Chemical evaluation of compounds as nitric oxide or peroxynitrite donors using the reactions with serotonin

The aim of this work was to assess the capacities of some .NO-donors to release .NO, and consequently NOx in aerobic medium, or to give peroxynitrite. The method was based on the differential reactivity of serotonin (5-HT) with either NO(x) or peroxynitrite, leading in phosphate-buffered solutions to 4-nitroso- and 4-nitro-5-HT formation, respectively. Yields and formation rates of 5-HT derivatives with .NO-donor were compared to those obtained with authentic .NO or peroxynitrite in similar conditions. Aside from the capacity of diazenium diolates (SPER/NO and DEA/NO) to release .NO spontaneously, converting 5-HT exclusively to 4-nitroso-5-HT, all other .NO donors must undergo redox reactions to produce .NO. S-nitrosoglutathione (GSNO) and sodium nitroprusside (SNP) modified 5-HT only in the presence of Cu2+, GSNO yielding 6 times more 4-nitroso-5-HT than SNP. Furthermore, in the presence of Cu+, the yield of .NO-release from GSNO was 45%. The molsidomine metabolite (SIN-1), which was presumed to release both .NO and O2(7-) at pH 7.4, reacted with 5-HT differently, depending on the presence of reductant or oxidant. Under aerobic conditions, SIN-1 acted predominantly as a 5-HT oxidant and also as a poor .NO and peroxynitrite donor (15% yield of .NO-release and 14 % yield of peroxynitrite formation). The strong oxidant Cu2+, even in the presence of air oxygen, accelerated oxidation and increased .NO release from SIN-1 up to 86%. Only a small part of SIN-1 gave simultaneously .NO and O2(7-) able to link together to give peroxynitrite, but other oxidants could enhance .NO release from SIN-1.

Electrochemical detection of nitroso-arginine as an intermediate between N-hydroxy-arginine and citrulline. An in vitro versus in vivo study using microcarbon electrodes in neuronal nitric oxide synthase and mice brain

The aim of the study was to describe in vivo and in vitro the transformation of N-hydroxy-arginine (NHA) into nitrite and citrulline. The products of NHA oxidation were studied by electrochemical methods. Cyclic voltammetry of NHA on microcarbon electrode showed an oxidation in two steps with one electron and one proton exchanged at each step. The first step gave a radical species NHA(.) with a half-life shorter than 1 micros and the second step gave nitroso-arginine (NA) with a half-life of about 1 s (1.5 s). Coulometric oxidation of NHA gave citrulline and nitrite. Differential pulse voltammetry (DPV) in vivo and in vitro gave a peak in reduction at -1.66 V vs Ag/AgCl for NA. After reductive adsorption of NA on the microelectrode surface in mice brain it gave the two peaks of NHA in oxidation plus another peak identified as nitrite. DPV in native and recombinant rat brain nitric oxide (NO)-synthase gave NA signal permitting K(m) and V(max) determination. All these results showed that NA was synthetized by NO-synthases before the final products, citrulline and nitrite.

Surface-enhanced Raman scattering: a structure-specific detection method for capillary electrophoresis

A new approach to detecting capillary electrophoresis (CE) eluent components by interfacing CE with a surface-enhanced Raman scattering (SERS) system is described. In this approach, CE-based separation of a mixture of trans-1,2-bis(4-pyridyl)ethylene and N,N-dimethyl-4-nitrosoaniline has been detected by SERS in a postcolumn geometry. The retention time obtained from SERS corresponds well with that from conventional UV-visible detection. Meanwhile, CE eluants are identified by their characteristic vibrational spectra, demonstrating the validity of SERS as a structure-specific detection method for CE. In addition, the ability to monitor SERS intensity changes at molecule-specific frequencies makes selective detection of individual analytes possible, even when separation is incomplete. Finally, CE-SERS is evaluated for separation of amino acids (tyrosine and tryptophan) and environmental pollutants (chlorophenol mixtures).

