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J.Health Sci., 48(2), 140-147, 2002
Low-level Nitric Oxide Blunts Oxidant Injury via Up-regulating Glutathione Synthesis
Risa Kurozumi and Shuji Kojima*
Faculty of Pharmaceutical Sciences, Tokyo University of Science, 2669 Yamazaki, Noda-shi, Chiba 278-0022, Japan
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 gamma-glutamylcysteine synthetase, the rate-limiting 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 (O2-)-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.
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