title: Molecular imaging of heparan sulfate expression with radiolabeled recombinant eosinophil cationic protein predicts allergic lung inflammation in a mouse model for asthma.
abstract: Heparan sulfate proteoglycans (HSPGs) are glycoproteins consisting of a core protein to which linear heparan sulfate (HS) side chains are covalently attached. These HS side chains mediate a variety of biologic functions involved in inflammation. Radionuclide imaging of HS side chains in tissues with inflammation may be used for the stratification of patients who would most likely benefit from HSPG-targeting therapy. The goal of this study was to evaluate the feasibility of in vivo radionuclide imaging of HS side chain expression in a mouse model of asthma using the recombinant eosinophil cationic protein (rECP).
  
  
  METHODS
  rECP was radioiodinated with (125)I or (123)I using the Chloramine-T method. The 50% inhibitory concentration value for (125)I-labeled rECP was determined in a competitive cell-binding assay using Beas-2B cells. The binding of radiolabeled rECP to HS side chains was evaluated both in vitro and in vivo. The biodistribution of radiolabeled rECP was assessed in asthma mice or in control mice using SPECT imaging, ex vivo biodistribution measurements, and microautoradiography.
  
  
  RESULTS
  The 50% inhibitory concentration value for (125)I-rECP was 7.4 ± 0.1 nM. The loss of HS side chains substantially inhibited the cellular and tissue uptake of (125)I- or (123)I-rECP, indicating that HS side chains of HSPGs are required for (125)I- or (123)I-eosinophil cationic protein binding and uptake both in vitro and in vivo. SPECT imaging demonstrated an appreciably higher accumulation of radioactivity in the lungs of asthma mice than in those of control mice. Ex vivo biodistribution studies also confirmed that there was at least a 4-fold increase in the lung-to-muscle ratio of asthma mice, compared with control mice. The accumulation of radiolabeled rECP was linearly correlated with leukocyte infiltration.
  
  
  CONCLUSIONS
  This study illustrates the feasibility of using radiolabeled rECP for the visualization of HS side chains of HSPGs and the evaluation of allergic lung inflammation in living subjects. Our data indicate that radiolabeled rECP is a novel imaging agent for HS side chains of HSPGs in predicting allergic lung inflammation in living mice.
authors.affiliation: Graduate Institute of Basic Medical Science, China Medical University, Taichung, Taiwan.
authors.forename: Hui-Chen
authors.initials: HC
authors.lastname: Chen
authors.forename: Hao-Teng
authors.initials: HT
authors.lastname: Chang
authors.forename: Po-Han
authors.initials: PH
authors.lastname: Huang
authors.forename: Margaret Dah-Tsyr
authors.initials: MD
authors.lastname: Chang
authors.forename: Ren-Shyan
authors.initials: RS
authors.lastname: Liu
authors.forename: Yu-Jung
authors.initials: YJ
authors.lastname: Lin
authors.forename: Chia-Hung
authors.initials: CH
authors.lastname: Hsieh
mesh_terms: D000485:Allergens / Q000276:immunology; D000818:Animals; D001249:Asthma / Q000150:complications* / Q000000981:diagnostic imaging / Q000276:immunology; D001692:Biological Transport; D045744:Cell Line, Tumor; D004195:Disease Models, Animal; D004355:Drug Stability; D047150:Eosinophil Cationic Protein / Q000378:metabolism / Q000493:pharmacokinetics; D005260:Female; D005786:Gene Expression Regulation; D006497:Heparan Sulfate / Q000378:metabolism*; D006801:Humans; D006967:Hypersensitivity / Q000150:complications*; D007249:Inflammation / Q000000981:diagnostic imaging / Q000276:immunology; D007457:Iodine Radioisotopes; D007553:Isotope Labeling; D007962:Leukocytes / Q000276:immunology; D051379:Mice; D057054:Molecular Imaging / Q000379:methods*; D064847:Multimodal Imaging; D049268:Positron-Emission Tomography; D011854:Radiochemistry; D011994:Recombinant Proteins / Q000378:metabolism / Q000493:pharmacokinetics; D014057:Tomography, X-Ray Computed
chemical_list: D000485:Allergens; D047150:Eosinophil Cationic Protein; D006497:Heparan Sulfate; D007457:Iodine Radioisotopes; D011994:Recombinant Proteins
keywords: allergic inflammation; asthma, single-photon emission computed tomography; heparan sulfate proteoglycans; recombinant eosinophil cationic protein