Radiosensitivity

Diethjidithiocarbamate [20624-25-3] (DDC) is both an inhibitor of SOD and a thiol, and exerts both radiosensitizing and radioprotective properties in mice, depending on factors such as the time of its adniinistration relative to irradiation. For neutrons, DDC shows only protective effects (141). DDC (1 mg/g ip) given 30 min before 15 Gy (1500 rad) also protects mouse jejunal crypt ceUs and reduces the frequency of micronuclei in splenic lymphocytes (134). 

TNE- a also protects mice against the lethal effects of radiation (164). TNE- a given before sublethal kradiation reduces the decline of neutrophils and total blood counts and accelerates the recovery of peripheral blood cells (190). TNE- a also alters the radiosensitivity of murine G1 progenitors (191). 

Whereas epidermal growth factor (EGF) enhances the radiosensitivity of human squamous ceU carcinoma cells in vitro (197), addition of EGF to hormone-deprived MCE-7 breast cancer cells prior to irradiation results ia iacreased radioresistance (198). An anti-EGE-receptor monoclonal antibody blocks the abiUty of EGE to enhance growth and radioresistance. Tumor cells, the growth of which is stimulated by EGE, appear to be protected those where growth is iohibited are sensitized (198). 

Sulphide and sulphoxide complexes have been extensively studied since cis-RuC12(DMSO)4 (DMSO, dimethyl sulphoxide, (Me)2SO) was found to have anti-tumour properties and to be a precessor for radiosensitizing agents. Such complexes can act as catalysts for the oxidation of sulphides with molecular oxygen. 

Again both S- and O-bonded sulphoxides are found. mer-[RuCl3(Ph2SO)3] has one S-bonded sulphoxide and two O-bonded sulphoxides (one trans to Cl, one trans to S) [112], The imidazole-substituted complexes are being studied as possible radiosensitizers and for anti-tumour activity. 

Taxanes (paclitaxel, docetaxel) are derivatives of yew tree bark (Taxus brevifolia). They stabilize microtubules in the polymerized state leading to nonfunctional microtubular bundles in the cell. Inhibition occurs during G2- and M-phases. Taxanes are also radiosensitizers. Unwanted effects include bone marrow suppression and cumulative neurotoxicity. 

Radiation sterilization Radiochromic chemical Plastic devices impregnated with radiosensitive chemicals which undergo colour changes at relatively low radiation doses Only indicate exposure to radiation... 

Redpath, J.L. et al. (1975). Role of metal ions in the radiosensitivity of mctalloproteins. Model experiments with bovine carbonic anhydrase. Int. J. Radiat. Biol. 26, 243. 

Lloyd RD, Taylor GN, Jee WSS, et al. 1999. Relative radiosensitivity of bone tumor induction among beagles as a function of age at injection of 239Pu or 226RA. Health Phys 76(l) 75-81. 

Schoeters GER, Vander Plaetse F, Van Den Heuvel RL. 1992. High radiosensitivity of the mineralization capacity of adult murine bone marrow in vitro to continuous a-irradiation compared to acute X-irradiation. Int J Radiat Biol 61(5) 675-683. 

Svoboda V, Kotaskova Z. 1983. Radiosensitivity and proliferative activity of vertebral CFU-S surviving in mice injected with oncogenic activities of 239Pu or 241Am. J Hyg Epidemiol Microbiol Immunol 27(3) 329-335. 

Van Den Heuvel R, Schoeters G, Vanderborght O. 1987. Radiosensitivity to 241 Am of bone marrow stromal cells in offspring of contaminated mice. In Age-related factors in radionuclide metabolism and dosimetry. Netherlands Kluwer Academic Publishers, 201-208. 

Radiosensitivity—Relative susceptibility of cells, tissues, organs, organisms, or any living substance to the injurious action of radiation. Radiosensitivity and its antonym, radioresistance, are currently used in a comparative sense, rather than in an absolute one. 

Some effects of irradiation on vitamins have been mentioned earlier. It appears that irradiation and heat treatment affect vitamins differendy. Apparendy, vitamins Br B6, B12 and folic acid decompose less under as high a radiation dose as 60 kGy than under autoclaving at 120°Cfor 20 minutes. On the other hand, vitamin C is much more sensitive to irradiation. Generally, the radiosensitive vitamins are also sensitive to light, heat, and oxygen. In fresh foods, the vitamins that are most susceptible to irradiation are A and E. There is also some decomposition of vitamins B, and C. Other vitamins are fairly stable under irradiation. However, for the most part, the vitamins are more susecptible to heat treatment than to irradiation. 

Acute biological effects of the Chernobyl accident on local natural resources were documented by Sokolov et al. (1990). They concluded that the most sensitive ecosystems affected at Chernobyl were the soil fauna and pine forest communities and that the bulk of the terrestrial vertebrate community was not adversely affected by released ionizing radiation. Pine forests seemed to be the most sensitive ecosystem. One stand of 400 ha of Pirns silvestris died and probably received a dose of 80 to 100 Gy other stands experienced heavy mortality of 10- to 12-year-old trees and up to 95% necrotization of young shoots. These pines received an estimated dose of 8 to 10 Gy. Abnormal top shoots developed in some Pirns, and these probably received 3 to 4 Gy. In contrast, leafed trees such as birch, oak, and aspen in the Chernobyl Atomic Power Station zone survived undamaged, probably because they are about 10 times more radioresistant than pines. There was no increase in the mutation rate of the spiderwort, (Arabidopsis thaliana) a radiosensitive plant, suggesting that the dose rate was less than 0.05 Gy/h in the Chernobyl locale. 

All plants are more radiosensitive during the growing season than during the dormant season. 

Reproductive stages are always more radiosensitive than vegetative stages. 

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