S-nitrosylation and S-glutathiolation of protein sulfhydryls by S-nitroso glutathione

PhICl2-Mediated Regioselective and Electrophilic Oxythio/Selenocyanation of o-(1-Alkynyl)benzoates: Access to Biologically Active S/SeCN-Containing Isocoumarins

The application of PhICl₂/NH₄SCN and PhICl₂/KSeCN reagent systems to the synthesis of the biologically active S/SeCN-containing isocoumarins via a process involving thio/selenocyanation, enabled by thio/selenocyanogen chloride generated in situ, followed with an intramolecular lactonization was realized. Gram-scale synthesis, further derivatization to access C4 thio/selenocyanated Xyridin A and anti-tumor activities of the obtained products highlight the potential use of this method.

Photosensitized co-generation of nitric oxide and singlet oxygen Enhanced toxicity against ovarian cancer cells

Near micromolar concentrations of nitric oxide (NO) induce tumor cells death. However, an appropriate NO load has to be delivered selectively to the tumor site in order to avoid NO loss and secondary NO-induced effects. The encapsulation of millimolar concentrations of a NO source and an appropriate trigger of NO release within phospatidylcholine-based liposomes should provide an efficient tool for the selective release of the needed NO payload. In this work we report the photosensitized generation of singlet oxygen and NO from folate-targeted PEGylated liposomes, containing AlPcS4 as the sensitizer and S-nitrosoglutathione (GSNO), in millimolar amounts, as the NO source. Amounts of singlet oxygen detected outside the liposome when using PEGylated liposomes are near 200 % larger when GSNO is present inside the liposomes as compared to its absence. These liposomes, conjugated to folate, were found to enhance the photosensitized cytotoxicity to A2780CP20 ovarian cancer cells as compared to liposomes containing the sensitizer but no GSNO (30 % as compared to 70 % cell viability) under the conditions of this work. Fluorescense of AlPcS4 was observed inside cells incubated with folate-conjugated liposomes but not with liposomes without folate. The photosensitized activity enhancement by GSNO increased when light fluence or liposome concentration were increased. The majority of ovarian cancer patients are initially diagnosed with disseminated intra-abdominal disease (stages III-IV) and have a 5-year survival of less than 20%. This work suggests a novel ovarian cancer nodules treatment via the use of tumor-targeted liposome nanoparticles with the capability of generating simultaneously reactive oxygen and nitrogen species upon illumination with near-infrared light.

Carbonic Anhydrases in Metazoan Model Organisms: Molecules, Mechanisms, and Physiology

During the past three decades, mice, zebrafish, fruit flies, and Caenorhabditis elegans have been the primary model organisms used for the study of various biological phenomena. These models have also been adopted and developed to investigate the physiological roles of carbonic anhydrases (CAs) and carbonic anhydrase-related proteins (CARPs). These proteins belong to eight CA families and are identified by Greek letters: α, β, γ, δ, ζ, η, θ, and ι. Studies using model organisms have focused on two CA families, α-CAs and β-CAs, which are expressed in both prokaryotic and eukaryotic organisms with species-specific distribution patterns and unique functions. This review covers the biological roles of CAs and CARPs in light of investigations performed in model organisms. Functional studies demonstrate that CAs are not only linked to the regulation of pH homeostasis, the classical role of CAs but also contribute to a plethora of previously undescribed functions.

Sirtuin Oxidative Post-translational Modifications

Increased sirtuin deacylase activity is correlated with increased lifespan and healthspan in eukaryotes. Conversely, decreased sirtuin deacylase activity is correlated with increased susceptibility to aging-related diseases. However, the mechanisms leading to decreased sirtuin activity during aging are poorly understood. Recent work has shown that oxidative post-translational modification by reactive oxygen (ROS) or nitrogen (RNS) species results in inhibition of sirtuin deacylase activity through cysteine nitrosation, glutathionylation, sulfenylation, and sulfhydration as well as tyrosine nitration. The prevalence of ROS/RNS (e.g., nitric oxide, S-nitrosoglutathione, hydrogen peroxide, oxidized glutathione, and peroxynitrite) is increased during inflammation and as a result of electron transport chain dysfunction. With age, cellular production of ROS/RNS increases; thus, cellular oxidants may serve as a causal link between loss of sirtuin activity and aging-related disease development. Therefore, the prevention of inhibitory oxidative modification may represent a novel means to increase sirtuin activity during aging. In this review, we explore the role of cellular oxidants in inhibiting individual sirtuin human isoform deacylase activity and clarify the relevance of ROS/RNS as regulatory molecules of sirtuin deacylase activity in the context of health and disease.

Inhibition of nitric oxide production enhances the activity of facial nerve tubulin polymerization and the ability of tau to promote microtubule assembly after neurorrhaphy

We previously reported that inhibition of nitric oxide (NO) production promotes rat reconnected facial nerve regeneration. However, the underlying mechanism is obscure. Microtubule assembly is known to be essential to axon regeneration; nevertheless, tubulins and microtubule-associated proteins (MAPs) have been demonstrated as targets for NO and peroxynitrite. Thus, we hypothesized that NO and/or peroxynitrite may affect facial nerve regeneration via influencing on microtubule assembly. First, tubulins and tau (a MAP) were extracted from facial nerves of normal rats, treated with NO donor or peroxynitrite, and processed for microtubule assembly assay. We found that peroxynitrite, DEA NONOate, and Angeli's salt reduced the tubulin polymerization activity to a greater extent than GSNO, SIN-1, and SNAP. Additionally, SIN-1, peroxynitrite, and Angeli's salt impaired the ability of tau to promote microtubule assembly. Next, nitrosative stress biomarkers 3-nitrotyrosine (3-NT) and S-nitrosylated cysteine (SNO-Cys) were immunolabeled in facial nerves. Both biomarkers were highly upregulated in proximal and distal stumps of reconnected facial nerves at 3 days and 1 week after neurorrhaphy. Notably, the expression of 3-NT was greatly reduced at 2 weeks, whereas that of SNO-Cys was maintained. Conversely, inhibition of NO production with L-NAME prevented the upregulation of SNO-Cys. Further, we used tubulins and tau extracted from facial nerves of sham-operated, nerve suture + vehicle treatment, and nerve suture + L-NAME treatment rats to perform microtubule assembly assay. We found that L-NAME treatment enhanced polymerization activity of tubulins and ability of tau to promote microtubule assembly. It is noteworthy that α-tubulin plays a more important role than β-tubulin since the activity of microtubule assembly using α-tubulin extracted from L-NAME-treated rats was greatly elevated, whereas that using β-tubulin extracted from L-NAME-treated rats was not. Overall, our findings support that inhibition of NO production reduces nitrosative stress, and may thus facilitate microtubule assembly and facial nerve regeneration.

Oxidative stress in oocyte aging and female reproduction

In a healthy body, reactive oxygen species (ROS) and antioxidants remain balanced. When the balance is broken toward an overabundance of ROS, oxidative stress appears and may lead to oocyte aging. Oocyte aging is mainly reflected as the gradual decrease of oocyte quantity and quality. Here, we aim to review the relationship between oxidative stress and oocyte aging. First, we introduced that the defective mitochondria, the age-related ovarian aging, the repeated ovulation, and the high-oxygen environment were the ovarian sources of ROS in vivo and in vitro. And we also introduced other sources of ROS accumulation in ovaries, such as overweight and unhealthy lifestyles. Then, we figured that oxidative stress may act as the "initiator" for oocyte aging and reproductive pathology, which specifically causes follicular abnormally atresia, abnormal meiosis, lower fertilization rate, delayed embryonic development, and reproductive disease, including polycystic ovary syndrome and ovary endometriosis cyst. Finally, we discussed current strategies for delaying oocyte aging. We introduced three autophagy antioxidant pathways like Beclin-VPS34-Atg14, adenosine 5'-monophosphate (AMP)-activated protein kinase/mammalian target of rapamycin (AMPK/mTOR), and p62-Keap1-Nrf2. And we also describe the different antioxidants used to combat oocyte aging. In addition, the hypoxic (5% O₂ ) culture environment for oocytes avoiding oxidative stress in vitro. So, this review not only contribute to our general understanding of oxidative stress and oocyte aging but also lay the foundations for the therapies to treat premature ovarian failure and oocyte aging in women.

