Quantitative Factors Introduced in the Feasibility Analysis of Reactive Oxygen Species (ROS)-Sensitive Triggers

Reactive oxygen species (ROS) are critical for cellular signaling. Various pathophysiological conditions are also associated with elevated levels of ROS. Hence, ROS-sensitive triggers have been extensively used for selective payload delivery. Such applications are predicated on two key functions: (1) a sufficient magnitude of concentration difference for the interested ROS between normal tissue/cells and intended sites and (2) appropriate reaction kinetics to ensure a sufficient level of selectivity for payload release. Further, ROS refers to a group of species with varying reactivity, which should not be viewed as a uniform group. In this review, we critically analyze data on the concentrations of different ROS species under various pathophysiological conditions and examine how reaction kinetics affect the success of ROS-sensitive linker chemistry. Further, we discuss different ROS linker chemistry in the context of their applications in drug delivery and imaging. This review brings new insights into research in ROS-triggered delivery, highlights factors to consider in maximizing the chance for success and discusses pitfalls to avoid.

A benzo BODIPY based fluorescent probe for selective visualization of hypochlorous acid in living cells and zebrafish

Hypochlorous acid (HOCl) is an essential endogenous reactive oxygen species in biological systems, playing a critical role in various physiological processes. Real-time monitoring of HOCl concentration in living organisms is essential for understanding its biological functions and pathological roles. In this study, we developed a novel fluorescent probe based on benzobodipy, BBDP, for rapid and sensitive detection of HOCl in aqueous solutions. The probe exhibited a significant fluorescence turn-on response to HOCl based on its specific oxidation reaction towards diphenylphosphine, with high selectivity, instantaneous response (less than 10 s), and low detection limit (21.6 nM). Furthermore, bioimaging results illustrated that the probe could be applied for real-time fluorescence imaging of HOCl in live cells and zebrafish. The development of BBDP may provide a new tool for exploring the biological functions of HOCl and its pathological roles in diseases.

Covalent Chemical Tools for Profiling Post-Translational Modifications

Nature increases the functional diversity of the proteome through posttranslational modifications (PTMs); a process that involves the proteolytic processing or catalytic attachment of diverse functional groups onto proteins. These modifications modulate a host of biological activities and responses. Consequently, anomalous PTMs often correlate to a host of diseases, hence there is a need to detect these transformations, both qualitatively and quantitatively. One technique that has gained traction is the use of robust chemical strategies to label different PTMs. By utilizing the intrinsic chemical reactivity of the different chemical groups on the target amino acid residues, this strategy can facilitate the delineation of the overarching and inclusionary roles of these different modifications. Herein, we will discuss the current state of the art in post-translational modification analysis, with a direct focus on covalent chemical methods used for detecting them.

Specific Reactions of RSNO, HSNO, and HNO and Their Applications in the Design of Fluorescent Probes

Nitric oxide (NO)-derived species play essential roles in regulating cellular responses. Among these species, S-nitrosothiols (including RSNO and HSNO) and nitroxyl (HNO) are especially interesting. Owing to their high reactivity and short survival time, the detection of these molecules in biological settings can be challenging. In this regard, much effort has been invested in exploring novel reactions of RSNO/HSNO/HNO and applying these reactions to develop fluorescence probes. Herein, reported specific reactions of RSNO/HSNO/HNO are summarized and strategies used in the design of fluorescent probes are illustrated. The properties and potential problems of representative probes are also discussed.

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.

Chemical probes for molecular imaging and detection of hydrogen sulfide and reactive sulfur species in biological systems

Hydrogen sulfide (H2S), a gaseous species produced by both bacteria and higher eukaryotic organisms, including mammalian vertebrates, has attracted attention in recent years for its contributions to human health and disease. H2S has been proposed as a cytoprotectant and gasotransmitter in many tissue types, including mediating vascular tone in blood vessels as well as neuromodulation in the brain. The molecular mechanisms dictating how H2S affects cellular signaling and other physiological events remain insufficiently understood. Furthermore, the involvement of H2S in metal-binding interactions and formation of related RSS such as sulfane sulfur may contribute to other distinct signaling pathways. Owing to its widespread biological roles and unique chemical properties, H2S is an appealing target for chemical biology approaches to elucidate its production, trafficking, and downstream function. In this context, reaction-based fluorescent probes offer a versatile set of screening tools to visualize H2S pools in living systems. Three main strategies used in molecular probe development for H2S detection include azide and nitro group reduction, nucleophilic attack, and CuS precipitation. Each of these approaches exploits the strong nucleophilicity and reducing potency of H2S to achieve selectivity over other biothiols. In addition, a variety of methods have been developed for the detection of other reactive sulfur species (RSS), including sulfite and bisulfite, as well as sulfane sulfur species and related modifications such as S-nitrosothiols. Access to this growing chemical toolbox of new molecular probes for H2S and related RSS sets the stage for applying these developing technologies to probe reactive sulfur biology in living systems.

A reductive ligation based fluorescent probe for S-nitrosothiols

A reductive ligation based fluorescent probe () for the detection of S-nitrosothiols (SNO) was developed. The probe showed good selectivity and sensitivity for SNO.

BR2BodPR2: highly fluorescent alternatives to PPh3and PhPCy2

The syntheses of highly fluorescent analogues of PPh₃and PhPCy₂based on the Bodipy chromophore are described.

