Unraveling peroxynitrite formation in biological systems

Peptide-Functionalized Fluorescent Particles for In Situ Detection of Nitric Oxide via Peroxynitrite-Mediated Nitration

Nitric oxide (NO) is a free radical signaling molecule that plays a crucial role in modulating physiological homeostasis across multiple biological systems. NO dysregulation is linked to the pathogenesis of multiple diseases; therefore, its quantification is important for understanding pathophysiological processes. The detection of NO is challenging, typically limited by its reactive nature and short half-life. Additionally, the presence of interfering analytes and accessibility to biological fluids in the native tissues make the measurement technically challenging and often unreliable. Here, a bio-inspired peptide-based NO sensor is developed, which detects NO-derived oxidants, predominately peroxynitrite-mediated nitration of tyrosine residues. It is demonstrated that these peptide-based NO sensors can detect peroxynitrite-mediated nitration in response to physiological shear stress by endothelial cells in vitro. Using the peptide-conjugated fluorescent particle immunoassay, peroxynitrite-mediated nitration activity with a detection limit of ≈100 × 10-9 m is detected. This study envisions that the NO detection platform can be applied to a multitude of applications including monitoring of NO activity in healthy and diseased tissues, localized detection of NO production of specific cells, and cell-based/therapeutic screening of peroxynitrite levels to monitor pronitroxidative stress in biological samples.

New tools for redox biology: From imaging to manipulation

Redox reactions play a key role in maintaining essential biological processes. Deviations in redox pathways result in the development of various pathologies at cellular and organismal levels. Until recently, studies on transformations in the intracellular redox state have been significantly hampered in living systems. The genetically encoded indicators, based on fluorescent proteins, have provided new opportunities in biomedical research. The existing indicators already enable monitoring of cellular redox parameters in different processes including embryogenesis, aging, inflammation, tissue regeneration, and pathogenesis of various diseases. In this review, we summarize information about all genetically encoded redox indicators developed to date. We provide the description of each indicator and discuss its advantages and limitations, as well as points that need to be considered when choosing an indicator for a particular experiment. One chapter is devoted to the important discoveries that have been made by using genetically encoded redox indicators.

Effects of β-Carotene and Its Cleavage Products in Primary Pneumocyte Type II Cells

β-Carotene has been shown to increase the risk of developing lung cancer in smokers and asbestos workers in two large scale trails, the Beta-Carotene and Retinol Efficacy Trial (CARET) and the Alpha-Tocopherol Beta-carotene Cancer Prevention Trial (ATBC). Based on this observation, it was proposed that genotoxic oxidative breakdown products may cause this effect. In support of this assumption, increased levels of sister chromatid exchanges, micronuclei, and chromosomal aberrations were found in primary hepatocyte cultures treated with a mixture of cleavage products (CPs) and the major product apo-8′carotenal. However, because these findings cannot directly be transferred to the lung due to the exceptional biotransformation capacity of the liver, potential genotoxic and cytotoxic effects of β-carotene under oxidative stress and its CPs were investigated in primary pneumocyte type II cells. The results indicate that increased concentrations of β-carotene in the presence of the redox cycling quinone dimethoxynaphthoquinone (DMNQ) exhibit a cytotoxic potential, as evidenced by an increase of apoptotic cells and loss of cell density at concentrations > 10 µM. On the other hand, the analysis of micronucleated cells gave no clear picture due to the cytotoxicity related reduction of mitotic cells. Last, although CPs induced significant levels of DNA strand breaks even at concentrations ≥ 1 µM and 5 µM, respectively, β-carotene in the presence of DMNQ did not cause DNA damage. Instead, β-carotene appeared to act as an antioxidant. These findings are in contrast with what was demonstrated for primary hepatocytes and may reflect different sensitivities to and different metabolism of β-carotene in the two cell types.

Aminoguanidine pretreatment prevents methotrexate-induced small intestinal injury in the rat by attenuating nitrosative stress and restoring the activities of vital mitochondrial enzymes

BACKGROUND

One of the major toxic side effects of methotrexate (MTX) is enterocolitis, for which there is no efficient standard treatment. Nitric oxide overproduction has been reported to play an important role in MTX-induced mucositis. This study was designed to investigate whether pretreatment with aminoguanidine (AG) - a selective iNOS inhibitor - prevents MTX-induced mucositis in rats.

METHODS

Rats were pretreated with AG (30 and 50 mg/kg body weight) i.p. daily 1 h before MTX (7 mg/kg body weight) administration for 3 consecutive days. After the final dose of MTX, the rats were killed, and the small intestines were used for analysis.

RESULTS

The small intestines of MTX-treated rats showed moderate to severe injury. Pretreatment with AG had a dose-dependent protective effect on MTX-induced mucositis. AG pretreatment reduced iNOS protein levels, mucosal nitric oxide levels, and protein tyrosine nitration. AG pretreatment also restored the activities of electron transport chain (ETC) complexes, vital tricarboxylic acid (TCA cycle) enzymes, and mitochondrial antioxidant enzymes.

CONCLUSIONS

These findings suggest that AG is beneficial in ameliorating MTX-induced enteritis in rats.

