Use of spin traps to detect superoxide production in living cells by electron paramagnetic resonance (EPR) spectroscopy

Accessing Properties of Molecular Compounds Involved in Cellular Metabolic Processes with Electron Paramagnetic Resonance, Raman Spectroscopy, and Differential Scanning Calorimetry

In this work, we review some physical methods of macroscopic experiments, which have been recently argued to be promising for the acquisition of valuable characteristics of biomolecular structures and interactions. The methods we focused on are electron paramagnetic resonance spectroscopy, Raman spectroscopy, and differential scanning calorimetry. They were chosen since it can be shown that they are able to provide a mutually complementary picture of the composition of cellular envelopes (with special attention paid to mycobacteria), transitions between their molecular patterning, and the response to biologically active substances (reactive oxygen species and their antagonists-antioxidants-as considered in our case study).

Sulfmyoglobin production by free cysteine during thermal treatment: Involvement of heme iron in the production of free radicals

The meat greening is an abnormal pigmentation related to microbiological contamination and lipid oxidation during storage. This color change results from sulfmyoglobin (SulfMb) production promoted by the reaction between metmyoglobin (MetMb), H₂O_2, and thiol compounds. Spectral studies on cooked meat suggested the production of SulfMb, probably due to the increment of free radicals during thermal treatment. Thus, we evaluated the involvement of free radicals and heme iron in the SulfMb production from horse MetMb and free cysteine (Cys) during thermal treatment. The results confirm that the reaction of SulfMb production at meat muscle pH (5.7-7.2) during heat treatment is a product of free radicals formed from Cys oxidation (SH) and reactive oxygen species (O₂^-, H₂O₂). This is catalyzed by the release of heme iron, thus promoting a consecutive reaction having MbFe(IV)O as a reaction intermediate.

Hydropersulfides (RSSH) attenuate doxorubicin-induced cardiotoxicity while boosting its anticancer action

Cardiotoxicity is a frequent and often lethal complication of doxorubicin (DOX)-based chemotherapy. Here, we report that hydropersulfides (RSSH) are the most effective reactive sulfur species in conferring protection against DOX-induced toxicity in H9c2 cardiac cells. Mechanistically, RSSH supplementation alleviates the DOX-evoked surge in reactive oxygen species (ROS), activating nuclear factor erythroid 2-related factor 2 (Nrf2)-dependent pathways, thus boosting endogenous antioxidant defenses. Simultaneously, RSSH turns on peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), a master regulator of mitochondrial function, while decreasing caspase-3 activity to inhibit apoptosis. Of note, we find that RSSH potentiate anticancer DOX effects in three different cancer cell lines, with evidence that suggests this occurs via induction of reductive stress. Indeed, cancer cells already exhibit much higher basal hydrogen sulfide (H2S), sulfane sulfur, and reducing equivalents compared to cardiac cells. Thus, RSSH may represent a new promising avenue to fend off DOX-induced cardiotoxicity while boosting its anticancer effects.

Luminescent Water-Dispersible Nanoparticles Engineered from Copper(I) Halide Cluster Core and P,N-Ligand with an Optimal Balance between Stability and ROS Generation

The present work introduces the solvent exchange procedure as a route for conversion of the Cu4I4L2 complex, where the Cu4I4 cluster core is coordinated with two P,N-ligands (L), into an aqueous colloid. The analysis of both colloidal and supernatant phases revealed some losses in CuI going from the initial Cu4I4L2 complex to Cu2I2L3-based nanoparticles. The comparative analysis of IR, 31P NMR spectroscopy, ESI mass-spectrometry and luminescence data argued for a contribution of the “butterfly”-like structures of the Cu2I2 cluster core to Cu2I2L3-based nanoparticles, although the amorphous nature of the latter restricted structure evaluation from the PXRD data. The green luminescence of the colloids revealed their chemical stability under pH variations in the solutions of some amino acids and peptides, and to specify the temperature and concentration conditions triggering the oxidative degradation of the nanoparticles. The spin trap-facilitated ESR study indicated that the oxidative transformations were followed by the generation of reactive oxygen species (ROS). The physiological temperature level (310 K) enhanced the ROS generation by nanoparticles, but the ROS level was suppressed in the solution of GSH at pH = 7.0. The cytotoxicity of nanoparticles was evaluated in the M-HeLa cell line and is discussed in correlation with their cell internalization and intracellular oxidative transformations.

