One- and two-electron oxidations of methionine by peroxynitrite

Catalytic Mechanism of Mycobacterium tuberculosis Methionine Sulfoxide Reductase A

The oxidation of Met to methionine sulfoxide (MetSO) by oxidants such as hydrogen peroxide, hypochlorite, or peroxynitrite has profound effects on protein function. This modification can be reversed by methionine sulfoxide reductases (msr). In the context of pathogen infection, the reduction of oxidized proteins gains significance due to microbial oxidative damage generated by the immune system. For example, Mycobacterium tuberculosis (Mt) utilizes msrs (MtmsrA and MtmsrB) as part of the repair response to the host-induced oxidative stress. The absence of these enzymes makes Mycobacteria prone to increased susceptibility to cell death, pointing them out as potential therapeutic targets. This study provides a detailed characterization of the catalytic mechanism of MtmsrA using a comprehensive approach, including experimental techniques and theoretical methodologies. Confirming a ping-pong type enzymatic mechanism, we elucidate the catalytic parameters for sulfoxide and thioredoxin substrates (kcat/KM = 2656 ± 525 M-1 s-1 and 1.7 ± 0.8 × 106 M-1 s-1, respectively). Notably, the entropic nature of the activation process thermodynamics, representing ∼85% of the activation free energy at room temperature, is underscored. Furthermore, the current study questions the plausibility of a sulfurane intermediate, which may be a transition-state-like structure, suggesting the involvement of a conserved histidine residue as an acid-base catalyst in the MetSO reduction mechanism. This mechanistic insight not only advances our understanding of Mt antioxidant enzymes but also holds implications for future drug discovery and biotechnological applications.

Plasma-Generated Nitric Oxide Water Mediates Environmentally Transmitted Pathogenic Bacterial Inactivation via Intracellular Nitrosative Stress

Over time, the proportion of resistant bacteria will increase. This is a major concern. Therefore, effective and biocompatible therapeutic strategies against these bacteria are urgently needed. Non-thermal plasma has been exhaustively characterized for its antibacterial activity. This study aims to investigate the inactivation efficiency and mechanisms of plasma-generated nitric oxide water (PG-NOW) on pathogenic water, air, soil, and foodborne Gram-negative and Gram-positive bacteria. Using a colony-forming unit assay, we found that PG-NOW treatment effectively inhibited the growth of bacteria. Moreover, the intracellular nitric oxide (NO) accumulation was evaluated by 4-amino-5-methylamino-2',7'-dichlorofluorescein diacetate (DAF-FM DA) staining. The reduction of viable cells unambiguously indicates the anti-microbial effect of PG-NOW. The soxR and soxS genes are associated with nitrosative stress, and oxyR regulation corresponds to oxidative stress in bacterial cells. To support the nitrosative effect mediated by PG-NOW, we have further assessed the soxRS and oxyR gene expressions after treatment. Accordingly, soxRS expression was enhanced, whereas the oxyR expression was decreased following PG-NOW treatment. The disruption of cell morphology was observed using scanning electron microscopy (SEM) analysis. In conclusion, our findings furnish evidence of an initiation point for the further progress and development of PG-NOW-based antibacterial treatments.

Interplay of carbon dioxide and peroxide metabolism in mammalian cells

The carbon dioxide/bicarbonate (CO₂/HCO₃^-) molecular pair is ubiquitous in mammalian cells and tissues, mainly as a result of oxidative decarboxylation reactions that occur during intermediary metabolism. CO₂ is in rapid equilibrium with HCO₃^-via the hydration reaction catalyzed by carbonic anhydrases. Far from being an inert compound in redox biology, CO₂ enhances or redirects the reactivity of peroxides, modulating the velocity, extent, and type of one- and two-electron oxidation reactions mediated by hydrogen peroxide (H₂O₂) and peroxynitrite (ONOO^-/ONOOH). Herein, we review the biochemical mechanisms by which CO₂ engages in peroxide-dependent reactions, free radical production, redox signaling, and oxidative damage. First, we cover the metabolic formation of CO₂ and its connection to peroxide formation and decomposition. Next, the reaction mechanisms, kinetics, and processes by which the CO₂/peroxide interplay modulates mammalian cell redox biology are scrutinized in-depth. Importantly, CO₂ also regulates gene expression related to redox and nitric oxide metabolism and as such influences oxidative and inflammatory processes. Accumulated biochemical evidence in vitro, in cellula, and in vivo unambiguously show that the CO₂ and peroxide metabolic pathways are intertwined and together participate in key redox events in mammalian cells.

