Tyrosine nitration by peroxynitrite formed from nitric oxide and superoxide generated by xanthine oxidase

Supersulfide biology and translational medicine for disease control

For decades, the major focus of redox biology has been oxygen, the most abundant element on Earth. Molecular oxygen functions as the final electron acceptor in the mitochondrial respiratory chain, contributing to energy production in aerobic organisms. In addition, oxygen-derived reactive oxygen species including hydrogen peroxide and nitrogen free radicals, such as superoxide, hydroxyl radical and nitric oxide radical, undergo a complicated sequence of electron transfer reactions with other biomolecules, which lead to their modified physiological functions and diverse biological and pathophysiological consequences (e.g. oxidative stress). What is now evident is that oxygen accounts for only a small number of redox reactions in organisms and knowledge of biological redox reactions is still quite limited. This article reviews a new aspects of redox biology which is governed by redox-active sulfur-containing molecules-supersulfides. We define the term 'supersulfides' as sulfur species with catenated sulfur atoms. Supersulfides were determined to be abundant in all organisms, but their redox biological properties have remained largely unexplored. In fact, the unique chemical properties of supersulfides permit them to be readily ionized or radicalized, thereby allowing supersulfides to actively participate in redox reactions and antioxidant responses in cells. Accumulating evidence has demonstrated that supersulfides are indispensable for fundamental biological processes such as energy production, nucleic acid metabolism, protein translation and others. Moreover, manipulation of supersulfide levels was beneficial for pathogenesis of various diseases. Thus, supersulfide biology has opened a new era of disease control that includes potential applications to clinical diagnosis, prevention and therapeutics of diseases.

Differential expression patterns of purinergic ectoenzymes and the antioxidative role of IL-6 in hospitalized COVID-19 patient recovery

Introduction

We have acquired significant knowledge regarding the pathogenesis of severe acute respiratory syndrome caused by coronavirus 2 (SARS-CoV-2). However, the underlying mechanisms responsible for disease recovery still need to be fully understood.

Methods

To gain insights into critical immune markers involved in COVID-19 etiopathogenesis, we studied the evolution of the immune profile of peripheral blood samples from patients who had recovered from COVID-19 and compared them to subjects with severe acute respiratory illness but negative for SARS-CoV-2 detection (controls). In addition, linear and clustered correlations between different parameters were determined.

Results

The data obtained revealed a significant reduction in the frequency of inflammatory monocytes (CD14+CD16+) at hospital discharge vs. admission. Remarkably, nitric oxide (NO) production by the monocyte compartment was significantly reduced at discharge. Furthermore, interleukin (IL)-6 plasma levels were negatively correlated with the frequency of NO+CD14+CD16+ monocytes at hospital admission. However, at the time of hospital release, circulating IL-6 directly correlated with the NO production rate by monocytes. In line with these observations, we found that concomitant with NO diminution, the level of nitrotyrosine (NT) on CD8 T-cells significantly diminished at the time of hospital release. Considering that purinergic signaling constitutes another regulatory system, we analyzed the kinetics of CD39 and CD73 ectoenzyme expression in CD8 T-cells. We found that the frequency of CD39+CD8+ T-cells significantly diminished while the percentage of CD73+ cells increased at hospital discharge. In vitro, IL-6 stimulation of PBMCs from COVID-19 patients diminished the NT levels on CD8 T-cells. A clear differential expression pattern of CD39 and CD73 was observed in the NT+ vs. NT-CD8+ T-cell populations.

Discussion

The results suggest that early after infection, IL-6 controls the production of NO, which regulates the levels of NT on CD8 T-cells modifying their effector functions. Intriguingly, in this cytotoxic cell population, the expression of purinergic ectoenzymes is tightly associated with the presence of nitrated surface molecules. Overall, the data obtained contribute to a better understanding of pathogenic mechanisms associated with COVID-19 outcomes.

Urinary Thioredoxin as a Biomarker of Renal Redox Dysregulation and a Companion Diagnostic to Identify Responders to Redox-Modulating Therapeutics

Significance: The development and progression of renal diseases, including acute kidney injury (AKI) and chronic kidney disease (CKD), are the result of heterogeneous pathophysiology that reflects a range of environmental factors and, in a lesser extent, genetic mutations. The pathophysiology specific to most kidney diseases is not currently identified; therefore, these diseases are diagnosed based on non-pathological factors. For that reason, pathophysiology-based companion diagnostics for selection of pathophysiology-targeted treatments have not been available, which impedes personalized medicine in kidney disease. Recent Advances: Pathophysiology-targeted therapeutic agents are now being developed for the treatment of redox dysregulation. Redox modulation therapeutics, including bardoxolone methyl, suppresses the onset and progression of AKI and CKD. On the other hand, pathophysiology-targeted diagnostics for renal redox dysregulation are also being developed. Urinary thioredoxin (TXN) is a biomarker that can be used to diagnose tubular redox dysregulation. AKI causes oxidation and urinary excretion of TXN, which depletes TXN from the tubules, resulting in tubular redox dysregulation. Urinary TXN is selectively elevated at the onset of AKI and correlates with the progression of CKD in diabetic nephropathy. Critical Issues: Diagnostic methods should provide information about molecular mechanisms that aid in the selection of appropriate therapies to improve the prognosis of kidney disease. Future Directions: A specific diagnostic method enabling detection of redox dysregulation based on pathological molecular mechanisms is much needed and could provide the first step toward personalized medicine in kidney disease. Urinary TXN is a candidate for a companion diagnostic method to identify responders to redox-modulating therapeutics. Antioxid. Redox Signal. 36, 1051-1065.

Non-peptide secondary metabolites from poisonous mushrooms: overview of chemistry, bioactivity, and biosynthesis

Covering: up to June 2021A wide variety of mushrooms have traditionally been recognized as edible fungi with high nutritional value and low calories, and abundantly produce structurally diverse and bioactive secondary metabolites. However, accidental ingestion of poisonous mushrooms can result in serious illnesses and even death. Chemically, mushroom poisoning is associated with secondary metabolites produced in poisonous mushrooms, causing specific toxicity. However, many poisonous mushrooms have not been fully investigated for their secondary metabolites, and the secondary metabolites of poisonous mushrooms have not been systematically summarized for details such as chemical composition and biosynthetic mechanisms. The isolation and identification of secondary metabolites from poisonous mushrooms have great research value since these compounds could be lethal toxins that contribute to the toxicity of mushrooms or could provide lead compounds with remarkable biological activities that can promote advances in other related disciplines, such as biochemistry and pharmacology. In this review, we summarize the structures and biological activities of secondary metabolites identified from poisonous mushrooms and provide an overview of the current information on these metabolites, focusing on their chemistry, bioactivity, and biosynthesis.

The relationship of polluted air and drinking water sources with the prevalence of systemic lupus erythematosus: a provincial population-based study

Environmental exposures interact with genetic factors has been thought to influence susceptibility of systemic lupus erythematosus (SLE) development. To evaluate the effects of environmental exposures on SLE, we conducted a population-based cohort study across Jiangsu Province, China, to examine the associations between the living environment including air and water pollution, population density, economic income level, etc. and the prevalence and mortality of hospitalized SLE (h-SLE) patients. A total of 2231 h-SLE patients were retrieved from a longitudinal SLE database collected by the Jiangsu Lupus Collaborative Group from 1999 to 2009. The results showed that: It existed regional differences on the prevalence of h-SLE patients in 96 administrative districts; The distribution of NO₂ air concentration monitored by atmospheric remote sensors showed that three of the ultra-high-prevalence districts were located in the concentrated chemical industry emission area; h-SLE patient prevalence was positively correlated with the excessive levels of nitrogen in drinking water; The positive ratio of pericarditis and proteinuria was positively correlated with the prevalence of h-SLE patients and pollution not only induced a high h-SLE patient prevalence but also a higher mortality rate, which might be attributed to NOx pollution in the air and drinking water. In summary, our data suggested that NOx in air and drinking water may be one of the important predispositions of SLE, especially for patients with renal involvement.

