title: Automatic labeling method for injectable 15O-oxygen using hemoglobin-containing liposome vesicles and its application for measurement of brain oxygen consumption by PET.
abstract: BACKGROUND
  The aim of this study was to develop an injectable (15)O-O(2) system using hemoglobin-containing vesicles (HbV), a type of artificial red blood cell, and to investigate the feasibility of (15)O(2)-labeled HbV ((15)O(2)-HbV) to measure cerebral metabolic rate of oxygen (CMRO(2)) in rats.
  
  
  METHODS
  The direct bubbling method was combined with vortexing to enhance labeling efficiency of HbV with (15)O-O(2) gas. L-Cysteine was added as a reductant to protect hemoglobin molecules in HbV from oxidation at different concentrations, and labeling efficiencies were also compared. Measurement of cerebral blood flow (CBF) and CMRO(2) in five normal rats was performed using a small animal PET scanner after the injection of H(2)(15)O and (15)O(2)-HbV to evaluate the precision of hemodynamic parameters quantitatively.
  
  
  RESULTS
  The labeling efficiency of HbV was significantly increased when vortexing and bubbling were combined compared with the simple bubbling method (P<.05). The most efficient method for labeling was bubbling of (15)O-O(2) combined with vortexing and the addition of 2.8 mM L-cysteine in HbV solution. The mean radioactivity of 214.4+/-7.8 MBq/mL HbV was obtained using this method. PET scans using (15)O(2)-HbV and H(2)(15)O yielded a mean CMRO(2) value of 6.8+/-1.4 (mL/min per 100 g) in rats with normal CBF of 51.4+/-7.9 (mL/min per 100 g).
  
  
  CONCLUSIONS
  Addition of l-cysteine to HbV and simple direct bubbling of (15)O-O(2) gas combined with vortexing was the most efficient method for preparation of (15)O(2)-HbV. The present injectable system using (15)O(2)-HbV was successfully utilized to measure CMRO(2) in rats, indicating that this new method could be useful for animal models to measure oxygen metabolism in the brain.
authors.affiliation: Biomedical Imaging Research Center, University of Fukui, Fukui, Japan. tiwaridr@u-fukui.ac.jp
authors.forename: Vijay Narayan
authors.initials: VN
authors.lastname: Tiwari
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Kiyono
authors.forename: Masato
authors.initials: M
authors.lastname: Kobayashi
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Mori
authors.forename: Takashi
authors.initials: T
authors.lastname: Kudo
authors.forename: Hidehiko
authors.initials: H
authors.lastname: Okazawa
authors.forename: Yasuhisa
authors.initials: Y
authors.lastname: Fujibayashi
mesh_terms: D000818:Animals; D001331:Automation; D001921:Brain / Q000000981:diagnostic imaging* / Q000378:metabolism*; D006454:Hemoglobins / Q000378:metabolism*; D007267:Injections; D007553:Isotope Labeling / Q000379:methods*; D007700:Kinetics; D008081:Liposomes / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism*; D010104:Oxygen Radioisotopes / Q000008:administration & dosage / Q000378:metabolism; D049268:Positron-Emission Tomography; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D006454:Hemoglobins; D008081:Liposomes; D010104:Oxygen Radioisotopes; D010100:Oxygen