Peroxynitrite: an endogenous oxidizing and nitrating agent

A novel di-functional fluorescent probe for ONOO- and Zn2+ imaging in cells

Peroxynitrite (ONOO-) is one of the most significant reactive oxygen species (ROS) in living cells. Zn2+ in living cells plays an essential part in different physiological processes. The abnormal concentration of ONOO- and Zn2+ in living cells are related to many kinds of diseases, such as anemia, epilepsy, diarrhea, Alzheimer's disease, and so on. The relationship of ONOO- and Zn2+ in living cells when the relative disease occurs remains unknown. So we develop the first probe H-1 for detecting ONOO- and Zn2+ at the same time. The probe H-1 shows high selectivity, good anti-interference capability, low detection limit and short response time to ONOO- and Zn2+. When the probe was applied to detect ONOO- and Zn2+ in HeLa cells, we could observe the fluorescence changing in the green and blue channels separately without interference in real time. It has the potential to employ the relation of ONOO- and Zn2+ in some disease mechanism research.

Visualization of peroxynitrite/GSH cross-talk in the oxidant-antioxidant balance by a dual-fluorophore and dual-site based mito-specific fluorescent probe

Peroxynitrite (ONOO-) and glutathione (GSH) play mutually regulating roles in the oxidant-antioxidant balance of organisms, which has a profound relationship with people's health and disease. In this study, we designed a two-photon fluorescent probe CD-NA that could simultaneously detect ONOO- and GSH via dual-fluorophore and dual-site properties. CD-NA shows different fluorescence responses to ONOO- (annihilated red fluorescence) and GSH (enhanced green emission) with high specificity and sensitivity. Notably, the response of CD-NA to ONOO- was unaffected by GSH, and the reverse is also true. It allows the ONOO-/GSH cross-talk to be successfully imaged. Given these excellent properties, CD-NA has been favorably employed in detecting ONOO- and GSH in living cells with the ability to target mitochondria. Therefore, CD-NA offers an efficient method for understanding the oxidant-antioxidant balance and interrelated physiological functions of ONOO- and GSH in living systems, and provides a new strategy to sort out the complex relationships and roles of various analytes in complex physiological processes.

A perylenemonoimide-based fluorescent probe: ultrasensitive and selective tracing of endogenous peroxynitrite in living cells

Peroxynitrite (ONOO-), a highly reactive species, plays a key role in various physiological and pathological processes. Herein, a red-emitting fluorescent reporter perylenemonoimide-boronate ester (PMI-BE) was synthesized and utilized for ultrasensitive detection of ONOO-. The unique feature of PMI-BE is its nanomolar sensitivity with high selectivity towards ONOO-. Moreover, PMI-BE also detects endogenously generated ONOO- in live cells.

Recent Progress of Spectroscopic Probes for Peroxynitrite and Their Potential Medical Diagnostic Applications

Peroxynitrite (ONOO-) is a crucial reactive oxygen species that plays a vital role in cellular signal transduction and homeostatic regulation. Determining and visualizing peroxynitrite accurately in biological systems is important for understanding its roles in physiological and pathological activity. Among the various detection methods, fluorescent probe-based spectroscopic detection offers real-time and minimally invasive detection, high sensitivity and selectivity, and easy structural and property modification. This review categorizes fluorescent probes by their fluorophore structures, highlighting their chemical structures, recognition mechanisms, and response behaviors in detail. We hope that this review could help trigger novel ideas for potential medical diagnostic applications of peroxynitrite-related molecular diseases.

A therapeutic probe for detecting and inhibiting ONOO- in senescent cells

Aging is an inevitable biological process, characterized by a general decline in the quality of all physiological functions and reactions involving all organs and tissues of the body. Oxidative stress is considered to be the main cause of aging, which may be caused by active nitrogen substances. ONOO^- is one of the important active nitrogen substances. Therefore, detecting the changes of ONOO^- in senescent cells is of great significance for the study of senescence. However, the study of ONOO^- in senescent cells is not deep enough. Here, we designed and synthesized a fluorescent probe FLASN based on flavonol, which integrates ONOO^- detection and aging treatment. Our probe FLASN was prepared by a simple synthesis process and was shown to have excellent spectral characteristics. Meanwhile, the results of bioimaging showed that the probe FLASN could detect endogenous/exogenous ONOO^- in cells and in vivo, and could reduce the production of ONOO^- in cells and in vivo stimulated by metformin. It is worth noting that for the first time, the change of ONOO^- in senescent cells and in vivo was detected, and the therapeutic effect of flavonol on senescent cells and in vivo was confirmed, by using the probe FLASN.