Air Pollution and Climate Change Effects on Allergies in the Anthropocene: Abundance, Interaction, and Modification of Allergens and Adjuvants

Air pollution and climate change are potential drivers for the increasing burden of allergic diseases. The molecular mechanisms by which air pollutants and climate parameters may influence allergic diseases, however, are complex and elusive. This article provides an overview of physical, chemical and biological interactions between air pollution, climate change, allergens, adjuvants and the immune system, addressing how these interactions may promote the development of allergies. We reviewed and synthesized key findings from atmospheric, climate, and biomedical research. The current state of knowledge, open questions, and future research perspectives are outlined and discussed. The Anthropocene, as the present era of globally pervasive anthropogenic influence on planet Earth and, thus, on the human environment, is characterized by a strong increase of carbon dioxide, ozone, nitrogen oxides, and combustion- or traffic-related particulate matter in the atmosphere. These environmental factors can enhance the abundance and induce chemical modifications of allergens, increase oxidative stress in the human body, and skew the immune system toward allergic reactions. In particular, air pollutants can act as adjuvants and alter the immunogenicity of allergenic proteins, while climate change affects the atmospheric abundance and human exposure to bioaerosols and aeroallergens. To fully understand and effectively mitigate the adverse effects of air pollution and climate change on allergic diseases, several challenges remain to be resolved. Among these are the identification and quantification of immunochemical reaction pathways involving allergens and adjuvants under relevant environmental and physiological conditions.

Bioapplications of Electrochemical Sensors and Biosensors

Recent progress in the electrochemical field enabled development of miniaturized sensing devices that can be used in biological settings to obtain fundamental and practical biochemically relevant information on physiology, metabolism, and disease states in living systems. Electrochemical sensors and biosensors have demonstrated potential for rapid, real-time measurements of biologically relevant molecules. This chapter provides an overview of the most recent advances in the development of miniaturized sensors for biological investigations in living systems, with focus on the detection of neurotransmitters and oxidative stress markers. The design of electrochemical (bio)sensors, including their detection mechanism and functionality in biological systems, is described as well as their advantages and limitations. Application of these sensors to studies in live cells, embryonic development, and rodent models is discussed.

Tyrosine-Nitrated Proteins: Proteomic and Bioanalytical Aspects

SIGNIFICANCE

"Nitroproteomic" is under active development, as 3-nitrotyrosine in proteins constitutes a footprint left by the reactions of nitric oxide-derived oxidants that are usually associated to oxidative stress conditions. Moreover, protein tyrosine nitration can cause structural and functional changes, which may be of pathophysiological relevance for human disease conditions. Biological protein tyrosine nitration is a free radical process involving the intermediacy of tyrosyl radicals; in spite of being a nonenzymatic process, nitration is selectively directed toward a limited subset of tyrosine residues. Precise identification and quantitation of 3-nitrotyrosine in proteins has represented a "tour de force" for researchers. Recent Advances: A small number of proteins are preferential targets of nitration (usually less than 100 proteins per proteome), contrasting with the large number of proteins modified by other post-translational modifications such as phosphorylation, acetylation, and, notably, S-nitrosation. Proteomic approaches have revealed key features of tyrosine nitration both in vivo and in vitro, including selectivity, site specificity, and effects in protein structure and function.

CRITICAL ISSUES

Identification of 3-nitrotyrosine-containing proteins and mapping nitrated residues is challenging, due to low abundance of this oxidative modification in biological samples and its unfriendly behavior in mass spectrometry (MS)-based technologies, that is, MALDI, electrospray ionization, and collision-induced dissociation.

FUTURE DIRECTIONS

The use of (i) classical two-dimensional electrophoresis with immunochemical detection of nitrated proteins followed by protein ID by regular MS/MS in combination with (ii) immuno-enrichment of tyrosine-nitrated peptides and (iii) identification of nitrated peptides by a MIDAS™ experiment is arising as a potent methodology to unambiguously map and quantitate tyrosine-nitrated proteins in vivo. Antioxid. Redox Signal. 26, 313-328.

Mechanisms of acetaminophen hepatotoxicity and their translation to the human pathophysiology

Acetaminophen (APAP) overdose is the most common cause of acute liver failure in the United States and mechanisms of liver injury induced by APAP overdose have been the focus of extensive investigation. Studies in the mouse model, which closely reproduces the human condition, have shown that hepatotoxicity is initiated by formation of a reactive metabolite N-acetyl-p-benzoquinone imine (NAPQI), which depletes cellular glutathione and forms protein adducts on mitochondrial proteins. This leads to mitochondrial oxidative and nitrosative stress, accompanied by activation of c-jun N-terminal kinase (JNK) and its translocation to the mitochondria. This then amplifies the mitochondrial oxidant stress, resulting in translocation of Bax and dynamin related protein 1 (Drp1) to the mitochondria, which induces mitochondrial fission, and ultimately induction of the mitochondrial membrane permeability transition (MPT). The induction of MPT triggers release of intermembrane proteins such as apoptosis inducing factor (AIF) and endonuclease G into the cytosol and their translocation to the nucleus, causing nuclear DNA fragmentation and activation of regulated necrosis. Though these cascades of events were primarily identified in the mouse model, studies on human hepatocytes and analysis of circulating biomarkers from patients after APAP overdose, indicate that a number of mechanistic events are identical in mice and humans. Circulating biomarkers also seem to be useful in predicting the course of liver injury after APAP overdose in humans and hold promise for significant clinical use in the near future.

Aldose reductase mediates endothelial cell dysfunction induced by high uric acid concentrations

BACKGROUND

Uric acid (UA) is an antioxidant found in human serum. However, high UA levels may also have pro-oxidant functions. According to previous research, aldose reductase (AR) plays a vital role in the oxidative stress-related complications of diabetes. We sought to determine the mechanism by which UA becomes deleterious at high concentrations as well as the effect of AR in this process.

METHOD

and vWF levels were measured in vivo.

RESULTS

production in hyperuricemic mice and protected endothelial cell function.

CONCLUSIONS

could protect endothelial function and maintain the antioxidant activities of UA. These findings provide new insight into the role of UA in chronic kidney disease.

