Determination of rate constants of the reactions of thiols with superoxide radical by electron paramagnetic resonance: critical remarks on spectrophotometric approaches

Protective effects of 2-aminoethylthiosulfuric acid and structurally analogous organosulfur compounds against ionizing radiation

High efficacy and minimal toxicity radioprotectors are desirable options for the hazards posed by nuclear medical and energy technologies and the dangers presented by nuclear weapons in an unstable global situation. Although cysteamine is an effective radioprotector, it has considerable toxicity. In this study, the protective effects of the less toxic organosulfur compounds 2-aminoethylthiosulfate (AETS), thiotaurine (TTAU), and hypotaurine (HTAU) against X-ray damage in mice were compared with that of cysteamine. Intraperitoneal injection of either AETS or cysteamine (2.2 mmol/kg body weight) 30 min before X-ray irradiation (7.0 Gy) provided 100% survival for 30 days, limited the decrease in erythrocytes and neutrophils over 9 days, and reduced damage to bone marrow and spleen over 9 days. Neither TTAU nor HTAU provided any protection. In mice, 30 min after AETS administration, non-protein thiol content increased in the spleen, indicating cysteamine generation by AETS hydrolysis, the active protective species of AETS. All examined compounds scavenged ^•OH under diffusion control in aqueous solution, which is inconsistent with the difference in the protective effects among the compounds. The results indicate that AETS protects animals from ionizing radiation by several mechanisms, including scavenging ^•OH as cysteamine.

Superoxide Anion Chemistry-Its Role at the Core of the Innate Immunity

Classically, superoxide anion O₂^•- and reactive oxygen species ROS play a dual role. At the physiological balance level, they are a by-product of O₂ reduction, necessary for cell signalling, and at the pathological level they are considered harmful, as they can induce disease and apoptosis, necrosis, ferroptosis, pyroptosis and autophagic cell death. This revision focuses on understanding the main characteristics of the superoxide O₂^•-, its generation pathways, the biomolecules it oxidizes and how it may contribute to their modification and toxicity. The role of superoxide dismutase, the enzyme responsible for the removal of most of the superoxide produced in living organisms, is studied. At the same time, the toxicity induced by superoxide and derived radicals is beneficial in the oxidative death of microbial pathogens, which are subsequently engulfed by specialized immune cells, such as neutrophils or macrophages, during the activation of innate immunity. Ultimately, this review describes in some depth the chemistry related to O₂^•- and how it is harnessed by the innate immune system to produce lysis of microbial agents.

Computational Modeling for the Oxidation Reactions of the Cysteine Residues with the Superoxide and the Organic Radical Species

The current computational study analyzes the oxidation reactions of the superoxide and hydroxyl radicals with cysteine residues due to their importance as natural targets to neutralize the harmful reactive oxygen species. Due to the high reactivity of the hydroxyl radicals with the surrounding environment, we also studied the oxidation reactions of organic radicals with cysteine. In addition, we explored the different reaction pathways between cysteine and the superoxide radicals in both anionic and protonated forms. All calculations were performed at the integrated quantum mechanical/molecular mechanical level in an explicit water box under periodic boundary conditions. Higher energy barriers were observed for the organic radicals than the hydroxyl radical, where the chemical nature of the organic radical and the branching pattern are the main factors contributing to the Gibbs energy barriers. The superoxide radical oxidation pathway exhibits a more complex nature due to the complicated interplay of various factors such as the underlying reaction mechanism, the involved oxidizing agent, the kinetic accessibility of the oxidation reaction, and the thermodynamics favorability of those oxidation reactions. We also examined the effect of the solvent-assisted hydrogen atom transfer on the different reaction barriers, which was found to be kinetically unfavorable.

A feasible approach for azo-dye methyl orange degradation in siderite/H2O2 assisted by persulfate: Optimization using response surface methodology and pathway

Siderite was applied to the binary oxidant system of siderite-catalyzed hydrogen peroxide (H₂O₂) and enhanced with persulfate (PS). In the absence of PS, methyl orange (MO) almost could not be degraded by the siderite/H₂O₂ process. However, adding PS significantly improved the capacity of MO to oxidize azo-dye. The influence of individual and interaction of reaction factors have been explored with a simple response surface methodology (RSM) based on central composite design (CCD). The quadratic model with low probabilities (<0.0001) at a confidence level of 95% was satisfactory to predict MO degradation in siderite/H₂O₂/PS system, whose correlation coefficients of R² and R²-adj were 0.9569 and 0.9264, respectively. Moreover, the optimum operation conditions of 21.20 mM, 2.75 g/L, 3.86 mM, and 4.69 for H₂O₂, siderite, PS and initial pH, respectively with the response of C/C₀ around 0.047. Radical scavenging experiments and electron spin resonance (ESR) determined that ·OH was crucial for MO degradation, while the contribution of SO₄^·- was minor. The surface morphology and iron content of siderite before and after the oxidation process showed clear differences. Possible intermediates and a degradation pathway were proposed based on the results of UV-Vis spectral and GC-MS analysis. Moreover, the toxicity to Vibrio fischeri bioluminescent bacterium has increased in the earlier degradation stage due to the generated by-products and weaken with the continuous treatment. This study demonstrated that the siderite/H₂O₂/PS system was effective over a relatively wide pH range without producing secondary pollutants, making it a promising technology and potential environmentally benign approach to azo-dye wastewater treatment.

Photo-Oxidation of Therapeutic Protein Formulations: From Radical Formation to Analytical Techniques

UV and ambient light-induced modifications and related degradation of therapeutic proteins are observed during manufacturing and storage. Therefore, to ensure product quality, protein formulations need to be analyzed with respect to photo-degradation processes and eventually protected from light exposure. This task usually demands the application and combination of various analytical methods. This review addresses analytical aspects of investigating photo-oxidation products and related mediators such as reactive oxygen species generated via UV and ambient light with well-established and novel techniques.

Sensitive and Selective Measurement of Hydroxyl Radicals at Subcellular Level with Tungsten Nanoelectrodes

Hydroxyl radical (^•OH) is an essential reactive oxygen species involved in critical cell functions. However, the mechanisms controlling its subcellular localization and intracellular level during health and disease remain poorly understood. This is due to the challenge of detecting ^•OH that are highly reactive and consequently short-lived (in vivo half-life of ∼10^-9 s). Herein, we present tungsten nanoelectrodes functionalized with stable 1-hexanethiol (HAT) for selective and sensitive detection of ^•OH at the subcellular level via the destruction of the self-assembled monolayer of HAT on the nanoelectrode tip. Taking advantage of the ultrasmall nanotip and the super mechanical toughness, the tungsten nanoelectrode could easily penetrate a single living cell without inducing any observable damage. Controlled by a high precision micromanipulator, the ^•OH level in RAW 264.7 murine macrophages under amyloid β (Aβ) induced oxidative stress were first investigated by the nanoelectrodes at the subcellular level. Moreover, the results revealed the cordycepin-mediated cytoprotection of macrophages through modulation of PI3K/Akt pathway activity and introduction of heme oxygenase-1 (HO-1). We believe that the developed nanoelectrochemical method has shown great capacities for the study of potential drugs for therapeutic intervention of Alzheimer's disease.

Effects of Acute Ethanol Administration on Brain Oxidative Status: The Role of Acetaldehyde

BACKGROUND

Ethanol (EtOH), one of the most widely consumed substances of abuse, can induce brain damage and neurodegeneration. EtOH is centrally metabolized into acetaldehyde, which has been shown to be responsible for some of the neurophysiological and cellular effects of EtOH. Although some of the consequences of chronic EtOH administration on cell oxidative status have been described, the mechanisms by which acute EtOH administration affects the brain's cellular oxidative status and the role of acetaldehyde remain to be elucidated in detail.

