Applications of electron spin resonance spectrometry for reactive oxygen species and reactive nitrogen species research

A neoteric antibacterial ceria-silver nanozyme for abiotic surfaces

Community-associated and hospital-acquired infections caused by bacteria continue to yield major global challenges to human health. Bacterial contamination on abiotic surfaces is largely spread via high-touch surfaces and contemporary standard disinfection practices show limited efficacy, resulting in unsatisfactory therapeutic outcomes. New strategies that offer non-specific and broad protection are urgently needed. Herein, we report our novel ceria-silver nanozyme engineered at a molar ratio of 5:1 and with a higher trivalent (Ce3+) surface fraction. Our results reveal potent levels of surface catalytic activity on both wet and dry surfaces, with rapid, and complete eradication of Pseudomonas aeruginosa, Staphylococcus aureus, and methicillin resistant S. aureus, in both planktonic and biofilm form. Preferential electrostatic adherence of anionic bacteria to the cationic nanozyme surface leads to a catastrophic loss in both aerobic and anaerobic respiration, DNA damage, osmodysregulation, and finally, programmed bacterial lysis. Our data reveal several unique mechanistic avenues of synergistic ceria-Ag efficacy. Ag potentially increases the presence of Ce3+ sites at the ceria-Ag interface, thereby facilitating the formation of harmful H2O2, followed by likely permeation across the cell wall. Further, a weakened Ag-induced Ce-O bond may drive electron transfer from the Ec band to O2, thereby further facilitating the selective reduction of O2 toward H2O2 formation. Ag destabilizes the surface adsorption of molecular H2O2, potentially leading to higher concentrations of free H2O2 adjacent to bacteria. To this end, our results show that H2O2 and/or NO/NO2-/NO3- are the key liberators of antibacterial activity, with a limited immediate role being offered by nanozyme-induced ROS including O2•- and OH•, and likely other light-activated radicals. A mini-pilot proof-of-concept study performed in a pediatric dental clinic setting confirms residual, and continual nanozyme antibacterial efficacy over a 28-day period. These findings open a new approach to alleviate infections caused by bacteria for use on high-touch hard surfaces.

Radical generation and bactericidal activity of nanobubbles produced by ultrasonic irradiation of carbonated water

Our previous study showed that nanobubbles (NBs) encapsulating CO2 gas have bactericidal activity due to reactive oxygen species (ROS) (Yamaguchi et al., 2020). Here, we report that bulk NBs encapsulating CO2 can be efficiently generated by ultrasonically irradiating carbonated water using a piezoelectric transducer with a frequency of 1.7 MHz. The generated NBs were less than 100 nm in size and had a lifetime of 500 h. Furthermore, generation of ROS in the NB suspension was investigated using electron spin resonance spectroscopy and fluorescence spectrometry. The main ROS was found to be the hydroxyl radical, which is consistent with our previous observations. The bactericidal activity lasted for at least one week. Furthermore, a mist generated by atomizing the NB suspension with ultrasonic waves was confirmed to have the same bactericidal activity as the suspension itself. We believe that the strong, persistent bactericidal activity and radical generation phenomenon are unique to NBs produced by ultrasonic irradiation of carbonated water. We propose that entrapped CO2 molecules strongly interact with water at the NB interface to weaken the interface, and high-pressure CO2 gas erupts from this weakened interface to generate ROS with bactericidal activity.

Spermine enhances the activity of anti-tuberculosis drugs

IMPORTANCE

This is the first study that attempted to demonstrate the mechanisms of reactive oxygen species (ROS) generation by spermine (Spm) in Mycobacterium tuberculosis (M.tb). Furthermore, this is the first study to demonstrate that it is able to enhance the activity of currently available and World Health Organization (WHO)-approved tuberculosis (TB) drugs. Spermine can easily be obtained since it is already found in our diet. Moreover, as opposed to conventional antibiotics, it is less toxic to humans since it is found in millimolar concentrations in the body. Finally, with the difficulty of curing TB with conventional antibiotics, this study suggests that less toxic molecules, such as Spm, could in a long-term perspective be incorporated in a TB regimen to boost the treatment.

Study on the Antioxidant Effect of Shikonin-Loaded β-Cyclodextrin Forming Host-Guest Complexes That Prevent Skin from Photoaging

When the skin is overexposed to ultraviolet rays, free radicals will accumulate in the skin, causing lipid damage and even inducing photoaging of the skin. Combination therapy with antioxidant drugs is a good choice for topical treatment of skin photoaging due to its special physiological structure. In this paper, shikonin was encapsulated in β-cyclodextrin (SH-β-CD) by the precipitation crystallization method, which delayed the release of the drug and increased drug solubility. The average diameter of SH-β-CD was 203.0 ± 21.27 nm with a zeta potential of -14.4 ± 0.5 mV. The encapsulation efficiency (EE%) was 65.9 ± 7.13%. The results of the in vitro permeation across the dialysis membrane and ex vivo transdermal release rates were 52.98 ± 1.21% and 88.25 ± 3.26%, respectively. In vitro antioxidant and antilipid peroxidation model assay revealed the antioxidant potential of SH and SH-β-CD. In the mice model of skin photoaging, SH and SH-β-CD had a recovery effect on the skin damage of mice, which could significantly increase the superoxide dismutase (SOD) activity in the skin. Briefly, SH-β-CD had an obvious therapeutic effect on the skin photoaging of mice caused by UV, and it is promising in skin disease treatment and skin care.

