Hemin as a Molecular Probe for Nitric Oxide Detection in Physiological Solutions: Experimental and Theoretical Assessment.

Given its pivotal role in modulating various pathological processes, precise measurement of nitric oxide (●NO) levels in physiological solutions is imperative. The key techniques include the ozone-based chemiluminescence (CL) reactions, amperometric ●NO sensing, and Griess assay, each with its advantages and drawbacks. In this study, a hemin/H2O2/luminol CL reaction was employed for accurately detecting ●NO in diverse solutions. We investigated how the luminescence kinetics was influenced by ●NO from two donors, nitrite and peroxynitrite, while also assessing the impact of culture medium components and reactive species quenchers. Furthermore, we experimentally and theoretically explored the mechanism of hemin oxidation responsible for the initiation of light generation. Although both hemin and ●NO enhanced the H2O2/luminol-based luminescence reactions with distinct kinetics, hemin's interference with ●NO/peroxynitrite- modulated their individual effects. Leveraging the propagated signal due to hemin, the ●NO levels in solution were estimated, observing parallel changes to those detected via amperometric detection in response to varying concentrations of the ●NO-donor. The examined reactions aid in comprehending the mechanism of ●NO/hemin/H2O2/luminol interactions and how these can be used for detecting ●NO in solution with minimal sample size demands. Moreover, the selectivity across different solutions can be improved by incorporating certain quenchers for reactive species into the reaction.

Development of bishydrazide-based fluorescent probes for the imaging of cellular peroxynitrite (ONOO-) during ferroptosis.

Peroxynitrite (ONOO-) is a critical ROS in living systems, and could induce lipid peroxidation which is the driver of ferroptotic cell death. Therefore, precise and rapid detection of cellular ONOO- is critical for the deep study of the biological functions of ONOO- during ferroptosis. Herein, we developed fluorescent probes (Rh-1, Rh-2 and Rh-3) for the rapid detection of intracellular ONOO- during ferroptosis. These probes used bishydrazide groups as the reactive sites for ONOO-. The response of these probes to ONOO- resulted in the production of the emissive xanthene fluorophore, providing a marked enhancement in the fluorescence intensity at 561 nm. The probe Rh-3 exhibited prominent selectivity and sensitivity towards ONOO-. Bioimaging experiments suggested that Rh-3 could be applied to image exogenous and endogenous ONOO- in living cells. By fluorescence imaging, it was demonstrated that erastin-induced ferroptosis caused increased levels of the endogenous ONOO-, and ferrostatin-1 (Fer-1) and vitamin E (VE) could markedly inhibit the excessive production of ONOO- during ferroptosis in living cells.

Multi-engineered Graphene Extended-Gate Field-Effect Transistor for Peroxynitrite Sensing in Alzheimer's Disease.

The expression of ß-amyloid peptides (Aß), a pathological indicator of Alzheimer's disease (AD), was reported to be inapparent in the early stage of AD. While peroxynitrite (ONOO-) is produced excessively and emerges earlier than Aß plaques in the progression of AD, it is thus significant to sensitively detect ONOO- for early diagnosis of AD and its pathological research. Herein, we unveiled an integrated sensor for monitoring ONOO-, which consisted of a commercially available field-effect transistor (FET) and a high-performance multi-engineered graphene extended-gate (EG) electrode. In the configuration of the presented EG electrode, laser-induced graphene (LIG) intercalated with MnO2 nanoparticles (MnO2/LIG) can improve the electrical properties of LIG and the sensitivity of the sensor, and graphene oxide (GO)-MnO2/Hemin nanozyme with ONOO- isomerase activity can selectively trigger the isomerization of ONOO- to NO3-. With this synergistic effect, our EG-FET sensor can respond to the ONOO- with high sensitivity and selectivity. Moreover, taking advantage of our EG-FET sensor, we modularly assembled a portable sensing platform for wireless tracking ONOO- levels in the brain tissue of AD transgenic mice at earlier stages before massive Aß plaques appeared, and we systematically explored the complex role of ONOO- in the occurrence and development of AD.

