The chemistry of the S-nitrosoglutathione/glutathione system

Interorgan, intraorgan and interplant communication mediated by nitric oxide and related species

Plant survival to a potential plethora of diverse environmental insults is underpinned by coordinated communication amongst organs to help shape effective responses to these environmental challenges at the whole plant level. This interorgan communication is supported by a complex signal network that regulates growth, development and environmental responses. Nitric oxide (NO) has emerged as a key signalling molecule in plants. However, its potential role in interorgan communication has only recently started to come into view. Direct and indirect evidence has emerged supporting that NO and related species (S-nitrosoglutathione, nitro-linolenic acid) are mobile interorgan signals transmitting responses to stresses such as hypoxia and heat. Beyond their role as mobile signals, NO and related species are involved in mediating xylem development, thus contributing to efficient root-shoot communication. Moreover, NO and related species are regulators in intraorgan systemic defence responses aiming an effective, coordinated defence against pathogens. Beyond its in planta signalling role, NO and related species may act as ex planta signals coordinating external leaf-to-leaf, root-to-leaf but also plant-to-plant communication. Here, we discuss these exciting developments and emphasise how their manipulation may provide novel strategies for crop improvement.

Cu(II)-Organic Coordination Polymer Networks for Persistent Nitric Oxide Release in Tumor Therapy

Nitric oxide (NO) plays a key role in regulating the immune system by polarizing macrophages toward the proinflammatory M1 phenotype, which is beneficial for cancer immunotherapy. We developed a Cu-organic coordination polymer network to sustainably release NO from endogenous donors. This robust polymer network was constructed through a dual-interaction process: complexation and cross-linking. The carboxylate groups of deprotonated 4-((6-(acryloyloxy)hexyl)oxy)benzoic acid (BA) served as bidentate ligands for the formation of Cu(II) complexes. The acrylate moiety of BA anchored these complexes in the polymer network, forming a cross-linked film. Cu ions within the network catalytically promoted NO release from S-nitrosoglutathione, maintaining this release even after 90 days in a physiological environment. The released NO effectively polarized both resting (M0) and tumor-promoting (M2) macrophages to the M1 phenotype. With their demonstrated physiological stability and sustained NO release performance, BA-Cu films hold potential as anticancer patches capable of continuously promoting antitumoral macrophages.

Generation of Thiosulfate, Selenite, Dithiosulfite, Perthionitrite, Nitric Oxide, and Reactive Chalcogen Species by Binuclear Zinc(II)-Chalcogenolato/-Polychalcogenido Complexes

A comparative bioinspired reactivity study of new binuclear Zn(II) complexes featuring coordinated thiolate, selenolate, trisulfide and diselenide in relation with (i) the generation of reactive sulfur/selenium species (RSS/RSeS), (ii) the oxygen dependent oxidation and disproportionation of polysulfide (Sn2-) to produce sulfite (SO32-), thiosulfate (S2O32-) and sulfide (S2-) by sulfur oxygenase reductase (SOR), and (iii) the reaction of Sn2- with nitrite (NO2-) to generate thionitrite (SNO-), perthionitrite (SSNO-) and nitric oxide (NO), is presented. The binuclear Zn(II)-thiolate/selenolate complexes could react with elemental sulfur to generate RSS/RSeS while similar reactions involving elemental selenium could not generate RSeS. The dizinc(II)-S3 and the dizinc(II)-Se2 complexes could react with dioxygen (O2) to generate binuclear Zn(II) complexes featuring coordinated thiosulfate (S2O32-) and selenite (SeO32-), respectively. Finally, unlike the nonreactive nature of the dizinc(II)-Se2 complex toward NO2-, reaction of the dizinc(II)-S3 complex with NO2- produced a new binuclear Zn(II) complex featuring a coordinated dithiosulfite (S3O2-) along with the formation of perthionitrite (SSNO-), of which the latter subsequently produced nitric oxide (NO) and S42-. The present work, thus, demonstrates the comparative reactivity of a series of binuclear Zn(II)-chalcogenolato/-polychalcogenido complexes for the generation of S2O32-, SeO32-, S3O2-, SSNO-, NO and RSS/RSeS.

Small molecule MarR modulators potentiate metronidazole antibiotic activity in aerobic E. coli by inducing activation by the nitroreductase NfsA

Antibiotic-resistant Enterobacterales pose a major threat to healthcare systems worldwide, necessitating the development of novel strategies to fight such hard-to-kill bacteria. One potential approach is to develop molecules that force bacteria to hyper-activate prodrug antibiotics, thus rendering them more effective. In the present work, we aimed to obtain proof-of-concept data to support that small molecules targeting transcriptional regulators can potentiate the antibiotic activity of the prodrug metronidazole (MTZ) against Escherichia coli under aerobic conditions. By screening a chemical library of small molecules, a series of structurally related molecules were identified that had little inherent antibiotic activity but showed substantial activity in combination with ineffective concentrations of MTZ. Transcriptome analyses, functional genetics, thermal shift assays, and electrophoretic mobility shift assays were then used to demonstrate that these MTZ boosters target the transcriptional repressor MarR, resulting in the upregulation of the marRAB operon and its downstream MarA regulon. The associated upregulation of the flavin-containing nitroreductase, NfsA, was then shown to be critical for the booster-mediated potentiation of MTZ antibiotic activity. Transcriptomic studies, biochemical assays, and electron paramagnetic resonance measurements were then used to show that under aerobic conditions, NfsA catalyzed 1-electron reduction of MTZ to the MTZ radical anion which in turn induced lethal DNA damage in E. coli. This work reports the first example of prodrug boosting in Enterobacterales by transcriptional modulators and highlights that MTZ antibiotic activity can be chemically induced under anaerobic growth conditions.

The C-terminal selenenylsulfide of extracellular/non-reduced thioredoxin reductase endows this protein with selectivity to small-molecule electrophilic reagents under oxidative conditions

Mammalian cytosolic thioredoxin reductase (TrxR1) serves as an antioxidant protein by transferring electrons from NADPH to various substrates. The action of TrxR1 is achieved via reversible changes between NADPH-reduced and non-reduced forms, which involves C-terminal selenolthiol/selenenylsulfide exchanges. TrxR1 may be released into extracellular environment, where TrxR1 is present mainly in the non-reduced form with active-site disulfide and selenenylsulfide bonds. The relationships between extracellular TrxR1 and tumor metastasis or cellular signaling have been discovered, but there are few reports on small-molecule compounds in targeted the non-reduced form of TrxR1. Using eight types of small-molecule thiol-reactive reagents as electrophilic models, we report that the selenenylsulfide bond in the non-reduced form of TrxR1 functions as a selector for the thiol-reactive reagents at pH 7.5. The non-reduced form of TrxR1 is resistant to hydrogen peroxide/oxidized glutathione, but is sensitive to certain electrophilic reagents in different ways. With 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB) and S-nitrosoglutathione (GSNO), the polarized selenenylsulfide bond breaks, and selenolate anion donates electron to the dynamic covalent bond in DTNB or GSNO, forming TNB-S-Se-TrxR1 complex or ON-Se-TrxR1 complex. The both complexes lose the ability to transfer electrons from NADPH to substrate. For diamide, the non-reduced TrxR1 actually prevents irreversible damage by this oxidant. This is consistent with the regained activity of TrxR1 through removal of diamide via dialysis. Diamide shows effective in the presence of human cytosolic thioredoxin (hTrx1), Cys residue(s) of which is/are preferentially affected by diamide to yield disulfide, hTrx1 dimer and the mixed disulfide between TrxR1-Cys497/Sec498 and hTrx1-Cys73. In human serum samples, the non-reduced form of TrxR1 exists as dithiothreitol-reducible polymer/complexes, which might protect the non-reduced TrxR1 from inactivation by certain electrophilic reagents under oxidative conditions, because cleavage of these disulfides can lead to regain the activity of TrxR1. The details of the selective response of the selenenylsulfide bond to electrophilic reagents may provide new information for designing novel small-molecule inhibitors (drugs) in targeted extracellular/non-reduced TrxR1.

