Glucose-dependent Insulinotropic Polypeptide Receptor Antagonist Research Articles

GIP-derived GIP receptor antagonists – a review of their role in GIP receptor pharmacology

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.

Regulation of energy metabolism through central GIPR signaling

In recent years, significant progress has been made to pharmacologically combat the obesity pandemic, particularly with regard to biochemically tailored drugs that simultaneously target the receptors for glucagon-like peptide-1 (GLP-1) and the glucose-dependent insulinotropic polypeptide (GIP). But while the pharmacological benefits of GLP-1 receptor (GLP-1R) agonism are widely acknowledged, the role of the GIP system in regulating systems metabolism remains controversial. When given in adjunct to GLP-1R agonism, both agonism and antagonism of the GIP receptor (GIPR) improves metabolic outcome in preclinical and clinical studies, and despite persistent concerns about its potential obesogenic nature, there is accumulating evidence indicating that GIP has beneficial metabolic effects via central GIPR agonism. Nonetheless, despite growing recognition of the GIP system as a valuable pharmacological target, there remains great uncertainty as to where and how GIP acts in the brain to regulate metabolism, and how GIPR agonism may differ from GIPR antagonism in control of energy metabolism. In this review we highlight current knowledge on the central action of GIP, and discuss open questions related to its multifaceted biology in the brain and the periphery.

Worth Their Weight? An Update on New and Emerging Pharmacologic Agents for Obesity and Their Potential Role for Persons with Cardiac Conditions.

Obesity is associated with cardiovascular (CV) conditions, including but not limited to atherosclerotic disease, heart failure, and atrial fibrillation. Despite this, the impact of intentional weight loss on CV outcomes for persons with obesity and established CV conditions remains poorly studied. New and emerging pharmacologic therapies for weight loss primarily targeting the incretin/nutrient sensing axes induce substantial and sustained weight loss. The glucagon-like-peptide 1 receptor agonists (GLP-1 RA) liraglutide and semaglutide have US FDA approval for the treatment of obesity, and the application for an obesity indication for the dual GLP-1/glucose-dependent insulinotropic polypeptide (GIP) receptor agonist tirzepatide is presently under FDA review. Extensive phase II and IIIa randomized controlled trials are underway evaluating permutations of combined GLP-1 RA, GIP receptor agonist, GIP receptor antagonist, and glucagon receptor agonists. Clinical outcome trials of these therapies in persons with obesity at high risk of established CV conditions should make it possible to estimate the role of intentional weight loss in managing CV risk via these medications. High-dose once weekly injectable semaglutide (2.4mg/week) use among persons with obesity and heart failure with preserved ejection fraction was effective at both reducing weight and improving health status; exercise capacity was also improved. Ongoing CV outcome trials of oral semaglutide and once weekly injectable tirzepatide will help to establish the role of these therapies among persons with other CV conditions. In addition to these two therapies targeting a CV claim or indication, many other new therapeutics for weight loss, as reviewed, are currently in development. The impact of pharmacologic-induced weight loss on CV conditions for persons with obesity and established CV conditions is currently under investigation for multiple agents. These therapies may offer new avenues to manage CV risk in persons with obesity and with established or at high risk for CV disease.

Contribution of GIP and GLP-1 to the Insulin Response to Oral Administration of Glucose in Female Mice

It has previously been shown that the incretin effect accounts for ≈50% of the insulin response to oral glucose in normal mice. Now, I have proceeded and studied the contribution of glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) to the insulin response to oral glucose in female mice by using receptor antagonists. A specific GIP receptor antagonist (mGIP(3-30); 50 or 500 nmol/kg), a specific GLP-1 receptor antagonist (exendin(9-39); 3 or 30 nmol/kg), the combination of mGIP (500 nmol/kg) and exendin(9-39) (30 nmol/kg), or saline was given intravenously four minutes after administration of glucose (50 mg) through a gastric tube in anesthetized C57/BL6J mice (n = 95) with samples obtained before glucose administration and after 15, 30 and 60 min. The insulinogenic index, determined as the area under the 60 min curve for insulin (AUCinsulin) divided by the AUCglucose, was used to reflect the insulin response. It was found that the insulinogenic index was reduced by 67 ± 4% by mGIP(3-30) (p < 0.001), by 60 ± 14% by exendin(9-39) (p = 0.007) and by 61 ± 14% by the combination of mGIP(3-30) and exendin(9-39) (p = 0.043), both at their highest doses, compared to animals injected with glucose in the same experimental series. It is concluded that both GIP and GLP-1 are required for a normal incretin effect in female mice, that they contribute similarly to the insulin response, and that it is unlikely that there is another incretin hormone in this species.

