Regulation of redox-sensitive exofacial protein thiols in CHO cells

D-cysteine ethyl ester and D-cystine dimethyl ester reverse the deleterious effects of morphine on arterial blood-gas chemistry and Alveolar-arterial gradient in anesthetized rats

We determined whether intravenous injections of the membrane-permeable ventilatory stimulants, D-cysteine ethyl ester (ethyl (2 S)– 2-amino-3-sulfanylpropanoate) (D-CYSee) and D-cystine dimethyl ester (methyl (2 S)– 2-amino-3-[[(2 S)– 2-amino-3-methoxy-3-oxopropyl]disulfanyl] propanoate) (D-CYSdime), could overcome the deleterious actions of intravenous morphine on arterial blood pH, pCO₂, pO₂ and sO₂, and Alveolar-arterial (A-a) gradient (i.e., the measure of exchange of gases in the lungs) in Sprague Dawley rats anesthetized with isoflurane. Injection of morphine (2 mg/kg, IV) caused pronounced reductions in pH, pO₂ and sO₂ accompanied by elevations in pCO₂, all which are suggestive of diminished ventilation, and elevations in A-a gradient, which suggests a mismatch of ventilation-perfusion. Subsequent boluses of D-cysteine ethyl ester (2 × 100 μmol/kg, IV) or D-cystine dimethyl ester (2 ×50 μmol/kg, IV) rapidly reversed of the negative actions of morphine on pH, pCO₂, pO₂ and sO₂, and A-a gradient. Similar injections of D-cysteine (2 × 100 μmol/kg, IV) were without effect, whereas injections of D-cystine (2 × 50 μmol/kg, IV) produced a modest reversal. Our data show that D-cysteine ethyl ester and D-cystine dimethyl ester readily overcome the deleterious effects of morphine on arterial blood gas (ABG) chemistry and A-a gradient by mechanisms that may depend upon their ability to rapidly enter cells. As a result of their known ability to enter the brain, lungs, muscles of the chest wall, and most likely the major peripheral chemoreceptors (i.e., carotid bodies), the effects of the thiolesters on changes in ABG chemistry and A-a gradient elicited by morphine likely involve central and peripheral mechanisms. We are employing target prediction methods to identify an array of in vitro and in vivo methods to test potential functional proteins by which D-CYSee and D-CYSdime modulate the effects of morphine on breathing.

Glutathione ethyl ester reverses the deleterious effects of fentanyl on ventilation and arterial blood-gas chemistry while prolonging fentanyl-induced analgesia

There is an urgent need to develop novel compounds that prevent the deleterious effects of opioids such as fentanyl on minute ventilation while, if possible, preserving the analgesic actions of the opioids. We report that L-glutathione ethyl ester (GSHee) may be such a novel compound. In this study, we measured tail flick latency (TFL), arterial blood gas (ABG) chemistry, Alveolar-arterial gradient, and ventilatory parameters by whole body plethysmography to determine the responses elicited by bolus injections of fentanyl (75 μg/kg, IV) in male adult Sprague-Dawley rats that had received a bolus injection of GSHee (100 μmol/kg, IV) 15 min previously. GSHee given alone had minimal effects on TFL, ABG chemistry and A-a gradient whereas it elicited changes in some ventilatory parameters such as an increase in breathing frequency. In vehicle-treated rats, fentanyl elicited (1) an increase in TFL, (2) decreases in pH, pO₂ and sO₂ and increases in pCO₂ (all indicative of ventilatory depression), (3) an increase in Alveolar-arterial gradient (indicative of a mismatch in ventilation-perfusion in the lungs), and (4) changes in ventilatory parameters such as a reduction in tidal volume, that were indicative of pronounced ventilatory depression. In GSHee-pretreated rats, fentanyl elicited a more prolonged analgesia, relatively minor changes in ABG chemistry and Alveolar-arterial gradient, and a substantially milder depression of ventilation. GSHee may represent an effective member of a novel class of thiolester drugs that are able to prevent the ventilatory depressant effects elicited by powerful opioids such as fentanyl and their deleterious effects on gas-exchange in the lungs without compromising opioid analgesia.

