The Role of Iron Chelators in Reducing Lipid Peroxidation

Abstract

Within biological systems, iron is tightly controlled by transferrin and ferritin, leaving only small amounts of chelatable and redox-active iron in the labile iron pool. Iron can participate in both critical (i.e. hemoglobin formation) and dangerous (i.e. Reactive Oxygen Species (ROS) generation) processes. When there is an increase in the labile iron pool, iron can readily catalyze Fenton Reactions, resulting in the formation of reactive oxygen species which can lead to oxidative stress. In the Fenton Reaction, Fe2+ is oxidized by hydrogen peroxide (H2O2) from the mitochondria, generating hydroxide ions and hydroxyl radicals, which are potent, non-selective oxidizing agents that react with biomolecules, such as DNA, amino acids, proteins and lipids. Lipid peroxidation is a chain reaction, initiated by the Fenton Reaction, that can eventually lead to cell death. Excess labile iron can result from various diseases, such as hemochromatosis and thalassemia. Chelators can be used in the treatment of these diseases because they remove iron from solution, thus preventing the Fenton Reaction, and consequently lipid peroxidation. Using an arachidonic acid model, this polyunsaturated fatty acid was exposed to both Fe3+ and Fenton Reaction conditions (i.e., Fe3+ and H2O2), to induce lipid peroxidation. The arachidonic acid model was also exposed to iron chelators (i.e. DIBI and deferiprone) to assess their ability to supress lipid peroxidation. Malondialdehyde (MDA), a stable by-product of lipid peroxidation, was used to quantify oxidative stress using a thiobarbituric acid reactive substance (TBARS) assay. In the TBARS assay, thiobarbituric acid (TBA) reacts with MDA to form a TBA-MDA chromogen. However, in the arachidonic acid model, increasing concentrations of hydrogen peroxide reduced the fluorescence signal from the TBA-MDA chromogen. The Fenton Reaction interferes with the TBARS assay because the colorimetric dye appears to be degraded by the presence of hydrogen peroxide. Fe3+ was sufficient to induce lipid peroxidation in arachidonic acid and was subsequently used in all experiments. Iron chelators, i.e., deferiprone and DIBI, a polymeric iron chelator, were used to inhibit lipid peroxidation. The multidentate chelator DIBI was more effective at reducing Fe3+ induced lipid peroxidation in an in vitro arachidonic acid model.