Membrane lipids and nuclear DNA are differently susceptive to Fenton reaction substrates in porcine thyroid

Fenton reaction (Fe2+ + H2O2 -> Fe3+ + center dot OH + OH-) is of special significance in the thyroid, as both substrates are indispensable for thyroid hormone synthesis, therefore being available presumably at high concentrations under physiological conditions. The study aimed at evaluation if both Fenton reaction substrates are required to induce oxidative damage to membrane lipids and nuclear DNA in porcine thyroid homogenates, and if these macromolecules are vulnerable to the same extent. Thyroid homogenates and nuclear DNA were incubated in the presence of H2O2 and/or Fe2+. Malondi-aldehyde + 4-hydroxyalkenals (MDA + 4-HDA) concentration (lipid peroxidation index) was measured spectrophotometrically, and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) concentration (DNA damage index) by HPLC. Whereas Fenton reaction substrates, used separately, did not affect lipid peroxidation, they increased 8-oxodG level for the highest H2O2 concentration (100 mM) and in Fe2+ concentration-dependent manner (300, 150, 30 and 15 mu M). If Fe2+ and H2O2 were applied together, lipid peroxidation increased significantly, however without H2O2 concentration- but with clear Fe2+ concentration-dependent effect. Concerning DNA damage, Fe2+ enhanced H2O2 effect, whereas Fe2+ concentration-dependent effect was not changed by H2O2. Excess of exclusively one of Fenton reaction substrates is sufficient to induce oxidative DNA damage, but not lipid peroxidation, in porcine thyroid. Comparing to H2O2, Fe2+ seems to be a stronger damaging substrate. (c) 2012 Elsevier Ltd. All rights reserved.