Nanoemulsions of Clove Oil Stabilized with Chitosan Oleate-Antioxidant and Wound-Healing Activity

Clove oil (CO) is a powerful antioxidant essential oil (EO) with anti-inflammatory, anesthetic, and anti-infective properties. It can be therefore considered a good candidate for wound-healing applications, especially for chronic or diabetic wounds or burns, where the balance of reactive oxygen species (ROS) production and detoxification is altered. However, EOs require suitable formulations to be efficiently administered in moist wound environments. Chitosan hydrophobically modified by an ionic interaction with oleic acid (chitosan oleate, CSO) was used in the present work to stabilize CO nanoemulsions (NEs). The dimensions of the NE were maintained at around 300 nm as the volume distribution for up to six months, and the CO content did not decrease to under 80% over 4 months, confirming the good stabilizing properties of CSO. The antioxidant properties of the CO NE were evaluated in vitro by a 2,2-diphenil-2-picrylhydrazyl hydrate (DPPH) assay, and in fibroblast cell lines by electron paramagnetic resonance (EPR) using α-phenyl-N-tert-butyl nitrone (PBN) as a spin trap; a protective effect was obtained comparable to that obtained with α-tocopherol treatment. In a murine burn model, the ability of CO formulations to favor macroscopic wound closure was evidenced, and a histological analysis revealed a positive effect of the CO NE on the reparation of the lesion after 18 days. Samples of wounds at 7 days were subjected to a histological analysis and parallel dosage of lipid peroxidation by means of a thiobarbituric acid-reactive substances (TBARS) assay, confirming the antioxidant and anti-inflammatory activity of the CO NE.

Wastewater treatment by anodic oxidation in electrochemical advanced oxidation process: Advance in mechanism, direct and indirect oxidation detection methods

Electrochemical Advanced Oxidation Process (EAOP) has been applied to the degradation of refractory pollutants in wastewater due to its strong oxidation capacity, high degradation efficiency, simple operation, and mild reaction. Among electrochemical processes, anodic oxidation (AO) is the most widely used and its mechanism is mainly divided into direct oxidation and indirect oxidation. Direct oxidation means that pollutants are oxidized at the anode by direct electron transfer. Indirect oxidation refers to the generation of active species during the electrolytic reaction, which acts on pollutants. The mechanism of AO process is controlled by many factors, including electrode type, electrocatalyst material, wastewater composition, pH, applied current and voltage levels. It is very important to explore the reaction mechanism of electrochemical treatment, which determines the efficiency of the reaction, the products of the reaction, and the extent of reaction. This paper firstly reviews the current research progress on the mechanism of AO process, and summarizes in detail the different mechanisms caused by influencing factors under common AO process. Then, strategies and methods to distinguish direct oxidation and indirect oxidation mechanisms are reviewed, such as intermediate product analysis, electrochemical test analysis, active species detection, theoretical calculation, and the limitations of these methods are analyzed. Finally some suggestions are put forward for the study of the mechanism of electrochemical advanced oxidation.

Electrochemical Sensors for the Detection of Reactive Oxygen Species in Biological Systems: A Critical Review

Reactive oxygen species (ROS) involving superoxide anion, hydrogen peroxide and hydroxyl radical play important role in human health. ROS are known to be the markers of oxidative stress associated with different pathologies including neurodegenerative and cardiovascular diseases, as well as cancer. Accordingly, ROS level detection in biological systems is an essential problem for biomedical and analytical research. Electrochemical methods seem to have promising prospects in ROS determination due to their high sensitivity, rapidity, and simple equipment. This review demonstrates application of modern electrochemical sensors for ROS detection in biological objects (e.g., cell lines and body fluids) over a decade between 2011 and 2021. Particular attention is paid to sensors materials and various types of modifiers for ROS selective detection. Moreover, the sensors comparative characteristics, their main advantages, disadvantages and their possibilities and limitations are discussed.

Defining roles of specific reactive oxygen species (ROS) in cell biology and physiology

'Reactive oxygen species' (ROS) is a generic term that defines a wide variety of oxidant molecules with vastly different properties and biological functions that range from signalling to causing cell damage. Consequently, the description of oxidants needs to be chemically precise to translate research on their biological effects into therapeutic benefit in redox medicine. This Expert Recommendation article pinpoints key issues associated with identifying the physiological roles of oxidants, focusing on H₂O₂ and O₂^.-. The generic term ROS should not be used to describe specific molecular agents. We also advocate for greater precision in measurement of H₂O₂, O₂^.- and other oxidants, along with more specific identification of their signalling targets. Future work should also consider inter-organellar communication and the interactions of redox-sensitive signalling targets within organs and whole organisms, including the contribution of environmental exposures. To achieve these goals, development of tools that enable site-specific and real-time detection and quantification of individual oxidants in cells and model organisms are needed. We also stress that physiological O₂ levels should be maintained in cell culture to better mimic in vivo redox reactions associated with specific cell types. Use of precise definitions and analytical tools will help harmonize research among the many scientific disciplines working on the common goal of understanding redox biology.

