Permeation of phospholipid membranes by peroxynitrite

Mitochondria Play Essential Roles in Intracellular Protection against Oxidative Stress-Which Molecules among the ROS Generated in the Mitochondria Can Escape the Mitochondria and Contribute to Signal Activation in Cytosol?

Questions about which reactive oxygen species (ROS) or reactive nitrogen species (RNS) can escape from the mitochondria and activate signals must be addressed. In this study, two parameters, the calculated dipole moment (debye, D) and permeability coefficient (Pm) (cm s-1), are listed for hydrogen peroxide (H2O2), hydroxyl radical (•OH), superoxide (O2•-), hydroperoxyl radical (HO2•), nitric oxide (•NO), nitrogen dioxide (•NO2), peroxynitrite (ONOO-), and peroxynitrous acid (ONOOH) in comparison to those for water (H2O). O2•- is generated from the mitochondrial electron transport chain (ETC), and several other ROS and RNS can be generated subsequently. The candidates which pass through the mitochondrial membrane include ROS with a small number of dipoles, i.e., H2O2, HO2•, ONOOH, •OH, and •NO. The results show that the dipole moment of •NO2 is 0.35 D, indicating permeability; however, •NO2 can be eliminated quickly. The dipole moments of •OH (1.67 D) and ONOOH (1.77 D) indicate that they might be permeable. This study also suggests that the mitochondria play a central role in protecting against further oxidative stress in cells. The amounts, the long half-life, the diffusion distance, the Pm, the one-electron reduction potential, the pKa, and the rate constants for the reaction with ascorbate and glutathione are listed for various ROS/RNS, •OH, singlet oxygen (1O2), H2O2, O2•-, HO2•, •NO, •NO2, ONOO-, and ONOOH, and compared with those for H2O and oxygen (O2). Molecules with negative electrical charges cannot directly diffuse through the phospholipid bilayer of the mitochondrial membranes. Short-lived molecules, such as •OH, would be difficult to contribute to intracellular signaling. Finally, HO2• and ONOOH were selected as candidates for the ROS/RNS that pass through the mitochondrial membrane.

Impact of Reactive Species on Amino Acids-Biological Relevance in Proteins and Induced Pathologies

This review examines the impact of reactive species RS (of oxygen ROS, nitrogen RNS and halogens RHS) on various amino acids, analyzed from a reactive point of view of how during these reactions, the molecules are hydroxylated, nitrated, or halogenated such that they can lose their capacity to form part of the proteins or peptides, and can lose their function. The reactions of the RS with several amino acids are described, and an attempt was made to review and explain the chemical mechanisms of the formation of the hydroxylated, nitrated, and halogenated derivatives. One aim of this work is to provide a theoretical analysis of the amino acids and derivatives compounds in the possible positions. Tyrosine, methionine, cysteine, and tryptophan can react with the harmful peroxynitrite or ^•OH and ^•NO₂ radicals and glycine, serine, alanine, valine, arginine, lysine, tyrosine, histidine, cysteine, methionine, cystine, tryptophan, glutamine and asparagine can react with hypochlorous acid HOCl. These theoretical results may help to explain the loss of function of proteins subjected to these three types of reactive stresses. We hope that this work can help to assess the potential damage that reactive species can cause to free amino acids or the corresponding residues when they are part of peptides and proteins.

Spirulina sp. LEB 18-extracted phycocyanin: Effects on liposomes' physicochemical parameters and correlation with antiradical/antioxidant properties

This study describes the physicochemical properties of soybean asolectin (ASO) liposomes loaded with phycocyanin (Phy) extracted from Spirulina sp. LEB 18. The effects of Phy in the liposomes' properties were investigated by Fourier transform infrared spectroscopy (FTIR), ¹H and ³¹P nuclear magnetic resonance (NMR), zeta (ζ)-potential, dynamic light scattering (DLS) and ultraviolet-visible (UV-vis) techniques. Phy restricted the motion of ASO polar and interface groups and disrupted the package arrangement of the lipid hydrophobic regions, as a likely effect of dipolar and π interactions related to its amino acid residues and pyrrole portions. These interactions were correlated to antiradical/antioxidant Phy responses obtained by 2,2-diphenyl-1-picrylhidrazil (DPPH) assay, thiobarbituric acid reactive substances (TBARS) and ferric reducing antioxidant power (FRAP) methods, and discussed to bring new chemical perspectives about Phy-loaded liposomes-related nutraceutical applications in inflammatory and viral infection processes.

Dissociations of free radicals to generate protons, electrophiles or nucleophiles: role in DNA strand breaks

The concept behind the research described in this article was that of marrying the 'soft' methods of radical generation with the effectiveness and flexibility of nucleophile/electrophile synthetic procedures. Classic studies with pulse radiolysis and laser flash photolysis had shown that free radicals could be more acidic than their closed shell counterparts. QM computations harmonised with this and helped to define which radical centres and which structural types were most effective. Radicals based on the sulfonic acid moiety and on the Meldrum's acid moiety (2,2-dimethyl-1,3-dioxane-4,6-dione) were found to be extreme examples in the superacid class. The ethyne unit could be used as a very effective spacer between the radical centre and the site of proton donation. The key factor in promoting acidity was understood to be the thermodynamic stabilisation of the conjugate anion-radicals released on deprotonation. Solvation played a key part in promoting this and theoretical microhydration studies provided notable support. A corollary was that heterolytic dissociations of free radicals to yield either electrophiles or nucleophiles were also enhanced relative to non-radical models. The most effective radical types for spontaneous releases of both these types of reagents were identified. Ethyne units were again effective as spacers. The enhancement of release of phosphate anions by adjacent radical centres was an important special case. Reactive oxygen species and also diradicals from endiyne antibiotics generate C4'-deoxyribose radicals from nucleotides. Radicals of these types spontaneously release phosphate and triphosphate and this is a contributor to DNA and RNA strand breaks.

Diffusion and Transport of Reactive Species Across Cell Membranes

This chapter includes an overview of the structure of cell membranes and a review of the permeability of membranes to biologically relevant oxygen and nitrogen reactive species, namely oxygen, singlet oxygen, superoxide, hydrogen peroxide, hydroxyl radical, nitric oxide, nitrogen dioxide, peroxynitrite and also hydrogen sulfide. Physical interactions of these species with cellular membranes are discussed extensively, but also their relevance to chemical reactions such as lipid peroxidation. Most of these species are involved in different cellular redox processes ranging from physiological pathways to damaging reactions against biomolecules. Cell membranes separate and compartmentalize different processes, inside or outside cells, and in different organelles within cells. The permeability of these membranes to reactive species varies according to the physicochemical properties of each molecule. Some of them, such as nitric oxide and oxygen, are small and hydrophobic and can traverse cellular membranes virtually unhindered. Nitrogen dioxide and hydrogen sulfide find a slightly higher barrier to permeation, but still their diffusion is largely unimpeded by cellular membranes. In contrast, the permeability of cellular membranes to the more polar hydrogen peroxide, is up to five orders of magnitude lower, allowing the formation of concentration gradients, directionality and effective compartmentalization of its actions which can be further regulated by specific aquaporins that facilitate its diffusion through membranes. The compartmentalizing effect on anionic species such as superoxide and peroxynitrite is even more accentuated because of the large energetic barrier that the hydrophobic interior of membranes presents to ions that may be overcome by protonation or the use of anion channels. The large difference in cell membrane permeability for different reactive species indicates that compartmentalization is possible for some but not all of them.

