title: Characterisation and biological activity of Glu3 amino acid substituted GIP receptor antagonists.
abstract: Glucose-dependent insulinotropic polypeptide (GIP) is an important gastrointestinal hormone, which regulates insulin release and glucose homeostasis, but is rapidly inactivated by enzymatic N-terminal truncation. Here we report the enzyme resistance and biological activity of several Glu(3)-substituted analogues of GIP namely; (Ala(3))GIP, (Lys(3))GIP, (Phe(3))GIP, (Trp(3))GIP and (Tyr(3))GIP. Only (Lys(3))GIP demonstrated moderately enhanced resistance to DPP-IV (p<0.05 to p<0.01) compared to native GIP. All analogues demonstrated a decreased potency in cAMP production (EC(50) 1.47 to 11.02 nM; p<0.01 to p<0.001) with (Lys(3))GIP and (Phe(3))GIP significantly inhibiting GIP-stimulated cAMP production (p<0.05). In BRIN-BD11 cells, (Lys(3))GIP, (Phe(3))GIP, (Trp(3))GIP and (Tyr(3))GIP did not stimulate insulin secretion with both (Lys(3))GIP and (Phe(3))GIP significantly inhibiting GIP-stimulated insulin secretion (p<0.05). Injection of each GIP analogue together with glucose in ob/ob mice significantly increased the glycaemic excursion compared to control (p<0.05 to p<0.001). This was associated with lack of significant insulin responses. (Ala(3))GIP, (Phe(3))GIP and (Tyr(3))GIP, when administered together with GIP, significantly reduced plasma insulin (p<0.05 to p<0.01) and impaired the glucose-lowering ability (p<0.05 to p<0.01) of the native peptide. The DPP-IV resistance and GIP antagonism observed were similar but less pronounced than (Pro(3))GIP. These data demonstrate that position 3 amino acid substitution of GIP with (Ala(3)), (Phe(3)), (Tyr(3)) or (Pro(3)) provides a new class of functional GIP receptor antagonists.
authors.affiliation: School of Biomedical Sciences, University of Ulster, Cromore Road, Coleraine BT52 1SA, Northern Ireland, UK.
authors.forename: Victor A
authors.initials: VA
authors.lastname: Gault
authors.forename: Kerry
authors.initials: K
authors.lastname: Hunter
authors.forename: Nigel
authors.initials: N
authors.lastname: Irwin
authors.forename: Brian D
authors.initials: BD
authors.lastname: Green
authors.forename: Brett
authors.initials: B
authors.lastname: Greer
authors.forename: Patrick
authors.initials: P
authors.lastname: Harriott
authors.forename: Finbarr P M
authors.initials: FP
authors.lastname: O'Harte
authors.forename: Peter R
authors.initials: PR
authors.lastname: Flatt
mesh_terms: D000243:Adenosine Deaminase / Q000502:physiology; D019943:Amino Acid Substitution / Q000235:genetics*; D000818:Animals; D006224:Cricetinae; D003412:Cricetulus; D018819:Dipeptidyl Peptidase 4 / Q000502:physiology; D005749:Gastric Inhibitory Polypeptide / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D018698:Glutamic Acid / Q000737:chemistry / Q000235:genetics*; D006023:Glycoproteins / Q000502:physiology; D006801:Humans; D051379:Mice; D008820:Mice, Obese; D011964:Receptors, Gastrointestinal Hormone / Q000037:antagonists & inhibitors*; D021241:Spectrometry, Mass, Electrospray Ionization
chemical_list: D006023:Glycoproteins; D011964:Receptors, Gastrointestinal Hormone; D018698:Glutamic Acid; D005749:Gastric Inhibitory Polypeptide; C041086:gastric inhibitory polypeptide receptor; C042807:DPP4 protein, human; D018819:Dipeptidyl Peptidase 4; D000243:Adenosine Deaminase