A new biomimetic model of free radical reactivity in lipids

The modeling of free radical reactions under naturally occurring conditions has become a basic step in the research of fundamental mechanisms of biological processes. Our current research is focused on the relationships between the structures and functions of lipids as affected by free radicals processes. The far most known process regarding polyunsaturated fatty acids (PUFA) is lipid peroxidation which is generally considered to be the major mechanism of cell injury in organisms subject to oxidative stress. A much recent research deals with the geometrical isomerization of PUFA. The double bond structures of natural unsaturated lipid molecules have almost invariably the cis geometry, which determines their properties and various biological activities. The conversion of lipids from cis to trans form occurs by a free radical process, which makes the examination of the underlying mechanism a challenging task accessible to radiation-chemical approach. In this context, in view of the fact that these processes in lipids are the most relevant chemical processes occurring to PUFA, studies of the lipid modification induced by irradiation can be carried out with biomimetic models that allow molecular processes of free radical reactions to be studied in a less complex environment, but respectful of the biological characteristics. We have established the simplest biomimetic model of cell membrane, the micelles of linoleic acid, prepared by addition of a non-ionic surfactant (TWEEN®-20) and the resulting solutions were irradiated by ionizing radiation up to 500 Gy under a variety of conditions where thiyl radicals are the main reactive species. The irradiation-induced peroxidation and trans isomerization in our model systems under controlled oxidation conditions represent a topic of our investigations. The concentrations of hydroperoxide of linoleic acid are determined using the spectrophotometric ferric thiocyanate method, while geometrical isomers are analyzed by GC (Rtx-2330 capillary column, FID) using known conditions for the separation of cis and trans isomers. Relative importance of these processes in this competitive environment will be considered. The effect of the natural antioxidants on the micelles supramolecular organization for the positional preference of the double bond isomerization will be also studied.