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Oxy‐Radicals and the Radiobiological Oxygen Effect
Author(s) -
Greenstock Clive L.
Publication year - 1984
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1002/ijch.198400001
Subject(s) - radiolysis , chemistry , oxygen , radical , oxygen enhancement ratio , redox , biophysics , reactive oxygen species , kinetics , dna damage , radiochemistry , photochemistry , biochemistry , dna , organic chemistry , physics , quantum mechanics , biology
Abstract The radiobiological oxygen effect can be separated into its biological and chemical components, using time‐resolved or kinetic studies. Rapid mix techniques show that the full oxygen enhancement ratio (OER) for radiation‐induced cell killing is expressed when oxygen is present or admitted 40 ms prior to irradiation. This predominant chemical action of oxygen, including direct and indirect action, is too fast to implicate processes other than those involving free radical species. The two principal hypotheses, “oxygen fixation” and “active oxygen”, are discussed. Pulse radiolysis studies of model systems provide kinetic data to indicate the principal damaging species and radiation targets, the kinetics and sequence of damaging events, and the role of redox processes involving oxygen, oxy‐radicals and radiation modifiers. Complementary steady‐state radiolysis studies enable the nature and extent of the physico‐chemical damage to be quantified. Mechanistic aspects of the radiobiological oxygen effect are inferred from in vitro studies of irradiated mammalian cells, comparing the different biological end‐points with specific forms of chemical damage, under a variety of physical, chemical and biological conditions. While this review stresses the role of oxygen in sensitizing the critical cellular target DNA, responsible for the acute biological effect of cell killing, it must be remembered that for cancer and other chronic effects, having a long latent period between radiation exposure and the biological expression of deleterious damage, there may not be an oxygen effect or if there is, it may be quite different in terms of the damaging species, principal radiation targets, and the sequence and kinetics of the damaging events. Although oxygen and oxy‐radicals may be involved in the initiation and development of cancer, their overall roles in influencing the chronic effects of radiation may be complex and dependent upon cellular and multicellular factors, making it difficult to unambiguously elucidate possible mechanisms.