Gamma-tocotrienol, a radiation prophylaxis agent, induces high levels of granulocyte colony-stimulating factor
Armed Forces Radiobiology Research Institute, USUHS, Bethesda, MD 20889-5603, United States. International Immunopharmacology
(Impact Factor: 2.47).
12/2012; 14(4):495-503. DOI: 10.1016/j.intimp.2012.09.001
Gamma-tocotrienol (GT3), a promising radioprotectant, is shown to protect CD2F1 mice from radiation-induced neutropenia and thrombocytopenia when given 24h prior to total-body irradiation. GT3 also is shown to increase white blood cells (WBC) and absolute neutrophil counts (ANC) transiently in peripheral blood. We hypothesized that increases in WBC and ANC may involve stimulation of hematopoiesis possibly by cytokines and growth factors. To evaluate the effects of GT3 on hematopoietic system, we measured various cytokines, chemokines and growth factors by cytokine array and Bio-Plex assays. Both showed strong induction of various cytokines and chemokines. GT3 treatment resulted in significant increases in G-CSF, IL-1α, IL-1β, IL-6, IL-12p70, IL-17, MIP-1α, and KC levels. G-CSF levels increased markedly within 12-24h after administration (5441 pg/ml in GT3-treated groups compared to 17 pg/ml in vehicle control). Most of these cytokine levels were elevated in the presence or absence of radiation. Time-course analysis of G-CSF and IL-6 induction showed that both cytokines were induced transiently after GT3 administration, and returned to normal levels by 48 h post-administration. For G-CSF, the peak was observed between 12 and 24h post-administration of GT3; however, the highest levels of IL-6 were obtained between 6 and 12h. These results demonstrate that GT3 induced high levels of G-CSF and other inflammatory cytokines and chemokines within 24h after administration. Survival studies reported showed that the most efficacious time for administering GT3 was 24h prior to irradiation, possibly because it induced key hematopoietic cytokines in that time window. These results also suggest a possible role of GT3-induced G-CSF stimulation in protecting mice from radiation-induced neutropenia and thrombocytopenia.
Available from: Vijay K Singh
- "We have tested several promising radiation countermeasures (5- androstenediol, CBLB502, CBLB612, and CBLB613, tocopherol succinate, and gamma-tocotrienol) and reported stimulation of G-CSF and other cytokines by these drugs in mice and also in nonhuman primates (CBLB502 (Singh et al., 2012a) and gamma-tocotrienol (unpublished observation)). DT3 induces high levels of cytokines comparable to other tocols, which are being developed as radiation countermeasures (GT3 and TS) (Singh et al., 2010, 2011; Kulkarni et al., 2012). DT3 stimulated significantly high levels of G-CSF in unirradiated as well as irradiated mice compared to respective vehicle controls. "
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ABSTRACT: The objective of this study was to determine the cytokine induction by delta tocotrienol (DT3, a promising radiation countermeasure) and to investigate the role of granulocyte colony-stimulating factor (G-CSF) in its radioprotective efficacy against ionizing radiation in mice.
Multiplex Luminex was used to analyze DT3- and other tocols (gamma-tocotrienol and tocopherol succinate)-induced cytokines in CD2F1 mice. Mice were injected with an optimal dose of DT3 and a G-CSF antibody, and their 30-day survival against cobalt-60 gamma-irradiation was monitored. Neutralization of G-CSF by administration of a G-CSF-specific antibody in DT3-injected mice was investigated by multiplex Luminex.
Our data demonstrate that DT3 induced high levels of various cytokines comparable to other tocols being developed as radiation countermeasures. DT3 significantly protected mice against ionizing radiation, and administration of a G-CSF neutralizing antibody to DT3-treated animals resulted in complete abrogation of DT3's radioprotective efficacy and neutralization of G-CSF in peripheral blood.
Our study findings suggest that G-CSF induced by DT3 mediates its radioprotective efficacy against ionizing radiation in mice.
Available from: Martin Hauer-Jensen
- "GT3 is also shown to increase serum interleukin-6 (IL-6) and G-CSF levels; these cytokines are known to stimulate hematopoiesis. Induction of these cytokines may contribute to radioprotective action of GT3 . In an attempt to enhance the radioprotective efficacy of GT3, we tested the effect of PTX, a methyl derivative of xanthine, in combination with GT3. "
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. This study was designed to determine the efficacy and mechanisms of radioprotection by the combination of gamma-tocotrienol (GT3) and pentoxifylline (PTX) against acute radiation injury.
Materials and Methods
. Post-irradiation survival was monitored to determine the most efficacious dose and time of administration of PTX. Dose reduction factor (DRF) was calculated to compare the radioprotective efficacy of the combination. To determine the mechanism of synergistic radioprotection by the combination, mevalonate or calmodulin were coadministered with the GT3-PTX combination. Mevalonate was used to reverse the inhibitory effect of GT3 on 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMGCR), and calmodulin was used to reverse the inhibition of phosphodiesterase (PDE) by PTX.
. The combination was most effective when 200 mg/kg of PTX was administered 15 min before irradiation along with 200 mg/kg of GT3 (−24 h) and resulted in a DRF of 1.5. White blood cells and neutrophil counts showed accelerated recovery in GT3-PTX-treated groups compared to GT3. Mevalonate had no effect on the radioprotection of GT3-PTX; calmodulin abrogated the synergistic radioprotection by GT3-PTX.
. The mechanism of radioprotection by GT3-PTX may involve PDE inhibition.
Available from: Michal Hofer
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ABSTRACT: The bone marrow syndrome represents the most probable manifestation of the acute radiation disease following medical application
of ionizing radiation, as well as contingent nuclear accidents. Protection and treatment of marrow damage induced by radiation
exposures in the range of sublethal and near lethal doses is, at present, a serious medical problem. Moreover, radiation-induced
haematopoietic suppression may serve as a model for studying the effects of other bone marrow damaging factors and medical
procedures, including cytostatic chemotherapy.
Among the compounds tested as potential stimulators of mammalian haematopoiesis damaged by ionizing radiation in the Institute
of Biophysics, Brno, Czech Republic, also clinically available medicaments belonging to non-steroidal anti-inflammatory drugs
(NSAIDs) or drugs used in cardiovascular medicine were used.
NSAIDs act on the principle of inhibition of prostaglandin production. Prostaglandins operate in negative feedback control
of haematopoiesis, especially granulopoiesis. Removal of this feedback enables to enhance production of functional blood cells.
Indomethacin, diclofenac, flurbiprofen, and nitroxybutylester of flurbiprofen have been successfully tested as haematopoietic
stimulators in irradiated mice. Administration of flurbiprofen nitroxybutylester, a newly synthesized flurbiprofen derivative,
appears to be especially promising from the point of view of decreased gastrointestinal toxicity of this compound.
Dipyridamole (DP) and adenosine monophosphate (AMP) used clinically for decreasing platelet aggregation (DP) and as vasodilators
and cardioprotectors (DP, AMP) operate as enhancers of extracellular concentration of adenosine. Receptor-based extra-cellular
action of adenosine has been found to stimulate haematopoiesis on the levels of stem and progenitor cell populations. Interesting
results on synergistic action of DP + AMP and granulocyte colony-stimulating factor (G-CSF) on mouse granulopoiesis have been
obtained as well. Haematopoiesis-enhancing effects of drugs elevating extracellular adenosine may be of clinical importance
both from the point of view of medical benefit as well as from the standpoint of contingent financial savings obtained when
using these unexpensive drugs.
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