Reactivity of disulfide bonds is markedly affected by structure and environment: implications for protein modification and stability

Disulfide bonds play a key role in stabilizing protein structures, with disruption strongly associated with loss of protein function and activity. Previous data have suggested that disulfides show only modest reactivity with oxidants. In the current study, we report kinetic data indicating that selected disulfides react extremely rapidly, with a variation of 10⁴ in rate constants. Five-membered ring disulfides are particularly reactive compared with acyclic (linear) disulfides or six-membered rings. Particular disulfides in proteins also show enhanced reactivity. This variation occurs with multiple oxidants and is shown to arise from favorable electrostatic stabilization of the incipient positive charge on the sulfur reaction center by remote groups, or by the neighboring sulfur for conformations in which the orbitals are suitably aligned. Controlling these factors should allow the design of efficient scavengers and high-stability proteins. These data are consistent with selective oxidative damage to particular disulfides, including those in some proteins.

Sensitive detection and estimation of cell-derived peroxynitrite fluxes using fluorescein-boronate

The specific and sensitive detection of peroxynitrite (ONOO^-/ONOOH) in biological systems is a great challenge due to its high reactivity towards several biomolecules. Herein, we validated the advantages of using fluorescein-boronate (Fl-B) as a highly sensitive fluorescent probe for the direct detection of peroxynitrite under biologically-relevant conditions in two different cell models. The synthesis of Fl-B was achieved by a very simply two-step conversion synthetic route with high purity (>99%) and overall yield (∼42%). Reactivity analysis of Fl-B with relevant biological oxidants including hydrogen peroxide (H₂O₂), hypochlorous acid (HOCl) and peroxynitrite were performed. The rate constant for the reaction of peroxynitrite with Fl-B was 1.7×10⁶M^-1s^-1, a million times faster than the rate constant measured for H₂O₂ (k=1.7M^-1s^-1) and 2,700 faster than HOCl (6.2×10²M^-1s^-1) at 37°C and pH 7.4. The reaction of Fl-B with peroxynitrite was significant even in the presence of physiological concentrations of CO₂, a well-known peroxynitrite reactant. Experimental and simulated kinetic analyses confirm that the main oxidation process of Fl-B takes place with peroxynitrite itself via a direct bimolecular reaction and not with peroxynitrite-derived radicals. Fl-B was successfully applied for the detection of endogenously-generated peroxynitrite by endothelial cells and in macrophage-phagocyted parasites. Moreover, the generated data allowed estimating the actual intracellular flux of peroxynitrite. For instance, ionomycin-stimulated endothelial cells generated peroxynitrite at a rate of ∼ 0.1μMs^-1, while immunostimulated macrophages do so in the order of ∼1μMs^-1 inside T. cruzi-infected phagosomes. Fl-B revealed not to be toxic in concentrations up to 1mM for 24h. Cellular peroxynitrite detection was achieved by conventional laboratory fluorescence-based methods including flow cytometry and epi-fluorescence microscopy. Fl-B was shown to be more sensitive than the coumarin boronate due to a higher molar absorption coefficient and quantum yield. Overall, our results show that Fl-B is a kinetically selective and highly sensitive probe for the direct detection of cell-derived peroxynitrite.

Role of Nitric Oxide in Cardiovascular Adaptation to Intermittent Hypoxia

Hypoxia is one of the most frequently encountered stresses in health and disease. The duration, frequency, and severity of hypoxic episodes are critical factors determining whether hypoxia is beneficial or harmful. Adaptation to intermittent hypoxia has been demonstrated to confer cardiovascular protection against more severe and sustained hypoxia, and, moreover, to protect against other stresses, including ischemia. Thus, the direct and cross protective effects of adaptation to intermittent hypoxia have been used for treatment and prevention of a variety of diseases and to increase efficiency of exercise training. Evidence is mounting that nitric oxide (NO) plays a central role in these adaptive mechanisms. NO-dependent protective mechanisms activated by intermittent hypoxia include stimulation of NO synthesis as well as restriction of NO overproduction. In addition, alternative, nonenzymic sources of NO and negative feedback of NO synthesis are important factors in optimizing NO concentrations. The adaptive enhancement of NO synthesis and/or availability activates or increases expression of other protective factors, including heat shock proteins, antioxidants and prostaglandins, making the protection more robust and sustained. Understanding the role of NO in mechanisms of adaptation to hypoxia will support development of therapies to prevent and treat hypoxic or ischemic damage to organs and cells and to increase adaptive capabilities of the organism.

Molecular visualizing and quantifying immune-associated peroxynitrite fluxes in phagocytes and mouse inflammation model

Reactions of peroxynitrite (ONOO^-) with biomolecules can lead to cytotoxic and cytoprotective events. Due to the difficulty of directly and unambiguously measuring its levels, most of the beneficial effects associated with ONOO^- in vivo remain controversial or poorly characterized. Recently, optical imaging has served as a powerful noninvasive approach to studying ONOO^- in living systems. However, ratiometric probes for ONOO^- are currently lacking. Herein, we report the design, synthesis, and biological evaluation of F₄₈₂, a novel fluorescence indicator that relies on ONOO^--induced diene oxidation. The remarkable sensitivity, selectivity, and photostability of F₄₈₂ enabled us to visualize basal ONOO^- in immune-stimulated phagocyte cells and quantify its generation in phagosomes by high-throughput flow cytometry analysis. With the aid of in vivo ONOO^- imaging in a mouse inflammation model assisted by F₄₈₂, we envision that F₄₈₂ will find widespread applications in the study of the ONOO^- biology associated with physiological and pathological processes in vitro and in vivo.