Diffusion of nitric oxide and oxygen in lipoproteins and membranes studied by pyrene fluorescence quenching

Oxygen and nitric oxide are small hydrophobic molecules that usually need to diffuse a considerable distance to accomplish their biological functions and necessarily need to traverse several lipid membranes. Different methods have been used to study the diffusion of these molecules in membranes and herein we focus in the quenching of fluorescence of pyrenes inserted in the membrane. The pyrene derivatives have long fluorescence lifetimes (around 200 ns) that make them very sensitive to fluorescence quenching by nitric oxide, oxygen and other paramagnetic species. Results show that the apparent diffusion coefficients in membranes are similar to those in water, indicating that diffusion of these molecules in membranes is not considerably limited by the lipids. This high apparent diffusion in membranes is a consequence of both a favorable partition of these molecules in the hydrophobic interior of membranes and a high diffusion coefficient. Altering the composition of the membrane results in slight changes in diffusion, indicating that in most cases the lipid membranes will not hinder the passage of oxygen or nitric oxide. The diffusion of nitric oxide in the lipid core of low density lipoprotein is also very high, supporting its role as an antioxidant. In contrast to the high permeability of membranes to nitric oxide and oxygen, the permeability to other reactive species such as hydrogen peroxide and peroxynitrous acid is nearly five orders of magnitude lower.

Effects of α-eleostearic acid on asolectin liposomes dynamics: relevance to its antioxidant activity

In this study, the effect of α-eleostearic acid (α-ESA) on the lipid peroxidation of soybean asolectin (ASO) liposomes was investigated. This effect was correlated to changes caused by the fatty acid in the membrane dynamics. The influence of α-ESA on the dynamic properties of liposomes, such as hydration, mobility and order, were followed by horizontal attenuated total reflection Fourier transform infrared spectroscopy (HATR-FTIR), nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC) and UV-vis techniques. The α-ESA showed an in vitro antioxidant activity against the damage induced by hydroxyl radical (OH) in ASO liposomes. The analysis of HATR-FTIR frequency shifts and bandwidths and (1)H NMR spin-lattice relaxation times, related to specific lipid groups, showed that α-ESA causes an ordering effect on the polar and interfacial regions of ASO liposomes, which may restrict the OH diffusion in the membrane. The DSC enthalpy variation analysis suggested that the fatty acid promoted a disordering effect on lipid hydrophobic regions, which may facilitate interactions between the reactive specie and α-ESA. Turbidity results showed that α-ESA induces a global disordering effect on ASO liposomes, which may be attributed to a change in the lipid geometry and shape. Results of this study may allow a more complete view of α-ESA antioxidant mode of action against OH, considering its influence on the membrane dynamics.

Nitro-fatty acids: formation, redox signaling, and therapeutic potential

SIGNIFICANCE

Nitrated derivatives of unsaturated fatty acids (nitro-fatty acids) are being formed and detected in human plasma, cell membranes, and tissue, triggering signaling cascades via covalent and reversible post-translational modifications of susceptible nucleophilic amino acids in transcriptional regulatory proteins and enzymes.

RECENT ADVANCES

Nitro-fatty acids modulate metabolic as well as inflammatory signaling pathways, including the p65 subunit of nuclear factor κB and the transcription factor peroxisome proliferator-activated receptor-γ. Moreover, nitro-fatty acids can activate heat shock as well as phase II antioxidant responses. As electrophiles, they also activate the Nuclear factor erythroid 2-related factor 2 pathway.

CRITICAL ISSUES

We first discuss the mechanisms of nitro-fatty acid formation as well as their key chemical and biochemical properties, including their capacity to release nitric oxide and exert antioxidant actions. The electrophilic properties of nitro-fatty acids to activate anti-inflammatory signaling pathways are discussed in detail. A critical issue is the influence of nitroarachidonic acid on prostaglandin endoperoxide H synthases, modulating inflammatory processes through redirection of arachidonic acid metabolism and signaling.

FUTURE DIRECTIONS

Based on this information, we analyze in vivo data supporting nitro-fatty acids as promising pharmacological tools to prevent inflammatory diseases associated with oxidative and nitrative stress conditions. A key future issue is to evaluate whether nitro-fatty acid supplementation would be useful for human diseases linked to inflammation as well as their potential toxicity when administered by long periods of time.

Nitro-fatty acids: novel anti-inflammatory lipid mediators

Nitro-fatty acids are formed and detected in human plasma, cell membranes, and tissue, modulating metabolic as well as inflammatory signaling pathways. Here we discuss the mechanisms of nitro-fatty acid formation as well as their key chemical and biochemical properties. The electrophilic properties of nitro-fatty acids to activate anti-inflammatory signaling pathways are discussed in detail. A critical issue is the influence of nitroarachidonic acid on prostaglandin endoperoxide H synthases, redirecting arachidonic acid metabolism and signaling. We also analyze in vivo data supporting nitro-fatty acids as promising pharmacological tools to prevent inflammatory diseases.

Antioxidative effects of extracts from Trifolium species on blood platelets exposed to oxidative stress

Clovers (Trifolium) may possess a significant therapeutic potential, but the effects of compounds from these plants on blood platelets and haemostasis have been poorly recognized. The present study was designed to evaluate the antioxidative action of extracts from three species of clovers: Trifolium pratense, Trifolium pallidum and Trifolium scabrum in the protection of human blood platelets in vitro. Platelet suspensions were pre-incubated with crude extract and phenolic fraction of T. pratense or phenolic fractions of T. scabrum and T. pallidum, at the final concentrations of 0.5-50 μg/ml. Then, for the induction of oxidative stress, 100 μM peroxynitrite was added. The antioxidative activity of plant extracts was assessed by measurements of the level of 3-nitrotyrosine, thiol groups and lipid peroxidation products (hydroperoxides and thiobarbituric acid-reactive substances). Despite the significant differences in the composition of the investigated extracts, we observed antioxidative effects of all used mixtures. The presence of Trifolium extracts considerably reduced the peroxynitrite-mediated modifications of proteins and diminished peroxidation of lipids in platelets. Our results indicate on a strong antioxidative activity of the tested extracts-statistically significant effects were found even for the lowest concentrations (0.5 μg/ml) of all extracts. This action may be useful in the protection of blood components, very susceptible to oxidative modifications. The obtained results suggest that the examined clovers are a promising source of compounds, valuable for the protection against oxidative stress-induced damage to blood platelets.

