Oxidation of 2-Cys Peroxiredoxins in Human Endothelial Cells by Hydrogen Peroxide, Hypochlorous Acid, and Chloramines

Aims: Reactive oxygen species released from neutrophils during vascular inflammation could contribute to endothelial dysfunction seen in diseases such as atherosclerosis. Activated neutrophils generate hydrogen peroxide (H2O2) and hypochlorous acid (HOCl), as well as chloramines that are formed when HOCl reacts with amino compounds. These oxidants preferentially target thiol groups and thiol-containing proteins. The peroxiredoxins (Prxs) are thiol proteins that have high reactivity with H2O2 and may also be sensitive to HOCl and chloramines. Results: We have investigated human umbilical vein endothelial cells and shown that their cytoplasmic (Prx1 and Prx2) and mitochondrial (Prx3) Prxs are oxidized when they are exposed to H2O2, HOCl, or cell-permeable chloramines. H2O2 converted the Prxs to hyperoxidized, inactive forms, with little accumulation of disulfide-linked dimers. The oxidized Prxs were reduced over hours, presumably due to the action of endothelial sulfiredoxin. In contrast to the hyperoxidation seen with H2O2, HOCl and the chloramine derivatives of glycine and ammonia converted the Prxs to disulfide-linked dimers and dimerization was reversed within 10-30 min of oxidant removal. HOCl treatment caused thioredoxin reductase (TrxR) inhibition with no reversal of dimerization. The cytotoxicity of ammonia chloramine was increased when cells were pretreated with H2O2 to hyperoxidize the Prxs, or when the chloramine was added in the presence of the TrxR inhibitor, auranofin. Innovation: We describe the novel observation that exposure of nucleated cells to inflammatory oxidants results in the accumulation of Prxs in the dimeric form. Conclusions: Endothelial cell Prxs are sensitive targets for neutrophil-derived oxidants and may protect against their damaging effects. Antioxid. Redox Signal. 17, 411-421.