP, GIP antibodies or antibodies against the GIPR. However, most of these have only been tested in rodents. In vitro, N- and C-terminally truncated GIP variants are potent and efficacious GIPR antagonists. Recently, GIP(3-30)NH2, a naturally occurring peptide, was shown to block the GIPR in humans and decrease GIP-induced insulin secretion as well as adipose tissue blood flow and TAG uptake. So far, there are no studies with a GIPR antagonist in patients with type 2 diabetes (T2D), but because the elevations in fasting plasma glucagon and paradoxical postprandial glucagon excursions, seen in patients with T2D, are aggravated by GIP, a GIPR antagonist could partly alleviate this and possibly improve the fasting and postprandial glycemia. Since the majority of patients with T2D are overweight, inhibition of GIP-induced fat deposition may be beneficial as well. Here we summarize the studies of GIPR antagonists and discuss the therapeutic potential of the GIP system in humans.
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Affiliation(s)
- Lærke Smidt Gasbjerg
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark; NNF Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark; Center for Diabetes Research, Gentofte Hospital, University of Copenhagen, Hellerup, Denmark.
| | - Maria Buur Nordskov Gabe
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark; NNF Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Bolette Hartmann
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark; NNF Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Mikkel Bring Christensen
- Center for Diabetes Research, Gentofte Hospital, University of Copenhagen, Hellerup, Denmark; Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark; Department of Clinical Pharmacology, Bispebjerg Hospital, University of Copenhagen, Copenhagen, Denmark
| | - Filip Krag Knop
- NNF Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark; Center for Diabetes Research, Gentofte Hospital, University of Copenhagen, Hellerup, Denmark; Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Jens Juul Holst
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark; NNF Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Mette Marie Rosenkilde
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark; NNF Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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7
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Sparre-Ulrich A, Gabe M, Gasbjerg L, Christiansen C, Svendsen B, Hartmann B, Holst J, Rosenkilde M. GIP(3–30)NH2 is a potent competitive antagonist of the GIP receptor and effectively inhibits GIP-mediated insulin, glucagon, and somatostatin release. Biochem Pharmacol 2017; 131:78-88. [DOI: 10.1016/j.bcp.2017.02.012] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2016] [Accepted: 02/14/2017] [Indexed: 12/31/2022]
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8
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Hansen LS, Sparre-Ulrich AH, Christensen M, Knop FK, Hartmann B, Holst JJ, Rosenkilde MM. N-terminally and C-terminally truncated forms of glucose-dependent insulinotropic polypeptide are high-affinity competitive antagonists of the human GIP receptor. Br J Pharmacol 2016; 173:826-38. [PMID: 26572091 PMCID: PMC4761099 DOI: 10.1111/bph.13384] [Citation(s) in RCA: 67] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2015] [Revised: 10/13/2015] [Accepted: 10/16/2015] [Indexed: 12/25/2022] Open
Abstract
Background and Purpose Glucose‐dependent insulinotropic polypeptide (GIP) affects lipid, bone and glucose homeostasis. High‐affinity ligands for the GIP receptor are needed to elucidate the physiological functions and pharmacological potential of GIP in vivo. GIP(1–30)NH2 is a naturally occurring truncation of GIP(1–42). Here, we have characterized eight N‐terminal truncations of human GIP(1–30)NH2. Experimental Approach COS‐7 cells were transiently transfected with human GIP receptors and assessed for cAMP accumulation upon ligand stimulation or competition binding with 125I‐labelled GIP(1–42), GIP(1–30)NH2, GIP(2–30)NH2 or GIP(3–30)NH2. Key Results GIP(1–30)NH2 displaced 125I‐GIP(1–42) as effectively as GIP(1–42) (Ki 0.75 nM), whereas the eight truncations displayed lower affinities (Ki 2.3–347 nM) with highest affinities for GIP(3–30)NH2 and GIP(5–30)NH2 (5–30)NH2. Only GIP(1–30)NH2 (Emax 100% of GIP(1–42)) and GIP(2–30)NH2 (Emax 20%) were agonists. GIP(2‐ to 9–30)NH2 displayed antagonism (IC50 12–450 nM) and Schild plot analyses identified GIP(3–30)NH2 and GIP(5–30)NH2 as competitive antagonists (Ki 15 nM). GIP(3–30) NH2 was a 26‐fold more potent antagonist than GIP(3–42). Binding studies with agonist (125I‐GIP(1–30)NH2), partial agonist (125I‐GIP(2–30)NH2) and competitive antagonist (125I‐GIP(3–30)NH2) revealed distinct receptor conformations for these three ligand classes. Conclusions and Implications The N‐terminus is crucial for GIP agonist activity. Removal of the C‐terminus of the endogenous GIP(3–42) creates another naturally occurring, more potent, antagonist GIP(3–30)NH2, which like GIP(5–30)NH2, was a high‐affinity competitive antagonist. These peptides may be suitable tools for basic GIP research and future pharmacological interventions.
