Decomposition of S-nitrosocysteine via S- to N-transnitrosation

Recycling 3D Printed Residues for the Development of Disposable Paper-Based Electrochemical Sensors

Here, we propose a recyclable approach using acrylonitrile-butadiene-styrene (ABS) residues from additive manufacturing in combination with low-cost and accessible graphite flakes as a novel and potential mixture for creating a conductive paste. The graphite particles were successfully incorporated in the recycled thermoplastic composite when solubilized with acetone and the mixture demonstrated greater adherence to different substrates, among which cellulose-based material made possible the construction of a paper-based electrochemical sensor (PES). The morphological, structural, and electrochemical characterizations of the recycled electrode material were demonstrated to be similar to those of the traditional carbon-based surfaces. Faradaic responses based on redox probe activity ([Fe(CN)6]3-/4-) exhibited well-defined peak currents and diffusional mass transfer as a quasi-reversible system (96 ± 5 mV) with a fast heterogeneous rate constant value of 2 × 10-3 cm s-1. To improve the electrode electrochemical properties, both the PES and the classical 3D-printed electrode surfaces were modified with a combination of multiwalled carbon nanotubes (MWCNTs), graphene oxide (GO), and copper. Both electrode surfaces demonstrated the suitable oxidation of nitrite at 0.6 and 0.5 V vs Ag, respectively. The calculated analytical sensitivities for PES and 3D-printed electrodes were 0.005 and 0.002 μA/(μmol L-1), respectively. The proposed PES was applied for the indirect amperometric analysis of S-nitroso-cysteine (CysNO) in serum samples via nitrite quantitation, demonstrating a limit of detection of 4.1 μmol L-1, with statistically similar values when compared to quantitative analysis of the same samples by spectrophotometry (paired t test, 95% confidence limit). The evaluated electroanalytical approach exhibited linear behavior for nitrite in the concentration range between 10 and 125 μmol L-1, which is suitable for realizing clinical diagnosis involving Parkinson's disease, for example. This proof of concept shows the great promise of this recyclable strategy combining ABS residues and conductive particles in the context of green chemical protocols for constructing disposable sensors.

Digital microfluidic platform assembled into a home-made studio for sample preparation and colorimetric sensing of S-nitrosocysteine

Digital microfluidics (DMF) is a versatile lab-on-a-chip platform that allows integration with several types of sensors and detection techniques, including colorimetric sensors. Here, we propose, for the first time, the integration of DMF chips into a mini studio containing a 3D-printed holder with previously fixed UV-LEDs to promote sample degradation on the chip surface before a complete analytical procedure involving reagent mixture, colorimetric reaction, and detection through a webcam integrated on the equipment. As a proof-of-concept, the feasibility of the integrated system was successfully through the indirect analysis of S-nitrosocysteine (CySNO) in biological samples. For this purpose, UV-LEDs were explored to perform the photolytic cleavage of CySNO, thus generating nitrite and subproducts directly on DMF chip. Nitrite was then colorimetrically detected based on a modified Griess reaction, in which reagents were prepared through a programable movement of droplets on DMF devices. The assembling and the experimental parameters were optimized, and the proposed integration exhibited a satisfactory correlation with the results acquired using a desktop scanner. Under the optimal experimental conditions, the obtained CySNO degradation to nitrite was 96%. Considering the analytical parameters, the proposed approach revealed linear behavior in the CySNO concentration range between 12.5 and 400 μmol L^-1 and a limit of detection equal to 2.8 μmol L^-1. Synthetic serum and human plasma samples were successfully analyzed, and the achieved results did not statistically differ from the data recorded by spectrophotometry at the confidence level of 95%, thus indicating the huge potential of the integration between DMF and mini studio to promote complete analysis of lowmolecular weight compounds.

