title: Inhibition of dipeptidyl peptidase-4 augments insulin secretion in response to exogenously administered glucagon-like peptide-1, glucose-dependent insulinotropic polypeptide, pituitary adenylate cyclase-activating polypeptide, and gastrin-releasing peptide in mice.
abstract: Inhibition of dipeptidyl peptidase-4 (DPP-4) is currently being explored as a new approach to the treatment of type 2 diabetes. This concept has emerged from the powerful and rapid action of the enzyme to inactivate glucagon-like peptide-1 (GLP-1). However, other bioactive peptides with potential influence of islet function are also substrates of DPP-4. Whether this inactivation may add to the beneficial effects of DPP-4 inhibition is not known. In this study, we explored whether DPP-4 inhibition by valine-pyrrolidide (val-pyr; 100 micromol/kg administered through gastric gavage at t = -30 min) affects the insulin and glucose responses to iv glucose (1 g/kg) together with GLP-1 (10 nmol/kg), glucose-dependent insulinotropic polypeptide (GIP; 10 nmol/kg), pituitary adenylate cyclase-activating polypeptide 38 (PACAP38; 1.3 nmol/kg), or gastrin-releasing peptide (GRP; 20 nmol/kg) given at t = 0 in anesthetized C57BL/6J mice. It was found that the acute (1-5 min) insulin response to GLP-1 was augmented by val-pyr by 80% (4.2 +/- 0.4 vs. 7.6 +/- 0.8 nmol/liter), that to GIP by 40% (2.7 +/- 0.3 vs. 3.8 +/- 0.4 nmol/liter), that to PACAP38 by 75% (4.6 +/- 0.5 vs. 8.1 +/- 0.6 nmol/liter), and that to GRP by 25% (1.8 +/- 0.2 vs. 2.3 +/- 0.3 nmol/liter; all P < 0.05 or less). This was associated with enhanced glucose elimination rate after GLP-1 [glucose elimination constant (K(G)) 2.1 +/- 0.2 vs. 3.1 +/- 0.3%/min] and PACAP38 (2.1 +/- 0.3 vs. 3.2 +/- 0.3%/min; both P < 0.01), but not after GIP or GRP. The augmented insulin response to GRP by val-pyr was prevented by the GLP-1 receptor antagonist, exendin(3) (9-39), raising the possibility that GRP effects may occur secondary to stimulation of GLP-1 secretion. We conclude that DPP-4 inhibition augments the insulin response not only to GLP-1 but also to GIP, PACAP38, and GRP.
authors.affiliation: Department of Medicine, Lund University, B11 BMC, SE-221 84 Lund, Sweden. bo.ahren@med.lu.se
authors.forename: Bo
authors.initials: B
authors.lastname: Ahrén
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Hughes
mesh_terms: D000818:Animals; D018819:Dipeptidyl Peptidase 4 / Q000502:physiology*; D005260:Female; D005749:Gastric Inhibitory Polypeptide / Q000494:pharmacology*; D019886:Gastrin-Releasing Peptide / Q000494:pharmacology*; D005934:Glucagon / Q000494:pharmacology*; D052216:Glucagon-Like Peptide 1; D005947:Glucose / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D051379:Mice; D008810:Mice, Inbred C57BL; D009414:Nerve Growth Factors / Q000494:pharmacology*; D009479:Neuropeptides / Q000494:pharmacology*; D018377:Neurotransmitter Agents / Q000494:pharmacology*; D010446:Peptide Fragments / Q000494:pharmacology*; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D011480:Protease Inhibitors / Q000494:pharmacology*; D011498:Protein Precursors / Q000494:pharmacology*; D011758:Pyrroles / Q000494:pharmacology*; D014633:Valine / Q000494:pharmacology*
chemical_list: C495402:Adcyap1 protein, mouse; D007328:Insulin; D009414:Nerve Growth Factors; D009479:Neuropeptides; D018377:Neurotransmitter Agents; D010446:Peptide Fragments; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D011480:Protease Inhibitors; D011498:Protein Precursors; D011758:Pyrroles; C112092:valine-pyrrolidide; D005749:Gastric Inhibitory Polypeptide; D019886:Gastrin-Releasing Peptide; D052216:Glucagon-Like Peptide 1; D005934:Glucagon; D018819:Dipeptidyl Peptidase 4; D014633:Valine; D005947:Glucose