Role of protein S-Glutathionylation in cancer progression and development of resistance to anti-cancer drugs

The survival, functioning and proliferation of mammalian cells are highly dependent on the cellular response and adaptation to changes in their redox environment. Cancer cells often live in an altered redox environment due to aberrant neo-vasculature, metabolic reprogramming and dysregulated proliferation. Thus, redox adaptations are critical for their survival. Glutathione plays an essential role in maintaining redox homeostasis inside the cells by binding to redox-sensitive cysteine residues in proteins by a process called S-glutathionylation. S-Glutathionylation not only protects the labile cysteine residues from oxidation, but also serves as a sensor of redox status, and acts as a signal for stimulation of downstream processes and adaptive responses to ensure redox equilibrium. The present review aims to provide an updated overview of the role of the unique redox adaptations during carcinogenesis and cancer progression, focusing on their dependence on S-glutathionylation of specific redox-sensitive proteins involved in a wide range of processes including signalling, transcription, structural maintenance, mitochondrial functions, apoptosis and protein recycling. We also provide insights into the role of S-glutathionylation in the development of resistance to chemotherapy. Finally, we provide a strong rationale for the development of redox targeting drugs for treatment of refractory/resistant cancers.

Human carbonic anhydrases and post-translational modifications: a hidden world possibly affecting protein properties and functions

Human carbonic anhydrases (CAs) have become a well-recognized target for the design of inhibitors and activators with biomedical applications. Accordingly, an enormous amount of literature is available on their biochemical, functional and structural aspects. Nevertheless post-translational modifications (PTMs) occurring on these enzymes and their functional implications have been poorly investigated so far. To fill this gap, in this review we have analysed all PTMs occurring on human CAs, as deriving from the search in dedicated databases, showing a widespread occurrence of modification events in this enzyme family. By combining these data with sequence alignments, inspection of 3 D structures and available literature, we have summarised the possible functional implications of these PTMs. Although in some cases a clear correlation between a specific PTM and the CA function has been highlighted, many modification events still deserve further dedicated studies.

Involvement of nitric oxide during in vitro oocyte maturation, sperm capacitation and in vitro fertilization in pig

The importance of porcine species for meat production is undeniable. Due to the genetic, anatomical, and physiological similarities with humans, from a biomedical point of view, pig is considered an ideal animal model for the study and development of new therapies for human diseases. The in vitro production (IVP) of porcine embryos has become widespread as a result of these qualities and there is significant demand for these embryos for research purposes. However, the efficiency of porcine embryo IVP remains very low, which hinders its use as a model for research. The high degree of polyspermic fertilization is the main problem that affects in vitro fertilization (IVF) in porcine species. Furthermore, oocyte in vitro maturation (IVM) is another important step that could be related to polyspermic fertilization and low embryo production. The presence of nitric oxide synthase (NOS), the enzyme that produces nitric oxide (NO), has been detected in the oviduct, the ovary, the oocyte and the sperm cell of porcine species. Its functions include regulating oviductal activity, ovulation, acquisition of meiotic competence, oocyte activation, sperm capacitation, and gamete interaction. Therefore, in this review, we summarize the current knowledge on the role of NO/NOS system in each of the steps that lead to the production of porcine embryos in an in vitro environment, i.e. IVM, sperm capacitation, IVF, and embryo culture. We also discuss the possible ways in which the NO/NOS system could be used to enhance IVP of porcine embryos.

Development of dual-tool nanosensor for cysteine based on N-(1-naphthyl)ethylenediamine cation functionalized silver nanoparticles

In an accomplishment of development of silver nanoparticles (AgNPs) based nanosensor for cysteine in its anionic and neutral forms, we have preferred N-(1-naphthyl)ethylenediamine cation (NEDA⁺) stabilized AgNPs (NEDA-AgNPs), because NEDA⁺ is a fluorescent active ion and it imparts excellent stability to AgNPs. Surface Plasmon resonance (SPR) of AgNPs and fluorescence property of NEDA⁺ are thus useful for presenting NEDA-AgNPs as a dual-tool nanosensor for cysteine molecules. The surface adsorbed NEDA⁺ cations interact selectively with cysteine as a consequence, the particles get aggregated, which was monitored using spectrophotometric method. The fluorescence property of NEDA⁺ is heavily quenched in NEDA-AgNPs, which could be reversed in presence of cysteine. The spectrofluorimetric method was thus used for quantification of cysteine as well. The detection limits (LOD to LOL) of anionic cysteine are 0.1784-1.598 μM and 0.0842-2.0 μM, respectively in spectrophotometric and spectrofluorimetric methods. From a real sample matrix, the recovery results are excellent, >95%. For neutral cysteine, the sensitivity is a bit low; 0.308-2.8 μM for spectrophotometric and 0.131-2.8 μM for spectrofluorimetric methods. It is found that the anionic cysteine (K_asso = 2.24 × 10⁵ M^-1/4.02 × 10⁵ M^-1) binds surface adsorbed NEDA⁺ cations strongly than that of neutral cysteine (K_asso = 3.69 × 10⁴ M^-1/1.24 × 10⁵ M^-1). Thus, NEDA-AgNPs show its potentials for being a dual-tool nanosensor as well as dual-form nanosensor for quantification of cysteine in a sample which may be the attractive system to an analyst.

Evolution of the Knowledge of Free Radicals and Other Oxidants

Free radicals are chemical species (atoms, molecules, or ions) containing one or more unpaired electrons in their external orbitals and generally display a remarkable reactivity. The evidence of their existence was obtained only at the beginning of the 20th century. Chemists gradually ascertained the involvement of free radicals in organic reactions and, in the middle of the 20th century, their production in biological systems. For several decades, free radicals were thought to cause exclusively damaging effects . This idea was mainly supported by the finding that oxygen free radicals readily react with all biological macromolecules inducing their oxidative modification and loss of function. Moreover, evidence was obtained that when, in the living organism, free radicals are not neutralized by systems of biochemical defences, many pathological conditions develop. However, after some time, it became clear that the living systems not only had adapted to the coexistence with free radicals but also developed methods to turn these toxic substances to their advantage by using them in critical physiological processes. Therefore, free radicals play a dual role in living systems: they are toxic by-products of aerobic metabolism, causing oxidative damage and tissue dysfunction, and serve as molecular signals activating beneficial stress responses. This discovery also changed the way we consider antioxidants. Their use is usually regarded as helpful to counteract the damaging effects of free radicals but sometimes is harmful as it can block adaptive responses induced by low levels of radicals.