Near-infrared Fluorescent Probes with Long-acting Cyclic Monitoring and Effectively Eliminating Peroxynitrite.

Two through-bond energy transfer fluorescent probes with a dihydroxyl naphthyl-pyrenyl conjugated system were synthesized for long-acting cyclic monitoring and eliminating peroxynitrite (ONOO- ). The probes exhibit large Stokes shifts (230 or 280 nm) and the fluorescence at 620 or 652 nm rapidly change in response to continuously variable concentrations of ONOO- under physiological conditions. The probes show good reversibility and can rapidly monitor the concentration changes of ONOO- in real time. In addition, with the additions of the probes, the decomposition of ONOO- is greatly accelerated. Therefore, the probes can effectively eliminate the excess ONOO- as well as sensing it. The biological studies showed that the probes can effectively and reversibly eliminate both exogenous and endogenous ONOO- in-situ as well as sensing its changes in cells, which can help to maintain the normal physiological concentration of ONOO- in organisms. This is the first system that a probe achieves multifunction including real-time detection, long-acting cyclic monitoring and in-situ elimination, thereby maintaining a normal physiological balance for ONOO- .

GC-MS Studies on Nitric Oxide Autoxidation and S-Nitrosothiol Hydrolysis to Nitrite in pH-Neutral Aqueous Buffers: Definite Results Using 15N and 18O Isotopes.

Nitrite (O=N-O-, NO2-) and nitrate (O=N(O)-O-, NO3-) are ubiquitous in nature. In aerated aqueous solutions, nitrite is considered the major autoxidation product of nitric oxide (●NO). ●NO is an environmental gas but is also endogenously produced from the amino acid L-arginine by the catalytic action of ●NO synthases. It is considered that the autoxidation of ●NO in aqueous solutions and in O2-containing gas phase proceeds via different neutral (e.g., O=N-O-N=O) and radical (e.g., ONOO●) intermediates. In aqueous buffers, endogenous S-nitrosothiols (thionitrites, RSNO) from thiols (RSH) such as L-cysteine (i.e., S-nitroso-L-cysteine, CysSNO) and cysteine-containing peptides such as glutathione (GSH) (i.e., S-nitrosoglutathione, GSNO) may be formed during the autoxidation of ●NO in the presence of thiols and dioxygen (e.g., GSH + O=N-O-N=O → GSNO + O=N-O- + H+; pKaHONO, 3.24). The reaction products of thionitrites in aerated aqueous solutions may be different from those of ●NO. This work describes in vitro GC-MS studies on the reactions of unlabeled (14NO2-) and labeled nitrite (15NO2-) and RSNO (RS15NO, RS15N18O) performed in pH-neutral aqueous buffers of phosphate or tris(hydroxyethylamine) prepared in unlabeled (H216O) or labeled H2O (H218O). Unlabeled and stable-isotope-labeled nitrite and nitrate species were measured by gas chromatography-mass spectrometry (GC-MS) after derivatization with pentafluorobenzyl bromide and negative-ion chemical ionization. The study provides strong indication for the formation of O=N-O-N=O as an intermediate of ●NO autoxidation in pH-neutral aqueous buffers. In high molar excess, HgCl2 accelerates and increases RSNO hydrolysis to nitrite, thereby incorporating 18O from H218O into the SNO group. In aqueous buffers prepared in H218O, synthetic peroxynitrite (ONOO-) decomposes to nitrite without 18O incorporation, indicating water-independent decomposition of peroxynitrite to nitrite. Use of RS15NO and H218O in combination with GC-MS allows generation of definite results and elucidation of reaction mechanisms of oxidation of ●NO and hydrolysis of RSNO.

Multifunctional Mitochondria-Targeting Near-Infrared Fluorescent Probe for Viscosity, ONOO-, Mitophagy, and Bioimaging.