Dynamics of photodissociation of nitric oxide from S-nitrosylated cysteine and N-acetylated cysteine derivatives in water

Cysteine and N-acetylated cysteine derivatives are ubiquitous in biological systems; they have thiol groups that bind NO to form S-nitrosothiols (RSNOs) such as S-nitrosocysteine (CySNO), S-nitroso-N-acetylcysteine (NacSNO), and S-nitroso-N-acetylpenicillamine (NapSNO). Although they have been utilised as thermally or catalytically decomposing NO donors, their photochemical applications are yet to be fully explored owing to the lack of photodissociation dynamics. To this end, the photoexcitation dynamics of these RSNOs in water at 330 nm were investigated using femtosecond time-resolved infrared (TRIR) spectroscopy over a broad time range encompassing the entire reaction, which includes the primary reaction, secondary reactions of the reaction intermediates, and product formation. We discovered that the acetate and amide groups in these RSNOs have strong vibrational bands sensitive to the bondage of NO and the electronic state of the compound, which facilitates the identification of reaction intermediates involved in photoexcitation. The simplest thiol available with the acetate group-thioglycolic acid-was nitrosylated; it produced S-nitrosothioglycolic acid (TgSNO) and was comparatively investigated. Transient absorption bands in the TRIR spectra of the RSNOs were assigned using quantum chemical calculations. Photoexcited cysteine-related RSNOs either decompose into RS and NO within 0.3 ps after excitation at 330 nm with a primary quantum yield (Φ1) of 0.46-1 or relax into an electronically excited intermediate state lying at 42 ± 3 kcal mol-1 above the ground state, which relaxes into the ground state with a time constant of 460-520 ps. A majority (62-80%) of the RS radical geminately rebinds with NO at a time constant of 3-7 ps. The remaining RS reacts with the neighbouring RSNO, which produces additional NO and RSSR with a (nearly) diffusion-limited rate constant that doubles the amount of NO produced; further, it remarkably extends the time window for the dissociated NO to react with the target compound. The final fraction of NO produced from these RSNOs at 330 nm was 0.32-0.58, and it depends on the geminate rebinding yield and Φ1. The detailed dynamics of the photoexcited RSNO can be utilised in the quantitative application of these RSNOs in practical use and in the synthesis of more efficient photoactivated NO precursors.

Copper-doped metal–organic frameworks for the controlled generation of nitric oxide from endogenous S-nitrosothiols

We report the synthesis of a catalyst, copper-doped zeolitic imidazolate framework ZIF-8, that generates nitric oxide from naturally occurring endogenous nitric oxide donors, S-nitrosoglutathione and S-nitrosocysteine.

Free radical-decellularized tissue promotes enhanced antioxidant and anti-inflammatory macrophage response

Oxidative stress leads to the progression of many diseases including chronic wounds, atherosclerosis, stroke and cancer. The modification of biomolecules with reactive nitrogen or oxygen species has been shown to trigger oxidative stress pathways that are beneficial for healing. Extracellular matrix scaffolds have been used successfully in reconstructive applications due to the beneficial host response they induce. To tailor extracellular matrix scaffolds to enhance antioxidant response, ECM were prepared using reactive nitrogen or oxygen species. These scaffolds were shown to be effectively decellularized and possess oxidative or nitroxidative protein modifications. Macrophage responses in vitro and in an in vivo muscle injury model were shown to have enhanced antioxidant phenotypes without impairment of long-term remodeling. These observations suggest that ECM decellularized with reactive oxygen or nitrogen species could provide better outcomes for the treatment of ischemic diseases.

Integrated microfluidic device for the separation, decomposition and detection of low molecular weight S-nitrosothiols

S-nitrosothiols (RSNOs) are very important biomolecules that play crucial roles in many physiological and physiopathological processes. They act as NO-donors and are candidates for future medicines. Their identification and quantitation are therefore important for biomedical applications. One, two or more RSNOs can then be combined to design a drug and therefore, the quantification of each is important to establish an acceptable quality control process. Till date, miniaturized devices have been used to detect RSNOs based on their total quantitation without a preceding separation step. This study reports on an original and integrated microdevice allowing for the successive electrokinetic separation of low molecular weight RSNOs, their decomposition under metal catalysis, and their quantitation by amperometric detection of the produced nitrite in the end-channel arrangement, leading to their quantitation in a single run. For this purpose, a commercial SU-8/Pyrex microfluidic system was coupled to a portable and wireless potentiostat. Different operating and running parameters were optimized to achieve the best analytical data, allowing for an LOD equal to 20 μM. The simultaneous separation of S-nitrosoglutathione and S-nitrosocysteine was successfully obtained within 75 s. The proposed methodology using SU-8/Pyrex microfluidic devices opens new possibilities to investigate future drug candidates for NO-donors.