ROLE OF THIOLS IN OXIDATIVE STRESS

A well-regulated redox state is essential for normal physiological function and cellular metabolism. In most eukaryotic cells, protein cysteine thiols are most sensitive to fluctuations in the cellular redox state. Under normal physiological conditions, the cytosol has a highly reducing environment, which is due to high levels of reduced glutathione and complex system of redox enzymes that maintain glutathione in the reduced state. The reducing environment of the cytosol maintains most protein thiols in the reduced state; although some non-exposed cysteine could be present as disulfides. Upon physiological increase in cellular oxidants, such as due to growth factors, cytokines and thiol-disulfide exchange reactions, specific proteins could act as redox switches that regulate the conformation and activity of different proteins. This reversible post translational modification enables redox-sensitive dynamic changes in cell signaling and function. Physiological oxidative stress could lead to the formation of sulfenic acids, which are usually intermediate states of thiol oxidation that are converted to higher order oxidation states, intramolecular disulfides or mixed disulfides with glutathione. Such glutathiolation reactions have been found to regulate the function of several proteins involved in intracellular metabolism, signal transduction and cell structure. Excessive oxidative stress results in indiscriminate and irreversible oxidation of protein thiols, depletion of glutathione and cell death. Further elucidation of the relationship between changes in cell redox and thiol reactivity could provide a better understanding of how redox changes regulate cell function and how disruption of these relationships lead to tissue injury and dysfunction and the development of chronic diseases such as cancer and cardiovascular disease.

Competing trends of ROS and RNS-mediated protein modifications during hypoxia as an alternate mechanism of NO benefits

Hypoxia, especially altitude associated hypoxia is known to cause severe physiological alterations and life-threatening conditions. Impaired redox balance along with oxidative stress, protein carbonylation and instigation of apoptotic events are common sub-cellular events that follow the hypoxic insult. The role of nitric oxide (NO) is very dynamic and versatile in preventing the ill effects of hypoxia vis-a-vis reacting with oxidative species and causing protein nitrosylation. Although several mechanisms of NO-mediated cytoprotection are known during hypoxic insult, limited pieces of evidence are available to support the relationship between two downstream events of oxidative stress, protein carbonylation (caused by carbonyl; CO radical) and protein nitrosylation/nitration (caused by NO/peroxynitrite; ONOO radical). In this study, we investigated an entirely new aspect of NO protection in hypoxia involving crosstalk between carbonylation and nitrosylation. Using standard NO inhibitor l-NAME and simulated hypoxic conditions in hypoxia-sensitive cell line H9c2, we evaluated the levels of radicals, cell death, mitochondrial membrane potential, levels of protein nitrosylation, protein nitration and carbonylation and glutathione content. The results were then carefully analyzed in light of NO bioavailability. Our study shows that reducing NO during hypoxia caused cell death via the increased degree of carbonylation in proteins. This provides a new aspect of NO benefits which furthers opens new possibilities to explore potential mechanisms and effects of cross-talk between nitrosylation, protein nitration and carbonylation, especially through some common antioxidant mediators such as glutathione and thioredoxin.

Regulation of protein function by S-nitrosation and S-glutathionylation: processes and targets in cardiovascular pathophysiology

Decades of chemical, biochemical and pathophysiological research have established the relevance of post-translational protein modifications induced by processes related to oxidative stress, with critical reflections on cellular signal transduction pathways. A great deal of the so-called ‘redox regulation’ of cell function is in fact mediated through reactions promoted by reactive oxygen and nitrogen species on more or less specific aminoacid residues in proteins, at various levels within the cell machinery. Modifications involving cysteine residues have received most attention, due to the critical roles they play in determining the structure/function correlates in proteins. The peculiar reactivity of these residues results in two major classes of modifications, with incorporation of NO moieties (S-nitrosation, leading to formation of proteinS-nitrosothiols) or binding of low molecular weight thiols (S-thionylation, i.e. in particularS-glutathionylation,S-cysteinylglycinylation andS-cysteinylation). A wide array of proteins have been thus analyzed in detail as far as their susceptibility to either modification or both, and the resulting functional changes have been described in a number of experimental settings. The present review aims to provide an update of available knowledge in the field, with a special focus on the respective (sometimes competing and antagonistic) roles played by proteinS-nitrosations andS-thionylations in biochemical and cellular processes specifically pertaining to pathogenesis of cardiovascular diseases.

Evidence towards the involvement of nitric oxide in drought tolerance of sugarcane

Exogenous supply of nitric oxide (NO) increases drought tolerance in sugarcane plants. However, little is known about the role of NO produced by plants under water deficit. The aim of this study was to test the hypothesis that drought-tolerance in sugarcane is associated with NO production and metabolism, with the more drought-tolerant genotype presenting higher NO accumulation in plant tissues. The sugarcane genotypes IACSP95-5000 (drought-tolerant) and IACSP97-7065 (drought-sensitive) were submitted to water deficit by adding polyethylene glycol (PEG-8000) in nutrient solution to reduce the osmotic potential to -0.4 MPa. To evaluate short-time responses to water deficit, leaf and root samples were taken after 24 h under water deficit. The drought-tolerant genotype presented higher root extracellular NO content, which was accompanied by higher root nitrate reductase (NR) activity as compared to the drought-sensitive genotype under water deficit. In addition, the drought-tolerant genotype had higher leaf intracellular NO content than the drought-sensitive one. IACSP95-5000 exhibited decreases in root S-nitrosoglutathione reductase (GSNOR) activity under water deficit, suggesting that S-nitrosoglutathione (GSNO) is less degraded and that the drought-tolerant genotype has a higher natural reservoir of NO than the drought-sensitive one. Those differences in intracellular and extracellular NO contents and enzymatic activities were associated with higher leaf hydration in the drought-tolerant genotype as compared to the sensitive one under water deficit.

Post-translational modifications of Medicago truncatula glutathione peroxidase 1 induced by nitric oxide

Plant glutathione peroxidases (Gpx) catalyse the reduction of various peroxides, such as hydrogen peroxide (H₂O₂), phospholipid hydroperoxides and peroxynitrite, but at the expense of thioredoxins rather than glutathione. A main function of plant Gpxs is the protection of biological membranes by scavenging phospholipid hydroperoxides, but some Gpxs have also been associated with H₂O₂ sensing and redox signal transduction. Nitric oxide (NO) is not only known to induce the expression of Gpx family members, but also to inhibit Gpx activity, presumably through the S-nitrosylation of conserved cysteine residues. In the present study, the effects of NO-donors on both the activity and S-nitrosylation state of purified Medicago truncatula Gpx1 were analyzed using biochemical assay measurements and a biotin-switch/mass spectrometry approach. MtGpx1 activity was only moderately inhibited by the NO-donors diethylamine-NONOate and S-nitrosoglutathione, and the inhibition may be reversed by DTT. The three conserved Cys of MtGpx1 were found to be modified through S-nitrosylation and S-glutathionylation, although to different extents, by diethylamine-NONOate and S-nitrosoglutathione, or by a combination of diethylamine-NONOate and reduced glutathione. The regulation of MtGpx1 and its possible involvement in the signaling process is discussed in the light of these results.

Change in the structure and function of lectin by photodissociation of NO

We have shown here that the structure and sugar-binding activity of lectin can be changed by the photodissociation of NO.