Enhanced Endosomal Signaling and Desensitization of GLP-1R vs GIPR in Pancreatic Beta Cells.

The incretin receptors, glucagon-like peptide-1 receptor (GLP-1R) and glucose-dependent insulinotropic polypeptide receptor (GIPR), are prime therapeutic targets for the treatment of type 2 diabetes (T2D) and obesity. They are expressed in pancreatic beta cells where they potentiate insulin release in response to food intake. Despite GIP being the main incretin in healthy individuals, GLP-1R has been favored as a therapeutic target due to blunted GIPR responses in T2D patients and conflicting effects of GIPR agonists and antagonists in improving glucose tolerance and preventing weight gain. There is, however, a recently renewed interest in GIPR biology, following the realization that GIPR responses can be restored after an initial period of blood glucose normalization and the recent development of dual GLP-1R/GIPR agonists with superior capacity for controlling blood glucose levels and weight. The importance of GLP-1R trafficking and subcellular signaling in the control of receptor outputs is well established, but little is known about the pattern of spatiotemporal signaling from the GIPR in beta cells. Here, we have directly compared surface expression, trafficking, and signaling characteristics of both incretin receptors in pancreatic beta cells to identify potential differences that might underlie distinct pharmacological responses associated with each receptor. Our results indicate increased cell surface levels, internalization, degradation, and endosomal vs plasma membrane activity for the GLP-1R, while the GIPR is instead associated with increased plasma membrane recycling, reduced desensitization, and enhanced downstream signal amplification. These differences might have potential implications for the capacity of each incretin receptor to control beta cell function.

Endogenous Glucose-Dependent Insulinotropic Polypeptide Contributes to Sitagliptin-Mediated Improvement in β-Cell Function in Patients With Type 2 Diabetes.

Dipeptidyl peptidase 4 (DPP-4) degrades the incretin hormones glucagon-like peptide 1 and glucose-dependent insulinotropic polypeptide (GIP). DPP-4 inhibitors improve glycemic control in type 2 diabetes, but the importance of protecting GIP from degradation for their clinical effects is unknown. We included 12 patients with type 2 diabetes (mean ± SD BMI 27 ± 2.6 kg/m2, HbA1c 7.1 ± 1.4% [54 ± 15 mmol/mol]) in this double-blind, placebo-controlled, crossover study to investigate the contribution of endogenous GIP to the effects of the DPP-4 inhibitor sitagliptin. Participants underwent two randomized, 13-day treatment courses of sitagliptin (100 mg/day) and placebo, respectively. At the end of each treatment period, we performed two mixed-meal tests with infusion of the GIP receptor antagonist GIP(3-30)NH2 (1,200 pmol/kg/min) or saline placebo. Sitagliptin lowered mean fasting plasma glucose by 1.1 mmol/L compared with placebo treatment. During placebo treatment, postprandial glucose excursions were increased during GIP(3-30)NH2 compared with saline (difference in area under the curve ± SEM 7.3 ± 2.8%) but were unchanged during sitagliptin treatment. Endogenous GIP improved β-cell function by 37 ± 12% during DPP-4 inhibition by sitagliptin. This was determined by the insulin secretion rate/plasma glucose ratio. We calculated an estimate of the absolute sitagliptin-mediated impact of GIP on β-cell function as the insulinogenic index during sitagliptin treatment plus saline infusion minus the insulinogenic index during sitagliptin plus GIP(3-30)NH2. This estimate was expressed relative to the maximal potential contribution of GIP to the effect of sitagliptin (100%), defined as the difference between the full sitagliptin treatment effect, including actions mediated by GIP (sitagliptin + saline), and the physiological response minus any contribution by GIP [placebo treatment + GIP(3-30)NH2]. We demonstrate insulinotropic and glucose-lowering effects of endogenous GIP in patients with type 2 diabetes and that endogenous GIP contributes to the improved β-cell function observed during DPP-4 inhibition.