Phenolic Melatonin-Related Compounds: Their Role as Chemical Protectors against Oxidative Stress

There is currently no doubt about the serious threat that oxidative stress (OS) poses to human health. Therefore, a crucial strategy to maintain a good health status is to identify molecules capable of offering protection against OS through chemical routes. Based on the known efficiency of the phenolic and melatonin (MLT) families of compounds as antioxidants, it is logical to assume that phenolic MLT-related compounds should be (at least) equally efficient. Unfortunately, they have been less investigated than phenols, MLT and its non-phenolic metabolites in this context. The evidence reviewed here strongly suggests that MLT phenolic derivatives can act as both primary and secondary antioxidants, exerting their protection through diverse chemical routes. They all seem to be better free radical scavengers than MLT and Trolox, while some of them also surpass ascorbic acid and resveratrol. However, there are still many aspects that deserve further investigations for this kind of compounds.

Peroxynitrite: From interception to signaling

Peroxynitrite is a strong oxidant and nitrating species that mediates certain biological effects of superoxide and nitrogen monoxide. These biological effects include oxidative damage to proteins as well as the formation of 3-nitrotyrosyl moieties in proteins. As a consequence, such proteins may lose their activity, gain altered function, or become prone to proteolytic degradation - resulting in modulation of cellular protein turnover and in the modulation of signaling cascades. In analogy to hydrogen peroxide, peroxynitrite may be scavenged by selenoproteins like glutathione peroxidase-1 (GPx-1) or by selenocompounds with a GPx-like activity, such as ebselen; in further analogy to H2O2, peroxiredoxins have also been established as contributors to peroxynitrite reduction. This review covers three aspects of peroxynitrite biochemistry, (i) the interaction of selenocompounds/-proteins with peroxynitrite, (ii) peroxynitrite-induced modulation of cellular proteolysis, and (iii) peroxynitrite-induced modulation of cellular signaling.

Peroxynitrite (ONOO-) Redox Signaling Molecule-Responsive Polymersomes

Designing specific-responsive polymer nanocapsules toward a definite cell signaling molecule for targeted therapy faces a great challenge. Here we demonstrate that new block copolymer appended trifluoromethyl ketone side groups can chemoselectively respond to an endogenous redox biosignal, peroxynitrite (ONOO^-), but shield the interference of other biogenic reactive oxygen, nitrogen, and sulfur species (ROS/RNS/RSS). The ONOO^- signaling molecule is capable of triggering cascade oxidation-elimination reactions to cleave the side functionalities from the polymer chain, which induces a large alteration of the polymer amphiphilicity and further leads to controllable disassembly of their self-assembled vesicular structure. Modulating the ONOO^- stimulus concentrations could readily control the vesicle dissociation rates for desirable drug delivery. We envisage that this polymer model would provide a new scenario to construct bioresponsive macromolecular systems for future biomedical nanotechnologies.

Peroxynitrite-mediated oxidation of plasma fibronectin

Fibronectin is a large dimeric glycoprotein present in both human plasma and in basement membranes. The latter are specialized extracellular matrices underlying endothelial cells in the artery wall. Peroxynitrous acid (ONOOH) a potent oxidizing and nitrating agent, is formed in vivo from superoxide and nitric oxide radicals by stimulated macrophages and other cells. Considerable evidence supports ONOOH involvement in human atherosclerotic lesion development and rupture, possibly via extracellular matrix damage. Here we demonstrate that Tyr and Trp residues on human plasma fibronectin are highly sensitive to ONOOH with this resulting in the formation of 3-nitrotyrosine, 6-nitrotryptophan and dityrosine as well as protein aggregation and fragmentation. This occurs with equimolar or greater levels of oxidant, and in a dose-dependent manner. Modification of Tyr was quantitatively more significant than Trp (9.1% versus 1.5% conversion with 500μM ONOOH) after accounting for parent amino acid abundance, but only accounts for a small percentage of the total oxidant added. LC-MS studies identified 28 nitration sites (24 Tyr, 4 Trp) with many of these present within domains critical to protein function, including the cell-binding and anastellin domains. Human coronary artery endothelial cells showed decreased adherence and cell-spreading on ONOOH-modified fibronectin compared to control, consistent with cellular dysfunction induced by the modified matrix. Studies on human atherosclerotic lesions have provided evidence for co-localization of 3-nitrotyrosine and fibronectin. ONOOH-mediated fibronectin modification and compromised cell-matrix interactions, may contribute to endothelial cell dysfunction, a weakening of the fibrous cap of atherosclerotic lesions, and an increased propensity to rupture.

Effect of peroxynitrite on human serum albumin: a multi technique approach

In this study, human serum albumin (HSA), the most abundant protein of blood plasma, was modified with varying concentrations of peroxynitrite. The peroxynitrite-induced changes in HSA was monitored by spectroscopy, SDS-PAGE, 1-anilinonaphthalene-8-sulfonic acid (ANS), thermal denaturation studies, and matrix-assisted laser desorption/inonization-time of flight mass spectrometry (MALDI-TOF MS). Aggregate formation was studied by thioflavin T binding and scanning electron microscopy (SEM). The results indicated formation of 3-nitrotyrosine, 6-nitrotryptophan, dityrosine, and carbonyls in modified samples and showed retarded mobility in SDS-polyacrylamide gel. Reduction in α-helicity and surface protein hydrophobicity confirmed the secondary and tertiary structure alterations in peroxynitrite-modified-HSA. Also, attachment of nitro group and increase in melting temperature was observed in modified sample. Furthermore, significant enhancement in the fluorescence intensity of ThT upon binding with peroxynitrite-modified-HSA and images under scanning electron microscope are suggestive of protein aggregation. It is, therefore, speculated that HSA modified by endogenously formed peroxynitrite might act as a trigger for nitration/aggregation and suggested the role of peroxynitrite-modified-HSA in SLE.

