Radioprotection by Antioxidantsa

Radioprotective potential of a novel therapeutic formulation of oligoelements Se, Zn, Mn plus Lachesis muta venom

In this study we evaluated in vivo the tolerance induced by the combination of Se, Zn and Mn (4 microg/ml each) plus Lachesis muta venom (4 ng/ml) (O-LM) to high doses of ionizing radiation. The protective effect of O-LM was investigated on the small-intestine and bone marrow of mice irradiated with a single whole-body dose of 10 Gy employing a (137)Cs source. Mice were sacrificed 3 days after irradiation. Mice receiving a subcutaneous daily O-LM injection starting 30 days before irradiation, showed a higher number of crypts, enhanced villous conservation and lack of edema or vascular damage in comparison to the untreated and irradiated group. In addition, O-LM treatment decreased vascular damage and the grade of aplasia preserving medullar progenies induced by ionizing radiation on mouse bone marrow. The protective effect of O-LM against radiation injury to the small intestine was associated with an increase in proliferation and a reduction of apoptosis in intestinal crypts and furthermore, to an enhanced intestinal immunoreactivity of MnSOD, and CuZnSOD, and also catalase. Based on the present results and taking into account that O-LM is being safely administered in phase I clinical trial as an immunomodulator, we suggest that O-LM could be an attractive candidate as a safe radioprotective agent for patients undergoing radiotherapy.

High dietary antioxidant intakes are associated with decreased chromosome translocation frequency in airline pilots

BACKGROUND

Dietary antioxidants may protect against DNA damage induced by endogenous and exogenous sources, including ionizing radiation (IR), but data from IR-exposed human populations are limited.

OBJECTIVE

The objective was to examine the association between the frequency of chromosome translocations, as a biomarker of cumulative DNA damage, and intakes of vitamins C and E and carotenoids in 82 male airline pilots.

DESIGN

Dietary intakes were estimated by using a self-administered semiquantitative food-frequency questionnaire. Translocations were scored by using fluorescence in situ hybridization with whole chromosome paints. Negative binomial regression was used to estimate rate ratios and 95% CIs, adjusted for potential confounders.

RESULTS

Significant and inverse associations were observed between translocation frequency and intakes of vitamin C, beta-carotene, beta-cryptoxanthin, and lutein-zeaxanthin from food (P < 0.05). Translocation frequency was not associated with the intake of vitamin E, alpha-carotene, or lycopene from food; total vitamin C or E from food and supplements; or vitamin C or E or multivitamin supplements. The adjusted rate ratios (95% CI) for > or =median compared with or =median compared with

CONCLUSION

High combined intakes of vitamins C and E, beta-carotene, beta-cryptoxanthin, and lutein-zeaxanthin from food, or a diet high in their food sources, may protect against cumulative DNA damage in IR-exposed persons.

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Key Words Collapse

MESH Headings

• Administration, Oral
• Aircraft
• Antioxidants/administration & dosage
• Antioxidants/pharmacology
• Ascorbic Acid/pharmacology
• Carotenoids/administration & dosage
• Carotenoids/pharmacology
• Chromosomes, Human/drug effects
• Chromosomes, Human/genetics
• Dietary Supplements
• Fruit
• Humans
• Interviews as Topic
• Male
• Occupations
• Surveys and Questionnaires
• Translocation, Genetic/drug effects
• Vegetables
• Vitamin E/pharmacology
• beta Carotene/administration & dosage

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Grants

• Y1CP802904 NCI NIH HHS
• Intramural NIH HHS

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Affiliation(s)

Lee C Yong National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention, Cincinnati, OH 45226, USA.
Martin R Petersen
Alice J Sigurdson
Laura A Sampson
Elizabeth M Ward

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Factors that modify radiation-induced carcinogenesis

It is known that numerous factors can influence radiation carcinogenesis in animals; these factors include the specific characteristics of the radiation (radiation type and dose, dose-rate, dose-fractionation, dose distribution, etc.) as well as many other contributing elements that are not specific to the radiation exposure, such as animal genetic characteristics and age, the environment of the animal, dietary factors and whether specific modifying agents for radiation carcinogenesis have been utilized in the studies. This overview focuses on the modifying factors for radiation carcinogenesis, in both in vivo and in vitro systems, and includes a discussion of agents that enhance (e.g., promoting agents) or suppress (e.g., cancer preventive agents) radiation-induced carcinogenesis. The agents that enhance or suppress radiation carcinogenesis in experimental model systems have been shown to lead to effects equally as large as other known modifying factors for radiation-induced carcinogenesis (e.g., dose-rate, dose-fractionation, linear energy transfer). It is known that dietary factors play an important role in determining the yields of radiation-induced cancers in animal model systems, and it is likely that they also influence radiation-induced cancer risks in human populations.

Pyridoxamine protects intestinal epithelium from ionizing radiation-induced apoptosis

Reactive oxygen species (ROS) and reactive carbonyl species (RCS) are the major causes of biological tissue damage during exposure to ionizing radiation (IR). The existing strategies to protect normal tissues from the detrimental effects of IR suffer from several shortcomings including highly toxic side effects, unfavorable administration routes, and low efficacy. These shortcomings emphasize a need for radioprotective treatments that combine effectiveness with safety and ease of use. In this paper, we demonstrate that pyridoxamine, a ROS and RCS scavenger with a very favorable safety profile, can inhibit IR-induced gastrointestinal epithelial apoptosis in cell culture and in an animal model. Pyridoxamine was more effective at protecting from radiation-induced apoptosis than amifostine, a synthetic thiol compound and the only FDA-approved radioprotector. We suggest that pyridoxamine has potential as an effective and safe radioprotective agent.

Mitochondrial targeting of a catalase transgene product by plasmid liposomes increases radioresistance in vitro and in vivo

To determine whether increased mitochondrially localized catalase was radioprotective, a human catalase transgene was cloned into a small pSVZeo plasmid and localized to the mitochondria of 32D cl 3 cells by adding the mitochondrial localization sequence of MnSOD (mt-catalase). The cell lines 32D-Cat and 32D-mt-Cat had increased catalase biochemical activity as confirmed by Western blot analysis compared to the 32D cl 3 parent cells. The MnSOD-overexpressing 32D cl 3 cell line, 2C6, had decreased baseline catalase activity that was increased in 2C6-Cat and 2C6-mt-Cat subclonal cell lines. 32D-mt-Cat cells were more radioresistant than 32D-Cat cells, but both were radioresistant relative to 32D cl 3 cells. 2C6-mt-Cat cells but not 2C6-Cat cells were radioresistant compared to 2C6 cells. Intratracheal injection of the mt-catalase-plasmid liposome complex (mt-Cat-PL) but not the catalase-plasmid liposome complex (Cat-PL) increased the resistance of C57BL/6NHsd female mice to 20 Gy thoracic irradiation compared to MnSOD-plasmid liposomes. Thus mitochondrially targeted overexpression of the catalase transgene is radioprotective in vitro and in vivo.