Attenuation of protein arginine dimethylation via S-nitrosylation of protein arginine methyltransferase 1

Upregulation of nitric oxide (NO) production contributes to the pathogenesis of numerous diseases via S-nitrosylation, a post-translational modification of proteins. This process occurs due to the oxidative reaction between NO and a cysteine thiol group; however, the extent of this reaction remains unknown. S-Nitrosylation of PRMT1, a major asymmetric arginine methyltransferase of histones and numerous RNA metabolic proteins, was induced by NO donor treatment. We found that nitrosative stress leads to S-nitrosylation of cysteine 119, located near the active site, and attenuates the enzymatic activity of PRMT1. Interestingly, RNA sequencing analysis revealed similarities in the changes in expression elicited by NO and PRMT1 inhibitors or knockdown. A comprehensive search for PRMT1 substrates using the proximity-dependent biotin identification method highlighted many known and new substrates, including RNA-metabolizing enzymes. To validate this result, we selected the RNA helicase DDX3 and demonstrated that arginine methylation of DDX3 is induced by PRMT1 and attenuated by NO treatment. Our results suggest the existence of a novel regulatory system associated with transcription and RNA metabolism via protein S-nitrosylation.

Advances in nitric oxide regulators for the treatment of ischemic stroke

Ischemic stroke (IS) is a life-threatening disease worldwide. Nitric oxide (NO) derived from l-arginine catalyzed by NO synthase (NOS) is closely associated with IS. Three isomers of NOS (nNOS, eNOS and iNOS) produce different concentrations of NO, resulting in quite unlike effects during IS. Of them, n/iNOSs generate high levels of NO, detrimental to brain by causing nerve cell apoptosis and/or necrosis, whereas eNOS releases small amounts of NO, beneficial to the brain via increasing cerebral blood flow and improving nerve function. As a result, a large variety of NO regulators (NO donors or n/iNOS inhibitors) have been developed for fighting IS. Regrettably, up to now, no review systematically introduces the progresses in this area. This article first outlines dynamic variation rule of NOS/NO in IS, subsequently highlights advances in NO regulators against IS, and finally presents perspectives based on concentration-, site- and timing-effects of NO production to promote this field forward.

Thiol-catalyzed formation of NO-ferroheme regulates intravascular NO signaling

Nitric oxide (NO) is an endogenously produced signaling molecule that regulates blood flow and platelet activation. However, intracellular and intravascular diffusion of NO are limited by scavenging reactions with several hemoproteins, raising questions as to how free NO can signal in hemoprotein-rich environments. We explore the hypothesis that NO can be stabilized as a labile ferrous heme-nitrosyl complex (Fe2+-NO, NO-ferroheme). We observe a reaction between NO, labile ferric heme (Fe3+) and reduced thiols to yield NO-ferroheme and a thiyl radical. This thiol-catalyzed reductive nitrosylation occurs when heme is solubilized in lipophilic environments such as red blood cell membranes or bound to serum albumin. The resulting NO-ferroheme resists oxidative inactivation, is soluble in cell membranes and is transported intravascularly by albumin to promote potent vasodilation. We therefore provide an alternative route for NO delivery from erythrocytes and blood via transfer of NO-ferroheme and activation of apo-soluble guanylyl cyclase.

Pyruvate dehydrogenase operates as an intramolecular nitroxyl generator during macrophage metabolic reprogramming

M1 macrophages enter a glycolytic state when endogenous nitric oxide (NO) reprograms mitochondrial metabolism by limiting aconitase 2 and pyruvate dehydrogenase (PDH) activity. Here, we provide evidence that NO targets the PDH complex by using lipoate to generate nitroxyl (HNO). PDH E2-associated lipoate is modified in NO-rich macrophages while the PDH E3 enzyme, also known as dihydrolipoamide dehydrogenase (DLD), is irreversibly inhibited. Mechanistically, we show that lipoate facilitates NO-mediated production of HNO, which interacts with thiols forming irreversible modifications including sulfinamide. In addition, we reveal a macrophage signature of proteins with reduction-resistant modifications, including in DLD, and identify potential HNO targets. Consistently, DLD enzyme is modified in an HNO-dependent manner at Cys477 and Cys484, and molecular modeling and mutagenesis show these modifications impair the formation of DLD homodimers. In conclusion, our work demonstrates that HNO is produced physiologically. Moreover, the production of HNO is dependent on the lipoate-rich PDH complex facilitating irreversible modifications that are critical to NO-dependent metabolic rewiring.

Near-infrared light-responsive Nitric oxide microcarrier for multimodal tumor therapy

Nitric oxide (NO) has shown great potential in tumor therapy, and the development of a platform for precise and controllable NO release still needs to be explored. Herein, a microfluidic electrospray strategy is proposed for the fabrication of hydrogel microspheres encapsulating NO donors (S-nitrosoglutathione, GSNO) together with black phosphorus (BP) and chemotherapeutic doxorubicin (DOX) as microcarriers for tumor therapy. Based on the excellent photothermal property of BP and thermal sensitivity of GSNO, the microcarriers exhibit a near-infrared light (NIR)-responsive NO release behavior. Besides, the photothermal performance of the microcarriers accelerates the release of DOX. All these contribute to the excellent tumor-killing effect of the microcarriers by combining multiple therapeutic strategies including NO therapy, photothermal therapy, and chemotherapy. Moreover, it was demonstrated that the NIR-responsive NO delivery microcarriers could significantly inhibit tumor growth without apparent side effects in vivo. Therefore, it is believed that the novel NIR-responsive NO microcarriers are promising candidates in clinical tumor therapy applications.

