The amplex red/horseradish peroxidase assay requires superoxide dismutase to measure hydrogen peroxide in the presence of NAD(P)H

NADPH Alters DUOX1 Calcium Responsiveness

Hydrogen peroxide is a key element in redox signaling and in setting cellular redox tone. DUOX1 and DUOX2, that directly synthesize hydrogen peroxide, are the most abundant NADPH oxidase transcripts in most epithelia. DUOX1 and DUOX2 hydrogen peroxide synthesis is regulated by intracellular calcium transients and thus cells can respond to signals and initiate responses by increasing cellular hydrogen peroxide synthesis. Nevertheless, many details of their enzymatic regulation are still unexplored. DUOX1 and DUOXA1 were expressed in HEK293T cells and activity was studied in homogenates and membrane fractions. When DUOX1 homogenates or membranes were pre-incubated in NADPH and started with addition of Ca2+, to mimic intracellular activation, progress curves were distinctly different from those pre-incubated in Ca2+ and started with NADPH. The Ca2+ EC50 for DUOX1's initial rate when pre-incubated in Ca2+, was three orders of magnitude lower (EC50 ∼ 10-6 M) than with preincubation in NADPH (EC50 ∼ 10-3 M). In addition, activity was several fold lower with Ca2+ start. Identical results were obtained using homogenates and membrane fractions. The data suggested that DUOX1 Ca2+ binding in expected physiological signaling conditions only slowly leads to maximal hydrogen peroxide synthesis and that full hydrogen peroxide synthesis activity in vivo only can occur when encountering extremely high concentration Ca2+ signals. Thus, a complex interplay of intracellular NADPH and Ca2+ concentrations regulate DUOX1 over a wide extent and may limit DUOX1 activity to a restricted range and spatial distribution.

Addressing Cardiovascular Toxicity Risk of Electronic Nicotine Delivery Systems in the Twenty-First Century: "What Are the Tools Needed for the Job?" and "Do We Have Them?"

Cigarette smoking is positively and robustly associated with cardiovascular disease (CVD), including hypertension, atherosclerosis, cardiac arrhythmias, stroke, thromboembolism, myocardial infarctions, and heart failure. However, after more than a decade of ENDS presence in the U.S. marketplace, uncertainty persists regarding the long-term health consequences of ENDS use for CVD. New approach methods (NAMs) in the field of toxicology are being developed to enhance rapid prediction of human health hazards. Recent technical advances can now consider impact of biological factors such as sex and race/ethnicity, permitting application of NAMs findings to health equity and environmental justice issues. This has been the case for hazard assessments of drugs and environmental chemicals in areas such as cardiovascular, respiratory, and developmental toxicity. Despite these advances, a shortage of widely accepted methodologies to predict the impact of ENDS use on human health slows the application of regulatory oversight and the protection of public health. Minimizing the time between the emergence of risk (e.g., ENDS use) and the administration of well-founded regulatory policy requires thoughtful consideration of the currently available sources of data, their applicability to the prediction of health outcomes, and whether these available data streams are enough to support an actionable decision. This challenge forms the basis of this white paper on how best to reveal potential toxicities of ENDS use in the human cardiovascular system-a primary target of conventional tobacco smoking. We identify current approaches used to evaluate the impacts of tobacco on cardiovascular health, in particular emerging techniques that replace, reduce, and refine slower and more costly animal models with NAMs platforms that can be applied to tobacco regulatory science. The limitations of these emerging platforms are addressed, and systems biology approaches to close the knowledge gap between traditional models and NAMs are proposed. It is hoped that these suggestions and their adoption within the greater scientific community will result in fresh data streams that will support and enhance the scientific evaluation and subsequent decision-making of tobacco regulatory agencies worldwide.

