Quantitative determination of trace hydrogen peroxide in the presence of sulfide using the Amplex Red/horseradish peroxidase assay

Novel lateral flow assay to detect H2O2 by utilizing self-biotinylation of G-quadruplex

We herein describe a novel lateral flow assay (LFA) to detect H2O2 by utilizing self-biotinylation of G-quadruplex (G4). In this strategy, the G4 strand promotes the self-biotinylation of G4 itself in the presence of H2O2, which is then allowed to bind to the FAM-labeled complementary detector probe. The resulting biotin-labeled G4/FAM-detector probe complex is captured on the test line, producing a red-colored band during lateral flow readout. Based on this unique approach, we achieved the naked-eye detection of target H2O2 at concentrations as low as 1 μM, with reliable quantification down to 0.388 μM. This method also demonstrated exceptional specificity in distinguishing H2O2 from other non-target molecules. We further verified its versatile applicability by reliably identifying another biomolecule, choline, by coupling with choline oxidase, which generates H₂O₂ during oxidation. This novel LFA strategy holds great promise as a powerful point-of-care testing (POCT) platform for detecting a large spectrum of target biomolecules by employing their corresponding oxidases.

Progress and limitations in reactive oxygen species quantitation

Reactive oxygen species (ROS) are a set of oxygen- and nitrogen-containing radicals. They are produced from a wide range of sources. In biological contexts, cellular stress leads to an overproduction of ROS, which can lead to genetic damage and disease development. In industry, ROS are often productively used for water purification or for analyzing the possible toxicity of an industrial process. Because of their ubiquity, detection of ROS has been an analytical goal across a range of fields. To understand complicated systems and origins of ROS production, it is necessary to move from qualitative detection to quantitation. Analytical techniques that combine quantitation, high spatial and temporal resolution, and good specificity represent detection methods that can fill critical gaps in ROS research. Herein, we discuss the continued progress and limitations of fluorescence, electrochemical, and electron paramagnetic resonance detection of ROS over the last ten years, giving suggestions for the future of the field.

Modified perylene diimide for femto molar level detection of glucose: smartphone-assisted colorimetric glucose detection kits

In this report, a functionalized hydroxyphenyl benzothiazole (HBT) derivative has been synthesized and anchored onto the perylene diimide (PDI) core at the -bay position (PHI). PHI has been explored for the generation of radical anions (PH1˙-) and dianions (PH12-) in 20% HEPES buffer-DMSO solution using H2S as a sacrificial electron donor. The PH1˙- has a half-life (t1/2) of 1.5 h and 3 h in oxygenated and hypoxic conditions, respectively. The formation of radical anions has been confirmed by optical (absorbance and fluorescence) methods, cyclic voltammetry (CV), differential pulse voltammetry (DPV), and femtosecond transient absorbance spectroscopy along with current-voltage (I-V) and NOBF4 studies. The PH1˙- showed peroxidase-like activity for the reduction of H2O2 as low as 170 fmol L-1 (fM) giving a colour change from sea green to pink. The biochemical assay which consists of PH1˙-+ GOx has been further utilized as a glucose sensor. Upon addition of glucose (0-8 nM) in the biochemical assay, the in-situ produced H2O2 (after oxidation of glucose with GOx) oxidized PH1˙- to PH1 giving a sea green to pink colorimetric read out along with a decrease in the absorption intensities at 720, 815, 880 and 950 nm and the emergence of absorption intensity at 541 nm. The lowest limit of detection is 85 fM. We also explored this biochemical assay for the detection of 860 fM of glucose in a 10% blood serum. Similarly, fluorometric, CV and DPV studies were carried out for the detection of glucose using this biochemical assay. The smartphone-assisted RGB colour analyser showed large variations in the red colour and this RGB based colour differentiation can be used for the detection of 1 nM of glucose.