The role of mitochondrial reactive oxygen species in insulin resistance

Insulin resistance is one of the earliest pathological features of a suite of diseases including type 2 diabetes collectively referred to as metabolic syndrome. There is a growing body of evidence from both pre-clinical studies and human cohorts indicating that reactive oxygen species, such as the superoxide radical anion and hydrogen peroxide are key players in the development of insulin resistance. Here we review the evidence linking mitochondrial reactive oxygen species generated within mitochondria with insulin resistance in adipose tissue and skeletal muscle, two major insulin sensitive tissues. We outline the relevant mitochondria-derived reactive species, how the mitochondrial redox state is regulated, and methodologies available to measure mitochondrial reactive oxygen species. Importantly, we highlight key experimental issues to be considered when studying the role of mitochondrial reactive oxygen species in insulin resistance. Evaluating the available literature on both mitochondrial reactive oxygen species/redox state and insulin resistance in a variety of biological systems, we conclude that the weight of evidence suggests a likely role for mitochondrial reactive oxygen species in the etiology of insulin resistance in adipose tissue and skeletal muscle. However, major limitations in the methods used to study reactive oxygen species in insulin resistance as well as the lack of data linking mitochondrial reactive oxygen species and cytosolic insulin signaling pathways are significant obstacles in proving the mechanistic link between these two processes. We provide a framework to guide future studies to provide stronger mechanistic information on the link between mitochondrial reactive oxygen species and insulin resistance as understanding the source, localization, nature, and quantity of mitochondrial reactive oxygen species, their targets and downstream signaling pathways may pave the way for important new therapeutic strategies.

Insights into the Pathogenesis of Neurodegenerative Diseases: Focus on Mitochondrial Dysfunction and Oxidative Stress

As the population ages, the incidence of neurodegenerative diseases is increasing. Due to intensive research, important steps in the elucidation of pathogenetic cascades have been made and significantly implicated mitochondrial dysfunction and oxidative stress. However, the available treatment in Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis is mainly symptomatic, providing minor benefits and, at most, slowing down the progression of the disease. Although in preclinical setting, drugs targeting mitochondrial dysfunction and oxidative stress yielded encouraging results, clinical trials failed or had inconclusive results. It is likely that by the time of clinical diagnosis, the pathogenetic cascades are full-blown and significant numbers of neurons have already degenerated, making it impossible for mitochondria-targeted or antioxidant molecules to stop or reverse the process. Until further research will provide more efficient molecules, a healthy lifestyle, with plenty of dietary antioxidants and avoidance of exogenous oxidants may postpone the onset of neurodegeneration, while familial cases may benefit from genetic testing and aggressive therapy started in the preclinical stage.

Nitric oxide homeostasis is maintained during acute in vitro hypoxia and following reoxygenation in naked mole-rat but not mouse cortical neurons

Reactive nitrogen species (RNS), including nitric oxide (NO), are important cellular messengers when tightly regulated, but unregulated production of RNS during hypoxia or ischemia and reoxygenation is deleterious to hypoxia-intolerant brain. Therefore, maintaining NO homeostasis during hypoxia/ischemia and reoxygenation may be a hallmark of hypoxia-tolerant brain. Unlike most mammals, naked mole-rats (NMRs; Heterocephalus glaber) are tolerant of repeated bouts of hypoxia in vivo. Although there is some evidence that NMR brain is tolerant of hypoxia/ischemia, little is known about the underlying neuroprotective mechanism(s), and their tolerance to reoxygenation injury has not been examined. We hypothesized that NMR brain would maintain NO homeostasis better than hypoxia-intolerant mouse brain during hypoxic/ischemic stresses and following reoxygenation. To test this, we exposed adult NMR and mouse cortical slices to transitions from normoxia (21% O₂) to hypoxia (< 1% O₂) or ischemia (oxygen glucose deprivation, OGD), followed by reoxygenation, while measuring neuronal NO production. We report that NMR cortical neurons maintain NO homeostasis during hypoxia/OGD and avoid bursts of NO upon reoxygenation. Conversely, mouse cortical neurons maintain NO homeostasis in OGD but not hypoxia and exhibit a burst of NO upon reperfusion. This suggests that maintenance of NO homeostasis during fluctuating O₂ availability may be a contributing neuroprotective mechanism against hypoxia/ischemia and reoxygenation injury in hypoxia-tolerant NMR brain.

One- and Two-Electron Oxidations of β-Amyloid25-35 by Carbonate Radical Anion (CO3•-) and Peroxymonocarbonate (HCO4-): Role of Sulfur in Radical Reactions and Peptide Aggregation

The β-amyloid (Aβ) peptide plays a key role in the pathogenesis of Alzheimer’s disease. The methionine (Met) residue at position 35 in Aβ C-terminal domain is critical for neurotoxicity, aggregation, and free radical formation initiated by the peptide. The role of Met in modulating toxicological properties of Aβ most likely involves an oxidative event at the sulfur atom. We therefore investigated the one- or two-electron oxidation of the Met residue of Aβ_25-35 fragment and the effect of such oxidation on the behavior of the peptide. Bicarbonate promotes two-electron oxidations mediated by hydrogen peroxide after generation of peroxymonocarbonate (HCO₄⁻, PMC). The bicarbonate/carbon dioxide pair stimulates one-electron oxidations mediated by carbonate radical anion (CO₃^•−). PMC efficiently oxidizes thioether sulfur of the Met residue to sulfoxide. Interestingly, such oxidation hampers the tendency of Aβ to aggregate. Conversely, CO₃^•− causes the one-electron oxidation of methionine residue to sulfur radical cation (MetS^•+). The formation of this transient reactive intermediate during Aβ oxidation may play an important role in the process underlying amyloid neurotoxicity and free radical generation.

pH-Dependent Nitrotyrosine Formation in Ribonuclease A is Enhanced in the Presence of Polyethylene Glycol (PEG)

Protein nitration can occur as a result of peroxynitrite-mediated oxidative stress. Excess production of peroxynitrite (PN) within the cellular medium can cause oxidative damage to biomolecules. The in vitro nitration of Ribonuclease A (RNase A) results in nitrotyrosine (NT) formation with a strong dependence on the pH of the medium. In order to mimic the cellular environment in this study, PN-mediated RNase A nitration has been carried out in a crowded medium. The degree of nitration is higher at pH 7.4 (physiological pH) compared to pH 6.0 (tumor cell pH). The extent of nitration increases significantly when PN is added to RNase A in the presence of crowding agents PEG 400 and PEG 6000. PEG has been found to stabilize PN over a prolonged period, thereby increasing the degree of nitration. NT formation in RNase A also results in a significant loss in enzymatic activity.

