Characterisation of the decomposition behaviour of S-nitrosoglutathione and a new class of analogues: S-Nitrosophytochelatins

Aspergillus awamori: potential antioxidant, anti-inflammatory, and anti-apoptotic activities in acetic acid-induced ulcerative colitis in rats

Ulcerative colitis (UC) is a chronic colonic inflammation with a significant health hazard. Aspergillus awamori (A. awamori) is a microorganism with various bioactive compounds with natural antioxidant and anti-inflammatory properties. The present work aimed to elucidate the protective and therapeutic effects of varying concentrations of A. awamori against acetic acid (AA)-induced ulcerative colitis (UC) in rats. Nine groups of albino male rats were established: a control negative group (G1), a control positive group (G2,AA), and preventive protocol groups (including G3A, G4A, and G5A) that received 100 mg, 50 mg, and 25 mg/kg b.w, respectively, of A. awamori orally and daily from the 1st day of the experiment and for 7 consecutive days. Then, they were subjected to one dose of AA intrarectally on day 8th. G3B, G4B, and G5B were termed as curative protocol groups that received one dose of AA on day 8th and then administered 100 mg, 50 mg, and 25 mg/kg b.w. of A. awamori, respectively, on day 9th and continued receiving these doses daily until day 16th. Rats in the AA group exhibited marked histopathological alterations of the distal colon, with an exaggeration of the DAI. In addition, a remarkable increase in oxidative stress was represented by the elevation of MDA and NO levels with a decline in SOD and GPx activities. In addition, upregulation of TNF-α, IL-6, and IL-1β mRNA expressions and downregulation of Muc2 and Nrf2 levels were detected. Unambiguously, a remarkable anti-inflammatory effect was noticed either in A. awamori prevented or treated groups expounded by reducing and regulating TNF-α, IL-6, and IL-1β with improved pathological lesion scoring. The Muc2, Nrf2, and bcl-2 gene levels were upregulated and restored also. In summary, the findings in this work reveal that A. awamori supplementation successfully alleviated the UC induced by AA, which had a better effect when administered before colitis induction.

Biomimetic catheter surface with dual action NO-releasing and generating properties for enhanced antimicrobial efficacy

Infection of indwelling catheters is a common healthcare problem, resulting in higher morbidity and mortality. The vulnerable population reliant on catheters post-surgery for food and fluid intake, blood transfusion, or urinary incontinence or retention is susceptible to hospital-acquired infection originating from the very catheter. Bacterial adhesion on catheters can take place during the insertion or over time when catheters are used for an extended period. Nitric oxide-releasing materials have shown promise in exhibiting antibacterial properties without the risk of antibacterial resistance which can be an issue with conventional antibiotics. In this study, 1, 5, and 10 wt % selenium (Se) and 10 wt % S-nitrosoglutathione (GSNO)-incorporated catheters were prepared through a layer-by-layer dip-coating method to demonstrate NO-releasing and NO-generating capability of the catheters. The presence of Se on the catheter interface resulted in a 5 times higher NO flux in 10% Se-GSNO catheter through catalytic NO generation. A physiological level of NO release was observed from 10% Se-GSNO catheters for 5 d, along with an enhanced NO generation via the catalytic activity as Se was able to increase NO availability. The catheters were also found to be compatible and stable when subjected to sterilization and storage, even at room temperature. Additionally, the catheters showed a 97.02% and 93.24% reduction in the adhesion of clinically relevant strains of Escherichia coli and Staphylococcus aureus, respectively. Cytocompatibility testing of the catheter with 3T3 mouse fibroblast cells supports the material's biocompatibility. These findings from the study establish the proposed catheter as a prospective antibacterial material that can be translated into a clinical setting to combat catheter-related infections.

Roles and current applications of S-nitrosoglutathione in anti-infective biomaterials

Bacterial infections can compromise the physical and biological functionalities of humans and pose a huge economical and psychological burden on infected patients. Nitric oxide (NO) is a broad-spectrum antimicrobial agent, whose mechanism of action is not affected by bacterial resistance. S-nitrosoglutathione (GSNO), an endogenous donor and carrier of NO, has gained increasing attention because of its potent antibacterial activity and efficient biocompatibility. Significant breakthroughs have been made in the application of GSNO in biomaterials. This review is based on the existing evidence that comprehensively summarizes the progress of antimicrobial GSNO applications focusing on their anti-infective performance, underlying antibacterial mechanisms, and application in anti-infective biomaterials. We provide an accurate overview of the roles and applications of GSNO in antibacterial biomaterials and shed new light on the avenues for future studies.

