1948-P: Secretion of the Short-Form Gastric Inhibitory Polypeptide in Nondiabetic and Diabetic Subjects

We previously reported that the short-form gastric inhibitory polypeptide (GIP) 1-30 is released from islet alpha cells and promotes insulin secretion in a paracrine manner in vitro. However, the role played by GIP 1-30 in glucose metabolism in vivo remains unclear. We developed an enzyme-linked immunosorbent assay (ELISA) specific for GIP 1-30 and measured GIP 1-30 secretion in nondiabetic subjects (ND, n = 8) and patients with type 2 diabetes (T2D, n = 9). We developed a sandwich ELISA by combining a novel antibody to the GIP C-terminus with the N-terminal anti-GIP 1-42 antibody that is already available. We explored cross-reactivities with incretins and glucagon-related peptides. We next subjected ND and T2D subjects to the cookie meal test (CMT: carbohydrates 75 g, lipids 28.5 g, proteins 8.5 g) and measured GIP 1-30 blood levels. Absorbance increased in a dose-dependent manner on addition of the GIP 1-30 amide but not GIP 1-42, GLP-1, or glucagon. Post-CMT loading, GIP 1-30 concentrations increased in both ND and T2D subjects; however, in ND subjects, the increases were much lower than those of GIP 1-42 (GIP 1-30, before loading: 1.4 ± 0.5 pmol/L, after: 1.9 ± 0.6 pmol/L; GIP 1-42, before: 8.2 ± 0.1 pmol/L, after: 204.0 ± 35.2 pmol/L, P<0.05). In T2D patients, the GIP 1-30 levels, as assessed by the areas under the curves, tended to be lower than those in ND patients. The DPP-4 inhibitor significantly increased both GIP 1-30 and GIP 1-42 secretion in T2D patients.

In conclusion, we developed a novel ELISA that is highly specific for GIP 1-30, the secretion of which was promoted by a mixed meal to a blood level lower than that of GIP 1-42. As is also true of the incretins, GIP 1-30 levels increased upon administration of DPP-4 inhibitor; GIP 1-30 secretion may differ between ND and T2D subjects.