Role of vitamin A and beta carotene in radiation protection: relation to antioxidant properties

The role of nutrition in space exploration: Implications for sensorimotor, cognition, behavior and the cerebral changes due to the exposure to radiation, altered gravity, and isolation/confinement hazards of spaceflight

Multi-year crewed space exploration missions are now on the horizon; therefore, it is important that we understand and mitigate the physiological effects of spaceflight. The spaceflight hazards-radiation, isolation, confinement, and altered gravity-have the potential to contribute to neuroinflammation and produce long-term cognitive and behavioral effects-while the fifth hazard, distance from earth, limits capabilities to mitigate these risks. Accumulated evidence suggests that nutrition has an important role in optimizing cognition and reducing the risk of neurodegenerative diseases caused by neuroinflammation. Here we review the nutritional perspective of how these spaceflight hazards affect the astronaut's brain, behavior, performance, and sensorimotor function. We also assess potential nutrient/nutritional countermeasures that could prevent or mitigate spaceflight risks and ensure that crewmembers remain healthy and perform well during their missions. Just as history has taught us the importance of nutrition in terrestrial exploration, we must understand the role of nutrition in the development and mitigation of spaceflight risks before humans can successfully explore beyond low-Earth orbit.

Radioprotection and Radiomitigation: From the Bench to Clinical Practice

The development of protective agents against harmful radiations has been a subject of investigation for decades. However, effective (ideal) radioprotectors and radiomitigators remain an unsolved problem. Because ionizing radiation-induced cellular damage is primarily attributed to free radicals, radical scavengers are promising as potential radioprotectors. Early development of such agents focused on thiol synthetic compounds, e.g., amifostine (2-(3-aminopropylamino) ethylsulfanylphosphonic acid), approved as a radioprotector by the Food and Drug Administration (FDA, USA) but for limited clinical indications and not for nonclinical uses. To date, no new chemical entity has been approved by the FDA as a radiation countermeasure for acute radiation syndrome (ARS). All FDA-approved radiation countermeasures (filgrastim, a recombinant DNA form of the naturally occurring granulocyte colony-stimulating factor, G-CSF; pegfilgrastim, a PEGylated form of the recombinant human G-CSF; sargramostim, a recombinant granulocyte macrophage colony-stimulating factor, GM-CSF) are classified as radiomitigators. No radioprotector that can be administered prior to exposure has been approved for ARS. This differentiates radioprotectors (reduce direct damage caused by radiation) and radiomitigators (minimize toxicity even after radiation has been delivered). Molecules under development with the aim of reaching clinical practice and other nonclinical applications are discussed. Assays to evaluate the biological effects of ionizing radiations are also analyzed.

Study logistics that can impact medical countermeasure efficacy testing in mouse models of radiation injury

PURPOSE

To address confounding issues that have been noted in planning and conducting studies to identify biomarkers of radiation injury, develop animal models to simulate these injuries, and test potential medical countermeasures to mitigate/treat damage caused by radiation exposure.

METHODS

The authors completed an intensive literature search to address several key areas that should be considered before embarking on studies to assess efficacy of medical countermeasure approaches in mouse models of radiation injury. These considerations include: (1) study variables; (2) animal selection criteria; (3) animal husbandry; (4) medical management; and (5) radiation attributes.

RESULTS

It is important to select mouse strains that are capable of responding to the selected radiation exposure (e.g. genetic predispositions might influence radiation sensitivity and proclivity to certain phenotypes of radiation injury), and that also react in a manner similar to humans. Gender, vendor, age, weight, and even seasonal variations are all important factors to consider. In addition, the housing and husbandry of the animals (i.e. feed, environment, handling, time of day of irradiation and animal restraint), as well as the medical management provided (e.g. use of acidified water, antibiotics, routes of administration of drugs, consideration of animal numbers, and euthanasia criteria) should all be addressed. Finally, the radiation exposure itself should be tightly controlled, by ensuring a full understanding and reporting of the radiation source, dose and dose rate, shielding and geometry of exposure, while also providing accurate dosimetry. It is important to understand how all the above factors contribute to the development of radiation dose response curves for a given animal facility with a well-defined murine model.

