title: Characterization of [¹²⁵I]GLP-1(9-36), a novel radiolabeled analog of the major metabolite of glucagon-like peptide 1 to a receptor distinct from GLP1-R and function of the peptide in murine aorta.
abstract: OBJECTIVE
  Glucagon-like peptide 1 (GLP-1) is an insulin secretagogue, released in response to meal ingestion and efficiently lowers blood glucose in Type 2 diabetic patients. GLP-1(7-36) is rapidly metabolized by dipeptidyl peptidase IV to the major metabolite GLP-1(9-36)-amide, often thought to be inactive. Inhibitors of this enzyme are widely used to treat diabetes. Our aim was to characterize the binding of GLP-1(9-36) to native mouse tissues and to cells expressing GLP1-R as well as to measure functional responses in the mouse aorta compared with GLP-1(7-36).
  
  
  METHODS
  The affinity of [(125)I]GLP-1(7-36) and [(125)I]GLP-1(9-36) was measured in mouse tissues by saturation binding and autoradiography used to determine receptor distribution. The affinity of both peptides was compared in binding to recombinant GLP-1 receptors using cAMP and scintillation proximity assays. Vasoactivity was determined in mouse aortae in vitro.
  
  
  RESULTS
  In cells expressing GLP-1 receptors, GLP-1(7-36) bound with the expected high affinities (0.1 nM) and an EC50 of 0.07 nM in cAMP assays but GLP-1(9-36) bound with 70,000 and 100,000 fold lower affinities respectively. In contrast, in mouse brain, both labeled peptides bound with a single high affinity, with Hill slopes close to unity, although receptor density was an order of magnitude lower for [(125)I]GLP-1(9-36). In functional experiments both peptides had similar potencies, GLP-1(7-36), pD2=7.40 ± 0.24 and GLP-1(9-36), pD2=7.57 ± 0.64.
  
  
  CONCLUSIONS
  These results suggest that GLP-1(9-36) binds and has functional activity in the vasculature but these actions may be via a pathway that is distinct from the classical GLP-1 receptor and insulin secretagogue actions.
authors.affiliation: Clinical Pharmacology Unit, Box 110, Addenbrooke's Hospital, Cambridge CB2 0QQ, UK.
authors.forename: Rhoda E
authors.initials: RE
authors.lastname: Kuc
authors.affiliation: Clinical Pharmacology Unit, Box 110, Addenbrooke's Hospital, Cambridge CB2 0QQ, UK.
authors.forename: Janet J
authors.initials: JJ
authors.lastname: Maguire
authors.affiliation: Clinical Pharmacology Unit, Box 110, Addenbrooke's Hospital, Cambridge CB2 0QQ, UK.
authors.forename: Keith
authors.initials: K
authors.lastname: Siew
authors.affiliation: Pfizer, Cardiovascular Medicine, Cambridge, MA, USA.
authors.forename: Sheena
authors.initials: S
authors.lastname: Patel
authors.affiliation: Pfizer, Cardiovascular Medicine, Cambridge, MA, USA.
authors.forename: David R
authors.initials: DR
authors.lastname: Derksen
authors.affiliation: Pfizer, Cardiovascular Medicine, Cambridge, MA, USA.
authors.forename: V
authors.initials: V
authors.lastname: Margaret Jackson
authors.affiliation: Clinical Pharmacology Unit, Box 110, Addenbrooke's Hospital, Cambridge CB2 0QQ, UK.
authors.forename: Kevin M
authors.initials: KM
authors.lastname: O'Shaughnessey
authors.affiliation: Clinical Pharmacology Unit, Box 110, Addenbrooke's Hospital, Cambridge CB2 0QQ, UK. Electronic address: apd10@medschl.cam.ac.uk.
authors.forename: Anthony P
authors.initials: AP
authors.lastname: Davenport
mesh_terms: D000818:Animals; D001013:Aorta, Thoracic / Q000378:metabolism*; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D005260:Female; D052216:Glucagon-Like Peptide 1 / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism / Q000502:physiology; D000067757:Glucagon-Like Peptide-1 Receptor; D006801:Humans; D007457:Iodine Radioisotopes / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009924:Organ Culture Techniques; D010455:Peptides / Q000737:chemistry* / Q000378:metabolism* / Q000502:physiology; D011485:Protein Binding / Q000502:physiology; D018027:Receptors, Glucagon / Q000737:chemistry* / Q000378:metabolism* / Q000502:physiology
chemical_list: C000593833:GLP1R protein, human; C000593834:Glp1r protein, mouse; D000067757:Glucagon-Like Peptide-1 Receptor; D007457:Iodine Radioisotopes; D010455:Peptides; D018027:Receptors, Glucagon; C114437:glucagon-like peptide-1 (9-36)-amide; D052216:Glucagon-Like Peptide 1
keywords: Cyclic AMP; Glucagon-like peptide 1 (GLP-1); Radioligand binding; Scintillation proximity assay; Vasoconstriction