Fluorescent probes for nitric oxide and hydrogen peroxide in cell signaling

Activity-Based Fluorescent Probes for Hydrogen Sulfide and Related Reactive Sulfur Species

Hydrogen sulfide (H2S) is not only a well-established toxic gas but also an important small molecule bioregulator in all kingdoms of life. In contemporary biology, H2S is often classified as a "gasotransmitter," meaning that it is an endogenously produced membrane permeable gas that carries out essential cellular processes. Fluorescent probes for H2S and related reactive sulfur species (RSS) detection provide an important cornerstone for investigating the multifaceted roles of these important small molecules in complex biological systems. A now common approach to develop such tools is to develop "activity-based probes" that couple a specific H2S-mediated chemical reaction to a fluorescent output. This Review covers the different types of such probes and also highlights the chemical mechanisms by which each probe type is activated by specific RSS. Common examples include reduction of oxidized nitrogen motifs, disulfide exchange, electrophilic reactions, metal precipitation, and metal coordination. In addition, we also outline complementary activity-based probes for imaging reductant-labile and sulfane sulfur species, including persulfides and polysulfides. For probes highlighted in this Review, we focus on small molecule systems with demonstrated compatibility in cellular systems or related applications. Building from breadth of reported activity-based strategies and application, we also highlight key unmet challenges and future opportunities for advancing activity-based probes for H2S and related RSS.

Hydrothermal synthesis of ZnZrO2/chitosan (ZnZrO2/CS) nanocomposite for highly sensitive detection of glucose and hydrogen peroxide

In this work, pure ZnZrO₂ and chitosan supported (ZnZrO₂/CS) nanocomposite have been synthesized at low coast by hydrothermal method. FT-IR, Micro Raman, PXRD, HR-SEM-EDAX, HR-TEM, AFM, BET and XPS were used to analyze the structural and morphological properties of the fabricated nanocomposites. The fabricated ZnZrO₂ and ZnZrO₂/CS nanocomposites were measured for their electrocatalytic activity towards glucose and hydrogen peroxide determinations. The ZnZrO₂/CS sensor exhibited wide detection range (5 μM to 5.85 mM), high sensitivity (6.78 μA mM^-1 cm^-2), LOD (2.31 μM), and long-term stability for glucose detection in alkaline solution. Also, as a multifunctional electrochemical sensor, ZnZrO₂/CS sensor exhibits excellent sensing ability towards hydrogen peroxide, with a wide dynamic range (20 μM to 6.85 mM), a high sensitivity (2.22 μA mM^-1 cm^-2), and a LOD (2.08 μM) (S/N = 3). The electrochemical measurement shows that the ZnZrO₂/CS sensor has excellent catalytic activity and a much LOD than ZnZrO₂. The modified electrode showed excellent anti interference nature. Furthermore, this ZnZrO₂/CS electrode was used to detection of glucose and H₂O₂ in human blood serum and HeLa cells respectively.

Highly sensitive benzothiazole-based chemosensors for detection and bioimaging of peroxynitrite in living cells

Fluorescent probes designed to sense and image peroxynitrite (ONOO−).

New strategy for detection of hydrogen peroxide based on bi-nucleophilic reaction

Two novel fluorescent probes based on 7-hydroxy-4-methyl-coumarin, FAA-MC-OH (2-fluoro-4-nitro-phenylacetyl hydroxyl coumarin) and FBA-MC-OH (2-fluoro-4-nitro-benzoyl hydroxyl coumarin) are first synthesized, and spectral studies confirm that both the probes display highly selective and sensitive to H₂O₂, especially FBA-MC-OH has a shorter response time. Moreover, it is worth noting that the reaction mechanism is based on bi-nucleophilic substitution instead of oxidation or hydrolysis, which is different from previous reported probes'.

MACA Fast and Efficient Method for Detecting H2O2 by a Dual-Locked Model Chemosensor

A pentafluorobenzene-containing fluorescent probe GW-1 was designed and synthesized for monitoring hydrogen peroxide. The probe's fluorescence was activated by a dual-locked model system that consists of a spiro location and a target analyte, which avoids the "alkalizing effect." The smart GW-1 exhibited high selectivity toward hydrogen peroxide over other reactive oxygen species (ROS) by a dual-controlled molecular switch. These features are favorable for H2O2 sensing and pH changes in bioanalytical and biomedical applications.