1362-P: Endogenous Glucose-Dependent Insulinotropic Polypeptide Facilitates Postprandial Intestinal Lipid Uptake in Healthy Men, but Not in Patients with Type 2 Diabetes

The gut hormone glucose-dependent insulinotropic polypeptide (GIP) stimulates glucose-induced insulin secretion and increases triglyceride deposition in subcutaneous adipose tissue, and these effects are attenuated in both type 2 diabetes (T2D) and obesity. Using the GIP receptor antagonist GIP (3-30) NH2, we investigated the effect of endogenous GIP on circulating lipoproteins (chylomicrons, VLDL, LDL, HDL) during a meal in healthy men and patients with T2D. We measured apolipoprotein B48 (ApoB48) (as a marker of chylomicron count) and plasma lipoprotein triglyceride and cholesterol content during two liquid meal tests (1,894 kJ) with double-blind infusions of GIP (3-30) NH2 or placebo (saline) in randomized order in 12 healthy men (19-65 years, BMI 20.3-25.5 kg/m2) and in patients with T2D (44-72 years, HbA1c 6.2-11% (37-70 mmol/mol) , BMI 27.4-41.2 kg/m2) . Compared to placebo, the GIP (3-30) NH2 infusion lowered postprandial responses of ApoB48 (incremental area under the curve (iAUC0-180 min) (median (95%CI)) : 215 (156-258) vs. 4 (363-541) mg×L-1×min, P=0.0049) , chylomicron-triglyceride content (iAUC0-270 min: 32.7 (-2.32-72.1) vs. 49.5 (1.21-170) mmol× L-1×min P=0.083) and HDL-triglyceride content (iAUC0-270min: -0.90 (-1.95-0.18) vs. 0.95 (-0.72-3.95) mmol× L-1×min, P=0.016) . In patients with T2D, infusion of GIP (3-30) NH2 did not change postprandial responses of ApoB48 or lipoprotein-triglyceride content. In both groups, there were no differences in lipoprotein-cholesterol contents. Disclosure L.S.Gasbjerg: Speaker's Bureau; Eli Lilly and Company, Stock/Shareholder; Antag Therapeutics. C.Christoffersen: None. F.K.Knop: Advisory Panel; Boehringer Ingelheim International GmbH, Eli Lilly and Company, Merck Sharp &amp; Dohme Corp., Novo Nordisk, Sanofi, ShouTi, Zucara Therapeutics, Consultant; AstraZeneca, Eli Lilly and Company, Novo Nordisk, Pharmacosmos A/S, Sanofi, ShouTi, Zealand Pharma A/S, Zucara Therapeutics, Research Support; AstraZeneca, Novo Nordisk, Sanofi, Zealand Pharma A/S, Speaker's Bureau; AstraZeneca, Bayer AG, Boehringer Ingelheim International GmbH, Eli Lilly and Company, Novo Nordisk, Sanofi, Stock/Shareholder; Antag Therapeutics. M.M.Rosenkilde: Research Support; Antag Therapeutics, Bainan Biotech, Stock/Shareholder; Antag Therapeutics, Bainan Biotech, Synklino ApS. M.M.Helsted: None. S.Stensen: Employee; Novo Nordisk A/S. L.S.L.Krogh: None. A.H.Sparre-ulrich: Other Relationship; Antag Therapeutics. B.Hartmann: Board Member; Bainan Biotech. T.Vilsbøll: Consultant; AstraZeneca, Bristol-Myers Squibb Company, Eli Lilly and Company, Gilead Sciences, Inc., GlaxoSmithKline plc., Merck Sharp &amp; Dohme Corp., Mundipharma, Novo Nordisk, Sun Pharmaceutical Industries Ltd. M.B.Christensen: None. J.J.Holst: Advisory Panel; Novo Nordisk, Board Member; Antag Therapeutics, Bainan Biotech. Funding EFSD (no. 94815) ; Novo Nordisk Foundation (no. 13777)

Activation of GIPR Exerts Analgesic and Anxiolytic-Like Effects in the Anterior Cingulate Cortex of Mice.