Vimentin as a Multifaceted Player and Potential Therapeutic Target in Viral Infections

Vimentin is an intermediate filament protein that plays key roles in integration of cytoskeletal functions, and therefore in basic cellular processes such as cell division and migration. Consequently, vimentin has complex implications in pathophysiology. Vimentin is required for a proper immune response, but it can also act as an autoantigen in autoimmune diseases or as a damage signal. Although vimentin is a predominantly cytoplasmic protein, it can also appear at extracellular locations, either in a secreted form or at the surface of numerous cell types, often in relation to cell activation, inflammation, injury or senescence. Cell surface targeting of vimentin appears to associate with the occurrence of certain posttranslational modifications, such as phosphorylation and/or oxidative damage. At the cell surface, vimentin can act as a receptor for bacterial and viral pathogens. Indeed, vimentin has been shown to play important roles in virus attachment and entry of severe acute respiratory syndrome-related coronavirus (SARS-CoV), dengue and encephalitis viruses, among others. Moreover, the presence of vimentin in specific virus-targeted cells and its induction by proinflammatory cytokines and tissue damage contribute to its implication in viral infection. Here, we recapitulate some of the pathophysiological implications of vimentin, including the involvement of cell surface vimentin in interaction with pathogens, with a special focus on its role as a cellular receptor or co-receptor for viruses. In addition, we provide a perspective on approaches to target vimentin, including antibodies or chemical agents that could modulate these interactions to potentially interfere with viral pathogenesis, which could be useful when multi-target antiviral strategies are needed.

Redox Proteomics Applied to the Thiol Secretome

SIGNIFICANCE

Secreted proteins are important both as signaling molecules and potential biomarkers. Recent Advances: Protein can undergo different types of oxidation, both in physiological conditions or under oxidative stress. Several redox proteomics techniques have been successfully applied to the identification of glutathionylated proteins, an oxidative post-translational modification consisting in the formation of a mixed disulfide between a protein cysteine and glutathione. Redox proteomics has also been used to study other forms of protein oxidation.

CRITICAL ISSUES

Because of the highest proportion of free cysteines in the cytosol, redox proteomics of protein thiols has focused, so far, on intracellular proteins. However, plasma proteins, such as transthyretin and albumin, have been described as glutathionylated or cysteinylated. The present review discusses the redox state of protein cysteines in relation to their cellular distribution. We describe the various approaches used to detect secreted glutathionylated proteins, the only thiol modification studied so far in secreted proteins, and the specific problems presented in the study of the secretome.

FUTURE DIRECTIONS

This review focusses on glutathionylated proteins secreted under inflammatory conditions and that may act as soluble mediators (cytokines). Future studies on the redox secretome (including other forms of oxidation) might identify new soluble mediators and biomarkers of oxidative stress. Antioxid. Redox Signal. 26, 299-312.

Clinical Relevance of Biomarkers of Oxidative Stress

SIGNIFICANCE

Oxidative stress is considered to be an important component of various diseases. A vast number of methods have been developed and used in virtually all diseases to measure the extent and nature of oxidative stress, ranging from oxidation of DNA to proteins, lipids, and free amino acids.

RECENT ADVANCES

An increased understanding of the biology behind diseases and redox biology has led to more specific and sensitive tools to measure oxidative stress markers, which are very diverse and sometimes very low in abundance.

CRITICAL ISSUES

The literature is very heterogeneous. It is often difficult to draw general conclusions on the significance of oxidative stress biomarkers, as only in a limited proportion of diseases have a range of different biomarkers been used, and different biomarkers have been used to study different diseases. In addition, biomarkers are often measured using nonspecific methods, while specific methodologies are often too sophisticated or laborious for routine clinical use.

FUTURE DIRECTIONS

Several markers of oxidative stress still represent a viable biomarker opportunity for clinical use. However, positive findings with currently used biomarkers still need to be validated in larger sample sizes and compared with current clinical standards to establish them as clinical diagnostics. It is important to realize that oxidative stress is a nuanced phenomenon that is difficult to characterize, and one biomarker is not necessarily better than others. The vast diversity in oxidative stress between diseases and conditions has to be taken into account when selecting the most appropriate biomarker.

