Incretins and other peptides in the treatment of diabetes

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Abstract
Glucagon‐like peptide‐1 (7‐36) amide (GLP‐1) is a gut hormone, released postprandially, which stimulates insulin secretion and insulin gene expression as well as pancreatic B‐cell growth. Together with glucose‐dependent insulinotropic polypeptide (GIP), it is responsible for the incretin effect which is the augmentation of insulin secretion following oral administration of glucose. Patients with Type 2 diabetes have greatly impaired or absent incretin‐mediated insulin secretion which is mainly as a result of decreased secretion of GLP‐1. However, the insulinotropic action of GLP‐1 is preserved in patients with Type 2 diabetes, and this has encouraged attempts to treat Type 2 diabetic patients with GLP‐1. GLP‐1 also possesses a number of potential advantages over existing agents for the treatment of Type 2 diabetes. In addition to stimulating insulin secretion and promoting pancreatic B‐cell mass, GLP‐1 suppresses glucagon secretion, delays gastric emptying and inhibits food intake. Continuous intravenous and subcutaneous administration significantly improves glycaemic control and causes reductions in both HbA1c and body weight. However, GLP‐1 is metabolized extremely rapidly in the circulation by the enzyme dipeptidyl peptidase IV (DPP‐IV). This is the probable explanation for the short‐lived effect of single doses of native GLP‐1, making it an unlikely glucose‐lowering agent. The DPP‐IV resistant analogue, exenatide, has Food and Drug Administration (FDA) approval for the treatment of Type 2 diabetes and selective DPP‐IV inhibitors are under development. Both approaches have demonstrated remarkable efficacy in animal models and human clinical studies. Both are well tolerated and appear to have advantages over current therapies for Type 2 diabetes, particularly in terms of the effects on pancreatic B‐cell restoration and potential weight loss.

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