The histopathological evaluation of the effectiveness of melatonin as a protectant against acute lung injury induced by radiation therapy in a rat model

PURPOSE

This study presents the histopathological evaluation of the effectiveness of melatonin as a protectant against acute lung injury induced by radiation therapy.

MATERIALS AND METHODS

Thirty-two Wistar rats were divided into four groups. The rats in Group 1 received melatonin and underwent radiation therapy. The rats in Group 2 received no melatonin and underwent radiation therapy. The rats in Group 3 received melatonin and underwent sham radiation therapy. The rats in Group 4 received no melatonin and underwent sham radiation therapy. Melatonin was administered at a dose of 100 mg/kg using an intraperitoneal injection. Radiation therapy was delivered on a Cobalt-60 unit using a single fraction of 18 Gy through an anterior portal covering the right lung in entirety. The rats underwent euthanasia at 6 weeks following radiation therapy. The lungs were dissected and blinded histopathological evaluation was performed.

RESULTS

Concerning the right lung, a decrease in intra-alveolar edema and intra-alveolar erythrocytes was observed despite an increase in activated macrophages, intra-alveolar fibrosis, hyaline arteriosclerosis and alveolar wall thickness for the rats in Group 1 as compared to the rats in Group 2. Concerning the left lung, a decrease in alveolar neutrophils and intra-alveolar erythrocytes was evident despite an increase in activated macrophages, hyaline arteriosclerosis and alveolar wall thickness for the rats in Group 1 as compared to the rats in Group 2.

CONCLUSIONS

This study puts forward the histopathological evidence regarding the effectiveness of melatonin as a protectant against acute lung injury induced by radiation therapy through restrained inflammation, regrettably at the expense of promoted fibrosis. The effectiveness of melatonin as a protectant against acute lung injury induced by radiation therapy needs to be evaluated further for the unresolved concerns regarding the safety.

Mechanisms underlying the radioprotective effect of histamine on small intestine

PURPOSE

To examine the protective effects of histamine on intestinal damage produced by gamma-radiation.

MATERIALS AND METHODS

56 mice were divided into 4 groups. Histamine and Histamine-10 Gy groups received a daily subcutaneous histamine injection (0.1 mg/kg) starting 20 hours before irradiation and continued until the end of the experimental period; the untreated group received saline. Histamine-10 Gy and untreated-10 Gy groups were irradiated with a single dose on whole-body using Cesium-137 source (7 Gy/min) and were sacrificed 3 days after irradiation. Small intestine was removed, fixed and stained with hematoxylin and eosin. The number of intestinal crypts per circumference, and other histological characteristics of intestinal cells were evaluated. We further determined by immunohistochemistry the expression of proliferating cell nuclear antigen (PCNA), Bax, Bcl-2 (pro- and anti-apoptotic protein, respectively), antioxidant enzymes (Superoxide dismutase (SOD), Catalase and Glutathione peroxidase), histamine content and apoptosis by terminal deoxynucleotidyl transferase mediated deoxyuridine triphosphate biotin nick end labeling (TUNEL) assay. Cells in the S phase of the cell cycle were identified by immunohistochemical detection of 5-bromo-2'-deoxyuridine (BrdU) incorporation.

RESULTS

Histamine treatment reduced mucosal atrophy, edema and preserved villi, crypts and nuclear and cytoplasmic characteristics of small intestine after radiation exposure. Additionally, histamine treatment increased PCNA expression and the BrdU-positive cell number, histamine content, decreased the number of apoptotic cells and significantly increased Catalase and copper-zinc-containing SOD of irradiated mice.

CONCLUSIONS

Histamine prevents radiation-induced toxicity by increasing proliferation of damaged intestinal mucosa and suppressing apoptosis that was associated with an increase in SOD and Catalase levels. This effect might be of clinical value in patients undergoing radiotherapy.

N-acetyl cysteine protects against ionizing radiation-induced DNA damage but not against cell killing in yeast and mammals

Ionizing radiation (IR) induces DNA strand breaks leading to cell death or deleterious genome rearrangements. In the present study, we examined the role of N-acetyl-L-cysteine (NAC), a clinically proven safe agent, for it's ability to protect against gamma-ray-induced DNA strand breaks and/or DNA deletions in yeast and mammals. In the yeast Saccharomyces cerevisiae, DNA deletions were scored by reversion to histidine prototrophy. Human lymphoblastoid cells were examined for the frequency of gamma-H2AX foci formation, indicative of DNA double strand break formation. DNA strand breaks were also measured in mouse peripheral blood by the alkaline comet assay. In yeast, NAC reduced the frequency of IR-induced DNA deletions. However, NAC did not protect against cell death. NAC also reduced gamma-H2AX foci formation in human lymphoblastoid cells but had no protective effect in the colony survival assay. NAC administration via drinking water fully protected against DNA strand breaks in mice whole-body irradiated with 1Gy but not with 4Gy. NAC treatment in the absence of irradiation was not genotoxic. These data suggest that, given the safety and efficacy of NAC in humans, NAC may be useful in radiation therapy to prevent radiation-mediated genotoxicity, but does not interfere with efficient cancer cell killing.

High-dose selenium for the mitigation of radiation injury: a pilot study in a rat model

The purpose of this study was to evaluate in an animal model the safety and efficacy of dietary supplementation with high doses of selenium for the mitigation of the type of radiation injury that might be sustained during a nuclear accident or an act of radiological terrorism. Age-matched male rats were exposed to 10 Gy (single dose) of total-body irradiation (TBI) followed by a syngeneic bone marrow transplant, then randomized to standard drinking water or drinking water supplemented with sodium selenite or seleno-l-methionine. At 21 weeks after TBI, most rats on standard drinking water had severe renal failure with a mean blood urea nitrogen (BUN) level of 124 +/- 29 mg/dl (geometric mean +/- SE) whereas rats on selenium-supplemented drinking water (100 microg/day) had a mean BUN level of 67 +/- 12 mg/dl. The mitigating effect of selenium was confirmed by histopathological analyses. None of the animals on high-dose selenium showed signs of selenium toxicity. Our results suggest that dietary supplementation with high-dose selenium may provide a safe, effective and practical way to mitigate radiation injury to kidneys.

