Nitric oxide and S-nitrosothiols in human blood

Study of the effect of thiols on the vasodilatory potency of S-nitrosothiols by using a modified aortic ring assay

Both low-molecular-mass thiols (LMM-SH) and protein thiols (P-SH) can modulate the biological activity of S-nitrosothiols (RSNO) via S-transnitrosation reactions. It has been difficult to evaluate the entity of this effect in blood circulation by in vitro assays with isolated aorta rings so far, because media rich in proteins cannot be used due to the foaming as a consequence of the needed gas bubbling. We have modified the original apparatus for organ bioassay in order to minimize foaming and to increase analytical performance. By using this modified bioassay we investigated the vasodilatory potency of various endogenous RSNOs in the presence of physiologically relevant concentrations of albumin and LMM-SH. Our results show that the sulfhydryl group of the cysteine moiety of albumin and LMM-SH has a dramatic effect on the vasodilatory potency of RSNO. Considering the equilibrium constants for S-transnitrosation reactions and the concentration of P-SH and LMM-SH we measured in healthy humans (aged 18-85 years), we infer that the age-dependency of hematic levels of LMM-SH may have a considerable impact in RSNO-mediated vasodilation. S-Nitrosoproteins such as S-nitrosoalbumin may constitute a relatively silent and constant amount of circulating RSNO. On the other hand, LMM-SH may mediate and control the biological actions of S-nitrosoproteins via S-transnitrosation reactions, by forming more potent nitric oxide-releasing LMM-S-nitrosothiols. Lifestyle habits, status of health and individual age are proven factors that, in turn, may influence the concentration of these compounds. These aspects should be taken into consideration when testing the vasodilatory effects of RSNO in pre-clinical studies.

Flow injection measurements of S-nitrosothiols species in biological samples using amperometric nitric oxide sensor and soluble organoselenium catalyst reagent

A novel flow injection analysis (FIA) system suitable for measurement of S-nitrosothiols (RSNOs) in blood plasma is described. In the proposed (FIA) system, samples and standards containing RSNO species are injected into a buffer carrier stream that is mixed with the reagent stream containing 3,3'-dipropionicdiselenide (SeDPA) and glutathione (GSH). SeDPA has been shown previously to catalytically decompose RSNOs in the presence of a reducing agent, such as GSH, to produce nitric oxide (NO). The liberated NO is then detected downstream by an amperometric NO sensor. This sensor is prepared using an electropolymerized m-phenylenediamine (m-PD)/resorcinol and Nafion composite films at the surface of a platinum electrode. Using optimized flow rates and reagent concentrations, detection of various RSNOs at levels in the range of 0.25-20 μM is possible. For plasma samples, detection of background sensor interference levels within the samples must first be carried out using an identical FIA arrangement, but without the added SeDPA and GSH reagents. Subtraction of this background sensor current response allows good analytical recovery of RSNOs spiked into animal plasma samples, with recoveries in the range of 90.4-101.0%.

Modeling the effect of oxygen on the amperometric response of immobilized organoselenium-based S-nitrosothiol sensors

Amperometric detection of S-nitrosothiols (RSNOs) at submicromolar levels in blood samples is of potential importance for monitoring endothelial function and other disease states that involve changes in physiological nitric oxide (NO) production. It is shown here that the elimination of dissolved oxygen from samples is critical when covalently attached diselenocystamine-based amperometric RSNO sensors are used for practical RSNO measurements. The newest generation of RSNO sensors utilizes an amperometric NO gas sensor with a thin organoselenium modified dialysis membrane mounted at the distal sensing tip. Sample RSNOs are catalytically reduced to NO within the dialysis membrane by the immobilized organoselenium species. In the presence of oxygen, the sensitivity of these sensors for measuring low levels of RSNOs (<μM) is greatly reduced. It is demonstrated that the main scavenger of the generated nitric oxide is not the dissolved oxygen but rather superoxide anion radical generated from the reaction of the reduced organoselenium species (the reactive species in the catalytic redox cycle) and dissolved oxygen. Computer simulations of the response of the RSNO sensor using rate constants and diffusion coefficients for the reactions involved, known from the literature or estimated from fitting to the observed amperometric response curves, as well as the specific geometric dimensions of the RSNO sensor, further support that nitric oxide and superoxide anion radical quickly react resulting in near zero sensor sensitivity toward RSNO concentrations in the submicromolar concentration range. Elimination of oxygen from samples helps improve sensor detection limits to ca. 10 nM levels of RSNOs.

S-nitroso-N-acetylcysteine: a promising drug for early ischemia/reperfusion injury in rat liver

BACKGROUND/AIMS

Ischemia-reperfusion (I/R) injury is among the major causes of poor graft function early after liver transplantation that adversely influences patient survival. A variety of mediators have been implicated in the pathogenesis of I/R vascular injury, including nitric oxide (NO). Because of the beneficial effects of NO during preconditioning and reperfusion, strategies to prevent or ameliorate I/R injury through the stimulation of hepatic NO production are an area of significant clinical interest. We evaluated the role of S-nitroso-N-acetylcysteine (SNAC) as an NO donor in the prevention of liver I/R injury in an animal model.

METHODS

Adult male Wistar rats were randomly assigned to 3 experimental groups containing 5 animals each: the University of Wisconsin (UW) solution group; SNAC solution group; and SNAC-containing UW solution (SNAC+UW) group. Aspartate aminotransferase (AST), alanine aminotransferase (ALT) and lactate dehydrogenase (LDH) were determined in samples of the cold storage solution at 2, 4, and 6 hours of preservation. After 6 hours of cold storage, We applied a 15-minute reperfusion period. Thereafter, the reperfusion was interrupted with blood samples obtained to measure AST, ALT, LDH, and thiobarbituric acid reactive substances (TBARS). Hepatic fragments were processed for histologic analysis, and to determine of TBARS, catalase, and glutathione levels.