Bacillus anthracis co-opts nitric oxide and host serum albumin for pathogenicity in hypoxic conditions

Bacillus anthracis is a dangerous pathogen of humans and many animal species. Its virulence has been mainly attributed to the production of Lethal and Edema toxins as well as the antiphagocytic capsule. Recent data indicate that the nitric oxide (NO) synthase (baNOS) plays an important pathogenic role at the early stage of disease by protecting bacteria from the host reactive species and S-nytrosylating the mitochondrial proteins in macrophages. In this study we for the first time present evidence that bacteria-derived NO participates in the generation of highly reactive oxidizing species which could be abolished by the NOS inhibitor L - NAME, free thiols, and superoxide dismutase but not catalase. The formation of toxicants is likely a result of the simultaneous formation of NO and superoxide leading to a labile peroxynitrite and its stable decomposition product, nitrogen dioxide. The toxicity of bacteria could be potentiated in the presence of bovine serum albumin. This effect is consistent with the property of serum albumin to serves as a trap of a volatile NO accelerating its reactions. Our data suggest that during infection in the hypoxic environment of pre-mortal host the accumulated NO is expected to have a broad toxic impact on host cell functions.

Peroxynitrite-driven mechanisms in diabetes and insulin resistance - the latest advances

Since its discovery, peroxynitrite has been known as a potent oxidant in biological systems, and a rapidly growing body of literature has characterized its biochemistry and role in the pathophysiology of various conditions. Either directly or by inducing free radical pathways, peroxynitrite damages vital biomolecules such as DNA, proteins including enzymes with important functions, and lipids. It also initiates diverse reactions leading eventually to disrupted cell signaling, cell death, and apoptosis. The potential role and contribution of this deleterious species has been the subject of investigation in several important diseases, including but not limited to, cancer, neurodegeneration, stroke, inflammatory conditions, cardiovascular problems, and diabetes mellitus. Diabetes, obesity, insulin resistance, and diabetes-related complications represent a major health problem at epidemic levels. Therefore, tremendous efforts have been put into investigation of the molecular basics of peroxynitrite-related mechanisms in diabetes. Studies constantly seek new therapeutical approaches in order to eliminate or decrease the level of peroxynitrite, or to interfere with its downstream mechanisms. This review is intended to emphasize the latest findings about peroxynitrite and diabetes, and, in addition, to discuss recent and novel advances that are likely to contribute to a better understanding of peroxynitrite-mediated damage in this disease.

Chemical biology of peroxynitrite: kinetics, diffusion, and radicals

Peroxynitrite is formed by the very fast reaction of nitric oxide and superoxide radicals, a reaction that kinetically competes with other routes that chemically consume or physically sequester the reagents. It can behave either as an endogenous cytotoxin toward host tissues or a cytotoxic effector molecule against invading pathogens, depending on the cellular source and pathophysiological setting. Peroxynitrite is in itself very reactive against a few specific targets that range from efficient detoxification systems, such as peroxiredoxins, to reactions eventually leading to enhanced radical formation (e.g., nitrogen dioxide and carbonate radicals), such as the reaction with carbon dioxide. Thus, the chemical biology of peroxynitrite is dictated by the chemical kinetics of its formation and decay and by the diffusion across membranes of the species involved, including peroxynitrite itself. On the other hand, most durable traces of peroxynitrite passing (such as 3-nitrotyrosine) are derived from radicals formed from peroxynitrite by routes that represent extremely low-yield processes but that have potentially critical biological consequences. Here we have reviewed the chemical kinetics of peroxynitrite as a biochemical transient species in order to estimate its rates of formation and decay and then its steady-state concentration in different intra- or extracellular compartments, trying to provide a quantitative basis for its reactivity; additionally, we have considered diffusion across membranes to locate its possible effects. Finally, we have assessed the most successful attempts to intercept peroxynitrite by pharmacological intervention in their potential to increment the existing biological defenses that routinely deal with this cytotoxin.

The effect of neighboring methionine residue on tyrosine nitration and oxidation in peptides treated with MPO, H2O2, and NO2(-) or peroxynitrite and bicarbonate: role of intramolecular electron transfer mechanism?

Recent reports suggest that intramolecular electron transfer reactions can profoundly affect the site and specificity of tyrosyl nitration and oxidation in peptides and proteins. Here we investigated the effects of methionine on tyrosyl nitration and oxidation induced by myeloperoxidase (MPO), H2O2 and NO2(-) and peroxynitrite (ONOO(-)) or ONOO(-) and bicarbonate (HCO3(-)) in model peptides, tyrosylmethionine (YM), tyrosylphenylalanine (YF) and tyrosine. Nitration and oxidation products of these peptides were analyzed by HPLC with UV/Vis and fluorescence detection, and mass spectrometry; radical intermediates were identified by electron paramagnetic resonance (EPR)-spin-trapping. We have previously shown (Zhang et al., J. Biol. Chem. 280 (2005) 40684-40698) that oxidation and nitration of tyrosyl residue was inhibited in tyrosylcysteine(YC)-type peptides as compared to free tyrosine. Here we show that methionine, another sulfur-containing amino acid, does not inhibit nitration and oxidation of a neighboring tyrosine residue in the presence of ONOO(-) (or ONOOCO2(-)) or MPO/H2O2/NO2(-) system. Nitration of tyrosyl residue in YM was actually stimulated under the conditions of in situ generation of ONOO(-) (formed by reaction of superoxide with nitric oxide during SIN-1 decomposition), as compared to YF, YC and tyrosine. The dramatic variations in tyrosyl nitration profiles caused by methionine and cysteine residues have been attributed to differences in the direction of intramolecular electron transfer in these peptides. Further support for the interpretation was obtained by steady-state radiolysis and photolysis experiments. Potential implications of the intramolecular electron transfer mechanism in mediating selective nitration of protein tyrosyl groups are discussed.

Peroxynitrite-mediated lipid oxidation and nitration: mechanisms and consequences

Lipid oxidation and nitration represents a novel area of research of relevance in the understanding of inflammatory processes. Peroxynitrite, the product of the diffusion-limited reaction between nitric oxide and superoxide anion, mediates oxidative modifications in lipid systems including cell membranes and lipoproteins. In this review, we discuss the mechanisms of lipid oxidation and nitration by peroxynitrite as well as the influence of physiological molecules and cell targets to redirect peroxynitrite reactivity. We also provide evidence to support that oxidation/nitration of lipids results in the formation of novel signaling modulators of key lipid-metabolizing enzymes.