Affinity Studies of Hemicyanine Derived Water Soluble Colorimetric Probes with Reactive Oxygen/Nitrogen/Sulfur Species

Peroxynitrite (ONOO^- ) is an essential endogenous reactive oxygen species (ROS) generated in mitochondria under various pathological and physiological conditions. An increase in its level in mitochondria is related to numerous diseases. Herein, we report a series of hemicyanine-derived water-soluble colorimetric probes (1-4) and the reactivity of which was studied with various reactive oxygen, nitrogen, and sulfur species. Probes 1-4 are formed by conjugating 1,2,3,3-tetramethyl-3H-indolium iodide and 4-hydroxybenzaldehyde or its derivatives through an alkene linkage formed by the Knoevenagel reaction. Oxidative cleavage of the electron-rich double bond of the conjugated hemicyanine dye revealed a discerning affinity of probe 3 towards peroxynitrite among all reactive oxygen species. The rapid change in color of 3 provides a sensitive and selective method for detecting peroxynitrite with a low detection limit of 180 nM. Notably, the water solubility of the probe displays excellent performance for the selective detection of peroxynitrite among ROS and reactive nitrogen (RNS)/sulfur species (RSS). UV-vis, ¹ H NMR, and ¹³ C NMR spectroscopic data and results from theoretical calculations provide further information on the interaction of peroxynitrite with probe 3.

Inducible Nitric Oxide Synthase Embedded in Alginate/Polyethyleneimine Hydrogel as a New Platform to Explore NO-Driven Modulation of Biological Function

Nitric oxide (NO), a small free radical molecule, turned out to be pervasive in biology and was shown to have a substantial influence on a range of biological activities, including cell growth and apoptosis. This molecule is involved in signaling and affects a number of physiologic functions. In recent decades, several processes related to cancer, such as angiogenesis, programmed cell death, infiltration, cell cycle progression, and metastasis, have been linked with nitric oxide. In addition, other parallel work showed that NO also has the potential to operate as an anti-cancer agent. As a result, it has gained attention in cancer-related therapeutics. The nitric oxide synthase enzyme family (NOS) is required for the biosynthesis of nitric oxide. It is becoming increasingly popular to develop NO-releasing materials as strong tumoricidal therapies that can deliver sustained high concentrations of nitric oxide to tumor sites. In this paper, we developed NO-releasing materials based on sodium alginate hydrogel. In this regard, alginate hydrogel discs were modified by adsorbing layers of polyethyleneimine and iNOS-oxygenase. These NO-releasing hydrogel discs were prepared using the layer-by-layer film building technique. The iNOS-oxygenase is adsorbed on the positively charged polyethyleneimine (PEI) matrix layer, which was formed on a negatively charged sodium alginate hydrogel. We show that nitric oxide is produced by enzymes contained within the hydrogel material when it is exposed to a solution containing all the components necessary for the NOS reaction. The electrostatic chemical adsorption of the layer-by-layer process was confirmed by FTIR measurements as well as scanning electron microscopy. We then tested the biocompatibility of the resulting modified sodium alginate hydrogel discs. We showed that this NOS-PEI-modified hydrogel is overall compatible with cell growth. We characterized the NOS/hydrogel films and examined their functional features in terms of NO release profiles. However, during the first 24 h of activity, these films show an increase in NO release flux, followed by a gradual drop and then a period of stable NO release. These findings show the inherent potential of using this system as a platform for NO-driven modulation of biological functions, including carcinogenesis.

The Balancing of Peroxynitrite Detoxification between Ferric Heme-Proteins and CO2: The Case of Zebrafish Nitrobindin

Nitrobindins (Nbs) are all-β-barrel heme proteins and are present in prokaryotes and eukaryotes. Although their function(s) is still obscure, Nbs trap NO and inactivate peroxynitrite. Here, the kinetics of peroxynitrite scavenging by ferric Danio rerio Nb (Dr-Nb(III)) in the absence and presence of CO₂ is reported. The Dr-Nb(III)-catalyzed scavenging of peroxynitrite is facilitated by a low pH, indicating that the heme protein interacts preferentially with peroxynitrous acid, leading to the formation of nitrate (~91%) and nitrite (~9%). The physiological levels of CO₂ dramatically facilitate the spontaneous decay of peroxynitrite, overwhelming the scavenging activity of Dr-Nb(III). The effect of Dr-Nb(III) on the peroxynitrite-induced nitration of L-tyrosine was also investigated. Dr-Nb(III) inhibits the peroxynitrite-mediated nitration of free L-tyrosine, while, in the presence of CO₂, Dr-Nb(III) does not impair nitro-L-tyrosine formation. The comparative analysis of the present results with data reported in the literature indicates that, to act as efficient peroxynitrite scavengers in vivo, i.e., in the presence of physiological levels of CO₂, the ferric heme protein concentration must be higher than 10⁻⁴ M. Thus, only the circulating ferric hemoglobin levels appear to be high enough to efficiently compete with CO₂/HCO₃⁻ in peroxynitrite inactivation. The present results are of the utmost importance for tissues, like the eye retina in fish, where blood circulation is critical for adaptation to diving conditions.

