A palette of fluorescent probes with varying emission colors for imaging hydrogen peroxide signaling in living cells

Electron spin resonance and fluorescence imaging assisted electrochemical approach for accurate and comprehensive monitoring of cellular hydrogen peroxide dynamics

A new analytical system combining electrochemistry, ESR, and fluorescence imaging for accurately and comprehensively measuring the dynamics of cellular H₂O₂.

Design, synthesis and properties of a reactive chromophoric/fluorometric probe for hydrogen peroxide detection

A succinct chromophoric/fluorometric probe, AVPM, for sensitive and selective H₂O₂detection.

An RGB color-tunable turn-on electrofluorochromic device and its potential for information encryption

RGB color-tunable electrofluorochromic devices with a turn-on mode were fabricated successfully and applied for the first time in encrypted information storage and display.

Reaction-based indicator displacement assay (RIA) for the colorimetric and fluorometric detection of hydrogen peroxide

Reaction-based indicator displacement assay for the optical cycle-monitoring of hydrogen peroxide.

Ratiometric Sensing of Hydrogen Peroxide Utilizing Conformational Change in Fluorescent Boronic Acid Polymers

We demonstrate that the copolymers containing boronic acid and pyrene units can be utilized for the fluorometric sensing of hydrogen peroxide (H₂O₂) in aqueous solutions. The copolymer exists in a relatively extended conformation in the absence of H₂O₂, whereas the polymer chain is contracted by the reaction of boronic acid moieties with H₂O₂ to form phenol groups. This conformational change induces aggregation of the originally isolated pyrene groups. As a result, relative intensity of excimer emission with respect to monomer emission increases with H₂O₂ concentration. Accordingly, the present methodology enables us to measure H₂O₂ by means of ratiometric fluorescence change in the range of 0-30 μM.

Long-wavelength fluorescent boronate probes for the detection and intracellular imaging of peroxynitrite

Two boronate fluorescent probes have been developed for the detection of peroxynitrite (TCFB1andTCFB2).

Effective killing of cancer cells and regression of tumor growth by K27 targeting sulfiredoxin

Cancer cells have been suggested to be more susceptible to oxidative damages and highly dependent on antioxidant capacity in comparison with normal cells, and thus targeting antioxidant enzymes has been a strategy for effective cancer treatment. Sulfiredoxin (Srx) is an enzyme that catalyzes the reduction of sulfinylated peroxiredoxins and thereby reactivates them. In this study we developed a Srx inhibitor, K27 (N-[7-chloro-2-(4-fluorophenyl)-4-quinazolinyl]-N-(2-phenylethyl)-β-alanine), and showed that it induces the accumulation of sulfinylated peroxiredoxins and oxidative stress, which leads to mitochondrial damage and apoptotic death of cancer cells. The effects of K27 were significantly reversed by ectopic expression of Srx or antioxidant N-acetyl cysteine. In addition, K27 led to preferential death of tumorigenic cells over non-tumorigenic cells, and suppressed the growth of xenograft tumor without acute toxicity. Our results suggest that targeting Srx might be an effective therapeutic strategy for cancer treatment through redox-mediated cell death.

Real-Time Fluorescence Measurements of ROS and [Ca2+] in Ischemic / Reperfused Rat Hearts: Detectable Increases Occur only after Mitochondrial Pore Opening and Are Attenuated by Ischemic Preconditioning