Caveolin-1 protects against hepatic ischemia/reperfusion injury through ameliorating peroxynitrite-mediated cell death

Nitrative stress is considered as an important pathological process of hepatic ischemia and reperfusion injury but its regulating mechanisms are largely unknown. In this study, we tested the hypothesis that caveolin-1 (Cav-1), a plasma membrane scaffolding protein, could be an important cellular signaling against hepatic I/R injury through inhibiting peroxynitrite (ONOO(-))-induced cellular damage. Male wild-type mice and Cav-1 knockout (Cav-1(-/-)) were subjected to 1h hepatic ischemia following 1, 6 and 12h of reperfusion by clipping and releasing portal vessels respectively. Immortalized human hepatocyte cell line (L02) was subjected to 1h hypoxia and 6h reoxygenation and treated with Cav-1 scaffolding domain peptide. The major discoveries included: (1) the expression of Cav-1 in serum and liver tissues of wild-type mice was time-dependently elevated during hepatic ischemia-reperfusion injury. (2) Cav-1 scaffolding domain peptide treatment inhibited cleaved caspase-3 expression in the hypoxia-reoxygenated L02 cells; (3) Cav-1 knockout (Cav-1(-/-)) mice had significantly higher levels of serum transaminases (ALT&AST) and TNF-α, and higher rates of apoptotic cell death in liver tissues than wild-type mice after subjected to 1h hepatic ischemia and 6hour reperfusion; (4) Cav-1(-/-) mice revealed higher expression levels of iNOS, ONOO(-) and 3-nitrotyrosine (3-NT) in the liver than wild-type mice, and Fe-TMPyP, a representative peroxynitrite decomposition catalyst (PDC), remarkably reduced level of ONOO(-) and 3-NT and ameliorated the serum ALT, AST and TNF-α levels in both wild-type and Cav-1(-/-) mice. Taken together, we conclude that Cav-1 could play a critical role in preventing nitrative stress-induced liver damage during hepatic ischemia-reperfusion injury.

Oxidative-Nitrosative Stress and Myocardial Dysfunctions in Sepsis: Evidence from the Literature and Postmortem Observations

BACKGROUND

Myocardial depression in sepsis is common, and it is associated with higher mortality. In recent years, the hypothesis that the myocardial dysfunction during sepsis could be mediated by ischemia related to decreased coronary blood flow waned and a complex mechanism was invoked to explain cardiac dysfunction in sepsis. Oxidative stress unbalance is thought to play a critical role in the pathogenesis of cardiac impairment in septic patients.

AIM

In this paper, we review the current literature regarding the pathophysiology of cardiac dysfunction in sepsis, focusing on the possible role of oxidative-nitrosative stress unbalance and mitochondria dysfunction. We discuss these mechanisms within the broad scenario of cardiac involvement in sepsis.

CONCLUSIONS

Findings from the current literature broaden our understanding of the role of oxidative and nitrosative stress unbalance in the pathophysiology of cardiac dysfunction in sepsis, thus contributing to the establishment of a relationship between these settings and the occurrence of oxidative stress. The complex pathogenesis of septic cardiac failure may explain why, despite the therapeutic strategies, sepsis remains a big clinical challenge for effectively managing the disease to minimize mortality, leading to consideration of the potential therapeutic effects of antioxidant agents.

Antioxidant Activity/Capacity Measurement. 3. Reactive Oxygen and Nitrogen Species (ROS/RNS) Scavenging Assays, Oxidative Stress Biomarkers, and Chromatographic/Chemometric Assays

There are many studies in which the antioxidant potential of different foods have been analyzed. However, there are still conflicting results and lack of information as a result of unstandardized assay techniques and differences between the principles of the methods applied. The measurement of antioxidant activity, especially in the case of mixtures, multifunctional or complex multiphase systems, cannot be evaluated satisfactorily using a simple antioxidant test due to the many variables influencing the results. In the literature, there are many antioxidant assays that are used to measure the total antioxidant activity/capacity of food materials. In this review, reactive oxygen and nitrogen species (ROS/RNS) scavenging assays are evaluated with respect to their mechanism, advantages, disadvantages, and potential use in food systems. On the other hand, in vivo antioxidant activity (AOA) assays including oxidative stress biomarkers and cellular-based assays are covered within the scope of this review. Finally, chromatographic and chemometric assays are reviewed, focusing on their benefits especially with respect to their time saving, cost-effective, and sensitive nature.

Evaluation of Antibacterial Activity and Reactive Species Generation of N-Benzenesulfonyl Derivatives of Heterocycles

Two N-benzenesulfonyl (BS) derivatives of 1,2,3,4-tetrahydroquinoline (THQ) were designed, prepared, and screened for antibacterial activity. This approach was based on combining the two privileged structures, BS and THQ, which are known to be active. The objective of this study was to evaluate the antibacterial activity of BS-THQ and its analogue 4-NH2BS-THQ, and to investigate the roles of reactive oxygen species and reactive nitrogen species in their lethality. Both showed bactericidal activity against Staphylococcus aureus ATCC 29213 and methicillin-resistant S. aureus (MRSA) ATCC 43300, with transmission electron microscopy revealing a disturbed membrane architecture. Furthermore, an increase of reactive oxygen species (ROS) in strains treated with BS-THQ with respect to the control was detected when fluorescent microscopy and spectrophotometric techniques were used. The analogue 4-NH2BS-THQ demonstrated a broader spectrum of activity than BS-THQ, with a minimum inhibitory concentration of 100 µg/mL against reference strains of S. aureus, Escherichia coli and Pseudomonas aeruginosa. The assayed compounds represent promising structures for the development of new synthetic classes of antimicrobials.

