Oxidation of ethidium-based probes by biological radicals: mechanism, kinetics and implications for the detection of superoxide

Ultrasonic controllable synthesis of sulfur-functionalized metal-organic frameworks (S-MOFs) and their application in piezo-photocatalytic rapid reduction of hexavalent chromium (Cr)

The United Nations' Sustainable Development Goals (SDGs) are significant in guiding modern scientific research. In recent years, scholars have paid much attention to MOFs materials as green materials. However, piezo catalysis of MOFs materials has not been widely studied. Piezoelectric materials can convert mechanical energy into electrical energy, while MOFs are effective photocatalysts for removing pollutants. Therefore, it is crucial to design MOFs with piezoelectric properties and photosensitivity. In this study, sulfur-functionalized metal-organic frameworks (S-MOFs) were prepared using organic sulfur-functionalized ligand (H2TDC) ultrasonic synthesis to enhance their piezoelectric properties and visible light absorption. The study demonstrated that the S-MOFs significantly enhanced the reduction of a 10 mg/L solution of hexavalent chromium to 99.4 % within 10 min, using only 15 mg of catalyst. The orbital energy level differences of the elements were analyzed using piezo response force microscopy (PFM) and X-ray photoelectron spectroscopy (XPS). The results showed that MOFs functionalized with sulfur atom ligands have a built-in electric field that facilitates charge separation and migration. This study presents a new approach to enhance the piezoelectric properties of MOFs, which broadens their potential applications in piezo catalysis and piezo-photocatalysis. Additionally, it provides a sustainable method for reducing hexavalent chromium, contributing to the achievement of sustainable development goals, specifically SDG-6, SDG-7, SDG-9, and SDG-12.

Hydroxylation of the indium tin oxide electrode promoted by surface bubbles

Adherent bubbles at electrodes are generally treated as reaction penalties. Herein, in situ hydroxylation of indium tin oxide surfaces can be easily achieved by applying a constant potential of +1.0 V in the presence of bubbles. Its successful hydroxylation is further demonstrated by preparing a ferrocene-terminated film, which is confirmed by cyclic voltammetry and X-ray photoelectron spectroscopy.

Health position paper and redox perspectives - Disease burden by transportation noise

Transportation noise is a ubiquitous urban exposure. In 2018, the World Health Organization concluded that chronic exposure to road traffic noise is a risk factor for ischemic heart disease. In contrast, they concluded that the quality of evidence for a link to other diseases was very low to moderate. Since then, several studies on the impact of noise on various diseases have been published. Also, studies investigating the mechanistic pathways underlying noise-induced health effects are emerging. We review the current evidence regarding effects of noise on health and the related disease-mechanisms. Several high-quality cohort studies consistently found road traffic noise to be associated with a higher risk of ischemic heart disease, heart failure, diabetes, and all-cause mortality. Furthermore, recent studies have indicated that road traffic and railway noise may increase the risk of diseases not commonly investigated in an environmental noise context, including breast cancer, dementia, and tinnitus. The harmful effects of noise are related to activation of a physiological stress response and nighttime sleep disturbance. Oxidative stress and inflammation downstream of stress hormone signaling and dysregulated circadian rhythms are identified as major disease-relevant pathomechanistic drivers. We discuss the role of reactive oxygen species and present results from antioxidant interventions. Lastly, we provide an overview of oxidative stress markers and adverse redox processes reported for noise-exposed animals and humans. This position paper summarizes all available epidemiological, clinical, and preclinical evidence of transportation noise as an important environmental risk factor for public health and discusses its implications on the population level.

