Versatile Histochemical Approach to Detection of Hydrogen Peroxide in Cells and Tissues Based on Puromycin Staining

Boronate-Based Probes for Biological Oxidants: A Novel Class of Molecular Tools for Redox Biology

Boronate-based molecular probes are emerging as one of the most effective tools for detection and quantitation of peroxynitrite and hydroperoxides. This review discusses the chemical reactivity of boronate compounds in the context of their use for detection of biological oxidants, and presents examples of the practical use of those probes in selected chemical, enzymatic, and biological systems. The particular reactivity of boronates toward nucleophilic oxidants makes them a distinct class of probes for redox biology studies. We focus on the recent progress in the design and application of boronate-based probes in redox studies and perspectives for further developments.

Activity-Based Sensing: A Synthetic Methods Approach for Selective Molecular Imaging and Beyond

Emerging from the origins of supramolecular chemistry and the development of selective chemical receptors that rely on lock-and-key binding, activity-based sensing (ABS)-which utilizes molecular reactivity rather than molecular recognition for analyte detection-has rapidly grown into a distinct field to investigate the production and regulation of chemical species that mediate biological signaling and stress pathways, particularly metal ions and small molecules. Chemical reactions exploit the diverse chemical reactivity of biological species to enable the development of selective and sensitive synthetic methods to decipher their contributions within complex living environments. The broad utility of this reaction-driven approach facilitates application to imaging platforms ranging from fluorescence, luminescence, photoacoustic, magnetic resonance, and positron emission tomography modalities. ABS methods are also being expanded to other fields, such as drug and materials discovery.

Ratiometric fluorescence determination of hydrogen peroxide using carbon dot-embedded Ag@EuWO4(OH) nanocomposites

A sheet-like carbon dot-embedded Ag@EuWO₄(OH) luminescent nanoprobe was successfully developed for assaying hydrogen peroxide. Firstly, the carbon dot-embedded EuWO₄(OH) nanosheets were prepared in a Eu(NO₃)₃·6H₂O-(NH₄)₁₀H₂(W₂O₇)₆·xH₂O-CS(NH₂)₂ hydrothermal synthetic system. Subsequently, the carbon dot-embedded EuWO₄(OH) was functionalized by Ag nanoparticles using an in situ photochemical deposition strategy upon ultraviolet light irradiation. Taking advantage of the dual emissions of the luminescence from carbon dots and characteristic red transitions of Eu³⁺ ions in the integrated system, the carbon dot-embedded Ag@EuWO₄(OH) luminescent composites exhibit ratiometric fluorescence responsive activity towards hydrogen peroxide. The luminescent intensity ratio of Eu³⁺ (614 nm) to carbon dots (389 nm) shows a polynomial function with changing hydrogen peroxide concentration. The corresponding detection limit is 60 μM at a signal-to-noise ratio of 3 (S/N = 3) implying the potential use of the carbon dot-embedded Ag@EuWO₄(OH) as nanoprobe. The method was applied to the quantification of H₂O₂ in real samples with satisfactory results. Graphical abstract A carbon dot-embedded Ag@EuWO₄(OH) luminescence ratiometric probe was successfully prepared through hydrothermal method and in situ photochemical deposition strategy. The luminescence intensity ratio of Eu³⁺ to carbon dots shows synergistic luminescence response activity towards H₂O₂ with detection limit of 60 μM.

Epileptic brain fluorescent imaging reveals apigenin can relieve the myeloperoxidase-mediated oxidative stress and inhibit ferroptosis