Uric acid: the oxidant-antioxidant paradox

Uric acid, despite being a major antioxidant in the human plasma, both correlates and predicts development of obesity, hypertension, and cardiovascular disease, conditions associated with oxidative stress. While one explanation for this paradox could be that a rise in uric acid represents an attempted protective response by the host, we review the evidence that uric acid may function either as an antioxidant (primarily in plasma) or pro-oxidant (primarily within the cell). We suggest that it is the pro-oxidative effects of uric acid that occur in cardiovascular disease and may have a contributory role in the pathogenesis of these conditions.

Influence of intramolecular electron transfer mechanism in biological nitration, nitrosation, and oxidation of redox-sensitive amino acids

Using both high-performance liquid chromatography (HPLC) and electron spin resonance (ESR) spin-trappng techniques, we developed an analytical methodology for investigating intramolecular electron transfer-mediated tyrosyl nitration and cysteine nitrosation in model peptides. Peptides N-acetyl-TyrCys-amide (YC), N-acetyl-TyrAlaCys-amide, N-acetyl-TyrAlaAlaCys-amide, and N-acetyl-TyrAlaAlaAlaAlaCys-amide were used as models. Product analysis showed that nitration and oxidation products derived from YC and related peptides in the presence of myeloperoxidase (MPO)/H(2)O(2)/NO(2)(-) were not detectable. The major product was determined to be the corresponding disulfide (e.g., YCysCysY), suggestive of a rapid electron transfer from the tyrosyl radical to the cysteinyl residue. ESR spin-trapping experiments with 5,5'-dimethyl-1-pyrroline N-oxide (DMPO) demonstrated that thiyl radical intermediates were formed from peptides (e.g., YC) treated with MPO/H(2)O(2) and MPO/H(2)O(2)/NO(2)(-). Blocking the thiol group in YC totally abrogated thiyl radical formation. Under similar conditions, we were, however, able to trap the tyrosyl radical using the spin trap dibromonitrosobenzene sulfonic acid (DBNBS). Competition spin-trapping experiments revealed that intramolecular electron transfer is the dominant mechanism for thiyl radical formation in YC peptides. We conclude that a rapid intramolecular electron transfer mechanism between redox-sensitive amino acids could influence both protein nitration and nitrosation reactions. This mechanism brings together nitrative, nitrosative, and oxidative mechanisms in free radical biology.

Nitrated fatty acids: mechanisms of formation, chemical characterization, and biological properties

Nitrated derivatives of unsaturated fatty acids are formed under oxidative and nitrative stress conditions, and are detected and structurally characterized in cell membranes, cardiac tissue, human plasma, and urine. Nitro-fatty acids display pleiotropic activities, including modulation of macrophage activation, prevention of leukocyte and platelet activation, and promotion of blood vessel relaxation. However, mechanisms of formation and levels reached in inflammatory milieu are poorly characterized. In this review, we discuss potential mechanisms of formation of nitro-fatty acids and their key chemical and biochemical properties. A major focus is to analyze nitrated lipids as novel signaling mediators leading to secondary changes in protein function via electrophilic-based modifications as well as inhibition of inflammatory cell function, thus representing the convergence of lipid and nitric oxide signaling pathways.

Melatonin location in egg phosphatidylcholine liposomes: possible relation to its antioxidant mechanisms

Although it is known that the antioxidant properties of melatonin can be modulated by its effect on membrane fluidity, there are few studies on this subject reported in the literature and they are controversial. In this study, viscosimetry and nuclear magnetic resonance (NMR) techniques were used to determine melatonin's effect and location on egg phosphatidylcholine bilayers mobility. Melatonin decreases the dynamic viscosity of the lipid dispersion. (31)P-NMR line width analysis indicated that melatonin induces a slight but uniform restriction of the lipid motional freedom in the polar head. However, melatonin changes in choline (13)C dynamics was only observed through chemical shift analysis. On the other hand, melatonin can induce an increase in the lipid nonpolar chain mobility, as observed by (13)C and (1)H relaxation time analysis. These results suggest the interfacial location of melatonin in the membrane. Additionally, the results of the analysis of the lipid (1)H-fitted exponential relaxation times suggest that melatonin promotes a molecular rearrangement of the bilayers. The melatonin effect and location in the lipid membrane may explain its antioxidant properties against lipid peroxidation induced by reactive species.

Adverse effects of the classic antioxidant uric acid in adipocytes: NADPH oxidase-mediated oxidative/nitrosative stress

Uric acid is considered a major antioxidant in human blood that may protect against aging and oxidative stress. Despite its proposed protective properties, elevated levels of uric acid are commonly associated with increased risk for cardiovascular disease and mortality. Furthermore, recent experimental studies suggest that uric acid may have a causal role in hypertension and metabolic syndrome. All these conditions are thought to be mediated by oxidative stress. In this study we demonstrate that differentiation of cultured mouse adipocytes is associated with increased production of reactive oxygen species (ROS) and uptake of uric acid. Soluble uric acid stimulated an increase in NADPH oxidase activity and ROS production in mature adipocytes but not in preadipocytes. The stimulation of NADPH oxidase-dependent ROS by uric acid resulted in activation of MAP kinases p38 and ERK1/2, a decrease in nitric oxide bioavailability, and an increase in protein nitrosylation and lipid oxidation. Collectively, our results suggest that hyperuricemia induces redox-dependent signaling and oxidative stress in adipocytes. Since oxidative stress in the adipose tissue has recently been recognized as a major cause of insulin resistance and cardiovascular disease, hyperuricemia-induced alterations in oxidative homeostasis in the adipose tissue might play an important role in these derangements.

Nitrotyrosine and protein carbonyls are equally distributed in HT22 cells after nitrosative stress

The generation of reactive oxygen and nitrogen species is an inevitable result of cellular metabolism and environmental influence. Such oxidation processes are always combined with the formation of various protein oxidation products. Environmental oxidants might either be activated inside the cell or act by themselves. Therefore, differences in the localization of oxidant formation might change the major compartment of oxidant action. Therefore, we employed NO donors (SNOC, DETA/NO, and Spe/NO) alone or in combination with the redox-cycling bipyridinium compound paraquat, the superoxide- and NO-releasing compound SIN-1, the relatively more lipophilic oxidants tert-butyl and cumene hydroperoxide, and peroxynitrite itself to test the ability of these compounds to generate oxidized and nitrated proteins in various cellular compartments. Combined treatment with oxidants and nitrating compounds led to the formation of protein carbonyls and nitrotyrosine with a severalfold higher concentration in the cytosol, compared to the nucleus. In fluorescence microscopy studies, the resulting protein modifications show a similar distribution of oxidized proteins and nitrotyrosine with highest concentrations in the perinuclear area. Studying the time- and concentration-dependent formation and degradation of protein carbonyls and nitrated proteins large similarities could be measured. Therefore, it can be concluded that formation, localization, and kinetics of protein carbonyl and nitrotyrosine formation parallel each other depending on the stress-inducing agent.