Redox Regulation of Ischemic Angiogenesis - Another Aspect of Reactive Oxygen Species

Antioxidants are expected to improve cardiovascular disease (CVD) by eliminating oxidative stress, but clinical trials have not shown promising results in chronic CVD. Animal studies have revealed that reactive oxygen species (ROS) exacerbate acute CVDs in which high levels of ROS are observed. However, ROS are also necessary for angiogenesis after ischemia, because ROS not only damage cells but also stimulate the cell signaling required for angiogenesis. ROS affect signaling by protein modifications, especially of cysteine amino acid thiols. Although there are several cysteine modifications, S-glutathionylation (GSH adducts; -SSG), a reversible cysteine modification by glutathione (GSH), plays an important role in angiogenic signal transduction by ROS. Glutaredoxin-1 (Glrx) is an enzyme that specifically removes GSH adducts in vivo. Overexpression of Glrx inhibits, whereas deletion of Glrx improves revascularization after mouse hindlimb ischemia. These studies indicate that increased levels of GSH adducts in ischemic muscle are beneficial in promoting angiogenesis. The underlying mechanism can be explained by multiple targets of S-gluathionylation, which mediate the angiogenic effects in ischemia. Increments in the master angiogenic transcriptional factor, HIF-1α, reduction of the anti-angiogenic factor sFlt1, activation of the endoplasmic reticulum Ca(2+)pump, SERCA, and inhibition of phosphatases may occur as a consequence of enhanced S-glutathionylation in ischemic tissue. In summary, inducing S-glutathionylation by inhibiting Glrx may be a therapeutic strategy to improve ischemic angiogenesis in CVD. (Circ J 2016; 80: 1278-1284).

Metabolomics for undergraduates: Identification and pathway assignment of mitochondrial metabolites

Metabolomics is a key discipline in systems biology, together with genomics, transcriptomics, and proteomics. In this omics cascade, the metabolome represents the biochemical products that arise from cellular processes and is often regarded as the final response of a biological system to environmental or genetic changes. The overall screening approach to identify all the metabolites in a given biological system is called metabolic fingerprinting. Using high-resolution and high-mass accuracy mass spectrometry, large metabolome coverage, sensitivity, and specificity can be attained. Although the theoretical concepts of this methodology are usually provided in life-science programs, hands-on laboratory experiments are not usually accessible to undergraduate students. Even if the instruments are available, there are not simple laboratory protocols created specifically for teaching metabolomics. We designed a straightforward hands-on laboratory experiment to introduce students to this methodology, relating it to biochemical knowledge through metabolic pathway mapping of the identified metabolites. This study focuses on mitochondrial metabolomics since mitochondria have a well-known, medium-sized cellular sub-metabolome. These features facilitate both data processing and pathway mapping. In this experiment, students isolate mitochondria from potatoes, extract the metabolites, and analyze them by high-resolution mass spectrometry (using an FT-ICR mass spectrometer). The resulting mass list is submitted to an online program for metabolite identification, and compounds associated with mitochondrial pathways can be highlighted in a metabolic network map.

Immunomodulatory potencies of isolated compounds from Crataegus azarolus through their antioxidant activities

The search of natural immunomodulatory agents has become an area of great interest in order to reduce damage to the human body. In this study, the immunomodulatory potential of Crataegus azarolus and its isolated hyperoside on mouse lymphocytes and macrophages in vitro was assessed. The effect of C. azarolus natural compounds on splenocytes proliferation, natural killer (NK) and cytotoxic T lymphocytes (CTL) activities, and on macrophage-mediated cytotoxicity were assessed by MTT test. Phagocytic activity and inhibition of nitric oxide (NO) release by macrophages were also evaluated. The antioxidant capacity of these products was evaluated by determining their cellular antioxidant activity (CAA) in splenocytes and macrophages. Depending on the concentrations, both ethyl acetate (EA) extract and hyperoside (Hyp) from C. azarolus affect macrophage functions by modulating their lysosomal enzyme activity and nitric oxide release. Whereas, the above-mentioned products significantly promote LPS and lectin-stimulated splenocyte proliferation, implying a potential activation of lymphocytes B and T enhancing humoral and cellular immune responses. Moreover, EA extract and Hyp could enhance the activity of NK and T lymphocytes cells, as well as the macrophages-mediated cytotoxicity against B16F10 cells. The anti-inflammatory activity was concomitant with the cellular antioxidant effect of the tested compounds against macrophages and splenocytes. Collectively, C. azarolus and its isolated hyperoside exhibited an immunomodulatory effect through their antioxidant activity. These findings suggest that C. azarolus should be explored as a novel potential immunomodulatory agent for the treatment of inflammatory diseases.

Glutathione plays an essential role in nitric oxide-mediated iron-deficiency signaling and iron-deficiency tolerance in Arabidopsis

Iron (Fe) deficiency is a common agricultural problem that affects both the productivity and nutritional quality of plants. Thus, identifying the key factors involved in the tolerance of Fe deficiency is important. In the present study, the zir1 mutant, which is glutathione deficient, was found to be more sensitive to Fe deficiency than the wild type, and grew poorly in alkaline soil. Other glutathione-deficient mutants also showed various degrees of sensitivity to Fe-limited conditions. Interestingly, we found that the glutathione level was increased under Fe deficiency in the wild type. By contrast, blocking glutathione biosynthesis led to increased physiological sensitivity to Fe deficiency. On the other hand, overexpressing glutathione enhanced the tolerance to Fe deficiency. Under Fe-limited conditions, glutathione-deficient mutants, zir1, pad2 and cad2 accumulated lower levels of Fe than the wild type. The key genes involved in Fe uptake, including IRT1, FRO2 and FIT, are expressed at low levels in zir1; however, a split-root experiment suggested that the systemic signals that govern the expression of Fe uptake-related genes are still active in zir1. Furthermore, we found that zir1 had a lower accumulation of nitric oxide (NO) and NO reservoir S-nitrosoglutathione (GSNO). Although NO is a signaling molecule involved in the induction of Fe uptake-related genes during Fe deficiency, the NO-mediated induction of Fe-uptake genes is dependent on glutathione supply in the zir1 mutant. These results provide direct evidence that glutathione plays an essential role in Fe-deficiency tolerance and NO-mediated Fe-deficiency signaling in Arabidopsis.

Elucidation of novel 13-series resolvins that increase with atorvastatin and clear infections

Endogenous mechanisms leading to host protection and resolution of infections without immunosuppression are of wide interest^1,2. Here we elucidated the structures of four new host-protective molecules produced in neutrophil-endothelial co-cultures, and present in human and mouse tissues after sterile inflammation or infection. These bioactive molecules contained conjugated triene and diene double bonds with each carrying a 13-carbon position alcohol and were derived from n-3 docosapentaenoic acid (DPA, C22:5). These compounds, termed 13-series resolvins (RvT), demonstrated potent protective actions increasing mice survival during Escherichia coli infections. RvT also regulated human and mouse phagocyte responses stimulating bacterial phagocytosis and regulating inflammasome components. Their biosynthesis during neutrophil-endothelial cell interactions was initiated by endothelial cyclooxygenase-2 (COX-2) and increased by atorvastatin via S-nitrosylation of COX-2. The actions of atorvastatin and RvT were additive in E. coli infections in mice where they accelerated resolution of inflammation and increased survival >60%. These results document novel host protective molecules in bacterial infections, namely 13-series resolvins, derived from n-3 DPA via transcellular biosynthesis and increased by atorvastatin. These novel molecules regulate key innate protective responses in the resolution of infectious-inflammation.