BackgroundChronic pain is defined as pain that persists typically for a period of over six months. Chronic pain is often accompanied by an anxiety disorder, and these two tend to exacerbate each other. This can make the treatment of these conditions more difficult. Glucose-dependent insulinotropic polypeptide (GIP) is a member of the incretin hormone family and plays a critical role in glucose metabolism. Previous research has demonstrated the multiple roles of GIP in both physiological and pathological processes. In the central nervous system (CNS), studies of GIP are mainly focused on neurodegenerative diseases; hence, little is known about the functions of GIP in chronic pain and pain-related anxiety disorders.MethodsThe chronic inflammatory pain model was established by hind paw injection with complete Freund’s adjuvant (CFA) in C57BL/6 mice. GIP receptor (GIPR) agonist (D-Ala2-GIP) and antagonist (Pro3-GIP) were given by intraperitoneal injection or anterior cingulate cortex (ACC) local microinjection. Von Frey filaments and radiant heat were employed to assess the mechanical and thermal hypersensitivity. Anxiety-like behaviors were detected by open field and elevated plus maze tests. The underlying mechanisms in the peripheral nervous system and CNS were explored by GIPR shRNA knockdown in the ACC, enzyme-linked immunosorbent assay, western blot analysis, whole-cell patch-clamp recording, immunofluorescence staining and quantitative real-time PCR.ResultsIn the present study, we found that hind paw injection with CFA induced pain sensitization and anxiety-like behaviors in mice. The expression of GIPR in the ACC was significantly higher in CFA-injected mice. D-Ala2-GIP administration by intraperitoneal or ACC local microinjection produced analgesic and anxiolytic effects; these were blocked by Pro3-GIP and GIPR shRNA knockdown in the ACC. Activation of GIPR inhibited neuroinflammation and activation of microglia, reversed the upregulation of NMDA and AMPA receptors, and suppressed the enhancement of excitatory neurotransmission in the ACC of model mice.ConclusionsGIPR activation was found to produce analgesic and anxiolytic effects, which were partially due to attenuation of neuroinflammation and inhibition of excitatory transmission in the ACC. GIPR may be a suitable target for treatment of chronic inflammatory pain and pain-related anxiety.

Deoxynivalenol (Vomitoxin)-Induced Anorexia Is Induced by the Release of Intestinal Hormones in Mice.

Deoxynivalenol (DON), also known as vomitoxin, is a mycotoxin that can cause antifeeding and vomiting in animals. However, the mechanism of DON inducing anorexia is complicated. Studies have shown that intestinal hormones play a significant part in the anorexia caused by DON. We adopted the “modeling of acute antifeeding in mice” as the basic experimental model, and used two methods of gavage and intraperitoneal injection to explore the effect of intestinal hormones on the antifeedant response induced by DON in mice. We found that 1 and 2.5 mg/kg·bw of DON can acutely induce anorexia and increase the plasma intestinal hormones CCK, PYY, GIP, and GLP-1 in mice within 3 h. Direct injection of exogenous intestinal hormones CCK, PYY, GIP, and GLP-1 can trigger anorexia behavior in mice. Furthermore, the PYY receptor antagonist JNJ-31020028, GLP-1 receptor antagonist Exendin(9-39), CCK receptor antagonist Proglumide, GIP receptor antagonist GIP(3-30)NH2 attenuated both intestinal hormone and DON-induced anorectic responses. These results indicate that intestinal hormones play a critical role in the anorexia response induced by DON.

85-LB: Glucose-Dependent Insulinotropic Polypeptide (GIP) Contributes Substantially to the Improved Beta-Cell Function during Sitagliptin Treatment in Persons with Type 2 Diabetes