METHODS

Swiss CD-I mice were pretreated with the acetaldehyde-sequestering agent d-penicillamine (DP; 75 mg/kg, i.p.) or the antioxidant lipoic acid (LA; 50 mg/kg, i.p.) 30 minutes before EtOH (2.5 g/kg, i.p.) administration. Animals were sacrificed 30 minutes after EtOH injection. Glutathione peroxidase (GPx) mRNA levels; GPx and glutathione reductase (GR) enzymatic activities; reduced glutathione (GSH), glutathione disulfide (GSSG), glutamate, g-L-glutamyl-L-cysteine (Glut-Cys), and malondialdehyde (MDA) concentrations; and protein carbonyl group (CG) content were determined in whole-brain samples.

RESULTS

Acute EtOH administration enhanced GPx activity and the GSH/GSSG ratio, while it decreased GR activity and GSSG concentration. Pretreatment with DP or LA only prevented GPx activity changes induced by EtOH.

CONCLUSIONS

Altogether, these results show the capacity of a single dose of EtOH to unbalance cellular oxidative homeostasis.

Free radical sensors based on inner-cutting graphene field-effect transistors

Due to ultra-high reactivity, direct determination of free radicals, especially hydroxyl radical (•OH) with ultra-short lifetime, by field-effect transistor (FET) sensors remains a challenge, which hampers evaluating the role that free radical plays in physiological and pathological processes. Here, we develop a •OH FET sensor with a graphene channel functionalized by metal ion indicators. At the electrolyte/graphene interface, highly reactive •OH cuts the cysteamine to release the metal ions, resulting in surface charge de-doping and a current response. By this inner-cutting strategy, the •OH is selectively detected with a concentration down to 10-9 M. Quantitative metal ion doping enables modulation of the device sensitivity and a quasi-quantitative detection of •OH generated in aqueous solution or from living cells. Owing to its high sensitivity, selectivity, real-time label-free response, capability for quasi-quantitative detection and user-friendly portable feature, it is valuable in biological research, human health, environmental monitoring, etc.

Redox Signaling by Reactive Electrophiles and Oxidants

The concept of cell signaling in the context of nonenzyme-assisted protein modifications by reactive electrophilic and oxidative species, broadly known as redox signaling, is a uniquely complex topic that has been approached from numerous different and multidisciplinary angles. Our Review reflects on five aspects critical for understanding how nature harnesses these noncanonical post-translational modifications to coordinate distinct cellular activities: (1) specific players and their generation, (2) physicochemical properties, (3) mechanisms of action, (4) methods of interrogation, and (5) functional roles in health and disease. Emphasis is primarily placed on the latest progress in the field, but several aspects of classical work likely forgotten/lost are also recollected. For researchers with interests in getting into the field, our Review is anticipated to function as a primer. For the expert, we aim to stimulate thought and discussion about fundamentals of redox signaling mechanisms and nuances of specificity/selectivity and timing in this sophisticated yet fascinating arena at the crossroads of chemistry and biology.

Identifying involvement of Lys251/Asp252 pair in electron transfer and associated proton transfer at the quinone reduction site of Rhodobacter capsulatus cytochrome bc1

Describing dynamics of proton transfers in proteins is challenging, but crucial for understanding processes which use them for biological functions. In cytochrome bc1, one of the key enzymes of respiration or photosynthesis, proton transfers engage in oxidation of quinol (QH2) and reduction of quinone (Q) taking place at two distinct catalytic sites. Here we evaluated by site-directed mutagenesis the contribution of Lys251/Asp252 pair (bacterial numbering) in electron transfers and associated with it proton uptake to the quinone reduction site (Qi site). We showed that the absence of protonable group at position 251 or 252 significantly changes the equilibrium levels of electronic reactions including the Qi-site mediated oxidation of heme bH, reverse reduction of heme bH by quinol and heme bH/Qi semiquinone equilibrium. This implicates the role of H-bonding network in binding of quinone/semiquinone and defining thermodynamic properties of Q/SQ/QH2 triad. The Lys251/Asp252 proton path is disabled only when both protonable groups are removed. With just one protonable residue from this pair, the entrance of protons to the catalytic site is sustained, albeit at lower rates, indicating that protons can travel through parallel routes, possibly involving water molecules. This shows that proton paths display engineering tolerance for change as long as all the elements available for functional cooperation secure efficient proton delivery to the catalytic site.

One- and two-electron oxidation of thiols: mechanisms, kinetics and biological fates

The oxidation of biothiols participates not only in the defense against oxidative damage but also in enzymatic catalytic mechanisms and signal transduction processes. Thiols are versatile reductants that react with oxidizing species by one- and two-electron mechanisms, leading to thiyl radicals and sulfenic acids, respectively. These intermediates, depending on the conditions, participate in further reactions that converge on different stable products. Through this review, we will describe the biologically relevant species that are able to perform these oxidations and we will analyze the mechanisms and kinetics of the one- and two-electron reactions. The processes undergone by typical low-molecular-weight thiols as well as the particularities of specific thiol proteins will be described, including the molecular determinants proposed to account for the extraordinary reactivities of peroxidatic thiols. Finally, the main fates of the thiyl radical and sulfenic acid intermediates will be summarized.

Degradation of trichloroethene by siderite-catalyzed hydrogen peroxide and persulfate: Investigation of reaction mechanisms and degradation products

A binary catalytic system, siderite-catalyzed hydrogen peroxide (H₂O₂) coupled with persulfate (S₂O₈^2-), was investigated for the remediation of trichloroethene (TCE) contamination. Batch experiments were conducted to investigate reaction mechanisms, oxidant decomposition rates, and degradation products. By using high performance liquid chromatography (HPLC) coupled with electron paramagnetic resonance (EPR), we identified four radicals (hydroxyl (HO·), sulfate (SO₄^-·), hydroperoxyl (HO₂·), and superoxide (O₂^-·)) in the siderite-catalyzed H₂O₂-S₂O₈^2- system. In the absence of S₂O₈^2- (i.e., siderite-catalyzed H₂O₂), a majority of H₂O₂ was decomposed in the first hour of the experiment, resulting in the waste of HO·. The addition of S₂O₈^2- moderated the H₂O₂ decomposition rate, producing a more sustainable release of hydroxyl radicals that improved the treatment efficiency. Furthermore, the heat released by H₂O₂ decomposition accelerated the activation of S₂O₈^2-, and the resultant SO₄^-· was the primary oxidative agent during the first two hours of the reaction. Dichloroacetic acid was firstly detected by ion chromatography (IC). The results of this study indicate a new insight to the reaction mechanism for the catalytic binary H₂O₂-S₂O₈^2- oxidant system, and the delineation of radicals and the discovery of the chlorinated byproduct provide useful information for efficient treatment of chlorinated-solvent contamination in groundwater.

Oxidative stress, mitochondrial permeability transition pore opening and cell death during hypoxia-reoxygenation in adult cardiomyocytes

Reactive oxygen species production is necessary to induce cell death following hypoxia/reoxygenation but the effect of reactive oxygen species produced during hypoxia on mitochondrial permeability transition pore (mPTP) opening and cell death is not established. Here we designed a model of hypoxia/reoxygenation in isolated cardiomyocytes measuring simultaneously reactive oxygen species production, mPTP opening and cell death in order (i) to establish a causal relationship between them, and (ii) to investigate the roles of various reactive oxygen species in mPTP opening. The percentage of cardiomyocytes exhibiting mPTP opening during reoxygenation increased with the duration of hypoxia. Antioxidants increased the time to mPTP opening when present during hypoxia but not at reoxygenation. This was associated with a drop in hydroxyl radical and hydrogen peroxide during hypoxia and the first minutes of reoxygenation. The increase in time to mPTP opening was accompanied by an improvement in cell viability reflected by maintenance of superoxide production at reoxygenation. Cyclosporin A delayed both the time to mPTP opening and cell death despite maintenance of reactive oxygen species production during hypoxia. These findings demonstrate that reactive oxygen species production precedes mPTP opening and that reactive oxygen species produced during hypoxia, particularly hydroxyl radicals and hydrogen peroxide, are necessary to induce mPTP opening which depends on hypoxia duration.