Emerging investigator series: contributions of reactive nitrogen species to transformations of organic compounds in water: a critical review

Reactive nitrogen species (RNS) pose a potential risk to drinking water quality because they react with organic compounds to form toxic byproducts. Since the discovery of RNS formation in sunlit surface waters, these reactive intermediates have been detected in numerous sunlit natural waters and engineered water treatment systems. This critical review summarizes what is known regarding RNS, including their formation, contributions to contaminant transformation, and products resulting from RNS reactions. Reaction mechanisms and rate constants have been described for nitrogen dioxide (˙NO₂) reacting with phenolic compounds. However, significant knowledge gaps remain regarding reactions of RNS with other types of organic compounds. Promising methods to quantify RNS concentrations and reaction rates include the use of selective quenchers and probe compounds as well as electron paramagnetic resonance spectroscopy. Additionally, high resolution mass spectrometry methods have enabled the identification of nitr(os)ated byproducts that form via RNS reactions in sunlit surface waters, UV-based treatment systems, treatment systems that employ chemical oxidants such as chlorine and ozone, and certain types of biological treatment processes. Recommendations are provided for future research to increase understanding of RNS reactions and products, and the implications for drinking water toxicity.

Cationic amino acid transporters and their modulation by nitric oxide in cardiac muscle cells

Cationic amino acid transporters (CATs) play a central role in the supply of the substrate L-arginine to intracellular nitric oxide synthases (NOS), the enzymes responsible for the synthesis of nitric oxide (NO). In heart, NO produced by cardiac myocytes has diverse and even opposite effects on myocardial contractility depending on the subcellular location of its production. Approximately a decade ago, using a combination of biophysical and biochemical approaches, we discovered and characterized high- and low-affinity CATs that function simultaneously in the cardiac myocyte plasma membrane. Later on, we reported a negative feedback regulation of NO on the activity of cardiac CATs. In this way, NO was found to modulate its own biosynthesis by regulating the amount of L-arginine that becomes available as NOS substrate. We have recently solved the molecular determinants for this NO regulation on the low-affinity high-capacity CAT-2A. This review highlights some biophysical and biochemical features of L-arginine transporters and their potential relation to cardiac muscle physiology and pathology.

Highly sensitive benzothiazole-based chemosensors for detection and bioimaging of peroxynitrite in living cells

Fluorescent probes designed to sense and image peroxynitrite (ONOO−).

A thiocarbonate-caged fluorescent probe for specific visualization of peroxynitrite in living cells and zebrafish

Peroxynitrite (ONOO^-), a highly reactive oxygen species (ROS), is implicated with many physiological and pathological processes including cancer, neurodegenerative diseases and inflammation. In this regard, developing effective tools for highly selective tracking of ONOO^- is urgently needed. Herein, we constructed a concise and specific fluorescent probe NA-ONOO for sensing ONOO^- by conjugating an ONOO^--specific recognition group ((4-methoxyphenylthio)carbonyl, a thiocarbonate derivative) with a naphthalene fluorophore. The probe, NA-ONOO, was in a dark state because the high electrophilicity of (4-methoxyphenylthio)carbonyl disturbs the intramolecular charge transfer (ICT) in the fluorophore. Upon treatment with ONOO^-, the fluorescent emission was sharply boosted (quantum yield Φ: 3% to 56.6%) owing to an ONOO^- triggered release of (4-methoxyphenylthio)carbonyl from NA-ONOO. Optical analyses showed that NA-ONOO presented high selectivity and sensitivity toward ONOO^-. With good cell permeability and biocompatibility, the NA-ONOO probe was successfully applied to imaging and tracing exogenous and endogenous ONOO^- in living cells and zebrafish. The probe NA-ONOO presents a new recognition group and a promising method for further investigating ONOO^- in living systems.

A novel p-dimethylaminophenylether-based fluorescent probe for the detection of native ONOO- in cells and zebrafish

Peroxynitrite (ONOO^-) is a highly reactive substance, and plays an essential part in maintaining cellular homeostasis. It is crucial to monitor the ONOO^- level in cells in normal and abnormal states. We introduced a p-dimethylaminophenylether-based fluorescent probe PDPE-PN, which could be synthesized readily. The new probe had prominent sensitivity and specificity, and a fast response towards ONOO^-. The spectral performance of probe PDPE-PN was outstanding and the limit of detection was 69 nM. Probe PDPE-PN with low toxicity was applied to detect endogenous/exogenous ONOO^- in RAW 264.7 macrophages and zebrafish. Importantly, successful application of the new receptor opens up new ideas for the design of ONOO^- probes.

Sequential Application of High-Voltage Electric Field Cold Plasma Treatment and Acid Blanching Improves the Quality of Fresh Carrot Juice (Daucus carota L.)