Mitochondrial permeability transition pore (mPTP) opening is critical for ischemia / reperfusion (I/R) injury and is associated with increased [Ca²⁺] and reactive oxygen species (ROS). Here we employ surface fluorescence to establish the temporal sequence of these events in beating perfused hearts subject to global I/R. A bespoke fluorimeter was used to synchronously monitor surface fluorescence and reflectance of Langendorff-perfused rat hearts at multiple wavelengths, with simultaneous measurements of hemodynamic function. Potential interference by motion artefacts and internal filtering was assessed and minimised. Re-oxidation of NAD(P)H and flavoproteins on reperfusion (detected using autofluorescence) was rapid (t_0.5 < 15 s) and significantly slower following ischemic preconditioning (IP). This argues against superoxide production from reduced Complex 1 being a critical mediator of initial mPTP opening during early reperfusion. Furthermore, MitoPY1 (a mitochondria-targeted H₂O₂-sensitive fluorescent probe) and aconitase activity measurements failed to detect matrix ROS increases during early reperfusion. However, two different fluorescent cytosolic ROS probes did detect ROS increases after 2–3 min of reperfusion, which was shown to be after initiation of mPTP opening. Cyclosporin A (CsA) and IP attenuated these responses and reduced infarct size. [Ca²⁺]_i (monitored with Indo-1) increased progressively during ischemia, but dropped rapidly within 90 s of reperfusion when total mitochondrial [Ca²⁺] was shown to be increased. These early changes in [Ca²⁺] were not attenuated by IP, but substantial [Ca²⁺] increases were observed after 2–3 min reperfusion and these were prevented by both IP and CsA. Our data suggest that the major increases in ROS and [Ca²⁺] detected later in reperfusion are secondary to mPTP opening. If earlier IP-sensitive changes occur that might trigger initial mPTP opening they are below our limit of detection. Rather, we suggest that IP may inhibit initial mPTP opening by alternative mechanisms such as prevention of hexokinase 2 dissociation from mitochondria during ischemia.

Sensitive detection and estimation of cell-derived peroxynitrite fluxes using fluorescein-boronate

The specific and sensitive detection of peroxynitrite (ONOO^-/ONOOH) in biological systems is a great challenge due to its high reactivity towards several biomolecules. Herein, we validated the advantages of using fluorescein-boronate (Fl-B) as a highly sensitive fluorescent probe for the direct detection of peroxynitrite under biologically-relevant conditions in two different cell models. The synthesis of Fl-B was achieved by a very simply two-step conversion synthetic route with high purity (>99%) and overall yield (∼42%). Reactivity analysis of Fl-B with relevant biological oxidants including hydrogen peroxide (H₂O₂), hypochlorous acid (HOCl) and peroxynitrite were performed. The rate constant for the reaction of peroxynitrite with Fl-B was 1.7×10⁶M^-1s^-1, a million times faster than the rate constant measured for H₂O₂ (k=1.7M^-1s^-1) and 2,700 faster than HOCl (6.2×10²M^-1s^-1) at 37°C and pH 7.4. The reaction of Fl-B with peroxynitrite was significant even in the presence of physiological concentrations of CO₂, a well-known peroxynitrite reactant. Experimental and simulated kinetic analyses confirm that the main oxidation process of Fl-B takes place with peroxynitrite itself via a direct bimolecular reaction and not with peroxynitrite-derived radicals. Fl-B was successfully applied for the detection of endogenously-generated peroxynitrite by endothelial cells and in macrophage-phagocyted parasites. Moreover, the generated data allowed estimating the actual intracellular flux of peroxynitrite. For instance, ionomycin-stimulated endothelial cells generated peroxynitrite at a rate of ∼ 0.1μMs^-1, while immunostimulated macrophages do so in the order of ∼1μMs^-1 inside T. cruzi-infected phagosomes. Fl-B revealed not to be toxic in concentrations up to 1mM for 24h. Cellular peroxynitrite detection was achieved by conventional laboratory fluorescence-based methods including flow cytometry and epi-fluorescence microscopy. Fl-B was shown to be more sensitive than the coumarin boronate due to a higher molar absorption coefficient and quantum yield. Overall, our results show that Fl-B is a kinetically selective and highly sensitive probe for the direct detection of cell-derived peroxynitrite.

A NIR fluorescent probe: imaging endogenous hydrogen peroxide during an autophagy process induced by rapamycin

In this work, a near-infrared probe (Cy-B) with high sensitivity, and good specificity as well as photo-stability has been developed for monitoring both exogenous and endogenous H₂O₂ in living cells. To the best of our knowledge, it was applied successfully for the first time to monitor spontaneous hydrogen peroxide in an autophagy process induced by the stimulation of rapamycin. The mice imaging experiments indicate that the probe has a good potential to be employed in the imaging of living biological systems.