Nitroxides protect against peroxynitrite-induced nitration and oxidation

Nitroxides are promising compounds for prevention of undesired protein modifications. The aim of this study was to compare the efficiency of 11 nitroxides, derivatives of 2,2,6,6-tetramethylpiperidine-1-oxide (TEMPO) and 2,2,5,5-tetramethylpirrolidine-1-oxyl (PROXYL) in prevention of nitration and oxidation of model compounds and human serum albumin (HSA). Most nitroxides were very efficient in preventing loss of fluorescein fluorescence induced by peroxynitrite (PN) (IC50 in the nanomolar range) and preventing HSA nitration. The loss of fluorescein fluorescence was demonstrated to be due to nitration. Nitroxides were more effective in prevention nitration than oxidation reactions. They showed a concentration window for preventing dihydrorhodamine (DHR) 123 oxidation but exerted a prooxidant effect at both high and low concentrations. No prooxidant effect of nitroxides was seen in prevention of DHR123 oxidation induced by SIN-1. In all essays hydrophobic nitroxides (especially 4-nonylamido-TEMPO and 3-carbamolyl-dehydroPROXYL) showed the lowest efficiency. An exception was the prevention of thiol group oxidation by PN and SIN-1 where hydrophobic nitroxides were the most effective, apparently due to binding to the protein. Nitroxides showed low toxicity to MCF-7 cells. Most nitroxides, except for the most hydrophobic ones, protected cells from the cytotoxic action of SIN-1 and SIN-1-induced protein nitration. These results point to potential usefulness of nitroxides for prevention of PN-induced oxidation and, especially, nitration.

Kinetics of reaction of peroxynitrite with selenium- and sulfur-containing compounds: Absolute rate constants and assessment of biological significance

Peroxynitrite (the physiological mixture of ONOOH and its anion, ONOO(-)) is a powerful biologically-relevant oxidant capable of oxidizing and damaging a range of important targets including sulfides, thiols, lipids, proteins, carbohydrates and nucleic acids. Excessive production of peroxynitrite is associated with several human pathologies including cardiovascular disease, ischemic-reperfusion injury, circulatory shock, inflammation and neurodegeneration. This study demonstrates that low-molecular-mass selenols (RSeH), selenides (RSeR') and to a lesser extent diselenides (RSeSeR') react with peroxynitrite with high rate constants. Low molecular mass selenols react particularly rapidly with peroxynitrite, with second order rate constants k2 in the range 5.1 × 10(5)-1.9 × 10(6)M(-1)s(-1), and 250-830 fold faster than the corresponding thiols (RSH) and many other endogenous biological targets. Reactions of peroxynitrite with selenides, including selenosugars are approximately 15-fold faster than their sulfur homologs with k2 approximately 2.5 × 10(3)M(-1)s(-1). The rate constants for diselenides and sulfides were slower with k2 0.72-1.3 × 10(3)M(-1)s(-1) and approximately 2.1 × 10(2)M(-1)s(-1) respectively. These studies demonstrate that both endogenous and exogenous selenium-containing compounds may modulate peroxynitrite-mediated damage at sites of acute and chronic inflammation, with this being of particular relevance at extracellular sites where the thiol pool is limited.

Peroxynitrous acid induces structural and functional modifications to basement membranes and its key component, laminin

Basement membranes (BM) are specialized extracellular matrices underlying endothelial cells in the artery wall. Laminin, the most abundant BM glycoprotein, is a structural and biologically active component. Peroxynitrous acid (ONOOH), a potent oxidizing and nitrating agent, is formed in vivo at sites of inflammation from superoxide and nitric oxide radicals. Considerable data supports ONOOH formation in human atherosclerotic lesions, and an involvement of this oxidant in atherosclerosis development and lesion rupture. These effects may be mediated, at least in part, via extracellular matrix damage. In this study we demonstrate co-localization of 3-nitrotyrosine (a product of tyrosine damage by ONOOH) and laminin in human atherosclerotic lesions. ONOOH-induced damage to BM was characterized for isolated murine BM, and purified murine laminin-111. Exposure of laminin-111 to ONOOH resulted in dose-dependent loss of protein tyrosine and tryptophan residues, and formation of 3-nitrotyrosine, 6-nitrotryptophan and the cross-linked material di-tyrosine, as detected by amino acid analysis and Western blotting. These changes were accompanied by protein aggregation and fragmentation as detected by SDS-PAGE. Endothelial cell adhesion to isolated laminin-111 exposed to 10 μM or higher levels of ONOOH was significantly decreased (~25%) compared to untreated controls. These data indicate that laminin is oxidized by equimolar or greater concentrations of ONOOH, with this resulting in structural and functional changes. These modifications, and resulting compromised cell-matrix interactions, may contribute to endothelial cell dysfunction, a weakening of the structure of atherosclerotic lesions, and an increased propensity to rupture.

Nitric oxide as a regulator of B. anthracis pathogenicity

Nitric oxide (NO) is a key physiological regulator in eukaryotic and prokaryotic organisms. It can cause a variety of biological effects by reacting with its targets or/and indirectly inducing oxidative stress. NO can also be produced by bacteria including the pathogenic Bacillus anthracis; however, its role in the infectious process only begins to emerge. NO incapacitates macrophages by S-nitrosylating the intracellular proteins and protects B. anthracis from oxidative stress. It is also implicated in the formation of toxic peroxynitrite. In this study we further assessed the effects of B. anthracis NO produced by the NO synthase (bNOS) on bacterial metabolism and host cells in experiments with the bNOS knockout Sterne strain. The mutation abrogated accumulation of nitrite and nitrate as tracer products of NO in the culture medium and markedly attenuated growth in both aerobic and microaerobic conditions. The regulatory role of NO was also suggested by the abnormally high rate of nitrate denitrification by the mutant in the presence of oxygen. Anaerobic regulation mediated by NO was reflected in reduced fermentation of glucose by the mutant correlating with the reduced toxicity of bacteria toward host cells in culture. The toxic effect of NO required permeabilization of the target cells as well as the activity of fermentation-derived metabolite in the conditions of reduced pH. The host cells demonstrated increased phosphorylation of major survivor protein kinase AKT correlating with reduced toxicity of the mutant in comparison with Sterne. Our global proteomic analysis of lymph from the lymph nodes of infected mice harboring bacteria revealed numerous changes in the pattern and levels of proteins associated with the activity of bNOS influencing key cell physiological processes relevant to energy metabolism, growth, signal transduction, stress response, septic shock, and homeostasis. This is the first in vivo observation of the bacterial NO effect on the lymphatic system.