Optimization of Lipophilic Metalloporphyrins Modifies Disease Outcomes in a Rat Model of Parkinsonism

Oxidative stress plays a crucial role in the pathogenesis of Parkinson disease (PD), and one strategy for neuroprotective therapy for PD is to scavenge reactive species using a catalytic antioxidant. Previous studies in our laboratory revealed that pretreatment of lipophilic metalloporphyrins showed protective effects in a mouse PD model. In this study, we optimized the formulations of these metalloporphyrins to deliver them orally and tested their efficacy on disease outcomes in a second species after initiation of an insult (i.e., disease modification). In this study, a pharmaceutical formulation of two metalloporphyrin catalytic antioxidants, AEOL11207 and AEOL11114, was tested for oral drug delivery. Both compounds showed gastrointestinal absorption, achieved high plasma concentrations, and readily penetrated the blood-brain barrier after intravenous or oral delivery. AEOL11207 and AEOL11114 bioavailabilities were calculated to be 24% and 25%, respectively, at a dose of 10 mg/kg via the oral route. In addition, both compounds significantly attenuated 6-hydroxydopamine (6-OHDA)-induced neurotoxic damage, including dopamine depletion, cytokine production, and microglial activation in the striata; dopaminergic neuronal loss in the substantia nigra; oxidative/nitrative stress indices (glutathione disulfide and 3-nitrotyrosine) in the ventral midbrain; and rotation behavioral abnormality in rats. These results indicate that AEOL11207 and AEOL11114 are orally active metalloporphyrins and protect against 6-OHDA neurotoxicity 1-3 days postlesioning, suggesting disease-modifying properties and translational potential for PD. SIGNIFICANCE STATEMENT: Two catalytic antioxidants showed gastrointestinal absorption, achieved high plasma concentrations, and readily penetrated the blood-brain barrier. Both compounds significantly attenuated dopamine depletion, cytokine production, microglial activation, dopaminergic neuronal loss, oxidative/nitrative stress indices, and behavioral abnormality in a Parkinson disease rat model. The results suggest that both metalloporphyrins possess disease-modifying properties that may be useful in treating Parkinson disease.

3-Nitrotyrosine and related derivatives in proteins: precursors, radical intermediates and impact in function

Oxidative post-translational modification of proteins by molecular oxygen (O2)- and nitric oxide (•NO)-derived reactive species is a usual process that occurs in mammalian tissues under both physiological and pathological conditions and can exert either regulatory or cytotoxic effects. Although the side chain of several amino acids is prone to experience oxidative modifications, tyrosine residues are one of the preferred targets of one-electron oxidants, given the ability of their phenolic side chain to undergo reversible one-electron oxidation to the relatively stable tyrosyl radical. Naturally occurring as reversible catalytic intermediates at the active site of a variety of enzymes, tyrosyl radicals can also lead to the formation of several stable oxidative products through radical-radical reactions, as is the case of 3-nitrotyrosine (NO2Tyr). The formation of NO2Tyr mainly occurs through the fast reaction between the tyrosyl radical and nitrogen dioxide (•NO2). One of the key endogenous nitrating agents is peroxynitrite (ONOO-), the product of the reaction of superoxide radical (O2•-) with •NO, but ONOO--independent mechanisms of nitration have been also disclosed. This chemical modification notably affects the physicochemical properties of tyrosine residues and because of this, it can have a remarkable impact on protein structure and function, both in vitro and in vivo. Although low amounts of NO2Tyr are detected under basal conditions, significantly increased levels are found at pathological states related with an overproduction of reactive species, such as cardiovascular and neurodegenerative diseases, inflammation and aging. While NO2Tyr is a well-established stable oxidative stress biomarker and a good predictor of disease progression, its role as a pathogenic mediator has been laboriously defined for just a small number of nitrated proteins and awaits further studies.

Microtubule alterations may destabilize photoreceptor integrity: Age-related microtubule changes and pattern of expression of MAP-2, Tau and hyperphosphorylated Tau in aging human photoreceptor cells

Photoreceptor cells undergo changes with aging. It is unknown if their microtubules are stable or not with aging. This study examined photoreceptor cell ultrastructure from 18 human donor retinas (32 eyes; age: 45-94 years) and quantified the photoreceptors with altered microtubules over six to ninth decades in four defined retinal regions. In addition, immunoreactivity (IR) to microtubule-associated protein-2 (MAP-2), tau and hyperphophorylated tau was performed in retinal sections from companion eyes. In young donor retinas below 75 years of age, microtubules appeared straight in photoreceptor inner segments and axons. With age, they appeared bent or misaligned in macular and mid-peripheral photoreceptors. In addition, dense granular materials were present in photoreceptor axons and synaptic terminals in advanced ages. In all decades, rod microtubules were affected more than their cone counterparts (28% vs 15%, p < 0.005). Both rods and cones were significantly affected in mid-peripheral retina (5-8 mm outside the macular border) in eighth decade, compared to other decades or retinal regions (parafoveal, perifoveal and nasal) examined (p < 0.005). IR showed a steady expression of MAP-2 in inner segments, and tau in inner segments to axons below 75 years of age, but was absent for both markers in scattered macular and mid-peripheral photoreceptors in advanced ages (>75 years). IR to hyperphosphorylated tau was present mainly in inner retina and increased with aging. Markers of oxidative stress, e.g., lipid peroxidation (4-hydroxy 2-nonenal) and nitrosative stress (nitrotyrosine) were immunopositive in aged photoreceptors. The sporadic loss of MAP-2 and tau-IR in photoreceptors may be due to microtubule changes; all these changes may affect intracellular transport and be partly responsible for photoreceptor death in aged human retina.

Nanosilver Targets the Bacterial Cell Envelope: The Link with Generation of Reactive Oxygen Radicals

The work describes the interactions of nanosilver (NAg) with bacterial cell envelope components at a molecular level and how this associates with the reactive oxygen species (ROS)-mediated toxicity of the nanoparticle. Major structural changes were detected in cell envelope biomolecules as a result of damages in functional moieties, such as the saccharides, amides, and phosphodiesters. NAg exposure disintegrates the glycan backbone in the major cell wall component peptidoglycan, causes complete breakdown of lipoteichoic acid, and disrupts the phosphate-amine and fatty acid groups in phosphatidylethanolamine, a membrane phospholipid. Consistent with the oxidative attacks, we propose that the observed cell envelope damages are inflicted, at least in part, by the reactive oxygen radicals being generated by the nanoparticle during its leaching process, abiotically, without cells. The cell envelope targeting, especially those on the inner membrane phospholipid, is likely to then trigger the rapid generation of lethal levels of cellular superoxide (O₂^•-) and hydroxyl (OH^•) radicals herein seen with a model bacterium. The present study provides a better understanding of the antibacterial mechanisms of NAg, whereby ROS generation could be both the cause and consequence of the toxicity, associated with the initial cell envelope targeting by the nanoparticle.