Myeloperoxidase (MPO)-mediated oxidative stress has been suggested to play an important role in the pathological dysfunction of epileptic brains. However, there is currently no robust brain-imaging tool to detect real-time endogenous hypochlorite (HClO) generation by MPO or a fluorescent probe for rapid high-throughput screening of antiepileptic agents that control the MPO-mediated chlorination stress. Herein, we report an efficient two-photon fluorescence probe (named HCP) for the real-time detection of endogenous HClO signals generated by MPO in the brain of kainic acid (KA)-induced epileptic mice, where HClO-dependent chlorination of quinolone fluorophore gives the enhanced fluorescence response. With this probe, we visualized directly the endogenous HClO fluxes generated by the overexpression of MPO activity in vivo and ex vivo in mouse brains with epileptic behaviors. Notably, by using HCP, we have also constructed a high-throughput screening approach to rapidly screen the potential antiepileptic agents to control MPO-mediated oxidative stress. Moreover, from this screen, we identified that the flavonoid compound apigenin can relieve the MPO-mediated oxidative stress and inhibit the ferroptosis of neuronal cells. Overall, this work provides a versatile fluorescence tool for elucidating the role of HClO generation by MPO in the pathology of epileptic seizures and for rapidly discovering additional antiepileptic agents to prevent and treat epilepsy.

A Novel Ratiometric Cationic Iridium(III) Complex Phosphorescent Probe for Hydrogen Peroxide

A novel cationic iridium(III) complex phosphorescent probe (Ir-BE) containing aromatic boronate ester moiety as recognition unit was designed and synthesized. The probe exhibits ratiometric emission variations (I₄₉₀/I₅₅₀) with the color change from yellow to green only toward H₂O₂ with a broad pH range of 4 - 13. Different from other aromatic boronate-based probes, Ir-BE possesses larger Stokes shift (320 nm) and exhibits good linear correlation (R² = 0.998) between the emission ratio (I₄₉₀/I₅₅₀) and the H₂O₂ concentration in a range of 0 - 300 μM. The detection limit was as low as 0.21 μM. Furthermore, the real water sample studied further proved Ir-BE has excellent selectivity for the quantitative detection of H₂O₂.

Reactive Oxygen Species (ROS)-Activatable Prodrug for Selective Activation of ATF6 after Ischemia/Reperfusion Injury

We describe here the design, synthesis, and biological evaluation of a reactive oxygen species (ROS)-activatable prodrug for the selective delivery of 147, a small molecule ATF6 activator, for ischemia/reperfusion injury. ROS-activatable prodrug 1 and a negative control unable to release free drug were synthesized and examined for peroxide-mediated activation. Prodrug 1 blocks activity of 147 by its inability to undergo metabolic oxidation by ER-resident cytochrome P450 enzymes such as Cyp1A2, probed directly here for the first time. Biological evaluation of ROS-activatable prodrug 1 in primary cardiomyocytes demonstrates protection against peroxide-mediated toxicity and enhances viability following simulated I/R injury. The ability to selectively target ATF6 activation under diseased conditions establishes the potential for localized stress-responsive signaling pathway activation as a therapeutic approach for I/R injury and related protein misfolding maladies.

High-Performance Quinoline-Malononitrile Core as a Building Block for the Diversity-Oriented Synthesis of AIEgens

In vivo fluorescent monitoring of physiological processes with high-fidelity is essential in disease diagnosis and biological research, but faces extreme challenges due to aggregation-caused quenching (ACQ) and short-wavelength fluorescence. The development of high-performance and long-wavelength aggregation-induced emission (AIE) fluorophores is in high demand for precise optical bioimaging. The chromophore quinoline-malononitrile (QM) has recently emerged as a new class of AIE building block that possesses several notable features, such as red to near-infrared (NIR) emission, high brightness, marked photostability, and good biocompatibility. In this minireview, we summarize some recent advances of our established AIE building block of QM, focusing on the AIE mechanism, regulation of emission wavelength and morphology, the facile scale-up and fast preparation for AIE nanoparticles, as well as potential biomedical imaging applications.

In vivo real-time tracking of tumor-specific biocatalysis in cascade nanotheranostics enables synergistic cancer treatment

Glucose oxidase (GOD)-based synergistic cancer therapy has aroused great research interest in the context of cancer treatment due to the inherent biocompatibility and biodegradability. However, this emerging therapeutic system still lacks a strategy to predict and regulate the in vivo biocatalytic behavior of GOD in real time to minimize the side effects on normal tissues. Herein, we developed a tumor-specific cascade nanotheranostic system (BNG) that combines GOD-catalyzed oxidative stress and dual-channel fluorescent sensing, significantly improving the synergistic therapeutic efficacy with real-time feedback information. The nanotheranostic system remains completely silent in the blood circulatory system and selectively releases GOD enzymes in the tumor site, with enhanced near-infrared (NIR) fluorescence at 825 nm. Subsequently, GOD catalyzes H2O2 production, triggering cascade reactions with NIR fluorescence at 650 nm as an optical output, along with GSH depletion, enabling synergistic cancer treatment. The designed nanotheranostic system, integrated with tumor-activated cascade reactions and triggering a dual-channel output at each step, represents an insightful paradigm for precise cooperative cancer therapy.

