Molecular imaging of peroxynitrite with HKGreen-4 in live cells and tissues

Caveolin-1 protects against hepatic ischemia/reperfusion injury through ameliorating peroxynitrite-mediated cell death

Nitrative stress is considered as an important pathological process of hepatic ischemia and reperfusion injury but its regulating mechanisms are largely unknown. In this study, we tested the hypothesis that caveolin-1 (Cav-1), a plasma membrane scaffolding protein, could be an important cellular signaling against hepatic I/R injury through inhibiting peroxynitrite (ONOO(-))-induced cellular damage. Male wild-type mice and Cav-1 knockout (Cav-1(-/-)) were subjected to 1h hepatic ischemia following 1, 6 and 12h of reperfusion by clipping and releasing portal vessels respectively. Immortalized human hepatocyte cell line (L02) was subjected to 1h hypoxia and 6h reoxygenation and treated with Cav-1 scaffolding domain peptide. The major discoveries included: (1) the expression of Cav-1 in serum and liver tissues of wild-type mice was time-dependently elevated during hepatic ischemia-reperfusion injury. (2) Cav-1 scaffolding domain peptide treatment inhibited cleaved caspase-3 expression in the hypoxia-reoxygenated L02 cells; (3) Cav-1 knockout (Cav-1(-/-)) mice had significantly higher levels of serum transaminases (ALT&AST) and TNF-α, and higher rates of apoptotic cell death in liver tissues than wild-type mice after subjected to 1h hepatic ischemia and 6hour reperfusion; (4) Cav-1(-/-) mice revealed higher expression levels of iNOS, ONOO(-) and 3-nitrotyrosine (3-NT) in the liver than wild-type mice, and Fe-TMPyP, a representative peroxynitrite decomposition catalyst (PDC), remarkably reduced level of ONOO(-) and 3-NT and ameliorated the serum ALT, AST and TNF-α levels in both wild-type and Cav-1(-/-) mice. Taken together, we conclude that Cav-1 could play a critical role in preventing nitrative stress-induced liver damage during hepatic ischemia-reperfusion injury.

Live-cell imaging approaches for the investigation of xenobiotic-induced oxidant stress

BACKGROUND

Oxidant stress is arguably a universal feature in toxicology. Research studies on the role of oxidant stress induced by xenobiotic exposures have typically relied on the identification of damaged biomolecules using a variety of conventional biochemical and molecular techniques. However, there is increasing evidence that low-level exposure to a variety of toxicants dysregulates cellular physiology by interfering with redox-dependent processes.

SCOPE OF REVIEW

The study of events involved in redox toxicology requires methodology capable of detecting transient modifications at relatively low signal strength. This article reviews the advantages of live-cell imaging for redox toxicology studies.

MAJOR CONCLUSIONS

Toxicological studies with xenobiotics of supra-physiological reactivity require careful consideration when using fluorogenic sensors in order to avoid potential artifacts and false negatives. Fortunately, experiments conducted for the purpose of validating the use of these sensors in toxicological applications often yield unexpected insights into the mechanisms through which xenobiotic exposure induces oxidant stress.

GENERAL SIGNIFICANCE

Live-cell imaging using a new generation of small molecule and genetically encoded fluorophores with excellent sensitivity and specificity affords unprecedented spatiotemporal resolution that is optimal for redox toxicology studies. This article is part of a Special Issue entitled Air Pollution, edited by Wenjun Ding, Andrew J. Ghio and Weidong Wu.

A Critical Review of Methodologies to Detect Reactive Oxygen and Nitrogen Species Stimulated by NADPH Oxidase Enzymes: Implications in Pesticide Toxicity

In this review, potential fluorescent probe applications for detecting reactive oxygen and nitrogen species (ROS/RNS) generated from NADPH oxidases (e.g., Nox2) and nitric oxide synthase enzymes are discussed in the context of pesticide toxicology. Identification of the specific marker products derived from the interaction between ROS/RNS and the fluorescent probes (e.g., hydroethidine and coumarin boronate) is critical. Due to the complex nature of reactions between the probes and ROS/RNS, we suggest avoiding the use of fluorescence microscopy for detecting oxidizing/nitrating species. We also critically examined the viability of using radiolabeling or positron emission tomography (PET) for ROS/RNS detection. Although these techniques differ in sensitivity and detection modalities, the chemical mechanism governing the reaction between these probes and ROS/RNS should remain the same. To unequivocally detect superoxide with these probes (i.e., radiolabeled and PET-labeled hydroethidine analogs), the products should be isolated and characterized by LC-MS/MS or HPLC using an appropriate standard.