Recent progress in developing fluorescent probes for imaging cell metabolites

Cellular metabolites play a crucial role in promoting and regulating cellular activities, but it has been difficult to monitor these cellular metabolites in living cells and in real time. Over the past decades, iterative development and improvements of fluorescent probes have been made, resulting in the effective monitoring of metabolites. In this review, we highlight recent progress in the use of fluorescent probes for tracking some key metabolites, such as adenosine triphosphate, cyclic adenosine monophosphate, cyclic guanosine 5'-monophosphate, Nicotinamide adenine dinucleotide (NADH), reactive oxygen species, sugar, carbon monoxide, and nitric oxide for both whole cell and subcellular imaging.

Fluorescent Probe for Monitoring Hydrogen Peroxide in COX-2-Positive Cancer Cells

Hydrogen peroxide (H₂O₂), an important marker for oxidative stress, plays a vital role in cellular biological functions. Overproduction of H₂O₂ causes oxidative damage to cellular functions and promotes cancer and other neurodegenerative diseases. Also, cyclooxygenase-2 (COX-2) enzyme is known to be expressed in several cancer types and exerts multifaceted roles in carcinogenesis and resistance to cancer treatment. Hence, it is important to monitor the H₂O₂ concentration changes in the COX-2-expressing cancer cells. Herein, we have developed a molecular fluorescent ratiometric H₂O₂-responsive probe (NPDIN) composed of indomethacin (COX-2 inhibitor) conjugated with 1,8-napthalimide boronate ester as fluorescent reporter through a chemical linker. The probe was capable of imaging the endogenous H₂O₂ in COX-2 overexpressing cancer cell lines (A549, LoVo, HT29, and Caco-2). Further studies revealed the critical role of the indomethacin moiety in the cellular uptake behavior of NPDIN in COX-2-overexpressing cancer cells. Collectively, our results demonstrated NPDIN as a COX-2-positive cancer-targeting sensitive ratiometric fluorescent probe (I₅₅₄/I₃₉₈) for H₂O₂ imaging and showed its promising biological applications in the future.

Facilitation of molecular motion to develop turn-on photoacoustic bioprobe for detecting nitric oxide in encephalitis

Nitric oxide (NO) is an important signaling molecule overexpressed in many diseases, thus the development of NO-activatable probes is of vital significance for monitoring related diseases. However, sensitive photoacoustic (PA) probes for detecting NO-associated complicated diseases (e.g., encephalitis), have yet to be developed. Herein, we report a NO-activated PA probe for in vivo detection of encephalitis by tuning the molecular geometry and energy transformation processes. A strong donor-acceptor structure with increased conjugation can be obtained after NO treatment, along with the active intramolecular motion, significantly boosting "turn-on" near-infrared PA property. The molecular probe exhibits high specificity and sensitivity towards NO over interfering reactive species. The probe is capable of detecting and differentiating encephalitis in different severities with high spatiotemporal resolution. This work will inspire more insights into the development of high-performing activatable PA probes for advanced diagnosis by making full use of intramolecular motion and energy transformation processes.

Immunological Techniques to Assess Protein Thiol Redox State: Opportunities, Challenges and Solutions

To understand oxidative stress, antioxidant defense, and redox signaling in health and disease it is essential to assess protein thiol redox state. Protein thiol redox state is seldom assessed immunologically because of the inability to distinguish reduced and reversibly oxidized thiols by Western blotting. An underappreciated opportunity exists to use Click PEGylation to realize the transformative power of simple, time and cost-efficient immunological techniques. Click PEGylation harnesses selective, bio-orthogonal Click chemistry to separate reduced and reversibly oxidized thiols by selectively ligating a low molecular weight polyethylene glycol moiety to the redox state of interest. The resultant ability to disambiguate reduced and reversibly oxidized species by Western blotting enables Click PEGylation to assess protein thiol redox state. In the present review, to enable investigators to effectively harness immunological techniques to assess protein thiol redox state we critique the chemistry, promise and challenges of Click PEGylation.

