Glutathione Peroxidase Protects against Peroxynitrite-mediated Oxidations

Abstract

There is a requirement for cellular defense against excessive peroxynitrite generation to protect against DNA strand breaks and mutations and against interference with protein tyrosine-based signaling and other protein functions due to formation of 3-nitrotyrosine. Here, we demonstrate a role of selenium-containing enzymes catalyzing peroxynitrite reduction using glutathione peroxidase (GPx) as an example. GPx protected against the oxidation of dihydrorhodamine 123 by peroxynitrite more effectively than ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one), a selenoorganic compound exhibiting a high second-order rate constant for the reaction with peroxynitrite, 2 ؋ 10 6 M ؊1 s ؊1 . Carboxymethylation of selenocysteine in GPx by iodoacetate led to the loss of "classical" glutathione peroxidase activity but maintained protection against peroxynitrite-mediated oxidation. The maintenance of protection by GPx against peroxynitrite requires GSH as reductant.When peroxynitrite was infused to maintain a 0.2 M steady-state concentration, GPx in the presence of GSH, but neither GPx nor GSH alone, effectively inhibited the hydroxylation of benzoate by peroxynitrite. Under these steady-state conditions peroxynitrite did not cause the loss of classical GPx activity. GPx, like selenomethionine, protected against protein 3-nitrotyrosine formation in human fibroblast lysates, shown in Western blots. The formation of nitrite rather than nitrate from peroxynitrite was enhanced by GPx or by selenomethionine. The results demonstrate a novel function of GPx and potentially of other selenoproteins containing selenocysteine or selenomethionine, in the GSH-dependent maintenance of a defense line against peroxynitritemediated oxidations, as a peroxynitrite reductase.Peroxynitrite is a potent biological oxidant (1) generated, e.g. by endothelial cells, Kupffer cells, neutrophils, and macrophages (see Beckman (2) for review). Peroxynitrite (ONOO Ϫ ) is a relatively stable species compared with free radicals, but peroxynitrous acid (ONOOH) decays with a rate constant of 1.3 s Ϫ1

Selenium in Biology: Facts and Medical Perspectives

“…The role of the cytoplasmic GPx as an 'emergency enzyme' to fight oxidative stress was verified by reverse genetics (Ho et al, 1997;Cheng et al, 1998;de Haan et al, 1998;Fu et al, 1999;Jaeschke et al, 1999) and, in this role, cGPx cannot be substituted by any of the other selenoproteins. Glutathione peroxidases, in particular the less ubiquitously distributed isozymes, are engaged in redox regulation of many metabolic processes (BrigeliusFlohé, 1999) and appear to be involved in peroxinitrite scavenging (Sies et al, 1997). PHGPx may, e. g., regulate the biosynthesis of leukotrienes, thromboxanes and prostaglandins and thus modulate inflammatory processes (Smith and Lands, 1972;Haurand and Flohé, 1988;Schnurr et al, 1996;Weitzel and Wendel, 1993;Imai et al, 1998).…”

Distinct Promoters Determine Alternative Transcription of gpx-4 into Phospholipid-Hydroperoxide Glutathione Peroxidase Variants

“…It was therefore considered to synergistically act with vitamin E in protecting membranes from lipid peroxidation (9). More recently, however, PHGPx has been implicated in regulating the synthesis of lipid mediators by silencing 5-and 15-lipoxygenase (10 -12), in suppressing hydroperoxideinduced apoptosis (13), in dampening cytokine-induced gene activation (14), in peroxynitrite scavenging (15), and in spermatogenesis (16).…”

Estrés oxidativo en la retina de la rata inducido por la administración crónica de etanol: tratamiento con el antioxidante ebselen

“…Posee actividad similar a la glutation peroxidasa y se ha documentado su efecto como secuestrante de peroxinitritos (12). Actualmente se investiga el papel de este antioxidante en enfermedades como la retinosis pigmentaria, la retinopatía diabética y la uveítis.…”