Flow injection measurements of S-nitrosothiols species in biological samples using amperometric nitric oxide sensor and soluble organoselenium catalyst reagent

A novel flow injection analysis (FIA) system suitable for measurement of S-nitrosothiols (RSNOs) in blood plasma is described. In the proposed (FIA) system, samples and standards containing RSNO species are injected into a buffer carrier stream that is mixed with the reagent stream containing 3,3'-dipropionicdiselenide (SeDPA) and glutathione (GSH). SeDPA has been shown previously to catalytically decompose RSNOs in the presence of a reducing agent, such as GSH, to produce nitric oxide (NO). The liberated NO is then detected downstream by an amperometric NO sensor. This sensor is prepared using an electropolymerized m-phenylenediamine (m-PD)/resorcinol and Nafion composite films at the surface of a platinum electrode. Using optimized flow rates and reagent concentrations, detection of various RSNOs at levels in the range of 0.25-20 μM is possible. For plasma samples, detection of background sensor interference levels within the samples must first be carried out using an identical FIA arrangement, but without the added SeDPA and GSH reagents. Subtraction of this background sensor current response allows good analytical recovery of RSNOs spiked into animal plasma samples, with recoveries in the range of 90.4-101.0%.

Modeling the effect of oxygen on the amperometric response of immobilized organoselenium-based S-nitrosothiol sensors

Amperometric detection of S-nitrosothiols (RSNOs) at submicromolar levels in blood samples is of potential importance for monitoring endothelial function and other disease states that involve changes in physiological nitric oxide (NO) production. It is shown here that the elimination of dissolved oxygen from samples is critical when covalently attached diselenocystamine-based amperometric RSNO sensors are used for practical RSNO measurements. The newest generation of RSNO sensors utilizes an amperometric NO gas sensor with a thin organoselenium modified dialysis membrane mounted at the distal sensing tip. Sample RSNOs are catalytically reduced to NO within the dialysis membrane by the immobilized organoselenium species. In the presence of oxygen, the sensitivity of these sensors for measuring low levels of RSNOs (<μM) is greatly reduced. It is demonstrated that the main scavenger of the generated nitric oxide is not the dissolved oxygen but rather superoxide anion radical generated from the reaction of the reduced organoselenium species (the reactive species in the catalytic redox cycle) and dissolved oxygen. Computer simulations of the response of the RSNO sensor using rate constants and diffusion coefficients for the reactions involved, known from the literature or estimated from fitting to the observed amperometric response curves, as well as the specific geometric dimensions of the RSNO sensor, further support that nitric oxide and superoxide anion radical quickly react resulting in near zero sensor sensitivity toward RSNO concentrations in the submicromolar concentration range. Elimination of oxygen from samples helps improve sensor detection limits to ca. 10 nM levels of RSNOs.

EPR detection of cellular and mitochondrial superoxide using cyclic hydroxylamines

Superoxide (O₂ⁱ⁻) has been implicated in the pathogenesis of many human diseases, but detection of the O(2)(•-) radicals in biological systems is limited due to inefficiency of O₂ⁱ⁻ spin trapping and lack of site-specific information. This work studied production of extracellular, intracellular and mitochondrial O₂ⁱ⁻ in neutrophils, cultured endothelial cells and isolated mitochondria using a new set of cationic, anionic and neutral hydroxylamine spin probes with various lipophilicity and cell permeability. Cyclic hydroxylamines rapidly react with O₂ⁱ⁻, producing stable nitroxides and allowing site-specific cO₂ⁱ⁻ detection in intracellular, extracellular and mitochondrial compartments. Negatively charged 1-hydroxy-4-phosphono-oxy-2,2,6,6-tetramethylpiperidine (PP-H) and positively charged 1-hydroxy-2,2,6,6-tetramethylpiperidin-4-yl-trimethylammonium (CAT1-H) detected only extramitochondrial O₂ⁱ⁻. Inhibition of EPR signal by SOD2 over-expression showed that mitochondria targeted mitoTEMPO-H detected intramitochondrial O₂ⁱ⁻ both in isolated mitochondria and intact cells. Both 1-hydroxy-3-carboxy-2,2,5,5-tetramethylpyrrolidine (CP-H) and 1-hydroxy-3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine (CM-H) detected an increase in cytoplasm O₂ⁱ⁻ stimulated by PMA, but only CM-H and mitoTEMPO-H showed an increase in rotenone-induced mitochondrial O₂ⁱ⁻. These data show that a new set of hydroxylamine spin probes provide unique information about site-specific production of the O₂ⁱ⁻ radical in extracellular or intracellular compartments, cytoplasm or mitochondria.

The role of EPR spectroscopy in studies of the oxidative status of biological systems and the antioxidative properties of various compounds

In this era of intense study of free radicals and antioxidants, electron paramagnetic resonance (EPR) is arguably the best-suited technique for such research, particularly when considering biochemical and biological systems. No attempt was made to cover all the topics of EPR application but instead attention was restricted to two areas that are both novel and received less attention in previous reviews. In the first section, the application of EPR in assessing the oxidative status of various biological systems, using endogenous stabile paramagnetic species, such as the ascorbyl radical, semiquinone, melanin, and oxidized pigments, is addressed. The second section covers the use of EPR in the emerging field of antioxidant development, using EPR spin-trapping and spin-probing techniques. In both sections, in addition to giving an overview of the available literature, examples (mostly from the authors? recent work) are also presented in sufficient detail to illustrate how to explore the full potential of EPR. This review aims at encouraging biologists, chemists and pharmacologists interested in the redox metabolism of living systems, free radical chemistry or antioxidative properties of new drugs and natural products to take advantage of this technique for their investigations.

Redox regulation of tumor necrosis factor signaling

Tumor necrosis factor-alpha (TNF) is a key cytokine that has been shown to play important physiologic (e.g., inflammation) and pathophysiologic (e.g., various liver pathologies) roles. In liver and other tissues, TNF treatment results in the simultaneous activation of an apoptotic pathway (i.e., TRADD, RIP, JNK) and a survival pathway mediated by NF-kappaB transcription of survival genes (i.e., GADD45beta, Mn-SOD, cFLIP). The cellular response (e.g., proliferation versus apoptosis) to TNF is determined by the balance between the apoptotic signaling pathway and the NF-kappaB survival pathway stimulated by TNF. Reactive oxygen species (ROS) are important modulators of signaling pathways and can regulate both apoptotic signaling and NF-kappaB transcription triggered by TNF. ROS are important in mediating the sustained activation of JNK, to help mediate apoptosis after TNF treatment. In some cells, ROS are second messengers that mediate apoptosis after TNF stimulation. Conversely, ROS can cause redox modifications that inhibit NF-kappaB activation, which can lead to cell death triggered by TNF. Consequently, the redox status of cells can determine the biologic response that TNF will induce in cells. In many liver pathologies, ROS generated extrinsically (e.g., inflammation) or intrinsically (i.e., drugs, toxins) may act in concert with TNF to promote hepatocyte death and liver injury through redox inhibition of NF-kappaB.