Reactive oxygen species drive foraging decisions in Caenorhabditis elegans

Environmental surveillance-mediated behavior integrates multiple cues through complex signaling mechanisms. In Caenorhabditis elegans, neurons coordinate perception and response through evolutionarily conserved molecular signaling cascades to mediate attraction and avoidance behaviors. However, despite lacking eyes, C. elegans was recently reported to perceive and react to the color blue. Here, we provide an explanation for this apparent color perception. We show that internally-generated reactive oxygen species (ROS) occurring in response to light are additive to exogenous sources of ROS, such as bacterial toxins or photosensitizers. Multiple sub-threshold sources of ROS are integrated to coordinate behavioral responses to the environment with internal physiologic cues, independent of color. We further demonstrate that avoidance behavior can be blocked by antioxidants, while ROS is both sufficient and scalable to phenocopy the avoidance response. Moreover, avoidance behavior in response to ROS is plastic and reversible, suggesting it may occur through a post-translation redox modification. Blue light affects C. elegans behavior through ROS generation by endogenous flavins in a process requiring the neuronal gustatory photoreceptor like protein, LITE-1. Our results demonstrate that LITE-1 is also required for ROS-mediated avoidance of pyocyanin and light-activated photosensitizers and this role is mediated through the modification of Cys44. Overall, these findings demonstrate that ROS and LITE-1 are central mediators of C. elegans foraging behavior through integration of multiple inputs, including light.

Novel NADPH Oxidase-2 Inhibitors as Potential Anti-Inflammatory and Neuroprotective Agents

A family of seven NADPH oxidase enzymes (Nox1-5, Duox1-2) has been implicated in a variety of diseases, including inflammatory lung diseases, neurodegenerative diseases, cardiovascular diseases, and cancer. Here, we report the results of our studies aimed at developing novel brain-permeable Nox2 inhibitors with potential application as neuroprotective agents. Using cell-based assays, we identified a novel Nox2 inhibitor, TG15-132, that prevents PMA-stimulated oxygen consumption and reactive oxygen species (superoxide radical anion and hydrogen peroxide) formation upon acute treatment in differentiated HL60 cells. Long-term treatment with TG15-132 attenuates the induction of genes encoding Nox2 subunits, several inflammatory cytokines, and iNOS in differentiated THP-1 cells. Moreover, TG15-132 shows a relatively long plasma half-life (5.6 h) and excellent brain permeability, with a brain-to-plasma ratio (>5-fold) in rodent models. Additionally, TG15-132 does not cause any toxic effects on vital organs or blood biomarkers of toxicity in mice upon chronic dosing for seven days. We propose that TG15-132 may be used as a Nox2 inhibitor and a potential neuroprotective agent, with possible further structural modifications to increase its potency.

Factors Important in the Use of Fluorescent or Luminescent Probes and Other Chemical Reagents to Measure Oxidative and Radical Stress

Numerous chemical probes have been used to measure or image oxidative, nitrosative and related stress induced by free radicals in biology and biochemistry. In many instances, the chemical pathways involved are reasonably well understood. However, the rate constants for key reactions involved are often not yet characterized, and thus it is difficult to ensure the measurements reflect the flux of oxidant/radical species and are not influenced by competing factors. Key questions frequently unanswered are whether the reagents are used under 'saturating' conditions, how specific probes are for particular radicals or oxidants and the extent of the involvement of competing reactions (e.g., with thiols, ascorbate and other antioxidants). The commonest-used probe for 'reactive oxygen species' in biology actually generates superoxide radicals in producing the measured product in aerobic systems. This review emphasizes the need to understand reaction pathways and in particular to quantify the kinetic parameters of key reactions, as well as measure the intracellular levels and localization of probes, if such reagents are to be used with confidence.

Practical Aspects in the Study of Biological Photosensitization Including Reaction Mechanisms and Product Analyses: A Do's and Don'ts Guide†

The interaction of light with natural matter leads to a plethora of photosensitized reactions. These reactions cause the degradation of biomolecules, such as DNA, lipids, proteins, being therefore detrimental to the living organisms, or they can also be beneficial by allowing the treatment of several diseases by photomedicine. Based on the molecular mechanistic understanding of the photosensitization reactions, we propose to classify them in four processes: oxygen-dependent (type I and type II processes) and oxygen-independent [triplet-triplet energy transfer (TTET) and photoadduct formation]. In here, these processes are discussed by considering a wide variety of approaches including time-resolved and steady-state techniques, together with solvent, quencher, and scavenger effects. The main aim of this survey is to provide a description of general techniques and approaches that can be used to investigate photosensitization reactions of biomolecules together with basic recommendations on good practices. Illustration of the suitability of these approaches is provided by the measurement of key biomarkers of singlet oxygen and one-electron oxidation reactions in both isolated and cellular DNA. Our work is an educational review that is mostly addressed to students and beginners.