Aspergillus awamori attenuates ochratoxin A-induced renal and cardiac injuries in rabbits by activating the Nrf2/HO-1 signaling pathway and downregulating IL1β, TNFα, and iNOS gene expressions

Ochratoxin A (OTA) is one of the most dangerous and that pollute agricultural products, inducing a variety of toxic effects in humans and animals. The current study explored the protective effect of different concentrations of Aspergillus awamori (A. awamori) against OTA (0.3 mg/kg diet) induced renal and cardiac damage by exploring its mechanism of action in 60 New Zealand white male rabbits. Dietary supplementation of A. awamori at the selected doses of 50, 100, and 150 mg/kg diet, respectively, for 2 months significantly improved the rabbit's growth performance; modulated the suppressed immune response and restored the altered hematological parameters; reduced the elevated levels of renal injury biomarkers such as urea, creatinine, and alkaline phosphatase; and increased serum total proteins concentrations. Moreover, it also declined enzymatic activities of cardiac injury biomarkers, including AST, LDH, and CK-MB. A. awamori alleviated OTA-induced degenerative and necrotic changes in the kidney and heart of rabbits. Interestingly, A. awamori upregulated Nrf2/OH-1 signaling pathway. Therefore enhanced TAC, CAT, and SOD enzyme activities and reduced OTA-induced oxidative and nitrosative stress by declining iNOS gene expression and consequently lowered MDA and NO levels. In addition to attenuating renal and cardiac inflammation via reducing IL-1β, TNF-α gene expressions in a dose-dependent response. In conclusion,this is the first report to pinpoint that dietary incorporation of A. awamori counteracted OTA-induced renal and cardiac damage by potentiating the rabbit's antioxidant defense system through its potent antioxidant, free radical scavenging, and anti-inflammatory properties in a dose-dependent response. Based on our observations, A. awamori could be utilized as a natural protective agent against ochratoxicosis in rabbits.

Buffer concentration dramatically affects the stability of S-nitrosothiols in aqueous solutions

S-nitrosothiols (RSNOs) are an important group of nitric oxide (NO)-donating compounds with low toxicity and wide biomedical applications. In this paper, we, for the first time, demonstrate that the concentration of buffer remarkably affects the stability of RSNOs including naturally occurring S-nitrosoglutathione (GSNO) and synthetic S-nitroso-N-acetylpenicillamine (SNAP). For a solution with a high concentration of GSNO (e.g., 50 mM) and an initial near-neutral pH, the optimal buffer concentration is close to the GSNO concentration under our experimental conditions. A lower buffer concentration does not have adequate buffer capacity to resist the pH drop caused by GSNO decomposition. The decreased solution pH further accelerates GSNO decomposition because GSNO is most stable at near-neutral pH according to our density functional theory (DFT) calculations. A higher-than-optimal buffer concentration also reduces the GSNO stability because buffer ingredients including phosphate, Tris base, and HEPES consume NO/N₂O₃. In contrast to GSNO, the highest SNAP stability is obtained when the starting solution at a neutral pH does not contain buffer species, and the stability decreases as the buffer concentration increases. This is because SNAP is more stable at mildly acidic pH and the SNAP decomposition-induced pH drop stabilizes the donor. When the RSNO concentration is low (e.g., 1 mM), the buffer concentration also matters because any excess buffer accelerates the donor decomposition. Since the effect of buffer concentration was previously overlooked and suboptimal buffer concentrations were often used, this paper will aid in the formulation of RSNO solutions to obtain the maximum stability for prolonged storage and sustained NO release.