The oxidation of glutathione by cobalt/tungsten carbide contributes to hard metal-induced oxidative stress

The occupational exposure to cobalt/tungsten carbide (Co/WC) dusts causes asthma and interstitial fibrosis. The International Agency for Research on Cancer (IARC) recently classified the mixture Co/WC as probably carcinogenic to humans (group 2A). The mechanism of action of Co/WC involves particle driven generation of Reactive Oxygen Species (ROS) with consequent oxidative damage. The present study evaluates the reactivity of Co/WC dust toward glutathione (GSH) and cysteine (Cys). Co/WC oxidized thiols through a mechanism involving the generation of sulphur-centred radicals. The results are consistent with the oxidation taking place at surface active sites, a part of which is accessible only to Cys S-H groups, but not to GSH ones. Such a reaction, with consequent irreversible depletion of antioxidant defenses of cells, will potentiate the oxidative stress caused by particle and cell generated ROS.

Active oxygen intermediates in the degradation of hematoporphyrin derivative in tumor cells subjected to photodynamic therapy

Hematoporphyrin derivative (HPD), a sensitizer used in photodynamic therapy (PDT) of malignancies, is progressively destroyed during the treatment. Prior studies suggested that upon PDT the photobleaching of HPD in tumor tissues is largely mediated by self-sensitized singlet oxygen. However, little is known about the role of other reactive oxygen species (ROS). The main aim of this work was to clarify the significance of H2O2, superoxide (O2.(-)) and hydroxyl (OH.) radicals in bleaching of HPD in tumor cells subjected to PDT. Experiments were performed on Ehrlich ascites carcinoma (EAC) cells, which were loaded with HPD in PBS and then irradiated with red light at 630 nm in the same buffer. Studies showed that photosensitization of EAC cells by HPD led to the formation of significant amounts of H2O2, O2.(-) and OH., and that these ROS could be involved in the photobleaching of HPD during PDT. In fact, we found that addition of catalase (CAT, a scavenger H2O2), Cu/Zn-superoxide dismutase (Cu/Zn-SOD) and Tiron (scavengers of O2.(-)), Na-benzoate, mannitol and deferoxamine (scavengers of OH.) caused a substantial decrease in the rate of HPD photobleaching in EAC cells. In these cells, the inhibitory effects of Na-benzoate, mannitol and deferoxamine on the photodegradation of HPD correlated well with suppression of the OH. generation, a highly active oxidizer. In EAC cells, the glutathione redox cycle and CAT (scavengers of H2O2) as well as Cu/Zn-SOD was found to suppress the photoinduced degradation of HPD. It was also established that HPD can directly scavenge H2O2 and oxygen free radicals; in a phosphate buffer its second-order rate constants were measured as 5.51+/-0.32 x 10(3)M(-1)s(-1) (for the reaction with O2.(-)), 5.08+/-0.31 x 10(4)M(-1)s(-1) (for H2O2), and 3.44+/-0.08 x 10(10)M(-1)s(-1) (for OH.). Thus, our data suggest that OH. could be one of the main oxidants mediating the photobleaching behavior of HPD in malignancies. Studies showed that photoexcited moieties of HPD can oxidize cell proteins with the formation of protein peroxides (PPO), which currently are regarded as a new form of ROS. Model experiments suggest that PPO could also participate in bleaching of HPD in tumors treated with PDT. It was found that HPD may destroy in tumor cells after cessation of photoirradiation and that this event is largely mediated by the presence of H2O2, a precursor of OH(.).

Alpha-lipoic acid differently affects the reserpine-induced oxidative stress in the striatum and prefrontal cortex of rat brain

Antioxidative properties of alpha-lipoic acid (LA) are widely investigated in different in vivo and in vitro models. The aim of this study was to examine whether LA attenuates oxidative stress induced in rats by reserpine, a model substance frequently used to produce Parkinsonism in animals. Male Wistar rats were treated with reserpine (5 mg/kg) and LA (50 mg/kg) separately or in combination. The levels of reduced glutathione (GSH), glutathione disulfide (GSSG), nitric oxide (NO) and S-nitrosothiols as well as activities of glutathione peroxidase (GPx), glutathione-S-transferase (GST) and L-gamma-glutamyl transpeptidase (gamma-GT) were determined in the striatum and prefrontal cortex homogenates. In the striatum and prefrontal cortex a single dose of reserpine significantly enhanced levels of GSSG and NO but not that of S-nitrosothiols when compared with control. In the striatum, LA administered jointly with reserpine markedly increased the concentration of GSH and decreased GSSG level. In the prefrontal cortex, such treatment produced only an increasing tendency in GSH level but caused no changes in GSSG content. In both structures LA injected jointly with reserpine markedly decreased NO concentrations but did not cause significant changes in S-nitrosothiol levels when compared with control. Enzymatic activities of GPx and GST were intensified by LA in the striatum. In the prefrontal cortex, GPx activity was not altered, while that of GST was decreased. Gamma-GT activity was attenuated by reserpine in the striatum while LA reversed this effect. Such changes were not observed in the prefrontal cortex. The mode of LA action in the striatum during the reserpine-evoked oxidative stress strongly suggests that this compound may be of therapeutic value in the treatment of Parkinson's disease.

Aspects of the biological redox chemistry of cysteine: from simple redox responses to sophisticated signalling pathways

The last decade has witnessed an increased interest in cysteine modifications such as sulfenic and sulfinic acids, thiyl radicals, sulfenyl-amides and thiosulfinates, which come together to enable redox sensing, activation, catalysis, switching and cellular signalling. While glutathionylation, sulfenyl-amide formation and disulfide activation are examples of relatively simple redox responses, the sulfinic acid switch in peroxiredoxin enzymes is part of a complex signalling system that involves sulfenic and sulfinic acids and interacts with kinases and sulfiredoxin. Although the in vivo evaluation of sulfur species is still complicated by a lack of appropriate analytical techniques, research into biological sulfur species has gained considerable momentum and promises further excitement in the future.

Characterization of the antioxidative activity of novel nontoxic neuropeptides by using capillary electrophoresis

In the present study, we have monitored the oxidation process of novel nontoxic neuropeptides and determined its rate constants, which describe the antioxidative potential of the peptides. A capillary electrophoretic method was implemented which ensures the simultaneity of analysis of reactants and products in a short time of analysis. The rate constants of oxidation of the four novel peptides, 4-methoxy-L-tyrosinyl-gamma-L-glutamyl-L-cysteinyl-glycine (UPF1), D-serinyl-gamma-L-glutamyl-L-cysteinyl-glycine (UPF6), 4-methoxy-L-tyrosinyl-alpha-L-glutamyl-L-cysteinyl-glycine and D-serinyl-alpha-L-glutamyl-L-cysteinyl-glycine, designed by us, were compared with those of oxidation of glutathione (reduced glutathione) by using capillary electrophoresis. The second-order rate constants were similar for all peptides if the oxidation was carried out with hydrogen peroxide (k(II) = 0.208 - 0.236 x 10(3)/M.min). The rate constants were also determined for the mixtures of peptides. When the oxidation is caused by hydroxyl radical (OH*), the gamma-glutamate containing peptides (UPF1 and UPF6) exhibited two to four times higher antioxidative activity (k(II) = 4.428 and 2.152 x 10(3)/M.min, respectively). The results suggest that the antioxidative potential of the peptides studied is not determined by the formation of disulphide bridge alone.