Revealing Dominant Oxidative Species in Reactive Oxygen Species-Driven Rapid Chemical Etching

Reactive oxygen species (ROS) widely participate in a variety of chemical reactions in biological and chemical applications. However, due to the extremely short lifetime of most ROS, conventional ROS-detecting techniques cannot show real-time dynamic changes of ROS-driven chemical reactions and identify the actual role of individual reactive species in these reactions. Herein, using in situ liquid cell TEM complemented by ex situ experiments, we directly visualize ROS-driven rapid etching of Prussian bule (PB) in real time and identify the dominant reactive species in etching processes. The results reveal that highly oxidative •OH is the dominant reactive radical in ROS-driven rapid chemical etching and hollow mesoporous PB nanoparticles can be synthesized on a minute-level time scale via •OH-dominated rapid etching. This work provides insight into ROS-related oxidation, which can continuously improve our understanding of ROS chemistry and make ROS more widely applicable in advanced chemical etching.

A Simulation Independent Analysis of Single- and Multi-Component cw ESR Spectra

The accurate analysis of continuous-wave electron spin resonance (cw ESR) spectra of biological or organic free-radicals and paramagnetic metal complexes is key to understanding their structure-function relationships and electrochemical properties. The current methods of analysis based on simulations often fail to extract the spectral information accurately. In addition, such analyses are highly sensitive to spectral resolution and artifacts, users' defined input parameters and spectral complexity. We introduce a simulation-independent spectral analysis approach that enables broader application of ESR. We use a wavelet packet transform-based method for extracting g values and hyperfine (A) constants directly from cw ESR spectra. We show that our method overcomes the challenges associated with simulation-based methods for analyzing poorly/partially resolved and unresolved spectra, which is common in most cases. The accuracy and consistency of the method are demonstrated on a series of experimental spectra of organic radicals and copper-nitrogen complexes. We showed that for a two-component system, the method identifies their individual spectral features even at a relative concentration of 5% for the minor component.

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.

The Effect of β-Carotene, Tocopherols and Ascorbic Acid as Anti-Oxidant Molecules on Human and Animal In Vitro/In Vivo Studies: A Review of Research Design and Analytical Techniques Used

Prolonged elevated oxidative stress (OS) possesses negative effect on cell structure and functioning, and is associated with the development of numerous disorders. Naturally occurred anti-oxidant compounds reduce the oxidative stress in living organisms. In this review, antioxidant properties of β-carotene, tocopherols and ascorbic acid are presented based on in vitro, in vivo and populational studies. Firstly, environmental factors contributing to the OS occurrence and intracellular sources of Reactive Oxygen Species (ROS) generation, as well as ROS-mediated cellular structure degradation, are introduced. Secondly, enzymatic and non-enzymatic mechanism of anti-oxidant defence against OS development, is presented. Furthermore, ROS-preventing mechanisms and effectiveness of β-carotene, tocopherols and ascorbic acid as anti-oxidants are summarized, based on studies where different ROS-generating (oxidizing) agents are used. Oxidative stress biomarkers, as indicators on OS level and prevention by anti-oxidant supplementation, are presented with a focus on the methods (spectrophotometric, fluorometric, chromatographic, immuno-enzymatic) of their detection. Finally, the application of Raman spectroscopy and imaging as a tool for monitoring the effect of anti-oxidant (β-carotene, ascorbic acid) on cell structure and metabolism, is proposed. Literature data gathered suggest that β-carotene, tocopherols and ascorbic acid possess potential to mitigate oxidative stress in various biological systems. Moreover, Raman spectroscopy and imaging can be a valuable technique to study the effect of oxidative stress and anti-oxidant molecules in cell studies.

Overview of oxidative stress findings in hepatic encephalopathy: From cellular and ammonium-based animal models to human data

Oxidative stress is a natural phenomenon in the body. Under physiological conditions intracellular reactive oxygen species (ROS) are normal components of signal transduction cascades, and their levels are maintained by a complex antioxidants systems participating in the in-vivo redox homeostasis. Increased oxidative stress is present in several chronic diseases and interferes with phagocytic and nervous cell functions, causing an up-regulation of cytokines and inflammation. Hepatic encephalopathy (HE) occurs in both acute liver failure (ALF) and chronic liver disease. Increased blood and brain ammonium has been considered as an important factor in pathogenesis of HE and has been associated with inflammation, neurotoxicity, and oxidative stress. The relationship between ROS and the pathophysiology of HE is still poorly understood. Therefore, sensing ROS production for a better understanding of the relationship between oxidative stress and functional outcome in HE pathophysiology is critical for determining the disease mechanisms, as well as to improve the management of patients. This review is emphasizing the important role of oxidative stress in HE development and documents the changes occurring as a consequence of oxidative stress augmentation based on cellular and ammonium-based animal models to human data.

Bisphenol A and Male Infertility: Role of Oxidative Stress

Bisphenol A (BPA) is an endocrine-disrupting chemical that is capable of mimicking, antagonizing, and interfering with the normal biological functioning of the endocrine system. BPA is used in diverse industries, hence its vast sources of exposure. Although the half-life of BPA is relatively short (<24 hours), studies have reported its detection in the urine of different populations. It, therefore, became important to investigate its effect on general health, including male reproductive health. The adverse effects of BPA on male fertility have been evaluated and reported from both in vivo and in vitro studies. Up to date, reports from randomized controlled trials remain controversial, as some revealed decreased sperm quality, sperm concentration, and total sperm count, while others reported that no adverse effect was seen after exposure. Findings from animal model studies and in vitro experiments have shown that exposure to BPA led to a reduction in sperm quality and increased sperm DNA fragmentation, and some even revealed altered expression of the gene that encodes gonadotropin-releasing hormone. This shows that BPA not only may adversely affect male fertility by acting as an endocrine disruptor but also can potentially impact male fertility via its possible contribution to oxidative stress. Therefore, this book chapter aims to identify and elucidate the effect of BPA exposure on male fertility, and to as well illustrate the mechanisms through which this occurs, while emphasizing the role of oxidative stress as a potential pathway.