Oxidized proteins: intracellular distribution and recognition by the proteasome

The formation of oxidized proteins is one of the highlights of oxidative stress. In order not to accumulate such proteins have to be degraded. The major proteolytic system responsible for the removal of oxidized proteins is the proteasome. The proteasome is distributed throughout the cytosolic and nuclear compartment of mammalian cells, with high concentrations in the nucleus. On the other hand a major part of protein oxidation is taking place in the cytosol. The present review highlights the current knowledge on the intracellular distribution of oxidized proteins and put it into contrast with the concentration and distribution of the proteasome.

NO* chemistry: a diversity of targets in the cell

NO(*) alone is a poorly reactive species; however, it is able to undergo secondary reactions to form highly oxidizing and nitrating species, NO(2)(*), N(2)O(3), and ONOO(-). These secondary reactive nitrogen species (RNS) are capable of modifying a diversity of biomolecular structures in the cell. The chemical properties of individual RNS will be discussed, along with their ability to react with amino acids, metal cofactors, lipids, cholesterol, and DNA bases and sugars. Many of the identified RNS-induced modifications have been observed both in vitro and in vivo. Several of these chemical modifications have been attributed with a functional role in the cell, such as the modulation of enzyme activity. Other areas in the field will be discussed, including the ability of RNS to react with metabolites, RNA, and substrates in the mitochondrion, and the cellular removal/repair of RNS-modified structures.

Antioxidant properties of violacein: Possible relation on its biological function

Violacein, a violet pigment produced by Chromobacterium violaceum, has attracted much attention in recent literature due to its pharmacological properties. In this work, the antioxidant properties of violacein were investigated. The reactivity with oxygen and nitrogen reactive species and 1,1-diphenyl-2-picryl-hydrazyl (DPPH), a stable free radical, was evaluated. EPR studies were carried out to evaluate the reactivity with the hydroxyl radical. The action of violacein against lipid peroxidation in three models of lipid membranes, including rat liver microsomes, Egg and Soy bean phosphathidylcholine liposomes were also evaluated. The compound reacted with DPPH (IC(50)=30microM), nitric oxide (IC(50)=21microM), superoxide radicals (IC(50)=125microM) and decreased the hydroxyl radical EPR signal. The compound protected the studied membranes against peroxidation induced by reactive species in the micromolar range. The reconstitution of violacein into the membranes increased its antioxidant effect. These results indicate that the compound has strong antioxidant potential. Based on these results we suggest violacein plays an important role with the microorganism membrane in defense against oxidative stress.

Protein tyrosine nitration in hydrophilic and hydrophobic environments

In this review we address current concepts on the biological occurrence, levels and consequences of protein tyrosine nitration in biological systems. We focused on mechanistic aspects, emphasizing on the free radical mechanisms of protein 3-nitrotyrosine formation and critically analyzed the restrictions for obtaining large tyrosine nitration yields in vivo, mainly due to the presence of strong reducing systems (e.g. glutathione) that can potently inhibit at different levels the nitration process. Evidence is provided to show that the existence of metal-catalyzed processes, the assistance of nitric oxide-dependent nitration steps and the facilitation by hydrophobic environments, provide individually and/or in combination, feasible scenarios for nitration in complex biological milieux. Recent studies using hydrophobic tyrosine analogs and tyrosine-containing peptides have revealed that factors controlling nitration in hydrophobic environments such as biomembranes and lipoproteins can differ to those in aqueous compartments. In particular, exclusion of key soluble reductants from the lipid phase will more easily allow nitration and lipid-derived radicals are suggested as important mediators of the one-electron oxidation of tyrosine to tyrosyl radical in proteins associated to hydrophobic environments. Development and testing of hydrophilic and hydrophobic probes that can compete with endogenous constituents for the nitrating intermediates provide tools to unravel nitration mechanisms in vitro and in vivo; additionally, they could also serve to play cellular and tissue protective functions against the toxic effects of protein tyrosine nitration.

Inorganic nitric oxide metabolites participating in no-dependent modifications of biopolymers

Biogenous nitric(II) oxide (NO), the higher nitrogen oxides (NO2, isomeric N2O3 and N2O4, ONOO-, etc.) that are NO-derived in vivo, and the products of their transformations are active compounds capable of reactions with biopolymers and low-molecular metabolites. The products of these reactions are often considered to be various NO-dependent modifications (NODMs). The nitrated, nitrosylated, nitrosated, and other NODMs play key roles in the regulation of the most important biochemical processes. In this review, we briefly discuss the metabolic reactions of nitrogen oxides that supply active intermediates for NODMs, the NODM reaction products, and some mechanisms of NODM reparation that allow the recovery of chemically intact biopolymer molecule from a modified (chemically damaged) NODM. For example, residues of 3-nitrotyrosine arising due to the NODM reactions of proteins can be reduced to unsubstituted Tyr residues as a result of alternative NODM reactions through intermediate diazotyrosine derivatives. The heterogeneity of a medium in vivo is an important factor controlling the proceeding of NODM reactions. We showed that many processes determining NODM efficiency proceed differently in the heterogeneous media of organisms and in homogeneous aqueous solutions.

Intramolecular Electron Transfer between Tyrosyl Radical and Cysteine Residue Inhibits Tyrosine Nitration and Induces Thiyl Radical Formation in Model Peptides Treated with Myeloperoxidase, H2O2, and NO2-

We investigated the effects of a cysteine residue on tyrosine nitration in several model peptides treated with myeloperoxidase (MPO), H(2)O(2), and nitrite anion (NO(2)(-)) and with horseradish peroxidase and H(2)O(2). Sequences of model peptides were acetyl-Tyr-Cys-amide (YC), acetyl-Tyr-Ala-Cys-amide (YAC), acetyl-Tyr-Ala-Ala-Cys-amide (YAAC), and acetyl-Tyr-Ala-Ala-Ala-Ala-Cys-amide (YAAAAC). Results indicate that nitration and oxidation products of tyrosyl residue in YC and other model peptides were barely detectable. A major product detected was the corresponding disulfide (e.g. YCysCysY). Spin trapping experiments with 5,5'-dimethyl-1-pyrroline N-oxide (DMPO) revealed thiyl adduct (e.g. DMPO-SCys-Tyr) formation from peptides (e.g. YC) treated with MPO/H(2)O(2) and MPO/H(2)O(2)/NO(2)(-). The steady-state concentrations of DMPO-thiyl adducts decreased with increasing chain length of model peptides. Blocking the sulfydryl group in YC with methylmethanethiosulfonate (that formed YCSSCH(3)) totally inhibited thiyl radical formation as did substitution of Tyr with Phe (i.e. FC) in the presence of MPO/H(2)O(2)/NO(2)(-). However, increased tyrosine nitration, tyrosine dimerization, and tyrosyl radical formation were detected in the MPO/H(2)O(2)/NO(2)(-)/YCSSCH(3) system. Increased formation of S-nitrosated YC (YCysNO) was detected in the MPO/H(2)O(2)/(*)NO system. We conclude that a rapid intramolecular electron transfer reaction between the tyrosyl radical and the Cys residue impedes tyrosine nitration and induces corresponding thiyl radical and nitrosocysteine product. Implications of this novel intramolecular electron transfer mechanism in protein nitration and nitrosation are discussed.

