Granulocyte colony-stimulating factor antibody abrogates radioprotective efficacy of gamma-tocotrienol, a promising radiation countermeasure

Radiation Countermeasures Program, Armed Forces Radiobiology Research Institute, Uniformed Services University of the Health Sciences, Bethesda, MD, USA.
Cytokine (Impact Factor: 2.66). 04/2013; 62(2). DOI: 10.1016/j.cyto.2013.03.009
Source: PubMed


This study aimed to determine the role of granulocyte colony-stimulating factor (G-CSF), induced by a promising radiation countermeasure, gamma tocotrienol (GT3), in protecting mice from lethal doses of ionizing radiation. CD2F1 mice were injected with an optimal dose of GT3 and a G-CSF antibody, and their 30-d survival was monitored. An appropriate antibody isotype was used as a control. Multiplex Luminex was used to analyze GT3-induced cytokines. G-CSF neutralization by exogenous administration of a G-CSF antibody was confirmed by analyzing serum cytokine levels. Our results demonstrate that GT3 significantly protected mice against ionizing radiation, and induced high levels of G-CSF in peripheral blood 24h after administration. Injection of a G-CSF neutralizing antibody to the GT3-treated mice resulted in complete neutralization of G-CSF and abrogation of its protective efficacy. Administration of a G-CSF antibody did not affect levels of other cytokines induced by GT3. Histopathology of bone marrow from GT3-treated and -irradiated mice demonstrated protection of the hematopoietic tissue, and also that such protection was abrogated by administering a G-CSF antibody. Our results suggest that induction of high levels of G-CSF by GT3 administration is responsible for its protective efficacy against radiation injury.

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Available from: Vijay K Singh, Mar 18, 2015
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    • "We also have reported that radiation exposure induces elevation of circulating G-CSF and that administering a neutralizing antibody to G-CSF exacerbates the deleterious effects of radiation exposure, suggesting that G-CSF induced in response to irradiation plays an important protective role in recovery (Singh et al., 2012d). Recently, we have demonstrated that the use of the G-CSF antibody abrogates the radioprotective efficacy of few radiation countermeasures (Singh et al., 2010; Kulkarni et al., 2013; Krivokrysenko et al., 2012; Grace et al., 2012). Our current study demonstrates that DT3 is a potent stimulator of several cytokines including G-CSF, and that the radioprotective efficacy of DT3 is mediated through G-CSF. "
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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.
    Life sciences 01/2014; 98(2). DOI:10.1016/j.lfs.2014.01.065 · 2.70 Impact Factor
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    • "Since then, several studies have undertaken the initiative to formulate tocotrienols in water soluble delivery systems to increase their solubility. The use of hydrophilic polymers such as cyclodextrin and emulsifiers including Tween 80 showed improved absorption and higher plasma concentrations when administered to rats [14,15]. Intravenous administration via tail vein injections was made possible for tocotrienols by formulating into suitable nano-carriers [16]. "
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    ABSTRACT: As a minor component of vitamin E, tocotrienols were evident in exhibiting biological activities such as neuroprotection, radio-protection, anti-cancer, anti-inflammatory and lipid lowering properties which are not shared by tocopherols. However, available data on the therapeutic window of tocotrienols remains controversial. It is important to understand the absorption and bioavailability mechanisms before conducting in-depth investigations into the therapeutic efficacy of tocotrienols in humans. In this review, we updated current evidence on the bioavailability of tocotrienols from human studies. Available data from five studies suggested that tocotrienols may reach its target destination through an alternative pathway despite its low affinity for alpha-tocopherol transfer protein. This was evident when studies reported considerable amount of tocotrienols detected in HDL particles and adipose tissues after oral consumption. Besides, plasma concentrations of tocotrienols were shown to be higher when administered with food while self-emulsifying preparation of tocotrienols was shown to enhance the absorption of tocotrienols. Nevertheless, mixed results were observed based on the outcome from 24 clinical studies, focusing on the dosages, study populations and formulations used. This may be due to the variation of compositions and dosages of tocotrienols used, suggesting a need to understand the formulation of tocotrienols in the study design. Essentially, implementation of a control diet such as AHA Step 1 diet may influence the study outcomes, especially in hypercholesterolemic subjects when lipid profile might be modified due to synergistic interaction between tocotrienols and control diet. We also found that the bioavailability of tocotrienols were inconsistent in different target populations, from healthy subjects to smokers and diseased patients. In this review, the effect of dosage, composition and formulation of tocotrienols as well as study populations on the bioavailability of tocotrienols will be discussed.
    Nutrition & Metabolism 01/2014; 11(1):5. DOI:10.1186/1743-7075-11-5 · 3.26 Impact Factor
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    • "G-CSF in particular and its related synthetic forms are used to protect against radiation-induced myelosuppression [10, 32, 33]. Recent studies show that radioprotection by GT3 may involve G-CSF induction [15, 34]. PTX had no beneficial effects on G-CSF, IL6 or KC. "
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    ABSTRACT: Purpose . 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. Results . 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. Conclusion . The mechanism of radioprotection by GT3-PTX may involve PDE inhibition.
    07/2013; 2013(7). DOI:10.5402/2013/390379
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