Comparative understanding of peroxide quantitation assays: a case study with peptide drug product degradation

Peroxide-mediated oxidation of drug molecules is a known challenge faced throughout the pharmaceutical development pathway-from early-stage stability studies to manufacturing processes. During the initial development stage, the major source of peroxide is the formulation excipients, whether they are pre-loaded or generated in situ due to slow degradation, and in the late phase, peroxides can be introduced during sanitization processes or generated via cavitation. In essence, a control strategy for peroxide mitigation often becomes a critical quality attribute for successful drug development. To this end, quantitation of peroxide is essential to monitor the peroxide level to ensure product quality and proposed shelf-life. However, methods for reliable and robust quantitation to detect trace levels of peroxide in a complex drug product matrix become increasingly challenging. This article discusses three high-throughput assays based on absorbance, fluorescence and chemiluminescence measurements to detect peroxide at a low level and compares the methods through validation studies in water. Selected methods have also been tested to understand the forced degradation of model peptide drug products with spiked hydrogen peroxide. Peptide degradation profiles and residual peroxide levels are presented to provide an understanding of the suitability of the quantitation methods and their performance.

A personal glucose meter-utilized strategy for portable and label-free detection of hydrogen peroxide

Rapid and precise detection of hydrogen peroxide (H2O2) holds great significance since it is linked to numerous physiological and inorganic catalytic processes. We herein developed a label-free and washing-free strategy to detect H2O2 by employing a hand-held personal glucose meter (PGM) as a signal readout device. By focusing on the fact that the reduced redox mediator ([Fe(CN)6]4-) itself is responsible for the final PGM signal, we developed a new PGM-based strategy to detect H2O2 by utilizing the target H2O2-mediated oxidation of [Fe(CN)6]4- to [Fe(CN)6]3- in the presence of horseradish peroxidase (HRP) and monitoring the reduced PGM signal in response to the target amount. Based on this straightforward and facile design principle, H2O2 was successfully determined down to 3.63 μM with high specificity against various non-target molecules. We further demonstrated that this strategy could be expanded to identify another model target choline by detecting H2O2 produced through its oxidation promoted by choline oxidase. Moreover, we verified its practical applicability by reliably determining extracellular H2O2 released from the breast cancer cell line, MDA-MB-231. This work could evolve into versatile PGM-based platform technology to identify various non-glucose target molecules by employing their corresponding oxidase enzymes, greatly advancing the portable biosensing technologies.

Advanced strategies in high-throughput droplet screening for enzyme engineering

Enzymes, as biocatalysts, play a cumulatively important role in environmental purification and industrial production of chemicals and pharmaceuticals. However, natural enzymes are limited by their physiological properties in practice, which need to be modified driven by requirements. Screening and isolating certain enzyme variants or ideal industrial strains with high yielding of target product enzymes is one of the main directions of enzyme engineering research. Droplet-based high-throughput screening (DHTS) technology employs massive monodisperse emulsion droplets as microreactors to achieve single strain encapsulation, as well as continuous monitoring for the inside mutant library. It can effectively sort out strains or enzymes with desired characteristics, offering a throughput of 108 events per hour. Much of the early literature focused on screening various engineered strains or designing signalling sorting strategies based on DHTS technology. However, the field of enzyme engineering lacks a comprehensive overview of advanced methods for microfluidic droplets and their cutting-edge developments in generation and manipulation. This review emphasizes the advanced strategies and frontiers of microfluidic droplet generation and manipulation facilitating enzyme engineering development. We also introduce design for various screening signals that cooperate with DHTS and devote to enzyme engineering.