Pivotal role of NOX‐2‐containing NADPH oxidase in early ischemic preconditioning

Reactive oxygen species (ROS)-mediated signaling is implicated in early ischemic preconditioning (PC). A NOX-2-containing NADPH oxidase is a recognized major source of ROS in cardiac myocytes, whose activity is augmented by preconditioning mimetics, such as angiotensin II. We hypothesized that this oxidase is an essential source of ROS in PC. Hearts from wild-type (WT) and NOX-2 knockout (KO) mice were Langendorff perfused and subjected to 35 min ischemia/reperfusion with or without preceding PC or drug treatment. Infarct size was measured by triphenyl tetrazolium chloride staining, and NADPH oxidase activity by lucigenin chemiluminescence. PC significantly attenuated infarct size in WT (26+/-2% vs. control, 38+/-2%, P<0.05) yet was ineffective in KO hearts (33+/-3% vs. control, 34+/-3%). Concomitantly, PC significantly increased NADPH oxidase activity in WT (+41+/-13%; P<0.05), but not in KO (-5+/-18%, P=NS). The ROS scavenger MPG (N-2-mercaptopropionyl glycine, 300 micromol/L) abrogated PC in WT (39+/-2% vs. control, 33+/-1%). CCPA (2-chloro N6 cyclopentyl adenosine, 200 nmol/L), a putative ROS-independent PC trigger, significantly attenuated infarct size in WT, MPG-treated WT and KO hearts (24+/-2, 23+/-1, and 20+/-3%, respectively, P<0.05). Furthermore, CCPA did not augment NADPH oxidase activity over control (+22+/-11%, P=NS). Inhibition of protein kinase C (PKC) with chelerythrine (CHE, 2 micromol/L) completely abrogated both PC (38+/-2% vs. CHE alone, 35+/-2%) and associated increases in oxidase activity (+3+/-10%, P=NS). PKC-dependent activation of a NOX-2-containing NADPH oxidase is pivotally involved in early ischemic PC. However, adenosine receptor activation can trigger a ROS and NOX-2 independent PC pathway.

Detection of intracellular superoxide formation in endothelial cells and intact tissues using dihydroethidium and an HPLC-based assay

Recently, it was demonstrated that superoxide oxidizes dihydroethidium to a specific fluorescent product (oxyethidium) that differs from ethidium by the presence of an additional oxygen atom in its molecular structure. We have adapted this new HPLC-based assay to quantify this product as a tool to estimate intracellular superoxide in intact tissues. Ethidium and oxyethidium were separated using a C-18 column and quantified using fluorescence detection. Initial cell-free experiments with potassium superoxide and xanthine oxidase confirmed the formation of oxyethidium from dihydroethidium. The formation of oxyethidium was inhibited by superoxide dismutase but not catalase and did not occur upon the addition of H(2)O(2), peroxynitrite, or hypochlorous acid. In bovine aortic endothelial cells (BAEC) and murine aortas, the redox cycling drug menadione increased the formation of oxyethidium from dihydroethidium ninefold (0.4 nmol/mg in control vs. 3.6 nmol/mg with 20 microM menadione), and polyethylene glycol-conjugated superoxide dismutase (PEG-SOD) significantly inhibited this effect. Treatment of BAEC with angiotensin II caused a twofold increase in oxyethidium formation, and this effect also was reduced by PEG-SOD (0.5 nmol/mg). In addition, in the aortas of mice with angiotensin II-induced hypertension and DOCA-salt hypertension, the formation of oxyethidium was increased in a manner corresponding to superoxide production estimated on the basis of cytochrome c reduction. Detection of oxyethidium using HPLC represents a new, convenient, quantitative method for the detection of superoxide in intact cells and tissues.

Improved superoxide-generating system suitable for the assessment of the superoxide-scavenging ability of aqueous extracts of food constituents using ultraweak chemiluminescence

In the interest of developing a simple and rapid ultraweak chemiluminescence assay for assessing the superoxide (O(2)(-))-scavenging activities of various aqueous extracts of food constituents, a specific and stable O(2)(-)-generating system was sought. Reported herein is the obtainment for the first time of a specific and stable O(2)(-)-generating system consisting of methylglyoxal (MG), a reactive 2-oxo aldehyde and arginine, which has been shown to produce much steadier lucigenin-based chemiluminesence (LBCL) than the conventional xanthine/xanthine oxidase system running in parallel and monitoring by an ultraweak chemiluminescence analyzer. Upon mixing of MG and arginine in a phosphate-buffered saline solution, pH 7.4, steady, time-dependent increments of LBCL can be visually observed. The plateau of LBCL can be reached in approximately 10 min and retained in a steadily stable state thereafter without fluctuation for the next 15 min. The lucigenin-based LBCL generation was shown to be specific since it could be effectively inhibited by active bovine SOD, but not by heat-inactivated enzyme or catalase. Conversely, the xanthine/xanthine oxidase system can merely produce a LBCL peak rapidly but decay instantaneously. To illustrate the application of the proposed method for assessing the O(2)(-)-scavenging ability of various food extracts, namely, Prunus mume (A), Lilum lancifolium (B), Creataegus pinnatifida (C), Tremella fuciformis (D), Fortunella margarita (E), and Scutellaria baicalensis (F), we used the following protocol: 12 min after monitoring of LBCL, 1 mg/mL of each of the test compounds was added to the assay system and various degrees of sudden drop of LBCL values were observed, indicating differences in O(2)(-)-scavenging abilities exerted by these food extracts that can be visually compared. Consequently, the percentages of inhibition of LBCL versus the concentrations of a test compound can be constructed. It follows that the concentration needed to inhibit 50% of LBCL (IC(50)) of a test compound can be extrapolated from the curve. Using this approach, we were able to obtain the IC(50) values of various compounds to be tested and the order of inhibitory efficiency of the above-mentioned food extracts was ranked, being A > B > C > D > E > F, respectively.

Functional analogues of the dioxygen reduction site in cytochrome oxidase: mechanistic aspects and possible effects of Cu(B)

Catalytic reduction of O(2) and H(2)O(2) by new synthetic analogues of the heme/Cu site in cytochrome c and ubiquinol oxidases has been studied in aqueous buffers. Among the synthetic porphyrins yet reported, those employed in this study most faithfully mimic the immediate coordination environment of the Fe/Cu core. Under physiologically relevant conditions, these biomimetic catalysts reproduce key aspects of the O(2) and H(2)O(2) chemistry of the enzyme. When deposited on an electrode surface, they catalyze the selective reduction of O(2) to H(2)O at potentials comparable to the midpoint potential of cytochrome c. The pH dependence of the half-wave potentials and other data are consistent with O-O bond activation at these centers proceeding via a slow generation of a formally ferric-hydroperoxo intermediate, followed by its rapid reduction to the level of water. This kinetics is analogous to that proposed for the O-O reduction step at the heme/Cu site. It minimizes the steady-state concentration of the catalytic intermediate whose decomposition would release free H(2)O(2). The maximum catalytic rate constants of O(2) reduction by the ferrous catalyst and of H(2)O(2) reduction by both ferric and ferrous catalysts are comparable to those reported for cytochrome oxidase. The oxidized catalyst also displays catalase activity. Comparison of the catalytic properties of the biomimetic complexes in the FeCu and Cu-free forms indicates that, in the regime of rapid electron flux, Cu does not significantly affect the turnover frequency or the stability of the catalysts, but it suppresses superoxide-releasing autoxidation of an O(2)-catalyst adduct. The distal Cu also accelerates O(2) binding and minimizes O-O bond homolysis in the reduction of H(2)O(2).