Tissue Derivation and Biological Sex Uniquely Mediate Endothelial Cell Protein Expression, Redox Status, and Nitric Oxide Synthesis

Human endothelial cells are routinely utilized in cardiovascular research to provide a translational foundation for understanding how the vascular endothelium functions in vivo. However, little attention has been given to whether there are sex specific responses in vitro. Similarly, it is unclear whether endothelial cells derived from distinct tissues behave in a homogenous manner. Herein, we demonstrate that marked sex differences exist within, and between, commonly utilized human primary endothelial cells from healthy donors, with respect to redox status, nitric oxide synthesis, and associated proteins that can mediate their expression. Further, we demonstrate that endothelial cells respond uniquely to inflammatory insult in a sex- and tissue origin-dependent manner. Our findings suggest sex and tissue derivation may need to be considered when studying endothelial cells in vitro as cells derived from distinct tissue and sexes may not behave interchangeably.

Effects of Silver Nanoparticles on Physiological and Proteomic Responses of Tobacco (Nicotiana tabacum) Seedlings Are Coating-Dependent

The harmful effects of silver nanoparticles (AgNPs) have been confirmed in many organisms, but the mechanism of their toxicity is not yet fully understood. In biological systems, AgNPs tend to aggregate and dissolve, so they are often stabilized by coatings that influence their physico-chemical properties. In this study, the effects of AgNPs with different coatings [polyvinylpyrrolidone (PVP) and cetyltrimethylammonium bromide (CTAB)] on oxidative stress appearance and proteome changes in tobacco (Nicotiana tabacum) seedlings have been examined. To discriminate between the nanoparticulate Ag form from the ionic one, the treatments with AgNO₃, a source of Ag⁺ ions, were also included. Ag uptake and accumulation were found to be similarly effective upon exposure to all treatment types, although positively charged AgNP-CTAB showed less stability and a generally stronger impact on the investigated parameters in comparison with more stable and negatively charged AgNP-PVP and ionic silver (AgNO₃). Both AgNP treatments induced reactive oxygen species (ROS) formation and increased the expression of proteins involved in antioxidant defense, confirming oxidative stress as an important mechanism of AgNP phytotoxicity. However, the mechanism of seedling responses differed depending on the type of AgNP used. The highest AgNP-CTAB concentration and CTAB coating resulted in increased H₂O₂ content and significant damage to lipids, proteins and DNA molecules, as well as a strong activation of antioxidant enzymes, especially CAT and APX. On the other hand, AgNP-PVP and AgNO₃ treatments induced the nonenzymatic antioxidants by significantly increasing the proline and GSH content. Exposure to AgNP-CTAB also resulted in more noticeable changes in the expression of proteins belonging to the defense and stress response, carbohydrate and energy metabolism and storage protein categories in comparison to AgNP-PVP and AgNO₃. Cysteine addition significantly reduced the effects of AgNP-PVP and AgNO₃ for the majority of investigated parameters, indicating that AgNP-PVP toxicity mostly derives from released Ag⁺ ions. AgNP-CTAB effects, however, were not alleviated by cysteine addition, suggesting that their toxicity derives from the intrinsic properties of the nanoparticles and the coating itself.