CONCLUSIONS

Many potential confounders that could impact the outcomes of studies to assess efficacy of a medical countermeasure for radiation-induced injuries are addressed, and recommendations are made to assist investigators in carrying out research that is robust, reproducible, and accurate.

Mechanisms of cardiac radiation injury and potential preventive approaches

In addition to cytostatic treatment and surgery, the most common cancer treatment is gamma radiation. Despite sophisticated radiological techniques however, in addition to irradiation of the tumor, irradiation of the surrounding healthy tissue also takes place, which results in various side-effects, depending on the absorbed dose of radiation. Radiation either damages the cell DNA directly, or indirectly via the formation of oxygen radicals that in addition to the DNA damage, react with all cell organelles and interfere with their molecular mechanisms. The main features of radiation injury besides DNA damage is inflammation and increased expression of pro-inflammatory genes and cytokines. Endothelial damage and dysfunction of capillaries and small blood vessels plays a particularly important role in radiation injury. This review is focused on summarizing the currently available data concerning the mechanisms of radiation injury, as well as the effectiveness of various antioxidants, anti-inflammatory cytokines, and cytoprotective substances that may be utilized in preventing, mitigating, or treating the toxic effects of ionizing radiation on the heart.

Characterization and radio-resistant function of manganese superoxide dismutase of Rubrobacter radiotolerans

Rubrobacter radiotolerans is the most radio-resistant eubacterium without spore-formation in the life cycle, and its D(37) is 16,000 Gy against gamma-rays. To understand the molecular mechanism of the high radio-resistance, we purified and characterized superoxide dismutase (SOD) of this organism as enzymatic radical scavenger, and then analyzed its genetic information. The purified SOD protein formed homo-tetramerization of 24,000 Da-monomer, while maintaining its enzymatic activity against potassium cyanide and hydrogen peroxide. We obtained a partial amino acid sequence of the protein and cloned the gene from it. Sequence analysis of the cloned gene indicated that the protein showed a similarity to other bacterial manganese SODs (Mn-SODs). Sequencing for adjacent regions of the gene showed that the gene had promoter elements with an open reading frame for putative PAS/PAC sensor protein at the 5'-adjacent region. Introduction of the gene into Escherichia coli cells lacking intrinsic SOD genes restored the cellular enzymatic activity and resistance to methyl viologen, indicating the gene at work. A mutant cell harboring this gene also became resistant against gamma-rays. The present results suggest that the protein in question is the Mn-SOD of R. radiotolerans, a good candidate as a radio-protection factor for this bacterial radio-resistance.

Effect of grape seed extract on lipid peroxidation, antioxidant activity and peripheral blood lymphocytes in rats exposed to x-radiation

The present studies were designed to evaluate supplemental grape seed extract (GSE) and vitamin E supplements on lipid peroxidation, on antioxidant systems and peripheral blood lymphocytes in rats exposed to x-rays. Three groups of rats were investigated: a control group (CG) received intraperitoneal (i.p.) physiological serum 1 mL/day (n=10), i.p.; a vitamin E group (VG) received 50 mg/kg/day (n=10); an i.p. grape seed extract group received 50 mg/kg/day (n=10). Four weeks later, a 6 Gy radiation dose was given to the rats. Blood samples were taken 24 h later after irradiation and lymphocyte, malondialdehyde (MDA), reduced glutathione (GSH), nitrate, nitrite, reduced ascorbic acid, retinol, beta-carotene and ceruloplasmin concentrations were analysed. The levels of GSH (p<0.05), retinol (p<0.001), beta-carotene (p<0.05) and ceruloplasmin concentration (p<0.001) in the GSE group were found to be higher than in the control group but the level of MDA (p<0.001) and nitrite concentration (p<0.05) in rats supplemented with GSE were found to be lower than in the control group. The results indicate that GSE enhanced the antioxidant status and decreased the incidence of free radical-induced lipid peroxidation in blood samples of rats exposed to x-radiation. The antioxidant effect of GSE given to animals was more effective than vitamin E administered before whole-body irradiation in rats.