In persons with type 2 diabetes (T2D), dipeptidyl peptidase 4 (DPP-4) inhibitor treatment improves glycemic control by raising the active levels of the insulinotropic gut hormones glucagon-like peptide 1 and glucose-dependent insulinotropic polypeptide (GIP). Using the GIP receptor antagonist GIP(3-30)NH2, we investigated endogenous GIP’s contribution to the insulinotropic effect of DPP-4 inhibition (assessed by insulin secretion rate (ISR) relative to plasma glucose). In a double-blind, placebo-controlled, cross-over study, 12 persons (eight men and four women) with T2D (mean ± SD; BMI 27.4 ± 2.6 kg/m2, HbA1c 7.1 ± 1.4% (54 ± 15 mmol/mol)) underwent two randomized 12-13-day treatment courses with DPP-4 inhibitor (sitagliptin 100 mg once-daily) and placebo, respectively, with an interposed 1-3-week washout period. In the end of each treatment period, two randomized 5-hour liquid mixed-meal tests with infusion of GIP(3-30)NH2 (1,200 pmol/kg/min) or saline (placebo) were performed. During placebo treatment, GIP(3-30)NH2 lowered postprandial serum C-peptide (determined as difference in baseline-subtracted area under curve (ΔbsAUC%) ± SEM: −31 ± 9%, P = 0.005) and increased postprandial plasma glucose excursions (ΔAUC% ± SEM: 7.3 ± 2.8%, P = 0.017) compared to saline. Sitagliptin increased concentrations of active GIP(1-42) (ΔAUC% ± SEM: 153 ± 21%, P &amp;lt; 0.0001) and lowered fasting plasma glucose (mean: 8.7 vs. 7.6 mmol/L, P &amp;lt; 0.0004), whereas postprandial glucose excursions were unchanged compared to placebo treatment. GIP(3-30)NH2 caused a reduction in AUCISR/AUCglucose ratio equivalent to 37 ± 12% of the increments due to sitagliptin. In conclusion, we demonstrate an insulinotropic and glucose-lowering effect of endogenous GIP in persons with T2D and show that endogenous GIP is responsible for more than one third of the improved beta cell function observed during DPP-4 inhibitor treatment. Disclosure S. Stensen: None. L. S. Gasbjerg: Stock/Shareholder; Self; Antag Therapeutics. M. M. Rosenkilde: Board Member; Self; Bainan Biotech, Synklino ApS, Board Member; Spouse/Partner; Antag Therapeutics, Bainan Biotech, Consultant; Self; Antag Therapeutics, Bainan Biotech, Synklino ApS, Stock/Shareholder; Self; Antag Therapeutics, Bainan Biotech, Synklino ApS, Stock/Shareholder; Spouse/Partner; Antag Therapeutics, Bainan Biotech. B. Hartmann: None. T. Vilsbøll: Consultant; Self; Amgen Inc., AstraZeneca, Boehringer Ingelheim Pharmaceuticals, Inc., Bristol-Myers Squibb Company, Gilead Sciences, Inc., Lilly Diabetes, Merck Sharp &amp; Dohme Corp., Mundipharma International, Novo Nordisk, Sanofi, Sun Pharmaceutical Industries Ltd. J. J. Holst: Consultant; Self; Novo Nordisk, Other Relationship; Self; Antag Therapeutics, Bainan Biotech, MSD Corporation, Novo Nordisk, Other Relationship; Spouse/Partner; Antag Therapeutics, Bainan Biotech, Synklino ApS. M. B. Christensen: None. F. K. Knop: Advisory Panel; Self; MSD Corporation, Novo Nordisk A/S, Sanofi, Consultant; Self; AstraZeneca, Boehringer Ingelheim Pharmaceuticals, Inc., Eli Lilly and Company, Novo Nordisk A/S, Pharmacosmos, Zealand Pharma A/S, Research Support; Self; Novo Nordisk A/S, Zealand Pharma A/S, Speaker’s Bureau; Self; AstraZeneca, Bayer AG, Boehringer Ingelheim Pharmaceuticals, Inc., Eli Lilly and Company, MSD Corporation, Novo Nordisk A/S. Funding European Foundation for the Study of Diabetes/Lilly European Diabetes Research Programme (2018); A.P. Møller Foundation

What combines best with GLP-1 for obesity treatment: GIP receptor agonists or antagonists?

Lu et al.1 previously demonstrated that antagonist antibodies against the GIP receptor promote weight loss combined with GLP-1. They now elegantly developed a conjugate of GIPR antibodies and GLP-1 and show effective weight loss in obese non-human primates.