Characterization of Fluorescein-Based Monoboronate Probe and Its Application to the Detection of Peroxynitrite in Endothelial Cells Treated with Doxorubicin

Boronate probes have emerged recently as a versatile tool for the detection of reactive oxygen and nitrogen species. Here, we present the characterization of a fluorescein-based monoboronate probe, a 4-(pinacol boronate)benzyl derivative of fluorescein methyl ester (FBBE), that proved to be useful to detect peroxynitrite in cell culture experiments. The reactivity of FBBE toward peroxynitrite as well hypochlorite, hydrogen peroxide, and tyrosyl hydroperoxide was determined. Second-order rate constants of the reactions of FBBE with peroxynitrite, HOCl, and H2O2 at pH 7.4 were equal to (2.8 ± 0.2) × 10(5) M(-1) s(-1), (8.6 ± 0.5) × 10(3) M(-1) s(-1), and (0.96 ± 0.03) M(-1) s(-1), respectively. The presence of glutathione completely blocked the oxidation of the probe by HOCl and significantly inhibited its oxidation by H2O2 and tyrosyl hydroperoxide but not by peroxynitrite. The oxidative conversion of the probe was also studied in the systems generating singlet oxygen, superoxide radical anion, and nitric oxide in the presence and absence of glutathione. Spectroscopic characterization of FBBE and its oxidation product has been also performed. The differences in the reactivity pattern were supported by DFT quantum mechanical calculations. Finally, the FBBE probe was used to study the oxidative stress in endothelial cells (Ea.hy926) incubated with doxorubicin, a quinone anthracycline antibiotic. In endothelial cells pretreated with doxorubicin, FBBE was oxidized, and this effect was reversed by PEG-SOD and L-NAME but not by catalase.

A rationally designed rhodamine-based fluorescent probe for molecular imaging of peroxynitrite in live cells and tissues

A novel fluorescent reporter HKYellow was rationally designed for the robust visualization of peroxynitrite production in live cells and tissues.

Herein, we present the rational design, synthesis, characterization, and biological applications of a new rhodamine-based fluorescent probe, HKYellow, for the detection and molecular imaging of peroxynitrite, an important highly reactive oxidant involved in a variety of physiological and pathological processes. HKYellow was rationally designed on the basis of the efficient fluorescence quenching effect of the N-phenyl group to the rhodamine core and a peroxynitrite-triggered N-dearylation reaction to achieve a sensitive and selective fluorescence turn-on response toward peroxynitrite in chemical and biological levels. This probe has been thoroughly evaluated for the robust imaging of peroxynitrite in live cells and tissues. By utilizing HKYellow, we provide the first visual evidence that peroxynitrite is generated in mouse liver tissues under an acute alcohol binge or ischemic–reperfusion condition. This probe should be a powerful molecular imaging tool for interrogating the complex biological roles of peroxynitrite under various biological settings.

The N-B Interaction through a Water Bridge: Understanding the Chemoselectivity of a Fluorescent Protein Based Probe for Peroxynitrite

Boronic acid and esters have been extensively utilized for molecular recognition and chemical sensing. We recently reported a genetically encoded peroxynitrite (ONOO(-))-specific fluorescent sensor, pnGFP, based on the incorporation of a boronic acid moiety into a circularly permuted green fluorescent protein (cpGFP) followed by directed protein evolution. Different from typical arylboronic acids and esters, the chromophore of pnGFP is unreactive to millimolar concentrations of hydrogen peroxide (H2O2). The focus of this study is to explore the mechanism for the observed unusual chemoselectivity of pnGFP toward peroxynitrite over hydrogen peroxide by using site-directed mutagenesis, X-ray crystallography, (11)B NMR, and computational analysis. Our data collectively support that a His residue on the protein scaffold polarizes a water molecule to induce the formation of an sp(3)-hybridized boron in the chromophore, thereby tuning the reactivity of pnGFP with various reactive oxygen and nitrogen species (ROS/RNS). Our study demonstrates the first example of tunable boron chemistry in a folded nonnative protein, which offers wide implications in designing selective chemical probes.

: a fluorescent hypochlorous acid probe for live-cell and in vivo imaging and quantitative application in flow cytometry and a 96-well microplate assay

We describe an ultra-selective and ultra-sensitive HOCI fluorescent probe HKOCl-3 for live-cell and in vivo imaging and quantitative applications.

