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N-terminally and C-terminally truncated forms of glucose-dependent insulinotropic polypeptide are high-affinity competitive antagonists of the human GIP receptor.

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 (125) I-labelled GIP(1-42), GIP(1-30)NH2 , GIP(2-30)NH2 or GIP(3-30)NH2 . KEY RESULTS:GIP(1-30)NH2 displaced (125) I-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 ((125) I-GIP(1-30)NH2 ), partial agonist ((125) I-GIP(2-30)NH2 ) and competitive antagonist ((125) I-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.

SUBMITTER: Hansen LS

PROVIDER: S-EPMC4761099 | biostudies-literature | 2016 Mar

REPOSITORIES: biostudies-literature

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N-terminally and C-terminally truncated forms of glucose-dependent insulinotropic polypeptide are high-affinity competitive antagonists of the human GIP receptor.

Hansen L S LS Sparre-Ulrich A H AH Christensen M M Knop F K FK Hartmann B B Holst J J JJ Rosenkilde M M MM

British journal of pharmacology 20160130 5

<h4>Background and purpose</h4>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 .<h4>Experimental approach</h4>COS-7 cells were transiently transfected with human GIP rec ...[more]

PMID: 26572091

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Project description:Context:In healthy individuals, glucose-dependent insulinotropic polypeptide (GIP) enhances insulin secretion and reduces bone resorption by up to 25% estimated by absolute placebo-corrected changes in carboxy-terminal type 1 collagen crosslinks (CTX) during GIP and glucose administration. In patients with type 2 diabetes (T2D), GIP's insulinotropic effect is impaired and effects on bone may be reduced. Objective:To investigate GIP's effect on bone biomarkers in patients with T2D. Design:Randomized, double-blinded, crossover study investigating 6 interventions. Patients:Twelve male patients with T2D. Interventions:A primed continuous 90-minute GIP infusion (2 pmol/kg/min) or matching placebo (saline) administered at 3 plasma glucose (PG) levels (i.e., paired days with "insulin-induced hypoglycemia" (PG lowered to 3 mmol/L), "fasting hyperglycemia" (mean PG ~8 mmol/L), or "aggravated hyperglycemia" (mean PG ~12 mmol/L). Main Outcome Measures:Bone biomarkers: CTX, procollagen type 1 N-terminal propeptide (P1NP) and PTH. Results:On days with insulin-induced hypoglycemia, CTX was suppressed by up to 40?±?15% during GIP administration compared with 12?±?11% during placebo infusion (P?<?0.0001). On days with fasting hyperglycemia, CTX was suppressed by up to 36?±?15% during GIP administration, compared with 0?±?9% during placebo infusion (P?<?0.0001). On days with aggravated hyperglycemia, CTX was suppressed by up to 47?±?23% during GIP administration compared with 10?±?9% during placebo infusion (P?=?0.0005). At all glycemic levels, P1NP and PTH concentrations were similar between paired days after 90 minutes. Conclusions:Short-term GIP infusions reduce bone resorption by more than one-third (estimated by absolute placebo-corrected CTX reductions) in patients with T2DM, suggesting preserved bone effects of GIP in these patients. Précis:Short-term GIP infusions reduce the bone resorption marker CTX by one-third in patients with type 2 diabetes independent of glycemic levels.

Project description:There is considerable interest in GIPR agonism to enhance the insulinotropic and extra-pancreatic effects of GIP, thereby improving glycaemic and weight control in type 2 diabetes (T2D) and obesity. Recent genetic epidemiological evidence has implicated higher GIPR-mediated GIP levels in raising coronary artery disease (CAD) risk, a potential safety concern for GIPR agonism. We therefore aimed to quantitatively assess whether the association between higher GIPR-mediated fasting GIP levels and CAD risk is mediated via GIPR or is instead the result of linkage disequilibrium (LD) confounding between variants at the GIPR locus. Using Bayesian multi-trait colocalisation, we identified a GIPR missense variant rs1800437 (G allele; E354) as the putatively causal variant shared between fasting GIP levels, glycaemic traits and adiposity-related traits (posterior probability for colocalisation, PPcoloc>0.97; PP explained by the candidate variant; PPexplained=1) that was independent from a cluster of CAD and lipid traits driven by a known missense variant in APOE (rs7412; distance to E354 ∼770Kb; R2 with E354 = 0.004; PPcoloc>0.99; PPexplained=1). Further, conditioning the association between E354 and CAD on the residual LD with rs7412, we observed slight attenuation in association, but it remained significant (OR per copy of E354 after adjustment 1.03; 95% CI, 1.02, 1.04; P=0.003). Instead, E354's association with CAD was completely attenuated when conditioning on an additional established CAD signal, rs1964272, (R2 with E354=0.27), an intronic variant in SNRPD2 (OR for E354 after adjustment for rs1964272: 1.01; 95% CI, 0.99, 1.03; P=0.06). We demonstrate that associations with GIP, anthropometric and glycaemic traits are driven by distinct genetic signals from those driving CAD and lipid traits in the GIPR region, and higher E354-mediated fasting GIP levels are not associated with CAD risk. These findings provide evidence that the inclusion of GIPR agonism in dual GIPR/GLP-1R agonists could potentiate the protective effect of GLP-1 agonists on diabetes without undue CAD risk, an aspect which has yet to be assessed in clinical trials.

Dataset Information

N-terminally and C-terminally truncated forms of glucose-dependent insulinotropic polypeptide are high-affinity competitive antagonists of the human GIP receptor.

Publications

N-terminally and C-terminally truncated forms of glucose-dependent insulinotropic polypeptide are high-affinity competitive antagonists of the human GIP receptor.

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