Modulation of radiation-induced life shortening by systemic intravenous MnSOD-plasmid liposome gene therapy

To determine whether systemic administration of MnSOD-PL protected mice from the acute hematopoietic syndrome and delayed death after total-body irradiation (TBI), C57BL/ 6J mice were injected intravenously with 100 microl liposomes containing 100 microg of human MnSOD-transgene plasmid 24 h prior to irradiation with 9.5 Gy or 1.0 Gy. The dose of 9.5 Gy was lethal to 42% of irradiated control female mice and 74% of irradiated control male mice at 30 days, with bone marrow hypocellularity consistent with the hematopoietic syndrome. A statistically significant increase in survival was observed in MnSOD-PL-treated female mice out to 400 days and in male mice out to 340 days. The incidence of tumors was similar between surviving groups. Between 350 and 600 days, the outcome was similar for both MnSOD-PL-treated and control irradiated groups, consistent with aging, with no difference in gross or microscopic pathological evidence of tumors. Male and female mice receiving 1.0 Gy TBI showed radiation-induced life shortening after 120 days that was decreased by MnSOD-PL administration and that was not associated with an increase in rate of tumor-associated death. Therefore, systemic MnSOD-PL radioprotective gene therapy is not associated with a detectably higher incidence of late carcinogenesis.

Quantum dots and nanoparticles for photodynamic and radiation therapies of cancer

Semiconductor quantum dots and nanoparticles composed of metals, lipids or polymers have emerged with promising applications for early detection and therapy of cancer. Quantum dots with unique optical properties are commonly composed of cadmium contained semiconductors. Cadmium is potentially hazardous, and toxicity of such quantum dots to living cells, and humans, is not yet systematically investigated. Therefore, search for less toxic materials with similar targeting and optical properties is of further interest. Whereas, the investigation of luminescence nanoparticles as light sources for cancer therapy is very interesting. Despite advances in neurosurgery and radiotherapy the prognosis for patients with malignant gliomas has changed little for the last decades. Cancer treatment requires high accuracy in delivering ionizing radiation to reduce toxicity to surrounding tissues. Recently some research has been focused in developing photosensitizing quantum dots for production of radicals upon absorption of visible light. In spite of the fact that visible light is safe, this approach is suitable to treat only superficial tumours. Ionizing radiation (X-rays and gamma rays) penetrate much deeper thus offering a big advantage in treating patients with tumours in internal organs. Such concept of using quantum dots and nanoparticles to yield electrons and radicals in photodynamic and radiation therapies as well their combination is reviewed in this article.

Radioprotection in vitro and in vivo by minicircle plasmid carrying the human manganese superoxide dismutase transgene

Manganese superoxide dismutase plasmid liposomes (MnSOD-PL) confer organ-specific in vivo ionizing irradiation protection. To prepare for potential intravenous clinical trials of systemic MnSOD-PL for radioprotection in humans, plasmid and bacterial sequences were removed and a new minicircle construct was tested. Minicircle MnSOD was purified and then cotransfected into 32D cl 3 murine interleukin-3-dependent hematopoietic progenitor cells along with another plasmid carrying the neo gene. Cells were selected in G418 (50 microg/ml) and cloned by limiting dilution. Biochemical analysis of minicircle MnSOD-transfected cells showed an MnSOD biochemical activity level of 5.8 +/- 0.5 U/mg compared with 2.7 +/- 0.1 U/mg for control 32D cl 3 cells (p = 0.0039). 32D-mc-MnSOD cells were as radioresistant as full-length MnSOD-PL transgene-expressing 2C6 cells, relative to 32D cl 3 parent cells, with an increased shoulder on the radiation survival curve (n = 4.8 +/- 0.2 and n = 4.6 +/- 0.2, respectively, compared with 1.5 +/- 0.5 for 32D cl 3 cells; p = 0.007). C57BL/6NHsd mice received intraoral mc-MnSOD-PL, mc-DsRed-PL control, full-length MnSOD-PL, or blank-PL and then were irradiated 24 hr later with 31 Gy to the esophagus. Mice receiving mc-MnSOD-PL showed increased survival compared with control mice or mice treated with mc-DsRed-PL (p = 0.0003 and 0.039, respectively), and comparable to full-length MnSOD-PL. Intravenous, systemic administration of mc-MnSOD-PL protected mice from total body irradiation (9.75 Gy). Therefore, minicircle DNA containing the human MnSOD transgene confers undiminished radioprotection in vitro and in vivo.

Radioprotective effects of ocimum flavonoids on leukocyte oxidants and antioxidants in oral cancer

Oxidants (NADPH oxidase and myeloperoxidase) and antioxidants (GSH,GSH peroxidase, SOD and glucose 6 phosphate dehydrogenase, that provides NADPH for antioxidants) were assayed in the neutrophils from oral cancer patients, in three stages viz, baseline samples,15 days after radiation and 30 days following radiation. These samples were obtained from 2 groups of patients. Group A that received radiation alone and Group B that received radiation and ocimum flavonoids,a radioprotector. The results showed a significant fall in the SOD levels in the second follow up of group B.Glucose 6 phosphate dehydrogenase showed significant increase only in the first follow up of patients who received Ocimum flavonoids. Except for these findings all other parameters remained statistically nonsignificant.

Heavy ion carcinogenesis and human space exploration

Before the human exploration of Mars or long-duration missions on the Earth's moon, the risk of cancer and other diseases from space radiation must be accurately estimated and mitigated. Space radiation, comprised of energetic protons and heavy nuclei, has been shown to produce distinct biological damage compared with radiation on Earth, leading to large uncertainties in the projection of cancer and other health risks, and obscuring evaluation of the effectiveness of possible countermeasures. Here, we describe how research in cancer radiobiology can support human missions to Mars and other planets.

Dietary antioxidants protect hematopoietic cells and improve animal survival after total-body irradiation

The purpose of this study was to determine whether a dietary supplement consisting of L-selenomethionine, vitamin C, vitamin E succinate, alpha-lipoic acid and N-acetyl cysteine could improve the survival of mice after total-body irradiation. Antioxidants significantly increased the 30-day survival of mice after exposure to a potentially lethal dose of X rays when given prior to or after animal irradiation. Pretreatment of animals with antioxidants resulted in significantly higher total white blood cell and neutrophil counts in peripheral blood at 4 and 24 h after 1 Gy and 8 Gy. Antioxidants were effective in preventing peripheral lymphopenia only after low-dose irradiation. Antioxidant supplementation was also associated with increased bone marrow cell counts after irradiation. Supplementation with antioxidants was associated with increased Bcl2 and decreased Bax, caspase 9 and TGF-beta1 mRNA expression in the bone marrow after irradiation. Maintenance of the antioxidant diet was associated with improved recovery of the bone marrow after sublethal or potentially lethal irradiation. Taken together, oral supplementation with antioxidants appears to be an effective approach for radioprotection of hematopoietic cells and improvement of animal survival, and modulation of apoptosis is implicated as a mechanism for the radioprotection of the hematopoietic system by antioxidants.