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Affiliation(s)
- L S Hansen
- Department of Neuroscience and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.,Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.,Center for Diabetes Research, Gentofte Hospital, University of Copenhagen, Copenhagen, Denmark
| | - A H Sparre-Ulrich
- Department of Neuroscience and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.,Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - M Christensen
- Center for Diabetes Research, Gentofte Hospital, University of Copenhagen, Copenhagen, Denmark
| | - F K Knop
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.,Center for Diabetes Research, Gentofte Hospital, University of Copenhagen, Copenhagen, Denmark
| | - B Hartmann
- NNF Center for Basic Metabolic Research, University of Copenhagen, Copenhagen, Denmark.,Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - J J Holst
- NNF Center for Basic Metabolic Research, University of Copenhagen, Copenhagen, Denmark.,Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - M M Rosenkilde
- Department of Neuroscience and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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9
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Tao YX, Liang XF. G Protein-Coupled Receptors as Regulators of Glucose Homeostasis and Therapeutic Targets for Diabetes Mellitus. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2014; 121:1-21. [DOI: 10.1016/b978-0-12-800101-1.00001-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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10
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Hewage CM, Venneti KC. Structural aspects of gut peptides with therapeutic potential for type 2 diabetes. ChemMedChem 2013; 8:560-7. [PMID: 23292985 DOI: 10.1002/cmdc.201200445] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2012] [Indexed: 12/25/2022]
Abstract
Gut hormones represent a niche subset of pharmacologically active agents that are rapidly gaining importance in medicine. Due to their exceptional specificity for their receptors, these hormones along with their analogues have attracted considerable pharmaceutical interest for the treatment of human disorders including type 2 diabetes. With the recent advances in the structural biology, a significant amount of structural information for these hormones is now available. This Minireview presents an overview of the structural aspects of these hormones, which have roles in physiological processes such as insulin secretion, as well as a discussion on the relevant structural modifications used to improve these hormones for the treatment of type 2 diabetes.
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Affiliation(s)
- Chandralal M Hewage
- School of Biomolecular and Biomedical Science, Conway Institute, University College Dublin, Belfield, Dublin 4, Ireland.
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11
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Fujita Y, Asadi A, Yang GK, Kwok YN, Kieffer TJ. Differential processing of pro-glucose-dependent insulinotropic polypeptide in gut. Am J Physiol Gastrointest Liver Physiol 2010; 298:G608-14. [PMID: 20185691 DOI: 10.1152/ajpgi.00024.2010] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Glucose-dependent insulinotropic polypeptide (GIP) is a hormone released from enteroendocrine K cells in response to meals. Posttranslational processing of the precursor protein pro-GIP at residue 65 by proprotein convertase subtilisin/kexin type 1 (PC1/3) in gut K cells gives rise to the established 42-amino-acid form of GIP (GIP(1-42)). However, the pro-GIP peptide sequence contains a consensus cleavage site for PC2 at residues 52-55 and we identified PC2 immunoreactivity in a subset of K cells, suggesting the potential existence of a COOH-terminal truncated GIP isoform, GIP(1-30). Indeed a subset of mouse and human K cells display GIP immunoreactivity with GIP antibodies directed to the mid portion of the peptide, but not with a COOH-terminal-directed GIP antibody, indicative of the presence of a truncated form of GIP. This population of cells represents approximately 5-15% of the total GIP-immunoreactive cells in mice, depending on the region of intestine, and is virtually absent in mice lacking PC2. Amidated GIP(1-30) and GIP(1-42) have comparable potency at stimulating somatostatin release in the perfused mouse stomach. Therefore, GIP(1-30) represents a naturally occurring, biologically active form of GIP.