RESULTS

During cold preservation, AST and LDH were significantly lower among the SNAC than the UW group or the SNAC+UW group (P = .004 and P = .03, respectively). ALT was comparable among the groups (P = .3). After reperfusion, serum levels of AST, ALT, and LDH, as well as of hepatic TBARS and catalase showed no differences among the groups. Glutathione concentration was lower in the SNAC and SNAC+UW group (P < .001) compared with the UW group. We did not observe histologic signs of preservation injury.

CONCLUSION

The SNAC solution showed a greater protective effect to preserve rat livers during cold storage, but it was comparable with UW.

Vascular Nitric Oxide: Formation and Function

Nitric oxide (NO) is a structurally simple, highly versatile molecule that was originally discovered over 30 years ago as an endothelium-derived relaxing factor. In addition to its vasorelaxing effects, NO is now recognized as a key determinant of vascular health, exerting antiplatelet, antithrombotic, and anti-inflammatory properties within the vasculature. This short-lived molecule exerts its inhibitory effect on vascular smooth muscle cells and platelets largely through cyclic guanosine monophosphate-dependent mechanisms, resulting in a multitude of molecular effects by which platelet activation and aggregation are prevented. The biosynthesis of NO occurs via the catalytic activity of NO synthase, an oxidoreductase found in many cell types. NO insufficiency can be attributed to limited substrate/cofactor availability as well as interactions with reactive oxygen species. Impaired NO bioavailability represents the central feature of endothelial dysfunction, a common abnormality found in many vascular diseases. In this review, we present an overview of NO synthesis and biochemistry, discuss the mechanisms of action of NO in regulating platelet and endothelial function, and review the effects of vascular disease states on NO bioavailability.

S-nitrosothiols as selective antithrombotic agents - possible mechanisms

S-nitrosothiols have a number of potential clinical applications, among which their use as antithrombotic agents has been emphasized. This is largely because of their well-documented platelet inhibitory effects, which show a degree of platelet selectivity, although the mechanism of this remains undefined. Recent progress in understanding how nitric oxide (NO)-related signalling is delivered into cells from stable S-nitrosothiol compounds has revealed a variety of pathways, in particular denitrosation by enzymes located at the cell surface, and transport of intact S-nitrosocysteine via the amino acid transporter system-L (L-AT). Differences in the role of these pathways in platelets and vascular cells may in part explain the reported platelet-selective action. In addition, emerging evidence that S-nitrosothiols regulate key targets on the exofacial surfaces of cells involved in the thrombotic process (for example, protein disulphide isomerase, integrins and tissue factor) suggests novel antithrombotic actions, which may not even require transmembrane delivery of NO.

Peroxynitrite and nitrosoperoxycarbonate, a tightly connected oxidizing-nitrating couple in the reactive nitrogen-oxygen species family: new perspectives for protection from radical-promoted injury by flavonoids

Peroxynitrite is the product of the reaction of nitric oxide with superoxide radical and is implicated in the pathogenesis of a wide variety of human diseases, being responsible for in-vivo oxidation/nitration events. Nitrosoperoxycarbonate anion, formed by the interaction of peroxynitrite with CO2/bicarbonate at physiological concentrations, provides a new interpretation of oxidative/nitrative processes formerly attributed to peroxynitrite. The aim of this review is to summarize the chemistry and biology of peroxynitrite and radical species related to nitrosoperoxycarbonate anion, as well as the information available regarding the molecular mechanisms that determine and regulate radical-promoted injury by the two tightly connected species at physiological concentrations. Interception of carbonate and nitro radicals produced by interaction of peroxynitrite with CO2/bicarbonate, as in-vivo prevention of pathological events, creates new perspectives for the evaluation of safe scavengers of oxidative/nitrative stress at the physiological level. In this respect, natural products such as flavonoids hold a preeminent position among the vast array of compounds endowed with such properties.

Metal ion-mediated nitric oxide generation from polyurethanes via covalently linked copper(II)-cyclen moieties

Polyurethanes are widely used in the manufacturing of biomedical catheters and other blood-contacting devices; however, thrombus formation still occurs, which renders these catheters ineffective unless systemic anticlotting agents are used. Nitric oxide (NO) is a well-known inhibitor of platelet activity. In the current study, two commercially available medical polyurethanes (Pellethane and Tecophilic) were derivatized to possess NO-generating Cu(II)-cyclen moieties pendant to the polymer backbone. A new three-step synthetic approach is used, that is simpler than a recently reported method to prepare Cu(II)-cyclen-polyurethane materials. Both derivatized polyurethanes were found to produce NO at levels at or above those of endothelial cells. A comparison between the modified commercial polyurethanes (hydrophobic vs. hydrophilic) is presented, including the synthetic scheme, extensive characterization, and coating application. These derivatized polymers may serve as useful coatings to prevent clotting on the surface of catheters and other blood-contacting biomedical devices.