Nitric Oxide and S-Nitrosylation in Cancers: Emphasis on Breast Cancer

Nitric oxide (NO) is a ubiquitous, endogenously produced, water-soluble signaling molecule playing critical roles in physiological processes. Nitric oxide plays pleiotropic roles in cancer and, depending on its local concentration, may lead to either tumor progression or tumor suppression. Addition of NO group to a cysteine residue within a protein, termed as S-nitrosylation, plays diverse regulatory roles and affects processes such as metabolism, apoptosis, protein phosphorylation, and regulation of transcription factors. The process of S-nitrosylation has been associated with development of different cancers, including breast cancer. The present review discusses different mechanisms through which NO acts, with special emphasis on breast cancers, and provides detailed insights into reactive nitrogen species, posttranslational modifications of proteins mediated by NO, dual nature of NO in cancers, and the implications of S-nitrosylation in cancers. Our review will generate interest in exploring molecular regulation by NO in different cancers and will have significant therapeutic implications in the management and treatment of breast cancer.

S-Nitrosothiol Signaling Is involved in Regulating Hydrogen Peroxide Metabolism of Zinc-Stressed Arabidopsis

Accumulation of heavy metals such as zinc (Zn) disturbs the metabolism of reactive oxygen (e.g. hydrogen peroxide, H2O2) and nitrogen species (e.g. nitric oxide, NO; S-nitrosoglutathione, GSNO) in plant cells; however, their signal interactions are not well understood. Therefore, this study examines the interplay between H2O2 metabolism and GSNO signaling in Arabidopsis. Comparing the Zn tolerance of the wild type (WT), GSNO reductase (GSNOR) overexpressor 35S::FLAG-GSNOR1 and GSNOR-deficient gsnor1-3, we observed relative Zn tolerance of gsnor1-3, which was not accompanied by altered Zn accumulation capacity. Moreover, in gsnor1-3 plants Zn did not induce NO/S-nitrosothiol (SNO) signaling, possibly due to the enhanced activity of NADPH-dependent thioredoxin reductase. In WT and 35S::FLAG-GSNOR1, GSNOR was inactivated by Zn, and Zn-induced H2O2 is directly involved in the GSNOR activity loss. In WT seedlings, Zn resulted in a slight intensification of protein nitration detected by Western blot and protein S-nitrosation observed by resin-assisted capture of SNO proteins (RSNO-RAC). LC-MS/MS analyses indicate that Zn induces the S-nitrosation of ascorbate peroxidase 1. Our data collectively show that Zn-induced H2O2 may influence its own level, which involves GSNOR inactivation-triggered SNO signaling. These data provide new evidence for the interplay between H2O2 and SNO signaling in Arabidopsis plants affected by metal stress.

Neuroprotective Effects of AEOL10150 in a Rat Organophosphate Model

Prolonged seizure activity or status epilepticus (SE) is one of the most critical manifestations of organophosphate exposure. Previous studies in our laboratory have demonstrated that oxidative stress is a critical mediator of SE-induced neuronal injury. The goal of this study was to determine if diisopropylflurorphoshate (DFP) exposure in rats resulted in oxidative stress and whether scavenging reactive oxygen species attenuated DFP-induced neurotoxicity. DFP treatment increased indices of oxidative stress in a time- and region- dependent manner. Neuronal loss measured by Fluoro-Jade B staining was significantly increased in the hippocampus, piriform cortex and amygdala following DFP. Similarly, levels of the proinflammatory cytokines, particularly TNF-α, IL-6, and KC/GRO were significantly increased in the piriform cortex and in the hippocampus following DFP treatment. The catalytic antioxidant AEOL10150, when treatment was initiated 5 min after DFP-induced SE, significantly attenuated indices of oxidative stress, neuroinflammation and neuronal damage. This study suggests that catalytic antioxidant treatment may be useful as a novel therapy to attenuate secondary neuronal injury following organophosphate exposure.

Localization of nitro-tyrosine immunoreactivity in human retina

Oxidative stress (OS) is associated with retinal aging and age-related macular degeneration (AMD). In both cases there are reports for the presence of markers of lipid peroxidation in retinal cells. We investigated if nitrosative stress also occurs in the human retina with aging. We examined the cellular localization of nitro-tyrosine, a biomarker of protein tyrosine nitration, in human donor retina (17-91 years; N = 15) by immunohistochemistry. Immunoreactivity (IR) to nitro-tyrosine was present in ten retinas and absent in five retinas. It was predominant in photoreceptor inner segments, cell bodies and axons. In six retinas, IR was present in abnormal, swollen axons of macular and peripheral cones. In the inner retina, weak immunoreactivity was detected in the outer and inner plexiform layer. Transmission electron microscopy revealed a variable degree of microtubule disorganization, abnormal outgrowth from the swollen macular axons (as the fibers of Henle) and few dead axons. The present study adds further evidence to the presence of aberrant photoreceptor axonal changes in the human retina and that nitro-tyrosine immunoreactivity is associated with the photoreceptor cells in select human retina.

Plant selenium toxicity: Proteome in the crosshairs

The metalloid element, selenium (Se) is in many ways special and perhaps because of this its research in human and plant systems is of great interest. Despite its non-essentiality, higher plants take it up and metabolize it via sulfur pathways, but higher amounts of Se cause toxic symptoms in plants. However, the molecular mechanisms of selenium phytotoxicity have been only partly revealed; the data obtained so far point out that Se toxicity targets the plant proteome. Besides seleno- and oxyproteins, nitroproteins are also formed due to Se stress. In order to minimize proteomic damages induced by Se, certain plants are able to redirect selenocysteine away from protein synthesis thus preventing Se-protein formation. Additionally, the damaged or malformed selenoproteins, oxyproteins and nitroproteins may be removed by proteasomes. Based on the literature this review sets Se toxicity mechanisms into a new concept and it draws attention to the importance of Se-induced protein-level changes.

Neuroprotective effects of a catalytic antioxidant in a rat nerve agent model

Persistent inhibition of acetylcholinesterase resulting from exposure to nerve agents such as soman, is associated with prolonged seizure activity known as status epilepticus (SE). Without medical countermeasures, exposure to soman and resultant SE leads to high morbidity and mortality. Currently available therapeutics are effective in limiting mortality, however effects on morbidity are highly time-dependent and rely on the ability to suppress SE. We have previously demonstrated significant protection from secondary neuronal injury in surrogate nerve agent models by targeting oxidative stress. However, whether oxidative stress represents a relevant therapeutic target in genuine nerve agent toxicity is unknown. Here, we demonstrate that soman exposure results in robust region- and time-dependent oxidative stress. Targeting this oxidative stress in a post-exposure paradigm using a small molecular weight, broad spectrum catalytic antioxidant, was sufficient to attenuate brain and plasma oxidative stress, neuroinflammation and neurodegeneration. Thus, targeting of oxidative stress in a post-exposure paradigm can mitigate secondary neuronal injury following soman exposure.

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Soman exposure results in time- and region- dependent oxidative stress in brain.

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A catalytic antioxidant inhibited oxidative stress, neuroinflammation and degeneration.

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Post-exposure treatment with the antioxidant attenuates secondary neuronal injury.