Nitric oxide synthase (NOS) inhibition during porcine in vitro maturation modifies oocyte protein S-nitrosylation and in vitro fertilization

Nitric oxide (NO) is a molecule involved in many reproductive processes. Its importance during oocyte in vitro maturation (IVM) has been demonstrated in various species although sometimes with contradictory results. The objective of this study was to determine the effect of NO during IVM of cumulus oocyte complexes and its subsequent impact on gamete interaction in porcine species. For this purpose, IVM media were supplemented with three NOS inhibitors: NG-nitro-L-arginine methyl ester (L-NAME), NG-monomethyl-L-arginine (L-NMMA) and aminoguanidine (AG). A NO donor, S-nitrosoglutathione (GSNO), was also used. The effects on the cumulus cell expansion, meiotic resumption, zona pellucida digestion time (ZPdt) and, finally, on in vitro fertilization (IVF) parameters were evaluated. The oocyte S-nitrosoproteins were also studied by in situ nitrosylation. The results showed that after 42 h of IVM, AG, L-NAME and L-NMMA had an inhibitory effect on cumulus cell expansion. Meiotic resumption was suppressed only when AG was added, with 78.7% of the oocytes arrested at the germinal vesicle state (P<0.05). Supplementation of the IVM medium with NOS inhibitors or NO donor did not enhance the efficiency of IVF, but revealed the importance of NO in maturation and subsequent fertilization. Furthermore, protein S-nitrosylation is reported for the first time as a pathway through which NO exerts its effect on porcine IVM; therefore, it would be important to determine which proteins are nitrosylated in the oocyte and their functions, in order to throw light on the mechanism of action of NO in oocyte maturation and subsequent fertilization.

Redox pioneer: professor Helmut Sies

Dr. Helmut Sies (MD, 1967) is recognized as a Redox Pioneer, because he authored five articles on oxidative stress, lycopene, and glutathione, each of which has been cited more than 1000 times, and coauthored an article on hydroperoxide metabolism in mammalian systems cited more than 5000 times (Google Scholar). He obtained preclinical education at the University of Tübingen and the University of Munich, clinical training at Munich (MD, 1967) and Paris, and completed Habilitation at Munich (Physiological Chemistry and Physical Biochemistry, 1972). In early research, he first identified hydrogen peroxide (H2O2) as a normal aerobic metabolite and devised a method to quantify H2O2 concentration and turnover in cells. He quantified central redox systems for energy metabolism (NAD, NADP systems) and antioxidant GSH in subcellular compartments. He first described ebselen, a selenoorganic compound, as a glutathione peroxidase mimic. He contributed a fundamental discovery to the physiology of GSH, selenium nutrition, singlet oxygen biochemistry, and health benefits of dietary lycopene and cocoa flavonoids. He has published more than 600 articles, 134 of which are cited at least 100 times, and edited 28 books. His h-index is 115. During the last quarter of the 20th century and well into the 21st, he has served as a scout, trailblazer, and pioneer in redox biology. His formulation of the concept of oxidative stress stimulated and guided research in oxidants and antioxidants; his pioneering research on carotenoids and flavonoids informed nutritional strategies against cancer, cardiovascular disease, and aging; and his quantitative approach to redox biochemistry provides a foundation for modern redox systems biology. Helmut Sies is a true Redox Pioneer.

Mass spectrometry-based quantitative proteomics for dissecting multiplexed redox cysteine modifications in nitric oxide-protected cardiomyocyte under hypoxia

AIMS

Distinctive states of redox-dependent cysteine (Cys) modifications are known to regulate signaling homeostasis under various pathophysiological conditions, including myocardial injury or protection in response to ischemic stress. Recent evidence further implicates a dynamic interplay among these modified forms following changes in cellular redox environment. However, a precise delineation of multiplexed Cys modifications in a cellular context remains technically challenging. To this end, we have now developed a mass spectrometry (MS)-based quantitative approach using a set of novel iodoacetyl-based Cys-reactive isobaric tags (irreversible isobaric iodoacetyl Cys-reactive tandem mass tag [iodoTMT]) endowed with unique irreversible Cys-reactivities.

RESULTS

We have established a sequential iodoTMT-switch procedure coupled with efficient immunoenrichment and advanced shotgun liquid chromatography-MS/MS analysis. This workflow allows us to differentially quantify the multiple redox-modified forms of a Cys site in the original cellular context. In one single analysis, we have identified over 260 Cys sites showing quantitative differences in multiplexed redox modifications from the total lysates of H9c2 cardiomyocytes experiencing hypoxia in the absence and presence of S-nitrosoglutathione (GSNO), indicative of a distinct pattern of individual susceptibility to S-nitrosylation or S-glutathionylation. Among those most significantly affected are proteins functionally implicated in hypoxic damage from which we showed that GSNO would protect.

INNOVATION

We demonstrate for the first time how quantitative analysis of various Cys-redox modifications occurring in biological samples can be performed precisely and simultaneously at proteomic levels.

CONCLUSION

We have not only developed a new approach to map global Cys-redoxomic regulation in vivo, but also provided new evidences implicating Cys-redox modifications of key molecules in NO-mediated ischemic cardioprotection.

Redox proteomics: from bench to bedside

In general protein posttranslation modifications (PTMs) involve the covalent addition of functional groups or molecules to specific amino acid residues in proteins. These modifications include phosphorylation, glycosylation, S-nitrosylation, acetylation, lipidation, among others (Angew Chem Int Ed Engl 44(45):7342-7372, 2005). Although other amino acids can undergo different kinds of oxidative posttranslational modifications (oxPTMs) (Exp Gerontol 36(9):1495-1502, 2001), in this chapter oxPTM will be considered specifically related to Cysteine oxidation, and redox proteomics here is translated as a comprehensive investigation of oxPTMs, in biological systems, using diverse technical approaches. Protein Cysteine residues are not the only amino acid that can be target for oxidative modifications in proteins (Exp Gerontol 36(9):1495-1502, 2001; Biochim Biophys Acta 1814(12):1785-1795, 2011), but certainly it is among the most reactive amino acid (Nature 468(7325):790-795, 2010). Interestingly, it is one of the least abundant amino acid, but it often occurs in the functional sites of proteins (J Mol Biol 404(5):902-916, 2010). In addition, the majority of the Cysteine oxidations are reversible, indicating potential regulatory mechanism of proteins. The global analysis of oxPTMs has been increasingly recognized as an important area of proteomics, because not only maps protein caused by reactive oxygen species (ROS) and reactive nitrogen species (RNS), but also explores protein modulation involving ROS/RNS. Furthermore, the tools and strategies to study this type oxidation are also very abundant and developed, offering high degree of accuracy on the results. As a consequence, the redox proteomics field focuses very much on analyzing Cysteine oxidation in proteins under several experimental conditions and diseases states. Therefore, the identification and localization of oxPTMs within cellular milieu became critical to understand redox regulation of proteins in physiological and pathological conditions, and consequently an important information to develop better strategies for treatment and prevention of diseases associated with oxidative stress.There is a wide range of techniques available to investigate oxPTMs, including gel-based and non-gel-based separation approaches to be combined with sophisticated methods of detection, identification, and quantification of these modifications. The strategies and approaches to study oxPTMs and the respective applications related to physiological and pathological conditions will be discussed in more detail in this chapter.

S-nitrosylation: specificity, occupancy, and interaction with other post-translational modifications

SIGNIFICANCE

S-nitrosylation (SNO) has been identified throughout the body as an important signaling modification both in physiology and a variety of diseases. SNO is a multifaceted post-translational modification, in that it can either act as a signaling molecule itself or as an intermediate to other modifications.

RECENT ADVANCES AND CRITICAL ISSUES

Through extensive SNO research, we have made progress toward understanding the importance of single cysteine-SNO sites; however, we are just beginning to explore the importance of specific SNO within the context of other SNO sites and post-translational modifications. Additionally, compartmentalization and SNO occupancy may play an important role in the consequences of the SNO modification.

FUTURE DIRECTIONS

In this review, we will consider the context of SNO signaling and discuss how the transient nature of SNO, its role as an oxidative intermediate, and the pattern of SNO, should be considered when determining the impact of SNO signaling.