Solvent-free synthesis of nitrone-containing template as a chemosensor for selective detection of Cu(II) in water

A state-of-the-art method was developed for repurposing nitrone-containing compounds in the chemosensory field, the ability of the designed molecules to chelate metal cations was evaluated, and their unprecedented solubility in water was confirmed. A facile, rapid, and solvent-free method of synthesizing small molecular mass chemosensors was developed by using a modulative α-aryl-N-aryl nitrone template. α-(Z)-Imidazol-4-ylmethylen-N-phenyl nitrone (Nit1) and α-(Z)-2-pyridyl-N-phenyl nitrone (Nit2) were prepared in 15 min, isolated in less than 60 min with ca. 90% yield, and screened against nine metal cations. Nit1 is a small-molecular-mass compound (188 g mol^-1) that is water-soluble and has specificity for sensing Cu²⁺ with an association constant of K = 1.53 × 10¹⁰ and a limit of detection (LOD) of 0.06 ppm. These properties make Nit1 a competitive chemosensor for the detection of Cu²⁺ in aqueous solution. The nitrone-containing template used in this study is a step forward for new and small chemosensory entities.

Silica-Supported Assemblage of CuII Ions with Carbon Dots for Self-Boosting and Glutathione-Induced ROS Generation

The present work introduces coordinative binding of CuII ions with both amino-functionalized silica nanoparticles (SNs) and green-emitting carbon dots (CDs) as the pregrequisite for the CuII-assisted self-assembly of the CDs at the surface of the SNs. The produced composite SNs exhibit stable in time stimuli-responsive green fluorescence derived from the CuII-assisted assemblage of CDs. The fluorescence response of the composite SNs is sensitive to the complex formation with glutathione (GSH), enabling them to detect it with the lower limit of detection of 0.15 μM. The spin-trap-facilitated electron spin resonance technique indicated that the composite SNs are capable of self-boosting generation of ROS due to CuII→CuI reduction by carbon in low oxidation states as a part of the CDs. The intensity of the ESR signals is enhanced under the heating to 38 °C. The intensity is suppressed at the GSH concentration of 0.35 mM but is enhanced at 1.0 mM of glutathione, while it is suppressed once more at the highest intracellular concentration level of GSH (10 mM). These tendencies reveal the concentrations optimal for the scavenger or reductive potential of GSH. Flow cytometry and fluorescence and confocal microscopy methods revealed efficient cell internalization of SNs-NH2-CuII-CDs comparable with that of “free” CDs.

Electron paramagnetic resonance and spin trapping to detect free radicals from allergenic hydroperoxides in contact with the skin: from the molecule to the tissue

A major research topic consists of revealing the contribution of radical-mediated reactions in dermatological diseases related to xenobiotic-induced stress, to succeed risk assessment procedures protecting producers and consumers. Allergic contact dermatitis is the clinically relevant consequence of skin sensitization, one of the most critical occupational and environmental health issues related to xenobiotics exposure. The first key event identified for the skin sensitization process to a chemical is its aptitude to react with epidermal proteins and form antigenic structures that will further trigger the immune response. Many chemical sensitizers are suspected to react through mechanisms involving radical intermediates. This review focuses on recent progress we have accomplished over the last few years studying radical intermediates derived from skin sensitizing chemicals by electron paramagnetic resonance in combination with the spin trapping technique. Our work is carried out "from the molecule", performing studies in solution, "to the tissue", by the development of a methodology on a reconstructed human epidermis model, very close in terms of histology and metabolic/enzymatic activity to real human epidermis, that can be used as suitable biological tissue model. The benefits are to test chemicals under conditions close to human use and real-life sensitization exposures and benefit from the 3D microenvironment. This article is protected by copyright. All rights reserved.