An artificial protein-probe hybrid as a responsive probe for ratiometric detection and imaging of hydrogen peroxide in cells

A novel fluorescent protein-probe hybrid was devised for ratiometric detection and imaging of intracellular H₂O₂ with high sensitivity and selectivity.

Synthesis and characterization of light-degradable bromocoumarin functionalized polycarbonates

The preparation, characterization and degradation properties of novel light-degradable bromocoumarin functionalized polycarbonates were investigated in the present work.

A novel ratiometric fluorescent probe for rapid detection of hydrogen peroxide in living cells

In this work, we present a new ratiometric fluorescent probe JNY-1 for rapid and convenient detection of H₂O₂. The probe could selectively and sensitively respond to H₂O₂ within 10 min. In addition, this probe was successfully applied for monitoring and imaging of H₂O₂ in liver cancer HepG2 cells under physiological conditions.

A new ratiometric fluorescent probe JNY-1 for sensitive detection of H₂O₂ is presented with selectivity over other reactive oxygen species, reactive nitrogen species, and biologically relevant species. Imaging of H₂O₂ in liver cancer HepG2 cells was achieved.

Near-Infrared Photoactivatable Semiconducting Polymer Nanoblockaders for Metastasis-Inhibited Combination Cancer Therapy

Inhibition of protein biosynthesis is a promising strategy to develop new therapeutic modalities for cancers; however, noninvasive precise regulation of this cellular event in living systems has been rarely reported. In this study, a semiconducting polymer nanoblockader (SPN_B ) is developed that can inhibit intracellular protein synthesis upon near-infrared (NIR) photoactivation to synergize with photodynamic therapy (PDT) for metastasis-inhibited cancer therapy. SPN_B is self-assembled from an amphiphilic semiconducting polymer which is grafted with poly(ethylene glycol) conjugated with a protein biosynthesis blockader through a singlet oxygen (¹ O₂ ) cleavable linker. Such a designed molecular structure not only enables generation of ¹ O₂ under NIR photoirradiation for PDT, but also permits photoactivation of blockaders to terminate protein translation. Thereby, SPN_B exerts a synergistic action to afford an enhanced therapeutic efficacy in tumor ablation. More importantly, SPN_B -mediated photoactivation of protein synthesis inhibition precisely and remotely downregulates the expression levels of metastasis-related proteins in tumor tissues, eventually contributing to the complete inhibition of lung metastasis. This study thus proposes a photoactivatable protherapeutic design for metastasis-inhibited cancer therapy.

A Metabolically Stable Boron-Derived Tyrosine Serves as a Theranostic Agent for Positron Emission Tomography Guided Boron Neutron Capture Therapy

