title: Delta-tocotrienol protects mouse and human hematopoietic progenitors from gamma-irradiation through extracellular signal-regulated kinase/mammalian target of rapamycin signaling.
abstract: BACKGROUND
  Exposure to γ-radiation causes rapid hematopoietic cell apoptosis and bone marrow suppression. However, there are no approved radiation countermeasures for the acute radiation syndrome. In this study, we demonstrated that natural δ-tocotrienol, one of the isomers of vitamin E, significantly enhanced survival in total body lethally irradiated mice. We explored the effects and mechanisms of δ-tocotrienol on hematopoietic progenitor cell survival after γ-irradiation in both in vivo and in vitro experiments.
  
  
  METHODS
  CD2F1 mice and human hematopoietic progenitor CD34(+) cells were treated with δ-tocotrienol or vehicle control 24 h before or 6 h after γ-irradiation. Effects of δ-tocotrienol on hematopoietic progenitor cell survival and regeneration were evaluated by clonogenicity studies, flow cytometry, and bone marrow histochemical staining. δ-tocotrienol and γ-irradiation-induced signal regulatory activities were assessed by immunofluorescence staining, immunoblotting and short-interfering RNA assay.
  
  
  RESULTS
  δ-tocotrienol displayed significant radioprotective effects. A single injection of δ-tocotrienol protected 100% of CD2F1 mice from total body irradiation-induced death as measured by 30-day post-irradiation survival. δ-tocotrienol increased cell survival, and regeneration of hematopoietic microfoci and lineage(-)/Sca-1(+)/ckit(+) stem and progenitor cells in irradiated mouse bone marrow, and protected human CD34(+) cells from radiation-induced damage. δ-tocotrienol activated extracellular signal-related kinase 1/2 phosphorylation and significantly inhibited formation of DNA-damage marker γ-H2AX foci. In addition, δ-tocotrienol up-regulated mammalian target of rapamycin and phosphorylation of its downstream effector 4EBP-1. These alterations were associated with activation of mRNA translation regulator eIF4E and ribosomal protein S6, which is responsible for cell survival and growth. Inhibition of extracellular signal-related kinase 1/2 expression by short interfering RNA abrogated δ-tocotrienol-induced mammalian target of rapamycin phosphorylation and clonogenicity, and increased γ-H2AX foci formation in irradiated CD34(+) cells.
  
  
  CONCLUSIONS
  Our data indicate that δ-tocotrienol protects mouse bone marrow and human CD34(+) cells from radiation-induced damage through extracellular signal-related kinase activation-associated mammalian target of rapamycin survival pathways.
authors.affiliation: Radiation Countermeasures Program, Armed Forces Radiobiology Research Institute, Uniformed Services University of the Health Sciences, 8901 Wisconsin Ave, Bethesda, MD 20889-5603, USA.
authors.forename: Xiang Hong
authors.initials: XH
authors.lastname: Li
authors.forename: Dadin
authors.initials: D
authors.lastname: Fu
authors.forename: Nabil H
authors.initials: NH
authors.lastname: Latif
authors.forename: Conor P
authors.initials: CP
authors.lastname: Mullaney
authors.forename: Patrick H
authors.initials: PH
authors.lastname: Ney
authors.forename: Steven R
authors.initials: SR
authors.lastname: Mog
authors.forename: Mark H
authors.initials: MH
authors.lastname: Whitnall
authors.forename: Venkataraman
authors.initials: V
authors.lastname: Srinivasan
authors.forename: Mang
authors.initials: M
authors.lastname: Xiao
mesh_terms: D000818:Animals; D018952:Antigens, CD34 / Q000378:metabolism; D015153:Blotting, Western; D001854:Bone Marrow Cells / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D002478:Cells, Cultured; D004307:Dose-Response Relationship, Radiation; D004789:Enzyme Activation / Q000187:drug effects / Q000528:radiation effects; D039561:Eukaryotic Initiation Factor-4E / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000235:genetics / Q000378:metabolism*; D005720:Gamma Rays; D006412:Hematopoietic Stem Cells / Q000187:drug effects* / Q000378:metabolism / Q000528:radiation effects; D006657:Histones / Q000378:metabolism; D006801:Humans; D008297:Male; D051379:Mice; D008856:Microscopy, Fluorescence; D010766:Phosphorylation / Q000187:drug effects / Q000528:radiation effects; D034622:RNA Interference; D038601:Ribosomal Protein S6 / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000528:radiation effects; D016019:Survival Analysis; D058570:TOR Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D014810:Vitamin E / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D018952:Antigens, CD34; D039561:Eukaryotic Initiation Factor-4E; D006657:Histones; D038601:Ribosomal Protein S6; C475961:gamma-H2AX protein, mouse; D014810:Vitamin E; C082097:tocotrienol, delta; D058570:TOR Serine-Threonine Kinases; D048049:Extracellular Signal-Regulated MAP Kinases
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