Randomized trial of antioxidant vitamins to prevent acute adverse effects of radiation therapy in head and neck cancer patients

PURPOSE

Many cancer patients take antioxidant vitamin supplements with the hope of improving the outcome of conventional therapies and of reducing the adverse effects of these treatments. A randomized trial was conducted to determine whether supplementation with antioxidant vitamins could reduce the occurrence and severity of acute adverse effects of radiation therapy and improve quality of life without compromising treatment efficacy.

PATIENTS AND METHODS

We conducted a randomized, double-blind, placebo-controlled trial among 540 head and neck cancer patients treated with radiation therapy. Patients were randomly assigned into two arms. The supplementation with alpha-tocopherol (400 IU/d) and beta-carotene (30 mg/d) or placebos was administered during radiation therapy and for 3 years thereafter. During the course of the trial, supplementation with beta-carotene was discontinued because of ethical concerns.

RESULTS

Patients randomly assigned in the supplement arm tended to have less severe acute adverse effects during radiation therapy (odds ratio [OR], 0.72; 95% CI, 0.52 to 1.02). The reduction was statistically significant when the supplementation combined alpha-tocopherol and beta-carotene for adverse effects to the larynx (OR, 0.38; 95% CI, 0.21 to 0.71) and overall at any site (OR, 0.38; 95% CI, 0.20 to 0.74). Quality of life was not improved by the supplementation. The rate of local recurrence of the head and neck tumor tended to be higher in the supplement arm of the trial (hazard ratio, 1.37; 95% CI, 0.93 to 2.02).

CONCLUSION

Supplementation with high doses of alpha-tocopherol and beta-carotene during radiation therapy could reduce the severity of treatment adverse effects. However, this trial suggests that use of high doses of antioxidants as adjuvant therapy might compromise radiation treatment efficacy.

Effects of Bambusae concretio Salicea (Chunchukhwang) on amyloid beta-induced cell toxicity and antioxidative enzymes in cultured rat neuronal astrocytes

Bambusae concretio Salicea (BCS; plant family name: Phyllostachys bambusoides Siebold et Zuccarinii) is a medicinal plant used in Korea for the treatment of various symptoms accompanying hypertension and cerebrovascular disorders. Previously, it was shown that BCS is an effective protectant against oxidative glutamate toxicity in the murine neuroblastoma cells and human neuroblastoma cells. Treatment with BCS increased the secretion of the non-amyloidogenic amyloid precursor protein fragment, and decreased the secretion of amyloid-beta (Abeta) peptides from neuronal cells [Jeong, J.C., Seo, Y.J., Kim, H.M., Lee, Y.C., Kim, C.H., 2003. Inhibitory effects of Bombusae concretio Salicea on neuronal secretion of Alzheimer's beta-amyloid peptides, a neuro-degenerative peptide. Neurochemical Research 28, 1785-1792.]. To further examine the pharmacological activity of BCS, we studied the protective effect of the water extracts on Abeta25-35 peptide-induced neuronal death by microscopic observation and lactate dehydrogenase (LDH) assay, and action on antioxidative enzymes using cultured astrocyte cells. Ten microM Abeta25-35-induced cell death was protected by the application of water extract of BCS in a dose-dependent manner, and concentrations of 1-10 microg/ml had a significant effect compared to exposure to Abeta25-35 only. When antioxidative enzyme activities such as catalase, superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione-S-transferase (GST) were assayed after Abeta25-35 treatment, the enzymes were decreased in a similar fashion. However, those activities were enhanced by BCS treatment and this may have resulted from the potentiation of antioxidative ability by BCS. The ability of BCS to reduce cellular cytotoxicity induced by 10 microM Abeta25-35 suggests that BCS may be a protective agent for free radical generating compounds such as Abeta25-35, and that Abeta25-35 is not only a potent lipid peroxide inducer, but also causes changes in antioxidative enzymes. From the results, it was concluded that BCS has a protective effect on Abeta-induced neuronal death in cultured astrocyte cells through the inhibition of lipid peroxidation and protection of antioxidative enzymes.