The chemistry of hydropersulfides (RSSH) as related to possible physiological functions

Hydropersulfides (RSSH) are oxidized thiol (RSH) derivatives that have been shown to be biologically prevalent with likely important functions (along with other polysulfur compounds). The functional utility of RSSH can be gleaned from their unique chemical properties. That is, RSSH possess chemical reactivity not present in other biologically relevant sulfur species that should allow them to be used in specific ways in biology as effector/signaling molecules. For example, compared to RSH, RSSH are considered to be superior nucleophiles, reductants and metal ligands. Moreover, unlike RSH, RSSH can be either reductants/nucleophiles or oxidants/electrophiles depending on the protonated state. It has also become clear that studies related to the chemical biology and physiology of hydrogen suflide (H₂S) must also consider the effects of RSSH (and related polysulfur species) as they are biochemically linked. Herein is a discussion of the relevant chemistry of RSSH that can serve as a basis for understanding how RSSH can be used by cells to, for example, combat stresses and used in signaling. Also, discussed are some current experimental studies regarding the biological activity of RSSH that can be explained by their chemical properties.

Nitric oxide-driven modifications of lipoic arm inhibit α-ketoacid dehydrogenases

Pyruvate dehydrogenase complex (PDHC) and oxoglutarate dehydrogenase complex (OGDC), which belong to the mitochondrial α-ketoacid dehydrogenase family, play crucial roles in cellular metabolism. These multi-subunit enzyme complexes use lipoic arms covalently attached to their E2 subunits to transfer an acyl group to coenzyme A (CoA). Here, we report a novel mechanism capable of substantially inhibiting PDHC and OGDC: reactive nitrogen species (RNS) can covalently modify the thiols on their lipoic arms, generating a series of adducts that block catalytic activity. S-Nitroso-CoA, a product between RNS and the E2 subunit's natural substrate, CoA, can efficiently deliver these modifications onto the lipoic arm. We found RNS-mediated inhibition of PDHC and OGDC occurs during classical macrophage activation, driving significant rewiring of cellular metabolism over time. This work provides a new mechanistic link between RNS and mitochondrial metabolism with potential relevance for numerous physiological and pathological conditions in which RNS accumulate.

Microneedles loaded with glutathione-scavenging composites for nitric oxide enhanced photodynamic therapy of melanoma

Photodynamic therapy (PDT) represents an attractive promising route for melanoma treatment. However, its therapeutic efficacy is compromised by inefficient drug delivery and high glutathione (GSH) levels in cancer cells. To overcome these challenges, microneedles (MNs) system loaded with GSH-scavenging nanocomposites was presented for nitric oxide (NO) enhanced PDT. The nanocomposites consisted of S-nitroso-N-acrylate penicillamine (SNAP; a NO donor) grafted fourth-generation polyamide amine dendrimer (G4) and chlorin e6 (Ce6). Upon local insertion of polyvinylpyrrolidone MNs, G4-SNAP/Ce6 composites were fast delivered and significantly amplified the therapeutic effects during PDT, via GSH depletion and reactive nitrogen species generation. Even with a single administration and low power light exposure, MNs with G4-SNAP/Ce6 effectively halt the tumor progression. The system demonstrated better cancer ablation efficacy than Ce6 alone toward melanoma. The strategy may inspire new ideas for future PDT-related therapy for skin tumors.

Hyperbaric oxygenation applied before or after mild or hard stress: effects on the redox state in the muscle tissue

The mechanism is unclear for the reported protective effect of hyperbaric oxygen preconditioning against oxidative stress in tissues, and the distinct effects of hyperbaric oxygen applied after stress. The trained mice were divided into three groups: the control, hyperbaric oxygenation preconditioning, and hyperbaric oxygenation applied after mild (fasting) or hard (prolonged exercise) stress. After preconditioning, we observed a decrease in basal levels of nitric oxide, tetrahydrobiopterin, and catalase despite the drastic increase in inducible and endothelial nitric oxide synthases. Moreover, the basal levels of glutathione, related enzymes, and nitrosative stress only increased in the preconditioning group. The control and preconditioning groups showed a similar mild stress response of the endothelial and neuronal nitric oxide synthases. At the same time, the activity of all nitric oxide synthase, glutathione (GSH) in muscle, declined in the experimental groups but increased in control during hard stress. The results suggested that hyperbaric oxygen preconditioning provoked uncoupling of nitric oxide synthases and the elevated levels of GSH in muscle during this study, while hyperbaric oxygen applied after stress showed a lower level of GSH but higher recovery post-exercise levels in the majority of antioxidant enzymes. We discuss the possible mechanisms of the redox response and the role of the nitric oxide in this process.

S-glutathionylation of fructose-1,6-bisphosphate aldolase confers nitrosative stress tolerance on yeast cells via a metabolic switch

Nitric oxide as a signaling molecule exerts cytotoxicity known as nitrosative stress at its excess concentrations. In the yeast Saccharomyces cerevisiae, the cellular responses to nitrosative stress and their molecular mechanisms are not fully understood. Here, focusing on the posttranslational modifications that are associated with nitrosative stress response, we show that nitrosative stress increased the protein S-glutathionylation level in yeast cells. Our proteomic and immunochemical analyses demonstrated that the fructose-1,6-bisphosphate aldolase Fba1 underwent S-glutathionylation at Cys112 in response to nitrosative stress. The enzyme assay using a recombinant Fba1 demonstrated that S-glutathionylation at Cys112 inhibited the Fba1 activity. Moreover, we revealed that the cytosolic glutaredoxin Grx1 reduced S-glutathionylation of Fba1 and then recovered its activity. The intracellular contents of fructose-1,6-bisphosphate and 6-phosphogluconate, which are a substrate of Fba1 and an intermediate of the pentose phosphate pathway (PPP), respectively, were increased in response to nitrosative stress, suggesting that the metabolic flow was switched from glycolysis to PPP. The cellular level of NADPH, which is produced in PPP and functions as a reducing force for nitric oxide detoxifying enzymes, was also elevated under nitrosative stress conditions, but this increase was canceled by the amino acid substitution of Cys112 to Ser in Fba1. Furthermore, the viability of yeast cells expressing Cys112Ser-Fba1 was significantly lower than that of the wild-type cells under nitrosative stress conditions. These results indicate that the inhibition of Fba1 by its S-glutathionylation changes metabolism from glycolysis to PPP to increase NADPH production, leading to nitrosative stress tolerance in yeast cells.

S-Nitroso-l-cysteine and ventilatory drive: A pediatric perspective

Though endogenous S-nitroso-l-cysteine (l-CSNO) signaling at the level of the carotid body increases minute ventilation (v̇E ), neither the background data nor the potential clinical relevance are well-understood by pulmonologists in general, or by pediatric pulmonologists in particular. Here, we first review how regulation of the synthesis, activation, transmembrane transport, target interaction, and degradation of l-CSNO can affect the ventilatory drive. In particular, we review l-CSNO formation by hemoglobin R to T conformational change and by nitric oxide (NO) synthases (NOS), and the downstream effects on v̇E through interaction with voltage-gated K+ (Kv) channel proteins and other targets in the peripheral and central nervous systems. We will review how these effects are independent of-and, in fact may be opposite to-those of NO. Next, we will review evidence that specific elements of this pathway may underlie disorders of respiratory control in childhood. Finally, we will review the potential clinical implications of this pathway in the development of respiratory stimulants, with a particular focus on potential pediatric applications.

