[The incretin effect: a new therapeutic target in type 2 diabetes].
ABSTRACT The two incretin hormones GLP-1 (Glucagon-Like Peptide-1) and GIP (Glucose-dependent Insulinotropic Peptide) are released by the gut in response to nutrient ingestion. Both of them potentiate glucose-induced insulin response, enhance insulin biosynthesis and, at least in rodents, preserve beta-cell mass through reduction of apoptosis and stimulation of beta-cell proliferation. In addition to its insulinotropic action, GLP-1 (but not GIP) suppresses glucagon secretion, delays gastric emptying and promotes satiety. Since in type 2 diabetes, the secretion of GLP-1 is dramatically reduced whereas its effects are retained, a number of pharmacological strategies aiming at restoring the incretin activity of this peptide have been explored. Because GLP-1 is rapidly degraded by the ubiquitous enzyme, dipeptidyl peptidase-IV (DPP-IV) and has a very short-lived action, DPP-IV resistant mimetics have been designed. Several randomized placebo-controlled studies with DPP-IV resistant GLP-1 analogues confirmed their efficacy to improve glycemic control in type 2 diabetic patients. The first one, exenatide, has been approved by the Food and Drug Administration (FDA) in 2005 for the treatment of type 2 diabetes. Longer-acting mimetics requiring only one injection per day or even per week are currently assessed in phase 3 trials. Another successful approach has been the development of orally active DPP-IV inhibitors which reversibly and selectively block the enzymatic activity. Many small-molecule DPP-IV inhibitors, called gliptins, have been shown to be effective as antihyperglycemic agents and, up to now, devoid of major adverse events. The first drug of this new therapeutic class having received FDA approval, sitagliptin, is now available for the treatment of type 2 diabetes in U.S. However, the efficacy/safety profile of these compounds and their positioning in the therapeutic algorithm of type 2 diabetes remains to be defined.