The antioxidant transcription factor Nrf2 contributes to the protective effect of mild thermotolerance (40°C) against heat shock-induced apoptosis

The exposure of cells to low doses of stress induces adaptive survival responses that protect cells against subsequent exposure to toxic stress. The ability of cells to resist subsequent toxic stress following exposure to low dose heat stress at 40°C is known as mild thermotolerance. Mild thermotolerance involves increased expression of heat shock proteins and antioxidants, but the initiating factors in this response are not understood. This study aims to understand the role of the Nrf2 antioxidant pathway in acquisition of mild thermotolerance at 40°C, and secondly, whether the Nrf2 pathway could be involved in the protective effect of thermotolerance against heat-shock (42°C)-induced apoptosis. During cell preconditioning at 40°C, protein expression of the Nrf2 transcription factor increased after 15-60min. In addition, levels of the Nrf2 targets MnSOD, catalase, heme oxygenase-1, glutamate cysteine ligase and Hsp70 increased at 40°C. Levels of these Nrf2 targets were enhanced by Nrf2 activator oltipraz and decreased by shRNA targeting Nrf2. Levels of pro-oxidants increased after 30-60min at 40°C. Pro-oxidant levels were decreased by oltipraz and increased by knockdown of Nrf2. Increased Nrf2 expression and catalase activity at 40°C were inhibited by the antioxidant PEG-catalase and by p53 inhibitor pifithrin-α. These results suggest that mild thermotolerance (40°C) increases cellular pro-oxidant levels, which in turn activate Nrf2 and its target genes. Moreover, Nrf2 contributes to the protective effect of thermotolerance against heat-shock (42°C)-induced apoptosis, because Nrf2 activation by oltipraz enhanced thermotolerance, whereas Nrf2 knockdown partly reversed thermotolerance. Improved knowledge about the different protective mechanisms that mild thermotolerance can activate is crucial for the potential use of this adaptive survival response to treat stress-related diseases.

Selenoprotein H is an essential regulator of redox homeostasis that cooperates with p53 in development and tumorigenesis

Selenium, an essential micronutrient known for its cancer prevention properties, is incorporated into a class of selenocysteine-containing proteins (selenoproteins). Selenoprotein H (SepH) is a recently identified nucleolar oxidoreductase whose function is not well understood. Here we report that seph is an essential gene regulating organ development in zebrafish. Metabolite profiling by targeted LC-MS/MS demonstrated that SepH deficiency impairs redox balance by reducing the levels of ascorbate and methionine, while increasing methionine sulfoxide. Transcriptome analysis revealed that SepH deficiency induces an inflammatory response and activates the p53 pathway. Consequently, loss of seph renders larvae susceptible to oxidative stress and DNA damage. Finally, we demonstrate that seph interacts with p53 deficiency in adulthood to accelerate gastrointestinal tumor development. Overall, our findings establish that seph regulates redox homeostasis and suppresses DNA damage. We hypothesize that SepH deficiency may contribute to the increased cancer risk observed in cohorts with low selenium levels.

Simultaneous fluorescence imaging of hydrogen peroxide in mitochondria and endoplasmic reticulum during apoptosis