A mitochondria-targeted nitroxide/hemigramicidin S conjugate protects mouse embryonic cells against gamma irradiation

PURPOSE

To evaluate the in vitro radioprotective effect of the mitochondria-targeted hemigramicidin S-conjugated 4-amino-2,2,6,6-tetramethyl-piperidine-N-oxyl (hemi-GS-TEMPO) 5-125 in gamma-irradiated mouse embryonic cells and adenovirus-12 SV40 hybrid virus transformed human bronchial epithelial cells BEAS-2B and explore the mechanisms involved in its radioprotective effect.

METHODS AND MATERIALS

Cells were incubated with 5-125 before (10 minutes) or after (1 hour) gamma-irradiation. Superoxide generation was determined by using dihydroethidium assay, and lipid oxidation was quantitated by using a fluorescence high-performance liquid chromatography-based Amplex Red assay. Apoptosis was characterized by evaluating the accumulation of cytochrome c in the cytosol and externalization of phosphatidylserine on the cell surface. Cell survival was measured by means of a clonogenic assay.

RESULTS

Treatment (before and after irradiation) of cells with 5-125 at low concentrations (5, 10, and 20 mum) effectively suppressed gamma-irradiation-induced superoxide generation, cardiolipin oxidation, and delayed irradiation-induced apoptosis, evaluated by using cytochrome c release and phosphatidylserine externalization. Importantly, treatment with 5-125 increased the clonogenic survival rate of gamma-irradiated cells. In addition, 5-125 enhanced and prolonged gamma-irradiation-induced G(2)/M phase arrest.

CONCLUSIONS

Radioprotection/mitigation by hemi-GS-TEMPO likely is caused by its ability to act as an electron scavenger and prevent superoxide generation, attenuate cardiolipin oxidation in mitochondria, and hence prevent the release of proapoptotic factors from mitochondria. Other mechanisms, including cell-cycle arrest at the G(2)/M phase, may contribute to the protection.

Melatonin mitigates oxidative damage and apoptosis in mouse cerebellum induced by high-LET 56Fe particle irradiation

Cerebellum is a vital organ responsible for the motor coordination and recently it has been reported to be involved in cognitive function. Reactive oxygen species are implicated in neurodegeneration and cognitive disorders because of higher vulnerability of neuronal tissues. Therefore, the present study aimed at investigating the role of melatonin against high-LET (linear energy transfer) (56)Fe particle irradiation-induced oxidative damage and apoptosis in the mouse cerebellum. Radiation-induced oxidative damage was examined using a neuronal-specific terminal deoxynucleotidyl transferase-mediated nick end-labeling (TUNEL), quantitative histopathology, DNA damage (comet assay), carbonyl content and 4-HAE + MDA (4-hydroxyalkenal + malondialdehyde) status of the cerebellum. Radiation exposure augmented the number of TUNEL positive cell, DNA migration in the comet tail and carbonyl and 4-HAE + MDA level in the cerebellum. Melatonin pretreatment significantly inhibited the oxidative damage to biomolecules as well as cerebellar apoptosis. Melatonin-treated irradiated mice showed higher counts of intact Purkinje cells as compared to vehicle-treated irradiated mice. In addition, radiation induced augmentation of 8-hydroxy-2'-deoxyguanosine (8-OHdG) and a decline in the total antioxidant capacity in serum; these changes were also ameliorated by melatonin pretreatment. The present results provide evidence supporting the antioxidant and neuroprotective function of melatonin.

[The biological effects of very low-doses of ionizing radiation at the occupational exposure level]

The knowledge of the biological effects of very low-doses of ionizing radiation is of particular interest in order to estimate the risk for occupational workers. The epidemiological studies are to date insufficient to predict the risk for doses below 100 mSv. The cellular and molecular interaction of ionizing radiation with the cells, and the mechanisms involved in cell defence allow understanding the cellular response to radiation. The transcriptome analysis in the range of low doses has shown different cell responses according to the dose and dose rate. Here are presented the cellular and molecular action of ionizing radiation, the cellular mechanisms of cell defence and their modulation by the dose and dose rate. A non-linear relationship is drawn in this area.

Free radical scavenging and radioprotective activity of dehydrozingerone against whole body gamma irradiation in Swiss albino mice

Dehydrozingerone (DZ) was explored for in vitro-in vivo antioxidant potential and in vivo radioprotective activity against whole body gamma irradiation in Swiss albino mice. DZ scavenged the ABTS (2, 2'-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) and DPPH (1, 1-dipehnyl-2-picrylhydrazyl) free radicals at room temp. DZ reduced Fe (III) to Fe (II) at pH 7.4 and scavenged the NADH/phenazine methosulfate generated superoxide radical in cell free system. DZ also scavenged the nitric oxide radical generated by sodium nitroprusside. To evaluate the radioprotective activity, mice were exposed to whole body gamma irradiation 30 min after the drug treatment at a dose rate of 1.66 Gy/min. Pretreatment with DZ 75, 100 and 125 mg/kg, i.p. reduced the radiation induced mortality and increased the mean survival times (MSTs). An i.p. dose of DZ 100 mg/kg was found the most effective dose in preventing radiation sickness and increasing the MST. Pretreatment DZ100 mg/kg maintained the spleen index (spleen weight/body weight x 100) and stimulates the endogenous spleen colony forming units (CFU). Pretreatment with DZ100 mg/kg maintained the villus height close to normal, prevents mucosal erosion and basement membrane damage in irradiated mice jejunum. However, no significant reductions in dead, inflammatory and mitotic cells were observed in DZ pretreated mice, but there was an increased in crypt cells proliferation and regeneration. Pretreatment with DZ100 mg/kg significantly elevated the endogenous antioxidant enzymes (GSH, GST and SOD) in mice at 2, 4 and 8 h post sham irradiation. Radiation induced fall in endogenous antioxidant enzymes was significantly prevented by DZ pretreatment. Pretreatment with DZ 75 and 100 mg/kg reduced the radiation induced micronucleated polychromatic erythrocytes (MPCE) and normochromatic erythrocytes (MNCE) in mice bone marrow. DZ also maintained the polychromatic erythrocytes (PCE) and normochromatic erythrocytes (NCE) ratio (P/N ratio) in irradiated mice. Dose modifying factor (DMF) was calculated by using the graded radiation dose (8.0, 9.0, 9.5 and 10 Gy). DZ 100 mg/kg elevated radiation LD(50) from 9.1 to 10.0 Gy, indicating the DMF of 1.09.