Ultra-selective and ultra-sensitive probes for hypochlorous acid (HOCl), one of the most poorly understood reactive oxygen species (ROS), are urgently needed to unravel the HOCl functions in important biological processes such as development and innate immunity. Based on a selective oxidative O-dearylation reaction of 2,6-dichlorophenol toward HOCl over other reactive oxygen species, we have developed a novel fluorescent probe HKOCl-3 for HOCl detection with ultra-selectivity, ultra-sensitivity and a rapid turn-on response. The functional robustness of HKOCl-3 for endogenous HOCl detection and imaging has been thoroughly scrutinized in multiple types of phagocytes and in vivo imaging of live intact zebrafish embryos. Furthermore, HKOCl-3 has been successfully applied to the detection of endogenous HOCl by a 96-well microplate assay and flow cytometry. Therefore, HKOCl-3 holds great promise as a versatile molecular tool that enables innovative investigation of HOCl biology and ROS-related diseases in multiple detection modalities.

Phenylboronic acid-based (19)F MRI probe for the detection and imaging of hydrogen peroxide utilizing its large chemical-shift change

Herein, we report on a new (19)F MRI probe for the detection and imaging of H2O2. Our designed 2-fluorophenylboronic acid-based (19)F probe promptly reacted with H2O2 to produce 2-fluorophenol via boronic acid oxidation. The accompanying (19)F chemical-shift change reached 31 ppm under our experimental conditions. Such a large chemical-shift change allowed for the imaging of H2O2 by (19)F chemical-shift-selective MRI.

Boronate based fluorescence (ESIPT) probe for peroxynitrite

A simple probe for the detection of peroxynitrite was developed incorporating a benzyl boronic ester unit.

Transforming the recognition site of 4-hydroxyaniline into 4-methoxyaniline grafted onto a BODIPY core switches the selective detection of peroxynitrite to hypochlorous acid

From peroxynitrite to HOCl: two probes are reported, sharing the same BODIPY core but differing only by a minimized variation in the recognition site.

Fluorescent probes for the selective detection of chemical species inside mitochondria

This feature article systematically summarizes the development of fluorescent probes for the selective detection of chemical species inside mitochondria.

Smart fluorescent probes for imaging macrophage activity

Smart fluorescent probes for macrophage activity make use of a broad range of chemical architectures to target different molecular targets.

Detection of Peroxynitrite in Plants Exposed to Bacterial Infection

Peroxynitrite is a highly reactive derivative of nitric oxide (NO) which is gaining attention in the plant biology community because it may play a role in NO signaling during biotic stress. Peroxynitrite can react with many different biomolecules, but its ability to nitrate the tyrosine residues of proteins is particularly important because this may regulate defense signaling in response to pathogens. The analysis of peroxynitrite levels in the context of its proposed defense role requires an accurate and specific detection method. Here, we describe a photometric assay using the fluorescent dye Hong Kong Green 2 as a specific and quantitative probe for peroxynitrite in Arabidopsis thaliana plants challenged with an avirulent strain of Pseudomonas syringae pv. tomato. This protocol includes the preparation of plant samples, the assay procedure, the measurement of peroxynitrite-specific fluorescence, and data presentation.

Visualizing peroxynitrite fluxes in endothelial cells reveals the dynamic progression of brain vascular injury

Accumulating evidence suggests that formation of peroxynitrite (ONOO(-)) in the cerebral vasculature contributes to the progression of ischemic damage, while the underlying molecular mechanisms remain elusive. To fully understand ONOO(-) biology, efficient tools that can realize the real-time tracing of endogenous ONOO(-) fluxes are indispensable. While a few ONOO(-) fluorescent probes have been reported, direct visualization of ONOO(-) fluxes in the cerebral vasculature of live mice remains a challenge. Herein, we present a fluorescent switch-on probe (NP3) for ONOO(-) imaging. NP3 exhibits good specificity, fast response, and high sensitivity toward ONOO(-) both in vitro and in vivo. Moreover, NP3 is two-photon excitable and readily blood-brain barrier penetrable. These desired photophysical and pharmacokinetic properties endow NP3 with the capability to monitor brain vascular ONOO(-) generation after injury with excellent temporal and spatial resolution. As a proof of concept, NP3 has enabled the direct visualization of neurovascular ONOO(-) formation in ischemia progression in live mouse brain by use of two-photon laser scanning microscopy. Due to these favorable properties, NP3 holds great promise for visualizing endogenous peroxynitrite fluxes in a variety of pathophysiological progressions in vitro and in vivo.