Oxidative Stress in Patients with Drug Resistant Partial Complex Seizure

Oxidative stress (OS) has been implicated as a pathophysiological mechanism of drug-resistant epilepsy, but little is known about the relationship between OS markers and clinical parameters, such as the number of drugs, age onset of seizure and frequency of seizures per month. The current study’s aim was to evaluate several oxidative stress markers and antioxidants in 18 drug-resistant partial complex seizure (DRPCS) patients compared to a control group (age and sex matched), and the results were related to clinical variables. We examined malondialdehyde (MDA), advanced oxidation protein products (AOPP), advanced glycation end products (AGEs), nitric oxide (NO), uric acid, superoxide dismutase (SOD), glutathione, vitamin C, 4-hydroxy-2-nonenal (4-HNE) and nitrotyrosine (3-NT). All markers except 4-HNE and 3-NT were studied by spectrophotometry. The expressions of 4-HNE and 3-NT were evaluated by Western blot analysis. MDA levels in patients were significantly increased (p ≤ 0.0001) while AOPP levels were similar to the control group. AGEs, NO and uric acid concentrations were significantly decreased (p ≤ 0.004, p ≤ 0.005, p ≤ 0.0001, respectively). Expressions of 3-NT and 4-HNE were increased (p ≤ 0.005) similarly to SOD activity (p = 0.0001), whereas vitamin C was considerably diminished (p = 0.0001). Glutathione levels were similar to the control group. There was a positive correlation between NO and MDA with the number of drugs. The expression of 3-NT was positively related with the frequency of seizures per month. There was a negative relationship between MDA and age at onset of seizures, as well as vitamin C with seizure frequency/month. We detected an imbalance in the redox state in patients with DRCPS, supporting oxidative stress as a relevant mechanism in this pathology. Thus, it is apparent that some oxidant and antioxidant parameters are closely linked with clinical variables.

Nitric Oxide Signalling in Yeast

Nitric oxide (NO) is a cellular signalling molecule widely conserved among organisms, including microorganisms such as bacteria, yeasts, and fungi, and higher eukaryotes such as plants and mammals. NO is mainly produced by the activities of NO synthase (NOS) or nitrite reductase (NIR). There are several NO detoxification systems, including NO dioxygenase (NOD) and S-nitrosoglutathione reductase (GSNOR). NO homeostasis, based on the balance between NO synthesis and degradation, is important for regulating its physiological functions, since an excess of NO causes nitrosative stress due to the high reactivity of NO and NO-derived compounds. In yeast, NO may be involved in stress responses, but the role of NO and the mechanism underlying NO signalling are poorly understood due to the lack of mammalian NOS orthologs in the yeast genome. NOS and NIR activities have been observed in yeast cells, but the gene-encoding NOS and the mechanism by which NO production is catalysed by NIR remain unclear. On the other hand, yeast cells employ NOD and GSNOR to maintain intracellular redox balance following endogenous NO production, treatment with exogenous NO, or exposure to environmental stresses. This article reviews NO metabolism (synthesis, degradation) and its regulation in yeast. The physiological roles of NO in yeast, including the oxidative stress response, are also discussed. Such investigations into NO signalling are essential for understanding how NO modulates the genetics and physiology of yeast. In addition to being responsible for the pathology and pharmacology of various degenerative diseases, NO signalling may be a potential target for the construction and engineering of industrial yeast strains.

The effects of hyperoxia on microvascular endothelial cell proliferation and production of vaso-active substances

BACKGROUND

Hyperoxia, an arterial oxygen pressure of more than 100 mmHg or 13% O2, frequently occurs in hospitalized patients due to administration of supplemental oxygen. Increasing evidence suggests that hyperoxia induces vasoconstriction in the systemic (micro)circulation, potentially affecting organ perfusion. This study addresses effects of hyperoxia on viability, proliferative capacity, and on pathways affecting vascular tone in cultured human microvascular endothelial cells (hMVEC).

METHODS

hMVEC of the systemic circulation were exposed to graded oxygen fractions of 20, 30, 50, and 95% O2 for 8, 24, and 72 h. These fractions correspond to 152, 228, 380, and 722 mmHg, respectively. Cell proliferation and viability was measured via a proliferation assay, peroxynitrite formation via anti-nitrotyrosine levels, endothelial nitric oxide synthase (eNOS), and endothelin-1 (ET-1) levels via q-PCR and western blot analysis.

RESULTS

Exposing hMVEC to 50 and 95% O2 for more than 24 h impaired cell viability and proliferation. Hyperoxia did not significantly affect nitrotyrosine levels, nor eNOS mRNA and protein levels, regardless of the exposure time or oxygen concentration used. Phosphorylation of eNOS at the serine 1177 (S1177) residue and ET-1 mRNA levels were also not significantly affected.

CONCLUSIONS

Exposure of isolated human microvascular endothelial cells to marked hyperoxia for more than 24 h decreases cell viability and proliferation. Our results do not support a role of eNOS mRNA and protein or ET-1 mRNA in the potential vasoconstrictive effects of hyperoxia on isolated hMVEC.

Covalent attachment of the heme to Synechococcus hemoglobin alters its reactivity toward nitric oxide

The cyanobacterium Synechococcus sp. PCC 7002 produces a monomeric hemoglobin (GlbN) implicated in the detoxification of reactive nitrogen and oxygen species. GlbN contains a b heme, which can be modified under certain reducing conditions. The modified protein (GlbN-A) has one heme-histidine C-N linkage similar to the C-S linkage of cytochrome c. No clear functional role has been assigned to this modification. Here, optical absorbance and NMR spectroscopies were used to compare the reactivity of GlbN and GlbN-A toward nitric oxide (NO). Both forms of the protein are capable of NO dioxygenase activity and both undergo heme bleaching after multiple NO challenges. GlbN and GlbN-A bind NO in the ferric state and form diamagnetic complexes (Fe^III-NO) that resist reductive nitrosylation to the paramagnetic Fe^II-NO forms. Dithionite reduction of Fe^III-NO GlbN and GlbN-A, however, resulted in distinct outcomes. Whereas GlbN-A rapidly formed the expected Fe^II-NO complex, NO binding to Fe^II GlbN caused immediate heme loss and, remarkably, was followed by slow heme rebinding and HNO (nitrosyl hydride) production. Additionally, combining Fe^III GlbN, ¹⁵N-labeled nitrite, and excess dithionite resulted in the formation of Fe^II-H¹⁵NO GlbN. Dithionite-mediated HNO production was also observed for the related GlbN from Synechocystis sp. PCC 6803. Although ferrous GlbN-A appeared capable of trapping preformed HNO, the histidine-heme post-translational modification extinguished the NO reduction chemistry associated with GlbN. Overall, the results suggest a role for the covalent modification in Fe^II GlbNs: protection from NO-mediated heme loss and prevention of HNO formation.

Peptide-Functionalized Fluorescent Particles for In Situ Detection of Nitric Oxide via Peroxynitrite-Mediated Nitration

Nitric oxide (NO) is a free radical signaling molecule that plays a crucial role in modulating physiological homeostasis across multiple biological systems. NO dysregulation is linked to the pathogenesis of multiple diseases; therefore, its quantification is important for understanding pathophysiological processes. The detection of NO is challenging, typically limited by its reactive nature and short half-life. Additionally, the presence of interfering analytes and accessibility to biological fluids in the native tissues make the measurement technically challenging and often unreliable. Here, a bio-inspired peptide-based NO sensor is developed, which detects NO-derived oxidants, predominately peroxynitrite-mediated nitration of tyrosine residues. It is demonstrated that these peptide-based NO sensors can detect peroxynitrite-mediated nitration in response to physiological shear stress by endothelial cells in vitro. Using the peptide-conjugated fluorescent particle immunoassay, peroxynitrite-mediated nitration activity with a detection limit of ≈100 × 10-9 m is detected. This study envisions that the NO detection platform can be applied to a multitude of applications including monitoring of NO activity in healthy and diseased tissues, localized detection of NO production of specific cells, and cell-based/therapeutic screening of peroxynitrite levels to monitor pronitroxidative stress in biological samples.