Plant Nitric Oxide Signaling under Drought Stress

Water deficit caused by drought is a significant threat to crop growth and production. Nitric oxide (NO), a water- and lipid-soluble free radical, plays an important role in cytoprotection. Apart from a few studies supporting the role of NO in drought responses, little is known about this pivotal molecular amendment in the regulation of abiotic stress signaling. In this review, we highlight the knowledge gaps in NO roles under drought stress and the technical challenges underlying NO detection and measurements, and we provide recommendations regarding potential avenues for future investigation. The modulation of NO production to alleviate abiotic stress disturbances in higher plants highlights the potential of genetic manipulation to influence NO metabolism as a tool with which plant fitness can be improved under adverse growth conditions.

The Use of Fluorescent Probes to Detect ROS in Photodynamic Therapy

Photodynamic therapy employs nontoxic dyes called photosensitizers (PS) that are excited by visible light of the correct wavelength to produce a variety of reactive oxygen species (ROS) by an interaction between the long-lived PS triplet states with ambient oxygen. The most important type of ROS in photodynamic therapy (PDT) is singlet oxygen, which is produced by a Type II energy transfer process. On the other hand, superoxide, hydrogen peroxide, and hydroxyl radicals can be produced by a Type I electron transfer process. This chapter describes a set of fluorescent probes that can be used to tease apart these different ROS produced when various PS are illuminated in solution. Singlet oxygen sensor green (SOSG) is used for singlet oxygen, 4-hydroxyphenyl-fluorescein (HPF) for hydroxyl radicals, Amplex Red for hydrogen peroxide, and nitroblue-tetrazolium or XTT for superoxide.

An update on the techniques used to measure oxidative stress in seminal plasma

Reactive oxygen species (ROS) are produced in significant amounts by spermatozoa and leucocytes. They are necessary to carry out various physiological functions such as sperm capacitation, hyperactivation, acrosome reaction, sperm-zona binding and cellular signalling pathways. Oxidative stress (OS) results when the ROS levels overwhelm the available antioxidant reserve. A number of direct and indirect tests have been developed to assess oxidative stress. In this manuscript, we discuss these common direct and indirect tests as well as their advantages and disadvantages. Tests measuring sperm dysfunction secondary to oxidative stress such as lipid peroxidation, DNA fragmentation and protein alterations are also described.

Self-assembled reduced graphene oxide–cerium oxide nanocomposite@cytochromechydrogel as a solid electrochemical reactive oxygen species detection platform

A new dimension for the selective detection of short-lived ROS by an electroactive reduced graphene oxide–cerium oxide nanocomposite@cytochromechydrogel.

Sonochemical One-Step Synthesis of Polymer-Capped Metal Oxide Nanocolloids: Antibacterial Activity and Cytotoxicity

Most antibacterial agents demand their action in the form of a liquid for compatibility and ease of use in biosystems, which are mainly composed of biological fluids. Controlling the colloidal stability of metal oxide nanocolloids, in parallel with minimizing the effect of using a large amount of surfactant on their biocidal activity and cytotoxicity, remains a challenge. Here, we address the stability of nanocolloids of ZnO and CuO in the presence of polymer surfactants and the influence of the surface capping on their antibacterial activity and cytotoxicity. The metal oxide nanoparticles (NPs) were synthesized sonochemically in a single step and tested against both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus to validate their biocidal efficacy. Cytotoxicity studies were performed on human alveolar epithelial cells. Polyethylene glycol- and polyvinyl alcohol-capped NPs are observed to show the minimum cytotoxicity whereas polyethylene imine-capped and pristine metal oxide NPs are toxic to the mammalian cells. The cytotoxic and antibacterial properties of the stable nanocolloids displayed an inverse relation, highlighting the role and significance of the polymer capping. The nontoxic biocidal nanocolloids showed an effective antibacterial efficacy of 99.9% in 2 h.

Detection of synergistic effect of superoxide dismutase and jujubosides on scavenging superoxide anion radical by capillary electrophoresis

A new capillary electrophoresis method was developed to study the synergistic effect of superoxide dismutase and jujuboside A or B on scavenging superoxide anion radical in serum matrix respectively, in which superoxide anion radical was generated from pyrogallol autoxidation. The electrophoresis conditions, and the factors affecting the productive rate of purpurogallin, such as pyrogallol autoxidation product and the activity of superoxide dismutase, were optimized. Under optimal conditions, the content of superoxide dismutase in Gibco newborn calf serum was 7.06 mg/L, RSD was 2.01% and the average recovery was 98.4%. The values of IC₅₀ for jujuboside A and B in the serum matrix were 157.67 and 31.60 mg/L respectively, and they both had synergy on scavenging superoxide anion radical with superoxide dismutase, but there was no the dose-dependency on this synergy.

Oxidation reduction potential: a new biomarker of male infertility

Oxidative stress is considered a major etiology for male infertility, more specifically idiopathic infertility. The causes of seminal oxidative stress can be intrinsic, such as varicocele or due to the presence of active leukocytes and immature germ cells. Reported external causes are smoking, alcohol or exposure to environmental toxins. Traditional methods to determine the seminal oxidative stress do not evaluate this status directly, but rather measure its components or intermediate products indirectly, instead. The major disadvantages of the traditional methods are related with time and cost as these methods are extremely time consuming and require expensive equipment, consumables and highly skilled laboratory personnel. To overcome these drawbacks, the MiOXSYS® system, a method which directly measures the oxidation-reduction potential (ORP), was developed. The evaluation of the ORP using MiOXSYS® is cost-effective, easy and quick. However, this newly introduced method to evaluate the oxidative status of semen still requires validation in different andrology laboratory settings across the world.