Simultaneous derivatization and quantification of the nitric oxide metabolites nitrite and nitrate in biological fluids by gas chromatography/mass spectrometry

Simultaneous quantification of nitrite and nitrate, the major oxidative metabolites of L-arginine-derived nitric oxide (NO), in biological fluids by GC or GC/MS methods is currently impossible. The separate analysis of these anions is associated with severe methodological problems. Therefore, a GC/MS method was developed which allows, for the first time, simultaneous quantification of nitrite and nitrate in various biological fluids. The method involves a single derivatization procedure, by which endogenous nitrite and nitrate and their externally added 15N-labeled analogues are simultaneously converted in aqueous acetone by pentafluorobenzyl bromide to the nitro and nitric acid ester pentafluorobenzyl derivatives, respectively, and a single GC/MS analysis. Nitrite and nitrate concentrations measured in plasma and urine of humans by this method correlated excellently with those from quantification of nitrite and nitrate in these matrixes using a previously reported GC/MS method that, however, requires reduction of nitrate to nitrite. Also, the present method enables discrimination between S-nitro- and S-nitroso-glutathione, which have identical chromatographic and spectrophotometric properties. The method is very useful to routinely study metabolism and reactions of NO and its metabolites in vitro and in vivo. It is accurate, interference-free, sensitive-50 fmol of [15N]-nitrite and [15N]nitrate were detected at signal-to-noise ratios of 870:1 and 95:1, respectively-and should be a reference method for nitrite and nitrate measurements.

Electrospray ionization mass spectrometry of low-molecular-mass S-nitroso compounds and their thiols

Low-molecular-mass S-nitroso compounds (R-S-N=O) are potent vasodilators and inhibitors of platelet aggregation. This work describes the electrospray ionization mass spectrometric (ESI-MS) analysis of physiological and synthetic low-molecular-mass S-nitroso compounds and their thiols including S-nitrosoglutathione, S-nitrosocysteine, glutathione and cysteine. Mass spectra of the unlabeled and S-15N-labeled low-molecular-mass S-nitroso compounds investigated are characterized by abundant cations due to [M+H]+, [M+Na]+, [(M+H)-NO]+, [2 M+H]+, and [(2 M+H)-2NO]+. Mass spectra of low-molecular-mass thiols are characterized by abundant cations due to [M+H]+, [M+Na]+ and [2M+H]+. Using off-line electrospray ionization tandem mass spectrometry we unequivocally identified S-[15N]nitrosoglutathione in human red blood cells formed after their incubation with S-[15N]nitrosocysteine. These results suggest that ESI-MS in combination with an appropriate liquid chromatographic system should be a useful analytical approach for the on-line quantitative determination of low-molecular-mass S-nitroso compounds in biological fluids in the presence of their thiols and nitrite. Considerations were made about on-line ESI-MS and quantitative measurements.

The effect of intra-gastric acidity and flora on the concentration of N-nitroso compounds in the stomach

BACKGROUND

Correa's hypothesis proposes that gastric carcinogenesis is due to atrophic gastritis and hypochlorhydria which permit gastric bacterial colonization, the reduction of dietary nitrates to nitrites and the formation of potentially carcinogenic N-nitroso compounds (NOCs).

OBJECTIVE

To test the hypothesis that omeprazole-induced hypochlorhydria is associated with increased intra-gastric concentrations of nitrate-reducing bacteria (NRB), nitrites and NOCs.

DESIGN

Single-blind study in healthy volunteers.

PARTICIPANTS

Fourteen healthy subjects (seven female, mean age 24 years), free of Helicobacter pylori infection, received a one-week course of placebo followed by a two-week course of omeprazole, 20 mg daily.

METHODS

Fasted gastric samples, aspirated using a sterile double-lumen nasogastric tube at the end of the 1 st week (placebo) and the 2nd and 3rd weeks (omeprazole), were cultured aerobically and anaerobically; gastric pH and intra-gastric concentrations of nitrates, nitrites and NOCs were also determined.

RESULTS

After weeks 1, 2 and 3, the intra-gastric concentrations of nitrate-reducing bacteria exceeded 10(5) colony-forming units (c.f.u.)/ml in 3, 7 and 9 subjects, respectively (P > 0.05). A gastric pH greater than 4.0 was associated with increased NRB (P < 0.05); however, neither increased gastric pH nor increased NRB, alone or in combination, was associated with increased intra-gastric concentrations of nitrites or NOCs (P > 0.05).