Modulating nitric oxide-generating activity of zinc oxide by morphology control and surface modification

Zinc oxide (ZnO) has emerged as a promising material for nitric oxide (NO) delivery owing to its intrinsic enzyme-mimicking activities to catalyze NO prodrugs S-nitrosoglutathione (GSNO) and β-gal-NONOate for NO generation. The catalytic performance of enzyme mimics is strongly dependent on their size, shape, and surface chemistry; however, no studies have evaluated the influence of the aforementioned factors on the NO-generating activity of ZnO. Understanding these factors will provide an opportunity to tune NO generation profiles to accommodate diverse biomedical applications. In this paper, for the first time, we demonstrate that the activity of ZnO towards catalytic NO generation is shape-dependent, resulting from the different crystal growth directions of these particles. We modified the surfaces of ZnO particles with zeolitic imidazolate framework (ZIF-8) by in situ synthesis and observed that ZnO/ZIF-8 retained 60% of its NO-generating potency. The newly formed ZnO/ZIF-8 particles were shown to catalytically decompose both endogenous (GSNO) and exogenous (β-gal-NONOate and S-nitroso-N-acetylpenicillamine (SNAP)) prodrugs to generate NO at physiological conditions. In addition, we design the first platform that combines NO-generating and superoxide radical scavenging properties by encapsulating a natural enzyme, superoxidase dismutase (SOD), into ZnO/ZIF-8 particles, which holds great promise towards combinatorial therapy.

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.

Zinc Oxide Particles Catalytically Generate Nitric Oxide from Endogenous and Exogenous Prodrugs

Nitric oxide (NO) is a potent biological molecule that contributes to a wide spectrum of physiological processes. However, the full potential of NO as a therapeutic agent is significantly complicated by its short half-life and limited diffusion distance in human tissues. Current strategies for NO delivery focus on encapsulation of NO donors into prefabricated scaffolds or an enzyme-prodrug therapy approach. The former is limited by the finite pool of NO donors available, while the latter is challenged by the inherent low stability of natural enzymes. Zinc oxide (ZnO) particles with innate glutathione peroxidase and glycosidase activities, a combination that allows to catalytically decompose both endogenous (S-nitrosoglutathione) and exogenous (β-gal-NONOate) donors to generate NO at physiological conditions are reported. By tuning the concentration of ZnO particles and NO prodrugs, physiologically relevant NO levels are achieved. ZnO preserves its catalytic property for at least 6 months and the activity of ZnO in generating NO from prodrugs in human serum is demonstrated. The ZnO catalytic activity will be beneficial toward generating stable NO release for long-term biomedical applications.

Polycaprolactone/gelatin degradable vascular grafts simulating endothelium functions modified by nitric oxide generation

Aim: Host remolding with scaffolds degradation and rapid formation of a complete endothelium, are prospective solutions for improving performance of small diameter vascular grafts. Materials & methods: For this purpose, microfibrous polycaprolactone (PCL)/gelatin scaffolds were prepared by electrospinning and subsequently functionalized with heparin and organoselenium-immobilized polyethyleneimine for nitric oxide generation through layer-by-layer self-assembly. Results: Our results showed that modified PCL/gelatin grafts had strong catalytic nitric oxide generation capacity and facilitated the enhanced attachment of endothelial cells, compared with control scaffold groups. Meanwhile, the modified grafts exhibited good hemocombatility, rapid endothelialization and smooth muscle cell regeneration. Conclusion: Modification of biodegradable scaffolds, proposed in this work, could enhance biological functions of vascular grafts and provides new strategies for the construction of small diameter vascular grafts.

S-Nitrosoglutathione exhibits greater stability than S-nitroso-N-acetylpenicillamine under common laboratory conditions: A comparative stability study