A magnetic electrode modified with hemoglobin for determination of hydrogen peroxide: distinctly improved response by applying a magnetic field

A facile and highly sensitive biosensor was developed for the determination of hydrogen peroxide (H₂O₂) via electrochemical catalytic reduction of H₂O₂ by hemoglobin (Hb). Hb was enriched and immobilized simply in a chitosan (Chit) membrane on a magnetic electrode to construct an enzyme-like biosensor. The biosensor catalyzes the electrochemical reduction of H₂O₂ under an external magnetic field. The response improved roughly twice as Hb was adsorbed by Chit in an alkaline medium. The response of the biosensor under the magnetic field increased by 16% owing to the paramagnetism of Hb. The effect of pH values on Hb adsorption by Chit, as well as the effect of an external magnetic field on Hb configuration were investigated by UV-vis spectroscopy. The reduction peak current has linear and log-linear relationships with H₂O₂ concentration in the range of 5-250 μmol∙L^-1 and 0.01-1 μmol∙L^-1, respectively. The detection limit was 0.003 μmol∙L^-1, with a good sensitivity of 0.227 μA∙μM^-1∙cm^-2. The biosensor was successfully applied to the determination of H₂O₂ in milk samples and in disinfectant solutions. Recoveries ranged from 96.3 to 105.4%, and from 95.3 to 107.7%, respectively. Graphical abstractConstruction of the biosensor, and principle of H₂O₂ determination based on Hb bioelectrocatalysis.

Development of a Nitric Oxide-Responsive Labeling Reagent for Proteome Analysis of Live Cells

Nitric oxide (NO) is a pleiotropic signaling molecule involved in the regulation of diverse physiological and pathophysiological mechanisms in cardiovascular, nervous, and immunological systems. To understand the biological functions of NO in detail, comprehensive characterization of proteins found in high-NO concentration environments is crucial. Herein, we describe the design of NO-responsive protein labeling reagents based on N-alkoxyacyl- o-phenylenediamine as an optimal reactive scaffold. The designed molecules can label proteins in murine macrophage cells in response to endogenously produced NO. The combination of NO-responsive protein labeling and liquid chromatography-tandem mass spectrometry technology allowed the characterization of the proteome under NO-generated conditions. Moreover, we demonstrated that our reagent was able to selectively mark and be used to fluorescently visualize NO-producing cells in a mixed cell culture system.

Challenges and Opportunities for Small-Molecule Fluorescent Probes in Redox Biology Applications

SIGNIFICANCE

The concentrations of reactive oxygen/nitrogen species (ROS/RNS) are critical to various biochemical processes. Small-molecule fluorescent probes have been widely used to detect and/or quantify ROS/RNS in many redox biology studies and serve as an important complementary to protein-based sensors with unique applications. Recent Advances: New sensing reactions have emerged in probe development, allowing more selective and quantitative detection of ROS/RNS, especially in live cells. Improvements have been made in sensing reactions, fluorophores, and bioavailability of probe molecules.

CRITICAL ISSUES

In this review, we will not only summarize redox-related small-molecule fluorescent probes but also lay out the challenges of designing probes to help redox biologists independently evaluate the quality of reported small-molecule fluorescent probes, especially in the chemistry literature. We specifically highlight the advantages of reversibility in sensing reactions and its applications in ratiometric probe design for quantitative measurements in living cells. In addition, we compare the advantages and disadvantages of small-molecule probes and protein-based probes.

FUTURE DIRECTIONS

The low physiological relevant concentrations of most ROS/RNS call for new sensing reactions with better selectivity, kinetics, and reversibility; fluorophores with high quantum yield, wide wavelength coverage, and Stokes shifts; and structural design with good aqueous solubility, membrane permeability, low protein interference, and organelle specificity. Antioxid. Redox Signal. 29, 518-540.

Monitoring dynamic release of intracellular hydrogen peroxide through a microelectrode based enzymatic biosensor

A high sensitive and selective hydrogen peroxide (H₂O₂) biosensor was fabricated on the basis of reduced hemoglobin (Hb) and single-walled carbon nanotubes (SWCNTs) for detecting the release of H₂O₂ from living HepG2 cancer cells in the process of the in situ biosynthesis of ZnO quantum. The modification of carbon fiber microelectrode (CFME) was carried out by physical adsorption. By the scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), the dense cover of surface and successful immobilization were characterized. Electrochemical investigation demonstrates that the as-prepared modified microelectrode showed a quasi-reversible process toward the reduction of H₂O₂, which exhibited a linear range from 0.51 to 10.6 μM, with a limit of detection of 0.23 μM. This microelectrode biosensor was applied for the quantification of the change of H₂O₂ concentration released from HepG2 cells through the in situ biosynthesis of ZnO quantum dots, which was further confirmed by the fluorescence staining.