Propelling the practical application of the intimate coupling of photocatalysis and biodegradation system: System amelioration, environmental influences and analytical strategies

The intimate coupling of photocatalysis and biodegradation (ICPB) possesses an enhanced ability of recalcitrant contaminant removal and energy generation, owing to the compact communication between biotic components and photocatalysts during the system operation. The photocatalysts in the ICPB system could dispose of noxious contaminants to relieve the external pressure on microorganisms which could realize the mineralization of the photocatalytic degradation products. However, due to the complex components in the composite system, the mechanism of the ICPB system has not been completely understood. Moreover, the variable environmental conditions would play a significant role in the ICPB system performance. The further development of the ICPB scheme requires clarification on how to reach an accurate understanding of the system condition during the practical application. This review starts by offering detailed information on the system construction and recent progress in the system components' amelioration. We then describe the potential influences of relevant environmental factors on the system performance, and the analytical strategies applicable for comprehending the critical processes during the system operation are further summarized. Finally, we put forward the research gaps in the current system and envision the system's prospective application. This review provides a valuable reference for future researches that are devoted to assessing the environmental disturbance and exploring the reaction mechanisms during the practical application of the ICPB system.

Prospects for More Efficient Multi-Photon Absorption Photosensitizers Exhibiting Both Reactive Oxygen Species Generation and Luminescence

The use of two-photon absorption (TPA) for such applications as microscopy, imaging, and photodynamic therapy (PDT) offers several advantages over the usual one-photon excitation. This creates a need for photosensitizers that exhibit both strong two-photon absorption and the highly efficient generation of reactive oxygen species (ROS), as well as, ideally, bright luminescence. This review focuses on different strategies utilized to improve the TPA properties of various multi-photon absorbing species that have the required photophysical properties. Along with well-known families of photosensitizers, including porphyrins, we also describe other promising organic and organometallic structures and more complex systems involving organic and inorganic nanoparticles. We concentrate on the published studies that provide two-photon absorption cross-section values and the singlet oxygen (or other ROS) and luminescence quantum yields, which are crucial for potential use within PDT and diagnostics. We hope that this review will aid in the design and modification of novel TPA photosensitizers, which can help in exploiting the features of nonlinear absorption processes.

Structure impact on photodynamic therapy and cellular contrasting functions of colloids constructed from dimeric Au(I) complex and hexamolybdenum clusters

Electrostatically driven self-assembly of [Au₂L₂]²⁺ (L is cyclic PNNP ligand) with [{Mo₆I₈}(L')₆]^2- (L' = I^-, CH₃COO^-) in aqueous solutions is introduced as facile route for combination of therapeutic and cellular contrasting functions within heterometallic colloids (Mo₆-Au₂). The nature of L' affects the size and aggregation behavior of crystalline Mo₆-Au₂ aggregates, which in turn affect the luminescence of the cluster units incorporated into Mo₆-Au₂ colloids. The spin trap facilitated electron spin resonance spectroscopy technique indicates that the level of ROS generated by Mo₆-Au₂ colloids is also affected by their size. Both (L' = I^-, CH₃COO^-) Mo₆-Au₂ colloids undergo cell internalization, which is enhanced by their assembly with poly-DL-lysine (PL) for L' = CH₃COO^-, but remains unchanged for L' = I^-. The colloids PL-Mo₆-Au₂ (L' = CH₃COO^-) are visualized as huge crystalline aggregates both outside and inside the cell cytoplasm by confocal microscopy imaging of the incubated cells, while the smaller sized (30-50 nm) PL-Mo₆-Au₂ (L' = I^-) efficiently stain the cell nuclei. Quantitative colocalization analysis of PL-Mo₆-Au₂ (L' = CH₃COO^-) in lysosomal compartments points to the fast endo-lysosomal escape of the colloids followed by their intracellular aggregation. The cytotoxicity of PL-Mo₆-Au₂ differs from that of Mo₆ and Au₂ blocks, predominantly acting through apoptotic pathway. The photodynamic therapeutic effect of the PL-Mo₆-Au₂ colloids on the cancer cells correlates with their intracellular trafficking and aggregation.

Electron paramagnetic resonance of sonicated powder suspensions in organic solvents