Copper Safeguards Dissolved Organic Matter from Sunlight-Driven Photooxidation

Sunlight plays a crucial role in the transformation of dissolved organic matter (DOM) and the associated carbon cycle in aquatic environments. This study demonstrates that the presence of nanomolar concentrations of copper (Cu) significantly decreases the rate of photobleaching and the rate of loss of electron-donating moieties of three selected types of DOM (including both terrestrial and microbially derived DOM) under simulated sunlight irradiation. Employing Fourier transform ion cyclotron resonance mass spectrometry, we further confirm that Cu selectively inhibits the photooxidation of lignin- and tannin-like phenolic moieties present within the DOM, in agreement with the reported inhibitory impact of Cu on the photooxidation of phenolic compounds. On the basis of the inhibitory impact of Cu on the DOM photobleaching rate, we calculate the contribution of phenolic moieties to DOM photobleaching to be at least 29-55% in the wavelength range of 220-460 nm. The inhibition of loss of electrons from DOM during irradiation in the presence of Cu is also explained quantitatively by developing a mathematical model describing hydrogen peroxide (a proxy measure of loss of electrons from DOM) formation on DOM irradiation in the absence and presence of Cu. Overall, this study advances our understanding of DOM transformation in natural sunlit waters.

Novel fluorometric protocol for assessing myeloperoxidase activity

Neutrophil myeloperoxidase (MPO) is an essential enzyme for the innate immune system. Measuring MPO activity is vital for understanding neutrophil characteristics and functions in various diseases. MPO activity can be measured using several methods, including spectrophotometric and fluorometric protocols. This paper introduces a fluorometric method for specifically quantifying MPO activity based on the H2O2-dependent oxidation of thiamine. We optimized this new method using the robust statistical approach response surface methodology (RSM) and Box Benken Design (BBD). We extensively examined the effects of several experimental parameters using the RSM methodology and determined the best conditions for accurate and sensitive MPO activity measurement. The optimal conditions were determined using the analysis of variance (ANOVA) for second-order polynomial equations. The resulting F-value (4.86) indicated that the model was significant. However, the lack-of-fitness F-value (1.79) suggested it did not differ significantly from the corresponding p-value. The greatest MPO activity (30 ± 2 U L-1) was obtained under optimum conditions, which were 1000 µM of H2O2, 10 min incubation time, and 1000 µM of thiamine. Our results suggest that this advanced fluorometric method has significant accuracy, sensitivity, and linearity up to 60 IU. The new and standard colorimetric methods also showed a good correlation. These results indicate that the new fluorometric method can be dependable and efficient for assessing MPO activity. The new method is characterized by excellent accuracy, sensitivity, and linearity, making it a valuable protocol for researchers and clinicians interested in assessing MPO activity.

Effects of electrospun fibers containing ascorbic acid on oxidative stress reduction for cardiac tissue engineering

Tissue engineering provides promise for regeneration of cardiac tissue following myocardial infarction. However, the harsh microenvironment of the infarct hampers the efficacy of regenerative therapies. Ischemia-reperfusion injury dramatically increases the levels of reactive oxygen species (ROS) within the infarcted area, causing a cascade of further cellular injury. Implantable tissue engineered grafts can target this oxidative stress by delivering pharmaceutical compounds directly into the diseased tissue. Herein, we successfully fabricated electrospun polycaprolactone (PCL) fibers containing varying concentrations of ascorbic acid, a potent antioxidant well known for its ROS-scavenging capabilities. The antioxidant scaffolds displayed significantly improved scavenging of DPPH radicals, superoxide anions and hydroxyl radicals, in a dose dependent manner. Mechanical properties testing indicated that incorporation of ascorbic acid enhanced the strength and Young's modulus of the material, correlating with a moderate but non-significant increase in the crystallinity. Moreover, the scaffolds supported adhesion and maintained survival of human umbilical vein endothelial cells in vitro, indicating good cytocompatibility. These results provide motivation for the use of ascorbic acid-containing fibrous scaffolds to regulate the highly oxidative microenvironment following myocardial infarction.

