GIP Contributes to Islet Trihormonal Abnormalities in Type 2 Diabetes

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Abstract

Context:

Research and clinical treatments on type 2 diabetes mainly focus on insulin deficiency with little attention paid to other islet hormones.

Objective:

This study tested the hypothesis that glucose-dependent insulinotropic polypeptide (GIP) is involved in diabetes-associated multiislet hormone dysregulation.

Design:

This paper included a case-control study involving 92 community-based volunteers from the Baltimore Longitudinal Study of Aging (BLSA): 23 with type 2 diabetes on glucose-lowering agents, 25 with newly diagnosed drug-naïve type 2 diabetes, 19 with prediabetes, and 25 with normal glucose tolerance; a separate intervention study with 13 non-BLSA volunteers with type 2 diabetes treated with diet alone, metformin, and/or metformin/sulfonylurea combination; a rodent study; and an in vitro cell line study.

Interventions:

An oral glucose tolerance test was performed in the BLSA participants. For the intervention study, saline (0.9% NaCl) or synthetic human GIP (20 ng · kg−1 · min−1) was administered to type 2 diabetes subjects for 180 minutes together with a meal, and plasma samples were obtained at predetermined intervals for 360 minutes. A bolus of GIP or placebo was given to C57BL/6 mice.

Main Outcome Measures:

Plasma glucose, insulin, glucagon, pancreatic polypeptide (PP), glucagon-like peptide-1 (GLP-1), and GIP were measured.

Results:

After an oral glucose tolerance test, glucose, glucagon, PP, GLP-1, and GIP levels were significantly elevated in type 2 diabetes groups, compared with normal and prediabetes groups. GIP infusion in type 2 diabetes subjects was associated with significantly elevated PP levels compared with placebo. The GIP bolus given to C57BL/6 mice was followed by increased PP levels. GIP receptors were found in both human and mouse PP cells.

Conclusions:

Up-regulation of GIP production may play an important role in multihormonal dysregulation in type 2 diabetes, most likely through interaction with GIP receptors on islets.

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