A scent of therapy: Synthetic polysulfanes with improved physico-chemical properties induce apoptosis in human cancer cells

Diallyl sulfanes derived from edible plants are highly potent compounds which at sub-millimolar concentrations are able to induce the formation of reactive oxygen species (ROS) in a variety of different cells, where they often cause an altered redox status. The loss of cellular thiols and/or formation of ROS subsequently triggers a range of cellular responses, including the induction of apoptosis. A great disadvantage of natural diallyl mono- and polysulfanes, however, is their inherent insolubility in water and the extremely bad odour which limits their practical use in humans. Here, we present the synthesis and biological evaluation of two new, especially designed polysulfanes, namely the trisulfide 1-Allyl-3-(2-ethoxyethyl)trisulfide (ATSEE) and the tetrasulfide Allyl-4-benzyltetrasulfide (ATTSB), which are nearly odourless. Both compounds produce O2•- radicals in HCT116 cells and both induce an oxidative defence signalling. Cell viability is especially reduced by the tetrasulfane ATTSB, with an arrest of the cell cycle in the G2-phase. In contrast, the trisulfane ATSEE does not inhibit the cell cycle. In agreement with these findings, treatment of HCT116 cells with ATTSB ultimately results in apoptosis whereas only limited induction of apoptosis has been detected for cells treated with ATSEE. We further show that antioxidative defence mechanisms and death response signalling run in parallel and the dominant pathway decides the fate of the cell. Thus, our results not only illuminate the intricate mode of action of certain polysulfanes; they also demonstrate that the new odourless tri- and tetrasulfanes exhibit a similar activity compared to their natural counterparts, yet are easier to handle and also deprived of the offensive odour which so far has prevented most practical applications of such polysulfanes, at least in the context of medicine.

Redox proteomics of the inflammatory secretome identifies a common set of redoxins and other glutathionylated proteins released in inflammation, influenza virus infection and oxidative stress

Protein cysteines can form transient disulfides with glutathione (GSH), resulting in the production of glutathionylated proteins, and this process is regarded as a mechanism by which the redox state of the cell can regulate protein function. Most studies on redox regulation of immunity have focused on intracellular proteins. In this study we have used redox proteomics to identify those proteins released in glutathionylated form by macrophages stimulated with lipopolysaccharide (LPS) after pre-loading the cells with biotinylated GSH. Of the several proteins identified in the redox secretome, we have selected a number for validation. Proteomic analysis indicated that LPS stimulated the release of peroxiredoxin (PRDX) 1, PRDX2, vimentin (VIM), profilin1 (PFN1) and thioredoxin 1 (TXN1). For PRDX1 and TXN1, we were able to confirm that the released protein is glutathionylated. PRDX1, PRDX2 and TXN1 were also released by the human pulmonary epithelial cell line, A549, infected with influenza virus. The release of the proteins identified was inhibited by the anti-inflammatory glucocorticoid, dexamethasone (DEX), which also inhibited tumor necrosis factor (TNF)-α release, and by thiol antioxidants (N-butanoyl GSH derivative, GSH-C4, and N-acetylcysteine (NAC), which did not affect TNF-α production. The proteins identified could be useful as biomarkers of oxidative stress associated with inflammation, and further studies will be required to investigate if the extracellular forms of these proteins has immunoregulatory functions.

Redox- and hypoxia-responsive MRI contrast agents

The development of responsive or "smart" magnetic resonance imaging (MRI) contrast agents that can report specific biomarker or biological events has been the focus of MRI contrast agent research over the past 20 years. Among various biological hallmarks of interest, tissue redox and hypoxia are particularly important owing to their roles in disease states and metabolic consequences. Herein we review the development of redox-/hypoxia-sensitive T1 shortening and paramagnetic chemical exchange saturation transfer (PARACEST) MRI contrast agents. Traditionally, the relaxivity of redox-sensitive Gd(3+) -based complexes is modulated through changes in the ligand structure or molecular rotation, while PARACEST sensors exploit the sensitivity of the metal-bound water exchange rate to electronic effects of the ligand-pendant arms and alterations in the coordination geometry. Newer designs involve complexes of redox-active metal ions in which the oxidation states have different magnetic properties. The challenges of translating redox- and hypoxia-sensitive agents in vivo are also addressed.

