Dose-rate and Oxygen Effects in Models of Lipid Membranes: Linoleic Acid

Cellular membranes have been suggested as possible loci for the development of the oxygen effect in radiobiology. Unsaturated lipids from membranes are subject to very efficient radiation-induced peroxidation, and the deleterious effects generally associated with lipid autoxidation could be initiated by ionizing radiation. Oxidative damage in lipids is characterized not only by high yields but also by a profound dose-rate effect. At dose-rates of X-irradiation below 100 rad/min, a very sharp rise occurs in oxidative damage. This damage has been quantified spectrophotometrically in terms of diene conjugation (O.D. 234 mm) and chromatographically in terms of specific 9- and 13-hydroperoxide formation in linoleic acid micelles. Radical scavenging experiments indicate that hydroxyl radical attack initiates the oxidative damage. Dimethyl sulphoxide is exceptional in that it does not protect, but sensitizes, linoleic acid to radiation induced peroxidation. The yields of hydroperoxides are substantial (G=10--40) and can be related to biological changes known to be effected by autoxidizing lipids.