Irregularities in mitochondrial viscosity and peroxynitrite (ONOO-) concentration can lead to mitochondrial dysfunction. It is still a great challenge to develop near-infrared (NIR) fluorescent probes to simultaneously detect viscosity, endogenous ONOO-, and mitophagy. Herein, a multifunctional mitochondria-targeting NIR fluorescent probe P-1 was first synthesized for simultaneously detecting viscosity, ONOO-, and mitophagy. P-1 used quinoline cations as a mitochondrial targeting moiety, arylboronate as an ONOO- responsive group, and detected the change of viscosity by the twisted internal charge transfer (TICT) mechanism. The probe has an excellent response to the viscosity during inflammation by lipopolysaccharides (LPSs) and mitophagy induced by starvation at 670 nm. The viscosity changes of the probe induced by nystatin in zebrafish showed that P-1 was able to detect microviscosity in vivo. P-1 also showed good sensitivity with a detection limit of 6.2 nM for ONOO- detection and was successfully applied to the endogenous ONOO- detection in zebrafish. Moreover, P-1 has the ability to distinguish between cancer cells and normal cells. All of these features make P-1 a promising candidate to detect mitophagy and ONOO- -associated physiological and pathological processes.

Human serum albumin-based supramolecular host-guest boronate probe for enhanced peroxynitrite sensing.

Peroxynitrite (ONOO-) is an important oxygen/nitrogen reactive species implicated in a number of physiological and pathological processes. However, due to the complexity of the cellular micro-environment, the sensitive and accurate detection of ONOO- remains a challenging task. Here, we developed a long-wavelength fluorescent probe based on the conjugation between a TCF scaffold and phenylboronate; the resulting conjugate is capable of supramolecular host-guest assembly with human serum albumin (HSA) for the fluorogenic sensing of ONOO-. The probe exhibited an enhanced fluorescence over a low concentration range of ONOO- (0-9.6 µM), whist the fluorescence was quenched when the concentration of ONOO- exceeded 9.6 µM. In addition, when human serum albumin (HSA) was added, the initial fluorescence of the probe was significantly enhanced, which enabled the more sensitive detection of low-concentrations of ONOO- in aqueous buffer solution and in cells. The molecular structure of the supramolecular host-guest ensemble was determined using small-angle X-ray scattering.

Quasi-LD-Targeted and ONOO--Responsive Fluorescent Probe for Investigating the Interaction of Nonalcoholic Fatty Liver with Drug-Induced Liver Injury.

Hepatic lipid droplets (LDs) and peroxynitrite (ONOO-) levels are closely related to nonalcoholic fatty liver disease (NAFLD). Additionally, some drug-induced liver injury (DILI) is often associated with ONOO-. Here, we constructed and screened the quasi-LDs-targeted and ONOO--responsive fluorescent probe MBDP-Py+ to investigate the interaction of NAFLD with DILI. By monitoring the upregulation of the ONOO- levels and the accumulation of LDs, MBDP-Py+ was more sensitive and efficient than tissue staining and serum markers detection in evaluating the early toxicity of NAFLD and diagnosing the anticancer-DILI. More importantly, the sensitive enhancement of fluorescence signals demonstrated that in different stages of NAFLD, the dominant element of liver injury was different in the NAFLD combined with DILI mice models. As the degree of NAFLD deepens, the synergistic effect of the two will lead to more serious liver damage.

Sensitive Detection of Nitrite and Nitrate in Seawater by 222 nm UV-Irradiated Photochemical Conversion to Peroxynitrite and Ion Chromatography-Luminol Chemiluminescence System.