Peroxynitrite-derived carbonate and nitrogen dioxide radicals readily react with lipoic and dihydrolipoic acid

Alpha-lipoic acid (LA) and dihydrolipoic acid (DHLA) may have a role as antioxidants against nitric oxide-derived oxidants. We previously reported that peroxynitrite reacts with LA and DHLA with second-order rate constants of 1400 and 500 M(-1) s(-1), respectively, but indicated that these direct reactions are not fast enough to protect against peroxynitrite-mediated damage in vivo. Moreover, the mechanism of the reaction of peroxynitrite with LA has been recently challenged (J. Biol. Chem.279:9693-9697; 2004). Pulse radiolysis studies indicate that LA and DHLA react with peroxynitrite-derived nitrogen dioxide (*NO2) (k2 = 1.3 x 10(6) and 2.9 x 10(7) M(-1) s(-1), respectively) and carbonate radicals (CO(3-)) (k2 = 1.6 x 10(9) and 1.7 x 10(8) M(-1) s(-1), respectively). Carbonate radical-mediated oxidation of LA led to the formation of the potent one-electron oxidant LA radical cation. LA inhibited peroxynitrite-mediated nitration of tyrosine and of a hydrophobic tyrosine analog, N-t-BOC L-tyrosine tert-butyl ester (BTBE), incorporated into liposomes but enhanced tyrosine dimerization. Moreover, while LA competitively inhibited the direct oxidation of glutathione by peroxynitrite, it was poorly effective against the radical-mediated thiol oxidation. The mechanisms of reaction defined herein allow to rationalize the biochemistry of peroxynitrite based on direct and free radical-mediated processes and contribute to the understanding of the antioxidant actions of LA and DHLA.

Facilitated nitration and oxidation of LDL in cigarette smokers

BACKGROUND

Cigarette smoking increases the risk of developing atherosclerosis and ischaemic heart disease. Smoking-induced oxidative stress is considered to favour oxidation of low-density lipoprotein (LDL) and subsequently promotes the atherogenic process. We investigated whether peroxynitrite, a reaction product of cigarette smoke, is involved in facilitated oxidation of LDL in smokers.

MATERIALS AND METHODS

Plasma LDL was obtained from 10 healthy asymptomatic cigarette smokers and 10 healthy nonsmokers. The state of enhanced oxidative stress in the plasma was assessed by LDL subfraction assay using anion-exchange high-performance liquid chromatography (AE-HPLC) and measurements of thiobarbituric acid-reactive substances (TBARS), 8-hydroxydeoxyguanosine (8-OHdG), vitamin E, 3-nitrotyrosine and 3-chlorotyrosine.

RESULTS

Smokers showed a significantly higher level of TBARS and 8-OHdG as well as a significantly lower level of vitamin E than nonsmokers, even after stopping smoking for 10 h or more. The LDL subfraction assay demonstrated an increase in oxidatively modified LDL, as expressed by lower levels of LDL1 and higher levels of LDL2. The 3-nitrotyrosine levels in apolipoprotein B in LDL were significantly higher in smokers than nonsmokers, while the 3-chlorotyrosine levels remained unchanged. In addition, these changes observed in the smokers were further accelerated within 30 min after resumption of cigarette smoking when compared with the levels before smoking resumption.

CONCLUSION

The present study suggests that peroxynitrite plays a significant role in oxidative modification of plasma LDL induced by cigarette smoking.

Relationship between the action of reactive oxygen and nitrogen species on bilayer membranes and antioxidants

Membrane lipid peroxidation (LPO) induced by hydroxyl (*OH) and ascorbyl (*Asc) radicals and by peroxynitrite (ONOO-) was investigated in asolectin (ASO), egg phosphatidylcholine (PC) and PC/phosphatidic acid mixtures (PC:PA) liposomes and rat liver microsomes (MC). Enthalpy variation (DeltaH) of PC:PA at different molar ratios were obtained by differential scanning calorimetry. It was also evaluated the LPO inhibition by quercetin, melatonin and Vitamin B6. The oxidant effect power follows the order *OH approximately *Asc > ONOO- on PC and MC; whilst on ASO liposomes, it follows *Asc > *OH approximately ONOO-. Increasing amounts of PA in PC liposomes resulted in lower levels of LPO. The DeltaH values indicate a more ordered membrane arrangement as a function of PA amount. The results were discussed in order to provide a complete view involving the influence of membranes, oxidants and antioxidants intrinsic behavior on the LPO dynamics.

Effect of hypercholesterolemia and of oxidative stress on the nitric oxide-cGMP pathway

Soluble guanylyl cyclase (sGC) is a key enzyme of the NO-cGMP pathway which is believed to mediate vasoprotective actions. In cardiovascular diseases such as hypercholesterolemia and atherosclerosis, these important functions of the vascular endothelium are strongly impaired. One of the major reasons for this so-called endothelial dysfunction is the increased vascular generation of reactive oxygen species such as superoxide and peroxynitrite. We aimed to investigate whether superoxide and peroxynitrite impacts on the expression and function of sGC and if such a mechanism occurs in a hypercholestemia-induced atherosclerosis. Our experiments with isolated rat aortic rings showed that extracellular superoxide has no effect on expression and function of sGC, while subjection of these rings to continuously generated extracellular peroxynitrite reduced sGC activity. Furthermore, intracellular superoxide as generated by LY85385 almost completely inhibited sGC-activity and increased its expression. In the cholesterol-fed White New Zealand rabbit, we found a 3.5-fold upregulation of sGC, while basal and NO-stimulated sGC-activities were only slightly enhanced and the vasodilator potency of SNAP was decreased by 10-fold. A great portion of the overexpressed dysfunctional sGC is located in intimal lesions. Finally, platelet sGC-activity and the anti-aggregatory effect of SNAP were not changed. These data suggest that endothelial dysfunction in hypercholesterolemia is associated with an oxidative stress-dependent and reversible overexpression of a dysfunctional vascular sGC, while inhibition of platelet sGC-activity is most likely not involved in hypercholesterolemia-induced platelet hyperreactivity.