Development of a Xanthene-Based Red-Emissive Fluorescent Probe for Visualizing H2O2 in Living Cells, Tissues and Animals

Hydrogen peroxide (H₂O₂) plays important roles in the regulation of many biological processes, and the abnormal level of H₂O₂ has close relation with the initiation and progression of many diseases. Herein, we describe a novel red-emissive fluorescence probe (RhoB) for the visualization of H₂O₂ in living cells, tissues and animals. RhoB was constructed on the basis of a xanthene-based red-emissive dye, and displayed nearly no fluorescence. After the treatment with H₂O₂, RhoB can exhibit red fluorescence with the emission wavelength at 638 nm. RhoB exhibited highly sensitive and selective response to H₂O₂. Density functional theory (DFT) calculations were conducted to shed light on the optical properties of RhoB, and natural bond orbital (NBO) calculations demonstrate that the boron atom shows the highest positive electricity and further support the response mechanism. RhoB was successfully applied for imaging of exogenous and endogenous H₂O₂ in living cells, and also can be utilized for visualizing H₂O₂ in living tissues and animals.

Theoretical Design of a Two-Photon Fluorescent Probe for Nitric Oxide with Enhanced Emission Induced by Photoninduced Electron Transfer

In the present work, we systematically investigate the sensing abilities of two recently literature-reported two-photon fluorescent NO probes, i.e., the o-phenylenediamine derivative of Nile Red and the p-phenylenediamine derivative of coumarin. The recognition mechanisms of these probes are studied by using the molecular orbital classifying method, which demonstrates the photoinduced electron transfer process. In addition, we have designed two new probes by swapping receptor units present on fluorophores, i.e., the p-phenylenediamine derivative of Nile Red and the o-phenylenediamine derivative of coumarin. However, it illustrates that only the latter has ability to function as off-on typed fluorescent probe for NO. More importantly, calculations on the two-photon absorption properties of the probes demonstrate that both receptor derivatives of coumarin possess larger TPA cross-sections than Nile Red derivatives, which makes a better two photon fluorescent probe. Our theoretical investigations reveal that the underlying mechanism satisfactorily explain the experimental results, providing a theoretical basis on the structure-property relationships which is beneficial to developing new two-photon fluorescent probes for NO.

Introduction

Primordial life forms on earth comprised oxygen-sensitive organisms: the anaerobic fermenters and cyanobacteria, which released oxygen as a metabolic by-product, causing the oxygen levels in the atmosphere to rise Benzie (Eur J Nutr 39:53–61, 2000 [1]), Halliwell (Free Radic Res 31:261–272, 1999 [2]).

A mitochondrial-targeted prodrug for NIR imaging guided and synergetic NIR photodynamic-chemo cancer therapy

Nontoxic prodrugs, especially activated by tumor microenvironment, are urgently required for reducing the side effects of cancer therapy. And combination of chemo-photodynamic therapy prodrugs show effectively synergetic therapeutic efficiency, however, this goal has not been achieved in a single molecule. In this work, we developed a mitochondrial-targeted prodrug PNPS for near infrared (NIR) fluorescence imaging guided and synergetic chemo-photodynamic precise cancer therapy for the first time. PNPS contains a NIR photosensitizer (NPS) and an anticancer drug 5'-deoxy-5-fluorouridine (5'-DFUR). These two parts are linked and caged through a bisboronate group, displaying no fluorescence and very low cytotoxicity. In the presence of H2O2, the bisboronate group is broken, resulting in activation of NPS for NIR photodynamic therapy and activation of 5'-DFUR for chemotherapy. The activated NPS can also provide a NIR fluorescence signal for monitoring the release of activated drug. Taking advantage of the high H2O2 concentration in cancer cells, PNPS exhibits higher cytotoxicity to cancer cells than normal cells, resulting in lower side effects. In addition, based on its mitochondrial-targeted ability, PNPS exhibits enhanced chemotherapy efficiency compare to free 5'-DFUR. It also demonstrated a remarkably improved and synergistic chemo-photodynamic therapeutic effect for cancer cells. Moreover, PNPS exhibits excellent tumor microenvironment-activated performance when intravenously injected into tumor-bearing nude mice, as demonstrated by in vivo fluorescence imaging. Thus, PNPS is a promising prodrug for cancer therapy based on its tumor microenvironment-activated drug release, synergistic therapeutic effect and "turn-on" NIR imaging guide.