Chemical radiosensitizers for use in radiotherapy

Radiosensitizers are intended to enhance tumour cell killing while having much less effect on normal tissues. Some drugs target different physiological characteristics of the tumour, particularly hypoxia associated with radioresistance. Oxygen is the definitive hypoxic cell radiosensitizer, the large differential radiosensitivity of oxic vs hypoxic cells being an attractive factor. The combination of nicotinamide to reduce acute hypoxia with normobaric carbogen breathing is showing clinical promise. 'Electron-affinic' chemicals that react with DNA free radicals have the potential for universal activity to combat hypoxia-associated radioresistance; a nitroimidazole, nimorazole, is clinically effective at tolerable doses. Hypoxia-specific cytotoxins, such as tirapazamine, are valuable adjuncts to radiotherapy. Nitric oxide is a potent hypoxic cell radiosensitizer; variations in endogenous levels might have prognostic significance, and routes to deliver nitric oxide specifically to tumours are being developed. In principle, many drugs can be delivered selectively to hypoxic tumours using either reductase enzymes or radiation-produced free radicals to activate drug release from electron-affinic prodrugs. A redox-active agent based on a gadolinium chelate is being evaluated clinically. Pyrimidines substituted with bromine or iodine are incorporated into DNA and enhance free radical damage; fluoropyrimidines act by different mechanisms. A wide variety of drugs that influence the nature or repair of DNA damage are being evaluated in conjunction with radiation; it is often difficult to define the mechanisms underlying chemoradiation regimens. Drugs being evaluated include topoisomerase inhibitors (e.g. camptothecin, topotecan), and the hypoxia-activated anthraquinone AQ4N; alkylating agents include temozolomide. Drugs involved in DNA repair pathways being investigated include the potent poly(ADP ribose)polymerase inhibitor, AG14,361. Proteins involved in cell signalling, such as the Ras family, are attractive targets linked to radioresistance, as are epidermal growth factor receptors and linked kinases (drugs including vandetanib [ZD6,474], cetuximab and gefitinib), and cyclooxygenase-2 (celecoxib). The suppression of radioprotective thiols seems to offer more potential with alkylating agents than with radiotherapy, although it remains a strategy worthy of exploration.

AFMK, a melatonin metabolite, attenuates X-ray-induced oxidative damage to DNA, proteins and lipids in mice

Antioxidant function of melatonin is well established. However, N(1)-acetyl-N(2)-formyl-5-methoxykynuramine (AFMK), a melatonin metabolite is a sparingly investigated biogenic amine, especially in relation to its in vivo antioxidant function. We have evaluated the oxidative damage to biomolecules (DNA, protein and lipid) induced by X-irradiation in C57BL mice and the prophylactic action of AFMK. The extent of DNA damage was analyzed by single-cell gel electrophoresis in cerebral cortex and serum 8-hydroxydeoxyguanosine (8-OHdG) levels by enzyme-linked immunosorbent assay. Oxidative modification of protein and lipid was measured in the terms of carbonyl content and 4-HAE + MDA (4-hydroxyalkenal + malondialdehyde) status of brain cortex. Radiation exposure dramatically augmented the level of 8-OHdG in serum as well as DNA migration in the comet tail. AFMK pretreatment significantly inhibited DNA damage. In addition, radiation-induced augmentation of protein carbonyl content and HAE + MDA was ameliorated by AFMK pretreatment. Whole-body exposure of mice to X-irradiation also reduced the level of brain sulfhydryl contents (protein-bound sulfhydryl, total sulfhydryl, and nonprotein sulfhydryl) which were significantly protected by AFMK. Radiation-induced decline in the total antioxidant capacity of plasma was significantly reversed in AFMK pretreated mice. Moreover, AFMK showed a very high level of in vitro hydroxyl radical scavenging potential which was measured by an electron spin resonance (ESR) study of the 2-hydroxy-5,5-dimethyl-1-pyrrolineN-oxide (DMPO-OH) adduct. IC(50) values resulting from ESR analysis was 338.08 nm. The present study indicate that AFMK is a potent antioxidant in both in vivo and in vitro systems.

Radiation-induced cognitive dysfunction and cerebellar oxidative stress in mice: Protective effect of α-lipoic acid

Reactive oxygen species are implicated in neurodegeneration and cognitive disorders due to higher vulnerability of neuronal tissues. The cerebellum is recently reported to be involved in cognitive function. Therefore, present study aimed at investigating the role alpha-lipoic acid against radiation-induced oxidative stress and antioxidant status in cerebellum and its correlation with cognitive dysfunction. We observed spontaneous motor activities and spatial memory task of mice using pyroelectric infrared sensor and programmed video tracking system, respectively. Whole body X-irradiation (6 Gy) of mice substantially impaired the reference memory and motor activities of mice. However, acute intraperitoneal treatment of mice with alpha-lipoic acid prior to irradiation significantly attenuated such cognitive dysfunction. Alpha-lipoic acid pretreatment exerted a very high magnitude of protection against radiation-induced augmentation of protein carbonyls and thiobarbituric acid reactive substance (TBARS) in mice cerebellum. Further, radiation-induced deficit of total, nonprotein and protein-bound sulfhydryl (T-SH, NP-SH, PB-SH) contents of cerebellum and plasma ferric reducing power (FRAP) was also inhibited by alpha-lipoic acid pre-treatment. Moreover, alpha-lipoic acid treated mice showed an intact cytoarchitecture of cerebellum, higher counts of intact Purkinje cells and granular cells in comparison to untreated irradiated mice. Results clearly indicate that alpha-lipoic acid is potent neuroprotective antioxidant.

Kojic acid and its manganese and zinc complexes as potential radioprotective agents

The naturally occurring fungal metabolite kojic acid and its manganese and zinc complexes have been evaluated as potential radioprotectors in mice. Their toxicity and radioprotective activity (survival rate) have been determined and compared with that of WR-2721 (amifostine). The results of in vivo radioprotection showed that these compounds exhibited significant radioprotective effects against lethal dose of gamma-irradiation in mice.

Protective effect of α-tocopherol on oxidative stress in experimental pulmonary fibrosis in rats

The study was undertaken to investigate the influence of alpha-tocopherol (vitamin E) on malondialdehyde (MDA) and glutathione (GSH) levels and catalase (CAT) activity in lung of rats with bleomycin-induced pulmonary fibrosis (PF). Fourteen Wistar-albino rats were randomly divided into two groups of seven animals each. The first group was treated intra-tracheally with bleomycin hydrochloride (BM group); the second group was also instilled with BM but received injections of alpha-tocopherol twice a week (BM + E group). The third group was treated in the same manner with saline solution only, acting as controls (C). There were decreases in GSH level and CAT activity while an increase in MDA level in BM group was found compared to the control group (p < 0.05). Vitamin E had a regulator effect on these parameters. After administration of alpha-tocopherol, the increase in GSH level and CAT activity and the decrease in MDA level were seen in BM + E group compared to BM group (p < 0.05). Distinct histopathological changes were found in the BM group compared to the untreated rats. Less severe fibrotic lesions were also observed in the BM + E group. The results show that vitamin E is effective on the prevention of BM-induced PF, as indicated by differences in the lung levels of oxidants and antioxidants.