Metabolic perturbations and cellular stress underpin susceptibility to symptomatic live-attenuated yellow fever infection

Flaviviral infections result in a wide spectrum of clinical outcomes, ranging from asymptomatic infection to severe disease. Although the correlates of severe disease have been explored^1-4, the pathophysiology that differentiates symptomatic from asymptomatic infection remains undefined. To understand the molecular underpinnings of symptomatic infection, the blood transcriptomic and metabolomic profiles of individuals were examined before and after inoculation with the live yellow fever viral vaccine (YF17D). It was found that individuals with adaptive endoplasmic reticulum (ER) stress and reduced tricarboxylic acid cycle activity at baseline showed increased susceptibility to symptomatic outcome. YF17D infection in these individuals induced maladaptive ER stress, triggering downstream proinflammatory responses that correlated with symptomatic outcome. The findings of the present study thus suggest that the ER stress response and immunometabolism underpin symptomatic yellow fever and possibly even other flaviviral infections. Modulating either ER stress or metabolism could be exploited for prophylaxis against symptomatic flaviviral infection outcome.

Peroxynitrite: cellular pathology and implications in autoimmunity

In inflamed tissues, the reaction of nitric oxide and superoxide leads to the formation of an extremely reactive peroxynitrite (ONOO-), which is a well known oxidizing and nitrating agent that exhibits high reactivity at physiological pH. The peroxynitrite formed can attack a wide range of biomolecules via direct oxidative reactions or indirect radical-mediated mechanisms thus triggering cellular responses leading to cell signaling, oxidative injury, committing cells to necrosis or apoptosis. Cellular DNA is an important target for ONOO- attack, and can react with deoxyribose, nucleobases or induces single strand breaks. The free radical-mediated damage to proteins results in the modification of amino acid residues, cross-linking of side chains and fragmentation. Free/protein-bound tyrosines are attacked by various reactive nitrogen species (RNS), including peroxynitrite, to form free/protein-bound nitrotyrosine (NT). The formation of NT represents a specific peroxynitrite-mediated protein modification, and the detection of NT in proteins is considered as a biomarker for endogenous peroxynitrite activity. The peroxynitrite-driven oxidation and nitration of biomolecules may lead to autoimmunity and age-related neurodegenerative diseases. Hence, peroxynitrite modified DNA and nitrated proteins can act as neoantigens and lead to the generation of autoantibodies against self-components in autoimmune disorders.

ROS and RNS signalling: adaptive redox switches through oxidative/nitrosative protein modifications

Over the last decade, a dual character of cell response to oxidative stress, eustress versus distress, has become increasingly recognized. A growing body of evidence indicates that under physiological conditions, low concentrations of reactive oxygen and nitrogen species (RONS) maintained by the activity of endogenous antioxidant system (AOS) allow reversible oxidative/nitrosative modifications of key redox-sensitive residues in regulatory proteins. The reversibility of redox modifications such as Cys S-sulphenylation/S-glutathionylation/S-nitrosylation/S-persulphidation and disulphide bond formation, or Tyr nitration, which occur through electrophilic attack of RONS to nucleophilic groups in amino acid residues provides redox switches in the activities of signalling proteins. Key requirement for the involvement of the redox modifications in RONS signalling including ROS-MAPK, ROS-PI3K/Akt, and RNS-TNF-α/NF-kB signalling is their specificity provided by a residue microenvironment and reaction kinetics. Glutathione, glutathione peroxidases, peroxiredoxins, thioredoxin, glutathione reductases, and glutaredoxins modulate RONS level and cell signalling, while some of the modulators (glutathione, glutathione peroxidases and peroxiredoxins) are themselves targets for redox modifications. Additionally, gene expression, activities of transcription factors, and epigenetic pathways are also under redox regulation. The present review focuses on RONS sources (NADPH-oxidases, mitochondrial electron-transportation chain (ETC), nitric oxide synthase (NOS), etc.), and their cross-talks, which influence reversible redox modifications of proteins as physiological phenomenon attained by living cells during the evolution to control cell signalling in the oxygen-enriched environment. We discussed recent advances in investigation of mechanisms of protein redox modifications and adaptive redox switches such as MAPK/PI3K/PTEN, Nrf2/Keap1, and NF-κB/IκB, powerful regulators of numerous physiological processes, also implicated in various diseases.

