Incretins: pathophysiological and therapeutic implications of glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1

Incretins such as glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) are intestinal postprandial hormones that stimulate insulin release from the pancreas as long as circulating glucose concentrations are raised. In addition to their effect on insulin secretion and consequent glucose lowering, GIP and GLP-1, especially the latter, have a number of physiological effects such as inhibition of glucagon release, gastric emptying and food intake, as well as a tropic action on pancreatic B-cell mass. There is currently a pandemic of obesity and diabetes, and existing treatments are largely inadequate both in regard to efficacy as well as their ability to tackle important factors in the pathogenesis of type 2 diabetes (T2D). There is increasing evidence that current treatments do not address the issue of progressive B-cell failure in T2D. Since obesity is the engine that is driving the epidemic of diabetes, it is disappointing that most treatments that succeed in lowering plasma glucose are also associated with weight gain. It is now well established that intensively treated T2D has a better outcome than standard treatment. Consequently, achieving better control of diabetes with lower HbA1c is the goal of optimal treatment. Despite the use of usual therapeutic agents in T2D, often in high doses and as combinations, such as metformin, sulphonylurea, α-glycosidase inhibitors, thiazolidinediones and a number of animal and human insulin preparations, optimal control of glycaemia is not achieved. The use of incretins as therapeutic agents offers a new approach to the treatment of T2D.