Quantification and characterization of radical production in human, animal and 3D skin models during sun irradiation measured by EPR spectroscopy

Sun radiation is indispensable to our health, however, a long term and high exposure could lead to erythema, premature skin aging and promotion of skin tumors. An underlying pathomechanism is the formation of free radicals. First, reactive oxygen species (*OH, *O₂^-) and then, secondary lipid oxygen species (C centered radicals, CCR) are formed. A high amount of free radicals results in oxidative stress with subsequent cell damage. In dermatological research different skin models are used, however, comparative data about the cutaneous radical formation are missing. In this study, the radical formation in porcine-, (SKH-1) murine-, human- ex vivo skin and reconstructed human skin (RHS) were investigated during simulated sun irradiation (305-2200 nm), with X-band EPR spectroscopy. The amount of radical formation was investigated with the spin probe PCA exposed to a moderate sun dose below one minimal erythema dose (MED, ~25 mJ/cm² UVB) in all skin models. Furthermore, the *OH and *CCR radical concentrations were measured with the spin trap DMPO within 0-4 MED (porcine-, human skin and RHS). The highest amount of radicals was found in RHS followed by murine and porcine, and the lowest amount in human ex vivo skin. In all skin models, more *OH than CCR radicals were found at 0-4 MED. Additionally, this work addresses the limitations in the characterization with the spin trap DMPO. The measurements have shown that the most comparable skin model to in vivo human skin could differ depending on the focus of the investigation. If the amount of radial production is regarded, RHS seems to be in a similar range like in vivo human skin. If the investigation is focused on the radical type, porcine skin is most comparable to ex vivo human skin, at an irradiation dose not exceeding 1 MED. Here, no comparison to in vivo human skin is possible.

Techniques to study phagocytosis and uptake of Leishmania tarentolae by J774 macrophages

Leishmaniasis is a vector borne parasitic disease affecting millions of people worldwide and is spreading into further areas because of global warming. The development of new active substances against these single-cell eukaryotic parasites is of great importance. Leishmania tarentolae promastigotes (LtP) are non-pathogenic for mammals and serve as model organisms for pathogenic Leishmania in basic research. However, it is important to refine methods to study the process of the infection of mammalian macrophages by LtP and pathogenic Leishmania. Important stages of the infection are phagocytosis by macrophages and multiplication of Leishmania amastigotes in the phagolysosome of macrophages. In this study, advanced methods using electron spin resonance (ESR) spectroscopy and genetically manipulated LtP were used to monitor the infection of adherent J774 macrophages with LtP. An ESR method was established to detect the formation of superoxide radicals directly in adherent J774 cells and to investigate the effect of LtP on this activity. J774 cells responded with a burst of superoxide radicals in the presence of phorbol myristate acetate as positive control. In contrast, challenging J774 cells with LtP resulted in a much lower burst of superoxide radicals. To facilitate LtP detection in the phagolysosome of J774 macrophages, LtP expressing enhanced green fluorescent protein (EGFP-LtP) were constructed. After different infection times with EGFP-LtP, the J774 cells were visualized by phase contrast microscopy and the cell number was determined. The intramacrophage Leishmania tarentolae amastigotes (LtA) expressing EGFP were detected by fluorescence microscopy and then counted with ImageJ. These experiments showed that LtP are taken up by J774 cells and form intraphagolysosomal amastigotes. LtA under our conditions multiplied intracellularly and were able to persist about 48 h in J774 cells. These experiments showed that ESR spectroscopy of attached macrophages and the use of the EGFP-LtP are suitable methods to study the initial phase of Leishmania infection in vitro.

Analysis of Short-Lived Reactive Species in Plasma-Air-Water Systems: The Dos and the Do Nots

This Feature addresses the analysis of the reactive species generated by nonthermal atmospheric pressure plasmas, which are widely employed in industrial and biomedical research, as well as first clinical applications. We summarize the progress in detection of plasma-generated short-lived reactive oxygen and nitrogen species in aqueous solutions, discuss the potential and limitations of various analytical methods in plasma-liquid systems, and provide an outlook on the possible future research goals in development of short-lived reactive species analysis methods for a general nonspecialist audience.

Electron Spin Resonance (ESR) for the study of Reactive Oxygen Species (ROS) on the isolated frog skin (Pelophylax bergeri): A non-invasive method for environmental monitoring

BACKGROUND

Reactive oxygen species (ROS) in biological tissues of elected biosentinels represent an optimal biomarker for eco-monitoring of polluted areas. Electron spin resonance (ESR) is the most definitive method for detecting, quantifying and possibly identifying radicals in complex systems.

OBJECTIVE

A non-invasive method for monitoring polluted areas by the quantitative determination of ROS in frog skin biopsy is presented.

METHODS

We assessed by ESR spectroscopy the ROS level in adult male of Pelophylax bergeri, specie not a risk of extinction, collected from the polluted Sarno River (SA, Italy) basin. The spin-trap ESR method was validated by immunohistochemical analysis of the well-assessed pollution biomarkers cytochrome P450 aromatase 1A (CYP1A) and glutathione S-transferase (GST), and by determining the poly(ADPribose) polymerase (PARP) and GST enzymatic activity.

RESULTS

ROS concentration in skin samples from frogs collected in the polluted area is significantly higher than that determined for the unpolluted reference area. Immunohistochemical analysis of CYP1A and GST supported the reliability of our approach, even in the absence of evident morphological and ultrastructural differences. PARP activity assay, connected to possible oxidative DNA damage, and the detoxification index by GST enzymatic assay give statistically significant evidence that higher levels of ROS are associated to alterations of the different biomarkers.

CONCLUSIONS

ROS concentration, measured by ESR on isolated frog skin, through the presented non-lethal method, is a reliable biomarker for toxicity screening and represents a useful basic datum for future modelling studies on environmental monitoring and biodiversity loss prevention.