Fundamentals on the biochemistry of peroxynitrite and protein tyrosine nitration

In this review we provide an analysis of the biochemistry of peroxynitrite and tyrosine nitration. Peroxynitrite is the product of the diffusion-controlled reaction between superoxide (O2•-) and nitric oxide (•NO). This process is in competition with the enzymatic dismutation of O2•- and the diffusion of •NO across cells and tissues and its reaction with molecular targets (e.g. guanylate cyclase). Understanding the kinetics and compartmentalization of the O2•- / •NO interplay is critical to rationalize the shift of •NO from a physiological mediator to a cytotoxic intermediate. Once formed, peroxynitrite (ONOO- and ONOOH; pKa = 6,8) behaves as a strong one and two-electron oxidant towards a series of biomolecules including transition metal centers and thiols. In addition, peroxynitrite anion can secondarily evolve to secondary radicals either via its fast reaction with CO2 or through proton-catalyzed homolysis. Thus, peroxynitrite can participate in direct (bimolecular) and indirect (through secondary radical intermediates) oxidation reactions; through these processes peroxynitrite can participate as cytotoxic effector molecule against invading pathogens and/or as an endogenous pathogenic mediator. Peroxynitrite can cause protein tyrosine nitration in vitro and in vivo. Indeed, tyrosine nitration is a hallmark of the reactions of •NO-derived oxidants in cells and tissues and serves as a biomarker of oxidative damage. Protein tyrosine nitration can mediate changes in protein structure and function that affect cell homeostasis. Tyrosine nitration in biological systems is a free radical process that can be promoted either by peroxynitrite-derived radicals or by other related •NO-dependent oxidative processes. Recently, mechanisms responsible of tyrosine nitration in hydrophobic biostructures such as membranes and lipoproteins have been assessed and involve the parallel occurrence and connection with lipid peroxidation. Experimental strategies to reveal the proximal oxidizing mechanism during tyrosine nitration in given pathophysiologically-relevant conditions include mapping and identification of the tyrosine nitration sites in specific proteins.

Methionine Ameliorates Polymyxin-Induced Nephrotoxicity by Attenuating Cellular Oxidative Stress

Polymyxins are a last line of defense against multidrug-resistant Gram-negative pathogens. Recent pharmacological data show that intravenous polymyxins can cause nephrotoxicity in up to 60% of patients, and the plasma concentrations of polymyxins achieved with the currently recommended dosage regimens are suboptimal in a large proportion of patients. Simply increasing the daily dose of polymyxins is not possible due to nephrotoxicity. This study aimed to examine the protective effect of methionine against polymyxin-induced nephrotoxicity. Methionine (400 mg/kg of body weight), polymyxin B (35 mg/kg), a combination of methionine (100 or 400 mg/kg) and polymyxin B, and saline were administered to mice twice daily over 3.5 days. Kidneys were collected immediately at the end of the experiment for histological examination. The effect of methionine on the pharmacokinetics of polymyxin B was investigated in rats. The attenuation of polymyxin B (0.75 mM)-induced mitochondrial superoxide production by methionine (10.0 mM) was examined in rat kidney (NRK-52E) cells. Histological results revealed that the polymyxin-induced nephrotoxicity in mice was ameliorated by methionine in a dose-dependent manner. The methionine doses were well tolerated in the mice and rats, and the pharmacokinetics of polymyxin B in rats were not affected by methionine. In the group receiving polymyxin B-methionine, the total body clearance of polymyxin B was very similar to that in the group receiving polymyxin B alone (3.71 ± 0.57 versus 3.12 ± 1.66 ml/min/kg, P > 0.05). A substantial attenuation of polymyxin-induced mitochondrial superoxide production in NRK-52E cells was observed following pretreatment with methionine. Our results demonstrate that coadministration of methionine significantly ameliorated polymyxin-induced nephrotoxicity and decreased mitochondrial superoxide production in renal tubular cells.

Preclinical and Clinical Studies on Antioxidative, Antihypertensive and Cardioprotective Effect of Marine Proteins and Peptides-A Review

High seafood consumption has traditionally been linked to a reduced risk of cardiovascular diseases, mainly due to the lipid lowering effects of the long chained omega 3 fatty acids. However, fish and seafood are also excellent sources of good quality proteins and emerging documentation show that, upon digestion, these proteins are sources for bioactive peptides with documented favorable physiological effects such as antioxidative, antihypertensive and other cardioprotective effects. This documentation is mainly from in vitro studies, but also animal studies are arising. Evidence from human studies evaluating the positive health effects of marine proteins and peptides are scarce. In one study, a reduction in oxidative stress after intake of cod has been documented and a few human clinical trials have been performed evaluating the effect on blood pressure. The results are, however, inconclusive. The majority of the human clinical trials performed to investigate positive health effects of marine protein and lean fish intake, has focused on blood lipids. While some studies have documented a reduction in triglycerides after intake of lean fish, others have documented no effects.

Biological signaling by small inorganic molecules

Small redox active molecules such as reactive nitrogen and oxygen species and hydrogen sulfide have emerged as important biological mediators that are involved in various physiological and pathophysiological processes. Advancement in understanding of cellular mechanisms that tightly regulate both generation and reactivity of these molecules is central to improved management of various disease states including cancer and cardiovascular dysfunction. Imbalance in the production of redox active molecules can lead to damage of critical cellular components such as cell membranes, proteins and DNA and thus may trigger the onset of disease. These small inorganic molecules react independently as well as in a concerted manner to mediate physiological responses. This review provides a general overview of the redox biology of these key molecules, their diverse chemistry relevant to physiological processes and their interrelated nature in cellular signaling.