GIPR antagonist antibodies conjugated to GLP-1 peptide are bispecific molecules that decrease weight in obese mice and monkeys

SummaryGlucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) regulate glucose and energy homeostasis. Targeting both pathways with GIP receptor (GIPR) antagonist antibody (GIPR-Ab) and GLP-1 receptor (GLP-1R) agonist, by generating GIPR-Ab/GLP-1 bispecific molecules, is an approach for treating obesity and its comorbidities. In mice and monkeys, these molecules reduce body weight (BW) and improve many metabolic parameters. BW loss is greater with GIPR-Ab/GLP-1 than with GIPR-Ab or a control antibody conjugate, suggesting synergistic effects. GIPR-Ab/GLP-1 also reduces the respiratory exchange ratio in DIO mice. Simultaneous receptor binding and rapid receptor internalization by GIPR-Ab/GLP-1 amplify endosomal cAMP production in recombinant cells expressing both receptors. This may explain the efficacy of the bispecific molecules. Overall, our GIPR-Ab/GLP-1 molecules promote BW loss, and they may be used for treating obesity.

Investigating GIPR (ant)agonism: A structural analysis of GIP and its receptor

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 invitro 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.

Glucose-dependent insulinotropic polypeptide modifies adipose plasticity and promotes beige adipogenesis of human omental adipose-derived stem cells.

The adipocyte precursors (APs) located in white adipose tissue (WAT) are functionally significant in adipose plasticity and browning. Modifying adipogenesis or WAT browning targeted on APs is a promising mechanism for anti-obesity drug. We herein explored the in vitro actions and mechanisms of glucose-dependent insulinotropic polypeptide (GIP), a gut-derived peptide, in human adipose-derived mesenchymal stem cells (hADSCs) isolated from omentum. The hADSCs were cotreated with 100nM GIP with or without equimolar concentration of GIP3-42 (a GIP receptor antagonist), and subsequently examined in vitro. CCK-8, EdU incorporation, and flow cytometry assays were used to assess cellular proliferation. Annexin V FTIC/PI double stain, TUNEL staining, and Western blot were applied for apoptosis evaluation. Adipogenesis was reflected by Western blot, real-time PCR, Oil Red O staining, mitochondrial staining, and mitochondrial DNA analysis. Results showed that GIP promoted proliferation and inhibited apoptosis of hADSCs via pleiotropiceffects. Besides, GIP facilitated de novo beige adipogenesis, by accelerating mitotic clonal expansion (MCE), upregulating core adipogenic regulators (C/EBPα and PPARγ), augmenting beige-related genes (UCP1, PGC1α, and PRDM16), increasing mitochondrial content and improving beige adipocyte functionalities. Above all, our study expands knowledge on the mechanisms of GIP modifying adipogenesis especially in inducing beige adipogenesis, and thus provides a theoretical support for clinical usage of GIP on obesity treatment.

Effects of endogenous GIP in patients with type 2 diabetes.

The insulinotropic effect of exogenous, intravenously infused glucose-dependent insulinotropic polypeptide (GIP) is impaired in patients with type 2 diabetes. We evaluated the effects of endogenous GIP in relation to glucose and bone metabolism in patients with type 2 diabetes using a selective GIP receptor antagonist and hypothesized that the effects of endogenous GIP were preserved. A randomized, double-blinded, placebo-controlled, crossover study. Ten patients with overweight/obesity and type 2 diabetes (mean±s.d.; HbA1c 52 ± 11 mmol/mol; BMI 32.5 ± 4.8 kg/m2) were included. We infused a selective GIP receptor antagonist, GIP(3-30)NH2 (1200 pmol/kg/min), or placebo (saline) during two separate, 230-min, standardized, liquid mixed meal tests followed by a meal ad libitum. Subcutaneous adipose tissue biopsies were analyzed. Compared with placebo, GIP(3-30)NH2 reduced postprandial insulin secretion (Δbaseline-subtracted area under the curve (bsAUC)C-peptide% ± s.e.m.; -14 ± 6%, P = 0.021) and peak glucagon (Δ% ± s.e.m.; -11 ± 6%, P = 0.046) but had no effect on plasma glucose (P = 0.692). Suppression of bone resorption (assessed by circulating carboxy-terminal collagen crosslinks (CTX)) was impaired during GIP(3-30)NH2 infusion compared with placebo (ΔbsAUCCTX; ±s.e.m.; -4.9 ± 2 ng/mL × min, P = 0.005) corresponding to a ~50% reduction. Compared with placebo, GIP(3-30)NH2 did not affect plasma lipids, meal consumption ad libitum or adipose tissue triglyceride content. Using a selective GIP receptor antagonist during a meal, we show that endogenous GIP increases postprandial insulin secretion with little effect on postprandial glycaemia but is important for postprandial bone homeostasis in patients with type 2 diabetes.