Nanostructured Organosilica Nitric Oxide Donors Intrinsically Regulate Macrophage Polarization with Antitumor Effect

Nitric oxide (NO) has many important biological functions; however, it has been a long-standing challenge to utilize the exogenous NO donor itself in the activation of macrophages for cancer immunotherapy. Herein, we report the synthesis of a nanoparticle-based NO delivery platform with a rational design for effective NO delivery and macrophage activation. S-Nitrosothiol (SNO) modified organosilica nanoparticles with a tetrasulfide-containing composition produced a higher level of intracellular NO than their bare silica counterparts in macrophages. Enhanced intracellular delivery of NO resulted in mitochondrial dysfunction and disruption of the tricarboxylic acid cycle, leading to macrophage activation and delayed tumor growth. This study provides insights on intracellularly delivered NO for regulating the polarization of macrophages and cancer immunotherapy.

S-Nitrosylation of OTUB1 Alters Its Stability and Ubc13 Binding

S-Nitrosylation is a reversible post-translational modification that regulates protein function involving the covalent attachment of the nitric oxide (NO) moiety to sulfhydryl residues of the protein. It is an important regulator in the cell signaling process under physiological conditions. However, the release of an excess amount of NO due to dysregulated NOS machinery causes aberrant S-nitrosylation of proteins, which affects protein folding, localization, and activity. Here, we have shown that OTUB1, a deubiquitinating enzyme, undergoes S-nitrosylation under redox stress conditions in vivo and in vitro. Previously, we have shown that OTUB1 forms an amyloid-like structure that promotes phosphorylation of α-synuclein and neuronal toxicity. However, the mechanistic insight into OTUB1 aggregation remains elusive. Here, we identified that OTUB1 undergoes S-nitrosylation in SH-SY5Y neuroblastoma cells under rotenone-induced stress, as well as excitotoxic conditions, and in rotenone-treated mouse brains. The in vitro S-nitrosylation of OTUB1 followed by mass-spectrometry analysis has identified cysteine-23 and cysteine-91 as S-nitrosylation sites. S-Nitrosylated OTUB1 (SNO-OTUB1) diminished its catalytic activity, impaired its native structure, promoted amyloid-like aggregation, and compromised its binding with Ubc13. Thus, our results demonstrated that nitrosylation of OTUB1 might play a crucial role in regulating the ubiquitin signaling and Parkinson's disease pathology.

Protein S-Nitrosylation Regulates Postmortem Beef Apoptosis through the Intrinsic Mitochondrial Pathway

The objective of the present study was to investigate the regulatory mechanism of protein S-nitrosylation on early postmortem beef muscle apoptosis. Beef semimembranosus (SM) muscles at 45 min postmortem were treated with nitric oxide (NO) donor, control (NaCl solution), or nitric oxide synthase (NOS) inhibitor for 24 h at 4 °C. Bcl-2 expression and mitochondrial membrane potential were significantly increased by the NO donor treatment at 6 h postmortem, while the NOS inhibitor group exhibited a lower Bcl-2 level and mitochondrial membrane potential in comparison with the control (P < 0.05). The cytochrome c expression analysis highlighted that NO donor incubation repressed cytochrome c release from mitochondria to the cytoplasm. Further, S-nitrosylation levels of caspase-3 and caspase-9 were elevated after incubation with the NO donor (P < 0.05), leading to decreased caspase-3 and caspase-9 activities (P < 0.05). The aforementioned findings imply that protein S-nitrosylation mediates postmortem apoptosis of beef SM through the mitochondrial apoptotic pathway.

Micelles Based on Lysine, Histidine, or Arginine: Designing Structures for Enhanced Drug Delivery

Natural amino acids and their derivatives are excellent building blocks of polymers for various biomedical applications owing to the non-toxicity, biocompatibility, and ease of multifunctionalization. In the present review, we summarized the common approaches to designing and constructing functional polymeric micelles based on basic amino acids including lysine, histidine, and arginine and highlighted their applications as drug carriers for cancer therapy. Different polypeptide architectures including linear polypeptides and dendrimers were developed for efficient drug loading and delivery. Besides, polylysine- and polyhistidine-based micelles could enable pH-responsive drug release, and polyarginine can realize enhanced membrane penetration and gas therapy by generating metabolites of nitric oxide (NO). It is worth mentioning that according to the structural or functional characteristics of basic amino acids and their derivatives, key points for designing functional micelles with excellent drug delivery efficiency are importantly elaborated in order to pave the way for exploring micelles based on basic amino acids.

Sodium borohydride and thiol mediated nitrite release from nitroaromatic antibiotics

Nitroaromatic antibiotics are used to treat a variety of bacterial and parasitic infections. These prodrugs require reductive bioactivation for activity, which provides a pathway for the release of nitrogen oxide species such as nitric oxide, nitrite, and/or nitroxyl. Using sodium borohydride and 2-aminoethanol as model reductants, this work examines release of nitrogen oxide species from various nitroaromatic compounds through several characterization methods. Specifically, 4- and 5-nitroimidazoles reproducibly generate higher amounts of nitrite (not nitric oxide or nitroxyl) than 2-nitroimidazoles during the reaction of model hydride donors or thiols. Mass spectrometric analysis shows clean formation of products resulting from nucleophile addition and nitro group loss. 2-Nitrofurans generate nitrite upon addition of sodium borohydride or 2-aminoethanethiol, but these complex reactions do not produce clean organic products. A mechanism that includes nucleophile addition to the carbon βto the nitro group to generate a nitronate anion followed by protonation and nitrous acid elimination explains the observed products and labeling studies. These systematic studies give a better understanding of the release mechanisms of nitrogen oxide species from these compounds allowing for the design of more efficient therapeutics.

Stability of S-nitrosothiols and S-nitrosylated proteins: A struggle for cellular existence!

Nitric oxide is a well-known gasotransmitter molecule that covalently docks to sulfhydryl groups of proteins resulting in S-nitrosylation of proteins and nonprotein thiols that serve a variety of cellular processes including cGMP signaling, vasodilatation, neurotransmission, ion-channel modulation, and cardiac signaling. S-nitrosylation is an indispensable modification like phosphorylation that directly regulates the functionality of numerous proteins. However, recently there has been a controversy over the stability of S-nitrosylated proteins (PSNOs) within the cell. It has been argued that PSNOs formed within the cell is a transient intermediate step to more stable disulfide formation and disulfides are the predominant end effector modifications in NO-mediated signaling. The present article accumulates state-of-the-art evidence from numerous research that strongly supports the very existence of PSNOs within the cell and attempts to put an end to the controversy. This review illustrates critical points including comparative bond dissociation energies of S-NO bond, the half-life of S-nitrosothiols and PSNOs, cellular concentrations of PSNOs, X ray crystallographic studies on PSNOs, and stability of PSNOs at physiological concentration of antioxidants. These logical evidence cumulatively support the endogenous stability and inevitable existence of PSNOs/RSNOs within the cell that directly regulate the functionality of proteins and provide valuable insight into understanding stable S-nitrosylation mediated cell signaling.

