The Role of Islet GLP-1 in the Pathogenesis of Prediabetes

We recently demonstrated that blockade of Glucagon-Like Peptide-1's (GLP-1) receptor (GLP1R) results in changes in islet function without changes in circulating GLP-1. This supports other evidence (rodents and humans) that through the (inducible) expression of a prohormone convertase (PC-1/3), the α-cell can process proglucagon to intact GLP-1. 'Islet' or 'pancreatic' GLP-1 acts in a paracrine fashion to regulate insulin and glucagon secretion. These effects are more pronounced in people with early type 2 diabetes (T2DM). Although pancreatic GLP-1 adapts to support islet function in T2DM, it is unclear if this mechanism is upregulated in prediabetes and whether it contributes to the phenotype(s) observed. Abnormal α-cell responsivity to glucose, measured using G50, is associated with Impaired Fasting Glucose (IFG); β-cell dysfunction is associated with Impaired Glucose Tolerance (IGT). Does IGT (or IFG) represent selective failure of intra-islet GLP-1 to support islet function? In this experiment we will use blockade of GLP1R to probe the contribution of endogenous GLP-1 secretion to the regulation of fasting glucose and islet function in prediabetes

Inclusion criteria

• People with stable weight and no history of diabetes.
• Fasting glucose < 126 mg/dL
• 2hr glucose after 75g OGTT < 200 mg/dL

Exclusion criteria

• Age < 25 or > 70 years (to avoid studying subjects who could have latent type 1 diabetes, or the effects of age extremes in subjects with normal or impaired fasting glucose).
• HbA1c > 6.5%
• Use of any glucose-lowering agents including metformin or sulfonylureas.
• For female subjects: positive pregnancy test at the time of enrollment or study
• History of prior upper abdominal surgery such as adjustable gastric banding, pyloroplasty and vagotomy.
• Active systemic illness or malignancy.
• Symptomatic macrovascular or microvascular disease.