Substituent effects on the stability and antioxidant activity of spirodiazaselenuranes

Spirodiazaselenuranes are structurally interesting compounds and the stability of these compounds depends highly on the nature of the substituents attached to the nitrogen atoms. Aromatic substituents are known to play important roles in stabilizing the Se-N bonds in spiro compounds. In this study, several spirodiazaselenuranes are synthesized by introducing benzylic and aliphatic substituents to understand their effect on the stability of the Se-N bonds and the antioxidant activity. Replacement of phenyl substituent by benzyl/alkyl groups significantly reduces the stability of the spirodiazaselenuranes and slows down the oxidative cyclization process. The selenium centre in the spiro compounds undergoes further oxidation to produce the corresponding selenurane oxides, which are stable at room temperature. Comparison of the glutathione peroxidase (GPx) mimetic activity of the compounds showed that the diaryl selenides having heterocyclic rings are significantly more active due to the facile oxidation of the selenium centre. However, the activity is reduced significantly for compounds having aliphatic substituents. In addition to GPx activity, the compounds also inhibit peroxynitrite-mediated nitration and oxidation reaction of protein and small molecules, respectively. The experimental observations suggest that the antioxidant activity is increased considerably upon substitution of the aromatic group with the benzylic/aliphatic substituents on the nitrogen atoms.

Influence of vitamin C and vitamin E on redox signaling: Implications for exercise adaptations

The exogenous antioxidants vitamin C (ascorbate) and vitamin E (α-tocopherol) often blunt favorable cell signaling responses to exercise, suggesting that redox signaling contributes to exercise adaptations. Current theories posit that this antioxidant paradigm interferes with redox signaling by attenuating exercise-induced reactive oxygen species (ROS) and reactive nitrogen species (RNS) generation. The well-documented in vitro antioxidant actions of ascorbate and α-tocopherol and characterization of the type and source of the ROS/RNS produced during exercise theoretically enable identification of redox-dependent mechanisms responsible for the blunting of favorable cell signaling responses to exercise. This review aimed to apply this reasoning to determine how the aforementioned antioxidants might attenuate exercise-induced ROS/RNS production. The principal outcomes of this analysis are (1) neither antioxidant is likely to attenuate nitric oxide signaling either directly (reaction with nitric oxide) or indirectly (reaction with derivatives, e.g., peroxynitrite); (2) neither antioxidant reacts appreciably with hydrogen peroxide, a key effector of redox signaling; (3) ascorbate but not α-tocopherol has the capacity to attenuate exercise-induced superoxide generation; and (4) alternate mechanisms, namely pro-oxidant side reactions and/or reduction of bioactive oxidized macromolecule adducts, are unlikely to interfere with exercise-induced redox signaling. Out of all the possibilities considered, ascorbate-mediated suppression of superoxide generation with attendant implications for hydrogen peroxide signaling is arguably the most cogent explanation for blunting of favorable cell signaling responses to exercise. However, this mechanism is dependent on ascorbate accumulating at sites rich in NADPH oxidases, principal contributors to contraction-mediated superoxide generation, and outcompeting nitric oxide and superoxide dismutase isoforms. The major conclusions of this review are: (1) direct evidence for interference of ascorbate and α-tocopherol with exercise-induced ROS/RNS production is lacking; (2) theoretical analysis reveals that both antioxidants are unlikely to have a major impact on exercise-induced redox signaling; and (3) it is worth considering alternate redox-independent mechanisms.

Reactive oxygen species, heat stress and oxidative-induced mitochondrial damage. A review

In recent years there has been enormous interest in researching oxidative stress. Reactive oxygen species (ROS) are derived from the metabolism of oxygen as by-products of cell respiration, and are continuously produced in all aerobic organisms. Oxidative stress occurs as a consequence of an imbalance between ROS production and the available antioxidant defence against them. Nowadays, a variety of diseases and degenerative processes such as cancer, Alzheimer's and autoimmune diseases are mediated by oxidative stress. Heat stress was suggested to be an environmental factor responsible for stimulating ROS production because of similarities in responses observed following heat stress compared with that occurring following exposure to oxidative stress. This manuscript describes the main mitochondrial sources of ROS and the antioxidant defences involved to prevent oxidative damage in all the mitochondrial compartments. It also deals with discussions concerning the cytotoxic effect of heat stress, mitochondrial heat-induced alterations, as well as heat shock protein (HSP) expression as a defence mechanism.

Ameliorating role of rutin on oxidative stress induced by iron overload in hepatic tissue of rats