Protein Transnitrosylation Signaling Networks Contribute to Inflammaging and Neurodegenerative Disorders

Significance: Physiological concentrations of nitric oxide (NO^•) and related reactive nitrogen species (RNS) mediate multiple signaling pathways in the nervous system. During inflammaging (chronic low-grade inflammation associated with aging) and in neurodegenerative diseases, excessive RNS contribute to synaptic and neuronal loss. "NO signaling" in both health and disease is largely mediated through protein S-nitrosylation (SNO), a redox-based posttranslational modification with "NO" (possibly in the form of nitrosonium cation [NO⁺]) reacting with cysteine thiol (or, more properly, thiolate anion [R-S^-]). Recent Advances: Emerging evidence suggests that S-nitrosylation occurs predominantly via transnitros(yl)ation. Mechanistically, the reaction involves thiolate anion, as a nucleophile, performing a reversible nucleophilic attack on a nitroso nitrogen to form an SNO-protein adduct. Prior studies identified transnitrosylation reactions between glyceraldehyde-3-phosphate dehydrogenase (GAPDH)-nuclear proteins, thioredoxin-caspase-3, and X-linked inhibitor of apoptosis (XIAP)-caspase-3. Recently, we discovered that enzymes previously thought to act in completely disparate biochemical pathways can transnitrosylate one another during inflammaging in an unexpected manner to mediate neurodegeneration. Accordingly, we reported a concerted tricomponent transnitrosylation network from Uch-L1-to-Cdk5-to-Drp1 that mediates synaptic damage in Alzheimer's disease. Critical Issues: Transnitrosylation represents a critical chemical mechanism for transduction of redox-mediated events to distinct subsets of proteins. Although thousands of thiol-containing proteins undergo S-nitrosylation, how transnitrosylation regulates a myriad of neuronal attributes is just now being uncovered. In this review, we highlight recent progress in the study of the chemical biology of transnitrosylation between proteins as a mechanism of disease. Future Directions: We discuss future areas of study of protein transnitrosylation that link our understanding of aging, inflammation, and neurodegenerative diseases. Antioxid. Redox Signal. 35, 531-550.

An intracellular assay for activity screening and characterization of glutathione-dependent oxidoreductases

The thioredoxin fold superfamily is highly diverse and contains many enzymatically active glutathione-dependent thiol-disulfide oxidoreductases, for example glutaredoxins and protein disulfide isomerases. However, many thioredoxin fold proteins remain completely uncharacterized, their cellular function is unknown, and it is unclear if they have a redox-dependent enzymatic activity with glutathione or not. Investigation of enzymatic activity traditionally involved time-consuming in vitro characterization of recombinant proteins, limiting the capacity to study novel mechanisms and structure-function relationships. To accelerate our investigation of glutathione-dependent oxidoreductases, we have developed a high-throughput and semi-quantitative assay in yeast. We combined overexpression of the glutathione transporter OPT1 with genetic fusion constructs between glutathione-dependent oxidoreductases and redox-sensitive green fluorescent protein 2 (roGFP2) to allow the rapid characterization of enzymatic activity with physiological substrates. We show that the kinetics of roGFP2 oxidation by glutathione disulfide correlate well with the in vitro-determined activity of the genetically fused glutaredoxins or mutants thereof. Our assay thus allows direct screening of glutaredoxin activity and rapid investigation of structure-function relationships. We also demonstrate that our assay can be used to monitor roGFP2 oxidation by S-nitrosoglutathione (GSNO). We show that glutaredoxins efficiently catalyze oxidation of roGFP2 by GSNO in both live yeast cells and in vitro. In summary, we have established a novel assay for activity screening and characterization of glutathione-dependent oxidoreductases.

Nanochemistry Modulates Intracellular Decomposition Routes of S-Nitrosothiol Modified Silica-Based Nanoparticles

Cellular delivery of nitric oxide (NO) using NO donor moieties such as S-nitrosothiol (SNO) is of great interest for various applications. However, understandings of the intracellular decomposition routes of SNO toward either NO or ammonia (NH₃ ) production are surprisingly scarce. Herein, the first report of SNO modified mesoporous organosilica nanoparticles with tetrasulfide bonds for enhanced intracellular NO delivery, ≈10 times higher than a commercial NO donor, is presented. The tetrasulfide chemistry modulates the SNO decomposition by shifting from NH₃ to NO production in glutathione rich cancer cells. This study provides a new strategy to control the NO level in biological systems.

Dual-signaling amplification strategy for glutathione sensing by using single gold nanoelectrodes

A new nanosensor for glutathione (GSH) detection by use of single nanoelectrodes has been developed through a dual-signaling ratiometric amplification strategy. Ag nanoparticles (Ag NPs) metalized DNA1 was modified on an Au nanoelectrode surface. Due to the strong affinity between Ag NP and GSH, Ag NPs could be removed by the addition of GSH. The remaining metalized DNA1 could hardly form a double strand, while the de-metalized DNA1 could hybrid with DNA2 and DNA3 to form a complex structure to adsorb methylene blue (MB), and then the electrochemical signal of differential pulse voltammetry (DPV) from MB oxidation could be observed. With the addition of GSH, the peak current of MB oxidation at about -0.27 V (I_MB) increases, while the signal of Ag oxidation at about 0.1 V (I_Ag) decreases. It was found that there had a linear relationship between the ratio of dual-signal (I_MB/I_Ag) and the GSH concentrations, which could be used to detect GSH. The ratiometric nanosensor is label-free, easy to operate, and can eliminate inherent system errors. Considering the advantages of nanoelectrodes, such as low IR drop, fast response, and small overall dimension, this developed nanosensor can be used for GSH detection living systems (e.g., cell lysate).

Nitric Oxide-Releasing Insert for Disinfecting the Hub Region of Tunnel Dialysis Catheters

The use of tunneled dialysis catheters (TDCs) for patients in need of hemodialysis treatments (HDs) causes a significant number of bloodstream infections (BSIs), with very few viable preventative/treatment methods. Use of antibiotics is relatively ineffective due to the development of multidrug-resistant bacterial strains and the inability to penetrate bacterial biofilms. Nitric oxide (NO) is an endogenous gas molecule that has broad-spectrum antimicrobial/antibiofilm activity. In this study, the potential of creating a NO-releasing insert device that is attached onto the hub region cap of TDCs and locally releases NO within the TDC hub is evaluated for its antimicrobial/antibiofilm effectiveness. The NO-releasing insert contains the natural NO donor S-nitrosoglutathione (GSNO), along with zinc oxide (ZnO) nanoparticles to accelerate NO release from the GSNO, within a short silicone tube that is sealed at both ends and attached to the catheter cap. An in vitro 3-d-long antimicrobial study using catheter hubs yielded >6.6 log reductions of both Pseudomonas aeruginosa and Staphylococcus aureus for the NO-releasing insert device compared to controls. Two 14-d-long sheep studies demonstrated that the NO-releasing insert devices are exceptionally potent at preventing bacteria/biofilm growth on the inner lumen walls of TDCs compared to controls that have no preventative treatment devices as well as implanted TDCs that have commercially available chlorhexidine-treated insert devices placed within the hub regions.