A H2O2-Responsive Theranostic Probe for Endothelial Injury Imaging and Protection

Overproduction of H₂O₂ causes oxidative stress and is the hallmark of vascular diseases. Tracking native H₂O₂ in the endothelium is therefore indispensable to gain fundamental insights into this pathogenesis. Previous fluorescent probes for H₂O₂ imaging were generally arylboronates which were decomposed to emissive arylphenols in response to H₂O₂. Except the issue of specificity challenged by peroxynitrite, boric acid by-produced in this process is actually a waste with unknown biological effects. Therefore, improvements could be envisioned if a therapeutic agent is by-produced instead. Herein, we came up with a "click-to-release-two" strategy and demonstrate that dual functional probes could be devised by linking a fluorophore with a therapeutic agent via a H₂O₂-responsive bond. As a proof of concept, probe AP consisting of a 2-(2'-hydroxyphenyl) benzothiazole fluorophore and an aspirin moiety has been prepared and confirmed for its theranostic effects. This probe features high specificity towards H₂O₂ than other reactive species including peroxynitrite. Its capability to image and ameliorate endothelial injury has been verified both in vitro and in vivo. Noteworthy, as a result of its endothelial-protective effect, AP also works well to reduce thrombosis formation in zebrafish model.

A lysosome targetable fluorescent probe for endogenous imaging of hydrogen peroxide in living cells

A lysosome targetable naphthalimide based fluorescent probe has been designed and synthesized for selective imaging of H₂O₂ in different cells, tissues and in vivo models.

NIR in, far-red out: developing a two-photon fluorescent probe for tracking nitric oxide in deep tissue

As a pivotal signalling molecule involved in various physiological and pathological processes, nitric oxide (NO) has motivated increasing interest in the last few decades. Although a considerable number of fluorescent probes have been developed for NO imaging, the in situ tracking of this gas molecule in biological events remains a big challenge, mainly because of the relatively short excitation and/or emission wavelengths, which are subject to background interference and lowered collection efficiency in deep-tissue imaging. Herein, we report a far-red emissive (650 nm) two-photon (TP) excitable NRNO probe, using Nile Red as the TP fluorophore, for NO detection and imaging both in vitro and in vivo. The NRNO probe shows a fast (within 180 s) and specific fluorescence response toward NO with a limit of detection (LOD) as low as 46 nM. The excellent properties of NRNO enable it to sensitively detect both exogenously and endogenously generated NO in living cells. The "NIR in" and "far-red out" lights lead to improved penetrating ability, thus endowing the probe with high resolution for the illumination of deep tissues. It is therefore able to visualize the NO generation in a lipopolysaccharide (LPS)-mediated inflammation process for the first time. Our results demonstrate that NRNO could be a practical tool for studying the NO-related biological events. Moreover, this study also suggests the possibility of using Nile Red and its derivatives to develop far-red emissive TP probes, which is an important, yet undeveloped area.

STAT3 Represses Nitric Oxide Synthesis in Human Macrophages upon Mycobacterium tuberculosis Infection

Mycobacterium tuberculosis is a successful intracellular pathogen. Numerous host innate immune responses signaling pathways are induced upon mycobacterium invasion, however their impact on M. tuberculosis replication is not fully understood. Here we reinvestigate the role of STAT3 specifically inside human macrophages shortly after M. tuberculosis uptake. We first show that STAT3 activation is mediated by IL-10 and occurs in M. tuberculosis infected cells as well as in bystander non-colonized cells. STAT3 activation results in the inhibition of IL-6, TNF-α, IFN-γ and MIP-1β. We further demonstrate that STAT3 represses iNOS expression and NO synthesis. Accordingly, the inhibition of STAT3 is detrimental for M. tuberculosis intracellular replication. Our study thus points out STAT3 as a key host factor for M. tuberculosis intracellular establishment in the early stages of macrophage infection.