L-Cysteine ethyl ester reverses the deleterious effects of morphine on, arterial blood-gas chemistry in tracheotomized rats

This study determined whether the membrane-permeable ventilatory stimulant, L-cysteine ethylester (L-CYSee), reversed the deleterious actions of morphine on arterial blood-gas chemistry in isoflurane-anesthetized rats. Morphine (2 mg/kg, i.v.) elicited sustained decreases in arterial blood pH, pO₂ and sO₂, and increases in pCO₂ (all responses indicative of hypoventilation) and alveolar-arterial gradient (indicative of ventilation-perfusion mismatch). Injections of L-CYSee (100 μmol/kg, i.v.) reversed the effects of morphine in tracheotomized rats but were minimally active in non-tracheotomized rats. L-cysteine or L-serine ethylester (100 μmol/kg, i.v.) were without effect. It is evident that L-CYSee can reverse the negative effects of morphine on arterial blood-gas chemistry and alveolar-arterial gradient but that this positive activity is negated by increases in upper-airway resistance. Since L-cysteine and L-serine ethylester were ineffective, it is evident that cell penetrability and the sulfur moiety of L-CYSee are essential for activity. Due to its ready penetrability into the lungs, chest wall muscle and brain, the effects of L-CYSee on morphine-induced changes in arterial blood-gas chemistry are likely to involve both central and peripheral sites of action.

ERp57/GRP58: a protein with multiple functions

The protein ERp57/GRP58 is a stress-responsive protein and a component of the protein disulfide isomerase family. Its functions in the endoplasmic reticulum are well known, concerning mainly the proper folding and quality control of glycoproteins, and participation in the assembly of the major histocompatibility complex class 1. However, ERp57 is present in many other subcellular locations, where it is involved in a variety of functions, primarily suggested by its participation in complexes with other proteins and even with DNA. While in some instances these roles need to be confirmed by further studies, a great number of observations support the participation of ERp57 in signal transduction from the cell surface, in regulatory processes taking place in the nucleus, and in multimeric protein complexes involved in DNA repair.

In vivo labeling of B16 melanoma tumor xenograft with a thiol-reactive gadolinium based MRI contrast agent

Murine melanoma B16 cells display on the extracellular side of the plasma membrane a large number of reactive protein thiols (exofacial protein thiols, EPTs). These EPTs can be chemically labeled with Gd-DO3A-PDP, a Gd(III)-based MRI contrast agent bearing a 2-pyridinedithio chemical function for the recognition of EPTs. Uptake of gadolinium up to 10(9) Gd atoms per cell can be achieved. The treatment of B16 cells ex vivo with a reducing agent such as tris(2-carboxyethyl)phosphine (TCEP) results in an increase by 850% of available EPTs and an increase by 45% of Gd uptake. Blocking EPTs with N-ethylmaleimide (NEM) caused a decrease by 84% of available EPTs and a decrease by 55% of Gd uptake. The amount of Gd taken up by B16 cells is therefore dependent upon the availability of EPTs, whose actual level in turn changes according to the extracellular redox microenvironment. Then Gd-DO3A-PDP has been assessed for the labeling of tumor cells in vivo on B16.F10 melanoma tumor-bearing mice. Gd-DO3A-PDP (or Gd-DO3A as the control) has been injected directly into the tumor region at a dose level of 0.1 μmol and the signal enhancement in MR images followed over time. The washout kinetics of Gd-DO3A-PDP from tumor is very slow if compared to that of control Gd-DO3A, and 48 h post injection, the gadolinium-enhancement is still clearly visible. Therefore, B16 cells can be labeled ex vivo as well as in vivo according to a common EPTs-dependent route, provided that high levels of the thiol reactive probe can be delivered to the tumor.

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.

Contribution of exofacial thiol groups in the reducing activity of Lactococcus lactis

Lactococcus lactis can decrease the redox potential at pH 7 (E(h7)) from 200 to -200 mV in oxygen free Man-Rogosa-Sharpe media. Neither the consumption of oxidizing compounds or the release of reducing compounds during lactic acid fermentation were involved in the decrease in E(h7) by the bacteria. Thiol groups located on the bacterial cell surface appear to be the main components that are able to establish a greater exchange current between the Pt electrode and the bacteria. After the final E(h7) (-200 mV) was reached, only thiol-reactive reagents could restore the initial E(h7) value. Inhibition of the proton motive force showed no effect on maintaining the final E(h7) value. These results suggest that maintaining the exofacial thiol (-SH) groups in a reduced state does not depend on an active mechanism. Thiol groups appear to be displayed by membrane proteins or cell wall-bound proteins and may participate in protecting cells against oxidative stress.