Cell apoptosis is a biochemical and molecular pathway essential for maintaining cellular homeostasis. It is an integrated process involving in a series of signal transduction cascades. Moreover, the apoptotic pathways may be initiated inside various subcellular organelles. Increasing evidence indicates that hydrogen peroxide (H2O2) is closely related to cell apoptosis, particularly in the mitochondria. However, during the apoptotic process, the synergetic variation of H2O2 levels in different compartments is seldom explored, particularly in two important organelles: mitochondria and endoplasmic reticulum (ER). To solve this problem, we developed two new organelle-specific fluorescent probes termed MI-H2O2 and ER-H2O2 that can detect H2O2 in mitochondria and ER, respectively or simultaneously. Experimental results demonstrated that MI-H2O2 and ER-H2O2 display distinguishable excitation and emission spectra, as well as excellent organelle targeting capabilities. Therefore, we used MI-H2O2 and ER-H2O2 to successfully image exogenous or endogenous hydrogen peroxide in the mitochondria and ER. Interestingly, during diverse apoptotic stimuli, dual-color fluorescence imaging results revealed that the changes of H2O2 levels in mitochondria and ER are different. The H2O2 levels are enhanced in both the mitochondria and ER during the l-buthionine sulfoximine (BSO)-treated cell apoptosis process. During mitochondria-oriented apoptosis induced by carbonyl cyanide m-chlorophenylhydrazone (CCCP) or rotenone, H2O2 levels prominently and continuously increase in the mitochondria, whereas the ER H2O2 levels were found to rise subsequently after a delay. Moreover, during ER-oriented apoptosis induced by tunicamycin, ER is the major site for overproduction of H2O2, and delayed elevation of the H2O2 levels was found in the mitochondria. Altogether, this dual-probe and multicolor imaging approach may offer a proven methodology for studying molecular communication events on H2O2-related apoptosis and also other physiological and pathological processes within different subcellular organelles.

Integrated High-Content Quantification of Intracellular ROS Levels and Mitochondrial Morphofunction

Oxidative stress arises from an imbalance between the production of reactive oxygen species (ROS) and their removal by cellular antioxidant systems. Especially under pathological conditions, mitochondria constitute a relevant source of cellular ROS. These organelles harbor the electron transport chain, bringing electrons in close vicinity to molecular oxygen. Although a full understanding is still lacking, intracellular ROS generation and mitochondrial function are also linked to changes in mitochondrial morphology. To study the intricate relationships between the different factors that govern cellular redox balance in living cells, we have developed a high-content microscopy-based strategy for simultaneous quantification of intracellular ROS levels and mitochondrial morphofunction. Here, we summarize the principles of intracellular ROS generation and removal, and we explain the major considerations for performing quantitative microscopy analyses of ROS and mitochondrial morphofunction in living cells. Next, we describe our workflow, and finally, we illustrate that a multiparametric readout enables the unambiguous classification of chemically perturbed cells as well as laminopathy patient cells.

[Development of Functional Multilayer Nanofilms and Microcapsules Based on Layer-by-Layer Deposition Techniques]

Functional multilayer thin films have been prepared by layer-by-layer (LbL) deposition for the development of sensors, separators, and drug delivery systems. In particular, glucose-sensitive LbL films have been widely studied for use as glucose sensors and in glucose-triggered drug delivery systems. In this work, I report on glucose-sensitive LbL films that consist of concanavalin A (ConA), phenylboronic acid (PBA), and glucose oxidase (GOx). ConA/glycogen LbL films were prepared by LbL deposition of ConA and glycogen through a lectin-sugar interaction. Similarly, PBA-modified poly(amidoamine) dendrimer/poly(vinyl alcohol) (PVA) LbL films were prepared through cyclic boronate ester bonds. Both types of films decomposed in the presence of glucose, by the competitive binding of glucose, although these LbL films did not show a satisfactory response to millimolar concentrations of glucose under physiological conditions. PBA-modified poly(allylamine hydrochloride) and PVA films were prepared on a GOx-modified quartz slide. The LbL film was stable over a wide pH range, from 3.0 to 9.0, in the absence of glucose. In contrast, the film decomposed upon exposure to 0.1-10 mM glucose solutions for 60 min at pH 7.4. The glucose-induced decomposition of the film can be explained by the scission of the carbon-boron bond of the PBA residues by hydrogen peroxide, which was produced through the GOx-catalyzed oxidation of glucose. These results suggest this multilayer film may be useful for the development of glucose-sensitive drug delivery systems.

