title: Investigation of the effect of oral metformin on dipeptidylpeptidase-4 (DPP-4) activity in Type 2 diabetes.
abstract: OBJECTIVE
  Glucagon-like peptide-1 (GLP-1) is an insulinotropic hormone and major component of the enteroinsular axis. Its therapeutic potential in human diabetes is limited by rapid degradation and inactivation by the enzyme dipeptidylpeptidase-4 (DPP-4). We investigated the acute effects of metformin with and without food on DPP-4 activity in Type 2 diabetes.
  
  
  METHODS
  Ten subjects with Type 2 diabetes (6 male/4 female, age 65.8 +/- 2.6 years, body mass index 30.0 +/- 1.2 kg/m2, glycated haemoglobin (HbA(1c)) 6.3 +/- 0.2%, mean +/- SEM) received metformin 1 g orally or placebo together with a standard mixed meal (SMM) in a random crossover design. Six subjects re-attended fasting and received metformin 1 g without a SMM.
  
  
  RESULTS
  Following SMM (n = 10), DPP-4 activity was not suppressed by metformin compared with placebo [area under curve (AUC)(0-4 h) 1574 +/- 4 vs. 1581 +/- 8 micromol/ml/min, respectively]. Plasma glucose, insulin and active GLP-1 were not different. However, DPP-4 activity was suppressed with metformin following fasting compared with a SMM (n = 6) (AUC(0-4 h) 1578 +/- 4 vs. 1494 +/- 9 micromol/min, P < 0.02). Metformin serum levels were significantly lower (P < 0.001) after SMM than fasting (AUC(0-4 h) 350 +/- 66 vs. 457 +/- 55 mg/ml/min).
  
  
  CONCLUSIONS
  Metformin inhibits DPP-4 activity in Type 2 diabetic patients in the fasting state but not when taken with a standard mixed meal. Metformin serum concentrations are lower if the drug is taken with food. These findings should be taken into account in establishing how to maximize efficacy of the drug.
authors.affiliation: Regional Centre for Endocrinology and Diabetes, Royal Victoria Hospital, Belfast BT12 6BA, Northern Ireland, UK.
authors.forename: J
authors.initials: J
authors.lastname: Cuthbertson
authors.forename: S
authors.initials: S
authors.lastname: Patterson
authors.forename: F P M
authors.initials: FP
authors.lastname: O'Harte
authors.forename: P M
authors.initials: PM
authors.lastname: Bell
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001786:Blood Glucose / Q000378:metabolism*; D018592:Cross-Over Studies; D003924:Diabetes Mellitus, Type 2 / Q000097:blood / Q000188:drug therapy*; D054873:Dipeptidyl-Peptidase IV Inhibitors / Q000097:blood; D004435:Eating / Q000502:physiology; D005215:Fasting / Q000097:blood; D005260:Female; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology / Q000627:therapeutic use*; D008297:Male; D008687:Metformin / Q000494:pharmacology / Q000627:therapeutic use*; D008875:Middle Aged
chemical_list: D001786:Blood Glucose; D054873:Dipeptidyl-Peptidase IV Inhibitors; D007004:Hypoglycemic Agents; D008687:Metformin