CONCLUSIONS

A two-week increase in gastric pH in healthy, H. pylori-negative subjects was associated with increased intra-gastric concentrations of nitrate-reducing bacteria but not of nitrites or N-nitroso compounds. These data suggest that reduced gastric acid secretion is not a necessary precursor to the formation of carcinogenic N-nitroso compounds and that other mechanisms should be invoked to explain gastric carcinogenesis.

Endogenous N-nitroso compounds, and their precursors, present in bacon, do not initiate or promote aberrant crypt foci in the colon of rats

Processed meat intake is associated with increased risk of colorectal cancer. This association may be explained by the endogenous formation of N-nitroso compounds (NOC). The hypothesis that meat intake can increase fecal NOC levels and colon carcinogenesis was tested in 175 Fischer 344 rats. Initiation was assessed by the number of aberrant crypt foci (ACF) in the colon of rats 45 days after the start of a high-fat bacon-based diet. Promotion was assessed by the multiplicity of ACF (crypts per ACF) in rats given experimental diets for 100 days starting 7 days after an azoxymethane injection. Three promotion studies were done, each in 5 groups of 10 rats, whose diets contained 7%, 14%, or 28% fat. Tested meats were bacon, pork, chicken, and beef. Fecal and dietary NOC were assayed by thermal energy analysis. Results show that feces from rats fed bacon-based diets contained 10-20 times more NOC than feces from control rats fed a casein-based diet (all p < 0.0001 in 4 studies). In bacon-fed rats, the amount of NOC input (diet) and output (feces) was similar. Rats fed a diet based on beef, pork, or chicken meat had less fecal NOC than controls (most p < 0.01). No ACF were detected in the colon of bacon-fed uninitiated rats. After azoxymethane injection, unprocessed but cooked meat-based diets did not change the number of ACF or the ACF multiplicity compared with control rats. In contrast, the bacon-based diet consistently reduced the number of large ACF per rat and the ACF multiplicity in the three promotion studies by 12%, 17%, and 20% (all p < 0.01). Results suggest that NOC from dietary bacon would not enhance colon carcinogenesis in rats.

Decreased levels of nitrosothiols in the lower airways of patients with cystic fibrosis and normal pulmonary function

Airway S-nitrosothiols (SNOs) are naturally occurring bronchodilators. SNOs, nitrate, and nitrite were measured in bronchoalveolar lavage fluid of 23 patients with cystic fibrosis (CF) and mild pulmonary disease (aged 6-16 years) and 13 healthy children (aged 8-15 years). Concentrations of SNOs were decreased in the lower airways of patients with CF and mild pulmonary disease (median, range: 0, 0-320 nmol/L vs 80, 0-970 nmol/L) despite normal levels of the inert nitric oxide metabolites nitrate and nitrite (mean +/- SEM: 3.7 +/- 0.5 micromol/L vs 4.8 +/- 0.9 micromol/L). S-nitrosolation- mediated bioreactivities may be impaired by depletion of the CF airway SNO reservoir.

Separation of N-nitrosoamino acids by C18 reversed-phase ion-pair high-performance liquid chromatography and compatible detection by electrospray ionization mass spectrometry

Four non-volatile N-nitrosoamino acids, namely N-nitrososarcosine, N-nitrosoproline, N-nitrosothiazolidine-4-carboxylic acid and N-nitroso-2-methyl-thiazolidine-4-carboxylic acid were separated by C18 reversed-phase ion-pair high-performance liquid chromatography (HPLC) using 1.4 mM C16-cetyltrimethylammonium chloride in methanol-water-acetonitrile (60:35:5, v/v) as the mobile phase. The N-nitrosoamino acids were sensitively detected by negative electrospray ionization mass spectrometry (ESI-MS) in the form of the deprotonated carboxylate anion, [M-H]-. Compatibility problems associated with HPLC separation and ESI-MS detection, such as formation of solvent cluster ions and the effects of co-eluting anions of the ion-pairing reagent, were systematically investigated. The optimized experimental conditions for separation and detection of N-nitrosoamino acids were described.