Inhibition of photosensitized degradation of organic contaminants by copper under conditions typical of estuarine and coastal waters

Dissolved organic matter (DOM) driven-photochemical processes play an important role in the redox cycling of trace metals and attenuation of organic contaminants in estuarine and coastal ecosystems. In this study, we evaluate the effect of Cu on 4-carboxybenzophenone (CBBP) and Suwannee River natural organic matter (SRNOM)-photosensitized degradation of seven target contaminants (TCs) including phenols and amines under pH conditions and salt concentrations typical of those encountered in estuarine and coastal waters. Our results show that trace amounts of Cu(II) (25 -500 nM) induce strong inhibition of the photosensitized degradation of all TCs in solutions containing CBBP. The influence of TCs on the photo-formation of Cu(I) and the decrease in the lifetime of transformation intermediates of contaminants (TC^•+/ TC^•_(-H)) in the presence of Cu(I) indicated that the inhibition effect of Cu was mainly due to the reduction of TC^•+/ TC^•_(-H) by the photo-produced Cu(I). The inhibitory effect of Cu on the photodegradation of TCs decreased with the increase in Cl^- concentration since less reactive Cu(I)-Cl complexes dominate at high Cl^- concentrations. The impact of Cu on the SRNOM-sensitized degradation of TCs is less pronounced compared to that observed in CBBP solution since the redox active moieties present in SRNOM competes with Cu(I) to reduce TC^•+/ TC^•_(-H). A detailed mathematical model is developed to describe the photodegradation of contaminants and Cu redox transformations in irradiated SRNOM and CBBP solutions.

Fluorescence coupling strategies in fluorescence-activated droplet sorting (FADS) for ultrahigh-throughput screening of enzymes, metabolites, and antibodies

Fluorescence-activated droplet sorting (FADS) has emerged as a powerful tool for ultrahigh-throughput screening of enzymes, metabolites, and antibodies. Fluorescence coupling strategies (FCSs) are key to the development of new FADS methods through their coupling of analyte properties such as concentration, activities, and affinity with fluorescence signals. Over the last decade, a series of FCSs have been developed, greatly expanding applications of FADS. Here, we review recent advances in FCS for different analyte types, providing a critical comparison of the available FCSs and further classification into four categories according to their principles. We also summarize successful FADS applications employing FCSs in enzymes, metabolites, and antibodies. Further, we outline possible future developments in this area.

Fe-catalyzed sulfide oxidation in hydrothermal plumes is a source of reactive oxygen species to the ocean

Historically, the production of reactive oxygen species (ROS) in the ocean has been attributed to photochemical and biochemical reactions. However, hydrothermal vents emit globally significant inventories of reduced Fe and S species that should react rapidly with oxygen in bottom water and serve as a heretofore unmeasured source of ROS. Here, we show that the Fe-catalyzed oxidation of reduced sulfur species in hydrothermal vent plumes in the deep oceans supported the abiotic formation of ROS at concentrations 20 to 100 times higher than the average for photoproduced ROS in surface waters. ROS (measured as hydrogen peroxide) were determined in hydrothermal plumes and seeps during a series of Alvin dives at the North East Pacific Rise. Hydrogen peroxide inventories in emerging plumes were maintained at levels proportional to the oxygen introduced by mixing with bottom water. Fenton chemistry predicts the production of hydroxyl radical under plume conditions through the reaction of hydrogen peroxide with the abundant reduced Fe in hydrothermal plumes. A model of the hydroxyl radical fate under plume conditions supports the role of plume ROS in the alteration of refractory organic molecules in seawater. The ocean's volume circulates through hydrothermal plumes on timescales similar to the age of refractory dissolved organic carbon. Thus, plume-generated ROS can initiate reactions that may affect global ocean carbon inventories.

Maintenance of complex I and its supercomplexes by NDUF-11 is essential for mitochondrial structure, function and health