Retinoids and TIMP1 prevent radiation-induced apoptosis of capillary endothelial cells

Radiation-induced changes in capillaries constitute a basic injury in the pathogenesis of chronic radiation damage to the heart, lung, liver, kidney and brain. It is important to identify new radioprotectors for capillary endothelial cells for use during radiotherapy to minimize normal tissue damage and possibly to increase the deliverable dose. Previously we demonstrated that exposure to ionizing radiation (10 Gy) results in death of bovine adrenal capillary endothelial cells in confluent monolayers by apoptosis. We also showed that retinoids inhibit the growth of endothelial cells, induce their differentiation, down-regulate matrix metalloproteinase (MMP) production, and up-regulate tissue inhibitors of matrix metalloproteinases (TIMPs). In the present studies, we demonstrated that radiation (10 Gy) induced an immediate increase in the amounts and activation of MMP1 and MMP2 in the cell fraction and medium of bovine capillary endothelial cells followed by an incidence of apoptosis. We also obtained data indicating that radiation-induced apoptosis can be inhibited by exposing bovine capillary endothelial cells to all-trans-retinol or all-trans-retinoic acid for 6 days before irradiation, even when the vitamins were removed 24 h before irradiation. Finally, we determined that inhibition of MMPs by TIMP was sufficient to block radiation-induced apoptosis, suggesting that the mechanism of protection by retinoids is through the alteration of levels of MMPs and TIMPs produced by the cells.

Protection against ionizing radiation by antioxidant nutrients and phytochemicals

The potential of antioxidants to reduce the cellular damage induced by ionizing radiation has been studied in animal models for more than 50 years. The application of antioxidant radioprotectors to various human exposure situations has not been extensive although it is generally accepted that endogenous antioxidants, such as cellular non-protein thiols and antioxidant enzymes, provide some degree of protection. This review focuses on the radioprotective efficacy of naturally occurring antioxidants, specifically antioxidant nutrients and phytochemicals, and how they might influence various endpoints of radiation damage. Results from animal experiments indicate that antioxidant nutrients, such as vitamin E and selenium compounds, are protective against lethality and other radiation effects but to a lesser degree than most synthetic protectors. Some antioxidant nutrients and phytochemicals have the advantage of low toxicity although they are generally protective when administered at pharmacological doses. Naturally occurring antioxidants also may provide an extended window of protection against low-dose, low-dose-rate irradiation, including therapeutic potential when administered after irradiation. A number of phytochemicals, including caffeine, genistein, and melatonin, have multiple physiological effects, as well as antioxidant activity, which result in radioprotection in vivo. Many antioxidant nutrients and phytochemicals have antimutagenic properties, and their modulation of long-term radiation effects, such as cancer, needs further examination. In addition, further studies are required to determine the potential value of specific antioxidant nutrients and phytochemicals during radiotherapy for cancer.

Bombycis corpus extract prevents amyloid-beta-induced cytotoxicity and protects superoxide dismutase activity in cultured rat astrocytes

Bombycis corpus(BC) or Bombyx Batryticatus, a batryticated silkworm and white-stiff silkworm, is a drug consisting of the dried larva of silkworm, Mobyz mori L., dead and stiffened due to the infection of Beauveria (Bals.) Vuill. In the present study, we have examined the protective effect of the water extracts against Amyloid- beta(A beta) 25-35 peptide-induced cytotoxicity by microscopic observation and LDH assay, and its action on antioxidative enzymes using cultured astrocyte cells. A beta 25-35-induced cell death was protected by the application of water extract of BC in a dose-dependent manner, and concentrations of 10(-6)to 10(-7)g ml(-1)showed a significant effect compared to exposure of A beta 25-35 alone. When antioxidative enzyme activities such as catalase, superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and glutathione-S transferase (GST) were assayed after A beta 25-35 treatment, most enzyme activities were decreased in a similar fashion. BC treatment of A beta 25-35-treated astrocytes did not affect the enzyme activities of catalase, GSH-Px and GST. However, only SOD activity was enhanced by BC treatment and this may result from the potentiation of the antioxidative ability of BC. The protective effect of BC against cytotoxicity induced by Abeta 25-35 strongly indicates that BC could be a protective agent for free radical generating compounds, and that Abeta 25-35 is not only a potent lipid peroxide inducer, but can also cause changes in antioxidative enzymes. From the results, it was concluded that BC has a protective effect against Abeta -induced cytotoxicity in cultured astrocyte cells through the inhibition of lipid peroxidation and protection of antioxidative enzymes.