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Affiliation(s)
- Yukihiro Fujita
- Department of Cellular and Physiological Sciences, Life Sciences Institute, University of British Columbia, Vancouver, Canada
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12
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Underwood CR, Parthier C, Reedtz-Runge S. Structural basis for ligand recognition of incretin receptors. VITAMINS AND HORMONES 2010; 84:251-78. [PMID: 21094903 DOI: 10.1016/b978-0-12-381517-0.00009-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The glucose-dependent insulinotropic polypeptide (GIP) receptor and the glucagon-like peptide-1 (GLP-1) receptor are homologous G-protein-coupled receptors (GPCRs). Incretin receptor agonists stimulate the synthesis and secretion of insulin from pancreatic β-cells and are therefore promising agents for the treatment of type 2 diabetes. It is well established that the N-terminal extracellular domain (ECD) of incretin receptors is important for ligand binding and ligand specificity, whereas the transmembrane domain is involved in receptor activation. Structures of the ligand-bound ECD of incretin receptors have been solved recently by X-ray crystallography. The crystal structures reveal a similar fold of the ECD and a similar mechanism of ligand binding, where the ligand adopts an α-helical conformation. Residues in the C-terminal part of the ligand interact directly with the ECD and hydrophobic interactions appear to be the main driving force for ligand binding to the ECD of incretin receptors. Obviously, the-still missing-structures of full-length incretin receptors are required to construct a complete picture of receptor function at the molecular level. However, the progress made recently in structural analysis of the ECDs of incretin receptors and related GPCRs has shed new light on the process of ligand recognition and binding and provided a basis to disclose some of the mechanisms underlying receptor activation at high resolution.
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Affiliation(s)
- Christina Rye Underwood
- Department of Chemistry, MEMPHYS Center for Biomembrane Physics, Technical University of Denmark, Kgs. Lyngby, Denmark, GLP-1 and Obesity Biology, Novo Nordisk, Måløv, Denmark
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13
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Parthier C, Kleinschmidt M, Neumann P, Rudolph R, Manhart S, Schlenzig D, Fanghänel J, Rahfeld JU, Demuth HU, Stubbs MT. Crystal structure of the incretin-bound extracellular domain of a G protein-coupled receptor. Proc Natl Acad Sci U S A 2007; 104:13942-7. [PMID: 17715056 PMCID: PMC1955799 DOI: 10.1073/pnas.0706404104] [Citation(s) in RCA: 194] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2007] [Indexed: 11/18/2022] Open
Abstract
Incretins, endogenous polypeptide hormones released in response to food intake, potentiate insulin secretion from pancreatic beta cells after oral glucose ingestion (the incretin effect). This response is signaled by the two peptide hormones glucose-dependent insulinotropic polypeptide (GIP) (also known as gastric inhibitory polypeptide) and glucagon-like peptide 1 through binding and activation of their cognate class 2 G protein-coupled receptors (GPCRs). Because the incretin effect is lost or significantly reduced in patients with type 2 diabetes mellitus, glucagon-like peptide 1 and GIP have attracted considerable attention for their potential in antidiabetic therapy. A paucity of structural information precludes a detailed understanding of the processes of hormone binding and receptor activation, hampering efforts to develop novel pharmaceuticals. Here we report the crystal structure of the complex of human GIP receptor extracellular domain (ECD) with its agonist, the incretin GIP(1-42). The hormone binds in an alpha-helical conformation in a surface groove of the ECD largely through hydrophobic interactions. The N-terminal ligand residues would remain free to interact with other parts of the receptor. Thermodynamic data suggest that binding is concomitant with structural organization of the hormone, resulting in a complex mode of receptor-ligand recognition. The presentation of a well structured, alpha-helical ligand by the ECD is expected to be conserved among other hormone receptors of this class.
