Effects of the novel (Pro3)GIP antagonist and exendin(9–39)amide on GIP- and GLP-1-induced cyclic AMP generation, insulin secretion and postprandial insulin release in obese diabetic (ob/ob) mice: evidence that GIP is the major physiological incretin

Abstract

Aims/hypothesis. This study examined the biological effects of the GIP receptor antagonist, (Pro 3 )GIP and the GLP-1 receptor antagonist, exendin(9-39)amide. Methods Cyclic AMP production was assessed in Chinese hamster lung fibroblasts transfected with human GIP or GLP-1 receptors, respectively. In vitro insulin release studies were assessed in BRIN-BD11 cells while in vivo insulinotropic and glycaemic responses were measured in obese diabetic (ob/ob) mice. Results. In GIP receptor-transfected fibroblasts, (Pro 3 )-GIP or exendin(9-39)amide inhibited GIP-stimulated cyclic AMP production with maximal inhibition of 70.0±3.5% and 73.5±3.2% at 10 −6 mol/l, respectively. In GLP-1 receptor-transfected fibroblasts, exendin-(9-39)amide inhibited GLP-1-stimulated cyclic AMP production with maximal inhibition of 60±0.7% at 10 −6 mol/l, whereas (Pro 3 )GIP had no effect. (Pro 3 )-GIP specifically inhibited GIP-stimulated insulin release (86%; p<0.001) from clonal BRIN-BD11 cells, but had no effect on GLP-1-stimulated insulin release. In contrast, exendin(9-39)amide inhibited both GIP and GLP-1-stimulated insulin release (57% and 44%, respectively; p<0.001). Administration of (Pro 3 )GIP, exendin(9-39)amide or a combination of both peptides (25 nmol/kg body weight, i.p.) to fasted (ob/ob) mice decreased the plasma insulin responses by 42%, 54% and 49%, respectively (p<0.01 to p<0.001). The hyperinsulinaemia of non-fasted (ob/ob) mice was decreased by 19%, 27% and 18% (p<0.05 to p<0.01) by injection of (Pro 3 )GIP, exendin(9-39)amide or combined peptides but accompanying changes of plasma glucose were small. Conclusions/interpretation. These data show that (Pro 3 )GIP is a specific GIP receptor antagonist. Furthermore, feeding studies in one commonly used animal model of obesity and diabetes, (ob/ob) mice, suggest that GIP is the major physiological component of the enteroinsular axis, contributing approximately 80% to incretin-induced insulin release. [Diabetologia (2003) 46:222-230] Keywords Enteroinsular axis, GIP receptor antagonist, glucagon-like peptide-1, glucose-dependent insulinotropic polypeptide, insulin release. The insulin secretory activity of pancreatic beta cells can be modulated in both a positive or negative manner by several peptide hormones and neurotransmitters [1,2,3]. The two intestinal hormones, glucosedependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1-(7-36)amide (GLP-1) have long been recognised as potent stimulators of insulin secretion under physiological conditions, and for that reason they are considered important incretin hormones [4,5,6]. The effects of both GIP and GLP-1 are glucose-dependent, providing a safeguard against potentially hazardous hypoglycaemic episodes, and as a

Early administration of the glucose-dependent insulinotropic polypeptide receptor antagonist (Pro3)GIP prevents the development of diabetes and related metabolic abnormalities associated with genetically inherited obesity in ob/ob mice

“…In normal mice, genetic knockout or chemical antagonism of the GIP receptor clearly results in mild impairments of glucose homeostasis and insulin secretion [34,45]. Similar effects were produced by acute as opposed to longer-term administration of (Pro 3 )GIP to adult ob/ob mice [36]. Viewed in simple terms, ablation of GIP receptor function in normal mice resulted in modest detrimental deficits in insulin release, as also observed when ob/ob mice were administered (Pro 3 ) GIP acutely.…”

“…injections (17:00 h) of either saline vehicle (0.9% [w/v] NaCl) or (Pro 3 )GIP (25 nmol/kg body weight). This dose of (Pro 3 ) GIP was chosen on the basis of earlier studies showing blockade of glucoregulatory effects of exogenous and endogenous GIP in ob/ob mice [35,36]. The once daily dosing regimen has also proved effective in longer-term studies [32,34].…”

Genetic variation of the adenylyl cyclase 3 (AC3) locus and its influence on type 2 diabetes and obesity susceptibility in Swedish men

“…19 ACs 1, 3 and 8, are most abundantly expressed in the brain and islets, where the cells need an elevated cAMP level to respond to multiple stimuli. [20][21][22] AC3 may play an interactive role with GLP-1, GIP and AR in control of insulin release and lipolysis. Therefore, a comprehensive analysis of AC3 in regulation of signaling by GLP-1, GIP and AR is necessary in order to understand the cellular mechanisms behind the postulated influence of AC3 genetic variation on BMI and other related metabolic features in T2D and obesity.…”

Functional expression of glucose-dependent insulinotropic polypeptide receptors is coupled to differentiation in a human adipocyte model

“…In a study using antagonists for the GLP1 and GIP receptors (GIPRs), it was shown that GIP is the major physiological incretin, contributing to 80% of the incretin-induced insulin release. 1 GIP is a 42-amino-acid peptide secreted by the lymphocyte K cells, which are located within the intestinal epithelium of the proximal deuodenum and is primarily regulated by ingestion of glucose or fat. 2,3 The molecular mechanisms whereby GIP potentiates glucosedependant insulin secretion by b-cells include increases in cAMP, inhibition of K ATP channels, increases in intracellular Ca 2 þ and stimulation of exocytosis.…”