S-Nitrosothiols (RSNOs) such as S-nitrosoglutathione (GSNO) and S-nitroso-N-acetylpenicillamine (SNAP) are susceptible to decomposition by stimuli including heat, light, and trace metal ions. Using stepwise isothermal thermogravimetric analysis (TGA), we observed that NO-forming homolytic cleavage of the S-N bond occurs at 134.7 ± 0.8 °C in GSNO and 132.8 ± 0.9 °C in SNAP, contrasting with the value of 150 °C that has been previously reported for both RSNOs. Using mass spectrometry (MS), nuclear magnetic resonance (NMR), and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), we analyzed the decomposition products from TGA experiments. The organic product of GSNO decomposition was glutathione disulfide, while SNAP decomposed to form N-acetylpenicillamine disulfide as well as other products, including tri- and tetrasulfides. In addition, we assessed the relative solution stabilities of GSNO and SNAP under common laboratory conditions, which include variable temperature, pH, and light exposure with rigorous exclusion of trace metal ions by chelation. GSNO exhibited greater stability than SNAP over a 7-day period except in one instance. Both RSNOs demonstrated an inverse relationship between solution stability and temperature, with refrigeration considerably extending shelf life. A decrease in pH from 7.4 to 5.0 also enhanced the stability of both RSNOs. A further decrease in pH from 5.0 to 3.0 resulted in decreased stability for both RSNOs, and is notably the only occasion in which SNAP proved more stable than GSNO. After 1 h of exposure to overhead fluorescent lighting, both RSNOs displayed high susceptibility to light-induced decomposition. After 7 h, GSNO and SNAP decomposed 19.3 ± 0.5% and 30 ± 2%, respectively.

Catalyzed Nitric Oxide Release Via Cu Nanoparticles Leads to an Increase in Antimicrobial Effects and Hemocompatibility for Short Term Extracorporeal Circulation

Devices used for extracorporeal circulation are met with two major medical concerns: thrombosis and infection. A device that allows for anticoagulant-free circulation while reducing risk of infection has yet to be developed. We report the use of a copper nanoparticle (Cu NP) catalyst for the release of nitric oxide (NO) from the endogenous donor S-nitrosoglutathione (GSNO) in a coating applied to commercial Tygon S3^™ E-3603 poly(vinyl chloride) tubing in order to reduce adhered bacterial viability and the occurrence thrombosis for the first time in an animal model. Cu GSNO coated material demonstrated a nitric oxide (NO) release flux ranging from an initial flux of 6.3 ± 0.9 ×10^-10 mol cm^-2 min^-1 to 7.1 ± 0.4 ×10^-10 mol cm^-2 min^-1 after 4 h of release, while GSNO loops without Cu NPs only ranged from an initial flux of 1.1 ± 0.2 ×10^-10 mol cm^-2 min^-1 to 2.3 ± 0.2 ×10^-10 mol cm^-2 min^-1 after 4 h of release, indicating that the addition of Cu NPs can increase NO flux up to five times in the same 4 h period. Additionally, a 3-log reduction in S. aureus and 1-log reduction in P. aeruginosa was observed in viable bacterial adhesion over a 24 h period compared to control loops. A Cell Counting Kit-8 (CCK-8) assay was used to validate no overall cytotoxicity towards 3T3 mouse fibroblasts. Finally, extracorporeal circuits were coated and exposed to 4 h of blood flow under an in vivo rabbit model. The Cu GSNO combination was successful in maintaining 89.3% of baseline platelet counts, while the control loops were able to maintain 67.6% of the baseline. These results suggest that the combination of Cu NPs with GSNO increases hemocompatibility and antimicrobial properties of ECC loops without any cytotoxic effects towards mammalian cells.

Long-term decomposition of aqueous S-nitrosoglutathione and S-nitroso-N-acetylcysteine: Influence of concentration, temperature, pH and light

Primary S-nitrosothiols (RSNOs) have received significant attention for their ability to modulate NO signaling in many physiological and pathophysiological processes. Such actions and their potential pharmaceutical uses demand a better knowledge of their stability in aqueous solutions. Herein, we investigated the effects of concentration, temperature, pH, room light and metal ions on the long-term kinetic behavior of two representative primary RSNOs, S-nitrosoglutathione (GSNO) and S-nitroso-N-acetylcysteine (SNAC). The thermal decomposition of GSNO and SNAC were shown to be affected by the auto-catalytic action of the thiyl radicals. At 25 °C in the dark and protected from the catalytic action of metal ions, GSNO and SNAC solutions 1 mM showed half-lives of 49 and 76 days, and apparent activation energies of 84 ± 14 and 90 ± 6 kJ mol^-1, respectively. Both GSNO and SNAC exhibited increased stability in the pH range 5-7. At high pH the decomposition pathway of GSNO involves the formation of an intermediate (GS-NO₂^2-), which decomposes generating GSH and nitrite. GSNO solutions displayed lower sensitivity to the catalytic action of metal ions than SNAC and the exposure to room light led to a 5-fold increase in the initial rates of decomposition of both RSNOs. In all comparisons, SNAC solutions showed higher stability than GSNO solutions. These findings provide strategic information about the stability of GSNO and SNAC and may open new perspectives for their use as experimental or therapeutic NO donors.