β-sitosterol decreases irradiation-induced thymocyte early damage by regulation of the intracellular redox balance and maintenance of mitochondrial membrane stability

Both radiation injury and oxidation toxicity occur when cells are exposed to ion irradiation (IR), ultimately leading to apoptosis. This study was designed to determine the effect of beta-sitosterol (BSS) on early cellular damage in irradiated thymocytes and a possible mechanism of effect on irradiation-mediated activation of the apoptotic pathways. Thymocytes were irradiated (6 Gy) with or without BSS. Cell apoptosis and apoptosis-related proteins were evaluated. BSS decreased irradiation-induced cell death and nuclear DNA strand breaks while attenuating intracellular reactive oxygen species (ROS) and increasing the activities of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx). BSS decreased the release of cytochrome c from mitochondria to the cytosol and the mitochondrio-nuclear translocation of apoptosis-inducing factor (AIF). Furthermore, BSS partially inhibited the radiation-induced increase of cleaved caspase 3 and cleaved PARP, and attenuated the activation of JNK and AP-1. In addition, evidence suggests that ROS generated by irradiation are involved in this course of cell damage. The results indicate that BSS confers a radioprotective effect on thymocytes by regulation of the intracellular redox balance which is carried out via the scavenging of ROS and maintenance of mitochondrial membrane stability.

Protective effect of triphlorethol-A from Ecklonia cava against ionizing radiation in vitro

We studied the cytoprotective effect of triphlorethol-A against gamma-ray radiation-induced oxidative stress. In this study, hydrogen peroxide, which is a reactive oxygen species (ROS), was detected using 2',7'-dichlorodihydrofluorescein diacetate (DCF-DA) assay. Triphlorethol-A reduced intracellular hydrogen peroxide generated by gamma-ray radiation. This compound provided protection against radiation-induced membrane lipid peroxidation and cellular DNA damage which are the main targets of radiation-induced damage. Triphlorethol-A protected the cell viability damaged by the radiation through inhibition of apoptosis. Triphlorethol-A reduced the expression of bax and activated caspase 3 induced by radiation, but recovered the expression of bcl-2 decreased by radiation. Taken together, the results suggest that triphlorethol-A protects cells against oxidative damage induced by radiation through reducing ROS.

Pycnogenol® protects against Ionizing radiation as shown in the intestinal mucosa of rats exposed to X-rays

X-rays and gamma radiation delivered to the abdominal region for cancer treatment encompasses severe damage to the intestinal mucosa, which significantly impairs a patient's quality of life. To a great extent the deleterious effects of x-radiation originate from radiolysis-induced reactive oxygen species. The well-researched powerful antioxidant Pycnogenol was administered orally to rats prior to x-irradiation with 15 Gy. Histological sections of the intestines showed a dramatically better condition of the mucosal layers compared with the irradiated control animals administered water without Pycnogenol. Pycnogenol treatment significantly preserved the height and number of villi as well as the glandular layer and a diminished number of congested vases were present. No intestinal alterations were seen in control animals receiving Pycnogenol in the absence of radiation. It is concluded that Pycnogenol provides significant protection from ionizing radiation damage.

Genistein stimulates hematopoiesis and increases survival in irradiated mice

Radiation protection from death and stimulating hematopoietic recovery by oral administrations of genistein, 160 mg/kg b.w., once daily for seven consecutive days before whole-body gamma-rays irradiation, were confirmed by tests with adult male BALB/c mice. Moreover, the protective action of genistein was compared to that of diethylstilbestrol (DES). Based on the studies of survival, behavior of hematograms, endogenous hematopoietic spleen colony formation (endoCFUs), and numbers of nucleated cell, granulocyte-macrophage colony forming units (CFU-GM) in bone marrow following irradiation, it was demonstrated that genistein was an effective radioprotector. The survival of irradiated mice protected by genistein was significantly increased and statistically higher than that of mice pre-treated with DES. Stimulated recovery of leukocytes, erythrocytes, lymphocytes and thrombocytes were observed in mice pre-treated with genistein or DES, however, the effects of genistein on promoting recovery of bone marrow nucleated cells, leukocytes and lymphocytes were significantly higher than those of DES. Enhanced endoCFUs, numbers of bone marrow nucleated cells and CFU-GM were also found in mice pre-treated with genistein as well as DES. Meanwhile, endoCFU numbers in mice pre-treated with genistein was 3.47-fold higher than that in the irradiated control group, although no significant difference was found between genistein administration and DES administration. It could be deduced that the radioprotective action against death is induced by a possible process of enhanced regeneration of the hematopoietic stem cells due to not only strengthened radioresistance and increased numbers of remained hematopoietic cells, but also enhanced post-irradiation repair or promoted proliferation of the hematopoietic stem cells. These effects of genistein may have some therapeutic implications for radiation-induced injuries.

A manganese porphyrin superoxide dismutase mimetic enhances tumor radioresponsiveness

PURPOSE

To determine the effect of the superoxide dismutase mimetic Mn(III) tetrakis(N-ethylpyridinium-2-yl)porphyrin (MnTE-2-PyP(5+)) on tumor radioresponsiveness.

METHODS AND MATERIALS

Various rodent tumor (4T1, R3230, B16) and endothelial (SVEC) cell lines were exposed to MnTE-2-PyP(5+) and assayed for viability and radiosensitivity in vitro. Next, tumors were treated with radiation and MnTE-2-PyP(5+)in vivo, and the effects on tumor growth and vascularity were monitored.

RESULTS

In vitro, MnTE-2-PyP(5+) was not significantly cytotoxic. However, at concentrations as low as 2 mumol/L it caused 100% inhibition of secretion by tumor cells of cytokines protective of irradiated endothelial cells. In vivo, combined treatment with radiation and MnTE-2-PyP(5+) achieved synergistic tumor devascularization, reducing vascular density by 78.7% within 72 h of radiotherapy (p < 0.05 vs. radiation or drug alone). Co-treatment of tumors also resulted in synergistic antitumor effects, extending tumor growth delay by 9 days (p < 0.01).

CONCLUSIONS

These studies support the conclusion that MnTE-2-PyP(5+), which has been shown to protect normal tissues from radiation injury, can also improve tumor control through augmenting radiation-induced damage to the tumor vasculature.