Effect of nitrosative stress on extracellular nucleotide metabolism in endothelial cells

Mechanisms of free radical injury involve chemical modification of proteins, lipid derivatives and nucleic acids and consequent loss of its function. However, specific targets and exact sequence of events has not been fully clarified. We determined whether extracellular enzymes that are involved in adenosine formation such as ecto-5'nucleotidase (e5N) and removal such as extracellular form of adenosine deaminase (eADA) could be affected by peroxynitrite. We used intact cell assay system that involves exposure of cultured HMEC-1 cells to substrates followed by HPLC analysis of conversion of substrates into products. We found that e5N and ADA activities decreased by 20-40% after incubation for 20 or 60 minutes with 30 μM peroxynitrite. Decrease of cellular ATP and NAD was also observed. We conclude that besides other cytotoxic effects modification of extracellular enzymes of nucleotide metabolism could be important target for free radical injury.

Free radicals: properties, sources, targets, and their implication in various diseases

Free radicals and other oxidants have gained importance in the field of biology due to their central role in various physiological conditions as well as their implication in a diverse range of diseases. The free radicals, both the reactive oxygen species (ROS) and reactive nitrogen species (RNS), are derived from both endogenous sources (mitochondria, peroxisomes, endoplasmic reticulum, phagocytic cells etc.) and exogenous sources (pollution, alcohol, tobacco smoke, heavy metals, transition metals, industrial solvents, pesticides, certain drugs like halothane, paracetamol, and radiation). Free radicals can adversely affect various important classes of biological molecules such as nucleic acids, lipids, and proteins, thereby altering the normal redox status leading to increased oxidative stress. The free radicals induced oxidative stress has been reported to be involved in several diseased conditions such as diabetes mellitus, neurodegenerative disorders (Parkinson's disease-PD, Alzheimer's disease-AD and Multiple sclerosis-MS), cardiovascular diseases (atherosclerosis and hypertension), respiratory diseases (asthma), cataract development, rheumatoid arthritis and in various cancers (colorectal, prostate, breast, lung, bladder cancers). This review deals with chemistry, formation and sources, and molecular targets of free radicals and it provides a brief overview on the pathogenesis of various diseased conditions caused by ROS/RNS.

Radical scavenging and antioxidant effects of Matricaria chamomilla polyphenolic-polysaccharide conjugates

Matricaria chamomilla L. (MC), a member of the Asteraceae family, is one of the oldest medicinal plants, widely used worldwide for a variety of healing applications. Its recommendations, derived from both traditional and modern medicine, include numerous disorders such as inflammation, ulcers, wounds, gastrointestinal disorders, stomach ache, pharyngitis, rheumatic pain, as well as the other ailments. This work is focused on another aspect of the biological activity of chamomile polyphenolic-polysaccharide conjugates--their antioxidant properties in the protection of blood plasma components against in vitro oxidative stress. Measurements of DPPH and ABTS radical scavenging indicated considerable anti-free radical action of MC. Pre-incubation of blood plasma with MC considerably diminished the extent of ONOO(-)-induced oxidative modifications such as protein carbonyl groups, SH groups, 3-nitrotyrosine, as well as the formation of lipid hydroperoxides. The analysis of the FRAP assay result shows a considerable increase of ferric reducing ability of blood plasma in the presence of MC. The results obtained in this study indicate that polyphenolic-polysaccharide conjugates isolated from M. chamomilla substances possess antioxidant properties. The M. chamomilla macromolecular glycoconjugates may be useful in the creation of new natural-based medications or dietary supplements, helpful in the prevention and treatment of oxidative stress-mediated disorders.

Posttranslational protein modifications by reactive nitrogen and chlorine species and strategies for their prevention and elimination

Proteins are subject to various posttranslational modifications, some of them being undesired from the point of view of metabolic efficiency. Prevention of such modifications is expected to provide new means of therapy of diseases and decelerate the process of aging. In this review, modifications of proteins by reactive nitrogen species and reactive halogen species, is briefly presented and means of prevention of these modifications and their sequelae are discussed, including the denitrase activity and inhibitors of myeloperoxidase.

Dynamics of nitric oxide, altered follicular microenvironment, and oocyte quality in women with endometriosis

OBJECTIVE

To study follicular microenvironment in terms of free radical dynamics, oocyte quality, and assisted reproductive technology (ART) outcomes among women with (group A) and without (group B) endometriosis.

DESIGN

Prospective cohort study.

SETTING

University ART center.

PATIENT(S)

Women with and without endometriosis undergoing ART (n=28).

INTERVENTION(S)

Follicular fluid (FF), granulosa cells (GCs), immature oocytes (IOs), and ART data on sibling cohort oocytes in groups A and B were compared.

MAIN OUTCOME MEASURE(S)

ART live birth outcomes, maturation, and aging among in vitro matured (IVM) oocytes, nitrate levels in FF, and nitrotyrosine (NT) footprints and apoptosis in the GCs.