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Affiliation(s)
| | | | | | - Rainer Rudolph
- *Institut für Biochemie und Biotechnologie and
- *Mitteldeutsches Zentrum für Struktur und Dynamik der Proteine, Martin–Luther–Universität Halle–Wittenberg, D-06120 Halle (Saale), Germany; and
| | - Susanne Manhart
- Probiodrug AG, Biocenter Halle, D-06120 Halle (Saale), Germany
| | | | - Jörg Fanghänel
- *Mitteldeutsches Zentrum für Struktur und Dynamik der Proteine, Martin–Luther–Universität Halle–Wittenberg, D-06120 Halle (Saale), Germany; and
| | | | | | - Milton T. Stubbs
- *Institut für Biochemie und Biotechnologie and
- *Mitteldeutsches Zentrum für Struktur und Dynamik der Proteine, Martin–Luther–Universität Halle–Wittenberg, D-06120 Halle (Saale), Germany; and
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14
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Irwin N, Green BD, Parker JC, Gault VA, O'Harte FPM, Flatt PR. Biological activity and antidiabetic potential of synthetic fragment peptides of glucose-dependent insulinotropic polypeptide, GIP(1-16) and (Pro3)GIP(1-16). ACTA ACUST UNITED AC 2006; 135:45-53. [PMID: 16675042 DOI: 10.1016/j.regpep.2006.03.006] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2006] [Accepted: 03/24/2006] [Indexed: 10/24/2022]
Abstract
Glucose-dependent insulinotropic polypeptide (GIP) is a key physiological insulin releasing peptide and potential antidiabetic agent. The present study was undertaken in an attempt to develop small molecular weight GIP agonist and antagonist molecules. The bioactivity of two modified C-terminally truncated fragment GIP peptides, GIP(1-16) and (Pro3)GIP(1-16), was examined in terms of insulin secretion and glucose homeostasis using BRIN-BD11 cells and type 2 diabetic mice. In vitro insulin release studies demonstrated that GIP(1-16) and (Pro3)GIP(1-16) possessed weak GIP-receptor agonist and antagonistic properties, respectively. Intraperitoneal administration of GIP(1-16) in combination with glucose to obese diabetic (ob/ob) mice did not effect the glycaemic excursion and had a marginal effect on insulin release. GIP(1-16) was substantially less effective than the native GIP(1-42). (Pro3)GIP(1-16) administration significantly curtailed (P < 0.05) the insulinotropic and glucose lowering effects of native GIP, but was significantly less effective than (Pro3)GIP. Based on the established concept of a therapeutic benefit of GIP receptor antagonism in obesity-diabetes, ob/ob mice received once daily injection of (Pro3)GIP(1-16) for 14 days. No significant effects were observed on food intake, body weight, HbA1c, glucose tolerance, metabolic response to feeding and either insulin secretion or insulin sensitivity following prolonged (Pro3)GIP(1-16) treatment. These data demonstrate that C-terminal truncation of GIP or (Pro3)GIP yields small molecular weight GIP molecules with significantly reduced biological activity that precludes therapeutic utility.
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Affiliation(s)
- Nigel Irwin
- Diabetes Research Group, School of Biomedical Sciences, University of Ulster, Coleraine BT52 1SA, Northern Ireland, UK.
