Reactive oxygen species and proinflammatory cytokine signaling in endothelial cells: effect of selenium supplementation

The release of superoxide (O2•−) and hydrogen peroxide (H2O2), induced by tumor necrosis factor-α (TNF-α) or interleukin-1β (IL-1β), has been studied in the endothelial cell line ECV 304 in the presence and absence of selenium (Se) supplementation. Both cytokines elicit the production of both species. Selenium supplementation, which increases Se-enzyme activity, decreases the amount of H2O2 but not O2•− detectable in the extracellular medium. Inhibition of reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase by diphenyliodonium (DPI) or phenylarsine oxide (PAO), largely prevents O2•− production, whereas H2O2 remains above the amount accounted for by disproportion of residual O2•−. Thus, a fraction of H2O2 found in the medium, derives from an intracellular pool, which is under control of selenium-dependent peroxidases. This is further supported by the observation that in Se-supplemented cells, the rate of intracellular glutathione (GSH) depletion induced by cytokine treatment is faster and more extensive. Because Se supplementation decreases cytokine-induced NF-κB activity, whereas added H2O2 is inactive and catalase does not affect the activation induced by TNF-α, it is concluded that only intracellularly generated H2O2 has a role in transcription factor activation by both TNF-α and IL-1β.