title: Specific Amyloid Binding of Polybasic Peptides In Vivo Is Retained by β-Sheet Conformers but Lost in the Disrupted Coil and All D-Amino Acid Variants.
abstract: OBJECTIVE
  The heparin-reactive, helical peptide p5 is an effective amyloid imaging agent in mice with systemic amyloidosis. Analogs of p5 with modified secondary structure characteristics exhibited altered binding to heparin, synthetic amyloid fibrils, and amyloid extracts in vitro. Herein, we further study the effects of peptide helicity and chirality on specific amyloid binding using a mouse model of systemic inflammation-associated (AA) amyloidosis.
  
  
  METHODS
  Peptides with disrupted helical structure [p5(coil)and p5(Pro3)], with an extended sheet conformation [p5(sheet)] or an all-D enantiomer [p5(D)], were chemically synthesized, radioiodinated, and their biodistribution studied in WT mice as well as transgenic animals with severe systemic AA amyloidosis. Peptide binding was assessed qualitatively by using small animal single-photon emission computed tomography/x-ray computed tomography imaging and microautoradiography and quantitatively using tissue counting.
  
  
  RESULTS
  Peptides with reduced helical propensity, p5(coil)and p5(Pro3), exhibited significantly reduced binding to AA amyloid-laden organs. In contrast, peptide p5(D)was retained by non-amyloid-related ligands in the liver and kidneys of both WT and AA mice, but it also bound AA amyloid in the spleen. The p5(sheet)peptide specifically bound AA amyloid in vivo and was not retained by healthy tissues in WT animals.
  
  
  CONCLUSIONS
  Modification of amyloid-targeting peptides using D-amino acids should be performed cautiously due to the introduction of unexpected secondary pharmacologic effects. Peptides that adopt a helical structure, to align charged amino acid side chains along one face, exhibit specific reactivity with amyloid; however, polybasic peptides with a propensity for β-sheet conformation are also amyloid-reactive and may yield a novel class of amyloid-targeting agents for imaging and therapy.
authors.affiliation: Departments of Medicine, Graduate School of Medicine, University of Tennessee, 1924 Alcoa Hwy, Knoxville, TN, 37920, USA. jwall@utmck.edu.|Departments of Radiology, Graduate School of Medicine, University of Tennessee, 1924 Alcoa Hwy, Knoxville, TN, 37920, USA. jwall@utmck.edu.
authors.forename: Jonathan S
authors.initials: JS
authors.lastname: Wall
authors.affiliation: Departments of Medicine, Graduate School of Medicine, University of Tennessee, 1924 Alcoa Hwy, Knoxville, TN, 37920, USA.
authors.forename: Angela
authors.initials: A
authors.lastname: Williams
authors.affiliation: Departments of Medicine, Graduate School of Medicine, University of Tennessee, 1924 Alcoa Hwy, Knoxville, TN, 37920, USA.
authors.forename: Tina
authors.initials: T
authors.lastname: Richey
authors.affiliation: Departments of Radiology, Graduate School of Medicine, University of Tennessee, 1924 Alcoa Hwy, Knoxville, TN, 37920, USA.
authors.forename: Alan
authors.initials: A
authors.lastname: Stuckey
authors.affiliation: Departments of Medicine, Graduate School of Medicine, University of Tennessee, 1924 Alcoa Hwy, Knoxville, TN, 37920, USA.
authors.forename: Craig
authors.initials: C
authors.lastname: Wooliver
authors.affiliation: Departments of Medicine, Graduate School of Medicine, University of Tennessee, 1924 Alcoa Hwy, Knoxville, TN, 37920, USA.
authors.forename: J
authors.initials: J
authors.lastname: Christopher Scott
authors.affiliation: Department of Pathobiology, University of Tennessee College of Veterinary Medicine, 2407 River Drive, Knoxville, TN, 37996, USA.
authors.forename: Robert
authors.initials: R
authors.lastname: Donnell
authors.affiliation: Departments of Medicine, Graduate School of Medicine, University of Tennessee, 1924 Alcoa Hwy, Knoxville, TN, 37920, USA.
authors.forename: Emily B
authors.initials: EB
authors.lastname: Martin
authors.affiliation: Departments of Medicine, Graduate School of Medicine, University of Tennessee, 1924 Alcoa Hwy, Knoxville, TN, 37920, USA.|Departments of Radiology, Graduate School of Medicine, University of Tennessee, 1924 Alcoa Hwy, Knoxville, TN, 37920, USA.
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Kennel
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000235:genetics*; D000682:Amyloid / Q000378:metabolism*; D000686:Amyloidosis / Q000000981:diagnostic imaging / Q000473:pathology; D000818:Animals; D001345:Autoradiography; D007457:Iodine Radioisotopes / Q000737:chemistry; D008822:Mice, Transgenic; D009154:Mutation / Q000235:genetics*; D010455:Peptides / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding; D000072757:Protein Conformation, beta-Strand; D000072098:Single Photon Emission Computed Tomography Computed Tomography; D014018:Tissue Distribution
chemical_list: D000596:Amino Acids; D000682:Amyloid; D007457:Iodine Radioisotopes; D010455:Peptides
keywords: AA amyloidosis; Amyloid binding; Biodistribution; Peptides; SPECT/CT