Redox Monitoring in Nuclear Medical Imaging

Significance: The imbalance in redox homeostasis is known as oxidative stress, which is relevant to many diseases such as cancer, arteriosclerosis, and neurodegenerative disorders. Overproduction of reactive oxygen species (ROS) is one of the factors that trigger the redox state imbalance in vivo. The ROS have high reactivity and impair biomolecules, whereas antioxidants and antioxidant enzymes, such as ascorbate and glutathione, reduce the overproduction of ROS to rectify the redox imbalance. Owing to this, redox monitoring tools have been developed to understand the redox fluctuations in oxidative stress-related diseases. Recent Advances: In an attempt to monitor redox substances, including ROS and radical species, versatile modalities have been developed, such as electron spin resonance, chemiluminescence, and fluorescence. In particular, many fluorescent probes have been developed that are selective for ROS. This has significantly contributed to understanding the relevance of ROS in disease onset and progression. Critical Issues: To date, the dynamics of ROS and radical fluctuation in in vivo redox states remain unclear, and there are a few methods for the in vivo detection of redox fluctuations. Future Directions: In this review, we summarize the development of radiolabeled probes for monitoring redox-relevant species by nuclear medical imaging that is applicable in vivo. In the future, translational research is likely to be advanced through the development of highly sensitive and in vivo applicable detection methods, such as nuclear medical imaging, to clarify the underlying dynamics of ROS, radicals, and redox substances in many diseases. Antioxid. Redox Signal. 36, 797-810.

Water-soluble cationic boronate probe based on coumarin imidazolium scaffold: Synthesis, characterization, and application to cellular peroxynitrite detection

Peroxynitrite (ONOO^-) has been implicated in numerous pathologies associated with an inflammatory component, but its selective and sensitive detection in biological settings remains a challenge. Here, the development of a new water-soluble and cationic boronate probe based on a coumarin-imidazolium scaffold (CI-Bz-BA) for the fluorescent detection of ONOO^- in cells is reported. The chemical reactivity of the CI-Bz-BA probe toward selected oxidants known to react with the boronate moiety was characterized, and the suitability of the probe for the direct detection of ONOO^- in cell-free and cellular system is reported. Oxidation of the probe results in the formation of the primary hydroxybenzyl product (CI-Bz-OH), followed by the spontaneous elimination of the quinone methide moiety to produce the secondary phenol (CI-OH), which is accompanied by a red shift in the fluorescence emission band from 405 nm to 481 nm. CI-Bz-BA reacts with ONOO^- stoichiometrically with a rate constant of ∼1 × 10⁶ M^-1s^-1 to form, in addition to the major phenolic product CI-OH, the minor nitrated product CI-Bz-NO₂, which is not formed by other oxidants tested or via myeloperoxidase-catalyzed oxidation/nitration. Both CI-OH and CI-Bz-NO₂ products were also formed in the presence of cogenerated fluxes of nitric oxide and superoxide radical anion produced during decomposition of a SIN-1 donor. Using RAW 264.7 cells, we demonstrate the ability of the probe to report endogenously produced ONOO^-via fluorescence measurements, including plate reader real time monitoring and two-photon fluorescence imaging. Liquid chromatography/mass spectrometry analyses of cell extracts and media confirmed the formation of both CI-OH and CI-Bz-NO₂ in macrophages activated to produce ONOO^-. We propose the use of a combination of real-time monitoring of probe oxidation using fluorimetry and fluorescence microscopy with liquid chromatography/mass spectrometry-based product identification for rigorous detection and quantitative analyses of ONOO^- in biological systems.

Detection of superoxide radical in all biological systems by Thin Layer Chromatography