S-glutathionylation in monocyte and macrophage (dys)function

Atherosclerosis is a chronic inflammatory disease involving the accumulation of monocytes and macrophages in the vascular wall. Monocytes and macrophages play a central role in the initiation and progression of atherosclerotic lesion development. Oxidative stress, which occurs when reactive oxygen species (ROS) overwhelm cellular antioxidant systems, contributes to the pathophysiology of many chronic inflammatory diseases, including atherosclerosis. Major targets of ROS are reactive thiols on cysteine residues in proteins, which when oxidized can alter cellular processes, including signaling pathways, metabolic pathways, transcription, and translation. Protein-S-glutathionylation is the process of mixed disulfide formation between glutathione (GSH) and protein thiols. Until recently, protein-S-glutathionylation was associated with increased cellular oxidative stress, but S-glutathionylation of key protein targets has now emerged as a physiologically important redox signaling mechanism, which when dysregulated contributes to a variety of disease processes. In this review, we will explore the role of thiol oxidative stress and protein-S-glutathionylation in monocyte and macrophage dysfunction as a mechanistic link between oxidative stress associated with metabolic disorders and chronic inflammatory diseases, including atherosclerosis.

Pros and cons of peptide isolectric focusing in shotgun proteomics

In shotgun proteomics, protein mixtures are proteolytically digested before tandem mass spectrometry (MS/MS) analysis. Biological samples are generally characterized by a very high complexity, therefore a step of peptides fractionation before the MS analysis is essential. This passage reduces the sample complexity and increases its compatibility with the sampling performance of the instrument. Among all the existing approaches for peptide fractionation, isoelectric focusing has several peculiarities that are theoretically known but practically rarely exploited by the proteomics community. The main aim of this review is to draw the readers' attention to these unique qualities, which are not accessible with other common approaches, and that represent important tools to increase confidence in the identification of proteins and some post-translational modifications. The general characteristics of different methods to perform peptide isoelectric focusing with natural and artificial pH gradients, the existing instrumentation, and the informatics tools available for isoelectric point calculation are also critically described. Finally, we give some general conclusions on this strategy, underlying its principal limitations.

S-nitrosoglutathione

BACKGROUND

S-Nitrosoglutathione (GSNO) is the S-nitrosated derivative of glutathione and is thought to be a critical mediator of the down stream signaling effects of nitric oxide (NO). GSNO has also been implicated as a contributor to various disease states.

SCOPE OF REVIEW

This review focuses on the chemical nature of GSNO, its biological activities, the evidence that it is an endogenous mediator of NO action, and implications for therapeutic use.

MAJOR CONCLUSIONS

GSNO clearly exerts its cellular actions through both NO- and S-nitrosation-dependent mechanisms; however, the chemical and biological aspects of this compound should be placed in the context of S-nitrosation as a whole.

GENERAL SIGNIFICANCE

GSNO is a central intermediate in formation and degradation of cellular S-nitrosothiols with potential therapeutic applications; thus, it remains an important molecule of study. This article is part of a Special Issue entitled Cellular functions of glutathione.

Antioxidant and anti-inflammatory activities of selected medicinal plants and fungi containing phenolic and flavonoid compounds

Background

This study aims to determine the relationship between the antioxidant and anti-inflammatory activities of the thirteen herbs and two fungi extracts, and their total phenolic and flavonoid contents.

Methods

Antioxidant activities were evaluated by four assays: an antioxidant activity assay using Saccharomyces cerevisiae, a DPPH ((2, 2-diphenyl-1-picrylhydrazyl) assay to assess free radical scavenging, an assay assessing ferrous ions or iron (II) chelating ability, and a ferric reducing antioxidant power (FRAP) assay. Total phenolic and flavonoid contents were determined using the Folin-Ciocalteu and aluminium chloride methods, respectively. Anti-inflammatory activities were determined by measuring the inhibition of nitric oxide and TNF-α production in lipopolysaccharide- and interferon-γ-activated J774A.1 macrophages. Their cytotoxicities against macrophages were determined by MTT assay.

Results

A positive linear correlation between antioxidant activities and the total phenolic and flavonoid content of the plant extracts was found. The plant extracts with high phenolic and flavonoid content also exhibited significant anti-inflammatory activity with good cell viability.

Conclusion

The selected herbs could be a rich source of antioxidants and free radical scavenging compounds. The levels of phenolic and flavonoid compounds were correlated with the antioxidant and anti-inflammatory activities of the extracts from the herbs.

Superoxide dismutase as a novel macromolecular nitric oxide carrier: preparation and characterization

Nitric oxide (NO) is an important molecule that exerts multiple functions in biological systems. Because of the short-lived nature of NO, S-nitrosothiols (RSNOs) are believed to act as stable NO carriers. Recently, sulfhydryl (SH) containing macromolecules have been shown to be promising NO carriers. In the present study, we aimed to synthesize and characterize a potential NO carrier based on bovine Cu,Zn-superoxide dismutase (bSOD). To prepare S-nitrosated bSOD, the protein was incubated with S-nitrosoglutathione (GSNO) under varied experimental conditions. The results show that significant S-nitrosation of bSOD occurred only at high temperature (50 °C) for prolonged incubation time (>2 h). S-nitrosation efficiency increased with reaction time and reached a plateau at ~4 h. The maximum amount of NO loaded was determined to be about 0.6 mol SNO/mol protein (~30% loading efficiency). The enzymatic activity of bSOD, however, decreased with reaction time. Our data further indicate that NO functionality can only be measured in the presence of extremely high concentrations of Hg²⁺ or when the protein was denatured by guanidine. Moreover, mildly acidic pH was shown to favor S-nitrosation of bSOD. A model based on unfolding and refolding of bSOD during preparation was proposed to possibly explain our observation.

Thiol-based posttranslational modifications in parasites

SIGNIFICANCE

Cysteine residues of proteins participate in the catalysis of biochemical reactions, are crucial for redox reactions, and influence protein structure by the formation of disulfide bonds. Covalent posttranslational modifications (PTMs) of cysteine residues are important mediators of redox regulation and signaling by coupling protein activity to the cellular redox state, and moreover influence stability, function, and localization of proteins. A diverse group of protozoan and metazoan parasites are a major cause of diseases in humans, such as malaria, African trypanosomiasis, leishmaniasis, toxoplasmosis, filariasis, and schistosomiasis.

RECENT ADVANCES

Human parasites undergo dramatic morphological and metabolic changes while they pass complex life cycles and adapt to changing environments in host and vector. These processes are in part regulated by PTMs of parasitic proteins. In human parasites, posttranslational cysteine modifications are involved in crucial cellular events such as signal transduction (S-glutathionylation and S-nitrosylation), redox regulation of proteins (S-glutathionylation and S-nitrosylation), protein trafficking and subcellular localization (palmitoylation and prenylation), as well as invasion into and egress from host cells (palmitoylation). This review focuses on the occurrence and mechanisms of these cysteine modifications in parasites.

CRITICAL ISSUES

Studies on cysteine modifications in human parasites are so far largely based on in vitro experiments.

FUTURE DIRECTIONS

The in vivo regulation of cysteine modifications and their role in parasite development will be of great interest in order to understand redox signaling in parasites.