Post-translational Activation of Glutamate Cysteine Ligase with Dimercaprol: A NOVEL MECHANISM OF INHIBITING NEUROINFLAMMATION IN VITRO

Neuroinflammation and oxidative stress are hallmarks of various neurological diseases. However, whether and how the redox processes control neuroinflammation is incompletely understood. We hypothesized that increasing cellular glutathione (GSH) levels would inhibit neuroinflammation. A series of thiol compounds were identified to elevate cellular GSH levels by a novel approach (i.e. post-translational activation of glutamate cysteine ligase (GCL), the rate-limiting enzyme in GSH biosynthesis). These small thiol-containing compounds were examined for their ability to increase intracellular GSH levels in a murine microglial cell line (BV2), of which dimercaprol (2,3-dimercapto-1-propanol (DMP)) was found to be the most effective compound. DMP increased GCL activity and decreased LPS-induced production of pro-inflammatory cytokines and inducible nitric-oxide synthase induction in BV2 cells in a concentration-dependent manner. The ability of DMP to elevate GSH levels and attenuate LPS-induced pro-inflammatory cytokine production was inhibited by buthionine sulfoximine, an inhibitor of GCL. DMP increased the expression of GCL holoenzyme without altering the expression of its subunits or Nrf2 target proteins (NQO1 and HO-1), suggesting a post-translational mechanism. DMP attenuated LPS-induced MAPK activation in BV2 cells, suggesting the MAPK pathway as the signaling mechanism underlying the effect of DMP. Finally, the ability of DMP to increase GSH via GCL activation was observed in mixed cerebrocortical cultures and N27 dopaminergic cells. Together, the data demonstrate a novel mechanism of GSH elevation by post-translational activation of GCL. Post-translational activation of GCL offers a novel targeted approach to control inflammation in chronic neuronal disorders associated with impaired adaptive responses.

IL-6 Improves the Nitric Oxide-Induced Cytotoxic CD8+ T Cell Dysfunction in Human Chagas Disease

Reactive oxygen and nitrogen species are important microbicidal agents and are also involved in lymphocyte unresponsiveness during experimental infections. Many of the biological effects attributed to nitric oxide are mediated by peroxynitrites, which induce the nitration of immune cells, among others. Our group has demonstrated that nitric oxide is involved in the suppressive activity of myeloid-derived suppressor cells in Trypanosoma cruzi-infected mice, with a higher number of CD8+ T cells suffering surface-nitration compared to uninfected controls. Studying the functional and phenotypic features of peripheral CD8+ T cells from chagasic patients and human cells experimentally infected with T. cruzi, we found that different regulatory mechanisms impaired the effector functions of T cytotoxic population from seropositive patients. Peripheral leukocytes from chagasic patients showed increased nitric oxide production concomitant with increased tyrosine nitration of CD8+ T cells. Additionally, this cytotoxic population exhibited increased apoptotic rate, loss of the TCRζ-chain, and lower levels of CD107a, a marker of degranulation. Strikingly, IL-6 stimulation of in vitro-infected peripheral blood mononuclear cells obtained from healthy donors, blunted T. cruzi-induced nitration of CD3+CD8+ cells, and increased their survival. Furthermore, the treatment of these cultures with an IL-6 neutralizing antibody increased the percentage of T. cruzi-induced CD8+ T cell nitration and raised the release of nitric oxide. The results suggest that the under-responsiveness of cytotoxic T cell population observed in the setting of long-term constant activation of the immune system could be reverted by the pleiotropic actions of IL-6, since this cytokine improves its survival and effector functions.

Direct measurement of actual levels of nitric oxide (NO) in cell culture conditions using soluble NO donors

Applying soluble nitric oxide (NO) donors is the most widely used method to expose cells of interest to exogenous NO. Because of the complex equilibria that exist between components in culture media, the donor compound and NO itself, it is very challenging to predict the dose and duration of NO cells actually experience. To determine the actual level of NO experienced by cells exposed to soluble NO donors, we developed the CellNO Trap, a device that allows continuous, real-time monitoring of the level of NO adherent cells produce and/or experience in culture without the need to alter cell culturing procedures. Herein, we directly measured the level of NO that cells grown in the CellNO Trap experienced when soluble NO donors were added to solutions in culture wells and we characterized environmental conditions that effected the level of NO in in vitro culture conditions. Specifically, the dose and duration of NO generated by the soluble donors S-nitroso-N-acetylpenicillamine (SNAP), S-nitrosoglutathione (GSNO), S-nitrosocysteine (CysNO) and the diazeniumdiolate diethyltriamine (DETA/NO) were investigated in both phosphate buffered saline (PBS) and cell culture media. Other factors that were studied that potentially affect the ultimate NO level achieved with these donors included pH, presence of transition metals (ion species), redox level, presence of free thiol and relative volume of media. Then murine smooth muscle cell (MOVAS) with different NO donors but with the same effective concentration of available NO were examined and it was demonstrated that the cell proliferation ratio observed does not correlate with the half-lives of NO donors characterized in PBS, but does correlate well with the real-time NO profiles measured under the actual culture conditions. This data demonstrates the dynamic characteristic of the NO and NO donor in different biological systems and clearly illustrates the importance of tracking individual NO profiles under the actual biological conditions.

[Host defense and oxidative stress signaling in bacterial infection ]

Nitric oxide (NO) and reactive oxygen species (ROS) produced during infection are involved critically in host defense mechanisms. It is quite important to physiologically regulate ROS, such as superoxide, and NO. These reactive species produced in excess may cause oxidative damage of biological molecules. An important cytoprotective and antimicrobial function of NO and ROS is mediated by induction of heme oxygenase (HO)-1. The signaling mechanism of this HO-1 induction has remained unclear, however. We discovered in 2007 a unique second messenger, 8-nitroguanosine 3',5'-cyclic monophosphate (8-nitro-cGMP), that mediates electrophilic signal transduction during oxidative stress and other cellular redox signaling in general. 8-Nitro-cGMP is formed via guanine nitration with NO and ROS, and in fact, NO-dependent 8-nitro-cGMP formation and HO-1 induction were identified in Salmonella-infected mice. HO-1 induction was regulated solely by 8-nitro-cGMP formed in cells, and more important, its potent anti-apoptotic function was evident in such a Salmonella infection. 8-Nitro-cGMP has a potent cytoprotective function, of which signaling appears to be mediated via protein sulfhydryls to generate a post-translational modification called protein S-guanylation. 8-Nitro-cGMP specifically S-guanylates Keap1, a negative regulator of transcription factor Nrf2, which in turn up-regulates transcription of HO-1. Our recent study revealed that the autophagy might be involved in the 8-nitro-cGMP-dependent antimicrobial effect. The 8-nitro-cGMP signaling was also found to be regulated by reactive sulfur species that have superior antioxidant activity and unique signaling function. This review will discuss a new paradigm of the host defense that operates via formation of a unique cell signaling molecule, 8-nitro-cGMP, during microbial infections.