Natural and man-made mutagens and carcinogens in the human diet

Around 40% of human cancers may relate to dietary factors, including both exogenous and endogenous mutagens. Of exogenous factors, alcohol, certain metals and certain pesticides (both naturally produced or manufactured by the chemical industry), N-nitroso compounds, heterocyclic amines and polycyclic aromatic hydrocarbons are all probable human carcinogens. Despite current negative publicity, genetic engineering appears to be a more precise process and no more likely to lead to cancer risks than conventional breeding processes. Many traditional assessments of cancer hazard from endogenous or exogenous chemicals ignore the presence of modifying factors in the human diet. For example, dietary fat and dietary fibre probably either enhance or protect against cancer, depending upon the exact amounts and chemical nature of the fat fibre. Considerable numbers of other types of antimutagen/anticarcinogens have been identified, with varying modes of action. Additionally, there is an interaction of dietary factors with genetics. Epidemiology will always be important in assessing relative risks, but it is essential to continue developing more sensitive biomonitoring methodologies. It would be desirable to compare precise measures of individual exposure to dietary carcinogens with levels of oxidative damage and evidence of genotoxic effects in a given tissue. Such experimental approaches might be expected to lead a better understanding of the interplay between different dietary factors and also between diet, hereditary and the environment.

N-Nitroso compounds in the diet

N-Nitroso compounds were known almost 40 years ago to be present in food treated with sodium nitrite, which made fish meal hepatotoxic to animals through formation of nitrosodimethylamine (NDMA). Since that time, N-nitroso compounds have been shown in animal experiments to be the most broadly acting and the most potent group of carcinogens. The key role of nitrite and nitrogen oxides in forming N-nitroso compounds by interaction with secondary and tertiary amino compounds has led to the examination worldwide of foods for the presence of N-nitroso compounds, which have been found almost exclusively in those foods containing nitrite or which have become exposed to nitrogen oxides. Among these are cured meats, especially bacon-and especially when cooked; concentrations of 100 micrograms kg(-1) have been found or, more usually, near 10 micrograms kg(-1). This would correspond to consumption of 1 microgram of NDMA in a 100-g portion. Much higher concentrations of NDMA (but lower ones of other nitrosamines) have been found in Japanese smoked and cured fish (more than 100 micrograms kg(-1)). Beer is one source of NDMA, in which as much as 70 micrograms l(-1) has been reported in some types of German beer, although usual levels are much lower (10 or 5 micrograms l(-1)); this could mean a considerable intake for a heavy beer drinker of several liters per day. Levels of nitrosamines have been declining during the past three decades, concurrent with a lowering of the nitrite used in food and greater control of exposure of malt to nitrogen oxides in beer making. There have been declines of N-nitroso compound concentrations in many foods during the past two decades. The small amounts of nitrosamines in food are nonetheless significant because of the possibility-even likelihood-that humans are more sensitive to these carcinogens than are laboratory rodents. Although it is probable that alkylnitrosamides (which induce brain tumors in rodents) are present in cured meats and other potentially nitrosated products in spite of much searching, there has been only limited indirect evidence of their presence.

Homocysteine decreases endothelin-1 production by cultured human endothelial cells

Hyperhomocysteinemia is believed to be responsible for the development of vascular disease via several mechanisms, including the impairment of endothelial-cell functionality. In-vitro studies have demonstrated that homocysteine decreases the production or bioavailability of vasodilator autacoids, such as prostacyclin and NO. Here, we show that the treatment of human endothelial cells with noncytotoxic homocysteine concentrations leads to a dose-dependent decrease in both the secretion of the vasoconstrictor agent endothelin-1 (ET-1) and the level of its mRNA. Homocysteine had an inhibitory effect at pathophysiological (0.1 and 0.5 mmol.L(-1)) and pharmacological noncytotoxic (1.0 and 2.0 mmol.L(-1)) concentrations. Mean percentage variation from control for ET-1 production was -36. 2 +/- 18.9% for 0.5 mmol.L(-1) homocysteine and -41.5 +/- 26.8% for 1.0 mmol.L(-1) homocysteine, after incubation for 8 h. Mean percentage variation from control for steady-state mRNA was -17.3 +/- 7.1% for 0.5 mmol.L(-1) homocysteine and -46.0 +/- 10.1 for 1.0 mmol.L(-1) homocysteine, after an incubation time of 2 h. ET-1 production was also reduced by incubation with various other thiol compounds containing free thiol groups, but not by incubation with thiol compounds with no free thiol group. Co-incubation of cells with homocysteine and the sulfhydryl inhibitor N-ethylmaleimide prevented the effect of homocysteine on ET-1 production, confirming a sulfhydryl-dependent mechanism. Based on the reciprocal feedback mechanism controlling the synthesis of vasoactive mediators, these preliminary data suggest a mechanism by which homocysteine may selectively impair endothelium-dependent vasodilation by primary inhibition of ET-1 production.

