Incretin-based therapies in type 2 diabetes mellitus.
BACKGROUND
Glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide are incretins secreted from enteroendocrine cells postprandially in part to regulate glucose homeostasis. Dysregulation of these hormones is evident in type 2 diabetes mellitus (T2DM). Two new drugs, exenatide (GLP-1 mimetic) and sitagliptin [dipeptidyl peptidase (DPP) 4 inhibitor], have been approved by regulatory agencies for treating T2DM. Liraglutide (GLP-1 mimetic) and vildagliptin (DPP 4 inhibitor) are expected to arrive on the market soon.


METHODS
The background of incretin-based therapy and selected clinical trials of these four drugs are reviewed. A MEDLINE search was conducted for published articles using the key words incretin, glucose-dependent insulinotropic polypeptide, GLP-1, exendin-4, exenatide, DPP 4, liraglutide, sitagliptin, and vildagliptin.


RESULTS
Exenatide and liraglutide are injection based. Three-year follow-up data on exenatide showed a sustained weight loss and glycosylated hemoglobin (HbA(1c)) reduction of 1%. Nausea and vomiting are common. Results from phase 3 studies are pending on liraglutide. Sitagliptin and vildagliptin are orally active. In 24-wk studies, sitagliptin reduces HbA(1c) by 0.6-0.8% as monotherapy, 1.8% as initial combination therapy with metformin, and 0.7% as add-on therapy to metformin. Vildagliptin monotherapy lowered HbA(1c) by 1.0-1.4% after 24 wk. Their major side effects are urinary tract and nasopharyngeal infections and headaches. Exenatide and liraglutide cause weight loss, whereas sitagliptin and vildagliptin do not.


CONCLUSIONS
The availability of GLP-1 mimetics and DPP 4 inhibitors has increased our armamentarium for treating T2DM. Unresolved issues such as the effects of GLP-1 mimetics and DPP 4 inhibitors on beta-cell mass, the mechanism by which GLP-1 mimetics lowers glucagon levels, and exactly how DPP 4 inhibitors lead to a decline in plasma glucose levels without an increase in insulin secretion, need further research.
Chia
Chee W
CW
National Institute on Aging, National Institutes of Health, Baltimore, MD 21224-6825, USA.
Egan
Josephine M
JM
D000595:Amino Acid Sequence; D003924:Diabetes Mellitus, Type 2 / Q000188:drug therapy*; D018819:Dipeptidyl Peptidase 4; D054873:Dipeptidyl-Peptidase IV Inhibitors; D004791:Enzyme Inhibitors / Q000009:adverse effects / Q000627:therapeutic use; D052216:Glucagon-Like Peptide 1 / Q000009:adverse effects / Q000031:analogs & derivatives; D006801:Humans; D007004:Hypoglycemic Agents / Q000009:adverse effects / Q000627:therapeutic use; D054795:Incretins / Q000009:adverse effects / Q000627:therapeutic use*; D008954:Models, Biological; D008969:Molecular Sequence Data
D054873:Dipeptidyl-Peptidase IV Inhibitors; D004791:Enzyme Inhibitors; D007004:Hypoglycemic Agents; D054795:Incretins; D052216:Glucagon-Like Peptide 1; C042807:DPP4 protein, human; D018819:Dipeptidyl Peptidase 4