Formation of 2-nitrophenol from salicylaldehyde as a suitable test for low peroxynitrite fluxes

There has been some dispute regarding reaction products formed at physiological peroxynitrite fluxes in the nanomolar range with phenolic molecules, when used to predict the behavior of protein-bound aromatic amino acids like tyrosine. Previous data showed that at nanomolar fluxes of peroxynitrite, nitration of these phenolic compounds was outcompeted by dimerization (e.g. biphenols or dityrosine). Using 3-morpholino sydnonimine (Sin-1), we created low fluxes of peroxynitrite in our reaction set-up to demonstrate that salicylaldehyde displays unique features in the detection of physiological fluxes of peroxynitrite, yielding detectable nitration but only minor dimerization products.

By means of HPLC analysis and detection at 380 nm we could identify the expected nitration products 3- and 5-nitrosalicylaldehyde, but also novel nitrated products. Using mass spectrometry, we also identified 2-nitrophenol and a not fully characterized nitrated dimerization product. The formation of 2-nitrophenol could proceed either by primary generation of a phenoxy radical, followed by addition of the NO₂-radical to the various resonance structures, or by addition of the peroxynitrite anion to the polarized carbonyl group with subsequent fragmentation of the adduct (as seen with carbon dioxide). Interestingly, we observed almost no 3- and 5-nitrosalicylic acid products and only minor dimerization reaction.

Our results disagree with the previous general assumption that nitration of low molecular weight phenolic compounds is always outcompeted by dimerization at nanomolar peroxynitrite fluxes and highlight unique features of salicylaldehyde as a probe for physiological concentrations of peroxynitrite.

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There are no specific probes for peroxynitrite formation in vivo.

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Salicylaldehyde reacts with peroxynitrite to form the product 2-nitrophenol.

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Only high/supraphysiological •NO or peroxidase/H₂O₂/NO₂^─ levels yield 2-nitrophenol.

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Salicylaldehyde is suitable for detection of nanomolar fluxes of peroxynitrite.

The Impact of Non-Enzymatic Reactions and Enzyme Promiscuity on Cellular Metabolism during (Oxidative) Stress Conditions

Cellular metabolism assembles in a structurally highly conserved, but functionally dynamic system, known as the metabolic network. This network involves highly active, enzyme-catalyzed metabolic pathways that provide the building blocks for cell growth. In parallel, however, chemical reactivity of metabolites and unspecific enzyme function give rise to a number of side products that are not part of canonical metabolic pathways. It is increasingly acknowledged that these molecules are important for the evolution of metabolism, affect metabolic efficiency, and that they play a potential role in human disease—age-related disorders and cancer in particular. In this review we discuss the impact of oxidative and other cellular stressors on the formation of metabolic side products, which originate as a consequence of: (i) chemical reactivity or modification of regular metabolites; (ii) through modifications in substrate specificity of damaged enzymes; and (iii) through altered metabolic flux that protects cells in stress conditions. In particular, oxidative and heat stress conditions are causative of metabolite and enzymatic damage and thus promote the non-canonical metabolic activity of the cells through an increased repertoire of side products. On the basis of selected examples, we discuss the consequences of non-canonical metabolic reactivity on evolution, function and repair of the metabolic network.

Oxidative stress in murine Theiler's virus-induced temporal lobe epilepsy

Temporal lobe epilepsy (TLE) is the most common form of acquired epilepsy that can be caused by several inciting events including viral infections. However, one-third of TLE patients are pharmacoresistant to current antiepileptic drugs and therefore, there is an urgent need to develop antiepileptogenic therapies that prevent the development of the disease. Oxidative stress and redox alterations have recently been recognized as important etiological factors contributing to seizure-induced neuronal damage. The goal of this study was to determine if oxidative stress occurs in the TMEV (Theiler's murine encephalomyelitis virus) model of temporal lobe epilepsy (TLE). C57Bl/6 mice were injected with TMEV or with PBS intracortically and observed for acute seizures. At various time points after TMEV injection, hippocampi were analyzed for levels of reduced glutathione (GSH), oxidized glutathione (GSSG) and 3-nitrotyrosine (3 NT). Mice infected with TMEV displayed behavioral seizures between days 3 and 7 days post-infection (dpi). The intensity of seizures increased over time with most of the seizures being a stage 4 or 5 on the Racine scale at 6 days p.i. Mice exhibiting at least one seizure during the observation period were utilized for the biochemical analyses. The levels of GSH were significantly depleted in TMEV infected mice at 3, 4 and 14 days p.i. with a concomitant increase in GSSH levels as well as an impairment of the redox status. Additionally, there was a substantial increase in 3 NT levels in TMEV infected mice at these time points. These redox changes correlated with the occurrence of acute seizures in this model. Interestingly, we did not see changes in any of the indices in the cerebellum of TMEV-infected mice at 3 dpi indicating that these alterations are localized to the hippocampus and perhaps other limbic regions. This is the first study to demonstrate the occurrence of oxidative stress in the TMEV model of infection-induced TLE. The redox alterations were observed at time points coinciding with the appearance of acute behavioral seizures suggesting that these changes might be a consequence of seizure activity. Our results support the hypothesis that redox changes correlate with seizure activity in acquired epilepsies, regardless of the inciting insults, and suggest oxidative stress as a potential therapeutic target for their treatment.

Protective effect of molecular hydrogen against oxidative stress caused by peroxynitrite derived from nitric oxide in rat retina

BACKGROUND

Oxidative and nitrative processes have an important role in the pathogenesis of glaucomatous neurodegeneration. Oxidative stress occurs when cellular production of reactive oxygen species outweighs the protective capacity of antioxidant defences. Reactive oxygen species are generated as by-products of cellular metabolism, primarily in the mitochondria. Herein, we present a novel investigation of the effects of molecular hydrogen (H2 ) on retinal cells exposed to oxidative stress.

METHODS

We cultured adult rat retinal tissues in an organotypic culture system with a nitric oxide donor, S-nitroso-N-acetylpenicillamine, in the presence or absence of H2 . Loss of mitochondrial membrane potential and apoptosis of retinal cells were analysed using a MitoTMRE detection kit and TdT-mediated dUTP nick end labeling (TUNEL) assay, respectively. Tyrosine nitration levels and oxidative stress damage in the retina were evaluated using immunohistochemical staining. Retinal damage was quantified by measuring the numbers of cells in the ganglion cell and inner nuclear layers and the thickness of the retina.

RESULTS

H2 suppressed loss of mitochondrial membrane potential and apoptosis in retinal cells. Moreover, H2 decreased the tyrosine nitration level and suppressed oxidative stress damage in retinal cells. S-nitroso-N-acetylpenicillamine treatment decreased the cell numbers in the ganglion cell layer and inner nuclear layer, but the presence of H2 inhibited this reduction. These findings suggest that H2 has a neuroprotective effect against retinal cell oxidative damage, presumably by scavenging peroxynitrite.

CONCLUSIONS

H2 reduces cellular peroxynitrite, a highly toxic reactive nitrogen species. Thus, H2 may be an effective and novel clinical tool for treating glaucoma and other oxidative stress-related diseases.

SR-135, a peroxynitrite decomposing catalyst, enhances β-cell function and survival in B6D2F1 mice fed a high fat diet

Peroxynitrite has been implicated in β-cell dysfunction and insulin resistance in obesity. Chemical catalysts that destroy peroxynitrite, therefore, may have therapeutic value for treating type 2 diabetes. To this end, we have recently demonstrated that Mn(III) bis(hydroxyphenyl)-dipyrromethene complexes, SR-135 and its analogs, can effectively catalyze the decomposition of peroxynitrite in vitro and in vivo through a 2-electron mechanism (Rausaria et al., 2011). To study the effects of SR-135 on glucose homeostasis in obesity, B6D2F1 mice were fed with a high fat-diet (HFD) for 12 weeks and treated with vehicle, SR-135 (5mg/kg), or a control drug SRB for 2 weeks. SR-135 significantly reduced fasting blood glucose and insulin levels, and enhanced glucose tolerance as compared to HFD control, vehicle or SRB. SR-135 also enhanced glucose-stimulated insulin secretion based on ex vivo studies. Moreover, SR-135 increased insulin content, restored islet architecture, decreased islet size, and reduced tyrosine nitration and apoptosis. These results suggest that a peroxynitrite decomposing catalyst enhances β-cell function and survival under nutrient overload.