Protective Mechanism and Treatment of Neurogenesis in Cerebral Ischemia

Stroke is the fifth leading cause of death worldwide and is a main cause of disability in adults. Neither currently marketed drugs nor commonly used treatments can promote nerve repair and neurogenesis after stroke, and the repair of neurons damaged by ischemia has become a research focus. This article reviews several possible mechanisms of stroke and neurogenesis and introduces novel neurogenic agents (fibroblast growth factors, brain-derived neurotrophic factor, purine nucleosides, resveratrol, S-nitrosoglutathione, osteopontin, etc.) as well as other treatments that have shown neuroprotective or neurogenesis-promoting effects.

ATP Suppression by pH-Activated Mitochondria-Targeted Delivery of Nitric Oxide Nanoplatform for Drug Resistance Reversal and Metastasis Inhibition

Mitochondria, which are important mediators for cancer initiation, growth, metastasis, and drug resistance, have been considered as a major target in cancer therapy. Herein, an acid-activated mitochondria-targeted drug nanocarrier is constructed for precise delivery of nitric oxide (NO) as an adenosine triphosphate (ATP) suppressor to amplify the therapeutic efficacy in cancer treatments. By combining α-cyclodextrin (α-CD) and acid-cleavable dimethylmaleic anhydride modified PEG conjugated mitochondria-targeting peptide, the nanocarrier shows prolonged blood circulation time and enhanced cellular uptake together with selectively restoring mitochondria-targeting capability under tumor extracellular pH (6.5). Such specific mitochondria-targeted delivery of NO proves crucial in inducing mitochondria dysfunction through facilitating mitochondrial membrane permeabilization and downregulating ATP level, which can inhibit P-glycoprotein-related bioactivities and formation of tumor-derived microvesicles to combat drug resistance and cancer metastasis. Therefore, this pioneering acid-activated mitochondria-targeted NO nanocarrier is supposed to be a malignant tumor opponent and may provide insights for diverse NO-relevant cancer treatments.

The role of glutathione and glutathione peroxidase in regulating cellular level of reactive oxygen and nitrogen species

Glutathione (GSH) and GSH/glutathione peroxidase (GPX) enzyme system is essential for normal intracellular homeostasis and gets disturbed under pathophysiologic conditions including endothelial dysfunction. Overproduction of reactive oxidative species (ROS) and reactive nitrogen species (RNS) including superoxide (O₂^•-), and the loss of nitric oxide (NO) bioavailability is a characteristic of endothelial dysfunction. The GSH/GPX system play an important role in eliminating ROS/RNS. Studies have provided important information regarding the interactions of ROS/RNS with the GSH/GPX in biological systems; however, it is not clear how this cross talk affect these reactive species and GSH/GPX enzyme system, under physiologic and oxidative/nitrosative stress conditions. In the present study, we developed a detailed endothelial cell kinetic model to understand the relationship amongst the key enzyme systems including GSH, GPX, peroxiredoxin (Prx) and reactive species, such as hydrogen peroxide (H₂O₂), peroxynitrite (ONOO^-), and dinitrogen trioxide (N₂O₃). Our simulation results showed that the alterations in the generation rates of O₂^•- and NO led to the formation of a wide range of ROS and RNS. Simulations performed by varying the ratio of O₂^•- to NO generation rates as well as GSH and GPX concentrations showed that the GPX reducing capacity was dependent on GSH availability, level of oxidative/nitrosative stress, and can be attributed to N₂O₃ levels, but not to H₂O₂ and ONOO^-. Our results showed that N₂O₃ mediated switch-like depletion in GSH and the incorporation of Prx had no considerable effect on the ROS/RNS species other than ONOO^- and H₂O₂. The analysis presented in this study will improve our understanding of vascular diseases in which the levels and oxidation states of GSH, GPX and/or Prx are significantly altered and pharmacological interventions show limited benefits.

Glutathione in Brain: Overview of Its Conformations, Functions, Biochemical Characteristics, Quantitation and Potential Therapeutic Role in Brain Disorders

Glutathione (GSH) is an important antioxidant found abundantly and synthesized intracellularly in the cytosol in a tightly regulated fashion. It has diverse physiological functions, including protection against reactive oxygen species and nitrogen species, antioxidant defense as well as maintenance of cellular thiol status. The human brain due to the high oxygen consumption is extremely susceptible to the generation of reactive oxygen species. GSH plays a paramount role in brain antioxidant defense, maintaining redox homeostasis. The depletion of brain GSH has also been observed from both autopsies as well as in vivo MRS studies with aging and varied neurological disorders (Alzheimer's disease, Parkinson's disease, etc.). Therefore, GSH enrichment using supplementation is a promising avenue in the therapeutic development for these neurological disorders. This review will enrich the information on the importance of GSH synthesis, metabolism, functions, compartmentation and inter-organ transport, structural conformations and its quantitation via different techniques. The transportation of GSH in the brain via different interventional routes and its potential role in the development of therapeutic strategies for various brain disorders is also addressed. Very recent study found significant improvement of behavioral deficits including cognitive decline, depressive-like behaviors, in APP (NL-G-F/NL-G-FG-) mice due to oral GSH administration. This animal model study put an emergent need to complete GSH supplementation trial in MCI and AD patients for cognitive improvement as proposed earlier.

Nitric oxide stimulates a PKC-Src-Akt signaling axis which increases human immunodeficiency virus type 1 replication in human T lymphocytes

Human immunodeficiency virus (HIV) infections are typically accompanied by high levels of secreted inflammatory cytokines and generation of high levels of reactive oxygen species (ROS). To elucidate how HIV-1 alters the cellular redox environment during viral replication, we used human HIV-1 infected CD4⁺T lymphocytes and uninfected cells as controls. ROS and nitric oxide (NO) generation, antioxidant enzyme activity, protein phosphorylation, and viral and proviral loads were measured at different times (2-36 h post-infection) in the presence and absence of the NO donor S-nitroso-N-acetylpenicillamine (SNAP). HIV-1 infection increased ROS generation and decreased intracellular NO content. Upon infection, we observed increases in copper/zinc superoxide dismutase (SOD1) and glutathione peroxidase (GPx) activities, and a marked decrease in glutathione (GSH) concentration. Exposure of HIV-1 infected CD4⁺T lymphocytes to SNAP resulted in an increasingly oxidizing intracellular environment, associated with tyrosine nitration and SOD1 inhibition. In addition, SNAP treatment promoted phosphorylation and activation of the host's signaling proteins, PKC, Src kinase and Akt. Inhibition of PKC leads to inhibition of Src kinase strongly suggesting that PKC is the upstream element in this signaling cascade. Changes in the intracellular redox environment after SNAP treatment had an effect on HIV-1 replication as reflected by increases in proviral and viral loads. In the absence or presence of SNAP, we observed a decrease in viral load in infected CD4⁺T lymphocytes pre-incubated with the PKC inhibitor GF109203X. In conclusion, oxidative/nitrosative stress conditions derived from exposure of HIV-1-infected CD4⁺T lymphocytes to an exogenous NO source trigger a signaling cascade involving PKC, Src kinase and Akt. Activation of this signaling cascade appears to be critical to the establishment of HIV-1 infection.