The study was aimed to investigate the combined effect of acid blanching (AB) and high-voltage electric field cold plasma (HVCP) on carrot juice quality. Before juice extraction, carrots were separated into three parts: control, blanched (100 °C for 5 min) with non-acidified water, and blanched with acidified water (35 g/L citric acid at pH 1.34). Carrot juice was then subjected to dielectric barrier discharge at 80 kV for 4 min. Results indicated that AB treatment significantly influenced the efficiency of HVCP. AB-HVCP resulted in antimicrobial synergism, which is an outcome of acidified NO₂^-, H₂O₂, O^-, and peroxynitrites (ONOO^-) or its precursor OH/NO₂, along with other species. In addition, plasma treatment also promotes the accumulation of coloring compounds, chlorogenic acid, and sugar contents by surface erosion of the epidermal layer, cis isomerization, rupturing of phenol-sugar and phenolic-cell matrix bonds, and depolymerized long-chain polysaccharides by cleavage of the glycoside bond. Therefore, AB-HVCP is a potential emerging hurdle strategy for fresh produce.

Visualization of ONOO- and Viscosity in Drug-Induced Hepatotoxicity with Different Fluorescence Signals by a Sensitive Fluorescent Probe

Drug-induced liver injury (DILI) is considered gradually as a serious public health issue, and hepatotoxicity has been regarded as the main clinical problem caused by it. We suspected that both the intracellular viscosity and peroxynitrite (ONOO^-) levels in drug-induced hepatotoxicity tissue are higher than those in a healthy liver. For this reason, we have presented a fluorescent probe VO for multichannel imaging viscosity and ONOO^- simultaneously. Experimental results showed that VO has satisfactory detection performance for both viscosity and ONOO^-, and based on the advantages of its lower cytotoxicity and pH-stabilities, VO was successfully employed to image viscosity and ONOO^- in living cells and animals. More importantly, we use the probe to successfully showcase drug-induced hepatotoxicity by imaging viscosity and ONOO^- induced by acetaminophen (APAP). All the results indicate that VO has great potential for the detection of viscosity and ONOO^- and to assay drug-induced hepatotoxicity. Overall, this work offers a new detection tool/method for a deeper understanding of drug-induced organism injury.

A novel highly selective fluorescent probe with new chalcone fluorophore for monitoring and imaging endogenous peroxynitrite in living cells and drug-damaged liver tissue

As a member of the reactive nitrogen species (RNS) family, peroxynitrite (ONOO^-) as an oxidant and nitrating mediator plays a significant role in some physiopathologic processes. The excessive production of peroxynitrite anion in a drug-damaged liver is a culprit of hepatotoxicity. The detection of peroxynitrite is of vital importance for the treatment of some diseases including cancer and liver injury. In this study, a novel turn-on fluorescent probe IC-ONOO with new chalcone fluorophore was designed and synthesized for the detection of in vitro and in vivo. The probe responded rapidly towards ONOO^- (only within 15 min did the fluorescent intensity maximize), and was endowed with high sensitivity and excellent selectivity. Given the fact that the linear correlation between the fluorescent intensity at 560 nm and the concentrations of the probe ranged from 0 to 9 μM, the limit of detection (LOD) was calculated to be 3.1 × 10^-8 M. With all the merits, probe IC-ONOO was qualified as a robust tool to monitor peroxynitrite anion under physiopathologic condition. Moreover, it was successfully applied in the imaging of endogenous peroxynitrite in living MCF-7 cells (Human breast carcinoma cells) and mouse drug-damaged liver tissue with low cytotoxicity. Given all the extraordinary merits, great potential has been seen in its application to other peroxynitrite related diseases.

A rapid response near-infrared ratiometric fluorescent probe for the real-time tracking of peroxynitrite for pathological diagnosis and therapeutic assessment in a rheumatoid arthritis model

Endogenous ONOO⁻ generation in rheumatoid arthritis mice was visualized and confirmed by the ratiometric fluorescent probe Ratio-A.

Antioxidants as Renoprotective Agents for Ischemia during Partial Nephrectomy

Small renal masses have been diagnosed increasingly in recent decades, allowing surgical treatment by partial nephrectomy. This treatment option is associated with better renal function preservation, in comparison with radical nephrectomy. However, for obtaining a bloodless field during surgery, occlusion of renal artery and veins is often required, which results in transitory ischemia. The renal ischemia-reperfusion injury is associated with increased reactive oxygen species production leading to renal tissue damage. Thus, the use of antioxidants has been advocated in the partial nephrectomy perioperative period. Several antioxidants were investigated in regard to renal ischemia-reperfusion injury. The present manuscript aims to present the literature on the most commonly studied antioxidants used during partial nephrectomy. The results of experimental and clinical studies using antioxidants during partial nephrectomy are reported. Further, alimentary sources of some antioxidants are presented, stimulating future studies focusing on perioperative antioxidant-rich diets.