Heparinized PCL/keratin mats for vascular tissue engineering scaffold with potential of catalytic nitric oxide generation

Heparins are capable of improving blood compatibility, enhancing HUVEC viability, while inhibiting HUASMC proliferation. Combination of biodegradable poly(ε-caprolactone) (PCL) with keratin and heparins would provide an anticoagulant and endothelialization supporting environment for vascular tissue engineering. Herein, PCL and keratin were first coelectrospun and then covalently conjugated with heparins. The resulting mats were surface-characterized by ATR-FTIR, SEM, WCA, and XPS. Cell viability data showed that the heparinized PCL/keratin mats could motivate the adhesion and growth of HUVEC, while inhibit HUASMC proliferation. In addition, these mats could prolong blood clotting time and reduce platelet adhesion as well as no erythrolysis. Interestingly, these mats could catalyze the NO donor in blood to release NO, which could enhance endothelial cell growth, while decrease smooth muscle cell proliferation and platelet adhesion. In summary, the heparinized mats would be a good candidate as a scaffold for vascular tissue engineering. This study is novel in that we prepared a type of heparinized tissue scaffold that could catalyze the NO donor to release NO to regulate endothelialization without angiogenesis and thrombus formation.

Regulation of macrophage polarization and promotion of endothelialization by NO generating and PEG-YIGSR modified vascular graft

As an effective clinic treatment for cardiovascular disease, vascular transplantation gains much acceptance recently. However, due to the acute thrombosis and intimal hyperplasia, long-term failure of synthetic grafts after implanted in small diameter blood vessel decelerates its commercial use. The continued acute inflammation and delayed endothelialization have been considered as fundamental reasons. To enhance the adhesion and organization of endothelial cells (ECs) and improve the vascular remodeling process, we have constructed a vascular graft based on electrospun polycaprolactone (PCL) matrix, on which organoselenium-immobilized polyethyleneimine (SePEI) for in situ nitric oxide (NO) generation and hyaluronic acid (HA) grafted with poly (ethylene glycol) (PEG) modified Tyr-Ile-Gly-Ser-Arg (YIGSR) for antifouling and EC adhesion were deposited through electrostatic layer-by-layer assembly. The in vitro results showed that SePEI deposited on the grafts could catalyze stable generation of NO. After in situ implantation in rats for 4 and 8weeks, the graft promoted the transformation of macrophages into an anti-inflammatory phenotype (M2), which helped endothelium remodeling. YIGSR on the outmost layer facilitated more rapid and organized EC adhesion compared to PCL and non-modified grafts. PEG polymer chain on the outmost layer mitigated nonspecific adsorption of undesirable blood components. In our study, we first demonstrated the regulation of macrophage polarization by an NO-generating vascular graft. The results indicated that the approach of anti-inflammatory macrophage polarization and enhanced endothelialization through NO generation and PEG-modified YIGSR in our study may provide a new perspective for the clinic application of cell-free small-diameter vascular grafts.

Electrospun poly-ε-caprolactone scaffold modified with catalytic nitric oxide generation and heparin for small-diameter vascular graft

Vascular grafts are significantly needed in peripheral vascular surgery; however, small diameter grafts are not always available, and synthetic grafts perform poorly because of acute thrombosis and neointimal proliferation after implantation.

In vivo pharmacological activity and biodistribution of S-nitrosophytochelatins after intravenous and intranasal administration in mice