Sensitive determination of RDX, nitroso-RDX metabolites, and other munitions in ground water by solid-phase extraction and isotope dilution liquid chromatography-atmospheric pressure electro-spray [correction of chemical] ionization mass spectrometry

Recent improvements in the LC-MS interface have increased the sensitivity and selectivity of this instrument in the analysis of polar and thermally-labile aqueous constituents. Determination of RDX, nitroso-RDX metabolites, and other munitions was enhanced using LC-MS with solid-phase extraction, 15N3-RDX internal standard, and electrospray ionization (ESI) in negative ion mode. ESI produced a five-fold increase in detector response over atmospheric pressure chemical ionization (APCI) for the nitramine compounds, while the more energetic APCI produced more than twenty times the ESI response for nitroaromatics. Method detection limits in ESI for nitramines varied from 0.03 microgram l-1 for MNX to 0.05 microgram l-1 for RDX.

Exposure to N-nitroso compounds in a population of high liver cancer regions in Thailand: volatile nitrosamine (VNA) levels in Thai food

The recent case-control studies in Thailand indicate that a high incidence of liver cancer in Thailand has not been associated with common risk factors such as hepatitis B infection, aflatoxin intake and alcohol consumption. While the infestation by the liver fluke Opisthorchis viverrini (OV) accounted for the high risk in north-east Thailand, there was no such exposure in the other regions of the country where the incidence of liver cancer is also high. Case-control studies suggest that exposure to exogenous and possibly endogenous nitrosamines in food or tobacco in betel nut and cigarettes may play a role in the development of hepatocellular carcinoma (HCC), while OV infestation and chemical interaction of nitrosamines may also be aetiological factors in the development of cholangiocarcinoma (CCA). Over 1800 samples of fresh and preserved food were systematically collected and tested between 1988 and 1996. All the food items identified by anthropological studies to be consumed frequently in four major regions of Thailand were analysed for volatile nitrosamines using gas chromatography combined with a thermal energy analyser. Relatively high levels of N-nitrosodimethylamine (NDMA), N-nitrosopiperidine (NPIP) and N-nitrosopyrrolidine (NPYR) were detected in fermented fish ("Plasalid"). NDMA was also detected at levels ranging from trace amounts to 66.5 microg/kg in several salted and dried fish ("Larb-pla" and "Pla-siu"). NDMA and NPYR were frequently detected in several vegetables, particularly fermented beans ("Tau-chiau") at levels ranging between 1 and 95.1 microg/kg and 0-146 microg/kg, respectively. The possible role of nitrosamines in Thai food in the aetiology of liver cancer (HCC, CCA) is discussed.

A new assay for the determination of low-molecular-weight nitrosothiols (nitrosoglutathione), NO, and nitrites by using a specific and sensitive solid-state amperometric gas sensor

Nitric oxide (NO) is generated in biological systems and plays an important role as a bioregulatory molecule. Its ability to bind hemoglobin and myoglobin is well known. Moreover, it may lose an electron forming the nitrosyl group involved in the formation of S-nitrosothiols. The main problem in analyzing NO is its extreme reactivity. We have tackled this task by using an amperometric sensor to determine free NO, S-nitrosothiols (such as S-nitrosoglutathione), and nitrite in cell-free systems and murine microglial cell cultures. The determination of nitrosothiols is of biochemical relevance and a difficult task particularly at low concentration values. In this article we describe a new method based on the reductive cleavage of the S-NO bond by cuprous ions followed by a solid-state amperometric determination. The system described by us is sensitive, rapid, does not require previous purification steps, is easy to perform, and is inexpensive. For this reason, we think that it may represent an important analytical improvement. It has been suggested that nitrosothiols may exert biological activity by acting as a reservoir of NO. We tested the production of nitrite and of RSNO in stimulated, cultured murine microglial cells and we have shown that nitrite accumulates in these conditions. GSNO also accumulates, provided that GSH is present in the medium.