RESULT(S)

Clinical characteristics and ART live birth outcomes were no different between groups A and B. Women from group A had significantly lower peak serum E2 (2,068.8±244.6 pg/mL vs. 2,756.2±205.0 pg/mL) and higher apoptosis (80.0% vs. 22.2%) and NT staining (70.0% vs. 22.2%) in GCs compared with group B. Fewer IOs underwent IVM to MII (0.6±0.3) in group A compared with group B (1.4±0.2). IVM oocytes had significantly higher incidence of cortical granule loss (83.3% vs. 24.0%) and spindle disruption (66.7% vs. 16.0%) and higher zona pellucida dissolution timing (133.8±9.4 s vs. 90.5±5.8 s) in group A compared with group B. FF nitrate levels were significantly higher in women who failed to conceive in group A (478.2±43.1 nmol/L) compared with those that did conceive (173.3±19.0 nmol/L).

CONCLUSION(S)

Increased protein nitration, GC apoptosis, resistance to IVM, and oocyte aging indicate the involvement of oxidative dysregulation of NO in the pathophysiology of altered follicular milieu and poor oocyte quality in women with endometriosis.

Study of the effects of oral zinc supplementation on peroxynitrite levels, arginase activity and NO synthase activity in seminal plasma of Iraqi asthenospermic patients

BACKGROUND

Low concentrations of nitric oxide (NO) are necessary for the biology and physiology of spermatozoa, but high levels of NO are toxic and have negative effects on sperm functions. Although several studies have considered the relationship between infertility and semen NO concentrations, no study on the effects of asthenospermia treatments such as oral zinc supplementation on concentrations of NO, which are important in fertility, has been reported. Studies have shown that oral zinc supplementation develops sperm count, motility and the physical characteristics of sperm in animals and in some groups of infertile men. The present study was conducted to study the effect of zinc supplementation on the quantitative and qualitative characteristics of semen, along with enzymes of the NO pathway in the seminal plasma of asthenospermic patients.

METHODS

Semen samples were obtained from 60 fertile and 60 asthenozoospermic infertile men of matched age. The subfertile group was treated with zinc sulfate; each participant took two capsules (220 mg per capsule) per day for 3 months. Semen samples were obtained (before and after zinc sulfate supplementation). After liquefaction of the seminal fluid at room temperature, routine semen analyses were performed. The stable metabolites of NO (nitrite) in seminal plasma were measured by nitrophenol assay. Arginase activity and NO synthase activity were measured spectrophotometrically.

RESULTS

Peroxynitrite levels, arginase activity, NO synthase activity and various sperm parameters were compared among fertile controls and infertile patients (before and after treatment with zinc sulfate). Peroxynitrite levels and NO synthase activity were significantly higher in the infertile patients compared to the fertile group. Conversely, arginase activity was significantly higher in the fertile group than the infertile patients. Peroxynitrite levels, arginase activity and NO synthase activity of the infertile patient were restored to normal values after treatment with zinc sulfate. Volume of semen, progressive sperm motility percentage and total normal sperm count were increased after zinc supplementation.

CONCLUSIONS

Treatment of asthenospermic patients with zinc supplementation leads to restored peroxynitrite levels, arginase activity and NO synthase activity to normal values and gives a statistically significant improvement of semen parameters compared with controls.

Three-electron two-centred bonds and the stabilisation of cationic sulfur radicals

Spin stabilisation of conjugated motifs and heteroatoms suggests that the primary mechanism for cationic thioether stabilisation is not three-electron two-centred bonds.

Peroxynitrite, a stealthy biological oxidant

Peroxynitrite is the product of the diffusion-controlled reaction of nitric oxide and superoxide radicals. Peroxynitrite, a reactive short-lived peroxide with a pKa of 6.8, is a good oxidant and nucleophile. It also yields secondary free radical intermediates such as nitrogen dioxide and carbonate radicals. Much of nitric oxide- and superoxide-dependent cytotoxicity resides on peroxynitrite, which affects mitochondrial function and triggers cell death via oxidation and nitration reactions. Peroxynitrite is an endogenous toxicant but is also a cytotoxic effector against invading pathogens. The biological chemistry of peroxynitrite is modulated by endogenous antioxidant mechanisms and neutralized by synthetic compounds with peroxynitrite-scavenging capacity.

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.

Teaching the basics of redox biology to medical and graduate students: Oxidants, antioxidants and disease mechanisms

This article provides a succinct but limited overview of the protective and deleterious effects of reactive oxygen and nitrogen species in a clinical context. Reactive oxygen species include superoxide, hydrogen peroxide, single oxygen and lipid peroxides. Reactive nitrogen species include species derived from nitric oxide. This review gives a brief overview of the reaction chemistry of these species, the role of various enzymes involved in the generation and detoxification of these species in disease mechanisms and drug toxicity and the protective role of dietary antioxidants. I hope that the graphical review will be helpful for teaching both the first year medical and graduate students in the U.S. and abroad the fundamentals of reactive oxygen and nitrogen species in redox biology and clinical medicine.