Tissue-specific differences in Ca2+ sensitivity of the mitochondrial permeability transition pore (PTP). Experiments in male rat liver and heart

Permeability transition pore (PTP) opening dissipates ion and electron gradients across the internal mitochondrial membrane (IMM), including excess Ca2+ in the mitochondrial matrix. After opening, immediate PTP closure must follow to prevent outer membrane disruption, loss of cytochrome c, and eventual apoptosis. Flickering, defined as the rapid alternative opening/closing of PTP, has been reported in heart, which undergoes frequent, large variations in Ca2+. In contrast, in tissues that undergo depolarization events less often, such as the liver, PTP would not need to be as dynamic and thus these tissues would not be as resistant to stress. To evaluate this idea, it was decided to follow the reversibility of the permeability transition (PT) in isolated murine mitochondria from two different tissues: the very dynamic heart, and the liver, which suffers depolarizations less frequently. It was observed that in heart mitochondria PT remained reversible for longer periods and at higher Ca2+ loads than in liver mitochondria. In all cases, Ca2+ uptake was inhibited by ruthenium red and PT was delayed by Cyclosporine A. Characterization of this phenomenon included measuring the rate of oxygen consumption, organelle swelling and Ca2+ uptake and retention. Results strongly suggest that there are tissue-specific differences in PTP physiology, as it resists many more Ca2+ additions before opening in a highly active organ such as the heart than in an organ that seldom suffers Ca2+ loading, such as the liver.

Dual-Mode Virus Detection: Combining Electrochemical and Fluorescence Modalities for Enhanced Sensitivity and Reliability

This study introduces a dual-mode biosensor specifically designed for the quantitative detection of viruses in rapid analysis. The biosensor is unique in its use of both optical (fluorescence) and electrochemical (impedance) detection methods using the same nanocomposites, providing a dual confirmation system for virus (norovirus-like particles) quantification. The system is based on using two antibody-conjugated nanocomposites: CdSeS quantum dots and Au-N,S-GQD nanocomposites. For optical detection, the principle relies on the fluorescence quenching of CdSeS by Au-N,S-GQD in a sandwich structure with the target. Conversely, electrochemical detection is based on the change in impedance caused by the formation of the same sandwich structure. The biosensor demonstrated exceptional sensitivity, capable of detecting norovirus at concentrations of as low as femtomolar in the electrochemical method and picomolar in the optical method. In the dual-responsive concentration range from 10-13 to 10-10 M, the sensor is highly sensitive in both methods, creating significant changes in fluorescence intensity and impedance in the presence of virus. Furthermore, the biosensor exhibits a high degree of specificity, with a negligible response to nontarget proteins, even within complex test solutions. This work represents a significant advancement in the field of biosensor technology, offering a fast, accurate, and reliable method for diagnosing viral infections and diseases.

Exploring the partial degradation of polysaccharides: Structure, mechanism, bioactivities, and perspectives

Polysaccharides are promising biomolecules with lowtoxicity and diverse bioactivities in food processing and clinical drug development. However, an essential prerequisite for their applications is the fine structure characterization. Due to the complexity of polysaccharide structure, partial degradation is a powerful tool for fine structure analysis, which can effectively provide valid information on the structure of backbone and branching glycosidic fragments of complex polysaccharides. This review aims to conclude current methods of partial degradation employed for polysaccharide structural characterization, discuss the molecular mechanisms, and describe the molecular structure and solution properties of degraded polysaccharides. In addition, the effects of polysaccharide degradation on the conformational relationships between the molecular structure and bioactivities, such as antioxidant, antitumor, and immunomodulatory activities, are also discussed. Finally, we summarize the prospects and current challenges for the partial degradation of polysaccharides. This review will be of great value for the scientific elucidation of polysaccharide fine structures and potential applications.