Amperometric S-nitrosothiol sensor with enhanced sensitivity based on organoselenium catalysts

A new S-nitrosothiol (RSNO) detection strategy based on an electrochemical sensor is described for rapidly estimating levels of total RSNOs in blood and other biological samples. The sensor employs a cellulose dialysis membrane covalently modified with an organoselenium catalyst that converts RSNOs to NO at the distal tip of an amperometric NO sensor. The sensor is characterized by very low detection limits (<20 nM), good long-term stability, and can be employed for the rapid detection of total low-molecular-weight (LMW) RSNO levels in whole blood samples using a simple standard addition method. A strategy for detecting macromolecular RSNOs is also demonstrated via use of a transnitrosation reaction with added LMW thiols allowing the estimation of total RSNO levels in blood. The sensor is shown to exhibit high selectivity over nitrosamines and nitrite. Such RSNO detection is potentially useful to reveal correlation between blood RSNO levels and endothelial cell dysfunction, which often is associated with cardiovascular diseases.

Nitric oxide-releasing/generating polymers for the development of implantable chemical sensors with enhanced biocompatibility

The development of reliable in vivo chemical sensors for real-time clinical monitoring of blood gases, electrolytes, glucose, etc. in critically ill and diabetic patients remains a great challenge owing to inherent biocompatibility problems that can cause errant analytical results upon sensor implantation (e.g., cell adhesion, thrombosis, inflammation). Nitric oxide (NO) is a well-known inhibitor of platelet activation and adhesion, and also a potent inhibitor of smooth muscle cell proliferation. In addition, NO mediates inflammatory response and promotes angiogenesis. Polymers that release or generate NO at their surfaces have been shown to exhibit greatly enhanced thromboresistance in vivo when in contact with flowing blood, as well as reduce inflammatory response when placed subcutaneously, and thus have the potential to improve the biocompatibility of implanted chemical sensors. Locally elevated NO levels at the surface of implanted devices can be achieved by using polymers that incorporate NO donor species that can decompose and release NO spontaneously when in contact with physiological fluids, or NO-generating polymers that possess an immobilized catalyst that decompose endogenous S-nitrosothiols to generate NO in situ. The potential use of such NO-releasing/generating materials for preparing in vivo sensors implanted either intravascularly or subcutaneously, is examined in this review.

Polyurethane with tethered copper(II)-cyclen complex: preparation, characterization and catalytic generation of nitric oxide from S-nitrosothiols

The preparation and characterization of a commercial biomedical-grade polyurethane (Tecophilic((R)), SP-93A-100) material possessing covalently linked copper(II)-cyclen moieties as a nitric oxide (NO) generating polymer are described. Chemiluminescence NO measurements demonstrate that the prepared polymer can decompose endogenous S-nitrosothiols (RSNOs) such as S-nitrosoglutathione and S-nitrosocysteine to NO in the presence of thiol reducing agents (RSHs; e.g., glutathione and cysteine) at physiological pH. Since such RSNO and RSH species already exist in blood, the proposed polymer is capable of spontaneously generating NO when in contact with fresh blood. This is demonstrated by utilizing the polymer as an outer coating at the distal end of an amperometric NO sensor to create a device that generates response toward the RSNO species in the blood. This polymer possesses the combined benefits of a commercial biomedical-grade polyurethane with the ability to generate biologically active NO when in contact with blood, and thus may serve as a useful coating to improve the hemocompatibility of various medical devices.

Molecular mechanisms and potential clinical significance of S-glutathionylation

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

The theoretical comparison between two model NO carriers, MeSNO and MeSeNO

In this study, we apply a hybrid DFT functional, MPW1LYP, to make a comparison between MeSNO and MeSeNO. Due to the mesomeric effect and negative hyperconjugation, Se-nitrososelenols seem to be more unstable than S-nitrosothiols regarding unimolecular decomposition. Interestingly, however, the barrier of the transnitrosation reaction of MeSeNO is larger than that of MeSNO, disregarding nucleophiles in the gas phase. Using the polarizable continuum model to consider the water solvent effect, the transnitrosation reactions of MeXNO and YMe- (X = S, Se; Y = S, Se) are found to undergo concerted reactions, in sharp contrast to the two-step reaction pathways concluded in the gas phase. Moreover, the barriers of the transnitrosation reactions of MeSNO for nucleophiles SMe- and SeMe- from the gas phase to the aqueous solution are found to be decreased, while the transnitrosation reactions of MeSeNO are essentially barrierless in aqueous solution.

B-type natriuretic peptide at early reperfusion limits infarct size in the rat isolated heart