Sensitive detection methods for nitrite (NO2-) and nitrate (NO3-) ions are essential to understand the nitrogen cycle and for environmental protection and public health. Herein, we report a detection method that combines ion-chromatographic separation of NO2- and NO3-, on-line photochemical conversion of these ions to peroxynitrite (ONOO-) by irradiation with a 222 nm excimer lamp, and chemiluminescence from the reaction between luminol and ONOO-. The detection limits for NO2- and NO3- were 0.01 and 0.03 µM, respectively, with linear ranges of 0.010-2.0 and 0.10-3.0 µM, respectively, at an injection volume of 1 µL. The results obtained by the proposed method for seawater analysis corresponded with those of a reference method (AutoAnalyzer based on the Griess reaction). As luminol chemiluminescence can measure ONOO- at picomolar concentrations, our method is expected to be able to detect NO2- and NO3- at picomolar concentrations owing to the high conversion ratio to ONOO- (>60%), assuming that contamination and background chemiluminescence issues can be resolved. This method has the potential to emerge as an innovative technology for NO2- and NO3- detection in various samples.

Mitochondrial targeted fluorescent nitrite peroxide probe for dynamic monitoring of cellular lung injury.

Herein, a mitochondrial targeted fluorescent nitrite peroxide probe CHP for dynamic monitoring of cellular lung injury was developed. For the practical delivery and selectivity, the structural features including pyridine head and borate recognition group were selected. CHP could respond to ONOO- with the 585 nm fluorescence signal. The detecting system indicated advantages such as wide linear range (0.0-30 µM), high sensitivity (LOD = 0.18 µM), high selectivity and steadiness under different environmental conditions including pH (3.0-10.0), time (48 h) and medium. In living A549 cells, the response of CHP towards ONOO- showed dose-dependent and time-dependent tendencies. The co-localization suggested that CHP could achieve mitochondrial targeting. Moreover, CHP could monitor the variation of endogenous ONOO- level and the cellular lung injury induced by LPS.

A highly selective red-emitting fluorescent probe and its micro-nano-assembly for imaging endogenous peroxynitrite (ONOO-) in living cells.

Endogenous peroxynitrite plays a very important role in the regulation of life activities. However, validated tools for ONOO- tests are currently insufficient. We designed a fluorescent probe TPA-F-NO2 with a low fluorescence background in water based on the D-π-A structure for the imaging of endogenous ONOO- in living cells. TPA-F-NO2 can realize the naked eye detection of ONOO- due to the obvious color change. TPA-F-NO2 has the advantages of large stokes shift, high signal-to-noise ratio, high selectivity and sensitivity. The quantitative detection can be achieved in the range of 0-14 µM ONOO-. Due to its solvatochromic characteristics, TPA-F-NO2 has the potential to be used in OLEDs and other fields. In addition, 4-methylumbelliferone has a wide range of anticancer effects as an inhibitor of hyaluronic acid. We prepared TPA-MU-NPs by assembling TPA-F-NO2 and 4-methylumbelliferone. It also endows TPA-MU-NPs with ONOO- imaging function and anti-proliferation effect on breast cancer cells and other cells. This 'probe-drug' assembly strategy provides ideas for the design and optimization of dual-functional probes.

Multiple oxidative post-translational modifications of human glutamine synthetase mediate peroxynitrite-dependent enzyme inactivation and aggregation.

Glutamine synthetase (GS), which catalyzes the ATP-dependent synthesis of L-glutamine from L-glutamate and ammonia, is a ubiquitous and conserved enzyme that plays a pivotal role in nitrogen metabolism across all life domains. In vertebrates, GS is highly expressed in astrocytes, where its activity sustains the glutamate-glutamine cycle at glutamatergic synapses and is thus essential for maintaining brain homeostasis. In fact, decreased GS levels or activity have been associated with neurodegenerative diseases, with these alterations attributed to oxidative post-translational modifications of the protein, in particular tyrosine nitration. In this study, we expressed and purified human GS (HsGS) and performed an in-depth analysis of its oxidative inactivation by peroxynitrite (ONOO-) in vitro. We found that ONOO- exposure led to a dose-dependent loss of HsGS activity, the oxidation of cysteine, methionine, and tyrosine residues and also the nitration of tryptophan and tyrosine residues. Peptide mapping by LC-MS/MS through combined H216O/H218O trypsin digestion identified up to 10 tyrosine nitration sites and five types of dityrosine cross-links; these modifications were further scrutinized by structural analysis. Tyrosine residues 171, 185, 269, 283, and 336 were the main nitration targets; however, tyrosine-to-phenylalanine HsGS mutants revealed that their sole nitration was not responsible for enzyme inactivation. In addition, we observed that ONOO- induced HsGS aggregation and activity loss. Thiol oxidation was a key modification to elicit aggregation, as it was also induced by hydrogen peroxide treatment. Taken together, our results indicate that multiple oxidative events at various sites are responsible for the inactivation and aggregation of human GS.