Radiation protectants: current status and future prospects

In today's heightened nuclear/biological/chemical threat environment, there is an increased need to have safe and effective means to protect not only special high-risk service groups, but also the general population at large, from the health hazards of unintended ionizing radiation exposures. An unfulfilled dream has been to have a globally effective pharmacologic that could be easily taken orally without any undue side effects prior to a suspected or impending nuclear/radiological event; such an ideal radioprotective agent has yet to be identified, let alone fully developed and approved for human use. No one would argue against the fact that this is problematic and needs to be corrected, but where might the ultimate solution to this difficult problem be found? Without question, representative species of the aminothiol family [e.g., Amifostine (MedImmune, Gaithersburg, Maryland)] have proven to be potent cytoprotectants for normal tissues subjected to irradiation or to radiomimetic chemicals. Although Amifostine is currently used clinically, drug toxicity, limited times of protection, and unfavorable routes of administration, all serve to limit the drug's utility in nonclinical settings. A full range of research and development strategies is being employed currently in the hunt for new safe and effective radioprotectants. These include: (1) large scale screening of new chemical classes or natural products; (2) restructuring/reformulating older protectants with proven efficacies but unwanted toxicities; (3) using nutraceuticals that are only moderately protective but are essentially nontoxic; (4) using low dose combinations of potentially toxic but efficacious agents that protect through different routes to foster radioprotective synergy; and (5) accepting a lower level of drug efficacy in lieu of reduced toxicity, banking on the premise that the protection afforded can be leveraged by post-exposure therapies. Although it is difficult to predict which of these strategies will ultimately prove to be successful, it is certain that the probability of a useful protectant being fielded is increased significantly. This is due to the resurgence of interest in radiation protection, increased resources being expended by federal agencies, and by the Food and Drug Administration's willingness to innovate relative to new approval guidance.

The Protective Role of Fruits and Vegetables against Radiation-Induced Cancer

The role of fruits and vegetables in protecting against radiation-induced cancer and the positive evidence from epidemiology and ancillary investigations are discussed in this review. The recently reported Hiroshima and Nagasaki atomic bomb survivor studies provide strong evidence for the protective role of fruits and vegetables against radiation-induced cancer. The anticarcinogenic substances contained in, and the anticarcinogenic mechanisms proposed for, fruits and vegetables are reviewed. The anticarcinogenic effectiveness of fruits and vegetables are compared with that of dietary supplements. The reasons for the observed superiority of fruits and vegetables are advanced.

Animal models for radiation injury, protection and therapy

Current events throughout the world underscore the growing threat of different forms of terrorism, including radiological or nuclear attack. Pharmaceutical products and other approaches are needed to protect the civilian population from radiation and to treat those with radiation-induced injuries. In the event of an attack, radiation exposures will be heterogeneous in terms of both dose and quality, depending on the type of device used and each victim's location relative to the radiation source. Therefore, methods are needed to protect against and treat a wide range of early and slowly developing radiation-induced injuries. Equally important is the development of rapid and accurate biodosimetry methods for estimating radiation doses to individuals and guiding clinical treatment decisions. Acute effects of high-dose radiation include hematopoietic cell loss, immune suppression, mucosal damage (gastrointestinal and oral), and potential injury to other sites such as the lung, kidney and central nervous system (CNS). Long-term effects, as a result of both high- and low-dose radiation, include dysfunction or fibrosis in a wide range of organs and tissues and cancer. The availability of appropriate types of animal models, as well as adequate numbers of animals, is likely to be a major bottleneck in the development of new or improved radioprotectors, mitigators and therapeutic agents to prevent or treat radiation injuries and of biodosimetry methods to measure radiation doses to individuals.

Rationale for using multiple antioxidants in protecting humans against low doses of ionizing radiation

Health risks of low doses of ionizing radiation (10 cGy or less) may not be accurately estimated in humans by epidemiological study or mathematical modelling because of several inherent confounding factors including environmental, dietary and biological variables that cannot be accounted for in any radio-epidemiological study. In addition, the expression of radiation-induced damage in humans not only depends upon total dose, dose rate, linear energy transfer (LET), and fractionation and protraction of total doses, but also on repair mechanisms, bystander effects, and exposure to chemical carcinogens, tumour promoters and other toxins. It also depends upon the levels of anti-carcinogenic and anti-tumour promoting agents. Low doses of ionizing radiation should not be considered insignificant with regard to increasing the incidence of somatic mutations (neoplastic and non-neoplastic diseases) and heritable mutations in humans owing to its interaction with other toxins that can enhance damage produced by irradiation. It is very prudent to continue to support the well-established radiobiological concept that no radiation dose can be considered completely safe, and that all efforts must be made to reduce both the radiation dose and biological damage, no matter how small that damage might be, without sacrificing the benefits of radiation. Based on the results of many scientific experiments, formulations containing multiple antioxidants for biological protection against radiation damage in humans can be developed, and this strategy together with the existing physical concept of radiation protection, should further reduce potential risks of low doses of ionizing radiation in humans.

Ionizing radiation‐induced damage on developing cerebellar granule cells cultures can be prevented by an early amifostine post‐treatment

Developing central nervous system (CNS) is highly sensitive to ionizing radiation due, in part, to reactive oxygen species (ROS) damage. A variety of compounds able to protect brain cells essentially by decreasing ROS production have been widely used to confirm ROS participation in different mechanisms of brain injury, as well as to evaluate them as therapeutic tools. To test if ionizing radiation-induced damage on immature cerebellar granule cells is mainly mediated by ROS accumulation, a free radical scavenger--amifostine (amf)--was used in an in vitro model. Moreover, the amf therapeutic effect was investigated. Results show that only an early (20-30 min) post-treatment with amf, acting through an antioxidant mechanism, has been effective in preventing cerebellar granule cell loss observed after ionizing radiation exposure in vitro. These data suggest that immature cerebellar granule cells grown in vitro are highly vulnerable to ROS damage and that a therapeutic intervention could be effective in a narrow temporal window. Moreover, radiation-induced cell death can be partially prevented by a complete limitation of ROS generation, suggesting that other mechanisms besides oxidative stress would also be responsible for the cellular damage found in this model.

The effects of ionizing radiation on DNA: The role of thiols as radioprotectors

Electron loss from N-(2-mercaptopropionyl) glycine (PSH) gave an EPR detectable radical anion, PS-.SP(-). When the PSH derivative was frozen in aqueous DNA solutions to 77 K and exposed to ionizing radiation, normal damage to the DNA was detected by EPR spectroscopy. However, on annealing above 77 K, central EPR features for the DNA base radical cations and anions gave central features assigned to PS-.SP(-) sigma*-radical anions, together with outer features for 5-6-dihydro-5-thymyl radicals, TH.. It is proposed that on freezing, the PSH molecules are constrained into a glassy region around the DNA, and that, on annealing, electron donation gives PS. radicals, with loss of quanine radical-cations, G(.+). The PS. radicals were not detectable, but on reaction with another PSH molecule, gave good EPR spectra for PS-.SP(-) radical-anions. These results indicate that PSH had little effect on the yield of the other base radicals C(.-)/T(.-). Also, growth of TH. radicals, formed from protonated thymine radical-anions, T(.-), were detected. We conclude that the primary effect of PSH is to capture the G(.+) centers, and thus could either prevent or repair radiation damage to DNA.