N-dansyl-S-nitrosohomocysteine a fluorescent probe for intracellular thiols and S-nitrosothiols

The fluorescence emission spectrum of N-dansyl-S-nitrosohomocysteine was enhanced approximately 8-fold upon removal of the NO group either by photolysis or by transnitrosation with free thiols like glutathione. The fluorescence enhancement was reversible in that it could be quenched in the presence of excess S-nitrosoglutathione. Attempts were then made to utilize N-dansyl-S-nitrosohomocysteine as an intracellular probe of thiols/S-nitrosothiols. Fluorescence microscopy of fibroblasts in culture indicated that intracellular N-dansyl-S-nitrosohomocysteine levels reached a maximum within 5 min. N-Dansyl-S-nitrosohomocysteine fluorescence was directly proportional to intracellular GSH levels, directly determined with HPLC. N-Dansyl-S-nitrosohomocysteine preloaded cells were also sensitive to S-nitrosoglutathione uptake as the intracellular fluorescence decreased as a function of time upon exposure to extracellular S-nitrosoglutathione.

Reductive assays for S-nitrosothiols: implications for measurements in biological systems

Bioactive SNOs are found in many tissues. We speculated SNOs might be misidentified in conventional assays which reduce NO-3 to NO. S-Nitrosothiols were exposed to saturated VCl3 in HCl, 1% KI in acetic acid, photolysis, or CuCl and CSH in He; NO was measured by chemiluminescence. S-Nitrosothiols were readily detected in VCl3 but not in KI. Reduction in CuCl/cysteine was linear (r2 = 1.0, n = 6), sensitive to 10 pmol, and eliminated by HgCl2; it did not detect NO-2, NO-3, or 3-nitrotyrosine. S-Nitrosothiols represented approximately 2.9% of NOx assayed by VCl3 in human serum, of which <5% were low-mass species. In summary, (i) conventional assays may misidentify NO-3, but not NO-2, as SNOs; and (ii) chemiluminescence/reduction systems may be sensitive and specific as SNO assays. We suggest that assay of the SNO fraction in biological NOx may be more relevant and feasible than is now appreciated.

Electrocatalytic reduction of S-nitrosoglutathione at electrodes modified with an electropolymerized film of a pyrrole-derived viologen system and their application to cellular S-nitrosoglutathione determinations

The preparation, electrochemical characterization, and analytical applications of glassy carbon (GC) electrodes modified with electropolymerized films of the cation N,N'-di(3-pyrrol-1-yl-propyl)-4,4'-bipyridine (DPPB) are described. Electropolymerized films of DPPB on GC electrodes exhibit two one-electron redox processes centered at -0.45 and -0.85 V, respectively. S-Nitrosoglutathione (GSNO) can be electrocatalytically reduced at electrodes modified with electropolymerized films of DPPB at approximately -0.4 V vs sodium-saturated calomel electrode, which represents a dramatic diminution of about 600 mV in the overpotential in comparison with the reaction carried out at a bare GC electrode. The kinetics of the catalytic reaction have been characterized using cyclic voltammetry and rotated disk electrode techniques from which a value of (1.3 +/- 0.2) x 10(3)M-1 s-1 was obtained. Using electrodes modified with an electropolymerized film of DPPB we have carried out preliminary studies of the determination of intracellular GSNO concentrations in two strains of the bacterium Rhodobacter sphaeroides.