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15
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Salhanick AI, Clairmont KB, Buckholz TM, Pellegrino CM, Ha S, Lumb KJ. Contribution of site-specific PEGylation to the dipeptidyl peptidase IV stability of glucose-dependent insulinotropic polypeptide. Bioorg Med Chem Lett 2005; 15:4114-7. [PMID: 15993590 DOI: 10.1016/j.bmcl.2005.06.002] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2005] [Revised: 05/27/2005] [Accepted: 06/02/2005] [Indexed: 01/12/2023]
Abstract
The effects of PEGylation of glucose-dependent insulinotropic polypeptide (GIP) on potency and dipeptidyl peptidase IV (DPPIV) stability are reported. N-terminal modification of GIP(1-30) with 40 kDa polyethylene glycol (PEG) abrogates functional activity. In contrast, C-terminal PEGylation of GIP(1-30) maintains full agonism and reasonable potency at the GIP receptor and confers a high level of DPPIV resistance. Moreover, the dual modification of N-terminal palmitoylation and C-terminal PEGylation results in a full agonist of comparable potency to native GIP that is stable to DPPIV cleavage. The results provide the basis for the development of long acting, PEGylated GIP, GIP variants, or GIP-based hybrid peptide therapeutics.
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Affiliation(s)
- Arthur I Salhanick
- Department of Metabolic Disorders Research, Bayer Pharmaceuticals Corporation, 400 Morgan Lane, West Haven, CT 06516, USA
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16
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Tyndall JDA, Pfeiffer B, Abbenante G, Fairlie DP. Over One Hundred Peptide-Activated G Protein-Coupled Receptors Recognize Ligands with Turn Structure. Chem Rev 2005; 105:793-826. [PMID: 15755077 DOI: 10.1021/cr040689g] [Citation(s) in RCA: 176] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Affiliation(s)
- Joel D A Tyndall
- Center for Drug Design and Development, Institute for Molecular Bioscience, University of Queensland, Brisbane, Qld 4072, Australia
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17
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Alaña I, Hewage CM, Malthouse JPG, Parker JC, Gault VA, O'Harte FPM. NMR structure of the glucose-dependent insulinotropic polypeptide fragment, GIP(1–30)amide. Biochem Biophys Res Commun 2004; 325:281-6. [PMID: 15522230 DOI: 10.1016/j.bbrc.2004.10.033] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2004] [Indexed: 11/27/2022]
Abstract
Glucose-dependent insulinotropic polypeptide is an incretin hormone that stimulates insulin secretion and reduces postprandial glycaemic excursions. The glucose-dependent action of GIP on pancreatic beta-cells has attracted attention towards its exploitation as a potential drug for type 2 diabetes. Use of NMR or X-ray crystallography is vital to determine the three-dimensional structure of the peptide. Therefore, to understand the basic structural requirements for the biological activity of GIP, the solution structure of the major biologically active fragment, GIP(1-30)amide, was investigated by proton NMR spectroscopy and molecular modelling. The structure is characterised by a full length alpha-helical conformation between residues F(6) and A(28). This structural information could play an important role in the design of therapeutic agents based upon GIP receptor agonists.
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Affiliation(s)
- Iñigo Alaña
- Department of Biochemistry, Centre for Synthesis and Chemical Biology, Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin 4, Ireland
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18
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Hinke SA, Manhart S, Speck M, Pederson RA, Demuth HU, McIntosh CHS. In depth analysis of the N-terminal bioactive domain of gastric inhibitory polypeptide. Life Sci 2004; 75:1857-70. [PMID: 15302229 DOI: 10.1016/j.lfs.2004.03.024] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2003] [Accepted: 03/29/2004] [Indexed: 11/27/2022]
Abstract
Gastric inhibitory polypeptide/glucose-dependent insulinotropic polypeptide (GIP) is an important gastrointestinal regulator of insulin release and glucose homeostasis following a meal. Strategies have been undertaken to delineate the bioactive domains of GIP with the intention of developing small molecular weight GIP mimetics. The molecular cloning of receptors for GIP and the related hormone GLP-1 (glucagon-like peptide-1) has allowed examination of the characteristics of incretin analogs in transfected cell models. The current report examines the N-terminal bioactive domain of GIP residing in residues 1-14 by alanine scanning mutagenesis and N-terminal substitution/modification. Further studies examined peptide chimeras of GIP and GLP-1 designed to localize bioactive determinants of the two hormones. The alanine scan of the GIP(1-14) sequence established that the peptide was extremely sensitive to structural perturbations. Only replacement of amino acids 2 and 13 with those found in glucagon failed to dramatically reduce receptor binding and activation. Of four GIP(1-14) peptides modified by the introduction of DP IV-resistant groups, a peptide with a reduced bond between Ala2 and Glu3 demonstrated improved receptor potency compared to native GIP(1-14). The peptide chimera studies supported recent results on the importance of a mid-region helix for bioactivity of GIP, and confirmed existence of two separable regions with independent intrinsic receptor binding and activation properties. Furthermore, peptide chimeras showed that binding of GLP-1 also involves both N- and C-terminal domains, but that it apparently contains only a single bioactive domain in its N-terminus. Together, these results should facilitate development of incretin based therapies using rational drug design for potential treatment of diabetes.