S-nitrosophytochelatins (SNOPCs) are novel analogues of S-nitrosoglutathione (GSNO) with the advantage of carrying varying ratios of S-nitrosothiol (SNO) moieties per molecule. Our aim was to investigate the in vivo pharmacological potency and biodistribution of these new GSNO analogues after intravenous (i.v.) and intranasal (i.n.) administration in mice. SNOPCs with either two or six SNO groups and GSNO were synthesized and characterized for purity. Compounds were administered i.v. or i.n. at 1 μmol NO/kg body weight to CD-1 mice. Blood pressure was measured and biodistribution studies of total nitrate and nitrite species (NOx) and phytochelatins were performed after i.v. administration. At equivalent doses of NO, it was observed that SNOPC-6 generated a rapid and significantly greater reduction in blood pressure (∼60% reduction compared to saline) whereas GSNO and SNOPC-2 only achieved a 30-35% decrease. The reduction in blood pressure was transient and recovered to baseline levels within ∼2 min for all compounds. NOx species were transiently elevated (over 5 min) in the plasma, lung, heart and liver. Interestingly, a size-dependent phytochelatin accumulation was observed in several tissues including the heart, lungs, kidney, brain and liver. Biodistribution profiles of NOx were also obtained after i.n. administration, showing significant lung retention of NOx over 15 min with minor systemic increases observed from 5 to 15 min. In summary, this study has revealed interesting in vivo pharmacological properties of SNOPCs, with regard to their dramatic hypotensive effects and differing biodistribution patterns following two different routes of administration.

Construction and evaluation of nitric oxide generating vascular graft material loaded with organoselenium catalyst via layer-by-layer self-assembly

A new biomimetic material for artificial blood vessel with in situ catalytic generation of nitric oxide (NO) was prepared in this study. Organoselenium immobilized polyethyleneimine as NO donor catalyst and sodium alginate were alternately loaded onto the surface of electrospun polycaprolactone matrix via electrostatic layer-by-layer self-assembly. This material revealed significant NO generation when contacting NO donor S-nitrosoglutathione (GSNO). Adhesion and spreading of smooth muscle cells were inhibited on this material in the presence of GSNO, while proliferation of endothelial cells was promoted. In vitro platelet adhesion and arteriovenous shunt experiments demonstrated good antithrombotic properties of this material, with inhibited platelet activation and aggregation, and prevention of acute thrombosis. This study may provide a new method of improving cellular function and antithrombotic property of vascular grafts.

Nitric oxide released from luminal s-nitroso-N-acetylcysteine increases gastric mucosal blood flow

Nitric oxide (NO)-mediated vasodilation plays a key role in gastric mucosal defense, and NO-donor drugs may protect against diseases associated with gastric mucosal blood flow (GMBF) deficiencies. In this study, we used the ex vivo gastric chamber method and Laser Doppler Flowmetry to characterize the effects of luminal aqueous NO-donor drug S-nitroso-N-acetylcysteine (SNAC) solution administration compared to aqueous NaNO2 and NaNO3 solutions (pH 7.4) on GMBF in Sprague-Dawley rats. SNAC solutions (600 μM and 12 mM) led to a rapid threefold increase in GMBF, which was maintained during the incubation of the solutions with the gastric mucosa, while NaNO2 or NaNO3 solutions (12 mM) did not affect GMBF. SNAC solutions (600 μM and 12 mM) spontaneously released NO at 37 °C at a constant rate of 0.3 or 14 nmol·mL-1·min-1, respectively, while NaNO2 (12 mM) released NO at a rate of 0.06 nmol·mL-1·min-1 and NaNO3 (12 mM) did not release NO. These results suggest that the SNAC-induced GMBF increase is due to their higher rates of spontaneous NO release compared to equimolar NaNO2 solutions. Taken together, our data indicate that oral SNAC administration is a potential approach for gastric acid-peptic disorder prevention and treatment.

Rapid in situ endothelialization of a small diameter vascular graft with catalytic nitric oxide generation and promoted endothelial cell adhesion

Rapidin situendothelialization of a small diameter vascular graft with catalytic nitric oxide generation and promoted endothelial cell adhesion.

Attenuated desensitization of β-adrenergic receptor by water-soluble N-nitrosamines that induce S-nitrosylation without NO release

RATIONALE

The clinical problem of loss of β-adrenergic receptor (β-AR) response, both in the pathogenesis of heart failure and during therapeutic application of β-agonists, is attributable, at least in part, to desensitization, internalization, and downregulation of the receptors. In the regulation of β-AR signaling, G protein-coupled receptor kinase 2 (GRK2) primarily phosphorylates agonist-occupied β-ARs, and this modification promotes desensitization, internalization, and downregulation of β-ARs. It has been demonstrated that GRK2 is inhibited by its S-nitrosylation. However, compounds that induce S-nitrosylation, such as S-nitrosoglutathione, simultaneously generate NO, which has been demonstrated to operate for cardiovascular protection.