Electron paramagnetic resonance spin trapping investigation into the kinetics of glutathione oxidation by the superoxide radical: re-evaluation of the rate constant

The ability of glutathione to scavenge the superoxide radical is a matter of serious contention in the literature: reported values for the second-order rate constant range from 10(2) to greater than 10(5) M(-1) s(-1). The physiological implications of this discrepancy will determine, for example, whether or not glutathione can compete with Mn-superoxide dismutase for reaction with the radical in the mitochondrial matrix, leading to formation of the potentially harmful glutathionyl radical. Several authors have investigated the kinetics of glutathione oxidation by superoxide using spectrophotometric assays, based on competition between either ferricytochrome c or epinephrine for reaction with the radical. However, these approaches have received criticism because the contributions of various secondary reactions to the overall kinetics have been largely overlooked (e.g., the reduction of ferricytochrome c by glutathione). In the present investigation, we have used electron paramagnetic resonance spectroscopy to monitor competition between GSH and the spin trap 5,5-dimethyl-1-pyrroline N-oxide for reaction with superoxide. This method has been used previously and a rate constant of 1.8 x 10(5) M(-1) s(-1) obtained (Dikalov, S.; Khramtsov, V.; Zimmer, G. Arch. Biochem. Biophys. 326:207-218; 1996). However, we demonstrate that this value is a gross overestimation because the spectrum of the hydroxyl radical adduct of the spin trap was incorrectly assigned to the glutathionyl radical adduct. The relatively high yield of the DMPO hydroxyl radical adduct is shown to be due to the two-electron reduction of the corresponding superoxide radical adduct by glutathione. Taking these factors into consideration, we estimate the second order rate constant for the oxidation of glutathione by superoxide to be approximately 200 M(-1) s(-1).

H(2)O(2) opens mitochondrial K(ATP) channels and inhibits GABA receptors via protein kinase C-epsilon in cardiomyocytes

Oxygen radicals and protein kinase C (PKC) mediate ischemic preconditioning. Using a cultured chick embryonic cardiomyocyte model of hypoxia and reoxygenation, we found that the oxygen radicals generated by ischemic preconditioning were H(2)O(2). Like preconditioning, H(2)O(2) selectively activated the epsilon-isoform of PKC in the particulate compartment and increased cell viability after 1 h of hypoxia and 3 h of reoxygenation. The glutathione peroxidase ebselen (converting H(2)O(2) to H(2)O) and the superoxide dismutase inhibitor diethyldithiocarbamic acid abolished the increased H(2)O(2) and the protection of preconditioning. PKC activation with phorbol 12-myristate 13-acetate increased cell survival; the protection of preconditioning was blocked by epsilonV(1-2), a selective PKC-epsilon antagonist. Similar to preconditioning, the protection of PKC activation was abolished by mitochondrial K(ATP) channel blockade with 5-hydroxydecanoate or by GABA receptor stimulation with midazolam or diazepam. In addition, PKC, mitochondrial ATP-sensitive K(+) (K(ATP)) channels, and GABA receptors had no effects on H(2)O(2) generated by ischemic preconditioning before prolonged hypoxia and reoxygenation. We conclude that H(2)O(2) opens mitochondrial K(ATP) channels and inhibits GABA receptors via activating PKC-epsilon. Through this signal transduction, preconditioning protects ischemic cardiomyocytes.

Superoxide modification and inactivation of a neuronal receptor-like complex

Excessive superoxide (O(-)(2)) formation is toxic to cells and organisms. O(-)(2) reacts with either iron-sulfur centers or cysteines (Cys) of cytoplasmic proteins. Reactions with membrane proteins, however, have not been fully characterized. In the present studies, the reaction of O(-)(2) with a protein complex that has glutamate/N-methyl-D-aspartate (NMDA) receptor characteristics and with one of the subunits of this complex was examined. Exposure of the complex purified from neuronal membranes and the recombinant glutamate-binding protein (GBP) subunit of this complex to the O(-)(2)-generating system of xanthine (X) plus xanthine oxidase (XO) caused strong inhibition of L-[3H]glutamate binding. Inhibition of glutamate binding to the complex and GBP by O(-)(2) was greater than that produced by H(2)O(2), another product of the X plus XO reaction. Mutation of two cysteine (Cys) residues in recombinant GBP (Cys(190,191)) eliminated the effect of O(-)(2) on L-[3H]glutamate binding. Both S-thiolation reaction of GBP in synaptic membranes with [35S]cystine and reaction of Cys residues in GBP with [3H]NEM were significantly decreased after exposure of membranes to O(-)(2). Inhibition of cysteylation of membrane GBP by O(-)(2) was still observed after iron chelation by desferrioxamine, albeit diminished, and was not altered by the presence of catalase. Overall, the results indicated that GBP exposure to O(-)(2) modified Cys residues in this protein. The modification was not characterized but it was probably that of disulfide formation.

Signal transduction of flumazenil-induced preconditioning in myocytes

The objective of this study was to examine the role of oxygen radicals, protein kinase C (PKC), and ATP-sensitive K(+) (K(ATP)) channels in mediating flumazenil-produced preconditioning. Chick cardiomyocyte death was quantified using propidium iodide, and oxygen radical generation was assessed using 2',7'-dichlorofluorescin oxidation. Preconditioning was initiated with 10 min of ischemia followed by 10 min of reoxygenation. Alternatively, flumazenil was infused for 10 min and removed 10 min before ischemia. Flumazenil (10 microM) and preconditioning increased oxygen radicals [1,693 +/- 101 (n = 3) and 1,567 +/- 98 (n = 3), respectively, vs. 345 +/- 53 (n = 3) in control] and reduced cell death similarly [22 +/- 3% (n = 5) and 18 +/- 2% (n = 6), respectively, vs. controls 49 +/- 5% (n = 8)]. Protection and increased oxygen radicals by flumazenil were abolished by pretreatment with the antioxidant thiol reductant 2-mercaptopropionyl glycine (800 microM; 52 +/- 10%, n = 6). Specific PKC inhibitors Go-6976 (0.1 microM) and chelerythrine (2 microM), given during ischemia and reoxygenation, blocked flumazenil-produced protection (47 +/- 5%, n = 6). The PKC activator phorbol 12-myristate 13-acetate (0.2 microM), given during ischemia and reoxygenation, reduced cell death similarly to that with flumazenil [17 +/- 4% (n = 6) and 22 +/- 3% (n = 5)]. Finally, 5-hydroxydecanoate (1 mM), a selective mitochondrial K(ATP) channel antagonist given during ischemia and reoxygenation, abolished the protection of flumazenil and phorbol 12-myristate 13-acetate. Thus flumazenil mimics preconditioning to reduce cell death in cardiomyocytes. Oxygen radicals activate mitochondrial K(ATP) channels via PKC during the process.

Oxidative degradation of pharmaceuticals: theory, mechanisms and inhibition

Oxidation is a common pathway for drug degradation in liquid and solid formulations. The present article reviews mechanistic details of autoxidation and chain oxidation processes, as well as the oxidation of selected functional groups commonly affected in drugs.

The reaction of superoxide radical with N-acetylcysteine

The interaction of superoxide radicals with N-acetylcysteine (RSH) in an aqueous solution of pH 7 using the technique of steady state radiolysis has been investigated in this paper. The radiolytic yield of the products (G value) of RSH consumption and disulfide of N-acetylcysteine (RSSR) formation has been determined. The G value of the products is not dependent on the concentration of RSH (at the plateau of dilution curve) or on the inverse of the square root of the dose rate (dose rate)(-1/2), from which it is concluded that in this reaction there is no character of chain reaction. The disulfide of N-acetylcysteine is the only sulfur final product. Hydrogen peroxide is not a reaction product, and accordingly the reaction of O(2)(*-) with RSH does not proceed via hydrogen atom abstraction from RSH. A reaction mechanism is proposed, and an overall rate constant of 68 M(-1) s(-1) has been estimated.

Nitric oxide-dependent modification of the sarcoplasmic reticulum Ca-ATPase: localization of cysteine target sites

Skeletal muscle contraction and relaxation is modulated through the reaction of sarcoplasmic reticulum (SR) protein thiols with reactive oxygen and nitrogen species. Here, we have utilized high-performance liquid chromatography-electrospray mass spectrometry and a specific thiol-labeling procedure to identify and quantify cysteine residues of the SR Ca-ATPase that are modified by exposure to nitric oxide (NO). NO and/or NO-derived species inactivate the SR Ca-ATPase and modify a broad spectrum of cysteine residues with highest reactivities towards Cys364, Cys670, and Cys471. The selectivity of NO and NO-derived species towards the SR Ca-ATPase thiols is different from that of peroxynitrite. The efficiency of NO at thiol modification is significantly higher compared with that of peroxynitrite. Hence, NO has the potential to modulate muscle contraction through chemical reaction with the SR Ca-ATPase in vivo.