Epidermal growth factor-induced hydrogen peroxide production is mediated by dual oxidase 1

Stimulation of mammalian cells by epidermal growth factor (EGF) elicits complex signaling events, including an increase in hydrogen peroxide (H2O2) production. Understanding the significance of this response is limited by the fact that the source of EGF-induced H2O2 production is unknown. Here we show that EGF-induced H2O2 production in epidermal cell lines is dependent on the agonist-induced calcium signal. We analyzed the expression of NADPH oxidase isoforms and found both A431 and HaCaT cells to express the calcium-sensitive NADPH oxidase, Dual oxidase 1 (Duox1) and its protein partner Duox activator 1 (DuoxA1). Inhibition of Duox1 expression by small interfering RNAs eliminated EGF-induced H2O2 production in both cell lines. We also demonstrate that H2O2 production by Duox1 leads to the oxidation of thioredoxin-1 and the cytosolic peroxiredoxins. Our observations provide evidence for a new signaling paradigm in which changes of intracellular calcium concentration are transformed into redox signals through the calcium-dependent activation of Duox1.

High Spatial Resolution Imaging of Endogenous Hydrogen Peroxide in Living Cells by Solid-State Fluorescence

Herein, we describe selective imaging of hydrogen peroxide using a precipitating dye conjugated to a boronic acid-based immolative linker. We achieved visualization of endogenous hydrogen peroxide in phagosomes by solid-state two-photon fluorescence imaging in living cells with exceptionally high spatial resolution.

Chemically Engineered Nanoparticle-Protein Interface for Real-Time Cellular Oxidative Stress Monitoring

A co-engineered nanoparticle/protein peroxide detector is created. This system features a gold nanoparticle functionalized with a galactose headgroup (AuNP-Gal) that reacts covalently with a boronate-modified green fluorescent protein (PB-GFP). Boronate acid-saccharide complexation between PB-GFP and AuNP-Gal affords a highly stable assembly. This complex is disrupted by peroxide, allowing quantitative and selective monitoring of hydrogen peroxide production in real time.

Physical, Chemical, and Biological Structures based on ROS-Sensitive Moieties that are Able to Respond to Oxidative Microenvironments

Reactive oxygen species (ROS) (H2 O2 , OCl(-) , (•) OH, O2 (-) ) are a family of reactive molecules that are generated intracellularly and are engaged in many biological processes. In physiological concentrations, ROS act as signaling molecules to a number of metabolic pathways; however, in excess they can be harmful to living organisms. Overproduction of ROS has been related to many pathophysiological conditions and a number of studies have been reported in elucidating their mechanism in these conditions. With the aim of harnessing this role, a number of imaging tools and therapeutic compounds have been developed. Here these imaging and therapeutic tools are reviewed and particularly those structures with ROS-sensitivity based on their biomedical applications and their functional groups. There is also a brief discussion about the method of preparation as well as the mechanism of action.

Increasing extracellular H2O2 produces a bi-phasic response in intracellular H2O2, with peroxiredoxin hyperoxidation only triggered once the cellular H2O2-buffering capacity is overwhelmed

Reactive oxygen species, such as H2O2, can damage cells but also promote fundamental processes, including growth, differentiation and migration. The mechanisms allowing cells to differentially respond to toxic or signaling H2O2 levels are poorly defined. Here we reveal that increasing external H2O2 produces a bi-phasic response in intracellular H2O2. Peroxiredoxins (Prx) are abundant peroxidases which protect against genome instability, ageing and cancer. We have developed a dynamic model simulating in vivo changes in Prx oxidation. Remarkably, we show that the thioredoxin peroxidase activity of Prx does not provide any significant protection against external rises in H2O2. Instead, our model and experimental data are consistent with low levels of extracellular H2O2 being efficiently buffered by other thioredoxin-dependent activities, including H2O2-reactive cysteines in the thiol-proteome. We show that when extracellular H2O2 levels overwhelm this buffering capacity, the consequent rise in intracellular H2O2 triggers hyperoxidation of Prx to thioredoxin-resistant, peroxidase-inactive form/s. Accordingly, Prx hyperoxidation signals that H2O2 defenses are breached, diverting thioredoxin to repair damage.