The chemical effects of the acoustic cavitation generated by ultrasound translates into the production of highly reactive radicals. Acoustic cavitation is widely explored in aqueous solutions but it remains poorly studied in organic liquids and in particular in liquid/solid media. However, several heterogeneous catalysis reactions take place in organic solvents. Thus, we sonicated trimethylene glycol and propylene glycol in the presence of silica particles (SiO₂) of different sizes (5-15 nm, 0.2-0.3 µm, 12-26 µm) and amounts (0.5 wt% and 3 wt%) at an ultrasound frequency of 20 kHz to quantify the radicals generated. The spin trap 5,5-dimethyl-1-pyrrolin-N-oxide (DMPO) was used to trap the generated radicals for study by electron paramagnetic resonance (EPR) spectroscopy. We identified the trapped radical as the hydroxyalkyl radical adduct of DMPO, and we quantified it using stable radical 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) as a quantitation standard. The concentration of DMPO spin adducts in solutions containing silica size 12-26 µm was higher than the solution without particles. The presence of these particles increased the concentration of the acoustically generated radicals by a factor of 1.5 (29 µM for 0.5 wt% of SiO₂ size 12-26 µm vs 19 µM for 0 wt%, after 60 min of sonication). Ultrasound produced fewest radicals in solutions with the smallest particles; the concentration of radical adducts was highest for SiO₂ particle size 12-26 µm at 0.5 wt% loading, reaching 29 µM after 60 min sonication. Ultrasound power of 50.6 W produced more radicals than 24.7 W (23 µM and 18 µM, respectively, at 30 min sonication). Increased temperature during sonication generated more radical adducts in the medium (26 µM at 75 °C and 18 µM at 61 °C after 30 min sonication). Acoustic cavitation, in the presence of silica, increased the production of radical species in the studied organic medium.

Oxidative Free Radicals and Other Species: Selective Messengers with a Reactive Capacity for Unselective Tissue Damage

Oxygen and nitrogen free radicals (RONS) form an exceptionally reactive molecular assembly within eukaryote cells. This perspective article gives a combined overview of different facets of research covering molecular reactivity, resultant tissue damage and final tissue outcomes as they relate to major disease. There is an emphasis on cardiovascular disease, as the damage processes are best liked to the pathology. The overriding importance of inflammation in driving damage across all tissues is highlighted. Brief coverage is also provided of measurement approaches, respectively for antioxidant status, using potentiometry, and voltammetry for selected target species. Whilst damage due to RONS is a common focus, the fundamental importance of RONS to biological signalling is also covered here as an indispensable basis for life. The article thus provides a global overview of this topic for anyone wishing to understand the current status across multiple fronts.

Melamine-Barbiturate Supramolecular Assembly as a pH-Dependent Organic Radical Trap Material

In the last two decades, a large number of self-assembled materials were synthesized and they have already found their way into large-scale industry and science. Hydrogen-bond-based supramolecular adducts are found to have unique properties and to be perfect host structures for trapping target molecules or ions. Such chemical systems are believed to resemble living matter and can substitute a living cell in a number of cases. Herein, a report on an organic material based on supramolecular assembly of barbituric acid and melamine is presented. Surprisingly, the structure is found to host and stabilize radicals under mild conditions allowing its use for biological applications. The number of free radicals is found to be easily tuned by changing the pH of the environment and it increases when exposed to light up to a saturation level. We describe a preparation method as well as stability properties of melamine-barbiturate self-assembly, potentiometric titration, and hydrogen ions adsorption data and EPR spectra concerning the composite.

Detection of Superoxide Radical in Adherent Living Cells by Electron Paramagnetic Resonance (EPR) Spectroscopy Using Cyclic Nitrones

Spin trapping with cyclic nitrones coupled to electron paramagnetic resonance (EPR) enables the detection and characterization of oxygen-derived free radicals, such as superoxide and hydroxyl radicals, in living cells. Detection is usually performed on cell suspensions introduced in glass capillaries, gas-permeable tubing, or flat cells, even when cells normally require attachment for growth. However, radical production may be influenced by cell adhesion, while enzymatic or mechanical cell harvesting may damage the cells and alter their metabolic rates. Here, we describe the detection on adherent cells attached to microscope coverslip glasses. This method preserves cell integrity, ensures near physiological conditions for naturally adherent cells, and is relatively simple to set up. Up to 12 conditions can be screened in half a day using a single batch of culture cells.

Quantitation of spin probe-detectable oxidants in cells using electron paramagnetic resonance spectroscopy: To probe or to trap?