Exogenous nitric oxide can trigger a preconditioned state through a free radical mechanism, but endogenous nitric oxide is not a trigger of classical ischemic preconditioning

Nitric oxide (NO) has been reported to play an important role in the late phase of ischemic preconditioning (PC) in the rabbit heart. However, the role of NO in the early phase of ischemic PC ("classical PC") is controversial. Accordingly, the present study was designed to determine whether NO contributes to the cardioprotective effect of classical PC in rabbits. Isolated hearts experienced 30 min of regional ischemia followed by 120 min of reperfusion. Infarct size was measured with triphenyltetrazolium chloride. In control hearts infarction was 30.2+/-3.3% of the risk zone. PC with 5 min of global ischemia and 10 min of reperfusion reduced infarct size to 10.2+/-2.4% (P<0.05). Perfusion with 2 microm S-nitroso-N-acetylpenicillamine (SNAP), a NO donor, in lieu of ischemia mimicked PC (4.4+/-1.9% infarction, P<0.01 v control). To determine whether this protection was dependent on either protein kinase C (PKC) as has previously been demonstrated for classical PC or free radicals known to be produced during exogenous NO administration, chelerythrine (5 microm), a PKC inhibitor, or N-(2-mercaptopropionyl)-glycine (300 microm), a free radical scavenger, was administered with or shortly after SNAP. Neither drug had any independent effect on infarct size, and each blocked SNAP's cardioprotection (31.0+/-5.1 and 25.7+/-5.2% infarction, resp.). N(omega)-nitro- L -arginine methyl ester (L -NAME, 100 microm), a NO synthase inhibitor, failed to block the cardioprotection from the above ischemic PC protocol (9.5+/-2.8% infarction, P<0.05 v control). L -NAME alone had no effect on infarct size (30.6+/-2.7%). These results suggest that the beneficial effect of exogenous NO production during SNAP pretreatment is mediated by a protein kinase C-dependent pathway via MPG-sensitive oxidants. However, we were unable to show any contribution of endogenous NO to classical PC's protection in isolated rabbit hearts.

Effect of calcium on reactive oxygen species in isolated rat cardiomyocytes during hypoxia and reoxygenation

It has been suggested that calcium (Ca(2+)) overload and oxidative stress damage the myocardium during ischemia and reperfusion. We investigated the possible effect of varying extracellular Ca(2+)and total cell Ca(2+)on reactive oxygen species (ROS) levels in resting adult rat cardiomyocytes. Cardiomyocytes were isolated by trypsin/collagenase digestion and exposed to 1 h of hypoxia (H) (95% N(2)/5% CO(2), no glucose) and 2 h of reoxygenation (R) (95% air/5% CO(2), glucose 5.5 m M) in suspension. Cell Ca(2+)was measured by uptake of(45)Ca(2+). ROS was measured by flow cytometry of ethidium's red fluorescence formed by oxidation of dihydroethidium mostly by superoxide anion. Cell viability decreased during H and R, expressed as uptake of trypan blue, loss of rod shape morphology and release of lactate dehydrogenase. Rapidly exchangeable cell Ca(2+)was closely correlated with extracellular Ca(2+)concentration. Cell Ca(2+)was unchanged during H but increased three to four times after R. This increase was attenuated by adding 3,4-dichlorobenzamil, 10 microm at R, and amplified by adding ouabain 1 m M (from start), respectively. Levels of ROS in hypoxic cells were unchanged or slightly reduced at the end of H and increased significantly by 20% compared to control after R. Levels of ROS were significantly decreased by lowering total extracellular Ca(2+)from 1 m M to 0.1 m M or by decreasing free extracellular Ca(2+)with EGTA 0.9 m M at the onset of R. Keeping extracellular Ca(2+)constant, ROS levels were neither affected by attenuating the increase in cell Ca(2+)by DCB nor by amplifying the increase in cell Ca(2+)by ouabain. In conclusion, ROS (superoxide anion) levels increase rapidly after reoxygenation, are correlated with extracellular-free Ca(2+)and are reduced by lowering extracellular-free Ca(2+). Levels of ROS are apparently not consistently correlated with total cell Ca(2+).

Reactivity of biologically important thiol compounds with superoxide and hydrogen peroxide

The reactivities of glutathione, cysteine, cysteamine, penicillamine, N-acetylcysteine, dithiothreitol and captopril with superoxide generated from xanthine oxidase and hypoxanthine, and with reagent hydrogen peroxide, have been investigated. Rates of thiol loss on adding hydrogen peroxide, and superoxide-dependent thiol loss and oxygen uptake were measured. The relative reactivities of the different thiols with both oxidants were inversely related to the pK of the thiol group, such that at pH 7.4, penicillamine was the most reactive. N-acetylcysteine weakly reactive and no reaction was seen with captopril. For hydrogen peroxide, the calculated rate constants for the reaction with the thiolate anion all fell within the range 18-26 M(-1) s(-1). With superoxide, our results are consistent with each thiol reacting via a short chain that consumes oxygen and regenerates superoxide. Only with some of the thiols, was the consumed oxygen recovered as hydrogen peroxide. Reported values for the rate constant for the reaction of thiols with superoxide vary over four orders of magnitude, with the highest being > 10(5) M(-1) s(-1). Due to the complexity of the chain reaction, no study so far has been able to obtain accurate values and we consider the best estimates to be in the 30 to 1000 M(-1) s(-1) range.

Alpha-lipoic acid supplementation: tissue glutathione homeostasis at rest and after exercise

Antioxidant nutrients have demonstrated potential in protecting against exercise-induced oxidative stress. alpha-Lipoic acid (LA) is a proglutathione dietary supplement that is known to strengthen the antioxidant network. We studied the effect of intragastric LA supplementation (150 mg/kg, 8 wk) on tissue LA levels, glutathione metabolism, and lipid peroxidation in rats at rest and after exhaustive treadmill exercise. LA supplementation increased the level of free LA in the red gastrocnemius muscle and increased total glutathione levels in the liver and blood. The exercise-induced decrease in heart glutathione S-transferase activity was prevented by LA supplementation. Exhaustive exercise significantly increased thiobarbituric acid-reactive substance levels in the liver and red gastrocnemius muscle. LA supplementation protected against oxidative lipid damage in the heart, liver, and red gastrocnemius muscle. This study reports that orally supplemented LA is able to favorably influence tissue antioxidant defenses and counteract lipid peroxidation at rest and in response to exercise.

Age-related chemical modification of the skeletal muscle sarcoplasmic reticulum Ca-ATPase of the rat

Much emphasis has been placed on the description of age-related changes in skeletal muscle physiology. The present paper summarizes the chemical characterization of age-related post-translational modifications of the rat skeletal muscle sarcoplasmic reticulum (SR) Ca-ATPase isoforms SERCA1 and SERCA2a obtained from 5- and 28-month-old male Fischer 344 rats. Whereas the SERCA1 isoform shows an age-dependent loss of Cys and Arg, the SERCA2a isoform displays a loss of Cys but also a significant accumulation of 3-nitrotyrosine. The in vitro exposure of SR vesicles particularly rich in SERCA1 (>90%) from 5-month-old rats to low levels of peroxyl radicals yielded SR vesicles with physical properties of the SR Ca-ATPase identical to those observed for the SR Ca-ATPase obtained from 28-month-old rats. The peroxyl radical-modified SR Ca-ATPase showed a loss of Cys and Arg but also of Ser and Met, indicating that peroxyl radicals, though a good model oxidant to generate 'aged' SR vesicles, may not be the only oxidant responsible for the chemical modification of the SR Ca-ATPase in vivo. In fact, efficient thiol modification of the SERCA1 was also observed after the exposure to peroxynitrite. Peroxynitrite selectively nitrated the tyrosine residues of the SERCA2a isoform even in the presence of an excess of SERCA1. Thus, peroxynitrite may be responsible for the age-dependent modification of the SR Ca-ATPase in vivo.