Gel-based methods in redox proteomics

BACKGROUND

The key to understanding the full significance of oxidants in health and disease is the development of tools and methods that allow the study of proteins that sense and transduce changes in cellular redox. Oxidant-reactive deprotonated thiols commonly operate as redox sensors in proteins and a variety of methods have been developed that allow us to monitor their oxidative modification.

SCOPE OF THE REVIEW

This outline review specifically focuses on gel-based methods used to detect, quantify and identify protein thiol oxidative modifications. The techniques we discuss fall into one of two broad categories. Firstly, methods that allow oxidation of thiols in specific proteins or the global cellular pool to be monitored are discussed. These typically utilise thiol-labelling reagents that add a reporter moiety (e.g. affinity tag, fluorophore, chromophore), in which loss of labelling signifies oxidation. Secondly, we outline methods that allow specific thiol oxidation states of proteins (e.g. S-sulfenylation, S-nitrosylation, S-thionylation and interprotein disulfide bond formation) to be investigated.

MAJOR CONCLUSIONS

A variety of different gel-based methods for identifying thiol proteins that are sensitive to oxidative modifications have been developed. These methods can aid the detection and quantification of thiol redox state, as well as identifying the sensor protein.

GENERAL SIGNIFICANCE

By understanding how cellular redox is sensed and transduced to a functional effect by protein thiol redox sensors, this will help us better appreciate the role of oxidants in health and disease. This article is part of a Special Issue entitled Current methods to study reactive oxygen species - pros and cons and biophysics of membrane proteins. Guest Editor: Christine Winterbourn.

Chemical methods for the direct detection and labeling of S-nitrosothiols

SIGNIFICANCE

Posttranslational modification of proteins through phosphorylation, glycosylation, and oxidation adds complexity to the proteome by reversibly altering the structure and function of target proteins in a highly controlled fashion.

RECENT ADVANCES

The study of reversible cysteine oxidation highlights a role for this oxidative modification in complex signal transduction pathways. Nitric oxide (NO), and its respective metabolites (including reactive nitrogen species), participates in a variety of these cellular redox processes, including the reversible oxidation of cysteine to S-nitrosothiols (RSNOs). RSNOs act as endogenous transporters of NO, but also possess beneficial effects independent of NO-related signaling, which suggests a complex and versatile biological role. In this review, we highlight the importance of RSNOs as a required posttranslational modification and summarize the current methods available for detecting S-nitrosation.

CRITICAL ISSUES

Given the limitations of these indirect detection methods, the review covers recent developments toward the direct detection of RSNOs by phosphine-based chemical probes. The intrinsic properties that dictate this phosphine/RSNO reactivity are summarized. In general, RSNOs (both small molecule and protein) react with phosphines to yield reactive S-substituted aza-ylides that undergo further reactions leading to stable RSNO-based adducts.

FUTURE DIRECTIONS

This newly explored chemical reactivity forms the basis of a number of exciting potential chemical methods for protein RSNO detection in biological systems.

Methodologies for the characterization, identification and quantification of S-nitrosylated proteins

BACKGROUND

Protein S-nitrosylation plays a central role in signal transduction by nitric oxide (NO), and aberrant S-nitrosylation of specific proteins is increasingly implicated in disease.

SCOPE OF REVIEW

Here, methodologies for the characterization, identification and quantification of SNO-proteins are reviewed, focusing on techniques suitable for the structural characterization and absolute quantification of isolated SNO-proteins, the identification and relative quantification of SNO-proteins from complex mixtures as well as the mass spectrometry-based identification and relative quantification of sites of S-nitrosylation (SNO-sites) in proteins.

MAJOR CONCLUSIONS

Structural characterization of SNO-proteins by X-ray crystallography is increasingly being utilized to understand both the relationships between protein structure and Cys thiol reactivity as well as the consequences of S-nitrosylation on protein structure and function. New methods for the proteomic identification and quantification of SNO-proteins and SNO-sites have greatly impacted the ability to study protein S-nitrosylation in complex biological systems.

GENERAL SIGNIFICANCE

The ability to identify and quantify SNO-proteins has long been rate-determining for scientific advances in the field of protein S-nitrosylation. Therefore, it is critical that investigators in the field have a good understand the utility and limitations of modern analytical techniques for SNO-protein analysis. This article is part of a Special Issue entitled: Regulation of cellular processes by S-nitrosylation.

Chemical 'omics' approaches for understanding protein cysteine oxidation in biology

Oxidative cysteine modifications have emerged as a central mechanism for dynamic post-translational regulation of all major protein classes and correlate with many disease states. Elucidating the precise roles of cysteine oxidation in physiology and pathology presents a major challenge. This article reviews the current, targeted proteomic strategies that are available to detect and quantify cysteine oxidation. A number of indirect methods have been developed to monitor changes in the redox state of cysteines, with the majority relying on the loss of reactivity with thiol-modifying reagents or restoration of labeling by reducing agents. Recent advances in chemical biology allow for the direct detection of specific cysteine oxoforms based on their distinct chemical attributes. In addition, new chemical reporters of cysteine oxidation have enabled in situ detection of labile modifications and improved proteomic analysis of redox-regulated proteins. Progress in the field of redox proteomics should advance our knowledge of regulatory mechanisms that involve oxidation of cysteine residues and lead to a better understanding of oxidative biochemistry in health and disease.

Fluorogenic click reaction

Fluorogenic Cu(I)-catalyzed alkyne-azide cycloaddition (CuAAC) reactions have emerged as a powerful tool for bioconjugation, materials science, organic synthesis and drug discovery. This review highlights the design of the recent development of fluorogenic CuAAC reactions as well as their applications.