Rational Design of a Dual-Channel Fluorescent Probe for the Simultaneous Imaging of Hypochlorous Acid and Peroxynitrite in Living Organisms.

Hypochlorous acid (HOCl) and peroxynitrite (ONOO-) are two important highly reactive oxygen/nitrogen species, which commonly coexist in biosystems and play pivotal roles in many physiological and pathological processes. To investigate their function and correlations, it is urgently needed to construct chemical tools that can track the production of HOCl and ONOO- in biological systems with distinct fluorescence signals. Here, we found that the coumarin fluorescence of coumarin-benzopyrylium (CB) hydrazides (spirocyclic form) is dim, and their fluorescence properties are controlled by their benzopyran moiety via an intramolecular photo-induced electron transfer (PET) process. Based on this mechanism, we report the development of a fluorescent probe CB2-H for the simultaneous detection of HOCl and ONOO-. ONOO- can selectively oxidize the hydrazide group of CB2-H to afford the parent dye CB2 (Absmax/Emmax = 631/669 nm). In the case of HOCl, it undergoes an electrophilic attack on the benzopyran moiety of CB2-H to give a chlorinated product CB2-H-Cl, which inhibits the PET process within the probe and thus affords a turn-on fluorescence response at the coumarin channel (Absmax/Emmax = 407/468 nm). Due to the marked differences in absorption/emission wavelengths between the HOCl and ONOO- products, CB2-H enables the concurrent detection of HOCl and ONOO- at two independent channels without spectral cross-interference. CB2-H has been applied for dual-channel fluorescence imaging of endogenously produced HOCl and ONOO- in living cells and zebrafish under different stimulants. The present probe provides a useful tool for further exploring the distribution and correlation of HOCl and ONOO- in more biosystems.

A Dual-Channel Fluorescent Nanoprobe for Sequential Detection of ATP and Peroxynitrite to Accurately Distinguish between Normal Cells and Cancer Cells.

Cancer is one of the biggest public enemies of global health with its high morbidity and mortality. Achieving early diagnosis is the most effective means of reducing cancer harm, which requires the use of powerful tools to accurately identify biomarkers. However, most of the reported fluorescent probes for cancer diagnosis can only detect one substance, which makes it difficult to meet the requirements of high accuracy. Here, a fluorescent nanoprobe (CPQ@ZIF-90) for sequential detection of ATP and ONOO- is constructed by encapsulating the ONOO- sensitive unit CPQ within ZIF-90. CPQ@ZIF-90 first reacts with ATP to release CPQ, which greatly enhances the fluorescence at 740 nm. Then, the released CPQ continues to react with ONOO- and is oxidatively cleaved by ONOO- to form a coumarin product with a small π-conjugated structure, which significantly enhances the fluorescence at 510 nm. CPQ@ZIF-90 shows high sensitivity and selectivity for the detection of ATP and then ONOO-. Moreover, CPQ@ZIF-90 has good biocompatibility and successfully realizes the sequential detection of a dual-channel fluorescence change of ATP and ONOO- in living cells and zebrafish and accurately distinguishes normal cells from cancer cells. CPQ@ZIF-90 is expected to be a potential tool for accurate cancer diagnosis through sequential detection of two cancer markers.