Live-cell imaging approaches for the investigation of xenobiotic-induced oxidant stress

BACKGROUND

Oxidant stress is arguably a universal feature in toxicology. Research studies on the role of oxidant stress induced by xenobiotic exposures have typically relied on the identification of damaged biomolecules using a variety of conventional biochemical and molecular techniques. However, there is increasing evidence that low-level exposure to a variety of toxicants dysregulates cellular physiology by interfering with redox-dependent processes.

SCOPE OF REVIEW

The study of events involved in redox toxicology requires methodology capable of detecting transient modifications at relatively low signal strength. This article reviews the advantages of live-cell imaging for redox toxicology studies.

MAJOR CONCLUSIONS

Toxicological studies with xenobiotics of supra-physiological reactivity require careful consideration when using fluorogenic sensors in order to avoid potential artifacts and false negatives. Fortunately, experiments conducted for the purpose of validating the use of these sensors in toxicological applications often yield unexpected insights into the mechanisms through which xenobiotic exposure induces oxidant stress.

GENERAL SIGNIFICANCE

Live-cell imaging using a new generation of small molecule and genetically encoded fluorophores with excellent sensitivity and specificity affords unprecedented spatiotemporal resolution that is optimal for redox toxicology studies. This article is part of a Special Issue entitled Air Pollution, edited by Wenjun Ding, Andrew J. Ghio and Weidong Wu.

A Critical Review of Methodologies to Detect Reactive Oxygen and Nitrogen Species Stimulated by NADPH Oxidase Enzymes: Implications in Pesticide Toxicity

In this review, potential fluorescent probe applications for detecting reactive oxygen and nitrogen species (ROS/RNS) generated from NADPH oxidases (e.g., Nox2) and nitric oxide synthase enzymes are discussed in the context of pesticide toxicology. Identification of the specific marker products derived from the interaction between ROS/RNS and the fluorescent probes (e.g., hydroethidine and coumarin boronate) is critical. Due to the complex nature of reactions between the probes and ROS/RNS, we suggest avoiding the use of fluorescence microscopy for detecting oxidizing/nitrating species. We also critically examined the viability of using radiolabeling or positron emission tomography (PET) for ROS/RNS detection. Although these techniques differ in sensitivity and detection modalities, the chemical mechanism governing the reaction between these probes and ROS/RNS should remain the same. To unequivocally detect superoxide with these probes (i.e., radiolabeled and PET-labeled hydroethidine analogs), the products should be isolated and characterized by LC-MS/MS or HPLC using an appropriate standard.

Flagellin-induced NADPH oxidase 4 activation is involved in atherosclerosis

It is widely accepted that bacterial infection-mediated inflammation facilitates development of atherosclerosis by activating toll-like receptor (TLR) signaling system. We reasoned that NADPH oxidases (Nox), required for TLR-mediated inflammatory response, are involved in atherogenesis. Here, we show that the activation of Nox4 through TLR5 regulates the inflammation of the endothelium and in atherogenesis. Flagellin-induced interaction between the COOH region of Nox4 and the TIR domain of TLR5 led to H2O2 generation, which in turn promoted the secretion of pro-inflammatory cytokines including IL-8, as well as the expression of ICAM-1 in human aortic endothelial cells (HAECs). Knockdown of the Nox4 in HAECs resulted in attenuated expressions of IL-8 and ICAM-1 leading to a reduction in the adhesion and trans-endothelial migration of monocytes. Challenge of recombinant FliC (rFliC) to the ApoE KO mice with high-fat diet (HFD) resulted in significantly increased atherosclerotic plaque sizes compared to the saline-injected mice. However, an injection of rFliC into the Nox4ApoE DKO mice with HFDs failed to generate atherosclerotic plaque, suggesting that Nox4 deficiency resulted in significant protections against rFliC-mediated atherogenesis. We conclude that TLR5-dependent Nox4 activation and subsequent H2O2 generation play critical roles for the development of atherosclerosis.