HIV/HAART-associated oxidative stress is detectable by metabonomics

Chronic human immunodeficiency virus (HIV) infection, separately and in combination with highly active antiretroviral therapy (HAART) is closely associated with oxidative stress (OS). Most studies demonstrating redox imbalances in HIV-infected individuals have done so using conventional biochemical methodologies. The limited simultaneous detection of multiple OS markers within one sample is a major drawback of these methodologies and can be addressed through the use of metabonomics. HIV-metabonomic studies utilizing biofluids from HAART cohorts as the investigative source, are on the increase. Data from many of these studies identified metabolic markers indicative of HIV-induced OS, usually as an outcome of an untargeted metabonomics study. Untargeted studies cast a wide net for any and all detectable metabolites in complex mixtures. Given the prevalence of OS during HIV infection and antiviral treatment, it is perhaps not surprising that indicators of this malady would become evident during metabolite identification. At times, targeted studies for specific (non-OS) metabolites would also yield OS markers as an outcome. This review examines the findings of these studies by first providing the necessary background information on OS and the main ways in which free radicals/reactive oxygen species (ROS) produced during OS, cause biomolecular damage. This is followed by information on the biomarkers which come about as a result of free radical damage and the techniques used for assaying these stress indicators. The established links between elevated ROS and lowered antioxidants during HIV infection and the subsequent use of HAART is then presented followed by a review of the OS markers detected in HIV metabonomic studies to date. We identify gaps in HIV/HAART-associated OS research and finally suggest how these research gaps can be addressed through metabonomic analysis, specifically targeting the multiple markers of HIV-induced OS.

Novel method for rapid toxicity screening of magnetic nanoparticles

Iron oxide nanoparticles have attracted a great deal of research interest and have been widely used in bioscience and clinical research including as contrast agents for magnetic resonance imaging, hyperthermia and magnetic field assisted radionuclide therapy. It is therefore important to develop methods, which can provide high-throughput screening of biological responses that can predict toxicity. The use of nanoelectrodes for single cell analysis can play a vital role in this process by providing relatively fast, comprehensive, and cost-effective assessment of cellular responses. We have developed a new method for in vitro study of the toxicity of magnetic nanoparticles (NP) based on the measurement of intracellular reactive oxygen species (ROS) by a novel nanoelectrode. Previous studies have suggested that ROS generation is frequently observed with NP toxicity. We have developed a stable probe for measuring intracellular ROS using platinized carbon nanoelectrodes with a cavity on the tip integrated into a micromanipulator on an upright microscope. Our results show a significant difference for intracellular levels of ROS measured in HEK293 and LNCaP cancer cells before and after exposure to 10 nm size iron oxide NP. These results are markedly different from ROS measured after cell incubation with the same concentration of NP using standard methods where no differences have been detected. In summary we have developed a label-free method for assessing nanoparticle toxicity using the rapid (less than 30 minutes) measurement of ROS with a novel nanoelectrode.

Combining experimental and modelling approaches to study the sources of reactive species induced in water by the COST RF plasma jet

The vast biomedical potential of cold atmospheric pressure plasmas (CAPs) is governed by the formation of reactive species. These biologically active species are formed upon the interaction of CAPs with the surroundings. In biological milieu, water plays an essential role. The development of biomedical CAPs thus requires understanding of the sources of the reactive species in aqueous media exposed to the plasma. This is especially important in case of the COST RF plasma jet, which is developed as a reference microplasma system. In this work, we investigated the formation of the OH radicals, H atoms and H₂O₂ in aqueous solutions exposed to the COST plasma jet. This was done by combining experimental and modelling approaches. The liquid phase species were analysed using UV-Vis spectroscopy and spin trapping with hydrogen isotopes and electron paramagnetic resonance (EPR) spectroscopy. The discrimination between the species formed from the liquid phase and the gas phase molecules was performed by EPR and ¹H-NMR analyses of the liquid samples. The concentrations of the reactive species in the gas phase plasma were obtained using a zero-dimensional (0D) chemical kinetics computational model. A three-dimensional (3D) fluid dynamics model was developed to provide information on the induced humidity in the plasma effluent. The comparison of the experimentally obtained trends for the formation of the species as a function of the feed gas and effluent humidity with the modelling results suggest that all reactive species detected in our system are mostly formed in the gas phase plasma inside the COST jet, with minor amounts arising from the plasma effluent humidity.

Laboratory assessment of oxidative stress in semen

Objectives

To evaluate different laboratory assessments of oxidative stress (OS) in semen and identify a cost-efficient and highly sensitive instrument capable of providing a comprehensive measure of OS in a clinical setting, as early intervention and an accurate diagnostic test are important because they help maintain a balance of free radicals and antioxidants; otherwise, excessive OS could lead to sperm damage and result in male infertility.

Materials and methods

A systematic literature search was performed through a MedLine database search using the keywords ‘semen’ AND ‘oxygen reduction potential’. We also reviewed the references of retrieved articles to search for other potentially relevant research articles and additional book chapters discussing laboratory assessments for OS, ranging from 1994 to 2017. A total of 29 articles and book chapters involving OS-related laboratory assays were included. We excluded animal studies and articles written in languages other than English.

Results

Direct laboratory techniques include: chemiluminescence, nitro blue tetrazolium, cytochrome C reduction test, fluorescein probe, electron spin resonance and oxidation–reduction potential (ORP). Indirect laboratory techniques include: measurement of Endtz test, lipid peroxidation, chemokines, antioxidants/micronutrients/vitamins, ascorbate, total antioxidant capacity, or DNA damage. Each of these laboratory techniques has its advantages and disadvantages.

Conclusion

Traditional OS laboratory assessments have their limitations. Amongst the prevalent laboratory techniques, ORP is novel and better option as it can be easily used in a clinical setting to provide a comprehensive review of OS. However, more studies are needed to evaluate its reproducibility across various laboratory centres.