Effect of Antioxidant Vitamins on Radiation-Induced Apoptosis in Cells of a Human Lymphoblastic Cell Line

Modulating the amount of radiation-induced apoptosis by administering antioxidant vitamins offers a possible way to influence radiation-induced side effects in normal tissues. Therefore, we investigated the effect of beta-carotene, vitamin C and alpha-tocopherol on radiation-induced apoptosis in cells in culture. Human T-lymphoblastic MOLT-3 cells were irradiated with a dose of 3 Gy 1 h after or immediately prior to the addition of vitamins in three concentrations (0.01 microM, 1 microM and 100 microM). Eight hours later, apoptosis was scored morphologically by staining the nuclear DNA with Hoechst 33342. When given prior to irradiation, beta-carotene and vitamin E reduced the amount of radiation-induced apoptosis significantly at concentrations of 0.01 microM and 1 microM. In contrast, vitamin C did not show any protective effect when given at these two concentrations and caused a slight but significant radiosensitization at 100 microM. At 0.01 microM, all combinations of two vitamins showed a protective effect. This was also observed for the combination of all three vitamins at concentrations of 0.01 and 1 microM. When given immediately after irradiation, each of the three vitamins showed a protective effect at 0.01 microM. In addition, the combination of alpha-tocopherol and vitamin C reduced radiation-induced apoptosis slightly when given at 1 microM. In all other cases, no statistically significant modulation of radiation-induced apoptosis was observed. In our experimental system, the protective effect of beta-carotene and vitamin E was dependent on concentration and occurred only in the micromolar and sub-micromolar concentration range, while vitamin C alone, but not in combinations, had a sensitizing effect, thus arguing for a careful consideration of vitamin concentrations in clinical settings.

Estudo morfológico do efeito radioprotetor da vitamina E (dl-alfa-tocoferil) na reparação tecidual em ratos

Esta pesquisa teve por finalidade avaliar a ação da vitamina E como radioprotetora no processo de reparação tecidual em ratos, após sofrerem um procedimento cirúrgico, que consistiu da produção de uma ferida na região dorsal anterior. Os animais foram divididos em cinco grupos: grupo CO (controle) - constituído de animais em que foi produzida somente a ferida; grupo VE - pré-tratamento com vitamina E (90 UI); grupo IR - irradiação três dias após a cirurgia; grupo VEIR - pré-tratamento com 90 UI de vitamina E e irradiação de suas bordas três dias após a cirurgia; grupo OIR - pré-tratamento com óleo de oliva e irradiação de suas bordas três dias após a cirurgia. A ação radioprotetora da vitamina E foi avaliada pela coloração por hematoxilina-eosina para análise morfológica do tecido de granulação, aos 4, 7, 14 e 21 dias após a cirurgia. A análise dos resultados mostrou que o retardo no processo de reparação tecidual causado por 6 Gy de radiação de elétrons com feixe de 6 MeV não ocorreu no grupo de animais que recebeu vitamina E, mostrando-se esta substância efetiva como radioprotetora.

In VivoPostirradiation Protection by a Vitamin E Analog, α-TMG

The water-soluble vitamin E derivative alpha-TMG is an excellent radical scavenger. A dose of 600 mg/kg TMG significantly reduced radiation clastogenicity in mouse bone marrow when administered after irradiation. The present study was aimed at investigating the radioprotective effect of postirradiation treatment with alpha-TMG against a range of whole-body lethal (8.5-12 Gy) and sublethal (1-5 Gy) doses of radiation in adult Swiss albino mice. Protection against lethal irradiation was evaluated from 30-day mouse survival and against sublethal doses was assessed from micronuclei and chromosomal aberrations in the bone marrow 24 h after irradiation. An intraperitoneal injection of 600 mg/kg TMG within 10 min of lethal irradiation increased survival, giving a dose modification factor (DMF) of 1.09. TMG at doses of 400 mg/kg and 600 mg/kg significantly reduced the percentage of aberrant metaphases, the different types of aberrations, and the number of micronucleated erythrocytes. DMFs of 1.22 and 1.48 for percentage aberrant metaphases and 1.6 and 1.98 for micronuclei were obtained for 400 mg/kg and 600 mg/kg TMG, respectively. No drug toxicity was observed at these doses. The effectiveness of TMG when administered postirradiation suggests its possible utility for protection against unplanned radiation exposures.

Protective effect of melatonin against fractionated irradiation-induced epiphyseal injury in a weanling rat model

The effects of melatonin, a free-radical scavenger and a general antioxidant, on radiation-induced growth plate injury have not been studied previously. The purpose of this study was to determine the potential benefits of sparing longitudinal bone growth by fractionated radiotherapy alone compared with pretreatment with melatonin that provides differential radioprotection of normal cells. Weanling 4-wk-old (75-100 g) male Sprague-Dawley rats were randomly assigned to one of three groups: Group R received fractionated radiation alone (n = 8); groups M5 (n = 8) and M15 (n = 7) received 5 or 15 mg/kg melatonin prior to fractionated radiation, respectively. The distal femur and proximal tibia in the right leg of each animal were exposed to a therapeutic X-irradiation dose (25 Gy total in three fractions) with the contralateral left leg as the non-irradiated control. Melatonin was administered intraperitoneally to the animals 30 min before radiation exposure. Six weeks after treatment, the rats were killed and the lower limbs disarticulated, skeletonized, radiographed, and bone growth was calculated based on measurement of the bone lengths. Fractionated radiation resulted in a mean percent overall limb growth loss of 41.2 +/- 9.5 and a mean percent overall limb discrepancy of 11.2 +/- 2.2. The administration of 5 or 15 mg/kg melatonin before each of the three fractions of radiotherapy reduced the mean percent overall limb growth loss to 33.9 +/- 5.8 and 32.2 +/- 4.5, respectively, and the mean percent overall limb discrepancy to 9.4 +/- 1.6 and 8.9 +/- 1.1, respectively; these values were significantly different compared with irradiation alone (range: P = 0.01-0.04). When compared with Group R, the growth arrest recovered by 5 or 15 mg/kg melatonin was 19.7 and 24.1% for the tibia, 7 and 18.6% for the femur, and 17.7 and 21.8% for the total limb, respectively. These results support further investigation of melatonin in combination with fractionation for potential use in growing children requiring radiotherapy to the extremity for malignant tumors.