Selective and Reversible Approaches Toward Imaging Redox Signaling Using Small-Molecule Probes

SIGNIFICANCE

Recent research has identified key roles for reactive oxygen species (ROS)/reactive nitrogen species (RNS) in redox signaling, but much remains to be uncovered. Molecular imaging tools to study these processes must not only be selective to enable identification of the ROS/RNS involved but also reversible to distinguish signaling processes from oxidative stress. Fluorescent sensors offer the potential to image such processes with high spatial and temporal resolution.

RECENT ADVANCES

A broad array of strategies has been developed that enable the selective sensing of ROS/RNS. More recently, attention has turned to the design of reversible small-molecule sensors of global redox state, with a further set of probes capable of reversible sensing of individual ROS/RNS.

CRITICAL ISSUES

In this study, we discuss the key challenges in achieving simultaneous detection of reversible oxidative bursts with unambiguous determination of a particular ROS/RNS.

FUTURE DIRECTIONS

We have highlighted key design features of small-molecule probes that show promise in enabling the study of redox signaling, identifying essential parameters that must be assessed for any new probe. Antioxid. Redox Signal. 24, 713-730.

1,4-Benzenediboronic-Acid-Induced Aggregation of Gold Nanoparticles: Application to Hydrogen Peroxide Detection and Biotin-Avidin-Mediated Immunoassay with Naked-Eye Detection

Hydrogen-peroxide (H2O2)-induced growth of small-sized gold nanoparticles (AuNPs) is often implemented for H2O2 sensing and plasmonic immunoassay. In contrast, there is little-to-no information in the literature regarding the application of H2O2-inhibited aggregation of citrate-capped AuNPs. This study discloses that benzene-1,4-diboronic acid (BDBA) was effective in driving the aggregation of citrate-capped AuNPs through an interaction between α-hydroxycarboxylate of citrate and boronic acids of BDBA. The H2O2-mediated oxidation of BDBA resulted in the conversion of boronic acid groups to phenol groups. The oxidized BDBA was incapable of triggering the aggregation of citrate-capped AuNPs. Thus, the presence of H2O2 prohibited BDBA-induced aggregation of citrate-capped AuNPs. The BDBA-induced aggregation of citrate-capped AuNPs can be paired with the glucose oxidase (GOx)-glucose system to design a colorimetric probe for glucose. Moreover, a H2O2·BDBA·AuNP probe was integrated with sandwich immunoassay, biotinylated antibody, and avidin-conjugated GOx for the selective naked-eye detection of rabbit immunoglobulin G (IgG) and human-prostate-specific antigen (PSA). The lowest detectable concentrations of rabbit IgG and human PSA by the naked eye were down to 0.1 and 4 ng/mL, respectively. More importantly, the proposed plasmonic immunoassay allowed the naked-eye quantification of 0-10 ng/mL PSA at an interval of 2 ng/mL in plasma samples.

[(11)C]Ascorbic and [(11)C]dehydroascorbic acid, an endogenous redox pair for sensing reactive oxygen species using positron emission tomography

Here we report the radiosynthesis of an endogenous redox pair, [(11)C]ascorbic acid ([(11)C]VitC) and [(11)C]dehydroascorbic acid ([(11)C]DHA), the reduced and oxidized forms of vitamin C, and their application to ROS sensing. These results provide the basis for in vivo detection of ROS using positron emission tomography (PET).

Nitro-Arachidonic Acid Prevents Angiotensin II-Induced Mitochondrial Dysfunction in a Cell Line of Kidney Proximal Tubular Cells