Characterization of Polysulfides, Polysulfanes, and Other Unique Species in the Reaction between GSNO and H2S

Glutathione-based products, GS_nX, of the reaction of hydrogen sulfide, H₂S, S-nitroso glutathione, and GSNO, at varied stoichiometries have been analyzed by liquid chromatography high-resolution mass spectrometry (LC-HRMS) and chemical trapping experiments. A wide variety of glutathione-based species with catenated sulfur chains have been identified including sulfanes (GSS_nG), sulfides (GSS_nH), and sulfenic acids (GS_nOH); sulfinic (GS_nO₂H) and sulfonic (GS_nO₃H) acids are also seen in reactions exposed to air. The presence of each species of GS_nX within the original reaction mixtures was confirmed using Single Ion Chromatograms (SICs), to demonstrate the separation on the LC column, and given approximate quantification by the peak area of the SIC. Further, confirmation for different GS_nX families was obtained by trapping with species-specific reagents. Several unique GS_nX families have been characterized, including bridging mixed di- and tetra-valent polysulfanes and internal trithionitrates (GSNHS_nH) with polysulfane branches. Competitive trapping experiments suggest that the polysulfane chains are formed via the intermediacy of sulfenic acid species, GSS_nOH. In the presence of radical trap vinylcyclopropane (VCP) the relative distributions of polysulfane speciation are relatively unaffected, suggesting that radical coupling is not a dominant pathway. Therefore, we suggest polysulfane catenation occurs via reaction of sulfides with sulfenic acids.

Copper ion vs copper metal-organic framework catalyzed NO release from bioavailable S-Nitrosoglutathione en route to biomedical applications: Direct 1H NMR monitoring in water allowing identification of the distinct, true reaction stoichiometries and thiol dependencies

Copper containing compounds catalyze decomposition of S-Nitrosoglutathione (GSNO) in the presence of glutathione (GSH) yielding glutathione disulfide (GSSG) and nitric oxide (NO). Extended NO generation from an endogenous source is medically desirable to achieve vasodilation, reduction in biofilms on medical devices, and antibacterial activity. Homogeneous and heterogeneous copper species catalyze release of NO from endogenous GSNO. One heterogeneous catalyst used for GSNO decomposition in blood plasma is the metal-organic framework (MOF), H₃[(Cu₄Cl)₃-(BTTri)₈, H₃BTTri = 1,3,5-tris(¹H-1,2,3-triazol-5-yl) benzene] (CuBTTri). Fundamental questions about these systems remain unanswered, despite their use in biomedical applications, in part because no method previously existed for simultaneous tracking of [GSNO], [GSH], and [GSSG] in water. Tracking these reactions in water is a necessary step towards study in biological media (blood is approximately 80% water) where NO release systems must operate. Even the balanced stoichiometry remains unknown for copper-ion and CuBTTri catalyzed GSNO decomposition. Herein, we report a direct ¹H NMR method which: simultaneously monitors [GSNO], [GSH], and [GSSG] in water; provides the experimentally determined stoichiometry for copper-ion vs CuBTTri catalyzed GSNO decomposition; reveals that the CuBTTri-catalyzed reaction reaches 10% GSNO decomposition (16 h) without added GSH, yet the copper-ion catalyzed reaction reaches 100% GSNO decomposition (16 h) without added GSH; and shows 100% GSNO decomposition upon addition of stoichiometric GSH to the CuBTTri catalyzed reaction. These observations provide evidence that copper-ion and CuBTTri catalyzed GSNO decomposition in water operate through different reaction mechanisms, the details of which can now be probed by ¹H NMR kinetics and other needed studies.

Reactive nitrogen species induced catalases promote a novel nitrosative stress tolerance mechanism in Vibrio cholerae

Vibrio cholerae faces nitrosative stress during successful colonization in intestine. Very little information is available on the nitrosative stress protective mechanisms of V. cholerae. Reports show that NorR regulon control two genes hmpA and nnrS responsible for nitric oxide (NO) detoxification in V. cholerae. In the present study we first time report a novel role of V. cholerae catalases under nitrosative stress. Using zymogram analysis of catalase we showed that KatB and KatG activity were induced within 30 min in V. cholerae in the presence of sodium nitroprusside (SNP), a NO donor compound. Surprisingly, V. cholerae cell survival was found to be decreased under nitrosative stress if catalase activities were blocked by ATz, a catalase inhibitor. Flow cytometry study was conducted to detect reactive oxygen species (ROS) and reactive nitrogen species (RNS) using DHE and DHR123, fluorescent probes respectively. Short exposure of SNP to V. cholerae did not generate ROS but RNS was detectable within 30 min. Total glutathione content was increased in V. cholerae cells under nitrosative stress. Furthermore, Superoxide dismutase (SOD) and Glutathione reductase (GR) activities remained unchanged under nitrosative stress in V. cholerae indicated antioxidant role of NO which could produce peroxynitrite. To investigate the role of catalase induction under nitrosative stress in V. cholerae, we conducted peroxynitrite reductase assay using cell lysates. Interestingly, SNP treated V. cholerae cell lysates showed lowest DHR123 oxidation compared to the control set. The extent of DHR123 oxidation was more in V. cholerae cell lysate when catalases were blocked by ATz.

Protein S-Nitrosylation: Determinants of Specificity and Enzymatic Regulation of S-Nitrosothiol-Based Signaling

SIGNIFICANCE

Protein S-nitrosylation, the oxidative modification of cysteine by nitric oxide (NO) to form protein S-nitrosothiols (SNOs), mediates redox-based signaling that conveys, in large part, the ubiquitous influence of NO on cellular function. S-nitrosylation regulates protein activity, stability, localization, and protein-protein interactions across myriad physiological processes, and aberrant S-nitrosylation is associated with diverse pathophysiologies. Recent Advances: It is recently recognized that S-nitrosylation endows S-nitroso-protein (SNO-proteins) with S-nitrosylase activity, that is, the potential to trans-S-nitrosylate additional proteins, thereby propagating SNO-based signals, analogous to kinase-mediated signaling cascades. In addition, it is increasingly appreciated that cellular S-nitrosylation is governed by dynamically coupled equilibria between SNO-proteins and low-molecular-weight SNOs, which are controlled by a growing set of enzymatic denitrosylases comprising two main classes (high and low molecular weight). S-nitrosylases and denitrosylases, which together control steady-state SNO levels, may be identified with distinct physiology and pathophysiology ranging from cardiovascular and respiratory disorders to neurodegeneration and cancer.