Phenolic antioxidants and the protection of low density lipoprotein from peroxynitrite-mediated oxidations at physiologic CO2

Dietary phenolic antioxidants have been shown to prevent LDL modifications mediated by several physiologic oxidants including peroxynitrite. However, more recent data demonstrated that CO(2) affected the fate of peroxynitrite in biological fluids and significantly reduced peroxynitrite scavenging by polyphenols, raising doubts concerning their antioxidant activity. We found that the oxidation of LDL lipids mediated by peroxynitrite decreased in the presence of bicarbonate, while Trp oxidation and 3-nitroTyr formation increased, suggesting a redirection of peroxynitrite reactivity toward the protein moiety. We therefore evaluated the protective activity of some phenolic antioxidants (quercetin, oleuropein, resveratrol, (+)-catechin, (-)-epicatechin, tyrosol, alpha- and gamma-tocopherol, ascorbate) on peroxynitrite-mediated oxidation of LDL aromatic residues. Some of these phenols protected LDL Trp from oxidation better than ascorbate or alpha-tocopherol, although protection at 100 microM did not exceed 30-40%. However, the same phenolic antioxidants were more active in inhibiting 3-nitroTyr formation and those with a catechin structure provided significant protection (IC(50%) 40-50 microM). Red wine, a polyphenol-rich beverage, showed a protective effect comparable to that of the most active phenolic antioxidants. Direct EPR studies showed that bicarbonate significantly increased the peroxynitrite-dependent formation of O-semiquinone radicals in red wine, supporting the hypothesis that polyphenols are efficient scavengers of radicals formed by peroxynitrite/CO(2). Ascorbate was a poor inhibitor of peroxynitrite/CO(2)-induced LDL tyrosine nitration, but the simultaneous addition to the most active polyphenols halved their IC(50%). In conclusion, although cooperation with other antioxidants can further decrease the IC(50%) of polyphenolics, as demonstrated for ascorbate, their antioxidant activity appears to occur at concentrations at least 1 order of magnitude higher than their bioavailability.

Spin trapping of glutathiyl and protein radicals produced from nitric oxide-derived oxidants

Despite the importance of protein radicals in cell homeostasis and cell injury, their formation, localization, and propagation reactions remain obscure, mainly because of the difficulties in detecting and characterizing radicals, in general, and protein radicals, in particular. New approaches based on spin trapping coupled with other methodologies are under development/testing but so far they have been applied mainly to the study of protein-tyrosyl and protein-tryptophanyl radicals. Here, our aim is to emphasize the importance of developing new methodologies for the detection of glutathyil and protein-cysteinyl radicals under physiological conditions. To this end, we summarize current EPR evidence supporting the view that glutathione and protein-cysteines are among the preferential targets of nitric oxide-derived oxidants and that they are oxidized to the glutathiyl and protein-cysteinyl radicals, respectively. The possible intermediacy of these species in the biological formation of mediators of protein-cysteine redox signaling, such as S-nitrosothiols and sulfenic acids, is also discussed.

Amphiphilic properties of (-)-epicatechin and their significance for protection of cells against peroxynitrite

The dietary flavanol (-)-epicatechin protects against nitration and oxidation reactions of the inflammatory mediator peroxynitrite in hydrophilic and hydrophobic environments. Bioavailability and cellular uptake of (-)-epicatechin are not yet fully characterized. Here, the octanol/buffer partition coefficient of (-)-epicatechin is observed to be 1.5, indicating that the flavanol is soluble in aqueous as well as lipophilic cellular phases, thus capable of permeating the cell membrane. In line with this, the ability of murine aortic endothelial cells (MAECs) to remove (-)-epicatechin from cell culture media is demonstrated. Epicatechin accumulates in cells, likely due to epicatechin binding to cellular proteins. Even after repeated washing, (-)-epicatechin accumulated by MAEC affords protection of the cells against peroxynitrite-induced nitration of protein tyrosyl residues and against oxidation of intracellular dichlorodihydrofluorescein.

Transmembrane nitration of hydrophobic tyrosyl peptides. Localization, characterization, mechanism of nitration, and biological implications

We have shown previously that peroxynitrite-induced nitration of a hydrophobic tyrosyl probe is greater than that of tyrosine in the aqueous phase (Zhang, H., Joseph, J., Feix, J., Hogg, N., and Kalyanaraman, B. (2001) Biochemistry 40, 7675-7686). In this study, we have tested the hypothesis that the extent of tyrosine nitration depends on the intramembrane location of tyrosyl probes and on the nitrating species. To this end, we have synthesized membrane spanning 23-mer containing a single tyrosyl residue at positions 4, 8, and 12. The location of the tyrosine residues in the phospholipid membrane was determined by fluorescence and electron spin resonance techniques. Nitration was initiated by slow infusion of peroxynitrite, co-generated superoxide and nitric oxide ((.)NO), or a myeloperoxidase/hydrogen peroxide/nitrite anion (MPO/H(2)O(2)/NO(2)(-)) system. Results indicate that with slow infusion of peroxynitrite, nitration of transmembrane tyrosyl peptides was much higher (10-fold or more) than tyrosine nitration in aqueous phase. Peroxynitrite-dependent nitration of tyrosyl-containing peptides increased with increasing depth of the tyrosyl residue in the bilayer. In contrast, MPO/H(2)O(2)/ NO(2)(-)-induced tyrosyl nitration decreased with increasing depth of tyrosyl residues in the membrane. Transmembrane nitrations of tyrosyl-containing peptides induced by both peroxynitrite and MPO/H(2)O(2)/NO(2)(-) were totally inhibited by (.)NO that was slowly released from spermine NONOate. Nitration of peptides in both systems was concentration-dependently inhibited by unsaturated fatty acid. Concomitantly, an increase in lipid oxidation was detected. A mechanism involving (.)NO(2) radical is proposed for peroxynitrite and MPO/H(2)O(2)/NO(2)(-)-dependent transmembrane nitration reactions.

Interactions of peroxynitrite and other nitrating substances with human platelets: the role of glutathione and peroxynitrite permeability

Platelets labeled with 2',7'-dihydrodichlorofluorescein diacetate (DCF-DA) and stimulated with 50-400nM peroxynitrite (ONOO(-)) produced a rapid increase of the fluorescence signal at 523nm with good linearity and reproducibility. Platelet fluorescence was inhibited by 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), suggesting that HCO(3)(-)/Cl(-) transporter mediated ONOO(-) transport into the platelets. Exposure of platelets to potassium superoxide, hydrogen peroxide, and sodium nitroprusside at concentrations of up to 100 microM did not generate a fluorescence signal. We also studied other nitrating compounds to establish the specificity of the DCF-DA-labeled platelet ONOO(-) assay. A rapid increase of fluorescence was observed when sodium hypochlorite (0.15 to 0.75mM) was added to platelets suspended in a buffered nitrite solution. Exposure of platelets to NO(2), nitroglycerin, and tetranitromethane produced a slow sustained increase of fluorescence. Endogenous glutathione appeared to be an essential factor in the generation of fluorescence by ONOO(-) and other nitrating compounds. We further studied other conditions that increased platelet fluorescence. Stimulation of platelets with thrombin (1U/mL) produced a rapid increase in fluorescence that corresponded to the formation of 20.5nmol ONOO(-) per 10(7) cells, whereas stimulation with collagen and arachidonic acid was without effect. Hypoxia of platelets for 20 and 40min followed by 5min of reoxygenation doubled the fluorescence from these platelets compared with control platelets. Thus, thrombin produced an effect that was likely due to the formation of ONOO(-) in platelets, whereas hypoxia-reoxygenation was likely to cause the formation of an active nitroglutathione-like molecule.

