Low-level Nitric Oxide Blunts Oxidant Injury via Up-regulating Glutathione Synthes.

Abstract

The elevation of cellular glutathione (GSH) level induced by low concentrations of an nitric oxide (NO)-donor, sodium nitroprusside (SNP), and its effect on oxidant-induced cell injury were examined in RAW264.7 cells. The cellular GSH level increased 6 hr after exposure of the cells to SNP at low concentrations ranging from 0.1 to 0.5 mM, and the elevation followed the induction of mRNA coding for γ-glutamylcysteine synthetase, the ratelimiting enzyme of the de novo glutathione synthesis pathway. Pre-treatment of cells with low concentration of SNP (less than 0.25 mM) at 12 hr prior to exposure to menadione (MEND), an superoxide anion (O 2 -)-donor, significantly suppressed the cell injury induced by MEND alone. Simultaneous treatment with a higher concentration of SNP (1.0 mM or more) also blunted the MEND-induced cell injury. Low and high doses of NO both seem to show a preventive effect against oxidant injury: NO may protect against oxidant injury by up-regulating GSH synthesis at low concentrations, while at high concentrations it may directly react with radical oxygen species (ROS), thus acting as a free radical scavenger and blunting oxidant injury. These results suggest that modulation of the cellular glutathione metabolism through intracellular NO is a potential mechanism for enhancing the antioxidant defense of cells.

Does Peroxynitrite Involve in the Elevation of Cellular Glutathione Induced by Sodium Nitroprusside (SNP) in RAW 264.7 Cells?

“…32) The effects of scavengers on the elevated g-GCS mRNA expression were also examined at 3 h after exposure to 0.25 mM SNP in order to elucidate the mechanisms responsible for the elevation of intracellular glutathione level in RAW 264.7 cells. Scavengers used in this study include an NO-specific scavenger (c-PTIO), NAC, and a hydrogen peroxide and/or peroxynitrite scavenger (Ebs).…”

“…32) Next, the involvement of secondary products in the induction of intracellular GSH synthesis after treatment with SNP was estimated in an indirect manner by using various scavengers. Inhibitors used in this study included an NO-specific scavenger (c-PTIO), an antioxidant (NAC), and a hydrogen peroxide and/or peroxynitrite scavenger (Ebs).…”

“…[27][28][29][30][31] In our previous study, changes in the endogenous GSH level in RAW 264.7 cells exposed to SNP were examined, and the GSH levels in the cells were found to be significantly increased via the de novo GSH pathway through transcriptional up-regulation of the g-GCS gene. 32) This phenomenon is considered to be an adaptive response of the cells to oxidative stress.…”