SERS nanoprobes for the monitoring of endogenous nitric oxide in living cells

Nitric Oxide (NO) is a significant gaseous signalling molecule in various pathological and physiological pathways, whereas many of its functions are still ambiguous in part because of the shortage of powerful detection approaches. Herein, we present a type of reaction-based surface-enhanced Raman scattering (SERS) nanoprobes, o-phenylenediamine-modified gold nanoparticles (AuNPs/OPD), to detect the level of the endogenous NO in living cells. The detection is achieved through the SERS variation of AuNPs/OPD caused by the reaction between NO and OPD on the surface of AuNPs. The proposed SERS nanoprobes have a good stability and a rapid response to NO within 30s Moreover, as a result of the reaction specificity coupled with SERS fingerprinting, AuNPs/OPD nanoprobes demonstrate high selectivity towards NO over other biologically relevant species with a sensitivity at 10(-7)M level. Thereby, this SERS strategy can be used for monitoring NO that is endogenously produced in living macrophages, indicating immense potential in studying NO-involved pathophysiological processes in biological systems.

Highly sensitive ratiometric fluorescence probes for nitric oxide based on dihydropyridine and potentially useful in bioimaging

Hantzsch dihydropyridine-based ratiometric fluorescent NO probes, viz.PyNO and TPANO, were synthesized and characterized.

Recent Progress in Fluorescent Imaging Probes

Due to the simplicity and low detection limit, especially the bioimaging ability for cells, fluorescence probes serve as unique detection methods. With the aid of molecular recognition and specific organic reactions, research on fluorescent imaging probes has blossomed during the last decade. Especially, reaction based fluorescent probes have been proven to be highly selective for specific analytes. This review highlights our recent progress on fluorescent imaging probes for biologically important species, such as biothiols, reactive oxygen species, reactive nitrogen species, metal ions including Zn²⁺, Hg²⁺, Cu²⁺ and Au³⁺, and anions including cyanide and adenosine triphosphate (ATP).

A Ratiometric Sensor Using Single Chirality Near-Infrared Fluorescent Carbon Nanotubes: Application to In Vivo Monitoring

Advances in the separation and functionalization of single walled carbon nanotubes (SWCNT) by their electronic type have enabled the development of ratiometric fluorescent SWCNT sensors for the first time. Herein, single chirality SWCNT are independently functionalized to recognize either nitric oxide (NO), hydrogen peroxide (H(2)O(2)), or no analyte (remaining invariant) to create optical sensor responses from the ratio of distinct emission peaks. This ratiometric approach provides a measure of analyte concentration, invariant to the absolute intensity emitted from the sensors and hence, more stable to external noise and detection geometry. Two distinct ratiometric sensors are demonstrated: one version for H(2)O(2), the other for NO, each using 7,6 emission, and each containing an invariant 6,5 emission wavelength. To functionalize these sensors from SWCNT isolated from the gel separation technique, a method for rapid and efficient coating exchange of single chirality sodium dodecyl sulfate-SWCNT is introduced. As a proof of concept, spatial and temporal patterns of the ratio sensor response to H(2)O(2) and, separately, NO, are monitored in leaves of living plants in real time. This ratiometric optical sensing platform can enable the detection of trace analytes in complex environments such as strongly scattering media and biological tissues.

A Chemical Approach for the Detection of Protein Sulfinylation

Protein sulfinic acids are formed by the reaction of reactive oxygen species with protein thiols. Sulfinic acid formation has long been considered an irreversible state of oxidation and is associated with high cellular oxidative stress. Increasing evidence, however, indicates that cysteine is oxidized to sulfinic acid in cells to a greater extent, and is more controlled, than first thought. The discovery of sulfiredoxin has demonstrated that cysteine sulfinic acid can be reversed, pointing to a vast array of potential implications for redox biology. Identification of the site of protein sulfinylation is crucial in clarifying the physiological and pathological effects of post-translational modifications. Currently, the only methods for detection of sulfinic acids involve mass spectroscopy and the use of specific antibodies. However, these methodologies are not suitable for proteomic studies. Herein, we report the first probe for detection of protein sulfinylation, NO-Bio, which combines a C-nitroso warhead for rapid labeling of sulfinic acid with a biotin handle. Based on this new tool, we developed a selective two-step approach. In the first, a sulfhydryl-reactive compound is introduced to selectively block free cysteine residues. Thereafter, the sample is treated with NO-Bio to label sulfinic acids. This new technology represents a rapid, selective, and general technology for sulfinic acid detection in biological samples. As proof of our concept, we also evaluated protein sulfinylation levels in various human lung tumor tissue lysates. Our preliminary results suggest that cancer tissues generally have higher levels of sulfinylation in comparison to matched normal tissues. A new ability to monitor protein sulfinylation directly should greatly expand the impact of sulfinic acid as a post-translational modification.