Nitro-arachidonic acid (NO₂-AA) is a cell signaling nitroalkene that exerts anti-inflammatory activities during macrophage activation. While angiotensin II (ANG II) produces an increase in reactive oxygen species (ROS) production and mitochondrial dysfunction in renal tubular cells, little is known regarding the potential protective effects of NO₂-AA in ANG II-mediated kidney injury. As such, this study examines the impact of NO₂-AA on ANG II-induced mitochondrial dysfunction in an immortalized renal proximal tubule cell line (HK-2 cells). Treatment of HK-2 cells with ANG II increases the production of superoxide (O₂^●-), nitric oxide (^●NO), inducible nitric oxide synthase (NOS2) expression, peroxynitrite (ONOO^-) and mitochondrial dysfunction. Using high-resolution respirometry, it was observed that the presence of NO₂-AA prevented ANG II-mediated mitochondrial dysfunction. Attempting to address mechanism, we treated isolated rat kidney mitochondria with ONOO^-, a key mediator of ANG II-induced mitochondrial damage, in the presence or absence of NO₂-AA. Whereas the activity of succinate dehydrogenase (SDH) and ATP synthase (ATPase) were diminished upon exposure to ONOO-, they were restored by pre-incubating the mitochondria with NO₂-AA. Moreover, NO₂-AA prevents oxidation and nitration of mitochondrial proteins. Combined, these data demonstrate that ANG II-mediated oxidative damage and mitochondrial dysfunction is abrogated by NO₂-AA, identifying this compound as a promising pharmacological tool to prevent ANG II–induced renal disease.

Sulfiredoxin inhibitor induces preferential death of cancer cells through reactive oxygen species-mediated mitochondrial damage

Recent studies have shown that many types of cancer cells have increased levels of reactive oxygen species (ROS) and enhance antioxidant capacity as an adaptation to intrinsic oxidative stress, suggesting that cancer cells are more vulnerable to oxidative insults and are more dependent on antioxidant systems compared with normal cells. Thus, disruption of redox homeostasis caused by a decline in antioxidant capacity may provide a method for the selective death of cancer cells. Here we show that ROS-mediated selective death of tumor cells can be caused by inhibiting sulfiredoxin (Srx), which reduces hyperoxidized peroxiredoxins, leading to their reactivation. Srx inhibitor increased the accumulation of sulfinic peroxiredoxins and ROS, which led to oxidative mitochondrial damage and caspase activation, resulting in the death of A549 human lung adenocarcinoma cells. Srx depletion also inhibited the growth of A549 cells like Srx inhibition, and the cytotoxic effects of Srx inhibitor were considerably reversed by Srx overexpression or antioxidants such as N-acetyl cysteine and butylated hydroxyanisol. Moreover, Srx inhibitor rendered tumorigenic ovarian cells more susceptible to ROS-mediated death compared with nontumorigenic cells and significantly suppressed the growth of A549 xenografts without acute toxicity. Our results suggest that Srx might serve as a novel therapeutic target for cancer treatment based on ROS-mediated cell death.

Carbazole-based two-photon fluorescent probe for selective imaging of mitochondrial hydrogen peroxide in living cells and tissues

The two-photon imaging in living cells and tissue demonstrated that the prepared probe possessed high specificity for mitochondrial H₂O₂.

Development of green to near-infrared turn-on fluorescent probes for the multicolour imaging of nitroxyl in living systems

The green to near-infrared turn-on fluorescent probes were developed for the multicolour imaging of nitroxyl in living systems.

Boranil dye based “turn-on” fluorescent probes for detection of hydrogen peroxide and their cell imaging application

The synthesis of boranil dye fluorescent probes for the detection of hydrogen peroxide has been described. The probes have been successfully applied for imaging of H₂O₂ in HeLa cells under physiological conditions.

Fluorescent probes for the selective detection of chemical species inside mitochondria

This feature article systematically summarizes the development of fluorescent probes for the selective detection of chemical species inside mitochondria.

A near-infrared fluorescent aza-bodipy probe for dual-wavelength detection of hydrogen peroxide in living cells

A boronic acid functionalized aza-borondipyrromethene dye (azaBDPBA) was applied to the dual-wavelength detection of hydrogen peroxide with high selectivity, which was loaded into cells to indicate the alteration of intracellular hydrogen peroxide during biological processes.

Label-free nanoprobe for antibody detection through an antibody catalysed water oxidation pathway

We developed a nanoprobe for the label-free detection of antibodies associated with infectious diseases, through a method based on the antibody catalyzed water oxidation pathway (ACWOP).