[Reactive oxygen species signaling and redox homeostasis regulated by 8-nitro-cGMP]

An emerging aspect of redox signaling is the signaling pathway mediated by electrophilic byproducts, such as nitrated cyclic nucleotide (8-nitro-cGMP), generated via reactions of reactive oxygen species (ROS), NO, and their secondary products. We recently clarified that enzymatically-generated hydrosulfide derivatives regulate the metabolism and signaling of 8-nitro-cGMP. Although hydrogen sulfide was proposed to be a gaseous signaling mediator, its exact nature and physiological functions remain obscure. We thus found that particular hydropersulfide derivatives rather than hydrogen sulfide greatly ameliorated chronic heart failure after myocardial infarction in vivo in mice. This potent cardioprotective effect resulted from strong suppression of H-Ras signaling activated by electrophilic stimulation with 8-nitro-cGMP functioning as a second messenger for the redox signaling induced by NO and ROS. A significant amount of 8-nitro-cGMP was formed in the heart tissue after myocardial infarction, and hydrogen sulfide exogenously administered completely nullified this formation. We have reportedly shown that hydropersulfide effectively thiolated electrophiles in cells, which is best represented by 8-nitro-cGMP. Our current study indicates that electrophile thiolation may be a unique mechanism regulating ROS signaling and redox homeostasis, which may thus promote further development of prophylactic and therapeutic options for oxidative stress-related diseases.

Structural and molecular basis of the peroxynitrite-mediated nitration and inactivation of Trypanosoma cruzi iron-superoxide dismutases (Fe-SODs) A and B: disparate susceptibilities due to the repair of Tyr35 radical by Cys83 in Fe-SODB through intramolecular electron transfer

Trypanosoma cruzi, the causative agent of Chagas disease, contains exclusively iron-dependent superoxide dismutases (Fe-SODs) located in different subcellular compartments. Peroxynitrite, a key cytotoxic and oxidizing effector biomolecule, reacted with T. cruzi mitochondrial (Fe-SODA) and cytosolic (Fe-SODB) SODs with second order rate constants of 4.6 ± 0.2 × 10(4) M(-1) s(-1) and 4.3 ± 0.4 × 10(4) M(-1) s(-1) at pH 7.4 and 37 °C, respectively. Both isoforms are dose-dependently nitrated and inactivated by peroxynitrite. Susceptibility of T. cruzi Fe-SODA toward peroxynitrite was similar to that reported previously for Escherichia coli Mn- and Fe-SODs and mammalian Mn-SOD, whereas Fe-SODB was exceptionally resistant to oxidant-mediated inactivation. We report mass spectrometry analysis indicating that peroxynitrite-mediated inactivation of T. cruzi Fe-SODs is due to the site-specific nitration of the critical and universally conserved Tyr(35). Searching for structural differences, the crystal structure of Fe-SODA was solved at 2.2 Å resolution. Structural analysis comparing both Fe-SOD isoforms reveals differences in key cysteines and tryptophan residues. Thiol alkylation of Fe-SODB cysteines made the enzyme more susceptible to peroxynitrite. In particular, Cys(83) mutation (C83S, absent in Fe-SODA) increased the Fe-SODB sensitivity toward peroxynitrite. Molecular dynamics, electron paramagnetic resonance, and immunospin trapping analysis revealed that Cys(83) present in Fe-SODB acts as an electron donor that repairs Tyr(35) radical via intramolecular electron transfer, preventing peroxynitrite-dependent nitration and consequent inactivation of Fe-SODB. Parasites exposed to exogenous or endogenous sources of peroxynitrite resulted in nitration and inactivation of Fe-SODA but not Fe-SODB, suggesting that these enzymes play distinctive biological roles during parasite infection of mammalian cells.

Antioxidant and neuronal cell protective effects of columbia arabica coffee with different roasting conditions

In vitro antioxidant activities and neuronal cell protective effects of ethanol extract from roasted coffee beans were investigated. Colombia arabica coffee (Coffea arabica) green beans were roasted to give medium (230°C, 10 min), city (230°C, 12 min) and french (230°C, 15 min) coffee beans. Total phenolics in raw green beans, medium, city and french-roasted beans were 8.81±0.05, 9.77±0.03, 9.92±0.04 and 7.76±0.01 mg of GAE/g, respectively. The content of 5-O-caffeoylquinic acid, the predominant phenolic, was detected higher in medium-roasted beans than others. In addition, we found that extracts from medium-roasted beans particularly showed the highest in vitro antioxidant activity on ABTS radical scavenging activity and FRAP assays. To determine cell viability using the MTT assay, extracts from medium-roasted beans showed higher protection against H₂O₂-induced neurotoxicity than others. Lactate dehydrogenase (LDH) leakage was also inhibited by the extracts due to prevention of lipid peroxidation using the malondialdehyde (MDA) assay from mouse whole brain homogenates. These data suggest that the medium-roasting condition to making tasty coffee from Columbia arabica green beans may be more helpful to human health by providing the most physiological phenolics, including 5-O-caffeoylquinic acids.

Functional hybrids of layered double hydroxides with hemin: synergistic effect for peroxynitrite-scavenging activity

The interaction between heme and LDHs results in a synergistic effect, which leads to an efficient ONOO⁻scavenging ability.

Temporal and spatial increase of reactive nitrogen species in the kainate model of temporal lobe epilepsy

Steady-state levels of reactive oxygen species (ROS) and oxidative damage to cellular macromolecules are increased in the rodent hippocampus during epileptogenesis. However, the role of reactive nitrogen species (RNS) in epileptogenesis remains to be explored. The goal of this study was to determine the spatial and temporal occurrence of RNS i.e. nitric oxide levels in a rat model of temporal lobe epilepsy (TLE). Rats were injected with a single high dose of kainate and monitored by video for behavioral seizures for 6weeks to determine the onset and severity of chronic seizures. RNS and tissue/mitochondrial redox status (glutathione redox couple and coenzyme A:glutathione redox couple) were measured in the hippocampus at 8h, 24h, 48h, 1wk, 3wk and 6wk following kainate to assess the level of reactive species in subcellular compartments. We observed a biphasic increase in RNS levels with a return to control values at the 48h time point. However, both tissue and mitochondrial redox status showed permanent and significant decreases during the entire time course of epilepsy development. 3 nitrotyrosine (3NT) protein adducts were found to gradually increase throughout epileptogenesis, conceivably as a result of the local environment under oxidative and nitrosative stress. Colocalization of 3NT immunostaining with neuron- or astrocyte-specific markers revealed neuron-specific localization of 3NT in hippocampal principal neurons. Persistent and concurrent glutathione oxidation and nitrosative stress occur during epileptogenesis suggesting a favorable environment for posttranslational modifications.