S-Nitroso-N-acetylcysteine Generates Less Carcinogenic N-Nitrosamines in Meat Products than Nitrite

Nitrite reacts with secondary amines to form N-nitrosamines (N-NA), which lead to gastrointestinal cancers. The aim of this study was to compare nitrite with S-nitrosocysteine (Cys-SNO) and S-nitroso-N-acetylcysteine (NAC-SNO) with respect to N-NA formation, which was evaluated by determining the conversion of N-methylaniline to N-nitrosomethylaniline. Under neutral and acidic pH conditions, N-NA formation rate was nitrite > Cys-SNO > NAC-SNO. In the presence of copper or nucleophiles, NAC-SNO generated much less N-NA than Cys-SNO. Nitrite and Cys-SNO produced higher amounts of N-NA in the presence of oxygen, whereas NAC-SNO was almost oxygen insensitive. In meat in the stomach medium, NAC-SNO produced much lower amounts of N-NA than other additives. In heated meat, Cys-SNO and NAC-SNO generated the nitrosyl-hemochrome pink pigment, better than nitrite. In conclusion, NAC-SNO was much less reactive for N-NA formation than nitrite and Cys-SNO in conditions relevant to meat production and stomach digestion.

Inorganic sulfur-nitrogen compounds: from gunpowder chemistry to the forefront of biological signaling

The reactions between inorganic sulfur and nitrogen-bearing compounds to form S-N containing species have a long history and, besides assuming importance in industrial synthetic processes, are of relevance to microbial metabolism; waste water treatment; aquatic, soil and atmospheric chemistry; and combustion processes. The recent discovery that hydrogen sulfide and nitric oxide exert often similar, sometimes mutually dependent effects in a variety of biological systems, and that the chemical interaction of these two species leads to formation of S-N compounds brought this chemistry to the attention of physiologists, biochemists and physicians. We here provide a perspective about the potential role of S-N compounds in biological signaling and briefly review their chemical properties and bioactivities in the context of the chronology of their discovery. Studies of the biological role of NO revealed why its chemistry is ideally suited for the tasks Nature has chosen for it; realising how the distinctive properties of sulfur can enrich this bioactivity does much to revive 'die Freude am experimentellen Spiel' of the pioneers in this field.

Colorimetric analysis of the decomposition of S-nitrosothiols on paper-based microfluidic devices

A disposable paper microfluidic device was developed to analyse different S-nitrosothiols simultaneously decomposed by Hg²⁺ as well as UV, Vis and IR lamps.

Ag2S quantum dots conjugated chitosan nanospheres toward light-triggered nitric oxide release and near-infrared fluorescence imaging

Nanoscaled light-triggered nitric oxide (NO) delivery vehicles with the ability of near-infrared (NIR) fluorescence imaging was presented, which consisted of chitosan (CS)-based S-nitrosothiols (SNO) and encapsulated silver sulfide quantum dots (Ag2S QDs). CS-SNO compounds that bore NO-storing functional groups were prepared via amino modification of chitosan. Water-soluble Ag2S QDs were synthesized and conjugated with the CS-SNO compounds with the aid of ethylenediaminetetraacetic acid (EDTA). The biocompatible Ag2S-CS-SNO nanospheres, with dimension of ∼117 nm, exhibited bright NIR fluorescence and satisfactory photostability under NIR irradiation. The Ag2S-CS-SNO nanospheres could release NO under irradiation of UV or visible light at physiological pH and temperature yet would hardly release NO if NIR irradiation was applied. Cell imaging was successfully performed, demonstrating that the Ag2S-CS-SNO nanospheres could emit readily observable NIR fluorescence and release NO in living cells. The NIR fluorescence imaging of the Ag2S-CS-SNO nanospheres did not interfere with the light-triggered NO release from them, which would provide new perspectives for the application of multifunctional nanostructured materials in diagnostics and imaging.