Boronophenylalanine (BPA) is the dominant boron delivery agent for boron neutron capture therapy (BNCT), and [¹⁸F]FBPA has been developed to assist the treatment planning for BPA-BNCT. However, the clinical application of BNCT has been limited by its inadequate tumor specificity due to the metabolic instability. In addition, the distinctive molecular structures between [¹⁸F]FBPA and BPA can be of concern as [¹⁸F]FBPA cannot quantitate boron concentration of BPA in a real-time manner. In this study, a metabolically stable boron-derived tyrosine (denoted as fluoroboronotyrosine, FBY) was developed as a theranostic agent for both boron delivery and cancer diagnosis, leading to PET imaging-guided BNCT of cancer. [¹⁸F]FBY was synthesized in high radiochemical yield (50%) and high radiochemical purity (98%). FBY showed high similarity with natural tyrosine. As shown in in vitro assays, the uptake of FBY in murine melanoma B16-F10 cells was L-type amino acid transporter (LAT-1) dependent and reached up to 128 μg/10⁶ cells. FBY displayed high stability in PBS solution. [¹⁸F]FBY PET showed up to 6 %ID/g in B16-F10 tumor and notably low normal tissue uptake (tumor/muscle = 3.16 ± 0.48; tumor/blood = 3.13 ± 0.50; tumor/brain = 14.25 ± 1.54). Moreover, administration of [¹⁸F]FBY tracer along with a therapeutic dose of FBY showed high accumulation in B16-F10 tumor and low normal tissue uptake. Correlation between PET-image and boron biodistribution was established, indicating the possibility of estimating boron concentration via a noninvasive approach. At last, with thermal neutron irradiation, B16-F10 tumor-bearing mice injected with FBY showed significantly prolonged median survival without exhibiting obvious systemic toxicity. In conclusion, FBY holds great potential as an efficient theranostic agent for imaging-guided BNCT by offering a possible solution of measuring local boron concentration through PET imaging.

An AIEgen-Peptide Conjugate as a Phototheranostic Agent for Phagosome-Entrapped Bacteria

The detection and elimination of intracellular bacteria remain a major challenge. In this work, we report an aggregation-induced emission (AIE) bioprobe that can detect bacterial infection and kill bacteria surviving inside macrophages through a dynamic process, notably specific molecular tailoring of the probe by caspase-1 activation in infected macrophages and accumulation of the residue on phagosomes containing bacteria, leading to light-up fluorescent signals. Moreover, the AIEgen can serve as a photosensitizer for generation of reactive oxygen species (ROS); and the average ROS indicator fluorescent signal intensity per unit area in the bacterial phagosomes is approximately 2.7-fold higher than that in the cytoplasm. This, in turn, induces bacteria killing with high efficiency and minimal cytotoxicity towards macrophages. We envision that this specific light-up bioprobe may provide a new approach for selective and sensitive detection and eradication of intracellular bacterial infections.

Imaging Dynamic Peroxynitrite Fluxes in Epileptic Brains with a Near-Infrared Fluorescent Probe

Epilepsy is a chronic neurodegenerative disease, and accumulating evidence suggests its pathological progression is closely associated with peroxynitrite (ONOO-). However, understanding the function remains challenging due to a lack of in vivo imaging probes for ONOO- determination in epileptic brains. Here, the first near-infrared imaging probe (named ONP) is presented for tracking endogenous ONOO- in brains of kainate-induced epileptic seizures with high sensitivity and selectivity. Using this probe, the dynamic changes of endogenous ONOO- fluxes in epileptic brains are effectively monitored with excellent temporal and spatial resolution. In vivo visualization and in situ imaging of hippocampal regions clearly reveal that a higher concentration of ONOO- in the epileptic brains associates with severe neuronal damage and epileptogenesis; curcumin administration can eliminate excessively increased ONOO-, further effectively protecting neuronal cells. Moreover, by combining high-content analysis and ONP, a high-throughput screening method for antiepileptic inhibitors is constructed, which provides a rapid imaging/screening approach for understanding epilepsy pathology and accelerating antiseizure therapeutic discovery.

Targeting Translation Activity at the Ribosome Interface with UV-Active Small Molecules

Puromycin is a well-known antibiotic that is used to study the mechanism of protein synthesis and to monitor ribosome activity due to its incorporation into nascent peptide chains. However, puromycin effects outside the ribosome catalytic core remain unexplored. Here, we developed two analogues (3PB and 3PC) of the 3'-end of tyrosylated-tRNA that can efficiently interact with several proteins associated with ribosomes. We biochemically characterized the binding of these analogues and globally mapped the direct small molecule-protein interactions in living cells using clickable and photoreactive puromycin-like probes in combination with in-depth mass spectrometry. We identified a list of proteins targeted by the molecules during ribosome activity (e.g., GRP78), and we addressed possible uses of the probes to sense the activity of protein synthesis and to capture associated RNA. By coupling genome-wide RNA sequencing methods with these molecules, the characterization of unexplored translational control mechanisms will be feasible.