The secretory omega-class glutathione transferase OvGST3 from the human pathogenic parasite Onchocerca volvulus

Onchocerciasis or river blindness, caused by the filarial nematode Onchocerca volvulus, is the second leading cause of blindness due to infectious diseases. The protective role of the omega-class glutathione transferase 3 from O. volvulus (OvGST3) against intracellular and environmental reactive oxygen species has been described previously. In the present study, we continue our investigation of the highly stress-responsive OvGST3. Alternative splicing of two exons and one intron retention generates five different transcript isoforms that possess a spliced leader at their 5'-end, indicating that the mechanism of mature mRNA production involves alternative-, cis- and trans-splicing processes. Interestingly, the first two exons of the ovgst3 gene encode a signal peptide before sequence identity to other omega-class glutathione transferases begins. Only the recombinant expression of the isoform that encodes the longest deduced amino acid sequence (OvGST3/5) was successful, with the purified enzyme displaying modest thiol oxidoreductase activity. Significant IgG1 and IgG4 responses against recombinantly expressed OvGST3/5 were detected in sera from patients with the generalized as well as the chronic hyperreactive form of onchocerciasis, indicating exposure of the secreted protein to the human host's immune system and its immunogenicity. Immunohistological localization studies performed at light and electron microscopy levels support the extracellular localization of the protein. Intensive labeling of the OvGST3 was observed in the egg shell at the morula stage of the embryo, indicating extremely defined, stage-specific expression for a short transient period only.

Molecular mechanisms and potential clinical significance of S-glutathionylation

Protein S-glutathionylation, the reversible binding of glutathione to protein thiols (PSH), is involved in protein redox regulation, storage of glutathione, and protection of PSH from irreversible oxidation. S-Glutathionylated protein (PSSG) can result from thiol/disulfide exchange between PSH and GSSG or PSSG; direct interaction between partially oxidized PSH and GSH; reactions between PSH and S-nitrosothiols, oxidized forms of GSH, or glutathione thiyl radical. Indeed, thiol/disulfide exchange is an unlikely intracellular mechanism for S-glutathionylation, because of the redox potential of most Cys residues and the GSSG export by most cells as a protective mechanism against oxidative stress. S-Glutathionylation can be reversed, following restoration of a reducing GSH/GSSG ratio, in an enzyme-dependent or -independent manner. Currently, definite evidence of protein S-glutathionylation has been clearly demonstrated in few human diseases. In aging human lenses, protein S-glutathionylation increases; during cataractogenesis, some of lens proteins, including alpha- and beta-crystallins, form both mixed disulfides and disulfide-cross-linked aggregates, which increase with cataract severity. The correlation of lens nuclear color and opalescence intensity with protein S-glutathionylation indicates that protein-thiol mixed disulfides may play an important role in cataractogenesis and development of brunescence in human lenses. Recently, specific PSSG have been identified in the inferior parietal lobule in Alzheimer's disease. However, much investigation is needed to clarify the actual involvement of protein S-glutathionylation in many human diseases.

Cell stress induced by the parkinsonian mimetic, 6-hydroxydopamine, is concurrent with oxidation of the chaperone, ERp57, and aggresome formation

Parkinson's disease (PD) involves an irreversible degeneration of the nigrostriatal pathway. As most cases of PD are sporadic, environmental risk factors may underlie neurodegeneration in dopaminergic neurons. One such factor is 6-hydroxydopamine (6-OHDA), which is widely used as a parkinsonian mimetic. Studies have shown that 6-OHDA generates reactive oxygen species and induces cell stress, the unfolded protein response, and apoptosis. Present findings show that 6-OHDA, but not hydrogen peroxide, MPP+, or rotenone, leads to the rapid formation of high-molecular-weight species of protein disulfide isomerase-associated protein 3 (ERp57) in a dose- and time-dependent fashion. Moreover, ERp57 conjugates are blocked by N-acetylcysteine and glutathione, suggesting that they represent oxidized forms of protein. Surprisingly, conjugates are complexed with DNA, because treatment with DNase reduces their appearance. Subcellular fractionation indicates that both nuclear and mitochondrial DNA are associated with the protein. Finally, toxin-treated ERp57 rapidly forms juxtanuclear aggresome-like structures in dopaminergic cells, suggesting that ERp57 plays an early adaptive response in toxin-mediated stress. Understanding the signaling mechanisms associated with parkinsonian mimetics, as well as their temporal induction, may aid in designing better interventions in models of PD.