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Chemical Ablation of Gastric Inhibitory Polypeptide Receptor Action by Daily (Pro³)GIP Administration Improves Glucose Tolerance and Ameliorates Insulin Resistance and Abnormalities of Islet Structure in Obesity-Related Diabetes

¹ School of Biomedical Sciences, University of Ulster, Coleraine, Northern Ireland, U.K
² School of Biology and Biochemistry, Queen’s University of Belfast, Belfast, Northern Ireland, U.K
³ School of Life and Health Sciences, Aston University, Birmingham, U.K
⁴ Department of Pharmaceutical and Medicinal Chemistry, Royal College of Surgeons in Ireland, Dublin, Ireland

Glucose-dependent insulinotropic polypeptide (gastric inhibitory polypeptide [GIP]) is an important incretin hormone secreted by endocrine K-cells in response to nutrient ingestion. In this study, we investigated the effects of chemical ablation of GIP receptor (GIP-R) action on aspects of obesity-related diabetes using a stable and specific GIP-R antagonist, (Pro³)GIP. Young adult ob/ob mice received once-daily intraperitoneal injections of saline vehicle or (Pro³)GIP over an 11-day period. Nonfasting plasma glucose levels and the overall glycemic excursion (area under the curve) to a glucose load were significantly reduced (1.6-fold; P < 0.05) in (Pro³)GIP-treated mice compared with controls. GIP-R ablation also significantly lowered overall plasma glucose (1.4-fold; P < 0.05) and insulin (1.5-fold; P < 0.05) responses to feeding. These changes were associated with significantly enhanced (1.6-fold; P < 0.05) insulin sensitivity in the (Pro³)GIP-treated group. Daily injection of (Pro³)GIP reduced pancreatic insulin content (1.3-fold; P < 0.05) and partially corrected the obesity-related islet hypertrophy and ß-cell hyperplasia of ob/ob mice. These comprehensive beneficial effects of (Pro³)GIP were reversed 9 days after cessation of treatment and were independent of food intake and body weight, which were unchanged. These studies highlight a role for GIP in obesity-related glucose intolerance and emphasize the potential of specific GIP-R antagonists as a new class of drugs for the alleviation of insulin resistance and treatment of type 2 diabetes.

Abbreviations: AUC, area under the curve; DPP, dipeptidyl peptidase; GIP, glucose-dependent insulinotropic polypeptide; GIP-R, GIP receptor; GLP-1, glucagon-like peptide 1

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