Reactions of amine and peroxynitrite: evidence for hydroxylation as predominant reaction and new insight into the modulation of CO2

Peroxynitrite is related to numerous diseases including cardiovascular diseases, inflammation, and cancer. In order to expand the understanding for the toxicology of peroxynitrite in biological system, the reactions of amine (morpholine as a probe) with peroxynitrite and the modulation of CO2 were investigated by using DFT methods. The results strongly indicate that the hydroxylation of amine by peroxynitrous acid ONOOH, which was previously overlooked by most studies, is predominant relative to the widely reported nitration and nitrosation in the absence of CO2. The product N-hydroxylamine is proposed to be mainly generated via nonradical pathway (two-electron oxidation). The modulation of CO2 exhibits two main functions: (1) inhibition of hydroxylation due to the promoted consumption of peroxynitrite via fast reaction of CO2 with ONOO¯ to form ONOOCO2¯; (2) dual effect (catalysis and inhibition) of CO2 toward nitration and nitrosation. As a new insight, amine does react with CO2 and produce inert amine carbamate R2NCOO¯. This reaction has the potential to compete with the reaction of CO2 and ONOO¯, which leads to inhibition of nitration and nitrosation. The concentration of CO2 could be a critical factor determining the final effect, catalysis or inhibition. As a new finding, HCO3¯ is probably an effective catalyst for the reaction of amine and CO2. Moreover, further studies on how the different types of the amine might affect the outcome of the reactions would be an interesting topic.

Antioxidant properties of aminoethylcysteine ketimine decarboxylated dimer: a review

Aminoethylcysteine ketimine decarboxylated dimer is a natural sulfur-containing compound detected in human plasma and urine, in mammalian brain and in many common edible vegetables. Over the past decade many studies have been undertaken to identify its metabolic role. Attention has been focused on its antioxidant properties and on its reactivity against oxygen and nitrogen reactive species. These properties have been studied in different model systems starting from plasma lipoproteins to specific cellular lines. All these studies report that aminoethylcysteine ketimine decarboxylated dimer is able to interact both with reactive oxygen and nitrogen species (hydrogen peroxide, superoxide anion, hydroxyl radical, peroxynitrite and its derivatives). Its antioxidant activity is similar to that of Vitamin E while higher than other hydrophilic antioxidants, such as trolox and N-acetylcysteine.

Neuroprotection by minocycline caused by direct and specific scavenging of peroxynitrite

Minocycline prevents oxidative protein modifications and damage in disease models associated with inflammatory glial activation and oxidative stress. Although the drug has been assumed to act by preventing the up-regulation of proinflammatory enzymes, we probed here its direct chemical interaction with reactive oxygen species. The antibiotic did not react with superoxide or (•)NO radicals, but peroxynitrite (PON) was scavenged in the range of ∼1 μm minocycline and below. The interaction of pharmacologically relevant minocycline concentrations with PON was corroborated in several assay systems and significantly exceeded the efficacy of other antibiotics. Minocycline was degraded during the reaction with PON, and the resultant products lacked antioxidant properties. The antioxidant activity of minocycline extended to cellular systems, because it prevented neuronal mitochondrial DNA damage and glutathione depletion. Maintenance of neuronal viability under PON stress was shown to be solely dependent on direct chemical scavenging by minocycline. We chose α-synuclein (ASYN), known from Parkinsonian pathology as a biologically relevant target in chemical and cellular nitration reactions. Submicromolar concentrations of minocycline prevented tyrosine nitration of ASYN by PON. Mass spectrometric analysis revealed that minocycline impeded nitrations more effectively than methionine oxidations and dimerizations of ASYN, which are secondary reactions under PON stress. Thus, PON scavenging at low concentrations is a novel feature of minocycline and may help to explain its pharmacological activity.

Formation, reactivity, and detection of protein sulfenic acids

It has become clear in recent decades that the post-translational modification of protein cysteine residues is a crucial regulatory event in biology. Evidence supports the reversible oxidation of cysteine thiol groups as a mechanism of redox-based signal transduction, while the accumulation of proteins with irreversible thiol oxidations is a hallmark of stress-induced cellular damage. The initial formation of cysteine-sulfenic acid (SOH) derivatives, along with the reactive properties of this functional group, serves as a crossroads whereby the local redox environment may dictate the progression of either regulatory or pathological outcomes. Protein-SOH are established as transient intermediates in the formation of more stable cysteine oxidation products both under basal conditions and in response to several redox-active extrinsic compounds. This review details both direct and multistep chemical routes proposed to generate protein-SOH, the spectrum of secondary reactions that may follow their initial formation and the arsenal of experimental tools available for their detection. Pioneering studies that have provided a framework for our current understanding of protein-SOH as well as state-of-the-art proteomic strategies designed for global assessments of this post-translational modification are highlighted.

Sulfate radical anion as a new reagent for fast photochemical oxidation of proteins

The focus is to expand the original design of fast photochemical oxidation of proteins (FPOP) and introduce SO(4)(-•), generated by 248 nm homolysis of low millimolar levels of persulfate, as a radical reactant in protein footprinting. FPOP is a chemical approach to footprinting proteins and protein complexes by "snapshot" reaction with free radicals. The radical used until now is the OH radical, and it provides a measure of residue-resolved solvent accessibility of the native protein. We show that FPOP can accommodate other reagents, increasing its versatility. The new persulfate FPOP system is a potent, nonspecific, and tunable footprinting method; 3-5 times less persulfate is needed to give the same global levels of modification as seen with OH radicals. Although solvent-exposed His and Tyr residues are more reactive with SO(4)(-•) than with (•)OH, oxidation of apomyoglobin and calmodulin shows that (•)OH probes smaller accessible areas than SO(4)(-•), with the possible exception of histidine. His64, an axial ligand in the heme-binding pocket of apomyoglobin, is substantially up-labeled by SO(4)(-•) relative to (•)OH. Nevertheless, the kinds of modification and residue selectivity for both reagent radicals are strikingly similar. Thus, the choice of these reagents relies on the physical properties, particularly the membrane permeability, of the radical precursors.