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Affiliation(s)
- Simon A Hinke
- Department of Physiology, Faculty of Medicine, University of British Columbia, 2146 Health Sciences Mall, Vancouver, British Columbia, V6T 1Z3, Canada
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19
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Manhart S, Hinke SA, McIntosh CHS, Pederson RA, Demuth HU. Structure-function analysis of a series of novel GIP analogues containing different helical length linkers. Biochemistry 2003; 42:3081-8. [PMID: 12627975 DOI: 10.1021/bi026868e] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Glucose-dependent insulinotropic polypeptide (GIP1-42) is a potent glucose-lowering intestinal peptide hormone. The equipotent GIP1-30NH2 was structurally modified by linking N- and C-terminal fragments with several different linkers. Substitution of the middle region of GIP by a flexible aminohexanoic linker resulted in greatly reduced binding affinity and reduction or complete loss of bioactivity. Connection of the bioactive domains GIP1-14 and GIP19-30NH2 by EKEK or AAAA linkers resulted in peptide agonists with approximately 3-4-fold increased bioactivity as compared to GIP1-30NH2. Conformational analysis by CD spectroscopy of GIP fragments and analogues suggests a helical region in the C-terminal (19-30) portion of GIP. It was demonstrated that stabilization of this C-terminal helical region by the introduction of helical linkers favored binding and activation of the GIP receptor. Our results suggest an important contribution of a direct interaction of the first 14 amino acids with the GIP receptor, an appropriate relative orientation of N- and C-terminal parts of GIP, and the presence of helical linkers to be essential for bioactivity.
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Affiliation(s)
- Susanne Manhart
- Department of Peptide Chemistry, probiodrug AG, Weinbergweg 22, 06120 Halle/Saale, Germany
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20
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Hinke SA, Gelling RW, Pederson RA, Manhart S, Nian C, Demuth HU, McIntosh CHS. Dipeptidyl peptidase IV-resistant [D-Ala(2)]glucose-dependent insulinotropic polypeptide (GIP) improves glucose tolerance in normal and obese diabetic rats. Diabetes 2002; 51:652-61. [PMID: 11872663 DOI: 10.2337/diabetes.51.3.652] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The therapeutic potential of glucose-dependent insulinotropic polypeptide (GIP) for improving glycemic control has largely gone unstudied. A series of synthetic GIP peptides modified at the NH(2)-terminus were screened in vitro for resistance to dipeptidyl peptidase IV (DP IV) degradation and potency to stimulate cyclic AMP and affinity for the transfected rat GIP receptor. In vitro experiments indicated that [D-Ala(2)]GIP possessed the greatest resistance to enzymatic degradation, combined with minimal effects on efficacy at the receptor. Thus, [D-Ala(2)]GIP(1--42) was selected for further testing in the perfused rat pancreas and bioassay in conscious Wistar and Zucker rats. When injected subcutaneously in normal Wistar, Fa/?, or fa/fa Vancouver Diabetic Fatty (VDF) Zucker rats, both GIP and [D-Ala(2)]GIP significantly reduced glycemic excursions during a concurrent oral glucose tolerance test via stimulation of insulin release. The latter peptide displayed greater in vivo effectiveness, likely because of resistance to enzymatic degradation. Hence, despite reduced bioactivity in diabetic models at physiological concentrations, GIP and analogs with improved plasma stability still improve glucose tolerance when given in supraphysiological doses, and thus may prove useful in the treatment of diabetic states.
