Mechanisms of the Antioxidant Effects of Nitric Oxide (original) (raw)
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Cellular antioxidant and pro-oxidant actions of nitric oxide
Free Radical Biology and Medicine, 1999
We describe a biphasic action of nitric oxide (NO) in its effects on oxidative killing of isolated cells: low concentrations protect against oxidative killing, while higher doses enhance killing, and these two effects occur by distinct mechanisms. While low doses of NO (from (Z)-1-[N-(3-ammonio propyl)-N-(n-propyl)-amino]-diazen-1-ium-1,2 2 diolate [PAPA/NO] or S-nitroso-N-acetyl-L-penicillamine [SNAP] prevent killing of rat hepatocytes by t-butylhydroperoxide (tBH), further increasing doses result in increased killing. Similar effects occur with rat hepatoma cells treated with PAPA/NO and tBH or H 2 O 2. Increased killing with higher concentrations of NO donor is due to both NO and tBH, because NO donor alone is without effect. Glutathione (GSH) is not involved in either of these actions. Based on measurements of thiobarbituric acid-reactive substances (TBARS) and effects of lipid radical scavenger (DPPD) and deferoxamine, the protective effect, but not the enhancing effect, involves peroxidative chemistry. Fructose has no effect on tBH killing alone but provides substantial protection against killing by higher concentrations of NO plus tBH, suggesting that the enhancing effect involves mitochondrial dysfunction. Hepatocytes, when stimulated to produce NO endogenously, become resistant to tBH killing, indicative of the presence of an NO-triggered antioxidant defensive mechanism. The finding that the protective effects of low concentrations of NO and the harmful effects of high concentrations of NO are fundamentally different in nature suggest that therapeutic interventions could be designed, which selectively prevent its pro-oxidant activity at high concentrations, thus converting NO from a "Janus-faced" modulator of oxidant injury into a "pure" protectant.
British Journal of Pharmacology, 1996
The effects of oxygen free radical scavengers and endothelial cell-derived nitric oxide (EDNO) on the death of porcine cultured aortic endothelial cells exposed to exogenous superoxide-[xanthine (0.4 mM)/ xanthine oxidase (0.04 unit ml-')+ diethylenetriaminepentaacetic acid (DTPA, 10 uM)] or hydroxyl radical-generating system(s) [superoxide generating system+ ferric iron (Fe3, 0.1 mM) or peroxynitrite (0-100 uM)] have been evaluated. 2 Spin trapping studies using 5,5-dimethyl-l-pyrroline-N-oxide (DMPO) with electron paramagnetic resonance spectrometry were also conducted to determine qualitatively the oxidant species generated by the oxidant generating systems. 3 Endothelial cell injury provoked by the exogenous superoxide generating system was inhibited by catalase, DTPA and a hydroxyl radical scavenger (dimethyl sulphoxide, DMSO), but not by superoxide dismutase (SOD). Addition of Fe3+ to the superoxide generating system enhanced the cell injury. These suggested that the direct cytotoxicity of exogenous superoxide is limited, and that endogenous transition metal-dependent hydroxyl radical formation is involved in the cell injury. 4 An inhibitor of the constitutive NO-pathway, NG-monomethyl-L-arginine, did not influence cell injury induced by the superoxide generating system, suggesting that basal NO production is not responsible for the cytotoxicity. 5 Stimulation of endothelial cells with bradykinin enhanced cell injury provoked by the exogenous superoxide generating system, but not by the exogenous hydroxyl radical generating system. The enhancement by bradykinin was inhibited by NG-monomethyl-L-arginine and bradykinin B2-receptor antagonist, D-Arg-[Hyp3, Thi5'8, D-Phe7] bradykinin, suggesting that an interaction of NO with superoxide is involved in the enhanced cytotoxicity. A possible intermediate of this reaction, peroxynitrite, also caused endothelial cell injury in a concentration-dependent manner. 6 The modulatory effects of NO on hydroxyl radical-like activity (=formaldehyde production) from the superoxide generating system was also evaluated in a cell-free superoxide/NO generating system, consisting of xanthine/xanthine oxidase, DTPA, DMSO, and various amounts of a spontaneous NO generator, sodium nitroprusside (SNP) and were compared with those of Fe3". At doses up to 10 gM, SNP concentration-dependently increased the formaldehyde production while the higher concentrations of SNP decreased. The maximum amount of formaldehyde produced by SNP was 5 fold less than that produced by Fe3+ (0.1 mM). Peroxynitrite-induced formaldehyde formation was concentrationdependently inhibited by SNP. 7 We conclude that agonist-stimulated but not basal NO production acts as cytotoxic hydroxyl radical donor as well as the endogenous transition metal when endothelial cells are exposed to exogenous superoxide anion, while the modulatory effect of EDNO is limited by a secondary reaction with hydroxyl radicals.