Mitochondrial supercomplexes form around a conserved core of monomeric complex I and dimeric complex III; wherein a subunit of the former, NDUFA11, is conspicuously situated at the interface. We identified nduf-11 (B0491.5) as encoding the Caenorhabditis elegans homologue of NDUFA11. Animals homozygous for a CRISPR-Cas9-generated knockout allele of nduf-11 arrested at the second larval (L2) development stage. Reducing (but not eliminating) expression using RNAi allowed development to adulthood, enabling characterisation of the consequences: destabilisation of complex I and its supercomplexes and perturbation of respiratory function. The loss of NADH dehydrogenase activity was compensated by enhanced complex II activity, with the potential for detrimental reactive oxygen species (ROS) production. Cryo-electron tomography highlighted aberrant morphology of cristae and widening of both cristae junctions and the intermembrane space. The requirement of NDUF-11 for balanced respiration, mitochondrial morphology and development presumably arises due to its involvement in complex I and supercomplex maintenance. This highlights the importance of respiratory complex integrity for health and the potential for its perturbation to cause mitochondrial disease. This article has an associated First Person interview with Amber Knapp-Wilson, joint first author of the paper.

Antioxidant/pro-oxidant and antiproliferative activities of phenolic-rich foods and extracts: A cell-based point of view

Phenolic compounds have demonstrated several in vitro beneficial properties by acting as antioxidant and pro-oxidant agents. This chapter approaches the relationship among oxidative stress, cancer, phenolic compounds and antiproliferative activity. Moreover, it discusses in vitro techniques and their biological applications, regarding cell viability and intracellular measure of reactive oxygen assays. The in vitro methods are important tools for screening and understanding the pathways involved on antiproliferative and antioxidant/pro-oxidant effects of phenolic compounds. These findings open avenues for the development of innovative food, chemical structures, technological applications and future perspectives in this research field.

Redox-based colorimetric sensing of H2O2 after removal of antioxidants with ABTS radical oxidation

Monitoring and determining H₂O₂ in many industries, treatment plants and biochemical media is important because of its harmful effects even at low concentrations. This work proposes a redox-based colorimetric sensor for the determination of hydrogen peroxide in the presence of antioxidants which are known interferents causing positive errors. On the other hand, the widely used peroxidase-based methods are interfered by enzyme inhibitors. The proposed method consists of two stages, namely antioxidant removal and H₂O₂ determination. In the first step, antioxidants were removed simply using ABTS radical (ABTS⁺) oxidant produced by persulfate. After antioxidant elimination, H₂O₂ in samples was determined by using the CUPRAC colorimetric sensor. The CUPRAC reagent, copper (II)-neocuproine (Cu(II)-Nc), immobilized on a Nafion persulfonate membrane was used for sensor preparation. The light blue Cu(II)-Nc was reduced by H₂O₂ to the yellow-orange colored Cu(I)-Nc chelate on the sensor, and the absorbance increase at 450 nm was recorded. The LOD and the LOQ values obtained for H₂O₂ were 0.33 and 1.10 µM, respectively. The proposed assay was validated in terms of linearity, additivity, precision and recovery. The H₂O₂ contents of spiked food extracts, synthetic serum and certain commercial products (i.e. food sterilization solution, whitening toothpaste and hair bleaching solution) were found to be comparable to the results of peroxidase-ABTS and titanyl sulfate reference assays. In addition, peroxide-type explosive triacetone triperoxide (TATP) was successfully determined in the presence of amine-type antioxidants. The proposed simple and low-cost assay is not inhibited by environmental agents (heavy metals, pesticides, sulfhydryl agents, etc.) adversely affecting enzymatic methods. It is additionally insensitive to turbidity and colored components of complex samples.

Unraveling the roles of the reductant and free copper ions in LPMO kinetics

BACKGROUND

Lytic polysaccharide monooxygenases (LPMOs) are monocopper enzymes that catalyze oxidative depolymerization of industrially relevant crystalline polysaccharides, such as cellulose, in a reaction that depends on an electron donor and O2 or H2O2. While it is well known that LPMOs can utilize a wide variety of electron donors, the variation in reported efficiencies of various LPMO-reductant combinations remains largely unexplained.

