Detection and identification of oxidants formed during •NO/O2•⁻ reaction: a multi-well plate CW-EPR spectroscopy combined with HPLC analyses

Oxidation of ethidium-based probes by biological radicals: mechanism, kinetics and implications for the detection of superoxide

Hydroethidine (HE) and hydropropidine (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {HPr}^{+}$$\end{document}HPr+) are fluorogenic probes used for the detection of the intra- and extracellular superoxide radical anion (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {O}_{ {2}}^{\bullet -}$$\end{document}O2∙-). In this study, we provide evidence that HE and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {HPr}^{+}$$\end{document}HPr+ react rapidly with the biologically relevant radicals, including the hydroxyl radical, peroxyl radicals, the trioxidocarbonate radical anion, nitrogen dioxide, and the glutathionyl radical, via one-electron oxidation, forming the corresponding radical cations. At physiological pH, the radical cations of the probes react rapidly with \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {O}_{ {2}}^{\bullet -}$$\end{document}O2∙-, leading to the specific 2-hydroxylated cationic products. We determined the rate constants of the reaction between \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {O}_{ {2}}^{\bullet -}$$\end{document}O2∙- and the radical cations of the probes. We also synthesized N-methylated analogs of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {HPr}^{+}$$\end{document}HPr+ and HE which were used in mechanistic studies. Methylation of the amine groups was not found to prevent the reaction between the radical cation of the probe and the superoxide, but it significantly increased the lifetime of the radical cation and had a substantial effect on the profiles of the oxidation products by inhibiting the formation of dimeric products. We conclude that the N-methylated analogs of HE and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {HPr}^{+}$$\end{document}HPr+ may be used as a scaffold for the design of a new generation of probes for intra- and extracellular superoxide.

Tracking isotopically labeled oxidants using boronate-based redox probes

Reactive oxygen and nitrogen species have been implicated in many biological processes and diseases, including immune responses, cardiovascular dysfunction, neurodegeneration, and cancer. These chemical species are short-lived in biological settings, and detecting them in these conditions and diseases requires the use of molecular probes that form stable, easily detectable, products. The chemical mechanisms and limitations of many of the currently used probes are not well-understood, hampering their effective applications. Boronates have emerged as a class of probes for the detection of nucleophilic two-electron oxidants. Here, we report the results of an oxygen-18-labeling MS study to identify the origin of oxygen atoms in the oxidation products of phenylboronate targeted to mitochondria. We demonstrate that boronate oxidation by hydrogen peroxide, peroxymonocarbonate, hypochlorite, or peroxynitrite involves the incorporation of oxygen atoms from these oxidants. We therefore conclude that boronates can be used as probes to track isotopically labeled oxidants. This suggests that the detection of specific products formed from these redox probes could enable precise identification of oxidants formed in biological systems. We discuss the implications of these results for understanding the mechanism of conversion of the boronate-based redox probes to oxidant-specific products.

Detection and Characterization of Reactive Oxygen and Nitrogen Species in Biological Systems by Monitoring Species-Specific Products

SIGNIFICANCE

Since the discovery of the superoxide dismutase enzyme, the generation and fate of short-lived oxidizing, nitrosating, nitrating, and halogenating species in biological systems has been of great interest. Despite the significance of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in numerous diseases and intracellular signaling, the rigorous detection of ROS and RNS has remained a challenge. Recent Advances: Chemical characterization of the reactions of selected ROS and RNS with electron paramagnetic resonance (EPR) spin traps and fluorescent probes led to the establishment of species-specific products, which can be used for specific detection of several forms of ROS and RNS in cell-free systems and in cultured cells in vitro and in animals in vivo. Profiling oxidation products from the ROS and RNS probes provides a rigorous method for detection of those species in biological systems.

CRITICAL ISSUES

Formation and detection of species-specific products from the probes enables accurate characterization of the oxidative environment in cells. Measurement of the total signal (fluorescence, chemiluminescence, etc.) intensity does not allow for identification of the ROS/RNS formed. It is critical to identify the products formed by using chromatographic or other rigorous techniques. Product analyses should be accompanied by monitoring of the intracellular probe level, another factor controlling the yield of the product(s) formed.

FUTURE DIRECTIONS

More work is required to characterize the chemical reactivity of the ROS/RNS probes, and to develop new probes/detection approaches enabling real-time, selective monitoring of the specific products formed from the probes. Antioxid. Redox Signal. 28, 1416-1432.

Tumor Catalytic-Photothermal Therapy with Yolk-Shell Gold@Carbon Nanozymes

Nanozymes, as a new generation of artificial enzymes, offer great opportunities in biomedical engineering and disease treatment. Synergizing the multiple intrinsic functions of nanozymes can improve their performance in biological systems. Here, we report a novel nanozyme with yolk-shell structure fabricated by combining a single gold nanoparticle core with a porous hollow carbon shell nanospheres (Au@HCNs). Au@HCNs exhibited enzyme-like activities similar to horseradish peroxidase and oxidase under an acidic environment, showing the ability of ROS generation. More importantly, the ROS production of Au@HCNs was significantly improved upon 808 nm light irradiation by the photothermal effect, which is often used for tumor therapy. Cellular and animal studies further demonstrated that the efficient tumor destruction was achieved through the combination of light-enhanced ROS and photothermal therapy. These results implied that the intrinsic enzyme-like activity and photothermal conversion of nanozymes can be synergized for efficient tumor treatment, providing a proof-of-concept of tumor catalytic-photothermal therapy based on nanozymes.

High-throughput assays for superoxide and hydrogen peroxide: design of a screening workflow to identify inhibitors of NADPH oxidases

Recent progress characterizing the reaction mechanism(s) of fluorescent probes with reactive oxygen species has made it possible to rigorously analyze these reactive species in biological systems. We have developed rapid high throughput-compatible assays for monitoring cellular production of superoxide radical anion and hydrogen peroxide using hydropropidine and coumarin boronic acid probes, respectively. Coupling plate reader-based fluorescence measurements with HPLC-based simultaneous monitoring of superoxide radical anion and hydrogen peroxide provides the basis for the screening protocol for NADPH oxidase (Nox) inhibitors. Using this newly developed approach along with the medium-throughput plate reader-based oximetry and EPR spin trapping as confirmatory assays, it is now eminently feasible to rapidly and reliably identify Nox enzyme inhibitors with a markedly lower rate of false positives. These methodological advances provide an opportunity to discover selective inhibitors of Nox isozymes, through enhanced conceptual understanding of their basic mechanisms of action.