The influence of antioxidants in the thiyl radical induced lipid peroxidation and isomerization processes in linoleic acid micelles

Abstract

Lipids are targets of various reactive oxygen, nitrogen and sulphur species. There are two main classes of reactions that are known in the context of reactivity of polyunsaturated fatty acids toward free radicals. One of the well known process is lipid peroxidation and the second one, much recent studied, is the process of geometrical isomerization of unsaturated lipids which can be catalysed by thiyl radicals (RS•). It has been shown that one process can be parallel with the occurence of the other and that lipid hydroperoxides and trans lipids can be the resulting effect of oxidative free radical conditions. In living organizms both lipid peroxidation and isomerization have damaging effects on cell membranes. The study of these processes in the biomimetic model of micelles of linoleic acid (LH) containing 2-mercaptoethanol as the thiol, has been extended in the presence of several natural occuring antioxidants. In order to study their protective properties against lipid peroxidation and trans isomerization, each of antioxidants -tocopherol, ascorbic acid and resveratrol, was added to the model systems. The systems were irradiated by gamma radiation up to 400 Gy, under a variety of conditions where RS• are the main reactive species. Preliminary results have shown that lipid peroxidation was retarded by ascorbic acid and -tocopherol, whereas this process was strongly inhibited by resveratrol. Furthermore, antioxidants have a much stronger inhibitory effect on the peroxidation in the presence of 2-mercaptoethanol. In model systems under anaerobic conditions, where process of geometrical isomerization prevails, the presence of antioxidants have influenced on decrease of the trans isomerization level. The ability of RS• scavenging was found to increase along the series resveratrol, -tocopherol, ascorbic acid. All results obtained in this study indicate that trans isomerization depends on the localization of the particular antioxidant in model LH system.