Relationships among indices of antioxidative activity in animals treated with selected prooxidants and antioxidants

Abstract

The aim of this study is to determine whether there are typical interactions and relationships among activities of indicative enzymes of free-radical scavenger system under the influence of environmental stressors. Animals representing various taxonomic groups: laboratory mice, rats, frogs, slugs of genus Agrolimax and Arion, earthworms Dendrobaena and Lumbricus, as well as Madagascar cockroach Gromphadorhina were treated with agents known for their prooxidative or antioxidative activity, such as: cadmium, paraquat, carbon tetrachloride, selenite and vitamin E. Diversified time schedules and ways of treatment with these agents were used in order to produce alterations of enzymatic activities and to assess whether there are essential relationships and signs of compensation among indices of antioxidative processes. The activity of superoxide dismutase, glutathione peroxidases, glutathione reductase, glutathione S-transferase, catalase as well as iron-ascorbate-stimulated lipid peroxidation and the content of thiobarbituric acid reactive substances were measured. When various doses of paraquat and cadmium were applied to mice, frog or invertebrate species the examined enzymes responded in a biphasic manner, characterised by an increase after lower and a decrease after higher doses. In some cases inverted biphasic pattern was also observed. The complex, “mosaic” alterations of enzyme activity within various organs, characterised by opposite changes of examined parameters were observed and explained as resulting from a diverse distribution of applied compounds within organism as well as from specific susceptibility of particular organs and enzymes. Additionally, the “mosaic” response pattern may reflect another aspect of biphasic dose-response relationships in the examined organs. Since a compensation of altered activity of peroxidase related pathway of free radical scavenger system by opposite alteration of superoxide dismutase and catalase activity was observed in several cases, the hypothesis on the mutual compensatory relations within antioxidative system was drawn and summarised as follows. An inhibition of Se-dependent glutathione peroxidase related pathway of free radical scavenger system in the organs of prooxidant-treated animals may provoke a stimulation of catalase and superoxide dismutase activity, which compensates for this inhibition. This mechanism possibly acts also in the opposite direction, compensating decreased activity of catalase with glutathione peroxidase or glutathione S-transferase activity. Additionally, some evidence was obtained for the compensation of decreased glutathione peroxidases activity by increasing reaction rate of these enzymes due to enhanced flux and availability of reduced glutathione, on condition that activity of glutathione reductase will rise sufficiently and the pool of reduced nicotinamide dinucleotide phosphate (NADPH) is maintained. The general frame of mutual compensatory mechanism within the antioxidative system postulated here seems to be common and universal, at least in the examined vertebrate species, insects and earthworms. Other observations and conclusions were also drawn on the basis of presented results.