The study presents a new method that detects O₂^•-, via quantification of 2-hydroxyethidium (2-ΟΗ-Ε⁺) as low as ∼30 fmoles by High-Performance Thin Layer Chromatography (HPTLC). The method isolates 2-ΟΗ-Ε⁺ after its extraction by the anionic detergent SDS (at 18-fold higher than its CMC) together with certain organic/inorganic reagents, and its HPTLC-separation from di-ethidium (di-Ε⁺) and ethidium (Ε⁺). Quantification of 2-OH-E⁺ is based on its ex/em maxima at 290/540 nm, and of di-E⁺ and E⁺ at 295/545 nm. The major innovations of the present method are the development of protocols for (i) efficient extraction (by SDS) and (ii) sensitive quantification (by HPTLC) for 2-OH-E⁺ (as well as di-E⁺ and E⁺) from most biological systems (animals, plants, cells, subcellular compartments, fluids). The method extracts 2-ΟΗ-Ε⁺ (by neutralizing the strong binding between its quaternary N⁺ and negatively charged sites on phospholipids, DNA etc) together with free HE, while protects both from biological oxidases, and also extracts/quantifies total proteins (hydrophilic and hydrophobic) for expressing O₂^•- levels per protein quantity. The method also uses SDS (at 80-fold lower than its CMC) to extract/remove/wash 2-ΟΗ-Ε⁺ from cell/organelle exterior membrane sites, for more accurate internal content quantification. The new method is applied on indicative biological systems: (1) artificially stressed (mouse organs and liver mitochondria and nuclei, ±exposed to paraquat, a known O₂^•- generator), and (2) physiologically stressed (cauliflower plant, exposed to light/dark).

Detection of extracellular superoxide in isolated human immune cells and in an animal model of arterial hypertension using hydropropidine probe and HPLC analysis

Superoxide formation is a hallmark of cardiovascular disease with the involvement of different tissues and cell types. Identification of the cellular sources and subcellular localization of superoxide formation is important to understand the underlying disease pathomechanisms. In the present study, we used HPLC quantification of the superoxide-specific oxidation products of hydroethidine (HE or DHE) and its derivative hydropropidine (HPr⁺) for measurement of intra- and extracellular superoxide formation in isolated leukocytes and tissues of hypertensive rats. Superoxide generation by isolated leukocytes from human subjects as well as tissue samples of hypertensive rats (infusion of angiotensin-II for 7 days) was investigated using HPr⁺ and HE fluorescent probes with HPLC or plate reader detection. Both fluorescent dyes were used to test for intra- and extracellular superoxide formation using the supernatant or cell/tissue pellet for analysis. We demonstrate the correlation of impaired functional parameters (blood pressure, vascular function, and oxidative burst) and increased superoxide formation in different organ systems of hypertensive rats using the HPr⁺/HPLC method. In the cell model, the differences between HE and HPr⁺ and especially the advantage of the extracellular specificity of HPr⁺, due to its cell impermeability, became evident. Plate reader-based assays showed much higher background signal and were inferior to HPLC based methods. In conclusion, the HPr⁺/HPLC assay for superoxide determination is highly reliable in isolated immune cells and an animal model of arterial hypertension. In particular, the cell impermeability of HPr⁺ made it possible to differentiate between intra- and extracellular superoxide formation.

Luminescent lanthanide complexes for reactive oxygen species biosensing and possible application in Alzheimer's diseases

Histopathological hallmarks of Alzheimer's disease (AD) are intracellular neurofibrillary tangles and extracellular formation of senile plaques composed of the aggregated amyloid-beta peptide along with metal ions (copper, iron or zinc). In addition, oxidative stress is considered as an important factor in the etiology of AD and a multitude of metalloproteins and transporters is affected, leading to metal ion misregulation. Redox-active metal ions (e.g., copper) can catalyze the production of reactive oxygen species (ROS) in the presence of molecular oxygen and a reductant such as ascorbate. The ROS thus produced, in particular the hydroxyl radical which is the most reactive one, may contribute to oxidative stress conditions. Thus, detecting ROS in vivo or in biological models of AD is of interest for better understanding AD etiology. The use of biocompatible and highly specific and sensitive probes is needed for such a purpose, since ROS are transient species whose steady-state concentrations are very low. Luminescent lanthanide complexes are sensitive probes that can meet these criteria. The present review focuses on the recent advances in the use of luminescent lanthanide complexes for ROS biosensing. It shows why the use of luminescent lanthanide complexes is of particular interest for selectively detecting ROS ( O 2 · - , HO^• , ¹ O₂ , H₂ O₂ , etc.) in biological samples in the µM-nM range. It particularly focuses on the most recent strategies and discusses what could be expected with the use of luminescent lanthanide complexes for better understanding some of the molecular mechanisms underlying the development of Alzheimer's disease.