OBJECTIVE

We examine whether S-nitrosylation without NO generation inhibits desensitization of β(2)-AR by GRK2. We thus aim to synthesize compounds that specifically induce S-nitrosylation.

METHODS AND RESULTS

We have developed water-soluble N-nitrosamines that have S-nitrosylating activity but lack NO-generating activity. These compounds, at least partly, rescue β-AR from desensitization in HEK 293 cells expressing FLAG-tagged human β(2)-AR and in rat cardiac myocytes. They inhibit isoproterenol-dependent phosphorylation and internalization of β(2)-AR. Indeed, they nitrosylate GRK2 in vitro and in cells, and their S-nitrosylation of GRK2 likely underlies their inhibition of β(2)-AR desensitization.

CONCLUSIONS

Compounds that induce S-nitrosylation without NO release inhibit GRK2 and attenuate β(2)-AR desensitization. Developing water-soluble drugs that specifically induce S-nitrosylation may be a promising therapeutic strategy for heart failure.

Increased stability of S-nitrosothiol solutions via pH modulations

S-nitrosothiol (RSNO) solutions represent a valuable source of nitric oxide and could be used as topical vasodilators, but their fast decomposition rate poses a serious obstacle to their potentially widespread therapeutic use. Our aim was to characterize and quantify the effect of pH on S-nitrosothiol formation and decomposition in simple aqueous solutions of S-nitrosoglutathione (GSNO), S-nitroso-N-acetylcysteine (SNAC) and S-nitroso-3-mercaptopropionic acid (SN3MPA). Furthermore, we investigated the effect of storage pH on the stability of GSNO incorporated in poly(ethylene glycol)/ poly(vinyl alcohol) matrices. S-nitrosothiol concentrations were measured spectrophotometrically and laser Doppler scanning method was used to assess dermal blood flow. GSH and NAC solutions reached a complete transformation to nitrosothiols when synthesized using acidic NaNO(2) solution. The initial concentration of all investigated RSNOs decreased more slowly with pH adjusted to mildly basic values (8.4-8.8) for the storage period. Polymer gels of PVA/PEG compositions at mildly basic storage pH further reduced the decomposition rate succeeding to contain 46.8% of the initial GSNO concentration for 25 days. This amount of topically administered GSNO was still capable of increasing the dermal blood flow over 200% in human subjects.

Are nitric oxide donors a valuable tool to study the functional role of nitric oxide in plant metabolism?

In the present work, we tested known nitric oxide (NO) modulators generating the NO+ (sodium nitroprusside, SNP) and NO˙ forms (S-nitroso-N-acetyl-D-penicillamine, SNAP and nitrosoglutathione, GSNO). This allowed us to compare downstream NO-related physiological effects on proteins found in leaves of pelargonium (Pelargonium peltatum L.). Protein modification via NO donors generally affects plant metabolism in a distinct manner, manifested by a lower thiobarbituric acid reactive substance (TBARS) content and lipoxygenase (LOX) activity in response to SNAP and GSNO. This is in contrast to the response observed for SNP treatment. Most changes in enzyme activity (GR, glutathione reductase; GST, glutathione-S-transferase; GPX, glutathione peroxidase) are most spectacular and repeatable during the first 8 h of incubation, which is explained by the half-life of the applied donors. In particular, a close dependence was found between the time-course of NO emission from the applied donors and the temporary inhibition of antioxidant enzymes, such as catalase (CAT) and ascorbate peroxidase (APX). The observed changes were accompanied by time-dependent alterations in protein accumulation as analysed by two-dimensional gel electrophoresis (2-DE) in pelargonium leaves treated with NO donors (SNP, SNAP and GSNO). Using proteomics, different proteins were found to be down- and up-regulated. However, no new protein spots characteristic of all three donors were found. These results indicate that the form of NO emitted from the donor structure plays a key role in switching on appropriate metabolic modifications. It has been noted that several NO-affected metabolomic changes induced by the used donors were not comparable, which confirms the need to maintain caution when interpreting results obtained using the pharmacological approach with different NO modulator compounds.