An integrated electrolysis - electrospray - ionization antimicrobial platform using Engineered Water Nanostructures (EWNS) for food safety applications

Engineered water nanostructures (EWNS) synthesized utilizing electrospray and ionization of water, have been, recently, shown to be an effective, green, antimicrobial platform for surface and air disinfection, where reactive oxygen species (ROS), generated and encapsulated within the particles during synthesis, were found to be the main inactivation mechanism. Herein, the antimicrobial potency of the EWNS was further enhanced by integrating electrolysis, electrospray and ionization of de-ionized water in the EWNS synthesis process. Detailed physicochemical characterization of these enhanced EWNS (eEWNS) was performed using state-of-the-art analytical methods and has shown that, while both size and charge remain similar to the EWNS (mean diameter of 13 nm and charge of 13 electrons), they possess a three times higher ROS content. The increase of the ROS content as a result of the addition of the electrolysis step before electrospray and ionization led to an increased antimicrobial ability as verified by E. coli inactivation studies using stainless steel coupons. It was shown that a 45-minute exposure to eEWNS resulted in a 4-log reduction as opposed to a 1.9-log reduction when exposed to EWNS. In addition, the eEWNS were assessed for their potency to inactivate natural microbiota (total viable and yeast and mold counts), as well as, inoculated E.coli on the surface of fresh organic blackberries. The results showed a 97% (1.5-log) inactivation of the total viable count, a 99% (2-log) reduction in the yeast and mold count and a 2.5-log reduction of the inoculated E.coli after 45 minutes of exposure, without any visual changes to the fruit. This enhanced antimicrobial activity further underpins the EWNS platform as an effective, dry and chemical free approach suitable for a variety of food safety applications and could be ideal for delicate fresh produce that cannot withstand the classical, wet disinfection treatments.

Clinical Relevance and Role of Neuronal AT1 Receptors in ADAM17-Mediated ACE2 Shedding in Neurogenic Hypertension

RATIONALE

Neurogenic hypertension is characterized by an increase in sympathetic activity and often resistance to drug treatments. We previously reported that it is also associated with a reduction of angiotensin-converting enzyme type 2 (ACE2) and an increase in a disintegrin and metalloprotease 17 (ADAM17) activity in experimental hypertension. In addition, while multiple cells within the central nervous system have been involved in the development of neurogenic hypertension, the contribution of ADAM17 has not been investigated.

OBJECTIVE

To assess the clinical relevance of this ADAM17-mediated ACE2 shedding in hypertensive patients and further identify the cell types and signaling pathways involved in this process.

METHODS AND RESULTS

Using a mass spectrometry-based assay, we identified ACE2 as the main enzyme converting angiotensin II into angiotensin-(1-7) in human cerebrospinal fluid. We also observed an increase in ACE2 activity in the cerebrospinal fluid of hypertensive patients, which was correlated with systolic blood pressure. Moreover, the increased level of tumor necrosis factor-α in those cerebrospinal fluid samples confirmed that ADAM17 was upregulated in the brain of hypertensive patients. To further assess the interaction between brain renin-angiotensin system and ADAM17, we generated mice lacking angiotensin II type 1 receptors specifically on neurons. Our data reveal that despite expression on astrocytes and other cells types in the brain, ADAM17 upregulation during deoxycorticosterone acetate-salt hypertension occurs selectively on neurons, and neuronal angiotensin II type 1 receptors are indispensable to this process. Mechanistically, reactive oxygen species and extracellular signal-regulated kinase were found to mediate ADAM17 activation.

CONCLUSIONS

Our data demonstrate that angiotensin II type 1 receptors promote ADAM17-mediated ACE2 shedding in the brain of hypertensive patients, leading to a loss in compensatory activity during neurogenic hypertension.

Detection of Reactive Oxygen and Nitrogen Species by Electron Paramagnetic Resonance (EPR) Technique

During the last decade there has been growing interest in physical-chemical oxidation processes and the behavior of free radicals in living systems. Radicals are known as intermediate species in a variety of biochemical reactions. Numerous techniques, assays and biomarkers have been used to measure reactive oxygen and nitrogen species (ROS and RNS), and to examine oxidative stress. However, many of these assays are not entirely satisfactory or are used inappropriately. The purpose of this chapter is to review current EPR (Electron Paramagnetic Resonance) spectroscopy methods for measuring ROS, RNS, and their secondary products, and to discuss the strengths and limitations of specific methodological approaches.

Electrochemical reactive oxygen species detection by cytochrome c immobilized with vertically aligned and electrochemically reduced graphene oxide on a glassy carbon electrode

Selective detection of hydrogen peroxide and superoxide based on a cytochrome c modified glassy carbon electrode.

Use of fluorescent probes for ROS to tease apart Type I and Type II photochemical pathways in photodynamic therapy

Photodynamic therapy involves the excitation of a non-toxic dye by harmless visible light to produce a long-lived triplet state that can interact with molecular oxygen to produce reactive oxygen species (ROS), which can damage biomolecules and kill cells. ROS produced by electron transfer (Type 1) include superoxide, hydrogen peroxide and hydroxyl radical (HO), while singlet oxygen (1O2) is produced by energy transfer. Diverse methods exist to distinguish between these two pathways, some of which are more specific or more sensitive than others. In this review we cover the use of two fluorescence probes: singlet oxygen sensor green (SOSG) detects 1O2; and 4-hydroxyphenyl-fluorescein (HPF) that detects HO. Interesting data was collected concerning the photochemical pathways of functionalized fullerenes compared to tetrapyrroles, stable synthetic bacteriochlorins with and without central metals, phenothiazinium dyes interacting with inorganic salts such as azide.