Cebpd Is Essential for Gamma-Tocotrienol Mediated Protection against Radiation-Induced Hematopoietic and Intestinal Injury

Gamma-tocotrienol (GT3) confers protection against ionizing radiation (IR)-induced injury. However, the molecular targets that underlie the protective functions of GT3 are not yet known. We have reported that mice lacking CCAAT enhancer binding protein delta (Cebpd^−/−) display increased mortality to IR due to injury to the hematopoietic and intestinal tissues and that Cebpd protects from IR-induced oxidative stress and cell death. The purpose of this study was to investigate whether Cebpd mediates the radio protective functions of GT3. We found that GT3-treated Cebpd^−/− mice showed partial recovery of white blood cells compared to GT3-treated Cebpd^+/+ mice at 2 weeks post-IR. GT3-treated Cebpd^−/− mice showed an increased loss of intestinal crypt colonies, which correlated with increased expression of inflammatory cytokines and chemokines, increased levels of oxidized glutathione (GSSG), S-nitrosoglutathione (GSNO) and 3-nitrotyrosine (3-NT) after exposure to IR compared to GT3-treated Cebpd^+/+ mice. Cebpd is induced by IR as well as a combination of IR and GT3 in the intestine. Studies have shown that granulocyte-colony stimulating factor (G-CSF), mediates the radioprotective functions of GT3. Interestingly, we found that IR alone as well as the combination of IR and GT3 caused robust augmentation of plasma G-CSF in both Cebpd^+/+ and Cebpd^−/− mice. These results identify a novel role for Cebpd in GT3-mediated protection against IR-induced injury, in part via modulation of IR-induced inflammation and oxidative/nitrosative stress, which is independent of G-CSF.

The dichotomous role of H2S in cancer cell biology? Déjà vu all over again

Nitric oxide (NO) a gaseous free radical is one of the ten smallest molecules found in nature, while hydrogen sulfide (H2S) is a gas that bears the pungent smell of rotten eggs. Both are toxic yet they are gasotransmitters of physiological relevance. There appears to be an uncanny resemblance between the general actions of these two gasotransmitters in health and disease. The role of NO and H2S in cancer has been quite perplexing, as both tumor promotion and inflammatory activities as well as anti-tumor and antiinflammatory properties have been described. These paradoxes have been explained for both gasotransmitters in terms of each having a dual or biphasic effect that is dependent on the local flux of each gas. In this review/commentary, I have discussed the major roles of NO and H2S in carcinogenesis, evaluating their dual nature, focusing on the enzymes that contribute to this paradox and evaluate the pros and cons of inhibiting or inducing each of these enzymes.

Detection of Nitric Oxide via Electronic Paramagnetic Resonance in Mollusks

Electronic paramagnetic resonance (EPR) is an appropriate tool to identify free radicals formed in tissues under normal as well as stressful conditions. Since nitric oxide (NO) as a free radical has paramagnetic properties it can be detected by EPR. The use of spin traps highly improves the sensitivity allowing NO identification, detection and quantification at room temperature in vitro and in vivo conditions. NO production in animals is almost exclusively associated to an enzyme family known as Nitric Oxide Synthases (NOSs). The digestive glands of mollusks are a major target for oxidative disruption related to environmental stress. A simple EPR-methodology to asses both, the presence of NO and its rate of generation in tissues from different mollusk species, is reported here.

Investigation of Drug-Induced Hepatotoxicity and Its Remediation Pathway with Reaction-Based Fluorescent Probes

Drug-induced liver injury (DILI) is considered a serious problem related to public health, due to its unpredictability and acute response. The level of peroxynitrite (ONOO^-) generated in liver has long been regarded as a biomarker for the prediction and measurement of DILI. Herein we present two reaction-based fluorescent probes (Naph-ONOO^- and Rhod-ONOO^-) for ONOO^- through a novel and universally applicable mechanism: ONOO^--mediated deprotection of α-keto caged fluorophores. Among them, Rhod-ONOO^- can selectively accumulate and react in mitochondria, one of the main sources of ONOO^-, with a substantial lower nanomolar sensitivity of 43 nM. The superior selectivity and sensitivity of two probes enable real-time imaging of peroxynitrite generation in lipopolysaccharide-stimulated live cells, with a remarkable difference from cells doped with other interfering reactive oxygen species, in either one- or two-photon imaging modes. More importantly, we elucidated the drug-induced hepatotoxicity pathway with Rhod-ONOO^- and revealed that CYP450/CYP2E1-mediated enzymatic metabolism of acetaminophen leads to ONOO^- generation in liver cells. This is the first time to showcase the drug-induced hepatotoxicity pathways by use of a small-molecule fluorescent probe. We hence conclude that fluorescent probes can engender a deeper understanding of reactive species and their pathological revelations. The reaction-based fluorescent probes will be a potentially useful chemical tool to assay drug-induced hepatotoxicity.