Iron is an essential element that participates in several metabolic activities of cells; however, excess iron is a major cause of iron-induced oxidative stress and several human diseases. Natural flavonoids, as rutin, are well-known antioxidants and could be efficient protective agents. Therefore, the present study was undertaken to evaluate the protective influence of rutin supplementation to improve rat antioxidant systems against IOL-induced hepatic oxidative stress. Sixty male albino rats were randomly divided to three equal groups. The first group, the control, the second group, iron overload group, the third group was used as iron overload+rutin group. Rats received six doses of ferric hydroxide polymaltose (100 mg kg(-1) b.wt.) as one dose every two days, by intraperitoneal injections (IP) and administrated rutin (50 mg kg(-1) b.wt.) as one daily oral dose until the sacrificed day. Blood samples for serum separation and liver tissue specimens were collected three times, after three, four and five weeks from the onset of the experiment. Serum iron profiles total iron, Total Iron Binding Capacity (TIBC), Unsaturated Iron Binding Capacity (UIBC), transferrin (Tf) and Transferrin Saturation% (TS%)}, ferritin, albumin, total Protein, total cholesterol, triacylglycerols levels and aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities were determined. Moreover, total iron in the liver, L-malondialdehyde (L-MDA), glutathione (GSH), Nitric Oxide (NO) and Total Nucleic Acid (TNA) levels and glutathione peroxidase (GPx), catalase (CAT) and superoxide dismutase (SOD) activities were also determined. The obtained results revealed that, iron overload (IOL) resulted in significant increase in serum iron, TIBC, Tf, TS% and ferritin levels and AST and ALT activities and also increased liver iron, L-MDA and NO levels. Meanwhile, it decreased serum UIBC, total cholesterol, triacylglycerols, albumin, total protein and liver GSH, TNA levels and Gpx, CAT and SOD activities when compared with the control group. Rutin administration to iron-overloaded rats resulted in significant decrease in serum total iron, TIBC, Tf, TS%, ferritin levels and AST and ALT activities and liver total iron, L-MDA and NO levels with significant increases in serum UIBC, albumin, total protein and total cholesterol levels and in liver GSH, CAT and SOD activities compared with the IOL group. This study provides in vivo evidence that rutin administration can improve the antioxidant defense systems against IOL-induced hepatic oxidative stress in rats. This protective effect in liver of iron-loaded rats may be due to both antioxidant and metal chelation activities.

Impact of acute Cd²⁺ exposure on the antioxidant defence systems in the skin and red blood cells of common carp (Cyprinus carpio)

Cd(2+)-induced oxidative stress and its effects on the expression of stress biomarkers and on macromolecule damage in the skin and blood of common carp were studied. Both tissues play important roles in the defence mechanisms against external hazards, serving as an anatomical barrier and as connecting tissue between the organs. In the skin, the production of peroxynitrite anion and hydrogen peroxide was almost doubled after exposure to 10 mg/L Cd(2+). The accumulation of these oxidant molecules suggests an intensive production of superoxide anion and nitrogen monoxide and the development of oxidative and/or nitrosative stress. Although the metallothioneins and the components of the glutathione redox system were activated in the skin, the accumulation of reactive intermediates led to the enhanced damage of lipid molecules after 24 h of metal exposure. In the blood, the basal levels of metallothionein messenger RNAs (mRNAs) were 2-2.5-fold of that measured in the skin. This high level of metallothionein expression could be the reason that the blood was less affected by an acute Cd(2+) challenge and the metallothionein and glutathione systems were not activated.

Changes in the conformational state of hemoglobin in hemodialysed patients with chronic renal failure

The aim of this study was to evaluate the properties of internal components of erythrocytes in chronic renal failure (CRF) patients undergoing hemodialysis (HD) in comparison to control subjects. For investigation of conformational state of hemoglobin and nonheme proteins (NHP) the maleimide spin label (MSL) in electron paramagnetic resonance (EPR) was applied. The studies were performed using MSL in whole cells and hemolysate as well as proteins separated by ion exchange chromatography and checked by electrophoresis. Additionally the level of –SH groups in hemolysate and isolated internal proteins of CRF erythrocytes was determined using 4,4′-dithiodipyridine. All measurements were performed before and after hemodialysis. Oxidative stress accompanying CRF/hemodialysed patients caused a significant decrease in the mobility of internal components inside erythrocytes indicated by MSL (P < 0.02). The significant decrease in mobility of spin labeled HbA_1c and HbA both before and after HD (P < 0.0002) as well as in nonheme proteins before hemodialysis (P < 0.05) versus control was indicated. Decrease in mobility of internal components of erythrocytes was accompanied by loss of thiols before and after hemodialysis versus control in NHP (P < 0.05), HbA_1c (P < 0.0002), and HbA (P < 0.0005). These findings showed oxidative influence of hemodialysis on hemoglobins and internal nonheme proteins in erythrocytes of CRF patients.

Nitric oxide signals postovulatory aging-induced abortive spontaneous egg activation in rats

OBJECTIVE

The aim of this study was to determine whether an increase of intracellular nitric oxide (NO) level signals postovulatory aging-induced abortive spontaneous egg activation (SEA) in rats.

METHODS

Freshly ovulated eggs (arrested at metaphase-II stage; M-II) were cultured in vitro for 3 hours to induce postovulatory egg aging. The morphological changes, inducible nitric oxide synthase (iNOS) expression, NO, cytosolic free Ca(2+), 3',5' cyclic guanosine monophosphate (cGMP), cell division cycle 25B (Cdc25B) and Wee1 levels, specific phosphorylation (pThr-14/Tyr-15) as well as total cyclin-dependent kinases-1 (Cdk1) (PSTAIRE) levels were analyzed.

RESULTS

Postovulatory aging induced generation of NO possibly through an iNOS-mediated pathway. The increase in NO level was associated with augmented cytosolic free Ca(2+) as well as cGMP levels in aged eggs. A significant increase in Wee1 level and decrease of Cdc25B level were observed in aged eggs. An accumulation of phosphorylated Cdk1 (pThr-14/Tyr-15) level was observed in aged eggs, while total Cdk1 (PSTAIR) level remained unchanged.

CONCLUSION

Our study demonstrates that generation of NO through an iNOS-mediated pathway increases cytosolic free Ca2+and cGMP levels. High levels of these signal molecules trigger the accumulation of phosphorylated Cdk1 in aged eggs. Thus, NO signals the accumulation of phosphorylated Cdk1 and induces postovulatory aging-induced abortive SEA in the rat.