Nitric oxide and reactive oxygen species in vascular injury
Biochemical Society symposium, 1995
Nitric oxide (.NO), a free radical species produced by several mammalian cell types, plays a role in regulation of vascular, neurological and immunological signal transduction and function. The role of .NO in cytotoxic events is acquiring increased significance. The high rate of production and broad distribution of sites of production of .NO, combined with its facile direct and indirect reactions with metalloproteins, thiols and various oxygen radical species, assures that .NO will play a central role in regulating vascular, physiological and cellular homoeostasis, as well as critical intravascular free radical and oxidant reactions. At the same time, there are contradictions as to whether .NO mediates or limits free-radical-mediated tissue injury, and uncertainty regarding its mechanisms of action. .NO has been portrayed as a pathogenic mediator during ischaemia-reperfusion, and inflammatory and septic tissue injury. In contrast, cell-, metal- and oxidant-induced lipoprotein oxidat...
Nitric oxide as a cellular antioxidant: A little goes a long way
Free Radical Biology and Medicine, 2006
Nitric oxide (NO • ) is an effective chain-breaking antioxidant in free radical-mediated lipid oxidation (LPO). It reacts rapidly with peroxyl radicals as a sacrificial chain-terminating antioxidant. The goal of this work was to determine the minimum threshold concentration of NO • required to inhibit Fe 2+ -induced cellular lipid peroxidation. Using oxygen consumption as a measure of LPO, we simultaneously measured nitric oxide and oxygen concentrations with NO • -and O 2 -electrodes. Ferrous iron and dioxygen were used to initiate LPO in docosahexaenoic acid-enriched HL-60 and U937 cells. Bolus addition of NO • (1.5 μM) inhibited LPO when the NO • concentration was greater than 50 nM. Similarly, using (Z)-1-[N-(3-ammoniopropyl)-N-(n-propyl)amino]diazen-1-ium-1,2diolate (PAPA/NO) as a NO • donor we found that an average steady-state NO • concentration of at least 72 ± 9 nM was required to blunt LPO. As long as the concentration of NO • was above 13 ± 8 nM the inhibition was sustained. Once the concentration of NO • fell below this value, the rate of lipid oxidation accelerated as measured by the rate of oxygen consumption. Our model suggests that the continuous production of NO • that would yield a steady-state concentration of only 10 -20 nM is capable of inhibiting Fe 2+ -induced LPO.
Biochemical and Biophysical Research Communications, 1991
The oxygenderived free radical superoxide anion (.Oz') plays an important role in the pathogenesis of various diseases. Recent demonstrations that .Ozs inactivates the potent vasodilator endotheliumderived relaxing factor (EDRF) and that EDRF is probably nitric oxide (NO) suggest that EDRF(N0) may act as an endogenous free radical scavenger. This hypothesis was tested in an in vitro system by analyzing the effect of authentic NO (dilutions of a saturated aqueous solution) on .Oz' production (detected spectrophotometrically as reduction of cytochrome @ by fMet-Leu-Phe-activated human leukocytes (PMN). NO depressed the rate of reduction of cytochrome g by ,Oz' released from PMN's or generated from the oxidation of hypoxanthine by xanthine oxkfase. This effect was concentration-dependent andoccurred at dilutions of the saturated NO solution (1:250 to 1 :lO) which inhibited platelet aggregation. NO had no direct effect on cytochrome g or on xanthine oxidase. These observations indicate that NO(EDRF) can be regarded as a scavenger of superoxide anion and they suggest that EDRF(N0) may provide a chemical barrier to cytotoxic free radicals u&-l.
The physiology and pathophysiology of the nitric oxide/superoxide system
Herz, 1997
Nitric oxide (NO) is a molecule with pleiotropic effects in different tissues. NO is synthesized by NO synthases (NOS), a family with four major types: endothelial, neuronal, inducible and mitochondrial. They can be found in almost all the tissues and they can even co-exist in the same tissue. NO is a well-known vasorelaxant agent, but it works as a neurotransmitter when produced by neurons and is also involved in defense functions when it is produced by immune and glial cells. NO is thermodynamically unstable and tends to react with other molecules, resulting in the oxidation, nitrosylation or nitration of proteins, with the concomitant effects on many cellular mechanisms. NO intracellular signaling involves the activation of guanylate cyclase but it also interacts with MAPKs, apoptosis-related proteins, and mitochondrial respiratory chain or anti-proliferative molecules. It also plays a role in post-translational modification of proteins and protein degradation by the proteasome. However, under pathophysiological conditions NO has damaging effects. In disorders involving oxidative stress, such as Alzheimer's disease, stroke and Parkinson's disease, NO increases cell damage through the formation of highly reactive peroxynitrite. The paradox of beneficial and damaging effects of NO will be discussed in this review. #
Archives of Biochemistry and Biophysics, 1996
NO do not protect. Similar results were observed for NO donors studied when hypoxanthine/xanthine oxi-The role that nitric oxide (NO) plays in various dedase was used as the source for ROS, although the Sgenerative and disease states has remained a mysnitrosothiol agents were much less protective. These tery since its discovery as a biological messenger, results demonstrate that NO possesses properties prompting the question, ''NO, friend or foe?'' Some which protect against ROS toxicity and demonstrate reports have suggested that NO is cytotoxic, and yet how the use of different NO donor compounds can others have shown that it possesses protective proplead to different conclusions about the role that NO erties against reactive oxygen species (ROS). Many can play in the cytotoxicity of ROS. ᭧ 1996 Academic Press, studies have used various NO donor complexes arriv-Inc.