Shock associated with endothelial dysfunction in omental microvessels

BACKGROUND

Impaired microvascular function leads to a poor outcome in a variety of medical conditions. Our aim was to determine whether vasodilator responses to acetylcholine (Ach) are impaired in human omental arterioles from patients with severe trauma.

MATERIALS AND METHODS

Patients with massive blood loss and severe shock requiring damage control procedures were included. Tissues were collected at the first (FEL) and the second explorative laparotomy (SEL). Control tissues were collected from nontrauma patients. Freshly isolated 50-200-μm-diameter omental arterioles were analysed using videomicroscopy. Dihydroethidine and DCF-DA fluorescence were used to assess reactive oxygen species (ROS) production. MnTBAP was used to determine the contribution of excess vascular superoxide contribution to endothelial dysfunction.

RESULTS

After constriction (30-50%) with endothelin-1, dilation to graded doses of Ach (10^-9 -10^-4 M) was greater in control vessels compared to FEL and SEL (max dilation at 10^-4 M (MD) = 25 ± 3%, n = 8; and 59 ± 8%, n = 8, respectively, and controls MD = 93 ± 10%, n = 6, P < 0·05). Fluorescence imaging of ROS production showed significant increases in superoxide (225·46 ± 12·86; 215·77 ± 10·75 vs. 133·75 ± 7·26, arbitrary units; P < 0·05) and peroxide-related ROS (240·8 ± 20·42; 234·59 ± 28·86, vs. 150·78 ± 15·65, arbitrary units; P < 0·05), in FEL and SEL microvessels compared to control, respectively. FEL pretreated with MnTBAP demonstrated significant improvement in Ach-induced vasodilation (25·5 ± 3·0% vs. 79·5 ± 8·2%; P < 0·05).

CONCLUSIONS

Severe shock associated with microvascular endothelial dysfunction enhances production of ROS in human omental tissues. The altered flow regulation may contribute to a mismatch between local blood supply and demand, exacerbating abnormal tissue perfusion and function.

Threshold levels of extracellular l-arginine that trigger NOS-mediated ROS/RNS production in cardiac ventricular myocytes

l-Arginine (L-Arg) is the substrate for nitric oxide synthase (NOS) to produce nitric oxide (NO), a signaling molecule that is key in cardiovascular physiology and pathology. In cardiac myocytes, L-Arg is incorporated from the circulation through the functioning of system-y⁺ cationic amino acid transporters. Depletion of L-Arg leads to NOS uncoupling, with O₂ rather than L-Arg as the terminal electron acceptor, resulting in superoxide formation. The reactive oxygen species (ROS) superoxide (O₂˙^-), combined with NO, may lead to the production of the reactive nitrogen species (RNS) peroxynitrite (ONOO^-), which is recognized as a major contributor to myocardial depression. In this study we aimed to determine the levels of external L-Arg that trigger ROS/RNS production in cardiac myocytes. To this goal, we used a two-step experimental design in which acutely isolated cardiomyocytes were loaded with the dye coelenterazine that greatly increases its fluorescence quantum yield in the presence of ONOO^- and O₂˙^- Cells were then exposed to different concentrations of extracellular L-Arg and changes in fluorescence were followed spectrofluorometrically. It was found that below a threshold value of ~100 µM, decreasing concentrations of L-Arg progressively increased ONOO^-/ O₂˙^--induced fluorescence, an effect that was not mimicked by d-arginine or l-lysine and was fully blocked by the NOS inhibitor l-NAME. These results can be explained by NOS aberrant enzymatic activity and provide an estimate for the levels of circulating L-Arg below which ROS/RNS-mediated harmful effects arise in cardiac muscle.

The dual role of iNOS in cancer

Nitric oxide (NO) is one of the 10 smallest molecules found in nature. It is a simple gaseous free radical whose predominant functions is that of a messenger through cGMP. In mammals, NO is synthesized by the enzyme nitric oxide synthase (NOS) of which there are three isoforms. Neuronal (nNOS, NOS1) and endothelial (eNOS, NOS3) are constitutive calcium-dependent forms of the enzyme that regulate neural and vascular function respectively. The third isoform (iNOS, NOS2), is calcium-independent and is inducible. In many tumors, iNOS expression is high, however, the role of iNOS during tumor development is very complex and quite perplexing, with both promoting and inhibiting actions having been described. This review will aim to summarize the dual actions of iNOS-derived NO showing that the microenvironment of the tumor is a contributing factor to these observations and ultimately to cellular outcomes.

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NO is pro- and anti-tumorigenic. High concentrations of NO maybe anti-tumorigenic.

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iNOS produces high concentrations of NO and relates to tumor growth or its inhibition.

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iNOS is associated with cytotoxicity, apoptosis and bystander anti-tumor effects.

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Tumor- and stromal-iNOS, and the ‘cell situation’ contribute to anti or pro-tumor effects.

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Dual role of iNOS is influenced by the cell situation and is environment dependent.