Calmodulin of the tropical sea cucumber: Gene structure, inducible expression and contribution to nitric oxide production and pathogen clearance during immune response

Calmodulin (CaM) is an essential second messenger protein that transduces calcium signals by binding calcium ions (Ca(2+)) and modulating its interactions with various target proteins. In contrast to vertebrates, where CaM is well established as a cofactor for Ca(2+)-dependent physiological and cellular functions including host defense, there is a paucity of understanding on CaM in invertebrates (such as echinoderms) in response to immune challenge or microbial infections. In this study, we obtained and described the gene sequence of CaM from the tropical sea cucumber Stichopus monotuberculatus, a promising yet poorly characterized aquacultural species. mRNA expression of StmCaM could be detected in the intestine and coelomic fluid after Vibrio alginolyticus injection. Transcriptional and translational expression of StmCaM was inducible in nature, as evidenced by the expression patterns in primary coelomocytes following Vibrio challenge. This response could be mimicked by the Vibrio cells membrane components or lipopolysaccharides (LPS), and blocked by co-treatment of the LPS-neutralizing agent polymyxin B (PMB). Furthermore, inhibition of CaM activity by incubation with its inhibitor trifluoroperazine dihydrochloride (TFP) blunted the production of Vibrio-induced nitric oxide (NO) and augmented the survival of invading Vibrio in coelomocytes. Collectively, our study here supplied the first evidence for echinoderm CaM participation in innate immunity, and provided a functional link between CaM expression and antibacterial NO production in sea cucumber.

Indirect detection of superoxide in RAW 264.7 macrophage cells using microchip electrophoresis coupled to laser-induced fluorescence

Superoxide, a naturally produced reactive oxygen species (ROS) in the human body, is involved in many pathological and physiological signaling processes. However, if superoxide formation is left unregulated, overproduction can lead to oxidative damage to important biomolecules, such as DNA, lipids, and proteins. Superoxide can also lead to the formation of peroxynitrite, an extremely hazardous substance, through its reaction with endogenously produced nitric oxide. Despite its importance, quantitative information regarding superoxide production is difficult to obtain due to its high reactivity and low concentrations in vivo. MitoHE, a fluorescent probe that specifically reacts with superoxide, was used in conjunction with microchip electrophoresis (ME) and laser-induced fluorescence (LIF) detection to investigate changes in superoxide production by RAW 264.7 macrophage cells following stimulation with phorbol 12-myristate 13-acetate (PMA). Stimulation was performed in the presence and absence of the superoxide dismutase (SOD) inhibitors, diethyldithiocarbamate (DDC) and 2-metoxyestradiol (2-ME). The addition of these inhibitors resulted in an increase in the amount of superoxide specific product (2-OH-MitoE(+)) from 0.08 ± 0.01 fmol (0.17 ± 0.03 mM) in native cells to 1.26 ± 0.06 fmol (2.5 ± 0.1 mM) after PMA treatment. This corresponds to an approximately 15-fold increase in intracellular concentration per cell. Furthermore, the addition of 3-morpholino-sydnonimine (SIN-1) to the cells during incubation resulted in the production of 0.061 ± 0.006 fmol (0.12 ± 0.01 mM) of 2-OH-MitoE(+) per cell on average. These results demonstrate that indirect superoxide detection coupled with the use of SOD inhibitors and a separation method is a viable method to discriminate the 2-OH-MitoE(+) signal from possible interferences.

Centella asiatica and lipoic acid, or a combination thereof, inhibit monocyte adhesion to endothelial cells from umbilical cords of gestational diabetic women

BACKGROUND AND AIMS

Diabetes mellitus is associated with inflammatory endothelial activation and increased vascular leukocyte adhesion molecule expression, both playing a prominent role in the development of vascular complications. Centella asiatica (CA) and Lipoic Acid (LA) have shown anti-inflammatory and anti-oxidant properties in a variety of experimental models; however, their action on human umbilical vein endothelial cells (HUVECs), chronically exposed to hyperglycemia and pro-inflammatory environment during pregnancy, is still unknown.