Non-Thermal Plasma in Contact with Water: The Origin of Species

Non‐thermal atmospheric pressure plasma has attracted considerable attention in recent years due to its potential for biomedical applications. Determining the mechanism of the formation of reactive species in liquid treated with plasma is thus of paramount importance for both fundamental and applied research. In this work, the origin of reactive species in plasma‐treated aqueous solutions was investigated by using spin‐trapping, hydrogen and oxygen isotopic labelling and electron paramagnetic resonance (EPR) spectroscopy. The species originating from molecules in the liquid phase and those introduced with the feed gas were differentiated by EPR and ¹H NMR analysis of liquid samples. The effects of water vapour and oxygen admixtures in the feed gas were investigated. All the reactive species detected in the liquid samples were shown to be formed largely in the plasma gas phase. It is suggested that hydrogen peroxide (determined by UV/Vis analysis) is formed primarily in the plasma tube, whereas the radical species ⋅OOH, ⋅OH and ⋅H are proposed to originate from the region between the plasma nozzle and the liquid sample.

Toxicity of metal oxide nanoparticles: mechanisms, characterization, and avoiding experimental artefacts

Metal oxide nanomaterials are widely used in practical applications and represent a class of nanomaterials with the highest global annual production. Many of those, such as TiO2 and ZnO, are generally considered non-toxic due to the lack of toxicity of the bulk material. However, these materials typically exhibit toxicity to bacteria and fungi, and there have been emerging concerns about their ecotoxicity effects. The understanding of the toxicity mechanisms is incomplete, with different studies often reporting contradictory results. The relationship between the material properties and toxicity appears to be complex and diifficult to understand, which is partly due to incomplete characterization of the nanomaterial, and possibly due to experimental artefacts in the characterization of the nanomaterial and/or its interactions with living organisms. This review discusses the comprehensive characterization of metal oxide nanomaterials and the mechanisms of their toxicity.

Rifampin induces hydroxyl radical formation in Mycobacterium tuberculosis

The antituberculosis (anti-TB) drug rifampin (RIF) binds to the beta subunit of the RNA polymerase (RpoB) of Mycobacterium tuberculosis, but the bactericidal responses triggered after target interaction are not known. To evaluate whether RIF induced an oxidative burst, lysates of RIF-treated M. tuberculosis were tested for determination of reactive oxygen species (ROS) by the electron paramagnetic resonance (EPR) technique using 1-hydroxy-3-carboxy-pyrrolidine (CPH) and 5,5-dimethyl-1-pyrrolidine-N-oxide (DMPO) as spin traps. M. tuberculosis killing by RIF stimulated an increase in the rate of formation of the CPH radical (CP·). Lysate pretreatment with the O2·(-) and ·OH scavengers superoxide dismutase (SOD) and thiourea (THIO), respectively, or with the metal chelator diethylene triamine pentaacetic acid (DTPA) inhibited CP· formation, arguing in favor of a metal-catalyzed ROS response. Formation of CP· did not increase following treatment of RIF-resistant strains with RIF, indicating that the ROS were induced after RpoB binding. To identify the ROS formed, lysates of RIF-treated bacilli were incubated with DMPO, a spin trap specific for ·OH and O2·(-), with or without pretreatment with SOD, catalase, THIO, or DTPA. Superoxide dismutase, catalase, and THIO decreased formation of the DMPO-OH adduct, and SOD plus DTPA completely suppressed it, suggesting that RIF activated metal-dependent O2·(-)-mediated mechanisms producing ·OH inside tubercle bacilli. The finding that the metal chelator DTPA reduced the bactericidal activity of RIF supported the possibility that ·OH was generated through these mechanisms and that it participated at least in part in M. tuberculosis killing by the drug.

Comparability of in vitro tests for bioactive nanoparticles: a common assay to detect reactive oxygen species as an example

The release of reactive oxygen species (ROS) during the electron transport of mitochondrial aerobic respiration is the major source of ROS. However, contact between cells and nanoparticles (NPs) can also induce release of ROS, leading to an imbalance towards the pro-oxidative state. At low levels of ROS production, cells initiate a protective response to guarantee their survival, but an excess of ROS can damage cellular compounds such as membranes and various organelles, or directly cause genotoxicity. Thus an elevated level of ROS is an important indicator of cellular stress and an accurate recording of this parameter would be very informative. ROS can be measured by various assays, but all known assays measuring and quantifying ROS possess certain weaknesses. The problems and challenges of quantitatively detecting ROS in vitro using the 2′,7′-dichlorodihydrofluorescein (DCF) assay is discussed as an example. In addition, we debate the difficulties in finding a suitable and stable chemical reaction control for the DCF assay (or other ROS-detecting assays). As a conclusion, we believe that using 3-morpholinosydnonimine hydrochloride (Sin-1) as a ROS inducer in the DCF assay is feasible only qualitatively. However, a quantitative measurement of the absolute amount of ROS produced and a quantitative comparison between experiments is (at the moment) impossible.

Oxidative stress in acute pancreatitis: lost in translation?

Oxidative stress has been implicated in the pathogenesis of acute pancreatitis, a severe and debilitating inflammation of the pancreas that carries a significant mortality, and which imposes a considerable financial burden on the health system due to patient care. Although extensive efforts have been directed towards the elucidation of critical underlying mechanisms and the identification of novel therapeutic targets, the disease remains without a specific therapy. In experimental animal models of acute pancreatitis, increased oxidative stress and decreased antioxidant defences have been observed, changes also detected in patients clinically. However, despite the promise of studies evaluating the effects of antioxidants in these model systems, translation to the clinic has thus far been disappointing. This may reflect many factors involved in the design of both preclinical and clinical evaluations of antioxidant therapy, not least the fact that most experimental studies have focussed on pre-treatment rather than post-injury assessment. This review has examined evidence relating to the involvement of oxidative stress in the pathophysiology of acute pancreatitis, focussing on experimental models and the clinical experience, including the experimental techniques employed and potential of antioxidant therapy.