Natriuretic peptides are regulatory autacoids in the mammalian myocardium whose functions, mediated via particulate guanylyl cyclase/cGMP, may include cytoprotection against ischaemia-reperfusion injury. Previous work has identified that B-type natriuretic peptide (BNP) limits infarct size when administered prior to and during coronary occlusion through a K(ATP) channel-dependent mechanism. The present study examined the hypothesis that the protection afforded by BNP is mediated specifically at reperfusion in a postconditioning-like manner. Langendorff-perfused rat hearts were subjected to 35 min coronary artery occlusion and 120 min reperfusion, and infarct size was determined by tetrazolium staining. Postconditioning was effected by applying six 10-second periods of global ischaemia at the onset of reperfusion.Treatment with either BNP 10 nM or the NO donor S-nitroso-N-acetylpenicillamine (SNAP) 1-10 microM was commenced 5 min prior to reperfusion and continued until 10 min after reperfusion. Control infarct size (% of ischaemic risk zone) was 40.8 +/- 3.7%.BNP at reperfusion induced a significant limitation of infarct size (BNP 22.9 +/- 4.1% P<0.05 vs. control). Co-treatment at reperfusion with BNP and the K(ATP) channel blockers 5-hydroxydecanote (5HD, 100 microM), glibenclamide (Glib; 10 microM) or HMR1098 (10 microM) abolished the infarct-limiting effect of BNP (BNP + 5HD 41.0 +/- 3.9%, BNP + Glib 39.8 +/- 5.6%, BNP + HMR 1098 46.0 +/- 7.1%,P < 0.05 vs. BNP). BNP given together with L-NAME (100 microM) at reperfusion resulted in a marked loss of protection (BNP + L-NAME 53.1 +/- 3.8% P < 0.001 vs. BNP). In a second series of experiments, SNAP (1-10 microM) given at reperfusion was found not to be protective (SNAP 1 microM 30.2 +/- 4.9%, SNAP 2 microM 27.5 +/- 9.5%, SNAP 5 microM 39.2 +/- 5.7%, SNAP 10 microM 33.7 +/- 6.4%, not significant vs. control). In a third series of experiments, postconditioning significantly limited infarct size (14.9 +/- 3.6 % vs. control 34.5 +/- 4.9%, P < 0.01) and this effect of postconditioning was abolished in the presence of isatin (100 microM), a non-specific blocker of particulate guanylyl cyclases (35.1 +/- 6%, P < 0.05 vs. postconditioning). In conclusion, pharmacological activation of pGC by BNP can effectively induce protection against reperfusion injury, by mechanisms involving K(ATP) channel opening and endogenous NO synthase activation. Furthermore, endogenous activation of pGC could play a role in the mechanism of postconditioning.

Effect of pH and Metal Ions on the Decomposition Rate of S-nitrosocysteine

S-nitrosothiols (RSNOs) have many biological functions including platelet deactivation, immunosupression, neurotransmission, and host defense. Most of the functions are attributed to nitric oxide (NO) release during S-nitrosothiol decomposition. As the simplest biologically occurring S-nitrosothiol, S-nitrosocysteine (CySNO) has been widely used as an NO donor and has also been incorporated into biomedical polymers. Knowledge of the CySNO decomposition rate is important for assessing the impact of CySNO on various bioengineering applications or biological systems. In this work, spectrophotometer measurements of CySNO decomposition in the presence of metal ions showed that the decomposition rate is highly susceptible to the pH. The maximum decomposition occurs near physiological pH (near 7.4) while in the acidic (pH < 6) and alkaline (pH > 9) condition CySNO is very stable. This demonstrates that blood provides an optimized environment for the decomposition of CySNO leading to the release of NO. The CySNO decomposition rate can also be affected by buffers with different purity levels in the presence and absence of metal ion chelators-although all buffers show the same pH phenomenon of maximizing near physiological pH. An equilibrium model of metal ions as a function of pH provides a plausible explanation for the pH dependence on the experimental decomposition rate.

Thiols in nitric oxide synthase-containing Nocardia sp. strain NRRL 5646

Mycothiol (MSH) [1-D-myo-inosityl-2-(N-acetyl-l-cysteinyl)amido-2-deoxy-alpha-D-glucopyranoside], isolated as the bimane derivative, was established to be the major thiol in Nocardia sp. strain NRRL 5646, a species most closely related to Nocardia brasiliensis strain DSM 43758(T). Thiol formation and detection of MSH-dependent formaldehyde dehydrogenase activity in cell extracts are relevant to the possible modulation of nitric oxide toxicity generated by strain NRRL 5646.

S-nitrosothiol detection via amperometric nitric oxide sensor with surface modified hydrogel layer containing immobilized organoselenium catalyst

A novel electrochemical device for the direct detection of S-nitrosothiol species (RSNO) is proposed by modifying an amperometric nitric oxide (NO) gas sensor with thin hydrogel layer containing an immobilized organoselenium catalyst. The diselenide, 3,3'-dipropionicdiselenide, is covalently coupled to primary amine groups in polyethylenimine (PEI), which is further cross-linked to form a hydrogel layer on a dialysis membrane support. Such a polymer film containing the organoselenium moiety is capable of decomposing S-nitrosothiols to generate NO(g) at the distal tip of the NO sensor. Under optimized conditions, various RSNOs (e.g., nitrosocysteine (CysNO), nitrosoglutathione (GSNO), etc.) are reversibly detected at </=0.1 microM levels, with sensor lifetimes of at least 10 days. The presence of reducing agents (e.g., glutathione) added to the test solution enhances the amperometric dynamic range output to approximately 25 microM levels of RSNO species. Sensitivities observed for different small molecule RSNO species are nearly equivalent, in sharp contrast to the behavior observed previously for a similar RSNO sensing configuration based on an immobilized Cu(I/II) catalytic layer. It is further shown that the new RSNO sensors can be used to assess the "NO-generating" ability of fresh blood samples by effectively detecting the total level of reactive low molecular-weight RSNO species present in such samples.

Hepatic gene expression profile associated with non-alcoholic steatohepatitis protection by S-nitroso-N-acetylcysteine in ob/ob mice

BACKGROUND/AIMS

To understand the molecular mechanisms underlying non-alcoholic steatohepatitis (NASH) prevention by S-nitroso-N-acetylcysteine (SNAC), an NO donor that inhibits lipid peroxidation, we examined hepatic differentially expressed genes between ob/ob mice receiving or not SNAC treatment concomitantly with a methionine-choline deficient (MCD) diet.

METHODS

Ob/ob mice were assigned to receive oral SNAC fed solution (MCD+SNAC group) or vehicle (MCD group) by gavage. After four weeks, histopathological analysis and microarray hybridizations were conducted in liver tissues from groups. GeneSifter system was used to identify differentially expressed genes and pathways according to Gene Ontology.