Reactive oxygen species and biological aging: a mechanistic approach

The experimental evidence for an age-dependent increased generation of reactive oxygen species and a progressive accumulation of oxidized biomolecules is growing. However, despite such facts there is no detailed mechanistic information on how the higher availability of reactive oxygen species translates into the accumulation of oxidized biomolecules. For example, open questions are which reactive oxygen species are responsible for what types of oxidation products in vivo, under what specific reaction conditions can we expect which reaction products, and why specifically are modified biomolecules eliminated whereas others accumulate? Mitochondria appear to serve as the major source for reactive oxygen species in aging tissue. Genetic experiments have demonstrated an effect of Cu,ZnSOD on life span and in the prevention of age-related oxidative damage, suggesting that extramitochondrial superoxide promotes biological aging. However, as superoxide does not easily cross membranes, potential chemical pathways that convert mitochondrial reactive oxygen species into superoxide outside the mitochondria are displayed. The chemical reactivity of individual reactive oxygen species with the amino acid side chain of methionine is surveyed to obtain mechanistic details on the oxidation pathways potentially leading to the age-dependent methionine oxidation of the protein calmodulin in vivo. It will evolve that the in vivo accumulation of oxidized calmodulin cannot be the result of the reaction of an individual reactive oxygen species with calmodulin in homogenous solution alone. Complexation of calmodulin to calmodulin-binding proteins and protein turnover are additional parameters likely contributing to the accumulation of specifically modified calmodulin.

Superoxide radical scavenging by phenolic bronchodilators under aprotic and aqueous conditions

Asthmatic airway disease is accompanied by the appearance of inflammatory cells which produce reactive oxygen species (ROS). Therefore, the radical scavenging properties of the bronchodilators reproterol, fenoterol, salbutamol and terbutaline toward superoxide anion radicals and hydroperoxyl radicals were investigated in a model system by electron paramagnetic resonance spectroscopy (EPR) and photometric approaches. The substances under study showed activity in superoxide radical scavenging under aprotic and protic conditions as well. The efficiency of the reaction decreased in the order: fenoterol > salbutamol > reproterol > terbutaline > oxyfedrine when DMSO was used as an aprotic solvent. In an aqueous system, the rate constants decreased in the order: fenoterol > reproterol > salbutamol. It is suggested that the antioxidant effect of these beta2-agonists is an additional advantage in treatment of asthmatic lung disease, reducing the negative consequences of airway inflammation.

Inactivation of yeast glutathione reductase by Fenton systems: effect of metal chelators, catecholamines and thiol compounds

Oxygen radical generating systems, namely, Cu(II)/ H2O2, Cu(II)/ascorbate, Cu(II)/NAD(P)H, Cu(II)/ H2O2/catecholamine and Cu(II)/H2O2/SH-compounds irreversibly inhibited yeast glutathione reductase (GR) but Cu(II)/H2O2 enhanced the enzyme diaphorase activity. The time course of GR inactivation by Cu(II)/H2O2 dependent on Cu(II) and H2O2 concentrations and was relatively slow, as compared with the effect of Cu(II)/ascorbate. The fluorescence of the enzyme Tyr and Trp residues was modified as a result of oxidative damage. Copper chelators, catalase, bovine serum albumin and HO. scavengers prevented GR inactivation by Cu(II)/H2O2 and related systems. Cysteine, N-acetylcysteine, N-(2-dimercaptopropionylglycine and penicillamine enhanced the effect of Cu(II)/H2O2 in a concentration- and time-dependent manner. GSH, Captopril, dihydrolipoic acid and dithiotreitol also enhanced the Cu(II)/H2O2 effect, their actions involving the simultaneous operation of pro-oxidant and antioxidant reactions. GSSG and trypanothione disulfide effectively protected GR against Cu(II)/H2O2 inactivation. Thiol compounds prevented GR inactivation by the radical cation ABTS.+. GR inactivation by the systems assayed correlated with their capability for HO. radical generation. The role of amino acid residues at GR active site as targets for oxygen radicals is discussed.

Quantitative determination and reversible modification of thiols using imidazolidine biradical disulfide label

Earlier we reported an ESR method of quantitative determination of sulfhydryl groups. The method is based on the application of the imidazoline biradical disulfide label, R1S-SR1, which participates in the reaction of thiol-disulfide exchange followed by dramatic changes in ESR spectra. One of the disadvantages of the application of R1S-SR1 at physiological conditions is the requirement of excess of the biradical compared with thiol content which results in the consumption of the thiols and irreversible damage of the system under study. In the present paper we propose imidazolidine biradical disulfide reagent, R2S-SR2, for ESR determination of thiols and provide an experimental basis for its application. This label has the advantages of the previously used biradical disulfide, R1S-SR1, such as high sensitivity down to 1 microM of thiols even in opaque samples and could possibly be used for reversible modification of proteins and enzymes. The particular properties of the R2S-SR2 are pH-sensitivity of its ESR spectrum, higher stability of the imidazolidine radical fragment towards biological reductants and low concentration of the label sufficient for thiol determination at physiological conditions. The latter makes it possible to use ESR spectroscopy for non-invasive thiol measurements in biological systems, in vivo applications included.

The pharmacology of the antioxidant lipoic acid

1. Lipoic acid is an example of an existing drug whose therapeutic effect has been related to its antioxidant activity. 2. Antioxidant activity is a relative concept: it depends on the kind of oxidative stress and the kind of oxidizable substrate (e.g., DNA, lipid, protein). 3. In vitro, the final antioxidant activity of lipoic acid is determined by its concentration and by its antioxidant properties. Four antioxidant properties of lipoic acid have been studied: its metal chelating capacity, its ability to scavenge reactive oxygen species (ROS), its ability to regenerate endogenous antioxidants and its ability to repair oxidative damage. 4. Dihydrolipoic acid (DHLA), formed by reduction of lipoic acid, has more antioxidant properties than does lipoic acid. Both DHLA and lipoic acid have metal-chelating capacity and scavenge ROS, whereas only DHLA is able to regenerate endogenous antioxidants and to repair oxidative damage. 5. As a metal chelator, lipoic acid was shown to provide antioxidant activity by chelating Fe2+ and Cu2+; DHLA can do so by chelating Cd2+. 6. As scavengers of ROS, lipoic acid and DHLA display antioxidant activity in most experiments, whereas, in particular cases, pro-oxidant activity has been observed. However, lipoic acid can act as an antioxidant against the pro-oxidant activity produced by DHLA. 7. DHLA has the capacity to regenerate the endogenous antioxidants vitamin E, vitamin C and glutathione. 8. DHLA can provide peptide methionine sulfoxide reductase with reducing equivalents. This enhances the repair of oxidatively damaged proteins such as alpha-1 antiprotease. 9. Through the lipoamide dehydrogenase-dependent reduction of lipoic acid, the cell can draw on its NADH pool for antioxidant activity additionally to its NADPH pool, which is usually consumed during oxidative stress. 10. Within drug-related antioxidant pharmacology, lipoic acid is a model compound that enhances understanding of the mode of action of antioxidants in drug therapy.