Specific S-nitrosothiol (thionitrite) quantification as solution nitrite after vanadium(III) reduction and ozone-chemiluminescent detection

Increasing evidence suggests that S-nitrosothiols (thionitrites) might represent naturally occurring nitric oxide surrogates and function as intermediates in nitrogen monoxide metabolism. A facile, sensitive, and selective micromethod has been developed and validated for quantification of S-nitrosothiols as their mercury-displaceable nitrogen monoxide content. In this method, brief (5-min), room-temperature pretreatment of S-nitrosothiol with a molar excess of aqueous mercuric chloride was used to liberate into solution, quantitatively, the nitrogen monoxide moiety, which rapidly and quantitatively converted to its stable solution end-product, nitrite. Solution nitrite was reduced back to nitric oxide with vanadium(III), and the nitric oxide was detected by gas-phase chemiluminescence after reaction with ozone in a commercial nitric oxide analyzer. A linear relationship was observed between S-nitrosothiol-bound nitrogen monoxide and ozone-chemiluminescent detector response over a wide range (16.3-3500 pmol) of nitric oxide, as generated by reaction of vanadium(III) with either nitrite standard or mercury-treated S-nitrosothiol. Assay response was quantitatively identical for equivalent amounts of nitrite and S-nitrosothiol-bound nitrogen monoxide. The method displayed 96% selectivity for nitrite vs. nitrate and negligible (<2%) interference by nitrosated compounds bearing nitrogen monoxide moieties bound to either nitrogen or carbon. The lower limits of quantitative sensitivity and qualitative detection were below 50 and 20 pmol S-nitrosothiol-bound nitrogen monoxide-equivalents, respectively. The intraday and interday coefficients of variation did not exceed 8%. This technique has been applied to quantify structurally diverse natural and synthetic S-nitrosothiols with quantitative recovery from complex biological samples such as culture media and plasma at levels of nitrogen monoxide-equivalents undetectable by the popular Saville colorimetric method.

Analysis of nanomolar S-nitrosothiol concentrations in physiological media

S-Nitrosothiols occur endogenously and are thought to function as storage forms and/or stable carriers of nitric oxide. Moreover, the S-nitrosothiols have been postulated to function as neurotransmitters and mediate the vasodilator action of glyceryl trinitrate. Because of the increasing pharmacological and physiological interest in S-nitrosothiols, a sensitive method for analysis of these substances is required. We describe a sensitive method based on adsorptive stripping voltammetry for measurement of two S-nitrosothiols, namely, S-nitroso-N-acetyl-D-penicillamine (SNAP) and S-nitrosoglutathione (SNOG), in Krebs' solution. The method is based on the irreversible electrochemical reduction of SNAP and SNOG at the hanging mercury drop electrode (HMDE). The analytes were adsorbed at the HMDE for 60 s at -0.100 V, then exposed to a cathodic linear potential scan of 100 mV s(-10) which resulted in the reduction of SNAP at -0.470 V and SNOG at -0.530 V. Under these conditions, 4 nM SNAP and 11 nM SNOG were readily quantified. Using the above method, we were able to confirm the rapid degradation of SNAP under UV irradiation. Reproducibility of the method as applied to the analysis of these S-nitrosothiols in Krebs' solution was demonstrated by the within-day and day-to-day coefficients of variation of 1.5% and 2.0%, respectively.

Development of chemiluminescence-based methods for specific quantitation of nitrosylated thiols

While nitrosothiol compounds have been hypothesized to be important in the transport and function of nitric oxide (NO) in biological systems many important questions regarding their mechanism of formation and functional importance remain. In view of these fundamental questions there has been a great need for simple, sensitive, and specific methods for quantitation of nitrosothiols in biological samples. We report the development of two methods, for the measurement of nitrosothiol compounds using a chemiluminescence nitric oxide analyzer with a standard purging vessel. The first method is based on treatment with acidified solutions of potassium iodide in the presence or absence of dissolved free iodine. Quantitative release of NO occurs either from both nitrite and nitrosothiols or from nitrite alone, respectively. Subtraction of the amount of NO released without iodine from NO released in the presence of iodine allows estimation of the nitrosothiol concentration. To selectively measure nitrosothiols, we developed a redox quinone-hydroquinone alkaline reactant that selectively releases NO from nitrosothiols. This reactant quantitatively converts nitrosothiols to NO at elevated temperature, > 60 degrees C. Both methods were shown to detect nitrosothiols in biological buffers or blood plasma down to 10 nM concentration with high accuracy and reproducibility, variability less than 5%. These assays should be a useful addition to techniques used to characterize the biochemistry of NO.