S-nitrosophytochelatins: investigation of the bioactivity of an oligopeptide nitric oxide delivery system

This study investigates the in vitro bioactivity of S-nitrosophytochelatins (SNOPCs), oligopeptide analogues of S-nitrosoglutathione (GSNO), and their mechanisms of nitric oxide (NO) delivery. SNOPCs were more potent than GSNO in inhibiting platelet aggregation and stimulating vasorelaxation. Their potency was related to the number of S-nitrosated moieties per mole compound. Transnitrosation reactions with cell membrane surface components were shown to be the primary mode of NO delivery to intracellular targets for SNOPCs, while delivery via γ-glutamyl transpeptidase was unique to GSNO. Due to rapid NO release, larger SNOPCs elicited a more transitory effect compared to smaller compounds. The duration of effect was influenced by compound molecular weight, NO release kinetics, ability to undergo transnitrosation, and incubation time with tissues. In summary, a new oligopeptide NO delivery system based on SNOPCs was shown to be biologically active and can be used to investigate the mechanisms of NO delivery to intracellular targets.

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

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

Increased nitrosoglutathione reductase activity in hypoxic pulmonary hypertension in mice

Altered S-nitrosothiols (RSNO) signaling is linked to pulmonary hypertension. Recent studies have shown that S-nitrosoglutathione (GSNO) reductase (GSNOR) catalyzes the degradation of GSNO and indirectly regulates the level of RSNO in vivo. Our present study tested the hypothesis that chronic hypoxia causes pulmonary hypertension, in part, by the change of GSNOR activity that contributes to the depletion of RSNO. Male mice were exposed to normobaric hypoxia in a ventilated chamber for 1 to 21 days or normoxia for 21 days. Right ventricular systolic pressure, right ventricle hypertrophy, and the number and media thickness of muscular pulmonary vessels increased significantly after 21 days of hypoxic exposure. Hypoxia induced the overexpression of endothelial nitric oxide synthase and inducible nitric oxide synthase. The mRNA expression of GSNOR decreased on day 1 of hypoxic exposure, but increased significantly on day 7 compared with the normoxic group. The protein expression of GSNOR increased significantly in the lung tissue after 7 days of hypoxic exposure and its enzymatic activities also increased. Both the ratios of glutathione to glutathione disulfide and nitrate to nitrite were significantly lower in the hypoxic groups than in the normoxic controls. The results suggest an increased GSNOR activity interfered with the metabolism of RSNO in mice with hypoxic pulmonary hypertension. An imbalanced of redox status is associated with the pathogenesis of hypoxic pulmonary hypertension.

Ochratoxin A-mediated DNA and protein damage: roles of nitrosative and oxidative stresses

Ochratoxin A (OTA) is a mycotoxin occurring in a variety of foods. OTA is nephrotoxic and nephrocarcinogenic in rodents. An OTA-mediated increase of the inducible nitric oxide synthase (iNOS) expression was observed in normal rat kidney renal cell line and in rat hepatocyte cultures, suggesting the induction of nitrosative stress. This was associated with an increased nuclear factor kappa-light chain enhancer of activated B cells activity. The potential consequences of iNOS induction were further investigated. A significant increase in the levels of protein nitrotyrosine residues was observed with OTA. In addition, OTA was found to increase the level of DNA abasic sites in both cell cultures system. This end point was used as an indirect measure of 8-nitroguanine formation. Treatment of the cells with L-N(6)-(1-iminoethyl) lysine, a specific inhibitor of iNOS activity, inhibited the OTA-mediated overnitration of proteins but did not reduce the level of DNA abasic sites. It was found previously that nuclear factor-erythroid 2 p45-related factor 2 (Nrf2) activators were able to restore the cellular defense against oxidative stress and could prevent DNA abasic sites in cell cultures. In the present study, pretreatment of the cells with activators of Nrf2 prevented OTA-mediated increase in lipid peroxidation, confirming the potential of Nrf2 activators to confer protection against OTA-mediated oxidative stress. In addition, it was found that Nrf2 activators could also prevent OTA-induced protein nitration and cytotoxicity. In conclusion, the present data further confirm oxidative stress as a key source of OTA-induced DNA damage and provide additional evidence for a role of this mechanism in OTA carcinogenicity. The exact role of nitrosative stress still remains to be established.

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.