METHODS AND RESULTS

In HUVECs from umbilical cords of gestational diabetic (GD) or healthy (C) women, both CA and LA affected tumor necrosis factor-α (TNF-α)-induced inflammation, being associated with a significant decrease in vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1) expression (western blot) and exposure (flow cytometry), as well as monocyte-HUVECs interaction (adhesion assay). Notably, this was associated with a significant reduction of an index of nitro-oxidative stress, such as the intracellular peroxynitrite levels (fluorescence detection by cytometric analysis), Mitogen-Activated Protein kinase (p44/42 MAPK) expression/phosphorylation levels and Nuclear Factor kappa-light-chain-enhancer of activated B cells (NF-κB p65) cytoplasm-nucleus translocation (flow cytometry). Overall our results indicate that both CA and LA used separately, and even better when combined, are effective to reduce the inflammatory response in TNF-α-treated HUVECs. Notably, this was more significant in GD than in C-HUVECs and also evident at baseline.

CONCLUSION

In conclusion, our in vitro study demonstrates that both CA and LA, or a combination thereof, are able to mitigate the potentially dangerous effects on the endothelium of chronic exposure to hyperglycemia in vivo.

Fluorescent Probe HKSOX-1 for Imaging and Detection of Endogenous Superoxide in Live Cells and In Vivo

Superoxide anion radical (O2(•-)) is undoubtedly the most important primary reactive oxygen species (ROS) found in cells, whose formation and fate are intertwined with diverse physiological and pathological processes. Here we report a highly sensitive and selective O2(•-) detecting strategy involving O2(•-) cleavage of an aryl trifluoromethanesulfonate group to yield a free phenol. We have synthesized three new O2(•-) fluorescent probes (HKSOX-1, HKSOX-1r for cellular retention, and HKSOX-1m for mitochondria-targeting) which exhibit excellent selectivity and sensitivity toward O2(•-) over a broad range of pH, strong oxidants, and abundant reductants found in cells. In confocal imaging, flow cytometry, and 96-well microplate assay, HKSOX-1r has been robustly applied to detect O2(•-) in multiple cellular models, such as inflammation and mitochondrial stress. Additionally, our probes can be efficiently applied to visualize O2(•-) in intact live zebrafish embryos. These probes open up exciting opportunities for unmasking the roles of O2(•-) in health and disease.

Locked-flavylium fluorescent dyes with tunable emission wavelengths based on intramolecular charge transfer for multi-color ratiometric fluorescence imaging

A new class of locked-flavylium fluorophores with tunable emission wavelengths based on intramolecular charge transfer were designed, synthesized, and evaluated. The optical studies indicate that sensor LF3 can display an intriguing character, fluorescence ratiometric response in three channels by tuning the ICT efficiencies.

A mitochondria-targetable fluorescent probe for peroxynitrite: fast response and high selectivity

A mitochondria-targetable fluorescence probe, methyl(4-hydroxyphenyl)amino-substituted pyronin (1), was exploited, which could highly selectively sense peroxynitrite (ONOO⁻) within seconds.

Nitric oxide as an antimicrobial molecule against Vibrio harveyi infection in the hepatopancreas of Pacific white shrimp, Litopenaeus vannamei

Nitric oxide (NO) is a key effector molecule produced in the innate immune systems of many species for antimicrobial defense. However, how NO production is regulated during bacterial infection in invertebrates, especially crustaceans, remains poorly understood. Vibrio harveyi, a Gram-negative marine pathogen, is among the most prevalent and serious threats to the world's shrimp culture industry. Its virulence typically manifests itself through shrimp hepatopancreas destruction. In the current study, we found that NO generated by an in vitro donor system (NOC-18) could rapidly and effectively kill V. harveyi. In addition, injection of heat-killed V. harveyi increased the concentration of NO/nitrite and the mRNA expression of nitric oxide synthase (NOS) in the hepatopancreas of Pacific white shrimp (Litopenaeus vannamei), the commercially most significant shrimp species. Live V. harveyi challenge also induced NO/nitrite production and NOS gene expression in primary L. vannamei hepatopancreatic cells in a time- and dose-dependent manner. Co-incubation of l-NAME, an inhibitor selective for mammalian constitutive NOSs, dose-dependently blocked V. harveyi-induced NO/nitrite production, without affecting V. harveyi-induced NOS mRNA expression. Furthermore, l-NAME treatment significantly increased the survival rate of infecting V. harveyi in cultured primary hepatopancreatic cells of L. vannamei. As a whole, we have demonstrated that endogenous NO produced by L. vannamei hepatopancreatic cells occurs in enzymatically regulated manners and is sufficient to act as a bactericidal molecule for V. harveyi clearance.

Luminescent probes for the bioimaging of small anionic species in vitro and in vivo

This comprehensive review examines recent developments in the use of fluorescent/luminescent probes for the bioimaging of anionic species. Images in cover art reproduced with permission from ref. 290 and 306.