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Affiliation(s)
- Simon A Hinke
- Department of Physiology, University of British Columbia, Vancouver, Canada
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21
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Hinke SA, Manhart S, Pamir N, Demuth H, W Gelling R, Pederson RA, McIntosh CH. Identification of a bioactive domain in the amino-terminus of glucose-dependent insulinotropic polypeptide (GIP). BIOCHIMICA ET BIOPHYSICA ACTA 2001; 1547:143-55. [PMID: 11343800 DOI: 10.1016/s0167-4838(01)00181-9] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The incretins are a class of hormones released from the small bowel that act on the endocrine pancreas to potentiate insulin secretion in a glucose-dependent manner. Due to the requirement for an elevated glucose concentration for activity, the incretins, glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1, have potential in the treatment of non-insulin-dependent diabetes mellitus. A series of synthetic peptide GIP fragments was generated for the purpose of elucidating the bioactive domain of the molecule. Peptides were screened for stimulation of cyclic AMP (cAMP) accumulation in Chinese hamster ovary cells transfected with the rat islet GIP receptor. Of the GIP fragments tested, GIP(1-14) and GIP(19-30) demonstrated the greatest cAMP-stimulating ability over the range of concentrations tested (up to 20 microM). In contrast, GIP fragments corresponding to amino acids 15-42, 15-30, 16-30 and 17-30 all demonstrated weak antagonism of GIP(1-42) activity. Competitive-binding displacement studies indicated that these peptides were low-affinity ligands for the GIP receptor. To examine biological activity in vivo, a bioassay was developed in the anesthetized rat. Intravenous infusion of GIP(1-42) (1 pmol/min/100 g) with a concurrent intraperitoneal glucose load (1 g/kg) significantly reduced circulating blood glucose excursions through stimulation of insulin release. Higher doses of GIP(1-14) and GIP(19-30) (100 pmol/min/100 g) also reduced blood glucose excursions.
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Affiliation(s)
- S A Hinke
- Department of Physiology, Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada
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22
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Gelling RW, Coy DH, Pederson RA, Wheeler MB, Hinke S, Kwan T, McIntosh CH. GIP(6-30amide) contains the high affinity binding region of GIP and is a potent inhibitor of GIP1-42 action in vitro. REGULATORY PEPTIDES 1997; 69:151-4. [PMID: 9226399 DOI: 10.1016/s0167-0115(97)00009-8] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
GIP (Glucose-dependent Insulinotropic Polypeptide) is an important regulator of insulin secretion. The effects of truncated forms of the peptide, GIP(10-30), GIP(6-30amide) and GIP(7-30), on binding of 125I-GIP(1-42) to GIP receptors in transfected CHO-KI cells, and on cyclic AMP responses to GIP(1-42), have been studied with a view to defining further the receptor binding region of GIP, and to establish whether such truncated peptides exhibit agonist or antagonist activity. All three peptides were found to be receptor antagonists, however GIP(6-30amide) exhibited receptor binding affinity equivalent to that of GIP(1-42) in competitive binding studies (IC50 = 3.08+/-0.57 nM). GIP(6-30amide) inhibited GIP(1-42)-induced cAMP production by 58% at a concentration of 100 nM, whereas GIP(10-30) and GIP(7-30), inhibited only in the microM range. GIP(6-30amide) therefore contains the high affinity binding region of GIP and is a potent inhibitor of GIP(1-42) action in vitro.
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Affiliation(s)
- R W Gelling
- Department of Physiology, Faculty of Medicine, University of British Columbia, Vancouver, Canada
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