RESULTS

NASH was absent in the MCD+SNAC group and no significant changes in food intake or body weight were observed in comparison to MCD group. After SNAC treatment, several genes belonging to oxidative phosphorylation, fatty acid biosynthesis, fatty acid metabolism and glutathione metabolism pathways were down-regulated in comparison to the MCD group.

CONCLUSIONS

SNAC treatment promotes down regulation of several genes from fatty acid (FA) metabolism related pathways, possibly through abrogation of the cytotoxic effects of reactive oxygen species and lipid peroxides with consequent prevention of mitochondrial overload. Further studies are required to investigate the clinical implications of these findings, in attempt to develop novel therapeutic strategies for NAFLD treatment.

Analysis of nitrite and nitrate in biological fluids by assays based on the Griess reaction: appraisal of the Griess reaction in the L-arginine/nitric oxide area of research

In the Griess reaction, first reported by Johann Peter Griess in 1879 as a method of analysis of nitrite (NO(2)(-)), nitrite reacts under acidic conditions with sulfanilic acid (HO(3)SC(6)H(4)NH(2)) to form a diazonium cation (HO(3)SC(6)H(4)-N[triple bond]N(+)) which subsequently couples to the aromatic amine 1-naphthylamine (C(10)H(7)NH(2)) to produce a red-violet coloured (lambda(max) approximately 540 nm), water-soluble azo dye (HO(3)SC(6)H(4)-NN-C(10)H(6)NH(2)). The identification of nitrite in saliva has been the first analytical application of this diazotization reaction in 1879. For a century, the Griess reaction has been exclusively used to identify analytically bacterial infection in the urogenital tract, i.e. to identify nitrite produced by bacterial reduction of nitrate (NO(3)(-)), the major nitrogen oxide anion in human urine. Since the discovery of the l-arginine/nitric oxide (l-Arg/NO) pathway in 1987, however, the Griess reaction is the most frequently used analytical approach to quantitate the major metabolites of NO, i.e. nitrite and nitrate, in a variety of biological fluids, notably blood and urine. The Griess reaction is specific for nitrite. Analysis of nitrate by this reaction requires chemical or enzymatic reduction of nitrate to nitrite prior to the diazotization reaction. The simplicity of the Griess reaction and its easy and inexpensive analytical feasibility has attracted the attention of scientists from wide a spectrum of disciplines dedicated to the complex and challenging L-Arg/NO pathway. Today, we know dozens of assays based on the Griess reaction. In principle, every laboratory in this area uses its own Griess assay. The simplest Griess assay is performed in batch commonly as originally reported by Griess. Because of the recognition of numerous interferences in the analysis of nitrite and nitrate in biological fluids and of the desire to analyze these anions simultaneously, the Griess reaction has been repeatedly modified and automated. In recent years, the Griess reaction has been coupled to HPLC, i.e. is used for post-column derivatization of chromatographically separated nitrite and nitrate. Such a HPLC-Griess system is even commercially available. The present article gives an overview of the currently available assays of nitrite and nitrate in biological fluids based on the Griess reaction. Special emphasis is given to human plasma and urine, to quantitative aspects, as well as to particular analytical and pre-analytical factors and problems that may be associated with and affect the quantitative analysis of nitrite and nitrate in these matrices by assays based on the Griess reaction. The significance of the Griess reaction in the L-Arg/NO pathway is appraised.

Measurement of nitric oxide levels in the red cell: validation of tri-iodide-based chemiluminescence with acid-sulfanilamide pretreatment

The tri-iodide-based chemiluminescence assay is the most widely used methodology for the detection of S-nitrosothiols (RSNOs) in biological samples. Because of the low RSNO levels detected in a number of biological compartments using this assay, criticism has been raised that this method underestimates the true values in biological samples. This claim is based on the beliefs that (i) acidified sulfanilamide pretreatment, required to remove nitrite, leads to RSNO degradation and (ii) that there is auto-capture of released NO by heme in the reaction vessel. Because our laboratories have used this assay extensively without ever encountering evidence that corroborated these claims, we sought to experimentally address these issues using several independent techniques. We find that RSNOs of glutathione, cysteine, albumin, and hemoglobin are stable in acidified sulfanilamide as determined by the tri-iodide method, copper/cysteine assay, Griess-Saville assay and spectrophotometric analysis. Quantitatively there was no difference in S-nitroso-hemoglobin (SNOHb) or S-nitroso-albumin (SNOAlb) using the tri-iodide method and a recently described modified assay using a ferricyanide-enhanced reaction mix at biologically relevant NO:heme ratios. Levels of SNOHb detected in human blood ranged from 20-100 nM with no arterial-venous gradient. We further find that 90% of the total NO-related signal in blood is caused by erythrocytic nitrite, which may partly be bound to hemoglobin. We conclude that all claims made thus far that the tri-iodide assay underestimates RSNO levels are unsubstantiated and that this assay remains the "gold standard" for sensitive and specific measurement of RSNOs in biological matrices.

Oral administration of S-nitroso-N-acetylcysteine prevents the onset of non alcoholic fatty liver disease in rats

AIM: To evaluate the potential of S-nitroso-N-acetylcysteine (SNAC) in inhibition of lipid peroxidation and the effect of oral SNAC administration in the prevention of nonalcoholic fatty liver disease (NAFLD) in an animal model.

