...REGULATION OF PHYSIOLOGICAL SYSTEMS BY NUTRIENTS Free Radicals, Antioxidants, and Nutrition Yun-Zhong Fang, Sheng Yang, and Guoyao Wu, PhD From the Department of Biochemistry and Molecular Biology, Beijing Institute of Radiation Medicine, Beijing, China; the Division of Animal Nutrition, Department of Animal Science, China Agricultural University, Beijing, China; and the Department of Animal Science and Faculty of Nutrition, Texas A&M University, College Station, Texas, USA Radiation hazards in outer space present an enormous challenge for the biological safety of astronauts. A deleterious effect of radiation is the production of reactive oxygen species, which result in damage to biomolecules (e.g., lipid, protein, amino acids, and DNA). Understanding free radical biology is necessary for designing an optimal nutritional countermeasure against space radiation–induced cytotoxicity. Free radicals (e.g., superoxide, nitric oxide, and hydroxyl radicals) and other reactive species (e.g., hydrogen peroxide, peroxynitrite, and hypochlorous acid) are produced in the body, primarily as a result of aerobic metabolism. Antioxidants (e.g., glutathione, arginine, citrulline, taurine, creatine, selenium, zinc, vitamin E, vitamin C, vitamin A, and tea polyphenols) and antioxidant enzymes (e.g., superoxide dismutase, catalase, glutathione reductase, and glutathione peroxidases) exert synergistic actions in scavenging free radicals. There has been growing evidence over the past three decades...
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