Conjugating S-nitrosothiols with glutathiose stabilized silver sulfide quantum dots for controlled nitric oxide release and near-infrared fluorescence imaging

Light-controllable nitric oxide (NO) delivery nanoparticles with the capability of near-infrared (NIR) fluorescence imaging were reported. Water-dispersible Ag2S quantum dots (QDs) were synthesized via a one-pot procedure using reduced glutathiose (GSH) as both sulfur source and stabilizer. S-nitrosothiols (RSNOs) were conjugated with the GSH stabilized Ag2S QDs at the amino groups of the GSH, leading to Ag2S-GSH-SNO nanoparticles with dimension of ~5.5 nm. The biocompatible Ag2S-GSH-SNO nanoparticles could release NO under UV or visible irradiation and emit NIR fluorescence under NIR excitation for bioimaging at physiological pH and temperature, yet could hardly release NO when NIR irradiation was applied. In vitro cell imaging and mice imaging experiments demonstrated that the Ag2S-GSH-SNO nanoparticles could emit readily observable NIR fluorescence and release NO in living cells and small animals. The NIR fluorescence imaging of the Ag2S-GSH-SNO nanoparticles would not interfere with the light-triggered NO release from them, as the excitation lights needed for these two functions were in different wavelength regions. This work provides new perspectives for the application of multifunctional nanostructured materials in diagnostics and imaging.

Detailed mechanistic investigation into the S-nitrosation of cysteamine

The nitrosation of cysteamine (H₂NCH₂CH₂SH) to produce cysteamine-S-nitrosothiol (CANO) was studied in slightly acidic medium by using nitrous acid prepared in situ. The stoichiometry of the reaction was H₂NCH₂CH₂SH + HNO₂ → H₂NCH₂CH₂SNO + H₂O. On prolonged standing, the nitrosothiol decomposed quantitatively to yield the disulfide, cystamine: 2H₂NCH₂CH₂SNO → H₂NCH₂CH₂S-SCH₂CH₂NH₂ + 2NO. NO₂ and N₂O₃ are not the primary nitrosating agents, since their precursor (NO) was not detected during the nitrosation process. The reaction is first order in nitrous acid, thus implicating it as the major nitrosating agent in mildly acidic pH conditions. Acid catalyzes nitrosation after nitrous acid has saturated, implicating the protonated nitrous acid species, the nitrosonium cation (NO⁺) as a contributing nitrosating species in highly acidic environments. The acid catalysis at constant nitrous acid concentrations suggests that the nitrosonium cation nitrosates at a much higher rate than nitrous acid. Bimolecular rate constants for the nitrosation of cysteamine by nitrous acid and by the nitrosonium cation were deduced to be 17.9 ± 1.5 (mol/L)^-1 s^-1 and 6.7 × 10⁴ (mol/L)^-1 s^-1, respectively. Both Cu(I) and Cu(II) ions were effective catalysts for the formation and decomposition of the cysteamine nitrosothiol. Cu(II) ions could catalyze the nitrosation of cysteamine in neutral conditions, whereas Cu(I) could only catalyze in acidic conditions. Transnitrosation kinetics of CANO with glutathione showed the formation of cystamine and the mixed disulfide with no formation of oxidized glutathione (GSSG). The nitrosation reaction was satisfactorily simulated by a simple reaction scheme involving eight reactions.

Nitrosylation of myoglobin and nitrosation of cysteine by nitrite in a model system simulating meat curing

Demand is growing for meat products cured without the addition of sodium nitrite. Instead of the direct addition of nitrite to meat in formulation, nitrite is supplied by bacterial reduction of natural nitrate often added as vegetable juice/powder. However, the rate of nitrite formation in this process is relatively slow, and the total ingoing nitrite is typically less than in conventional curing processes. The objective of this study was to determine the impact of the rate of addition of nitrite and the amount of nitrite added on nitrosylation/nitrosation reactions in a model meat curing system. Myoglobin was preferentially nitrosylated as no decrease in sulfhydryl groups was found until maximum nitrosylmyoglobin color was achieved. The cysteine-myoglobin model retained more sulfhydryl groups than the cysteine-only model (p < 0.05). The rate of nitrite addition did not alter nitrosylation/nitrosation reactions (p > 0.05). These data suggest that the amount of nitrite but not the rate of addition impacts the nitrosylation/nitrosation reactions this system.