METHODS: NAFLD was induced in Wistar male rats by choline-deficient diet for 4 wk. SNAC-treated animals (n=6) (1.4 mg/kg/day of SNAC, orally) were compared to 2 control groups: one (n=6) received PBS solution and the other (n=6) received NAC solution (7 mg/kg/d). Histological variables were semiquantitated with respect to macro and microvacuolar fat changes, its zonal distribution, foci of necrosis, portal and perivenular fibrosis, and inflammatory infiltrate with zonal distribution. LOOHs from samples of liver homogenates were quantified by HPLC. Nitrate levels in plasma of portal vein were assessed by chemiluminescence. Aqueous low-density lipoprotein (LDL) suspensions (200 µg protein/mL) were incubated with CuCl₂ (300 µmol/L) in the absence and presence of SNAC (300 µmol/L) for 15 h at 37 °C. Extent of LDL oxidation was assessed by fluorimetry. Linoleic acid (LA) (18.8 µmol/L) oxidation was induced by soybean lipoxygenase (SLO) (0.056 µmol/L) at 37 °C in the presence and absence of N-acetylcysteine (NAC) and SNAC (56 and 560 µmol/L) and monitored at 234 nm.

RESULTS: Animals in the control group developed moderate macro and microvesicular fatty changes in periportal area. SNAC-treated animals displayed only discrete histological alterations with absence of fatty changes and did not develop liver steatosis. The absence of NAFLD in the SNAC-treated group was positively correlated with a decrease in the concentration of LOOH in liver homogenate, compared to the control group (0.7±0.2 nmol/mg vs 3.2±0.4 nmol/mg protein, respectively, P<0.05), while serum levels of aminotransferases were unaltered. The ability of SNAC in preventing lipid peroxidation was confirmed in in vitro experiments using LA and LDL as model substrates.

CONCLUSION: Oral administration of SNAC prevents the onset of NAFLD in Wistar rats fed with choline-deficient diet. This effect is correlated with the ability of SNAC to block the propagation of lipid peroxidation in vitro and in vitro.

Metabolism of oxidants by blood from different mouse strains

Haemoglobins bearing reactive sulfhydryl groups have been shown to be able to interplay with glutathione in some detoxification processes. Blood from different mouse strains commonly used as experimental animal models, i.e., C57, DBA and ICR, was treated with oxidants with the aim of evaluating: (i) the involvement of protein SH groups in oxido-reductive reactions that are commonly carried out by glutathione and (ii) the impact of this phenomenon on blood-mediated metabolism of thiol reactants. All the main forms of glutathione (reduced, disulfide, and mixed disulfide with haemoglobin) were measured after oxidant treatment. Significant differences were found among the studied strains: DBA mice formed preferably mixed disulfides instead of glutathione disulfide, whereas the opposite behaviour was shown by C57 mice. Unexpectedly, the ICR strain resulted to be composed of three different subgroups (ICRa, ICRb, and ICRc), with the ICRa behaving similarly to the DBA strain, ICRc to the C57 strain, and ICRc showing an intermediate behaviour. These results are due to the different number of haemoglobin SH groups in the studied mouse strains. In particular, additional fast-reacting SH groups were found in haemoglobin from DBA, ICRa, and ICRb mice, but not in the C57 and ICRc strain. These differences were also reflected in the susceptibility of haemoglobin to dimerize and in its ability to react with S-nitrosocysteine. Because of the widely different reactivity of haemoglobin cysteinyl residues, the mouse strains examined are an interesting but complicated model in which to study the pharmacological and toxicological action of some drugs.

Leishmanicidal activity of primary S-nitrosothiols against Leishmania major and Leishmania amazonensis: implications for the treatment of cutaneous leishmaniasis

Nitric oxide (NO) is considered a key molecule in the defense against intracellular pathogens, particularly Leishmania. The expression of inducible nitric oxide synthase and consequent production of NO by infected macrophages has been shown to correlate with leishmaniasis resistance in the murine model as well as in human patients. Nitric oxide donors have been used successfully in the treatment of cutaneous leishmaniasis in humans, although their mechanisms of action are not fully understood. In the present work, the dose-dependent cytotoxic effects of the NO-donors S-nitroso-N-acetyl-l-cysteine (SNAC) and S-nitrosoglutathione (GSNO) against Leishmania were evaluated. GSNO inhibited the growth of Leishmania major and Leishmania amazonensis with in vitro 50% inhibitory concentrations (IC(50)) of 68.8+/-22.86 and 68.9+/-7.9 micromol L(-1), respectively. The IC(50) for SNAC against L. major and L. amazonensis were, respectively, 54.6+/-8.3 and 181.6+/-12.5 micromol L(-1). The leishmanicidal activity of GSNO, but not of SNAC, was reversed by ascorbic acid (AA) and dithiothreitol (DTT), suggesting that the mechanism of action of GSNO is related to the transnitrosation of parasite proteins. These results demonstrate that SNAC and GSNO have leishmanicidal activity, and are thus potential therapeutic agents against cutaneous leishmaniasis.

N-acetylcysteine for prevention of radiographic contrast material-induced nephropathy: is the intravenous route best?