Activated Two-Photon Near-Infrared Ratiometric Fluorescent Nanoprobe for ONOO- Detection and Early Diagnosis and Assessment of Liver Injury.

Liver injury poses a serious threat to human health and growing evidence suggests that it is closely associated with a biomarker (peroxynitrite, ONOO-). Therefore, considering that the relationship of ONOO- levels with the occurrence and development of liver injury disease remains a challenge, an urgent need exists to develop a reliable and robust tool for its visual rapid diagnosis and assessment. Herein, a two-photon near-infrared (TP-NIR) ratiometric fluorescent nanoprobe (NTC) based on a fluorescence resonance energy transfer (FRET) strategy was designed, synthesized, and characterized, which had the advantages of good water solubility, low background interference, deep tissue penetration, and high imaging resolution. Specially, NTC was constructed by self-assembly of an alkynyl group of a small-molecule fluorescent probe (NR) via click chemistry grafting onto azide chitosan (natural polymeric nanomaterial). NR contained acceptor 1 (NIR fluorophore) and donor 3 (D-π-A structure of naphthalimide derivative fluorophore) with outstanding TP properties that could be activated by ONOO- for the ratiometric detection of ONOO-. Furthermore, in the presence of ONOO-, NTC exhibited a short response time (∼10 s) and high selectivity and sensitivity toward ONOO- with an excellent detection limit as low as 15.3 nM over other reactive oxygen/nitrogen species. Notably, NTC has been successfully employed for ONOO- detection and imaging in living HepG2 cells, liver injury mice tissues, and mice models with satisfactory results. Thus, the construction of this NTC nanoprobe can provide a robust molecule tool for enabling early diagnosis and assessment of liver injury in the future.

A ratiometric fluorescent nanoprobe for ultrafast imaging of peroxynitrite in living cells.

For ratiometrically imaging peroxynitrite (ONOO-) in living cells, we devised and fabricated a novel fluorescent nanoprobe, NC-NP530/460, in this study. To achieve ratiometric fluorescence response towards ONOO-, NC-NP530/460 used 3-(2-benzothiazolyl) coumarin (Cou-Bz) as the internal reference and 1,8-naphthimide derivative (Naph-PN) as a fluorescent ONOO- probe. These compounds were incorporated into an amphiphilic block polymer called Pluronic F-127. In addition to an ultrafast response to ONOO-, NC-NP530/460 also showed great selectivity and sensitive detection (detection limit was 4.51 µM). It was important to note that NC-NP530/460 demonstrated solid performance for ONOO- fluorescence ratio imaging in living cells, highlighting its potential for ONOO--related chemical biology research.

Development of Probes with High Signal-to-Noise Ratios Based on the Facile Modification of Xanthene Dyes for Imaging Peroxynitrite during the Liver Ischemia/Reperfusion Process.

Xanthene-based fluorescence probes with high signal-to-noise ratios are highly useful for bioimaging. However, current strategies for improving the signal-to-noise ratios of xanthene fluorescence probes based on the replacement of oxygen group elements and extension of conjugation always require complicated modifications or time-consuming synthesis, which unfortunately goes against the original intention owing to the alteration of the parent structure and outstanding properties. Herein, a facile strategy is presented for developing a unique class of high signal-to-noise ratio probes by modifying the 2' position of a rhodol scaffold with different substituents. Systematic studies have shown that the probe named Rhod-CN-B with a strong electron-withdrawing methylene malononitrile functional group (-CH═(CN)2) at the 2' position displayed a high signal-to-noise ratio and excellent photostability in aqueous solutions and could detect peroxynitrite (ONOO-) without interference from other biologically active species. In addition, the excellent selectivity and sensitivity of Rhod-CN-B displayed satisfactory properties in tracking the endogenous production of ONOO- in the apoptosis process of liver cells stimulated by lipopolysaccharides. Moreover, we utilized Rhod-CN-B to perform imaging of ONOO- in the course of the liver ischemia/reperfusion (I/R) process, revealing that high ONOO- levels were associated with aggravation of hepatocyte damage. All of the experimental data and results demonstrated that Rhod-CN-B could be a powerful tool for imaging ONOO- in more physiological and pathological processes.

