title: Insulinotropic actions of nateglinide in type 2 diabetic patients and effects on dipeptidyl peptidase-IV activity and glucose-dependent insulinotropic polypeptide degradation.
abstract: BACKGROUND
  Nateglinide restores early-phase insulin secretion to feeding and reduces postprandial hyperglycaemia in type 2 diabetes. This study evaluated the effects of nateglinide on dipeptidyl peptidase-IV (DPP-IV) activity and glucose-dependent insulinotropic polypeptide (GIP) degradation. Research design and methods Blood samples were collected from type 2 diabetic subjects (n=10, fasting glucose 9.36+/-1.2 mmol/l) following administration of oral nateglinide (120 mg) 10 min prior to a 75 g oral glucose load in a randomised crossover design.
  
  
  RESULTS
  Plasma glucose reached 18.2+/-1.7 and 16.7+/-1.7 mmol/l at 90 min in control and placebo groups (P<0.001). These effects were accompanied by prompt 32% inhibition of DPP-IV activity after 10 min (19.9+/-1.6 nmol/ml per min, P<0.05), reaching a minimum of 1.9+/-0.1 nmol/ml per min at 120 min (P<0.001) after nateglinide. Insulin and C-peptide levels increased significantly compared with placebo, to peak after 90 min at 637.6+/-163.9 pmol/l (P<0.05) and 11.8+/-1.4 mg/l (P<0.01) respectively. DPP-IV-mediated degradation of GIP was significantly less in patients receiving nateglinide compared with placebo. Inhibition of DPP-IV activity corresponded with a time- and concentration-dependent inhibitory effect of nateglinide on DPP-IV-mediated truncation of GIP(1-42) to GIP(3-42) in vitro. Comparison of in vitro inhibition of DPP-IV by nateglinide and vildagliptin revealed IC(50) values of 17.1 and 2.1 microM respectively.
  
  
  CONCLUSIONS
  Although considerably less potent than specified DPP-IV inhibitors, the possibility that some of the beneficial actions of nateglinide are indirectly mediated through DPP-IV inhibition and increased bioavailability of GIP and other incretins merits consideration.
authors.affiliation: School of Biomedical Sciences, University of Ulster, Coleraine BT52 1SA, Northern Ireland, UK. am.mckillop@ulster.ac.uk
authors.forename: Aine M
authors.initials: AM
authors.lastname: McKillop
authors.forename: Nicola A
authors.initials: NA
authors.lastname: Duffy
authors.forename: John R
authors.initials: JR
authors.lastname: Lindsay
authors.forename: Brian D
authors.initials: BD
authors.lastname: Green
authors.forename: S
authors.initials: S
authors.lastname: Patterson
authors.forename: Finbarr P M
authors.initials: FP
authors.lastname: O'Harte
authors.forename: Patrick M
authors.initials: PM
authors.lastname: Bell
authors.forename: Peter R
authors.initials: PR
authors.lastname: Flatt
mesh_terms: D000218:Adamantane / Q000031:analogs & derivatives / Q000494:pharmacology; D003510:Cyclohexanes / Q000494:pharmacology* / Q000627:therapeutic use; D003924:Diabetes Mellitus, Type 2 / Q000188:drug therapy / Q000378:metabolism*; D018819:Dipeptidyl Peptidase 4 / Q000378:metabolism*; D054873:Dipeptidyl-Peptidase IV Inhibitors / Q000494:pharmacology* / Q000627:therapeutic use; D005260:Female; D005749:Gastric Inhibitory Polypeptide / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D008297:Male; D008875:Middle Aged; D000077715:Nateglinide; D009570:Nitriles / Q000494:pharmacology; D010649:Phenylalanine / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000627:therapeutic use; D011759:Pyrrolidines / Q000494:pharmacology; D000077597:Vildagliptin
chemical_list: D003510:Cyclohexanes; D054873:Dipeptidyl-Peptidase IV Inhibitors; D007328:Insulin; D009570:Nitriles; D011759:Pyrrolidines; D000077715:Nateglinide; D010649:Phenylalanine; D005749:Gastric Inhibitory Polypeptide; D018819:Dipeptidyl Peptidase 4; D000077597:Vildagliptin; D000218:Adamantane