Electron Paramagnetic Resonance (EPR) spectroscopy coupled with spin traps/probes enables quantitative determination of reactive nitrogen and oxygen species (RNOS). Even with numerous studies using spin probes, the methodology has not been rigorously investigated. The autoxidation of spin probes has been commonly overlooked. Using the spin probe 1-hydroxy-3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine (CMH), the present study has tested the effects of metal chelators, temperature, and oxygen content on the autoxidation of spin probes, where an optimized condition is refined for cell studies. The apparent rate of CMH autoxidation under this condition is 7.01 ± 1.60 nM/min, indicating low sensitivity and great variation of the CMH method and that CMH autoxidation rate should be subtracted from the generation rate of CMH-detectable oxidants (simplified as oxidants below) in samples. Oxidants in RAW264.7 cells are detected at an initial rate of 4.0 ± 0.7 pmol/min/10⁶ cells, which is not considered as the rate of basal oxidants generation because the same method has failed to detect oxidant generation from the stimulation of phorbol-12-mysirate-13-acetate (PMA, 0.1 nmol/10⁶ cells) in cells (2.5 ± 0.9 for PMA vs. 2.1 ± 1.5 pmol/min/10⁶ cells for dimethyl sulfoxide (DMSO)-treated cells). In contrast, the spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), which exhibits minimal autoxidation, reveals differences between PMA and DMSO treatment (0.26 ± 0.09 vs. -0.06 ± 0.12 pmol/min/10⁶ cells), which challenges previous claims that spin probes are more sensitive than spin traps. We have also found that low temperature EPR measurements of frozen samples of CMH autoxidation provide lower signal intensity and greater variation compared to RT measurements of fresh samples. The current study establishes an example for method development of RNOS detection, where experimental details are rigorously considered and tested, and raises questions on the applications of spin probes and spin traps.

Formation and Inhibition of Lipid Alkyl Radicals in Roasted Meat

Free radicals are ubiquitous in roasted foods. In this work, lipid-derived carbon-centered alkyl radical formation was first studied in roasted meat by electron spin resonance (ESR). The influence of antioxidants on the inhibition of free radicals was investigated. The results showed that the high temperature, high heat transfer rate, and high polyunsaturated fatty acid (PUFA) content resulted in high radical content in roasted meat, while the high water content in meat retarded radical formation. The 0.03% addition of tea polyphenols (TPP) significantly reduced radical formation during roasting (p < 0.05), whereas the 0.03% rosemary extract (RE) had no significant inhibitory effect (p > 0.05). These results suggested that water retention and the addition of TPP would decrease radical generation during the roasting of meat.

An LC-MS Assay to Measure Superoxide Radicals and Hydrogen Peroxide in the Blood System

Red blood cells are constantly exposed to reactive species under physiological or pathological conditions or during administration of xenobiotics. Regardless of the source, its accurate quantification is paramount in the area of theragnostics, which had been elusive up until now. Even if there are a lot of approaches to evaluate the oxidative stress, very sensitive methods are missing for the blood system. We therefore sought to apply a highly sensitive approach, by liquid chromatography coupled to mass spectrometry (UPLC–MS), for the quantification of reactive species such as superoxide radical and hydrogen peroxide using dihydroethidium (DHE) and coumarin boronic acid (CBA) probes respectively through the detection of 2-hydroxyethidium (2OH-E⁺) and 7-hydroxycoumarin (COH). The use of the high-resolution mass spectrometry associated to UPLC ensured a selective detection of superoxide and hydrogen peroxide in the blood system under diverse conditions such as oxidized red blood cells (RBCs), untreated and treated parasitized RBCs. Moreover, this technique allowed the determination of reactive species in human plasma. This protocol provides a huge opportunity for in-depth study of several pathological conditions vis-a-vis their treatment in modern medicine.

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.

Detection and Characterization of Reactive Oxygen and Nitrogen Species in Biological Systems by Monitoring Species-Specific Products

SIGNIFICANCE

Since the discovery of the superoxide dismutase enzyme, the generation and fate of short-lived oxidizing, nitrosating, nitrating, and halogenating species in biological systems has been of great interest. Despite the significance of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in numerous diseases and intracellular signaling, the rigorous detection of ROS and RNS has remained a challenge. Recent Advances: Chemical characterization of the reactions of selected ROS and RNS with electron paramagnetic resonance (EPR) spin traps and fluorescent probes led to the establishment of species-specific products, which can be used for specific detection of several forms of ROS and RNS in cell-free systems and in cultured cells in vitro and in animals in vivo. Profiling oxidation products from the ROS and RNS probes provides a rigorous method for detection of those species in biological systems.

CRITICAL ISSUES

Formation and detection of species-specific products from the probes enables accurate characterization of the oxidative environment in cells. Measurement of the total signal (fluorescence, chemiluminescence, etc.) intensity does not allow for identification of the ROS/RNS formed. It is critical to identify the products formed by using chromatographic or other rigorous techniques. Product analyses should be accompanied by monitoring of the intracellular probe level, another factor controlling the yield of the product(s) formed.