Detecting and monitoring NO, SNO and nitrite in vivo

The detection and quantification of nitric oxide and related reactive nitrogen species in vivo is vital to the understanding of the pathology and/or treatment of numerous conditions. To that end, several detection and quantification methods have been developed to study NO, as well as its redox relatives, nitrite and S-nitrosothiols. While no single technique can offer a complete picture of the nitrogen cycle in a given system in vivo, familiarity with the benefits and limitations of several common tools for NO_x determination can assist in the development of new diagnostics and therapeutics.

New reagents for detecting free radicals and oxidative stress

Free radicals and oxidative stress play important roles in the deterioration of materials, and free radicals are important intermediates in many biological processes. The ability to detect these reactive species is a key step on the road to their understanding and ultimate control. This short review highlights recent progress in the development of reagents for the detection of free radicals and reactive oxygen species with broad application to materials science as well as biology.

Visualization of endogenous and exogenous hydrogen peroxide using a lysosome-targetable fluorescent probe

Reactive oxygen species (ROS) play crucial roles in diverse physiological processes; therefore, the efficient detection of ROS is very crucial. In this study, we report a boronate-based hydrogen peroxide (H2O2) probe having naphthalimide fluorophore. This probe also contained a morpholine moiety as a directing group for lysosome. The recognition property indicated that the probe exhibited high selectivity towards H2O2 not only in the solution but also in the living cells. Furthermore, it was used to monitor the level of endogenous and exogenous H2O2. These results support that the probe can function as an efficient indicator to detect H2O2.

A highly selective fluorescent probe for fast detection of nitric oxide in aqueous solution

A naphthalimide-based fluorescent probe NPA exhibits fast detection rate for NO was synthesized.

Mitochondrially targeted redox probe reveals the variations in oxidative capacity of the haematopoietic cells

NpFR2 is a fluorescent sensor that can reversibly measure changes in the mitochondrial redox environment.

H2O2-activated triplet–triplet annihilation upconversion via modulation of the fluorescence quantum yields of the triplet acceptor and the triplet–triplet-energy-transfer efficiency

H₂O₂-activatable TTA upconversion was achieved with non-fluorescent 9,10-bis(diphenylphosphino)anthracene as a triplet acceptor/emitter, which can be oxidized to a fluorescent product by H₂O₂.

Regulation of protein tyrosine phosphatase oxidation in cell adhesion and migration

SIGNIFICANCE

Redox-regulated control of protein tyrosine phosphatases (PTPs) through inhibitory reversible oxidation of their active site is emerging as a novel and general mechanism for control of cell surface receptor-activated signaling. This mechanism allows for a previously unrecognized crosstalk between redox regulators and signaling pathways, governed by, for example, receptor tyrosine kinases and integrins, which control cell proliferation and migration.

RECENT ADVANCES

A large number of different molecules, in addition to hydrogen peroxide, have been found to induce PTP inactivation, including lipid peroxides, reactive nitrogen species, and hydrogen sulfide. Characterization of oxidized PTPs has identified different types of oxidative modifications that are likely to display differential sensitivity to various reducing systems. Accumulating evidence demonstrates that PTP oxidation occurs in a temporally and spatially restricted manner. Studies in cell and animal models indicate altered PTP oxidation in models of common diseases, such as cancer and metabolic/cardiovascular disease. Novel methods have appeared that allow characterization of global PTP oxidation.

CRITICAL ISSUES

As the understanding of the molecular and cellular biology of PTP oxidation is developing, it will be important to establish experimental procedures that allow analyses of PTP oxidation, and its regulation, in physiological and pathophysiological settings. Future studies should also aim to establish specific connections between various oxidants, specific PTPs, and defined signaling contexts.

FUTURE DIRECTIONS

Modulation of PTP activity still appears as a valid strategy for correction or inhibition of dys-regulated cell signaling. Continued studies on PTP oxidation might present yet unrecognized means to exploit this regulatory mechanism for pharmacological purposes.