Distinct effects of form selective cytochrome P450 inhibitors on cytochrome P450-mediated monooxygenase and hydrogen peroxide generating NADPH oxidase

A characteristic of cytochrome P450 (CYP) enzymes is their ability to generate H₂O₂, either directly or indirectly via superoxide anion, a reaction referred to as "NADPH oxidase" activity. H₂O₂ production by CYPs can lead to the accumulation of cytotoxic reactive oxygen species which can compromise cellular functioning and contribute to tissue injury. Herein we determined if form selective CYP inhibitors could distinguish between the activities of the monooxygenase and NADPH oxidase activities of rat recombinant CYP1A2, CYP2E1, CYP3A1 and CYP3A2 and CYP1A1/2-enriched β-naphthoflavone-induced rat liver microsomes, CYP2E1-enriched isoniazide-induced rat liver microsomes and CYP3A subfamily-enriched dexamethasone-induced rat liver microsomes. In the presence of 7,8-benzoflavone (2.0 μM) for CYP1A2 and 4-methylpyrazole (32 μM) or DMSO (16 mM) for CYP2E1, monooxygenase activity was blocked without affecting NADPH oxidase activity for both the recombinant enzymes and microsomal preparations. Ketoconazole (1.0 μM), a form selective inhibitor for CYP3A subfamily enzymes, completely inhibited monooxygenase activity of rat recombinant CYP3A1/3A2 and CYP3A subfamily in rat liver microsomes; it also partially inhibited NADPH oxidase activity. 7,8-benzoflavone is a type I ligand, which competes with substrate binding, while 4-methylpyrazole and DMSO are type II heme binding ligands. Interactions of heme with these type II ligands was not sufficient to interfere with oxygen activation, which is required for NADPH oxidase activity. Ketoconazole, a type II ligand known to bind multiple sites on CYP3A subfamily enzymes in close proximity to heme, also interfered, at least in part, with oxygen activation. These data indicate that form specific inhibitors can be used to distinguish between monooxygenase reactions and H₂O₂ generating NADPH oxidase of CYP1A2 and CYP2E1. Mechanisms by which ketoconazole inhibits CYP3A NADPH oxidase remain to be determined.

Free radical-mediated degradation of polysaccharides: Mechanism of free radical formation and degradation, influence factors and product properties

Increasing studies focus on the degradation of polysaccharides by free radicals. The review mainly provides an overview of degradation of polysaccharides by free radicals generated from hydrogen peroxide (H₂O₂). Evidence suggests that free radicals generated from H₂O₂ can be generated by various mechanisms. It broke glycosidic bonds mainly through hydrogen abstraction, causing the degradation of polysaccharides. Its degradation efficiency is affected by many factors, such as the concentration of polysaccharides and H₂O₂, temperature and pH. In addition, free radical degradation could change the physicochemical and structural properties of polysaccharides, such as water solubility, thermal stability, molecular weight, monosaccharide composition, apparent morphology, and chain conformation, but it had little effects on the primary structure of polysaccharides. Besides, free radical degradation could also improve the bioactivities of polysaccharides, including antioxidant, antitumor and anticoagulant activities.

Photooxidation-induced fluorescence amplification system for an ultra-sensitive enzyme-linked immunosorbent assay (ELISA)

This report suggests a method of enhancing the sensitivity of chemifluorescence-based ELISA, using photooxidation-induced fluorescence amplification (PIFA). The PIFA utilized autocatalytic photooxidation of the chemifluorescent substrate, 10-acetyl 3,7-dihydroxyphenoxazine (ADHP, Amplex Red) to amplify the fluorescent product resorufin, initially oxidized by horse radish peroxidase (HRP). As the amplification rate is proportional to the initial level of resorufin, the level of antigen labeled by HRP is quantified by analyzing the profile of fluorescence intensity. The normalized profile was interpolated into an autocatalysis model, and the rate of increase at half-maximum time was quantified by the use of an amplification index (AI). The lower limit of detection, for resorufin or HRP, was less than one-tenth that of the plate reader. It requires only slight modification of the fluorescence reader and is fully compatible with conventional or commercial ELISA. When it is applied to a commercial ELISA kit for the detection of amyloid beta, it is verified that the PIFA assay enhanced the detection sensitivity by more than a factor of 10 and was compatible with a conventional 96-well ELISA assay kit. We anticipate this PIFA assay to be used in research for the detection of low levels of proteins and for the early diagnosis of various diseases with rare protein biomarkers, at ultra-low (pg/mL) concentrations.