Delta-tocotrienol protects mouse and human hematopoietic progenitors from gamma-irradiation through extracellular signal-regulated kinase/mammalian target of rapamycin signaling.
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.
Li
Xiang Hong
XH
Radiation Countermeasures Program, Armed Forces Radiobiology Research Institute, Uniformed Services University of the Health Sciences, 8901 Wisconsin Ave, Bethesda, MD 20889-5603, USA.
Fu
Dadin
D
Latif
Nabil H
NH
Mullaney
Conor P
CP
Ney
Patrick H
PH
Mog
Steven R
SR
Whitnall
Mark H
MH
Srinivasan
Venkataraman
V
Xiao
Mang
M
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
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
Nature. 2006 May 25;441(7092):424-30
16724053
Int J Cancer. 2008 Aug 15;123(4):739-52
18512238
Carcinogenesis. 2008 Dec;29(12):2279-88
18809972
Life Sci. 2006 Mar 27;78(18):2088-98
16458936
Expert Rev Anticancer Ther. 2006 Sep;6(9):1179-93
17020453
Genes Dev. 2001 Apr 1;15(7):807-26
11297505
J Nutr Biochem. 2009 Feb;20(2):79-86
19071006
DNA Repair (Amst). 2006 Sep 8;5(9-10):1042-8
16822724
Cell Mol Life Sci. 2008 Nov;65(22):3525-44
18668205
Oncogene. 2003 Sep 1;22(37):5885-96
12947395
Biochem Pharmacol. 2008 Aug 1;76(3):330-9
18599020
Drug Resist Updat. 2008 Jun;11(3):63-76
18440854
Biochim Biophys Acta. 2007 Aug;1773(8):1299-310
17188374
Cancer Lett. 2008 Oct 8;269(2):388-95
18504069
Radiat Prot Dosimetry. 2006;122(1-4):124-7
17351270
J Immunol. 1998 Jun 1;160(11):5579-87
9605163
Mol Cell Biol. 2009 Nov;29(21):5645-56
19704005
Biochem J. 2007 Apr 15;403(2):217-34
17376031
J Anim Sci. 2008 Apr;86(14 Suppl):E36-50
17998426
Radiat Res. 2009 May;171(5):596-605
19580495
Adv Space Res. 2009;43(8):1171-1178
20046946
Int J Radiat Biol. 2007 Mar;83(3):141-51
17378522
Mol Cell Biol. 2004 Mar;24(5):1823-35
14966265
Mol Pharmacol. 2007 Aug;72(2):370-9
17473057
Mol Biotechnol. 2005 Oct;31(2):151-74
16170216
Nature. 2006 May 25;441(7092):431-6
16724054
Blood. 2009 Oct 15;114(16):3402-12
19667405
Curr Mol Pharmacol. 2009 Jan;2(1):122-33
20021452
Mol Cancer Ther. 2007 Mar;6(3):789-801
17363476
Leukemia. 2005 Sep;19(9):1543-9
16001087
PLoS Biol. 2007 Apr;5(4):e92
17373858
Kidney Int. 2001 Mar;59(3):866-75
11231341
Science. 2004 Apr 30;304(5671):693-4
15118152
Am J Physiol Endocrinol Metab. 2007 Jun;292(6):E1647-55
17284572
Health Phys. 2010 Jun;98(6):894-7
20445401
Mol Cell Biochem. 1997 May;170(1-2):131-7
9144327
Nat Rev Cancer. 2006 Sep;6(9):702-13
16929324
Immunopharmacol Immunotoxicol. 2008;30(2):271-90
18569084