Monoclonal antibody against protein-bound glutathione: use of glutathione conjugate of acrolein-modified proteins as an immunogen

Acrolein shows a facile reactivity with the ε-amino group of lysine to form N(ε)-(3-formyl-3,4-dehydropiperidino)lysine (FDP-lysine) as the major product. In addition, FDP-lysine generated in the acrolein-modified protein could function as an electrophile, reacting with thiol compounds, to form an irreversible thioether adduct. In the present study, to establish the utility of this irreversible conjugate, we attempted to use it as an immunogen to raise a monoclonal antibody (mAb), which specifically recognized protein-bound thiol compounds. Using the glutathione (GSH) conjugate of the acrolein-modified protein as an immunogen, we raised the mAb 2C4, which cross-reacted with the GSH conjugate of acrolein-modified proteins. Specificity studies revealed that mAb 2C4 recognized both the GSH conjugate of an acrolein-lysine adduct, FDP-lysine, and oxidized GSH (GSSG). In addition, mAb 2C4 cross-reacted not only with the GSH conjugates of the acrolein-modified protein but also with the GSH-treated, oxidized protein (S-glutathiolated protein), suggesting that the antibody significantly recognized the protein-bound GSH as the epitope. An immunohistochemical analysis of the atherosclerotic lesions from the human aorta showed that immunoreactive materials with mAb 2C4 were indeed present in the macrophage-derived foam cells and migrating smooth muscles. In addition, using mAb 2C4, we analyzed the GSH-treated, oxidized low-density lipoproteins by agarose gel electrophoresis under reducing or nonreducing conditions followed by immunoblot analysis and found that the majority of the GSH was irreversibly incorporated into the proteins. The results of this study not only showed the utility of the antibody raised against the GSH conjugate of the acrolein-modified proteins but also suggested that the irreversible binding of GSH and other redox molecules to the oxidized LDL might represent the process common to the modification of LDL during atherogenesis.

Electronic and spatial structures of water-soluble dinitrosyl iron complexes with thiol-containing ligands underlying their ability to act as nitric oxide and nitrosonium ion donors

The ability of mononuclear dinitrosyl iron commplexes (M-DNICs) with thiolate ligands to act as NO donors and to trigger S-nitrosation of thiols can be explain only in the paradigm of the model of the [Fe(+)(NO(+))(2)] core ({Fe(NO)(2)}(7) according to the Enemark-Feltham classification). Similarly, the {(RS(-))(2)Fe(+)(NO(+))(2)}(+) structure describing the distribution of unpaired electron density in M-DNIC corresponds to the low-spin (S = 1/2) state with a d(7) electron configuration of the iron atom and predominant localization of the unpaired electron on MO(d(z2)) and the square planar structure of M-DNIC. On the other side, the formation of molecular orbitals of M-DNIC including orbitals of the iron atom, thiolate and nitrosyl ligands results in a transfer of electron density from sulfur atoms to the iron atom and nitrosyl ligands. Under these conditions, the positive charge on the nitrosyl ligands diminishes appreciably, the interaction of the ligands with hydroxyl ions or with thiols slows down and the hydrolysis of nitrosyl ligands and the S-nitrosating effect of the latter are not manifested. Most probably, the S-nitrosating effect of nitrosyl ligands is a result of weak binding of thiolate ligands to the iron atom under conditions favoring destabilization of M-DNIC.

Redox regulation in plant programmed cell death

Programmed cell death (PCD) is a genetically controlled process described both in eukaryotic and prokaryotic organisms. Even if it is clear that PCD occurs in plants, in response to various developmental and environmental stimuli, the signalling pathways involved in the triggering of this cell suicide remain to be characterized. In this review, the main similarities and differences in the players involved in plant and animal PCD are outlined. Particular attention is paid to the role of reactive oxygen species (ROS) as key inducers of PCD in plants. The involvement of different kinds of ROS, different sites of ROS production, as well as their interaction with other molecules, is crucial in activating PCD in response to specific stimuli. Moreover, the importance is stressed on the balance between ROS production and scavenging, in various cell compartments, for the activation of specific steps in the signalling pathways triggering this cell suicide process. The review focuses on the complexity of the interplay between ROS and antioxidant molecules and enzymes in determining the most suitable redox environment required for the occurrence of different forms of PCD.

Thioredoxin 1-mediated post-translational modifications: reduction, transnitrosylation, denitrosylation, and related proteomics methodologies

Despite the significance of redox post-translational modifications (PTMs) in regulating diverse signal transduction pathways, the enzymatic systems that catalyze reversible and specific oxidative or reductive modifications have yet to be firmly established. Thioredoxin 1 (Trx1) is a conserved antioxidant protein that is well known for its disulfide reductase activity. Interestingly, Trx1 is also able to transnitrosylate or denitrosylate (defined as processes to transfer or remove a nitric oxide entity to/from substrates) specific proteins. An intricate redox regulatory mechanism has recently been uncovered that accounts for the ability of Trx1 to catalyze these different redox PTMs. In this review, we will summarize the available evidence in support of Trx1 as a specific disulfide reductase, and denitrosylation and transnitrosylation agent, as well as the biological significance of the diverse array of Trx1-regulated pathways and processes under different physiological contexts. The dramatic progress in redox proteomics techniques has enabled the identification of an increasing number of proteins, including peroxiredoxin 1, whose disulfide bond formation and nitrosylation status are regulated by Trx1. This review will also summarize the advancements of redox proteomics techniques for the identification of the protein targets of Trx1-mediated PTMs. Collectively, these studies have shed light on the mechanisms that regulate Trx1-mediated reduction, transnitrosylation, and denitrosylation of specific target proteins, solidifying the role of Trx1 as a master regulator of redox signal transduction.

Characterization of inhibitors of glucocorticoid receptor nuclear translocation: a model of cytoplasmic dynein-mediated cargo transport

Agonist-induced glucocorticoid receptor [GR] transport from the cytoplasm to the nucleus was used as a model to identify dynein-mediated cargo transport inhibitors. Cell-based screening of the library of pharmacologically active compound (LOPAC)-1280 collection identified several small molecules that stalled the agonist-induced transport of GR-green fluorescent protein (GFP) in a concentration-dependent manner. Fluorescent images of microtubule organization, nuclear DNA staining, expression of GR-GFP, and its subcellular distribution were inspected and quantified by image analysis to evaluate the impact of compounds on cell morphology, toxicity, and GR transport. Given the complexity of the multi-protein complex involved in dynein-mediated cargo transport and the variety of potential mechanisms for interruption of that process, we therefore developed and validated a panel of biochemical assays to investigate some of the more likely intracellular target(s) of the GR transport inhibitors. Although the apomorphine enantiomers exhibited the most potency toward the ATPase activities of cytoplasmic dynein, myosin, and the heat-shock proteins (HSPs), their apparent lack of specificity made them unattractive for further study in our quest. Other molecules appeared to be nonspecific inhibitors that targeted reactive cysteines of proteins. Ideally, specific retrograde transport inhibitors would either target dynein itself or one of the other important proteins associated with the transport process. Although the hits from the cell-based screen of the LOPAC-1280 collection did not exhibit this desired profile, this screening platform provided a promising phenotypic system for the discovery of dynein/HSP modulators.

The disulfide proteome and other reactive cysteine proteomes: analysis and functional significance

Ten years ago, proteomics techniques designed for large-scale investigations of redox-sensitive proteins started to emerge. The proteomes, defined as sets of proteins containing reactive cysteines that undergo oxidative post-translational modifications, have had a particular impact on research concerning the redox regulation of cellular processes. These proteomes, which are hereafter termed "disulfide proteomes," have been studied in nearly all kingdoms of life, including animals, plants, fungi, and bacteria. Disulfide proteomics has been applied to the identification of proteins modified by reactive oxygen and nitrogen species under stress conditions. Other studies involving disulfide proteomics have addressed the functions of thioredoxins and glutaredoxins. Hence, there is a steadily growing number of proteins containing reactive cysteines, which are probable targets for redox regulation. The disulfide proteomes have provided evidence that entire pathways, such as glycolysis, the tricarboxylic acid cycle, and the Calvin-Benson cycle, are controlled by mechanisms involving changes in the cysteine redox state of each enzyme implicated. Synthesis and degradation of proteins are processes highly represented in disulfide proteomes and additional biochemical data have established some mechanisms for their redox regulation. Thus, combined with biochemistry and genetics, disulfide proteomics has a significant potential to contribute to new discoveries on redox regulation and signaling.