Decomposition of S-Nitrosothiols Induced by UV and Sunlight

Photochemical release of nitric oxide (NO) from the S-nitroso derivatives of glutathione, L-cysteine, N-acetyl-L-cysteine, L-cysteinemethylester, D,L-penicillamine, N-acetyl-D,L-penicillamine, and N-acetylcysteamine has been investigated at neutral and acidic pH. The release of NO from RSNO is one of the key reactions that could be utilized in photodynamic therapy. The UV-VIS and HPLC analyses have shown that under argon saturated conditions, disulfide (RSSR) is the major product of UV as well as sunlight induced decomposition. While in aerated conditions, nitirite—the end product of the oxidation of NO—was also observed along with disulfide. The formation of thiyl radical as the intermediate was reconfirmed by laser flash photolysis. The initial rate of formation of NO was on the order of 10−10dm3mol−1s−1. The quantum yields of these reactions were in the range of 0.2–0.8. The high quantum yields observed in the photo induced release of NO from RSNO using both UV and sunlight demonstrate the potential application of these reactions in photodynamic therapy.

Nitric oxide and airway epithelial barrier function: regulation of tight junction proteins and epithelial permeability

Acute airway inflammation is associated with enhanced production of nitric oxide (NO(.)) and altered airway epithelial barrier function, suggesting a role of NO(.) or its metabolites in epithelial permeability. While high concentrations of S-nitrosothiols disrupted transepithelial resistance (TER) and increased permeability in 16HBE14o- cells, no significant barrier disruption was observed by NONOates, in spite of altered distribution and expression of some TJ proteins. Barrier disruption of mouse tracheal epithelial (MTE) cell monolayers in response to inflammatory cytokines was independent of NOS2, based on similar effects in MTE cells from NOS2-/- mice and a lack of effect of the NOS2-inhibitor 1400W. Cell pre-incubation with LPS protected MTE cells from TER loss and increased permeability by H2O2, which was independent of NOS2. However, NOS2 was found to contribute to epithelial wound repair and TER recovery after mechanical injury. Overall, our results demonstrate that epithelial NOS2 is not responsible for epithelial barrier dysfunction during inflammation, but may contribute to restoration of epithelial integrity.

Nitric oxide regulation of MMP-9 activation and its relationship to modifications of the cysteine switch

Matrix metalloproteases (MMPs) are Zn-containing endopeptidases involved in the degradation of extracellular matrix components and are typically secreted in a latent (pro-MMP) form and activated either by proteolytic or oxidative disruption of a conserved cysteine switch. Several recent studies have suggested that nitric oxide (NO) can contribute to the activation of MMPs, but the mechanisms involved are incompletely understood. We investigated the ability of NO to regulate the activation of (pro)MMP-9 using a variety of NO-donor compounds and characterized modifications of the cysteine switch using a synthetic peptide (PRCGVPDLGR) representing the cysteine switch domain of MMP-9. Among the NO-donors used, only S-nitrosocysteine (SNOC) was found to be capable of modest activation of proMMP-9, but S-nitrosoglutathione (GSNO) or the NONOates, DEA-NO, SPER-NO, or DETA-NO, were ineffective. In fact, high concentrations of DETA-NO were found to inhibit MMP-9 activity, presumably by direct interaction with the active-site Zn (2+). Analysis of chemical modifications within the Cys-containing peptide, PRCGVPDLGR, revealed rapid and transient S-nitrosylation by SNOC and GSNO, and formation of mixed disulfides and dimerized peptide as major final products. Similarly, NONOates induced transient S-nitrosylation and primarily peptide dimerization. Coordination of the peptide Cys with a synthetic Zn (2+) complex, to more closely mimic the structure of the active site in proMMP-9, reduced peptide nitrosylation and oxidation by NONOates, but enhanced peptide nitrosylation by SNOC and GSNO. Collectively, our results demonstrate that NO is incapable of directly activating proMMP-9 and that S-nitrosylation of MMP-9 propeptide by NO-donors is unrelated to their ability to regulate MMP-9 activity.