Antioxidant nutrients: current dietary recommendations and research update

OBJECTIVE

To review the importance of antioxidant nutrients in the maintenance of health and the prevention and treatment of disease, with a focus on data pertaining to vitamin C, vitamin E, selenium, and carotenoids. A secondary objective was to discuss the new Dietary Reference Intakes released by the Institute of Medicine (IOM) for these nutrients.

DATA SOURCES

IOM reports on the use of antioxidant vitamins were reviewed for nutrient recommendations. In addition, a MEDLINE search was performed to identify recent research and review articles on the topic, which were analyzed to identify key research findings in the area.

DATA SYNTHESIS

The review discusses the biologic processes of oxidation reactions and antioxidants in biologic systems, provides an overview of information on selected antioxidant nutrients, and explores their role in the prevention and treatment of cancer, cardiovascular disease, ocular disorders, and respiratory disorders.

CONCLUSION

There appear to be significant health benefits from dietary antioxidants, as can be found in fruits and vegetables. Some prospective assessment of the effect of supplemental antioxidants also suggests benefit, especially for vitamin E; however, there are conflicting results in this area. Overall, it appears that antioxidant nutrients, especially those from food sources, have important roles in preventing pathogenic processes related to cancer, cardiovascular disease, macular degeneration, cataracts, and asthma, and may enhance immune function.

Antioxidant micronutrients and childhood malignancy during oncological treatment

Serum antioxidant vitamins A (retinol) and E (alpha-tocopherol), beta-carotene, zinc, and selenium, and cholesterol and related proteins for 170 children with newly diagnosed malignancy were measured at diagnosis and 6 months after initiation of treatment, and compared with those of 632 cancer-free controls. Incident cancer cases and controls were 1-16 years old and recruited between 1986 and 1989. At diagnosis, age- and sex-adjusted serum concentrations of retinol, beta-carotene, zinc, and alpha-tocopherol were significantly inversely associated with cancer. No significant decreases in mean values were observed at 6 month, except for the alpha-tocopherol-to-cholesterol ratio in patients with bone tumors and serum zinc in bone tumors and central nervous system malignancies. An increase during the period of treatment was found for retinol and selenium in leukemia patients. beta-carotene was maintained at the initial concentrations determined prior to therapy. These findings provide further information about micronutrient requirements in children with cancer.

Can alpha-tocopherol and beta-carotene supplementation reduce adverse radiation effects on salivary glands?

In this study, we evaluated whether supplementation with antioxidant vitamins can reduce the adverse effects of irradiation on the salivary glands in the rat. Four groups of adult Sprague-Dawley rats were given a basic diet providing 0.6 mg alpha-tocopherol and no beta-carotene per day. In two groups the basic diet was supplemented with 3.4 mg alpha-tocopherol and 6 mg beta-carotene per day from 14 days before irradiation until 12 days after completed irradiation. One group of rats given basic diet and one group given supplemented diet were irradiated with 7 Gy daily for five consecutive days. Isoproterenol and pilocarpine-stimulated whole saliva was collected from all rats 2, 4 and 26 weeks after irradiation. Vitamin-supplemented irradiated rats had higher secretion rates on all three occasions compared with those of irradiated rats given basic diet. The changes in saliva composition seen in irradiated rats were less accentuated in vitamin-supplemented, irradiated rats. The proportions of acinar cells were significantly decreased both in parotid and submandibular glands 26 weeks after irradiation. Supplementation with alpha-tocopherol and beta-carotene did not alter the morphology of the glands.