Use of oral N-acetylcysteine for preventing radiographic contrast material-induced nephropathy (RCIN) has become widespread, despite conflicting results from clinical trials and meta-analyses. The variability in study results may reflect differences in baseline risks in study patients, hydration regimens, choice of contrast agent, definition of RCIN, and the oral dosage formulation of N-acetylcysteine used. Injectable N-acetylcysteine recently has become available in the United States. Although oral N-acetylcysteine regimens are typically administered during a 48-hour period, more rapid intravenous administration could offer an important advantage for urgent procedures such as coronary angiography. However, the three published studies in which intravenous N-acetylcysteine protocols were used have produced divergent results, likely because of substantially different dosage regimens. With few intravenous studies available, clinicians may look to more broadly studied oral regimens to estimate equivalent intravenous dosages. In the oral studies, however, a wide range of formulations were used, and the bioavailability of each product was uncertain. In addition, the intravenous route circumvents first-pass metabolism, resulting in less glutathione production, perhaps compromising the antioxidant effects of N-acetylcysteine administration. Overall, little evidence exists that any studied N-acetylcysteine protocol improves clinical outcomes in terms of reducing length of hospital stay, need for dialysis, or mortality. Furthermore, N-acetylcysteine may directly affect serum creatinine level, which all clinical trials to date have used as a primary outcome measure. If oral or intravenous N-acetylcysteine is used with the intention of preventing RCIN, more established preventive measures should not be overlooked, including adequate hydration with isotonic saline, avoidance of potentially nephrotoxic drugs, and use of iso-osmolar radiographic contrast media.

S-nitrosoglutathione incorporated in poly(ethylene glycol) matrix: potential use for topical nitric oxide delivery

Incorporation of nitric oxide (NO) donors in non-toxic polymeric matrices can be a useful strategy for allowing topical NO delivery. We have incorporated the NO-donor S-nitrosoglutathione (GSNO) into a liquid poly(ethylene glycol) (PEG)/H2O matrix through the S-nitrosation of GSH by a NO/O2 gas mixture. Kinetic measurements of GSNO decomposition associated with NO release were performed at 25, 35, and 45 degrees C in the dark and under irradiation with UV/Vis light, lambda>480 nm and lambda=333 nm. NO release from the liquid matrix to the gas phase was confirmed by mass spectrometry. The PEG/H2O matrix stabilizes GSNO leading to expressive reductions in the initial rates of thermal and photochemical NO release, compared to aqueous GSNO solution. This matrix effect is assigned to diffusional constrains imposed on the escape of the NO and GS radicals formed in the solvent cage. This effect allows the storage of PEG-GSNO formulations for extended periods (more than 65 days at freezer) with negligible decomposition. PEG-GSNO formulation seems therefore to be applicable in topical NO delivery and GSNO displays potential as a percutaneous absorption enhancer. Moreover, the rate of NO release can be locally increased by irradiation with visible light.

Polynitrosated Polyesters: Preparation, Characterization, and Potential Use for Topical Nitric Oxide Release

New nitric oxide (NO) donor macromolecules, containing multiple S-nitrosothiol (S-NO) groups covalently attached to the polymer backbone, were prepared through the polycondensation reaction of diols (ethylene glycol and poly(ethylene glycol)) with mercaptosuccinic acid, followed by the S-nitrosation of the SH groups by a gaseous NO/O2 mixture. The polynitrosated polyesters (PNPEs) obtained were characterized by IR spectroscopy and gel permeation chromatography and displayed biological activity as vasodilators, leading to local hyperaemia when applied topically on healthy skin. Kinetic measurements in either dry or aqueous conditions have shown that PNPEs can provide sustained NO release for more than 20 h at physiological temperature. Their increased viscosity at low temperatures greatly reduces the rate of NO release, allowing for their storage for more than 90 days at -20 degrees C without decomposition. These results indicate that PNPEs have potential for topical delivery of NO in biomedical applications.

Detection of human red blood cell-bound nitric oxide

Major disparities in reported levels of basal human nitric oxide metabolites have resulted in a recent literature focusing almost exclusively on methods. We chose to analyze triiodide chemiluminescence, drawn by the prospect of identifying why the most commonly employed assay in nitric oxide biology typically yielded lower metabolite values, compared with several other techniques. We found that the sensitivity of triiodide was greatly affected by the auto-capture of nitric oxide by deoxygenated cell-free heme in the reaction chamber. Potential contaminants and signal losses were also associated with standard sample purification procedures and the chemistry involved in nitrite removal. To inhibit heme nitric oxide auto-capture, we added potassium ferricyanide to the triiodide reagent, reasoning this would provide a more complete detection of any liberated nitric oxide. From human venous blood samples, we established nitric oxide levels ranging from 0.000178 to 0.00024 mol nitric oxide/mol hemoglobin. We went on to find significantly elevated nitric oxide levels in venous blood taken from diabetic patients in comparison to healthy controls (p < 0.0001). We concluded that the lack of signals reported of late by several groups using triiodide chemiluminescence for the detection of hemoglobin-bound nitric oxide may not represent levels on the border of assay sensitivity but rather underestimated values because of methodological limitations. We therefore stress the need for assay systems to be developed that differentiate between individual nitric oxide metabolite species and overcome the limitations we outline, allowing accurate conclusions to be drawn regarding physiological nitric oxide metabolite levels.

Transnitrosation of nitrosothiols: characterization of an elusive intermediate

We report an investigation of the reaction between (S)-nitroso-l-cysteine ethyl ester and l-cysteine ethyl ester as a model of physiologically relevant transnitrosation processes. Our theoretical and experimental evidence clearly supports the existence of a nitroxyl disulfide intermediate in solution.

Nitric oxide and blood: a review

Nitric oxide (NO) was identified as a physiological mediator of vascular tone in 1987. NO produced by endothelial cells causes vasodilatation and also inhibits platelet aggregation and leucocyte adhesion. Red cells metabolize NO to nitrate but may possibly carry and release, or even produce, NO in hypoxic conditions. NO physiology may have important implications for transfusion medicine, ranging from adverse effects of haemoglobin substitutes to preservation of stored platelets and to detrimental effects of stored red cells.