FUTURE DIRECTIONS

More work is required to characterize the chemical reactivity of the ROS/RNS probes, and to develop new probes/detection approaches enabling real-time, selective monitoring of the specific products formed from the probes. Antioxid. Redox Signal. 28, 1416-1432.

A possible role for selenoprotein glutathione peroxidase (GPx1) and thioredoxin reductases (TrxR1) in thyroid cancer: our experience in thyroid surgery

Background

Oxidative stress is responsible for some alterations in the chemical structure and, consequently, in the function of proteins, lipids, and DNA. Recent studies have linked oxidative stress to cancers, particularly thyroid cancer, but the mechanisms remain unclear. Here, we further characterize the role of oxidative stress in thyroid cancer by analyzing the expression of two selenium antioxidant molecules, glutathione peroxidase (GPx1) and thioredoxin reductase (TrxR1) in thyroid cancer cells.

Methods

Samples of both healthy thyroid tissue and thyroid tumor were taken for analysis after total thyroidectomy. The expression of GPx1 and TrxR1 was revealed by Western blot analysis and quantified by densitometric analyses, while the evaluation of free radicals was performed by Electron Paramagnetic Resonance (EPR)-spin trapping technique.

Results

Our results show a decrease in the expression of GPx1 and TrxR1 (− 45.7 and − 43.2% respectively, p < 0.01) in the thyroid cancer cells compared to the healthy cells. In addition, the EPR technique shows an increase of free radicals in tumor tissue, significantly higher than that found in healthy thyroid tissue (+ 116.3%, p < 0.01).

Conclusions

Our findings underscore the relationship between thyroid cancer and oxidative stress, showing the imbalance of the oxidant/antioxidant system in thyroid cancer tissue. These results suggest that either the inability to produce adequate antioxidant defense or an increased consumption of antioxidants, due to the hyper-production of free radicals, may play a crucial role in thyroid cancer.

A novel flow cytometry assay using dihydroethidium as redox-sensitive probe reveals NADPH oxidase-dependent generation of superoxide anion in human platelets exposed to amyloid peptide β

Reactive oxygen species (ROS) generation is critical in the regulation of platelets, which has important implications in the modulation of hemostasis and thrombosis. Nonetheless, despite several assays have been described and successfully utilized in the past, the analysis of ROS generation in human platelets remains challenging. Here we show that dihydroethidium (DHE) allows the characterization of redox responses upon platelet activation by physiological and pathological stimuli. In particular, the flow cytometry assay that we describe here allowed us to confirm that thrombin, collagen-related peptide (CRP) and arachidonic acid but not adenosine diphosphate (ADP) stimulate superoxide anion formation in a concentration-dependent manner. 0.1unit/ml thrombin, 3 μg/ml CRP and 30 μM arachidonic acid are commonly used to stimulate platelets in vitro and here were shown to stimulate a significant increase in superoxide anion formation. The ROS scavenger N-acetylcysteine (NAC) abolished superoxide anion generation in response to all tested stimuli, but the pan-NADPH oxidase (NOX) inhibitor VAS2870 only inhibited superoxide anion formation in response to thrombin and CRP. The involvement of NOXs in thrombin and CRP-dependent responses was confirmed by the inhibition of platelet aggregation induced by these stimuli by VAS2870, while platelet aggregation in response to arachidonic acid was insensitive to this inhibitor. In addition, the pathological platelet stimulus amyloid β (Aβ) 1-42 peptide induced superoxide anion formation in a concentration-dependent manner. Aβ peptide stimulated superoxide anion formation in a NOX-dependent manner, as proved by the use of VAS2870. Aβ 1-42 peptide displayed only moderate activity as an aggregation stimulus, but was able to significantly potentiate platelet aggregation in response to submaximal agonists concentrations, such as 0.03 unit/ml thrombin and 10 μM arachidonic acid. The inhibition of NOXs by 10 μM VAS2870 abolished Aβ-dependent potentiation of platelet aggregation in response to 10 μM arachidonic acid, suggesting that the pro-thrombotic activity of Aβ peptides depends on NOX activity. Similar experiments could not be performed with thrombin or collagen, as NOXs are required for the signaling induced by these stimuli. These findings shed some new light on the pro-thrombotic activity of Aβ peptides. In summary, here we describe a novel and reliable assay for the detection of superoxide anion in human platelets. This is particularly important for the investigation of the pathophysiological role of redox stress in platelets, a field of research of increasing importance, but hindered by the absence of a reliable and easily accessible ROS detection methodology applicable to platelets.