A Doubly-Quenched Fluorescent Probe for Low-Background Detection of Mitochondrial H2O2

Hydrogen peroxide (H₂O₂) is an important product of oxygen metabolism and plays a crucial role in regulating a variety of cellular functions. Fluorescent probes have made a great contribution to our understanding of the biological role of endogenous H₂O₂. However, fluorescent probes for H₂O₂ featuring aryl boronates can suffer from moderate turn-on fluorescence responses. Strategies that can reduce the background fluorescence of these boronate-masked probes would significantly improve the sensitivity of endogenous H₂O₂ detection. In this work, we propose a general and reliable double-quenching concept for the design of fluorescent probes with low background fluorescence. A new fluorescent probe was developed for the detection of endogenous H₂O₂ in mitochondria of live cancer cells. This probe exploits a boronate-driven lactam formation and an eliminable quenching moiety simultaneously (i.e., the double-quenching effect) to reduce the background fluorescence, which ultimately results in the achievement of a >50-fold fluorescence turn-on. A linear concentration range of response between 1 and 60 μM and a detection limit of 0.025 μM can be obtained. This study not only presents a highly sensitive fluorescent probe for the detection of H₂O₂ but also provides a new concept for the design of fluorescent probes with a previously unachievable fluorescence off-on response ratio for other types of ROS and many other biologically relevant analytes.

UV cell stress induces oxidative cyclization of a protective reagent for DNA damage reduction in skin explants

UV irradiation is a major driver of DNA damage and ultimately skin cancer. UV exposure leads to persistent radicals that generate ROS over prolonged periods of time. Toward the goal of developing long-lasting antioxidants that can penetrate skin, we have designed a ROS-initiated protective (RIP) reagent that, upon reaction with ROS (antioxidant activity), self-cyclizes and then releases the natural product apocynin. Apocynin is a known antioxidant and inhibitor of NOX oxidase enzymes. A key phenol on the compound 1 controls ROS-initiated cyclization and makes 1 responsive to ROS with a EC50 comparable to common antioxidants in an ABTS assay. In an in vitro DNA nicking assay, the RIP reagent prevented DNA strand breaks. In cell-based assays, the reagent was not cytotoxic, apocynin was released only in cells treated with UVR, reduced UVR-induced cell death, and lowered DNA lesion formation. Finally, topical treatment of human skin explants with the RIP reagent reduced UV-induced DNA damage as monitored by quantification of cyclobutane dimer formation and DNA repair signaling via TP53. The reagent was more effective than administration of a catalase antioxidant on skin explants. This chemistry platform will expand the types of ROS-activated motifs and enable inhibitor release for potential use as a long-acting sunscreen.

Selectively light-up hydrogen peroxide in hypoxic cancer cells with a novel fluorescent probe

A novel fluorescent turn-on probe (HCyHP) was developed in a simple two-step synthesis for monitoring of exogenous and endogenous H2O2 levels in biological samples and hypoxic cancer diagnosis.

Fabrication of Liquid-Crystal-Based Optical Sensing Platform for Detection of Hydrogen Peroxide and Blood Glucose

Rapid and accurate determination of H₂O₂ is of great importance in practical applications. In this study, we demonstrate construction of liquid-crystal (LC)-based sensing platforms for sensitive and real-time detection of H₂O₂ with high accuracy for the first time. Single-stranded DNA (ssDNA) adsorbed onto the surface of nanoceria is released to the aqueous solution in the presence of H₂O₂, which disrupts arrangement of the self-assembled cationic surfactant monolayer decorated at the aqueous/LC interface. Thus, the orientation of LCs changes from a homeotropic to planar state, leading to change in the optical response from dark-to-bright appearance. As H₂O₂ can be produced during oxidation of glucose by glucose oxidase (GOx), detection of glucose is also fulfilled by employing the H₂O₂ sensing platform. Our system can detect H₂O₂ and glucose with concentrations as low as 28.9 nM and 0.52 μM, respectively. It shows high promise of using LC-based sensors for the detection of H₂O₂ and its relevant biomarkers in practical applications.