Radicals in the reaction between peroxynitrite and uric acid identified by electron spin resonance spectroscopy and liquid chromatography mass spectrometry

Peroxynitrite is a reactive oxidant produced in vivo in response to oxidative and other stress by the diffusion-limited reaction of nitric oxide and superoxide. This article is focused on the identification of free radical intermediates of uric acid formed during its reaction with peroxynitrite. The experimental approach included the ESR spin trapping of the radical generated from the reaction between uric acid and peroxynitrite at pH 7.4 and mass spectrometry studies of the trapped radicals. Using PBN (N-tert-butyl-alpha-phenylnitrone) as the spin trapping agent, a six-line ESR spectrum was obtained and its hyperfine coupling constants, a(N)=15.6 G and a(H)=4.4 G, revealed the presence of carbon-based radicals. Further structural identification of the PBN-radical adducts was carried out using liquid chromatography-mass spectrometry. After comparison with the control reactions, two species were identified that correspond to the protonated molecules (M+1) at m/z 352 and 223, respectively. The ions of m/z 352 were characterized as the PBN-triuretcarbonyl radical adduct and the m/z 223 ion was identified as the PBN-aminocarbonyl radical adduct. Their mechanism of formation is discussed.

A top-down LC-FTICR MS-based strategy for characterizing oxidized calmodulin in activated macrophages

A liquid chromatography-mass spectrometry (LC-MS)-based approach for characterizing the degree of nitration and oxidation of intact calmodulin (CaM) has been used to resolve approximately 250 CaM oxiforms using only 500 ng of protein. The analysis was based on high-resolution data of the intact CaM isoforms obtained by Fourier-transform ion cyclotron resonance mass spectrometry (FTICR MS) coupled with an on-line reversed-phase LC separation. Tentative identifications of post-translational modifications (PTMs), such as oxidation or nitration, have been assigned by matching observed protein mass to a database containing all theoretically predicted oxidation products of CaM and verified through a combination of tryptic peptide information (generated from bottom-up analyses) and on-line collisionally induced dissociation (CID) tandem mass spectrometry (MS/MS) at the intact protein level. The reduction in abundance and diversity of oxidatively modified CaM (i.e., nitrated tyrosines and oxidized methionines) induced by macrophage activation has been explored and semiquantified for different oxidation degrees (i.e., no oxidation, moderate, and high oxidation). This work demonstrates the power of the top-down approach to identify and quantify hundreds of combinations of PTMs for single protein target such as CaM and implicate competing repair and peptidase activities to modulate cellular metabolism in response to oxidative stress.

Mechanisms of peroxynitrite-mediated nitration of tyrosine

The mechanisms of tyrosine nitration by peroxynitrous acid or nitrosoperoxycarbonate were investigated with the CBS-QB3 method. Either the protonation of peroxynitrite or a reaction with carbon dioxide gives a reactive peroxide intermediate. Peroxynitrous acid-mediated nitration of phenol occurs via unimolecular decomposition to give nitrogen dioxide and hydroxyl radicals. Nitrosoperoxycarbonate also undergoes unimolecular decomposition to give carbonate and nitrogen dioxide radicals. The reactions of tyrosine with the hydroxyl or carbonate radicals give a phenoxy radical intermediate. The reaction of the nitrogen dioxide with this radical intermediate followed by tautomerization gives nitrated tyrosine in both cases. According to CBS-QB3 calculations, the rate-limiting step for the nitration of phenol is the decomposition of peroxynitrous acid or nitrosoperoxycarbonate.

Peroxynitrite mild nitration of albumin and LDL–albumin complex naturally present in plasma and tyrosine nitration rate–albumin impairs LDL nitration

In blood, peroxynitrite (ONOO- ) and CO2 react to form NO2* and CO3* through the short-lived adduct ONOOCO2-, leading to protein-bound tyrosine nitration. ONOO(-) -modified LDL is atherogenic. Oxidatively modified LDL generally appears in the vessel wall surrounded by antioxidants. Human serum albumin (HSA) is one of them, partly associated to LDL as a LDL-albumin complex (LAC). The purpose was to study the effect of a mild nitration on LAC and whether albumin may interfere with LDL nitration. To do so, SIN-1 was used as ONOO- generator in the presence or absence of 25 mM HCO3-. The human serum albumin (HSA)-bound tyrosine nitration rate was found to be 4.4 x 10(-3) mol/mol in the presence of HCO3-. HSA decreased the LAC-tyrosine nitration rate from 2.5 x 10(-3) to 0.6 x 10(-3) mol/mol. It was concluded that HSA impaired the apoB-bound tyrosine nitration. These findings raise the question of the patho-physiological significance of these nitrations and their interactions which may potentially prevent both atheromatous plaque formation and endothelium dysfunction in particular and appear to be beneficial in terms of atherogenic risk.