Peroxynitrite activates kinases of the src family and upregulates tyrosine phosphorylation signaling

The hypothesis that peroxynitrite may act as a signaling molecule able to upregulate protein tyrosine phosphorylation is discussed. This article focuses on the mechanisms for activating kinases of the src family, an important class of nonreceptor tyrosine kinases implicated in the regulation of cell communication, proliferation, migration, differentiation, and survival. Recent in vitro findings show that in erythrocytes, synaptosomes, and cerebellar primary culture cells peroxynitrite is able to inhibit phosphatases and to activate different members of the src kinase family through different mechanisms involving cysteine-dependent and -independent processes. The ability of nitrotyrosine-containing peptides with SH2 binding affinity to activate src kinases is also discussed.

Focusing of nitric oxide mediated nitrosation and oxidative nitrosylation as a consequence of reaction with superoxide

The impact of nitric oxide (NO) synthesis on different biological cascades can rapidly change dependent on the rate of NO formation and composition of the surrounding milieu. With this perspective, we used diaminonaphthalene (DAN) and diaminofluorescein (DAF) to examine the nitrosative chemistry derived from NO and superoxide (O2-) simultaneously generated at nanomolar to low micromolar per minute rates by spermine/NO decomposition and xanthine oxidase-catalyzed oxidation of hypoxanthine, respectively. Fluorescent triazole product formation from DAN and DAF increased as the ratio of O2- to NO approached equimolar, then decreased precipitously as O2- exceeded NO. This pattern was also evident in DAF-loaded MCF-7 carcinoma cells and when stimulated macrophages were used as the NO source. Cyclic voltammetry analysis and inhibition studies by using the N2O3 scavenger azide indicated that DAN- and DAF-triazole could be derived from both oxidative nitrosylation (e.g., DAF radical + NO) and nitrosation (NO+ addition). The latter mechanism predominated with higher rates of NO formation relative to O2-. The effects of oxymyoglobin, superoxide dismutase, and carbon dioxide were examined as potential modulators of reactant availability for the O2- + NO pathway in vivo. The findings suggest that the outcome of NO biosynthesis in a scavenger milieu can be focused by O2- toward formation of NO adducts on nucleophilic residues (e.g., amines, thiols, hydroxyl) through convergent mechanisms involving the intermediacy of nitrogen dioxide. These modifications may be favored in microenvironments where the rate of O2- production is temporally and spatially contemporaneous with nitric oxide synthase activity, but not in excess of NO generation.

Induction of SOS response in Salmonella typhimurium TA4107/pSK1002 by peroxynitrite-generating agent, N-morpholino sydnonimine

Salmonella typhimurium TA4107/pSK1002 strain was used to measure the SOS response induced by peroxynitrite. The parent strain TA4107 (oxydelta1[oxydelta(oxyR argH)1]) is sensitive to oxidative stress and the plasmid of pSK1002 carries a fused gene umuC'-'lacZ, in which umu and lacZ genes are involved in the induction of mutagenesis and beta-galactosidase activity, respectively. Therefore, the level of SOS response was monitored via beta-galactosidase activity. A bolus addition of authentic peroxynitrite (0.3-0.6 mM) increased about eight times the enzyme activity. In N-morpholino sydnonimine (SIN-1), which produces peroxynitrite from superoxide and nitric oxide generated through hydrolysis, addition of over 1mM SIN-1 induced four-five-fold activity. The SIN-1-induced SOS response was scarcely influenced by superoxide dismutase (SOD), catalase or a combination of both, removing the possibility of induction by superoxide, hydrogen peroxide and hydroxyl radical. Two types of peroxynitrite scavengers, mannitol (type I) and glutathione (type II), decreased the response. Mannitol showed a constant inhibition (70%) at a concentration up to 20 mM, exhibiting kinetics that are zero-order in mannitol and first-order in peroxynitrite. On the other hand, glutathione sharply reduced the response dependent on concentration up to 2 mM (90%), indicating second-order kinetics, first-order in both glutathione and peroxynitrite. Dihydrorhodamine (DHR)123, which traps peroxynitrite in a molar ratio of 1:1, efficiently inhibited the SOS response. These effects suggest that peroxynitrite, generated gradually from SIN-1, penetrates through the cell membrane, damages the DNA and induces the SOS response. This strain can thus, be used in screening of antioxidants against peroxynitrite-induced DNA damage in cells.

Nitrogen dioxide and carbonate radical anion: two emerging radicals in biology

Nitrogen dioxide and carbonate radical anion have received sporadic attention thus far from biological investigators. However, accumulating data on the biochemical reactions of nitric oxide and its derived oxidants suggest that these radicals may play a role in various pathophysiological processes. These potential roles are also indicated by recent studies on the high efficiency of urate and nitroxides in protecting cells and whole animals against the injury associated with conditions of excessive nitric oxide production. The high protective effects of these antioxidants are incompletely defined at the mechanistic level but some of them can be explained by their efficiency in scavenging peroxynitrite-derived radicals, particularly nitrogen dioxide and carbonate radical anion. In this review, we provide a framework for this hypothesis and discuss the potential sources and properties of these radicals that are likely to become increasingly recognized as important mediators of biological processes.

Oxidant-induced signaling: effects of peroxynitrite and singlet oxygen

Following the requirement for cells to cope with oxidative stress, there are cellular adaptation mechanisms at the level of gene expression. Much of what is known about oxidant-induced signaling in mammalian cells was found in experiments using hydrogen peroxide as an oxidant. However, since the biochemical reactivities of various oxidants significantly differ, 'oxidative stress' is not necessarily identical independent of the oxidant employed to bring it about. Here, the biological actions of peroxynitrite and singlet oxygen are presented, focusing on signaling effects. Peroxynitrite is generated in biological systems in the diffusion-controlled reaction of superoxide with nitrogen monoxide and is thus likely to be produced in the vicinity of activated macrophages. Singlet oxygen is generated by stimulated neutrophils in vivo and may further be generated photochemically, e.g. upon exposure of cells to ultraviolet A radiation. Exposure of cells to either of these oxidants elicits a cellular stress response, entailing the activation of signaling cascades that regulate proliferative and apoptotic responses, such as mitogen-activated protein kinase cascades or the phosphoinositide 3-kinase/Akt cascade. Two mechanisms for the oxidant-induced activation of a signaling cascade may be envisaged: (i) the indirect targeting of the cascade by interrupting negative regulation, and (ii) an activating oxidation of one of the constituting components of the cascade. Examples for both mechanisms in relation to peroxynitrite and singlet oxygen are discussed.