RESULTS

In this study, we describe a novel two-domain cellulose-active family AA10 LPMO from a marine actinomycete, which we have used to look more closely at the effects of the reductant and copper ions on the LPMO reaction. Our results show that ascorbate-driven LPMO reactions are extremely sensitive to very low amounts (micromolar concentrations) of free copper because reduction of free Cu(II) ions by ascorbic acid leads to formation of H2O2, which speeds up the LPMO reaction. In contrast, the use of gallic acid yields steady reactions that are almost insensitive to the presence of free copper ions. Various experiments, including dose-response studies with the enzyme, showed that under typically used reaction conditions, the rate of the reaction is limited by LPMO-independent formation of H2O2 resulting from oxidation of the reductant.

CONCLUSION

The strong impact of low amounts of free copper on LPMO reactions with ascorbic acid and O2, i.e. the most commonly used conditions when assessing LPMO activity, likely explains reported variations in LPMO rates. The observed differences between ascorbic acid and gallic acid show a way of making LPMO reactions less copper-dependent and illustrate that reductant effects on LPMO action need to be interpreted with great caution. In clean reactions, with minimized generation of H2O2, the (O2-driven) LPMO reaction is exceedingly slow, compared to the much faster peroxygenase reaction that occurs when adding H2O2.

Simple Electrochemical Synthesis of Polyethylenimine-Encapsulated Ag Nanoparticles from Solid AgCl Applied in Catalytic Reduction of H2O2

We report a simple and environmentally friendly synthesis of polyethylenimine (PEI)-encapsulated Ag nanoparticles (AgNPs) by a direct electroreduction of solid AgCl. The AgNPs, characterized by field-emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), and energy dispersive X-ray spectroscopy (EDS), revealed that AgNPs diameters (100–500 nm) depended on the loading of the AgCl precursor. Using cyclic voltammetry (CV), it was confirmed that the AgNPs had a catalytic effect on the electrochemical reduction of H2O2. The obtained AgNPs were subsequently used to construct an electrochemical H2O2 sensor exhibiting a low detection limit (1.66 μM) and a wide linear response range, with real-life tests indicating an insensitivity to common interferents and confirming the potential use of the developed technique in diverse applications.

Expression of the Tyrosine Hydroxylase Gene from Rat Leads to Oxidative Stress in Potato Plants

Catecholamines are biogenic aromatic amines common among both animals and plants. In animals, they are synthesized via tyrosine hydroxylation, while both hydroxylation or decarboxylation of tyrosine are possible in plants, depending on the species, though no tyrosine hydroxylase-a counterpart of the animal enzyme-has been identified yet. It is known that in potato plants, it is the decarboxylation of tyrosine that leads to catecholamine production. In this paper, we present the effects of the induction of an alternative route of catecholamine production by introducing the tyrosine hydroxylase gene from rat. We demonstrate that an animal system can be used by the plant. However, it does not function to synthesize catecholamines. Instead, it leads to elevated reactive oxygen species content and a constant stress condition in the plant, which responds with elevated antioxidant levels and improved resistance to infection.

Distinct effects of copper on the degradation of β-lactam antibiotics in fulvic acid solutions during light and dark cycle

This study revealed the dual roles of Cu(II) on the β-lactam antibiotics degradation in Suwannee River fulvic acid (SRFA) solution during day and night cycle. Amoxicillin (AMX) and ampicillin (AMP) were selected as the representative β-lactam antibiotics. Cu(II) played a key role in the dark degradation of AMX and AMP via catalytic hydrolysis and oxidation. However, Cu(II) mainly exhibited an inhibitory effect on SRFA-involved photochemical degradation of AMX and AMP. In the presence of 500 nM of Cu(II), the degradation rate of AMX and AMP in the light condition were around 5 times higher than that in the dark condition, suggesting the photodegradation of β-lactam antibiotics was much more pronounced than catalyzed hydrolysis and oxidation. The triplet excited state of SRFA (³SRFA∗) primarily contributed to AMX and AMP photodegradation. Hydroxyl radicals (^•OH) and singlet oxygen (¹O₂) exhibited limit impacts. The redox cycle of Cu(II)/Cu(I) restricted the electron transfer pathway of ³SRFA∗ with AMX and AMP. During the day and night cycles for 48 h, Cu(II) served as a stronger inhibitor rather than a promotor. These findings highlight the interactions between Cu(II) and SRFA are distinct under day and night conditions, which could further affect the fate of β-lactam antibiotics in natural environments.