NO to cancer: The complex and multifaceted role of nitric oxide and the epigenetic nitric oxide donor, RRx-001

The endogenous mediator of vasodilation, nitric oxide (NO), has been shown to be a potent radiosensitizer. However, the underlying mode of action for its role as a radiosensitizer – while not entirely understood – is believed to arise from increased tumor blood flow, effects on cellular respiration, on cell signaling, and on the production of reactive oxygen and nitrogen species (RONS), that can act as radiosensitizers in their own right. NO activity is surprisingly long-lived and more potent in comparison to oxygen. Reports of the effects of NO with radiation have often been contradictory leading to confusion about the true radiosensitizing nature of NO. Whether increasing or decreasing tumor blood flow, acting as radiosensitizer or radioprotector, the effects of NO have been controversial. Key to understanding the role of NO as a radiosensitizer is to recognize the importance of biological context. With a very short half-life and potent activity, the local effects of NO need to be carefully considered and understood when using NO as a radiosensitizer. The systemic effects of NO donors can cause extensive side effects, and also affect the local tumor microenvironment, both directly and indirectly. To minimize systemic effects and maximize effects on tumors, agents that deliver NO on demand selectively to tumors using hypoxia as a trigger may be of greater interest as radiosensitizers. Herein we discuss the multiple effects of NO and focus on the clinical molecule RRx-001, a hypoxia-activated NO donor currently being investigated as a radiosensitizer in the clinic.

•NO radiosensitizer activity is complex with variable results in clinical and non-clinical studies

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NO radiosensitizes by reaction with DNA radicals, by its metabolites and by impact on the vasculature.

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Understanding the local and context-specific activity of NO is key for radiosensitizer development

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RRx-001 induces NO production under hypoxia with promising radiosensitizing activity.

Low SOD activity is associated with overproduction of peroxynitrite and nitric oxide in patients with acute coronary syndrome

OBJECTIVE

The present study was undertaken to evaluate the variation of the oxidative/nitrosative stress status in a population of subjects; with acute coronary syndrome (ACS), and examine its possible implication in plaque rupture which is the main mechanism in the pathophysiology of ACS.

PATIENTS AND METHODS

We made this study on 50 men with ACS and 50 age and sex matched healthy controls. Nitrosative/oxidative stress markers including; nitric oxide, superoxide anion levels, superoxide dismutase (SOD) activity and peroxynitrite levels were evaluated in blood samples of patients and controls.

RESULTS

Compared with healthy subjects, coronary patients had significantly higher nitric oxide, peroxynitrite and superoxide anion concentrations in both plasma and erythrocytes associated to significant decrease of SOD activity. Erythrocytes peroxynitrite concentration was negatively correlated with the antioxidant enzyme activity (SOD).

CONCLUSION

Our results show a significant accumulation of both intracellular and plasma pro-oxidants with a concomitant decrease in the SOD scavenging activity in ACS patients. Both seem to be associated with plaque rupture and ischemia observed in ACS.

Role of nitric oxide in the genotoxic response to chronic microcystin-LR exposure in human-hamster hybrid cells

Microcystin-LR (MC-LR) is the most abundant and toxic microcystin congener and has been classified as a potential human carcinogen (Group 2B) by the International Agency for Research on Cancer. However, the mechanisms underlying the genotoxic effects of MC-LR during chronic exposure are still poorly understood. In the present study, human-hamster hybrid (AL) cells were exposed to MC-LR for varying lengths of time to investigate the role of nitrogen radicals in MC-LR-induced genotoxicity. The mutagenic potential at the CD59 locus was more than 2-fold higher (p<0.01) in AL cells exposed to a cytotoxic concentration (1 μmol/L) of MC-LR for 30 days than in untreated control cells, which was consistent with the formation of micronucleus. MC-LR caused a dose-dependent increase in nitric oxide (NO) production in treated cells. Moreover, this was blocked by concurrent treatment with the NO synthase inhibitor NG-methyl-L-arginine (L-NMMA), which suppressed MC-LR-induced mutations as well. The survival of mitochondrial DNA-depleted (ρ0) AL cells was markedly decreased by MC-LR treatment compared to that in AL cells, while the CD59 mutant fraction was unaltered. These results provided clear evidence that the genotoxicity associated with chronic MC-LR exposure in mammalian cells was mediated by NO and might be considered as a basis for the development of therapeutics that prevent carcinogenesis.