Redox regulation of insulin degradation by insulin-degrading enzyme

Insulin-degrading enzyme (IDE) is a thiol sensitive peptidase that degrades insulin and amyloid β, and has been linked to type 2 diabetes mellitus and Alzheimer's disease. We examined the thiol sensitivity of IDE using S-nitrosoglutathione, reduced glutathione, and oxidized glutathione to distinguish the effects of nitric oxide from that of the redox state. The in vitro activity of IDE was studied using either partially purified cytosolic enzyme from male Sprague-Dawley rats, or purified rat recombinant enzyme. We confirm that nitric oxide inhibits the degrading activity of IDE, and that it affects proteasome activity through this interaction with IDE, but does not affect the proteasome directly. Oxidized glutathione inhibits IDE through glutathionylation, which was reversible by dithiothreitol but not by ascorbic acid. Reduced glutathione had no effect on IDE, but reacted with partially degraded insulin to disrupt its disulfide bonds and accelerate its breakdown to trichloroacetic acid soluble fragments. Our results demonstrate the sensitivity of insulin degradation by IDE to the redox environment and suggest another mechanism by which the cell's oxidation state may contribute to the development of, and the link between, type 2 diabetes and Alzheimer's disease.

Regulation of mitochondrial processes by protein S-nitrosylation

BACKGROUND

Nitric oxide (NO) exerts powerful physiological effects through guanylate cyclase (GC), a non-mitochondrial enzyme, and through the generation of protein cysteinyl-NO (SNO) adducts-a post-translational modification relevant to mitochondrial biology. A small number of SNO proteins, generated by various mechanisms, are characteristically found in mammalian mitochondria and influence the regulation of oxidative phosphorylation and other aspects of mitochondrial function.

SCOPE OF REVIEW

The principles by which mitochondrial SNO proteins are formed and their actions, independently or collectively with NO binding to heme, iron-sulfur centers, or to glutathione (GSH) are reviewed on a molecular background of SNO-based signal transduction.

MAJOR CONCLUSIONS

Mitochondrial SNO-proteins have been demonstrated to inhibit Complex I of the electron transport chain, to modulate mitochondrial reactive oxygen species (ROS) production, influence calcium-dependent opening of the mitochondrial permeability transition pore (MPTP), promote selective importation of mitochondrial protein, and stimulate mitochondrial fission. The ease of reversibility and the affirmation of regulated S-nitros(yl)ating and denitros(yl)ating enzymatic reactions support hypotheses that SNO regulates the mitochondrion through redox mechanisms. SNO modification of mitochondrial proteins, whether homeostatic or adaptive (physiological), or pathogenic, is an area of active investigation.

GENERAL SIGNIFICANCE

Mitochondrial SNO proteins are associated with mainly protective, bur some pathological effects; the former mainly in inflammatory and ischemia/reperfusion syndromes and the latter in neurodegenerative diseases. Experimentally, mitochondrial SNO delivery is also emerging as a potential new area of therapeutics. This article is part of a Special Issue entitled: Regulation of cellular processes by S-nitrosylation.

Role of quinones in the ascorbate reduction rates of S-nitrosoglutathione

Quinones are one of the largest classes of antitumor agents approved for clinical use, and several antitumor quinones are in various stages of clinical and preclinical development. Many of these are metabolites of, or are, environmental toxins. Because of their chemical structure they are known to enhance electron transfer processes such as ascorbate oxidation and NO reduction. The paraquinones 2,6-dimethyl-1,4-benzoquinone (DMBQ), 1,4-benzoquinone, methyl-1,4-benzoquinone, 2,6-dimethoxy-1,4-benzoquinone, 2-hydroxymethyl-6-methoxy-1,4-benzoquinone, trimethyl-1,4-benzoquinone, tetramethyl-1,4-benzoquinone, and 2,3-dimethoxy-5-methyl-1,4-benzoquinone; the paranaphthoquinones 1,4-naphthoquinone, menadione, 1,4-naphthoquinone-2-sulfonate, 2-ethylsulfanyl-3-methyl-1,4-naphthoquinone and juglone; and phenanthraquinone (PHQ) all enhance the anaerobic rate of ascorbate reduction of GSNO to produce NO and GSH. Rates of this reaction were much larger for p-benzoquinones and PHQ than for p-naphthoquinone derivatives with similar one-electron redox potentials. The quinone DMBQ also enhances the rate of NO production from S-nitrosylated bovine serum albumin upon ascorbate reduction. Density functional theory calculations suggest that stronger interactions between p-benzo- or phenanthrasemiquinones and GSNO than between p-naphthosemiquinones and GSNO are the major causes of these differences. Thus, quinones, and especially p-quinones and PHQ, could act as enhancers of NO release from GSNO in biomedical systems in the presence of ascorbate. Because quinones are exogenous toxins that could enter the human body via a chemotherapeutic application or as an environmental contaminant, they could boost the release of NO from S-nitrosothiol storages in the body in the presence of ascorbate and thus enhance the responses elicited by a sudden increase in NO levels.

The redox switch: dynamic regulation of protein function by cysteine modifications

Reactive oxygen intermediates (ROIs) and reactive nitrogen intermediates (RNIs) have now become well established as important signalling molecules in physiological settings within microorganisms, mammals and plants. These intermediates are routinely synthesised in a highly controlled and transient fashion by NADPH-dependent enzymes, which constitute key regulators of redox signalling. Mild oxidants such as hydrogen peroxide (H(2)O(2)) and especially nitric oxide (NO) signal through chemical reactions with specific atoms of target proteins that result in covalent protein modifications. Specifically, highly reactive cysteine (Cys) residues of low pK(a) are a major site of action for these intermediates. The oxidation of target Cys residues can result in a number of distinct redox-based, post-translational modifications including S-nitrosylation, S-glutathionylation; and sulphenic acid, sulphinic acid and disulphide formation. Importantly, such modifications precisely regulate protein structure and function. Cys-based redox switches are now increasingly being found to underpin many different signalling systems and regulate physiological outputs across kingdoms.

Protocols for the detection of s-glutathionylated and s-nitrosylated proteins in situ

The oxidation of protein cysteine residues represents significant posttranslational modifications that impact a wide variety of signal transduction cascades and diverse biological processes. Oxidation of cysteines occurs through reactions with reactive oxygen as well as nitrogen species. These oxidative events can lead to irreversible modifications, such as the formation of sulfonic acids, or manifest as reversible modifications such as the conjugation of glutathione with the cysteine moiety, a process termed S-glutathionylation (also referred to as S-glutathiolation, or protein mixed disulfides). Similarly, S-nitrosothiols can also react with the thiol group in a process known as S-nitrosylation (or S-nitrosation). It is the latter two events that have recently come to the forefront of cellular biology through their ability to reversibly impact numerous cellular processes. Herein we describe two protocols for the detection of S-glutathionylated or S-nitrosylated proteins in situ. The protocol for the detection of S-glutathionylated proteins relies on the catalytic specificity of glutaredoxin-1 for the reduction of S-glutathionylated proteins. The protocol for the detection of S-nitrosylated proteins represents a modification of the previously described biotin switch protocol, which relies on ascorbate in the presence of chelators to decompose S-nitrosylated proteins. These techniques can be applied in situ to elucidate which compartments in tissues are affected in diseased states whose underlying pathologies are thought to represent a redox imbalance.