title: Ultrastructural characterization of mesenchymal stromal cells labeled with ultrasmall superparamagnetic iron-oxide nanoparticles for clinical tracking studies.
abstract: BACKGROUND
  To evaluate survival and engraftment of mesenchymal stromal cells (MSCs) in vivo, it is necessary to track implanted cells non-invasively with a method, which does not influence cellular ultrastructure and functional characteristics. Iron-oxide particles have been applied for cell tracking for years, but knowledge regarding possible cytotoxic ultrastructural changes subsequent to iron-oxide particle labeling is limited. Hence, the purpose of this study was to label MSCs with dextran-coated ultrasmall super-paramagnetic iron-oxide (USPIO) particles conjugated with the transduction sequence of trans-activator of transcription (TAT) (IODEX-TAT) and evaluate the effect of labeling on ultrastructure, viability, phenotype and proliferative capacity of the cells.
  
  
  METHODS
  MSCs were labeled with 5 and 10 μg IODEX-TAT/10(5) cells for 2, 6 and 21 hours. IODEX-TAT uptake and cellular ultrastructure were determined by electron microscopy. Cell viability was determined by propidium iodide staining and cell proliferation capacity by 5-bromo-2-deoxyuridine (BrdU) incorporation. Maintenance of stem cell surface markers was determined by flow cytometry. Results. IODEX-TAT labeling for 2, 6 and 21 h did not influence cellular ultrastructure or viability. Moreover, neither stem cell surface markers nor cell proliferation capacity was affected by labeling with IODEX-TAT.
  
  
  CONCLUSIONS
  Our results demonstrate that labeling of MSCs for 21 h with a clinically relevant dose of 10 μg IODEX-TAT/10(5) cells is feasible and does not affect MSC ultrastructure, viability, phenotype or proliferation capacity.
authors.affiliation: Cardiology Stem Cell Centre, The Heart Centre, Rigshospitalet, University Hospital Copenhagen , Copenhagen , Denmark.
authors.forename: Louise
authors.initials: L
authors.lastname: Hansen
authors.forename: Alastair B
authors.initials: AB
authors.lastname: Hansen
authors.forename: Anders B
authors.initials: AB
authors.lastname: Mathiasen
authors.forename: Michael
authors.initials: M
authors.lastname: Ng
authors.forename: Kishore
authors.initials: K
authors.lastname: Bhakoo
authors.forename: Annette
authors.initials: A
authors.lastname: Ekblond
authors.forename: Jens
authors.initials: J
authors.lastname: Kastrup
authors.forename: Tina
authors.initials: T
authors.lastname: Friis
mesh_terms: D049109:Cell Proliferation; D002470:Cell Survival; D058948:Cell Tracking / Q000379:methods*; D002478:Cells, Cultured; D003911:Dextrans / Q000737:chemistry* / Q000633:toxicity; D005434:Flow Cytometry; D006801:Humans; D058185:Magnetite Nanoparticles / Q000737:chemistry* / Q000633:toxicity; D059630:Mesenchymal Stem Cells / Q000648:ultrastructure*; D013194:Staining and Labeling
chemical_list: D003911:Dextrans; D058185:Magnetite Nanoparticles; C097921:ferumoxtran-10
keywords: Electron microscopy; MSC; SPIO; USPIO; labeling; stem cells; toxicity; ultrastructure