Recent Developments in the Probes and Assays for Measurement of the Activity of NADPH Oxidases

NADPH oxidases are a family of enzymes capable of transferring electrons from NADPH to molecular oxygen. A major function of NADPH oxidases is the activation of molecular oxygen into reactive oxygen species. Increased activity of NADPH oxidases has been implicated in various pathologies, including cardiovascular disease, neurological dysfunction, and cancer. Thus, NADPH oxidases have been identified as a viable target for the development of novel therapeutics exhibiting inhibitory effects on NADPH oxidases. Here, we describe the development of new assays for measuring the activity of NADPH oxidases enabling the high-throughput screening for NADPH oxidase inhibitors.

Fundamental mechanisms and reactions in non-catalytic subcritical hydrothermal processes: A review

The management and disposal of solid waste is of increasing concern across the globe. Hydrothermal processing of sludge has been suggested as a promising solution to deal with the considerable amounts of sludge produced worldwide. Such a process not only degrades organic compounds and reduces waste volume, but also provides an opportunity to recover valuable substances. Hydrothermal processing comprises two main sub-processes: wet oxidation (WO) and thermal hydrolysis (TH), in which the formation of various free radicals results in the production of different intermediates. Volatile fatty acids (VFAs), especially acetic acid, are usually the main intermediates which remain as a by-product of the process. This paper aims to review the fundamental mechanism for hydrothermal processing of sludge, and the formation of different free radicals and intermediates therein. In addition, the proposed kinetic models for the two processes (WO and TH) from the literature are reviewed and the advantages and disadvantages of each model are outlined. The effect of mass transfer as a critical component of the design and development of the processes, which has been neglected in most of these proposed models, is also reviewed, and the effect of influencing parameters on the processes' controlling step (reaction or mass transfer) is discussed.

European contribution to the study of ROS: A summary of the findings and prospects for the future from the COST action BM1203 (EU-ROS)

The European Cooperation in Science and Technology (COST) provides an ideal framework to establish multi-disciplinary research networks. COST Action BM1203 (EU-ROS) represents a consortium of researchers from different disciplines who are dedicated to providing new insights and tools for better understanding redox biology and medicine and, in the long run, to finding new therapeutic strategies to target dysregulated redox processes in various diseases. This report highlights the major achievements of EU-ROS as well as research updates and new perspectives arising from its members. The EU-ROS consortium comprised more than 140 active members who worked together for four years on the topics briefly described below. The formation of reactive oxygen and nitrogen species (RONS) is an established hallmark of our aerobic environment and metabolism but RONS also act as messengers via redox regulation of essential cellular processes. The fact that many diseases have been found to be associated with oxidative stress established the theory of oxidative stress as a trigger of diseases that can be corrected by antioxidant therapy. However, while experimental studies support this thesis, clinical studies still generate controversial results, due to complex pathophysiology of oxidative stress in humans. For future improvement of antioxidant therapy and better understanding of redox-associated disease progression detailed knowledge on the sources and targets of RONS formation and discrimination of their detrimental or beneficial roles is required. In order to advance this important area of biology and medicine, highly synergistic approaches combining a variety of diverse and contrasting disciplines are needed.

Glutathione Fine-Tunes the Innate Immune Response toward Antiviral Pathways in a Macrophage Cell Line Independently of Its Antioxidant Properties

Glutathione (GSH), a major cellular antioxidant, is considered an inhibitor of the inflammatory response involving reactive oxygen species (ROS). However, evidence is largely based on experiments with exogenously added antioxidants/reducing agents or pro-oxidants. We show that depleting macrophages of 99% of GSH does not exacerbate the inflammatory gene expression profile in the RAW264 macrophage cell line or increase expression of inflammatory cytokines in response to the toll-like receptor 4 (TLR4) agonist lipopolysaccharide (LPS); only two small patterns of LPS-induced genes were sensitive to GSH depletion. One group, mapping to innate immunity and antiviral responses (Oas2, Oas3, Mx2, Irf7, Irf9, STAT1, il1b), required GSH for optimal induction. Consequently, GSH depletion prevented the LPS-induced activation of antiviral response and its inhibition of influenza virus infection. LPS induction of a second group of genes (Prdx1, Srxn1, Hmox1, GSH synthase, cysteine transporters), mapping to nrf2 and the oxidative stress response, was increased by GSH depletion. We conclude that the main function of endogenous GSH is not to limit inflammation but to fine-tune the innate immune response to infection.