Genetically encoded fluorescent redox probes

Redox processes are involved in almost every cell of the body as a consequence of aerobic life. In the past decades, redox biology has been increasingly recognized as one of the key themes in cell signaling. The progress has been accelerated by development of fluorescent probes that can monitor redox conditions and dynamics in cells and cell compartments. This short paper focuses on fluorescent redox probes that are genetically encoded, and discusses their properties, molecular mechanism, advantages and pitfalls. Our recent work on reaction-based encoded probes that are responsive to particular redox signaling molecules is also reviewed. Future challenges and directions are also commented.

Endothelial NO and O₂·⁻ production rates differentially regulate oxidative, nitroxidative, and nitrosative stress in the microcirculation

Endothelial dysfunction causes an imbalance in endothelial NO and O₂·⁻ production rates and increased peroxynitrite formation. Peroxynitrite and its decomposition products cause multiple deleterious effects including tyrosine nitration of proteins, superoxide dismutase (SOD) inactivation, and tissue damage. Studies have shown that peroxynitrite formation during endothelial dysfunction is strongly dependent on the NO and O₂·⁻ production rates. Previous experimental and modeling studies examining the role of NO and O₂·⁻ production imbalance on peroxynitrite formation showed different results in biological and synthetic systems. However, there is a lack of quantitative information about the formation and biological relevance of peroxynitrite under oxidative, nitroxidative, and nitrosative stress conditions in the microcirculation. We developed a computational biotransport model to examine the role of endothelial NO and O₂·⁻ production on the complex biochemical NO and O₂·⁻ interactions in the microcirculation. We also modeled the effect of variability in SOD expression and activity during oxidative stress. The results showed that peroxynitrite concentration increased with increase in either O₂·⁻ to NO or NO to O₂·⁻ production rate ratio (QO₂·⁻/QNO or QNO/QO₂·⁻, respectively). The peroxynitrite concentrations were similar for both production rate ratios, indicating that peroxynitrite-related nitroxidative and nitrosative stresses may be similar in endothelial dysfunction or inducible NO synthase (iNOS)-induced NO production. The endothelial peroxynitrite concentration increased with increase in both QO₂·⁻/QNO and QNO/QO₂·⁻ ratios at SOD concentrations of 0.1-100 μM. The absence of SOD may not mitigate the extent of peroxynitrite-mediated toxicity, as we predicted an insignificant increase in peroxynitrite levels beyond QO₂·⁻/QNO and QNO/QO₂·⁻ ratios of 1. The results support the experimental observations of biological systems and show that peroxynitrite formation increases with increase in either NO or O₂·⁻ production, and excess NO production from iNOS or from NO donors during oxidative stress conditions does not reduce the extent of peroxynitrite mediated toxicity.

Protein tyrosine nitration and thiol oxidation by peroxynitrite-strategies to prevent these oxidative modifications

The reaction product of nitric oxide and superoxide, peroxynitrite, is a potent biological oxidant. The most important oxidative protein modifications described for peroxynitrite are cysteine-thiol oxidation and tyrosine nitration. We have previously demonstrated that intrinsic heme-thiolate (P450)-dependent enzymatic catalysis increases the nitration of tyrosine 430 in prostacyclin synthase and results in loss of activity which contributes to endothelial dysfunction. We here report the sensitive peroxynitrite-dependent nitration of an over-expressed and partially purified human prostacyclin synthase (3.3 μM) with an EC₅₀ value of 5 μM. Microsomal thiols in these preparations effectively compete for peroxynitrite and block the nitration of other proteins up to 50 μM peroxynitrite. Purified, recombinant PGIS showed a half-maximal nitration by 10 μM 3-morpholino sydnonimine (Sin-1) which increased in the presence of bicarbonate, and was only marginally induced by freely diffusing NO₂-radicals generated by a peroxidase/nitrite/hydrogen peroxide system. Based on these observations, we would like to emphasize that prostacyclin synthase is among the most efficiently and sensitively nitrated proteins investigated by us so far. In the second part of the study, we identified two classes of peroxynitrite scavengers, blocking either peroxynitrite anion-mediated thiol oxidations or phenol/tyrosine nitrations by free radical mechanisms. Dithiopurines and dithiopyrimidines were highly effective in inhibiting both reaction types which could make this class of compounds interesting therapeutic tools. In the present work, we highlighted the impact of experimental conditions on the outcome of peroxynitrite-mediated nitrations. The limitations identified in this work need to be considered in the assessment of experimental data involving peroxynitrite.

Targeting hepatoma using nitric oxide donor strategies

AIMS

The study evaluated the role of increased intracellular nitric oxide (NO) concentration using NO donors or stably NO synthase-3 (NOS-3) overexpression during CD95-dependent cell death in hepatoma cells. The expression of cell death receptors and caspase activation, RhoA kinase activity, NOS-3 expression/activity, oxidative/nitrosative stress, and p53 expression were analyzed. The antitumoral activity of NO was also evaluated in the subcutaneous implantation of NOS-3-overexpressing hepatoma cells, as well NO donor injection into wild-type hepatoma-derived tumors implanted in xenograft mouse models.

RESULTS

NO donor increased CD95 expression and activation of caspase-8 and 3 in HepG2, Huh7, and Hep3B cells. NOS-3 overexpression increased oxidative/nitrosative stress, p53 and CD95 expression, cellular Fas-associated death domain (FADD)-like IL-1beta converting enzyme (FLICE) inhibitory protein long (cFLIP(L)) and its short isoform (cFLIP(S)) shift, and cell death in HepG2 (4TO-NOS) cells. The inhibition of RhoA kinase and p53 knockdown using RNA interference reduced cell death in 4TO-NOS cells. The supplementation with hydrogen peroxide (H(2)O(2)) increased NOS-3 activity and cell death in 4TO-NOS cells. NOS-3 overexpression or NO donor injection into hepatoma-derived tumors reduced the size and increased p53 and cell death receptor expression in nude mice.

INNOVATION AND CONCLUSIONS

The increase of intracellular NO concentration promoted oxidative and nitrosative stress, Rho kinase activity, p53 and CD95 expression, and cell death in cultured hepatoma cells. NOS-3-overexpressed HepG2 cells or intratumoral NO donor administration reduced tumor cell growth and increased the expression of p53 and cell death receptors in tumors developed in a xenograft mouse model.

Vascular E-selectin expression correlates with CD8 lymphocyte infiltration and improved outcome in Merkel cell carcinoma

Merkel cell carcinoma (MCC) is an aggressive, polyomavirus-linked skin cancer. Although CD8 lymphocyte infiltration into the tumor is strongly correlated with improved survival, these cells are absent or sparse in most MCCs. We investigated whether specific mechanisms of T-cell migration may be commonly disrupted in MCC tumors with poor CD8 lymphocyte infiltration. Intratumoral vascular E-selectin, critical for T-cell entry into skin, was downregulated in the majority (52%) of MCCs (n=56), and its loss was associated with poor intratumoral CD8 lymphocyte infiltration (P<0.05; n=45). Importantly, survival was improved in MCC patients whose tumors had higher vascular E-selectin expression (P<0.05). Local nitric oxide (NO) production is one mechanism of E-selectin downregulation and it can be tracked by quantifying nitrotyrosine, a stable biomarker of NO-induced reactive nitrogen species (RNS). Indeed, increasing levels of nitrotyrosine within MCC tumors were associated with low E-selectin expression (P<0.05; n=45) and decreased CD8 lymphocyte infiltration (P<0.05, n=45). These data suggest that one mechanism of immune evasion in MCC may be restriction of T-cell entry into the tumor. Existing therapeutic agents that modulate E-selectin expression and/or RNS generation may restore T-cell entry and could potentially synergize with other immune-stimulating therapies.