Indazoles: a new top seed structure in the search of efficient drugs against Trypanosoma cruzi

For years, Chagas disease treatment has been limited to only two drugs of highly questionable and controversial use (Nifurtimox® and Benznidazole®). In the search of effective drugs, many efforts have been made, but only a few structures have emerged as actual candidates. Heading into this, the multitarget-directed approach appears as the best choice. In this framework, indazoles were shown to be potent Trypanosoma cruzi growth inhibitors, being able to lead both the formation of reactive oxygen species and the inhibition of trypanothione reductase. Herein, we discuss the main structural factors that rule the anti-T. cruzi properties of indazoles, and how they would be involved in the biological properties as well as in the action mechanisms, attempting to make parallels between the old paradigms and current evidences in order to outline what could be the next steps to follow in regard to the future drug design for Chagas disease treatment.

Positive effect of propolis on free radicals in burn wounds

Concentration and properties of free radicals in the burn wounds treated with propolis were examined by the use of electron paramagnetic resonance spectroscopy. Magnetic spin-spin interactions and complex free radicals structures in wound beds were studied. The results were compared to those obtained for silver sulphadiazine used as a standard pharmaceutical agent. The changes of free radicals in the matrix of injury with time of exposition on these substances were tested. The aim of this study was to check the hypothesis about the best influence of propolis on the burn wounds healing. It was confirmed that a relatively lower concentration of free radicals exists in the burn wounds treated with propolis. The homogeneously broadened spectra and a complex free radical system characterize the tested tissue samples. The fastening of spin-lattice relaxation processes in the matrix of injury after treatment with propolis and silver sulphadiazine was observed. Practical usefulness of electron paramagnetic resonance spectroscopy in alternative medicine was proved.

Detection of superoxide anion and hydrogen peroxide production by cellular NADPH oxidases

BACKGROUND

The recent recognition that isoforms of the cellular NADPH-dependent oxidases, collectively known as the NOX protein family, participate in a wide range of physiologic and pathophysiologic processes in both the animal and plant kingdoms has stimulated interest in the identification, localization, and quantitation of their products in biological settings. Although several tools for measuring oxidants released extracellularly are available, the specificity and selectivity of the methods for reliable analysis of intracellular oxidants have not matched the enthusiasm for studying NOX proteins.

SCOPE OF REVIEW

Focusing exclusively on superoxide anion and hydrogen peroxide produced by NOX proteins, this review describes the ideal probe for analysis of O2(-) and H2O2 generated extracellularly and intracellularly by NOX proteins. An overview of the components, organization, and topology of NOX proteins provides a rationale for applying specific probes for use and a context in which to interpret results and thereby construct plausible models linking NOX-derived oxidants to biological responses. The merits and shortcomings of methods currently in use to assess NOX activity are highlighted, and those assays that provide quantitation of superoxide or H2O2 are contrasted with those intended to examine spatial and temporal aspects of NOX activity.

MAJOR CONCLUSIONS

Although interest in measuring the extracellular and intracellular products of the NOX protein family is great, robust analytical probes are limited.

GENERAL SIGNIFICANCE

The widespread involvement of NOX proteins in many biological processes requires rigorous approaches to the detection, localization, and quantitation of the oxidants produced. This article is part of a Special Issue entitled Current methods to study reactive oxygen species - pros and cons and biophysics of membrane proteins. Guest Editor: Christine Winterbourn.

Hyperuricemia induces endothelial dysfunction via mitochondrial Na+/Ca2+ exchanger-mediated mitochondrial calcium overload

BACKGROUND

Uric acid (UA) has proven to be a causal agent in endothelial dysfunction in which ROS production plays an important role. Calcium overload in mitochondria can promote the mitochondrial production of ROS. We hypothesize that calcium transduction in mitochondria contributes to UA-induced endothelial dysfunction.

METHODS AND RESULTS

We first demonstrated that high concentrations of UA cause endothelial dysfunction, marked by a reduction in eNOS protein expression and NO release in vitro. We further found that a high concentration of UA increased levels of [Ca2+]mito, total intracellular ROS, H2O2, and mitochondrial O2·-, and Δψmito but not the [Ca2+]cyt level. When the mitochondrial calcium channels NCXmito and MCU were blocked by CGP-37157 and Ru360, respectively, the UA-induced increases in the levels of [Ca2+]mito and total intracellular ROS were significantly reduced. Mitochondrial levels of O2·- and Δψmito were reduced by inhibition of NCXmito but not of MCU. Moreover, inhibition of NCXmito, but not of MCU, blocked the UA-induced reductions in eNOS protein expression and NO release.

CONCLUSIONS

The increased generation of mitochondrial O2·- induced by a high concentration of UA is triggered by mitochondrial calcium overload and ultimately leads to endothelial dysfunction. In this process, the activation of NCXmito is the major cause of the influx of calcium into mitochondria. Our results provide a new pathophysiological mechanism for UA-induced endothelial dysfunction and may offer a new therapeutic target for clinicians.

Targeting mitochondrial function for the treatment of acute spinal cord injury

Traumatic injury to the mammalian spinal cord is a highly dynamic process characterized by a complex pattern of pervasive and destructive biochemical and pathophysiological events that limit the potential for functional recovery. Currently, there are no effective therapies for the treatment of spinal cord injury (SCI) and this is due, in part, to the widespread impact of the secondary injury cascades, including edema, ischemia, excitotoxicity, inflammation, oxidative damage, and activation of necrotic and apoptotic cell death signaling events. In addition, many of the signaling pathways associated with these cascades intersect and initiate other secondary injury events. Therefore, it can be argued that therapeutic strategies targeting a specific biochemical cascade may not provide the best approach for promoting functional recovery. A "systems approach" at the subcellular level may provide a better strategy for promoting cell survival and function and, as a consequence, improve functional outcomes following SCI. One such approach is to study the impact of SCI on the biology and function of mitochondria, which serve a major role in cellular bioenergetics, function, and survival. In this review, we will briefly describe the importance and unique properties of mitochondria in the spinal cord, and what is known about the response of mitochondria to SCI. We will also discuss a number of strategies with the potential to promote mitochondrial function following SCI.