Proteins as biomarkers of oxidative/nitrosative stress in diseases: the contribution of redox proteomics

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) contribute to the pathogenesis and/or progression of several human diseases. Proteins are important molecular signposts of oxidative/nitrosative damage. However, it is generally unresolved whether the presence of oxidatively/nitrosatively modified proteins has a causal role or simply reflects secondary epiphenomena. Only direct identification and characterization of the modified protein(s) in a given pathophysiological condition can decipher the potential roles played by ROS/RNS-induced protein modifications. During the last few years, mass spectrometry (MS)-based technologies have contributed in a significant way to foster a better understanding of disease processes. The study of oxidative/nitrosative modifications, investigated by redox proteomics, is contributing to establish a relationship between pathological hallmarks of disease and protein structural and functional abnormalities. MS-based technologies promise a contribution in a new era of molecular medicine, especially in the discovery of diagnostic biomarkers of oxidative/nitrosative stress, enabling early detection of diseases. Indeed, identification and characterization of oxidatively/nitrosatively modified proteins in human diseases has just begun.

Determinants of basal nitric oxide concentration in the renal medullary microcirculation

In this study, we modeled the production, transport, and consumption of nitric oxide (NO) in the renal medullary microcirculation under basal conditions. To yield agreement with reported NO concentrations of ∼60–140 nM in medullary tissues (Zou AP and Cowley AW Jr. Hypertension 29: 194–198, 1997; Am J Physiol Regul Integr Comp Physiol 279: R769–R777, 2000) and 3 nM in plasma (Stamler JS, Jaraki O, Osborne J, Simon DI, Keaney J, Vita J, Singel D, Valeri CR, and Loscalzo J. Proc Natl Acad Sci USA 89: 7674–7677, 1992), the permeabilities of red blood cells (RBCs), vascular walls, and pericytes to NO are all predicted to lie between 0.01 and 0.1 cm/s, and the NO production rate by vasa recta endothelium is estimated to be on the order of 10−14μmol·μm−2·s−1. Our results suggest that the concentration of NO in RBCs, which is essentially controlled by the kinetics of NO scavenging by hemoglobin, is ∼0.01 nM, that is, 103times lower than that in plasma, pericytes, and interstitium. Because the basal concentration of NO in pericytes is on the order of 10 nM, it may be too low to active guanylate cyclase, i.e., to induce vasorelaxation. Our simulations also indicate that basal superoxide concentrations may be too low to affect medullary NO levels but that, under pathological conditions, superoxide may be a very significant scavenger of NO. We also found that although oxygen is a negligible NO scavenger, medullary hypoxia may significantly enhance NO concentration gradients along the corticomedullary axis.

Depletion of Endogenous Nitric Oxide Enhances Cisplatin-induced Apoptosis in a p53-dependent Manner in Melanoma Cell Lines

The expression of inducible nitric-oxide synthase in melanoma tumor cells was recently shown to correlate strongly with poor patient survival after combination biochemotherapy (p<0.001). Furthermore, evidence suggests that nitric oxide, a reaction product of nitric oxide synthase, exhibits antiapoptotic activity in melanoma cells. We therefore hypothesized that nitric oxide antagonizes chemotherapy-induced apoptosis. Whether nitric oxide is capable of regulating cell growth and apoptotic responses to cisplatin treatment in melanoma cell lines was evaluated. We demonstrate herein that depletion of endogenously produced nitric oxide can inhibit melanoma proliferation and promote apoptosis. Moreover, our data indicate that the depletion of nitric oxide leads to changes in cell cycle regulation and enhances cisplatin-induced apoptosis in melanoma cells. Strikingly, we observed that the depletion of nitric oxide inhibits cisplatin-induced wild type p53 accumulation and p21(Waf1/Cip1/Sdi1) expression in melanoma cells. When cisplatin-induced p53 binding to the p21(Waf1/Cip1/Sdi1) promoter was examined, it was found that nitric oxide depletion significantly reduced the presence of p53-DNA complexes after cisplatin treatment. Furthermore, dominant negative inhibition of p53 activity enhanced cisplatin-induced apoptosis. Together, these data strongly suggest that endogenously produced nitric oxide is required for cisplatin-induced p53 activation and p21(Waf1/Cip1/Sdi1) expression, which can regulate melanoma sensitivity to cisplatin.

An improved HPLC measurement for GSH and GSSG in human blood

The pathophysiological sequelae of oxidative/nitrosative stress are notoriously difficult to quantify. Despite these impediments, the medical significance of oxidative/nitrosative stress has become increasingly recognized to the point that it is now considered to be a component of virtually every disease. The level of oxidative stress can be quantified in blood by the measurement of the increase in glutathione disulfide (GSSG) and the decrease in the GSH/GSSG ratio, which has been shown to be altered in a variety of human diseases such as lung inflammation, amyotrophic lateral sclerosis, chronic renal failure, malignant disorders, and diabetes. Among the proposed methods for GSH/GSSG detection, the amino group derivatization with 2,4-dinitrofluorobenzene followed by HPLC separation has the advantage of allowing evaluation of both parameters within a single run contemporaneously. However, it has been shown that the application of this method on blood samples is not reproducible. In this report, we offer an explanation for these experimental limits and suggest some modifications that allow the application of this method to blood samples. The modified method has a low detection limit (0.5 microM, i.e., 1.4 pmoles) and a high reproducibility with a within-run imprecision of less than 2%. It could have a wide application as it is simple, virtually artifact-free, and not time-consuming, especially for large-scale screening studies.