CRITICAL ISSUES

The target specificity of protein S-nitrosylation and the stability and reactivity of protein SNOs are determined substantially by enzymatic machinery comprising highly conserved transnitrosylases and denitrosylases. Understanding the differential functionality of SNO-regulatory enzymes is essential, and is amenable to genetic and pharmacological analyses, read out as perturbation of specific equilibria within the SNO circuitry.

FUTURE DIRECTIONS

The emerging picture of NO biology entails equilibria among potentially thousands of different SNOs, governed by denitrosylases and nitrosylases. Thus, to elucidate the operation and consequences of S-nitrosylation in cellular contexts, studies should consider the roles of SNO-proteins as both targets and transducers of S-nitrosylation, functioning according to enzymatically governed equilibria.

Development of Cu-Modified PVC and PU for Catalytic Generation of Nitric Oxide

Nitric oxide (NO) generating surfaces are potentially promising for improving haemocompatibility of blood-contacting biomaterials. In the present report, Cu-modified poly(vinyl chloride) (PVC) and polyurethane (PU) were prepared via polydopamine (pDA)-assisted chelation. The copper content on the PVC and PU modified surfaces, assessed by inductively coupled plasma - optical emission spectrometry (ICP-OES), were about 3.86 and 6.04 nmol·cm−2, respectively. The Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) data suggest that copper is attached to the polymer surface through complex formation with pDA. The cumulative leaching of copper from modified PVC and PU during the five day incubation in phosphate buffered saline (PBS), measured by inductively coupled plasma mass spectrometry (ICP-MS), was about 50.7 ppb and 48 ppb, respectively which is within its physiological level. Modified polymers were tested for their ability to catalytically generate NO by decomposing of endogenous S-nitrosothiol (GSNO). The obtained data show that Cu-modified PVC and PU exhibited the capacity to generate physiological levels of NO which could be a foundation for developing new biocompatible materials with NO-based therapeutics.

S-Nitrosothiols: Materials, Reactivity and Mechanisms

The article provides a comprehensive view of S-nitrosothiols, chemical behaviour, the pathways leading to their synthesis, their spectral properties, analytical methods of detection and determination, chemical and photochemical reactivity, kinetic aspects and suggested mechanisms. The structure parameters of S-nitrosothiols and the parent thiols are analysed with respect to their effect on the strengthening or weakening the S–NO bond, and in consequence on the S-nitrosothiol stability. This depends also on the ease of S–S bond formation in the product disulphide. These structural features seem to be crucial both to spontaneous as well as to Cu-catalysed decomposition. Principal emphasis is given here to the S-nitrosothiols’ ability to act as ligands and to the effect of coordination on the ligand properties. The chemical and photochemical behaviours of the complexes are described in more detail and their roles in chemical and biochemical systems are discussed.

The aim of the article is to demonstrate that the contribution of S-nitrosothiols to chemical and biochemical processes is more diverse than supposed hitherto. Nevertheless, their role is predictable and, based on the correlation between structure and reactivity, many important mechanisms of biochemical processes can be interpreted and various applications designed.

Urban Particulate Matter-Induced Decomposition of S-Nitrosoglutathione Relevant to Aberrant Nitric Oxide Biological Signaling

Exposure to airborne particulate matter (PM) is associated with hazardous effects on human health. Soluble constituents of PM may be released in biological fluids and disturb the precisely tuned nitric oxide signaling processes. The influence of aqueous extracts from two types of airborne urban PM (SRM 1648a, a commercially available sample, and KR PM2.5, a sample collected "in-house" in Krakow, Poland) on the stability of S-nitrosoglutathione (GSNO) was investigated. The particle interfaces had no direct effect on the studied reaction, but extracts obtained from both samples facilitated NO release from GSNO. The effectiveness of NO release was significantly affected by glutathione (GSH) and ascorbic acid (AscA). Examination of the combined influence of Cu²⁺ , Fe³⁺ , and reductants on GSNO stability revealed copper to be the main GSNO decomposing species. Computational models of nitrosothiols interacting with metal oxide substrates and solvated metal ions support these claims. The study stresses the importance of the interplay between metal ions and biological reductants in S-nitrosothiols decomposition.

S-Alk(en)ylmercaptocysteine suppresses LPS-induced pro-inflammatory responses in murine macrophages through inhibition of NF-κB pathway and modulation of thiol redox status

The Allium vegetable-derived metabolite, S-alk(en)ylmercaptocysteine (CySSR), has been reported to modulate oxidative stress and inflammatory responses. However, the underlying mechanisms of action and structure-activity relationships are not completely understood. We investigated the mechanistic basis of the protective effects of CySSR on pro-inflammatory responses involving redox/oxidative stress induced by E. coli lipopolysaccharide (LPS) using RAW 264.7 cells. CySSR (R = allyl, "A" or 1-propenyl, "Pe") pre-treatments conferred concentration-dependent reductions in cytokines (TNF-α, IL-1β and IL-6), NO production and iNOS (inducible nitric synthase) overexpression, and attenuated oxidant production in LPS-stimulated RAW 264.7 cells where viability remained > 90%. These protective effects were manifested through inhibited activation of the nuclear factor-kappa B (NF-κB) signaling pathway via suppression of the IκB kinases (IKK) phosphorylation possibly by transforming growth factor β-activated kinase 1 or a kinase further upstream the canonical NF-κB signaling pathway. The attenuation of LPS-induced inflammation by CySSRs was associated with enhanced levels of cellular cysteine (CySH) and glutathione (GSH) mediated by cellular import/reduction of CySSR and the induction of glutamate cysteine ligase (GCL), one of > 200 nuclear factor erythroid 2-related factor 2 (Nrf2) regulated proteins. The reduction of anti-inflammatory effect of CySSR following pretreatment of cells with L-buthionine-S,R-sulfoximine (BSO) implicates GSH having a major role in reducing inflammation, likely in the context of other Nrf2-regulated antioxidant enzymes that scavenge H₂O₂ and peroxides using GSH as co-substrate. The anti-inflammatory effect of CySSPe was significantly greater than CySSA for almost all indicators measured, and cell metabolites of CySSRs may have a role in attenuating NF-κB signaling.

Gas Therapy: An Emerging “Green” Strategy for Anticancer Therapeutics

As an emerging area, gas therapy has attracted more and more attention in treating many diseases including cancer. The fabrication of stimuli‐responsive delivery systems with on‐demand release behavior is very promising for precision gas therapy, which can obtain optimal therapeutic performance without gas poisoning risks. In this review, the authors introduce the recent progress in the preparation of different kinds of gas carriers for efficient delivery of gaseous molecules (NO, H2S, CO, O2). Particularly, in order to achieve targeted accumulation of gaseous molecules in tumor tissues, gaseous molecules–integrated nanoparticles were constructed. Most importantly, by combination of gas therapy with other therapeutic modalities such as chemotherapy, photodynamic therapy (PDT), and radiotherapy, various multifunctional nanocarriers have been designed for synergistic cancer therapy. Especially, the recent developments of multifunctional gas‐carrying nanocarriers for synergistic cancer therapy are discussed in detail.