Copper(II) and iron(III) ions inhibit respiration and increase free-radical mediated lipid peroxidation in rat liver mitochondria: effect of antioxidants

Abstract

Rat liver mitochondria (1.5–2.1 mg protein·mL− 1) supplemented with either 25 and 100 μM Cu2 + or 100 and 500 μM Fe3 + show inhibition of active respiration (O2 consumption in state 3) and increased phospholipid peroxidation. Liver mitochondria were supplemented with the antioxidants reduced glutathione, N-acetylcysteine or butylated hydroxitoluene, to evaluate their effects on the above-mentioned alterations. Although the mitochondrial dysfunction is clearly associated to phospholipid peroxidation, the different responses to antioxidant supplementation indicate that the metal ions have differences in their mechanisms of toxicity. Mitochondrial phospholipid peroxidation through the formation of hydroxyl radical by a Fenton/Haber-Weiss mechanism seems to precede the respiratory inhibition and to be the main fact in Fe-induced mitochondrial dysfunction. In the case of Cu2 +, it seems that the ion oxidizes glutathione, and low molecular weight protein thiol groups in a direct reaction, as part of its intracellular redox cycling. The processes involving phospholipid peroxidation, protein oxidation and mitochondrial respiratory inhibition characterize a redox dyshomeostatic situation that ultimately leads to cell death. However, Cu2 + exposure involves an additional, yet unidentified, toxic event as previous reduction of the metal with N-acetylcysteine has only a minor effect in preventing the mitochondrial damage.