Chronic peptide-based GIP receptor inhibition exhibits modest glucose metabolic changes in mice when administered either alone or combined with GLP-1 agonism.

Combinatorial gut hormone therapy is one of the more promising strategies for identifying improved treatments for metabolic disease. Many approaches combine the established benefits of glucagon-like peptide-1 (GLP-1) agonism with one or more additional molecules with the aim of improving metabolic outcomes. Recent attention has been drawn to the glucose-dependent insulinotropic polypeptide (GIP) system due to compelling pre-clinical evidence describing the metabolic benefits of antagonising the GIP receptor (GIPR). We rationalised that benefit might be accrued from combining GIPR antagonism with GLP-1 agonism. Two GIPR peptide antagonists, GIPA-1 (mouse GIP(3-30)NH2) and GIPA-2 (NαAc-K10[γEγE-C16]-Arg18-hGIP(5-42)), were pharmacologically characterised and both exhibited potent antagonist properties. Acute in vivo administration of GIPA-1 during an oral glucose tolerance test (OGTT) had negligible effects on glucose tolerance and insulin in lean mice. In contrast, GIPA-2 impaired glucose tolerance and attenuated circulating insulin levels. A mouse model of diet-induced obesity (DIO) was used to investigate the potential metabolic benefits of chronic dosing of each antagonist, alone or in combination with liraglutide. Chronic administration studies showed expected effects of liraglutide, lowering food intake, body weight, fasting blood glucose and plasma insulin concentrations while improving glucose sensitivity, whereas delivery of either GIPR antagonist alone had negligible effects on these parameters. Interestingly, chronic dual therapy augmented insulin sensitizing effects and lowered plasma triglycerides and free-fatty acids, with more notable effects observed with GIPA-1 compared to GIPA-2. Thus, the co-administration of both a GIPR antagonist with a GLP1 agonist uncovers interesting beneficial effects on measures of insulin sensitivity, circulating lipids and certain adipose stores that seem influenced by the degree or nature of GIP receptor antagonism.

GIP Receptor Antagonist, SKL-14959 Indicated Alteration of the Lipids Metabolism to Catabolism by the Inhibition of Plasma LPL Activity, Resulting in the Suppression of Weight Gain on Diets-Induced Obesity Mice.

IntroductionGlucose-dependent insulinotropic polypeptide (GIP) plays a crucial role in the regulation of lipid metabolism via lipoprotein lipase (LPL). GIP receptor antagonist, SKL-14959, suppressed the weight gain in the diet-induced obesity model. However, the mechanism is not unclear. Therefore, we aimed to give insight into the reason.MethodsMice were divided into three groups of the low-fat diet, high-fat diets mixture with or without SKL-14959 for 151 days, and were monitored body weight and food consumption through the test. Oral glucose tolerance test (OGTT) and insulin tolerance test (ITT) were also performed. After that, blood, liver, muscle and adipose tissue were collected. Blood samples were measured glycosylated hemoglobin A1c (HbA1c), glucose, insulin, GIP level and plasma LPL activity. Triacylglycerol (TG) contents of liver and muscles were also measured. Moreover, a simple correlation analysis was performed.ResultsSKL-14959 suppressed the body weight gain, decreased body mass index (BMI), HbA1c, and fasting glucose level, and trended to decline adipose tissues weight and TG contents compared with the vehicle, and inhibited plasma LPL activity. OGTT and ITT in the SKL-14959 group were not significantly changed relative to the vehicle. Additionally, upon treatment with SKL-14959 treatment, weight gain had weak correlation with lipase activity. Furthermore, lipase activity was associated with the fat mass and not white but red muscle TG contents and liver TG contents were not associated with lipase activity but HbA1c.In ConclusionSKL-14959 might direct lipids metabolism to catabolism by inhibition of plasma LPL activity, resulting in the suppression of weight gain on diets-induced obesity mice.

Incretin Hormones and Type 2 Diabetes-Mechanistic Insights and Therapeutic Approaches.