Lysin cell-binding domain-functionalized magnetic beads for detection of Staphylococcus aureus via inhibition of fluorescence of Amplex Red/hydrogen peroxide assay by intracellular catalase

Accurate and rapid identification of Staphylococcus aureus (S. aureus) is of great significance for controlling the food poisoning and infectious diseases caused by S. aureus. In this study, a novel strategy that combines lysin cell-binding domain (CBD)-based magnetic separation with fluorescence detection was developed for the specific and sensitive quantification of S. aureus in authentic samples. The S. aureus cells were separated from the sample matrix by lysin CBD-functionalized magnetic beads. Following lysis by lysostaphin, intracellular catalase was released from S. aureus cells and detected by a fluorometric system composed of horseradish peroxidase (HRP), hydrogen peroxide (H₂O₂), and Amplex Red. S. aureus was quantified via the inhibitory effect of the released intracellular catalase on the fluorometric system since the catalase could decompose the H₂O₂. Optimized conditions afforded a calibration curve for S. aureus ranging from 1.0 × 10² to 1.0 × 10⁷ CFU mL^-1. The detection limit was as low as 78 CFU mL^-1 in phosphate-buffered saline (PBS), and the total detection process could be completed in less than 50 min. Other bacteria associated with common food-borne and nosocomial infections negligibly interfered with S. aureus detection, except for Staphylococcus epidermidis, which may have slightly interfered. Moreover, the potential of this proposed method for practical applications has been demonstrated by detection assays of sterilized milk and human serum. Graphical abstract.

UV-C irradiated gallic acid exhibits enhanced antimicrobial activity via generation of reactive oxidative species and quinone

A novel light-enhanced antimicrobial treatment was developed by exposing gallic acid (GA) to UV-C light. GA (15 mM) solution was exposed to UV-C for 30 min and subsequently incubated with E. coli O157:H7 for 30 min to achieve a 3.2 ± 0.2 log CFU/mL reduction. The antimicrobial activity is affected by the irradiation duration, wavelength, and pH of solution. The addition of benzenesulfinic acid (BSA) to UV-C irradiated GA lowered (P < 0.05) its antimicrobial activity, indicating that quinones contributed to its overall antimicrobial effect. In addition, the attenuated (P < 0.05) antimicrobial activity of UV-C exposed GA in the presence of reactive oxidative species (ROS) quenchers, the generation of hydrogen peroxide, and increased levels of intracellular oxidative stress detected in E. coli O157:H7 illustrated that ROS also played a role in the antimicrobial effect of UV-C irradiated GA. UV-C irradiated GA could be applied as a novel antimicrobial in food systems.

Exhaled breath condensate hydrogen peroxide, pH and leukotriene B4 are associated with lower airway inflammation and airway cytology in the horse

BACKGROUND

Exhaled breath condensate (EBC) analysis is a noninvasive method to assess the lower respiratory tract. In human subjects, EBC hydrogen peroxide (H₂ O₂ ), pH and leukotriene B₄ (LTB₄ ) are useful for detection and monitoring of inflammatory lung diseases, including asthma.

OBJECTIVES

To determine associations between EBC biomarkers and cytological and endoscopic definitions of lower airway inflammation (LAI) while controlling for sampling and environmental variables.

STUDY DESIGN

Prospective, cross-sectional study.

METHODS

Clinical, endoscopic and airway cytological findings from 47 horses were compared with EBC pH and concentrations of H₂ O₂ and LTB₄ by univariate and multivariable analyses. Dichotomous (presence/absence of airway inflammation) and continuous outcome variables (differential cell counts in tracheal aspirate and bronchoalveolar lavage fluid, BALF) were evaluated and potential effects of collection and methodological factors were included.

