A biomimetic model of free radical reactivity: The influence of antioxidants in the thiyl radical induced lipid peroxidation and isomerization processes

Biomimetic models provide basic molecular mechanisms studies that are closer to the biological environment such as living organism. 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 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.1 Both processes have damaging effects on cell membranes of living organisms. In this study, the biomimetic model of micelles of linoleic acid containing 2-mercaptoethanol (RSH) were irradiated by gamma radiation under a variety of conditions where RS• are the main reactive species. The study of these processes has been extended in the presence of several natural occuring antioxidants which have shown their protective properties against lipid peroxidation and trans isomerization. Lipid peroxidation was retarded by ascorbic acid and α-tocopherol, whereas this process was strongly inhibited by resveratrol and the ascorbic acid/α-tocopherol mixture. Furthermore, antioxidants have a much stronger inhibitory effect on the peroxidation in the presence of 2-mercaptoethanol. Under anaerobic conditions, where lipid peroxidation is suppresed, the presence of antioxidants have influenced on a decrease of the trans isomerization level along the series resveratrol  -tocopherol  ascorbic acid. All results indicate that trans isomerization depends on the localization of the particular antioxidant in model system. In order to protect lipid structures from the thiyl radical damage a new role of the essential antioxidants can be assessed.