The selective cytotoxic effect of carotenoids and alpha-tocopherol on human cancer cell lines in vitro

This study compares the toxic effects of the carotenoids, beta-carotene and canthaxanthin, and alpha-tocopherol (vitamin E) on human tumor cells and their normal counterparts in vitro. Seven different malignant cell lines were examined: oral carcinoma (two cell lines), breast (two cell lines), lung carcinoma (two cell lines), and malignant melanoma. The in vitro cell culture assays showed a consistent morphologic change in the affected tumor cells following treatment with carotenoid or vitamin E. A rounding of the tumor cells and eventual lifting off the tissue culture plate were observed. These changes were apparent after 1 to 5 hours of treatment depending on the tumor cell line. Associated with these observable cellular changes were quantitative reductions in proliferation (3H-thymidine proliferation) and succinic dehydrogenase activity (MTT assay). In addition, there was a noticeable change in protein expression, with an increased expression of a 70-kD protein following treatment with beta-carotene. This protein was associated with tumor cells showing a decrease in proliferation (oral carcinoma, malignant melanoma) but not with normal keratinocytes or melanocytes. These studies substantiate a selective cytotoxic effect on human tumor cell growth by carotenoids and alpha-tocopherol in vitro, and may provide an explanation of the therapeutic activity of these agents and their possible use in the treatment of premalignancy or early oral carcinoma.

Beta-carotene and/or vitamin E as modulators of alkylating agents in SCC-25 human squamous carcinoma cells

Dietary levels of beta-carotene and vitamin E have been associated with cancer prevention and to a lesser extent, with therapeutic enhancement of cancer treatment. We report on the cytotoxicity of beta-carotene, vitamin E, and the combination of beta-carotene and vitamin E in human SCC-25 squamous carcinoma cells under various environmental conditions found in solid tumor masses. Beta-Carotene was selectively cytotoxic toward normally oxygenated cells and was generally more cytotoxic at normal pH than at acidic pH (6.45). Vitamin E was selectively cytotoxic toward normally oxygenated cells following 6 h exposure at normal pH and was generally equally cytotoxic toward normally oxygenated and hypoxic cells under the other conditions tested. Beta-Carotene was an effective modulator of cisplatin (CDDP) cytotoxicity toward SCC-25 cells, whereas vitamin E was not. Both beta-carotene and vitamin E were effective modulators of melphalan cytotoxicity toward SCC-25 cells. Treatment of SCC-25 cells with beta-carotene (70 microM, 2h) resulted in a reduction in superoxide dismutase activity, in glutathione-S-transferase activity, and in nonprotein sulfhydryl levels in the cells. Exposure to vitamin E or to a combination of beta-carotene and vitamin E increased the glutathione-S-transferase activity in SCC-25 cells by 40%-45% over the control value. Treatment with beta-carotene, vitamin E, or canthaxanthin reduced the incorporation of [3H]-thymidine into SCC-25 cells but not that into normal human keratinocytes. The most marked reduction in [3H]-thymidine incorporation into SCC-25 cells occurred following treatment with the combination of beta-carotene and melphalan. We hope to continue to explore the mechanisms of this effect and to study these combinations in vivo.

New protective agents for bone marrow in cancer therapy

WR-2721 is a unique bone marrow protective agent which also protects other normal tissues against the toxic effects of radiation therapy and chemotherapy, especially with cisplatin and alkylating agents. In addition to protection against acute toxicities, WR-2721 has also been shown to protect against mutagenesis, cell transformation, and carcinogenesis which might be termed subacute and late toxicities. The protective mechanisms are not fully elucidated but oxygen free radical scavenging certainly plays a role and effects of enzymatic DNA repair mechanisms have also been reported. In the field of reduction of toxicity from anticancer treatment modalities, the properties of CSFs and other substances have been contrasted with WR-2721 the former being stimulators of bone marrow (and the immune system) rather than true protectors. Nonetheless, they also have a clinical role and combinations of a protector and stimulator may prove useful in the future. WR-2721 offers the prospect of increasing the therapeutic index of current cancer treatment and may allow the administration of higher than currently would be considered maximal tolerated doses (MTD). This may, in turn, lead to improved efficacy and the full potential of this agent is now being explored in a variety of randomized, controlled clinical trials.