Solvent Cage Concept for the Homolytic Fragmentation of the Peroxynitrite-CO2 Adduct, ONOOCO2.

The toxicity of peroxynitrite, ONOO-, is directed by carbon dioxide via the formation of the corresponding adduct, ONOOCO2-. Entity ONOOCO2- is believed to be a highly unstable compound that primarily decomposes to nitrate and carbon dioxide, but it also undergoes fractional homolysis to generate carbonate radical anion, CO3•-, and nitrogen dioxide, NO2•, in a so-called solvent (radical) cage reaction. Recently, Koppenol et al. reviewed their proposal that ONOOCO2- is a relatively long-lived intermediate, arguing that "the solvent cage as proposed is physically not realistic". To further address whether ONOOCO2- could be a long-lived species, bond dissociation enthalpies (BDE) were calculated by the composite reference method (SMD)W1BD. Anion ONOOCO2- can exist in two conformers, s-cis-gauche and s-trans-gauche with predicted gas-phase O-O BDEs of about 10.8 and 9.5 kcal mol-1, respectively. Therefore, both conformers should have very short lifetimes. The (SMD)W1BD method was also used to evaluate the thermodynamic parameters of interest, revealing that the homolytic decomposition of ONOOCO2- is the most reasonable pathway. Moreover, previously reported experimental chemically induced dynamic nuclear polarization data also support the intermediacy of the radical cage and the formation of products CO2 and NO3- at a total yield of about 70%. Because the solvent radical cage concept for the decay of ONOO- in the presence of CO2 is supported by a variety of spectrometric methods as well as by quantum chemical calculations at high levels of theory, it provides strong evidence against the "out-of-cage" construct. For clarification of the nature of the transient UV/vis absorption(s) between 600 and 700 nm, as observed by Koppenol et al., several experimental approaches are suggested.

Construction of a Mitochondria-Endoplasmic Reticulum Dual-Targeted Red-Emitting Fluorescent Probe for Imaging Peroxynitrite in Living Cells and Zebrafish.

Peroxynitrite (ONOO- ) is one of the important reactive oxygen species, which plays a vital role in the physiological process of intracellular redox balance. Revealing the biological functions of ONOO- will contribute to further understanding of the oxidative process of organisms. In this work, we designed and synthesized a novel red-emitting fluorescent probe MCSA for the detection of ONOO- , which could rapidly respond to ONOO- within 250 s and exhibited high sensitivity to ONOO- with a low detection limit of 78 nM. Co-localization experiments demonstrated MCSA had the ability to localize into the mitochondria and endoplasmic reticulum. What's more, MCSA enabled monitoring ONOO- level changes during tunicamycin-induced endoplasmic reticulum stress. We have also successfully achieved the visual detection of exogenous and endogenous ONOO- in living cells and zebrafish. This work presented a chemical tool for imaging ONOO- in vitro and in vivo.

A Fluorogenic ONOO--Triggered Carbon Monoxide Donor for Mitigating Brain Ischemic Damage.

Ischemia-reperfusion (I/R) injuries are from the secondary radicals of ONOO-. Direct radical scavenging is difficult because of their high reactivity. ONOO- is longer-lived than the radicals in the biological milieu. Scavenging ONOO- suppresses radical generation preventively. CO is neuroprotective during ischemia. With the scaffold of carbon-caged xanthene, we designed an OONO--triggered CO donor (PCOD585). Notably, PCOD585 exhibited a concomitant fluorescence turn-on upon ONOO-detection, facilitating microscopic monitoring. PCOD585 was cytoprotective in oxygen-glucose deprivation (OGD)-insulted PC-12 cells. It was permeable to the blood-brain barrier and further exhibited neuroprotective effects to MCAO rats by reducing infarction volume, cell apoptosis, and brain edema.