Mass spectrometry and 3-nitrotyrosine: strategies, controversies, and our current perspective

Reactive-nitrogen species (RNS) such as peroxynitrite (ONOO(-)), that is, the reaction product of nitric oxide ((•)NO) and superoxide (O2(-•)), nitryl chloride (NO2Cl) and (•)NO2 react with the activated aromatic ring of tyrosine to form 3-nitrotyrosine. This modification, which has been known for more than a century, occurs to both the free form of the amino acid (i.e., soluble/free tyrosine) and to tyrosine residues covalently bound within the backbone of peptides and proteins. Nitration of tyrosine is thought to be of biological significance and has been linked to health and disease, but determining its role has proved challenging. Several key questions have been the focus of much of the research activity: (a) to what extent is free/soluble tyrosine nitrated in biological tissues and fluids, and (b) are there specific site(s) of nitration within peptides/proteins and to what extent (i.e., stoichiometry) does this modification occur? These issues have been addressed in a wide range of sample types (e.g., blood, urine, CSF, exhaled breath condensate and various tissues) and a diverse array of physiological/pathophysiological scenarios. The accurate determination of nitrated tyrosine is, however, a stumbling block. Despite extensive study, the extent to which nitration occurs in vivo, the specificity of the nitration reaction, and its importance in health and disease, remain unclear. In this review, we highlight the analytical challenges and discuss the approaches adopted to address them. Mass spectrometry, in combination with either gas chromatography (GC-MS, GC-MS/MS) or liquid chromatography (LC-MS/MS), has played the central role in the analysis of 3-nitrotyrosine and tyrosine-nitrated biological macromolecules. We discuss its unique attributes and highlight the role of stable-isotope labeled 3-nitrotyrosine analogs in both accurate quantification, and in helping to define the biological relevance of tyrosine nitration. We show that the application of sophisticated mass spectrometric techniques is advantageous if not essential, but that this alone is by no means a guarantee of accurate findings. We discuss the important analytical challenges in quantifying 3-nitrotyrosine, possible workarounds, and we attempt to make sense of the disparate findings that have been reported so far.

A boronate-based fluorescent probe for the selective detection of cellular peroxynitrite

A boronate-based fluorescent probe 1 for the selective monitoring of intracellular peroxynitrite has been developed. The probe takes advantage of the fast reaction of an arylboronate group with peroxynitrite, yielding a corresponding phenol that undergoes spontaneous subsequent reactions to produce a strongly fluorescent product associated with a large turn-on signal.

A ratiometric fluorescent probe for fast and sensitive detection of peroxynitrite: a boronate ester as the receptor to initiate a cascade reaction

We have developed a fluorescent probe connecting boronate ester oxidation and in situ cyclization together for the sensitive and selective detection of ONOO⁻.

The reduction of EPSC amplitude in CA1 pyramidal neurons by the peroxynitrite donor SIN-1 requires Ca2+ influx via postsynaptic non-L-type voltage gated calcium channels

The peroxynitrite free radical (ONOO(-)) modulation of miniature excitatory postsynaptic currents (mEPSCs) and spontaneous excitatory postsynaptic currents (sEPSCs) was investigated in rat CA1 pyramidal neurons using the whole-cell patch clamp technique. SIN-1(3-morpholino-sydnonimine), which can lead the simultaneous generation of superoxide anion and nitric oxide, and then form the highly reactive species ONOO(-), induced dose-dependent inhibition in amplitudes of both mEPSCs and sEPSCs. The SIN-1 action on mEPSC amplitude was completely blocked by U0126, a selective MEK inhibitor, suggesting that MEK contributed to the action of ONOO(-) on mEPSCs. The effect of SIN-1 was completely occluded either in the presence of the calcium chelator EGTA or the non-selective calcium channel antagonist Cd(2+). Furthermore, the application of nifedipine (20 μM), the L-type calcium channel blocker, had no effect on the ONOO(-)-induced decrease in mEPSC amplitude, excluding a role for L-type voltage-gated Ca(2+) channels in this process. SIN-1 inhibited the frequency of sEPSCs but had no effect on mEPSC frequency, which suggested a presynaptic action potential-dependent the action of ONOO(-) at CA1 pyramidal neuron synapses. The best-known glutamatergic input to CA1 pyramidal neurons is via Schaffer collaterals from CA3 area. However, no changes were observed in slices treated with SIN-1 on the spontaneous firing rates of CA3 pyramidal neurons. These findings suggested that SIN-1 inhibited glutamatergic synaptic transmission of CA1 pyramidal neurons by a postsynaptic non-L-type voltage gated calcium channel-dependent mechanism.

Uric acid in multiple sclerosis

Peroxynitrite, a reactive oxidant formed by the reaction of nitric oxide with superoxide at sites of inflammation in multiple sclerosis (MS), is capable of damaging tissues and cells. Uric acid, a natural scavenger of peroxynitrite, reduces inflammatory demyelination in experimental allergic encephalomyelitis. Some studies reported lower serum levels of uric acid in MS patients compared with controls, whereas other studies found no difference. A critical appraisal of these studies favors the view that reduced uric acid in MS is secondary to its peroxynitrite scavenging activity during inflammatory disease activity, rather than a primary deficiency. Serum uric acid levels could be used as a biomarker for monitoring disease activity in MS. Therapeutic strategies aimed at raising serum uric acid levels may have a glial/neuroprotective effect on MS patients.