Simple SummaryWhen we ingest a meal, our intestine secretes hormones that are released into the bloodstream. Amongst these hormones are the incretins hormones which stimulate the release of insulin from the pancreas which is essential for the regulation of in particular postprandial glucose concentrations. In patients with type 2 diabetes, the effect of the incretins is diminished. This is thought to contribute importantly to the pathophysiology of the disease. However, in pharmacological amounts, the incretins may still influence insulin secretion and metabolism. Much research has therefore been devoted to the development of incretin-based therapies for type 2 diabetes. These therapies include compounds that strongly resemble the incretins, hereby stimulating their effects as well as inhibitors of the enzymatic degradation of the hormones, thereby increasing the concentration of incretins in the blood. Both therapeutic approaches have been implemented successfully, but research is still ongoing aimed at the development of further optimized therapies. Glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are secreted from the gut upon nutrient stimulation and regulate postprandial metabolism. These hormones are known as classical incretin hormones and are responsible for a major part of postprandial insulin release. The incretin effect is severely reduced in patients with type 2 diabetes, but it was discovered that administration of GLP-1 agonists was capable of normalizing glucose control in these patients. Over the last decades, much research has been focused on the development of incretin-based therapies for type 2 diabetes. These therapies include incretin receptor agonists and inhibitors of the incretin-degrading enzyme dipeptidyl peptidase-4. Especially the development of diverse GLP-1 receptor agonists has shown immense success, whereas studies of GIP monotherapy in patients with type 2 diabetes have consistently been disappointing. Interestingly, both GIP-GLP-1 co-agonists and GIP receptor antagonists administered in combination with GLP-1R agonists appear to be efficient with respect to both weight loss and control of diabetes, although the molecular mechanisms behind these effects remain unknown. This review describes our current knowledge of the two incretin hormones and the development of incretin-based therapies for treatment of type 2 diabetes.

Chronic glucose-dependent insulinotropic polypeptide receptor (GIPR) agonism desensitizes adipocyte GIPR activity mimicking functional GIPR antagonism

Antagonism or agonism of the glucose-dependent insulinotropic polypeptide (GIP) receptor (GIPR) prevents weight gain and leads to dramatic weight loss in combination with glucagon-like peptide-1 receptor agonists in preclinical models. Based on the genetic evidence supporting GIPR antagonism, we previously developed a mouse anti-murine GIPR antibody (muGIPR-Ab) that protected diet-induced obese (DIO) mice against body weight gain and improved multiple metabolic parameters. This work reconciles the similar preclinical body weight effects of GIPR antagonists and agonists in vivo, and here we show that chronic GIPR agonism desensitizes GIPR activity in primary adipocytes, both differentiated in vitro and adipose tissue in vivo, and functions like a GIPR antagonist. Additionally, GIPR activity in adipocytes is partially responsible for muGIPR-Ab to prevent weight gain in DIO mice, demonstrating a role of adipocyte GIPR in the regulation of adiposity in vivo.

Dose-dependent efficacy of the glucose-dependent insulinotropic polypeptide (GIP) receptor antagonist GIP(3-30)NH2 on GIP actions in humans.

The glucose-dependent insulinotropic polypeptide (GIP) fragment GIP(3-30)NH2 is a selective, competitive GIP receptor antagonist, and doses of 800 to 1200 pmol/kg/min inhibit GIP-induced potentiation of glucose-stimulated insulin secretion by >80% in humans. We evaluated the effects of GIP(3-30)NH2 across a wider dose range in eight healthy men undergoing six separate and randomized 10-mmol/L hyperglycaemic clamps (A-F) with concomitant intravenous infusion of GIP (1.5 pmol/kg/min; A-E) or saline (F). Clamps A to E involved double-blinded, infusions of saline (A) and GIP(3-30)NH2 at four rates: 2 (B), 20 (C), 200 (D) and 2000 pmol/kg/min (E), respectively. Mean plasma concentrations of glucose (A-F) and GIP (A-E) were similar. GIP-induced potentiation of glucose-stimulated insulin secretion was reduced by 44 ± 10% and 84 ± 10% during clamps D and E, respectively. Correspondingly, the amounts of glucose required to maintain the clamp during D and E were not different from F. GIP-induced suppression of bone resorption and increase in heart rate were lowered by clamps D and E. In conclusion, GIP(3-30)NH2 provides extensive, dose-dependent inhibition of the GIP receptor in humans, with most pronounced effects of the doses 200 to 2000 pmol/kg/min within the tested range.