RESULTS

EBC pH and H₂ O₂ concentrations were higher in horses with LAI and both were positively associated with the percentage of neutrophils in BALF (P<0.05). Mast cell percentage in BALF was negatively associated with EBC pH, and BALF eosinophil percentage was positively associated with EBC LTB₄ (P<0.05). Ambient temperature, relative humidity and assay methodology significantly impacted some analytes.

MAIN LIMITATIONS

LAI is challenging to categorise due to a variety of clinical and cytological phenotypes. Although the study was designed to overcome this limitation, numbers of horses were small in some categories.

CONCLUSIONS

EBC pH and H₂ O₂ concentrations are altered by airway inflammation, suggesting a role for these biomarkers in the diagnosis and monitoring of airway disease. Environmental and methodological factors can influence these biomarkers and should be considered in the interpretation of results.

Copper Inhibition of Triplet-Induced Reactions Involving Natural Organic Matter

The triplet excited state of natural organic matter (³NOM*) is an important reactive intermediate in sensitizing transformation of a wide range of environmentally relevant organic compounds, but the impact of trace metals on the fate and reactivity of ³NOM* is poorly understood. In this study, we investigate the effect of low concentrations of copper on ³NOM*-mediated oxidation (electron transfer) and energy transfer reactions. The oxidative efficiency of ³NOM* from Suwannee River NOM (SRNOM) and the widely used model triplet sensitizer 4-carboxybenzophenone were determined by measuring the photooxidation of 2,4,6-trimethylphenol (TMP). The pseudo-first-order photooxidation rate constants of TMP decreased markedly in the presence of trace amounts of Cu(II) (25-500 nM) with the decrease associated with the continuous reduction of the oxidation intermediates of TMP (i.e., TMP^•_(-H)) by the photochemically produced Cu(I). A kinetic model is developed that adequately describes the Cu inhibition effect in TMP photooxidation in irradiated SRNOM solutions. The ³NOM* energy transfer ability was assessed by measuring the isomerization of sorbic acid with the rate of this process markedly retarded in the presence of significantly higher (micromolar) concentrations of Cu(II) than previously used. This result is attributed to (i) decreased formation of high energy ³NOM* due to formation of Cu-NOM complexes and (ii) increased loss of ³NOM* as a result of quenching by Cu. Since ³NOM* is the precursor to singlet oxygen (¹O₂) formation, the steady-state concentrations of ¹O₂ also decreased in the presence of micromolar concentrations of Cu(II) with the quenching rate constant of ³NOM* by Cu calculated to be 1.08 × 10¹⁰ M^-1 s^-1.

Evaluation of colorimetric assays for determination of H2O2in planta during fungal wood decomposition

Hydrogen peroxide (H₂O₂) plays a critical role in generating oxygen radicals as fungi attack and deconstruct plant cell walls. Its concentrations in planta, however, are often low during decomposition and evade detection by traditional methods. Here, we compared relevant methods and selected the best based on detection limits and selectivity.

Overcoming Reductant Interference in Peroxidase-Based Assays for Hydrogen Peroxide Quantification

A problem commonly encountered when using peroxidase-based methods for hydrogen peroxide quantification in biobased matrixes is interference due to the presence of endogenous reductants. Such assays are typically based on the generation of an oxidized reporter molecule in direct proportion to the amount of hydrogen peroxide reduced in the peroxidase-catalyzed reaction. Endogenous reductants confound such assays by reducing the oxidized reporter molecule, thus resulting in underestimates of hydrogen peroxide content. In the present work, we demonstrate how this problem can be circumvented by selectively oxidizing offending compounds by treatment with the oxidized reporter molecule prior to initiating the peroxidase reaction for hydrogen peroxide quantification. The approach is demonstrated using horseradish peroxidase, 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), as the reporter molecule and a representative garlic paste as the hydrogen peroxide-containing biobased matrix. The approach is expected to be generally applicable to a wide range of peroxidase-based assays when applied to complex biobased systems.